nature scapes

7/31/2019 Nature Scapes

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Published July

The High Dynamic Range (HDR) Landscape Photography TutorialText and images copyright Royce Howland, all rights reserved

Table of Contents1. Overview

The Situation

A New(-ish) Approach

2. What is HDR?

Definition of HDR

HDR vs. 8- or 16-bit Formats

Capturing HDR Image Data

What Is HDR Good For?

3. Setting Up the Input Images

Physical Setup

Camera Setup

Determining the Exposure Sequence

RAW Conversion

Single Frame Scenes vs. Multi-frame Stitched Panoramas

4. Processing a Single Frame HDR Image

Tools Used

Workflow 1 Photoshop CS2

Workflow 2 Photomatix Pro

Comparison of Workflow Results

5. Processing a Multi-Frame Stitched HDR Image

Tools Used

Differences from the Single Frame Workflow

Workflow Overview

6. Gallery of HDR Images

7. Conclusion

Wish List

References


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1. OverviewAs a wildlife and landscape photography enthusiast with a couple of years of serious digital shooting under my belt, I doclaim to be an expert with High Dynamic Range (HDR) imaging or photography in general. But I have fun in the field, enlearning as much as I can about the art and science of photography, and have produced some images that are personrewarding, as well as enjoyed by others. I currently derive particular satisfaction from working with stitched panoramas takesunrise or sunset, printed on roll stock.Late in 2005 I began adding HDR processing into my workflow. This was done to gain greater access to the tonality presenwide and dramatically lit vistas. I mostly bypassed the usual digital exposure blending route as it seemed labor intensalthough I know the technique can produce results. Naturally I posted several HDR images to Naturescapes.Net (NSN), several people expressed interest in the technique used to create these images. At the request of the NSN editorial teamorganized my learning and thinking about HDR, and this article is the result.For at least a few of those who read this, I hope for two things. First, I would like to add some fuel to your own creative fireworking with HDR images. Second, I hope you will post your results and share questions, ideas and techniques that workyou. There is still much to learn as this new imaging capability, its tools, and our creative use matures.

The SituationSay I have an image that looks like this:

I captured the image at sunrise, a great time to be out in the field. My senses soaking up everything before me, I tripped shutter, hoping to capture an image that would evoke wonder and appreciation a hint of the moment.Back at my workstation, I eagerly began sorting through the captures. However, despite the presence of a fair amoundramatic light and lots of interesting tonality and detail across the original scene, images like the one above just do not evothe experience. The clouds lack drama, detail and color; portions of the sky are far over-exposed; distant trees have turned muddy blur; and the ice does not reveal the snappy surface detail it showed in the early morning glow.


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Of course, I realized while out shooting that there was a lot of contrast (or dynamic range) in the scene, and that the camcould only capture a small subset of that range. So I shot different exposures (bracketing), some optimized for the sky, sofor the foreground ice, others for the far, shadowy trees. Not surprisingly, none of these single images really grabs me ureview.I considered that I could use a graduated neutral density filter in situations like this. At capture time, these filters are useblock some light in the brightest part of the frame, often the sky. This effectively expands the captured dynamic range by onthree stops. Of course that does not help now, with images that I have already taken. And considering the irregular line of mountains and the dynamic range reflected across the ice and water, I am unsure if filters would be workable for this scene.

Using an exposure blending technique, I could combine several digital files with different exposures of the scene. It seeworth trying, so I put in some effort with three exposures taken across a 4-stop range using automatic exposure bracketThe images are layered, luminance masked and blended in Photoshop CS2, together with some curves and contenhancements. This produced the following image:

This is a definite improvement, and with more work I could fine tune this image further. For example, some ghosting inmoving clouds could be cloned or masked out, more work with contrast and curves could increase the drama in the clousome selective saturation or white point adjustments could improve the whites of the ice and snow, and so on. The exposblending technique is used to good effect by many photographers, but it can mean a lot of work. And I feel it will leave wanting more from this image.

A New(-ish) ApproachEven with all of the above techniques, plus a lot of effort, the results may not have maximum impact. Perhaps you, like mhave wondered if there is another way. Enter High Dynamic Range (HDR). HDR imaging has been around for at least a couof decades, but has been popularized more recently by new software tools. Using one such tool, the Photomatix Pro HDR processing application, I tried again with the example image. On the same thbracketed exposures, I can produce this image:


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This result better represents the feeling I had at the scene, represented by the title Stormy Sunrise. As a bonus, creating image required no use of filters in the field, and minimal fine tuning work in Photoshop. The heavy lifting was done by tmapping, a process of converting an HDR image back into an 8-bit or 16-bit image file that can be worked with convention(as the HDR image itself can not). In total it took less than 30 minutes of processing time after converting the RAW filesignificantly less time than for the blended exposure version of the image, which honestly still needs more work.The HDR image reveals more of the original scenes drama than does the exposure blended version. More detail is visthroughout the sky, mountains and ice, in large part due to what are called local contrast enhancements adjustments temphasize tonal transitions and details within a very small space rather than strictly preserving the overall relationship of brand dark tones across the entire image. Overall contrast and color tone is more expressive.As for the original single frame with its middle-of-the-road, neutral exposure? While it could be tweaked, it is not remotely insame league for expressing the impact of the original scene.To see how you can use HDR as part of your workflow to create images with a large dynamic range, read on! This article gia landscape photographers view of the theory behind HDR, describes how to capture the input images, and shows how to two popular HDR tools: Photoshop CS2 and Photomatix Pro. It will also show how to use these tools to process both sinframes and stitched panoramic images.

2. What is HDR?Before getting into the tutorial, it would help to have some terms of reference. In brief, dynamic range (DR) is the rangeluminance values from the darkest to the brightest. The original, real-world scene has a certain inherent DR which mayquite large a ratio of 100,000:1 or more as DR is measured. Your eyes can perceive a subset of the scenes DR (ab10,000:1), while your camera can record a smaller subset than your eyes can see perhaps 400:1 for a DSLR. The DR omonitor or a printed photograph is smaller yet.High dynamic range (HDR) in photography means representing the full range of tonality present in the scene with hperceptual faithfulness. Most HDR techniques currently use software to combine several different exposures of a scene intsingle file that maps the full range of luminance at every pixel. This HDR image is then processed in various ways dependon the ultimate usage. For most of us this means tone mapping the HDR image into a 16-bit or 8-bit digital file such as a JPor TIFF image.


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If this is enough definition for you and you want to get into the part that shows how to get things done, feel free to skip aheathe next section on shooting technique. The rest of this section provides the details of what HDR is for those who prefeknow what before getting into the how.Key points covered in the rest of this section:

Definition of HDR HDR vs. 8-bit or 16-bit file formats

Capturing HDR images

What is HDR good for?Definition of HDR

Dynamic range (DR) is a fairly generic term used in a variety of disciplines. As described above, for our purposesphotography, DR is the range of luminance values from the darkest to the brightest . The DR of the real-world scenfront of you is the range of darkest to brightest portions available to your eye, film or imaging sensor. The DR of a camerthe subset of the scenes DR that can be captured without being clipped on the highlight end, or reduced to noise or outrblocked up on the shadow end. Conversely, the DR of a monitor is the luminance range it can display from black to white. High dynamic range (HDR) must mean a lot of DR. But how much is a lot? The standard unit for measuring luminanccandelas per square meter, or cd/m2. You may have seen this unit used in monitor specifications. According to the FAQ

www.hdrsoft.com (the web site for Photomatix Pro), the luminance of starlight is around 0.001 cd/m2, that of a sunlit scenaround 100,000 cd/m2, [ and] the luminance of the sun itself is approximately 1,000,000,000 cd/m2.Without getting into the debates about which medium truly has precisely what DR, this chart summarizes some rule-of-thuDR values for different stages of dealing with a scene:

One clear conclusion from this chart is that the experience of seeing the original scene, then capturing it, to reproducing itothers to see, is one of progressively losing DR. DR lost at capture time is gone for good, as it can never be regained after tpoint. If it can be captured as close as possible to what was present in the original scene, then perhaps something can be dto present the image to viewers with a better interpretation of the source scenes tonality and detail.Loosely speaking, then, HDR is the ability to capture and represent the full DR found in a scene with high perceptaccuracy and precision. To pin it down further, we need to look at digital file formats and how they represent luminavalues.Norman Korens web site has a good discussion of some of this information, specifically DR from digital capture throu

reproduction on screen or in print; see www.normankoren.com/digital_tonality.html . Sean McHughs web site also has a logood information about this subject; see for example www.cambridgeincolour.com/tutorials/dynamic-range.htm .

HDR vs. 8- or 16-bit FormatsAn HDR image is represented using what can be considered a 32-bit per RGB channel format. The 32-bit numbers are deci(or floating point) values, not integer values. The format records the luminosity of every point in the source scene, regardlof its level of brightness. There are several different HDR file formats in existence, including Radiance RGBE and Open-EXEach format encodes image data in a different way, with corresponding advantages and disadvantages.

STAGE DYNAMIC RANGE STOPS

Typical outdoor, sunlit scene 100,000:1 or more ~17 EV

Human eye 10,000:1 ~14 EV

Film camera up to ~2000:1 ~11 EV

Digital camera typically ~400:1 ~8.5 EV

Good computer monitor 500:1 to 1000:1 9 - 10 EV

Typical photo print 100:1 up to 250:1 7 - 8 EV


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Radiance RGBE and Open-EXR seem to be fairly dominant in terms of support in various applications. Both are supportedthe tools discussed in this article. However the applications implementations of the formats are not necessarily compatible one another.Radiance RGBE was developed in the late 1980s by Greg Ward as part of his Radiance imaging application, while Open-Ewas developed by Industrial Light and Magic and published as an open format around 2002. The key trade-off between the formats appears to be that Radiance RGBE covers a much larger DR than Open-EXR, while Open-EXR offers more precisthan Radiance RGBE. In truth both formats likely represent DR overkill for landscape shooting and most other formsphotography. But at least they provide the elbow room that is lacking in 8-bit and 16-bit formats.The image formats with which we are all familiar, such as the JPEG and TIFF, supply a relatively small number of luminavalues for each of the red, green and blue channels. Here is how the 8-bit, 16-bit, 32-bit Radiance RGBE and 32-bit Open-Eformats break down:

Note that I am glossing over a few things here since this is not primarily a technical article. For example, the Radiance RGand Open-EXR file formats do not actually use 32 bits per channel in the file saved to disk, for storage size reasons. Also DR ratios are not apples-to-apples comparisons since the darkest and lightest luminance values vary widely. I am also attempting to address color space or gamma encoding which affect the image data encoded within the file. For minformation on this topic, see the paper High Dynamic Range Image Encodings by Greg Ward.There are several pragmatic benefits of the HDR formats over the 8-bit and 16-bit formats. When the source scene exceeds the luminance values the 8-bit and 16-bit formats can represent on either or both ends of the range, the DR is clippShadows below the low end of the range block up to black (luminance value 0), while highlights above the top end of the ranblow out to white (luminance value 255 or 65,535 depending on the format).In addition, luminance values within the representable range must snap to the integral values within the formats range. This no way to represent a luminance value of 2.3 or 2.9, so these values both may be represented as 2. Thus, in addition torange being limited potentially on both ends of the spectrum, the values it can represent are not necessarily very precImage processing functions that affect luminance may introduce increasing levels of error.Finally, the integer luminance values are not mapped to the actual light from the source scene in a linear fashion. Some pof the scenes tonal range are compressed into fewer values while other parts of the scenes range get a larger block of valuThus the non-HDR format effectively applies a tone curve that biases the DR. Compressing part of the DR can cause isslike posterization and banding when image processing is done later.In contrast (no pun intended), the HDR formats do not impose a practical limit on the DR that can be represented. (There limit, just not one that a landscape or indeed almost any type of photographer is likely to hit.) This is not only because Huses more bits to represent a wider range of luminance values, but also because these bits represent floating point valrather than integer values. Thus HDR can represent very small and very large luminance values, such as 0.00001 1,000,000,000 within the same file. And because the HDR formats have decimal precision, they can represent luminavalues such as 2.3, 2.9 or 2.543635. Image processing functions that affect luminance introduce fewer errors.Finally, the various HDR formats luminance values correspond linearly to the amount of light present at each point. There iscurve applied to compress part of the DR into a limited span of values. Posterization and banding are unlikely to occur wworking with HDR files.All of this sounds like great theory as long as there is a way to actually capture this image data and get it into an HDR form

Capturing HDR Image DataThe ability to capture the source scene luminance information is a critical point. Just because a file format has a latheoretical maximum DR, does not mean that the image data contained in the file truly spans that DR. For example, a DSRAW file contains imaging sensor data that typically has 12 bits of total information, for maximum DR of 4095:1. (Very digital cameras currently capture more than 12 bits of data at the sensor.)

8-bit 16-bit 32-bit Radiance RGBE 32-bit Open-EXR

Maximum DR 255:1 65,535:1 1x1076:1 107,000,000,000:1

Luminance value range 0, 1, 2, , 255 0, 1, 2, , 65,535 0, 1x10-38, , 1x1038 0, 0.0000012, , 65,000


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Converting the RAW file to a 16-bit TIFF does not somehow expand the captured DR upwards. The RAW conversion proccan not manufacture more luminance information than was actually contained within the RAW data. While the theoremaximum DR of a 16-bit TIFF is 65,535:1, the real maximum DR of the image data it contains is far less. In fact it is exactly same as the original RAW image data, 4095:1 at best. The TIFF data takes up more space but it does not contain any eluminance information.In fact, the DR of the data is even more limited, since the usable luminance range is only a subset of the original 12 bitRAW image data from the sensor. A typical DSLR may have around 8.5 EV of usable DR, say about 400:1. (Read some of Askeys current DSLR camera reviews at www.dpreview.com to see how real-world DR performance works out with cur

digital cameras.) DR typically is lost in the shadows when image detail becomes indistinguishable from noise, and it is losthe highlights when sensors cease to respond to brightness and just blow out to white or to incorrect colors due to uneqclipping of the RGB channels.So how can HDR image data be captured, assuming you are not using a camera such as the Spheron SpheroCam HDR tcan natively capture HDR images of 26-stops? As stated above, the human eye can perceive a DR of about 10,000:1 isingle view. But the eye has a useful range greater than that think of what you can see in bright daylight versus at night wyour vision night-adjusted. The eyes DR is like a sliding window of perception that can be moved across scenes from very dto very bright, taking in a certain amount of DR as a subset of a much larger operating range.A camera is the same in this respect. As stated, a good DSLR can capture a range of perhaps 8.5 stops of luminance in image, or about 400:1 of DR. By altering the exposure to take images that range from very under-exposed to very oexposed, a series of slices can be captured across the source scenes DR. These slices will form a much larger DR w

combined together in software.So the mechanism for capturing HDR image data comes down to shooting multiple exposures of the scene. For best resthe exposure series should cover the entire DR of the scene, properly exposed, from shadows to highlights. With this serieexposures and software to process them, a single HDR image file can be produced. There is some technique involvedcapturing and processing the images, described in the rest of this article.

What Is HDR Good For?Before getting into the shooting technique section, some final thoughts about the what of HDR what kind of photographHDR good for? Until recently, HDR has found most of its use in synthetic imaging applications (ray-tracing, 3D scene modeland computer generated imaging such as gaming) as well as video post-production work.In still photography, HDR can be used to create images from scenes that possess a broad range of tonal values from shadoto highlights. This situation is typical to landscapes and other outdoor settings, since sunlit scenes may have a DR of 100,00or more. Besides traditional landscapes, other outdoor images that might benefit from HDR include those with significhighlights such as strongly lit reflective surfaces. I have seen some great HDR images of cars for example, where the mand glass have incredible pop. HDR also can be applied to good effect with indoor or outdoor architectural photograpwhere natural and artificial light combined with shadows can produce a wide DR over various materials and surfaces.Naturally, just because a scene contains significant DR does not mean that it all must be reproduced. We have all seen mstunning landscapes or other scenes where the photographer selects exposures to clip highlights or block up shadows in a that enhances impact. There is no guarantee that HDR technique by itself can produce a better interpretation of a giscene. For decades, photographers have made artistic decisions about what is truly important, composing and exposingthat, and letting the rest go. HDR provides another tool to use, but the artistic judgment remains as important as ever. Michael Reichmann said in his introductory luminous-landscape.com article on HDR, I fully expect to see some really si

not downright ugly [HDR] images in the months ahead.)Since HDR technique involves taking several exposure bracketed images and combining them into a single file, it works bwith relatively static situations. If there is motion within the frame such as wind blowing the branches of a tree, or anskater moving across the field of view the software will create ghosts or blurriness. Interestingly, moving water does necessarily pose a problem to HDR tools they may introduce a pleasing blur to the water. Landscape compositions obenefit from the inclusion of water elements; feel free to experiment with HDR when moving water is in the frame. Personally I use HDR for landscape and scenic shots including both single frame images and multiple frame stitcpanoramas. This tutorial shows examples of both. Classic cases are sunrises and sunsets. Shooting panoramas at sunrisesunset unavoidably introduces a challenging amount of DR in part because of the large field of view. HDR is a nattechnique to use for many such scenes, and this is why I first began experimenting with the process.


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Even with single frame images, I use HDR where the sky has a lot of interesting cloud formations with detail and tonality thwant to capture, without giving up detail in the middle or foreground areas that are much darker in tone. I am also startinguse HDR for winter scenes involving irregular mountainscapes of ice, snow, trees and rock. Here, I do not want to blow out highlights in the ice and snow, while the darker tones of rocks and trees may contain a lot of detail that I want to show as we

There are many other possible uses for HDR. The rule of thumb I would suggest is this: if you have a scene with a wide raof tonalities, and there is engaging detail across both shadows and highlights that supports the vision you wishcommunicate, then HDR may be the right technique for the job. This is especially true if irregular form in the subject maprohibits use of filters, and the DR to be dealt with would involve an excessive number of layers and adjustments using

exposure blending technique.What examples can you think of? One place to start is thinking about those scenes containing a large tonal range that have so far struggled to capture to your satisfaction. Even if you have successfully used exposure blending techniquesPhotoshop, you may find HDR to be a valuable approach in similar situations.

3. Setting Up the Input ImagesBefore you can create an HDR image you must first capture and prepare the input images that will feed the process. As thwill be several images to process even without getting into stitched panoramas, some points on setup are worth considerinproduce the best source material you can for the software to handle later on.The recommendations in this section may sound excessive, and certainly you can work more casually in some circumstancMy own goal often is to create images rich in detail that will be printed on large media, possibly several feet in length in case of stitched panoramas. Quality issues not visible in online image posts or small prints become more readily apparent, take steps to avoid them from the beginning.The condensed description of setting up is to first get stable support for the camera. Multiple exposure blending techniqueseasier to use and produce higher quality results when software does not have to attempt to compensate for alignment errorbetween frames, caused by camera motion. Then set up the camera so that the only settings changing during the imsequence are the specific exposure changes you need to capture the target DR. Once those elements are configured, determine the number of images and exposure interval you want to shoot, and shoot

sequence. Back at the workstation, use a consistent RAW conversion to process the images for input to the HDR tool.

If you are already experienced in these areas, feel free to jump ahead to the first HDR tutorial section covering PhotosCS2. The rest of this section provides more background on setting up and capturing the image sequence for those readwho may be newer to this type of photography. Key points covered in this section:

Physical setup Camera setup Determining the exposure sequence RAW conversion

Single frame scenes vs. multi-frame stitched panoramas

Physical SetupStable physical support of the camera is relatively important. Because the HDR software needs to map the luminance valueeach corresponding pixel from the series of input frames, it is important to have the images lined up with each other as cloas possible. Both HDR tools described in this tutorial have functions to align the input images if they are slightly off. Howeregistration errors can still occur if the camera moves too much between images. This is particularly a problem if the imagplane rotates vertically or horizontally, as this will cause perspective shifts in between bracketed frames for which the Hsoftware cannot compensate.


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If the shutter speeds across the bracketed exposure range are all relatively fast and your hands are steady, you may be ablhand-hold the camera. It is a simple way to start trying HDR whether or not you already have a good tripod. As long as you shooting only a single automatically bracketed sequence of images that does not require manually changing any camsettings, you should be able to at least get at least some good approximations of what HDR can do for you. The best way to avoid alignment problems is to have the camera mounted on a stable tripod and head. Depending on hslow the shutter speed is across the range of exposures, and whether there are ambient sources of vibration such as wind, may need to put more or less effort into stabilizing the camera support. Most of these measures are the same as for any loexposure shooting:

Consider lowering the tripod legs. If that would block the shots, then hang a weight from the center column hook if this one.

Lay a bean bag over the camera and lens to damp vibration as long as this does not block any sensors on the cambody.

Do not let the camera strap flap around in the breeze. Remove it, or wrap it securely around the tripod. Shoot with a remote release rather than pressing the shutter button directly, so you do not vibrate or misalign

camera. If you do not have a remote release, you can try using the camera's self timer (often available with 3 or 10 sec

delays). The delay allows time for vibrations caused by pressing the shutter button to damp. Be on guard with tthough, because the timer also will significantly increase the elapsed time needed to capture all frames in the expossequence. If the light or any subject elements are changing, blurring and ghosting as well as exposure inconsistenccan result, especially for multi-frame panoramas.

If you are manually changing exposure settings to create your bracketed sequence, or are directly pressing the shubutton on the camera, do so carefully. Even minor shifts in the camera's orientation can create registration errors latethe HDR software.

If shutter speeds are slow, enable the mirror lock-up function on the camera if it has one.Camera Setup

Some basic camera settings also need to be determined. Most fundamental is the number of images and exposure intervathe sequence whether taken by automatic bracketing or manually changing exposure between shots. Your priority iscontrol the camera. Regardless of how many exposures you need, put the camera in manual exposure mode and select eexposure (or each base exposure if auto-bracketing) by hand. In particular you do not want the aperture or ISO settings bechanged.Most modern cameras have an automatic exposure bracketing function. Canon non-professional DSLRs, which I use, can ta sequence of three images bracketed up to -2 and +2 EV around a base exposure. (On the high end of the scale, the Canoseries cameras can be set to bracket up to seven shots at +/- 3 EV. Nikon professional DSLRs like the D2X can bracket unine shots at +/- 1 EV.)Using one of these cameras in the simplest way, you would select the auto bracketing function for +/- 2 EV (or greatesupported), select the base exposure, and then capture three images to have your set of input frames. This is a convenient fast way to begin working with HDR.Why immediately jump to +/- 2 EV? The goal is to capture a wide DR. The source scene easily may contain enough DRexceed what you can record in three images at +/- 2 EV. This might amount to 12.5 EV in total for a typical DSLR, or sroughly 6000:1. Recalling that a well-lit outdoor scene may have a DR of 100,000:1, clearly 12.5 stops is not enough to capt

everything from shadows to highlights. Thus if you limit yourself to a small number of exposures, you want to record as mDR in them as possible. Stepping at 1 EV likely would be insufficient. See the next section for more about choosing exposure sequence.A side note: The Photoshop CS2 help entry on its Merge to HDR function states, In general, dont use your cameras abracket feature, because the exposure changes are usually too small. This may apply to digital point and shoot camehowever all DSLRs should support exposure stepping up to 2 EV or more when auto-bracketing.If you shoot digital, I recommend that you shoot RAW for HDR work. The point is to capture DR. If you shoot JPEG out of camera, some amount of DR has already been sacrificed within each given image as the camera compresses the sensor d(usually 12 bits) down to 8 bits. Further, the camera applies a tone curve, compressing shadow tones in order to fahighlights. Since I personally find that shadow tones contribute a lot to my HDR work, I would not like to sacrifice them. Finaintroducing JPEG compression artifacts (however slight) into the HDR process may degrade image quality.


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I understand there are arguments in favor of shooting JPEG. Typically the benefits raised are to get more continuous frammore storage capacity, and potentially minimize subsequent workflow effort in RAW conversion. However, in my opinion, thfactors are not particularly relevant for HDR work, especially landscape photography as discussed here. However, if you wto do so, you can shoot JPEG images and process them using the HDR tools described in this article. For most other settings, the rule of thumb is to keep the camera in manual mode for each function. This ensures that noththe camera does will vary the image sequence in a way you do not purposely intend. When shooting the sequence,

essentially want only the exposure changing to capture the range of tonality you need. Everything else should remain consto prevent more work later, or loss of image quality.Here are a few final points:

For digital shooters, set the ISO to as low a setting as conditions will allow. Any noise introduced by higher ISO mayexaggerated by the HDR tone mapping process. If the source scene contains moving elements that blur at sloshutter speeds, you can try increasing ISO to get faster shutter speeds, and take your chances with noise reductools later.

Ensure white balance stays the same across the images fed into the HDR process, since it is important to preseconsistent color. If you are shooting RAW, leave the camera set for automatic white balance and later convert all inimages with the same white balance setting. Or you can set a specific white balance in the camera and adjust late

required.

If you are manually bracketing any portion of the exposure sequence, use manual focus. If auto-focus is left enabledifferent focal point may be selected between one frame and the next. This will create image combination problems tcannot be resolved by the HDR software.

Determining the Exposure SequenceHow do you know what that best exposure sequence is? Clearly this depends on the source scene. It also involves how mshadow and highlight detail you decide to capture high DR does not necessarily mean all the DR there is. Finalldepends on how many images at what exposure interval you choose to shoot with your preferred bracketing technique.Examine the scene looking for shadow and highlight areas. In those areas, use an external light meter, the cameras smeter if it has one, or some test shots consulting the histogram (if you shoot digital). This will give you some potential expos

values on each end of the DR spectrum that you ultimately need to capture. You will then have to do some quick exposmath to figure out how many frames at what EV stepping you will need to capture the scene.You can cover the scenes DR in fewer exposures by stepping at a higher EV interval, but it is not desirable to use a larinterval than 2 EV even if your camera supports it. Stepping by 1 EV may be preferable depending on the HDR tool. As wany software function that is interpolating reality between one recorded point and another, more data points sampled clotogether produce better and smoother final results.For example, if a given scenes highlights meter at 1/2000s at your chosen aperture and the shadows meter at 1/4s, thenexposures taken at an interval of 1 EV would cover the range. You could possibly eliminate one or two of the exposures onfar ends of the range if you shot RAW and can depend on your camera for good shadow and highlight detail capture. Fexposures shot 2 stops apart also would do the job, at the risk of providing a bit less smooth result. With only a little effort, you can extend the automatic bracketed approach described in the previous section to cover five shat a 2 EV interval, even if your camera is limited to a three shot burst using auto-bracketing. Enable auto-bracketing at +/- 2 and select a good central exposure based on the cameras meter. Prior to shooting, dial in -2 EV exposure compensation shoot three frames. Now quickly dial up to +2 EV compensation and shoot three more frames. At this point you haveframes, two of which are exposed the same; discard one of them later. This leaves you with five frames covering -4 to +4 roughly 16.5 stops, which approaches DR of 100,000:1. If your camera supports exposure compensation of +/- 3 EV, you use the same technique without throwing away one of the exposures. You end up with six frames covering -5 to +5 EVabout 18.5 stops of DR.Here is an example showing the same scene processed twice via HDR, from two image sequences taken seconds apart. first sequence contains three exposures covering -2 to +2 EV, while the second contains five images covering -4 to +4 Both sequences have the same central exposure, and both use an interval of 2 EV. Both were tone mapped with the saparameters in Photomatix Pro, with no further retouching done.


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In this case, there is not much difference between the resulting tone mapped images. The one based on the five imasequence is a little more contrasty due to slightly deeper blacks. For that reason it has slightly better definition in the clouBut on the whole the two are close, and the three exposure version likely could be touched up to become even closer. For scene three exposures at +/- 2 EV were sufficient to capture the available DR. In part this is because the sun is not direwithin the frame, and there are no extreme shadows or highlights.Outdoor scenes can have DR of 100,000:1 or more, but many have less. Learning to read the scene can reduce the needmetering and calculating a longer exposure sequence. Likewise, gaining that experience improves on the just shoot a buof exposures and hope for the best approach.Note that by shifting the exposure range, for example by moving the base exposure up or down when using auto-bracketyou can bias the eventual results towards the darker or lighter tones. If manually bracketing, you can choose to leave off soof the exposures on the bottom or top end of the range. You can also shoot the exposures and then simply not include them

the HDR input. This lets you adjust the mood, block up some shadows or clip some highlights for creative reasons. Some experimentation and experience with a variety of scenes will give you a baseline for the number and steppingexposures you need to produce pleasing results. So far I have been using three or five frames shot at a 2 EV step and habeen happy enough with my results. With only three frames, some highlights and shadows are lost but often even this smasequence produces pleasing results.

RAW ConversionFor those who shoot in RAW mode, another setup issue that must be considered involves how to configure the Rconverter. There are numerous RAW conversion applications out there, each with its strengths, weaknesses and proponeWhich one you use is not really that important for the purposes of HDR processing. What is more important is how you do conversion.

Three Image Sequence Five Image Sequence


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One key factor, as previously indicated, is to ensure that all of the images in a sequence are processed with the same wbalance. Tone mapping HDR images is challenging enough without throwing different color balances into the mix. Picrepresentative exposure from the input sequence, get its color temperature and tint right, and then apply the same settingthe entire sequence. Do the same with any other color enhancements that you make in the RAW conversion. Many RAconverters with strong workflow support make it easy to copy settings across a series of images.The main point of HDR tone mapping is to set levels, apply a tone curve and make contrast enhancements to the final imcontaining DR information compiled from all input images. Therefore it is best to avoid making any significant exposchanges to the RAW files during conversion. If the initial exposures were set up reasonably well, most of the changes that might make to an individual input image will be trumped by the changes later made during HDR processing.The main reason you might be tempted to adjust exposure in the RAW conversion is to shift the entire input sequence updown, to bias the final tone mapped HDR image. As with many digital processing functions, use a light hand. This is especitrue if you are increasing the exposure as this will bring out noise that the HDR processing may emphasize further. Howebefore even trying this, recall that shifting the exposure during RAW conversion can not bring out any more real luminainformation than existed in the original RAW data. Since the HDR image is going to include all of that data by mapping all ofinput images, it may be less work to perform a straight forward RAW conversion, process and tone map the HDR image, then make final exposure adjustments to the end result.

Single Frame Scenes vs. Multi-frame Stitched PanoramasFor stitching multiple frames to work well as input to HDR processing, it is even more important to ensure that camera suppis stable and all non-essential camera functions are on manual as recommended above. Stitching software can compensatea number of things that are not quite synchronized between images across the field of view. However, the more work software has to do, the more the quality of the final product may be jeopardized. Keeping in mind that HDR tone mapping mexaggerate undesirable details in the input images, you do not want stitching artifacts to be introduced and subsequentlymagnified.One other thing to consider when planning for both stitching and HDR work on an image sequence is the shooting time facIf you are shooting outside at sunrise or sunset for example, the light may be changing relatively quickly in your critical shoowindow. The more fiddling you have to do to capture the sequence across the field of view, the more likely it is that the lquality may change perceptibly between the beginning and the end of the sequence. It is also possible that moving elemesuch as clouds or water will shift enough that seamless processing will be made more difficult.Some examples of things that can help decrease the time taken to shoot the entire sequence include:

Use automatic exposure bracketing with a larger EV interval to speed up the capture of exposures taken at each rota

point. Fewer manual exposure changes means less time taken. Make sure you have chosen a good focal point that works across the field of view, and disabled auto-focus on the le

You do not want to wait for auto-focus to hunt for a new lock at each rotation point. Use a lens focal length that gives a wider angle, which may cut several one or more rotation points from the sequen

You can crop later for compositional reasons if you do not mind losing the resolution. The risk here is gettingincreased amount of rectilinear distortion with some lenses.

If you normally shoot vertical frames for stitching, consider whether the composition will support horizontal shots insteThis will cover the field of view even faster.

Ensure that your exposure sequence is not filling up your camera buffer faster than it can write. Find ways to shfewer exposures, in order not to be waiting on the camera while the light is changing in front of you.

4. Processing a Single Frame HDR ImageOkay, enough theory! In this section, two HDR workflows will be shown that produce a single frame (i.e. non-stitched) fimage from several input images. One workflow is based on Photoshop CS2, then other on Photomatix Pro. In both cases, example will show how to initially create the HDR image file, and then how to tone map it into a final image.Key points covered in this section:

Tools used Workflow 1 PS CS2 Workflow 2 PS CS2 + Photomatix

Comparison of workflow results


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The examples will produce a tone mapped image from this sequence:

The base image was shot at 1/15s, f/22, ISO 100. The camera used was a Canon EOS 10D with Sigma 12-24mm f/4.5lens zoomed to 13mm. The camera was tripod mounted, and the shutter was tripped with a remote release cable. exposure sequence was taken using auto-bracketing at an interval of +/- 2 EV. The images were shot RAW and converte16-bit TIFF files using Rawshooter Premium at default settings except for +20 detail, +10 saturation and +3 vibrance.

Tools UsedThe example screenshots in this section are taken from a desktop workstation (AMD Athlon 64 X2 4800+ dual core systwith 3 GB of RAM visible) running Windows XP SP2.Application software versions include:

Rawshooter Premium 1.0.3 build 77 Adobe Photoshop CS2 9.0.1 Photomatix Pro 2.2.3

Workflow 1 Photoshop CS2The first workflow shows how to produce a tone mapped HDR image using only the tools found within Photoshop CS2. Atmoment, CS2 probably can be considered the preeminent tool for image processing and it is the workhorse applicationmany photographers. When CS2 was introduced, it contained new support for HDR image processing and so it is likely to

the first point of contact with HDR.There are two key functions to use. The first is Merge to HDR, accessed via the File>Automate>Merge to HDR menu in Cor the Tools>Photoshop>Merge to HDR menu in Bridge. This function is how you initially combine several images takedifferent exposures into a single HDR 32-bit image file.The second function is HDR Conversion, accessed via the Image>Mode>16 Bits/Channel menu in CS2 while a previocreated HDR 32-bit image is open in the editor. Dropping the image mode below 32-bit triggers CS2 to get you to specify hto tone map the HDR image, in this case to get it to fit within a 16-bit DR. (HDR Conversion can also be accessed by droppthe image mode to 8-bit.)

CS2 Merge to HDRTo get the first example rolling, the first thing to do is process the above three example images into a single HDR file. With Copen, select the Merge to HDR function via the File>Automate>Merge to HDR menu. This brings up the following panel:

0 EV (base image) -2 EV +2 EV


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With the drop-down list showing Files, I have browsed to my source images and included the three of them. The drop-docan be used instead to select Folder which permits adding an entire folder of images, or Open Files which will add the currently open in the editor.The only other control is a check-box to enable alignment of the input images. I recommend selecting the check-box unthere is a specific reason not to. While it will add processing time, it will help ensure that any minor image alignment erpresent in the input images will be eliminated, or at least minimized. If you are sure your images will match 100%, or are worried about ghosting and blurriness from registration problems, you can uncheck the box to speed up processing.Clicking the OK button kicks off the first stage of processing and produces a single HDR image. This process takes 15 seconds on my workstation for this example. Most of that time is spent aligning the input images. Once alignment and inprocessing are done, a second large window is displayed:

This window shows a preview of the HDR image, incorporating the full DR of the original sequence. Since your compmonitor is essentially an 8-bit device, and no tone mapping has yet been done, you are able to see only a limited subset of full DR at any one time.The histogram on the right hand side of the window gives a snapshot of the total DR of the combined image. Each red mark on the horizontal axis of the histogram represents about 1 stop of DR. The white point slider beneath the histogcontrols the subset of DR displayed on the monitor. Adjust the slider left and right to examine detail in different tonal areathe image. Using the histogram, slider and image preview, it is quickly possible to tell where the interesting image detail and roughly how well the merge worked (including the image alignment).Down the left hand side, thumbnails of the input image are shown with an estimate of the relative exposure of each. Eimage also has a check-box controlling whether that images information is included in the merged image. You can toggle

individual image on and off to roughly determine the contribution its data makes to the overall look.


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Be sure to leave the bit depth drop-down showing 32 Bit/Channel in order to generate an actual HDR image. Selecting 168 bits will immediately drop the DR of the merged image by clipping shadows and highlights to fit the selected bit depth, bason the position of the white point slider. When 32-bit is selected, the position of the white point slider does not affect the sadata in any way, but the sliders position will be remembered the next time the HDR file is opened.The size of the preview can be adjusted using the zoom controls at the bottom if you need to examine some details mclosely. When the input images have been selected and the preview examined to your satisfaction, click OK and the Himage will be generated. This process takes only a few seconds. At the end, the generated HDR image is open in CS2, reafor further work:

Before doing anything else, you can save the HDR image in case you want to come back to the pre-tone mapped version later date. Several formats are available to choose from, including Radiance RGBE (which uses the extension .hdr) Open-EXR (which uses .exr). This example saved as an .hdr file runs about 18.5 MB in size compared to about 36 MBust one of the input images in 16-bit TIFF format. In .exr format, the HDR image comes in just over 13 MB in size. Ftechnical comparison of the HDR formats, see Greg Wards paper High Dynamic Range Image Encodings linked at the of this article.While many CS2 capabilities are not available with HDR files, including layers and most of the tools, some filters and a other functions can be used with 32-bit files. Personally I am not sure what adjustments I would wish to make at this pogiven the lack of layers and the inability to directly see the full image at once because of its expanded DR. Perhaps 32image processing will continue to be an area of innovation in future versions of Photoshop. For now we will simply move ontone mapping the HDR image into a 16-bit file.

CS2 HDR ConversionIn some ways everything up to this point really has just been preparation. Now it is finally time to get a concrete result abit image that can be edited, displayed or printed just like any conventional image. However, the tone mapped HDR imageshow an interpretation of the original scene in a way that is difficult (perhaps even impractical) to achieve using other me

involving comparable time, effort or cost.Following the above actions, CS2 is sitting with the merged (and saved) HDR image open in the editor. To perform the t


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mapping process, you trigger the HDR Conversion function by selecting the Image>Mode>16 Bits/Channel menu item. Tbrings up the following panel:

CS2 permits tone mapping an HDR image using four different methods, available in the drop-down list of this panel. The three methods are not satisfactory, at least for the type of HDR images I work with. While easy to use, they may produce usresults only in limited circumstances. This is because they provide simplistic global effects, with few or no control points,compressing the DR of the 32-bit image into the target bit depth.As you select each method, the HDR image open in CS2 will show a preview of what the conversion will look like. Feel freexplore these methods on your own HDR images, but they will not be discussed further in this article.

The interesting conversion method is called Local Adaptation and this is what I will focus on. When you select this metfrom the drop-down list and also click the small arrow icon labeled Toning Curve and Histogram, the HDR Conversion panow looks like this:

This provides a familiar looking curves control, with some differences from the standard curves adjustment tool. The Load aSave buttons perform a familiar function. A custom set of parameters can be set up for an image, saved (using the file na

CONVERSION METHOD DESCRIPTION

Exposure and Gamma Two sliders for exposure and gamma values. Lets you manually adjust tbrightness and contrast of the HDR image.

Highlight CompressionNo controls. Compresses the highlight values in the HDR image so they fall witthe luminance values range of the 16-bits-per-channel image file.

Equalize HistogramNo controls. Compresses the dynamic range of the HDR image while trying preserve some contrast.


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extension .hdt), and then reloaded as a starting point in future editing sessions. As in other editing panels, pressing thekey (Option key on a Mac) switches the Cancel button to Reset. Clicking Reset returns the entire panel to its default stawhich means the Exposure and Gamma method with its default control values.The panel provides no ability to select just the red, green or blue channels the curve is applied to the entire image becaHDR is about working with luminance, not color. Also, there are no black, gray or white point eyedroppers, nor any automfunctions or freehand curve drawing. The curve can be edited by moving the initial black and white end points, and by addand dragging new points.Editing points on the curve is one of the two main attractions of using this conversion method. It permits direct control overtranslation of the HDR images wide DR into something that will fit within 16 (or 8) bits, and also present a desirable balance

tonality and contrast. Thus editing the curve here is done for the same reason as making a curve adjustment on a norimage.The difference here is that the curve is affecting a much greater initial DR than normal (see the red tick marks of histogram), and will redistribute contrast as well as actually compress the DR when you hit OK. To get the look you want it mbe necessary to do a more than simply apply a bit of traditional S-curve. The greater the DR, the more work you will havdo to prevent CS2s automatic functions from deciding for you how to compress the DR. You may have several tonal regithat you need to adjust in different ways, rather than simply focus on a simple shadows-midtones-highlights break down as wnormal images.Looking at the unfamiliar controls on this panel, first there is the Corner check-box below the curves control. Not available wthe standard curves tool, this check-box controls whether the next point added to the curve creates a smooth change along curve where it joins other existing points, or creates a sharp and angular join. This effect can be used to create a shtransition in the tone of the image at certain levels, rather than a transition that is smoothed out over a broader luminanrange. Again, because this curve potentially must compress the DR by a large margin, you may not have the luxury of maksmooth tonal transitions in some cases. Having a sharp transition can protect tonalities that you have already adjusted fbeing skewed by further adjustments along other parts of the curve.As with the normal curves tool, you can move the mouse cursor over the main image window, where the pointer turns intoeyedropper. Clicking and holding over a point in the image highlights, on the curve, where that image point falls. Dragging eyedropper around on the image, the highlight point on the curve tracks the mouse movement. This lets you target areas of image tone you may wish to fine tune on the curve. The principles of adjusting the curve here are the same as when editing curves in a non-HDR image. Move the bottom left atop right end points closer to the tails of the histogram, to set the black and white points where image data starts to appeThen use one or more points along the curve to adjust its slope. Likely you often will use several points, reflecting the fact you have more than one area of tonal range with significant detail you wish to enhance. Make the slope of the curve stee(more vertical) to increase contrast where important image detail lies. Make the slope shallower (more horizontal) to comprtone where little or less important image detail lies. Remember that the large DR present is going to get compressed insmaller range as a result of this tone mapping exercise, so you may have to sacrifice contrast in some areas that have gdetail in order to preserve detail in other areas.The other main attraction of this panel besides editing the curve is using the Radius and Threshold controls to alter the degof local contrast enhancement performed. As described much earlier, local contrast enhancement increases the contrast wivery small regions of the image in order to enhance the appearance of detail there. Even if you spend considerable efediting the curve, because it is a global effect across the image it is still possible to get areas of contrast that do not work visually. By changing these numeric values, you can exercise a different form of control over the tonal quality of the convers

The Radius control specifies the number of pixels that the conversion function will consider to mean local. A small radsuch as the default value of 16 pixels, means that contrast enhancement is applied in very tight regions across the image. T

will result in hard edged, sharply defined tonal shifts that occur on a small scale. The advantage is that this tends to emphasfine detail. The downside is that it tends to look less natural and over-processed, something that is often levied as a criticismtone mapped HDR images.The range of the radius is from 1 250 pixels. If you set the radius too low, the result will look very flat across much of the fof view because the contrast enhancements have fallen below the threshold that your eye can readily pick up. If you setradius too high, the result often will look more natural in tonality but may seem a little plastic and lacking in fine details tare enhanced by strong local contrast. To determine the right radius for a given image, move the control between extremthat are clearly wrong until you find a region of values that works.The Threshold control also affects the local contrast enhancement, and sets the difference in luminance between adjacpixels for them to be included or excluded from the current local region. Similar to the threshold value in the Unsharp Mfilter, this control relates to edge detection. This is a key part of the human visual systems ability to perceive detail a

apparent sharpness. Changing the threshold value affects how contrasty the resulting image will be.


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The threshold can range from 0.1 to 4.0. If you set the threshold too low, once again the converted image may appear wasout and flat. A lot of the inherent detail will be softened because very slight tonal differences between pixels are enoughexclude some of them from the region being enhanced. However the results will appear smoother and more natural. Setthe threshold too high, conversely, certainly will emphasize detail and make everything stand out. But the results likely wiltoo stark. I often set the threshold somewhere between 0.5 and 1.0.Here is a small selection of images showing the visual trade-offs involved with three settings for radius, and three for threshall using the same adjusted curve:

SETTING IMAGE

Radius 8, Threshold 0.5




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Both of these contrast enhancement settings, as well as any edits you make to the curve, are very much season to tasadjustments. Which values work best will depend on the scene (its breadth of DR and areas of detail) and the interpretatyou intend to show. There is no right answer, although naturally there are many wrong answers.

Threshold 0.1, Radius 50




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In the end I wound up with these HDR Conversion panel settings:

These settings produced a tone mapped image looking like this:

CS2 Final Touch-upA tone mapped HDR image can not be considered final any more than images straight out of the camera or RAW converterfinal. After some consideration and editing, here is my final result:


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The following adjustments were made to the converted HDR image to produce the above image: brightness increased slightly via an adjustment layer black point increased via a levels layer midtones punched up slightly via a curves layer selective brightness of trees increased slightly via a masked layer snowy / icy parts brightened (white point dropped slightly), via a masked levels layer whites of selected small areas of snow and ice increased further via a masked saturation adjustment layer a bit more snap added via a high pass overlay layer at 20% opacity noise reduction and selective sharpening on the base layer

I like the final image a lot more than the one that came straight out of the HDR Conversion. However, I am still not satisgiven the 2 hours of work that went into the image. I like the sky, and the flat gray of the midtones has been minimized. Butice in particular is still not as punchy and detailed as I would like, and a lot of the whites have been compromised.Working things to this point has taken quite a bit of time and involved numerous trials especially with the curve and contenhancement settings in the HDR Conversion panel. I do not know how much better a result could be achieved with additiowork, at least at my level of expertise. In my experience so far with CS2 HDR processing this is not an isolated situatRather, it seems that each attempt I make gets to a certain point and then no further. Depending on the image, this point mbe more or less satisfying, but generally I am left wanting more.Instead of proceeding with more efforts to tweak this image in CS2, I will switch gears and see what results can be obtaiusing a different tool Photomatix Pro.

Workflow 2 Photomatix ProThis second example is based on using Photomatix Pro to do the HDR processing. Other aspects of the workflow

performed as usual, including in my case Rawshooter Premium for RAW conversion and Photoshop CS2 for final touch-up.

Photomatix Pro is a stand-alone application from the French company MultimediaPhoto SARL. It may be new to you, bsuspect currently the Photomatix application is the most popular HDR tool among people actively working with Hphotography. The first version came out in early 2003, and I have been using it since late 2005. A free trial version is availait is fully functional but applies a watermark to all generated images. Note: I have no connection with the company other tbeing a happy customer.


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One advantage of using a stand-alone application for HDR processing is that it does not require you to have Photoshop CWhen I began working with HDR, I was still using Photoshop Elements 3. Using Photomatix Pro, which can import JPEG TIFF images created elsewhere and output 8- or 16-bit TIFF images in turn, was a much cheaper way to get into the gathan purchasing CS2. (In the end I got CS2 anyway, one of the biggest reasons being to work with 16-bit layers, a necessitythis kind of work.) In general, I am a fan of using best of breed tools. CS2 is an incredibly capable application, but it is not best at everything.Another advantage of Photomatix Pro is that it contains several exposure processing functions besides HDR tone mappThe tone mapper used for HDR images can even be applied to a single 16-bit TIFF image. Depending on the DR present inoriginal capture, tone mapping a single image can potentially add some interesting pop. For multi-image processingaddition to an HDR work-up, the images can be run through more traditional exposure blending functions that do not do twork in a 32-bit HDR mode. Photomatix Pro also has some batch processing functions that can automate the processconverting several groups of input images.If you prefer to stay within CS2, the Photomatix tone mapper is available as a plug-in that can be used in place of CS2s oHDR Conversion function. You still use CS2s Merge to HDR function to create the HDR image, however you then use Photomatix plug-in to generate a tone mapped 8- or 16-bit image file. Most of the other Photomatix Pro features are available in the plug-in, including batch processing and the highlights and shadows exposure blending functions.The main focus of this section is to look at how the stand-alone Photomatix Pro application can be used as an alternative H

processing tool. As with CS2, there are two key functions to work with. The first is Generate HDR, accessed via HDRI>Generate HDR menu item in Photomatix Pro. This is how you initially combine several input images taken at diffeexposures into a single HDR image. The second function is Tone Mapping, accessed via the HDRI>Tone Mapping menu itwhen a previously created HDR 32-bit image is open.

Photomatix Generate HDRThe initial step is to process the same three example images into a single HDR file. With Photomatix open, select HDRI>Generate HDR menu item. This brings up the Generate HDR Step One panel:

I have navigated to the folder containing the input images and selected them. There is nothing else to do in this panel, proceed by clicking OK to get to the next step:


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The purpose of this Exposure Values panel is to confirm the estimates the software made about the exposure range of input images. If you shoot the input series with a consistent exposure interval such as 1 or 2 EV, Photomatix normally accurately guess the relative exposure values. If it does not get them right, select the EV interval from the drop-down listmanually enter the relative EV values beside each image thumbnail. Once these values are entered, clicking OK proceeds

the final step:

In this Generate HDR Step Two panel, the only option I normally change is to enable alignment of the input images. discussed previously in the CS2 example, this ensures that minor registration errors do not creep into the combined image to any slight misalignment of the camera during the capture of the input sequence.From the three options for camera response curve, I keep the recommended default selection, Use standard response curMultimediaPhoto recommends this since they feel modern digital camera sensors are close enough to linear in their luminaresponse that calibrating a curve for a specific camera is of little benefit. Furthermore, the Gamma 2.2 curve (the standcurve referred to by this setting) applied to the sRGB and Adobe RGB 1998 color spaces is well defined and does introduce a need for calibration. Photomatix is unlike most HDR tools in this regard. Most of the others calculate a curvedefault, and many of them require an explicit curve calibration step that creates a saved profile for the camera.If you choose, you can calculate a response curve using the setting Attempt to calculate response curve. Or if you know


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input images came from a linear RAW conversion, you can select Use linear response curve. If you calculate the cuPhotomatix does not permit you to save and recall it. It simply calculates the response from each image sequence process; the results of this are likely to be variable depending on how many images are in the sequence and the exposinterval between them. Note: CS2 does not provide any options regarding response curve. It appears to calculate a respocurve from each image sequence; like Photomatix it also does not permit saving the curve.Upon clicking OK at this point, Photomatix will compute the HDR image. On my workstation this takes about 10 seconaround half of which is spent on image alignment. When the HDR image is created, it is opened for viewing in the mwindow:

As with other applications that display an HDR image on normal hardware, the monitor does not have sufficient DR to rendcomplete view. With the image open in Photomatix, functions are available in HDRI>Adjust View to step the exposure up down. This provides a similar ability to view the image as does the exposure slider in CS2. In addition, Photomatix providesmall full-resolution viewing window that can be enabled or disabled. As the mouse pointer is moved over the HDR image, viewer shows a normalized view of the image data from a small area around the pointer. You can quickly check detail aluminance across the image without having to adjust the base exposure of the entire image.Some DR statistics are available by selecting the HDRI>HDR Histogram menu item:

This window shows a histogram, the range of 32-bit luminance values, and a mapping of luminance values onto relaexposure values. The histogram shown for this example looks pretty comparable in distribution to the one seen in Calthough it appears to have clipped the luminance range on the bottom and top ends where no image data exists. As you


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see, this example has a DR of almost 1500:1, essentially all of which is available for use during tone mapping as the next stwill show.This is a good time to save the HDR image in case you want to come back to it later. As with CS2, there are two princformats: Radiance RGBE and Open-EXR. The default is Radiance RGBE. Saving in that format here, the resulting file sizabout 18.8 MB. Saving as Open-EXR with ZIP compression produces a file about 13.8 MB in size. This file sizes are similathose generated from CS2.As noted before, even though both applications support the .hdr and .exr file formats, the way the applications encodeimage data is not necessarily compatible. Thus it is best to use the same application to both encode and tone map the Himage file rather than try to cross-process HDR files between applications. (An exception to this rule is the Photomatix t

mapping plug-in, which works on HDR images created by the CS2 Merge to HDR function.)

Photomatix Tone MappingHere is where the heavy lifting occurs with the Photomatix workflow. After the above steps, there is an HDR image open inmain window. I select the HDRI>Tone Mapping menu item and the following window appears:

At this point, in contrast to the CS2 approach, Photomatix provides just one function. However, this one function provides aof creative control. While controls may appear complex at first glance, the sliders and drop-down lists, in fact, make it very to iterate through the choices.A preview of the tone mapped image is shown. For screen capture size reasons it is shown here at the minimum resolutio

512 pixels wide. Selection buttons at the lower left of the window enable widths of 768 and 1024 pixels. The preview dimens


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is always width; it does not adjust to the longest axis depending on whether the image is portrait or landscape.

There is no choice of arbitrary resolution or zoom ratio, such as zoom percentage or actual pixels. In part this is because preview shown here is only an approximation of what the final tone mapped image will look like. The Photomatix developmay have felt that looking at actual pixels of a simulated view is of limited value. Once the image is generated, it canexamined at higher zoom levels, and if necessary the tone mapping can be revisited. However this cycle takes time andflexible preview sizing is one feature that I wish was present in the Photomatix tone mapper. Even the 1024 pixel width (added in release 2.2.3) is small to work with for large files such as stitched panoramas.Fortunately the other tone mapping controls are to the tools credit. The familiar histogram is present to the left of the imapreview. Unlike the CS2 histogram which shows the luminance distribution of the HDR image, this histogram shows

distribution of the final tone mapped image. As you make changes, you can watch the histogram to determine how ysettings affect the distribution.Starting at the top right and moving counter-clockwise, there are two radio buttons that allow you to select 8- or 16-bit outThe default can be specified in an application preference; I have chosen a default for 16-bit as seen here.To the left of the bit-depth buttons is a slider labeled Strength which ranges from 0 100%. This control adjusts the levelocal contrast enhancement. Moving the slider left produces more natural tones, but results look flatter and do not emphafine details. Moving the slider right intensifies contrast, punching up detail and adding dramatic tone. However overdoing creates an unnatural appearance.Below 50%, I find the Strength control produces results comparable to the CS2 HDR Conversion Local Adaptation methodhigher settings, it produces enhanced contrast results that I have not been able to duplicate in CS2. Strength defaults to 8

which I do often find to be too high. For some images, though, having that top range may give a dramatic visual that you wa

To the left of the Strength slider is the Luminosity slider. This control brightens the image if moved to the right, or darkens moved to the left. Consider it to be similar to the midtones slider found in the CS2 levels adjustment. The default value is 0, the range is -10 to +10. I find that pushing the Strength slider higher often darkens the over-all tone, so I raise Luminositlittle to compensate.Below Luminosity is the Color Saturation slider. Defaulted at 46%, this control ranges from 20% to 100%. I find the defslightly low for my taste, but rarely adjust it by more than a few points. You may know how easy it is to overdo saturatespecially if your intended final output is a print. Photographers new to digital processing sometimes dial in too much saturato make an image look good, when the issue is poor midtone contrast, sub-par black and white points, etc. HDR processinvery much about dealing with over-all image tone, enhancing local contrast, and picking good black and white points.having to fall back on big saturation boosts to punch up an image should not be required. However, the control is here if y

need it.

Immediately below the histogram are two more sliders that control the white and black points. White Clip defaults to 0.25while Black Clip defaults to 0.00%. I often put the Black Clip slider up a notch or two. Unlike CS2, Photomatix appears to pprocess the HDR luminance range to filter it down to a smaller subset in which image detail exists. Therefore it shouldunnecessary to make big adjustments to the clipping points. But if you need to fine tune the image, the controls are here.Below the clipping controls is the Smoothing drop-down list, containing four entries: High, Medium, Low and Very Lowith the default being Medium. The higher the selection, the larger the regions over which the contrast enhancements smoothed. Smoother results look more natural. This control is analogous to setting the Radius value in the CS2 HConversion panel, with similar effect. I normally use High or Medium, as I find the other settings look too unnatural landscape scenes.As an aside, one key difference between CS2 and Photomatix in this adjustment is that Photomatix provides only four discsettings instead of a range from 1 250 pixels. Four settings may not be quite sufficient (six or eight would give a little mcontrol), but it is a good approach for the types of images I work on. I honestly do not agonize in CS2 whether the smoothradius should be 80, 82 or 83. Having that level of fine grained control adds little or nothing to the creative process for me, aam focused on qualitative results.This same effect often causes photographers to struggle with editing points on curves in CS2. There is a lot of precise conpossible, but correlating that control to the qualitative results you want can be a challenge. Having fine grained controls is nbad thing. However, difficulty making an initial selection that gets in the zone can make the tool time consuming frustrating to use. Initial information indicates that Adobe is making improvements in this area with its Lightroom softwHopefully software vendors continue to improve most photographers want to concentrate on making beautiful photograpnot twiddling bits.Below Smoothing is the Microcontrast control. Microcontrast defaults to High, and has the additional choices of MediuLow and Very Low. I normally leave the setting on High. Sometimes small detail needs to be less emphasized. T


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application help file gives examples such as noisy input images and stitched images containing stitching artifacts. In thcases the control can be set lower. MultimediaPhoto is currently working on enhancements to this control that will permit higsettings without emphasizing image noise as much.Finally, underneath the Microcontrast control is a set of buttons for dealing with parameter sets. The Previous button will uthe current change, while Default resets everything. The Load and Save buttons permit saving and recalling settings. Savsettings creates a small file with the extension .xmp. A library of these files can be built up to create a series of default lothat can be customized for individual images. This is a little harder to do with saved settings in CS2 because the curve eare much more image-specific.Here is a final look at the tone mapping window with the parameters I have chosen for conversion:

The key changes from the default settings include: Strength of 70% Luminosity of 2 Saturation of 55% Smoothing of High

When I am satisfied with the settings, I hit the OK button and Photomatix performs the real tone mapping. This takes less t20 seconds on my machine. The final results will look somewhat different than the preview, but I find generally they are cloenough to achieve the look I want without a lot of iterations back and forth.When the conversion completes, the final image (a 16-bit TIFF in this case) is opened in the main Photomatix window.


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At this point the image can be saved for finishing work back in CS2. Here is what the final generated image looks like usingabove tone mapping settings:

There are some interesting things going on here, and to my eye this is a better starting point than was the result that cadirectly out of the CS2 HDR Conversion function. I particularly like the ice in this version. However, the image is not finishedback to CS2 for the final touch-up work.

Photomatix Final Touch-UpWith the tone mapped HDR image saved as a 16-bit TIFF from Photomatix, it can be loaded into CS2 for the finishing touchWhen I did this the first time to create the tone mapped image seen at the beginning of the article, I did minimal touch-up win CS2. This time around, to have a more level playing field in comparing the results between CS2 and Photomatix, I touchup both versions using similar adjustments.Here is the final rendition of the Photomatix image:


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The following adjustments were made to the converted image:

brightness increased slightly via an adjustment layer black point increased slightly via a levels layer midtones punched up slightly via a curves layer brightness of trees increased slightly via a masked layer snowy / icy parts brightened (white point dropped slightly), via a masked levels layer whites of selected small areas of snow and ice increased further via a masked saturation adjustment layer

a bit more snap added via a high pass overlay layer at 20% opacity

noise reduction and selective sharpening on the base layerHaving gone through both workflows with the same example image, we can look at a head-to-head comparison of the result

Comparison of Workflow ResultsHere are the final images from each workflow once more:

CS2 version Photomatix version


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Certainly it is possible that either image could be improved further. However, I feel those improvements would be sincrements, and not favor either version of the image over the other. This would leave the Photomatix version with advantage. Having worked through numerous HDR images over the past six months, as well as reading a lot of commenon the Internet, in my opinion the tone mapper in Photomatix simply produces more interesting results with less work. Here some general critiques between the two versions:

The Photomatix version has more drama in the sky. The CS2 version has possibly more natural tonal range (less blabut seems washed out, gray and a touch plastic in comparison.

The Photomatix version contains better detail in the trees, especially visible from the center to the right. The Cversion is more blocked up.

The Photomatix version shows better contrast, color tone and detail across the ice surface. Again, the CS2 versiodull, gray and generally lacking in sharp, punchy details.

The CS2 version has a smoother tonal appearance over-all but this comes at the cost of contrast, where the Photomversion is better.

There is one notable downside with the Photomatix version of this image that I had to deal with during processing, remnantwhich will be seen below in the 100% crops. That downside is emphasis of noise and other fine grained artifacts in the souimages (such as JPEG compression or Bayer mask anti-aliasing artifacts). The Photomatix algorithms which emphasmicrocontrast in desirable image detail can also really bring up the less desirable details. The CS2 version of the image d

not exhibit this condition.

MultimediaPhoto is aware of this situation and the support FAQ for Photomatix mentions some potential work-aroundsaddition to simply post-processing the tone mapped image with your favorite noise reduction tool. A pending release of application is slated to include a new option for the microcontrast setting that reportedly will minimize the effects of noise. Tfunctionality was not available in time for this article.Here are some 100% crops from the two versions of the image:

Actual image data looks very comparable between the two versions. The Photomatix version has more drama (darker tone a bit more contrast), while some remaining artifacts are visible. The CS2 version is flatter in tone and a bit washed out; mwork might improve it.



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The CS2 version has a bit less detail, and the trees have blocked up. Some artifacts are evident around the top edges of up-slope groups of trees, which look like registration errors. Some whites are a bit too strong, probably clumsiness on my pColor tone in the trees is better in the Photomatix version, but here the noise-like artifacts are again visible.

Registration errors are again visible along the ridge line in the CS2 version. This is not adjustable in the HDR Conversfunction so would have to be fixed afterwards in post-processing. The Photomatix version shows minimal hints of registraerrors along the ridge line as well. The clouds and trees again are better, although the trees still show some noise.




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The CS2 version again lacks detail and tone compared to the Photomatix version.

Color tone and apparent detail were quite lacking in the lower right corner of the CS2 version. The Photomatix version is mpreferable, despite the noise.




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The CS2 version has blocked up again here and lost detail in the trees and rocks. The registration errors show up again althe ridge line. Possibly some heavy handed adjustments of mine need to be backed off. The Photomatix version is mpleasing over-all, but the noise shows here in the trees as an annoying blast of speckling.

The open ice on the far left is smooth in the CS2 version, but again lacks punchy detail. The Photomatix version has the dbut also shows the noise again. At least here the noise is less distracting; not all noise is bad, sometimes it can add desiratexture.




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When examined at the level of 100% crops, it appears that both CS2 and Photomatix have their pluses and minuses. Acimage detail present is comparable between the two versions. The major differences are in the results of tone mapping. Ovemy preference for the results of Photomatix is borne out by looking at the details as well as at the whole. However, I am trying to do a sell job on Photomatix. It is a tool like any other and if it does something you need, give it a shot. If not, usomething else.For example, while CS2s registration errors were significant in this example, I have found cases where CS2s alignm

function did a better job than Photomatix. This might be a situation where using the Photomatix plug-in would allow the besboth worlds HDR 32-bit file generation (including alignment) using CS2, and tone mapping using Photomatix.Note: Photomatix Pro does have a partially manual alignment mode that may help with a troublesome series of input imagUsing this mode, two control points can be specified, as with various image stitching applications, to help the alignmfunction figure out how to register the successive images.Here are two more images of a different scene that provide another view of the differences between CS2 and Photomatix tmapping. Both images were processed from a series of three exposures taken at an interval of 2 EV. Nearly identical finishwork was done on both, although the effort was not as extensive as for the main example images above.

Since the images were shot hand-held (using a Canon 5D), I went up to ISO 400 to keep the shutter speeds a bit faste1/320s, 1/80s and 1/20s. This contributes to more noise in the Photomatix version of the image; the CS2 version is noticeasmoother at full resolution. In most respects, both images examined at this down-sampled size look fairly equivalent. Wcant be seen is the processing time. The CS2 HDR conversion took much longer since I had to iterate over the parameterthe Local Adaptation method several times, dealing with problems (described below) and trying to get the look I wanted. I able to get the sky fairly close in the end, but could not achieve quite the same results in the rest of the image, as I was ablget in Photomatix in just a few minutes.Despite the greater effort spent on the CS2 version, the Photomatix version has more dramatic contrast throughout thankthe darker blacks. The snow also has much better definition than in the CS2 version. I attribute this to the microcontcomponent of the Photomatix tone mapping algorithm. The CS2 version of the image simply does not hold the same levedetail in the snow.Looking at a few 100% crops of both versions will emphasize the above points, plus provide a close look at one other critshort-coming of the CS2 version that has not been discussed so far.



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The CS2 version is a little smoother, but the Photomatix version is a little more dramatic.

Again, the CS2 version is smoother while the grain can really be seen in the Photomatix version. When I ran noise removaboth images (around half strength on the CS2 version), I excluded the snow as I wanted to preserve maximum detail thSome moderate noise removal in the snow would give the Photomatix version a clearer advantage due to its improcontrast, at the cost of some detail.




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The CS2 version wins for reduced noise, but the Photomatix version wins for detail.

Other Comparative Notes on the ToolsHere are a few miscellaneous points about the tools that may be worth noting.CS2 enforces a minimum DR span on the input images. In some cases I have heard about, this seems to erroneously blthe ability to merge files that contain sufficient DR. So far I have not personally encountered this issue. Photomatix Pro, in event, does not attempt to force any minimum amount of DR on the images and will let you combine pretty much sequence. In fact, you can tone map a single 16-bit TIFF image if you want to see what additional contrast and detail mighpulled out of it.A few weeks before writing this article, I upgraded my landscape camera to a Canon EOS 5D. After a while I got through

backlog of 10D images, and started working on new images taken with the 5D. It quickly became apparent that 5D ima




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were not being properly processed by Photomatix Pro. In discussion with the folks at MultimediaPhoto (who were vresponsive), it appears that two known issues are going on. First, the Photomatix tone mapping algorithms work best when image width and height are both multiples of a high power of two, such as 256 1024. In the case of the 5D, the size multiple of only 16 or 32, and this causes problems when the Smoothing control is set to High. Setting this to Mediinstead appears to avoid the issue. Also cropping, upsampling or down-sampling the input images are possible work-arounif a higher power of 2 is the result.Second, a large number of very dark pixels in the under-exposed images can bias the tone mapping algorithm to produce dareas in the final image, or even to take the final image completely to black. Because 5D images have a resolution of 12.8 they may have a larger absolute number of dark pixels and trigger the black tone issue. The web site has an FAQ entrythis issue and there are some work-arounds. Again, this may occur in its most extreme form when Smoothing is set to Hig

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