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Theme : Primary image processing

Lina Adel FituriPoligraphyфак. № 24159621b

Contens:

1.What is the purpose of image processing?

2. Мethods in image processing. Correction of histogram.Сonvolution methods. Binarization.

3. Adjustments in Adobe Photoshop

Brightness/Contrast

Lightness channel and adjustments curves

Levels

The Photoshop Curves tool

The Exposure tool

Vibrance

Hue/ Saturation

Color Balance

Black & White film

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What is the purpose of image processing?

Image processing has multiple purpose.

• To improve the quality of an image in subjective way, usually by increasing its contrast. This is called image enhancement.

• To use az few bits as possible to represent the image, with minimum deterioration in its quality. This is called image compression.

• To improve an image in an objective way, for axample by reducing its blurring. This is called image restoration.

• To make explicit certain characteristics of the image which can be used to identify the contents of the image. This is called feature extraction.

http://www.google.bg/patents?hl=bg&lr=&vid=USPAT4677465&id=6BM-AAAAEBAJ&oi=fnd&dq=correction+of+histogram&printsec=abstract#v=onepage&q=correction%20of%20histogram&f=falsehttp://www.photocolorcorrection.com/histogram.html http://www.mini.pw.edu.pl/~kotowski/Grafika/Images/

Methods in image processing

Correction of histogram

The definition of a histogram is:

A bar graph of a frequency distribution in which the widths of the bars are proportional to the classes into which the variable has been divided and the heights of the bars are proportional to the class frequencies.

Methods3

http://www.mini.pw.edu.pl/~kotowski/Grafika/Images/Index.html

Convolution

Convolution is the modification of a pixel’s value on the basis of the value of neighbouring pixels.

Convolution FiltersOne of the most powerful techniques in all of image processing is convolution.

Convolution is the modification of a pixel's value on the basis of the value of neighboring pixels.

Images are convolved by multiplying each pixel and its neighbors by a numerical matrix, called a kernel. This matrix is essentially moved over each pixel in the image, each pixel under the matrix is multiplied by the appropriate matrix value, the total is summed and normalized, and the central pixel is replaced by the result.

Cx,y = å(å(Pi,j*Mi,j))/(å(å(Mi,j))

Binary Images Binary images are images that have been quantised to two values, usually denoted 0 and 1, but often with pixel values 0 and 255, representing black and white.

Binary images are used in many applications since they are the simplest to process, but they are such an impoverished representation of the image information that their use is not always possible. However, they are useful where all the in-formation you need can be provided by the silhouette of the object and when you can obtain the silhouette of that object easily.

Figure 2: The histogram of an image showing the frequen-cy of occurrence of each grey scale value.

Figure 1: The ideal histogram of a light object on a darker plain background.

http://www.cs.technion.ac.il/~blayvas/PAPERS/binarization_CVPR.pdf

http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/OWENS/LECT2/node3.html

Methods4

Adj

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tsBrightness/Contrast

What are brightness and

contrast?

Photoshop allows you to adjust the brightness and contrast of your image. If an image is too light or too dark, you can use the brightness and contrast controls to improve the picture. Below is an example of an image before and after the brightness and contrast were adjusted.

for more information :http://iit.bloomu.edu/vthc/photoshop/enhancing/brightness&contrast.

htm

http://www.bairarteditions.com/pages/tutorials/photoshop/excontrast.html

Levels Levels is a tool in Photoshop and other image editing programs which can move and stretch the brightness levels of an image histogram. It has the power to adjust brightness, contrast, and tonal range by specify-ing the location of complete black, complete white, and midtones in a histogram. Since every photo’s histogram is unique, there is no single way to adjust the levels for all your photos. A proper understanding of how to adjust the levels of an image histogram will help you better represent tones in the final image.The levels tool can move and stretch brightness levels in a histogram using three main components: a black point, white point and midtone slider. The position of the black and white point sliders redefine the histo-gram’s “Input Levels” so they are mapped to the “Output Levels” (default is black (0) or white (255), respectively), whereas the midtone slider redefines the loca-tion of middle gray (128). Each slider is shown below as they appear in Photoshop’s levels tool, with added blue labels for clarity:

How it wokrs ?

http://www.cambridgeincolour.com/tutorials/levels.htm

Adjustments5

The Photoshop Curves tool

The Photoshop curves tool is perhaps the most powerful and flexible image transformation, yet it may also be one of the most intimidating.

Similar to Photoshop levels, the curves tool can take input tones and selectively stretch or compress them. Unlike levels however, which only has black, white and midpoint control, a tonal curve is controlled using any number of anchor points (small squares below, up to a total of 16). The result of a given curve can be visualized by following a test input tone up to the curve, then over to its resulting output tone. A diagonal line through the center will therefore leave tones unchanged.

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Using Levels

Using curves

Original

Lightness channel

and adjustments curves

Performing curves to just the light-ness/luminosity channel - either in LAB mode or as an adjustment layer can help reduce changes in hue and color saturation. Move your mouse over each of the im-ages below to see what would have happened if this curve had been applied to the RGB channel.

http://www.cambridgeincolour.com/tutorials/photoshop-curves.htm

Adjustments

Using Levels

Calibrated in stops, it increases brightness throughout the image but affects the shadow areas far less than the highlights. Increase the Exposure sufficiently though and the image will turn solid white. Set it low enough and you will end up with solid black.

The Exposure tool

The oddly named Off- set slider seems to primarily do the opposite, stretching the ton-al range downward to dark- en the shadows without overly influencing the highlights. Af-ter adjusting the Exposure, Offset can be used to tweak the shadow and quarter-tone areas of the image while only moderately affect-ing the rest of the image.

The Gamma slider works in a similar fash-ion to the Brightness slider in Adobe Camera Raw. Moving it to the right increases the mid-tone brightness of the image, while sliding it to the left will darken the overall appearance of the image

Over exposureUnder exposureh t t p : / / w w w . b a i r a r t e d i t i o n s . c o m / p a g e s / t u t o r i a l s / p h o t o s h o p / e x p o s u r e . h t m lhttp://help.adobe.com/en_US/Photoshop/11.0/WSA0E099D7-EB39-40f5-A99E-2F95526904CCa.html

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Vibrance

One of the new features in Pho-toshop CS4 is

a Vibrance adjust-ment, a feature

borrowed from light-room's development module. It's fair-ly intuitive to use,

but have you ever wondered what exactly this handy little ad-justment does?

7 Adjustments

Vibrance

50% Vibrance 100% Vibrance OriginalVibrance: Adjusts the saturation so that clipping is minimized as colors approach full saturation. This setting changethe saturation of all lower-saturated colors with less effect on the higher-saturated colors. Vibrance also prevents skintones from becoming oversaturated.

for more information :

http://help.adobe.com/en_US/Photoshop/11.0/WSC799D0E1-38B5-4edf-A136-2ABE147063AC.htmlhttp://www.digitalphoton.net/color-vibrance-in-photoshop/http://www.miraztutorials.com/photo-vibrance-photoshop-cs4-tutorial/

Hue/ Saturation

Adjustments8

Hue is another name for color. When an im-age’s hue is ad-justed, the base color of that im-age changes in correlation with the color wheel. The image’s saturation re-fers to the inten-sity of its colors.

http://iit.bloomu.edu/vthc/photoshop/enhancing/hue&saturation.htmhttp://www.zuberphotographics.com/content/photoshop/hue-saturation.htmhttp://www.picturecorrect.com/tips/huesaturation-without-losing-exposure-in-photoshop/

Hue/Saturation

Original 50% 100%

9 Adjustments

Colors In photography and im-age processing, color balance is the global adjustment of the in-tensities of the colors (typically red, green, and blue primary colors). An important goal of

this adjustment is to render spe-cific colors – particularly neutral colors – correctly; hence, the gen-eral method is sometimes called gray balance, neutral balance, or white balance. Color balance changes the overall mixture of col-ors in an image and is used for col-or correction; generalized versions of color balance other than neutrals to also appear correct or pleasing

Color Balance

http://www.bairarteditions.com/pages/tutorials/photoshop/cblevels.htmlhttp://iit.bloomu.edu/vthc/photoshop/enhancing/colorbalance.htmhttp://www.geofflawrence.com/photoshop_tutorial_color.php Black & White

film

http://www.outdooreyes.com/photo73.php3http://www.earthboundlight.com/phototips/black-and-white-photo-

shop.htmlhttp://digital-photography-school.com/forum/post-processing-

printing/7630-black-white-adjustment-layers-blending-modes-photoshop.html

10 Adjustments