Research Summary - 1)PhysicsOverview: What does the light do?

Surface Effects- Light hits object.Reflection - Some bounces backDiffraction - Some curves aroundRefraction - Some enters the structure and is slowed Absorbtion - Some light is absorbed / object takes on colourDispersion - The light beam is split up (prism)Polarization - The light’s orientation is alteredPlechorism - Observed colour changes with viewing angle - also Dichroism/TrichroismBirefrigence - The light beam (can) splitInterference - Small scale reflections create colour effectFlourescence - Invisible (UV) converted to visible lightPhosphorescence - continued emission after removal of sourceChatoyancy, Asterism - “Cat’s Eye” & Starring effects

Surface Effects//Fresnel / Reflection / Glare / Gamma

Digital Technology Design II Year Two Major Assignment : Progress

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Summarize researchOutline tasks to completeRevise timelineEstablish presentation format

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Caustics (note dispersion within caustics)

Optical Effects -Lens Flare, Halo, Glow (Hyperreality)

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Diffraction//Just make it visible in the shadow edges

Refraction//Refractive Index of material ie 1.5=water 2.4=Diamond

//Singly Refractive vs Doubly Refractive & AmorphousAmorphous = lack of crystalline structure

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///a.k.a. -- Uniaxial, Biaxial & Isotropic refraction

“There are two types of optical crystals, isotropic and aniso-tropic crystal. The isotropic crystals have the same refractive index for all directions. The anisotropic crystal has a different refractive index in a different direction, and has two different values for the same direction. However, there are one or two particular directions where these two refractive indices have the same value.

These particular directions are called optic axes and the crystal having one optic axis is called uniaxial or monoaxial crystal, while the one having two optic axes is called biaxial crystal. Since the anisotropic crystal has two refractive indi-ces, there are two refracted rays in crystal for one incident ray and so-called double refraction or birefringence occurs”

Hayamitzu, Y. Analysis of internal conical refraction using ray tracing formulas for the biaxial crystal. Optical review 13, No. 4, pp.169–183, 2006.

algorithm to render isotropic and uniaxial crystalline aggre-gatesDebelov, V.A., Kozlov, D.S. A local model of light interaction with iso-tropic and uniaxial transparent media. Vestnik of Novosibirsk State University, Series: Information Technologies, vol. 10, No. 1, pp. 5–23, 2012, (in Russian)

paper devoted to rendering of uniaxial monocrystalsWeidlich, A. and Wilkie, A. Realistic rendering of birefringency in uni-axial crystals. ACM Transactions on Graphics 27, (1):6:1–6:12

refracted rays in biaxial crystals.[Lat12] Latorre, P., Seron, F. J., and Gutierrez, D. Birefringence: cal-culation of refracted ray paths in biaxial crystals. The Visual Computer 28, No. 4, pp. 341-356, 2012.

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Absorbtion//Manner in which gems aquire colour

“As a general rule, a fraction of the light traveling inside a transparent material is absorbed. The absorption along a path (x0, x) is ruled by the Bouguer-Lambertian law [Wyszecki and Stiles 1982], giving the resulting intensity after a distance ...is called the absorbance of the medium and depends on the wavelength. Absorption is responsible for the color of gem-stones, and the absorbance spectrum acts as a tracer for the chemical nature, geographic source and applied treatments of a stone.”

“Many gemstones display this behavior (e.g.,sapphires, ru-bies, tourmalines [Hughes 1997; Nassau 2001]). Other gem-stones (like andalusite) display three distinct colors. This comes from their crystal structure, which has two optical axes instead of one. The computation of absorption in this context is beyond the scope of this paper.”

“This is because it modifies the color of the ray “at the sur-face” of the object, whereas real colored transparent object modify the color of the ray gradually as it travels through the medium. Looking at the gems above (rubies, perhaps?), the small ones are just as deeply red as the big one, and the tip ofthe big one is just as deeply red as the thickest part of it. That doesn’t look... correct. What we need to do is to enable at-tenuation through the medium instead. To do this we need to set our transparency color back to white (basically, treat the surface itself as completely transparent), and move to the falloff settings within the material:”

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Dispersion//Splitting of Light into constituent colours

Violets refract more than reds, thereby splitting the light into it’s constituent colours

nb: lotta work been done here already!

“extended simulations of gems beyond refraction & dispersion that are the dominant effect for Diamonds.”

Stefane Guy & Cyril SolerGraphics Gems Revisited: Fast and Physically-Based Rendering of Gem-stones (2004)

Ray Tracing & Dispersion (Diamond)Sun, Fracchia, Calvert, DrewDeriving Spectra from Colours and Rendering Light Interference

above: looking through a spinel at a lightbulb 6 feet away

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Polarization, Plechorism & Dichroism

//Polarization

“Although the polarization state of light is, for most rendering applications, an expensive and unnecessary feature, it does play a critical role in the interaction of light with gemstones, and therefore must be incorporated into any rendering mod-el that wants to reproduce these effects. Indeed, while the naked eye is not trained for detecting light polarization, the path of light through a faceted transparent object involves a number of selective changes in the polarization. This succes-sion of changes is responsible for the darkening ofsome re-gions and, in the case of anisotropic crystalstructures, a color change depending on the direction of propogation.”Graphics Gems RevisitedGuy & Soler Fast and Physically-Based Rendering of Gemstones

Wolff proposes one of the first attempts to incorporate polar-ization effectsin ray tracing

WOLFF, L., AND KURLANDER, D. J. 1990. Ray tracing with po-larization parameters.IEEE Computer Graphics and Applications 10, 6 (november/december), 44–55.

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// Plechorism, Dichroism

“Anisotropic crystals will have optical properties that vary with the direction of light. The polarization of light determines the direction of the electric field, and crystals will respond in different ways if this angle is changed. These kinds of crystals have one or two optical axes. If absorption of light varies with the angle relative to the optical axis in a crystal then pleoch-roism results.[2]Anisotropic crystals have double refraction of light where light of different polarizations is bent different amounts by the crystal, and therefore follows different paths through the crystal. The components of a divided light beam follow differ-ent paths within the mineral and travel at different speeds. When the mineral is observed at some angle, light following some combination of paths and polarizations will be present, each of which will have had light of different colors absorbed. At another angle, the light passing through the crystal will becomposed of another combination of light paths and polariza-tions, each with their own color. The light passing through the mineral will therefore have different colors when it is viewed from different angles, making the stone seem to be of differ-ent colors.”

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gem

gem

render

render

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//Polarization & Dichroism

Tetragonal, trigonal and hexagonal minerals can only show two colors and are called dichroic. Orthorhombic, monoclinic and triclinic crystals can show three and are trichroic.

BORGES, C. F. 1991. Trichromatic ap-proximation for computer graphics illu-mination models. In Proceedings of the 18th annual conference on Computer graphics and interactive techniques, ACM Press, Eurographics, 101–104.

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Birefrigence“Birefringence is the degree to which a doubly refractive gemseparates the doubled images or rainbows”

In 1994, Tannenbaum gave some details about the implemen-tation of the birefringency phenomenon [Tannenbaum et al. 1994] for computing images of highly birefringent media such as calcite. As we explain below, birefringency is responsible for color variations in many stones.TANNENBAUM, D. C., TANNENBAUM, P., AND WOZNY, M. J. 1994. Polarization and birefringency considerations in rendering. In Comp. Graphics (SIGGRAPH ’94 Proceedings), ACM Press, 221–222 (Extended version available on CD–ROM).

Left: Ruby Right: Not a Ruby

Birefrigence in gem identification - Double rainbow with the yellow and grees aspects of the spectrum having been ab-sorbed by the material

nb - find this one!!

K. Nassau, The Physics and Chemistry of Color: The Fifteen Causes of Color, John Wiley and Sons, New York, 1983.

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Light Interference

Light Interference In PearlsNagata, Dobashi, Wanabe, Usami, InokuchiModelling & Visualization for a Pearl Quality Evaluation Simulator Transacions on Visualization & Computer Graphics

Deriving Spectra from Colors and Rendering Light Interference Yinlong Sun, F. David Fracchia, Thomas W. Calvert, and Mark S. Drew - Simon Fraser University

real

render

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Fluorescence aka Luminescence (Maya)

//When the material converts invisible UV and XRay light to visible light (One electron absorbs two photons) it’s fluores-cent. If the material continues to emit light after the light source has been removed it’s phosphorescent. (Some Dia-monds)

“Diamonds are also evaluated on the parameters of the fluo-rescence. Most diamonds when the held under the ultraviolet light or black light it will emit a colored glow known as fluo-rescence. This fluorescence causes diamond to change its color when subjected to the ultraviolet light. Ultraviolet light surrounds us as part of the sunlight and is also present in the light of the fluorescent light-bulbs. This light may cause the diamond to look whiter or yellowish. Diamonds that emit blue fluorescence in ultraviolet light may correct the actual yellow tint of the stone making the stone look white. It can also be said that the diamonds graded yellow emit blue fluorescence degree may vary. On the contrary, a diamond that emits yel-low fluorescence may look very white under incandescent lights.

This attribute may cause the diamond to look different in the normal light at home. It is suggested to buy diamonds from a reputable retailer, to avoid any cheating on color and qual-ity. An important fact to note, a strong fluorescence in the diamond may cause the stone to appear cloudy.”

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Another formalism (Stokes light vectors) was used by Wilkie in 2001 to get rid of complex numbers [Wilkie et al.2001] and to incorporate polarization along with fluorescence effects in a ray tracer, with convincing results on semi-transparent ob-jectsWILKIE, A., TOBLER, R. F., AND PURGATHOFER, W. 2001. Combined rendering of polarization and fluorescence effects. Tech. Rep. 186-2-01-11. Available at www.cg.tuwien.ac.at/research/TR/01/.

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Chatoyancy & Asterism

ChatoyancyImura, Abe, Kanaya, Yasumuro, Wanabe, ChiharaRendering “Play of Colour” Using Stratified Model Based on Amorphous Structure of Opal - Changming Sun

Yokoi et al. propose an algorithm [Yokoi et al. 1986] aimed particularly at the reproduction of asterism (i.e., the effect seen on star sapphires) and chatoyancy effects. YOKOI, S., KURASHIGE, K., AND ICHIRO TORIWAKI, J. 1986. Rendering gemswith asterism and chatoyancy. The Visual Computer 2, 5 (Sept.), 307–312.

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Summary - 2)Not Physics//Profound relationship btw CGI and Diamond industry - cus-tom computer graphics applications used to optimize poten-tial of uncut stones, appraise/quantify quality of cut stones, and create representations of stones to aid in design and sales.

“The use of the term ‘Ideal’ is thus confusing,” GIA President William E. Boyajian says in the introduction to the study, pub-lished in the Fall 1998 issue of Gems & Gemology. “Although it is not GIA’s role to discredit the concept of an ‘Ideal’ cut, on the basis of our research to date, we cannot recommend its use modern times.”

To come to its conclusions, GIA created a computer-gener-ated three dimensional model of a round brilliant colorless flawless 58-facet diamond with perfect symmetry and polish. It entered eight cut factors and several physical factors that affect the way light interacts with diamond. These calcula-tions resulted in more than 20,000 proportion combinations which were measured for brilliance through a numerical evaluation GIA calls weighted light return (WLR). The WLR numbers were reached by tracing and weighting rays of light as they followed their paths through the diamond.”

Metrics created for “Brilliance” -- variations on proportions of diamond cuts evaluated via CGIHemphill, Reinitz, Johnson, Shigley. Modelling the Appearance of the Round Brilliant Cut Diamond : An Analysis of Brilliance Gems & Ge-ology (1998)

Metrics created for “Fire” ++Hemphill, Reinitz, Johnson, Shigley, Gilbertson, Geuts, Green. Model-ling the Appearance of the Round Brilliant Cut Diamond : An Analysis of Fire and More About Brilliance Gems & Geology (2001)

You can’t photograph ‘Scintillation’ as it’s a dynamic effect - requires animation (also photograph then rotate)

“This static view is only 1/45th of the overall impression these graphics give. When the animation is seen the diamond graphics rotate through 45 degrees of tilt. As they rotate you can see the different appearance of angular spectrum..”

“..of the hundreds of types of gems, simulation of only a few have been reported” (2008) pg 157

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//Just tell me where can I download a shader from!!It’s all academic - nobody’s showing you “how to pull it off in Maya” unless it’s a diamond - How the heck do I input your physics equation into my application?

“Up to now, the academic solutions which have been proposed for rendering gemstones have all been based on more or less complex ray tracing implementations... In the specifications of the two software packages JewelSpace TM (see www.jew-elspace.net) and JewelCAD TM (see www.jacadcam.com), for instance, one learns that the first combines radiosity and ray tracing while the second uses OpenGL and ray tracing, which gives nice, but not instant, results.”

// Guy and Soler own it - definitive textGraphics Gems RevisitedGuy & Soler Fast and Physically-Based Rendering of Gemstones---check your focus! -- light effects and how to pull them off...

Guy & Soler Criticizing own work -

“However one can complain that the luster of the stone? (responsible for the irridescent col-ors on the top faces in the photography) is not simu-lated, which would be a challenging problem to solveusing graphics hardware”

“Other important features of gemstones, such as in-clusions, color zoning? and luster would be interesting to incorporate as well”

At the end of the day.. *takes long swig for dramatic effect

IT’S ALL BEEN DONE BEFORE* - BUT THE RESULTS ALL SEEM TO BE IN THE FORM OF COMPLEX PHYSICS EQUATIONS - EVIDENCE THAT IT HAS BEEN DONE, NOT TOOLS TO HELP DESIGNERS DO IT..*nobody’s mentioned optical effects or the hyperreality we expect from modern cgi wheres the glow and the halo we expect to see from our flashy sparkly stuff?

Tasks To Complete- Finish planning format - Storyboard - how to “tell light’s story” - Establish format / template- Obtain examples (reference footage?) of effects in real life- Build Models- Play! Figure out your f/x, project style- Replicate effects in 3d- Render time!- Graphic design / Typography- AE compositing, post-production- Audio

Revised Timeline//Key Dates //Plan

asap: approval for final format2/9: Break9/9: Break16/9: Formative (wed)23/9: -- Summative (fri)31/9: --7/10: --14/10: --21/10:--28/10:--*Exam weeks - 29 October-15 November 2013*Last day of semester - 15 November 2013

Presentation Format//What do I want at the end of this?- one animated document (it’s going to be presented on a screen & then live in my folio)- focus on “telling light’s story” as it interacts with crystalwhat happens at every step- simulations shown alongside real world examples of same phenomena- viewer “take out” = Master of replicating the ethereal in CGIcontrasting beauty of imagery with advanced scientific con-cepts explained.

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Best thing I’ve written today...

1) collect reference!2)storyboard & design 3)play! 4) models and shaders models and shaders5) graphics and type6) compositing/post7) moving type/polish8) audio