Announcement Upcoming graphics courses: Color Computer Animation: Algorithms & Techniques (Winter) Procedural Shading (Spring) Applications in VR (Virtual Theatre) (Fall) AI for Interactive Environments (Spring) Logistics Projects Approx 26-28 projects Listing of projects now on Web Checkpoint 4 Presentation schedule Grading started Presentations (15 min max) Checkpoint 5 Last 4 classes (week 9 + week 10 + finals week) Due Wednesday (Hey, that’s today!) Sign up Checkpoint 6 Email me with 1 st , 2 nd , 3 rd choices First come first served. Given today RenderMan Mid-quarter report due today Due May 14 Drop in dropbox. Mac problems…see me after class. Finals date has been set Announcement Saturday, May 19th As promised: 8:00am -- 10am THE ILLUSION OF LIFE, REVISITED Room 70-1620 Ken Perlin Thursday, May 10th @ 12 noon Project presentations. Golisano Building Auditorium Conflicts? Let me know. 1
Announcement Computer Graphics as Virtual Photography Many years ago Walt Disney spoke of the quest to create the real camera photo Photographic Photography: “Illusion of Life”. In fact, in every era of human history this scene (captures processing print quest has evolved new kinds of literacy; from the first cave light) paintings to the written word, music, drama, cinema, animation and beyond. Recently it has become possible to create this illusion interactively. But what makes for an effective processing experience, once an audience can respond back? What makes us care about an interactive character? We will show some recently developed techniques for breathing life into interactive characters. These techniques may point the way to a new era camera Computer 3D synthetic tone where cinema intersects with interactive narrative and on-line model Graphics: models reproduction image community. (focuses simulated And we’re also going to make sheep waltz. lighting) Photographic Pipeline (back in Photography and Light the day) pho•tog•ra•phy, n ., the process or art of Follow the path of light from scene to photo to viewer! producing images of objects by the action of light on a sensitized surface, e.g., a film in a camera. enlarger film Photography = writing with light print viewer camera scene Photographic Pipeline (for the new millenium!) What we’re missing Lighting values Follow the path of light from scene to photo to viewer! Currently 0 - 1…what is 0? What is 1? Camera model CCD JPEG array Current a pinhole Color RGB…which RGB? No postprocessing print Current directly from scene to image. Post viewer digital scene process camera 2
Light and Color Light -- What it is “Indeed rays, properly expressed, Electromagnetic radiation are not colored” induction radio ultra gamma secondary power infrared x-rays heating waves violet rays cosmic rays -- Sir Isaac Newton 10 10 10 8 10 16 10 14 10 12 10 6 10 4 10 2 10 -2 10 -4 10 -6 10 -8 1 Wavelength visible light (nm) Red 700 nm orange 650 nm yellow 600 nm green 550 nm I.e., light rays are not colored; we blue 450 nm violet 400 nm perceive them as colored! Light - Color Light – Spectral Density Functions (SDF) Color is the perceptual response to AKA spectral power distributions light of wavelengths 400 - 700 nm Describes the distribution of the strengths hitting the retina. of light at given wavelengths emitted from a source. Spectral power distributions exist in the physical world but color exists only in the eye and brain, e.g., there is no real white light! Light - Color Light - Color Black Body Radiators and daylight Daylight from the sun & total sky (5000K - Black Body Radiators 7000K) Spectrum resulting from heating a standard D 65 - Average daylight (6504K) “body” to a given temperature Daylight w/occluded sun (> 7000K) Planck’s formula: Daylight from sun alone (< 5000K) c M ( , T ) 1 � = 5 c / T ( e � 1 ) � 2 � 2 c 1 . 4388 10 � c 3 . 7418 10 16 = � � = � 2 1 3
Light -- Color Light - Color Black Body Radiators and other light sources Not all lighting sources have smooth SDFs Light -- Color Light and color Light Filters Absorbs light at given wavelengths Allows light at other wavelengths through Using filters Absorption Actual SDF is determined SDF for a filter by multiply SDF of light by Material can absorb light on a wavelength by SDF of filter wavelength by wavelength basis wavelength. Responsible for object color Light and color Light and color The “color” of an object we see is a function Color appearance applets of: http://www.cs.rit.edu/~ncs/color/a_spectr.html Spectral qualities of the material being viewed: Absorption http://www.cs.brown.edu/exploratories/freeS Reflection oftware/repository/edu/brown/cs/exploratorie Diffraction s/applets/spectrum/reflection_guide.html Etc. Spectral qualities of the illuminating light. 4
Light and Color Light and Color Color is the perceptual response to light CIE Experiments – used X,Y,Z values to quantify chromatic characteristics of color stimuli of wavelengths 400 - 700 nm hitting the retina. When rendering, spectrum must be sampled. Color vision is inherently trichromatic. Who is the CIE? Light and Color International Commission on Illumination Color matching applet In French http://www.cs.rit.edu/~ncs/color/a_game.html Commission internationale de l'éclairage Thus, CIE an organization devoted to international cooperation and exchange of information among its member countries on all matters relating to the There are lots of color spaces and most of the science and art of lighting. time we can convert between them, but not Founded 90 years ago… always. Headquartered in Vienna, Austria Light and Color Light and Color CIE RGB curves CIE XYZ color matching curves 40 30 200 20 150 R y 10 G 100 x B 0 z 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 50 7 0 2 5 7 0 2 5 7 0 2 5 7 0 2 5 -10 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 0 -20 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 Wavelength 7 0 2 5 7 0 2 5 7 0 2 5 7 0 2 5 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 Wavelength 5
Light and Color Chromaticity Coordinates Chromaticity coordinates (X,Y,Z have no often given in xyY perceptual correlates, although Y is xy give the luminance, and x and z provide hue chromaticity information) y Y gives brightness X Y Z x = y z = = X Y Z + + X Y Z X Y Z + + + + x y z 1 + + = x Light and Color Light and Color sRGB RGB (or any primary set) can be Standard proposed by Microsoft and HP determined from XYZ Based on ITU-R 709.BT Need chromaticies of primaries and white It is a lighting model for “many” CRTs point. Primaries generally determined by R 3 . 2410 X 1 . 5374 Y 0 . 4986 Z = � � device . G 0 . 9692 X 1 . 8760 Y 0 . 0416 Z RGB values are incomplete without = � + + specification of primaries & white point. B 0 . 0556 X 0 . 2040 Y 1 . 0570 Z = � + Light and Color Light and Color sRGB Other color spaces HSV (hue-saturation-value) CMYK (printing) CIELAB / CIELUV (perceptual) Why does CG use RGB? Convenience http://www.cs.rit.edu/~ncs/color/a_chroma.html 6
Light -- Color Light - Color Full spectral renderers are hard to Converting from SDF to RGB. find Expensive in time and memory 40 Most renderers specify color using RGB 30 triplet (red, green, blue) 20 R For accuracy, must convert from SDF 10 G to RGB B 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 7 0 2 5 7 0 2 5 7 0 2 5 7 0 2 5 -10 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 Full spectral rendering going on at -20 RIT Munsell Color Lab (Mark Wavelength Fairchild) Light - Color Light - Color Converting from SDF to RGB Converting from SDF (S) to RGB R r ( ) S ( ) d = � � � � = R * � G g ( ) S ( ) d = � � � � = G * � B b ( ) S ( ) d = � � � � * = B � Based on how “average” eye works Light - Color Light - Color Converting SDF to XYZ Problems with direct conversion to RGB Negative values 200 Which RGB? (may not match RGB of 150 y monitor) 100 x z Solution: Use XYZ space 50 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 7 0 2 5 7 0 2 5 7 0 2 5 7 0 2 5 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 Wavelength 7
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