CS 445 / 645 Introduction to Computer GraphicsToday we talk about lightingWhat can we sense? Review of lecture notes about colorEngineer a Solution CIE Color SpaceSlide 5Engineer a Solution Devices Have Unique Color GamutsEngineer a Solution RGB Color Space (Color Cube)Engineer a Solution RGB Color GamutsEngineer a Solution RGB Color SpaceEngineer a Solution HSV Color SpaceHSV Color SpaceSolving the Lighting ProblemOptical IllusionLightingSlide 15DefinitionsSlide 17Slide 18Components of IlluminationSlide 20Simplifications for Interactive GraphicsAmbient Light SourcesSlide 23Slide 24Directional Light SourcesSlide 26Point Light SourcesSlide 28Other Light SourcesSlide 30The Physics of ReflectionLambert’s Cosine LawLambert’s LawComputing Diffuse ReflectionDiffuse Lighting ExamplesSpecular ReflectionSlide 37The Optics of ReflectionNon-Ideal Specular ReflectanceNon-Ideal Specular Reflectance: An Empirical ApproximationSlide 41Phong LightingPhong Lighting: The nshiny TermCalculating Phong LightingCalculating The R VectorPhong ExamplesThe Phong Lighting ModelPhong Lighting: Intensity PlotsLighting ReviewCS 445 / 645Introduction to Computer GraphicsLecture 14Lecture 14LightingLightingLecture 14Lecture 14LightingLightingToday we talk about lightingTypical three-step development processTypical three-step development process1.1.Understand the real system – how does light work (Physics)Understand the real system – how does light work (Physics)2.2.Determine what matters to us – what can we sense (Psyc)Determine what matters to us – what can we sense (Psyc)3.3.Engineer a system that remains true to the portion of reality Engineer a system that remains true to the portion of reality we can appreciatewe can appreciateTypical three-step development processTypical three-step development process1.1.Understand the real system – how does light work (Physics)Understand the real system – how does light work (Physics)2.2.Determine what matters to us – what can we sense (Psyc)Determine what matters to us – what can we sense (Psyc)3.3.Engineer a system that remains true to the portion of reality Engineer a system that remains true to the portion of reality we can appreciatewe can appreciateWhat can we sense?Review of lecture notes about colorWhat color do we see the best?What color do we see the best?•Yellow-green at 550 nmYellow-green at 550 nmWhat color do we see the worst?What color do we see the worst?•Blue at 440 nmBlue at 440 nmHow many fully saturated hues can be distinguished?How many fully saturated hues can be distinguished?•128 fully saturated hues128 fully saturated huesHow many saturations can be distinguished for a given hue?How many saturations can be distinguished for a given hue?•16 to 23 depending on hue16 to 23 depending on hueWhat color do we see the best?What color do we see the best?•Yellow-green at 550 nmYellow-green at 550 nmWhat color do we see the worst?What color do we see the worst?•Blue at 440 nmBlue at 440 nmHow many fully saturated hues can be distinguished?How many fully saturated hues can be distinguished?•128 fully saturated hues128 fully saturated huesHow many saturations can be distinguished for a given hue?How many saturations can be distinguished for a given hue?•16 to 23 depending on hue16 to 23 depending on hueEngineer a SolutionCIE Color SpaceInternational standard for describing a color (1931)International standard for describing a color (1931)Empirically determined parameterization (X, Y, Z)Empirically determined parameterization (X, Y, Z)Any pure wavelength Any pure wavelength can be matched perceptually by can be matched perceptually by positive positive combinations combinations of X,Y,Zof X,Y,ZInternational standard for describing a color (1931)International standard for describing a color (1931)Empirically determined parameterization (X, Y, Z)Empirically determined parameterization (X, Y, Z)Any pure wavelength Any pure wavelength can be matched perceptually by can be matched perceptually by positive positive combinations combinations of X,Y,Zof X,Y,ZEngineer a SolutionCIE Color SpaceThe The gamutgamut of all colors perceivable is thus a three- of all colors perceivable is thus a three-dimensional shape in X,Y,Zdimensional shape in X,Y,ZThe The gamutgamut of all colors perceivable is thus a three- of all colors perceivable is thus a three-dimensional shape in X,Y,Zdimensional shape in X,Y,ZEngineer a SolutionDevices Have Unique Color GamutsSince X, Y, and Z are hypothetical light sources, no real Since X, Y, and Z are hypothetical light sources, no real device can produce the entire gamut of perceivable device can produce the entire gamut of perceivable colorcolorSince X, Y, and Z are hypothetical light sources, no real Since X, Y, and Z are hypothetical light sources, no real device can produce the entire gamut of perceivable device can produce the entire gamut of perceivable colorcolorEngineer a SolutionRGB Color Space (Color Cube)Define colors with (r, g, b) amounts of red, green, Define colors with (r, g, b) amounts of red, green, and blueand blueDefine colors with (r, g, b) amounts of red, green, Define colors with (r, g, b) amounts of red, green, and blueand blueEngineer a SolutionRGB Color GamutsThe RGB color cube sits within CIE color space The RGB color cube sits within CIE color space something like this:something like this:The RGB color cube sits within CIE color space The RGB color cube sits within CIE color space something like this:something like this:Engineer a SolutionRGB Color SpaceRGB may be counter intuitiveRGB may be counter intuitive•Must think about mixing colorsMust think about mixing colors•Small changes in RGB value may have large or small perceived Small changes in RGB value may have large or small perceived color changescolor changesRGB may be counter intuitiveRGB may be counter intuitive•Must think about mixing colorsMust think about mixing colors•Small changes in RGB value may have large or small perceived Small changes in RGB value may have large or small perceived color changescolor changesEngineer a SolutionHSV Color SpaceA more intuitive color spaceA more intuitive color spaceHSV is an alternative:HSV is an alternative:•HueHue - The color we see (red, green, purple) - The color we see (red, green, purple)•SaturationSaturation - How far is the color from gray (pink is less - How far is the color from gray (pink is less saturated than red, sky blue is less
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