1. Color Models (Review) (from CPSC 453)

2. Color ModelsColor Models –Introduction –Describing Colors –Color Perception –Color Spaces Color ModelsColor Models –Introduction –Describing Colors –Color Perception –Color Spaces Overview ch 15, pp 418-435

3. Study the nature of color and its numerical descriptionStudy the nature of color and its numerical description Examine some standards for representing colorExamine some standards for representing color Define and use various color spacesDefine and use various color spaces Study the nature of color and its numerical descriptionStudy the nature of color and its numerical description Examine some standards for representing colorExamine some standards for representing color Define and use various color spacesDefine and use various color spaces Goals

4. IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) Overview

5. How are colors described accurately in numerical terms?How are colors described accurately in numerical terms? How do the numerical descriptions relate to everyday ways of describing color?How do the numerical descriptions relate to everyday ways of describing color? How does one compare color?How does one compare color? What range of colors can a CRT display or a printed page reveal?What range of colors can a CRT display or a printed page reveal? How are colors described accurately in numerical terms?How are colors described accurately in numerical terms? How do the numerical descriptions relate to everyday ways of describing color?How do the numerical descriptions relate to everyday ways of describing color? How does one compare color?How does one compare color? What range of colors can a CRT display or a printed page reveal?What range of colors can a CRT display or a printed page reveal? Important Questions

6. Color Models : Introduction Wavelength  : Distance light travels during one cycle of its vibration Electromagnetic phenomenon Waves that lie in a narrow band of wavelengths

7. Color Models : Introduction Spectral density S( ) (power per unit wavelength) “Pure spectral” light : light sources which emit light of essentially a single wavelength (ex: laser)

8. Most light sources: Contain power of various amounts over a continuous set of wavelengths Their spectral densities (“spectra”) cover a band of wavelengths The spectral power distribution of a light source is the amount of energy it emits at each wavelength in the visible spectrum. Idealized daylight Color Models : Introduction

9. IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) Overview

10. Precise characterization of the colorPrecise characterization of the color One color : many different spectral shapesOne color : many different spectral shapes How many numbers? Just three!How many numbers? Just three! –Color perception is three-dimensional What “coding” scheme?What “coding” scheme? –Several conventions –Current international standard Precise characterization of the colorPrecise characterization of the color One color : many different spectral shapesOne color : many different spectral shapes How many numbers? Just three!How many numbers? Just three! –Color perception is three-dimensional What “coding” scheme?What “coding” scheme? –Several conventions –Current international standard Describing Colors

11. Color Models : Describing Colors W Dominant Wavelength : W Dominant Wavelength : hue of the color L Luminance: L Luminance: total power of the light (area under the entire spectrum) S Saturation: S Saturation: (purity of the light) percentage of luminance in the dominant component Strength of the spike spike Strength of the white light spectrum Bandwidth Capitalizes on the variety of spectra that produce the same (perceived) color

12. Previous method: given a color, it is not clear how to measure saturation, luminance, and dominant wavelength Let’s compare colors with a set of color standards and find the closest match Density a, b, c : test colors Color Models : Describing Colors

13. Remember: color perception is three-dimensional : Any color can be constructed as the superposition of just three primary colors, R, G, B r, g, b: scalars describing the amounts of primary colors Why Red, Green, Blue? Sensitivity of our cones (eye cells) to these three colors Color Models : Describing Colors

14. Experiment: how people match colors? Pure spectral color mono  )  ? ? One cannot remove light that isn’t there! C alone cannot be constructed as the superpositions of POSITIVE amounts of the THREE primary colors (r, g, b) Color Models : Describing Colors

15. IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) Overview

16. Color Models : Color Perception C alone cannot be constructed as the superpositions of POSITIVE amounts of the THREE primary colors (r, g, b)

17. Commission on illumination (CIE) defined three special “supersaturated” primary color X, Y, Z Color Models : Color Perception

18. Standard CIE chromaticity diagram (1931) Human Visual System Color Models : Color Perception

20. Complementary colors Color Models : Color Perception

22. IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) IntroductionIntroduction –Why study it? What is light? Describing ColorsDescribing Colors –Dominant Wavelength, Color Matching Color PerceptionColor Perception –CIE chromaticity diagram, Color Gamuts Color SpacesColor Spaces –Physical (RGB, CMY), Perceptual (HLS, HSV) Overview

23. Color Models : Color Spaces RGB

24. CMY(K) RGB

27. RGB, CMY : Physical Spaces Color Models : Color Spaces

28. HLS, HSV : Perceptual Spaces Painter’s palette Color Models : Color Spaces

29. HLS : Hue, Lightness, Saturation Primary wavelength Perceived luminance Purity or vividness Color Models : Color Spaces

30. HSV : Hue, Saturation, Value Color Models : Color Spaces

32. RGB // r,g,b values are from 0 to 1 // h = [0,360], s = [0,1], v = [0,1] void RGBtoHSV ( float r, float g, float b, float *h, float *s, float *v ) void HSVtoRGB ( float *r, float *g, float *b, float h, float s, float v ) HSV Color Models : Color Spaces

33. RGBHLS void RGBtoHLS (float r, float g, float b, float *hue, float *light, float *satur ) void HLStoRGB (float hue, float light, float satur, float *r, float *g, float *b) Color Models : Color Spaces