Color

1. Color Color Tsung-Yi Wu Color

2. Introduction • Color is a subjective sensation produced in a brain. • In the RGB color model, a color is represented by 3 values (red (R), green (G) and blue (B) light). • The color depth of an image is number of bits used to represent a color value.

3. Introduction • The CMYK (Cyan, Magenta, Yellow, and Key (black)) model is used for printing, as it models the way color is produced by mixing ink or paint. • Other color models include YCrCb, etc.

4. Introduction • A 24-bit image can be thought of as being made up of three 8-bit channels, one each for red, green and blue in RGB color.

5. Physiology • Color is a subjective sensation produced in a brain. • Color Blindness

6. Physiology • Light is a form of electromagnetic radiation, we can measure its wavelength. • Visible light: 400nm-700nm

7. Physiology • Receptor Cells

8. Physiology • Receptor Cells Cones Response

9. Tristimulus Theory • Any colors can be specified by just 3 values, giving weights of 3 components. • Each type of cone responds to R, G, B

10. Tristimulus Theory • RGB color model

11. Color Depth • Color depth • 24, 30, 36, 48 bits • Grey scale image: R=G=B • Millions of colors, true color: 24 bitsThousands of colors, hi-color: 16 bits256 colors: 8 bits • Grey-level: 256 = 8 bits

12. Indexed Color • Direct color • Indexed color • Palette of 256 colors • Color lookup table (CLUT) • Logical colors => physical colors • 24 bits color => indexed color • 1/3 of data • BMP, TGA, TIFF: palette 0 Direct Color 50,50,50 100,100,100 255,255,255 0,0,0 90, 122, 0, 16 Palette (R,G,B) 255

13. Color Temperature • Color Temperature Model • relationship between the temperature of a theoretical standardized material and the energy distribution of its emitted light as the radiator is brought to increasingly higher temperatures • measured in Kelvin (K).

14. Color Temperature • Color Temperature Model

15. Complementary Color • Either one of two colors whose mixture in the right proportions produces white (in the case of light) or gray (in the case of pigment).Read more: http://www.answers.com/topic/complementary-color#ixzz1H2VM0p2g

16. Complementary Color • Complementary Color (pigment) • The complementarycolor of a primary color (R, B, and Y) is the color you get by mixing the other two (red + blue = purple; blue + yellow = green; red + yellow = orange). • So the complementarycolor for red is green, for blue it's orange, and for yellow it's purple.

17. Complementary Color • Lab

18. Complementary Color • Lab

19. Complementary Color • Original

20. Complementary Color • Example • http://www.johnsadowski.com/big_spanish_castle.php

21. Other Color Models • CMYK (for printing) • C = G+B = W-RM = R+B = W-GY = R+G = W-B • Complementary color • Such a model is called subtractive because inks “subtract”brightness from white

22. Other Color Models • CMYK’s Example

23. Other Color Models • YUV standard (also called CCIR 601), known before as YCrCb (YCrCb) • a colour representation model dedicated to analogue video • Y parameter represents the luminance (i.e. information in black and white) • U and V make it possible to represent the chrominance (i.e. information regarding the color).

24. Other Color Models • YUV (for SDTV) • Y = 0.299R + 0.587 G + 0.114 B • U = -0.169R - 0.331 G + 0.5B = 0.564(B - Y) • V = 0.5R -0.419G -0.081B = 0.713(R-Y) • R/G/B: [0, 1]  Y: [0, 1], U/V: [-0.5, 0.5] • U is sometimes written as Cb and V is sometimes written as Cr

25. Other Color Models • YUV (for SDTV)

26. Other Color Models • CbCr Scaled (Y=0.5) BUG

27. Other Color Models • CbCr Scaled

28. Other Color Models • Example for YCbCr ? Y Cb Cr

29. HSB • HSB: hue, saturation, and brightness • Hue is the actual color. It is measured in angular degrees counter-clockwise around the cone starting and ending at red = 0 or 360 (so yellow = 60, green = 120, etc.). • Saturation is the purity of the color, measured in percent from the center of the cone (0) to the surface (100). At 0% saturation, hue is meaningless. • Brightness is measured in percent from black (0) to white (100). At 0% brightness, both hue and saturation are meaningless.

30. HSB • Saturation is an expression for the relative bandwidth of the visible output from a light source. In the diagram, the saturation is represented by the steepness of the slopes of the curves • the red curve represents a color having low saturation, • the green curve represents a color having greater saturation, • the blue curve represents a color with fairly high saturation • As saturation increases, colors appear more "pure." As saturation decreases, colors appear more "washed-out."

31. HSB • Diagrams

32. HSB • PhotoImpact

33. Gamma Correction • Consistent Color

34. Gamma Correction • Example

35. Gamma Correction • Example

36. References • http://livedocs.adobe.com/en_US/Photoshop/10.0/images/sca_white_balance.png • http://www.qualityorientalrug.com/designer/color.html • http://www.hitachi.co.jp/Prod/vims/e_rlad/tech/lcos/image/point8.gif • http://graphics.stanford.edu/gamma.html • http://www.bem.fi/book/28/fi/2802.gif