1. Color
Color
Color
Tsung-Yi Wu

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 bits Thousands of colors, hi-color: 16 bits 256 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
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:

16. Complementary Color Complementary Color (pigment)
The complementary color 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 complementary color 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

21. Other Color Models CMYK (for printing)
C = G+B = W-R M = R+B = W-G Y = 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 (Y Cr Cb)
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 G B
U = R G + 0.5B = 0.564(B - Y)
V = 0.5R G B = 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