Color

Tsung-Yi Wu

Color

Color

Introduction Color is a subjective sensation produc

ed in a brain. In the RGB color model, a color is repr

esented 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.

Introduction The CMYK (Cyan, Magenta, Yellow, a

nd 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.

Introduction A 24-bit image can be thought of as be

ing made up of three 8-bit channels, one each for red, green and blue in RGB color.

Physiology Color is a subjective sensation produc

ed in a brain.– Color Blindness

Physiology Light is a form of electromagnetic radiation,

we can measure its wavelength. Visible light: 400nm-700nm

Physiology Receptor Cells

Physiology Receptor Cells

Response

Cones

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

Tristimulus Theory RGB color model

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 bits256 colors: 8 bits

– Grey-level: 256 = 8 bits

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

50,50,50100,100,100255,255,255

0,0,0

(R,G,B)

90,122,

0,16

DirectColor

Palette

0

255

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).

Color Temperature Color Temperature Model

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

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.

Complementary Color Lab

Complementary Color Lab

Complementary Color Original

Complementary Color Example

– http://www.johnsadowski.com/big_spanish_castle.php

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 in

ks “subtract” brightness from white

Other Color Models CMYK’s Example

Other Color Models YUV standard (also called CCIR 601),

known before as YCrCb (Y Cr Cb) – a colour representation model dedicated t

o 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).

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

Other Color Models YUV (for SDTV)

Other Color Models CbCr Scaled (Y=0.5)

BUG

Other Color Models CbCr Scaled

Other Color Models Example for YCbCr ?

Y

Cb

Cr

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.

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."

HSB Diagrams

HSB PhotoImpact

Gamma Correction Consistent Color

Gamma Correction Example

Gamma Correction Example

References http://livedocs.adobe.com/en_US/Photosho

p/10.0/images/sca_white_balance.png http://www.qualityorientalrug.com/designer/c

olor.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