color tsung-yi wu color. introduction color is a subjective sensation produced in a brain. in the...
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Color
Tsung-Yi Wu
Color
Color
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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.
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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.
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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.
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Physiology Color is a subjective sensation produc
ed in a brain.– Color Blindness
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Physiology Light is a form of electromagnetic radiation,
we can measure its wavelength. Visible light: 400nm-700nm
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Physiology Receptor Cells
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Physiology Receptor Cells
Response
Cones
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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
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Tristimulus Theory RGB color model
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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
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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
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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).
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Color Temperature Color Temperature Model
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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
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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.
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Complementary Color Lab
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Complementary Color Lab
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Complementary Color Original
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Complementary Color Example
– http://www.johnsadowski.com/big_spanish_castle.php
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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
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Other Color Models CMYK’s Example
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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).
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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
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Other Color Models YUV (for SDTV)
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Other Color Models CbCr Scaled (Y=0.5)
BUG
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Other Color Models CbCr Scaled
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Other Color Models Example for YCbCr ?
Y
Cb
Cr
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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.
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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."
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HSB Diagrams
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HSB PhotoImpact
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Gamma Correction Consistent Color
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Gamma Correction Example
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Gamma Correction Example
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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