Color Models

Color Models

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AM RadioFM Radio + TVMicrowave

Infrared

UltravioletVisible

Colorimetry

Color Perception involve Hue, Saturation, and Lightness

Hue:distinguish among colors such as red, green, and purple.Saturation:refer to how color far from gray.Lightness: the perceived intensity of a reflecting object.Brightness:refer to the perceived intensity of self-luminous.

White “Pure” color

Black

GraysShades

Tones

Artists TermsTint: results of adding white pigments pure pigmentsShade: comes from adding black pigments to pure pigmentsTone:results of adding both black and white pigments to pure pigments

Color Perception

Dominant Wavelength: the wave length of the color we “see”.Excitation: the saturation of the colorLuminance: the amount or intensity of light

Hue Dominant WavelengthSaturation ExcitationLightness LuminanceBrightness Luminance

Color SystemsSpectral Colors

• The separation of colors by a prism expose a continuous range of spectral colors

• A spectral color is composed of a single wavelength • The helium-neon laser monochromatic light is red (632 nm). • Most colored objects give off a range of wavelengths and the

characterization of color is much more than the statement of wavelength.

Courtesy:hyperphysics.phy-astr.gsu.edu/hbase/vision/colsys.html

Color SystemsThe Newton Color Circle

• The Newton color circle provides a convenient way to perceive the additive mixing properties of colors.

• The R,G,B and their complementary colors C,M,Y are placed on the circle in the order of the wavelengths of the corresponding spectral colors.

Green

Cyan

Blue

Yellow

Red

Magenta

Color SystemsMunsell

• The Munsell color systems match colors to a set of standard samples. • It divides hue into 100 equal steps around a color circle. • This color circle differs form Newton Color Circle by a distortion resulting of

assigning a unit of radial distance to each perceptible difference in saturation• The perceptible difference for hues range from 10 to 18 for the various colors. • Perpendicular to the plane formed by hue and saturation is the brightness

scale divided into a scale of "value" from 0 (black) to 10 (white). • A point in the color space so defined is specified by hue, value, and chroma in

the form H V/C.

Courtesy:hyperphysics.phy-astr.gsu.edu/hbase/vision/colsys.html

Color SystemsOstwald

• The Ostwald color systems match colors to a set of standard samples. • It creates a color space based on dominant wavelength, purity, and

luminance, mapping the values of hue, saturation and brightness. • Establishing the values for these parameters is done with a disc colorimeter

which mixes on a disk amounts of the pure spectral color at the dominant wavelength with white, and black

• A point in the Ostwald color space is represented by values C,W, and B to represent the percentages of the circle. For example 35,15,50 represents 35% full color, 15% white, and 50% black.

Courtesy:hyperphysics.phy-astr.gsu.edu/hbase/vision/colsys.html

Color Models For Raster GraphicsCommission Intenationale de l’Eclairage (CIE), 1931 defined three standard primaries, called X,Y,Z to replace Red, Green, Blue.

The primaries are used to match color by using three corresponding color-matching functions

CIE Chromatic DiagramThe right Figure show the XYZ space

Chromatic values depend on dominant wavelength and saturation and independentof luminous energy.Consider a color C, the we can Write C = XX + YY + ZZ Normalize Against X+Y+Zx = X/(X+Y+Z) y = Y/(X+Y+Z) z = Z/(X+Y+Z) We know that x+y+z = 1, and the luminanceinformation usually in Y (Y cef.), thus we can recover X,Y,Z X = Y (x/y) ; Y = Y ; Z = Y(1-x-y)/y Plotting these parameters

XYZ Color Space

About XYZ SpaceWhen two color A and B are addedtogether new color C lies on the lineconnects both colors.In the side Figure, B defines the dominantwavelength, and the ratio AC to BC expressedas a percent of the excitation purity of A.The closer A to C the more light A includes.

Complementary colors are those that can bemixed to produce white light. D and E on the side Figure are complementary colors.Nonspectral color are those that can not be defined by dominant wavelength such as F.Color gamuts or color ranges is the effect of adding colors together

RGB Color Model

Blue (0,0,1)

Black (0,0,0)

Yellow (1,1,0)

Green (0,1,0)

Cyan (0,1,1)

Red (1,0,0)

Magenta(1,0,1) White (1,1,1)

The color range (gamut) RGB model is defined by the CRT’s phosphor.

C = RR + GG + BB

Let us look at these colors in XYZ spaceRGB NTSC CIE MonitorR (0.67, 0.33) (0.73, 0.26) (0.62, 0.34)G (0.21, 0.71) (0.27, 0.71) (0.26, 0.59)B (0.14, 0.08) (0.16, 0.01) (0.15, 0.07)

RGB Cube

CMY Color Model

Cyan, magenta, and blue are the complements of red, green, blue. CMY is important when dealing with hardcopy that deposit color pigments onto paper.

CMY =

111

RGB -

CMY =

111

RGB -

YIQ Color Model

• YIQ model exploits two properties of the visual system– More sensitive to changes luminance than to change hue or

saturation– Object that cover an extremely small part of our field of view,

produce a limit color sensation.• Y is the luminance (the same Y in XYZ space).• The chromaticity is encoded encoded in I and Q • Only Y component will show black/White TV• More bits are used for Y, and either I or Q has less bits than the other.

YIQ is used by the US commercial TV.

YIQ =

RGB

0.299 0.587 0.114-.596 -0.275 -0.3210.212 -0.528 0.311

HSV Color Model

• HSV model is based on the intuitive appeal of the artists model of tint, shade, and tone.

HSV is a user oriented color model

Using Color Models