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Color

Color. 2011, Fall. Colorimetry : Definition (1/2). Colorimetry Light is perceived in the visible band from 380 to 780 nm distribution of wavelengths (light's spectrum) Human  distinguish 10 million different colors three different types of cone( 원추체 ) receptors in the retina

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Color

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  1. Color 2011, Fall

  2. Colorimetry: Definition (1/2) • Colorimetry • Light is perceived in the visible band • from 380 to 780 nm • distribution of wavelengths (light's spectrum) • Human  distinguish 10 million different colors • three different types of cone(원추체) receptors in the retina • Standard condition for measuring color • Proposed by CIE(Commission Internationale d’Eclairage) Retina (망막) Lens (수정체)

  3. Human Eye • Retina(망막) • The photosensitive part of the eye • composed of two types of cells, called rods and cones • Only the cones are responsible for color perception. • Cones are most densely packed within a region of the eye called the fovea.

  4. Wavelength vs. Frequency • 사이클(cycle) : 일정한 시간 간격마다 반복되는 동일한 모양 • 주기(period) : 한 사이클이 걸리는 시간 (주파수와 역수관계) • 주파수(Frequency(): 1초에 사이클이 몇번 반복되는가? • 파장(Wavelength) : 한 사이클의 간격 Wavelength = C / Frequency C= 3*108 m/s (빛의속도) the speed of light ( 300 million meters per second) Frequency

  5. Colorimetry: Definition (2/2) 긴 파장 (저주파) 짧은 파장 (고주파)

  6. Colorimetry: Visible Light • Visible light • from 380 to 780 nm • The lowest visible frequency : red • the highest : violet. • White light is an even distribution of all visible frequencies. • Rainbows and prisms divide • white light into the colors of the spectrum. • Black : the absence of light

  7. Colorimetry: Color Model (RGB Color) • Color Matching (Color Models) • RGB Color Model (Fig12-11) • Primary colors: RED, GREEN, BLUE. • Secondary colors: YELLOW = red + green, CYAN = green + blue, MAGENTA = blue + red. • WHITE = red + green + blue. • BLACK = no light. • Disadv • cannot directly represent all visible colors (negative value) 빛의 삼원색 (가산혼합)

  8. Colorimetry: Color Model (Grayscale) • Grayscale • BLACK = 0% brightness, 100% grey. • WHITE = 100% brightness, 0% grey. • NTSC phosphors (older) • Y=0.30R+0.59G+0.11B • CRT and HDTV phosphors (modern) • Y=0.2125R+0.7154G+0.0721B

  9. Colorimetry: Color Model (Paint Color) • Paint colors • Primary colors: • red, yellow, blue • Secondary colors: • orange = red + yellow,green = yellow + blue,purple = blue + red. • All colors: • red + yellow + blue = muddy brown. • Black and white are separate colors, which may be mixed with others to make lighter or darker shades or tones.

  10. Colorimetry: Color Model (CIE XYZ Color) • CIE XYZ Color Model • defined three new hypothetical light sources, x, y, and z, which yield positive matching curves

  11. Colorimetry: Color Model (CIE XYZ Color) • chromaticity diagram (색도도) • curved line  color of the spectrum • purple line  line connecting the ends of the spectrum • white point  x=y=z=1/3 • Saturation(채도) • The relative distance of the color point compared to the distance to the edge of the region • Hue(색상) • the point on the region edge

  12. Colorimetry: Color Model (CIE XYZ Color) • Gamut • specify ranges of colors that can be produced by a particular model

  13. Colorimetry: Color Model (CIE XYZ Color) • Disadvantage • the 2D diagram failed to give a uniformly-spaced visual representation of what is actually a three-dimensional color space

  14. Colorimetry: Color Model (CIE LUV) • CIE LUV CIE LUV CIE LU’V’

  15. Colorimetry: Color Model (CIE LAB) • CIE LAB • retinal color stimuli are translated into distinctions • between light and dark • between red and green • between blue and yellow. • CIE LAB indicates these values with three axes: L*, a*, and b*.

  16. Colorimetry: Color Model (HSV) • HSV (=HSB) • Hue, Saturation, Value (=Brightness) • HUE(색상) : the actual color. • measured in angular degrees around the cone • Ex) red = 0 or 360 (so yellow = 60, green = 120, etc.). • SATURATION(채도) : 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(명도) • measured in percent from black (0) to white (100). • At 0% brightness, both hue and saturation are meaningless. 색의 삼속성 (삼요소)

  17. Colorimetry: Color Model (HLS) • HLS • Hue, Lightness, Saturation (similar to the HSV cone) • the primary colors located at L = 0.5 • the colors of black and white acting as ends of the cones.

  18. Colorimetry: Color Model (CMYK) • CMYK • Primary colors • CYAN, MAGENTA, and YELLOW. • Secondary colors • BLUE = cyan + magenta • RED = magenta + yellow • GREEN = yellow + cyan. • BLACK • = cyan + magenta + yellow (in theory). • BLACK (K) INK is used in addition to C,M,Y to produce solid black. • WHITE • no color (on white paper, of course). • Standard Color Printer 색의 삼원색 (감산혼합)

  19. Colorimetry: Color Model (YIQ) • YIQ • Used by US commercial color television broadcasting (Used by NTSC standard) • Y: encodes luminance • I, Q: encode color (chromaticity) • For black and white TV, only the Y channel is used • People are more sensitive to the illuminance difference • We can use more bits (bandwidth) to encode Y • and less bits to encode I and Q

  20. Color Models for ComputerGraphics

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