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  Standard condition for measuring color Proposed by CIE(Commission Internationale d’Eclairage) Retina ( 망막 ) Lens ( 수정체 )

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.

Wavelength vs. Frequency  사이클 (cycle) : 일정한 시간 간격마다 반복되는 동일한 모양  주기 (period) : 한 사이클이 걸리는 시간 ( 주파수와 역수관계 )  주파수 (Frequency(): 1 초에 사이클이 몇번 반복되는가 ?  파장 (Wavelength) : 한 사이클의 간격 Frequency Wavelength = C / Frequency C= 3*10 8 m/s ( 빛의속도 ) the speed of light ( 300 million meters per second)

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

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

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 )

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 G B

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.

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

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

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

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

Colorimetry : Color Model (CIE LUV) CIE LUV CIE LU’V’

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*.

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 )

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.

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 )

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

Color Models for Computer Graphics