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*108 m/s ( 빛의속도 )the speed of light
( 300 million meters per second)
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+0.7154G+0.0721B
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 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