1. Color
2015, Fall

2. Colorimetry : Definition (1/2)
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 = C / Frequency
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)
짧은 파장
(고주파)
긴 파장
(저주파)

6. Colorimetry : 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)
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

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)

15. Colorimetry : Color Model (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)
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)
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)
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 Model Applet:

20. Color Models for Computer Graphics