Color

1
Color

• Current Issues
• Realistic and accurate rendering in digital media
  (monitor, printer, camera)
• E-commerce, internet application, video games,
  animation
• Digital photography replacing traditional
  Film-based Photography, digital darkroom, web
  photobook, digital photo developing service

2
RGB Color Space
G
Green (1,0,0)
Yellow (1,1,0)
White (1,1,1)
Cyan (0,1,1)
Red (1,0,0)
R
Blk
Blue (0,0,1)
Magenta (1,0,1)
B
3
Color Frame Buffer
CRT
Red D/A
Green D/A
Blue D/A
Bit n
1
0
1
1
0
0
1
1
0
1
0
1
Bit 4
Bit 3
Bit 2
Bit 1
4
RGB Color Space12 Bit Encoding Example
G
111111110000
Green (0, 1, 0)
Yellow (1,1,0)
White (1,1,1)
Cyan (0,1,1)
Red (1,0,0)
R
Blk
Blue (0,0,1)
111100000000
000000001111
Magenta (1,0,1)
111100001111
B
5
Video Look-up Table forIndexed Color
179
CRT
Look Up Table
Red D/A
Green D/A
Blue D/A
177
178
1
0
1
1
0
0
1
1
0
1
0
1
1
0
1
1
0
0
1
1
0
1
0
1
179
180
6
Color perception

• Color perception involves three quantities
• 1. Hue colors (e.g. red, green, purple, yellow)
• 2. Saturation pastel colors versus vivid pure
  colors
• (e.g. red is highly saturated, pink is relatively
  un
• saturated)
• 3. Lightness perceived intensity (of a
  reflecting ob
• ject)
• Brightness perceived intensity (of
  lightemitting
• objects such as light bulb, sun, CRT)

7
Color perception-- HSL
8
Colormatching functions

• Colors can be specified by weighted sums of red,
  green, and blue
• C T1R T2G T3B
• where T1 T2 T3 are the amounts of R GB colors
  respectively together they formed the
  tri-stimulus values.

9
Basic Tenet of Three-color Theory

• If two colors produce the same tristimulus values
  they are visually indistinguishable.
• Color Gamut
• The range of colors that we can produce on a
  given system with a given set of primaries is
  called the systems color gamut.

10
Chromaticity Coordinates
11
RGB Color Model

• Used in color CRT monitor
• Employ Cartesian coordinate system
• Additive system

12
CMY Color Model

• Cyan, Magenta, and Yellow are the complements of
  red, green and blue
• Subtractive primaries
• Used in Hardcopy devices,e.g. Color printer
• CMYK includes black as another component to
  improve printing quality

13
Additive and Subtractive System
14
HSV Color model

• RGB, CMY color model are oriented towards
  hardware devices
• Human users find the system non-intuitive
• A new system based on the following 3 primaries
• Hue (color)
• Saturation (purity)
• Value (lightness)

15
OpenGL Color Models

• RGBA or Color Index

color index mode
Red
Green
Blue
0
Display
1
1
2
2
4
8
3
ww
www
16
24
123
219
74
ww
25
26
RGBA mode
www
16
OpenGL Colour Related Functions

• Set the current colour and colour index
• void glColor3bsifd ububuiv(TYPE red, TYPE
  green, TYPE blue)
• void glColor4bsifd ububuiv(TYPE red, TYPE
  green, TYPE blue, TYPE alpha)
• void glIndexsifd ubv(TYPE index)