Raster Graphics and Color. Aaron Bloomfield CS 445: Introduction to Graphics Fall 2006. Overview. Display hardware How are images displayed? Raster graphics systems How are imaging systems organized? Color models How can we describe and represent colors?
CS 445: Introduction to Graphics
Mask for separating beams for RGB part of displayed image
Phosphor layer with RGB zones
Close-up of the phos-phor-coated inner side of the screenCathode Ray Tube (CRT)
Figure 2.16 from H&B
Figure 2.29 from H&B
Refresh rate is usually 60-120 Hz for CRTs
Figure 1.3 from FvDFH
Monochromatic is a gray-scale image that uses another color instead of whiteRed component vs. monochromatic
Figure 2.8 from H&B
BlackHow Do Artists Do It?
H S V Color
0 1.0 1.0 Red
120 1.0 1.0 Green
240 1.0 1.0 Blue
* 0.0 1.0 White
* 0.0 0.5 Gray
* * 0.0 Black
60 1.0 1.0 ?
270 0.5 1.0 ?
270 0.0 0.7 ?
Figure 15.16&15.17 from H&B
Figures 15.1 from H&B
Figures 15.3-4 from H&B
2C = 2R + 2G + 2B
C1 + C2 = (R1 + R2) + (G1 + G2) + (B1 + B2)
Y matches luminance
These functions are defined tabularly at 1-nm intervals
Linear combinations of the R,G,B matching functionsXYZ Matching Functions
Converting from RGB
to XYZ is a snap:
Given x, y, and Y, we can
recover the X,Y,Z coordinates
add greenA Problem With XYZ Colors
Colored printer ink is more expensive
Notice how much less CMY is needed in the CMYK version
One of the reasons printers use CMYK
And color mixing…CMY vs CMYK