Video Raster Graphics

[Hill: p. 22-29. Foley & van Dam: p. 145-184]
virtual raster device
real device
video signal format
gamma correction
component and composite video

Other display devices

Definitions

Pixel aspect ratio
width / height: usually 1
Image aspect ratio
m/n: 4/3 for NTSC, 16/9 for HDTV
Refresh rate
NTSC: 30Hz (interlaced)
PAL, SECAM: 25Hz (interlaced)
most displays: 60 or 72Hz non-interlaced
film?
 
 
Phosphorescence
light given off after electron beam has passed
Critical Fusion Frequency
Image refresh frequency at which image appears steady (no perceptable flicker)
Monitor bandwidth
Rate at which electron beam can turn on and off
Spot size
diameter of a single dot on the output device
Bloom
phosphor excitation beyond area of electron excitement
Resolution
Density of lines that can be resolved

Basic display architecture

Pixels

Colour maps

[Hill: 26-29. Foley & vanDam: p. 564-573, 599-600]
Colour maps are commonly employed to reduce the memory requirements for the framebuffer. Desired RGB display colours are numbered and stored in the corresponding row of the colour map. The framebuffer need only store the colour numbers in this way. The compromise is that the number of simultaneously displayable colours is limited.

What algorithms might one use to generate a colour-map?

Halftoning

Many screens and printers produce are capable of producing only black or white. Nevertheless, one would like to be able to display approximations of continuous-tone images on these devices. A solution is available by relying on the spatial integration that our eyes perform.

The following image is an example of the use of dithering to create an approximation of a continuous-tone image.


Napoleon Visual by www.PDImages.com