Club Amiga de Montreal - CAM/CAM_CD_1.iso/files/231.lha/dither8.doc

Text File | 1989-04-12 | 2KB | 35 lines

m            DITHER-DEMO 8

    Dithering is a technique used to fool the human eye into seeing
more colors than are actually being displayed. Dithering works by placing
different colors so close together that the eye 'mixes' them and perceives
a third color. The dither demo program opens a high resolution interlaced
screen that uses two bit-plans: it is limited to display 4 colors, just
like a standard WorkBench screen. Three of these four colors ('white' the
background color is not used) are mixed to yield 9 different 'perceived'
colors. By using a trick of the Amiga hardware we are able to change
the color palette many times during a display field, which lets us use
a different set of 4 colors on EVERY horizontal line. The demo program
only changes the color palette once every 4 lines, giving us 9 colors
per row by 80 rows, or over 1000 colors! This program is the latest in
a series of graphics demos, and the first to use 'animation'.

    Graphics programming using dithering is not nearly as complex
as programming using the Amiga's 'Hold and Modify' (or HAM) mode, so it
provides an economical way to increase the number of displayable colors
without using a lot of memory and caffeine. You'll notice that the demo
program is just over 3000 bytes long; it was written in 'C' and could
easily be reduced further in assembly language.

    This demo program is Copyright © 1989 by Lake Forest Logic Inc.,
publisher of The Disk Mechanic utility package for the Amiga.
Permission is hereby granted to freely re-distribute the program provided
this document file accompanies it and neither file is modified.

        3/15/89  Erik C. Quackenbush

    mCall the Lake Forest Logic BBS at [phone].
     All Amiga, 24 hours, 2400 baud, 20 mb on-line storage.
            PC-PURSUITABLE!