🚀 go-pugleaf

In <1ish70INNco6@shelley.u.washington.edu> rberteig@shelley.u.washington.edu (Rolf Berteig) writes:

>A quick way to do this with results better than bliting (getting the 
>20 system colors) but with quality still lacking is to create a standard
>256 color pallet and an inverse pallet (with say 2^5 entries). To display 
>an image, for every pixel you take the 8 bits for red,green,blue and shift 
>right 3 bits (now you have 15 bit color) and use this number as an index 
>into your inverse color map. Your inverse color map then gives the closest 
>fit to your standard pallet. Now you are ready to blit your device dependent
>8 bits per pixel bit map.

This is the way old Color QuickDraw did it on the Mac, and
believe me, it's NOT PRETTY.

However, you can implement error diffusion which calculates
the error from one translated pixel and spreads it to
neighbouring pixels with very little performance degradation;
all you have to do is an extra suctraction after you get the
color, and add that difference to the next "real" color you
want to display. Clear the value for each scanline...

Cheers,

							/ h+
-- 
 -- Jon W{tte, h+@nada.kth.se, Mac Hacker Deluxe --
   This signature is kept shorter than 4 lines in the interests of UseNet
   S/N ratio.