On Thu, May 25, 2000 at 12:12:58AM -0700, Doug Coward wrote:
A couple of years ago, after reading the chapter on
ASCII art
in "The New RTTY Handbook", I wrote a quick and dirty program
to to convert .BMP files into non-overstrike ASCII pictures
I could send in emails. From the book, I created my levels of
"gray" in 8 levels with this character array:
M H I : " , . [SP] (from dark to light)
Do any of the line printer art programs attempt to distribute the error to
neighboring pixels? I always assumed those systems (the commercial ones
anyway, like the outfits that used to make line-printer T-shirts from photos)
used something like Floyd-Steinberg halftoning, where you use the value of
the current pixel to choose a level of gray, then figure out by how much
that level differs from the value you *really* wanted, and distribute that
error to neighboring pixels which you'll visit later on in the sequence.
Having a cumulative error of only one level of gray per line lets you get
really nice pictures from lousy output devices, all with integer math...
John Wilson
D Bit