bits/pixel) monochrome image files to GIF image files. It is not robust
in the TIF formats it will accept; I wrote it for the two cases I
needed. I am open to suggestions on additional TIFF variations to support.
You have the option if stretching the image in the X direction, making
the resulting file more suitable for the benighted non-square pixels of
a CGA, EGA or Hercules display board.
If the same number of bits is used for the GIF file, no dithering is
used. Otherwise, you have a choice of Floyd-Steinberg or Stucki
dithering. FS is quick, and gives reasonable results. Stucki will give
better detailing, at the expense of some time.
For multi-bit output, the dithering uses gray-levels, and a "color"
table is written to the file for use by display programs. Try using 3
bits on a VGA, or 2 bits for an EGA. ( Be wary of some VGA programs
which do not set color tables correctly! For example, CSHOW5 only allows
4 shades per primary, just like an EGA.) Most EGA/VGA monitors/cards I have
seen have a disproportionally bright "full white", which gives poor
results, though you could try adjusting the contrast & brightness. The
IBM 8514, for those of you with $, looks wonderful with 4 bits. I
have added an option (for Stucki dithering only) to disuse the brightest
level, which helps EGAs with the above problem considerably.
Please direct comments/complaints to me, CompuServe 7377,1761.