> Do all dithering routines mess up at 49, 50, and 51%?
> In PhotoShop, dithering makes an annoying mess line at these
> tones, which looks stupid on for instance faces or bodies
> with lots of soft tones.
>
See page 62 of Dan Burkholder's book, "Making Digital Negatives for Contact
Printing" (Bladed Iris Press, 7003 Forest Meadow, San Antonio Texas 78240
USA; bladediris@aol.com):
"Nothing is perfect in this world, including bitmaps. You might discover a
bit of noise in 50% dot areas of your image. This can show up in blends made
with the gradient tool. At the exact 50% density, PhotoShop tries to decide
which way to randomize, while at the same time maintaining the film with a
50% white/50% black dot ratio. If this is a problem, try adding some noise
of your own to the affected areas (Filter>Noise>Add Noise) while still in
grayscale mode. Usually only 1 or 2 units of noise is enough....The Color
Partnership has released Icefields 2.3, a stochastic screening (random
microdots) software package that addresses the diffusion dither anomalies,
particularly the grainy appearance in 50% dot and highlight areas."
The Color Partnership, Ice Fields 2.3
2002 Jimmy Durante Blvd. #315
Del Mar, California 92014
800-554-8688
I haven't tried this myself, as I use 400 LPI linescreen instead of the
dithering method for my negatives. Hope you find this helpful.
Charlie Palmer
Albuquerque NM USA