Re: flexfax: Tiff formats.

[David Woolley <david@djwhome.demon.co.uk>]

> just wondering if anyone has really experimented with what sort of formats
> are good for faxing with hylafax.... I want to have some tiff files to send
> and am not having very much luck in terms of quality of fax, what sort of

TIFF files for faxing should be bi-level at either the normal or fine
resolution sampling rates.  If you want continuous tone, you would be
best advised to use an external tool to convert the image to bi-level,
preferably one that does Floyd-Steiner dithering.

Complicating factors are that the printing technology for faxes is not
tightly specified.  Some may print non-overlapping dots and therefore
have a linear transfer function for dithered images, but others may
use technology where the dots overlap, in which case the image will be
too dark if encoded for the ideal case.

Also, faxes are often printed these days on printers that are 300 dpi,
and therefore cannot accurately represent 200 dpi, with the result that
there may be artefacts on finely patterned areas.

Getting rid of these effects can probably only be done by using a coarse
half-tone screen (rather than dithering), but ghostscript is the only 
free tool that I know to be capable of this and the screening pattern
would be very visible like in old (UK printing technology) newspapers.