28 Jun
2004
28 Jun
'04
2:35 a.m.
>>>> "Paul" == Paul Williams
<paul(a)frixxon.co.uk> writes:
Paul> Tom Owad wrote:
> I was doing 150dpi greyscale jpegs. I've
changed to 400dpi 1bpp
> tiffs, and now I'm ending up with each page about 700K... (scan
> as greyscale tiff (unknown compression), convert to 1-bit with lzw
> compression, save as pdf in Photoshop).
Paul> You need to scan at 1bpp, not grayscale. When you are
Paul> converting from grayscale to 1bpp, you are probably getting
Paul> dithering (a pseudo-random scattering of black and white
Paul> pixels) in order to approximate the original grays at the edges
Paul> of characters. This dithering will ruin the achievable
Paul> compression in G4, which is a fax algorithm optimised for runs
Paul> of white and black pixels.
That certainly would do it, and it will also wreck the appearance of
the resulting files. For black and white material, the conversion
method you need is "Threshold" -- you do NOT want "dither".
paul