Re: Scanning?

[Eric Smith <eric@brouhaha.com>]

Mike Maginnis <maginnis@tarnover.org> writes:
> Don't know if this has been addressed before. I'm planning to re-scan
> the Computist magazines that I've already done so far, and get moving
> on finishing the rest sometime this decade.
> 
> Any thoughts on the best way to scan these?  I can't seem to get a
> decent image down to less than ~200K.  Anything smaller and it image
> incurs serious quality loss.

For pages that only contain text and line art, *please* use Group 4 fax
lossless compression.  This is a natively supported format in TIFF,
Postscript, and PDF files, and results in 30K-50K sizes for a typical
page (though more for pages with lots of small type or fine drawing
details).  Any good scanning software can do it.  Since it's lossless,
the quality is identical to the original scan.

However, G4 compression is not good for photographs or other continuous-tone
images, because that's not what it's designed for.  Pages that have such
images (other than relatively unimportant incidental ones) should be
compressed with JPEG compression, which is what it sounds like you've
been doing.  Unfortunately JPEG compression blurs text and line art.

Ideally, for pages that consist of a mix of text and line art, and
continuous-tone images, you'd use a graphic editor (e.g., Gimp or
Photoshop) to separate the continuous-tone images into a separate layer,
apply JPEG compression to those only, and G4 to the text and line art.
Then you can composite the result in either Postscript or PDF.

That process yields really nice looking results, but takes a lot of
work.

Eric