Re: [hpoj-devel] Ghostscript, Gamma, Color Management

[Robert G. B. <rg...@ph...>]

On Wed, 6 Dec 2000, Gerhard Fuernkranz wrote:

> "Robert G. Brown" wrote:
>
> > I'm going to spend some time trying to fix the printer resolution and
> > gamma problem next.  When I print photos, the gamma is without exception
> > too dark (which isn't the printer per se, which works "perfectly" on a
> > color copy process).  Pictures come out looking muddy and dark.  Even at
> > 300dpi, the printer should be able to do much better, especially on the
> > more expensive smooth finish inkjet photo paper.  I don't know if this
> > is just an incongruity between the cdj550 postscript translator and this
> > printer or if it is a real problem with the printer itself, but I assume
> > the former.
>
> I could obtain reasonable result for printing sRGB (see below) color
> images

<some excellent prose deleted>

> Gerhard

I never did thank you for all of this, but thanks tremendously.  It is
always as useful to know the background you provided as the temporary
fix, so one can fix things that the fix doesn't fix, for example.

It also provides a fairly clear map for those who want to contribute
further (to e.g. SANE or to the manifold printer filter installations)
to follow.  If I understand your explanation correctly the short term
fix for photos (jpegs) is to convert the jpegs to pnm's via e.g. djpeg,
correct the gamma with pnmgamma, convert the result to postscript, and
them send the result to the printer via the cdf550.upp (if possible)
ghostscript driver.  The longer term fix is to determine the appropriate
color transformations required for a given printer device in some sort
of standard form (e.g. relative to sRGB) and then integrate a
transformation engine SOMEWHERE into the scanner/printer path.

Is it safe to assume that the pictures taken by a typical digital camera
these days have color output mapped to sRGB?  I note that for my camera
at least they typically look about correct (reasonable colors and gamma)
on the monitor...

   rgb

-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rg...@ph...