> One thing that strikes me right away about the difficulty getting the
> steps you want from an imagesetter. By making fairly radical adjustments
> to the file in the curves dialog of PhotoShop, you may be ending up with
> far fewer than 255 steps in the file's histogram. When you ask for a
> histogram from your output file, does it show a ragged shape like a comb
> with missing teeth? If so, and the missing teeth are in the areas where
> you have posterization in the imagesetter output, there could be a
> connection.
>
Yes, you do get missing values by applying the compensation curve in
Photoshop.
> Color management systems like KCMS use "Precision Transforms" to tailor
> the data in a file that looks good on a calibrated monitor to the
> precise needs of specific output devices, without the data loss
> inherent in a curves adjustment within the program. PT's for
> Palladiotype, Cyanotype, etc, could do the job, but I don't expect Kodak
> is about to write them for us.
>
> Another possibility for less data loss would be to do as much as
> possible of the needed adjustments in the scanning module of a scanner
> with "extra" (10 or 12 bit) bit depth. The idea is that by applying the
> "alt.proc. curve" within the scanning module you bring a histogram of
> the right curve shape into PShop with a full set of 255 levels. The less
> manipulation in PShop, the more data that goes to the imagesetter. The
> difference is clearly visible in files intended for 4/C output. The
> disadvantage is that your monitor image will not look good (KCMS files
> look terrible on screen after they have been through their PT's, too).
> But spotting and retouching would still be digital-easy. I don't *know*
> that the posterization is due to relatively empty sections in the
> histogram, but it's worth investigating.---Carl
>
Using a different program to apply the curve may work, however I would
not want to apply the curve before going into Photoshop -- that really
defeats a lot of the powerfull editing capabilities of Photoshop. Now
you may be able to edit the file in Photoshop, and then use another
program to apply the curve at the end...
David