QTR-Quadtone RIP

Hi Jeff,

Nice analysis.  It looks like you have covered a lot of bases.
I must confess I'm not a regular Qimage user -- I use PS on a Mac for all my work.
But a little over a year ago I did coordinate with QImage and this looks surprising
like some of the issues then.  Any chance you are using a relatively old version of
Qimage?   The issue at the time was that Black Point Compensation was working
differently in Qimage than Photoshop.   Internally to Qimage is a color management
called LittleCMS which is actually doing these conversions.

Anyway I wonder if you have an old version or the issue has re-cropped up.

Roy

--- In QuadtoneRIP@yahoogroups.com, "jkohn_home" <jkohn@...> wrote:
>
> 
> Roy (and other interested parties),
> 
> You may recall my discussion about whether or not it was wise to 
> convert to the QTR-CreateICC generated profiles using perceptual  intent
> or not before printing, and I speculated that this could be a  source of
> "double profiling" that would compromise the DMAX of the  print. I
> posted this graph comparing 3 different methods of printing  (using
> graylab, using ICC with perceptual, and using ICC with rel- col). It
> shows the behavior that led me to believe using the profile  with
> perceptual intent might not be such a good idea:
> 
> http://www.pbase.com/jkohn/image/65715318
> <http://www.pbase.com/jkohn/image/65715318>
> 
> Well I decided to do some further testing since you didn't think the 
> results I was getting were correct/expected. This time I decided to 
> take QImage out of the loop by doing any profile conversions directly in
> Photoshop. The results were very different this time:
> 
> http://www.pbase.com/jkohn/image/65974462
> <http://www.pbase.com/jkohn/image/65974462>
> 
> As you can see, using the profile with perceptual intent now yields  the
> most accurate results. I did a little more digging and it sure seems  to
> me that the ICC handling in QImage is broken, at least as it  relates to
> printing to file with grayscale images. I found that you  can take the
> 21x4 random test file, print it to file in QImage with  Printer ICC
> disabled, and the gray steps in the resulting file will  have changed
> from what they should be. Likewise, enabling Printer ICC  and printing
> to file using one of the QTR profiles (either gray-lab  or
> curve-specific) will yield completely different results from doing  the
> conversion in Photoshop.
> 
> I haven't determined exactly what's going on here and whether it just
> affects printing to file, or just happens with grayscale files.  But
> right now, I do not recommend QTR users to use QImage for
> layout/interpolation if you care about getting accurate tonality in your
> prints.
> 
> As the second chart above shows, the ICC profile with perceptual  intent
> seemed to yield the most accurate results when printing a  grayscale
> step chart. But when I repeated the test using a real world  image, I
> found that the deep shadows were too murky and didn't have  the detail
> in them that I wanted. Conversely, printing directly from gray-lab gave
> better shadow separation, but also lightens the midtones too much. So I
> did one final test using gray- lab instead of the profile, but boosting
> the gamma setting in QTR to +4 in order to  darken the midtones some.
> This proved to  be "just right", as the real-world image now showed
> excellent shadow  detail and the midtone values were closer to where
> they should be:
> 
> http://www.pbase.com/image/66139883
> <http://www.pbase.com/image/66139883>
> 
> So in the case of my HPR curves for the 2400, it looks like I'm going 
> to be printing directly from gray-lab using gamma=+4, unless the image
> has no shadows to be concerned with (which is rare for me). The
> resulting  prints look amazing, it was definitely worth all the work (I
> can't  tell you how many step charts I've printed in the last few
> weeks). My  HPR curves are finished, I'll try to write up some notes on
> their  usage and post to the group tomorrow.  The I guess I'll have to
> start testing with QImage's ICC handling is also broken for printing
> color directly to the print...
>