QTR-Quadtone RIP

Jeff Kohn wrote:
> I'm running the latest version of QImage, 2007.208. What I don't get is that
> even with Printer ICC disabled (in which case no profile conversion at all
> should be taking place), there was still a change to the L* values in the
> step chart image. It makes me wonder if when printing to file (instead of to
> a printer) there's some intermediate profile conversion taking place that
> shouldn't be (maybe to sRGB?).
>  
> Jeff

Jeff,

You are correct. With CM off in Qimage and an "RGB" greyscale 
target without embedded profile loaded there is no change in 
the step values according to Photoshop. It is different 
however with a true greyscale target like you discovered. It 
doesn't have to be a profile related shift, it could well be a 
shift that happens when Qimage translates greyscale to RGB.
I think it is a new problem as I have tested this in the past 
and  then there were no problems with the CM off (enough with 
CM on though). Doesn't look like a BPC  related issue either 
as the whole range shifts, even up to 4 or 5% at some points 
along the range. Most likely a shift to sRGB + BPC as far as I 
can simulate it with other Qimage settings.

This has to discussed again with Mike Chaney. The problem is
that Qimage is upgrading often and bugs that are only revealed
in odd printing methods are not always discovered right away.

3 possibilities:
The greyscale is getting a profile treatment when it is 
converted to RGB on loading (Qimage internally is RGB only)
The "Honor EXIF color space tag when no profile is embedded" 
is still working on greyscales when CM is off, it is alright 
with RGB files though when it is switched off :-). I have 
discussed this feature with Mike in July 2005 on the Qimage 
list. There are more dangers in that feature.
The greyscale/RGB file gets an sRGB profile treatment when it 
is saved as Print to File. The Web version of Print to File 
may interfere and that one converts to sRGB..

Ernst
-- 

                    --
           Ernst Dinkla


www.pigment-print.com
(         unvollendet         )