QTR-Quadtone RIP

jkohn_home wrote:
> 
> --- In QuadtoneRIP@yahoogroups.com, Ernst Dinkla <E.Dinkla@...> wrote:
>> Roy Harrington wrote:
>>
>>> I think Ernst may have pinpointed the issue.
>>
>> Roy,
>>
>> I'm not so sure about that right now. I have done this before
>> and I think I made the same mistake again. Qimage actually
>> does exactly the same as Photoshop does when CM is off in both
>> applications. When CM is off in PS the Greyscale one will
>> convert to the same RGB numbers the Qimage conversion makes
>> when CM is off. So Qimage and Photoshop behave the same when
>> CM is off. The plain TIFF converter of my website that has no
>> CM at all produces the same numbers.
> 
> 
> Here's how I tested. I took the 21-step gray chart from QTR's Eye-One
> folder and printed it to file with CM turned off. Now open both the
> original file and the QImage-generated file in Photoshop, choosing
> "don't color manage" when prompted. Then I looked at the LAB values in
> the Info palette to compare the two images. The values from the QImage
> file had changed and were no longer correct.
> 
> But now that I think about it, the QImage version is actually RGB data,
> not grayscale. On a lark, I decided to "assign" the "qtr-rgb-lab"
> profile to the image. Once I did that, the L* values for the gray steps
> were correct. I'm not entirely sure I understand this result but it does
> seem to indicate that printing grayscale images to file in QImage with
> Prtr ICC disabled works. Printing the two images in QTR and measuring
> indicated that the results were indeed consistent.
> 
> That said it still looks like there are problems in the case of actually
> trying to use Prtr ICC in QImage so for now I'll be leaving it disabled.
> I've settled on keeping my images in gray-lab anyway, as opposed to
> converting them to curve-specific ICC profiles before printing so this
> shouldn't cause too many problems.

Don't think you used the right solution to get the test 
correct as far as I can understand it.

I also think that you throw away the best part of QTR's ICC 
profiling this way. There's very little difference between 
keeping the images in Gamma 2.2 or Gray Lab and what it brings 
is may be only visible in a CM environment when editing. But 
there's a lot more control by using (custom or generic) QTR 
printer profiles for editing in a CM application (softproof) 
and after conversion to the profile in printing with QTR or 
with Epson's ABW.

Ernst
-- 

                    --
           Ernst Dinkla


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