QTR-Quadtone RIP

--- 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.