QTR-Quadtone RIP

Hi Gottlieb,
This is a good set of questions and I think leads to a good introduction on
color management.
The idea of color management -- i.e. using display and printer ICC profiles
-- is to match
L values from the original file.  This is different than making L values
linear.  The
stepwedges have K values that are linear but depending on the profile the L
values
may or may not be linear.  When a file such as the steps you're using has no
embedded profile
it inherits the gray working space defined in Color Settings.  Not knowing
your settings
makes it hard to evaluate your results.

So what you see on the screen depends on the Color Settings -- vary the
workspace and you'll see.
Printing however depends on the selections on the Print page -- No Color
Management means
the Color Settings have no effect on the result.  A Print Profile means that
the workspace
is involved in the output.  The idea being that you want the display and the
print to match.

The idea in making the ICC profile with (1) and (2) is to have a "known"
value sent to the driver,
hence the linear K values are sent to the driver.  But in using the profile
in (7) and (8) the CMS
is trying to match the L values of the input in the print by changing the K
values sent to the
driver.  (Note in (7) "without CMS" isn't really true because the working
space will be used).

So it's hard to say whether the new densities you got are "better".  The
most important criteria
is which stepwedge print matches (i.e. looks) the closest to what you see on
the screen.  I suspect that
the random stepwedge is not a very good image to evaluate this.  Possibly
the "21step" file with
the steps in order is better or maybe a real image.

It's a bit hard to accurately measure this because the idea is a
"perceptual" intent not a straight-line.
But since you using a photo paper with a very dark dMax you can get pretty
close to the straight-line
test by using the QTR-Gray Lab profile for the gray working space in Color
Settings.  This still
isn't perfect since the mapping of L=0 of the file to L=3.xx of the print
adds some non-linearity.

Roy

On Jan 6, 2008 2:57 PM, g.bossert <g.bossert@...> wrote:

> Hello,
>
> my name is Gottlieb and I'm new in this group.
>
> I'm trying to create some grayscale ICC profiles for the Epson 3800
> ABW driver using the QTR-Create-ICC.exe and Datacolor Spyder3Print
> (also knwon as PrintFix PRO with the Datacolor 1005 device).
>
> On my glossy proof paper the Epson 3800 ABW (dark setting) is almost
> linear as it should be.
>
> The generated Grayscale ICC Profile should only correct the L* curve
> only marginally. But instead it seems that the calibration does the
> contrary.
>
> But may be the caibration does all right and I make an error in
> reasoning or calibrating.
>
> The way I created the grayscale ICC profiles was the following:
>
> 1) Open the file "Step-21-gray.tif" in Photoshop CS2 without CMS
>
> 2) Print it with no CMS and the Epson 3800 ABW driver set to the
> setting "Dark"
>
> 3) Let the print dry over night
>
> 4) Read the 21 Patches with Spyder3Print and save it to an Create-ICC
> formated file.
>
> 5) Drag the file to QTR-Create-ICC.exe
>
> 6) Install the Profile
>
> 7) Open "Step-21-gray.tif" in Photoshop CS2 without CMS
>
> 8) Print it with CMS managed by Photoshop, the QTR-ICC pofile and the
> Epson 3800 ABW driver set to the setting "Dark" with the same media
> settings
>
> 9) Read the 21 Patches with Spyder3Print and save the L* vaules to an
> file.
>
> 10) Import the L* Values from the file of step 4 and 9 into an
> spreadsheet an compare them
>
> The resulting graph and the L* values can be found here:
>
> http://www.ironsys.de/pub/yahoo_qtr_group/profile-graph-1.gif
>
> (The color profile was generated with Spyder3Print)
>
> I hope someone can help me.
>
> Thanks,
>  Gottlieb
>
>
>


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