Digital BW, The Print

Olivier

Roy should step in here but (1) the ICC spec discusses how the kTRC data
should be scaled for media white point-relative colorimetry and (2) in the
documents section of www.color.org you will also find a discussion paper on
Adobe black point compensation.  Roy has done both the black and white point
scaling.


> From: odesmais <odesmais@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Sun, 07 Aug 2005 12:13:25 -0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: [Digital BW] QTR ICC still in the dark...
> 
> I have been trying hard to understand the QTR ICC tool. I thought I
> got it but... no!!!
> 
> When the stepwedge is printed linearised and profile converted I got
> values far lighter than when non profil-converted :  
> 
> DEN Linear Linear+converted
> 0 96,45 96,14
> 5 92,9 93,59
> 10 89,24 90,35
> 15 85,27 86,92
> 20 81,34 83,99
> 25 77,4 80,57
> 30 73,61 77,03
> 35 70,04 73,91
> 40 66,63 70,39
> 45 62,3 66,99
> 50 58,03 63,17
> 55 53,54 58,76
> 60 50,04 55,38
> 65 45,97 51,15
> 70 41,94 46,6
> 75 37,92 42,89
> 80 34,08 38,01
> 85 30,44 31,62
> 90 25,85 26,12
> 95 21,73 21,11
> 100 17,7 17,89
> 
> Basically it looks like it applies a higher gamma...
> 
> I just took the QTR stepwedge, opened it with no color managed
> conversion (CS then assumes it will have the default grey profile
> e.g. 15% dot in my color settings), converted to QTR ICC and print it
> in QTR. 
> 
> Anyway, when visualizing the kTRC tag of the QTR profile, the curve
> does look like it maps destination values lighter than the source
> ones in a nice below the 45° line curve.

The kTRC should look convex/bowed upwards.  So for a given input (vertical
axis) a lesser (than 1:1) pixel value is read from the curve and hence, for
the most part, the image is printed darker than with the simple linear
output.
> 
> Last to make it easier : kTRC seems (from ICC spec.) to be build from
> XYZ. 

XYZ_Y or L* with scaling done in XYZ_Y

>I don't have PM, so I just past Lab values in a PM measurement
> file I got. PM XYZ look pretty strange with double digit figures
> while XYZ range from 0 to 1.99... ?
> 
> So 2 questions :
> 
> 1. Do I need to also input XYZ in PM file to feed QTR create ICC and
> if so how do I convert "real" XYZ to the PM XYZ format ?

I am sorry but I don't follow this at all.  You should be feeding QTR Create
ICC an Eye One Measure Tool file simply by dragging and dropping it.  You
don't need to change anything.


> 2. Is that normal QTR ICC lightens a file ?

His does not seem correct.  Workflow:

1. Build a QTR ink descriptor file to generate a greyscale (curve).
2. Linearize the greyscale by measuring a printed step wedge and inserting
the LINEARIZE function into the ink descriptor file.
3.  Print another step wedge using this newly linearized ink curve and use
MeasureTool to measure it.
4.  Drag the MeasureTool output file to QTR Create ICC.  The output ICC
profile is named the same as the MeasureTool file but its use-name is
QTR-[MeasureTool output file name]

I would expect the opposite of the results above.