Hello Hermann-Josef
The LAB values displayed in Info (or the color picker) when using RGB or CMYK
profiles use the rendering intent (RI) that is set in PS Color Settings. If the
RGB profile is of class (not Claas ;) input or monitor - meaning if the wtpt of
the ICC is already LAB 100/0/0 - then changing the RI won‘t affect the values.
When using printer profiles (RGB, CMYK) and if you set PS Color Setting‘s RI to
abs.col. the Info window or color picker will display „real“ LAB values of the
device. If it‘s set to rel.col., then you‘ll notice that the device white point
will be scaled (media relative) to LAB 100/0/0 as well.
I always set PS Color Setting‘s RI to abs.col. to make sure I see the
real-world LAB values associated to the specific printer profile.
It is curious however that you seem to observe the same thing also with your
scanner profile (input), possibly because the RGB whitepoint isn‘t LAB 100/0/0
natively.
Best,
Joe
Am 15.07.2020 um 14:28 schrieb Hermann-Josef Röser
<posts@xxxxxxxxxxxxxxxxxxxxxxxxx>:
Hello Claas,
thank you very much for your answer.
look at the conversion which Photoshop has to do to get to the numbersdisplayed in the "Info" palette.
ImageRGB -> CIELAB
This conversion, as far as I understand color management, is provided by the
transform using the ICC-profile. This specifies the conversion scannerRGB
(which is identical to imageRGB) to CIELab. Why would I need a rendering
intent here? I do not change the color space. So going from imageRGB to Lab
should be uniquely defined.
Display on the screen is a different issue. I just want to understand, why
the Lab-value displayed by PS is being influenced by the rendering intent.
They are certainly not the values sent to the monitor. This is a separate
path in color management. I am just interested in the Lab-values
corresponding to the RGB-values from the scanner.
Therefore the change of the default RI doesn't influence the imagerendering on screen.
To my understanding, the Lab-value uniquely specifies the color of the patch
in the target. So this should not change, but it does.
Best wishes
Hermann-Josef
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