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
Therefore the change of the default RI doesn't influence the imagerendering on screen.
--- Begin Message ---Hello,
- From: Claas Bickeböller <lists@xxxxxxxxxxxxxxxxx>
- To: <argyllcms@xxxxxxxxxxxxx>
- Date: Wed, 15 Jul 2020 13:48:21 +0200
look at the conversion which Photoshop has to do to get to the numbers
displayed in the "Info" palette.
ImageRGB -> CIELAB
Which rendering intent should Photoshop use to do this conversion?
Photoshop takes the one from the colour presets.
To display the image on screen Photoshop makes these conversions:
ImageRGB -> CIELAB -> DisplayRGB
The rendering intent to go to DisplayRGB is always relative colorimetric with
black point compensation until you activate softproofing and specify a
different one
by activating the checkboxes for black and papersimulation.
The checkbox for black turns the RI to rel.col., papersim to abs.col.
Therefore the change of the default RI doesn't influence the image rendering on
screen.
Does this explain what you see?
Best regards
Claas
Hermann-Josef Röser schrieb am 15.07.20 um 09:19:
Hello,
according to the literature, the rendering intent "tells the color
management system how to handle the issue of converting color between color
spaces when going from a larger gamut to a smaller one" (e.g. Fraser, Murphy
& Bunting 2005, Real World Color Management).
With this definition I have a problem understanding the following
experiment:
1) Scanning an IT8-target with my scanner
2) Producing an ICC-profile with colprof: colprof -v -Z t -Zp -qh -bn -ax
KR_Target_IT8_g22
3) Embedding this profile into the image of the target from which the
profile was created
4) Opening the image in PhotoShop and choosing the color space of this
profile as the color space
instead of the working colour space (which is Adobe RGB).
If I now read out the Lab-values of the different patches in PS I would have
expected to obtain the values from the reference table. But this is not the
case. There are large discrepancies. However, if I go to the color settings
tab and change the rendering intent from the default value "perceptual" to
"absolute colorimetric" the Lab values quoted by PS are very close to the
values in the reference table.
Furthermore, in changing the intent, the visual appearance on the screen
does not change, although e.g. the L value of patch GS02 are changing from
97 to 77, which should be easily spotted by eye.
Since I was not changing the color space in what I did (I chose the scanner
profile as working space) I do not understand why the rendering intent comes
into play here and how. Obviously I have not really understood the role of
the rendering intents. :-(
Any explanation of this would be very much appreciated.
Hermann-Josef
--- End Message ---
