How does RT editor window rendering intent work?

[KarlMagnusLarsson (Magnus Larsson)]

How does RT editor window rendering intent work? Is it broken in latest dev source 5.8-3107-gd92f5f7ca, or am I misunderstanding something?

Background:
I am using latest dev source 5.8-3107-gd92f5f7ca on Debian 11.4. using a calibrated wide gamut EIZO monitor. In the Debian GNOME settings | color, i have selected the ICC profile from EIZO screen calibration. In RT have the ‘system default (from GDK)’ selected in RT main edit window. This sets up a color managed system. I have almost always used ‘relative colorimetric’ as RT main window editor rendering intent.

In the RT main editor window there are combo boxes for monitor profile, rendering intent, soft proofing and highlight pixels (out of gamut).

Rendering intent is the second combo box from the left in the picture above.

For a RAW file (Canon 5D mk IV CR2) do we have this proces?:

RAW → RT working profile (ProPhoto) → Monitor profile

and RT rendering intent (perceptual, relative colorimetric, absolute colorimetric) converts between the RT working profile and the Monitor profile? This means that if my RAW-file + RT edits and settings push some colors out of monitor gamut then I might get different visual rendering results in RT main editor depending on ‘rendering intent’ settings. Is this correct?

An attempt to test:
In my test, if I highlight pixels out of gamut relative to the monitor profile (for a very saturated set of colors in a RAW file) I do get out of gamut warning relative to monitor profile. (I use the button with the exclamation mark !. Edit: ‘soft proofing’ button is not active.

However changing ‘rendering intent’ from perceptual to relative colorimetric to absolute colorimetric, does not change anything for me in terms how the RT main editor renders the picture. I understand the changes could be subtle and not so obvious, but I ought to be able to detect something.

[kofa (István Kovács)]

That may be because the intents only have an effect if the profiles support them. Simple matrix profiles don’t.

See this informative response:

Colour management - intents

Hi @kofa, thank you for sharing this experiment. Color management and ICC profiles are confusing so it makes sense to probe things like this to gain an understanding. Personally I kind of expected this result. Elle Stone’s profiles from the repo you linked are matrix profiles and as such don’t contain any intent look-up tables (LUTs). It is also stated on Elle’s page: As a very relevant aside, using perceptual intent when converting to sRGB for photographic image editing does not magically ma…

[KarlMagnusLarsson (Magnus Larsson)]

Thank you @kofa, for pointing this out. I also noticed this reply further down in your thread:

@ggbutcher

LCMS2 will silently default to an attainable rendering intent if the one specified in the transform call is not available. So, you need to know the contents of both the input and output profiles to know how it’ll go…

If I do:
./iccDumpProfile 'CG279X(35945120)10Display-100-D65.icc'
I get:

Profile:          'CG279X(35945120)10Display-100-D65.icc'
Profile ID:       Profile ID not calculated.
Size:             8480(0x2120) bytes

Header
------
Attributes:       Reflective | Glossy
Cmm:              Unknown 'MSFT' = 4D534654
Creation Date:    1/27/2022  20:03:28
Creator:          'Eizo' = 45697A6F
Data Color Space: RgbData
Flags             EmbeddedProfileFalse | UseAnywhere
PCS Color Space:  XYZData
Platform:         Microsoft
Rendering Intent: Perceptual
Type:             DisplayClass
Version:          4.20
Illuminant:       X=0.9642, Y=1.0000, Z=0.8249

Profile Tags
------------
                      Tag    ID      Offset	    Size
                     ----  ------    ------	    ----
    profileDescriptionTag  'desc'       276	     172
             copyrightTag  'cprt'       448	     152
   chromaticAdaptationTag  'chad'       600	      44
       mediaWhitePointTag  'wtpt'       644	      20
             luminanceTag  'lumi'       664	      20
           redColorantTag  'rXYZ'       684	      20
         greenColorantTag  'gXYZ'       704	      20
          blueColorantTag  'bXYZ'       724	      20
Unknown 'vcgt' = 76636774  'vcgt'       744	    1554
                redTRCTag  'rTRC'      2300	    2060
              greenTRCTag  'gTRC'      4360	    2060
               blueTRCTag  'bTRC'      6420	    2060

Where I find:
Rendering Intent: Perceptual

Is that the verdict? The calibration result icc profile for an EIZO CG279X using their ColorNavigator7 software hard codes Rendering Intent: Perceptual? (I calibrate using Windows dual boot, but prefer Linux, so I transfer the monitor profile icc result to Debian Gnome Color management). Calibrated state is stored semi-persistently in monitor.

If I do:
./iccDumpProfile 'CG279X(35945120)10Display-100-D65.icc' ALL
I get several ‘LUTs’ but I do not know what to look for.

On the input side I am using Canon 5D mk IV with RT | Color tab | Color management | Auto matched color profile selected. This point to ‘Canon EOS 5D Mark IV.dcp’.

Edit: Are color profiles with multiple rendering intent rare? This not discussed very often, as I see it.

[ggbutcher (Glenn Butcher)]

I found this treatise helpful:

https://www.argyllcms.com/doc/iccgamutmapping.html

Essentially, matrix/shaper profiles are always colorimetric, not enough information to to anything other than a “dump 'em just inside the gamut” gamut transform. It takes a LUT to do a Perceptual or Saturation gamut transform.

[KarlMagnusLarsson (Magnus Larsson)]

Thank you @ggbutcher. I have browsed your reference, but I need to read again, more carefully.

Meanwhile, does anyone know what is normal to have in an ICC profile from EIZO ColorNavigator calibration? My current monitor ICC profile is attached:
CG279X(35945120)10Display-100-D65.icc (8.2 KB)

Is my monitor profile limiting rendering intents? Is Rendering Intent: Perceptual normal in a monitor calibration result? I am calibrating periodically using EIZO software using the native gamut of monitor as target. I am following a standard process from EIZO.

Is it the RT ‘Canon EOS 5D Mark IV.dcp’. file that is limiting rendering intents, somehow?

[kofa (István Kovács)]

@KarlMagnusLarsson

Where I find:
Rendering Intent: Perceptual

The rendering intent specified in the header of an ICC profile is the intent that is recommended to be used when converting from that profile to some other profile, not to that profile from some other profile.

ICC Profile Conversion Intents

[priort (Todd Prior)]

I also wonder if there is any interplay with windows…you can choose rendering intent in the os color management say for different types of content. It might be interesting if you create a test profile in windows and change the intent and then calibrate and see if your icc still ends up with perceptual or if that has been drawn from the OS settings?? I really have no idea but just wondering…

EDIT: THere are gamut mapping profiles and advanced settings …default for photography is perceptual…

This is win 11 but I recall 10 is much the same…

[KarlMagnusLarsson (Magnus Larsson)]

Hello @priort and all,

Thank you for the advice.

@priort

I also wonder if there is any interplay with windows…you can choose rendering intent in the os color management say for different types of content. It might be interesting if you create a test profile in windows and change the intent and then calibrate and see if your icc still ends up with perceptual or if that has been drawn from the OS settings?? I really have no idea but just wondering…

I do indeed have Windows 10 color management set as exactly the same as the Windows 11 settings you show;

@priort

This is win 11 but I recall 10 is much the same…

Ok, I will change my Windows 10 settings and recalibrate using EIZO ColorNavigator7 and analyse what happens.

[KarlMagnusLarsson (Magnus Larsson)]

I get ‘intent’=‘perceptual’ in my color profiles from ColorNavigator 7 regardless of changes to ‘ICC rendering Intent to WCS Gamut mapping’.

The CG279X has a built in calibration sensor and ColorNavigator 7 does not have rendering intent settings. EIZO do describe in documentation how to change rendering intent in different applications. EIZO does not mention any restrictions regarding application side rendering settings. I have sent a question to EIZO support.

My latest profile is here:
CG279X(35945120)10Display-100-D65.icc (8.2 KB)

./iccDumpProfile 'CG279X(35945120)10Display-100-D65.icc' 

Profile:          'CG279X(35945120)10Display-100-D65.icc'
Profile ID:       Profile ID not calculated.
Size:             8416(0x20e0) bytes

Header
------
Attributes:       Reflective | Glossy
Cmm:              Unknown 'MSFT' = 4D534654
Creation Date:    7/30/2022  19:29:32
Creator:          'Eizo' = 45697A6F
Data Color Space: RgbData
Flags             EmbeddedProfileFalse | UseAnywhere
PCS Color Space:  XYZData
Platform:         Microsoft
Rendering Intent: Perceptual
Type:             DisplayClass
Version:          4.20
Illuminant:       X=0.9642, Y=1.0000, Z=0.8249

Profile Tags
------------
                      Tag    ID      Offset	    Size
                     ----  ------    ------	    ----
    profileDescriptionTag  'desc'       276	     172
             copyrightTag  'cprt'       448	      88
   chromaticAdaptationTag  'chad'       536	      44
       mediaWhitePointTag  'wtpt'       580	      20
             luminanceTag  'lumi'       600	      20
           redColorantTag  'rXYZ'       620	      20
         greenColorantTag  'gXYZ'       640	      20
          blueColorantTag  'bXYZ'       660	      20
Unknown 'vcgt' = 76636774  'vcgt'       680	    1554
                redTRCTag  'rTRC'      2236	    2060
              greenTRCTag  'gTRC'      4296	    2060
               blueTRCTag  'bTRC'      6356	    2060

Question1: Is this profile ‘CG279X(35945120)10Display-100-D65.icc’ limited in rendering intents? How to analyze and conclude what the profile supports?

Btw all of these RT output profile have ‘intent’ = ‘perceptual’ as well:

• RTv4_Large.icc
• RTv4_Medium.icc
• RTv4_sRGB.icc
  (I have not checked the other RT output profiles)

This means that RT TIFF and JPG result files have ‘Rendering Intent: Perceptual’ embedded in them. Question2: What does this mean when RT renders such a TIFF and JPG in main edit window?