applying color profile followed by converting color profile results in noticeable color cast

[numberonesoniafan]

Expected behavior: In Affinity Photo, apply a scanner profile to a raw scan with no profile, then convert to a working space such as ROMM RGB. 1) Results should be very similar to doing the same steps in an external app (I don't expect that they'd be pixel-perfect, but any differences should not be perceptible). 2) There shouldn't be any visible color casts in the result.

Actual behavior: Results are perceptibly different between Affinity Photo's result and argyllcms' cctiff. Given a scanned IT8/7.2 target with the profile applied and then converted to ROMM RGB (once in Affinity, and then once with cctiff on a copy of the image), for Affinity Photo the dark grey rectangles in the image have a reddish color cast to them, whereas the output of cctiff has those squares as a neutral grey.

Repro steps:

To generate the Affinity Photo output:

1. Open the unprofiled image ("raw0010_2019-5-20-downsampled.tiff").
2. Document->Assign ICC Profile... then Assign the desired scanner profile ("2019-10-27_qh_as_u").
3. Document->Convert Format/ICC Profile... then Convert to the desired working space profile ("ProPhoto RGB"--see Note 1). Rendering Intent is Relative Colourimetric. Black Point Compensation is on (it also repros with BPC off... doesn't matter).
4. Observe that the grey rectangles at the bottom of the image have a reddish color cast to some of them, #19-21 in particular. (The RGB values confirm that there's more red present.)

To generate the cctiff output (can use GIMP instead--see Note 3):

1. Install cctiff. I downloaded the source code, v2.1.1, at https://www.argyllcms.com/downloadsrc.html and compiled it on my Mac.
2. Run cctiff like so:

~/Argyll_V2.1.1/imdi/cctiff -e ~/Argyll_V2.1.1/icc/ProPhoto.icm -ir /PATH/TO/2019-10-27_qh_as_u.icc -ir ~/Argyll_V2.1.1/icc/ProPhoto.icm /PATH/TO/raw0010_2019-5-20-downsampled.tiff /PATH/TO/2019-5-20-downsampled-output_of_cctiff.tiff

Observe that the grey rectangles at the bottom of the image are all neutral grey.

Notes:

1. ProPhoto.icm (which displays as "ProPhoto RGB" in Affinity Photo) is argyll's included ProPhoto color profile (which I imported into Affinity's color profiles by just opening some existing file that already had that profile embedded). However, this still repros if I instead convert to the included ROMM RGB profile in Affinity.
2. The scanner profile was generated by argyll separately (scanin and colprof). (I actually used this exact raw image to generate the profile.)
3. I can also generate the expected output (i.e. no reddish color cast in the dark greys) with GIMP (it's using argyllcms under the hood). Just apply the scanner profile, then convert. I don't have Photoshop so I can't do this experiment there.
4. I'm on Affinity Photo 1.8.3, but this repros on 1.7.x as well.
5. I've also attached the output of Affinity Photo's Preferences->Color menu, just in case those settings matter.

ProPhoto.icm 2019-10-27_qh_as_u.icc raw0010_2019-5-20-downsampled.tiff 2019-5-20-downsampled-output_of_affinity_photo.tiff 2019-5-20-downsampled-output_of_cctiff.tiff

Edited April 5, 2020 by numberonesoniafan

[Chris B]

Hey numberonesoniafan, welcome to the Affinity Forums.

Thank you for an excellent post. I am currently discussing this after reproducing it. Please accept my apologies about the late reply. Hopefully we can get to the bottom of this one.

[Justin]

Hi numberonesoniafan

Thanks for reporting this. I'm not sure exactly what's wrong as yet, but I note that if I change the format to RGB/32 (HDR) before converting from the scanner profile to ProPhoto, then it seems to work correctly.

Regards

Justin

[Patrick Connor]

We have made fixes/improvements to this area ("Colour cast after conversion (ProPhoto)") of the program in the latest release.

The fixes and how to update are described in these forum posts.

• Affinity Photo 1.8.4 for Windows                ( Microsoft Store and Affinity Store )
• Affinity Photo 1.8.4 for macOS                   ( Mac App Store and Affinity Store )
• Affinity Photo 1.8.4 for iOS                          ( Apple iPad Store )
    

We would appreciate you checking that this issue has now been resolved for you,

[numberonesoniafan]

This still repros on 1.8.4; i.e there is still a reddish color cast for the dark greys when converting from the scanner profile to some RGB/16 profile. The workaround of converting to a 32-bit profile still works.

[numberonesoniafan]

I've confirmed this is resolved in Affinity 1.9.0, i.e. you can apply the profile, then convert (in 16-bit) to ProPhoto, and the colors are as expected (no color casts in dark colors). It wasn't mentioned in the patch notes, but I went and verified this myself because I was curious... 😁

Thanks to the devs for their hard work!