Problems with Prophoto RGB, if the graphics processor is enabled

[gianlucam18089686]

Hello
I have a problem with photoshop v22.5 (also with previous versions)
If I open an image from lightroom classic(v10.4)to photoshop using  "Prophoto RGB" in PS as a workspace, some colors of the image look different in photoshop than what i see in lightroom Classic.
in fact if i open Photoshop and Lightroom together and I make a side by side comparison, in photoshop there is a chromatic difference, especially in the cold tones and in the shadows.
The strange thing is that if I disable the graphics processor in photoshop preferences, the colors are identical in both programs.
I also tried to create a new blank document in PS using Prophoto RGB as workspace and keeping the graphics processor enabled, I drew on it a radial gradient from Black to White, the result is that there is a strange color banding, but even on this occasion if I disable the graphics processor in PS then restart it and redraw the same radial gradient, the color banding disappears.
I had this problem in previous versions of photoshop too, but i got around this by setting the "Basic drawing mode" in the advanced settings for the graphics processor. But it seems that in the latest version of photshop this option has been removed.
Summarizing, the problem I described occurs only if I set Prophoto RGB as workspace and activate the graphics accelerator in photoshop. Instead I don't have this problem with PS if I use AdobeRGB or sRGB as working space even if I keep the graphics processor enabled.
Sorry for my bad English.

System specifications:
Windows 10 Pro x64 21H1 Build 19043.1165
CPU: Intel i7-6700K RAM:16Gb DDR4
VGA:Nvidia GTX 1070Ti 8gb VRAM. Nvidia Driver studio 471.68
Monitor: Primary BenQ PD2500Q - Secondary Dell U2515H. Both Connected via Displayport and Calibrated with Xrite i1Display Pro colorimeter.

I am attaching some screenshots to help you understand the problem better.

[D Fosse · Accepted solution]

Yes, this is an old and familiar bug, first reported back with CS5 ten years ago.

It happens when the GPU does the conversion from ProPhoto into the monitor profile. It does not happen when GPU is off (or previously in Basic mode), as the conversion is then performed by the CPU in the traditional way.

It also does not happen with Adobe RGB or sRGB. That's because ProPhoto is an extremely large color space, and so rounding errors are amplified and exaggerated when converted into a much smaller space.

Where these inaccuracies and rounding errors actually originate I don't know. I first thought it was OpenGL code - but it still happens, when OpenGL is no longer used and these things are done with DirectX (Windows) or Metal (Mac). Perhaps some of the same functions and calls have been maintained for portability.

In any case, we've had to live with this for a long time. There's no workaround, other than not using ProPhoto, or turn off GPU in preferences. The latter was workable when we still had the "Basic" option, without disablig GPU processing completely, but that's gone now.

It should be said, though, that some monitor profiles are more affected than others. If your calibrator gives you a choice, use matrix-based profiles instead of LUT (table) based. I use Eizo ColorNavigator, and I see this with LUT profiles but not at all with matrix profiles. Other calibrators may give different results, but generally matrix profiles seem safer.

Oh, and to be clear: the data are not affected, the file itself won't have this banding. This is only the display in Photoshop.

[gianlucam18089686]

Thanks for the clarification.
To calibrate my monitors I have always used the displaycal software with its calibration loader and with it I have always created a "curves + Matrix" profile, I suppose it is a normal matrix profile.
Now I will try to calibrate the monitor again using this time the xrite i1profiler software and the Windows profile loader and see if the situation changes.
If the situation doesn't improve I'll use Adobe RGB as my workspace in PS.
Thanks again

[TheDigitalDog]

If turning OFF GPU works, it's a GPU bug and you need to contact the manufacturer or find out if there's an updated driver for it. 
Also see: https://helpx.adobe.com/photoshop/kb/acr-gpu-faq.html

I've never seen this, good to know. I'm on a Mac plus using a display with internal calibration (SpectraView) so maybe that would be a solution for you if you ever upgrade the display system.

[D Fosse]

Yes, Spectraview makes matrix profiles (with no option for LUT IIRC). It's also completely absent using matrix profiles with Colornavigator, but pops up with LUT profiles.

and the Windows profile loader

By @gianlucam18089686

That's irrelevant. The calibration doesn't play a part in this. It's the monitor profile, the icc profile used by Photoshop to convert the data before sending to screen. It's happening in that conversion. Photoshop gets this profile from the operating system, and loads it at application startup.

Over the years we've had many threads about this, and many variables have been tested. The only one that proved significant is the monitor profile itself. Type and manufacturer of the GPU never seemed to matter, nor the driver version. Nvidia, AMD, Windows, Mac, all affected equally. This is deeply embedded in code somewhere, but I'd really like to know where.

Chris Cox (since retired engineer) promised to look into it. And that was the last we heard.

[gianlucam18089686]

I'm definitely not a software engineer, I'm just a hobby photographer but at this point i just can't understand adobe's choice to remove the "BASIC Draw" option in photoshop.
No doubt Adobe made a technically correct choice by removing that old option in PS.
But there is a bug that has been known for a long time and it also seems very popular and that option seems to be the one and only way around that problem.
Mine is not a criticism, it is not my intention, I just cannot understand the reason for this choice.
Anyway..
I hope adobe will fix this bug soon even though it's been ten 10 years already. or at least that Adobe decides to put back the "BASIC draw" option in Photoshop.
Thank you all for the help.

Sorry for my bad English

[davescm]

"I'm definitely not a software engineer, I'm just a hobby photographer but at this point i just can't understand adobe's choice to remove the "BASIC Draw" option in photoshop."

The old options were associated with the old GPU functions (OpenGL/CL). Photoshop's graphics routines are being rewritten and updated to use Direct X and Metal. This is forced by changes in the operating systems which are deprecating those functions. I can only presume the removal of those old drawing options is associated with that rewrite.

Dave

[D Fosse]

Yes, that makes sense.