QT Gamma Compensation LUT .cube file not available

[youthful_teacher8457]

Hi Caroline,

We stumbled upon an old post about QT Gamma Compensation where your files were being referenced. That was this link: https://web.archive.org/web/20240524125853/https://community.adobe.com/t5/user/viewprofilepage/user-... (this is web archive).

Since the recent Cloud Files change in Adobe (I thought from May) these files are not accessible anymore. I have managed to find the original QT Gamma file that adds the correction, but I am missing the 'undo' file still.

Is there a way for you to retrieve these files?

We would be thrilled if it's possible to still get the undo file.

Kind regards,

Joost Adams

[R Neil Haugen]

I have never heard of an "undo". Which technically would be called an inverse transform.

The gamma compensation is of course totally needed by some users because Apple, on some systems, applies an incorrect display transform for SDR/Rec.709 video files playback in any apps that use the Apple Colorsync color management utililty. Such as QuickTime Player,  and Chrome and Safari browsers.

Other players and browsers used on that same Mac, will not use the wrong display transform. Such as VLC and Potplayer, and Firefox browser.

The image seen in VLC, Potplayer, and Firefox is pretty much the same as all other systems will see.

So in QuickTime player, you get the lighter image. In VLC/Potplayer, you don't.

[youthful_teacher8457]

Hi Neil,

Thank you for your response! I am referring to these files attached. So in a previous post there was a .cube file to add the needed compensation, and there also was an undo .cube file to remove that compensation if it was already in the file.

The problem we faced was on our website. We had thumbnails that were static images. Upon hover, the animation would play exactly from the start-off point of the static image and would transition smoothly to the animation (in mp4 format, with Vimeo's CDN so it would load fast). You could then see a noticeable change in color when hovered.

I have attached an example of that behavior as well. 

TL;DR: We managed to retrieve the .cube file (from another platform) but if it would be possible to retrieve the undo .cube file we could save them in our archives. If that is not possible, only the .cube file that adds it will work too. 

Kind regards,

Joost

[R Neil Haugen]

LUTs are simply look-up tables ... and actually, you do have the LUT in the text file format.

Perhaps that could be used in Lattice (Macs) or LutCalc (PCs) to reformat as a .cube file.

[youthful_teacher8457]

Hi Neil,

Thank you for the clarification. You're 100% correct, and I realize now that the .txt file I had was effectively the LUT itself. I do have the working .cube file for the compensation.

I agree that an inverse transform LUT is unnecessary for our main workflow, since we can always re-export from the original source files. My reason for asking about the "undo" file was purely for archival completeness. I was thinking of a future scenario where we might only have a compensated MP4—without the source—and would need a way to reverse the gamma shift.

Ultimately, the reason I started this new thread was that the original files in Caroline's post became inaccessible after the Adobe Cloud changes in May. I managed to find the compensation LUT elsewhere and wanted to make it available again for any other users searching for it.

Thanks again for your expert insight!

Kind regards,
Joost

[R Neil Haugen]

I see your point about needing an inverse transform LUT to use with "archival" media. I've got Premiere back through 2018 on my current rig, my older backup rig through the original CC2014 version. 

So I should have the inverse LUT on both machines is would think. I'll check today.

When they instituted their algorithm tonemapping the older process wasn't needed for current work of course, and was removed.

But as another user has noted and requested, Premiere needs several inverse transforms that it doesn't presently have. This should be added also.