Premiere Pro 25.5 Wide Gamut Tone Mapping Export Issue working with Lumetri Gamma compensation LUT

Ok ... I work for/with/teach pro colorists, mostly based in Resolve. I've a long time of hearing about the mess Apple made with their improper Rec.709 display transform built into their ColorSync utility. Hours of listening to and talking with full color scientists ... colorist presentations and all. To the nth degree.

But before going into the deep tech, please understand ... there is no uniform "accurate" color shared across screens and devices as that is physically impossible. All colorists are taught this to begin with. They setup according to the standards only so that their produced media falls in the general area on other machines, that other professionally produced media does. "You can't fix gramma's green TV." is still applicable.

Every screen out there is at least a little if not a lot different from any other screens. That's just Life at this time.

To the Mac issues.

ColorSync applies a display transform essentially equivalent to gamma 1.96, instead of the specified Rec.709/Bt.1886 display transform essentially gamma 2.4. But only on Macs without Reference modes that are set to the HDTV setting. Which do show the correct transforms.

But wait ... there's more!

According to testing by a number of colorists, they don't do a good job remapping Rec.709 hue values within the monitor's native P3 space. So Apple by design blows both the tonal and chromal transforms on many Macs.

But again, only on Macs not using the Reference mode setting of HDTV, which does apply correct transforms.

So the issue you have is only on some Macs, is specific only to those computers/devices, and will show a different, lighter image of the Rec.709 file than all other screens/devices, including all broadcast compliant machines/systems, most PCs, Androids, and TVs.

That is the cause of the issue and you need to realize how specific it is. 

Try viewing the files in VLC or Potplayer, and you will see much closer to the image other systems, including many Macs, will see.

That ancient LUT ... was Adobe's attempt to satisfy Mac geeks who wanted equivalent views on their Macs, no matter what the image was like everywhere else. As on all 'normal' Rec.709 screens, the image will be way too dark and over-saturated.

BlackMagic's Resolve has the Rec.709-A export option, which yes A is specifically meaning Apple. It changes the NCLC header tags in the file, using a totally unspecified (and non-standard) second value, that for some odd reason causes many Mac rigs to apply the correct Rec.709 transform. 

Unfortunately, as that second digit is an odd thing, on other screens it can cause unexpected things to happen. Not always, but I've seen some where that causes a very dark image. So ... it is maybe better than the Adobe ancient 'Gamma Compensation LUT' ... but not by too much.

I do not recommend continuuing to use the ancient LUT. As there is a better process for that within Premiere for the last two major versions.

Premiere now has all the color management options in ONE place, thankfully ... the Lumetri panel's Settings  tab ... the tab named Settings.

Go to the Viewing Options section, and set the viewing gamma to 1.96/QuickTime, and that will present the lighter image in Premiere. And export without worrying about that stupid ancient LUT.

Do check for the difference between QuickTime, a totally bonkers player, and VLC and Potplayer though. As the latter two will show you what most others will see of that file.