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Graphics Cards

Journeyman III

2019 iMac with Radeon Pro Vega 48 and Adobe Lightroom Classic shadow posterization.

I've been battling this issue since Oct 22. I've been back and forth with Adobe support as well as Apple. I've been patient with waiting for OS updates and Adobe updates, hoping the problem would be resolved, but it hasn't as of yet.

In the fall of 2022, Adobe had a major release to Lightroom. It went from version 11.5 to 12. With this release, my machine experiences crushed shadows or posterization when working in the Develop module if Lightroom's Graphic Acceleration is enabled via Preferences. This is NOT an issue in the Library module. If I choose to disable the Graphics Acceleration option, the problem goes away. I'm able to perform my work just fine with the GA disabled, but ultimately, I'd prefer to be using the feature as designed. Adobe also gives a warning that in the near future, the Graphic Acceleration will no longer be an option and will be on by default. If I revert back to Lightroom 11.5, the problem doesn't exist. So it seems something was changed in the Graphics Processor design, causing this issue. I started a thread in the Adobe Support Community, and most responses there led to the graphics processor being the issue and needing an update.

I'm at a loss. From my understanding, it's not possible to update the graphics processor on an iMac. That is only done during OS updates released by Apple, correct? 

Thank You! Devin

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