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With "Use GPU for image processing" checked, Lightroom uses >75% of available VRAM and will not release it after completing edits. Specific issue: Transferring RAW files to DXO Photolab for DeepPrime noise reduction results in processing times going from 7 seconds for a 20MB files to six or seven times that.
Lightroom version: 12.1
OS: Windows 10 22H2
GPU: AMD RX 5500, 4GB VRAM
To reproduce the issue:
1) With "Use GPU for image processing" and "Use GPU for export" in Lightroom unchecked, send file to Photolab via plug-in.
2) Process file in Photolab with GPU enabled, apply DeepPrime, export DNG back to Lightroom. Note export time (in my case,7 seconds).
3) Check "Use GPU for image processing" in Lightroom and make adjustments to any file in the Develop module. Return to the Library module.
4) Export a new file via plug-in to Photolab. Repeat step 2. Export time back to Lightroom (or to another program, or to disk) is now 42 seconds or longer.
Windows performance monitor shows Lightroom using around 2GB VRAM with just "Use GPU for display" checked. With "Use GPU for image processing" enabled, VRAM usage is 3GB or more and is not released until GPU image processing is disabled or until Lightroom is closed.
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I meant to post this as a bug, but for some reason it got sent to Discussions instead.
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You stated, “ 3) Check "Use GPU for image processing" in Lightroom and make adjustments to any file in the Develop module. Return to the Library module.“
As far as I am aware when you make a change in LrC Preferences you need to exit the application and reboot for the change to take effect.
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I don't believe what you're seeing is a bug. Instead, it's a reminder of how VRAM hungry LrC is when the GPU is operating in Image Processing mode, and it's even more hungry when full acceleration is enabled.
You can check the LrC System Requirements at https://helpx.adobe.com/uk/lightroom-classic/system-requirements.html
Note that 4GB of VRAM is the minimum for Imaging Processing acceleration, and 8GB is the minimum when full acceleration is enabled. You may also wish to scroll down to the Mac requirements and see that for shared memory systems (i.e. M1/M2) the minimum for full acceleration is doubled to 16GB.
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