Denoise is not using GPU even if Lightroom preferences says that my system supports full acceleration

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Description of Issue: I recently upgraded Lightroom classic to version 15.6. Before that it used to take around 10 seconds to run Denoise in one of my files (photos from Nikon Z8). Now it takes around 25 to 30 seconds. This time does not change if I set the “Use Graphics Processor” preferences to off or custom. It seems that the software is always using the CPU instead of GPU. In spite of this behaviour, the application is recognising my processor (Apple M1 Ultra) and it says that it supports full acceleration.

Lightroom Classic Version 15.6

OS version 26.7.1

Camera model: Nikon Z8

Hardware: Mac Studio M1 Ultra, 128 GB

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António Gil250908655h1gAuthor

Participating Frequently

The information I got from the net is that Apple Neural Engine (ANE) support for Denoise was re-enabled starting in version 15.4 (and maintained in 15.6) for Bayer and X-Trans RAW files on Apple Silicon devices. Is this wrong?

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GilSantos

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António Gil250908655h1gAuthor

Participating Frequently

Thank you, Johan, for your reply.

Adobe did this several times before. This time is also temporary, or permanent? Because it makes a big diference when denoising batches of files.

Regards,

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GilSantos

JohanElzenga

Community Expert

AFAIK, denoise always uses the GPU, regardless of that setting. The real reason for the slow down is that Lightroom Classic is no longer using the Apple Neural Engine for denoise, because that still caused quality issues.

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-- Johan W. Elzenga

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António Gil250908655h1gAuthor

Participating Frequently

Thank you for your answer.

I just checked the issue and what I got from the net is that Apple Neural Engine (ANE) support for Denoise was re-enabled starting in version 15.4 (and maintained in 15.6) for Bayer and X-Trans RAW files on Apple Silicon devices.

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GilSantos

JohanElzenga

Community Expert

Yes, it was enabled in 15.4 (resulting in a major speed increase), but unfortunately that info is not complete. It has been disabled again because of quality issues (faint blocks were visible sometimes). If the Neural Engine was still taking care of denoise, then you would not have seen such a drop in speed. By the way; the Neural Engine is a separate processor. It is not the same as the GPU. If denoise was still done by the Neural Engine, then disabling/enabling the GPU would have nothing to do with this speed problem, because the GPU would not be used for denoise in the first place.

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-- Johan W. Elzenga

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