P: Photoshop 27.8 & later Rendering Artifacts, Exposed Previews and Color Banding

Hello,

I have encountered what appears to be a GPU-related rendering bug when converting RGB images to CMYK in Photoshop.

System

• Photoshop 27.8
• macOS Tahoe 26.5.2
• Mac Studio M2 Ultra
• Apple Silicon GPU

Problem

Whenever GPU acceleration is enabled, converting an RGB image to CMYK produces severe black rendering artifacts across the image. The artifacts appear immediately after the color conversion and make the document unusable.

The issue occurs with multiple images and is fully reproducible on my system.

Steps to Reproduce

1. Open an RGB image.
2. Make sure Use Graphics Processor is enabled under Preferences > Performance.
3. Convert the document to CMYK (either Image > Mode > CMYK Color or Edit > Convert to Profile).
4. Large black artifacts appear throughout the image.

Expected Result

The RGB image should convert normally to CMYK without any visual corruption.

Actual Result

The converted image contains large black rendering artifacts that were not present in the original RGB document.

Workaround

Disabling Use Graphics Processor completely resolves the issue.

After restarting Photoshop with GPU acceleration disabled, the exact same RGB image converts to CMYK correctly with no artifacts.

Additional Information

• The problem started recently. Earlier Photoshop versions on the same hardware did not show this behavior.
• The issue does not appear to be related to a specific image.
• Since disabling GPU acceleration immediately fixes the problem, this seems to be related to Photoshop's Metal GPU rendering pipeline rather than the color conversion itself.
• I can provide the original RGB file, the corrupted CMYK result, screenshots, the GPU Compatibility Report, and the Photoshop System Information if needed.

Has anyone else experienced this issue on Apple Silicon Macs, particularly on an M2 Ultra?

Thank you.