GPU preview desaturates saturated colors after Adobe RGB to Lab conversion on Apple M1 Pro

Summary

When I convert a 16-bit Adobe RGB (1998) document to Lab Color in Photoshop, highly saturated colors appear slightly duller/desaturated. The issue disappears completely when “Use Graphics Processor” is disabled in Photoshop. This appears to be a GPU/Metal preview issue rather than a change caused by the color conversion itself.

System information

• Computer: 16-inch MacBook Pro with Apple M1 Pro

• macOS: 26.6.2, build 25G83

• Photoshop: 27.9.1

• Graphics processor: Apple M1 Pro

• Document: 16 bits/channel, Adobe RGB (1998), one rasterized pixel layer

• External display: calibrated Eizo ColorEdge CG, connected via USB-C to DisplayPort

• The issue is also visible on the MacBook Pro’s internal display

• Proof Colors is disabled

Steps to reproduce

1. Create or open a 16-bit Adobe RGB (1998) document containing a single rasterized pixel layer.

2. Add saturated test patches with these RGB values:

   • 255, 90, 0

   • 0, 255, 90

   • 0, 90, 255

3. Include a normal photographic image without extremely saturated colors in the same document.

4. Ensure that View > Proof Colors is disabled.

5. Convert the document to Lab Color using Image > Mode > Lab Color.

6. Observe the saturated test patches.

7. Convert the document back to Adobe RGB (1998).

8. Repeat the test after disabling “Use Graphics Processor” in Photoshop’s Performance settings and restarting Photoshop.

Expected result

The color-managed appearance should remain essentially unchanged when converting from Adobe RGB (1998) to Lab, apart from negligible conversion precision differences.

The approximate Lab values of the test colors are:

• RGB 255, 90, 0: Lab 68, 74, 81

• RGB 0, 255, 90: Lab 84, -123, 62

• RGB 0, 90, 255: Lab 42, 29, -93

These colors are within Photoshop’s Lab encoding range.

Actual result

With “Use Graphics Processor” enabled, all three saturated test patches appear slightly duller or less saturated after conversion to Lab. The photographic background, which contains less saturated colors, appears almost unchanged.

When the document is converted back to Adobe RGB, the test patches appear vivid again.

The problem disappears completely when “Use Graphics Processor” is disabled and Photoshop is restarted.

Additional troubleshooting

• Photoshop and macOS are fully updated.

• The problem occurs on both the calibrated external Eizo display and the MacBook Pro’s internal display.

• The external display connection is therefore unlikely to be the cause.

• Disabling only OpenCL, GPU Compositing, and Anti-Alias Guides and Paths does not resolve the issue.

• The 30 Bit Display option is greyed out.

• Converting the same Adobe RGB document to ProPhoto RGB does not produce a visible change.

• Proof Colors is not enabled.

Impact

This makes GPU preview unreliable for color-critical Lab work. Disabling the graphics processor restores correct appearance, but reduces performance and disables or limits GPU-dependent Photoshop features.

Please investigate whether Photoshop’s GPU/Metal canvas renderer applies a different or incorrect display-color transform to Lab documents on Apple Silicon.

I can provide a small PSD test file, screen photographs, and Photoshop System Info if needed.