I found an issue with macOS Reference Modes where a recreated custom preset does not match the grayscale response of the original Apple-provided preset, even when all visible settings appear to be identical.
For example, when duplicating the built-in Apple Display P3-600 nits Reference Mode preset, the duplicated preset does not produce the same grayscale luminance response as the original system preset.
The comparison is performed under the same physical display brightness setting. The difference is not caused by different brightness levels. The native Reference Mode preset and the recreated preset are tested at the same display brightness, but the grayscale response is still different.
The same behavior also occurs when manually creating a new Reference Mode preset with equivalent parameters, including using Pure Gamma settings. Even when the gamma value and other visible parameters are matched, the grayscale transfer function in the shadow region does not match the original Apple preset.
The difference can be observed using grayscale test patterns, including:
- BarsAndBlack_16bit.TIFF
- CT ColorBar test pattern
With these test images, the recreated preset shows lifted dark tones compared with the original Apple Display P3-600 nits preset. The darker grayscale steps become brighter, indicating that the EOTF/grayscale response is not identical between the built-in preset and the recreated preset.
This behavior can be reproduced using the built-in macOS Preview application. Opening the same test image and switching between the native Reference Mode preset and the recreated preset shows differences in the black level and shadow grayscale response.
The issue can be reproduced on both macOS 26.4 and macOS 15.
Environment:
- macOS: 26.4 (also reproducible on macOS 15)
- Mac: 14-inch MacBook Pro
- Display: Built-in XDR Display
- Reference Mode tested: Apple Display P3-600 nits
The main question is:
When there is a difference between the built-in Apple Reference Mode preset and a recreated preset with the same visible parameters, which one represents the intended and accurate gamma/EOTF response?
Specifically:
- Is the built-in Apple Display P3-600 nits Reference Mode using additional internal calibration data or hidden parameters that are not exposed in the Reference Mode configuration UI?
- Is the recreated preset actually applying the requested gamma curve correctly, while the Apple preset includes additional processing?
- Or is the Apple built-in preset the accurate reference implementation, and the recreated preset cannot reproduce it because some internal display calibration information is unavailable?
Is there a documented way to create a custom Reference Mode preset that exactly matches the grayscale response of an Apple system preset?
Thank you.