Big ColorSync Bug? macOS Interprets Rec 705 Profile Differently Between 15 and 14

ColorSync throughout the system interprets the Rec. ITU-R BT.709-5 color profile differently in macOS 15 than it did on macOS 14 leading to severe color differences. This is breaking/problem-causing color change.

Here's a comparison of one way the results can appear different.

Steps to Reproduce

1. Open this image above (named here as sRGB_Bars.png) in ColorSync Utility. (This should be an sRGB profiled image if the forums don't mess with that.)

2. With Digital Color Meter open and set to "Display in sRGB" [0-255] you can see the gray bars progress left-to-right as 0, 23, 46, 69, 92, 115, etc... ] Those are the correct reference values.

3. At the bottom of the window in ColorSync use [Match to Profile] [Display -> Rec. ITU-R BT.709-5], then click the Apply Button. You can verify the image now uses the Rec 709 profile with the (i) Get Info button in the toolbar.

4. Use "Save As…" to save the image with a different name.

**) Do the steps above on macOS 14 and macOS 15 to create two images. Rec709_CreatedOnMacOS14, and Rec709_CreatedOnMacOS15.

**) Compare the two images on BOTH operating system versions, and you'll see they are significantly different from each other.

Rec709_CreatedOnMacOS14.png when viewed on macOS 15 has the gray values of: [0, 1, 18, 43, 67, ...]

Rec709_CreatedOnMacOS14.png when viewed on macOS 15 has the gray values of: [0, 51, 72, 94, 115, ... ]

These are MASSIVE differences.

Significance

This is not just a problem that affects ColorSync Utility or Preview, etc. This same gamma interpretation difference is affecting the Core Video, Core Image, Video Toolbox, etc pipelines as well. That gets complicated to talk about, and this is example is the simplest I can boil it down to.

Conclusion

Significant bug? What's going on?