With the help of Claude and Codex, I've tried upgrading a screen magnification, capture, and pixel peeping app (SnoopX, from Stanford's software repository) to be HDR-aware. For images that are truly HDR (displayed in Apple Photos, Google Photos in Chrome, or Mac Preview), and on an HDR monitor with plenty of EDR headroom (Apple XDR display), I should see pixel values well above 1.0. Apple's Digital Color Meter does. However, my app does not. I think the code is doing all the right things with ScreenCaptureKit, but it never returns values above 1.0. Has anybody gotten this to work? Here is what Codex says about the code it helped me build in my app:
• Set captureDynamicRange: We set config.captureDynamicRange = SCCaptureDynamicRangeHDRLocalDisplay (when available). Note: Gemini’s SCCaptureModeHDRLocalDisplay isn’t a real symbol — the actual API is SCCaptureDynamicRange.
• Use preset: We try initWithPreset: SCStreamConfigurationPresetCaptureHDRStreamLocalDisplay, but your runtime crashes on initWithPreset: (unrecognized selector), so we fall back to manual config. That means your system SDK headers mention the preset, but the runtime doesn’t implement it.
• Pixel format: We explicitly set kCVPixelFormatType_64RGBAHalf. Your logs show the stream buffer is 64RGBAHalf.
• Enable HDR on display: EDR headroom logs show current=6.40, so HDR is active.
• Color space: We set Extended Linear Display P3 for stream, and we forced the screenshot sampler to convert into extended‑linear P3 before reading. The screenshot itself reports Extended sRGB, but conversion doesn’t yield >1.0 either.
Despite all of that, the OS is still delivering tone‑mapped values (max 1.0000) for both the stream and the screenshot path.
So I don’t think there’s a missing knob here; it looks like a system‑level limitation on Tahoe for desktop capture.