When capturing RAW (not ProRAW) photos using AVCapturePhotoOutput, the resulting images are subject to a strange overexposed effect when viewed in Apple software. I have been able to recreate this in multiple iOS apps which allow RAW capture.
Some users report previously normal images transforming over the span of a few minutes. I have actually watched this happen in real-time: if you observe the camera roll after taking a few RAW photos, the highlights in some will randomly **** (edit: this just says b l o w, nice job profanity filter) out of proportion after whatever is causing this issue kicks in.
The issue can also be triggered by zooming in to one of these images from the stock Photos app. Once the overexposure happens on a given image, there doesn't appear to be a way to get it to display normally again. However, if you AirDrop an image to a different device and then back, you can see it display normally at first and then break once more.
Interestingly, the photo displays completely fine when viewed in Affinity photo or random photo viewers on Ubuntu.
Sometimes the issue is not that bad, but it is often egregious, resulting in completely white areas of a previously balanced photo (see https://discussions.apple.com/thread/254424489).
This definitely seems like a bug, but is there any way to prevent it? Could there be an issue with color profiles?
This is not the same issue in which users think RAW photos are broken because they are viewing the associated JPG – this happens even with photos that have no embedded JPG or HEIC preview.
Very similar (supposedly fixed) issue on MacOS: https://www.macworld.com/article/1444389/overexposed-raw-image-export-macos-monterey-photos-fixed.html
Numerous similar complaints:
https://discussions.apple.com/thread/254424489 https://discussions.apple.com/thread/253179308 https://discussions.apple.com/thread/253773180 https://discussions.apple.com/thread/253954972 https://discussions.apple.com/thread/252354516
Finally figured out the cause. Behind the scenes, iOS and MacOS apply a strong tone curve to RAW images. Many default methods of loading and displaying an image (including those used in the stock apps) don't allow you to change this setting.
I imagine that this tone curve is appropriate for ProRAW images, but breaks earlier RAW formats. Unfortunate that it's applied indiscriminately in most Apple software.
However, there is a way to display these RAW images properly in your own apps. Just load data into a CIRAWFilter and set the boostAmount to 0.
