Volen
As already discussed, the root cause is that Google Camera does all the processing on its own and uses special SELinux domain for hardware acceleration. That SELinux domain is removed in GOS for security reasons.
It is removed because we don't give special privileged access to Google apps. It would only be possible to do it behind a special toggle which is not planned since nearly everything works fine without it. Portrait mode on 7th generation Pixels is the only thing there have been complaints about and they're working on fixing it in Google Camera.
GOS camera (and any other 3rd party camera) are using the same (restricted) API that lacks all the processing Google Camera offers hence the quality is not comparable. It doesn't matter what 3rd party Camera app we will use - they all use the same API so the quality will be more or less the same (and not good vs Google Camera).
This is completely wrong. Google Camera on the stock Pixel OS has no special access to any additional camera APIs. Other apps can provide the same features and quality. Features and quality vary quite a lot across apps. There is no special magic in Google Camera that's unavailable to others in terms of features and quality. The only special access it has is to hardware acceleration features for more quickly doing the processing when treated by the OS as a specifically privileged app.
GrapheneOS Camera provides hardware accelerated HDR+ on Pixels via the standard Camera2 APIs since the OS and hardware implement it. Google Camera implements their own comparable HDR+ although they have more control over it, meaning they can adjust it to be more aggressive in low light conditions. HDR+ provided by the OS can and should do that too, and they're working on improving it to match Google Camera in all conditions. Night mode, Portrait mode, etc. will be provided via CameraX extensions via the OS in the future. There won't be any special access required to use them, because the OS camera service will implement them itself. Google Camera will almost certainly continue doing it separately in the short term. In the long term, they may move most of the features into the OS instead of doing the processing in Google Camera and only needing the APIs needed to obtain the data in the OS.
Currently, Google Camera is really slow in processing images, especially, portrait pictures or when taking multiple pictures at once.
GrapheneOS Camera provides hardware accelerated HDR+ on Pixels via the standard Camera2 APIs since the OS and hardware implement it. It will have hardware accelerated Night and Portrait modes on Pixels when those CameraX extensions are available. This is our focus.