Although I aimed to get it working only on Galaxy S7 Exynos, there are reports that it is working on other devices like S7 Snapdragon, S8, Note 8 etc...
Working list on S7 Exynos:
-Portrait mode front/back cam
-HDR+ front/back cam
Bugs on S7 Exynos:
-after clean install or clear data when you enter then exit settings the first time, you will get a black screen. Kill the app and start again and everything should be OK.
-if the app hangs during processing a HDR+ or portrait shot, memory leak (500-600 MB) could happen. If it is leaked by GCam, a force close in settings can eliminate it (a swipe away is not enough). However if it is leaked by cameraserver, cameraserver needs to be killed i.e. a reboot is needed for non-rooted users. Memory leak could be observed by looking at 'cat /d/ion/buffer' using adb or root shell.
-in auto HDR+ mode, sometimes HDR+ doesn't want to activate anymore, only normal shots are taken. Workaround: restart the app (swipe away from recents)
-front cam video recording crash
-incorrect EXIF data if denoise is set higher than 100%.
Working/not working for other galaxys:
Note 8: Rear camera touch to focus not working
Settings to be used:
Auto exposure-mode: "Slow shutter" if you are taking pics of static objects in low light environment. In good light it doesn't matter.
B-S-G mod settings:
HDR+ front camera: on
HDR+ front camera fix: on if you have a Galaxy S7 Exynos. If HDR+ works for you without this on front cam, don't turn this on, because it will degrade dynamic range in good light!!!!
Model: Pixel XL Marlin+Taimen
Config camera HDR+: Nexus 6 hdr+ Auto
HDR+ parameters: Default
Fix black level front camera: 0.00
Portrait Mode on all models: enabled
Changes vs. V6:
-HDR+ setting (off,auto or on) should be permanent now
Changes vs. V5:
-fixed bug which caused hdr+ shot failure sometimes!
-attempted to fix HDR+ portrait mode (can be activated by disabling portrait ZSL mode).
-added some description to "HDR+ parameters". For example: 8/10 burst, 1500 MB means: HDR+ operates with 8 shot bursts. Portrait mode (ZSL) operates with 10 shot bursts at most. Estimated total memory usage: 1500 MB (including camera2 api buffers).
Changes vs. V4:
-added more shutter options. Selecting "Stock camera2 api" will get rid of rainbow effect, but dynamic range is poor, because camera can't underexpose fast enough if auto shutter control is on.
-added antibanding modes. Works up to 1/149 sec shutter speed. Only select 50hz or 60hz in case of banding problems, because it can cause suboptimal shutter speed otherwise!
-denoise strength for HDR+ and portrait. For front cam you need to select about 2-300% to really see the difference. Back cam is much more sensitive to this setting.
-HDR+ dynamic range control (called Underexposure multiplier). Reduce below 100% to decrease rainbow effect.
-added Samsung specific metering modes. To enable touch to expose, select "Controlled by GCam".
-added Samsung Live HDR mode. Adds some dynamic range to modes where HDR+ is not available like zero shutter Portrait mode. No Rainbow effect in HDR+ mode if this is selected, but noise is too much unfortunately!
-you can enable HDR+ for Portrait mode by disabling "Portrait ZSL mode". Better dynamic range, custom shutter control, but no zero shutter lag.
-custom white balance. I set greens to 96% to get rid of the greenish look where I sit right now, but it is a matter of taste probably.
-modified HDR+ quality settings. Choose "Very high" if you were using "Medium" before (unstable for me). The recommended "Default" setting is the same as before, it is somewhere between medium and high.
Changes vs. V3:
-front cam HDR+ workaround for S7. Still to be tested in very bright conditions. Turn on "HDR+ front camera fix" if you have an S7.
-front cam: normal pics in auto HDR+ mode are saved now
-front cam: improved non-HDR+ quality
-added a custom auto-exposure mode for HDR+ (only HDR+, so not for portrait). It is called "Slow shutter" because it will decrease shutter speed as much as possible (1/10 secs on S7) in bad light. The result: much lower ISO and noise. Of course fast moving objects will probably get blurry more easily. Only tested this on S7, on other devices it might need some tuning.
Changes vs. V2:
-purple colour on highly exposed areas in front camera fixed
-front cam HDR+
-made medium-very high HDR+ settings work again