[G4 Q&A, Help & Troubleshooting] AquariumVitae:
Thoughts on how (not) to compare image quality especially with third party apps

Preambel:

in this context "stock camera" means whatever LG packaged into the official LG G4 stock roms, in my case Marshmallow. So no V10 backport/sideport or likewise

"third party camera app" refers mostly to me using "ProShot", but in some cases also "FreeDCam"; but is not limited to

third party is simplified an app not from LG; it is mostly available through Play store or via apk sideload. The point is that for comparison it must be available to - and run on - any custom/AOSP based ROM.

honestly I did not yet go to any custom ROM, neither Stock nor AOSP. My 2016 built G4 (H815) didn't boot loop yet and my 2 years warranty is void in a few months. Therefor and because I might have time in late summer I will go from theoretical to practical.

if and when you use automatic modes and respective filter settings of a camera app, you might not be interested in the detail that I am going into. Honestly, that's nothing wrong and maybe a healthy decision!

as I work very often in manual mode and I constantly adjust these settings to get specific results, it is very important to judge in detail, also doing pixel peeping :cyclops:

These are more hypothetical methods for comparison the stock ROM and custom ROM camera performance. It is a subject that bothers me for quite some time. As I stumbled upon this thread I decided to dump methods on how I would - or better will - do the comparison. Please don't be offended because of me ripping apart the previously mentioned methods.

I believe that the methods presented in this thread - to determine quality difference between Stock and Custom/AOSP based ROM - are quite flawed.

Just to analyze the quality it needs most complete EXIF data. Which isn't available in the posted images. (Again, you might be fine by "just looking" at the automatic mode results .) As I use the stock camera app now and then and mainly ProShot I know that these apps differently set Shutterspeed and ISO under same conditions. I guess, which is done by the expectation and goals of the respective developers. So a good comparison would require to set the values manually. Also focus, as far as it can be done precisely (eg. macro and infinite; as I know only "FreeDCam" provides setting it by values in %)

Yes, the basis for comparison should be a raw image. Example: ProShot has an option for noise reduction. It can be set to "NR HQ/LQ/Off". When taking pictures with these settings you (most of the time) can easily distinguished each from the other. Therefor ProShot either uses different and own algorithms, or it can say to Camera2 API (wild guess...) to do more/less noise reduction. Just by this fact, a comparison between the stock camera JPGs and ProShots JPGs isn't enlightening.

Therefor raw/dng files should be better for comparison. BUT there is the next thing: The stock camera saves DNGs with a different bit depth than ProShot. (I just now cannot name a tool to read the bit depth, but you'll find one). Stock camera creates 10bit files where ProShot creates 16bit files (btw, size is about 20MB vs 30MB). I do not know if ProShot just converts the 10bit data and puts it into a 16bit file. But therefor even a comparison between stock and third party RAW/DNG might not be valid, too!!! FreeDCam offers in its "complex" user interface different RAW bitdepths but I never gave it a try.

Btw, I read once (TL;DR) that modern professional cameras "nowadays output 14bit or even 16bit depth" raws. Therefor another wild guess(!) is that the LG G4 truely outputs only 10bit raws - even for ProShot. I got not the slightest idea on how to determine. Do you? Help appreciated!

Not to compare apples and oranges I would rule out in-depth comparison between stock and third party camera apps as the stock app won't be available. As I am already almost only using third party apps even on stock ROM this makes it in the future much easier for me to determine if and how much custom ROMs influence the LG G4 camera and photo quality.

Until now it's theoretical and addresses the methods that I will use myself in the near future. Sorry for making such a fuzz about it. That's all I can offer for now.