Did some photo observation and it's.. almost disappointing but not surprising.
Bare in mind this is still preliminary.
Low light non-HDR the GS4 has less noise. HDR mode (on not auto on the DT) the DT has less noise than the
GS4 does in HDR or non, and takes HDR photo's considerably faster. From a few brief comparison shots with the flash inside, the DT
pics looked bad, plenty well lit but just bad.
Outside well-lit is a mixed bag so far, you can tell the higher resolution sensor in the DT but that isn't really that important unless
you are trying to print images really large, for regular internet or display on even a large TV they both have plenty.
The DT is faster than the GS4 stock camera but only by a hair, the drag to focus then tap to shoot is superior on the DT,
and (a major plus), the DT is able to adjust balance and such for a specified point on the screen and the GS4 cannot(which is a huge
failing and the GS3 shared it too, don't know about the GS5) If your shot is a room with a window outside where it's bright, on the GS3/4
you have to actually re-frame the shot to have the camera either use the light level of the window(and the room is then pitch black), or use the lower light level of the room, you can't tap where you want it to sample from). So huge win for the DT out of the gate on that score.
Honestly they both look so (relatively) crappy compared to even a couple hundred dollar or less point and shoot, it's hard to get too excited or disappointed either way.
The DT camera works fine for a cell phone, and other than the point sample function, I'd have to say the GS4 is easier to get nice shots with at the moment, but with some effort the DT is capable of better. I might try and setup to do some comparison shots, but unless you have a well calibrated and known display, you aren't going to see what I see or anyone else see's either. Differences between the two, yes, but not a true representation.
Further, with the lack of manual control and inconsistent nature of non-dedicated software, you can take two shots back to back and they will look like two different cameras from the same device which is super annoying trying to compare things.
Unless one is coming from a phone with a really outstanding camera I would not let any of this deter one from going with the DT.
You'd be far better served by a small pocket point and shoot in your glovebox or backpack and having the great screen and huge battery and
fast cpu on the DT IMO. Maybe Android L will have a better camera and/or they will update the firmware or something, part of the problem is there is very little lens/hardware and a lot of software going on with these things and that is a recipe for crappy photos.
I have high hopes the OIS helps out with low light on the Nexus 6, but it's still too big for me.