Let's say I want to take the highest dynamic range pictures with a smartphone camera. Do I need to look for a specific sensor with better hardware for HDR photos, or find the best camera app because the sensor doesn't matter?
For instance, the ISOCELL camera in the Samsung Galaxy S5 takes significantly more dramatic HDR pictures than the Exmor sensor in the Sony Xperia Z2, but unfortunately has much lower low light sensitivity.
Since many smart phone "HDR apps" don't actually do any real HDR so it's useful to define what we are talking about.
HDR stands for "high dynamic range", it's designed for situations where the highlights are too bright and the dark areas are too dark so the camera can't capture the entire range of brightness in a single shot.
HDR is done in two steps:
In the first step the software creates an image that does have the entire brightness range, usually by combining multiple shots at different brightness levels - the result from this step is usually an image that looks bland and boring if viewed directly.
In the second step the software takes the result from the first step and process it to enhance details, colors and local contrast - the produces the "HDR look" of images with saturated colors and details everywhere.
Many HDR apps only perform the second step, they take a single non-HDR image and process it to look HDR-ish, you can recognize them easily because they take just one image - for those apps you need a good camera that is capable of capturing the entire dynamic range of the scene (there are no "good" apps in this category since this is all cheating but you do want the better apps because the not-very-best in the category tend to push the saturation and processing way too far into "clown puke" territory and behind).
The real HDR apps take multiple shots - traditionally at least 3 - and combine them, if you have one of those the app is more important because as the entire HDR technique was invented to overcome camera limitations - so it works pretty well with limited cameras.
Obviously the camera does matter, you can get by with a bad camera and a good app but you'll get better results from a good camera with a good app.
HDR is always software, not hardware. The concept behind HDR is that you take multiple images at different exposures and then combine them to produce a wider dynamic range than the sensor itself could do.
All that really matters is if the HDR app is able to control the exposure settings on the camera. As long as the app can adjust the shutter speed of the camera, it can then produce over and under exposed images in addition to the normal exposure and these image are then combined in HDR software to pull out the details that come out most clearly in each.
I know this is an older post but I have a Samsung Note 3. I have an HDR app on the phone that takes 3 different pictures all at difference exposure settings.
It then combines the three images and allows me to tweak the settings for the look I want.
The process of taking 3 separate pictures is slow. This is a HARDWARE limitation. If anything in your shot is moving that object tends to either blur out or disappear altogether. This reduces the sharpness of the image slightly.
Ideally, you would want hardware that can change exposure settings VERY rapidly and take a shot 3 times, all in the blink of an eye.
