I'm trying to find apps for my rooted Galaxy S3 mini that will override the software involved in image processing so that instead of jpg files, the readout from the sensor will be stored. I was expecting to find a lot of results, but unfortunately I didn't find anything so far.
A lot of people would like it, unfortunately raw date is only available in Android since Lollipop, and then only if the phone manufacturers support it in their drivers.
Any software on a phone is dependant on the hardware access layer (firmware), and if it isn't implemented there, there isn't really a chance to access the data.
To clarify, the jpeg compression is not performed by the applications, but already by the API.