Interestingly, in this particular case, although the photo was the same resolution as before, Google Photos decided to not only reduce the size of the file, but scale down the image as well. After the compression, we are left with an image with a resolution of 2268 x 3024, which is roughly equivalent to 7 MP, down from the original 12 MP. Ouch. It doesn't look bad or anything, but this seemingly per-photo type of compression may not be to the liking of some people out there (I can vouch for this). We tried running this particular image through Google Photos twice and the results were identical both times.