These are calibrated B-V images from JD2455945.17, as explained at this link.
The one on the left is generated WITH flatfielding of the B and V images used, while the one on the right is generated WITHOUT flatfielding. They are almost identical, but not quite. Here is the difference between the two:
The pattern is the expected pattern from the CCD chip. The histogram of the values is here:
So there is a difference which is distributed around 0 with S.D. 5 millimagnitudes. The effect of flattening would appear to be small – but recall that these are difference images.
Apart from various problems related to aligning images it is rather nice to work with difference images – problems tend to cancel out! However, note in the above how some of the structure on the DS in the B-V image looks like the features of the falt field – as if perhaps the flatfield we used did nothave enoughj ‘amplitude’ in the stripes.