>>14319531They're just flatfielding artifacts combined with doing a mosiac, the instruments haven't been properly calibrated yet. That is the next phase. Note that these same detectors are very widely used, the previous generation is currently in use on Hubble's WFC3/IR. They are quite capable of making high quality data and pretty images.
If you've never looked at raw telescope data you probably have no idea how ugly it stars. Here is an example image from Hubble's ACS camera, which did the famous Ultra Deep Field as well as most pretty images. The typical exposure on the left is fucking horrible, note this is after basic processing. The stars in the image are all streaked by something called Charge Transfer Inefficiency which is caused by radiation damage to the CCD. You can also see striping caused the bias fluctuating. While these things look bad they are correctable.
