Apparently they have been transmitting low quality and small pixel count images at the initial trials of the cameras while training themselves to run the system. It was interesting and worried us all.
There is a set of alteration software programs in the rover to make panoramas and composite images from individual images. That and the multiple selection of quality for the cameras is new on this rover, and only a limited set of choices was available on the prior rovers.
The efficiency of taking and sending lessor time consuming images was estimated to make the travel less cumbersome with multiple cameras and with those that are multiple megabyte in pixel count.
The images seem to be better as the weeks pass.
If you look carefully at these of sol 46 and 47, the focused areas show a fine linear pattern throughout the stone which appears much like a 'fingerprint pattern' of ridges and color differences. The image was altered in color balance to aid in seeing the pattern, and is a standard white balance in a simple photo editor. It makes a very unusual stone pattern which is internal to the layered material. It both complements and complexes the vacuosities and crystalline larger scale patterns of repeats.
Download and view the full sized image in a photo viewer or editor. The host gives a slightly smaller view online.
Sol 46 MAHLI camera
I'll hope someone can answer your final question.
These individual point of interest questions should be on a single running topic dialog with the archives compromised as it is. Just a suggestion, based on the limited introduction index page size.