As my DSI is uncooled, "bracketing" lights with darks for each frame/segment is recommended.
Basically, take darks often, and a lot of them.
For the entire mosaic, I took 174 lights, and 144 darks.
I did take flats and Bias frames, and used them to calibrate the darks.
I tried using just the darks from each segment for each segment, but they didn't match color and brightness.
When I used all the darks for all the lights, they matched right up.
I used MaximDL to Calibrate and Combine, then FITS Liberator.
I do a full range stretch in MaximDL to get all data. Then after combining and opening in FITS Liberator, I use the same exact stretch settings for each segment. Then save as a .TIF for Photoshop.
Imaging: 8" f/5 Newt on a Celestron AVX mount
Meade DSI Color with ATIK .5 focal reducer / Celestron UHC/LPR filter.
Guiding: 60mm Meade Telestar refractor
Logitech Quickcam Pro 3000 / PHD Guiding