Stacking with coverage correction

A feature request for AstroArt 5:

• Center the images to stack by some means (here using the weighted average of all pixels brighter than some threshhold)
• Track the number of images covering every individual pixel of the resulting image while stacking
• Compensate for uneven coverage by scaling the values in the regions with non-maximum coverage
• (nice to have: allow images of different sizes. this is usually not needed.)

Example: Chunks to center and stack

Uncorrected stack

Coverage corrected stack