Copy metadata during rgbcomp and pixelmath operations
The rgbcomp
command (from #798 (closed)) creates a blank image in which pixels from other images are copied. We lose all header information. The command should copy the header from the luminance image if any, or add more data in the comments/history from all images, maybe preserving observation dates and number of combined images too.
WCS information from any image should be preserved if found.
We might look at the same problem for the RGB composition GUI module some day.
Edited by Cyril Richard