Dark frame (substraction): gui & pipe priority
Introduce DT_MIPMAP_FULL_UNSCALED - raw data without black/white prescaling
Cache per-channel black levels
Lighttable: sum and average buttons (works on unscaled raw)
rawscale: template, non-functional
Darkframe: added divider
rawscale: gui
Divider now works!
wip
divider fixed