I am trying to create a pseudo LRGB image from Ha and OIII masters. In pixel math I identify my Ha to R/K channel and my OIII to G and B channels. I have both images open in the workspace. When I hit apply I get an error message stating that the OIII file can't be found which is rather baffling as it is open on the screen. Can anyone advise what I am doing wrong? Any suggestons will be very much appreciated.
Regards
Gordon