Bug in Pixel Math

[Dimitris Platis]

I am trying to do harry's trick for switching narrowband stars with RGB stars (same algorithm like when changing Masked Stretch stars with HT stars).....however, it doesnt work unless I click Replace Image.
When I click New Image it just creates the image written on Pixel Math.
Is it a bug or am I missing something?

[pfile]

you apply this thru a mask, right?

i guess what's happening is that when you don't use "replace image" you get a copy of the original image, which is correct. if you were to use replace image without a mask, you'd overwrite the whole target image with the source image. but since you are using a mask, only those pixels exposed by the mask are written by pixelmath.

i think if you want a new image of just the changes, you'd have to use the pixelmath expression star_mask*rgb_stars (or maybe ~star_mask*rgb_stars).

rob