While I was playing around with adaptive stretch on a grayscale image that is to be used as a mask, I noted an unexpected behaviour.
Here are two screen captures of the issue.
The image is the L channel from an rgb (dslr) image of M45. The original image is a stack of 7 subs with full calibration frames. The stack is dithered and there is no indication of anything out of the ordinary with the subs. Dithering was approximately 15 pixels per frame, so what you see in the image is definitely no edge effect.
The original image had dbe applied, cropped to exclude edges and masked stretch + curves transformation applied.
After adaptive stretch of the L channel, suddenly a band appears in the middle of the image. It seems as if adaptive stretch was not applied to this area of the image.
Has anyone seen anything similar before and knows what can cause this?
