Strange "waves" in my image after integration

[jirestre]

Hello community, first post here and a beginner with PI and to the hobby.

This is the stretched image of my 40 lights and 20 blacks integration (30s each at ISO 800). I have stretched it to emphasize the problem, those brown and purple waves across the picture, more visible in the bottom half. I shot other targets that night and none of them present this problem. I have processed other 6 or 7 targets with other problems, but not this one, this is new to me.

Previous to stretch this image was DynamicCropped, DynamicBackgroundExtracted, BackgroundNeutralized, ColorCalibrated, and SCRN green removed.

The lights were taken at a dark site, other targets that night (M31, M45 came out decent).
Any clues?

As always thanks a lot for the help.

[pfile]

seems like correlated 'walking noise' - there are a few possible contributors here.

1) hot pixels left in calibrated images - this can be due to mismatched darks (length of dark vs. length of light) or scaling darks (in which case it's normal to have some hot/warm pixels left over as the master dark is multiplied by some scaling factor < 1
    1a) dark sub temperatures don't match light sub temperatures leading to a similar under/over correction of dark/thermal signal in the calibrated lights.
2) lack of dithering - residual hot pixels (and by extension, fixed pattern thermal noise) march along in a line due to slight polar alignment errors causing each successive frame to be offset from the prior by some constant X/Y step
3) in this specific case, 30s is likely too short; 30s might have been OK for your other targets (but in any case at a dark site you should probably do longer subs since skyfog glow is not a limiting factor)

if you asked for dark scaling during imageintegration, you might try again with that turned off provided your dark subs are also 30s. if not, you might try CosmeticCalibration to clean up the hot/warm pixels before registration and integration. however that won't really fix the underlying problem of no dithering (if that's what happened here.)

rob