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[Sticky] Colored centering of the stars, align channels

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Red Giant Customer
Joined: 2 years ago
Posts: 118

Useful technique. another powerful option in APP that is not as obvious as maybe it could/should be.

I find it almost always necessary using quad band filter with OSC to fix color issue with red and blue sides of stars from those filters. Luckily, my broadband OSC data never had this issue yet. But always with filters and it works quite well, although takes a long time to save all the aligned images. 


Main Sequence Star Customer
Joined: 3 years ago
Posts: 74

Reviving this thread...

I was under the impression never had this issue in APP before, but a recent M31 image stacked with 2.0.0 beta 6had this RGB misalignment. Thanks Daniel for the great video, that workaround resolved this problem. But I cannot confirm this has anything to do with atmospheric refraction. M31 was 60°-80° up in the sky and I had massive misalignment(2-3 px shift between each R,G,B). This issue also showed up in both clear filter and duoband filter stacks, so should have to do with the optics used neither.

However 2 1/2 years later this bug still doesn't   seem to be targeted. Before I bought APP, I used DeepSkyStacker which had an Align channels function if I am not mistaken. I am not sure if there is any reasonable use case where one would want an RGB channel misalignment in stacking. Anyway, it is clearly a bug as the "align channels" function only works when saving&reloading calibrated files. It does NOT work as an option of the usual workflow though, giving the user the incorrect expectation of a channel aligned result.

When the box is ticked, the channels should be aligned in the stack. If system restrictions would require a save/reload to do so, the user should be alerted (and/or system should automatically deroute such path using temp saved calib frames). I feel the worst case option is to have APP simply spit out a faulty result without any user alert or instruction how to circumvent that.

Clear Skies,


Main Sequence Star Customer
Joined: 7 months ago
Posts: 43

I agree that it should be clear that align channels does not, in fact, align channels unless you take specific extra steps.

Nearly all of my OSC stacks have channel misalignment even if I’m shooting at fairly high altitudes so there really is a fundamental need here for OSCs.  So it would be a great benefit to me if the default one click “integrate” option allowed align channels to operate.

Perhaps I’m missing something where the default workflow should not attempt to align the color channels.  Possibly it’s an architectural limitation in how the overall system was designed and didn’t include OSC channel alignment as a fundamental basic step.  That would be unfortunate, but understandable at this point.

This post was modified 2 weeks ago by Steven Miller
This post was modified 1 week ago 2 times by Steven Miller

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