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Problem while merging RGB in PS5

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I've just merged the R G and B channels from my last nights session with M63, having processed each channel in DSS (each was 2 x 10 mins subs with 3 x 10 mins darks). Did not do any levels or anything else in DSS. Each of the images looked fine in itself, but for some reason appear to have shifted very slightly when combined. I've included a close up to show the effect.

Is this indicative of a guiding problem (phd seemed to be working well all last night, and the graphs were no worse than normal)?

Is there any way of correcting the problem? I've only done a bit of processing on the L channel (6x10mins with 3 darks) but I thought it was worth persevering if I can correct the error.

Thanks for any help you can provide




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You may need to do a second pass at alignment. My current process (which is in a state of refinement) is:

- align each channel separately

- stack each channel to produce master channel images

- align each master channel (I align to the L band image)

- combine aligned master channels in PS.

The other possibility is some sort of optical artefact. Is it worse at the edges of the image? Perhaps the image field isn't completely flat for all wavelengths?


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I was using a focal reducer on the C925, wihch I believe acts as a field flattener, so I hope it's not that. How do you do the aligning? Is that in PS? I was using the Merge CHannels RGB option to get the 3 separate images combined, but could not see how to manipulate alignment as part of that.


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I like the star alignment algorithm in PixInsight, but there are lots of other choices. You could do it manually in Photoshop using the transform tool on each channel - might be a bit time consuming thought


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You can do it in PS but it is not very accurate, proper aligning software is to be preferred.

Open your colour image and go to the Channels palette. Select the Move tool (letter V) and then press the key to the left of the number one. You can now select any channel and show all three at the same time. Move the active channel one pixel at a time with the move tool.

If you need to rotate you have to use Image Transform and drag the object by its corner handles. Things usually go from bad to worse then.


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