Fixing RGB channel shifts in long moon exposures?

Acquisition Gradient Removal Mosaic Processing Solar System Moon
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Arny avatar
Arny avatar

On Nov 8th I had the most perfect night for a shot of the moon on its 17th day:

Little wind from top to bottom atmosphere, thus seeing was excellent and my scope was finally well collimated.

So I went for a long desired full moon disk shot in best quality possible.

Taking my 2my pixel size color Asi678 would have taken ages to get all 38 tiles plus the risk of missing an overlap.

So I went for my Asi2600mono for best use of the 3,76my pixel size and tool R, G and B channels across full sensor. Worked fine, but only at 3fps, so taking 4 panels for 3 colors took several hours.

A first processing of the red channel yielded a great result (see below) - but trying to combine a RGB image from the channels failed due to nasty gradients. Apparently the first red channel tiles had soo much delay to last taken blue and green channels that the colors got distorted across the image.

(I first took red channel tiles counter clockwise NE-NE-SW-SE and then took G and B in pairs working my way up SE-SW-NE-NE, as this was more efficient. Thus time delay between R and B,G is maximum for NE tile)

What have I tried to get rid of the gradients

  • RGB alignment- does not work as gradient differ across image, neither In Pixinsight, Photoshop nor AstroSurface

  • More detailed alignment of RGB channel using star alignment and DynamicAlignement in Pixinsight for combining RGB tiles individually and then to combine as RGB image - did not help either

  • Color calibration also did not help

Any idea what else I could try to get the B and G data well integrated?

Arny

Graded RGB image before postprocessing

📷 image.jpegimage.jpegfully processed Red channel

📷 image.jpegimage.jpeg

andrea tasselli avatar
andrea tasselli avatar
Why would you bother with RGB at all?
Arny avatar
Arny avatar

andrea tasselli · Nov 13, 2025, 12:50 PM

Why would you bother with RGB at all?

First of all in this case to make use of all the data I acquired :-)

But in the first place I was aiming for a mineral moon image for which you need color.
In hindsight a color camera would have been a good advice, but I also wanted to work out how to take RGB seperately, ie. for planets.

So any advice or experience in this case?

andrea tasselli avatar
andrea tasselli avatar
Yes, a color camera would have been highly recommended in these cases but too late now. It *might* be doable but a lot depends on the final stacked frames/panels for each of the color channels. Without them there isn't much I can do or advise. Most likely it will require manual handling off the beaten path (e.g., using Siril and/or Iris) but again it is just my guess (and experience having done it before, if I may be so bold in saying)…
Arny avatar
Arny avatar

andrea tasselli · Nov 13, 2025, 04:06 PM

Yes, a color camera would have been highly recommended in these cases but too late now. It *might* be doable but a lot depends on the final stacked frames/panels for each of the color channels. Without them there isn't much I can do or advise. Most likely it will require manual handling off the beaten path (e.g., using Siril and/or Iris) but again it is just my guess (and experience having done it before, if I may be so bold in saying)…

So would go as far as to recommend to do the moon always, or at least when doing full disc, with a color cam to avoid the issue or properly aligning the channel of a panels in the aftermath, Andrea?

andrea tasselli avatar
andrea tasselli avatar
Yes, I would. And I would recommend doing the same for Jupiter too.
Well written Respectful
Brian Puhl avatar
Brian Puhl avatar

I’ve tried this before, and the only way I was able to do it was a completely manual alignment in photoshop. Absolute PITA, and still wasn’t quite perfect, I don’t know of any other way really.

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