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Thread: Comet Registration using PixInsight with RGB

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    Default Comet Registration using PixInsight with RGB



    I have a question about using the Comet Alignment process in PI. I'm following Warren's process in his book, 'Inside PixInsight', to process the comet against a background of non-trailed stars. I have used this process many times, but always with a OSC camera (QHY10). The results were usually very good.

    I am now using a monochrome camera (ASI1600mm) and have RGB subs that have been calibrated and registered based on the best Green sub. I have integrated each filter set into a RedMaster, GreenMaster and BlueMaster to prepare for the subtraction process later on. Because of bad gradients in the images (mostly due to the light pollution in the area of the sky) I want to apply DBE on each. But because of the movement during the image capture time each of the masters is slightly shifted. To compensate I wanted to apply Dynamic Crop on the master that has the black borders (in my case, I believe it was the RedMaster but that is not important to the question) and then make sure they are all aligned by applying the same crop to each of the other two masters. This works fine to get the final CometMaster via Channel Combination, but later when I try to subtract the CometMaster during the integration of the star images to get the final 'stars only' master the geometry of the frames is different and PI fails. I understand why, but if don't crop the initial masters I'm assuming the black borders around the RedMaster will mess up the DBE process.

    Assuming I'm making myself clear, is there a way to do this and still end up with a Cometmaster that can be subtracted in the final integration step? Or am I worrying about the DBE process messing up and it will be OK. I could then crop the final later.
    Scopes/Mounts: Celestron EdgeHD-11 on HyperTuned CGEM-DX mount; William Optics GT102 on iOptron iEQ30 Pro; Criterion Dynamax-8 SCT
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    Default Re: Comet Registration using PixInsight with RGB

    I'll try to help. (The comet that Warren uses in his book as an example is mine)

    Don't try to DBE the masters--it will only screw you up. If you do, and you crop out the black bits, you have to crop the star master also.
    My recommendation is to do your channel combination, create your color comet and your star master, then do your comet subtraction. Clone stamp out the residual comet bits if they're in the way

    At this point, you should have a color comet and and color star image. Here, you can do the dynamic crop to get them to size and do your DBE, etc if you want to. However, all you really have to do is just to DBE on your star image. Lighten the background on the star image so that it's brighter than the comet, and then use pixelmath to do max (comet,star). That way only the comet will be added to the final image and you don't need to worry about the background of the comet at all.

    That's one way. There are certainly other approaches.
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    Stuart Forman


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    Default Re: Comet Registration using PixInsight with RGB

    Thanks Stuart - I'll give your suggestions a go; certainly sounds simpler. And I like the idea of essentially eliminating the comet image's background in the processing. I just took a bunch more LRGB subs of 46P early this morning, so I have a lot of data to play with.
    Scopes/Mounts: Celestron EdgeHD-11 on HyperTuned CGEM-DX mount; William Optics GT102 on iOptron iEQ30 Pro; Criterion Dynamax-8 SCT
    Lenses: Hyperstar-III; Celestron 0.7x FR; WO Flat/Reducer 0.8x
    Guiding: Orion ST80; WO 50mm; Celestron OAG
    Cameras and Filters: ZWOASI1600mm Pro (ZWO LRGB and NB), QHY10, Canon 50D; ASI120MC
    Misc: Feather-Touch focuser w/remote; ZWO 31mm FW; Kendrick Dew System, Temp-est Fans
    Software: SN7; SGP; APT; BYE; PHD; MG; FlexRX; PSP; PI; Registax; FireCapture

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    Default Re: Comet Registration using PixInsight with RGB

    The issue with that is your star field will be different. But good luck!
    Stuart Forman


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    Default Re: Comet Registration using PixInsight with RGB

    Quote Originally Posted by s24man View Post
    The issue with that is your star field will be different. But good luck!
    Oh, I'm not going to combine the two sessions - just that I have another set of data to process.
    Scopes/Mounts: Celestron EdgeHD-11 on HyperTuned CGEM-DX mount; William Optics GT102 on iOptron iEQ30 Pro; Criterion Dynamax-8 SCT
    Lenses: Hyperstar-III; Celestron 0.7x FR; WO Flat/Reducer 0.8x
    Guiding: Orion ST80; WO 50mm; Celestron OAG
    Cameras and Filters: ZWOASI1600mm Pro (ZWO LRGB and NB), QHY10, Canon 50D; ASI120MC
    Misc: Feather-Touch focuser w/remote; ZWO 31mm FW; Kendrick Dew System, Temp-est Fans
    Software: SN7; SGP; APT; BYE; PHD; MG; FlexRX; PSP; PI; Registax; FireCapture

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    Default Re: Comet Registration using PixInsight with RGB

    I'm looking forward to seeing the result
    Stuart Forman


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