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Adding RGB Stars to NB Image

Patrick Sparkman
in PixInsight
Hi Adam,

I have really enjoyed learning how to use Pixinsight from your video's and articles.  It has helped my image processing quality immensely.  I have paid for both Fundamentals, and Horizons.  I have to admit that I have not watched every video, but am trying to focus on the ones needed to help me solve problems.  My current issue is wanting to add an RGB star field to my NB processed images to get a natural star color instead of the mostly white stars I get with the NB combination.  Can you point me to some specific videos where you might address that issue.  I looked and I don't see anything specific, but I might have missed something.

Thanks again for the wonderful work you do!  The money that I spent on your videos improved my final image quality more than anything else that I have purchased in this hobby!

Comments

  • BlockHeadBlockHead
    Hi Patrick,

    I plan on adding some NB processing to Horizons soon.
    The method I think I would use I do  cover...but no promises...I do not have your data... is one I show in many different forms. Screen blending will do the trick. Make a version of your RGB data that is black clipped..or has a very dark background so that only the stars are seen. Blend this image into your NB image using Screen blending (now accessible as a Pixel math expression combine(NB_image,RGB_stars,op_screen())   ) . 

    It is a good experiment to try...and "Adam BLock" way.
    -the Blockhead


  • Patrick Sparkman
    Hmmm...I tried that Pixel math expression, and did not get the expected results.  The background of the NB image actually got darker, and the stars stayed the same.  The background of the Stars image is 0 0 0.  Do you want to see the files?  If so, what format do you want and how should I send them.
  • BlockHeadBlockHead
    Screen never creates darker pixels in the blended result.. 
    You should provide the permanently stretched NB color image and the Linear RGB image that has stars. The RGB image should already be registered to the NB color image. Both files should be saved as XISF files. 
    You need to upload the files to a cloud server (there are free ones... or perhaps you have something already like OneDrive, GoogleDrive, DropBox...etc etc. 

    I wonder if you remembered to stretch the RGB image before the pixel math blend?

    Anyway, if you can do my first paragraph... I will take a look.

    -the Blockhead
  • Patrick Sparkman
    Thanks Adam.  I played with it again, and this time the background didn't change...so I must have done something wrong the first time.  However, the stars didn't really get the color from the RGB file (I had stretched it), and only got larger.  I will post the files to GoogleDrive for you to pick up and post the link here.
  • Patrick Sparkman
    Oh...do you have a way that I can privately send you the link.  I would prefer to not have the full resolution .xisf files freely available.
  • BlockHeadBlockHead
    ngc1535@caelumobservatory.com
  • Patrick Sparkman
    Awesome!  Thank you Adam.  I will send it now.

  • BlockHeadBlockHead
    HI Patrick,

    So... I went ahead and made a PixInsight Horizons lesson on this. I did not personally identify you, but obviously used your two images to do this thing. May I publish this as a tutorial?

    Thanks in advance for the consideration.
    -the Blockhead
  • Patrick Sparkman
    Absolutely!  I am honored to have my images used.  Any way that I can get a preview of the video though?  :)
  • Patrick Sparkman

  • BlockHeadBlockHead
    I will publish it likely tomorrow. 
    (The raw recording is done... now there is "post processing" of the video... lol)

    As a sneak peek... what I did was the following:
    1. Applied the CorrectMagentaStars script. In my opinion... this does a majority of the work.
    2.. Took your RGB image and permanently stretched with Maskedstretch.
    3. Adjusted that image so only the stars are showing with a black background.. 
    4. Used the screenblend operation I indicated earlier. combine(NB,RGB,op_screen())

    I found that I couldn't make the background as dark as necessary to prevent the blended image from losing some color saturation due to the lightening of the background. Re-raising the saturation is a fine fix. But I felt bad- so I then did a variation where I created this new image with RGB stars in your NB image..but only wrote those stars to your original NB image with a mask.

    At that point. you have RGB stars in your NB image. Your RGB stars are not super colorful- but they are appropriately added. On #2... another variation instead of using MaskedStretch... Arcsinhstretch could be used. Something to try perhaps.

    -the Blockhead
  • BlockHeadBlockHead
    Hi Patrick,

    The video is published here:


    Thank you again for letting me use your image and example.
    -the Blockhead
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