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Pixel Math Not Working

Mossyback
in PixInsight
I've been trying to combine an RGB image with a Luminance using pixel math. I've asked for help on the PI site and the responders say that the formula that I'm using should work --- but it doesn't. 

I used the Expression Editor and parse and got the following information.       

Parsed 1 PixelMath expression(s)
2referenced images(s)
2 referenced image(s):

Master_Lum: 2723x2186, Gray

RGB_Image05: 2723x2186, RGB

Expression #1:

Infix: combine(Master_Lum,RGB_Image05,op_screen())

Postfix: Master_Lum,RGB_Image05,op_screen(0),combine(3)

I'm new to all of this but apparently it's saying that all is well.

The error message that I get when processing in PI is "Error: Invalid symbol identifier"

Help!
Hank

Comments

  • BlockHeadBlockHead
    There is something more going on... Can you post screen shots of your PixelMath screen..and make certain you do not have anything in the "Symbols" tab?? (this is the likely culprit)

    -the Blockhead
  • Mossyback
    Hi Adam,

    This is driving me crazy. I just set up the pixel math screen to send to you and I first applied it to my images. Now nothing happens - no response from PI except the RGB image goes grey.

    Hank
    Screenshot 2023-02-23 at 8.51.54 AM.png
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  • BlockHeadBlockHead
    Well... this isn't the typical usage of the screen blending mode.
    Note that you are trying to combine a greyscale luminance with a color image. This is not the usage I suspect you want. BUT... if you REALLY do want this.. you need to convert your Luminance image to an RGB image. 
    Then it will blend exactly as you want. This is your issue..and I win the prize for getting the answer!

    Use Image->Color Spaces->Convert to RGB 

    -the Blockhead


  • Mossyback
    "This is not the usage I suspect you want."

    What I would like to do is end up with my LRGB image. I thought that putting these two together with Pixel Math was the way to proceed, but apparently not. If I try LRGB combination, that doesn't work. I spent quite a lot of time trying to work through your processing of M42 and I learned a lot but you didn't put things together perhaps because it involved other filters. At this point I'm dead in the water. It sounds like I've gone down a dead end.

    Hank 
  • Mossyback
    Maybe my solution is to take up basket weaving. I would probably be less expensive. ;-)
  • BlockHeadBlockHead
    Well... the point of the M42 tutorial was not to be a complete session..but to learn how to manage the detail and color in bright objects (especially with HDRMT).

    The pixel math you were trying to do is not the same as what LRGB combination does. 
    So, as I understand it, your REAL issue is LRGB combination.

    When you need to do is make available (or at least show screen shots) of your M42 Luminance and RGB image. You will have already stretched them presumably.

    Here is your homework, what values do you have in the bulk (core) of M42 in your stretched image?
    Have you watched my video on LRGB?


    -the Blockhead
  • Mossyback
    Hi Adam,

    I went back and read your article on LRGB/RGB combination and I think I now understand what you are saying.
    Before we go any further, I took my two images and followed your instructions and I believe it worked. (See screen shot below). If this is the case, I'm a happy camper. However, I was expecting a third, combined image rather than having what appears to be the original RGB and Luminance.

    Hank 
    Screenshot 2023-02-24 at 9.36.24 AM.png
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  • Mossyback
    Also:

    Screenshot 2023-02-24 at 9.51.52 AM.png
    1902 x 1536 - 2M
    Screenshot 2023-02-24 at 9.51.40 AM.png
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  • BlockHeadBlockHead
    Your screen shot looks very odd (the one that shows the history of what you did). 
    You have ChannelCombination where you combined Red, Green, and LUMINANCE. This doesn't make sense. I would expect you to combine Red, Green, and Blue. Do you see why I am confused?

    -the Blockhead
  • Mossyback
    Yes I do and that makes two of us. I don't understand how I could have made such a stupid mistake. I went back to channel combination and now the Blue channel isn't there. I'm not sure to which point I'll have to go back to in order to rectify this.

    Sorry to have wasted your time.

    Hank
  • BlockHeadBlockHead
    You need to find your integrated Red, Green, and Blue data.
    Then do channel combination and the steps you that show in your history.
    As you did, the final step at this point is LRGB Combination of the stretched RGB and stretched L. Only the Lumniance in populated in the LRGBCombination process and you drag that over to your RGB stretched image. The brightnesses levels of your stretched images matter in terms of creating a nice blend. This takes some understanding of the stuff I explain...but also a little practice.

    -the Blockhead
  • Mossyback
    Thanks, Adam. I will continue to work on it.

    Hank
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