Resolved LRGB stacking using png files

Discussion in 'Image Processing' started by Jesse, Feb 18, 2019.

  1. Jesse

    Jesse Cyanogen Customer

    Oct 11, 2014
    Why can't I color stack png files? (Combine Color and Color Stack are both grayed out - see attached screenshot.)

    I start with four FITS images taken in separate colors then run them through an image processing program that writes (only) png files. I can open them in MDL but it won't allow me to align/stack them. I've not had this issue using FITS images. The only thing I can think of is headers(?) but I don't see why header information should be necessary for alignment and stacking.


    Attached Files:

  2. William B

    William B Cyanogen Customer

    Jan 8, 2015
    Christchurch, Dorset UK
    Hello Jesse.

    As a MaxIm user (not staff) I can confirm that MaxIm does read and allow Color Combine and Color Stack of 8bit and 16bit PNG files provided the format of the PNG is a single channel MONO image.

    MaxIm can not Color Combine or Color Stack PNG images that are saved as RGB format PNG files, i.e, already in 'color' format. If you load PNG files that are RGB coded the Color Combine and Color Stack commands remain 'greyed' out.

    When you save your PNG's in your (unspecified) image processing program ensure you are saving the files in single channel mono format and not multi channel RGB encoded.

    In Photoshop for example you would need to set Image > Mode > Greyscale before saving the image as a PNG.

    Alternatively, after importing the RGB encoded PNG's into MaxIm use the 'Convert to Mono' command from the 'Color' menu first on each of the four LRGB images, then you will be able to use the Color Combine and Color Stack commands.

    Since we don't know which image processing program you used before importing the PNG into MaxIm it is not possible to give any additional tips.

    If you are still having problems suggest you upload a folder of the four PNG files to Diffraction Limited's FTP server, or place them in a Dropbox or Google Drive and post back with a link here, plus, provide additional information such as which program was used to generate the PNG files, what operating system and which version number of MaxIm you are using.


    Last edited: Feb 19, 2019
  3. Doug

    Doug Staff Member

    Sep 25, 2014
    They're color images, even though all three planes are the same so they look black-and-white. You'll need to convert them to monochrome.

    Use the Color menu Convert To Mono command on each of your frames. Then you'll be able to color stack them. (Tip: View menu Batch Process command will be handy for this.)
  4. Jesse

    Jesse Cyanogen Customer

    Oct 11, 2014
    Indeed that was the issue. Thanks for both replies!

    Since the image processing program is a one trick pony that only accepts 16 bit single channel FITS I blindly assumed it wrote out grayscale. I suppose since Convert To Mono was an option (per the screenshot) that making that assumption made an ass out of me and me :) Thanks again, Jesse

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