FITS Image Size

Discussion in 'STX and STXL' started by Mike Hambrick, Jun 30, 2019.

  1. Mike Hambrick

    Mike Hambrick Cyanogen Customer

    Joined:
    Jul 13, 2016
    Messages:
    167
    Hi to all

    This is more of a curiosity than anything else, but is it common for the stacked FITS images to be larger than the sub-frames that went into the stack.
    The screen shot below is from a stack of 45 sub frames. Each sub frame is 30 MB which I suppose is not unexpected for a 16 megapixel camera (STXL16200), but it seems curious that the more sub frames I stack together, the larger the final image is. I would have expected the stacked image to be about the same as the sub frames.

    upload_2019-6-30_8-10-56.png
     
  2. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    3,455
    A couple of things that may account for it:
    FITS data format - whether the final image is stored as a 16 bit integer, 32 bit integer, or IEEE Floating point.
    FITS data format - uncompressed or compressed
    Also keep in mind that the processing history is included in the FITS header by MaxIm and some other programs, although this doesnt grow the size as significantly as taking an 8 or 16bit image and converting to 32bit.
     

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