Binning artefact on bright stars

Discussion in 'STT Series' started by letteri, Jul 1, 2016.

  1. letteri

    letteri Standard User

    Joined:
    Aug 2, 2015
    Messages:
    69
    With my STT-8300M, saturated stars binned 2x2 are showing an aliasing artefact on their right side, as you can see in the attached image. The JPEG compression is exaggerating it, but it is there in the original data.

    The artefacts don't appear at binning 1x1, so I am guessing that this is a buffer overflow when binning, but I wanted to confirm that. And if so, is there anything that can be done about it apart from lowering the exposure time (or post-processing)?

    Cheers,
    Joe
     

    Attached Files:

  2. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,590
    Location:
    Earth
    It's not a "buffer overflow", but you are on the right track - it looks like the CCD chip pixels may be blooming - basically when the pixel's electron well is full (too many photons hit), the electron charge may spill over to neighbouring pixels. Not unusual if the star is overexposed. Nothing to be done about it.
    If you upload a FITS sample (crop it to make it under 2MB) and upload, might be able to analyse and confirm. You could tell if the artifacts are the same saturation level right next to where the circular edge of the star would be. Also, to confirm, you need to verify that the artifact is running along a column of the chip.
     
  3. letteri

    letteri Standard User

    Joined:
    Aug 2, 2015
    Messages:
    69
    I was under the impression that blooming happened in the vertical direction, whereas this artefact is happening along the rows and only on the right side of the saturated wells, so I thought it might be something that is happening while the chip is reading out the lines.

    Either way, it appears to be inherent in the hardware, and as you say, probably not much to be done about it.

    I have attached a crop from a raw FITS files that shows the artefact more clearly.
     

    Attached Files:

  4. Colin Haig

    Colin Haig Staff Member

    Joined:
    Oct 27, 2014
    Messages:
    4,590
    Location:
    Earth
    Your bright stars are saturated, and only artifacts I see are from the secondary spider vanes. Where in the image is the artifact ?
     

Share This Page