Loading ...
Sorry, an error occurred while loading the content.

54529Re: [ccd-newastro] I'm about to smash my ST2k........Please stop me!

Expand Messages
  • Terry Platt
    Oct 1, 2006
    • 0 Attachment
      Hi Frank,

      Random 'hot pixels' are usually data errors of some kind. For example, they could be due to interruptions of the camera download as other computer processes capture the bus. Is you control computer running free of other intensive applications? Network activity is a classic cause of random effects.

      Regards,
      Terry

      ----- Original Message -----
      From: Photon Collector
      To: ccd-newastro@yahoogroups.com
      Sent: Sunday, October 01, 2006 7:13 AM
      Subject: [ccd-newastro] I'm about to smash my ST2k........Please stop me!


      People, I'm at wit's end.
      I have been imaging with my ST2k imager for a couple years now. I have always had big problems with random hot (or bright) pixels. My images and darks have the usual consistent hot pixels that subtract out as they should. But both the images and the darks also have a large quantity of random hot pixels that differ from image to image and dark to dark. These random hot pixels do not subtract out because they pop up at random throughout the images and darks. The result is an image with many bright and dark pixels. Bright pixels remain in the image because the dark frame doesn't contain a corresponding bright pixel to subtract out. Dark pixels appear in the reduced image because the dark frame has bright pixels where there are none on the image.
      To prove to myself that the problem is real, I subtracted one dark frame from another dark frame shot in sequence. The resultant image should be very smooth. Instead it has bright and dark pixels, just like my images. As another test, I shot 10 darks in a row, of course all with the same temp and time settings. Then I opened them up in both Maxim and CCDSoft and ran a blink comparison. During the blink comparison, you can see that about 1/2 of the hot pixels are fixed in their position while the rest jump around all over the image. The same is true when doing a blink comparison of a series of raw images shot in sequence.
      I even went as far as upgrading my imaging chip from the older 2001 chip to the new and (supposedly) less noisy 2020 chip at great cost to me. The results are exactly the same.
      Here is an example of a completed image: http://publicmissiles.com/franku/2020_-25_f55_processed_NGC_7331.jpg
      It is a combination of 8, 20 minute exposures median combined after reduction using 10 median combined dark frames and the appropriate flat fields.
      If someone out there has a broadband connection (12 meg file!) and is willing to help, I have up-loaded a zip file containing a raw image, a flat field, and 3 dark frames. Try processing the image with the data I provided to see if you can get a clean image......I sure can't. Here is the zip file with everything you need: http://publicmissiles.com/franku/Raw_stuff.zip
      In the past I would spend an hour or two with the clone tool cleaning up every bad pixel. But I just can't believe this is what everyone else goes through. I never hear about problems similar to what I'm having. I hope it's just something I'm doing wrong but I can't imagine what it is. Is it possible that something in the observatory environment is causing the random hot pixels?

      ---Frank Rocketman Uroda

      [Non-text portions of this message have been removed]





      [Non-text portions of this message have been removed]
    • Show all 25 messages in this topic