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54580Re: [ccd-newastro] I'm about to smash my ST2k........Please stop me!

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  • Wodaski - Yahoo
    Oct 3, 2006
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      That's not how CCD sensors actually work in the real world. Yes, you can
      have pixels that are routinely and regularly hot or cold. But you can
      also have pixels that vary in how hot or cold they are. Your statement:

      "Random pixels that pop up hot in one photo and then don't in another
      photo can _only_ be due to random noise."

      is just not true, and I want to correct the error before others start
      assuming it is true. What is true is that the manufacturer must tune the
      electronics for the camera to make sure that these variations are
      minimized. The STL-11000 camera, for example, had a notorious problem
      with these hot pixels until SBIG changed the camera driver to deal with
      the problem. Even so, there is still a small population of these varying
      pixels on most STL-11000 cameras, but the count is WAY down to a
      reasonable number.

      Such pixels are also going to occur on the ST-2000 series of cameras -
      they seem to be harder to control in a certain generation of Kodak ABG
      chips, but the camera drivers have all been revised to minimize this issue.

      This isn't to say that there aren't other causes of random hot pixels,
      and varying populations of hot pixels (such as the ones you cite). I
      just want to be clear that there can be conditions other than readout
      noise that determine this.

      Ron

      W. W. Mathis wrote:
      > Frank: I've been thinking about your problem. I can see that a chip might have something wrong with a pixel that would give a "hot" pixel. But this hot pixel will be hot from now until doomsday, since it is an inherent defect in the chip. Random pixels that pop up hot in one photo and then don't in another photo can _only_ be due to random noise. So it seems to me that you should be looking for electrical problems that make the transmission "noisy". Poor connections, bad grounding, cross talk between wires, etc.
      > . The computer will not accept info until it is ready to deal with it, so one program "Locking" another program out of memory really can't happen.
      >
      > Ward Mathis
      > ----- Original Message -----
      > From: Photon Collector
      > To: ccd-newastro@yahoogroups.com
      > Sent: Sunday, October 01, 2006 11:59 AM
      > Subject: Re: [ccd-newastro] I'm about to smash my ST2k........Please stop me!
      >
      >
      > The hot and cold pixel removal tools in MaxIM didn't do much at all. Instead I used the median kernel filter in MaxIM on each of my subframe right after initial reduction. I then did a median combine of the 8 subframes.
      > The image is MUCH better! Take a look but please excuse my quick post-processing. Nothing was done to remove bad pixels in PS.
      > http://publicmissiles.com/franku/2020_-25_f55_processed2_NGC_7331.jpg
      >
      > Of course, this is not a fix of the root cause but it's many times better than ever before. I'm still running my equipment tests.
      >
      > ---Frank Rocketman Uroda
      >
      > ----- Original Message -----
      > From: Bert Katzung
      > To: ccd-newastro@yahoogroups.com
      > Sent: Sunday, October 01, 2006 11:52 AM
      > Subject: Re: [ccd-newastro] I'm about to smash my ST2k........Please stop me!
      >
      > Hi Frank:
      > I've had that sort of salt & pepper artifact problem on occasion with my
      > ST10-XME; don't know what causes it or cures it, seems to have its own
      > schedule.
      > On the positive side, I find I can get rid of them with the hot and cold
      > pixel removal tools in MaxIm. Extra steps, but they clean up pretty
      > well---never have to use the clone tool in Photoshop.
      > Bert
      >
      > katzung1@...
      > www.astronomy-images.com
      > www.visionlightgallery.com/katzung/
      >
      > ----- Original Message -----
      > From: "Photon Collector" <photoncollector@...>
      > To: <ccd-newastro@yahoogroups.com>
      > Sent: Saturday, September 30, 2006 11:13 PM
      > 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
      > >
      >
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      --

      Ron Wodaski
      New Astronomy Press
      http://www.newastro.com
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