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Old 11-09-2012, 02:19 PM
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PRejto (Peter)
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Hot Pixel Problem

Hello,

I'm having trouble removing the effect of a hot pixel (producing a verticle line on image) from my Moravian G2-8300 camera.

Dark frame reduction ought to remove it but it doesn't entirely. I'm not sure what to do. I made a dark frame master composed of 10 seperate 4 min exposures at -20C by median combining. The light frames show the line but the dark fram only removes some of the line intensity. The single reduced frames show very slight streaking but of course when I try to combine the light frames trhe streak becomes more pronounced. Yes, the light frames and darks have the same time and temperature. I tried doing this in two different programs, CCDSoft, and SIPS (the imaging/capture) program made by Moravian. Both gave similar results.

Any advice much appreciated!!

Peter
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Old 11-09-2012, 04:27 PM
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multiweb (Marc)
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If darks won't remove it try dithering your subs. It will be rejected when stacking.
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Old 11-09-2012, 04:36 PM
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Some hot pixels will have a variable output from frame to frame. This means that they will not properly dark subtract. The line is just from the readout time from the hot pixel. It will also have variability due to the variable output of the hot pixel. Some software use a pixel map of dodgy pixels at the same time as dark subtracting. This then replaces the hot pixel with an average of nearby pixels. This solves the problem.
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Old 11-09-2012, 06:30 PM
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Use Median combine for flats.

Use sigma reject for darks. It gets rid of outliers but not repeating pixel values.

There is also a pixel map feature in the latest version of CCDstack. I have never used it as it seemed not very user friendly.

I believe Astroart has a defective column removal tool. You just tell it which column (they are numbered and move the cursor along in CCDstack and it will show the column number along the bottom of the image).

Other programs may have a column removal tool. Perhaps Maxim.
Later verions of Photoshop also have a clone tool that can replace a line.

Greg.
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Old 11-09-2012, 06:30 PM
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PRejto (Peter)
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Thanks for both suggestions! I'm curious as to what software mentioned can recognize the bad pixel and get rid of it during dark subtraction?

Thanks!
Peter
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Old 11-09-2012, 07:12 PM
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troypiggo (Troy)
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You haven't mentioned PixInsight, but it has a CosmeticCorrection module that can detect and remove hot and cold pixels that may remain after bias/dark calibration.
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Old 11-09-2012, 07:23 PM
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Quote:
Originally Posted by PRejto View Post
Thanks for both suggestions! I'm curious as to what software mentioned can recognize the bad pixel and get rid of it during dark subtraction?

Thanks!
Peter
Of the programmes I use;
MIRA
IRIS
AIP4WIN
IRAF (if you are a massochist)
All have defect map functions. I'm sure others would as well.
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