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  #1  
Old 13-06-2018, 06:51 PM
E_ri_k (Erik)
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Are these hot pixels?

Hey guys, I'm having trouble with an LRGB image.....

In my RGB combination the image is littered with red and green spots. Most subs have the artefacts present, some worse than others, and they are very prominent in the integrations.

My Blue and Luminous frames are clean though. I checked the FITS header to see if the CCD cooling shut off for some reason during the R and G exposures, but no.

I can clone stamp them out, but there are hundreds! I have had a play with the pixel rejection settings, but not to a great success. Hoping some experts (maybe Rick) might have a suggestion!

Erik
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  #2  
Old 13-06-2018, 07:34 PM
glend (Glen)
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Perhaps a registration issue. All the green and red problems have the same orientation, which seems to suggest they are not stacked correctly.
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  #3  
Old 13-06-2018, 08:03 PM
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RickS (Rick)
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Hi Erik,

Looks like a combination of hot pixels and the interpolation algorithm creating ringing artefacts around them.

Assuming you're using PI, try CosmeticCorrection with a master dark or auto detect to clean up the subs after calibration and before registration. If you still have a few hot pixels left and registration makes them even uglier, you can adjust the clamping parameter in StarAlignment. If that doesn't work then try a different interpolation algorithm that doesn't create ringing, like Bilinear.

Cheers,
Rick.
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  #4  
Old 13-06-2018, 08:44 PM
E_ri_k (Erik)
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Quote:
Originally Posted by glend View Post
Perhaps a registration issue. All the green and red problems have the same orientation, which seems to suggest they are not stacked correctly.
Thanks Glen, Im not sure....I tried re calibrating and registering with the same results. The hot spots only appear in the red and green subs?
Erik

Quote:
Originally Posted by RickS View Post
Hi Erik,

Looks like a combination of hot pixels and the interpolation algorithm creating ringing artefacts around them.

Assuming you're using PI, try CosmeticCorrection with a master dark or auto detect to clean up the subs after calibration and before registration. If you still have a few hot pixels left and registration makes them even uglier, you can adjust the clamping parameter in StarAlignment. If that doesn't work then try a different interpolation algorithm that doesn't create ringing, like Bilinear.

Cheers,
Rick.
Hi Rick, thank you. Yes using PI. Ill the functions you suggested in the morning and let you know I go. Thanks.
Erik
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  #5  
Old 14-06-2018, 02:12 PM
E_ri_k (Erik)
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Thanks Rick. I applied CosmeticCorrection to the R&G subs and it did its magic.
The Auto Detect option worked the best.

Still wondering why the R&G subs were so badly affected? Some subs worse than others..

Erik
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  #6  
Old 14-06-2018, 02:39 PM
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Perhaps your darks need updating. They go off over time as new hot pixels appear.

With CCDstack I notice I would get those type of colour speckles sometimes if I did not do data rejection of hot and cold pixels which is all I do in data rejection. I don't find the other methods of data rejection do anything.

Greg.
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  #7  
Old 14-06-2018, 02:43 PM
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RickS (Rick)
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Glad you got it sorted out, Erik!

I don't know why the red and green subs would most affected. Lum sometimes looks cleaner just because the signal levels are higher and defects get buried. I guess it is possible that the temperature sensor has an intermittent fault and just happened to be reading wrong when you did the red and green. Might be worth taking a few darks at different times and comparing them to see if you get unexpected variation.

Cheers,
Rick.
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