Author Topic: Problem with CosmeticCorrection module  (Read 6053 times)

Offline jerrymacon

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Problem with CosmeticCorrection module
« on: 2016 May 20 09:05:50 »
There appears to be a specific arrangement of hot pixels that the CosmeticCorrection module cannot handle.  The following dropbox link is a zip of 5 images (small crops) taken with my QHY10 color ccd.
https://www.dropbox.com/s/o6p1525yy18yyjr/NGC3718-HotPixelCosmeticCorrection.zip?dl=0
Three are the target NGC3718: a raw frame, CC applied, and no CC.  These show that the CC process did a fabulous job of perfectly correcting all the approximately 100 hot pixels in this crop, with the exception of a close pair of hot pixels.  This crop is from the center of the image and shows one of these pairs.  There were a total of 4 pairs exactly like this in the entire image.  All 4 had exactly the same problem:  both hot pixels show up prominently as white and are made worse than expected by being surrounded by hot blue pixels what were not in the raw images.
The condition that triggers this is a pair of hot pixels separated by 2 pixels in both x and y.
I also included the master dark I used and the same crop from M51 which shows the exact same hot pixel locations.
Here are 2 smaller crops just showing the CC version and the non-CC version.
« Last Edit: 2016 May 20 09:11:01 by jerrymacon »

Offline TobiasLindemann

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Re: Problem with CosmeticCorrection module
« Reply #1 on: 2016 May 20 09:40:35 »
Hi Jerry,
this is an known issue. When two, or more hotpixels are too close, they are not detected by CC. But if the Hotpixels are always on the same location, you can correct the pixels via defect list.
Open CC and activate "user defect list". Than open your masterdark and zoom in to maximum, locate the hotpixels and click on it. Now click on "add defect" in CC. Repeat it with the next hotpixel. After applying it on your images, it should correct all hotpixels.
If you wish, you can save the defect list in a file.

Greetings
Tobias

Sorry, I have forgotten one thing: You should activate "Limit". Otherwise the defect list corrects one whole row, or column.


Offline jerrymacon

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Re: Problem with CosmeticCorrection module
« Reply #2 on: 2016 May 20 10:01:05 »
Wonderful!  Thanks for the detailed solution.  I tried the defect list but did not see the Limit checkbox and thought it only worked on entire rows or columns.