I am looking into a problem with speckles on my images and wondered if anybody had similar problems or solutions. Occasionally I get a pixel values of say 4K surrounded by ones of 2K - several in an image of various deltas. There are not that many but for DSOs etc. they stand out. I am using my own calibration software and have checked the darks, flats, dark flats and image and the weird pixels are only in the image and are not (or near) 'bad' pixels (bad is outwith 50 to 200% of normal dark level on any dark & there are 16 darks forming a Master dark). The images, etc. are binned 2x2 and the CCD temperature is -30 degC & the cooler was operating at 80%. I am going to do some 1x1 darks and see if they have a problem in the associated 2x2 area.
Yep .. the raw image file attached no processing at all ... but there is a lot of 'warm' pixels in it ... Its better seen in the processed image (dark subtracted and flat fielded.
Could just be a cosmic ray strike. That does happen all the time on a large array. Often these are literally cosmic ray radiation, though it can also be low-level ionizing radiation from materials near the camera (concrete, drywall, etc.).
Hmm ... cosmic rays tend to leave a trail, I'll look into it some more, ... seems like to many to me. Thanks for the quick responses though - do you ever sleep ? G.
Yes, but I'm a bit of a night owl... something about astronomy. That said... I'm not sure the server has the right time zone! Will have to check that.
I have done some more work on the images and it looks like it is as you say, cosmic rays, as there is no immediate correlation between the calibrated images and speckles. I implemented a de-speckle routine to find and fix them. Seems to work a treat (but gets a few of the background 'outliers' as well). They range from about 600 to 800 per image (including the background ones). The report file is attached FYI.
