New unremoved hot pixels have popped up.

[Vanderbei]

I bought a ZWO ASI2400MC Pro camera last January and I started using SharpCap to operate the camera. Back in February, I took photos of the Rosette Nebula. I did 30 second exposures autostacked and saved every 5 minutes. Total exposure time was one hour. The individual 5 minute long fits files only showed a few wiggly unremoved hot pixels. They were easy to remove from the final stacked image using Photoshop. More recently, I've been taking pics of the Western Veil Nebula. I'm using the same exposure/stacking setup: 30 secs saved every 5 minutes. The individual 5 minute long files now show lots (let's say about 20) of unremoved hot pixels. Here's one 50 minute stack of the 5 minute images...
https://vanderbei.princeton.edu/tmp/ngc6960-HaOIII.jpg
Obviously the unremoved hot pixels can be seen as short little streaks. My Rosette picture only had 3 similar streaks. I'm wondering what has changed. Is it the camera? It's new and I never take it off from the telescope. Is it the software? I'm currently running version 4.0.8949.0. Back in February I was running version 4.0.8604.0. Or, did I maybe change some settings and that's decreasing the ability of the software to detect/remove hot pixels. Here's a screenshot showing a side-by-side comparison of the CameraSettings text files on the two dates...
https://vanderbei.princeton.edu/tmp/Cam ... mpared.jpg
I really really really hope we can figure out how to get things working the they were back in February.

[admin]

Hi,

nothing obvious changing in your camera settings (apart from a slight difference in temperature, which shouldn't really matter much). I can see you have a stronger display stretch in one set of settings, which would make warm pixels appear hot, but I'm not sure that has anything to do with it.

It's possible that the camera may have started creating a few more hot pixels - have you created new dark frames recently? If you have the original dark frames and compare them with the new you can possibly spot any changes. If more hot pixels have appeared in the dark frame then it would definitely point the finger at the camera sensor changing its behaviour slightly.

cheers,

Robin

[Vanderbei]

Thanks Robin. I'll grab some new darks tonight. I'll also tinker with the display stretch. Hopefully one of those two things will help me understand what's happening.

[Vanderbei]

PS. I'm also wondering if there is a way to tell SharpCap to ignore the hot pixels. I'm not using a guide scope, so things do move (aka dither) a bit over the 5 minutes of exposure. So, I'm surprised that SharpCap is not identifying them as outliers and removing/ignoring them.

[admin]

Hi,

SharpCap will remove them based on detection in the dark frame (it looks for statistical outliers in the dark frame, then will ignore the values from those pixels and take a value from a nearby pixel). If the dark frames are older and for one reason or another don't have those new hot pixels in them, then they will not be removed.

I did try to work out a way of removing hot pixels based on analysis of the light frames only, but was unable to find a robust way of doing it that wasn't sometimes fooled by real features in the image.

cheers,

Robin

[Vanderbei]

Ok. That's good to know. I'll be sure to grab good dark frames.