Pixel Streaks - What's Causing Them?

Discussion of using SharpCap for Deep Sky Imaging
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poolemarkw
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Joined: Mon Mar 26, 2018 5:49 pm
Location: Indialanatic, FL

Pixel Streaks - What's Causing Them?

#1

Post by poolemarkw »

Hi Everyone,

See the attached picture...I'm getting Pixel Streaks in my stacked images. What would be causing this? Here are the details:

- SharpCap Polar Alignment
- SharpCap Live Stacking
- Dark Frame Subtraction
- No Flats
- PHD Auto Guiding
- ZWO ASI 294MC Pro Camera cooled to -10C
- Gain 200, Exposure 60s

Added Comment - I just compared this image with other pictures taken that do NOT have these streaks. I found that this image was generated using a Master Dark that was saved as a .FITS file, and the pictures that do NOT have this problem were created using Master Darks that were saved as a .png file. I don't know what would have made SharpCap start saving my darks as .FITS versus .png files.......

Thanks! Mark
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admin
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Re: Pixel Streaks - What's Causing Them?

#2

Post by admin »

Hi,

I think I can see two green streaks and a blue streak there, which would tend to imply that what you are seeing is hot pixels that are not being fully corrected by the dark subtraction being streaked out by the drift. This can often happen if for instance the temperature at which the dark frame was taken doesn't match the temperature of the sensor when taking the light frames.

Cheers, Robin
poolemarkw
Posts: 119
Joined: Mon Mar 26, 2018 5:49 pm
Location: Indialanatic, FL

Re: Pixel Streaks - What's Causing Them?

#3

Post by poolemarkw »

Hi Robin,

The darks were taken at a different time than the lights, but in both cases the camera was being cooled to -10C. The file name for the darks indicates a temperature of -9.4C and the file containing the capture info for the lights indicates -10C, so very little difference. What about the .fits versus .png file format? Could that have caused it? I've never seen this issue when darks were saved in the .png format.

Thanks,

Mark
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Re: Pixel Streaks - What's Causing Them?

#4

Post by admin »

Hi Mark,

As long as you are using the same bit depth for both captures then the choice of file save format shouldn't be an issue. I've got quite a bit of trouble to make sure that SharpCap can save and reload files in both PNG and fits format and get the pixel values exactly right after reloading for both 8-bit and 16-bit bit depths.

Cheers, Robin
poolemarkw
Posts: 119
Joined: Mon Mar 26, 2018 5:49 pm
Location: Indialanatic, FL

Re: Pixel Streaks - What's Causing Them?

#5

Post by poolemarkw »

Ok, thanks. Still, I'm going to change my settings so that my darks are saved as .png files again and see if the issue goes away.
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