Small green, blue and red lines in images when livestacking

[Moonstruck]

Hello Robin,
Lately when I have been livestacking there have been some very small blue, green and red lines in my images. Any idea what they are? Do you think this might be a camera sensor issue? I have a ZWO asi 294 MC camera. Any help will be appreciated. I have attached a link to an image showing these lines.

https://drive.google.com/file/d/1AXrnMz ... sp=sharing

John

[admin]

Hi John,

those are tracks from hot pixels on the sensor, being stretched out to wiggly lines by the stacking and stretching process. It's fairly normal to have hot pixels and the usual mechanisms to deal with them are

1) Dark subtraction (making sure the darks are captured at the same settings and temperature as the light frames)
2) Automatic hot pixel correction (select 'Hot and Cold Pixel Removal' in the 'Subtract Dark' preprocessing control in SharpCap).

If you go for the automatic correction, you may need to tweak the sensitivity - let the camera run capturing dark frames with a fairly strong display stretch and adjust the sensitivity until you can no longer see them in the individual frames.

cheers,

Robin

[Moonstruck]

Thanks, I didn't know about automatic hot pixel correction. I'll check that out.

[stbkaiser]

HI Robin
I understand about the HOT pixels present in the imager.
I'm curious though why the software does not throw them out when stacking.
When I run LIVE stacking on my ASIAIR with the same camera , the hot pixels do not show up.
Same thing if I stack frames in DSS (and I always dither). Noise reduction and no hot pixels.
Are these other programs doing more intensive processing to eliminate the hot pixels.
Also a thought. If I have characterized the camera/imager in your software, could that not be used to mask out the hot pixels.
Thanks
Steve

[admin]

Hi Steve,

I guess that the thing is that there are several things that you can do in SharpCap to address these hot pixels, but they are all 'off' by default. Those things include

* Sigma clipped stacking, which will reject hot pixel values after the first few frames of a stack if they occur at new locations in the stacked image
* Hot pixel correction as mentioned above
* Dark frame subtraction (which also includes some automatic hot pixel correction for where hot pixels are found in the dark - this does not help if hot pixels are intermittent and only occur maybe one frame in 30 or so).

This is kind of the 'SharpCap way' - that is that you get to choose what processing happens to your image rather than it all being turned on for you as ASI Air might be doing.

cheers,

Robin

[stbkaiser]

Thanks for the information Robin
I am finally starting to play around with live stacking .
I will try the Sharpcap methods .
Curious to see how well it stacks up (pun intended) to the manual processing I am so trained on.
Doing more sessions at night with an audience so this is a great way to wow them more quickly..
Take care
Steve