Removing Bad Pixels

[SB]

Hi All,
I am noticing bright or dark pixels in my subs. These do not go away with stacking (see attached images).

The first two images show Hot pixels that have been detected, however there are bright and dark pixels that are not detected (either hot or cold detection). These pixels do not appear in the same location in every sub so they multiply out in the stacked image (see image 3 - a section of stacked Ha of the Helix Nebula showing bright pixels).

Any ideas what these pixels are or how to remove them.

Many thanks

Chris

[multiweb]

A master dark or a bad pixel map will take care of that.

[SB]

Hi Marc
I tried that. I stacked in DSS and Affinity with the same result (using Bias and Darks).

Chris

[multiweb]

:confused2:

Not sure then. That's the only way I know how to remove hot pixels. Otherwise you could use data rejection with a range of ADU over a certain value but you have to be careful not to clip your stars.

[SB]

Hi Marc,
Looks like that solves the problem. I see what you mean about being careful not to clip the stars.

I set the Threshold (standard deviations) lower while keeping the clipping iterations default.

Further to this , renewing my Darks completely fixed the problem!

Many thanks

Chris.

[multiweb]

Yeah a set of new darks for a master that has a total integration time longer than the longest of your sub should do the trick. Cameras develop more hot pixels over time. So get a new set of darks every 6 or 12 months. Bad pixel maps are easier to use. You just need one dark to make one. The rest of blotches are mostly cosmic rays. They reject fine while stacking. Otherwise you can use an algo such as PI cosmetic process. That takes care of hot pixels and outliers nicely too.