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Extraneous Red, Blue & Green pixels showing up before and after I process the image

Paul Stubenrauch

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Thanks in advance for any help anyone can offer…

I’ve downloaded the Bubble Nebula that contains a total of 6 files (2 Ha, 2 SII, and 2 OIII)… When I run the script in Siril, I get a huge amount of extraneous Red, Blue & Green pixels showing up before and after I process the image. See screenshot… If you know how to get rid of these using Siril or Gimp, please enlighten me for they are truly wrecking the image. I can probably get access to Photoshop too if need be… Again, thanks in advance for helping this newbie..  Regards, Paul SRed-Green-Blue-Pixels.thumb.png.6b98c1526a593705b4711ad87e4eba8b.png

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Hi Paul, 

What you're seeing here is "noise" from the camera expressed as hot pixels, since these are random for each exposure, the red, green and blue channels will have a random assortment of noise on each image, this corresponds to the red green and blue pixels that you are seeing.

Luckily there are a couple of ways to resolve this. I'm guessing that you are only stacking a few frames per colour channel, by increasing the number of frames that you integrate you can average out the noise. (While usually a single one-click dataset is OK to obtain a nice colour image, many datasets are optimal to have a greater signal. That's why we image the same target many times, these are what we call the Bundles with many one-clicks datasets per sky target that it is possible to grab).

Pixinsight also has some algorithms and processes that you can use to help remove these hot pixels:

The first is cosmetic correction, using the auto detect for hot and cold pixels (default parameters) on the images before you start alignment or stacking can greatly reduce the noise in the image.

You can also use the Winsorized sigma clipping in pixel rejection (1) in the image integration process to help remove hot pixels.


There should be a cosmic correction feature in SIRIL too:




Kind regards,


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