We spent a couple of hours last night researching how to remove the hot pixels from our ST237A allsky camera.

hotpixels/noise

hotpixels/noise


These are the bright spots on an image that are noise or hot pixels, that do not move during the night. As a result they can be confused with real stars and possibly other objects. So, while seeing if the linux imagemagick package we use to annotate the image had any other parameters and operations that could be used, we stumbled across:
-interlace none
This prevents imagemagic from creating a progressive JPG by default
-comment “copywrite StarlightCascade Observatory”
which puts it into the exif comment section
and finally
-noise radius (eg -noise 1)

Add or reduce noise in an image.
The principal function of noise peak elimination filter is to smooth the objects within an image without losing edge information and without creating undesired structures. The central idea of the algorithm is to replace a pixel with its next neighbor in value within a pixel window, if this pixel has been found to be noise. A pixel is defined as noise if and only if this pixel is a maximum or minimum within the pixel window.
Use -noise radius to specify the width of the neighborhood when reducing noise.
We used this on an image and got the following result:
The first image is from September 22nd at 05:45 am and is not processed for noise. The second images is from September 24th at 05:44am and is processed with -noise 1
sco-20090922_0545_23.fit-a
sco-20090924_0544_30

The only issue now is to see if the -noise function will remove real data as well. We can go back in time and process some of the original “specials” and see how they react.