Combining sub-frames with MaxIm v5

Let's say you have ten sub-frames that have been aligned as described here. The job now is to combine them so as to make the best possible composite. In general this can be done in several ways. Sum, Average, Median, SD Mask, Sigma Clip and Drizzle are all available in MaxIm. Some of these methods are worse than useless if you have frames containing noise such as sat trails, aircraft, hot pixels, cosmic rays and so on. You might think it acceptable to throw away all the bad ones but if the combine method can eradicate the problems why not keep all the frames? See here for notes and noise values for the different methods.

From the tests shown it is clear that SD Mask is in the lead and is always my first choice. It works by finding the standard deviation for each pixel in the frame set and puts the median value into the output for values greater than the sigma factor and the average for values inside the sigma factor.

Typical values are shown below.

I always set 16bit Integer for the output as you cannot see 100 shades of grey on screen, never mind 65,000 of them. Check the values as MaxIm has an annoying habit of re-setting them when you are not looking. Click on 'Go' and your aligned frames will be combined.

 

Here is a very rough example of combining 5x5m subs using SD Mask as above.