Stacking with AstroCrop in Linux

Back in 2014 Nicola wrote the code for the first version of AstroCrop. This was for Windows. We worked on the algorithms for precisely cropping a series of images, and controlling the precision of the cropping. We were motivated by capturing Lunar and solar images with 60 x and 40 x optical zoom Bridge cameras using a static tripod and burst mode capture. We were capturing about 100 images over a very short period of time and wanted to stack the images.

With this technique of capture, it is almost inevitable that there will be some movement of the object of interest (Sun or Moon) between bursts of capture. Moreover, the images captured contain a relatively large amount of black space surrounding the object. The result of this was that there was frequently too much movement of the object among the images for stacking software such as Registax and Autostakkert! to be able to cope. Moreover, the large amount of black space around the object was undesirable.

This image has been re-scaled to about 1/4 its original size for display here if clicked on

Note the large amount of wasted back space in the image.

We wanted to crop precisely, every image to exactly the same, user defined size.
So, Nicola coded AstroCrop and it is available at https://www.linux-astro-imaging.uk/  .Both Windows and Linux versions are available for download.

When the original program was written, an automatic stacking function was included after the images had been cropped. However, it was decided to comment out all of the stacking functions in the initial release as software such as Registax and Autostakkert! were available in Windows.

Whilst there is stacking software available in Linux such a lxnstack, and Registax & Autostakkert run perfectly under Wine, We decided to un-comment the stacking code in the Linux version of AstroCrop for testing purposes, but not to release it at this stage. The reason for this is that we intend to implement a quality estimator so that the user can specify a stack of the best x% of the cropped images. Moreover, with the techniques that Nicola has developed for the rapid handling of images whilst developing AstroDMx Capture for Linux, she has decided to re-write the whole AstroCrop project to use some of these techniques and increase the efficiency of AstroCrop even further.

A data set of 60 bridge camera images of the Moon captured on March 4th 2015 was used to test the cropping and stacking in the version of AstroCrop for Linux with the un-commented code. The pixel search perimeter (which is user selected from 5 pixels up to 60 pixels) was set to 30 pixels. This will give better correlations between the cropped images. The resulting stacked, cropped image was wavelet processed in Registsx 5.1 and post processed in the Gimp 2.10.

The process worked well and we look forward to the time when a stacking version of AstroCrop is released for Linux