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Old 11-06-2017, 03:13 PM
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Linux image preprocessing - Asterism

I have been working on a Linux preprocessing utility for about two years, primarily for my own use as an educational tool and the essential ingredients, curiosity and fun. Now in its fourth iteration, it is a more functional package with a new name features and interface.

Noted: there are plenty of excellent preprocessing programs out there... and I use PixInsight for many tasks. I am just sharing what I have been doing in astrophotography - DIY software.

Primarily intended for consumer digital camera RAW data, the Asterism user manual explains far more than I should include here.

Asterism is a bash script that performs a number of tasks more clearly arranged in a tabbed user interface - compared to previous versions.

Asterim uses existing programs to do the preprocessing work. Yad (GUI) ImageMagick (Q16) and Panotools are required. Hugin MacroFusion and Enfuse are optional. Note: libtiff should be installed on most Linux distros - if not it is also a requirement.

Asterism's primary function is preprocessing. That is image reduction / calibration deBayer alignment and stacking. Secondary processes are stand-alone image calibration, without alignment and stacking. Master frame creation. Conversion (16 bit monochrome Bayer) - not that useful unless you have special requirements.

There are range of other options, again better explained by viewing the documentation and playing with a small image set to illustrate the various functions.

Not much more to say on the topic. It's a work in progress, but functional, all the same.

Last edited by rcheshire; 15-06-2017 at 10:50 AM.
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Old 19-06-2017, 04:54 PM
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Update: I've added a polynomial stacking routine. Essentially a noise rejection filter. Removes satellite trails and hot pixels. Before and after shots. These are low resolution jpg normalized gamma 2.2 to illustrate the effect.
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Last edited by rcheshire; 27-06-2017 at 02:40 PM.
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Old 24-06-2017, 12:14 PM
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A new version. No major changes. Largely bug fixes, code tidy up and provision for setting ImageMagick in-built resources - threads and memory - on a per-session basis. Removed unnecessary parallel processing routines, letting ImageMagick handle the resources.

EDIT: with reference to the first post, dcraw is also required

Last edited by rcheshire; 27-06-2017 at 02:44 PM.
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Old 01-07-2017, 08:04 AM
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New version and manual - minor bug fix. LLRGB has been remodelled and Bayer non-raw images can be processed. Asterism manual refers.
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Old 06-07-2017, 12:05 PM
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Asterism_superbias creates what might be called a superbias, significantly reducing random noise in the master bias
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Old 08-07-2017, 05:05 PM
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Added a standalone alignment and stacking utility. User manual refers.

EDIT: Documentation update

Last edited by rcheshire; 09-07-2017 at 12:21 PM.
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Old 19-07-2017, 09:15 AM
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New version.

Last edited by rcheshire; 19-07-2017 at 01:44 PM.
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Old 22-07-2017, 01:54 PM
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Tweaks and bug fix. Super-bias process modified.

EDIT: this process is essentially a large kernel median filter. The larger the kernel the longer the process. Comparing histograms of various kernel sizes, the latest iteration should be a good compromise between noise reduction in the bias and processing time.

Last edited by rcheshire; 25-07-2017 at 07:39 AM.
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Old 31-07-2017, 10:45 AM
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Added channel (matrix) sRGB multiplier capability... user manual refers.

Obtain channel matrix values here, for example

Last edited by rcheshire; 31-07-2017 at 11:19 AM.
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Old Today, 07:49 PM
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Hot pixel map correction

This latest version includes hot pixel map correction. Certainly removes hot pixels. Flat illumination correction method reviewed and simplified, hopefully. Not to mention a significant manual rewrite.

The interface has seen change as well as the inclusion of links to documentation and other resources from the Documentation tab.

Last edited by rcheshire; Today at 09:20 PM.
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