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Linux image preprocessing project - Asterism


geoland

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Hi.

I've been playing around with image preprocessing in Linux, using freely available tools.

As a DIY project I wrote a bash script to get things orchestrated to perform various tasks. It's been an interesting and at times complex task, but fun all the same

It is of course open source and free. DCRAW ImageMagick and Panotools  are the core programs. Yad provides a GUI.

My bash and C++ skills are a little better than entry level and hopefully improving - I'm sure a discerning eye will find reason to be critical.

You can read about the project here

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Looks just the thing I`ve been looking for Rowland!. I`m wondering if the stacking tool requires multiple stars as I mainly do spectroscopy with usually a single spectrum in the fits. Other apps I`ve tried require a minimum number of stars to proceed whereas I just have the spectrum and nothing else. I`ve just come across your post so I`ll have a browse of the manual and see.

cheers

Steve

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Steve. I think you will find the alignment method is not star dependent, it just requires recognisable control points. If you know Hugin panorama stitcher, Asterism uses a very similar algorithm. 

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Steve, you can use fits tif png jpg and pretty much any other format you can think of.

Asterism, given no options, except a project name and project directory, will process non-raw files without dark frames and mean stack all frame types - this is default.

By adding switches (check boxes and options) processing can be configured to do an array of tasks. 

For your needs, first determine whether the fits files are bayered or debayered. 

If already debayered, refer to the 'Preprocessing NO RAW DeBayered minimalist with dark frames' image below.

If the files are bayer fits; that is, they are not debayered, refer to the 'Preprocessing NO RAW Bayer minimalist with dark frames' image.

PREPROCESS triggers DeBayer - whether raw or otherwise.

Leave 'RAW files' unchecked

Enter fit or fits, as preferred, in 'Output format' - column 3 - or just accept the default tiff output.

'Preprocessing NO RAW DeBayered minimalist with dark frames'

1i-minimalnorawbayerdarks.thumb.png.59798996bf7077bd3853c2262cb3b85c.png

'Preprocessing NO RAW Bayer minimalist with dark frames' - PREPROCESS triggers DeBayer

1i-minimalnorawdarks.thumb.png.8c8ca1c94b165cbb0a1f1496e12693ea.png

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While I think of it the debayer pattern or matrix is set to RGGB - depending on your camera you may need to select a different matrix. Most DLSRs are RGGB...

EDIT: Documentation update

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Hi Steve. Your Nikon - RGGB - select PREPROCESS, RAW files^, Dark frames^ (optional). Bias and flats are processed by default. 

Your mono Atik - no bayer matrix - select Dark frames^ (optional) - bias and flats as above.

If you would like to upload to a file share,  1 fits for each channel - bias dark flat and light - I am happy to take a look.

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Hi Steve.

Here are your stacked images. No problem aligning the frames.

Having no experience whatsoever in spectroscopy, I took the calibration and noise results at face value, besides having only two light frames

At first look I thought the bright spots in the image were hot pixels, but the dark frames made no difference. On closer inspection they appear to be constellations?

The bias dark and flat frames were median stacked. The stacked light frames are mean and median combined. Polynomial stacking doesn't  work well with low count frames.

Given that the 314l is monochrome, debayer is not required and I take it you have a series of L R G and B filter images, which all need processing.

An earlier version of Asterism is configured to process 3 channels separately. A fourth channel, as in LRGB, should be simple enough to add, if you wish to colour process, which is I guess desirable?

EDIT: thinking on a work flow for 4 channels. Each can be separately processed and stacked in Asterism. The four channels could then be combined using the standalone PMStack utility, included in Asterism - modified to ensure proper colour channel combination. And while a lot more work, LRGB processing could be integrated.

mean_stack_steve.jpg.0f5a2c87577b18bcbbdf90e66a27aa79.jpg5965bc8a8cf9f_median_stack_steve.jpg.7ba4003393817fa9090ad5c8ea249fbb.jpg

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Will do will have to find it on my other laptop?. I am running latest Kubuntu 17.04 and usually use ISIS under Wine for all the spectrum processing which seems to work ok but Rowland's app looks very useful.

Cheers

Steve

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Yes it does a bit doesn't it, When Isis does its thing I'm often amazed what pops out its so powerful. For the calibration I simply give it a 120sec fits of an Argon/Neon lamp spectrum (from a fluorescent starter) and Isis automatically calculates the wavelength's,clever stuff ☺.

Steve

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Ah yes, that X axis is just pixel coordinates. The Y axis is the sum of all pixel values along the  Y, and the X axis is just the position in the image..

For example, that peak at 950 something is the sum of all pixel values where x=950 and y>500 and y < 550.

Knowing that 950 = 6562A and maybe 1 other peak it would be possible to map the Y pixel values to actual wavelengths.

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EDIT: the superbias 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

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  • 3 weeks later...

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.

EDIT: uploaded a revision - same link.

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