Improvements for Calcium SHG processing

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thesmiths
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Improvements for Calcium SHG processing

Post by thesmiths »

It has been apparent to us for some time that reconstructing images from the Calcium K and H lines is more difficult than for the Hydrogen alpha and beta lines. There are several reasons for this. The first reason is how broad the lines are:

Calcium K (left) and H (right). They are spaced 34.8 angstroms apart.
Calcium K (left) and H (right). They are spaced 34.8 angstroms apart.
Calcium K and H.png (227.66 KiB) Viewed 1235 times

The slopes of the lines are not very steep (i.e. they are broad, not narrow) so tracking the centre of the line is more prone to error. Second, the contrast features within the line is very high:

Ca-H spectral line
Ca-H spectral line
CaH scan 5.JPG (33.88 KiB) Viewed 1235 times

This means if the spectral line fitting program looks to locate the centre of the line by only assuming it is the darkest, it could make errors. In fact, this often seemed to happen, with the result that the spectral line fitting was slightly incorrect when using this darkest line = centre of the line assumption.

We therefore recently developed a more sophisticated line fitting routine that is more robust to the particular character of the Calcium lines. It seems to do a more accurate job of finding the correct shape and position of the Calcium lines, without degrading the performance for the narrower (and lower contrast) lines like H-alpha and H-beta. My analogy is finding the correct tilt of a filter to get it on band.

Here is an example of the old spectral line fitting vs the new one. What it does is eliminate potential problem points and determine the polynomial fit using only good points.

New vs old spectral line fit for Ca-H
New vs old spectral line fit for Ca-H
095348_spectral_line.gif (113.2 KiB) Viewed 1235 times

This leads to an improved rendering of the surface details (note the right hand side):

New vs old Ca-H SHG reconstruction
New vs old Ca-H SHG reconstruction
100617_CaH-old-new.gif (934.19 KiB) Viewed 1195 times

The problems were not always so severe in every case: it depended on the particular surface features and the exposure chosen. But we noticed that some quite good data could not be processed effectively using the old line fitting routine. Below is an example of the new routine in action (using the dataset above):

Image
This image from viewtopic.php?t=41324

We will shortly be coming out with a new version of our SHG reconstruction software (likely to be called v3.8). My son is back home from university so has some time now to help me implement new features that we had been thinking about for a while.
Last edited by thesmiths on Tue Jul 04, 2023 2:07 pm, edited 4 times in total.


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Re: Improvements coming for Calcium SHG processing

Post by Montana »

Superb work Douglas, many thanks for all your hard work you put into this software. The SHG has really been transformed recently :bow :hamster: :bow

Alexandra


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Re: Improvements for Calcium SHG processing

Post by christian viladrich »

Great work !


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Re: Improvements for Calcium SHG processing

Post by NM_mike »

I was just showing a neighbor how "easy" it is to capture details of our star... in very large part because of clever software developed by theSmiths.

Thank you for your time and effort!


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Re: Improvements for Calcium SHG processing

Post by rsfoto »

Hi Douglas,

Excellent work. I prefer your software over INTI. YOur software is much more stable.

I have seen today that not changing anything in the hardware at all by just making a sequence of H-alpha images the software reported me differente angles of the H-alpha lñine itself varygin from 0.5 to 0.9 as an example.

regards Rainer


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