Kstars-devel Digest, Vol 229, Issue 17

Tue Mar 28 17:21:12 BST 2023

Hi All,

A proof of concept stand-alone application for the exposure calculator 
is available in new repository github. I have not yet started to 
integrate the calculator into a branch on KStars.  I was hoping some of 
you might do some testing with this tool, and give me some feedback 
before I move forward with integration.

The branch with my initial commit is here:

https://github.com/Stingray65/KStars-ExposureCalculator/tree/master

(I have not yet applied the standard artistic style to the code, so 
please ignore any odd formatting at this time).

The project includes a set of 16 xml camera files that provide some 
needed data to the calculator, like the gain (or ISO) to read-noise values.

I also wrote a doc that would be an initial draft for changes to the 
KStars user guide. There are some comments for the development team in 
this document, the comments are enclosed with "[]". One of which 
explains how new camera files can be created.

https://github.com/Stingray65/KStars-ExposureCalculator/blob/master/Documentation/HelpManualDraft.pdf

The proof of concept is a straight Qt app, and I think that anyone who 
pulls it will need to edit the SubExposureCalculatorPOC.pro.user file to 
change some values of directories.

Thanks

On 3/12/23 22:48, joseph.mcgee at sbcglobal.net wrote:
>
> Hi All:
>
> Sorry, for long email...
>
> I've built a Qt app as a proof of concept for the optimal sub exposure 
> calculation. The Qt project source can be found on my google drive, (I 
> did not want to "pollute" the Kstars git with what might be considered 
> pool quality design and my sloppy (java-like) code: my last real c++ 
> project was in 1998, and this was my first experience with Qt).
>
> A link to this project is here: 
> https://drive.google.com/drive/folders/11BIS5tyPeJcZeoysgjdrG2j_J8Cbu0zj?usp=sharing
>
> I may be have bugs in this code... I have not taken the time to 
> validate all test results back to Dr Glover calculations. But the 
> results this tool is producing for my camera are matching what my old, 
> (and validated), Java code produced.
>
> Before you run it, please be aware that this implementation does not 
> include any compensation for the effect of a filter in the optical 
> train. So the results of the calculation would only be relevant for an 
> unfiltered exposure.  My Java code from years ago attempted to apply 
> compensation for two broadband filters that I use, but my calculation 
> method for filters was only based on some comments found on cloudy 
> nights web site; it was not from the presentation of Dr Glover.
>
> Since I'm not applying filter compensation in this POC application, 
> the results will not translate to your real-world experience of 
> imaging with filters.  It is likely that the calculated exposure times 
> from this application could be on the order of 10x lower that what you 
> would expect with a filtered exposure.  I plan to continue my research 
> on how best to implement filter compensation.  (I might be sending a 
> separate email on this topic).
>
> This POC application relies upon gain to read-noise data for a few 
> specific ZWO cameras.  I've created xml files to provide this data, 
> (in a folder named "ImageSensorData"). This POC app will read the 
> folder and add the files names into a QComboBox for ease of selection. 
> The format of the xml files is simple, and new files can be added to 
> the folder to expand the options for testing.
>
> When launched, the application will present a window with two frames. 
> The small frame on the left represents data that we might pull from 
> KStars Ekos/Indi.  This will be used to initialize the calculator in 
> the frame on the right.  The panel on the right would be the only 
> display a user would experience in KStars.   So there are two SQM 
> controls in this application for a reason, the SQM control on the left 
> frame would not exist in KStars, the SQM control on the "user" 
> interface (right frame) will present to the user and allow the user to 
> experiment with SQM values of different locations.
>
> To initialize the calculator, select an imaging camera, a focal ratio 
> and the desired "initial" SQM value, then click "Apply". The 
> calculator will present a graph of the optimal sub-exposures based on 
> the initial data, (I have gain defaulted to 50).
>
>
> To find an optimal exposure time for a given gain, simply adjust the 
> gain slider relative to the x-axis values on the graph. For this 
> example camera, notice there is a severe step in the exposure times 
> caused by the camera read-noise having a prominent step at gain 100. 
> For this camera, moving gain just above 100 will drastically reduce 
> the exposure time, and the noise for the sub-exposure.
>
> To calculate for a different location, the (right) SQM control can be 
> adjusted. A higher SQM will naturally produce longer optimal 
> exposures, since there will be reduced light pollution. Here is the 
> same case in a darker sky; the optimal exposure graph and results 
> changed to a longer exposure. Notice that the exposure noise remained 
> the same, but we have a longer exposure... so the proportion  signal 
> to noise is better.  And the predicted noise on the stacked images is 
> significantly reduced for roughly the same integration times.
>
> The calculations by Dr Glover also included a value for a tolerance of 
> the increased noise. The default is 5% which he stated was a good 
> "general" value. This value can be adjusted based upon personal 
> preference. Adjusting this will effect the allowed noise for the 
> single exposure, and that will also effect the stack noise.
>
> On the subject of trying to capture read-noise data from bias frames; 
> I encountered a hurdle, so I may be sending another email in a day or so.
>
> Finally,  I don't claim to fully comprehend the physics that Dr Glover 
> presented. But as I have tested his equations with this application, 
> the results seem make sense, his equations lead to exposures times 
> that provide a higher signal to noise value.
>
> Please feel free to openly criticize what I'm suggesting with this 
> tool being added to KStars.  I think it will add some value, but 
> supporting data for cameras may not be easy, and so the implementation 
> of this tool may need to be limited to only those cameras where we can 
> easily find the needed gain read-noise data.
>
> Please experiment with this tool, let me know what you think, (good or 
> bad).
>
> Thanks
>
>
> Qt Project source code can be found here:
>
> https://drive.google.com/drive/folders/11BIS5tyPeJcZeoysgjdrG2j_J8Cbu0zj?usp=sharing
>
> On 3/7/23 04:00, kstars-devel-request at kde.org wrote:
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>>     1. Re: Optimal Exposure and Noise Calculator (Jens Scheidtmann)
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