Bias files causing new problems.

Questions and answers about processing in StarTools and how to accomplish certain tasks.

Bias files causing new problems.

Postby mikey2000 » Sat Dec 09, 2017 8:27 pm

I've incorporated bias files into my DSS/Startools workflows for ages.

Just out of interest, I thought I'd try a new ISO setting on my Sony A6000 camera. I've been using ISO400 all year and re-using the master bias file I made ages ago with DSS.

So, I set it to ISO1000 and took some photos last night. The lights/darks/flats all came out OK but when I included the bias files in the stack, it takes ***Ages*** to load into star tools and then the first AutoDev gives a very weird mottley blotchy image. If I drop the bias files from the stack and try again, it comes out OK and loads into StartTools in a reasonable amount of time.

it seems the bias files are causing my stack to go 'bad' somehow.

Is there any thing I need to be aware of here?
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Re: Bias files causing new problems.

Postby admin » Sat Dec 23, 2017 12:45 am


It sounds like whatever is happening in DSS is corrupting your data and is introducing a lot of anomalous values. Anomalous values are values that are outside of the bounds of the max/min values specified in a FITS header, or are encoded as NaN (Not-a-number) or plus or minus infinity. Other types of anomalous data would be data that does not vary over large areas (e.g. has the same value in a large part of the image).

In all these cases, StarTools substitutes the anomalies with "plausible" replacements, in order to make sure that ST's algorithms don't create artefacts as a result of the discontinuities. If there are many of these anomalies, this may take some time.

The blotchiness may be explained by the distribution of the replacement values.

If you are absolutely sure the data is fine though and the issue is with StarTools, I would happily have a look at it!
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Re: Bias files causing new problems.

Postby mikey2000 » Tue Jan 02, 2018 6:14 pm

Thanks for the help. I'll double check all the DSS stuff and maybe reshoot the bias files too.
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