Opening 32bits FITs file failed on SIRL...

[pe78420]

Hi,

I have a problem when opening 32-bit FITS files generated by SharpCap's live stacking (v4.1.13193.0-64bit) in SIRIL (v1.2.6).
The 16-bit version opens fine, but the 32-bit version displays a completely black and empty screen!

SIRIL support told me: "The problem comes from the way SharpCap saved the file. It wrote -32 in the BITPIX keyword when it should have written 32 because it uses integers." They also said: "If I change the value of the header keyword, I can open it."

Is this a known issue? Any advice?

For reference, the 32-bit FITS file opens correctly in GIMP (v3.0.0-1) and ASIFitsView (v1.14).

Many thanks in advance.

Best regards,

[admin]

Hi,

I don't think I agree witht the analysis from the Siril support folks. SharpCap has two options for writing out a 32 bit FITS file (because there are two ways to do it and some software doesn't handle one of the options when trying to read the file).

1) Leave the 'Save 32 bit FITS files as floating point' option unchecked in the 'Saving' settings - in that case, SharpCap will save the FITS file with integer values and write a BITPIX header of 32

2) Tick that 'Save 32 bit FITS files as floating point' - when that is ticked, SharpCap will save the FITS file with floating point values and write a BITPIX header of -32

This all ties in with the specification of the BITPIX header (https://archive.stsci.edu/fits/fits_sta ... 0000000000).

Now, the actual pixel values are the same numbers (to within the accuracy supported by the floating point format) in both cases - that is, if the pixel value is the integer value 123456 in the integer save, it will be a floating point value of 123456.0000 (or the closest floating point to that value) in the floating point save. That fact might have confused the analysis by the Siril people, and it also might be the underlying cause of why the image appears black - Siril may not handle the floating point range of values that SharpCap outputs.

Anyway, that's the situation as I am seeing it (both from checking the code and my testing). It's probably worth trying both possibilities for the option about 32 bit saving to see if one works properly in your use case.

cheers,

Robin

[pe78420]

Hi Robin,

Thanks for your quick answer.

I forgot to mention that the Siril support team also told me the following: "Or try to see if you can change the settings."

So, according to your response (and that of the Siril support team), that’s what I need to do—change the settings (which I didn’t know at the time).

I will try with "Save 32-bit FITS files from Live Stacking as floating point" unchecked.

Regards,

Phil

[pe78420]

... and it works
Sorry, I forgot to positively close this post !