GIMP cannot read SharpCap 32 bit FITS files

[Borodog]

I like to do my stretching in GIMP. It has no problem reading the 32 bit FITS files produced by Autostakkert and DSS. But the SharpCap 32 bit FITS files produced under the "Save" drop down in live stacking do not import correctly into GIMP. They come in as a uniform gray. I have confirmed that the data is in there, because I used DSS as a translator; I can import a SharpCap 32 bit FITS file as a light and "stack" a single frame, which also produces a 32 bit FITS file, and GIMP has no problem reading that, and it has all the data in it.

[admin]

Hi,

could you share some sample files that show this please? I just tested with GIMP 2.10 and got the same results with a SharpCap saved 32 bit FITS as with a DSS saved one (32 bit integer). FITS (32 bit rational) from DSS come through much better in GIMP, but that format misses the point of saving as 32 bit as it does not record all possible pixel value detail.

cheers,

Robin

[Borodog]

Thanks for your reply, Robin. The forums here only allow me to attach files less than 1 MB, and I cannot seem to generate a 32bit FITS file from SharpCap that meets that limitation, even zipped. If you PM me an email address I will send one to you, or you should be able to generate it yourself; I made it using the Deep Sky test camera, live stacked a few frames, and saved as 32 bit FITS. The behavior upon opening in GIMP is slightly different from the uniform gray I saw before, but still unusable. It opens in GIMP as mostly uniform gray with a coupled of posterized levels that are black, red, green, and yellow:

SharpCap 32 bit FITS file opened in GIMP

Stack_32bits_15frames_15s.png (12.8 KiB) Viewed 584 times

[admin]

Hi,

yes, that's pretty much what I saw when I tried a 32 bit FITS from DSS and SharpCap in Gimp 2.10. What would be interesting is to see one that does work properly so I can have a dig through the FITS file headers to see what is different. I will PM you an email address.

cheers,

Robin

[astromaurizio]

Hi, I have exactly the same problem. I just updated SharpCap and GIMP to the latest versions available but the problem is still present.

Additional info:
- when I import in GIMP the FITS (both 16 and 32 bit) generated with SharpCap, they are showed reflected vertically (this is visible also in the sample image posted by Borodog). The same happens when opening such files with ASTAP (Astrometric STAcking Program). Is it expected?
- I tried to import the 32 bit FITS generated by SharpCap in ASTAP, and they are visualized correctly (even if still upside down).
- I checked the 32 bit FITS with https://fits.gsfc.nasa.gov/fits_verify.html and everything seems ok.

Let me know if there are news on this and if you have found a solution.

Thank you so much

[admin]

Hi,

there is now an option in the 'Saving Settings' that you can enable to make the 32-bit FITS files get saved as floating point 32-bit FITS rather than integer 32-bit. This makes them compatible with GIMP.

The upside down thing is actually common to a lot of FITS software - almost all other image formats start top-left, but FITS starts bottom left. Lots of people who implmenet FITS support (me included) don't spot that, so end up writing the FITS files the wrong way up. It's not something I plan to correct since if I do correct it, it will break the workflow of everyone who currently uses FITS files created by SharpCap. SharpCap does write a semi-standardised 'ROWORDER=TOPDOWN' header, which lets other applications work out the inverted view if they also support that header.

cheers,

Robin