Are the Default 16-bit FITS Files Stretched?
Posted: Fri Jul 12, 2019 9:07 pm
I am using SharpCap 3.2 with a ZWO ASI1600mm Pro camera, and the software seems to be working great when taking Live Stack data. I saved the LRGB images to the default 16-bit FITS file. I now think that was a mistake, since I want to combine the LRGB data in PixInsight, and the files stored in the 16-bit format are rescaled (or stretched) according to SharpCap manual statements below. It appears that I should be using the Raw (32-bit) Stack instead. Is that correct? Is there any information in my stored (16-bit) that would allow me to "un-scale" the scaled data? (The 16-bit files seem to be combining OK, and maybe I already had a few saturated stars that were already at the 65535 level, which prevented the rescaling?)
From the SharpCap manual:
"• Save as 16 Bit Stack will rescale the stacked data linearly between the 0 and the maximum pixel value into the range 0 to 65535 and save this as a 16-bit FITS file. The 16-bit FITS option is the default as it gives a high bit depth image with the full range of the image used (i.e. brightest pixel is 65535).
• Save as Raw (32-bit) Stack will save the full 32-bit stack data without any scaling as a 32-bit FITS file. The maximum value in it will depend on the number of frames stacked, meaning more adjustments will be needed when viewing (without further adjustment this FITS file will probably appear black when opened into a FITS viewing application)."
SharpCap is a pleasure to use. Thanks for its development.
From the SharpCap manual:
"• Save as 16 Bit Stack will rescale the stacked data linearly between the 0 and the maximum pixel value into the range 0 to 65535 and save this as a 16-bit FITS file. The 16-bit FITS option is the default as it gives a high bit depth image with the full range of the image used (i.e. brightest pixel is 65535).
• Save as Raw (32-bit) Stack will save the full 32-bit stack data without any scaling as a 32-bit FITS file. The maximum value in it will depend on the number of frames stacked, meaning more adjustments will be needed when viewing (without further adjustment this FITS file will probably appear black when opened into a FITS viewing application)."
SharpCap is a pleasure to use. Thanks for its development.