Floating point FIT not displaying correctly

[nickg]

My workflow involves saving the stack as a 32-bit float FIT in CCDstack and importing it in PI. Sometimes it will display correctly using the default settings in STF, and others the white point is clipped and the image appears over exposed. In fact it seems no matter what adjustment I make in the STF makes no difference in the image looking normal. Saving it as a 16-bit TIFF seems to work every time. Any ideas?

Thanks,

Nick

[pfile]

PI writes 32b float images with values in the range 0.0 to 1.0, and by default the fits reader expects to find the same range in fits files that it opens.

what is the range in your CCDstack file? if you open PI and then click the "format explorer" tab on the left, then double-click "FITS", what does the "floating point out-of-range policy" pane show?

imho it's likely that the CCDstack file has values greater than 1.0...

rob

[nickg]

It says:

Minimum: -2.118679531250000e+005
Maximum: +6.598108593750000e+004

If I rescale it, I get the result I mentioned before. If I truncate it, it's all white. Is there a fix?

[pfile]

can you post one of the images? it's hard to say anything without taking a look...

rob

[jkmorse]

Nick,

Welcome to the world of FITS incompatibilities.  I know exactly what you are experiencing since I have run into that problem many times myself.  After some fairly exhaustive research, here is a post setting out the fixes that should work under any circumstances:

http://pixinsight.com/forum/index.php?topic=8021.msg52728#msg52728

Love to hear if that fixes things and which step did the trick (for me its the input hints that usually do it, either singly or, in some tough cases, together).

Best,

Jim 

[nickg]

Thanks for all the suggestions. As others have mentioned this happens sort of randomly, so when it does it seems that saving it as a 16-bit unsigned TIFF and converting it back to 32-bit FIT in PI seems to do the trick.

Regards,
Nick

[jkmorse]

Nick,

Only risk is that you lose the acquisition FITS header information which, depending on your processing techniques, may or may not be important.

Best,

Jim