https://bugs.kde.org/show_bug.cgi?id=397993
Bug ID: 397993
Summary: Kstars : FitsViewer does not respect Fits standard
Product: kstars
Version: unspecified
Platform: Other
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: general
Assignee: mutla...@ikarustech.com
Reporter: ashash...@gmail.com
Target Milestone: ---
When you visualize a fits file with personalized min/max value, FITS keywords
DATAMIN and DATAMAX are changed in file concerned.
But DATAMIN and DATA MAX are fits standards keywords
https://fits.gsfc.nasa.gov/fits_standard.html
KEYWORD: DATAMAX
REFERENCE: FITS Standard
STATUS: reserved
HDU: image
VALUE: real
COMMENT: maximum data value
DEFINITION: The value field shall always contain a floating point
number, regardless of the value of BITPIX. This number shall give the
maximum valid physical value represented by the array, exclusive of any
special values.
So DATAMIN and DATAMAX can't be used to store theses values as it correspond to
camera numeric depth. (for example, for a 16 nits camera, value are DATAMIN = 0
and DATAMAX = 65535 )
For example, Audela store it in MIPS-MAX mans MIPS-MIN keywords. (not in
standards...)
May be Kstars can do the same... or store it in other non-standards keywords.
Comments to read from this very bad placed bug from TallFurryMan
https://github.com/indilib/indi/issues/693
I agree, DATAMIN/DATAMAX do not relate to the actual minimum/maximum values of
FITS data, but indicate what the dynamic range of the physical equivalent of
the FITS data is. So they can't be changed at all.
Not that I trust particularly that plug-in, but here's a side reference on the
GIMP plug-in reading FITS files:
https://gitlab.gnome.org/GNOME/gimp/blob/master/plug-ins/file-fits/. That
plug-in didn't change much since 1999...
FITS header is read in
https://gitlab.gnome.org/GNOME/gimp/blob/master/plug-ins/file-fits/fits-io.c.
There are two modes, stated "automatic" and "by DATAMIN/DATAMAX":
With "automatic", FITS data is applied a reference change from the
minimum/maximum value of FITS data to the [0,DATAMAX] interval. This is just
weird as an automatic mode.
With "by DATAMIN/DATAMAX", FITS data is applied a reference change from
origin BZERO and scale BSCALE. The minimum/maximum value of FITS data is
considered to be the inverse reference change of DATAMIN/DATAMAX. This is
proper conversion to physical data values.
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