I need to check the code, but the following is what I remember.
The display routine will first create a seperate image
by scaling the data down within the window level and window
width constraints so it has the same number of bits
as the colormap has. Then it will try to get/allocate as many gray
color as possible from the colormap, and substitue with closest colors
when color runs out. Obviously this is a problem only for
non-private pseudoColor colormaps. For private colormap,
all entries in the map will be mapped to gray.
With a shared pseudoColor colormap, it's not easy to say
how many shades of gray to use as the display routine may
simply not able to honor it. One thing you may want to do
is to play with the window level and width that indirectly
affects how many grays are used.
--- Michal Szymanski <msz@bulge.astrouw.edu.pl> wrote:
> # To subscribers of the xforms list from Michal Szymanski
> <msz@bulge.astrouw.edu.pl> :
>
> Hello,
>
> I've read the chapter about images in XForms' manual, but apparently
> either I missed it or it is not there:
>
> If I try to display GRAY16 image (e.g. read from a 16-bit FITS file)
> in a PseudoColor visual (e.g. in a canvas window), what kind
> of colormap is used? Does the display routine change the colormap?
> Should the user prepare it manually? Can the user control how
> many grey levels are used?
>
> thanks in advance for any hints,
>
> regards, Michal.
>
> --
> Michal Szymanski (msz@sirius.astrouw.edu.pl)
> Warsaw University Observatory, Warszawa, POLAND
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