-------------------------------------------
entry variable: $rgb -- abs name output bitmap file
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default: */rgb/<scandir>-cor.tiff

The "rgb:" entry shows the proposed name of a
saved bitmap (usu. tiff).

Session directory can be abbreviated as an
asterisk (*).  Absolute name OK, too.  Relative
name appended to $session/rgb.  Must confirm
overwrite, or use save_rgb directly (doesn't
ask).  Alternatively, set target rgb directory
($named_rgbdir) and write rgb file with function:
save_rgb_named <relative_name>.

The default bitmap output format is now tiff (3
bytes per pixel, lossless LZW compression, no
transparency).  To obtain an SGI rgb file, unset
$tiffoutflag by unlicking the unlabled check at
end of entry, which will update output file
suffix), or restart tkmedit from csurf with
Preferences -> Save .tiff selected.

The csurf Preferences -> Black->Transparent
option has no effect on tkmedit (the background
of a structural scan is not exactly black).
