ION and color mapping bug ?

[Udo Grabowski <udo.grabowski(at)imk.fzk.de>]

Hello again !

A similar problem to the one reported shortly before ('object graphics
colormap bug?') arises in our ION 1.2/Java1.2 code when using the IONgr2Canvas
interface together with the addIONGR2drawable idl interface (the Canvas 
turns out to be a IDLgrbuffer on the Idl side). RGB colors can be retrieved
with the NEAREST_COLOR function of IDLgrPalette with a predefined colormap,
and the indices are correct when comparing with the appearance in xpalette.
But on the screen (8 bit) some of the colors appear completely wrong (eg., 
Blue->yellow). It seems that ION does not know about switching colormaps to 
private mode (we never saw that for any ION program), but instead tries to 
map the full colortable to the shared one available with minimum color
distortion. 
This mapping code seems to fail for the object graphics colors. We also 
recognize that the white background is covered with patches of grey dithering
artefacts. Seems that this mapping is done by a lousy dithering code.
When specifying colors and printing, everything looks perfect. When using direct
graphics with the ION(j)grDrawable interface, colors are also fine.
Does anyone has experiences with that ? Is there any cure apart from getting
a fix from RSI ?
-- 
Dr. Udo Grabowski                           email: udo.grabowski@imk.fzk.de
Institut f. Meteorologie und Klimaforschung II, Forschungszentrum Karslruhe
Postfach 3640, D-76021 Karlsruhe, Germany           Tel: (+49) 7247 82-6026
http://www.fzk.de/imk/imk2/ame/grabowski/           Fax:         "    -6141