Re: when use RGB and when use RGBA?

Hi Helen,

> I need some help on how to determine  when and where use RGB  and RGBA.

You would use RGBA when you want at least some pixels
to be partially transparent. Otherwise use RGB.

> Suppose  the normal range of a flat field is between 0 and 100, but some
> points are with negative values.
> How can I make a color display but use grey color represent  the
> negative values?

Call setRange() on your ScalarMap to RGB to set a range from
your most negative value (e.g., -10.0) to 100.0. Then get
the ColorControl from the call to getControl() on that
ScalarMap, and call its setTable() method with a table that
assigns gray values to all the negative values in the
range.

Good luck,
Bill