>    What he is suggesting is to invert the color value, so white 
> becomes black, and black areas become white, so that the bumpmap
> will take a different height field to achieve the "inverse" effect..
> I have tried it before but do not quite like the result..
>    IMHO, the PS Lighting effects did it more "politically correct".
> If you press the "inverse bumpmap" there, the effect is different
> from the "Invert" Bump Map in Gimp.. Just try it out yourself and
> see if you agree... don't ask me to explain, I can't .. ;-)

The Bumpmap plug-in works by taking the intensity values to be height
values and computing the surface normal at each point.  Then it does
simple Gouraud-like shading on the destination image.  Inverting the
bumpmap source is exactly the same as using the "invert" button on the
plug-in's dialog box; the intensity values are inverted and the
surface normals will point in the opposite direction.

I.e. it is essentially a cheap embossing effect.

Photoshop's Lighting Effects produces much better results because it
actually does Phong shading of the image, and it general it has better
lighting models that you can choose.  You can do this in the GIMP with
Tom Bech's plug-in of the same name.


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