[gdal-dev] merge ground and elevation image

[Jan Tappenbeck]

Hi !

i have two  black/white images with ground and elevation - and the 
background is white.

when i merge this two with gdal_merge i see in the result only one of 
this informations ground or elevation.

did anybody now a way to merge both informations with a white background 
in the result?

regards Jan :-)