Usage: add_images [options] file1 file2 [file3]

	This script will read two sgi rgb images and add them to one sgi rgb
	image. The rgb values of the in-images will be scaled down to yield an
	image of normal brightness.

	options:	-h    => this help screen 
			-s XX => Normally a scaling factor of 128 for both
				 images is used (0=black 256=white). 
				 You can choose a different scale factor (XX)
				 between 0 and 256 for the first image. The
				 second image will get a factor of 256 - XX.
				 If XX is 0 the resulting image will equal the
				 second image but perfectly white colors will
				 become black.
				 If you add mutiple -s options the second scale
				 will be used for the second picture: 
				 (e.g. -s 160 -s 160)
			-b    => Black mode: In both images convert white to
				 black; add both images without color scaling.

	Uses sgi image commands: cscale and add.

Author: Olaf Corten, the Netherlands
E-Mail: olafc@molding.fico.nl or ocorten@knoware.nl

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# History:
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# first version	februari 1997
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