post.trm image max colors patch

[Daniel J S. <dan...@ie...>]

Attached is a bug fix for the PostScript image using the five operand form (i.e., no palette).  The bug was that the max colors was not set to 2^N, where N is 1, 2, 4, 8, or 12.  So if the gray scale max was 128 (2^7) the brightness was lower than it should have been.

Dan