A user posted in comp.graphics.rendering.raytracing that ugly artifacts
were showing up in heightfields in POV-Ray for Linux but not in POV-Ray
for Solaris.  Examples were put up on a web site (using the example of
crater.pov), and I was able to reproduce the artifacts in the Linux
version.   The problem appears to stem from a failure to write a 16-bit
PNG (despite the hf_gray_16).  We're producing an 8-bit PNG, which shows
a lot more faceting than 16-bit.  Output as TGA works fine, so that's a
workaround.  I suspect (but have not confirmed) that the Solaris version
was outputting a TGA that was converted to PNG (16-bit) with an external
program.  This bug has been seen in the Windows version (3.1g) by
another user on c.g.r.r.

-Mark Gordon

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