I built pov 3.7 rc6 beta on my Raspberry PI.

The first time I built, openexr was enabled by default; the second time 
I built with '--without-openexr'. For each build I ran povray on the 
biscuit.pov file as done by 'make check'. Perhaps this is by design, but 
when built with openexr, the 8-bit color PNG exhibits weird artifacts. I 
would expect to see this if I used '+fn16' (I actually used +fn) and 
pnginfo displays the same info for both PNG's:

[openexr enabled povray]
   $ pnginfo biscuit-withexr.png
   Image Width: 320 Image Length: 240
   Bitdepth (Bits/Sample): 8
   Channels (Samples/Pixel): 3
   Pixel depth (Pixel Depth): 24
   Colour Type (Photometric Interpretation): RGB
   Image filter: Single row per byte filter
   Interlacing: No interlacing
   Compression Scheme: Deflate method 8, 32k window
   Resolution: 0, 0 (unit unknown)
   FillOrder: msb-to-lsb
   Byte Order: Network (Big Endian)
   Number of text strings: 2 of 9
     Software (tEXt uncompressed): POV-Ray 3.7.0.RC6
     Comment (tEXt uncompressed): Render Date: 2012-08-16 
06:02:06Z\nPlatform: armv6l-unknown-linux-gnueabi\nCompiler: g+
+ 4.6\n

[--without-openexr]
   $ pnginfo biscuit-noexr.png
   Image Width: 320 Image Length: 240
   Bitdepth (Bits/Sample): 8
   Channels (Samples/Pixel): 3
   Pixel depth (Pixel Depth): 24
   Colour Type (Photometric Interpretation): RGB
   Image filter: Single row per byte filter
   Interlacing: No interlacing
   Compression Scheme: Deflate method 8, 32k window
   Resolution: 0, 0 (unit unknown)
   FillOrder: msb-to-lsb
   Byte Order: Network (Big Endian)
   Number of text strings: 2 of 9
     Software (tEXt uncompressed): POV-Ray 3.7.0.RC6
     Comment (tEXt uncompressed): Render Date: 2012-08-17 
12:20:06Z\nPlatform: armv6l-unknown-linux-gnueabi\nCompiler: g+
+ 4.6\n

Furthermore, there are still artifacts in the no-exr image when compared 
to a PNG rendered on Win7x64 using povray 3.7 RC6. I've attached all 
three images for comparison.

For you information, when I first got the Raspberry PI up and running, I 
ran an ancient program 'paranoia.c' which tests floating point accuracy. 
The program can still be found here:
   http://www.netlib.org/paranoia/paranoia.c
The program reported no abnormalities on the Raspberry PI, so I would 
expect that the PNG's produced by both x86 and arm (--without-openexr) 
would be >close< to identical. But they are not...?

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Attachments:
Download 'biscuit-withexr.png' (165 KB) Download 'biscuit-noexr.png' (164 KB) Download 'biscuit-win7x64.png' (163 KB)

Preview of image 'biscuit-withexr.png'

Preview of image 'biscuit-noexr.png'

Preview of image 'biscuit-win7x64.png'