I am able to reliably reproduce a bug in POV-Ray 3.5
which affects Win32 and probably on other platforms.

Loaded imagemaps using grayscale PNG files
of 4 bpp or less appear near-black.

The bug is in the module png_pov.cpp,
function Read_Png_Image(), near line 1550.
The problem is that the colormap's RGB color
channels are mapped directly to palette indices,
which is okay for 8-bit files but not for
lower bit depths, since the palette indices
don't go all the way up to 255. e.g., A 4-bit file
will have a maximum white color of rgb(15,15,15)
instead of rgb(255,255,255).

The code fragment

    for (index = 0; index < cmap_len; index++)
    {
      cmap[index].Red =
      cmap[index].Green =
      cmap[index].Blue = index;
      cmap[index].Filter = 0;
      cmap[index].Transmit = 0;
    }

should read

    for (index = 0; index < cmap_len; index++)
    {
      cmap[index].Red =
      cmap[index].Green =
      cmap[index].Blue = index * 255 / (cmap_len - 1);
      cmap[index].Filter = 0;
      cmap[index].Transmit = 0;
    }


Ray Gardener
Daylon Graphics Ltd.
http://www.daylongraphics.com/products/leveller/
"Heightfield modeling perfected"

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