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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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In article <3e91529e$1@news.povray.org> , "Ray Gardener"
<ray### [at] daylongraphics com> wrote:
> 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).
Will be fixed in POV-Ray 3.51.
Thorsten
____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde
Visit POV-Ray on the web: http://mac.povray.org
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