Wasn't it Christoph Hormann who wrote:
>Mike Williams wrote:
>
>> The documentation suggests that you can use an externally generated PPM
>> file to store suitable 16-bit data, but PPM files created by POVRay with
>> hf_gray_16 switched on are not in this format (and they're not simple
>> grey images either).
>
>Why do you think so?  Last time i checked POV-Ray generated correct 
>binary 16bit PGM with hf_gray_16 and +fp.

When I use POVRay to generate a hf_gray_16 TGA file, it works as a
height_field.

When I do exactly the same thing with a PPM file generated with
hf_gray_16 and +fp. I get an error "Parse Error: File is not in PPM
format (type 53)" when I try to use it as a height_field. (POVRay 3.6
Windows 98se).

Some image editors think that the hf_gray_16 PPM file has 8 bits per
pixel (and don't display it correctly). Other image editors think that
it's an 8-bit greyscale PGM file with an incorrect extension (and do
display it correctly).

The documentation only mentions generating TGA hf_gray_16 files from
within POV. The only bit that mentions using 16-bit PPM files says that
they can be "generated with special custom-made programs".


However, the significant point for the original poster is that you can't
do it with BMP files.

-- 
Mike Williams
Gentleman of Leisure

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