> Date: Mon, 11 Dec 2000 14:56:08 -0500
> From: Joe Boccanfuso <[EMAIL PROTECTED]>
>
> I am particularly concerned with the words "... with very little loss in
> object quality". My concern/question is as follows. Does this refer to
> (possibly) losing the actual co-ordinate (i.e. x, y, z) and color data or
> does this refer to losing Appearance attributes above and beyond color (e.g.
> Polygon fill mode, Texturing, Transparency, etc.)? My hope is that the
> actual geometric/co-ordinate data is NOT lost. What data may be lost?
Geometry compression is lossy. Positions, colors, normals (and in Level II,
texture coordinates) are quantized.
The intent is to effectively produce perceptually lossless compression, as in
JPEG and MP3. Quality is controlled by setting quantization levels (up to 16
bits per component for positions, colors, and textures, and up to a total of 18
bits for normals).
Although it works well for many applications, it's not appropriate for those
that must retain the exact bit-for-bit representation after decompression.
You can get an idea of the quality by playing around with the example programs
provided for compressing .obj files.
-- Mark Hood
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