"JeffBTX" <nomail@nomail> wrote:
> Antialias_Clipped is not covered in the documentation (revision.txt says that
> the documentation WAS changed, but searching the CHM file I cannot find +ac,
> +AC, or Antialias_Clipped). Would appreciate an explanation, I can't even guess
> what "CLIPPING" is in relation to antialiasing...

FYI: This refers to the clipping of overly-bright colors to the displayable
range (0.0 to 1.0 in POV-Ray terms, or 0..255 in 8-bit RGB terms).

With anti-aliasing active, "prehistoric" versions of POV-Ray clipped such colors
on a *per-ray* basis, instead of the resulting pixel value. This seems to have
been changed in the course of introduction of proper gamma handling, so that
POV-Ray 3.6.1 clipped the colors on a per-pixel basis; note that this has the
same effect as generating HDR output, and converting the image to 8-bit in a
post-processing step.

However, in some situations - especially with extremely-overly-bright objects in
the scene - this approach may seem to give inferior results, which may be the
reason why it was re-introduced later (as an option) in 2007 (but never
released before; interestingly, it has also never been re-introduced to 3.7).

However, I think it was an oversight to include the 2007 change into 3.6.2
without at least changing the default to "off", as this has been the standard
for years now.

As already mentioned, POV-Ray 3.7 also invariably uses per-pixel clipping
(unless HDR output is used of course, in which no clipping is performed at
all).

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