I think that this may be a bug.

I've had a look at the source code and it reveals that POV-Ray behaves in a
strange way when anti-aliasing is used with field rendering.

If you have anti-aliasing switched off, it behaves the way most people
expect. It calculates and renders only the odd-numbered lines of a frame -
on the screen the even numbered lines appear as black lines, but in the
output file they are an exact copy of the calculated lines. In other words
line 1 is calculated and output as line 1 and 2, then line 3 is calculated
and output as line 3 and 4, and so on. For the next frame only the
even-numbered lines are calculated and duplicated in a similar way.

However, when you switch on anti-aliasing the behaviour changes. For a
particular frame, POV-Ray calculates and renders ALL of the lines (odd and
even) individually as if field rendering was not switched on! But then it
anti-aliases the odd-numbered lines, leaving the even lines with no
anti-aliasing. For the next frame all of the lines are calculated and
rendered, and then the even lines are anti-aliased with the odd lines left
with no anti-aliasing.

This can be seen in the function Start_Non_Adaptive_Tracing() in render.c

This is very strange. The whole point of using the field rendering feature
of POV-Ray is to save time by only calculating HALF of the lines in each
image, but when anti-aliasing is switched on ALL of the lines are being
calculated (although only half are anti-aliased). So it seems that POV-Ray
is wasting a lot of time unnecessarily calculating the "unused" lines!

If any of the POV-Ray development team read this, can you comment on whether
this  is a BUG?

Thanks

Colin




"PovRAY" <cbd### [at] my-dejacom> wrote in message
news:3ccc7162@news.povray.org...
> I've just completed the rendering of a cyclical animation which took
several
> days to complete. As the output is to be for television I switched on
> povray's field rendering and also antialiasing.
>
> I was expecting to see each generated image having sets of duplicated
> consective lines which happens with field rendering when antialiasing is
> switched off (i.e. line 1 and 2 identical, 3 and 4 identical, etc...).
>
> However with antialising switched on, I was surpised to see every line was
> uniquely different. And zooming into an image I can see that each line is
> antialiased, but when viewed in total the image looks pixelated as if
there
> was little of no antialiasing present. I suspect that the antialiasing
with
> field rendering is not working "correctly" - perhaps a bug?
>
> Is there anyone who knows how povray is supposed to perform antialiasing
> when field rendering is switched on?
>
> Thanks
>
> Colin
>
>
>
>
>

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