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John VanSickle wrote:
> JSR wrote:
> 
>> Hi,
>> I'm trying to improve aliasing in my small images. The problem is that
>> when
>> I render at small resolutions (< 800x600) the result always has
>> aliasing in
>> the thin lines, but when I render at high (> 3000x1500) the problem is
>> solved.
>>
>> I've tried with:
>> Option 1: +a0.1
>> Option 2: +am2 +r8 +a0.01
>> And the problem persist in both images (as you can see in attached file).
> 
> It's simple.  At the lower resolution, one pixel will be to one side of
> the thin line of grout, and the other pixel will be to the other side of
> the thin line of grout.  Both pixels hit the tile instead, and because
> they come out with very close rgb values, the renderer sees no reason to
> anti-alias further.
> 
> At the higher resolution levels, the thin line gets hit at least once by
> a pixel, and the aa settings see it through to the right result after that.
> 
> Your solutions are:
> 
> 1.  Set the aa threshold to zero, and the sampling method and depth so
> that every primitive gets hit when it is part of any pixel.  This will
> make things take longer.
> 
> 2.  Render at a much higher resolution with no aa at all, and then use
> some kind of post-processing to combine each block of pixels into a
> final pixel.
> 
	Those two solutions are equivalent: rendering with a aa threshold
of 0 means that POV will always go to the maximum depth and average
the results, which is more or less equivalent to rendering at a
higher resolution and downscaling.

	The best solution is to combine the two: render at a slightly
higher resolution so that at least one ray will always hit the thin
groves, but with some aa so that the results are refined where
needed. Then downscale in an image processing app. This is more or
less equivalent to being able to specify a minimum aa level (which
AFAIK isn't possible).

		Jerome
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+------------------------- Jerome M. BERGER ---------------------+
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