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).

Render at high resolution and resize is a solution, but I ask:

(In order to don't lose time)

Thanks,

JSR.

P.D.: Someone knows if Kari Kivisalo has a web page? I saw his name in
pov-news a long time ago... I think he was one of the best pov-raiders...

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Attachments:
Download 'antialias.jpg' (99 KB)

Preview of image 'antialias.jpg'

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.

3.  Patch POV-Ray so that you can specify a higher level of aa for 
certain regions, and lower settings for others.

Regards,
John

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> 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.
> 
> 3.  Patch POV-Ray so that you can specify a higher level of aa for 
> certain regions, and lower settings for others.

Indeed, I was under the impression that there are commandline switches 
to set the minimum and maximum supersampling amount. But, apparently, 
there is only a switch for the maximum; the minimum is always 1 (mode=1) 
or 4 (mode=2). Pitty...

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Have you tried focal blur instead of antialiasing?


-- 
-Nekar Xenos
"The truth is out there"

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> Have you tried focal blur instead of antialiasing?

That way you can have two problems instead of one...

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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

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
- --
+------------------------- Jerome M. BERGER ---------------------+
|    mailto:jeb### [at] freefr      | ICQ:    238062172            |
|    http://jeberger.free.fr/     | Jabber: jeb### [at] jabberfr   |
+---------------------------------+------------------------------+
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>> 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.

Well, it depends.

If you render at a higher resolution and then use a nice image 
modification package, you could do a Lanczos resample or something, 
which looks slightly nicer. But that's about it.

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