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Hey all,
I'm working on a scene where I have a problem with some horizontal lines,
and yes, the problem is antialiasing. The thing is, I've tried +a0.0 +am2
and there's really not a lot of difference in this particular part of the
scene, still jaggies even though the scene as a whole does look better.
Anyway, these horizontal lines are really probably about 15 - 20 degrees
to the horizontal in the actual image - hence the jaggies.
Now to the point. ;) I did a few experiments* where I used +a0.0 +am1
and the same but with +am3, and there was a significant difference in speed:
o- +a0.0 +am1 = 35 secs
o- " +am2 = 2:30 secs
o- " +am3 = 36 secs
o- +a0.0 --- = 39 secs
* These experiments included a small selection in the winPoV render
window - I used the exact select dimensions for each render used in this
mini-experiment.
Does PoV-Ray not recognise +am1, +am3?
The scene still rendered with +am1, +am3, but what did it really
render? Also, +a0.0 on its own took longer(!) I thought when I tried it, it
would be quicker than +am1 or +am3.
Second from last question, (silly question too): what does the 'am'
stand for?
Lastly, how can I improve these jaggies?
~Steve~
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St. <dot### [at] dot com> wrote:
> Now to the point. ;) I did a few experiments* where I used +a0.0 +am1
> and the same but with +am3, and there was a significant difference in speed:
There's no method 3. I guess povray is reverting to method 1.
> Second from last question, (silly question too): what does the 'am'
> stand for?
Antialiasing method.
> Lastly, how can I improve these jaggies?
If rendering time is not an issue, you can increase the number of
samples using the +r option. The default is +r3 (which means 3x3 rays).
Try with +r4 or +r5 (and expect heavy slowdown of the rendering).
--
- Warp
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"Warp" <war### [at] tagpovrayorg> wrote in message
news:46c7416d@news.povray.org...
> St. <dot### [at] dotcom> wrote:
>> Now to the point. ;) I did a few experiments* where I used +a0.0 +am1
>> and the same but with +am3, and there was a significant difference in
>> speed:
>
> There's no method 3. I guess povray is reverting to method 1.
So, method 1 is recognised by PoV-Ray but not method 3. It still
leaves the question of what method 1 is good for compared to +a0.0?
>
>> Second from last question, (silly question too): what does the 'am'
>> stand for?
>
> Antialiasing method.
Dang... :o/
>
>> Lastly, how can I improve these jaggies?
>
> If rendering time is not an issue, you can increase the number of
> samples using the +r option. The default is +r3 (which means 3x3 rays).
> Try with +r4 or +r5 (and expect heavy slowdown of the rendering).
Phew! Well, this is an image that I have to go through with. But,
you've taught me something new there Warp. Thanks.
I'll give that a try and hope it comes good. ;)
~Steve~
>
> --
> - Warp
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St. <dot### [at] dotcom> wrote:
> So, method 1 is recognised by PoV-Ray but not method 3.
Methods 1 and 2 are two different sampling algorithms. There's no
method 3.
> It still
> leaves the question of what method 1 is good for compared to +a0.0?
There's nothing to compare. The +a and the +am options are two different
parameters of antialiasing (the fact that both start with "+a" is a mere
question of syntax). The option +a turns on antialiasing calculations, and
it can take a threshold value as parameter. The +am option specifies the
algorithm to use for antialiasing (1 being the default when this option
is not given).
The threshold given to +a means how much adjacent pixels must differ
before antialiasing samples are taken. The antialiasing method simply
tells how those samples are taken. They are basically different and
independent settings.
--
- Warp
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
St. wrote:
> Hey all,
>
> I'm working on a scene where I have a problem with some horizontal lines,
> and yes, the problem is antialiasing. The thing is, I've tried +a0.0 +am2
> and there's really not a lot of difference in this particular part of the
> scene, still jaggies even though the scene as a whole does look better.
>
> Anyway, these horizontal lines are really probably about 15 - 20 degrees
> to the horizontal in the actual image - hence the jaggies.
>
> Now to the point. ;) I did a few experiments* where I used +a0.0 +am1
> and the same but with +am3, and there was a significant difference in speed:
>
> o- +a0.0 +am1 = 35 secs
> o- " +am2 = 2:30 secs
> o- " +am3 = 36 secs
> o- +a0.0 --- = 39 secs
>
In addition to what Warp already said:
- +am1 is the default, therefore "+a0.0 +am1" and "+a0.0" are
identical;
- with the default recursion depth of 3, method 1 will use 9
samples per pixels, whereas method 2 will use 81 samples per pixel.
This explains the timing differences you see.
To improve the jaggies, I would suggest rendering at a higher
resolution (say multiplying the image dimensions by 2), then
downscaling the image. At the same time, you should raise the AA
threshold to 0.1 or 0.2 in order to improve the rendering speed.
Jerome
- --
+------------------------- Jerome M. BERGER ---------------------+
| mailto:jeb### [at] freefr | ICQ: 238062172 |
| http://jeberger.free.fr/ | Jabber: jeb### [at] jabberfr |
+---------------------------------+------------------------------+
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> whereas method 2 will use 81 samples per pixel.
A *maximum* of 81 samples per pixel.
--
- Warp
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Warp wrote:
> "J�r�me M. Berger" <jeb### [at] freefr> wrote:
>> whereas method 2 will use 81 samples per pixel.
>
> A *maximum* of 81 samples per pixel.
>
With +a0.0, the maximum is always reached isn't it?
Jerome
- --
+------------------------- Jerome M. BERGER ---------------------+
| mailto:jeb### [at] freefr | ICQ: 238062172 |
| http://jeberger.free.fr/ | Jabber: jeb### [at] jabberfr |
+---------------------------------+------------------------------+
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=5qxz
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> So, method 1 is recognised by PoV-Ray but not method 3. It still
> leaves the question of what method 1 is good for compared to +a0.0?
>
+a0.0 is useless. It will supersample even if there is a completely
color. Even +a0.001 could be useful in some cases, but +a0.0 is simply a
waste of CPU time...
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Nicolas Alvarez wrote:
> It will supersample even if there is a completely color.
OK that got messed up... I meant "It will supersample even if there is a
completely plain color." Even if your whole image is the exact same
color, +a0.0 will supersample it...
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Wasn't it Nicolas Alvarez who wrote:
>Nicolas Alvarez wrote:
>> It will supersample even if there is a completely color.
>
>OK that got messed up... I meant "It will supersample even if there is a
>completely plain color." Even if your whole image is the exact same
>color, +a0.0 will supersample it...
It is sometimes useful to supersample images for which the colour is
exactly the same at integer pixel positions, but which have sub-pixel
features.
For example:
camera {location <0,0,-10> look_at 0}
plane {z,0
pigment {gradient x
colour_map {[0.005 rgb 0][0.005 rgb 1]}
}
finish {ambient 1}
}
If you render that with any non-zero antialias threshold then it will
miss some of the lines where the line happens to squeeze between pixels.
How many lines are missed depends on the image size: at 320x240 all the
lines are missed.
If you render it with +a0.0 then it finds all the lines.
That's a bit of an extreme example, but it's possible to encounter the
same sort of effect in real scenes.
--
Mike Williams
Gentleman of Leisure
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