Hi all,

This idea came about earlier, while I was drawing with and ink. The 
technique isn't new, but I can't remember who originated it. Basically, 
it involves a sphere with high transmittance placed around the camera. 
The textures are gradients. They are turned into lines under the 
influence of the contrast-inducing sphere mentioned beforehand.

Rendered in a single pass. Sized and framed with the Gimp. Questions and 
comments are always welcome!

~Sam

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Samuel Benge wrote:
> Hi all,
>
> This idea came about earlier, while I was drawing with and ink. The
> technique isn't new, but I can't remember who originated it.
> Basically, it involves a sphere with high transmittance placed around
> the camera. The textures are gradients. They are turned into lines
> under the influence of the contrast-inducing sphere mentioned
> beforehand.
>
> Rendered in a single pass. Sized and framed with the Gimp. Questions
> and comments are always welcome!

Ooh, that looks nice! Even knowing the technique, I can't quite figure out 
how the image must look before the contrast enhancement.

The technique is demonstrated in the POV-Ray demo files 
\scenes\textures\pigments\transmitfx.pov and scenes\advanced\bwstripe.pov

Unfortunately, since POV-Ray 3.6, when using really high contrast, the 
effects looks aliased even if antialias is used. This is because of the 
controversial decision to make POV-Ray do clipping *after* antialiasing 
rather than before. In POV-Ray 3.5 it looked perfect. However, you can 
always render at a higher resolution and scale down.

Rune
-- 
http://runevision.com

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"Rune" <new### [at] runevisioncom> schreef in bericht 
news:469b48f6$1@news.povray.org...
>
> The technique is demonstrated in the POV-Ray demo files 
> \scenes\textures\pigments\transmitfx.pov and scenes\advanced\bwstripe.pov
>
> Unfortunately, since POV-Ray 3.6, when using really high contrast, the 
> effects looks aliased even if antialias is used. This is because of the 
> controversial decision to make POV-Ray do clipping *after* antialiasing 
> rather than before. In POV-Ray 3.5 it looked perfect. However, you can 
> always render at a higher resolution and scale down.
>

I think this is addressed in Megapov's Clip_Colors() if I am not mistaken.

Thomas

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Thomas de Groot wrote:
> "Rune" schreef in bericht:
>> Unfortunately, since POV-Ray 3.6, when using really high contrast,
>> the effects looks aliased even if antialias is used. This is because
>> of the controversial decision to make POV-Ray do clipping *after*
>> antialiasing rather than before. In POV-Ray 3.5 it looked perfect.
>> However, you can always render at a higher resolution and scale down.
>
> I think this is addressed in Megapov's Clip_Colors() if I am not
> mistaken.

That's a workaround, but as far as I remember, the post-processing in 
MegaPOV is rather slow. Or has that changed since I last used it?

Rune
-- 
http://runevision.com

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"Rune" <new### [at] runevisioncom> schreef in bericht 
news:469ca853$1@news.povray.org...
>
> That's a workaround, but as far as I remember, the post-processing in 
> MegaPOV is rather slow. Or has that changed since I last used it?
>

Well I am not sure. As far as I can tell this workaround does not seem 
slower. However, I didn't test speed really.

Thomas

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Rune wrote:

> Ooh, that looks nice! 

Hey, thanks!

> Even knowing the technique, I can't quite figure out 
> how the image must look before the contrast enhancement.

It's a reflective eye which has an outside surface with an ior of 1.33.
A simple gradient z for the sclera, radial for the iris.

> The technique is demonstrated in the POV-Ray demo files 
> \scenes\textures\pigments\transmitfx.pov and scenes\advanced\bwstripe.pov

Hmm, what do you know. I'll have to look at it.

> Unfortunately, since POV-Ray 3.6, when using really high contrast, the 
> effects looks aliased even if antialias is used. This is because of the 
> controversial decision to make POV-Ray do clipping *after* antialiasing 
> rather than before. In POV-Ray 3.5 it looked perfect. However, you can 
> always render at a higher resolution and scale down.
> 
> Rune

Gah, I don't know why it was changed!

Speaking of odd aa behavior, I don't even use +am1 anymore because of 
the strange artifacts. Is that also due to post-clipping of averaged 
samples? It's unfortunate, since method 2 is faster.... at least I think 
it is.

~Sam

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Samuel Benge wrote:
> Rune wrote:
>> Unfortunately, since POV-Ray 3.6, when using really high contrast,
>> the effects looks aliased even if antialias is used. This is because
>> of the controversial decision to make POV-Ray do clipping *after*
>> antialiasing rather than before. In POV-Ray 3.5 it looked perfect.
>> However, you can always render at a higher resolution and scale down.
>>
>> Rune
>
> Gah, I don't know why it was changed!

Thorsten (I believe it was) explained something along the lines that the 
pixels in the raytraced image should simulate the light-sensitive cells in a 
digital camera, which covers an area, but which can be over-exposed even if 
just one small sub-pixel dot is really bright. In effect, it meant that you 
can create a scene with stars in the sky that are much smaller than one 
pixel but still show up if they are sufficiently bright.

This then is the justification for a feature that makes all very bright 
things with sharp edges look jagged.

> Speaking of odd aa behavior, I don't even use +am1 anymore because of
> the strange artifacts. Is that also due to post-clipping of averaged
> samples?

Hmm, I don't know...

Rune
-- 
http://runevision.com

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