andrel <a_l### [at] hotmailcom> wrote:
> I think I agree with Thorsten and Christoph that 3.6 behaviour is
> mathematically correct and that 3.5 had a bug/feature.

  The 3.6 behaviour might be *mathematically* correct given some
premises (which might not be realistic). However, the 3.6 behaviour
is not *physically* correct, which is the most important thing here
(but neither is the 3.5 behaviour, for that matter).

  The raytracing algorithm tries to simulate a photographic film which
is hit by light. The aim of POV-Ray is photorealism, not light absolute
intensity measurement at each pixel.
  If the goal of the rendering was to measure the intensity of light
hitting each pixel, the 3.6 antialiasing would be more correct than 3.5,
but it would not be perfect either: Brightness is clipped to a certain
maximum value, which renders even this goal useless.

  However, that is not the goal of POV-Ray in the first place. The goal
is to simulate photorealism.
  What happens when light hits the film of a camera, and this light is
much more intense than what the camera/film is configured for? The film
gets overexposed at that point. Overexposure manifests itself by color
bleeding: The spot which is too bright will spread to its surroundings in
the film.

  So neither the 3.5 nor the 3.6 antialiasing methods are physically
correct.
  The question which remains is: Which one produces better images?

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
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-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Slime <fak### [at] emailaddress> wrote:
> The previous behavior was correct; the current behavior is broken.

  Not true. Neither one is correct.

  The only question is which one looks better.

> Well, duh. If an object is 1/10000 of the image's width, then of course it
> should be nearly invisible!

  Not true. At least not in photography.

-- 
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-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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Thorsten Froehlich <tho### [at] trfde> wrote:
> Get over it and fix your scenes!

  This is an incorrect solution.

  Have you ever heard of film exposure times and overexposures?
Overexposure is not always a mistake in photography, nor is it in
raytracing either.

  Here's an example of intentional overexposure in a photograph:
http://www.students.tut.fi/~warp/photos/patikka2/35.jpg
  If the shutter speed of the camera would have been set so that the
brightest part of the image (in this case the Sun) would have the
maximum intensity the camera could measure, then everything in the
photograph except the Sun would be almost completely black. Letting
the Sun overexpose the photograph was completely intentional and
in fact gives a good photographical effect.

  The photo also gives a hint about the truely correct solution to
the problem.

-- 
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Eli <eli### [at] jehoelnet> wrote:
> I hardly use the built-in antialiasing. I use the focal blur trick instead, 
> although it doesn't work if the aperture is too small. 

  What is "the focal blur trick"?

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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Rafal 'Raf256' Maj <spa### [at] raf256com> wrote:
> Imho this *is* the correct behaviour in most cases

  Not in photography. Neither solution is physically correct.

> if only *10 times 
> brighter object occupies 1/10 (or more) of pixel - enitre pixel should be 
> white.

  But what happens if an object which occupies an entire pixel is 10 times
brighter than what the pixel can represent?

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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war### [at] tagpovrayorg news:4132edfb@news.povray.org

>   But what happens if an object which occupies an entire pixel is 10
>   times 
> brighter than what the pixel can represent?

If he eye is not accomodated - it will only represent the maximum value.

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Rafal Maj 'Raf256', home page - http://www.raf256.com/me/
Computer Graphics

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In article <4132ed5f@news.povray.org> , Warp <war### [at] tagpovrayorg>  wrote:

>   Here's an example of intentional overexposure in a photograph:
> http://www.students.tut.fi/~warp/photos/patikka2/35.jpg
>   If the shutter speed of the camera would have been set so that the
> brightest part of the image (in this case the Sun) would have the
> maximum intensity the camera could measure, then everything in the
> photograph except the Sun would be almost completely black. Letting
> the Sun overexpose the photograph was completely intentional and
> in fact gives a good photographical effect.
>
>   The photo also gives a hint about the truely correct solution to
> the problem.

Indeed.  And the correct solution can only be implemented if the
anti-aliasing occurs prior to clipping colors.

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

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Warp wrote:

>   Have you ever heard of film exposure times and overexposures?
> Overexposure is not always a mistake in photography, nor is it in
> raytracing either.

Slightly OT, but:

In my opinion "overexposure" or "underexposure" is allways a mistake and 
not intentional. "Increasing exposure" or "decreasing exposure", on the 
other hand, IS intentional and gives the desired result and the result 
is then a correctly exposed image. And all this relates allways to the 
usage of a light meter which gives some initial values for shutter speed 
and aperture that we can alter.

In your image, it is hard to say whether it is overexposed or 
underexposed or both/neither. The scene itself (expect the sun) is maybe 
underexposed as there is no detail in the trees. The sun is overexposed 
because it is very bright. The whole scene is probably quite correctly 
exposed to give desired effect. With small P&S digital cameras it is 
quite common that deepest shadows are "blocked" (ie. black, no detail) 
and brightest highlights are "blown out" (white, no detail). With good 
B&W film it is possible to capture a wider dynamic range with some detail.

> Letting the Sun overexpose the photograph was completely intentional 
> and in fact gives a good photographical effect.

Actually sun is not "overexposing the photograph" but sun "gets 
overexposed in the photograph".


Severi

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Severi Salminen <sev### [at] not_thissibafi> wrote:
> Actually sun is not "overexposing the photograph" but sun "gets 
> overexposed in the photograph".

  Whatever... :P

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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Rafal 'Raf256' Maj <spa### [at] raf256com> wrote:
> >   But what happens if an object which occupies an entire pixel is 10
> >   times 
> > brighter than what the pixel can represent?

> If he eye is not accomodated - it will only represent the maximum value.

  It will appear larger than it really is, even in the human eye (and
specially in a photograph).

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
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-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -

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