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.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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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.

-- 
http://www.raf256.com/3d/
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]
[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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Thorsten Froehlich <tho### [at] trfde> wrote:
> Indeed.  And the correct solution can only be implemented if the
> anti-aliasing occurs prior to clipping colors.

  The problem is that when there's overexposure, the "antialias
before clipping" gets only half-way to the solution and thus what you
are seeing is the result of an algorithm which is incomplete and shows
artifacts as a result.

-- 
#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:41332a06@news.povray.org

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

So that's a task for post-processing.

I even write such a progam :) It needs input as 2 images (one normal, and 
second much darker - to compress input, but array of floats would also be 
good), and it can add some small lens-flare-like reflections etc.



-- 
http://www.raf256.com/3d/
Rafal Maj 'Raf256', home page - http://www.raf256.com/me/
Computer Graphics

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