"Rafal 'Raf256' Maj" <spa### [at] raf256com> wrote in message
news:Xns9555A63CFFB51raf256com@203.29.75.35...
> 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.

Why post-processing ?  Can't the 'bleeding' be computed while tracing ? When a
pixel is brighter than can be represented, just add some of that color to the
surrounding pixels.  Won't this solve the AA-problem?

Or am I talking nonsense here? :)

cu!
--
camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
<.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf

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Zeger Knaepen <zeg### [at] studentkuleuvenacbe> wrote:
> Why post-processing ?  Can't the 'bleeding' be computed while tracing ? When a
> pixel is brighter than can be represented, just add some of that color to the
> surrounding pixels.  Won't this solve the AA-problem?

  It will probably require changing the way POV-Ray handles the rendered
image. It would need to be able to change previously traced pixels (which
currently might already have been saved to the destination file) and
pixels yet to be traced.

-- 
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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Warp wrote:

> 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.

I suspect that the colour bleeding around the sun
in this photo is caused by inperfections in the
camera lens.

One has "correct exposure" when the film has the
desired densities for certain object(s)/area(s).

Many automatic exposure systems tries to achieve a
certain density on the film for objects with
"medium tones".

-- 
Tor Olav
http://subcube.net
http://subcube.com

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war### [at] tagpovrayorg news:4133696d@news.povray.org

>   It will probably require changing the way POV-Ray handles the rendered
> image. It would need to be able to change previously traced pixels (which
> currently might already have been saved to the destination file) and
> pixels yet to be traced.
> 

So IMHo adding post-processing would be very useffull.

Perhaps I could provide an patch (that maybe later would be included in 
MegaPOV then Pov Official)

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

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Tor Olav Kristensen <tor### [at] toberemovedhotmailcom> wrote:
> I suspect that the colour bleeding around the sun
> in this photo is caused by inperfections in the
> camera lens.

  No, it's a property of the film (well, in this case the CCD of the
digital camera, but it works the same way there). Sometimes when you
have extreme overexposure at the border of a frame in a film, the
brightness might even bleed partially to the adjacent frame.

  Without this natural property it would be impossible to photograph
things which are smaller than what the film would normally record, no
matter how bright these things are. However, as we know, if the thing
is bright enough, it will imprint the film no matter how small it is.

-- 
#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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In article <4133a71f$1@news.povray.org> , Tor Olav Kristensen 
<tor### [at] TOBEREMOVEDhotmailcom>  wrote:

> I suspect that the colour bleeding around the sun
> in this photo is caused by inperfections in the
> camera lens.

Not necessarily  keep in mind that film also is not infinitely thin.  For
color film the depth light has to penetrate to reach all three layers is
about three times the films resolution.  And the light scatters in each
layer as well.  This creates a natural blur effect at sharp light/dark
transitions.  I.e. <http://mac.povray.org/rhein.jpg> is (a after two JPEG
compressions) scan of a positive film and the resolution in the image is
about 80 lines per millimeter*.  Looking at the two bell towers clearly
shows a kind of blur. But, the sunlight entered at about a 30 degree angle,
so even without refraction it did pass at least two pixels.  Add scattering
and you get exactly the blur effect seen.

> One has "correct exposure" when the film has the
> desired densities for certain object(s)/area(s).

Yes, but keep in mind that film also has a very high dynamic range (for film
in the dark regions) compared to a digital display.  I.e. the image linked
above was edited to correct for the bad display dynamic range to make the
dark areas visible approximately as they are to the human eye.

> Many automatic exposure systems tries to achieve a
> certain density on the film for objects with
> "medium tones".

I think this is what most people come to expect nowadays due to point and
shot cameras.  It is only natural to expect the same for computer generated
images.

    Thorsten

* About half the scanner resolution - the image was scaled down before.
Film resolution for the film that was used is 135 lines per millimeter
according to manufacturer at 1000:1 contrast ratio.

____________________________________________________
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:


>   No, it's a property of the film (well, in this case the CCD of the
> digital camera, but it works the same way there). Sometimes when you
> have extreme overexposure at the border of a frame in a film, the
> brightness might even bleed partially to the adjacent frame.
> 
>   Without this natural property it would be impossible to photograph
> things which are smaller than what the film would normally record, no
> matter how bright these things are. However, as we know, if the thing
> is bright enough, it will imprint the film no matter how small it is.

Actually it is imperfections both in the lens and in the film/sensor. 
Even the best lenses have many different aberrations (like spherical 
aberration, chromatic aberration etc.) which cause a point in the scene 
render a circle/disc/ellipse/whatever to the film. Also the film is not 
perfect: there are many layers in the film. These cause inner 
reflections which spread the light that hits the film.

Question is: should POV-Ray try to simulate an imperfect optical system? 
And is antialiasing the right place to do it?

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In article <41342dd8@news.povray.org> , Warp <war### [at] tagpovrayorg>  wrote:

>  No, it's a property of the film (well, in this case the CCD of the
> digital camera, but it works the same way there).

Actually, with a CCD you get many problem in case of overexposure.  The CCD
elements have a charge limit.  And you get charge transfers to neighboring
pixels in the same line.

Even worse, all but the most expensive CCDs depend on a filter grid and the
camera later interpolating to get the final resolution image (the CCD
resolution quoted for digital cameras is always that of a monochrome
CCD!!!).  As color samples are distributed in a gird getting a good
approximation very close to the CCD resolution works, but it also adds a
slight blur, which later comes in very handy when having to use JPEG
compression, which is more effective with a certain level of blur.

> Sometimes when you
> have extreme overexposure at the border of a frame in a film, the
> brightness might even bleed partially to the adjacent frame.

Which is an effect of scattering inside the camera...

    Thorsten

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

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

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In article <4133696d@news.povray.org> , Warp <war### [at] tagpovrayorg>  wrote:

>   It will probably require changing the way POV-Ray handles the rendered
> image. It would need to be able to change previously traced pixels (which
> currently might already have been saved to the destination file) and
> pixels yet to be traced.

Nope, just trace a few (four perhaps) more pixels one pixel off in each
direction.  Would be slower, yes, but also simulate film more accurately.

    Thorsten

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

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

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Severi Salminen <sev### [at] not_thissibafi> wrote:
> Question is: should POV-Ray try to simulate an imperfect optical system? 

  POV-Ray is already doing that.
  Antialiasing brings the image closer to what a photograph would look like.
Why stop half-way?

-- 
#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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