news: chr### [at] netplexaussieorg...
> But it is still less accurate than radiosity could be, as far as I can
> tell.
Accuracy here is really a non-issue given the benefits...

>Why use a high dynamic range environment map instead of sampling
> the actual environment?
> Speed? The ability to use real-world samples
> instead of coding a background?

Creating complex environments just to make them look nice in reflections and
project the right lights is rarely done :
for practical purposes, you just don't code the whole St Peters Basilic to
make a background (or you've really been raytracing too long...). There's a
example by Jaime who did a fake HDRI that way, but he used a complete scene
he had done before.
Speed is of course a big issue there too, since maps render very fast.
Also, natural light environments taken from photographs have a complexity
and a richness that is unmatched by usual 3D lighting, which is why people
go ooh and aah in front of these pics.
Now HDR isn't the solution to all lighting problems, and is only valuable in
certain circumstances, like "packshot" images (close ups of objects), but
then it is very good and extremly simple to set up using regular radiosity
parameters.

G.

--
**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters

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I'm starting to get interested...

-- 
#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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On Mon, 30 Dec 2002 13:02:54 -0500
Christopher James Huff <chr### [at] maccom> wrote:

> The ability to use real-world samples 
> instead of coding a background?

  Yes, I think it's main purpouse is to create "augmented reality", but
it's good also for some other interesting things, as Gilles said.

-- 
Jaime Vives Piqueres
		
La Persistencia de la Ignorancia
http://www.ignorancia.org

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Can you tell me a bit more about the implementation here? For example, I
have rendered a few scenes using an HDR file and I would like to "mask out"
the actual original scene that the HDR file contains. Is there a way to do
that? If I put a plane or perhaps a wall in front of the "background" image
that appears in my scene, will that block out the light coming from the HDR
file? In other words, does the placement of the HDR file in the scene act
exactly like a light-emitting source? That's the part I don't quite get.
In effect, the probes I have used are of a campus, a beach, a kitchen, etc.
and you can always see some part of that original scene in the POV scene.
I'd like to "sample" the illumination of the HDR file but leave the kitchen
(or the beach) out of my own picture.

Thanks much,
Dennis


"Gilles Tran" <git### [at] wanadoofr> wrote in message
news:3e10983b@news.povray.org...
>

> news: chr### [at] netplexaussieorg...
> > But it is still less accurate than radiosity could be, as far as I can
> > tell.
> Accuracy here is really a non-issue given the benefits...
>
> >Why use a high dynamic range environment map instead of sampling
> > the actual environment?
> > Speed? The ability to use real-world samples
> > instead of coding a background?
>
> Creating complex environments just to make them look nice in reflections
and
> project the right lights is rarely done :
> for practical purposes, you just don't code the whole St Peters Basilic to
> make a background (or you've really been raytracing too long...). There's
a
> example by Jaime who did a fake HDRI that way, but he used a complete
scene
> he had done before.
> Speed is of course a big issue there too, since maps render very fast.
> Also, natural light environments taken from photographs have a complexity
> and a richness that is unmatched by usual 3D lighting, which is why people
> go ooh and aah in front of these pics.
> Now HDR isn't the solution to all lighting problems, and is only valuable
in
> certain circumstances, like "packshot" images (close ups of objects), but
> then it is very good and extremly simple to set up using regular radiosity
> parameters.
>
> G.
>
> --
> **********************
> http://www.oyonale.com
> **********************
> - Graphic experiments
> - POV-Ray and Poser computer images
> - Posters
>
>
>
>
>

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In article <3e10983b@news.povray.org>,
 "Gilles Tran" <git### [at] wanadoofr> wrote:


> news: chr### [at] netplexaussieorg...
> > But it is still less accurate than radiosity could be, as far as I can
> > tell.
> Accuracy here is really a non-issue given the benefits...

Well, since my interests are mainly in simulation, "better" == "more 
accurate", "less accurate" == "worse". Speed is only part of my equation 
for judging a simulation if the quality is a constant. Like glows or 
fog, this is a compromise of quality vs. speed...it isn't "better than 
radiosity", just faster without being a lot worse, like what ambient was 
originally for.

Since you are an artist, you have different criteria about which is 
"better".

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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3e15d35a$1@news.povray.org...
> file? In other words, does the placement of the HDR file in the scene act
> exactly like a light-emitting source? That's the part I don't quite get.
> In effect, the probes I have used are of a campus, a beach, a kitchen,
etc.
> and you can always see some part of that original scene in the POV scene.
> I'd like to "sample" the illumination of the HDR file but leave the
kitchen
> (or the beach) out of my own picture.

Well, HDR maps really behave like any other map apart the high range stuff
(mildy reflective objects will show proper highlights, radiosity effects
will be more natural-looking etc.). I don't see a way to use only the
illumination but not the image itself, apart carefully setting up the scene
so that the HDR map doesn't show up in the frame and the non-HDR parts shown
are consistent with the rest of the lighting (the sort of trick we use with
regular maps). And no_image only works for the reflective parts, not the
illumination itself (just checked...). Possibly the best would be to use
Jaime's trick, setting up a complete scene and then using it as a map with
the "fake HDR" method(s) he describes.

G.

--
**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters

Post a reply to this message

Thank for your reply. Where is the message in which Jamie describes this
technique> I must have missed it.
But to be clear, if I put a plane on the Y axis beyond my object, I should
still be able to use the illumination from the map even if the map image is
not showing in my scene?
thanks again,
D.

"Gilles Tran" <git### [at] wanadoofr> wrote in message
news:3e162bfa@news.povray.org...

> 3e15d35a$1@news.povray.org...
> > file? In other words, does the placement of the HDR file in the scene
act
> > exactly like a light-emitting source? That's the part I don't quite get.
> > In effect, the probes I have used are of a campus, a beach, a kitchen,
> etc.
> > and you can always see some part of that original scene in the POV
scene.
> > I'd like to "sample" the illumination of the HDR file but leave the
> kitchen
> > (or the beach) out of my own picture.
>
> Well, HDR maps really behave like any other map apart the high range stuff
> (mildy reflective objects will show proper highlights, radiosity effects
> will be more natural-looking etc.). I don't see a way to use only the
> illumination but not the image itself, apart carefully setting up the
scene
> so that the HDR map doesn't show up in the frame and the non-HDR parts
shown
> are consistent with the rest of the lighting (the sort of trick we use
with
> regular maps). And no_image only works for the reflective parts, not the
> illumination itself (just checked...). Possibly the best would be to use
> Jaime's trick, setting up a complete scene and then using it as a map with
> the "fake HDR" method(s) he describes.
>
> G.
>
> --
> **********************
> http://www.oyonale.com
> **********************
> - Graphic experiments
> - POV-Ray and Poser computer images
> - Posters
>
>
>
>

Post a reply to this message

Program ended abnormally on 1/3/03 8:02 PM, Due to a catastrophic Dennis
Miller error:
> Thank for your reply. Where is the message in which Jamie describes this
> technique> I must have missed it.

I think it was in povray.binaries.images.

> But to be clear, if I put a plane on the Y axis beyond my object, I should
> still be able to use the illumination from the map even if the map image is
> not showing in my scene?

The parts of the HDR map behind the camera, yes.
The parts hidden by the plane, no.


> thanks again,
> D.
> 

-- 
/*Francois Labreque*/#local a=x+y;#local b=x+a;#local c=a+b;#macro P(F//
/*    flabreque    */L)polygon{5,F,F+z,L+z,L,F pigment{rgb 9}}#end union
/*        @        */{P(0,a)P(a,b)P(b,c)P(2*a,2*b)P(2*b,b+c)P(b+c,<2,3>)
/*   videotron.ca  */}camera{orthographic location<6,1.25,-6>look_at a }

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On Fri, 3 Jan 2003 20:02:03 -0500
"Dennis Miller" <dhm### [at] attbicom> wrote:

> Thank for your reply. Where is the message in which Jamie describes
> this technique> I must have missed it.

 The basic trick consists on using a surrounding sphere with a
multilayer texture like this one (more or less, I'm still
experimenting with it):

--
// "back-lighting" layer
texture{
 pigment{
  image_map{
   jpeg "test.jpg" 
   map_type 1 
   interpolate 2
  }
 }
 finish{
  diffuse 0 
  ambient light_ambient
 }
}
// 254 layers to fake the HDR behavoir
texture{
 pigment{
  image_map{
   gif "test.gif"  // grayscale version of the original map 
   map_type 1 
   #while (il<254)
//    transmit 255-il max_intensity/(pow(il+1,2))
    filter 255-il max_intensity/(pow(il+1,2))
    #local il=il+1;
   #end
  }
 } 
 finish{
  diffuse 0 
  ambient 0
 }
}
// final layer to hide the grayscale maps 
texture{
 pigment{
  image_map{
   jpeg "test.jpg" 
   map_type 1 
   interpolate 2 
//   filter all .5
   filter all .9
  }
 } 
 finish{
  diffuse 1 
  ambient 1
 }
}
--

  The problem is that each map needs diferent settings that must be
found by trial and error. The advantage is that it can work with any 
image where the brightness levels are somewhat proportional to real
luminance. Aditionally, you need a program to convert the image to a
grayscale one with ordered palette (255=white, 0=black). I've done it
with The Gimp, simply saving the grayscale version as gif.

-- 
Jaime Vives Piqueres
		
La Persistencia de la Ignorancia
http://www.ignorancia.org

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