Nicolas George nous apporta ses lumieres en ce 2007/10/22 07:34:
> "Bill Pragnell"  wrote in message
> <web.471c85bad8eb8586731f01d10@news.povray.org>:
>> However, you can adjust gray_threshold in the radiosity settings. This
>> specifies how much colour to include in the radiosity calculations (1 = no
>> colours, 0 = full colour radiosity).
> 
> Thanks, that does exactly what I was hoping.
> 
>> 					Obviously, if you get rid of the sky
>> colour you will also lose colours emitted from nearby objects, so you can't
>> have it both ways I'm afraid!
> 
> That is ok for me in that particular scene.
> 
> As a more theoretical question, would it be possible, with the radiosity
> algorithm, to have different gray_threshold for each object?
> 
>> One more point - it's best to set all objects' ambient to 0, otherwise they
>> actively emit light in radiosity calculations.
> 
> Is it enough to set the global_settings ambient_light to 0, or is it
> necessary to add a finish { ambient 0 } to each object in the scene.
> 
>> 
Beter to use:
#default{finish{ambient 0}} and to override the provided ambient of ready-made 
finishes to ambient 0.

Seting ambient_lights 0 will also turn off any lighting by high ambient object 
you may have.

-- 
Alain
-------------------------------------------------
  "Having a smoking area in a restaurant is like having a peeing area in a pool."
   --Thomas Pfeffer, American Heart Association

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scott wrote:
>> I wrote a minimal example to show the amount of difference I get. It 
>> is at
>> the end.
> 
> How are you choosing the RGB values to use for the sky, sunlight and 
> sand? Those are probably not physically accurate...  Unless you have 
> some sophisticated optical measurement equipment, I suggest you just 
> tweak with these values until your scene looks the way you want it.  
> Also check your gamma settings...
> 

Maybe increasing the brightness of the "sun" could also help. Or 
diminishing that of the sky_sphere. I would have thought that on a sunny 
day you get a lot more light from the Sun than from the rest of the 
sky... Not a mere 3 times more.

-- 
Vincent

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Vincent Le Chevalier  wrote in message <471d1c2f$1@news.povray.org>:
>								Or 
> diminishing that of the sky_sphere.

I do not know how to do that. Is it possible?

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Bill Pragnell wrote:
> 
> From the documentation:
> 
> "The actual ambient used is: Ambient = Finish_Ambient * Global_Ambient."
> 
> So if you set global ambient = 0 then it will work fine. If you want nonzero
> ambient light then it's better to use the #default finish { } and only
> specify the ambient values you want to override.
> 

Something that's sometimes useful is to give each object's finish some 
ambient value that will look OK for test renders (ambient 0.3 works 
pretty well).  If you then set the global ambient value to 0 for a 
radiosity render, the ambient value for the objects' textures will 
revert to 0.  If you need something in the final scene to have a 
non-zero ambient (for example, a glowing LED), set its ambient really 
high and then set the global ambient to something like 0.001, which will 
effectively kill the ambient in the other textures.

Hope that's slightly useful...

--Sherry Shaw


-- 
#macro T(E,N)sphere{x,.4rotate z*E*60translate y*N pigment{wrinkles scale
.3}finish{ambient 1}}#end#local I=0;#while(I<5)T(I,1)T(1-I,-1)#local I=I+
1;#end camera{location-5*z}plane{z,37 pigment{granite color_map{[.7rgb 0]
[1rgb 1]}}finish{ambient 2}}//                                   TenMoons

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Nicolas George nous apporta ses lumieres en ce 2007/10/22 18:14:
> Vincent Le Chevalier  wrote in message <471d1c2f$1@news.povray.org>:
>> 								Or 
>> diminishing that of the sky_sphere.
> 
> I do not know how to do that. Is it possible?
Just reduce the rgb values that you use for the sky_shere.
You can also reduce the brightness in the radiosity block, it default to 1 if 
you don't set it yourself.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you've convinced your boss that 
raytracing is really an integral part of your job title (and you really don't 
work in a position that requires it).
Quietly Watching

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Sherry Shaw nous apporta ses lumieres en ce 2007/10/22 19:16:
> Bill Pragnell wrote:
>>
>> From the documentation:
>>
>> "The actual ambient used is: Ambient = Finish_Ambient * Global_Ambient."
>>
>> So if you set global ambient = 0 then it will work fine. If you want 
>> nonzero
>> ambient light then it's better to use the #default finish { } and only
>> specify the ambient values you want to override.
>>
> 
> Something that's sometimes useful is to give each object's finish some 
> ambient value that will look OK for test renders (ambient 0.3 works 
> pretty well).  If you then set the global ambient value to 0 for a 
> radiosity render, the ambient value for the objects' textures will 
> revert to 0.  If you need something in the final scene to have a 
> non-zero ambient (for example, a glowing LED), set its ambient really 
> high and then set the global ambient to something like 0.001, which will 
> effectively kill the ambient in the other textures.
> 
> Hope that's slightly useful...
> 
> --Sherry Shaw
> 
> 
Even beter: use this "trick"
#declare Rad = 1;

have:
#if(Rad)radiosity{ your_radiosity_settings }#end

and add this to your finishes:
... #if(Rad)ambient 0 #else ambient 0.3 #end

Now, set Rad to 0 for the test renders and to 1 for the radiosity renders.
No ugly trick, only 1 variable to set.

-- 
Alain
-------------------------------------------------
Stay out of my head, its a bad neighborhood.

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> Vincent Le Chevalier  wrote in message <471d1c2f$1@news.povray.org>:
>> 								Or 
>> diminishing that of the sky_sphere.
> 
> I do not know how to do that. Is it possible?

It is not possible with a sky_sphere because you cannot specify a 
finish. However, you can do that with a really big hollow sphere 
centered on the origin.

With this method, you can specify an ambient value, but you must set 
diffuse to 0, otherwise the sky sphere will be illuminated by the sun, 
and it becomes impossible to adjust their brightness separately.

And then you can play with the diffuse component of the objects (that 
can be done in the #default block).

The next problem is that POV-Ray has no exposure control, so in fact it 
will not necessarily look right when you diminish the ambient value of 
the sky sphere. It will get you a very dark sky...

In my experience it is better to first adjust the ambient of the 
sky_sphere to obtain the right color in the places where you see the 
sky. Then, set the sunlight and the diffuse component to get the 
lighting you like. Playing with these three things it's possible to 
obtain many results...

I'm not quite sure it's the right way to do it though ;-)

Here is an example:

#if(1)
global_settings {
     radiosity {}
}
#default {finish{ambient 0}}
#end
// Use this to control the brightness of the shadows
#default {finish{diffuse 0.35}}

plane {
   y, 0
   pigment { rgb <0.804, 0.569, 0.494> }
   normal { bumps 0.5 }
}

union{
     sphere{y,1}

     cylinder {
         0,3*y,0.5
         translate <2,0,-2>
     }
     pigment{rgb 1}
     scale 30
}

camera {
   location <220, 50, 0> look_at <0, 0, 0>
}

sphere {
     0,1
     texture {
         pigment {
             gradient y
             color_map {
             [ 0.0 rgb <0.9, 0.9, 1> ]
             [ 0.5 rgb <0.3, 0.3, 1> ]
             }
         }
         finish {
             // Use this to adjust the brightness of the sky
             ambient 1
             diffuse 0 }
     }

   scale 200000
   hollow
}

light_source {
     <100000, 100000, -100000>
     rgb <1,1,0.9>*6 // And this to adjust the sunlight
}


-- 
Vincent

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"Vincent Le Chevalier" <gal### [at] libertyALLsurfSPAMfr> wrote in 
message news:471e1c7b$1@news.povray.org...

>> Vincent Le Chevalier  wrote in message <471d1c2f$1@news.povray.org>:
>>> Or diminishing that of the sky_sphere.
>>
>> I do not know how to do that. Is it possible?
>
> It is not possible with a sky_sphere because you cannot specify a finish. 
> However, you can do that with a really big hollow sphere centered on the 
> origin.

or you could of course just multiply the color-values of your sky_sphere...

cu!
-- 
#macro G(b,e)b+(e-b)*C/50#end#macro _(b,e,k,l)#local C=0;#while(C<50)
sphere{G(b,e)+3*z.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1;
#end#end _(y-x,y,x,x+y)_(y,-x-y,x+y,y)_(-x-y,-y,y,y+z)_(-y,y,y+z,x+y)
_(0x+y.5+y/2x)_(0x-y.5+y/2x)            // ZK http://www.povplace.com

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Vincent Le Chevalier  wrote in message <471e1c7b$1@news.povray.org>:
> It is not possible with a sky_sphere because you cannot specify a 
> finish. However, you can do that with a really big hollow sphere 
> centered on the origin.
<snip details>

Thanks, I will try to look into it when I have time.

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Alain wrote:
> Even beter: use this "trick"
> #declare Rad = 1;
> 
> have:
> #if(Rad)radiosity{ your_radiosity_settings }#end
> 
> and add this to your finishes:
> ... #if(Rad)ambient 0 #else ambient 0.3 #end
> 
> Now, set Rad to 0 for the test renders and to 1 for the radiosity renders.
> No ugly trick, only 1 variable to set.
> 


If you check the flag *inside* the global_settings block--

global_settings{
   // assumed_gamma etc.
   #if (Rad)
     ambient_light 0.001
     radiosity {
       // Radiosity settings
     }
   #end
   }
}

--then you have only one variable to set and no changes to the finishes. 
  But it's all good.  ;)  The "best" approach depends on things like the 
length of your scene code, whether you're using textures from an 
#include file, whether or not you're already basing textures on the 
state of a flag (like "#if (test-mode) Little_Texture #else Big_Texture 
#end"), and the way you like to do things.

--Sherry Shaw


-- 
#macro T(E,N)sphere{x,.4rotate z*E*60translate y*N pigment{wrinkles scale
.3}finish{ambient 1}}#end#local I=0;#while(I<5)T(I,1)T(1-I,-1)#local I=I+
1;#end camera{location-5*z}plane{z,37 pigment{granite color_map{[.7rgb 0]
[1rgb 1]}}finish{ambient 2}}//                                   TenMoons

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