Help, gurus!

I have several indoor scenes where the primary source of illumination is
sunlight coming through one (or several windows).  After playing with
gigantic white spheres outside my building, parallel lights coming through
the windows, and every radiosity setting combination I can think of, I
cannot get the room to look real.  Some typical results:

- If I crank my "sunlight" (a parallel light) up to rgb<100,100,100> I get
very blotchy results, though the room is lit reasonably well
- If I crank my "ambient white sphere" (a gigantic sphere outside my
building) to have ambient 100, I get strange artifacts
- If I leave lighting values down where they are reasonable (2 being a
maximal value) my room is too dark, the light doesn't bounce in the room at
all
- If I turn recursion up to 20 and increase my count to 500, my results get
a bit better... but it is REALLY slow and still very dark
- Using a light INSIDE my room gives me great results!  It is just the
sunlight that I am having trouble with.

Some notes:

- My materials all have a diffuse value from 0.9 to 1.0 - so they should be
scattering the light around the room nicely
- I tried playing with "Brightness" above values of 1.0 which light up my
room, but make my contrast levels look strange

... my goal here is to have a generic "sunlight" method that I can use with
several indoor scenes, which does not require an hour for each frame.  Is
this a feasible task?  Please tell me that I don't need to add area lights
to each window.  :)

Any suggestions greatly appreciated, sample scenes, anything.

Cheers,
JP

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Hi John,

I haven't tried myself, but JRG seems to know the trick and he just
explained it in p.b.i. in the tread "ACE".. Here's a direct link:

http://news.povray.org/povray.binaries.images/25857/?mtop=183588&moff=10


Regards,
Hugo

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John Pallett wrote:
>
> my goal here is to have a generic "sunlight" method that I can use with
> several indoor scenes

Here is one which uses realistic energies for sun and sky.
The net diffuse value for concrete is realistic 0.4.
http://luxlab.com/tmp/balance.jpg

Same method applied to a model where the materials of the
outside structures were at some random default values resulting
from multiple conversions. The inside materials were ok (net diffuse
0.25 for sandstone) so it's mostly realistic.

http://luxlab.com/tmp/church2.jpg


> which does not require an hour for each frame

Very high quality radiosity was used in the first scene because
measurements from the color probes needed to be accurate. Lower
quality settings give faster but less accurate results. It's still
going to be slow and difficult to use. If interested mail me.


_____________
Kari Kivisalo

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It's no doubt something that can't be described easily, it kind of sounds
like you expect radiosity to be a light source.

When you say "too dark" that means you aren't seeing a brightness you
expect, something which others might not expect to see in a sunlit room with
no other light sources except for the Sun through a window. If the room has
dark texturing it will of course still be darkened even though sunlight
shines in, and if it is a bright white interior it could almost glow in
places where the sunlight shines. However, it's a visual thing. The eyes
adjust to it in various ways. Try the following scene and see what you
think; you'll probably need to show a rendering of what you don't want and
describe how it should be altered, or make changes to it to show how it
ought to look.
You mentioned diffuse values up to 1 but not over one. Perfectly legal to
use diffuse 1.1 and beyond. I'm thinking that the problem there is how the
radiosity is going to blend everything together. It usually shows most at
very short distances and tapers off abruptly. I'm not sure of how to go
about counteracting that effect and instead get a uniform, farther reaching
effect.

#version 3.5;

global_settings {
        radiosity {
                brightness 0.9
                recursion_limit 3
                gray_threshold 0.3
                media on
        }
}

// ----------------------------------------

camera {
  location  <-1, 2, -6>
  right     x*image_width/image_height
  look_at   <0,0,0>
}

// sky
sphere {
        0,1
  pigment {
    gradient y
    color_map {
      [0 rgb <0.8,0.9,1.0>]
      [0.7 rgb <0.3,0.5,0.9>]
      [1 rgb <0.2,0.4,0.7>]
    }
  }
  finish {ambient 0.9 diffuse 0.1}
  scale 9999
 hollow
}

// sunlight
light_source {
        0,<1.5,1.3,1.1>
        looks_like {
                sphere {0,99 pigment {rgb 1} finish {ambient 1 diffuse 1}}
                }
        parallel
        point_at z
 translate -999*z rotate <30,45,0>
}

// ground
plane {
  y, -0.01
  pigment { color rgb <0.3,0.7,0.4> }
}

// ----------------------------------------

// visibility test objects
#local W=5;
#while (W>-5)
sphere {
  0,0.5
  translate W*z
        pigment {checker color rgb 0 color rgb 1 scale 0.25}
        finish {ambient 0.1 diffuse 0.6} // defaults
}
#local W=W-1;
#end

// room with 4 windows
difference {
box {
        <-3,0,-9>,<3,3,3>
}
box {
        <-3,0.1,-9>/1.1,<3,3,3>/1.1
}
box {
        <-3.1,1,-2>,<3.1,2,-1>
}
box {
        <-3.1,1,1>,<3.1,2,2>
}

        pigment {rgb 0.9}
        finish {ambient 0.25 diffuse 0.75 specular 0.1 roughness 0.1}
 hollow
}

// air in room
box {
        <-3,0,-9>,<3,3,3>
        pigment {rgbf 1}
        interior {
                media {
                        emission 0.6
                        absorption 0.9
                        scattering {
                                5,3
                                eccentricity 0.3 // use with type 5
                                extinction 0
                        }
                        density {
                                rgb 0.1
                        }
                        samples 30,60
                }
        }
 hollow
}

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John Pallett <joh### [at] chiefarchitectcom> wrote:
> - If I crank my "sunlight" (a parallel light)

  Btw, sunlight is not parallel.

-- 
#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 -

Post a reply to this message

In article <3d417105@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

> John Pallett <joh### [at] chiefarchitectcom> wrote:
> > - If I crank my "sunlight" (a parallel light)
> 
>   Btw, sunlight is not parallel.

It's close enough for most purposes...

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

Post a reply to this message

Try setting assumed_gamma to somthing very low, like 1 or 0.5. This will 
brighten everything up, hopfully simulating the natural adjustment our 
eyes make in low-light situations.

John Pallett wrote:

> Help, gurus!
> 
> I have several indoor scenes where the primary source of illumination is
> sunlight coming through one (or several windows).  After playing with
> gigantic white spheres outside my building, parallel lights coming through
> the windows, and every radiosity setting combination I can think of, I
> cannot get the room to look real.  Some typical results:
> 
> - If I crank my "sunlight" (a parallel light) up to rgb<100,100,100> I get
> very blotchy results, though the room is lit reasonably well
> - If I crank my "ambient white sphere" (a gigantic sphere outside my
> building) to have ambient 100, I get strange artifacts
> - If I leave lighting values down where they are reasonable (2 being a
> maximal value) my room is too dark, the light doesn't bounce in the room at
> all
> - If I turn recursion up to 20 and increase my count to 500, my results get
> a bit better... but it is REALLY slow and still very dark
> - Using a light INSIDE my room gives me great results!  It is just the
> sunlight that I am having trouble with.
> 
> Some notes:
> 
> - My materials all have a diffuse value from 0.9 to 1.0 - so they should be
> scattering the light around the room nicely
> - I tried playing with "Brightness" above values of 1.0 which light up my
> room, but make my contrast levels look strange
> 
> ... my goal here is to have a generic "sunlight" method that I can use with
> several indoor scenes, which does not require an hour for each frame.  Is
> this a feasible task?  Please tell me that I don't need to add area lights
> to each window.  :)
> 
> Any suggestions greatly appreciated, sample scenes, anything.
> 
> Cheers,
> JP
> 
> 
> 


-- 
Samuel Benge

sbe### [at] caltelcom

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In article <3D4### [at] caltelcom>,
 Samuel Benge <sbe### [at] caltelcom> wrote:

> Try setting assumed_gamma to somthing very low, like 1 or 0.5. This will 
> brighten everything up, hopfully simulating the natural adjustment our 
> eyes make in low-light situations.

Very low? 1 is the recommended value..."For new scenes, you should use 
an assumed gamma value of 1.0 as this models how light appears in the 
real world more realistically."

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

Post a reply to this message

> Any suggestions greatly appreciated, sample scenes, anything.

Just an idea: You ought to need a realistic sky for a realistic scene. At
least, the sun shouldn't be a white sphere (or spherical pattern) in a black
sky, but in a blue-to-white sky. This will lighten up your room a bit...

cukk

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Hi guys -

Some more notes -

I was surrounding my entire scene with a gigantic white sphere, not creating
a 'spherical sun'.  The problem, as it turns out, was that the light wasn't
getting scattered around the room enough for it to properly simulate
sunlight coming in a window (which scatters all over the room).  So the
scene consisted of:

- A huge white sphere, ambient 0.5
- A parallel white light (sunlight) (parallel lighting for the sun is good
enough for our purposes)
- A room with a window, all materials set to (ambient 0, diffuse 0.9) so
that they aren't emitting light into the scene
- My camera inside the room

Thanks to everyone for suggestions thus far.  The missing ingredient seems
to have been media, which can be used to scatter light.  What I am doing now
is using media inside my rooms to scatter the sunlight as it comes in the
window and as it bounces around the room.  Very subtle scattering gives me
great results.

I'll post images to PBI once I get something put together that demonstrates
the problem clearly.

Can anyone suggest another way to solve the problem of having the light
coming in the window scatter around the room appropriately?  Note that my
camera points TOWARDS the window, so making the window's wall invisible is
not an option.

JP

Post a reply to this message

"John Pallett" wrote:
> Hi guys -
>
> Some more notes -
>
> I was surrounding my entire scene with a gigantic white sphere, not creating
> a 'spherical sun'.  The problem, as it turns out, was that the light wasn't
> getting scattered around the room enough for it to properly simulate
> sunlight coming in a window (which scatters all over the room).  So the
> scene consisted of:
>
> - A huge white sphere, ambient 0.5
> - A parallel white light (sunlight) (parallel lighting for the sun is good
> enough for our purposes)
> - A room with a window, all materials set to (ambient 0, diffuse 0.9) so
> that they aren't emitting light into the scene
> - My camera inside the room
>
> Thanks to everyone for suggestions thus far.  The missing ingredient seems
> to have been media, which can be used to scatter light.  What I am doing now
> is using media inside my rooms to scatter the sunlight as it comes in the
> window and as it bounces around the room.  Very subtle scattering gives me
> great results.
>
> I'll post images to PBI once I get something put together that demonstrates
> the problem clearly.
>
> Can anyone suggest another way to solve the problem of having the light
> coming in the window scatter around the room appropriately?  Note that my
> camera points TOWARDS the window, so making the window's wall invisible is
> not an option.

Ah. Too bad. Then you have to:
1) Raise the count to appropriate value.
2) Raise the recursion limit to appropriate value (3).
3) Raise the brightness to appropriate value (2.5, 3 or even more)
4) Be very patient.

Otherwise you could put a huge area_light right where the window is. This, with just
a bit of tweaking, should give you very soft shadows which, together with just a bit
of radiosity, might look nice nonetheless. This can be very slow too.

Anyway ambient 0.5 is pretty low for a skysphere. Use a real sky_sphere with a
gradient from white (bright white: rgb 1.25) to sky blue.

--
Jonathan.

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So no value in using scattering media to help "scatter" the sunlight around
the room...?

JP

"JRG" <jrg### [at] hotmailcom> wrote in message
news:3d41b4f1@news.povray.org...
> "John Pallett" wrote:
> > Hi guys -
> >
> > Some more notes -
> >
> > I was surrounding my entire scene with a gigantic white sphere, not
creating
> > a 'spherical sun'.  The problem, as it turns out, was that the light
wasn't
> > getting scattered around the room enough for it to properly simulate
> > sunlight coming in a window (which scatters all over the room).  So the
> > scene consisted of:
> >
> > - A huge white sphere, ambient 0.5
> > - A parallel white light (sunlight) (parallel lighting for the sun is
good
> > enough for our purposes)
> > - A room with a window, all materials set to (ambient 0, diffuse 0.9) so
> > that they aren't emitting light into the scene
> > - My camera inside the room
> >
> > Thanks to everyone for suggestions thus far.  The missing ingredient
seems
> > to have been media, which can be used to scatter light.  What I am doing
now
> > is using media inside my rooms to scatter the sunlight as it comes in
the
> > window and as it bounces around the room.  Very subtle scattering gives
me
> > great results.
> >
> > I'll post images to PBI once I get something put together that
demonstrates
> > the problem clearly.
> >
> > Can anyone suggest another way to solve the problem of having the light
> > coming in the window scatter around the room appropriately?  Note that
my
> > camera points TOWARDS the window, so making the window's wall invisible
is
> > not an option.
>
> Ah. Too bad. Then you have to:
> 1) Raise the count to appropriate value.
> 2) Raise the recursion limit to appropriate value (3).
> 3) Raise the brightness to appropriate value (2.5, 3 or even more)
> 4) Be very patient.
>
> Otherwise you could put a huge area_light right where the window is. This,
with just
> a bit of tweaking, should give you very soft shadows which, together with
just a bit
> of radiosity, might look nice nonetheless. This can be very slow too.
>
> Anyway ambient 0.5 is pretty low for a skysphere. Use a real sky_sphere
with a
> gradient from white (bright white: rgb 1.25) to sky blue.
>
> --
> Jonathan.
>
>
>
>

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I have (had?) a complete animation with this church scene. My bro almost
couldn't believe it was done using computer(s). Absolutely stunning.

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"John Pallett" wrote:
> So no value in using scattering media to help "scatter" the sunlight around
> the room...?

Although "media on" in the radiosity block makes media affect radiosity, I doubt it
would be of any help here.


--
Jonathan.

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Not sure about that, remember the "god's fingers" situation when light
crawls through small openings in dusty/smoky areas?

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Some good news actually regarding scattering media - I'm getting some good
results from this.

I tried adding a very simple scattering media to my room and it made a huge
difference - even without any emissive characteristics, the scattering
effect caused rays to bounce more or less as I'd expect sunlight to interact
with my room.  It's almost as if the 'scattering' of a single radiosity ray
simulates the effect of the sunlight bouncing around the room several times.

Unfortunately it's very tweaky - small changes in radiosity settings mean
you have to modify the media - but I'm still working on it.  The good news
is that using media, I can get good results in much less time than by
cranking up my radiosity settings.  I may not be able to get a reliable
framework out of it - but I will let you know if I do.

JP

"JRG" <jrg### [at] hotmailcom> wrote in message
news:3d41d1cb$1@news.povray.org...
> "John Pallett" wrote:
> > So no value in using scattering media to help "scatter" the sunlight
around
> > the room...?
>
> Although "media on" in the radiosity block makes media affect radiosity, I
doubt it
> would be of any help here.
>
>
> --
> Jonathan.
>
>
>
>

Post a reply to this message

In article <3d41d1fb$1@news.povray.org>,
 "Apache" <apa### [at] yahoocom> wrote:

> Not sure about that, remember the "god's fingers" situation when light
> crawls through small openings in dusty/smoky areas?

That is not due to beam divergence, it would happen with truely parallel 
light. It is caused by perspective: the rays come through the clouds at 
a distance and pass to each side. If the sun was close enough for 
divergence to be visible, there probably wouldn't be clouds and you 
wouldn't be there to see it.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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What else can be used to simulate the adaption the eye makes in 
low-light situations?

Christopher James Huff wrote:

> In article <3D4### [at] caltelcom>,
>  Samuel Benge <sbe### [at] caltelcom> wrote:
> 
> 
>>Try setting assumed_gamma to somthing very low, like 1 or 0.5. This will 
>>brighten everything up, hopfully simulating the natural adjustment our 
>>eyes make in low-light situations.
>>
> 
> Very low? 1 is the recommended value..."For new scenes, you should use 
> an assumed gamma value of 1.0 as this models how light appears in the 
> real world more realistically."
> 
> 


-- 
Samuel Benge

sbe### [at] caltelcom

Post a reply to this message

In article <3D4### [at] caltelcom>,
 Samuel Benge <sbe### [at] caltelcom> wrote:

> What else can be used to simulate the adaption the eye makes in 
> low-light situations?

You could use an external program to process the contrast of the image 
(or do it in POV using functions, see the recent find_edges images for 
an example), or you could use a patch that allows you to adjust the 
dynamic range of the image. The raw_image and curves patches of MegaPOV 
could be used for this.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

Post a reply to this message

On Fri, 26 Jul 2002 18:47:15 -0500, Christopher James Huff wrote:
> In article <3d41d1fb$1@news.povray.org>,
>  "Apache" <apa### [at] yahoocom> wrote:
> 
>> Not sure about that, remember the "god's fingers" situation when light
>> crawls through small openings in dusty/smoky areas?
> 
> That is not due to beam divergence, it would happen with truely parallel 
> light. It is caused by perspective: the rays come through the clouds at 
> a distance and pass to each side. If the sun was close enough for 

And in fact, on particularly good days you can see convergence on the 
other side of the sky as well; APOD has had a few examples of this 
phenomenon. 

-- 
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbf 1}hollow interior{media{emission 3-T}}}#end 
Z(-x-x.2x)camera{location z*-10rotate x*90normal{bumps.02scale.05}}

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