ambient light

Hi,
I am using Radiance to simulate objects with various glossy parameters.
But I found no matter how did I set up the material properties of the
objects, they all look the same under the light. I guess there must be
too much ambient light so the highlights on the objects are invisible. I
want to turn off the ambient light in the scene and only keep a few area
light sources. How shall I set up the parameters? Also, how do I include these parametesr in the .rad file?
thanks.

Bei

Hi,

do you have an example picture that you can publish on the net? AFAIK you can't switch off the ambient from a rad file, the ambient settings don't describe the scene. So they are passed as command line parameters to rpic or set in the rif-file (if you use rad or trad). You might try -ab 0... however, it sounds not clear why your surfaces are all looking the same, even with ambient light :wink: BTW, do you calculate the ambient (-ab ?) or pass values you got somewhere else?

CU Lars.

···

--
Lars O. Grobe
[email protected]

Hi Bei,

Did you set the -st paramater (specular treshhold) ?
If you have a specular value of, say, 0.01, your -st value should be also 0.01, otherwise you will not see any
specular reflections.

Succes,

Iebele

Bei Xiao wrote:

···

Hi,
I am using Radiance to simulate objects with various glossy parameters.
But I found no matter how did I set up the material properties of the
objects, they all look the same under the light. I guess there must be
too much ambient light so the highlights on the objects are invisible. I
want to turn off the ambient light in the scene and only keep a few area
light sources. How shall I set up the parameters? Also, how do I include these parametesr in the .rad file?
thanks.

Bei

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi,
   I passed the value "-ab 1" to the rad file because I want to use 1 indirect light source.
The problem is when I am using single light source, the scene looks okey( shinny objects are
shinny). But in order to create softer shadows, I am using area lights now. But It seems now
the shinny objects look the same as the matt ones. I also lost all the shading of the scene.

Thanks.

Bei

>

Hi, > > do you have an example picture that you can publish on the net? AFAIK > you can't

switch off the ambient from a rad file, the ambient settings > don't describe the scene. So
they are passed as command line parameters > to rpic or set in the rif-file (if you use rad or
trad). You might try > -ab 0... however, it sounds not clear why your surfaces are all looking

the same, even with ambient light :wink: BTW, do you calculate the ambient > (-ab ?) or pass

values you got somewhere else? > > CU Lars. > -- > Lars O. Grobe > [email protected] > > >
_______________________________________________ > Radiance-general mailing list >
[email protected] >
http://www.radiance-online.org/mailman/listinfo/radiance-general

···

Hi,
No, i didn't set it. HOw did you set it in .rif file? I am rendering hyperspectral images.
So i have to passing these values in .rif to use rad commend to render them. Thanks.

Bei

···

Hi Bei,

Did you set the -st paramater (specular treshhold) ?
If you have a specular value of, say, 0.01, your -st value should be also 0.01, otherwise you will not see any
specular reflections.

Succes,

Iebele

Bei Xiao wrote:

> Hi,
> I am using Radiance to simulate objects with various glossy parameters.
> But I found no matter how did I set up the material properties of the
> objects, they all look the same under the light. I guess there must be
> too much ambient light so the highlights on the objects are invisible. I
> want to turn off the ambient light in the scene and only keep a few area
> light sources. How shall I set up the parameters? Also, how do I include these parametesr in the .rad file?
> thanks.
>
> Bei
>
> _______________________________________________
> Radiance-general mailing list
> [email protected]
> http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hello,

I am trying to render an image using only ambient light. I noticed that the
reflected light appears to be non-uniform across the objects in the scene.
The scene is a open box with the open part facing the viewer and only
surfaces inside the box are lit (outside of the box is dark). It appears
that the light has some directionality to it. I'm guessing that there is a
setting value that I have not appropriately set or something. I wondered if
anyone had an idea what might be problem. The rpict parameters are listed as
the following:

rpict -t 12 -vf view_files/rightview.vf -x 1600 -y 1600 -ps 3 -pt .08 -dp
512 -ar 48 -ms 0.71 -ds .2 -dj .5 -dt .1 -dc .5 -dr 1 -sj .7 -st .1 -ab 1
-aa .15 -ad 800 -as 128 -av 0.5 0.5 0.5 -lr 8 -lw .002 -dj 0.6 -dt 0.01 -dr
3 -ds 0.1 -sj 0.7 -st 0.15 -dc 0.5 -lr 1 -aw 0 -av 0.02317 0.02317 0.02317

Any ideas would be appreciated.

Thank you,

Bei

···

--

Bei Xiao
Room 330 C
3401 Walnut Street C Wing
Department of Neuroscience
University of Pennsylvania
Philadelphia, PA 19104, USA
Web: www.psych.upenn.edu/~beixiao
flickr:www.flickr.com/photos/slowtempo

When you say that you are rendering using only ambient light, do you
mean that there are no sources in your scene (no sky definition, no
surfaces with materials such as light, glow, source) and only the
contribution due to -av 0.02317? If so, your directionality might be due
to the ambient bounce, which is not uniformly distributing light because
of the one open side of the box. Try again with -ab 0 instead of -ab 1
and see if that gives what you had wanted. It seems you are only trying
to render a purely theoretical scene?

...

I am trying to render an image using only ambient light. I noticed that
the reflected light appears to be non-uniform across the objects in the
scene. The scene is a open box with the open part facing the viewer and
only surfaces inside the box are lit (outside of the box is dark). It
appears that the light has some directionality to it. I'm guessing that
there is a setting value that I have not appropriately set or something.
I wondered if anyone had an idea what might be problem. The rpict
parameters are listed as the following:

rpict -t 12 -vf view_files/rightview.vf -x 1600 -y 1600 -ps 3 -pt .08
-dp 512 -ar 48 -ms 0.71 -ds .2 -dj .5 -dt .1 -dc .5 -dr 1 -sj .7 -st .1
-ab 1 -aa .15 -ad 800 -as 128 -av 0.5 0.5 0.5 -lr 8 -lw .002 -dj 0.6 -dt
0.01 -dr 3 -ds 0.1 -sj 0.7 -st 0.15 -dc 0.5 -lr 1 -aw 0 -av 0.02317
0.02317 0.02317

···

____________________________________________________________
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What is your light source? Even an ambient light has to begin somewhere. Maybe an overcast sky without a sun?
Are you using rad with a rif file? If so, increase the quality...
Your -ad and -as settings are pretty small
QUALITY=h
DETAIL= h
VARIABILITY= m

Rob

···

-----Original Message-----
From: [email protected] on behalf of [email protected]
Sent: Tue 11/25/2008 8:49 AM
To: [email protected]
Subject: [Radiance-general] ambient light

Hello,

I am trying to render an image using only ambient light. I noticed that the
reflected light appears to be non-uniform across the objects in the scene.
The scene is a open box with the open part facing the viewer and only
surfaces inside the box are lit (outside of the box is dark). It appears
that the light has some directionality to it. I'm guessing that there is a
setting value that I have not appropriately set or something. I wondered if
anyone had an idea what might be problem. The rpict parameters are listed as
the following:

rpict -t 12 -vf view_files/rightview.vf -x 1600 -y 1600 -ps 3 -pt .08 -dp
512 -ar 48 -ms 0.71 -ds .2 -dj .5 -dt .1 -dc .5 -dr 1 -sj .7 -st .1 -ab 1
-aa .15 -ad 800 -as 128 -av 0.5 0.5 0.5 -lr 8 -lw .002 -dj 0.6 -dt 0.01 -dr
3 -ds 0.1 -sj 0.7 -st 0.15 -dc 0.5 -lr 1 -aw 0 -av 0.02317 0.02317 0.02317

Any ideas would be appreciated.

Thank you,

Bei

--

Bei Xiao
Room 330 C
3401 Walnut Street C Wing
Department of Neuroscience
University of Pennsylvania
Philadelphia, PA 19104, USA
Web: www.psych.upenn.edu/~beixiao
flickr:www.flickr.com/photos/slowtempo

Hello Bei.

Hello,

I am trying to render an image using only ambient light. I noticed that the reflected light appears to be non-uniform across the objects in the scene. The scene is a open box with the open part facing the viewer and only surfaces inside the box are lit (outside of the box is dark). It appears that the light has some directionality to it.

The ambient light setting in Radiance is different to other renderers
- or maybe it's not if I think about it. Anyway, it's not supposed to replace
a proper light source in your scene (a 'light' or 'source' material for
example). It's just there to 'take over' when the proper ray tracing
does not produce a light source in an acceptable time. That means
it's only applied it the renderer has not found a light source after
tracing a ray for '-ab' bounces through the scene.

In your case with a box open to the dark void every ray that leaves
the box adds nothing to the illuminance level of a point. The closer
you are to the (front) edge the more rays escape the box and the
darker this point will be in the image.

The points at the back of the box are only 'bright' because the
renderer assigns an artificial brightness to the ray after the first
bounce (-ab 1). You can probably achieve a smoother gradient
in your image by increasing the -ab value.

If you enclose your open box and the camera with another
closed box you will probably see that there is no directionality
to the ambient light and everything will be uniformly grey (if
there is only one material). Every ray not hits a surface and
the brightness is only modified by the reflectance of the
material.

Regards,
Thomas

···

On 25 Nov 2008, at 16:49, [email protected] wrote:

Thank you very much! I will try this and get back to you about the result.

Bei

···

On Tue, Nov 25, 2008 at 12:55 PM, Thomas Bleicher <[email protected]>wrote:

Hello Bei.

On 25 Nov 2008, at 16:49, [email protected] wrote:

Hello,

I am trying to render an image using only ambient light. I noticed that
the reflected light appears to be non-uniform across the objects in the
scene. The scene is a open box with the open part facing the viewer and
only surfaces inside the box are lit (outside of the box is dark). It
appears that the light has some directionality to it.

The ambient light setting in Radiance is different to other renderers
- or maybe it's not if I think about it. Anyway, it's not supposed to
replace
a proper light source in your scene (a 'light' or 'source' material for
example). It's just there to 'take over' when the proper ray tracing
does not produce a light source in an acceptable time. That means
it's only applied it the renderer has not found a light source after
tracing a ray for '-ab' bounces through the scene.

In your case with a box open to the dark void every ray that leaves
the box adds nothing to the illuminance level of a point. The closer
you are to the (front) edge the more rays escape the box and the
darker this point will be in the image.

The points at the back of the box are only 'bright' because the
renderer assigns an artificial brightness to the ray after the first
bounce (-ab 1). You can probably achieve a smoother gradient
in your image by increasing the -ab value.

If you enclose your open box and the camera with another
closed box you will probably see that there is no directionality
to the ambient light and everything will be uniformly grey (if
there is only one material). Every ray not hits a surface and
the brightness is only modified by the reflectance of the
material.

Regards,
Thomas

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

--
Quote of the Day

Writing your PHD thesis is one chance that you can be bold at your arguments
because it will receive no reviews!

-David Brainard (my advisor)

Bei Xiao
Room 330 C
3401 Walnut Street C Wing
Department of Neuroscience
University of Pennsylvania
Philadelphia, PA 19104, USA
Web: www.psych.upenn.edu/~beixiao
flickr:www.flickr.com/photos/slowtempo

We tried placing the scene and camera within the context of a larger box and
this seemed to solve the problem that we were having. Thank you everyone
for all your help.
-Bei

···

On Tue, Nov 25, 2008 at 2:02 PM, <[email protected]> wrote:

Thank you very much! I will try this and get back to you about the result.

Bei

On Tue, Nov 25, 2008 at 12:55 PM, Thomas Bleicher <[email protected]>wrote:

Hello Bei.

On 25 Nov 2008, at 16:49, [email protected] wrote:

Hello,

I am trying to render an image using only ambient light. I noticed that
the reflected light appears to be non-uniform across the objects in the
scene. The scene is a open box with the open part facing the viewer and
only surfaces inside the box are lit (outside of the box is dark). It
appears that the light has some directionality to it.

The ambient light setting in Radiance is different to other renderers
- or maybe it's not if I think about it. Anyway, it's not supposed to
replace
a proper light source in your scene (a 'light' or 'source' material for
example). It's just there to 'take over' when the proper ray tracing
does not produce a light source in an acceptable time. That means
it's only applied it the renderer has not found a light source after
tracing a ray for '-ab' bounces through the scene.

In your case with a box open to the dark void every ray that leaves
the box adds nothing to the illuminance level of a point. The closer
you are to the (front) edge the more rays escape the box and the
darker this point will be in the image.

The points at the back of the box are only 'bright' because the
renderer assigns an artificial brightness to the ray after the first
bounce (-ab 1). You can probably achieve a smoother gradient
in your image by increasing the -ab value.

If you enclose your open box and the camera with another
closed box you will probably see that there is no directionality
to the ambient light and everything will be uniformly grey (if
there is only one material). Every ray not hits a surface and
the brightness is only modified by the reflectance of the
material.

Regards,
Thomas

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

--
Quote of the Day

Writing your PHD thesis is one chance that you can be bold at your
arguments because it will receive no reviews!

-David Brainard (my advisor)

Bei Xiao
Room 330 C
3401 Walnut Street C Wing
Department of Neuroscience
University of Pennsylvania
Philadelphia, PA 19104, USA
Web: www.psych.upenn.edu/~beixiao
flickr:www.flickr.com/photos/slowtempo

--
Quote of the Day

Writing your PHD thesis is one chance that you can be bold at your arguments
because it will receive no reviews!

-David Brainard (my advisor)

Bei Xiao
Room 330 C
3401 Walnut Street C Wing
Department of Neuroscience
University of Pennsylvania
Philadelphia, PA 19104, USA
Web: www.psych.upenn.edu/~beixiao
flickr:www.flickr.com/photos/slowtempo