Radiance Digest Volume 3, Number 0

Dear Radiance Users,

It's been some time since I last put out a Radiance Digest -- almost a year!
It has been a very busy time for me (and probably for you as well), so let
me bring you up to date with a few changes.

First, I am leaving LBNL to work for Silicon Graphics, Inc. starting
May 5th.  I am taking this opportunity to normalize my name usage
everywhere to "Gregory Ward Larson," which has been my legal name since
1985 when I was married, though I never bothered to change it at work.
(My wife and I picked this new, neutral last name to share with our two
daughters, now 4 and 6 years of age.  Larson is actually Cindy's maternal
grandmother's maiden name, so you can think of it as a kind of affirmative
action in a paternal society.)  My new e-mail address at SGI is
"gregl@sgi.com", but the old addresses should continue to work for some time.
I will send out my official mailing address as soon as I figure out what it is.

Second, "Rendering with Radiance: The Art and Science of Lighting
Visualization," is nearly completed.  We have a new publisher, which
makes us very happy -- Morgan Kaufmann.  The book, which will be accompanied
by a CD-ROM, shall be available for purchase sometime in early 1998.  We
expect the list between $80 and $90, which is a lot for a book, but not
much for software.  We don't expect to sell a whole lot of them, or to get
rich from it.  Six authors have worked on the project.  Rob Shakespeare of
Indiana University and I wrote the bulk of it, with Charles Ehrlich, John
Mardaljevic, Peter Apian-Bennewitz and Erich Phillips lending their expertise
in the application chapters.

Third, Charles Ehrlich will be taking over most of my Radiance support
duties in my stead, though technically, we were never supposed to be doing
support, anyway.  His e-mail address is "CKEhrlich@lbl.gov", for those of
you who don't know.  He has been the ADELINE contact person for over a year
now, and knows quite a bit about Radiance as he has been using the software
intensively since 1988 or so.  I will still be working on Radiance as time
permits in my new job, and I hope that SGI will support it as part of their
optional software distribution with their machines.

And now, without further ado, the index for this digest:

       OPACITY MAPPING                - using mixfunc to make holey materials
       RPIECE                        - best use questions for parallel rendering
       3D STUDIO                - translating from 3D Studio to Radiance
       COMPUTING REFLECTANCES        - what is the total reflectance of a material?
       RTRACE QUESTIONS        - using the -I option and computing radiosities
       PROCEDURAL TEXTURES        - displacement mapping and efficiency issues
       MIST                        - questions about the new mist type
       MKILLUM QUESTIONS        - how best to apply mkillum to daylighting
       COLORED LIGHT SOURCES        - accounting for colored light sources

All the best,

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To: greg@hobbes.lbl.gov
Date: Thu, 27 Jun 1996 19:29:02 EDT
From: Takehiko Nagakura <takehiko@MIT.EDU>


How are you? 

I am the MIT professor using radiance for architecture space rendering,
if you remember me.  I have a quick question. I would be glad if you could
give me a tip.  Is there any way to do opacity map in radiance?  All I would 
like to do is to make a greyscale image and use the greyness to be translated
into degree of transparency.  I know how to do a color map, but cannot figure 
out how to do opacity map.  Hope I am not bothering you.  Thanks very much.

Takehiko Nagakura (Assist. Prof. of architecture, MIT)

Date: Sat, 29 Jun 96 17:45:10 PDT
From: greg (Gregory J. Ward)
To: takehiko@MIT.EDU
Subject: opacity maps in Radiance

Yes, I remember you, and yes, there is a way.  In 3.0 (available at our
ftp site, hobbes.lbl.gov), use the "mixdata" primitive with a converted
image file, using "void" as one of your two modifiers.  In version 2.5,
you could do the same thing, but you would have to use a trans primitive
with 100% transmittance instead of "void".

To convert the image, I suggest you use pvalue, and edit the output.
Something like this:

% pvalue -d -b Radiance_picture > data_file
% vi data_file

The top of the file will look something like this:

ra_tiff -r
pfilt -x /3 -y /3 -1 -r .6 
pvalue -d -b 

-Y 133 +X 270
... and so on

Edit it so that you have a valid data file, i.e.:

# Data file produced from a picture:
#ra_tiff -r
#pfilt -x /3 -y /3 -1 -r .6 
#pvalue -d -b 

2		# Number of dimensions
1 0 133		# U image coordinate, decreasing
0 2.03 270	# V image coordinate, increasing

... and so on

Then, apply this in a opacity map as follows:

void plastic my_material
5 .5 .3 .7 .05 .02

void mixdata my_mixture
7 my_material void mymapping data_file mymapping.cal my_v my_u

The file "mymapping.cal" then contains definitions of the function mymapping(b),
my_u and my_v, which indicate the mapping from grey pixel value to opacity,
and the U and V picture coordinates, respectively.  A really simple example
is as follows:

       mymapping(b) = min(b,1);
       my_u = Px;
       my_v = Py;

This assumes the object in question is located in the positive quadrant of
the XY plane in world coordinates, and its size corresponds to the dimensions
we entered for the image, namely 2.03 units in X and 1 unit in Y.  The image
pixel brightness values also equal the opacity we desire.  (The min function
is just to limit the range from 0 to 1, to avoid any confusion even though
the routines don't break if we go over 1.)  You could then add a transformation
to the end of the mixdata primitive's string arguments to move it to a
different location and size.

I hope this gives you the idea.  If you do this in 2.5, you should leave off
the #-delimited comments in the data file, and use a transparent primitive
rather than "void", i.e.:

void trans invisible
7 0 0 0 0 0 1 1



From: "Alois Goller" <goller@icg.tu-graz.ac.at>
Date: Mon, 2 Sep 1996 14:39:05 -0600
To: "Gregory J. Ward" <greg@hobbes.lbl.gov>
Subject: Parallel Radiance

Hi Greg,

back from holidays, I did some timing measurements. I got similar figures in
the range you report in "Parallel Rendering on the ICSD SPARC-10's"
(radiance/doku/Notes/parallel.html): Dividing the image in rather large
patches, (about 5 to 10 per processor) and having each processor to render more
than 20 minutes per patch, it results in a good CPU utilization (more than 98%
continuously). As you already mentioned, some of the processors are idle at the
very end. This causes the efficiency to be at about 85% in my cases.

However, rendering smaller files, and using many pieces, there was a surprise:
       | rpict (1)     | rpiece (1)    | rpiece (3)    | rpiece (10)
A      | 1:49.66       | 19:02.09      | 14:22.93      | 14:48.25
B      | 5:26.79       | 17:38.85      | 12:49.82      | 14:23.04
C      |17:03.23       | 29:11.56      | 14:15.85      | 15:12.59

C is 2 times larger than B (x and y, resulting in the fourfold number of
pixels), B is 2 times larger than A. This fact can be also obtained by looking
at the second column (rpict(1)) denoting rpict running on a single processor.
Involving rpiece with 1, 3, and 10 processors needs constantly about 15
minutes, at different CPU utilization levels ranging from 1% to 60%.

Have you experienced similar results?
Is there something wrong with our NFS, rpiece, etc.?

| Alois GOLLER                                                         |
| Parallel and Distributed Computing (for Remote Sensing Applications) |
| Institute f. Computer Graphics and Vision, Technical University Graz | 
| Muenzgrabenstrasse 11, A-8010 Graz, Austria                          |
| Tel. +43 (316) 873-50 25                 \  FAX  +43 (316) 873-50 50 |    
| E-mail goller@icg.tu-graz.ac.at           \  Home +43 (316) 80 46-67 |
| WWW http://www.icg.tu-graz.ac.at/alGo.html \  or   +43 (4842) 67 51  |

Date: Tue, 3 Sep 96 09:50:09 PDT
From: greg (Gregory J. Ward)
To: goller@icg.tu-graz.ac.at
Subject: Re:  Parallel Radiance

Hi Alois,

I would never attempt to render with rpiece any job that used less than an
hour of CPU time on a single processor -- I don't think it's worth
distributing such a small job.

In particular, you should not break a short job into too many small pieces,
as each piece will complete too quickly and you'll end up with NFS lock
manager bottlenecks, which is what I assume you are seeing here.  Rpiece
is waiting around for I/O completion most of the time.  Either use larger
pieces on a shorter job, or else don't use rpiece at all if it's too short.

I haven't done exetensive enough testing to give you more accurate information
than this, but I expect if you did some parametric runs that you would find
an optimum somewhere around a 5-10 minutes per piece in rpiece -- longer if
you have more rpiece jobs running.  The NFS lock manager can be VERY slow
on some systems.


P.S.  Thanks for sharing your results with me!


Date: Mon, 16 Sep 1996 14:47:25 -0400
From: James_F_Todd@email.whirlpool.com (James F Todd)
Subject: Radiance File Translators
To: gjward@lbl.gov
 I have just begun looking at the Radiance Website, and I had a question:
 Does there exist a translator in existence that allows the import of POV, 
 DXF, or 3DS models into the Radiance renderer?
 This may be a very stupid question, but I'm more involved with the 
 creative side of things, not the technical.
 The reason I ask about those three is that I work with 3DStudio, and I 
 have utilities to convert between its native 3DS format and either DXF or 
 Thanks in advance for any information you can provide.

Date: Mon, 16 Sep 96 13:49:25 PDT
From: greg (Gregory J. Ward)
To: James_F_Todd@email.whirlpool.com
Subject: Re:  Radiance File Translators

Hi JT,

There are a couple of programs by which you can get from 3DS to Radiance.
The first converts 3DS into MGF -- a format I developed which is physically-
based and fairly compatible with Radiance.  From there, we have a translator
into Radiance.

I recommend this route rather than going from DXF, which loses most of
the pertinent material information needed for rendering.



Date: Fri, 20 Sep 1996 17:57:33 -0400 (EDT)
To: greg@hobbes.lbl.gov (Gregory J. Ward)
From: jedev@visarc.com (John E. de Valpine)
Subject: Material Reflectances


I'll give the parallel rendering a try soon. I'll probably try doing a
network rendering first before footing the bill for a new cpu.

On another note, I am trying to get a better understand of how reflectance
values relate to Radiance material definitions. I gleaned the following from
the digests:

        refl = (0.3)(r) + (0.59)(g) + (0.11)(b)

        refl = [(0.263)(r) + (0.655)(g) + (0.082)(b)](1 - spec) + spec

        refl = (0.263)(r) + (0.655)(g) + (0.082)(b)

How are these derived? How do these relate to ro_d ro_si ro_s ro_a in the
reflection model described in materials.1? How are the weights derived? 

If I understand correctly in the case of plastic the diffuse reflectance
would be:
        pC(1-r_subS) where
                p = <1,1,1>
                C = <r,g,b.
                r_subS = spec + (1 - spec)e^-6cos_sub1

As always if there is something that I should read first please point me in
the right direction?


Date: Fri, 20 Sep 96 15:35:05 PDT
From: greg (Gregory J. Ward)
To: jedev@visarc.com
Subject: Re:  Material Reflectances

Hi Jack,

Well, I'll admit that it's confusing -- especially when I keep changing the
conversion from RGB to luminance all the time.  The problem is that there's
no standard RGB color system, unless you count NTSC, which is not appropriate
for computer monitors due to the different phosphors employed in early

The correct, up-to-date conversion from RGB to luminance/efficacy is:

       lb = .265*r + .670*g + .065*b

This formula may be found (indirectly) in src/common/color.h, which is the
ultimate reference.  Small changes in RGB space should not create large
changes in the result.

The relationship between reflectance and Radiance material parameters is
more complicated than it probably should be, but it was done this way so
that the parameters had clear legal ranges (i.e., 0-1 usually).  A more
sensible specification would have required the user to figure out what
all the components added up to to insure that they were not specifying
a reflectance value greater than 1.  Even so, there are instances where
parameter values greater than 1 are the best approximation to a color that
is outside of the RGB gamut, for example.

Anyway, getting back to your formulas, most of what you have written here
is correct, except for the RGB coefficients, which should be as I have
given them here, and the final formula, which must have come from an
outdated version of material.1, back when I had a Fresnel approximation
in there.  Now, r_subS = spec, with no exponential factor in there.


Date: Fri, 15 Nov 1996 17:31:00 GMT
From: Rosinda Duarte <rduarte@lge3.dee.uc.pt>
To: greg@hobbes.lbl.gov
Subject: Reflectance factor

  Hi Greg!
  When I have a material type plastic, Could I say its reflectance is the
 three components RGB?  For example:

  void plastic material
 3 0.64 .064 0.63
 This material is not completely white, how can I define reflectance value?
Because if it was white I think I could say its reflectanve is equal the value
of three components RGB, couldn't I?



Date: Fri, 15 Nov 96 09:31:54 PST
From: greg (Gregory J. Ward)
To: rduarte@lge3.dee.uc.pt
Subject: Re:  Reflectance factor

Hi Rosinda,

It's nice to hear from you again.  I thought you had left the university,
because your e-mails have been bouncing from the Radiance discussion group,
and I had to remove you from the list.  If this gets through, I'll add
you back in again.  In the meantime, you can look at the /pub/discuss
directory on hobbes.lbl.gov to see what you've missed.

The reflectance of plastic can be computed from the RGB, specularity and
roughness as follows:

total_reflectance = arg4 + (1-arg4)*(.265*arg1+.67*arg2+.065*arg3)

where arg1-arg4 are the first four of five real arguments to the primitive.



Date: Wed, 25 Sep 96 19:14 MDT
From: dxs@november.diac.com
To: gjward@lbl.gov

i have a question about rtrace.  i ran the program with the following
input points and command options in a options file.  i noticed that the
input value for the x coodinate in  the output data was incorrect,
it was 8.5 instead of 7.5.  my question is:  is rtrace using my
input value of 7.5 and calculating with it and just not outputing it
correctly?  or am i using incorrect options?  i am running on linux,
using a pentium.  (this machine is new, so i am sure that it does
not have the divide error).
dan stanger
 7.5  7.5  2.6  1.0  0.0  0.0

oconv sc3.rad
rtrace -oodv -I -dp 128 -ar 52 -ds 0.25 -dt 0.1 -dc 1.0 -dr 1 -sj 0 -st 1 -aa
0 -ab 10 -as 0 -lw .02
SOFTWARE= RADIANCE 3.0 official release June 19, 1996

8.500000e+00    7.500000e+00    2.600000e+00    -1.000000e+00   -0.000000e+00
-0.000000e+00   2.995701e+00    2.995701e+00    2.995701e+00

Date: Thu, 26 Sep 96 09:11:40 PDT
From: greg (Gregory J. Ward)
To: dxs@november.diac.com
Subject: rtrace -I weirdness

Hi Dan,

You're not doing anything incorrectly, and there's nothing wrong with your
system.  In fact, the -I option of rtrace causes some of the output to
appear a bit strange because of the way it's computed.  Normally, ray
tracing starts from a point and heads in some direction.  With the -I
option to rtrace, we are asking it to start from an intersection at
a virtual surface and look at the hemisphere centered on some normal vector.

To trick the calculation into doing what we want, we create a virtual ray
intersection with this virtual surface by starting off a ray 1 unit above
the surface point and directing it towards are desired "origin."  In fact,
this means that the ray origin is 1 unit above our specified point, so
that is why the -oo output option gives you this difference.  I suggest
instead that you use -op to get the point echoed in the case of rtrace -I.


From: "Valois Jean-Sebastien" <valois@cim.mcgill.ca>
Date: Thu, 26 Sep 1996 08:56:47 -0400
To: GjWard@lbl.gov
Subject: Question.

Hi Mr Ward,
       How are you ?  I was wondering if it is possible to:

       1. "print" the values of the variables in a ".cal" file ? (debugger)
        2. simulate the noise (sampling) effect of a lens of a camera ?
       3. simulate the various behavior of a camera to different lighting
conditions ?

Thank you.

From greg Thu Sep 26 09:25:53 1996
Return-Path: <greg>
Date: Thu, 26 Sep 96 09:25:35 PDT
From: greg (Gregory J. Ward)
To: valois@cim.mcgill.ca
Subject: Re:  Question.
Status: R

Hi Jean-Sebastien,

In answer to your questions:

>        1. "print" the values of the variables in a ".cal" file ? (debugger)

There is a shell script called "debugcal.csh" that may be found in the
ray/src/util directory of the Radiance distribution.  Copy it from there
to your bin directory with the name "debugcal" then set the mode to
execute with "chmod 755 {bin_directory}/debugcal".  Run the "rehash"
command then in your scene directory call:

       % ximage {picture} | debugcal {octree} -f {calfile} -e '{rcalc_code}'

Where {picture} is a picture rendered with your problem {calfile}, and
{rcalc_code} is a set of assignments to output variables you want to look
at, e.g. '$1=wood_dx;$2=wood_dy;$3=wood_dz' -- that sort of thing.

Once your picture is displayed, hit the middle mouse button on points in
the image where you want to see the computed variables.

>        2. simulate the noise (sampling) effect of a lens of a camera ?

If you mean the depth of field, there is a script in the Radiance 3.0
distribution called "pdfblur" that may be used in conjunction with
pinterp to produce depth of field blurring.  Motion blur is possible
using a similar technique with the "pmblur" script, but this is usually
applied within the new animation control program, "ranimate."

>        3. simulate the various behavior of a camera to different lighting
>              conditions?

I'm not sure exactly which effects you mean.  Can you be more specific?  I
am working at this moment on some techniques and algorithms for adaptive
display based on the human visual system, so you can look for that in the
next release.


From: bits1@teil.soft.net (BITS TRAINEES grp-1)
Subject: rtrace and meshing
To: greg@hobbes.lbl.gov
Date: Thu, 17 Oct 1996 09:57:17 -0800 (PST)

Hello Greg,

I am doing a project in Visual simulation which involves adding diffuse
lighting values to the scene model before it can be used for visual
simulation purpose. I am using  RADIANCE for the above purpose. I
really find Radiance a very cool package for the purpose. I however
have some doubts in using it for my project.  They are :

     1)  I am computing the radiosity at each vertex in the scene.
In order to find the radiosity I use rtrace to find the Irradiance
at each vertex. I fire a ray from each vertex in the direction of
the normal. However I am a bit doubtful as to how I should find
the radiosity from the irradiance. I am having the only the color of
the face and no material properties. Since all the faces in my scene
are diffuse I assume the color to be the diffuse reflectance function.
I therefore multiply the irradiance with the reflectance function to
get the radiosity which I use for display. Is this method correct?  Can
you suggest as to how I can compute the radiosity from the irradiance
if I am having the material properties or the BRDF data?

     2)  My next doubt is does rtrace return the values in RGB space or
in HSV space because I am at present assuming that it returns the values
in RGB space.

     3)  Before my scene is taken up by the rtrace program I mesh the scene
suitably so that the lighting appears smooth. So I use some
triangulation such as Delaunay triangulation to mesh the scene. However
I knowe that Radiance also meshes the scene. Therefore can you please
tell me as to how I can control the meshing done by Radiance. In my
case I may want Radiance to override the meshing part because I am
already doing it.

     4)  Can you suugest as to what parameters I should use for rtrace so
that it yields the best results. At present I am using rtrace in the
following fashion :
     rtrace -av 0.1 0.1 0.1 -ab 5 -ad 5 -as 5 -lr 5 -aw 4 -st 0.1 -dv -I\
-h -w temp.oct < rayinput.dat > radiance.out
     Here rayinput.dat is the input file of ray org. & dir.
the output is kept in radiance.out

     5)  Finally Can you please send me an example file in which you apply
texture to one of the polygons in the scene. I want to know as to how
this is done. A simple example with one polygon and one RGB image as
texture would suffice.
     I know that I am asking a lot but please do find time to answer my doubts.
It would help me in my project greatly if you could reply  quickly.

     Thanking You.

- Mahaboob Ali
( bits1@teil.soft.net )

Date: Thu, 17 Oct 96 09:51:03 PDT
From: greg (Gregory J. Ward)
To: bits1@teil.soft.net
Subject: Re:  rtrace and meshing

Hello Mahaboob,

I will do my best to answer your queries....

>      1)  I am computing the radiosity at each vertex in the scene.
> ...

Your current method is sound.  The radiosity is in fact the diffuse irradiance
multiplied by the diffuse reflectance.  Radiosity for non-diffuse surfaces
is undefined, so I cannot recommend a method for computing vertex radiosities
considering specular reflection.  Your renderings wouldn't work anyway,
since you are relying on the radiosities being the same from all directions,
which cannot be the case with specular surfaces.

>      2)  My next doubt is does rtrace return the values in RGB space or
> in HSV space because I am at present assuming that it returns the values
> in RGB space.

All computations in Radiance are carried out and represented in RGB space.

>      3)  Before my scene is taken up by the rtrace program I mesh the scene
> ...

Radiance does not do any explicit meshing, and it is not possible to control
how Radiance samples the scene at this level.  All you can do is adjust
the rendering parameters to achieve denser (more accurate) sampling or
sparser (less accurate) sampling.  The placement of samples is dictated
by accuracy requirements rather than absolute spacing, which is one of
the main advantages of Radiance over traditional radiosity codes.

>      4)  Can you suugest as to what parameters I should use for rtrace so
> ...

These parameters will most certainly produce poor results.  In particular,
the value of -ad 5 is much too low to get an accurate sampling of indirect
diffuse radiation.  You really should use the "rad" program, with its more
intuitive control variables, to come up with options for rtrace.  To do
this, read the rad man page carefully, set up your rad input file, then
set an OPTFILE=render.opt line in it and run:

       rad -v 0 myscene.rif
       rtrace @render.opt -I temp.oct < rayinput.dat > irradiance.out

>      5)  Finally Can you please send me an example file in which you apply
> texture to one of the polygons in the scene. I want to know as to how
> this is done. A simple example with one polygon and one RGB image as
> texture would suffice.

This doesn't seem related to your project, since textures have no direct
effect on irradiance values.  Nevertheless, here is a simple example of
applying a "texture" (which we call a "pattern") in Radiance:

void colorpict oakfloor_pat
9  red green blue  oakfloor.pic  picture.cal  tile_u tile_v  -s 1.16670
1  .578313253

oakfloor_pat plastic wood_floor
5  .2  .2  .2  .02  .05

This was taken from the draft Radiance user's manual by Cindy Larson.  Wiley
is publishing a book on Radiance, which will hopefully be on the shelves by
next summer, and this will offer a much more extensive guide to the software.
In the meantime, please avail yourself of the materials that exist in the
ray/doc directory, which includes this manual (called "usman1.doc").

I hope this helps!


Date: Thu, 10 Oct 1996 13:25:28 -0400 (EDT)
To: greg@hobbes.lbl.gov (Gregory J. Ward)
From: jedev@visarc.com (John E. de Valpine)
Subject: Procedural Textures


As I understand it texfunc perturbs the surface normal for a material by
modifying the normal with the results of the xfunc yfunc zfunc in some
texture.cal file. This results in what I understand as 2-d bump mapping. Is
there any way to do displacement mapping where the normal at the rayhit may
or may not be displaced according to some set of parameters. I am trying to
simulate the effects of concrete formwork, ie a panels size and the holes
for form ties within a given panel. I made a procedural material that
accomplishes this as a colorfunc. But I would like to be able to achieve 3d
effects using displacement mapping.

On a similar note, in writing code for procedural materials, is there a
time/evaluation trade off between the two folowing:

Tx = arg(1);
Ty = arg(2);


T(xy) = select(xy,arg(1),arg(2));

How does the evaluation occur? Everytime Tx or Ty is evaluated is arg(n)
executed or are Tx and Ty instantiated on first evaluation?


Date: Thu, 10 Oct 96 10:53:59 PDT
From: greg (Gregory J. Ward)
To: jedev@visarc.com
Subject: Re:  Procedural Textures

Hi Jack,

There is no displacement mapping in the current release of Radiance, nor is
any expected in the forseeable future.  This is because doing displacement
mapping correctly is HARD!  My only suggestion is if you really want this
effect, that you generate the geometry for one panel and put it in an octree
to instantiate throughout your scene to keep the memory costs down.  The
additional time spent ray tracing should not be that great, especially if
you instantiate the little holes instead of the whole panel.  (You'll have
to cut holes in the panels of an appropriate size, but this won't add too
much time so long as they are rectangular.)

As for your procedural materials, the first method of assigning separate
variables is faster because variables are only evaluated once during each
ray execution cycle, whereas a function is reevaluated on each call.



Date: Wed, 8 Jan 1997 18:41:37 -0500 (EST)
From: Mark Stock <mstock@engin.umich.edu>
To: radiance-discuss@hobbes.lbl.gov
Subject: Mist Question


I have a simple question: Why can I not get a mist sphere to rpict 
properly with a user-defined albedo?

void mist cloudstuff
1 sky
6 0.005 0.005 0.005 0.8 0.8 0.8 

cloudstuff sphere cloud1
0 0 4  -100 -150 100 180

...plus other stuff in the scene

rpict -vp -700 -700 20 -vd 1 1 0.2 -ab 1 scene.oct > image1.pic
rpict: fatal - bad arguments for mist "cloudstuff"
rpict: 8904 rays, 22.85% after 0.001u 0.000s 0.001r hours on ......

The mist material works when only the extinction coefficients are used.

Any help will be appreciated!


Mark Stock

Date: Wed, 8 Jan 97 15:50:15 PST
From: greg (Gregory J. Ward)
To: mstock@engin.umich.edu
Subject: Re:  Mist Question

Hi Mark,

There was a bug in release 3.0 regarding mist arguments, that has been fixed
in a patch.  Be sure to install all the patches in the /pub/patch directory
on hobbes.lbl.gov.  The process has been automated to make it easier.

I'm not positive, but I'm pretty sure that putting "sky" as your scattering
source is not going to work.  This is only meant for normal, non-glow sources.
This should work anyway without it to give you a spherical cloud.

Do you still want me to post this to the rest of the group, or shall I just
stick it in the digest for the next distribution?


Date: Wed, 8 Jan 1997 18:55:01 -0500 (EST)
From: Mark Stock <mstock@engin.umich.edu>
To: greg@hobbes.lbl.gov
Subject: Re: Mist Question


Naw, I don't think there's a need to post it to the group, I just
hadn't realized that there were patches that weren't installed on our
system here. If you've recieved enough questions about it, though, you
may want to.

Thanks for the quick reply!

Mark Stock


Date: Tue, 7 Jan 97 10:10:58 GMT
From: milan@esru.strath.ac.uk (Milan Janak)
To: greg@hobbes.lbl.gov

Dear Greg,

First of all I would like to wish you a Happy New Year.

I am once again back here in ESRU Glasgow working on
couple European Daylighting and Glazing research project.

A part of this work involves detailed simulation of the
daylight linking controls by run-time coupling of 
the thermal simulation (ESP-r) and the lighting simulation

Here I would appreciate to get little more insight to the
"mkillum" treatment of the highly directional light sources
such as a sun or any virtual light sources by specular reflection
from external surfaces.

I have carry out simple test with sky with sun and
calculated window light distribution (window facing sun)
by mkillum and then
couple of internal point illuminances (e.g. 13000 lx and 476 lx)

Then I have deleted sun from the model and repeated the calculation
of the internal point illuminance with the same window light distribution
calculated previously (model with sun) (e.g. 2000 lx and 475 lx).

The results suggest to me that:

mkillum does not "map" such highly directional sources (e.g. sun) into the 
light distribution? These are probably moved to the direct calculation
as that is in my opinion the most effective way to handle them.

I am right to think that light distribution calculated by mkillum
will not contain direct and specular contributions to the window

I would suppose that for direct and specular contribution mkillum
window model reverts back to the primary material e.g. glass to
calculate these direct contributions into the internal illuminance?

With best regards,

Milan Janak,
University of Strathclyde, Glasgow.

Date: Tue, 7 Jan 97 09:32:05 PST
From: greg (Gregory J. Ward)
To: milan@esru.strath.ac.uk
Subject: mkillum

Hi Milan,

Yes, you are correct.  Mkillum only computes the directional diffuse
component of light coming in through a window system -- the specular
(beam) component is best handled by the default algorithm.  Actually,
if you are only computing a few point values, there is no sense in
using mkillum at all.  You are better off just using the ambient
calculation unless you plan to produce one or more renderings.

I can provide you with draft chapters from the Radiance book explaining
all this, if you have a PDF viewer.

I am very busy this week, working on a Siggraph paper.  You might do better
to write back to me after the 13th.


Date: Wed, 26 Mar 97 14:12:39 GMT
From: milan@esru.strath.ac.uk (Milan Janak)
To: greg@hobbes.lbl.gov
Subject: Light shelf-ceiling and mkillum

Dear Greg,

I would appreciate very your help with following:

As explained in your paper "The RADIANCE Lighting Simulation System" it
is a good idea to treate illuminated part of the ceiling (e.g. from
reflecting light shelf in my case) as illum source with precalculated
light distribution.  As you said, this (ceiling) is in reality
important light source.

Up till now everything is clear. Its starts to be little more difficult
to get it right in all details.

The best probably is to give example:
Let's say we have room with external specular light shelf and want to
assess its performance under overcast and clear sky conditions.

So firstly we run mkillum to precalculate light distribution for
external windows. So as mkillum will include only diffuse directional
contributions, for overcast sky it will map all external contributions
(also from specular surfaces??) but for clear sky conditions (with sun)
it will omitt beam contributions from sun or reflected from specular
light shelf, as these are handled by default calculations.

Then we build up octree with precalculated light outputs for external

Secondly, we run mkillum for part of illuminated ceiling by light
reflected from light shelf.  So for overcast sky, ceiling will actually
see only external window's illum light sources as there should not be
any beam contributions? For clear sky conditions there will be
additional beam contribution from sun reflected in light shelf which
will be now included in ceiling illum light output?

Base on my understanding, secondary light sources are not participating
in specular and diffuse sampling (they revert to the original material)
and therefore mkillum for ceiling should be calculated with -ab 0, as
otherwise there would be double counting for ambient contribution from
this part of the ceiling???

Thank you ones again very much.

ESRU, Glasgow.

Date: Wed, 26 Mar 97 09:27:29 PST
From: greg (Gregory J. Ward)
To: milan@esru.strath.ac.uk
Subject: Re:  Light shelf-ceiling and mkillum

Hi Milan,

Your understanding of the secondary light sources in Radiance using mkillum
seems to be quite good, and I'll be the first to agree that this is a very
confusing topic!

Do not worry about double-counting in Radiance -- these things are pretty
well taken care of so you don't have to think about it.  If you compute
the distribution from your ceiling with -ab 0, then the ceiling output
will not include these interreflections, because illum's do NOT participate
as their original materials in the indirect calculation.  Therefore, I
recommend that you set -ab at 1 or two when your run mkillum.  Also, you
can save on calculation later if you set d=0 in the mkillum scene input
file for the ceiling if it is a diffuse material.

I hope this helps.


Date: Wed, 9 Apr 97 19:19:08 BST
To: greg@hobbes.lbl.gov
Subject: Lamp colors in Radiance RGB format
From: Jeff.Shaw@arup.com

My name is Jeff Shaw, and I work with Steve Walker and Andy Sedgwick for Ove
Arup & Partners in London.  I have been doing a lot of work with Radiance
lately, and Steve thought you may be able to offer some advice on a recent
problem that I have encountered.

Essentially what I am attempting to do is to accurately model the color of the
lamps in some luminaires which I have modelled in Radiance for a particular
project.  So far I hove gone about this in the following way:

I have started with the Spectral Power Distributions of the fluorescent lamp 
phospors which I am interested (provided to me by a lamp manufacturer). Using
spreadsheet, I have converted these tables of values (between 400nm and 760nm)
producing, for each lamp color, a single set of x and y CIE chromaticity
chart coordinates.  I have used the CIE 1931 color-matching Functions
(Distribution Coefficients) to do this, and am confident that this process
has given me reasonable output.

The problem I have is how then to proceed with the conversion of these x and y
color chart coordinates into RGB values readable by Radiance which produce an
accurate color for each lamp.  I first attempted this using an in-house C
script (rgb.c - attached for your information) I believe written some time ago
by a colleague who is no longer here.  The script, however seems incomplete
and only converts to RGB according to NTSC standard rather than CIE standard.

As it is, I used the script to covert my x and y color chart coordinates to
RGB values.  For instance:
For a 3500K fluorescent lamp:
x = 0.4022 ; y = 0.3639 > R = 0.4531 ; G = 0.3251 ; B = 0.2219
For a 5400K fluorescent lamp:
x = 0.3318 ; y = 0.3478 > R = 0.3238 ; G = 0.2987 ; B = 0.3775

When I applied these values to my Radiance scene and viewed the resulting 
octrees, the 3500K lamp seemed too yellow/pink and the 5400K lamp seemed much
too purple, as you may expect.  This could be for three reasons:
1) The colors really are like that, the brainm just perceives them differently 
in real life.
2) The monitor is distorting/not properly showing the colors.
3) The RGB values are wrong.

Steve and I had a look at the new ra_xyze script which you wrote, and when we
applied it to our pictures with the -r -p options (using the values on your man
page for -p) the picture did appear slightly whiter as we wanted.  But we
are not entirely sure what ra_xyze does and whether we used it correctly.

Sorry to write a rather long and rambling email, but I hope I adequately
explained the situation.  We thought that as you have been doing a lot of
work on color recently for Version 3.0 of Radiance, you may be able to help.
I would appreciate any comments or suggestions that you have.


Jeff Shaw


Date: Wed, 9 Apr 97 11:39:42 PDT
From: greg (Gregory J. Ward)
To: Jeff.Shaw@arup.com
Subject: Re:  Lamp colors in Radiance RGB format

Hi Jeff,

Indeed, Radiance RGB values are not the same as NTSC RGB.  There are routines
within Radiance for converting from CIE colors to Radiance RGB values, but
it is probably easiest just to use the "lampcolor" program, providing it
with your own lamp table with CIE (x,y) chromaticities.  This table is
explained a bit in the manual page for ies2rad, and I can explain it further
if it doesn't make sense to you after reading that and looking at the
default "lamp.tab" file included in the ray/src/cv directory.

Failing this, you can use the .cal file ray/src/cal/cal/xyz_rgb.cal to
convert between XYZ and RGB values.  Again, let me know if you need help
with this or the "calc" or "rcalc" programs.

The resulting image will not look correct unless you adjust it for your
particular monitor primaries, unless they just happen to match the canonical
ones chosen for Radiance.  (This was the idea.)  To do this, you will have
to either measure the monitor primaries or obtain this data from the

Finally, I think you may be disappointed in your results for the other
reason you mentioned, which is that the eye peforms an unconscious color
(white) balancing operation when we view a scene.  This is why most
color video cameras have a white balance feature, also, and color films
are selected based on the expected illumination source.  Otherwise, all
pictures taken under incandescent lighting would look orange, and/or
outdoor images would look bluish.  Again, we don't perceive them that way,
because our eye/brain system compensates for the prevalent illumination
over a wide range of dominant spectra.

This is why most renderings are performed with equal-energy white
illuminants (i.e., RGB all equal), because a final white-balancing
operation would divide by the dominant illuminant color, yielding
the exact same result.  (See the -t option to pfilt.)  The only
case where it really makes sense to use different lamp colors
is when you are mixing different types of illumination in the same
environment, or letting in daylight with incandescents, etc.
(I assume this is what you are doing, or you wouldn't be asking.)
Unfortunately, in this case, white balancing is problematic, since
there is no one dominant spectrum to divide the result by.

I hope this is helpful to you.  By the way, I recently got some bounced
mail from "radiance@arup.com" -- is this alias no longer in action?
I removed it from our mailing list, but if you are still using Radiance
there, then you probably want to be on the list.  Shall I put your e-mail
on the list, instead?


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