accurate light levels (Thomas Bleicher)

william_reynolds · January 15, 2006, 1:51pm

thanks thomas and francesco for your comments.

my question about brightness was about not knowing the actual brightness in the real world, precisely because the monitor can't show you all the detail. i just wanted to check that that the original .pic image is not scaled at all by the exposure setting.

thanks again
will

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Today's Topics:

   1. Re: accurate light levels (Thomas Bleicher)
   2. Re: trad - TclTk (Thomas Bleicher)
   3. Re: splitting a render by light sources (Thomas Bleicher)
   4. Re: lightpipes/ports (Francesco Anselmo)
   5. Re: splitting a render by light sources (Francesco Anselmo)
   6. Re: lightpipes/ports (Jan Wienold)

----------------------------------------------------------------------

Message: 1
Date: Sat, 14 Jan 2006 20:06:01 +0100
From: Thomas Bleicher <[email protected]>
Subject: Re: [Radiance-general] accurate light levels
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

On 14.01.2006, at 16:59, william reynolds wrote:

Welcome to Radiance.

hi there

As I said in my other question today (spliting a render by light sources)
I am quite new to radiance, and I am having some issues setting up my
renderings. I have radiance installed and working fine, but I dont quite
understand how I make sure the brightness of the final render is realistic.
There are a few reasons for this:

You don't have to worry much about the "brightness" of images. The Radiance
image file format can store a much greater dynamic range than your monitor
can display or your eyes can see.

I'm not sure what exposure setting to use with pfilt - is it as simple
as setting '-e 1' so as not to adjust the exposure? I have tried this
and my images all come out very dark, but this might be because I don't
have enough light in the scene (see next paragraph, below).

The information within the images is not lost until you convert
the Radiance image (traditionally called *.pic, more resently *.hdr)
to *.tga (or similar) format which may loose all the details. You can
convert to some *.tif formats that support the full range but this
depends on the application you will use to process these images
afterwards.

And yes, using ra_t16 (for *.tga) or ra_tiff (for *.tif) it is as
simple as "-e +2" or "-e -2" to make the image brighter or darker.
Your images may in fact appear dark at the first glance when you render
a scene designed for 100 sources with one active source only.

Open your rendered image in "ximage" which is designed to handle
*.pic images. Hit the "a" key or "h" key to perform an adjustment
of the image exposure on screen, which should give you a better
rendering (on screen) of the image information. Read the man-page
of ximage for further details on the controls. Then read the man-page
of "pcond" which will create an new addjusted image.

Please note that most image manipulation tools bundled with Radiance
will work as filters and dump their output to your terminal window
when not told otherwise. Usually you will redirect the output to a
new file or "pipe" it into another program. These are basic Unix
concepts you should know to get the most out of your new Linux box.

Examples:

     pcond -h+ oldimage.pic > newimage.pic

     pcond -h+ oldimage.pic | ra_t16 -3 > newimage.tga

Has anyone used radiance with any theatrical light fixtures?
and would they be prepared to share the .rad files for them?
I have found the .rad descriptions of architectural fixtures,
but i'm not familiar with any of them, and even if I was I need
to be able to use accurate models of the specific instruments
I'll be using in theatres. I would simply build my own files,
using the iestorad utility, but rather unhelpfully the instrument
manufacturers dont seem willing to give out ies data.

Rob Shakespeare, coauthor of "Rendering with Radiance" (see below)
has experiance in this field, as have some others here on the list.

IIRC there was a post a few weeks ago about theatrical lights.
I'm not shure if the poster was willing to share his homemade
messurments of some fixtures. Hope he will answer personally.

Has anyone made any more materials information available to the
public? I have looked through the material.rad list of materilas
in the lib folder, but I'm specifically looking black paint and
heavy black cloth type materials. If not, then does anyone have
any recomendations of how to go about determining good values to
use in my own materials definitions? I dont have access to any
way of measuring reflected light levels in an experiment.

You can find a short introduction to the radiance materials
at other things here:

     http://radsite.lbl.gov/radiance/refer/usman1.pdf

and here (follow link "Documentation" and start with the
"radcourse_basic.pdf" document)

     http://luminance.londonmet.ac.uk/learnix/

While browsing for the link to Axel Jacobs more resent tutorials
I found this overview of materials:

http://www.learn.londonmet.ac.uk/student/resources/radiance/ material_db.shtml

Everyone highly recommends "The Book" about Radiance:

     http://radsite.lbl.gov/radiance/book/

It even includes a chapter about "Dramatic Lighting" (stage lighting).

Thanks for your help with my probably rather basic questions
Will

Everyone has his/her share of problems with Radiance

Thomas

------------------------------

Message: 2
Date: Sat, 14 Jan 2006 20:27:10 +0100
From: Thomas Bleicher <[email protected]>
Subject: Re: [Radiance-general] trad - TclTk
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII; format=flowed

On 14.01.2006, at 17:08, william reynolds wrote:

From looking over the past posts it seems that something has been
changed in the Tcl/Tk language that means that the trad utility
will no longer run with more recent versions. Does anyone know
with which version of Tcl/Tk this issue frst raised its head?
I've only tried the most recent versions. I also tried to install
the version I believe trad is meant to run under (Tcl 7.4, Tk 4)
but the source for these no longer under the new gcc!

Don't waste your preciouse time with old dead scripts. (Or do
it right and update the code for current releases if you know
enough about TCL/TK).

I'm pretty new to the linux system im running (fresh from windows)
and I dont really know what I'm doing changing code, so I thought
I'd appeal to this list for advice about any other front-ends for
Radiance.

You don't need much of a front end for Radiance except if you're
afraid of the command line. Most documentation you will find on
the LNBL homepage will use tipped out commands and a text editor
to create the scene files.

You can try the Radiance_on_a_Disk LEARNIX distribution by
Axel Jacobs:

     http://luminance.londonmet.ac.uk/learnix/

The documentation (including the "radcourse" PDFs I mentioned in
my other post) should match this environment so you don't have
to wrestle with the installation to get examples running.

A usefull front-end for the Radiance bundle of tools is the
programm "rad" which will controll the creation of octrees etc.
for you. It's included in the Radiance distribution. Read the
man-page about how to use it.

And start learning bash.

I'm aware of Rayfront, but unfortunately I dont have much budget
to spend on this project (it's my 4th year undergraduateEngineering
degree final project) and I am hoping for a free version!

Rayfront is one of the best front ends I know about. Perhaps
you can convince your department to invest in an educational licence?
Would be good for the development of Rayfront, too.

Thomas

------------------------------

Message: 3
Date: Sat, 14 Jan 2006 20:55:57 +0100
From: Thomas Bleicher <[email protected]>
Subject: Re: [Radiance-general] splitting a render by light sources
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII; format=flowed

On 14.01.2006, at 16:23, william reynolds wrote:

hi there
i'm fairly new to the radiance package, and to rendering in
general, but i have a fairly specific project on the go, with
which i need some help.

i am trying to use radiance to render a relatively simple model
geometrically - just a simple room, with a box sitting on the
floor - but with up to 100 or so light sources. but the difference
is that i want to get a separte image file for each light
source - i.e. hundred or so images, with only 1 light on in each.
i will then use superposition and recombine the images later,
allowing me to vary the intensities of each light source.

I hope you are aware of the fact that a incandescent light source
will have a shift of the spectrum in it's output when you change
the intensity (reduce the power for the lamp). But I don't think
you're bothered about this (small) aspect, so let's move on.

is there any kind of built in functionality in radiance to
allow me to do this, or do i have to write a shell script or
something (and if so, can anyone point me towards a good place
to learn how! i come from a very winndows based background)

The "build in functionality" of Radiance is it's simplicity.
Small tools for small tasks. And yes, you will have to write
a script for your problem. But it will be a simple script.

First you have to organize your scene data:

a) everything that is static in the scene in one file
b) a bunch of files containing everything that isn't
    (in your case 100 files with the description of 1 light
     source each).
c) definitions of i.e. viewpoints or render parameters

The basic steps to create one image are:

1) Compile a scene octree from the static and one dynamic file
2) Render the image with the created octree as input

I don't know much about your light so I assume you have
created a "static.rad" file, 100 "dynamic.001" etc. files
and a file with render options "render.opt".

Creating your images is as simple as:

for i in `seq -w 100`
do
   oconv static.rad dynamic.\{i\} > tmp\_scene\.oct    rpict @render\.opt tmp\_scene\.oct > image\_{i}.pic
done

Not as bad as it sounds, eh?

There is plenty of room for improvements: in particular, you don't
need all the 100 files for light sources if the vary only in
position or in other small details. That could be done within
the "for ..." loop, too. All depends on your needs.

For a simple introduction to bash google for "bash tutorial"
and try a few of the hits. It depends on you what's the right
introduction level. You can use any other scripting language
as well (Python, Perl, TCL) if you already know one.

HTH,
Thomas

------------------------------

Message: 4
Date: Sat, 14 Jan 2006 22:32:15 +0000
From: Francesco Anselmo <[email protected]>
Subject: Re: [Radiance-general] lightpipes/ports
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"

Hi Erico

Thanks for the pointer. I've downloaded the pmap 4.3 version and tried
to compile/install (after performing a fresh installation of radiance
3.7), but the pmap installation is unsuccessful.

If you're using linux, you can download the new pmap binaries from this page:
http://www.bozzograo.net/radiance/modules.php?op=modload&name=Downloads&file=index&req=viewdownload&cid=4