[Radiance-general] HDR & Isocontour help.

[Chris Foster]

Hi everybody...again

Im a regular nuisance on here, please dont kick me off Greg!

In addition to my last email, i have a query regarding light measurement within radiance. When viewing an .oct in rvu if i type t and then click on a point, it will give me a few values, the last of which, i assume, is luminance in nits.

Firstly is this assumption correct?

Is there a way to measure illuminance as opposed to luminance?

Thanks in advance

Chris




-----Original Message-----
From: radiance-general-bounces at radiance-online.org on behalf of Bleicher, Thomas
Sent: Wed 7/26/2006 2:01 PM
To: Radiance general discussion
Subject: RE: [Radiance-general] HDR & Isocontour help.
 
Hi Matt.

Answering for Greg here as he may be sound asleep in
another part of the world.

Greg assumed that you had a 3D scene in Radiance format
from which the HDR images have been generated. So his
answer was to use that scene (the input.oct file) to
create a "luximage.pic" from the same viewpoint as the
first HDR image. The "luximage.pic" file contains the
information needed for contour lines showing lux levels.

If you don't have this information you can't create
contour plots of lux level!

However, you still can create contour plots from the
original images. These lines will have "Nits" as unit
and show the "brightness" of an element in the scene
instead of the illuminace on that element (i.e. the
quantity of light reflected from a table vs. the light
falling on that table). The command for this is

$ falsecolor -cl -s 1000 -i rendering.pic -p rendering.pic > cline.pic

As you see input data ("-i" option) and background image
("-p" option) are the same file here. I think you can omit
the "-p" option in this case, but I can't check it now.
You may have to change the value of the "-s" ("scale")
option so it contains all the levels of your image. See
the man page of falsecolor for details and further useful
options.

Regards,
Thomas
 

> -----Original Message-----
> From: radiance-general-bounces at radiance-online.org 
> [mailto:radiance-general-bounces at radiance-online.org] On 
> Behalf Of Matt Parker
> Sent: 26 July 2006 13:35
> To: radiance-general at radiance-online.org
> Subject: Re: [Radiance-general] HDR & Isocontour help.
> 
> > Hi Matt,
> > 
> > The falsecolor command will create iso lines using the -cl or -cb 
> > options.  Try the following sequence:
> > 
> > % rpict -x 512 -y 512 [view and other options] input.oct > 
> > rendering.pic % rpict -i -x 512 -y 512 [same options] intput.oct > 
> > luximage.pic % falsecolor -cl -s 1000 -i luximage.pic -p 
> rendering.pic 
> > | ra_tiff - contours.tif
> > 
> > You'll need to play with the falsecolor options to get it like you 
> > want.  See <http://radsite.lbl.gov/radiance/man_html/falsecolor.
> > 1.html> for details.
> > 
> > -Greg
> > 
> 
> Greg,
> 
> Thanks so much for you very fast reply. All of the commands 
> look simple enough. My question now is, what is the .oct file 
> and how do I create it? I have been given a series of .HDR 
> images that were created using PhotoSphere from a series of 
> shots. What do I need to do to convert this to a .oct file or 
> do I just substitute my .hdr file where you indicate .oct.
> 
> Again, I apologize if this a stupid question.
> 
> Thanks for your help.
> 
> Matt 
> 
> 
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general
> 

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