I have run into a problem that I think Mehlika Nur Inanici had a couple of year's back.
I am trying to use rtrace to get luminance values on top of a desk surface. The command I'm using is:
cnt 6 12 1 | rcalc -e '$1=51+((72/6)*$1+6);$2=96+((144/12)*$2+6);$3=30' \
-e '$4=0;$5=0;$6=1' | rtrace -h -ov @../options_aa08_ab5 -af b_b_m_2_bare_aa08_ad1024_ab5.amb -e b_b_m_2_bare_illumgrid_task_08_l.out b_b_m.oct \
rcalc -e '$1=179*(.265*$1+.670*$2+.065*$3)' >
b_b_m_2_bare_illumgrid_task_08_l.dat
The values reported by rtrace are in the range of 0.1 to 0.2 candela/meter squared. However, in an image, I am getting values in the range of 1.5 to 2.5 candela/meter squared (which is much more reasonable).
In response to Mehlika's question, Schorsch had mentioned that the header to the pic file would give an exposure value, and that luminance = 179*(.265*R+.670*G+.065*B) / e. But I can't seem to find the exposure.
What am I missing? Where am I not looking?
Thanks.
Hello John. You can use the getinfo command to look at the exposure of an Radiance image. The exposure value is given as EXPOSURE=.... If there is no exposure line, exposure is 1.00 by default.
Hope it helps...
Mehlika
John An wrote:
···
I have run into a problem that I think Mehlika Nur Inanici had a couple of year's back.
I am trying to use rtrace to get luminance values on top of a desk surface. The command I'm using is:
cnt 6 12 1 | rcalc -e '$1=51+((72/6)*$1+6);$2=96+((144/12)*$2+6);$3=30' \
-e '$4=0;$5=0;$6=1' | rtrace -h -ov @../options_aa08_ab5 -af b_b_m_2_bare_aa08_ad1024_ab5.amb -e b_b_m_2_bare_illumgrid_task_08_l.out b_b_m.oct \
> rcalc -e '$1=179*(.265*$1+.670*$2+.065*$3)' > b_b_m_2_bare_illumgrid_task_08_l.dat
The values reported by rtrace are in the range of 0.1 to 0.2 candela/meter squared. However, in an image, I am getting values in the range of 1.5 to 2.5 candela/meter squared (which is much more reasonable).
In response to Mehlika's question, Schorsch had mentioned that the header to the pic file would give an exposure value, and that luminance = 179*(.265*R+.670*G+.065*B) / e. But I can't seem to find the exposure.
What am I missing? Where am I not looking?
Thanks.
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Thanks Mehlika for the explanation. I was using getinfo to find the exposure information, and there was nothing regarding exposure. Can you think of any other reason why this may be happening, and what I might do to remedy this problem?
John
Mehlika wrote:
Hello John. You can use the getinfo command to look at the exposure of
an Radiance image. The exposure value is given as EXPOSURE=.... If there
is no exposure line, exposure is 1.00 by default.
Hope it helps...
Mehlika
John An wrote:
> I have run into a problem that I think Mehlika Nur Inanici had a
> couple of year's back.
>
> I am trying to use rtrace to get luminance values on top of a desk
> surface. The command I'm using is:
>
> cnt 6 12 1 | rcalc -e '$1=51+((72/6)*$1+6);$2=96+((144/12)*$2+6);$3=30' \
···
-e '$4=0;$5=0;$6=1' | rtrace -h -ov @../options_aa08_ab5 -af
> b_b_m_2_bare_aa08_ad1024_ab5.amb -e
> b_b_m_2_bare_illumgrid_task_08_l.out b_b_m.oct \
> > rcalc -e '$1=179*(.265*$1+.670*$2+.065*$3)' >
> b_b_m_2_bare_illumgrid_task_08_l.dat
>
> The values reported by rtrace are in the range of 0.1 to 0.2
> candela/meter squared. However, in an image, I am getting values in
> the range of 1.5 to 2.5 candela/meter squared (which is much more
> reasonable).
>
> In response to Mehlika's question, Schorsch had mentioned that the
> header to the pic file would give an exposure value, and that
> luminance = 179*(.265*R+.670*G+.065*B) / e. But I can't seem to find
> the exposure.
>
> What am I missing? Where am I not looking?
>
> Thanks.
>
John,
Are you sure you are sending the rays in the right direction ?
From the two first lines of your script:
cnt 6 12 1 | rcalc -e '$1=51+((72/6)*$1+6);$2=96+((144/12)*$2+6);$3=30' \
-e '$4=0;$5=0;$6=1' | ....
it seems you are sending rays from a regular grid in a xy plane in the upward direction ($6=1) !
I guess you should ensure your calculation grid is located above your desk (e.g. by setting $3=30.5) and then trace rays downwards ($6=-1). Then rtrace will calculate the luminance values at the rays intersections with your desk plane which is what you expect I think...
Hope this will help you.
Raphaël Compagnon
it seems you are tracing rays
···
At 01.05.2004 01:40, you wrote:
Thanks Mehlika for the explanation. I was using getinfo to find the exposure information, and there was nothing regarding exposure. Can you think of any other reason why this may be happening, and what I might do to remedy this problem?
John
Thank Raphael,
I had always simply taken illuminance values, so I simply thought that taking the -I parameter out would do the trick. It makes much more sense that I would need to send the ray toward the surface I want to evaluate.
John
···
On May 3, 2004, at 6:01 AM, Raphael Compagnon wrote:
----------------------------------------------------------------------
Message: 1
Date: Mon, 03 May 2004 08:57:32 +0200
From: Raphael Compagnon <[email protected]>
Subject: Re: [Radiance-general] Re: rtrace for luminance values
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
John,
Are you sure you are sending the rays in the right direction ?
From the two first lines of your script:
cnt 6 12 1 | rcalc -e '$1=51+((72/6)*$1+6);$2=96+((144/12)*$2+6);$3=30' \
-e '$4=0;$5=0;$6=1' | ....
it seems you are sending rays from a regular grid in a xy plane in the
upward direction ($6=1) !
I guess you should ensure your calculation grid is located above your desk
(e.g. by setting $3=30.5) and then trace rays downwards ($6=-1). Then
rtrace will calculate the luminance values at the rays intersections with
your desk plane which is what you expect I think...
Hope this will help you.
Raphaël Compagnon
it seems you are tracing rays
At 01.05.2004 01:40, you wrote:
Thanks Mehlika for the explanation. I was using getinfo to find the
exposure information, and there was nothing regarding exposure. Can you
think of any other reason why this may be happening, and what I might do
to remedy this problem?
John
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