Hi!
I am new to Desktop Radiance and wish to ask if anybody knows why I could
not get any differences in luminance rendering clear and dark glass. I have
2 types of glass, one is clear with below transmittance:
void glass Clear
0
0
3 0.890 0.961 0.961
Another glass is darker with below transmittance:
void glass Project_SC_0_2
0
0
3 0.308 0.308 0.308
We wish to know how dark would the rooms be with a glass shading coefficient
of 0.20 and visible light transmittance of 0.28. The above radiance
transmission numbers were generated by Ecotect. I tried editing them to:
void glass Project_SC_0_2
0
0
3 0.28 0.28 0.28
But I get the same image rendered, the objects behind the glass looks the
same. Looks like there is no difference in the transmission thru the glass,
or is there something wrong with my approach? But when I click on the image
to display luminance I get different cd/m2 numbers.
Any advise would be helpful. Thanks in advance!
Rgds,
Jun
Hi!
I am new to Desktop Radiance and wish to ask if anybody knows why I could
not get any differences in luminance rendering clear and dark glass.
[...]
But I get the same image rendered, the objects behind the glass looks the
same. Looks like there is no difference in the transmission thru the glass,
or is there something wrong with my approach? But when I click on the image
to display luminance I get different cd/m2 numbers.
Any advise would be helpful. Thanks in advance!
I think you only have a problem in understanding the image format and its
representation on screen.
Radiance stores the calculation result as an image where every pixel has
RGB value and an exponent giving the 'brightness' of the point. This
format can store an illuminance range that exceeds the capabilities of your
display by far. To get a visual impression (the image you would expect
from the rendering) the image viewer has to convert the real values in the
picture file to RGB values for your computer screen.
If you have two different pictures with the same scene but lit with different
amounts of light this adjustment will present you the image optimised for
the display, which probably means that the real brightness of the scene
is changed to something that gives the best representation for your eyes.
The images 'look' similar (or indeed identical) but the real content of the
image is different (as you have found out with the cd/m2 values).
You can think of this process of something like your eyes do in different
lighting conditions: At first you will feel blinded in a bright room but after
a while your eyes adjust to the light levels and you can see normally. If
you move to an identical but dimly lit room you will think it's too dark. After
some time you will get used to it and you can see in this room just like in
the room before.
To help you with your problem:
While you view the image in an image viewer for Radiance *.pic file
format you have to set the 'exposure' to the same value for both images.
If you use ximage (on Unix) use the '-e' option for this.
If you can't do this in your picture viewer use the tool 'pcompos' to combine
the two pictures into one and view them at the same time:
pcompos -a 2 bright.pic dark.pic > brigh_and_dark.pic
Regards,
Thomas
···
On 7 Oct 2008, at 04:11, Jhun Calixihan wrote:
Ah.. I see.
This is great! Thanks Thomas for the help!
Rgds,
Jun
···
-----Original Message-----
From: Thomas Bleicher [mailto:[email protected]]
Sent: Tuesday, October 07, 2008 5:17 PM
To: [email protected]; Radiance general discussion
Subject: Re: [Radiance-general] Glass Transmittance not showing
Importance: High
On 7 Oct 2008, at 04:11, Jhun Calixihan wrote:
Hi!
I am new to Desktop Radiance and wish to ask if anybody knows why I
could
not get any differences in luminance rendering clear and dark glass.
[...]
But I get the same image rendered, the objects behind the glass
looks the
same. Looks like there is no difference in the transmission thru
the glass,
or is there something wrong with my approach? But when I click on
the image
to display luminance I get different cd/m2 numbers.
Any advise would be helpful. Thanks in advance!
I think you only have a problem in understanding the image format and
its
representation on screen.
Radiance stores the calculation result as an image where every pixel has
RGB value and an exponent giving the 'brightness' of the point. This
format can store an illuminance range that exceeds the capabilities
of your
display by far. To get a visual impression (the image you would expect
from the rendering) the image viewer has to convert the real values
in the
picture file to RGB values for your computer screen.
If you have two different pictures with the same scene but lit with
different
amounts of light this adjustment will present you the image optimised
for
the display, which probably means that the real brightness of the scene
is changed to something that gives the best representation for your
eyes.
The images 'look' similar (or indeed identical) but the real content
of the
image is different (as you have found out with the cd/m2 values).
You can think of this process of something like your eyes do in
different
lighting conditions: At first you will feel blinded in a bright room
but after
a while your eyes adjust to the light levels and you can see
normally. If
you move to an identical but dimly lit room you will think it's too
dark. After
some time you will get used to it and you can see in this room just
like in
the room before.
To help you with your problem:
While you view the image in an image viewer for Radiance *.pic file
format you have to set the 'exposure' to the same value for both images.
If you use ximage (on Unix) use the '-e' option for this.
If you can't do this in your picture viewer use the tool 'pcompos' to
combine
the two pictures into one and view them at the same time:
pcompos -a 2 bright.pic dark.pic > brigh_and_dark.pic
Regards,
Thomas