rvu exposure setting

Hi,

I've a basic question which I haven't really succeeded to get answer to from the different tutorials. When I visualize an octree with rvu I usually set -av and -ab as first parameters.
As far as I understand, the "ambient value" should set the brightness of the scene, but I don't see any change by setting it to different values, and to get a nice image I usually use the -pe option to set the exposure.
Could you please enlighten me on the usage of "ambient vale" option to get a good exposure in my images?

Thanks,
Stefano

···

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

Hi Stefano,

The ambient value is used as a proxy estimate for the interreflected light, to be used for pixels when the other ambient investigation methods have been exhausted (ab, as, ad, lw, etc). It's a "value of last resort", if you will. So in one sense, if you drive the simulation with aggressive ambient parameters, the av setting becomes fairly irrelevant because a "good" av will be derived deterministically. Of course in keeping with the "there's no such thing as a free lunch" theme, cranking up the other ambient parameters results in long simulation times. There are some rules of thumb regarding "good" av settings for indoor and outdoor scenes that you can start with (consultation of the "rad" manual page will reveal these), but for a good image or numeric result you should be asking Radiance to do some raytracing to tease these values out for all the little corners of your space.

As far as using rvu for a testbed, this is an excellent way to interactively see the effects of the various parameters on appearance and render time. If you change a setting though, you need to redraw the image with the "new" command, or by clicking "redraw" on the new Qt-based rvu that comes with the NREL installers, to see the effect. Speaking of the NREL Radiance installers, we are posting updated packages tomorrow that address the missing .cal files issue that is present in the current installers.

- Rob

···

________________________________________
From: Stefano Moret [[email protected]]
Sent: Monday, May 14, 2012 6:47 PM
To: [email protected]
Subject: [Radiance-general] rvu exposure setting

Hi,

I’ve a basic question which I haven’t really succeeded to get answer to from the different tutorials. When I visualize an octree with rvu I usually set –av and –ab as first parameters.
As far as I understand, the “ambient value” should set the brightness of the scene, but I don’t see any change by setting it to different values, and to get a nice image I usually use the –pe option to set the exposure.
Could you please enlighten me on the usage of “ambient vale” option to get a good exposure in my images?

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

Dear Rob,

Thanks for clarifying this. So which would be the best way of getting a good image with a "correct" exposure if I want, for example, to automate the images production process with a script?
My question ultimately ends up referring to the Ruby script Daylightsim.rb for Openstudio exported models (which was probably written by you?) which is giving me in output very dark/bad quality .hdr images.

Thanks,
Stefano

···

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

On 14/mag/2012, at 18.47, Guglielmetti, Robert wrote:

Hi Stefano,

The ambient value is used as a proxy estimate for the interreflected light, to be used for pixels when the other ambient investigation methods have been exhausted (ab, as, ad, lw, etc). It's a "value of last resort", if you will. So in one sense, if you drive the simulation with aggressive ambient parameters, the av setting becomes fairly irrelevant because a "good" av will be derived deterministically. Of course in keeping with the "there's no such thing as a free lunch" theme, cranking up the other ambient parameters results in long simulation times. There are some rules of thumb regarding "good" av settings for indoor and outdoor scenes that you can start with (consultation of the "rad" manual page will reveal these), but for a good image or numeric result you should be asking Radiance to do some raytracing to tease these values out for all the little corners of your space.

As far as using rvu for a testbed, this is an excellent way to interactively see the effects of the various parameters on appearance and render time. If you change a setting though, you need to redraw the image with the "new" command, or by clicking "redraw" on the new Qt-based rvu that comes with the NREL installers, to see the effect. Speaking of the NREL Radiance installers, we are posting updated packages tomorrow that address the missing .cal files issue that is present in the current installers.

- Rob

________________________________________
From: Stefano Moret [[email protected]]
Sent: Monday, May 14, 2012 6:47 PM
To: [email protected]<mailto:[email protected]>
Subject: [Radiance-general] rvu exposure setting

Hi,

I’ve a basic question which I haven’t really succeeded to get answer to from the different tutorials. When I visualize an octree with rvu I usually set –av and –ab as first parameters.
As far as I understand, the “ambient value” should set the brightness of the scene, but I don’t see any change by setting it to different values, and to get a nice image I usually use the –pe option to set the exposure.
Could you please enlighten me on the usage of “ambient vale” option to get a good exposure in my images?

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

_______________________________________________
Radiance-general mailing list
[email protected]<mailto:[email protected]>
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi Stefano,

The short answer is that it's unnecessary as long as you run the simulation with reasonable parameters. The fact that you are getting lousy images is probably because you don't have a proper view set up for DaylightSim, and the error handling for that is lousy/non-existent, because, yes, I did write it. =8-/

We have also focused on numeric grids since the implementation of the 3-phase method, and it may be that something is simply broken. Can you do me a favor and repost this question on the OpenStudio forum and we can hash out the script issues over there, since this isn't really a Radiance problem? Thanks!

- Rob

Rob Guglielmetti IESNA, LEED AP
Commercial Buildings Research Group
National Renewable Energy Laboratory
15013 Denver West Parkway MS:RSF202
Golden, CO 80401
303.275.4319
[email protected]

···

On 5/15/12 1:49 PM, "Stefano Moret" <[email protected]<mailto:[email protected]>> wrote:

Dear Rob,

Thanks for clarifying this. So which would be the best way of getting a good image with a "correct" exposure if I want, for example, to automate the images production process with a script?
My question ultimately ends up referring to the Ruby script Daylightsim.rb for Openstudio exported models (which was probably written by you?) which is giving me in output very dark/bad quality .hdr images.

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

On 14/mag/2012, at 18.47, Guglielmetti, Robert wrote:

Hi Stefano,

The ambient value is used as a proxy estimate for the interreflected light, to be used for pixels when the other ambient investigation methods have been exhausted (ab, as, ad, lw, etc). It's a "value of last resort", if you will. So in one sense, if you drive the simulation with aggressive ambient parameters, the av setting becomes fairly irrelevant because a "good" av will be derived deterministically. Of course in keeping with the "there's no such thing as a free lunch" theme, cranking up the other ambient parameters results in long simulation times. There are some rules of thumb regarding "good" av settings for indoor and outdoor scenes that you can start with (consultation of the "rad" manual page will reveal these), but for a good image or numeric result you should be asking Radiance to do some raytracing to tease these values out for all the little corners of your space.

As far as using rvu for a testbed, this is an excellent way to interactively see the effects of the various parameters on appearance and render time. If you change a setting though, you need to redraw the image with the "new" command, or by clicking "redraw" on the new Qt-based rvu that comes with the NREL installers, to see the effect. Speaking of the NREL Radiance installers, we are posting updated packages tomorrow that address the missing .cal files issue that is present in the current installers.

- Rob

________________________________________
From: Stefano Moret [[email protected]<mailto:[email protected]>]
Sent: Monday, May 14, 2012 6:47 PM
To: [email protected]<mailto:[email protected]>
Subject: [Radiance-general] rvu exposure setting

Hi,

I’ve a basic question which I haven’t really succeeded to get answer to from the different tutorials. When I visualize an octree with rvu I usually set –av and –ab as first parameters.
As far as I understand, the “ambient value” should set the brightness of the scene, but I don’t see any change by setting it to different values, and to get a nice image I usually use the –pe option to set the exposure.
Could you please enlighten me on the usage of “ambient vale” option to get a good exposure in my images?

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]><mailto:[email protected]>

_______________________________________________
Radiance-general mailing list
[email protected]<mailto:[email protected]>
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi Stefano,

It sounds to me that you think exposure needs to be set before rendering. It doesn't. The image format used by Radiance contains more data than typical image formats allowing you to adjust exposure after rendering. With rvu you can type "e", then enter then click on any pixel to adjust the overall image exposure to the value of that pixel. Or you can type "e 1" to adjust to the exposure to the image average (" e 2 " is twice the image average). Or "e -1" to reduce exposure by one f-stop (+1 to increase). You can adjust exposure as much as you like in rvu.

For a rendered hdr image you can adjust exposure after rendering with pfilt.

Andy

···

On May 15, 2012, at 12:49 PM, Stefano Moret wrote:

Dear Rob,

Thanks for clarifying this. So which would be the best way of getting a good image with a "correct" exposure if I want, for example, to automate the images production process with a script?
My question ultimately ends up referring to the Ruby script Daylightsim.rb for Openstudio exported models (which was probably written by you?) which is giving me in output very dark/bad quality .hdr images.

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]

On 14/mag/2012, at 18.47, Guglielmetti, Robert wrote:

Hi Stefano,

The ambient value is used as a proxy estimate for the interreflected light, to be used for pixels when the other ambient investigation methods have been exhausted (ab, as, ad, lw, etc). It's a "value of last resort", if you will. So in one sense, if you drive the simulation with aggressive ambient parameters, the av setting becomes fairly irrelevant because a "good" av will be derived deterministically. Of course in keeping with the "there's no such thing as a free lunch" theme, cranking up the other ambient parameters results in long simulation times. There are some rules of thumb regarding "good" av settings for indoor and outdoor scenes that you can start with (consultation of the "rad" manual page will reveal these), but for a good image or numeric result you should be asking Radiance to do some raytracing to tease these values out for all the little corners of your space.

As far as using rvu for a testbed, this is an excellent way to interactively see the effects of the various parameters on appearance and render time. If you change a setting though, you need to redraw the image with the "new" command, or by clicking "redraw" on the new Qt-based rvu that comes with the NREL installers, to see the effect. Speaking of the NREL Radiance installers, we are posting updated packages tomorrow that address the missing .cal files issue that is present in the current installers.

- Rob

________________________________________
From: Stefano Moret [[email protected]]
Sent: Monday, May 14, 2012 6:47 PM
To: [email protected]
Subject: [Radiance-general] rvu exposure setting

Hi,

I’ve a basic question which I haven’t really succeeded to get answer to from the different tutorials. When I visualize an octree with rvu I usually set –av and –ab as first parameters.
As far as I understand, the “ambient value” should set the brightness of the scene, but I don’t see any change by setting it to different values, and to get a nice image I usually use the –pe option to set the exposure.
Could you please enlighten me on the usage of “ambient vale” option to get a good exposure in my images?

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Thanks for your replies.

@Andy: I'm aware of that thing, but I was wondering how to get good exposures in cases in which I couldn't interactively set it, like when I'm using scripts to automate the images creation process;
@Rob: ok, I'm posting it on Openstudio forum.

Cheers,
Stefano

···

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

On 15/mag/2012, at 14.04, Andy McNeil wrote:

Hi Stefano,

It sounds to me that you think exposure needs to be set before rendering. It doesn't. The image format used by Radiance contains more data than typical image formats allowing you to adjust exposure after rendering. With rvu you can type "e", then enter then click on any pixel to adjust the overall image exposure to the value of that pixel. Or you can type "e 1" to adjust to the exposure to the image average (" e 2 " is twice the image average). Or "e -1" to reduce exposure by one f-stop (+1 to increase). You can adjust exposure as much as you like in rvu.

For a rendered hdr image you can adjust exposure after rendering with pfilt.

Andy

On May 15, 2012, at 12:49 PM, Stefano Moret wrote:

Dear Rob,

Thanks for clarifying this. So which would be the best way of getting a good image with a "correct" exposure if I want, for example, to automate the images production process with a script?
My question ultimately ends up referring to the Ruby script Daylightsim.rb for Openstudio exported models (which was probably written by you?) which is giving me in output very dark/bad quality .hdr images.

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

On 14/mag/2012, at 18.47, Guglielmetti, Robert wrote:

Hi Stefano,

The ambient value is used as a proxy estimate for the interreflected light, to be used for pixels when the other ambient investigation methods have been exhausted (ab, as, ad, lw, etc). It's a "value of last resort", if you will. So in one sense, if you drive the simulation with aggressive ambient parameters, the av setting becomes fairly irrelevant because a "good" av will be derived deterministically. Of course in keeping with the "there's no such thing as a free lunch" theme, cranking up the other ambient parameters results in long simulation times. There are some rules of thumb regarding "good" av settings for indoor and outdoor scenes that you can start with (consultation of the "rad" manual page will reveal these), but for a good image or numeric result you should be asking Radiance to do some raytracing to tease these values out for all the little corners of your space.

As far as using rvu for a testbed, this is an excellent way to interactively see the effects of the various parameters on appearance and render time. If you change a setting though, you need to redraw the image with the "new" command, or by clicking "redraw" on the new Qt-based rvu that comes with the NREL installers, to see the effect. Speaking of the NREL Radiance installers, we are posting updated packages tomorrow that address the missing .cal files issue that is present in the current installers.

- Rob

________________________________________
From: Stefano Moret [[email protected]<mailto:[email protected]>]
Sent: Monday, May 14, 2012 6:47 PM
To: [email protected]<mailto:[email protected]>
Subject: [Radiance-general] rvu exposure setting

Hi,

I’ve a basic question which I haven’t really succeeded to get answer to from the different tutorials. When I visualize an octree with rvu I usually set –av and –ab as first parameters.
As far as I understand, the “ambient value” should set the brightness of the scene, but I don’t see any change by setting it to different values, and to get a nice image I usually use the –pe option to set the exposure.
Could you please enlighten me on the usage of “ambient vale” option to get a good exposure in my images?

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]><mailto:[email protected]>

_______________________________________________
Radiance-general mailing list
[email protected]<mailto:[email protected]>
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]<mailto:[email protected]>
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]<mailto:[email protected]>
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi Stefano,

Sorry, I thought maybe you were coming from one of the other rendering tools where you need to set exposure as a rendering parameter. get it wrong and you wasted valuable computation time.

There are two options for automated post-processing in Radiance: pfilt sets the exposure to the image average and pcond mimics human visual response. You could just run your images through one of those tools and they would select a good exposure for each image.

rpict -ab ... mymodel.oct > image.hdr
pfilt image.hdr > exposureadjusted_image.hdr
or
pcond image.hdr > humanvision_image.hdr

If you want all your images to use the same exposure, you can use pfilt with a single pass (-1) and set exposure with "-e". In this case, I'd suggest having separate render and post process scripts so you can easily change the exposure - it might require a bit of fiddling to find a single exposure that gives decent results for all images.

Andy

···

On May 15, 2012, at 4:07 PM, Stefano Moret wrote:

Thanks for your replies.

@Andy: I'm aware of that thing, but I was wondering how to get good exposures in cases in which I couldn't interactively set it, like when I'm using scripts to automate the images creation process;
@Rob: ok, I'm posting it on Openstudio forum.

Cheers,
Stefano

--

Stefano Moret
California Lighting Technology Center
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]

On 15/mag/2012, at 14.04, Andy McNeil wrote:

Hi Stefano,

It sounds to me that you think exposure needs to be set before rendering. It doesn't. The image format used by Radiance contains more data than typical image formats allowing you to adjust exposure after rendering. With rvu you can type "e", then enter then click on any pixel to adjust the overall image exposure to the value of that pixel. Or you can type "e 1" to adjust to the exposure to the image average (" e 2 " is twice the image average). Or "e -1" to reduce exposure by one f-stop (+1 to increase). You can adjust exposure as much as you like in rvu.

For a rendered hdr image you can adjust exposure after rendering with pfilt.

Andy

On May 15, 2012, at 12:49 PM, Stefano Moret wrote:

Dear Rob,

Thanks for clarifying this. So which would be the best way of getting a good image with a "correct" exposure if I want, for example, to automate the images production process with a script?
My question ultimately ends up referring to the Ruby script Daylightsim.rb for Openstudio exported models (which was probably written by you?) which is giving me in output very dark/bad quality .hdr images.

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]

On 14/mag/2012, at 18.47, Guglielmetti, Robert wrote:

Hi Stefano,

The ambient value is used as a proxy estimate for the interreflected light, to be used for pixels when the other ambient investigation methods have been exhausted (ab, as, ad, lw, etc). It's a "value of last resort", if you will. So in one sense, if you drive the simulation with aggressive ambient parameters, the av setting becomes fairly irrelevant because a "good" av will be derived deterministically. Of course in keeping with the "there's no such thing as a free lunch" theme, cranking up the other ambient parameters results in long simulation times. There are some rules of thumb regarding "good" av settings for indoor and outdoor scenes that you can start with (consultation of the "rad" manual page will reveal these), but for a good image or numeric result you should be asking Radiance to do some raytracing to tease these values out for all the little corners of your space.

As far as using rvu for a testbed, this is an excellent way to interactively see the effects of the various parameters on appearance and render time. If you change a setting though, you need to redraw the image with the "new" command, or by clicking "redraw" on the new Qt-based rvu that comes with the NREL installers, to see the effect. Speaking of the NREL Radiance installers, we are posting updated packages tomorrow that address the missing .cal files issue that is present in the current installers.

- Rob

________________________________________
From: Stefano Moret [[email protected]]
Sent: Monday, May 14, 2012 6:47 PM
To: [email protected]
Subject: [Radiance-general] rvu exposure setting

Hi,

I’ve a basic question which I haven’t really succeeded to get answer to from the different tutorials. When I visualize an octree with rvu I usually set –av and –ab as first parameters.
As far as I understand, the “ambient value” should set the brightness of the scene, but I don’t see any change by setting it to different values, and to get a nice image I usually use the –pe option to set the exposure.
Could you please enlighten me on the usage of “ambient vale” option to get a good exposure in my images?

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected]>

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Dear Stefano, et al,

My rendering pipeline often contains a call to pfilt to set the exposure as
if the picture was taken with a particular fstop and exposure. Look at this
reference:
http://radsite.lbl.gov/radiance/refer/Notes/filmspeed.html

Here is the example from that site. You can see the "1/60" and "4" in the
call to ev. Very handy.

So, if you were trying to produce an image as it would appear shot at 1/60
sec. on ASA 100 (ISO 21) film at f-4, you would apply pfilt thusly:

  pfilt -1 -e `ev "2.81*1/60*21/4^2"` raw.pic > fin.pic

Hope that helps,
Tim

PS: here it is in action. Note I do not save the original file and direct
standard error to /dev/null. Both of these are probably a bad idea.

rpict $VIEWPOINT \
                       -ps 1 -pt 0.15 -pj 0.6 \
                       -dj 0.7 -ds 0.5 -dt -0.5 -dc 0.75 -dr 1 -dp 256 \
                       -ss 0.3 -st 0.02 \
                       -ab 3 -aa 0.05 -ar 64 -ad 2048 -as 1024 \
                       -lr 4 -lw 0.0001 \
                       -x 2500 -y 2500 \
                       clock.oct 2> /dev/null \
                           > pfilt -1 -e `ev "2.81*1/60*21/4^2"` -x /4 -y
/4 -r 0.6 > $filtFile

···

On Tue, May 15, 2012 at 4:32 PM, Andy McNeil <[email protected]> wrote:

Hi Stefano,

Sorry, I thought maybe you were coming from one of the other rendering
tools where you need to set exposure as a rendering parameter. get it
wrong and you wasted valuable computation time.

There are two options for automated post-processing in Radiance: pfilt
sets the exposure to the image average and pcond mimics human visual
response. You could just run your images through one of those tools and
they would select a good exposure for each image.

rpict -ab ... mymodel.oct > image.hdr
pfilt image.hdr > exposureadjusted_image.hdr
or
pcond image.hdr > humanvision_image.hdr

If you want all your images to use the same exposure, you can use pfilt
with a single pass (-1) and set exposure with "-e". In this case, I'd
suggest having separate render and post process scripts so you can easily
change the exposure - it might require a bit of fiddling to find a single
exposure that gives decent results for all images.

Andy

On May 15, 2012, at 4:07 PM, Stefano Moret wrote:

Thanks for your replies.

@Andy: I'm aware of that thing, but I was wondering how to get good
exposures in cases in which I couldn't interactively set it, like when I'm
using scripts to automate the images creation process;
@Rob: ok, I'm posting it on Openstudio forum.

Cheers,
Stefano

    --

Stefano Moret
California Lighting Technology Center <http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]

On 15/mag/2012, at 14.04, Andy McNeil wrote:

Hi Stefano,

It sounds to me that you think exposure needs to be set before
rendering. It doesn't. The image format used by Radiance contains more
data than typical image formats allowing you to adjust exposure after
rendering. With rvu you can type "e", then enter then click on any pixel
to adjust the overall image exposure to the value of that pixel. Or you can
type "e 1" to adjust to the exposure to the image average (" e 2 " is twice
the image average). Or "e -1" to reduce exposure by one f-stop (+1 to
increase). You can adjust exposure as much as you like in rvu.

For a rendered hdr image you can adjust exposure after rendering with
pfilt.

Andy

On May 15, 2012, at 12:49 PM, Stefano Moret wrote:

Dear Rob,

Thanks for clarifying this. So which would be the best way of getting a
good image with a "correct" exposure if I want, for example, to automate
the images production process with a script?
My question ultimately ends up referring to the Ruby script Daylightsim.rb
for Openstudio exported models (which was probably written by you?) which
is giving me in output very dark/bad quality .hdr images.

Thanks,
Stefano

    --

Stefano Moret
California Lighting Technology Center <http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]

On 14/mag/2012, at 18.47, Guglielmetti, Robert wrote:

Hi Stefano,

The ambient value is used as a proxy estimate for the interreflected
light, to be used for pixels when the other ambient investigation methods
have been exhausted (ab, as, ad, lw, etc). It's a "value of last resort",
if you will. So in one sense, if you drive the simulation with aggressive
ambient parameters, the av setting becomes fairly irrelevant because a
"good" av will be derived deterministically. Of course in keeping with the
"there's no such thing as a free lunch" theme, cranking up the other
ambient parameters results in long simulation times. There are some rules
of thumb regarding "good" av settings for indoor and outdoor scenes that
you can start with (consultation of the "rad" manual page will reveal
these), but for a good image or numeric result you should be asking
Radiance to do some raytracing to tease these values out for all the little
corners of your space.

As far as using rvu for a testbed, this is an excellent way to
interactively see the effects of the various parameters on appearance and
render time. If you change a setting though, you need to redraw the image
with the "new" command, or by clicking "redraw" on the new Qt-based rvu
that comes with the NREL installers, to see the effect. Speaking of the
NREL Radiance installers, we are posting updated packages tomorrow that
address the missing .cal files issue that is present in the current
installers.

- Rob

________________________________________
From: Stefano Moret [[email protected]]
Sent: Monday, May 14, 2012 6:47 PM
To: [email protected]
Subject: [Radiance-general] rvu exposure setting

Hi,

I’ve a basic question which I haven’t really succeeded to get answer to
from the different tutorials. When I visualize an octree with rvu I usually
set –av and –ab as first parameters.
As far as I understand, the “ambient value” should set the brightness of
the scene, but I don’t see any change by setting it to different values,
and to get a nice image I usually use the –pe option to set the exposure.
Could you please enlighten me on the usage of “ambient vale” option to get
a good exposure in my images?

Thanks,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618

530-747-3846
[email protected]<mailto:[email protected] <[email protected]>>

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