[Radiance-general] rvu exposure setting

Tue May 15 16:07:50 PDT 2012

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
smoret at ucdavis.edu<mailto:smoret at ucdavis.edu>

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
smoret at ucdavis.edu<mailto:smoret at ucdavis.edu>

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 [smoret at ucdavis.edu<mailto:smoret at ucdavis.edu>]
Sent: Monday, May 14, 2012 6:47 PM
To: radiance-general at radiance-online.org<mailto:radiance-general at radiance-online.org>
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
smoret at ucdavis.edu<mailto:smoret at ucdavis.edu><mailto:smoret at ad3.ucdavis.edu>

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