[Radiance-general] rvu exposure setting
Tim Perry
tim.v2.0 at gmail.com
Tue May 15 16:40:52 PDT 2012
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 <amcneil at lbl.gov> 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
> 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
>
> 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]
> Sent: Monday, May 14, 2012 6:47 PM
> To: 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 ad3.ucdavis.edu <smoret at ad3.ucdavis.edu>>
>
>
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