[Radiance-general] Update on image based lighting

Tue, 25 Nov 2003 05:19:09 +0900

Hi Rob,

My camera takes 5 exposures, from +2 to -2, so the result would be the same
only with fewer pictures (which can be an advantage) The problem is that the
mid exposure is calculated from the whole scene light. Additionally, you can
set the under/over-exposure option to offset all the bracketing (in my
camera up to 2 stops), so you can get for example from 0 to +/-5.

Still I found situations where this was not enough. Not only daylight,
direct sun and so on, but even in a relatively dark room with only one
bright lamp, the lamp can be out of range. I use the colormeter in osx to
make sure that the brightest zones are below 255 in the darkest picture, and
the darkest above 0 in the brightest. This can be really bad if for instance
you had gone to a remote place to take some images and then back at home you
find out that they`re no good... (I know why I`m saying this)

The best thing would be to test the camera`s latitude (the difference in
f-stops between the minimum and maximum registerable values) so you can
meter the exposure in the highlights and shadows and find out if
auto-bracketing is enough.
Hope this helps. All this is not so complicated, but it`s tricky to explain
in writing (at least for me)
Regards,

Santiago.

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of
> Rob Guglielmetti
> Sent: Monday, November 24, 2003 11:43 PM
> To: [email protected]
> Subject: Re: [Radiance-general] Update on image based lighting
>
>
> Santiago Torres wrote:
> > Hi all,
> > As promised, I am posting the last results I got with image
> based lighting,
> > especially about illuminance values under a mapped sky.
>
> Hi Santiago,
>
> Thanks for taking the time to write that up.  I need more coffee this
> morning before I fully digest all the numbers there, but one statement
> at the end bears comment:
>
> "One thing to consider is that the camera has a built-in bracketing
> option that can take up to 5 images, with up to 1 stop increments. If
> the scene has high contrast, this can be insufficient to capture the
> whole range, so manual set up might be needed."
>
> I'm actually looking to buy a new camera for the office so that we can
> use HDR photography for survey work, mostly lower contrast stuff.  But
> I'm wondering, what is the contrast threshold where you would need to go
> manual?  I'm looking at the Canon digital rebel, which only does the
> three shot autobracket but can separate each exposure by two stops.
> Greg Ward & I discussed this off-list and he said that that is
> sufficient for what I'm looking to do.  But I assume you're talking
> about much higher contrast scenes, such as landscapes with direct sun,
> that would require a manual exposure?
>
> ----
>
>       Rob Guglielmetti
>
> e. [email protected]
> w. www.rumblestrip.org
>
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