[Radiance-general] Problems using hdrgen for hdri generation

[Rob Guglielmetti]

Greg Ward wrote:

> It's probably because the sequence didn't capture enough dynamic range,
> or there were no smooth gradients.  The best strategy is to use a good
> sequence to get the camera response, then store it and reuse it via
> hdrgen's -r option.  (See the related tips in the attachment.)

Hi Greg and everyone,

Greg, I've been meaning to ask you about this.  I have been shopping for a
new digital camera lately, and one of the criteria I have is the ability
to easily capture workable HDR images.  Now, at the Berkeley workshop you
demonstrated doing this wth your Olympus 3030, which has the ability to
take a 5-image autobracketed sequence, all separated by a stop.  This
gives you the ability to shoot a rough HDR sequence, handheld.  This is
what I was looking for, and I recall you saying that for these kind of
quickie HDR sequences one needed to make sure the midrange exposure was
separated by at least two stops from the endpoints.  I assumed this was to
ensure capturing the "entire range" of a "typical scene" (we have
discussed the limitations of this method in capturing the immense dynamic
range of a scene with direct sun, etc).

Of course when one looks at the current crop of digicams, the field
quickly gets thinned out when applying this criteria.  All too often a
nice camera (like the new Sony V3) is eliminated because its autobracket
function consists of a three shot maximum, separated by a single stop --
not enough.  At work, we have a Canon Rebel, which also only does three
shots for an autobracket sequence, but can separate them by two stops a
piece.

So, I'm wondering.  If I got a camera like the V3, which only goes one
stop to either side of the ideal exposure, but *first* use a tripod and
create an excelent HDR sequence as per your (excellent) quickstart guide,
and create and save a camera response curve for my V3 from that sequence,
would my crude handheld three-shot/1-stop HDR sequences be reasonably
accurate (assuming again, moderate dynamic range scenes)?

That was a long and winding sentence, but I hope you get the idea. (?)

P.S.
Just today I saw your camera for $225 on a closeout special at a store in
Manhattan that's not even known for low camera prices.  Ahh, technology.

P.P.S.
I was in the aforementioned store looking to purchase a power supply for
my work computer because the cooling fan in its power supply rolled over
and died 30 minutes into my workday this morning, a morning when I was
just finally getting caught up.  Ahh, technology.  =8-)

- Rob Guglielmetti
www.rumblestrip.org