proj-imim:
[proj-imim] Underwater Panoramas
malcolm yeo 1970-Jan-01 01:00:00
Hello.
I've been lurking on this list for some time now.
Firstly I would like to thank Prof. Dersch for his wonderfull Pano Tools,
Philo, Ben, Joost & Max Lyons to name a few of the laterally minded people
on the list who contribute to the collective knowledge.
Unfortunately I'm slow in reading the digests, so usually when I find
something I'd like to comment on all the discussions have been and gone.
This is in response to Renaud's 25th August note about underwater panoramas.
YES it is possible.
History:
I started a few years ago after seeing the frustrating efforts a friend went thought
with his homemade underwater panoramic camera - by the time he set it up the
subjects moved and wouldn't come back into shot. As I'd just learnt of Panorama
Tools I tried hand holding my housed SLR and 16mm fullframe fisheye. I proceeded
to shoot three rolls of panorama sequences and learn about Panorama Tools in
earnest. One of these attempted panoramas worked!!
It is hard and SLOW to produce anything of merit underwater.
At first hand held sequences resulted in most panoramas being failures after
tinkering for several weeks with PTOptimiser, PTGui and Photoshop masks. I
attempted to use the Philopod next but it was frustrating trying to correct for
the slightest water movement. Now I'm using a cheap monopod; a little like what's
mentioned at www.outsidethelines.com with the compass glued to the bubble level.
This is small, flexable, and quick to use. I'm still using my SLR/16mm with Fuji
ISO800 Pro negative film (Pushed to ISO3200). I have almost succeeded with ISO800
film but occasional exposures of 1/15sec @ f/2.8 handheld don't really work even
though water density and the camera mass aids hand holding.
Subjects:
360' is such a large area to fill with interesting subjects!
In fact I no longer shoot land panoramas unless there is an unsettled or cloudy
sky. Why waste 50% of your image? I've considered generating taylor-made skies
using Terragen and incorporating them in the pano but I'm not patient enough to
wait for the rendering to complete.
Panoramas best display the feel and expanse of the underwater scene but the best
subjects (schools of fish) move too quickly and are unpredictable. I find I shoot
fixed geographic features (narrow channels or wrecks) where interesting life
congregates. Finding wrecks around where I live: Sydney, Australia is a problem also
as they mainly occur in deep water (40-50m) and nitrogen narcosis at this depth can
lead to surprises when you see your developed sequences.
Be careful, an apparently interesting vertical submarine cliff will only fill 180'
at best as it will look similar to an interesting, flat & horizontal substrate.
Method:
I note a reference spot on the bottom and shoot the basic pano around that (aproximately
60' between images and a zenith/nadir), then I withdraw and await the people/animal
subjects moving into a more photogenic position, I then swoop in quickly, roughly
line up to my reference point and shoot the "talent" for inclusion as extra shots.
The good thing about this method is I don't need as high positional accuracy for the
extra shots as the actual panorama shots, this allows me to respond to the subjects.
Output:
I aim to generate high quality spherical panoramas for print & transparencies as
I don't have any web presence. Some underwater images are best converted to
circular fisheye projection (pitch=-90'). Others are best displayed as two side by
side 180' circular fisheyes (pitch=0' yaw=+/-90').
Lately I've started mixing psphere and circular fisheyes:
I start with two side by side 180' circular fisheyes (yaw=+/-90'), then I add a
psphere 180x180' layer (at yaw=0'). So instead of having a rectanglular image
(ratio 2:1) I get a sausage shaped image (also ratio 2:1 but with round left
and right ends). This seems to work OK as at the join at yaw=+/-90' the two
projections match. Sometimes the extreme stretching at the top and bottom of the
psphere ends too abruptly but it works best if nadir & zenith are a low detailed
region of the image. This really does improve the composition of some images!
Is this 'Mal-Projection'?? I'm certain the French speakers will enjoy this term!!
Currently I'm working on adding artificial illumination to show the glorious colours
in my panos. I'm thinking of using a large sub-reflector to give even lighting but
the bulk of the equipment can detract from my safety in waves and currents.
More on that, if I'm successful.....
Renaud the most important skill to learn first is your diving skills before attempting
any photography underwater. It's nice to shoot panoramas but you want to stay alive!
I hope this has been of interest to you all.
Cheers.
Mal Yeo
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