[photo-3d] Answer to Quiz: Movement of clouds/direction of shoot

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

Thank you for participating in the quiz!  I think almost
everyone got the answer right, but Abram Klooswyk explained
all aspects to it... The correct answer is "IT DEPENDS".
The conservative answer (the one likely to work most
times) is "RECORD IN THE SAME DIRECTION OF CLOUD MOVEMENT"
This will make the clouds the further object in the scene
and it will work well in most typical situations.

I will now summarize Abram's answer with a few personal
comments:

The question was:

>>100 feet separation hyperstereo with a single camera.
>>...clouds are drifting very slowly from left to right. 
>>Should you take the LEFT picture first or the RIGHT, 
>>and why?

What happens if you take the Left picture first:

>The cloud separation will become _larger_ then 
>the separation of the farthest "ground target", so will be 
>in a farther plane in 3D viewing.

So the clouds will be pushed back and most likely will
be the furthest object in your picture.

What happens if you take the right picture first:

>separation of the clouds will become _less_ then far point 
>separation, so will be closer in the 3D percept. 

So the clouds will be pulled forward.

Here is a very important point:

>How far closer depends on cloud speed etc.

(more precisely it depends on how much the clouds moved
between the two shots... so the time it takes you to
record the pictures is a factor too)

So, back to our question:  Which one is better and why? 

>Complications occur when close clouds overlap more distant 
>hills or mountains. 

AHA!  So which method is better depends on how are the
clouds positioned with respect to closer and more
distant objects in the scene!

1. If the clouds are behind a nearby object (like tall
buildings in Manhattan - yes it has happened to me!)
then by all means you want to push them back.

2. If the clouds are in front of distant hills, then
pushing them back will be a problem... You are better
off bringing them closer.

3. If the clouds and distant hills do not overlap
(this happened to me in Grand Canyon) then either
method will work but bringing them closer will add an
extra layer of depth in front of the very distant
hills and it might be attractive. Or, as Abram said:

>a few close clouds only in the middle of the scene can be nice. 
>However, in many, maybe most cases non-background-overlapping clouds 
>a little more distant than horizon mountains are fine.
>
>So I believe the answer to "which first" is not always the same.

Yes, thank you Abram and all of you who participated.

Now, be prepared for the continuation of this quiz...
in my next posting.

George Themelis

 

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