Which is the best projection for a "flat" panorama?  

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alfapapa
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Which is the best projection for a "flat" panorama?

by alfapapa » Sun May 04, 2014 3:27 pm

Hello,
I've worked with spherical panoramas since today with only little problems.
Now I've tried to stitch a simple 3 photo vertical sequence but all my attempts produced very poor results.
I can't understand which projection is the best choice for such a "simple" task.
I guessed the planar projection was the best, and as a matter of fact it looks so, but it cause a large progressive stretch in the upper and lower section of the panorama (you can play a bit with the pitch angle setting to "center" the panorama, but stretch persists).
All others projections give unappceptable distortions in the upper and lower section of the resulting panorama.
Obviously some projections (spherical, cylindrical, little planet, mirror ball) are surely unfit for this goal, but, as I wrote, all the others seem not better in my newbie experience.
Paradoxically I get much better results with a "generic" (even though top level) software like Photoshop.
Which is your experience about this matter?
Thank you in advance for your attention.

Andrea

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mediavets
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Re: Which is the best projection for a "flat" panorama?

by mediavets » Sun May 04, 2014 5:14 pm

alfapapa wrote:Hello,
I've worked with spherical panoramas since today with only little problems.
Now I've tried to stitch a simple 3 photo vertical sequence but all my attempts produced very poor results.
I can't understand which projection is the best choice for such a "simple" task.
I guessed the planar projection was the best, and as a matter of fact it looks so, but it cause a large progressive stretch in the upper and lower section of the panorama (you can play a bit with the pitch angle setting to "center" the panorama, but stretch persists).
All others projections give unacceptable distortions in the upper and lower section of the resulting panorama.
Obviously some projections (spherical, cylindrical, little planet, mirror ball) are surely unfit for this goal, but, as I wrote, all the others seem not better in my newbie experience.
Paradoxically I get much better results with a "generic" (even though top level) software like Photoshop.
Which is your experience about this matter?
Thank you in advance for your attention.

Andrea

Welcome to the forum...

If these three standard photo images were not shot using pano head then you will probably get a better result from something like Photoshop.

If you would like to make the image set available as ZIP file for download then I expect there will be people here who would be happy to take a look and do a trial stitch so as to be able to offer better advice.

Meanwhile here are links to some information about projection types:
http://www.autopano.net/wiki-en/action/ ... ting_Modes

http://www.cambridgeincolour.com/tutori ... ctions.htm

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Re: Which is the best projection for a "flat" panorama?

by alfapapa » Mon May 05, 2014 9:07 am

Thank you Mediavets,

I'm going to read the pages you linked about projections...
As you suggest I attach a zip file encluding the images set and a low-res rendering of my best effort with planar projection (pitch angle = 15).
The images aren't particulary nice, it's only for testing this kind of stitching (I guess I'll need to tune it soon).
As you foresee, the photos were not shot using a panohead. I believed it's not the main problem as the control points and stitching areas look fine. The main issue is the progressive stretching of the upper and lower images (i.e. it leaps out that people in the lower-left part is dramatically distorted compared to the "original" image).
May be it's an unavoidable peculiarity of projections =(
Attachments
test_images.ZIP
(10.69 MiB) Downloaded 22 times

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mediavets
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Re: Which is the best projection for a "flat" panorama?

by mediavets » Mon May 05, 2014 9:36 am

IMO the issue is entirely related to the pano field of view.

If you view the stitched image as part of a Panotour virtual tour the distortion is 'corrected'.

Where you hoping to print the stitched pano image?
Attachments
2-pt21-zoom-oxford-partial.jpg
1-ptp21-oxford-partial-spherical.jpg
[Group 1]-_01__03-3 images-oxford-partial-03.jpg

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mediavets
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Re: Which is the best projection for a "flat" panorama?

by mediavets » Mon May 05, 2014 10:11 am

If you want to print the pano you may like to 'play' with the Pannini projection:
Attachments
1-apg-panini.jpg

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Re: Which is the best projection for a "flat" panorama?

by mediavets » Mon May 05, 2014 10:33 am


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alfapapa
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Re: Which is the best projection for a "flat" panorama?

by alfapapa » Mon May 05, 2014 3:16 pm

Tank you for your posts,

My goal was to generate a pano similar as a single photo I could shot if could walk back till entire subject was included in a single shot (exclusive of the image resolution of course) possibly printed on paper and not to be used as a virtual tour.
It looks a very complex matter indeed!
As I read in one of your links "If you are looking for a single projection, that will map a spherical (even partial) panorama on a flat surface without bending lines: This won't work!".
I tried with Panini projection parameters too, but I can't minimize the "bubble" distortions at the pano extremity (as in your sample jpg).
I'll try to take some shots extending the photo coverage up and down in order to use only the best part of the images (center section=less parallax?) and cut away the stretched extremities...Hmmm... no, the crucial point should be the (wide) FOV.

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Re: Which is the best projection for a "flat" panorama?

by mediavets » Mon May 05, 2014 4:54 pm

alfapapa wrote:Tank you for your posts,

My goal was to generate a pano similar as a single photo I could shot if could walk back till entire subject was included in a single shot (exclusive of the image resolution of course) possibly printed on paper and not to be used as a virtual tour.
It looks a very complex matter indeed!
As I read in one of your links "If you are looking for a single projection, that will map a spherical (even partial) panorama on a flat surface without bending lines: This won't work!".
I tried with Panini projection parameters too, but I can't minimize the "bubble" distortions at the pano extremity (as in your sample jpg).
I'll try to take some shots extending the photo coverage up and down in order to use only the best part of the images (center section=less parallax?) and cut away the stretched extremities...Hmmm... no, the crucial point should be the (wide) FOV.


Yes, you'll need to shoot a larger view and then crop into it.

The alternative would be to use tilt-shift lens I believe?:

http://en.wikipedia.org/wiki/Perspective_control_lens

http://en.wikipedia.org/wiki/Tilt%E2%80 ... hotography


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