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Old 7th January 2020, 13:18   #1  |  Link
nji
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Filter for changing field of view (FOV)?

Does someone knows about a filter which makes it possible
to change the FOV?
I searched ... but to no success.
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Old 7th January 2020, 15:04   #2  |  Link
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There is no "neutral" projection that you can map to. It might work if you stuck to a single axis but you then couldn't correct for rotation or have any translation in the other axis.
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Old 7th January 2020, 15:41   #3  |  Link
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I'm afraid your answer is too short for me to understand.
What I mean is something like the pics shown here:
https://webuser.hs-furtwangen.de/~de...Panoramas.html

In my simple words:
How would a scene look like if not taken with a wide angle lens but with telephoto?
Of course it would be a kind of "artifical" result (due to hidden/ unrevealing effects).
In image manipulation I do have the "panorama tools" (as plugin).
Changing the FOV changes a grid to a kind of spherical projection (and vice versa).
You do find me confused.
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Old 7th January 2020, 16:57   #4  |  Link
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I'm not aware of any for vdub . But shotcut (free, open source) has the bigsh0t plugin, which can manipulate several types of projections, FOV adjustment . Since it's a NLE, adjustments are keyframeable (changes over time) and you can "see" what you're doing with feedback . (There are more complicated open source programs like natron that can do this too)

Make sure you download the 2.1 release

https://monochrome.sutic.nu/2018/09/17/bigsh0t.html
https://bitbucket.org/leo_sutic/bigsh0t/src/master/



"The artist formerly known as DH" also wrote the avisynth plugin defish with FOV adjustments
https://forum.doom9.org/showthread.php?t=152860
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Old 7th January 2020, 18:32   #5  |  Link
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You're confusing two concepts - changing the projection and changing the FOV. You can change the projection easily enough, but you can't change the FOV of an image (except for the trivial case of cropping, but then you're deleting information).
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Old 7th January 2020, 19:59   #6  |  Link
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I assume you do mean both of us?

Yes, I do agree, I also have the impression that I'm confusing the two concepts.
Because actually I do not understand why it should be a problem to change FOV.
To quote from my post #3 from above:

How would a scene look like if not taken with a wide angle lens but with telephoto?
Of course it would be a kind of "artifical" result (due to hidden/ unrevealing effects).

Well, it's showy that there can't be found such a filter.
And even the panotools don't offer a ... "FOV conversion".
Only a changing from one projection to the other, and to specify FOV for rectangular.
(BTW.
What if I would map from a rectangular with FOV_src to fisheye,
then back from fisheye to rectangular with FOR_dst?)
In OpenGL there seems do be a method for FOV changing,
to do the dolly effect for example (??).
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Old 7th January 2020, 21:54   #7  |  Link
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Changing the FOV of an image, other than simply cropping or expanding (which is just deleting or inpainting information, and doesn't change the FOV of the actual content), means changing the (virtual) distance to the camera - and that means reconstructing the scene in 3D. And if you can do that, you may as well just have whatever AI you've used to stabilise the camera motion for you and re-render it entirely.

Quote:
(BTW.
What if I would map from a rectangular with FOV_src to fisheye,
then back from fisheye to rectangular with FOR_dst?)
Then your output image wouldn't be rectangular, but some distorted projection.

Quote:
In OpenGL there seems do be a method for FOV changing,
to do the dolly effect for example (??).
In OpenGL the "scene" is already 3D - it hasn't yet been rendered so the camera can be moved and the lens parameters changed. A video just doesn't have the required information, because the camera position has already been decided and the image is already captured.
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Old 7th January 2020, 22:11   #8  |  Link
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Believe it or not ... I do understand that. Thank you!

But then I'm really wondering what kind of magic you do in your AviSynth plugin.
It uses the FOV, but hasn't the 3D info.

BTW:
As far I know now your plugin is the only one that does the trick.
It's a pity it can't take rolling shutter effect into account,
and can't exclude/ refill areas (borders, logos etc.).
So you have unsteady moving border/ dubbing-ons.

EDIT:
Maybe the "distorted projection" I described above
(doing directly without the detour to fisheye of course)
would result to better results when DeShaking wide angle movies?

Last edited by nji; 7th January 2020 at 22:28.
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Old 12th January 2020, 13:20   #9  |  Link
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Quote:
Originally Posted by nji View Post
How would a scene look like if not taken with a wide angle lens but with telephoto?
Besides crop you have second option. Zoom out. Which again, means loss of information.

Last edited by redfordxx; 12th January 2020 at 13:36.
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Old 12th January 2020, 13:42   #10  |  Link
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Rethinking the idea from my other thread:
Making spherical projection before deshaker analysis...would probably favor all direction rotations, zoom so so ...but definitely not moving the camera (changing to PoV x and y axes)
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Old 12th January 2020, 14:02   #11  |  Link
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If there is spherical projection suitable for rotation and for example rectangular projection for camera movement... why not run on one video deshaker for two projections after each other.

I didn't give it second thought.
Do i smoke too much?
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Old 12th January 2020, 17:28   #12  |  Link
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Changing from one central projection to another central projection is more or less fail-safe as long as you keep the center the same. Once you move PoV you need distances to pixels and also reconstruct revealing areas. This is much more challenging. AFAIK this part of research is called "structure from motion".
Have you tried to find any software which already does that? Like Microsoft Hyperlapse for example.
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Old 12th January 2020, 19:03   #13  |  Link
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nji: Maybe something like defish() will help to achieve what you had in mind.
Edit: I'm too late to the party, I just saw poisondeathray's post.
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Last edited by Emulgator; 12th January 2020 at 23:29.
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Old 12th January 2020, 23:04   #14  |  Link
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Quote:
Originally Posted by shekh View Post
Once you move PoV you need distances to pixels and also reconstruct revealing areas. This is much more challenging. AFAIK this part of research is called "structure from motion".
OK...that looks like a no go.
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Old 13th January 2020, 00:29   #15  |  Link
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After defish, what projection I will have?
Rectangular?
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Old 13th January 2020, 01:25   #16  |  Link
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Quote:
Originally Posted by redfordxx View Post
After defish, what projection I will have?
Rectangular?
?
It would probably depend on what you start with, and what settings you use
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Old 13th January 2020, 08:38   #17  |  Link
redfordxx
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Quote:
Originally Posted by poisondeathray View Post
?
It would probably depend on what you start with, and what settings you use
I start with 65 FoV 16:9 smartphone.

So, defish doesnot change the projection? Just straightens lines etc. a little?

So, in that case...
... how do I apply that projection change script with xyreap?
https://forum.doom9.org/showthread.php?t=171922

Last edited by redfordxx; 13th January 2020 at 08:42. Reason: https://forum.doom9.org/showthread.php?t=171922
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Old 13th January 2020, 16:44   #18  |  Link
poisondeathray
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Quote:
Originally Posted by redfordxx View Post
I start with 65 FoV 16:9 smartphone.

So, defish doesnot change the projection? Just straightens lines etc. a little?

So, in that case...
... how do I apply that projection change script with xyreap?
https://forum.doom9.org/showthread.php?t=171922
??

"Straightening lines" - the way it's done with any of these types of filters - is changing the projection. So is causing lens distortion. Any type of lens distortion manipulation that causes "warping" in post is , by definition. But it might not fall neatly within some named category

Why are you doing this ? The common reason is to reverse the lens distortion, do whatever manipulations, then add back the same lens distortion (if desired) to match the original footage. The reason is many types of manipulations require flat or equirectangular to work properly. Compositing for example.

If you can't get what you want with one of those listed above, try natron. It's got several models in it's lens distortion node including panotools
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Old 13th January 2020, 18:07   #19  |  Link
redfordxx
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Sorry maybe for me being slow:
I made defish using a,b,c parameters.
Now I am asking what is the resulting projection supposed to be?
Rectangular?

Because when I am going to change the projection using the tools mentioned, I need to know what I am starting with.

That's what I've asked few posts above.
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Old 13th January 2020, 18:27   #20  |  Link
poisondeathray
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Quote:
Originally Posted by redfordxx View Post
Sorry maybe for me being slow:
I made defish using a,b,c parameters.
Now I am asking what is the resulting projection supposed to be?
Rectangular?

Because when I am going to change the projection using the tools mentioned, I need to know what I am starting with.

That's what I've asked few posts above.

?????
Maybe I'm the one that is slow...

It can be anything depending what your values are , and what you start with

eg. If you start with "normal" equirectangular projection, you can impose a lens distortion. Create one. If you start with a "fisheye" you can "undo" it or make it more pronounced (pincushion / barrel) . You can do whatever you want

If you cannot find your camera lens profile somewhere, if you don't know what you have - normally you would need to do a lens calibration. Essentially you shoot a grid pattern. Then measure or estimate what you have.

Last edited by poisondeathray; 13th January 2020 at 18:36.
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