find focal length from image

[Mark Serena]

Hey guys,

Not a Maya question, but wanted to know if anyone knew of any software that was able to solve camera data from a single image. 

I only know the building height in my images, but thought if there was software where i could draw perspective lines and feed the heights in, it would spit out info of the camera? 

Probably simple enough trying to do some trig or something, but I'm not that keen on it.

Any tips would be helpful.

Cheers,

Mark

[matt estela]

I'd say most 3d trackers these days would offer that, have a look at syntheyes and/or 3dequaliser. Nuke might even have that too, in v8, there was a bunch of tracker related stuff in the latest release.

--
You received this message because you are subscribed to the Google Groups "maya_he3d" group.
To unsubscribe from this group and stop receiving emails from it, send an email to maya_he3d+...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[Mark Serena]

yeah, been a while since i was in syntheyes, so was in quickly and out, basically just want a perspective matcher like the one in 3dsmax...might just get the trial and run through them that.

not a problem doing it in maya, just thought i might of been missing something. i'll try nuke now.

cheers matt

[Anthony Tan]

If you've access to it, you can also have a stab at PFTrack. I distinctly recall drawing perspective lines in it for some reason..

[Keith Rogers]

There is a focal length finder in pftrack. You just pin the corners of a cube to similar points in the image.

[Johan Forsgren]

In many images the focal lenght is stored in the image's metadata, just rightclick and go into the details tab (if your on windows)

JOHAN FORSGREN
CG ARTIST
Phone + 46 31 752 20 00	johan.f...@edithouse.se
Direct + 46 31 752 20 07	Follow us at facebook.com/edithousefilmworks

edithouse FILM WORKS	www.edithouse.se
Lilla Bommen 4a, S-411 04 Göteborg, Sweden	www.facebook.com/edithousefilmworks

[Ivan&Ana]

But focal length does not change perspective, so ...you can only roughly guesstimate the focal length. Wide or tele.

Tccin3D

[Milos Vukotic]

Logically, deriving focal length info from a single image is practically impossible unless we know the dimension of each object in the scene and it's distance from the camera (which we simply don't :D).

But deriving it from video, or at the very least 2 frames, where computer can calculate movement and deformation of each significant target area and compare them to one another, sounds definitely positive, and I believe that motion tracking tools should be able to do that.

[Milos Vukotic]

Ivan&Ana, how do you mean it doesn't change perspective? As far as I know focal length and other lens related modifications are the only things that affect perspective...

Am I missing something?

[Ivan&Ana]

Perspective is changed when you change position, 45mm and 100mm lenses render perspective the same.

 Lines of perspective stay same if you hold your position. Often when you change focal length you also change your position in space to frame subjects better, so it looks like perspective has changed, in reality lens did not do anything, only distance to subject is different, and thus perspective is not the same.  

--
You received this message because you are subscribed to the Google Groups "maya_he3d" group.
To unsubscribe from this group and stop receiving emails from it, send an email to maya_he3d+...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

--

Tccin3D

[Milos Vukotic]

Yes, focal length in it's essence is a distance from the center of the lens, I do understand that, and yes lines of perspective will stay the same if position is preserved. However, doesn't it go without saying that one will automatically want to change the position and get closer in order to compensate for the "zoom out" effect of it. Once one does that, he'll notice a big change, everything will look more distorted and "funky".

So yeah I get your point, but I guess it depends on how you view it (no pun intended :D).

[Mark Serena]

i was waiting to hear back from PFTrack about using their demo, because you have to request it, and was just given the flick, denied. Guess that option is out the door.

I have been able to use the metadata on some of the images and reclaim some by doing an reverse image search but some I can't.

found something with the right word search this time around, looks like the guy working with soup that made the copier node.

http://vimeo.com/24130335

[matt estela]

What was the tracker that autodesk bought? Isn't that bundled with maya these days? Surely that'd be capable of this?

I vaguely recall a blender video doing the same as that vimeo thing... *quick search later...*   Ah:

https://www.youtube.com/watch?v=yeWzQYh7iH0

Means loading blender though... ew... ;)

[Ryan O'Phelan]

Check this out. This popped up on a nuke discussion list the other day. I think you can get focal length. 
It's a capture of a FXPHD article. 

https://www.evernote.com/shard/s7/sh/70dcb995-c062-4b11-a9de-3a238159ef55/4f2ff05a1d359877f9aea494a05905fe

[Ryan O'Phelan]

http://www.fxphd.com/tips/finding-the-cameras-position-tutorial/

[Ryan O'Phelan]

Ok,  so you can't get focal length directly,  but if you derive the cam position,  and know the film back,  you can build an accurate set,  and get the FL quickly.

R