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View Full Version : Camera Perspective Match help



Rhothgar
01-09-2010, 01:55 PM
I have tried and tried. I'm just not sure what else to do.

Unfortunately I have no information about the live action camera other than it was shot DV on a Sony DSR500 no lens information.

I need to add digital extras to this shot and I have not been able to match the perspective.

The first example is what I've started with. As you can see in frame 205 things look close not perfect but close. The 3D character is supposed to be a little taller than the last one in line whom he is following. (once I can match the camera several more will be added later)

The problem is that in frame 450 the 3D character shrinks quite a bit as they travel away from the camera....

Version 2 is the closest I've been able to come but if you look at frame 205 the 3D character looks warped stretched out and too big but frame 405 is still off but looks closer.

I'm not sure what else to do here.

Any suggestions?

Thanks.

Rhothgar
01-09-2010, 01:56 PM
Here are the camera properties used in each example...

walfridson
01-09-2010, 02:11 PM
focal length is too low..
i would merge your frame 200 with the last in PS.. bring it in LW, place out boxes far and near.. test untill you find the perfect setting.
you could even upload the background image here and people can help you.
if you look at my page I had a "grass" project like that many years ago :D... know the feeling

Sekhar
01-09-2010, 03:34 PM
You could try matchmoving. I did a test once for this kind of thing and got some decent results as I remember. Usually, the objects are stationary and the camera moves, so you solve for the camera movement. But if you constrain the camera (as locked down, fixed focal length, etc.) and track the people and surroundings, solving can yield some movement info for the people. You can then take that into LW and parent your CG character to a tracked human, placing it relatively as necessary.

There're a bunch of matchmoving software (Voodoo is free, Syntheyes is inexpensive, etc.), but I'd tried my little experiment with Matchmover. Regardless of how you proceed with this, please do post back your findings.

gordonrobb
01-10-2010, 01:11 AM
In my experience 'matchmoving' software will not help you at all. It is for either 'matching' the movement of the camera, or an object. I can only speak for Syntheyes, but unless there is proper camera movement, it will not be able to give you any information about the camera (focal length etc.).

My guess is that you need to make the focal length longer (as wolfridson said), but also I think the angle is slightly too shallow (unless these guys are going up a hill). So tilt the camera down a little, increase the focal length. In short align the ground plane better, then move your camera to get the guy in position better.

CC Rider
01-10-2010, 08:43 AM
If you have access to the original location of the shot or if someone happened to take measurments or stills, you may be able to get some measurements of the area. Still cameras may have some METADATA that could be helpful... (you may be able to estimate it and get close enough but real world measurments would be the most helpful)
If you figure out the distance from one side of the frame to the other, that's one big variable out of the way which gets you a lot closer to your goal...
Figure out how far they walked, etc and build a scale environment. A simple ground plane with a couple of boxes the same size as the actors. One box for each edge of the frame and at near and far distances.
Once you have this, it will be much simpler to experiment and find the correct focal length of the lens. Keep in mind that every time you change the focal length of the lens, of course you'll need to move the camera to compensate for the framing. ex. every time you zoom in, you'll need to move the camera back to compensate.

CC Rider
01-10-2010, 08:49 AM
Also, the first set of pictures look to be fairly close. The biggest problem seems to be the ground plane more than the focal length...notice that the second shot where the CG character seems to be too short, he isn't that much shorter but rather he isn't walking on the same plane as the others. His feet or lower than the rest.
Perhaps a careful banking of the camera and reframing might be in order?

Rhothgar
01-12-2010, 06:12 AM
Thanks all for your replies.

I merged the two frames

Added a second character and placed each one at A and B

I moved the camera up on Y (a little higher) and further away from the characters. Then rotated down a bit as suggested.

I've also increased the focal length to 33. I was going the opposite direction :stumped:

This has all taken less than an hour. It's not perfect but I think it's getting close.

Thanks again! :)