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Tracking live action—how important are markers?

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Kim TaylorTracking live action—how important are markers?
by on Jan 29, 2012 at 10:13:09 pm

Hi guys, I need your expert advice!

I've just got one of the biggest commissions of my career to date. I come from a straight design background, but I've been steering my career more towards motion graphics of late. This particular project is for a music video, which involves live action. My client will send me the filmed and edited video and I will composite some of the song lyrics on top of the action, as if they were there in the scene.

I've done a bit of motion tracking before in After Effects, however only from shots where the cameraman was stationary. In this video the camera will be moving around on streets, inside houses etc. I plan to use Mocha AE to achieve this, however it is going to be a new experience.

MY QUESTION: The filming is taking place in a few weeks and I am currently researching planar tracking techniques. Would it be wise to ask the production company to put tracking markers in the scene, and then clone them out afterwards? How accurate will the tracking process be without markers?

This video is a prime example of what I want to achieve.




(jump to the middle to see some of the composited elements). Would the 3d tracking here have been achieved using markers?

Furthermore, the video will ultimately be converted to black and white. Will removing colour information decrease tracking accuracy and should I ask for a full colour cut of the video to work with?

Thanks for any advice! :)


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Andrew SomersRe: Tracking live action—how important are markers?
by on Jan 29, 2012 at 11:19:09 pm

You normally do NOT need tracking markers, IF there are enough high contrast stationary points in your set. In the video you showed as an example, there is more than enough detail in the bridges and buildings .

I have seen all too often in footage, well meaning people in production putting tracking marks all of the the place where not needed - inly to create a HUGE problem in post in painting them out.

You need specific markers:

1) On green/blue screen backgrounds, when the camera is moving - you need tracking marks to define the screen.

2) On moving subjects *if* those subjects are going to be replaced with CGI. (i.e. face dots for face replacement, and body dots for body mocap/replacement).

3) On things that need to be tracked that have no high contrast and stable geometry that is trackable, such as smooth monotone surfaces.


One place people often put tracking markers where they are typically NOT needed is on monitor faces. This is a HUGE pet peeve of mine. If you can see at least three of the monitor corners in the footage, then you do NOT NEED MARKERS. You mainly need markers on a monitor face if you cannot see the monitor's frame. in fact, you cane use a green image in the monitor with rectangles of same saturation but different luminance, and have the best for tracking and for keying.


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Kim TaylorRe: Tracking live action—how important are markers?
by on Jan 30, 2012 at 9:34:19 am

Thanks, that's an incredibly helpful response. Clearly tracking markers aren't going to be needed on any reasonably detailed scene.

I'd rather avoid having to paint out unnecessary markers if I don't have to. Appreciate the write up


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Roland R. KahlenbergRe: Tracking live action—how important are markers?
by on Jan 30, 2012 at 4:50:59 am

I agree with Andrew that those shots do not require markers as there are sufficient objects at different z-space in the imagery and the camera movements do provide sufficient parallax and lateral changes for tracking.

Other than mocha, you'll want to pick up 3D tracking using Camera Tracker or syntheyes.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Kim TaylorRe: Tracking live action—how important are markers?
by on Jan 30, 2012 at 9:37:42 am

Thanks, I will look into the camera tracking software and perhaps try the demos.

I'm not sure I understand their purposes so well though, surely in performing 3D tracking this is something Mocha already covers? At $300+ is it essential for this kind of project?

Thanks


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Roland R. KahlenbergRe: Tracking live action—how important are markers?
by on Jan 30, 2012 at 11:23:08 am

mochaAE/mochaPro are 2D/2.5D tracking apps. With respect to the video, the text inserts are doable with either of the mocha products. Where you will need a 3D tracker is the part where the woman walks/stumbles across the bridge. You can rent the Camera Tracker instead of making an outright purchase.

With regards to either working with BW graded footage or the original, most trackers work with luminance values either within the composite RGB or the individual RGB channels. So, generally speaking, high contrast imagery allows for more stringent tracking results.

If you're new to tracking then it's best to get up to speed ASAP. It's an art as much as it is a science, which means that experience counts a lot! There are lots of tutorials at the COW, the Imagineer Systems Website and also on lynda.com. Stay away from tuts from youtube - there are of course good ones but due to the sheer numbers and the fact that quality is always a premium, you're bound to find more of the bad ones.

Of course, once you're 'tuned' to tracking, check the youtube vids - by then you'll be able to pick up some useful tips (technically and artistically).

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Kim TaylorRe: Tracking live action—how important are markers?
by on Jan 30, 2012 at 1:09:31 pm

Ok thanks. I am doing my best to get up to speed quickly. Like I say, I have done motion tracking before, but not really with regard to planar tracking or 3D tracking. I have access to Lynda so I will have a search on there!

Just one last thing: My client recently threw a bit of a curveball in his last email saying that they plan to use a special effects lens on some of the shots. The lens is made by Lensbaby. These lenses create a 'targeted lens blur' allowing you to focus on a specific part of the frame, blurring and distorting the rest. Examples here -> http://christophermartinphotography.com/tag/lensbaby-muse/

I realize this isn't a standard question, but could this make tracking a nightmare? I am tempted to push back and request that any tracked shots are filmed without this lens. What do you think?


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Michael SzalapskiRe: Tracking live action—how important are markers?
by on Jan 30, 2012 at 2:47:38 pm

It would really depend on where in the shot they want the element tracked and how they're using that lens. However, I'd suggest doing the blur effect in post for any shots they want tracked, if possible.

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.


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Roland R. KahlenbergRe: Tracking live action—how important are markers?
by on Jan 31, 2012 at 12:39:01 am

As long as the tracking region is free from the lens effect, you should be fine. But do take note that this requires lots of QC on-set. If the tracking region gets into the blurred region then you are going to lose the track. Further, if they want you to insert text in both the lens-free and lens-affected areas then you've got to match the blurred effect too. Of course, all these will preclude rack focus effects as well.

I would rather do this in post but it'll will add quite a bit of time to your post work. Take a look at Maltanon's site for presets that mimic such camera effects.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Kim TaylorRe: Tracking live action—how important are markers?
by on Feb 1, 2012 at 4:25:50 pm

Great, very helpful thanks. Checking out Maltaannon's site now


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