Monday, June 6, 2011

Match Moving Tutorial Part II

Import your image sequence. This part is about as self explanatory as it gets. You may have to create a 'new project' or 'new folder' depending on your tracking software.
With your sequence imported let's start. Now some applications have a 'wizard' or guide that will take you from start to finish and get you a fairly decent Auto track. Every now and then an auto track will come out clean and won't need a re-track or re-solve but don't count on it. The purpose of the tutorial is to teach you the terms and how to adjust settings and not rely on automated tracking. Which likely wont work if you have subject in the scene moving in relation to your ground plane. I'll explain this in the next section.

The next step is to actually do the tracking. This will likely be call something along the lines of "Track Features" as it is in Boujou, and I believe Icarus. Now, if your footage includes something along the lines of maybe a guy running down a street and you plan on compositing a monster chasing him we might have some more work to do before we hit that magic 'track' button. If your main character is running, you don't want the software thinking his is a part of the environment and take that motion into consideration when creating your ground plane. You're going to have to mask him out. An autotrack can to a pretty good job in most apps of realizing when if you have a subject moving in relation to a background but it's not worth risking the possibility of a useless track.  Boujou's button is called 'Create Poly-Mask' which I would apply frame by frame around my moving subject until he is masked out of my footage.

Now you can track your footage. At this point you can either grab a latte or sit and watch those little colored dots wiggle around your screen a top your footage. These dots are called points or locators. You can change the number, relation distance, min./max. search distance, and all sorts of settings  so better suit your track. For the most part, the default settings have suited me just fine. If you are having issues with footage that has a lot of movement for example, try bumping up the search distance to allow the locators more area to search for their intended target. Number of locators will give you more points to work with but also take longer to track.

If you planned ahead, you may have stuck objects in your scene to help your application with tracking.
You can attach specific locators to these points if you wish.

Once your footage is done tracking (this time varies depending on length of footage and speed of machine) you should be able to scroll through your footage and see a bunch of those locators "stuck" to your footage.
We're almost done with this part!

If you have a clean track it is time to move on and 'Solve' for your 3D camera. All this means is your locator points' movement in relation to eachother will be taken and used to re-create the movement of your actually camera. Pretty cool stuff. This is another "sit back and wait" parts of the process.
Now if you remembered what I said about including x, y, and z reference lines in your footage you should have no problem with this part.
In order to orient your virtual camera (tell it which way is up, down, left, right, front and back) you need to create 'Scene Geometry'. This will either be selecting  points along known X, Y, or Z axis or drawing your own lines. Again, this part varies according to application.
After solving for your camera, you are basically finished (as long as you have a clean track, solve, and your camera is correctly oriented).

To test that your track worked correctly your application should give you an option to add 'Test objects' such as a cube or ground plane. If your ground plane looks accurate, congratulations you are finished with this stage.

Your last step is just to export the track to a workable format for your 3D application like Maya or 2D such as After Effects.

Part 3 Next.

No comments:

Post a Comment