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Camera tracking tips!!

Posted by Marius Oberholster on Thursday, August 23, 2012 Under: General
Hey all!!

I want to give you all a freebie on account of all the visitors to the site. 65 per week is a good number so far and I really appreciate every reader!!

The last week or so, I've done work with camera tracking, to try and figure out how I can best work with it and get a great result and HE has given some great advice on working with them and some features you may not know about in Blender.

- Plan your shot
There are many things to consider, one of them is the amount of complex shapes you may have in your scene (that will need to be replicated for shading purposes) as well as if you will need to key colors and what those colors should be. Lighting and tracking points remain the most important for any scene, imo.

- Reduce your tracking video's resolution and replace it in the compositor for rendering (if your PC is slower than most)
When HE showed me this, I was ecstatic!! I had tried to track full 720p HD and it just took so long per frame and that only on a single track. Until HE told me to take the original video and export it to half the resolution at least and then track that. The scene will retain it's size and the proportions will remain as well, so just finish the video with the full-res footage.

- Blender can track image sequences
I wanted to use OGG video for my tracking and so on, but Blender does not support tracking with it, so HE suggested I use PNG sequence from the sequence editor and it worked extremely well. A useful feature, especially if you are going to track your own scenes for practice.

- Remember to adjust your motion blur to match your footage
Whenever you do have Blender rebuild your scene, it does some compositing for you, which includes the Vector Blur node. Make sure your blur from your scene matches the blur from your footage. Too little or too much and it will be immediately obvious.

- The edges of high-contrast points work really well too
I've noticed while working that the tracker sometimes prefers the edges of high contrast points, instead of the points themselves, so you can try that if you'd like.

- Keyframe matching is more accurate
While tracking, I saw that my markers would move off of their place and especially so when set to match the previous frame. If you do use previous frame, instead of keyframe, it has a looser point of reference. Fluid reference if you will, so moving off course is not so easy to avoid. Using the keyframe is much much more accurate.

- Masking works well, but remember the motion-caused-feather moves to the direction of the animation, not neutrally across it's borders like some blurs do
Noticed this one in compositing. After HE showed me how to work with the tracking, I thought my scene was finished, until I saw my sleeve was also being keyed out of the scene (it was the same color as what I made transparent). I immediately knew that I had to use masking to fix it (did not feel like it). So this is where HE showed me that you draw using Ctrl+LMB. Had no idea at all. But remember that it does not remain sharp if you add the Vector Blur to it, it does reduce and expand based on direction of the blur. Just play around with it and you'll see.

- Use more than the bare minimum tracking points
The more you use, the more accurate your track will be (that is if you take care to make sure that the tracking does go right for each point).

- Refine everything during camera solving
In the Camera Solve section, you can find refine options. By default it is set to nothing, but this is very useful when you don't have your camera's full specs (like a cellphone camera for example). Refining is always a good idea.

- When a tracker goes dead (for whatever reason), it does not become wasted for the rest of the video
Let's say I track a scene where I turn around in 360'. That means that every tracking point will go off-screen at some point and will return again if I turn around at least twice. If you make sure to watch what tracker does what (by doing them one at a time), you will find that you can keyframe the tracker for the first time the tracking point shows up again. Currently, Blender is not equipped to bring it back for you, but you can still use the same tracker for the same reference point, even if it went off-screen. You add a new keyframe for it, by turning it on again (clicking on the eye) and moving it with G (Grab). Just make sure the eye is off for the duration the point is not on-screen.

- Choose your keying color wisely!
I did a scene this week that was very simple and although I keyed out blue, the rest of the scene was pretty much blue as well. So I had to use masking. If you do choose your keying color wisely and make sure that you have your scene excluding that color (from most of the original footage that should stay opaque), you should be set for an easy task. Again, this comes down to planning you scene and knowing what Blender can do, though practice.

- If a tracker stops tracking, reactivate, adjust and continue
Sometimes Blender tracks a point and for no apparent reason, just goes dead. While I think that has something to do with the math involved in matching, I know it's easily fixed by activating it again, adjusting it and continuing the track. Sometimes you may have to adjust and activate for a few frames, but the effort is worth it.

- Make sure everything looks right before rendering
You can do this by going into the compositor and using the Viewer Node and you can render a few frames you can see may present a problem.
  Doing so, prevents issues like I had with my sleeve being the same color (and that I only saw after rendering the whole sequence), which meant more work following that. So consider your scene and what is required before going to your final sequence render.

- You can animate the Compositor for adjustments in the scene.
For example if the light changes (it affects pretty much everything) and that means you will need to key frame those adjustments.

Hope all of the above tips are useful to you when doing camera tracking!!

Thank YOU for showing me the above! I really very much appreciate it!!

In : General 


Tags: tips  camera  camera tracking  tracking  help 

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