Tracking features successfully

(claus_01) #1


right now, I’m about to learn how to use the Blender tracker. I want to track a moving ball in front of a red background, but most of the markers aren’t following the ball. What do I have to do to be successful?



P.S.: Here’s the .blend file:

Ball Test 01.blend (460 KB)

(claus_01) #2

So, no one has got any ideas? I want to make the markers following the ball. Until now, only one marker is tracking the ball, the others stay where they are. :no:


(colkai) #3

Without the actual footage files, it’s impossible to tell what is the problem. Basically, any marker needs ot be at a point of high contrast so that it can be tracked. That’s why markers tend to be white or black dots / crosses. Also, depending on the camera work of the footage you want tracked, depends if you would get a good result. If there isn’t enough parallax, you never get a decent track solve.
I highly recommed watching this:

It is excellent for going in depth about tracking and the pitfalls to watch for.

(3pointEdit) #4

Also blender won’t allow you to pack video into blend file. You would have to upload that separately somewhere to test. At least provide a few example frames of the video to see what you are expecting to track.

(claus_01) #5

This is a screenshot of the first frame. The white ball is moving from left to right, but only one marker is following the ball.


(kesonmis) #6

You are trying to track untrackable features. Random point on edge is very prone to sliding because all positions around it look the same. I would create one tracker for whole ball shape.

(colkai) #7

Either that, or make certain faces black so there is sufficient contrast to follow the whole shape. Seems something of a redundant exercise to track this. You’d normally want it to place 3D into live footage. What exactly are you hoping to produce here? What is the goal? If it’s just a tracking excercise, I’d get some footage from the net and practice on that. As I say, watch the Track, Match, Blend series, it covers all aspects.

(hype) #8

You could track the ball as a whole, or try tracking the point where the string attaches to the ball.

You could also check out my little course on tracking for compositing.

(claus_01) #9

This is merely some tracking exercise from the Blender book by Thomas Beck.



(kesonmis) #10

An excercise should still have a target to reach. Tracking is one of the areas where the process itself is pretty useless, you measure the quality of track through its application and end result. Sometimes you need this, sometimes that, sometimes crap will do the job. So it would be helpful to know what this excercise is about. Do you attach something to the ball in comp?

(claus_01) #11

No, I want to shoot a video & want to colorize the sky (dark blue). I thought that for this purpose I would need tracking because the masks I want to create are moving. The ball is merely an exercise because I’m new to tracking & post.

Here’s a photograph to give you an idea what I am trying to achieve:

(3pointEdit) #12

I think that you might have to look up rotoscope technique.

(kesonmis) #13

For sky modification you probably need a mix of keying (luma, channels etc depending on video) and roto. You are right that tracking is useful here, because you can attach masks to trackers and remove the tedious work of animating camera wobble manually. In Blender this kind of work is a bit contorted, but just to lay out a general idea I would do it somewhat like this:

  • pull some keys (from luma, different color channels with bigger separation, maybe try chroma key) and see which areas will work with keyed mask and which ones need additional roto. Mix different keys together using rough masks to get the best key for each area. You rarely get one good key for whole image.
  • depending on camera movement track the footage and create a transform;
  • attach created transform to masks and animate masks where necessary (for example if there are moving objects);
  • mix masks with keys using for example Maximum operation;
  • use the resulting mask as a factor in color operation or better yet, do all color ops you want for sky and in the end use the mask to merge modified sky over unmodified background (in Nuke this is called keymix operation and it helps to prevent problems which creep out when all color ops are done through mask)

Some more ideas: sometimes it is useful to stabilize the image before roto, then do roto, then re-apply transformation to masks. This is helpful because you get a better idea if your masks actually stick to their focus objects without slipping.