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Dealing with lens distortion

From: mocha 2.6 Essential Training

Video: Dealing with lens distortion

Lens distortion can cause the image to slip relative to the tracking data. Here, we'll see how to use the planar grid to check for and to fix it. I want to make my planar grid larger, so I'll come over to the windows track and make it visible and then using the planer surface controls I'll adjust it larger, like so. I'll even scrub down to a different frame. Find my best frame to see what I want to see. And I'm going to make the grid cover most of the front of the building.

Dealing with lens distortion

Lens distortion can cause the image to slip relative to the tracking data. Here, we'll see how to use the planar grid to check for and to fix it. I want to make my planar grid larger, so I'll come over to the windows track and make it visible and then using the planer surface controls I'll adjust it larger, like so. I'll even scrub down to a different frame. Find my best frame to see what I want to see. And I'm going to make the grid cover most of the front of the building.

I'd like to have some more precision in the grid I want to increase the number of grid points. So to do that, we go to this popup here and we can set the number of Grid divisions for example to 24 tab 24, close. Now I have a lot more lines to work with, so I'll continue aligning things up here. I want the gridlines over here to be parallel to the windowpane which looks good and over here which does not look so good. So I'm going to adjust this bottom edge a little bit.

You see how the planar surface controls the planar grid? Okay, I want this top edge up here to be parallel with the building. So I'll pull this down here and then scooch this down, so that's nice and even up there. I want to get it even with this fence railing. So I'll drop that down there a tiny bit. Rechecking my right grid, I need to tuck that up a little bit, so I'll move that up tiny amount.

Rechecking my left, I'll need to tune that up a little bit. Okay, let's say that's good and now we'll Play. Now most clips are going to have lens distortion and it will be most notorious in the corners. Watch what happens here, see how the grid is slipping in this part of the picture. It's not that the tracking data is slipping. It's that the picture is warped. This tracking data is correct for the sweet spot here in the middle of the frame, so the image is actually bending underneath the tracking data.

So let's see what kind of a problem that will create. Let's say I want to put a roto on this window and I want to use this tracking data. Let's watch what happens. I'll turn off the Planer Grid and the Planar Surface. I'll hide my windows track spline. Push in here, move over, and I'll pick any frame that gives me the best view of my target. I'll get my X spline, I'll just draw a real quick thing here.

No great precision, pull the corners sharp, select all of these, bring in the edges a little bit to make them nice and round, relaxing the tension. Okay, let's say we like that and we're going to name this spline left window. Now right now, it's not connected to any tracker and you notice it has the cog turned on. So I'm going to come down to Link to track, do the pop up and say connect this to the windows track.

Notice it jumped a little bit. Now if I play it, you'll see it's drifting off especially at the bottom of the frame. So this spline is linked to tracking data that doesn't track the warped art of the picture. So I'm going to need to do a new track. I'll jump to the first frame, I'm going to hide my left window spline for a moment. Come down here to get a better look. Again, I can go to any frame that gets me the best view of my target for tracking.

So I am just going to draw a real quick and dirty tracking spline here. Now before I do anything I'm going to rename it. So I'm going to call this the left window track. Okay, I'm ready to track, but before I begin, I need to check over here. See these cogs? If the cog is turned on that means when you start doing the tracking that shape will be tracked. The problem is the windows track is already tracked.

I do not want to re-track it, for two reasons, I want to turn this off. one, I don't want to destroy my tracking data and two, the system slows down, because now it's tracking two different splines, or three, or four, however many you have turned on. So you have to get into the habit of turning off the cogs and turn on the cog for only the one spline you want to track at the moment. All right! So, cogs are set, spline is drawn, this is my start point so I'll track forward from here and the tracker will follow the image even though it's got lens warp in it.

Once the tracking is done, I'll pull the playhead back to where I started then I'll track backwards to get the front part of the picture. Okay, tracking is all done. We'll play that and say hmm, that looks good. All right, we'll stop that. I'll scrub to a convenient frame that gives me my gives me my best view of the target. So I'll turn on the Planar Surface. So I'll set my Planar Surface in order to check the quality of my track.

Make sure I am happening here. Now my problem is the corner that I would like to put my Planar Surface on over here is actually out of frame. So I can use the Planar Grid, I'll turn on the Planar Grid and make sure that the plane grid lines up okay, and I'll see, I'm off over here. So now I can use the Planar Grid to help line up my Planar Surface.

Okay, now the Planar Surface and the planar grid are locked to the window, let's play that and see if it all looks good. You bet, I'm tracking on this part of picture. So this part of the grid is slipping and sliding, because this area is not warped. All right, fine. We are done with that, we'll stop, jump to the first frame and home the viewer. I'm now ready to attach the left window roto to my new left window tracking data. So I'll turn off the Planar Grid and the Planar Surface.

I'll hide my window track. I'll open up my left window spline. Again this guy was attached to the other tracking data and of course it's slipping and sliding as you can see right here, let me push it on that to get you a better view. You can see how it's slipping and sliding right there okay, because again this part of the picture has got lens distortion, but the tracking was done over here in the sweet part the lens. All right, what I'm going to do is I'm going to switch this roto from the windows track to the left window track, very simple.

The left window spline is selected. I'll come down to Link to track pop up, and I'll select the left window track and the spline jumps into place. And now it's beautifully locked to this part of the picture, because the tracking data is now tracked on the warped part of picture. All right, we'll stop that and hold the viewer. So use the Planar Grid to confirm your tracking data and even to help you line up the Planar Surface when you need to.

Show transcript

This video is part of

Image for mocha 2.6 Essential Training
mocha 2.6 Essential Training

49 video lessons · 7736 viewers

Steve Wright
Author

 
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  1. 5m 23s
    1. Welcome
      1m 40s
    2. Getting to know the user interface
      3m 43s
  2. 1h 7m
    1. Drawing X-splines
      8m 2s
    2. Drawing B-splines
      5m 4s
    3. Editing splines
      3m 52s
    4. Keyframing splines
      6m 33s
    5. Discovering the timeline controls
      5m 52s
    6. Walking through the New Project window
      4m 23s
    7. Working with interlaced clips
      8m 19s
    8. Setting the color space
      4m 46s
    9. Defining mocha preferences
      3m 46s
    10. Walking through the Layer Control panel
      3m 22s
    11. Walking through the Layer Properties panel
      3m 29s
    12. Viewing mattes
      3m 41s
    13. Walking through the Edge Properties panel
      6m 24s
  3. 1h 8m
    1. A planar tracking demo
      6m 36s
    2. Setting motion options
      13m 12s
    3. Adjusting the tracking spline
      8m 51s
    4. Tracking awkward surfaces
      6m 3s
    5. Understanding the planar grid
      6m 50s
    6. Dealing with lens distortion
      7m 43s
    7. An AdjustTrack demo
      5m 49s
    8. Keyframing the AdjustTrack
      7m 48s
    9. Offsetting reference points
      5m 49s
  4. 1h 8m
    1. Strategizing shape distribution
      11m 21s
    2. Working with large areas
      2m 44s
    3. Selecting a start frame
      10m 38s
    4. Replacing a shape
      2m 54s
    5. Keyframing: Bifurcation
      4m 38s
    6. Keyframing: Straight ahead
      5m 17s
    7. Keyframing: Extremes
      9m 22s
    8. Keyframing: Maximum digression
      6m 45s
    9. Converting to stereo
      2m 54s
    10. Inspecting your rotos
      4m 43s
    11. Rendering mattes
      4m 45s
    12. Exporting shapes
      2m 54s
  5. 1h 30m
    1. Moving the camera with parallax
      5m 30s
    2. Moving the camera without parallax
      3m 58s
    3. Using multiple splines in a layer
      7m 23s
    4. Subtracting shapes
      7m 6s
    5. Stabilizing the viewer
      5m 46s
    6. Keyframing during tracking
      7m 24s
    7. Unlinking the tracker
      5m 8s
    8. Tracking manually
      12m 35s
    9. Defining corner pinning
      5m 4s
    10. Going further into the Track tab
      6m 53s
    11. Utilizing the more advanced AdjustTrack features
      8m 40s
    12. Working with the Stabilize tab
      6m 11s
    13. Exporting track data
      8m 53s

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