10 Replies Latest reply on Mar 16, 2011 6:07 AM by JesseHarris

    Stabilizing a dolly/tracking shot

    D_Watts

      Hi,

       

      I have a shot I filmed in a studio environment - the camera was on a skateboard tracking into the action like so:

      track.jpg

       

      The problem is that the movement bumps at several points. I've tried the standard stabilize tracker (position/rotation), using the base of the chairs as tracking points - it stabilizes the image a bit but it also ends up zooming into the left side chair. Is there a particular technique to stabilizing such a shot except manually adjusting for each bump?

       

      Thanks,

      David

        • 1. Re: Stabilizing a dolly/tracking shot
          Mylenium Most Valuable Participant

          mochaAE. Comes free with AE ever since CS4. There's enough "planes" in your image to feed its planar algorithm with stable references. You should be able to get a stable track using AE's tracker just as well, you just may have picked the wrong reference points. Ratehr than the feet of the chairs, use more constant points liek the intersections of the BG/ floor line with the table's pillar and the chair supports.

           

          Mylenium

          1 person found this helpful
          • 2. Re: Stabilizing a dolly/tracking shot
            D_Watts Level 1

            My problem wasn't that I was lacking a stable track, but that it was trying to correct it by gradually moving the image across to the left. I tried Mocha and reversed the track (using the anchor point/adding a rotation*-1 expresion to the rotation value) and it did the same. I've just had to manually adjust for the drift.

            • 3. Re: Stabilizing a dolly/tracking shot
              JesseHarris Level 1

              Hi,

               

              I asked a very similar question on this forum a few days ago and it was never addressed, much less answered.  I have a camera tilt and dolly-in and I need to stabilize some bobbles ie; unwanted camera movement with in the desired camera move.  How can I accomplish this stabilization/smoothing of the motion?

              • 4. Re: Stabilizing a dolly/tracking shot
                bogiesan-xSdJwH

                I've never used Mocha, never had to. Every stabilization project I've pushed through the standard tools in AE has worked beyond my expectations and I've had some truly awful work in Betacam, DV and 720 to correct. Wish I had something better to offer you guys but without seeing what you're up to, I cannot imagine why the basic trackers are not satisfying your needs.

                 

                Thanks for posting your suggestion of using expression values, sorry that didn't work.

                 

                bogiesan

                • 5. Re: Stabilizing a dolly/tracking shot
                  richiericardo

                  hmmm, tricky one.  Just my opinion but theres not anything particular in your shot that i'd say was ideal for tracking.  Tracking the corners of the chair bases not necessarily best as they are round, and are 3D shapes rather than 2d track points and your camera movement over the shot is changing the perspective.

                   

                  Also you can't rely on any points that are where two areas cross in different depths due to the parallax.

                   

                  For tracking a 2 point track you want the points to be as far apart as possible to reduce rotation jitter, so ideally two tracking markers on the back curtain would have been ideal but never mind.  You could try maybe increase the contrast of the shot to bring out the detail in the back curtain.  Theres a few creases on it on the left hand side, and if you make the search region big enough after effects may track it.  The right side looks abit trickier as theres less definition.

                   

                  Long shot but maybe worth a try.  I once had a shot similar to this and got it working this way, however i had to track it in small sections and you have to watch to make sure theres no movement in the curtain creases.

                  1 person found this helpful
                  • 6. Re: Stabilizing a dolly/tracking shot
                    D_Watts Level 1

                    Jesse, I'm having hard time visualising the shot, could you post a couple screenshots from various points of the move? Maybe I can try to help.

                     

                     

                    Also thanks for the other replies, Mocha did a decent job of tracking where the chair pushes against the curtain (not ideal due to parralax, but it's only to remove the bumps in the footage). Though the built in AE tracker did a decent job of it too, but both produced an awkward effect that pulled the image across to the left:

                    Untitled-1.jpg

                    Maybe it was because of the parralax effect or something. I used the anchor point and rotation values from the Mocha track so I just keyframed the position to correct for it, after a bit of work it seemed to smooth out the shot.

                     

                    Markers would have been ideal but we only used them for handheld shots, I didn't think to use them on the dolly (an misjudgement of mine thinking that it would be smooth).

                    • 7. Re: Stabilizing a dolly/tracking shot
                      JesseHarris Level 1

                      DW,

                       

                      Thanks very much for replying.  I have a somewhat different shot, but with many similarities.  I hope you'll be able to view the vimeo clip I'm posting.  This clip is a RAM preview render of a small section of my camera move.  It's a tilt down from the top of the building.  About halfway through this clip you'll see a jump, a bobble, where the camera was evidently jolted somehow. 

                       

                      I'd like to maintain my smooth tilt...  When I apply standard stabilization, on the lights under the overhang, AE tries to nullify my beautiful slow tilt...  Am I missing something very obvious?  I am a little inexperienced with Motion Tracking, is this a case where I need to manually set points?  And how would I do that to maintain the tilt down?

                       

                      http://vimeo.com/21097215

                       

                      Thanks again for taking an interest!

                      • 8. Re: Stabilizing a dolly/tracking shot
                        richiericardo Level 1

                        Basically a stabilize does exactly that, it removes all movement from the shot, by shifting the frame in the opposite direction.

                         

                        So by doing a stabilize on your shot you'd end up with a static image (if the stabilize worked perfectly).  Essentially what you need to do is stabilize the shot to remove all the jitter and movement, then track the shot and match the move back on.

                         

                        This would (in an ideal track situation) give you the same result as you started with, however your camera moves is now animated with the tracking data.  You just need to go into the keyframes and either smooth out or find the keyframes with the bump and move them about to elimate the shake.

                         

                        This would work best normally if this was only a pan, or a pan and zoom.  However since yours is a tilt as well then it makes it alot more tricky as your dealing with 4 point tracks + the perspective shift.

                         

                        - Hope that makes sense am not always very good at explaining myself.

                         

                        ** A solution for your shot which i'd try first tho is this:

                         

                        Your shot is timelapse right, and since the jolt is only on 1 or two frames, why not go in and adjust those couple of frames individually?  Shift them up down a little bit to compensate for the bump on just those frames.

                         

                        Without trying it myself, i can't say for certain whether it would def work but worth trying, its easier than stabilizing then tracking the move back on

                        • 9. Re: Stabilizing a dolly/tracking shot
                          D_Watts Level 1

                          I think Richie might be right - since it's a timelapse and it only seems to affect 1-3 frames it might be more accurate to do it manually.

                           

                          Here's how I would do it - in Photoshop load up the frame before the jolt, all the frames during it, and the one afterwards - layer them over eachother and make each one slightly transparent. Then try to get an even spacing between the first and last frame, which should maintain the smooth pan and sort out any jolt. Then import back into AE.

                           

                          Hope that makes sense. The alternative is to track the lights with Mocha, copy the transform data to a null object, disable everything except the "Anchor point" and "Rotation" (incase the jolt rotates the camera too) - that should give you a steady shot. You'd have to add in the smooth camera move again though.

                           

                          I'd still opt for the manual method though, because it would give you much more control.

                          • 10. Re: Stabilizing a dolly/tracking shot
                            JesseHarris Level 1

                            RR, DW,

                             

                            Thanks a lot!  Seems like I'll be able to make something work from your ideas.  Frustratingly, I've been diverted by another project, but I'll get back to the time lapse work and let you know how I manage.

                             

                            Thanks again!