8 Replies Latest reply on Jun 12, 2008 8:23 AM by Navarro Parker

    Automatic motion tracker dot removal?

    Navarro Parker Level 3
      I recently did some motion tracking with Mocha for a shoot. Mocha is awesome, by the way.

      Anywho, I had placed some red markers on my green screen for improved motion tracking. I had seen some behind-the-scene footage for Lord of the Rings and I noticed they used red and green markers on of their blue screen elements. It's makes sense that red and green are two of the RGB primaries so they should be easy to remove. However, I ran in to trouble because this was shot on XDCAM EX which has 4:2:0 color sampling as well as some heavy compression (35Mbit/sec VBR for 1080p). The red markers smeared into orange around the borders. So when I tried to do a replace color or color key on the red, I was left with an orange halo -- expanding the color tolerance started to affect the color of the actors. Unfortunately, their hair often passed in front of the markers, which made masking out the markers impossible. In the end, I had to manually roto paint way too many frames in order to remove the markers completely.

      Do you have any tips for automatically removing markers from a green screen?
        • 1. Re: Automatic motion tracker dot removal?
          Level 1
          100% automatic - no

          I usually run two instances of a keyer, one for the actors and one for the markers, then screen the masks together. If the camera is moving there are almost always instances when you must do a little roto by hand to clean up a few frames here and there.
          • 2. Re: Automatic motion tracker dot removal?
            Navarro Parker Level 3
            Rick -- Do you run into the same color sampling halos around your markers? How do you get rid of them with a keyer?
            • 3. Re: Automatic motion tracker dot removal?
              Level 1
              A complete step by step won't fit in a single post but the basic procedure using Keylight would be something like this.

              1. Duplicate your green screen footage 3 times.
              2. Apply Keylight to the top two layers then solo the top layer.
              3. Adjust Keylight for the top layer to create the best key you can for the green background. You may need to add garbage mattes. View the combined matte, not the final result.
              4. Solo the second layer and adjust Keylight to remove the red trackers. Make the best key that you can. You may or may not need garbage mattes. Again, select combined matte and not final result.
              5. Pre-compose the top two layers, open the pre-comp and set the blend mode to the top layer to multiply or apply invert to both layers and set the blend mode to screen. Add an adjustment layer with either levels or curves above the two to adjust the matte. You'll want the best black and white matte you can get here. Don't worry if it infringes on the actors a bit as the tracking marks move behind the actors.
              6. Back in your main comp use the pre-comp as a luma matte for the bottom copy of your footage and check the key. If you need to do a little roto to fix some edges, duplicate the footage again and use the mask tool to fix the areas that need to be fixed. on the bottom copy of the footage.

              I hope this helps. What you are trying to do is combine the mattes for two different colors, clean them up with masks, and then add in your background and do the color matching.

              If you can post a still frame, and I get some time in the next few days I'll build you a sample comp with CS3.
              • 4. Re: Automatic motion tracker dot removal?
                Navarro Parker Level 3
                Consider it done! I really appreciate your help!


                The Red Dots are for motion tracking. The blue dots are for corner pinning (they are the corners of the obscured screen)
                • 5. Re: Automatic motion tracker dot removal?
                  Level 1
                  If you had anything to do with the shooting of this footage there are a few things that you can learn right off the top. When you have great corners as you do in this example, there's no need for tracking marks.

                  Secondly, If the cameras are moving it's going to be moving you're going to need more than AE's simple tracker to corner pin video into frames that are partially offscreen.

                  Thirdly, if you have to use tracking marks make sure that they are not the same basic color as primary elements on your set. In this case, the red is almost the same color as a bunch of the set so you have to resort to garbage mattes to clean up the marks.

                  I've attached a quick project that shows the technique. I simply keyed out the blue dots, the red dots, and the green, then multiplied their mattes and used that comp as a luma track matte for the original. Keylight has a fairly good spill removal tool so I also used keylight as a spill removal tool in the master comp.

                  Hope this helps.

                  You'll find the project file here.
                  • 6. Re: Automatic motion tracker dot removal?
                    Navarro Parker Level 3
                    Thanks Rick! I really appreciate it! Interesting method of multiplying Keylight's Combined Matte function. (I haven't played around with any function except Screen Matte and Status when building a key)

                    Yeah, I used Mocha for the tracking (which is just incredible!). I wouldn't have dreamed of doing it with AE's tracker! I added the tracking markers because the camera was often zooming into the screen where there was nothing but solid green. I felt the markers would help Mocha keep track of the zoom -- which it did.

                    Next time, I'll use all blue dots if the set is warmly lit like this one.
                    • 7. Re: Automatic motion tracker dot removal?
                      Level 1
                      All you needed was the corners of the frame. Also, dots don't track as well as squares or + shapes.