3 Replies Latest reply on Jan 4, 2016 6:38 AM by Rick Gerard

    Candle Fire - Motion Tracker problem

    jacobo_friso Level 1

      Hello guys I need your help with one specific shot in my movie ... In the shot is moving candle that we recorded not lit up so we can add fire, smoke and wick of a candle in postproduction. But I came to a problem in After Effects, the motion tracker doesnt track the movement of a candle correctly and the mask (fire, smoke and wick of a candle) that I parented to the null object later on wiggles around pretty visibly. Is there any way that I can track the movement better? I tried many methods but they didnt worked ...

       

      link to problematic footage

      https://www.dropbox.com/s/87l9jhrm2s...0shot.mp4?dl=0

        • 1. Re: Candle Fire - Motion Tracker problem
          Rick Gerard Adobe Community Professional & MVP

          I don't think that tracking is the biggest problem with your shot. You might not have to do as much correction to the track if you used a bigger target. The thing that makes it look fake is that the flame doesn't react to the movement of the candle and it doesn't blend with the background as a real flame would. The flame would bend as the candle is moved into the shot because of air resistance. you could fix the blending problem by trying the Add or Screen blend mode for the flame and working the project in 32 bit. You may need to duplicate the flame layer to get the blend working properly. There is also a change in the scale of the candle due to the changing distance from the camera. Single point tracking would not add that scale change to the flame. There is also no glow from the flame on the top of the candle. When a candle burns the tip of the wick is also glowing red (white in in your shot). That's a subtle thing but it should be there. I just don't think there was enough thought put into the composite. It takes a lot of elements to sell something as simple as a candle flame. It looks to me like you just did some tracking, added a flame and then did some roto work on the thumb. Here's how I probably would have approached that shot.

           

          Rather than track the shot I would have stabilized the shot for rotation and scale and used as big a target as I could. Something like this:
          Screen Shot 2015-12-29 at 3.15.51 AM.png

          If I were going to track the shot my tracking target would probably be even bigger than the top box and include the top and bottom curvy lines in the candle. If I were to just track the shot I would also try and track scale and rotation.

           

          After stabilizing the shot I would have checked the position, made any adjustments, necessary by adding nulls like this:

          Screen Shot 2015-12-29 at 3.55.38 AM.png

          Then I would have used mesh warp to bend the flame as the candle moves and then removed the stabilization and added the motion back to the flame using this animation preset. You could do the same thing with tracking but it's harder to see errors when tracking than it is when stabilizing. Here's an animation preset that I use all the time to remove stabilization and add the motion to the added elements. All you have to do is name your footage layer "stabilized" apply the preset to a null layer and then parent the footage and the added elements to the null. Dropbox - destabilize Rotation Scale.ffx

           

          My final composite would also have included a glow on the top of the candle and some light effects on the fingers as they put out the flame. I'm guessing the final composite would have the following layers:

          1. Destabilize Null
          2. Modified thumb roto as track matte for
          3. Glow for the thumb
          4. Thumb roto
          5. Flame with distortion using Screen Blend mode (duplicate if necessary)
          6. Thumb roto as track matte for
          7. Finger glow
          8. Candle top roto for track matte to keep candle glow from bleeding onto background
          9. Glow for candle top
          10. Glowing tip for wick
          11. Footage

          All of those layers would be parented to the destabilize null to put the motion back into the shot.

           

          You could also have tracked the candle in Mocha and carefully analyzed the position scale and rotation there, then used that track to position the flame on the candle. From the quick test that I did with the footage AE's Stabilize Motion tool would do the job in just a few minutes.

           

          I'm assuming that the camera original was in color and not an MP4. It's very important to use the original footage or a 10 bit or better digital intermediate for tracking. You want as much detail in the shot as you can get. If I were shooting this shot I would have made absolutely sure that the candle was in focus or at least racked into focus because it's very difficult to track something that is out of focus and has compression artifacts and noise in the shot. Remember that for next time. I would have also shot a reference frame on location with the candle burning so I would have something to work from when doing the composite.

          • 2. Re: Candle Fire - Motion Tracker problem
            jacobo_friso Level 1

            Hello Rick, first of all thank you so much for your help


            I did the tracking and I think it ended up well. But I can came to another problem ... Can you please help me by telling me how can I create (simulate) glow of the candle on the the hand and thumbs which put out the fire of candle? I did rotobrush of hand but  I dont know how do I have to combine different layer blends to achieve the look ...

            Please how would you approach this problem?

             

            Link to problematic footage:

            Dropbox - Sequence.mov

             

             

             

            Sending pictures of my composition and different layers i hope that will help you. If you will need any more informatiom just tell me ...

             

            Raw Comp

            Raw comp.jpg

            Comp with added layers

            Edited comp.jpg

            Different layers

            Layers.jpg

            Hand that needs to be rotobrushed (i didnt add roto yet because i want to know how will I make hand glow with mask)

            Rotobrush.jpg

            • 3. Re: Candle Fire - Motion Tracker problem
              Rick Gerard Adobe Community Professional & MVP

              I would add a white shape layer between the flame layer and the finger layer, then add some blur to the shape layer and change the blend mode to ADD. You will probably also have to rotoscope the entire hand to put it on a separate layer. I gave you a list of the minimum layers that would be required in the previous post. This footage will probably require a fair amount of hand roto.

               

              1. Destabilize Null
              2. Modified thumb roto as track matte for
              3. Glow for the thumb
              4. Thumb roto
              5. Flame with distortion using Screen Blend mode (duplicate if necessary)
              6. Thumb roto as track matte for
              7. Finger glow
              8. Candle top roto for track matte to keep candle glow from bleeding onto background
              9. Glow for candle top
              10. Glowing tip for wick
              11. Footage