4 Replies Latest reply on Jul 21, 2008 11:09 AM by Mylenium

    Need understanding bout Auto trace function

      hi.. ive problems understanding the real purpose of auto trace.. im actually new to AE.. i can understand keying out the background.. but what if i want to key out a background which is not the empty blue/green matte.. is auto trace the right tool to use? if yes.. how? tq in advance
        • 1. Re: Need understanding bout Auto trace function
          Dan Jacobsen Level 1
          auto trace automatically draws a mask around an area. this area can be defined by luminance, red, green, blue or alpha.

          this is useful if you need to edit a shape that is based on an area in a frame.

          for example, you can use auto trace on a line of text to change it into a few masks on a white solid. you can then pull vertices out to give it a distorted look. Set the channel to alpha for this.

          or set the channel to luminance to let it draw around a lighter part of of screen, perhaps the sky, and generate a mask for the sky. because it's then a mask you can tweak it or animate it

          it's probably not what you're after. it sounds like you need to cut something out that isn't a different colour or lum to the bgnd.

          what is it exactly? maybe you need to rota scope it. which is manually drwing a mask around an object then animating it manually.

          ps. i love the way colour shows up as a spelling mistake!
          • 2. Re: Need understanding bout Auto trace function
            David Wigforss-Hv1BNN Level 2
            Auto Trace is very similar to using the magic wand in PS and converting the selection to a Path. Actually, I wish they'd bring the wand into AE, it would make things much easier than trying to key out the BG (in order to generate the alpha for Auto Trace).

            I use Auto Trace VERY often. I'm really glad that they upgraded it to bezier curves. Whenever I do highlights in my scenes, I'll trace the object, and then tweak the feather/expansion of the mask. Works really great.

            But like Dan says, you probably need to draw/animate it by hand... You might be able to key out stuff to generate the alpha, but probably not. Much easier with cell animation, with flat colors...
            • 3. Re: Need understanding bout Auto trace function
              David Wigforss-Hv1BNN Level 2
              Actually, I do have one qualm with AutoTrace.. Whenever it generates multiple masks, it seems that they aren't consistant.. One mask 'level' almost never encircles the main object I want to trace for the entire timeline. It seems to dance around to other parts of the object. For example, say I was tracing a house with windows cut out.. Sometimes Mask 1 would cover the house, some frames it moves to inside the windows..

              Anyone know a way of overcoming that? It gets to be hard to figure out which mask keyframes to delete. Cause sometimes I'll delete some, and then my entire mask is messed up. Isn't there an option in prefs to not keep a consistant vertice count? Maybe that'd help. Best solution I've had is to create a garbage mask encircling the stuff I don't want, and re-Auto Tracing it. Sometimes that's not possible and I need to go frame by frame figuring out which mask right.. (I very much like the preference option of generating a new color for each mask. I recommend enabling that!)
              • 4. Re: Need understanding bout Auto trace function
                Mylenium Most Valuable Participant
                Nope, not that I know of. The masks are "intrinsic" based on the actual info in the frame they are generated at. Keeping the vertex count constant would mean that the algorithm itself would need to do sub-pixel motion analysis or tracking of individual knots. I guess that's still the domain of tools like motor or Silhouette. Maybe one day it will come to AE, but probably later than sooner, unfortunately...