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It is indeed about a good 20 minutes later, and I'm going to set my Roto Brush effect and type PP and show you that I've made 173 strokes total to define from my Base Frame back to time zero (x0). So I don't want you to be under any illusions that this is a automated process. Roto Brush greatly reduces the amount of work you need to do but you still need to do some work. Saving the Propagation parameters early on will help reduce that amount of work. And now as I drag my time indicator, through my timeline, you can see I have set up a propagation boundary for all these frames.
Tricky areas was in here where his little finger is moving inside the shadows of his hand, a little gap here, managing the gap here between the thumb, the laptop and the shirt sleeve but I worked my way through all those frames. Now let's go back to the Base Frame and think about propagating forward in time. I want to see how far this Base Frame provides good information going forward making corrective strokes as I go, as close to the Base Frame as I can, propagating outward and then see if I might need to create another Base Frame with an entirely separate Roto Brush Span later in time to join up with this one.
We'll go one frame forward. Actually, it looks pretty good. Another frame forward. Good. Another frame forward, things are going much better propagating forward than they were backward. That's why I chose the Base Frame that I did. In subsequent frames, we actually see less of the foreground than we're worried about; his arm blocks his hand, his hands close up where the gaps between his fingers close up and there's less work away from that Base Frame. I'm going to zoom in here and improve the gap until there.
I'll keep moving forward. Now we need some Roto Brush corrective work to improve these gaps. Again, I'm just making a centerline here. And subtract around this thumb tip there. A little bit of the keyboard here. In general, not bad. And keep stepping forward in fixing these little problems from frame to frame. Now I am searching around to the entire segmentation boundary, every frame and making corrective strokes.
But you could choose to a divide and conquer, maybe do one pass working in just the left side, go back to Base Frame then make another pass just working on the right side. This isn't too bad though. A little bit of the keyboard here. Less critical through here where we're not actually over the screen. The viewer's attention probably won't be down here. I'm just trying to keep a consistent line so that any matte line between my Roto Brushed foreground and the untouched background isn't too obvious.
Press Page Down or the number 2 to step forward and continue to make corrective strokes. Up a little bit of these fingers appearing underneath here. Let's make sure we grab that. Take out some on the keyboard and a little bit there. I know some of you will probably find it instructive to watch me go through every frame of the shot and see what it is I'm looking for.
I'm sure others of you are probably going to get bored stiff watching me go through every single frame. So there will come a point here soon enough, that I'm going to go ahead and just cut the video, finish the rest of the shot and then move forward to my next important technique to discuss. Basically, when do you give up one span and start creating the second span. It's several minutes later and I have been propagating strokes away from my Base Frame in the direction of the Roto Brush Span arrows and I'm getting to a point where I see some major changes in motion.
These few frames are indeed being tracked pretty well by Roto Brush but I see that I have his left hand raising. I'm starting to see some gaps open up between the fingers of his hand. Indeed, I need to zoom in here and do another background stroke in this gap that's opening up between his fingers. From this frame forward, I see I'm getting significant movement and Roto Brush is missing information as gaps open up. I could keep making corrective strokes and propagating that information forward but at some point when you find yourself making major changes on every frame, you have to ask yourself, "Is more of the foreground being revealed? Is that why Roto Brush is having trouble? Would I be better off picking a new Base Frame later in time and propagating that information back to join this one?" And indeed in this shot, since he is raising his hands, I think I would go to a new pose somewhere around here where his hands are the most open and I've got a clear shot defining the gaps between his fingers and start a brand new Base Frame there.
So I would back up my Roto Brush Span back to around 0:00:01:27, my last good frame of my previous look, which is right around there, then move to here and start all over, again, larger brush and defining a new Base Frame. You'll see that Roto Brush has created a brand new yellow dash for my base and a new propagation span going forward in time and going back to join my previous span.
You might think you'd have a lot of trouble around that boundary but if you've done your job of defining foreground and background strokes, Roto Brush is using the same algorithms underneath the hood and you actually get a really good seam right in that area. So to really finish this shot off, you'd indeed want to create as many spans as necessary to pick different points in time as his hands open and close. For now I'm just going to go ahead and go back to this last good propagation frame at 0:00:01:27, press N to end my work area at this point and focus on getting a good look through here and then you can repeat the same concepts later on throughout the shot.
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