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After Effects CS6 New Features
Illustration by John Hersey

Exploring the Rolling Shutter Repair effect


From:

After Effects CS6 New Features

with Chris Meyer

Video: Exploring the Rolling Shutter Repair effect

Another nice addition to After Effects CS6 is a Rolling Shutter Repair effect. Rolling shutter is an artifact caused by CMOS sensors in cameras, where the top of the image is scanned earlier in time than the bottom of the image. If there is any motion inside this image, you may notice some leaning or other skewing or distortion in the shot, because different areas were taken at different points in time, and therefore those pixels were in different positions. Well, let's look at a few cases where Rolling Shutter repair can fix this and frankly, not fix it.

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After Effects CS6 New Features
2h 13m Appropriate for all Apr 11, 2012

Viewers: in countries Watching now:

Get up to speed quickly with the new features in After Effects CS6. Join veteran After Effects user Chris Meyer as he explores the key enhancements to this industry standard visual effects and motion graphics software. Chris shares creative ideas and important production advice while covering the strengths of features such as memory optimization with the new global performance cache, 3D motion tracking with the 3D Camera Tracker, and the new 3D rendering engine for ray-traced 3D rendering.

Topics include:
  • Understanding the global performance cache
  • Using ray-traced rendering with beveling and extrusion
  • Working with 3D Camera Tracker
  • Performing rolling shutter repairs
  • Adding variable mask feathering
  • Working with CycoreFX HD plug-in
  • Touring Imagineer Systems mocha AE and Adobe SpeedGrade
  • Round-tripping between After Effects and MAXON CINEMA 4D
Subject:
Video
Software:
After Effects
Author:
Chris Meyer

Exploring the Rolling Shutter Repair effect

Another nice addition to After Effects CS6 is a Rolling Shutter Repair effect. Rolling shutter is an artifact caused by CMOS sensors in cameras, where the top of the image is scanned earlier in time than the bottom of the image. If there is any motion inside this image, you may notice some leaning or other skewing or distortion in the shot, because different areas were taken at different points in time, and therefore those pixels were in different positions. Well, let's look at a few cases where Rolling Shutter repair can fix this and frankly, not fix it.

If you have access to the exercise files that came with this video training, open up the Rolling Shutter Repair folder inside your exercise files, then open up the project Rolling Shutter CS6. We have three different examples. Let's start with Rolling Shutter 1 - hand held because this is the most obvious case and the one where Rolling Shutter helps perhaps most. Here is a handheld shot of the building. This could have been shot with a DSLR, a cell phone, et cetera. There's no tripod, steady camera, otherwise good support. You might mind notice, particularly around this marker 1, that this building appears to change in size from frame to frame. It stretches, it squashes; it stretches, it squashes. Unless it's a rubber building in earthquake country, that's not supposed to happen.

Let's go down here to marker 2 as well, and you will see difference between that frame and the frame after. You have a bit of leaning in addition to a stretch going on between those two frames. Let's select our footage and apply Effect > Distort > Rolling Shutter Repair. If you can't remember it's in there, you can always use the Effects and Presets panel to search for it. I will select the effect and you will notice that building straighten up a little bit. Let's compare those frames. Next frame, earlier frame. Better, but still a little bit of stretching. That's the case where you want to go to the Rolling Shutter Ray parameter inside of this effect.

Increase it a little bit. I'm going to go up to around 90, 95 for now. Then we compare your frames. Now this building is holding its shape much better. I will go back to marker 1, look at before, and step through this point, and that's pretty good, a little bit of stretch to the bottom. Let's see if we backed it off a little bit to be may be the 80 area. That's holding up a bit better. So what you would do is try out different rates-- 50 to 70 is common for DSLRs, 100 is what you are going to need for cell phones--until your objects hold their shape from frame to frame.

Again, this is before, where you are really seeing some strange stretching going on, and after. And with a little bit of tweaking, I could get that even better. Speaking of tweaking, there's not a lot of parameters in the Rolling Shutter Repair effect. There's Scan Direction. Most sensors scan from the top to the bottom, but if you have some footage that's been rotated ahead of time or a different type of sensor in a particular camera or a cell phone, you can go ahead and try out these different options till you find one that works. And also two different methods: Warp or Pixel Motion.

Where you have this scene that's planar like this is, Warp works fine and frankly renders faster as well. However, if you have what they refer to as local motion in the shot, say a person or object moving by the screen in a different direction than the rest of the actions happening in the shot, or maybe something like a panning shot where you have got a lot of parallax objects that are close and objects that are far away, moving at different rates, that's where you might want to use Pixel Motion. Warp is a good default. If you are noticing some tearing or other problems you can go to Detailed Analysis, which takes a little bit longer but might give you a better result.

And in the case of Pixel Motion, it has a parameter for Pixel Motion Detail. How detailed was the vector field where it's trying to determine the motion in the shot? Higher numbers give a more detailed analysis but also take a lot longer to render. I will step a frame at a time here. And I can see this is taking much longer to render. Although the building is holding up pretty good here with Pixel Motion, that has actually, I think, an even better result than we are getting with Warp. So if you have the render time, you can try that alternative.

Anyway, Rolling Shutter Repair is great for handheld shots, but let's look at another common example. I will go to Project panel and open up Rolling Shutter 2 pan. This is the case of the camera that has been mounted on a tripod and is going through panning motion. Initially, things look okay; however, these windows, which are nice squares, and this is pole to the right, which is nice and vertical, they are supposed to stay that way throughout the whole shot. But as the pan picks up speed, you will notice that these windows really start leaning. I mean we have a little bit lens distortion going on here, but that's quite a bit.

And all these poles are leaning to the right. What's going on with the CMOS sensor is, again, the lines up here are earlier in time than the lines down here. As this building moves from the right to the left, the lines further down the frame are going to be further to the left. That's why you have this leaning. Well, let's select our footage and apply Rolling Shutter Repair, and you will see building straightens up. Before and after. I might further increase the rate here, till I get things to stand up a little bit better. Somewhere around there seems to work nicely for this shot. Before and after.

Now if I had to do something such as composite something into the walls or windows of this building, it's going be much easier to do it to objects that actually keep their corrected dimension compared to object which have an artificial lean during the middle of the shot. And that's why we are covering Rolling Shutter Repair here in the visual effects portion of this course. It's really a pre-processing you might want to do shots before you need to perform visual effects, such as adding things to the scene. Okay, let's look at the third example that on the surface you think should work fine but in reality, doesn't. I have a camera mounted on a tripod. No panning, no motion, no shaky cam.

I have a car driving by actually rather slowly in the scene. It seems like a pretty easy shot; it should be easy to repair. But since I'm familiar with this car, I do know that in reality, its front grill doesn't slope that far back. I also know that its wheels are supposed to be round, and you can tell that these wheels are leaning quite a bit. They have a bit of shape to them. Also, the spokes inside those wheels are supposed to be straight, not have these little bends to them. Well, let's select the footage and apply Rolling Shutter Repair.

And at first, it is seems like the car does stand up better, and I can make it stand up even straighter, somewhere around there. But however, notice not only the car is straightened up, the trees have been bent as well. This is before and after. Before and after. You note that the trees are bending, and you notice that the asphalt is moving, and also that is getting softer. Before after. So what Rolling Shutter Repair is doing in this case in Warp mode is it's warping the entire frame based on the motion of just the car, but in reality it should only be warping a portion of the frame, just where the car is.

Well, initially you might think, that sounds like a job for Pixel Motion, since it's supposed to deal with local motion in the shot. Well, it seemed like this has a little bit too strong of motion, even for Pixel Motion. I will go ahead and apply this and you will notice that things get further straightened out. The wheels are a bit better. But as I turn this off and on, watch what's happening to the road in particular. Before and after. Before and after. Some of the scene, like this portion of the trees, are staying where they are suppose to, but other portions of the scene, such as the trees right above the back of the car here and the asphalt right underneath the car, are moving, whereas rest of the scene is stationary.

I will turn the effect on and RAM Preview this, take a moment to calculate. But even during this preview, you can see that these waves of distortion are going through the shot, and this would just not be acceptable. And here's the playback. No good. Now in a case like this, you can try increasing Motion Detail and that might help. Go up to 100% here. It takes longer to render. The wheels look even better than they did before. This before and after.

But you will a segment of this roadway is still moving along with the car. Even though less of the trees are moving, we saw a bit of shrubbery behind the car moving as well. So this is a case where you might just have to live with shot the way it is. And frankly, it's not all that bad way it is. Don't start throwing Rolling Shutter Repair on every single shot from a DSLR or a cell phone. It may do more harm than good. However, for some shots, particularly handheld shots, but also things such as a nice tripod pan, it will indeed improve the production value for shots and make it easier for you to integrate other things into these scenes.

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