If you’ve watched the other video in this course, you learned that slit scan photography was used extensively at the race tracks to determine the winner in close contests. This is because slitscan photography is record not of spatial relationships but of temporal relationships – with lines recorded at different times composing the picture.
Creating these time shifted images can lead to some bizarre and otherworldly visual effects. But how do we get that look in motion pictures? That’s where After Effects comes in. And as you’ll see in a minute, After Effects is capable of creating some slitscan effects that frankly aren’t even possible in the real world.
I’ll assume you’re relatively familiar with After Effects’ interface. Even if you’re not, stick around and you’ll get sense of what this tool can do because it is really worth learning if you want to play with visual effects.
I’ve dropped in some footage of me doing a very slow walk and twist. This was recorded at 60 frames per second. The slowness of the move has been sped up using After Effects’ Time remapping tool. The purpose of this is to give us as many frames to work with because once we start applying the slit scan effect, we’ll need as much temporal resolution as possible to get a smooth result.
The effect we’ll use to create the slitscan can be found under the Effects Menu – Time – Time Displacement. In the effects window we see a few property options- the first is the layer you want to use for the Time Displacement Map.
The displacement map is how you want after effects to assemble the slitscan effect. I like to create my displacement maps, also called a gradient maps, by using Photoshop – jumping over to Photoshop, I created a file that’s the same size as my video and applied a vertical gradient going from black to white.
Now what After Effects does is lay the map on top of the footage and examine the displacement map’s luminance. All the pixels that are white or brighter than 50% gray are displaced FORWARD in time, all the pixels that are black or darker than 50% gray are displaced BACKWARD in time. If you want to imagine an analog to the real world- think of all the pixels that share the same gray value, this is your slit for the slit scan and it moves across the image.
A quick note here… It’s a good idea to create these displacement maps in 16 bit color which gives you thousands of levels of gray to work with rather than the 256 levels of gray with 8 bit color. More gray resolution means you’ll have a smoother animation.
So back into after effects. Let’s make sure we’re working in 16 bit color, although you can leave it 8 bit for speed while you’re working and turn it up to 16 for the final render. I’ll drop my displacement map under the original video and turn off it’s visibility. Next I select this layer which I just added as the Time Displacement Layer in my Time Displacemnt effect.
The next two settings are the maximum amount of time displacement and the Time Resolution. The maximum time displacement is how far ahead and behind you want the pixels to be shifted. The resolution is how many different frames per second you want to use. This is where having a lot of frames to work with will help – if you shot in 24p and had fast motion, you would get a lot of banding as there just aren’t a lot of inbetween frames for this effect to work with. Because I shot 60p and exagerrated the slowness of the motion so I could speed it up later I have a lot of frames to work with to create a smooth result. Just realize that the higher you push the time resolution, the harder your computer has to work to calculate the different frames.
Give it a quick render – and there you have it, the traditional slitscan video effect.
Let’s go Nuts
This is where I see a lot of slitscan tutorials stop. That’s really a shame because we’ve only just scratched the surface of what you can do with this tool and in my opinion the up down displacement map can yield results that are a little predicatble. But you’re not stuck with just one kind of displacement map…
What if you tried a horizontal gradient – this creates some picasso-esque shots that look like they’re shot from multiple angles. Or how about some swirly gradients for some unpredicatable results. You can even use this effect to create tears in the video by using solid blocks of color. Or even create vortices using swirls or circular gradients.
And of course – there’s nothing stopping you from animating your displacement maps for more unpredicatable behavior.
This time displacement effect may not be an everyday tool but it’s a neat way of creating some otherworldly images with sometimes unexpected results. Just remember to shoot as high a frame rate as you can – keep the motion slow for a smoother effect, work in 16 bit color and experiment with different kinds of Time displacement Gradient Maps. You may not use it on every film you make, but it’s another tool to store in the back of your mind while you’re on your quest to make something great.