[Class Assembling]
Hi, John Hess here and today I'm going to demonstrate how to create digital slit scan video using Adobe After Effects.
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 Displacement 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.
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.
I'm John Hess, I'll see you at Filmmaker IQ.com