Exploration Of A Powerful After Effects Filter
by Brian Maffitt, MAFF/x Inc. & Total AE
What's this all about?
First of all, the Gradient Wipe
filter is part of After Effects. All of the techniques in this
tutorial depend on the use of this program.
Many After Effects users have posted
questions online regarding tricky animation needs--needs that
were easily addressed with the use of this filter. Recently
someone needed to animate pulses of light traveling along a
winding roadway. The request drew a wide range of responses,
many of them functional suggestions, but none of them easy to
execute; it became clear that not many people understood the
potential of the Gradient Wipe effect, for it offers the simplest
solution to this particular problem.
I threw the following animation
together in about half an hour. It consists of three Photoshop
pict files, manipulated in AE using only the Gradient Wipe effect.
All of the source files are included in this folder for reference.
Click to play me (164k .mov)
In this brief tutorial we'll examine
the basics of the Gradient Wipe effect. I'll explain how it
works, give some tips for creating effective gradients in Photoshop,
show a few advanced animation techniques, and give you a step-by
step walkthrough of the above sequence. I hope it sparks your
Gradient Wipe Basics
Or, "Yeah, Yeah, I Know all this Stuff, Right?"
Note: This chapter
approaches the Gradient Wipe filter from ground zero. If you
know the general theory behind its operation, you may want to
skip to the next chapter. You will, of course, miss out on my
prose, but suit yourself.
Briefly, the Gradient Wipe uses
a grayscale file to generate an animated transition between
two layers. The pixels of the destination layer replace the
source layer according to the pixel value of the gradient layer.
All right, forget the words. It
takes a thousand of them to describe a picture, so let's just
look at some pictures. This is a visual medium, right?
Let's call this the "A" Layer
and this the "B" Layer
and this handsome fellow
we'll call "Mr. Gradient".
Using the Gradient Wipe filter,
you can create a transition between the A Layer and the B Layer
by using Mr. Gradient as the transition layer. All three of
them need to be present in the comp for this to work.
Hint: The gradient
layer need not be visible--in fact it probably shouldn't be.
Although in most cases you can just hide it at the bottom of
the stack of layers, there are cases when you don't want it
hanging around mucking up your composition, like when you're
animating a tranparent alpha. Click the layer's little "V"
box in the timeline to turn off its video. This works for any
filter that uses another layer as a source of information, such
as the "Displacement Map" filter.
White pixels lead the transition,
followed by successive shades of gray, and finishing up when
the wipe reaches the black pixels. In the case of a simple ramp
like Mr. Gradient here, you get a simple left-right wipe, thus:
Note that the transition has
a soft edge--this is adjustable
via the Gradient Wipe controls.
You can adjust the ease-in ease-out
of this sort of linear transition by varying the midpoint of
the gradient. If you're using Photoshop you can do this within
the Gradient Tool Options palette:
Drag the slider like so.
Your gradients might now look like
The top midpoint's set to about 20%...
And on the bottom it's set to about 80%.
...and if you were to apply this
to layers A and B, your results
would look something like this.
Now of course you can use After
Effects' Linear Wipe effect to do simple left-right transitions.
And yes, you can use AE's ease-in ease-out keyframes to control
the gradient wipe--but here's where things get interesting:
in the example directly above us, a single pict contains two
gradients, one above the other. This means you could have TWO
wipes going on simultaneously -- one easing in and one easing
out -- from the same layer, using ONE effect--Gradient Wipe.
To further illustrate, have a look
at this file:
This started as a linear gradient,
followed by the Polar Coordinates
filter. This wipe would result
in a clockwise radial sweep.
Big whoop. AE already has a radial
wipe effect, right? But add a gradient bar to the top of the
...and something nifty happens.
Now you can radial-wipe an
image on in the bottom area
of the screen while simultaneously
wiping a title on left- right across the top.
Cool, eh? Are the idea lights beginning
to go off yet? In the next chapter we'll look at some more advanced
techniques and some good tricks for making gradient picts. Having
Advanced Gradient Design
Or, "All Roads Lead to Photoshop"
The fun and power of this filter
depend on creative gradient design. Photoshop and its many filters
are an obvious choice for creating interesting grayscale files.
Take a look at this example:
This is a simple 45+ linear gradient...
except that for fun I applied
a Xaos Paint Alchemy filter to
it to simulate brush strokes...
...so now when I use it for a
transition, the wipe "paints"
Paint Alchemy is terrific for generating
"natural-looking" gradient effects--it simulates an
infinite number of brush-stroke styles. It only works on color
files, though, so you'll need to convert your grayscale gradient
files to RGB to apply the effect and then back to grey again.
The KPT Gradient Designer tool
is another very powerful member of the gradient arsenal. Its
ability to do radial sweeps, a variety of bursts, and--most
importantly--do cycles (black to white-back to black again ,
for example) make it the starting point of choice for most of
my gradient work.
Look at this next wipe map:
What the heck is going on here?
Well--this is a Gradient Wipe map
that simulates the "drafting" of the image below.
These are the informational outlines of part of the "Rubino"
font family, which is designed to look like a font-in-creation,
complete with the "artist's" original source lines.
In creating the above gradient the circular lines were all designed
to wipe on with a circular sweep gradient, and the straight
lines all wipe on straight.
Hint: In a multiple-gradient
wipe like this, it's desireable to have some of the areas start
or end on something other than pure white or black--this, in
effect, adjusts the timing of the wipe so that all of the lines
aren't drawing at the same time. This can look more "natural".
By animating these lines with the
above wipe, then "sketching in" the font's outline
and fill with the "brushy" gradient at the top of
the chapter, I got a movie that looked like this:
Click on the above image to play the movie. (200k .mov)
Obviously, there was a great deal
of work involved here in designing the gradient--but it was
much quicker to apply (and render) this technique than animating
fifty different elements in After Effects.
There are literally-and I'm not
exaggerating here--about eighty bazillion different ways of
generating interesting gradients. One really nice tool is Adobe
Illustrator: play with the blend tool and let your imagination
go wild. Another is KPT's Gradients on Paths, which was recently
rolled into the KPT Gradient Designer. This tool is a bit of
a bear to use effectively but can be useful in certain situations.
Or you can render gradients directly onto objects in a 3-D Program
like ElectricImage, then composite some "running lights"
or other moving patterns later in AE... the possibilities are
The next chapter will be a specific
step-by step approach to animating a gradient transition along
a path-- and gets into the very powerful technique of layering
offset gradient wipes to animate repeating pulses of light.
Almost through! Hang in there!
The Roadway Pulse Project
Or, "How I Got Inspired at my 4th of July Cookout"
Some time ago somebody posted a
problem on-line. I'll call the person "Greg" (although
his real name is Doug and he works for Digital Knight Productions).
"Greg" had a client who
wanted pulses of light travelling along a winding highway. Several
suggestions were posted before I got to the question, and rather
than throw in my two cents at the time I decided to give the
idea some thought. In spite of the suggestions for hand-drawing
mattes and carefully tweaking polygon wipes, I felt the easiest
solution had to lie in the Gradient Wipe filter. But I had only
used the filter to wipe on a line or an object; the trick was
how to get the necessary pulses?
While I was cleaning my grill it
hit me--if you can wipe something on, you can wipe it off. The
key to the pulses is to use multiple, offset Gradient Wipes.
The front of the pulse wipes on, gets a few frames into the
animation, then immediately begins to wipe off. The two effects
chase each other across the scene. Of course, the effect can
be offset to include as many on-screen pulses as you want.
First of all, I created the source
files. The base was a Corel Stock PhotoCD Image of a nice windy
I used the pen tool to define the
roadway path, then used that path to create the rest of the
files. Once you've defined a pen path you can "stroke"
it with any of the photoshop paint tools. I used the airbrush
tool to create the eventually-pulsing glow. The result is a
solid green photoshop file with the following alpha channel:
To create the most important image,
the gradient blend, I again used the pen path as a source. This
time, however, I stroked it with the paintbrush tool--and here's
where some experimentation is called for. You have to find the
best combination of several settings to achieve an optimum blend.
There are 256 possible shades of
gray in an 8-bit gradient. The Options palette for several of
the Photoshop tools lets you choose a "fade" amount--set
this to 256 to obtain the smoothest possible effect. Make sure
your paint colors are reset to full black and full white, and
that your opacity is set to 100%. Selecting "Background"
or "Transparent" really depends on your situation--I
usually set it to "Background".
Your basic settings for creating a
nice, smooth gradient.
Your next step is to define a custom
brush size appropriate for your path and your task. You create
a custom brush by clicking in any empty box in the Brushes palette,
...which pops up the following
The two things we care about in
this window are "Diameter" (for now) and "Spacing"
(which we'll get to in a minute).
The main thing to worry about in
choosing a diameter is that it's big enough to accomodate the
effect you're going to be wiping on. Be careful about getting
TOO big, however--particularly if your path has sharp corners,
as the following example illustrates:
This path has been stroked with
a too-fat brush. The overlapping
gradient will result in unwanted
artifacts. It's bad.
This path is better. It's wide enough
to accomodate the glow effect but
not so wide it overlaps itself.
We like this one.
Now that we have a width we like,
all that's left is to stroke the path--but what's happening?
The stroke is coming up too short! Or too long!
This is where the "Spacing"
slider comes into play (see above). Increase the spacing and
the line goes further before fading out-- decrease it and the
line tightens up. You'll have to stroke the path, see which
way you need to adjust, undo, adjust the spacing amount accordingly,
and stroke again until you're satisfied with the results.
My path ultimately looked like
Now all that was left was to animate
it in AE. Let's have a quick look at the Gradient Wipe interface:
The only goofy thing about the
interface, to my sensibilities at least, is that the effect
seems to have been designed to wipe layers OFF rather than ON.
This means, when the transition is "100% complete"
(top slider), the layer is GONE, rather than fully on. This
is not a problem, it just seems backwards to me, because I usually
think in terms of bringing a new element in.
I created a 640 x 480 comp, and
dragged the files into it in the following order: Gradient Path,
Monaco, Glow. I selected the "Glow" layer, applied
the Gradient Wipe effect, set the Gradient Layer to "Gradient
Path", set the transition softness to roughly match the
sides of the glow (so the front of the glow would look like
the sides) and made the transition about five seconds long.
Result: a green glowing line wiped itself neatly on, following
Satisfied, I added another "Monaco"
layer, again applied the Gradient Wipe effect, selecting "Gradient
Path" as the Gradient Layer. I then copied the keyframes
from the "Glow" layer, offset the timeline by about
ten frames, and pasted the keyframes into the second "Monaco"
layer. Now the Green glow appeared to wipe off ten frames after
it wiped on. I adjusted the Transition Softness setting of the
second Monaco layer to a value of "6" which gave it
a nice motion-blur-trail look.
Now it was a simple matter of duplicating
and offsetting these top two layers as many times as I liked
to create multiple "pulses" of light. Project done.
Let's look at it again!
Click to play me. (164k .mov)
Of course, layering dozens of these
effects would start slowing things down a bit. If this is the
case, you can create the "pulse" as a separate layer
keyed with an alpha channel, then pre-render the pulse as a
QT movie using these settings: Animation, best quality, Milltions+.
This saves the effect with no loss of image quality and with
an intact alpha channel. You can then bring it in, loop it,
copy and offset it as many times as you'd like and it will render
In Closing... Or, "Thank Heaven
it's Finally Over"
Well, that's it! More than you
ever wanted to know about the Gradient Wipe filter. I've typed
the word "gradient" more times in the creation of
this tutorial than in the rest of my life combined. I hope it
Have fun and keep exploring!
Special thanks to Total
Training for allowing us to re-print this tutorial