The Directional Blur effect gives a layer the illusion of motion in a given direction. Let’s take a look at this little space scene. Just a few position and rotation keyframes make a rocket fly in an arc through the screen. But we want to give it the illusion that it is moving faster, or maybe warping through space. First, we should turn on Motion Blur for the layer. That’s already nice, but I want to really make these pixels look stretched out. So I’m going to duplicate this layer, and apply a Directional Blur by going to Effect, Blur & Sharpen, Directional Blur.
There are only two editable properties for a Directional Blur: Direction and Blur Length. Blur Length determines how much your image will be blurred. So I’m going to turn that way up, to 200. Since the Direction is set to 0 degrees, my image is being blurred vertically. So I’m going to go to our first rotation keyframe, and drag the direction until it matches the direction of the ship. Now it really looks like this thing is moving fast. But it’s a little too intense, so I’m going to turn the opacity down to 60.
Since our ship travels in an arc, our blur isn’t going to match up the whole time. So while we are still on our first rotation keyframe, hit the stopwatch next to Direction to turn on keyframes. Go to the last rotation keyframe and drag the rotation to match up with the ship again. Now we can just go back through our animation and touch up the rotation to match.
Finally, I really only want this blur to be coming off the tail end of the ship, and the Directional Blur works in all directions on a given angle. So I’m just going to draw a mask around where I want the blur to stay. You will notice that there is still blur outside of my mask here. That is because the mask is applied before the effect, so we need to adjust our mask until the blur disappears from the top.
Now that the basis of the effect is done, you can try turning off the motion blur if you just want that blurred tail. You can also change the order of the layers to see some different results.