Fog, Smoke, or Mist Rolls In
An animated layer of translucent clouds is easily enough re-created in After Effects. The basic element can be fabricated by applying the Fractal Noise effect to a solid, and then using a Blending mode such as Add or Screen to layer it in with the appropriate Opacity setting.
Fractal Noise at its default settings already looks smoky (see Figure 10); switching Noise Type setting from the default, Soft Linear, to Spline, improves it. The main thing to add is motion.
An Evolution animation creates internal movement, although Transform animations cause the overall layer to move as if being blown by wind. Offset Turbulence can be used to reposition infinitely without running out of space.
Figure 10 Fractal Noise (shown at the default setting, with Noise Type set to Spline) is a decent stand-in for organic-looking fog. You can try varying the Fractal Type or Noise Type to get different looks, and you must animate the Evolution if you want any billowing of the element. Several Fractal Types are available, as seen in the pull-down menu.
Brightness, Contrast, and Scale settings determine the apparent scale and density of the noise layer. Complexity and Sub Settings also affect apparent scale and density, but with all kinds of undesirable side effects that make the smoke look artificial.
The look is greatly improved by layering at least two separate passes via a Blending mode.
Masking and Adjusting
When covering the entire foreground evenly with smoke or mist, a more realistic look is achieved using two or three separate overlapping layers with offset positions (see Figure 11).
The unexpected byproduct of layering 2D particle layers in this manner is that they take on the illusion of depth and volume. The eye perceives changes in parallax between the foreground and background, and automatically assumes these to be a byproduct of full three-dimensionality, yet you save the time and trouble of a 3D volumetric particle render. Of course, you're limited to instances in which particles don't interact with movement from objects in the scene; otherwise, you instantly graduate to some very tricky 3D effects.
Figure 11 The smoke in this shot is made up of one large rendered fractal noise element that's sliced up, staggered (as seen with the layer outlines), and animated in pseudo-3D.
Particle layers can be combined with the background via Blending modes, or they can be applied as a Luma Matte to a colored solid (allowing you to specify the color of the particles without having a Blending mode change it). To add smoke to a generalized area of the frame, a big elliptical mask with a high feather setting (in the triple digits even for video resolution) will do the trick; if the borders of the smoke area are apparent, increase the mask feather even further (see Figure 12).
Figure 12 This mask of a single smoke element from the shot in Figure 10 has a 200-pixel feather, despite the fact that the resolution of the shot is D1 video (720 × 486). The softness of the mask helps to sell the element as smoke and works well overlaid with other, similarly feathered masked elements.
Moving Through the Mist
The same effect you get when you layer several instances of Fractal Noise can aid in the illusion of moving forward through a misty cloud. That's done simply enough, but how often does your shot consist of just moving through a misty cloud? Most of the time, clouds of smoke or mist are added to an existing shot. You can emulate 3D tracking to make the smoke hold its place in a particular area of the scene as the camera moves through (or above) it. To make this work, keep a few points in mind:
- Each instance of Fractal Noise should have a soft elliptical mask around it. The mask should be large enough to overlap with another masked instance, but small enough that it doesn't slide its position as the angle of the camera changes.
- A small amount of Evolution animation goes a long way, and too much will blow the gag. Let the movement of the camera create the interest of motion.
- Depending on the length and distance covered in the shot, be willing to create at least a half-dozen individual masked layers of Fractal Noise.
Mist and smoke seem to be a volume, but they actually often behave more like overlapping, translucent planes—individual clouds of mist and smoke.