Showing Fog

Today I have to crack the mystical formula of ... fog.

Fog is a series of particles, primarily water vapor, that obscures our vision.
(source: http://www.corelmag.com/0703/foggy/intofog.html)

As such it is a great attribute in film making, to (dis-)cover part of a scene or set focus to the main object of interest (such as your knight riding through the forest).




'Knight in the mist' by Coen de Moor;
Fog used as a storytelling attribute

Fog seems to want to lay flat in the lower areas of a scene, whereas smoke tends to move upward. Obviously the further away from the viewer, the thicker the fog.

Now here is why I had to learn how to show fog. I am drawing a storyboard for a story named "Stealers of Light", by Martin Yuille. The opening scene is as follows:

FADE IN

Fog obscures our view and we can hear inaudible menacing whispers 
in the distance. A figure enters from the left, wandering 
and searching as if lost. 

Confused he moves into the fog, we follow. 

The whispers gradually grow nearer and the fog grows thicker...

From the previously cited website I found out that to show/draw fog we need to layer two effects on top of each other;

1) The fog - a blurred shape that moves from side to side.

2) The actor - a silhouette who changes in opacity (see-through vs solid colours) and possibly moves as well.

Starting with the first layer, the fog itself. For this layer I have used the photo editing software called Photoshop (www.adobe.com). To end with the image underneath, I applied the Filter > Render > Clouds effect to a black rectangle a couple of times (see tip). Then to make the left and right edge form a seamless joint, I widened the rectangle's canvas by 200 percent and stuck the previously generated clouds on the righthand side in reverse.



Fog, created in Photoshop (75% transparant)

This foggy layer we can then move from left to right continuously to act as the fog.

Next, we need fixed objects (e.g. a tree) and our actor on layers below the fog.



Silhouette of our actor.

Now if above image is reduced in size (smaller if further away) and made slightly transparant during the movement, the illusion of this person walking through fog is achieved.

In addition, to increase awareness of where this person is walking we add a tree, that alternates in transparancy too.



Tree image, courtesy cornell college



Illusion of a figure walking through fog