Digital Artform

Here's a square rotated 45 degrees.

Here's some turbulence. This type of image makes a useful displacement map for achieving digital "heat shimmer" or "heat ripple" effects in post production.

Here's the result - a displacement only in the diagonal direction.

Notice how two of the diagonal edges have remained straight. Why? Because they have been displaced in the same direction in which they are already pointing.

The red values of a displacement map control horizontal displacemement. The green values control vertical displacement. The exact method varies from program to program, but in Photoshop, middle red is the "zero displacement" for horizontal motion. Middle green is the "zero displacement" for vertical motion. Darker values go up, or left, as the case may be. Lighter values go down, or right, as the case may be.

Let's work with a new source image. In this case, it's a simple, unrotated square.

Here's red turbulence. It displaces the source image horizontally.

Here's the results of the red turbulence displacement. The overall vertical drop comes from the fact that the green channel is all black. Black is not the null displacement. Middle green (0 127 0) is.

Here's green turbulence. It displaces images vertically.

Here's the results of the green turbulence displacement. Note the overall horizontal shift. This is caused by the fact that the red channel is not set to 127, the null displacement, but to zero, a strong lateral displacement. Overlooking this detail is easy to do!

Here's turbulence in the red channel combined with the zero offset value (127) in the green channel. Remember I'm using Photoshop for this.

Here's the "zero offset" in action.

Finally, here's turbulence in the red channel, and completely unrelated turbulence in the green channel.

This is a good basis on which to build a heat ripple effect.