Homework 3: Due Midnight on Tuesday October 20th.

Making Visual Illusions

Write a single matlab script to generate the illusions below in separate figures. Full credit will be given for the first three figures. The fourth one is a little bit harder. We encourage you to give the fourth one a try - but it is optional.

Figure 1:

This is called the peripheral drift illusion. This image has a sawtooth luminance profile as a function of polar angle. It produces a sensation of motion when viewed in the periphery. Direction of apparent motion is clockwise.

See (Faubert, J and Herbert, A. (1999). The peripheral drift illusion: A motion illusion in the visual periphery. Perception, 28, 617-622)

(For fun, check out what it looks like with different colormaps)

Figure 2:

This is the same thing, but with the direction of the ramps reversed. Which direction does it appear to move?

Figure 3:

This image demonstrates lightness constancy. It is a uniform bar placed on a luminance ramp. The bar appears to vary from light to dark because its ratio with the background varies. (from Mike Harris, Birmingham, UK)

(Again for fun, check out what it looks like with different colormaps)

Figure 4:

This one is optional. The bottom bar is the same as in the previous figure. The top bar varies physically in luminance to offset the illusion so that it looks uniform. Its actual luminance varies as a ramp from dark to light just like the background but with a shallower slope. (i.e. lum bar = k*lum background).