The hues in this photograph1 are slowly and steadily changing. The effect is achieved by running a small program. The program is not playing a movie file; it is changing the hues of the pixels in a still image. About five times a second, the program makes a small step. At each step, the hue of each pixel is changed to a closely related hue. Eventually, after many steps, the hue of each pixel moves all the way round the colour wheel, back to its original position. The cycle begins again.
- As the hues change, the difference between the hues of distinct pixels remains constant—the total information in the picture is maintained—but the picture appears to lose detail at some stages. This demonstrates how the human eye is more attuned to some differences than to others. In particular, we often have a more acute discrimination in hues close to orange. Look at the spectrum or the colour wheel and notice how we see broad and narrow bands of colour in what is, in fact, a uniform gradation of hues. (Admittedly the bands of colour have fuzzy edges.)