White lines on black, one behind another, each rising into a hump of sharp peaks: the sleeve of Joy Division's debut album Unknown Pleasures (1979) is one of the best-known images of its century. Fewer people know it is a scientific plot of successive radio pulses from CP 1919, the first pulsar ever found.
How it works
Each line is a profile raised above its own baseline. The envelope E lifts the middle and holds down the ends (“Hump width”), f supplies the relief and “Peak height” its scale. The trick is the order: lines are drawn from back to front, each filled beneath with the background colour, so nearer lines hide farther ones and a flat stack of curves reads as a mountain ridge. This is the painter's algorithm, the oldest way of hiding lines.
With “Source” at “noise”, a profile is fractal noise plus four pulses at fixed places whose strength drifts from line to line, much as a pulsar's pulses vary from turn to turn; “Smoothness” drops the finer octaves. With “track spectrum” each line is the mel spectrum of its own slice of a song: low frequencies left, high right, the start of the track at the back and the end at the front, a portrait of the whole song at once. The “mirrored spectrum” option puts the bass in the middle, and “Perspective” makes the back rows narrower and lower.
A bit of history
The pulsar was found by the PhD student Jocelyn Bell Burnell in Cambridge on 28 November 1967. Its signal came every 1.337 seconds so regularly that the source was jokingly dubbed LGM-1, for “little green men”; it proved to be a spinning neutron star whose beam sweeps past the Earth like a lighthouse's. The radio astronomer Harold Craft made the plot at Arecibo for his 1970 dissertation, to see smaller pulses within larger ones. The band found it in The Cambridge Encyclopaedia of Astronomy, and the designer Peter Saville reversed it to white on black. It is not a Fourier transform, as often claimed, just pulse intensities stacked up; statisticians now call such charts ridgeline plots.
What to tweak
- A black background, a white “Line colour”, 60–90 “Lines” and “Perspective” at 0 come close to the sleeve.
- “Smoothness” near 0 gives spiky peaks like the pulsar's; near 1, soft hills like dunes.
- Switch “Occlusion” off and the lines turn transparent and tangle, which shows how much one rule does.
- Load a track and choose “track spectrum”: the intro, the choruses and the bridge settle into separate ridges.
- Add the “Grain” effect on top for the rough card of the first pressing.
Guilloché and spirograph
Harmonograph
Phyllotaxis
Gielis superformula
Flow lines