Technique · Fields

Bokeh

Out-of-focus lights: glowing discs strung along curves, laid on a slanted grid or scattered, in warm and neon colours.

Bokeh is a field drawn for every pixel by the graphics chip. Every piece on Synapse Drip is made from a recipe that layers techniques like this one, and you can change any of it in the Studio.

Good to know

  • Photographers prize bokeh, and reviews of lenses now compare how smoothly each one renders out-of-focus lights.
  • The discs of light in bokeh are images of the light sources themselves, blurred into the shape of the lens opening; any bright point that is out of focus becomes one.
  • Fairy lights, car headlights and the lit windows of a distant city all make good bokeh because each is a small, bright, separate source.
  • Bokeh comes from the Japanese boke, meaning blur; the photographer Mike Johnston popularised the word in English in 1997.
  • A bokeh disc is the shape of the lens aperture: a lens with a five-bladed aperture makes pentagon-shaped highlights, and a perfectly round aperture makes round ones.
  • The brighter rim of many bokeh discs comes from spherical aberration, a flaw in simple lenses that makes light from the edges of the lens land differently from light through the middle.

The mathematics

  • Each disc has radius r = about 0.059 of the frame and brightness 1 - smoothstep over its edge, with a ring at 88 percent of the radius added on top for the brighter rim; the overlap of two discs is simply their sum.
  • The slanted grid imitates perspective: positions are divided by a scale that grows toward one corner, so discs get bigger and further apart there, exactly as a wall of lights would when seen at an angle.
  • The discs are placed on a jittered grid, one candidate per cell displaced by a random amount, and kept with a probability that depends on the distance to the nearest string.

In art

  • The Impressionist painters, Monet above all, worked in blurred patches of light, and photographers who shoot bokeh are in a sense painting with the same patches.
  • Gold and amber light feels warm because it matches candlelight and tungsten bulbs, whose colour temperature is roughly 1,900 to 3,000 kelvin.

More ways to use it

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