Thursday, August 19, 2010

Pattern-Induced Flicker Colours

When I were a young lad down at t'mill, this was the Benham Effect. Then it became "Fechner-Benham colours", or even "Prevost-Fechner-Benham colours". For Evans' Ache, people, sort out this business of priority. What is wrong with the Terrordrome approach? Three dead 19th-century psychophysicists with imposingly respectable beards go in; one comes out. In the meantime I shall call it the Benham Effect because, hello, Fechner and Prevost did NOT SPEAK ENGLISH.

It is all about using black and white to induce the experience of seeing colour. Traditionally this involved a spinning disk, half black, with a pattern of concentric arcs drawn on the white half. If you stare past the disk in one direction as it spins you might see a flickering cycle of black - striped pattern - white - black. Or black - white - stripes - black. For some of these cycles there is a subtle sense of colour laid over that zone of the disk like a watercolour wash. It doesn't have to be a disk (a drum works just as well), and the pattern doesn't have to be concentric arcs -- what's important is a black / white pattern. The more edges the better.

Irritating flickering pattern below! Black-&-White nemesis, epileptogenesis!

What is happening here is an artefact of spatial contrast. The visual system is all about contrasts and relative levels of colour and lightness rather than absolute levels. When a lighter and a darker area adjoin, the visual system runs a sharpness-enhancement algorithm with hard-wired lateral interactions that make the lighter side of the edge look lighter still and the darker side, darker. The same for chromatic edges.

When the pattern of edges is changing rapidly, there are transients percolating through the system, because some components of this hard-wired circuitry respond to each change more slowly than others. The blueness or yellowness sort of oozes out and gets everywhere.

Can we use this to simulate colour on black-&-white TVs? Yes we can!
If Substance McG had waved his black-and-white crayons around rapidly, perhaps he would have seen colours, and then he wouldn't be envying the entitled kids today.


mikey said...

For fucks sake, Bimler, I don't have a job and I'm frequently time-constrained. You seem to have access to an additional 12 hours a day that the rest of us can only aspire to. Is this some kind of "Pluterday" artifact?

And as to the substance (sorry), two questions come to mind. First, why go through some weird process with black and white patterns on a disk or drum when you can, oh I dunno, just kind of look around and SEE COLOR? If your goal is to see color, might I suggest going outside and looking around? I know, wacky, right?

Second, if you do want to explore the far reaches of the spectrum, again, your black and white patterns are of limited consequence next to 1500-2000 micrograms of LSD. Now THATS color. Sorry, colour.

Do carry on....

zombie rotten mcdonald said...

i am intrigued by your concepts, mikey, and would like to subscribe to your newsletter and monthly sample club.

Another Kiwi said...

Do not complain to the Riddled staff the next time you are trapped in a themepark spinning around thing (how the fuck do I know what they are called) and you want to press the black stop button not the white super boost button.
"oooh should I go for the slightly red button or the slightly yellow button, I shall ring the good Herr Doctor Bimler, I hope he doesn't have caller recognition"

Another Kiwi said...

T'mill called to say one of cross beams has come out of skew ont treadle

Jennifer said...

Contrast makes the world go 'round, baby!

ifthethunderdontgetya™³²®© said...

I bow down to my spinning Spirograph master.

Big Bad Bald Bastard said...

I watched the spinning "tops" and, all of a sudden, I have this urge to ship a pallet of Scotch to an address in New Zealand.

Prevost-Fechner-Benham Effect" would be a great band name.

77south said...

B^4 I'm not sure an MC yelling out "Posse in Prevost-Fechner-Benham Effect" to get the crowd hyped up at a hip hop concert would have the desired effect.

merc said...

If you look closely a harlequin pop pops out and says...nothing.

Smut Clyde said...

If your goal is to see color, might I suggest going outside and looking around?

Consider the perspective of a vision scientist, mikey. There are neddling busy-body 'ethics committees' placing limits on how much they can observe people's brains directly. I have argued over and over that the whole point of a 'twin study' is that with twins, one of them is a SPARE and is basically disposable, but do the Ethics Committee listen? Do they bogroll.

So the only way we can work out what's going on inside the Black Box is to play silly-buggers with the input and trick the output into doing strange things.

all of a sudden, I have this urge to ship a pallet of Scotch to an address in New Zealand.
It worked!