Saturday, April 13, 2013

Colours out of space (and time)

Back with Another Kiwi and I were young, the world was monochrome as shown in old photographs, and if we wanted any colours we had to make them ourselves, by taking a spatial pattern of black-&-white edges and overlaying it with time variations. Kids today have everything handed to them on a plate but you try telling them that and they just laugh. I think they're laughing, anyway; it's hard to be sure until they give my ear trumpet back.

The effect was noticed in 1831 by Wheatstone when he was waving a page of lines and letters in front of his eyes, as was the custom of the time. I AM NOT MAKING THIS UP.
The prototype of the Wedgwood Patent Ceramic Bong -- designed by Brewster -- had recently been presented to King William IV at the latter's coronation for the greater glory of the Commonwealth, and all over England the physicists were staring intently at the Paisley wallpaper or asking one another "Have you ever looked at your hand? I mean, really LOOKED at it?" In fact Prévost had discovered the same flicker effect several years earlier, but he failed to publish it (being distracted at the time by his "Looking-at-the-world-through-a-cardboard-tube-at-each-eye-pointing-in-slightly-different-directions" experimental program) so he has only recently received the credit he deserves.

Here is one I made earlier... it is Benham's Top. Each zone is black half the time, white for 1/3 of the time, and a spatial pattern for 1/6 of the time, with the critical parameter being the timing of that 1/6 relative to the black / white alternation. The effect is strongest for a flicker of about 7 Hz and a spatial frequency of about 15'. This is close enough to the size of receptive fields of chromatic-opponent ganglion cells in the retina, for some theories to invoke those cells to account for the lateral interactions.

The edges consist of concentric arcs in the physical spinning version but when it comes to a computer display the pattern can be anything. Zebra stripes, tiger stripes, polka dots, whatever. Perhaps there are people who spend their computer cycles generating elaborate black-&-white GIFs who can make use of this valuable information.

But there is no reason to restrict the patterns to black-&-white. They can be black-&-colour, or colour-&-white, or colour-&-colour. There are different kinds of colour-opponent retinal ganglion cells, and the various theories lead to different predictions as to whether any phase-dependent effect on appearance will occur when both components are chromatic and the same luminance. It all lends itself to cruel and unethical experiments which a Herr Doktor guy is currently supposed to be writing up.

These Pattern-Induced Flicker Colours are of interest to Riddled because of the names of two researchers, which fit so neatly into the Nominal Determinism theory of scientific careers.


Big Bad Bald Bastard said...


Smut Clyde said...

I confess, much of my parenting approach is modelled after Calvin's dad.

ifthethunderdontgetya™³²®© said...

What's all this about kids being made in pate?

Smut Clyde said...

It's the new artform, ITTDGY. No-one's making butter sculpture any more.

Big Bad Bald Bastard said...

I confess, much of my parenting approach is modelled after Calvin's dad.

How do you like in bike shorts? AFAF

tigris said...



Substance McGravitas said...

Gifwise it's pretty hard to get a lot of frames going at high speeds...OBS should do some kind of javascript rotation.