Thursday, August 28, 2008

Noticing is remembering

In last week's post on fan color appearance, I wrote that in low light conditions today's top cameras do not reproduce faithfully color appearance because they remain photopic, in opposition to the human visual system which becomes scotopic. The result shown in the photographs was that while we humans see the crowd achromatic and the LED fans chromatic, the camera reproduced the fans achromatically and the crowd chromatically.

Reality is always more complex. For the camera, the image is flat, i.e., each photosite or pixel has the same importance. However, for the human visual system an object that attracts attention by being bright, colorful, and rapidly moving gets more memory resources allocated, i.e., it is more memorable. This fact makes the photopic/photopic confusion more striking for the photographers themselves than for viewers not present at the event.

The lesson is actually more general. Color scientists who are serious about their research still do psychophysics experiments. When designing these experiments, it is important not to overstretch the observer's memory capacity, because it might skew the experiment.

For more on this topic, the recent paper Dynamic Shifts of Limited Working Memory Resources in Human Vision by Paul M. Bays and Masud Husain in Science 8 August 2008: Vol. 321. no. 5890, pp. 851-854 presents the results of recent research on visual memory. Here is the editor's summary:

The dominant model of human visual working memory allows for the simultaneous representation of only three or four objects. With what precision is each visual object stored as a function of the number of items in a scene? Bays and Husain tested the ability of human subjects to remember the location and orientation of multiple visual items after a brief disappearance of the stimulus array, and found that visual working memory is a flexibly allocated resource. Making an eye movement toward an object, or directing covert attention to it, caused a greater proportion of memory resources to be allocated to that object, allowing the memory of its presence to be retained with far greater precision than other objects in the scene.

Saturday, August 23, 2008

Fan color appearance

One of the key accessories for 盆踊り (bon odori) is the flat fan or 団扇 (uchiwa). The best ones are made by creating a bone skeleton with bamboo from 四国 (Shikoku), on which 和紙 (washi, Japanese paper) is glued.

At this year's パロアルト (Palo Alto) お盆 (obon), I noticed that instead of the usual artistic fans with delicate designs, many dancers were wearing plastic fans like those handed out in hot summer nights by beer companies as marketing tools. I was surprised—with the consul here, why something so tacky?

It was only as the dance progressed and dusk had my vision switch from photopic to mesopic, that I discovered the secret. Today's flat fans are made with designs created by elaborate multicolored LED patterns and wave guides molded in the plastic fan. As the day wanes and vision progresses towards scotopic, these modern 団扇 (uchiwa) become eerie, creating an atmosphere where the living look more like the dead ancestors coming to visit us during お盆 (obon).

Scary! Has 四国 (Shikoku) been unsealed and become 死国 (Shikoku)?

And now to the challenge for color imaging. Below are photographs of paroaruto's bon odori in chronological order. As you note, the camera remains photopic. It cannot render correctly the fan color appearance and the scariness has completely disappeared.

Back to the drawing board! We need color rendering algorithms that can reproduce accurately the color appearance of contemporary flat fans.