Tricking the Eye

As visual displays get smaller and smaller, in order to accompany us wherever we go, playing movies or games on portable devices, the need to wring the most amount of information using the least amount of electricity grows larger and larger. On the desktop or in the home, such constraints are relatively unimportant; but when you are carrying your display unit, they become crucial. Thankfully, engineers today are developing new display technologies that reduce power consumption and use a technique called biomimetics to literally trick your eyes into seeing just the amount of information needed to perceive a perfect likeness. In this month's cover story, visual display expert Joel Pollack explains how they pull it off, in "Displays of a Different Stripe".

Biomimicry is well known to audio engineers, who have long employed it to design microphones, amplifiers, and speakers for frequency ranges that match the human auditory system. For the human visual system, such compression algorithms are being designed to take advantage of the photoreceptors in the eye. Known as cones, these receptors come in three types, each defined by a special protein they produce, called a photopigment. The two dominant photopigments, one that detects photons in the reddish-yellow band of wavelengths and the second in the greenish-yellow band, do almost all the work of resolving an image—its luminance, edges, and other structural detail—as well as its color, partially. The third type of cone senses only color in the blue wavelengths and fills out the full picture.

In conventional visual displays, however, images are produced by using a ratio of 1:1:1 of red, green, and blue picture element pieces, or subpixels. Because the blue subpixels do almost nothing to help the eye resolve images, most of them go to waste, Pollack writes. To take advantage of this imbalance, contemporary display designers are changing the ratios of the subpixels and even adding new ones, such as white, to produce images that are more tuned to the actual working of the visual system. For example, Pollack's firm has found ways to render a pixel with an average of just two subpixels—two-thirds as many as in the conventional RGB pattern—by using algorithms to create, in effect, virtual pixels. Basically, the algorithm fools the eye. It defines an edge of an object in an image with the red, green, and white subpixels, and adds the requisite dash of blue off to the side.

Pollack writes that the bottom line is that brightness and color can be conveyed in more than one combination of red, green, blue, and white. The benefit is that these enhancements to displays provide about twice the brightness for a given draw of power. The savings in manufacturing costs more than balances any increase occasioned by the addition of a fourth, clear, color filter. Engineers can use the gains to save power or to intensify the brightness.

The expansion of information technology into new domains means that engineers must now learn to make products that conform to the needs of the mind and the senses to best improve them, Pollack concludes. It's an object lesson in mind over matter.

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