There are two big problems with computing devices small enough to put into your pocket: input and output. Solutions to the input problem include things like Palm's Graffiti and the BlackBerry's thumb keypad. Solutions to the output problem include . . . uh, well, I guess there aren't really any solutions, just a lot of tiny, tiny screens. But a company called Microvision this week showed off something promising: a video projector small enough to be built into a cellphone.Microvision brought out its PicoP at the Society of Information Display's (SID) meeting this week in San Francisco

The PicoP is a thumb-nail-sized module (Microvisions calls it an Integrated Photonics Module) designed to be embedded inside portable computing devices like cell phones and PDAs. Details are scanty and the demos were apparently of prototypes, but the goal is a device that would project an image the size of a laptop display on any convenient surface.

A company press release explains the technology this way: "Unlike most matrix-display technologies, such as a LCD or DLP, we modulate laser light temporally and spatially using a single tiny vibrating silicon mirror to produce an image. . . . Because PicoP is using a collimated beam of laser light to produce a full-color, high resolution and contrast image it exhibits an 'infinite' depth of focus. As a result, this product will not require a projection lens which further reduces its form factor and cost."

Moving-mirror technologies have been used for nearly 20 years to produce virtual displays by modulating beams of light directed into goggle-wearing viewer's eyes. More recently Texas Instruments developed Digital Light Processing (DLP) technology that put millions of "micromirrors" on silicon chips -- one for each pixel in a projected display. Microvision has evidently combined the two approaches with a laser light source that's bright enough to be seen without being so power-hungry it drains the device's battery.

"Bright enough" is the crux of the problem. If Microvision has created something that can fit in a cell phone and project a page-sized image we can see in room light, that would be a real break-through. Can I get one retrofitted to my PDA?