BUENA PARK, Calif. -- The player pianos that were so popular in the early part of this century are making a comeback -- this time with a high-tech twist. Although computerized player pianos that store live performances and play them back note for note have been around for several years, a new piano from Yamaha Corp. of America goes one step further by integrating stringless optical sensor technology. Optical hammer-speed (top) and key-position (bottom) sensors work together in the Yamaha GranTouch piano to convert keystrokes into digital data. The Disklavier GranTouch Digital Grand Piano features a traditional keyboard but is equipped with optical sensors instead of strings and an iron plate. When the user plays the instrument, a sensor on the bottom of each key breaks a beam of light, indicating which key is being played. Another optical sensor on the hammer tells the system the velocity at which the key is being struck, converts the information into digital data and selects the appropriate sound. The result? An electronic reproduction of sound that is surprisingly similar to the real thing. The idea for the GranTouch was developed at the company's Japanese headquarters with the hope of revitalizing the piano market, which has been in a slump for two decades. At only 273 lbs, the GranTouch is less than half the weight of a traditional grand piano; its stringless structure makes it more compact as well. The company expects that these features will attract a segment of buyers who previously shied away from owning a piano because of space limitations. In addition to sensor technology, the piano has a floppy disk drive that allows users to listen to recordings from its 400-disk music library, make their own multitrack recordings or receive digital signals from across the country. Concert pianists may find the GranTouch lacking some of the subtle nuances that characterize traditional instruments, but at a cost of less than $16,000, the photonic piano could prove to be an affordable alternative.