Optical mouse

An optical mouse is a computer mouse which uses a light source, typically a light-emitting diode (LED), and a light detector, such as an array of photodiodes, to detect movement relative to a surface. Variations of the optical mouse have largely replaced the older mechanical mouse design, which uses moving parts to sense motion. An optical mouse is a computer mouse which uses a light source, typically a light-emitting diode (LED), and a light detector, such as an array of photodiodes, to detect movement relative to a surface. Variations of the optical mouse have largely replaced the older mechanical mouse design, which uses moving parts to sense motion. The earliest optical mice detected movement on pre-printed mousepad surfaces. Modern optical mice work on most opaque diffusely reflective surfaces like paper, but most of them do not work properly on specularly reflective surfaces like polished stone or transparent surfaces like glass. Optical mice that use dark field illumination can function reliably even on such surfaces. Though not commonly referred to as optical mice, nearly all mechanical mice tracked movement using LEDs and photodiodes to detect when beams of infrared light did and didn't pass through holes in an incremental rotary encoder wheel. Thus, the primary distinction of “optical mice” is not their use of optics, but their complete lack of moving parts to track mouse movement, instead employing an entirely solid-state system. The first two optical mice, first demonstrated by two independent inventors in December 1980, had different basic designs:One of these, invented by Steve Kirsch of MIT and Mouse Systems Corporation, used an infrared LED and a four-quadrant infrared sensor to detect grid lines printed with infrared absorbing ink on a special metallic surface. Predictive algorithms in the CPU of the mouse calculated the speed and direction over the grid. The other type, invented by Richard F. Lyon of Xerox, used a 16-pixel visible-light image sensor with integrated motion detection on the same chip and tracked the motion of light dots in a dark field of a printed paper or similar mouse pad. The Kirsch and Lyon mouse types had very different behaviors, as the Kirsch mouse used an x-y coordinate system embedded in the pad, and would not work correctly when the pad was rotated, while the Lyon mouse used the x-y coordinate system of the mouse body, as mechanical mice do. The optical mouse ultimately sold with the Xerox STAR office computer used an inverted sensor chip packaging approach patented by Lisa M. Williams and Robert S. Cherry of the Xerox Microelectronics Center. Modern surface-independent optical mice work by using an optoelectronic sensor (essentially, a tiny low-resolution video camera) to take successive images of the surface on which the mouse operates. As computing power grew cheaper, it became possible to embed more powerful special-purpose image-processing chips in the mouse itself. This advance enabled the mouse to detect relative motion on a wide variety of surfaces, translating the movement of the mouse into the movement of the cursor and eliminating the need for a special mouse-pad. A surface-independent coherent light optical mouse design was patented by Stephen B. Jackson at Xerox in 1988. The first commercially available, modern optical computer mice were the Microsoft IntelliMouse with IntelliEye and IntelliMouse Explorer, introduced in 1999 using technology developed by Hewlett-Packard. It worked on almost any surface, and represented a welcome improvement over mechanical mice, which would pick up dirt, track capriciously, invite rough handling, and need to be taken apart and cleaned frequently. Other manufacturers soon followed Microsoft’s lead using components manufactured by the HP spin-off Agilent Technologies, and over the next several years mechanical mice became obsolete. The technology underlying the modern optical computer mouse is known as digital image correlation, a technology pioneered by the defense industry for tracking military targets. A simple binary-image version of digital image correlation was used in the 1980 Lyon optical mouse. Optical mice use image sensors to image naturally occurring texture in materials such as wood, cloth, mouse pads and Formica. These surfaces, when lit at a grazing angle by a light emitting diode, cast distinct shadows that resemble a hilly terrain lit at sunset. Images of these surfaces are captured in continuous succession and compared with each other to determine how far the mouse has moved. To understand how optical flow is used in optical mice, imagine two photographs of the same object except slightly offset from each other. Place both photographs on a light table to make them transparent, and slide one across the other until their images line up. The amount that the edges of one photograph overhang the other represents the offset between the images, and in the case of an optical computer mouse the distance it has moved.