Optical Mice

Developed by Agilent Technologies and introduced to the
world in late 1999, the optical mouse­ actually uses a tiny
camera to take thousands of pictures every second.

Able to work on almost any surface without a mouse pad, most
optical mice use a small, red light-emitting diode (LED) that
bounces light off that surface onto a complimentary
metal-oxide semiconductor (CMOS) sensor. In addition to LEDs,
a recent innovation are laser-based optical mice that detect
more surface details compared to LED technology. This results
in the ability to use a laser-based optical mouse on even
more surfaces than an LED mouse.

Here's how the sensor and other parts of an optical mouse
work together

# The CMOS sensor sends each image to a digital signal
processor (DSP) for analysis.
# The DSP detects patterns in the images and examines how the
patterns have moved since the previous image.
# Based on the change in patterns over a sequence of images,
the DSP determines how far the mouse has moved and sends the
corresponding coordinates to the computer.
# The computer moves the cursor on the screen based on the
coordinates received from the mouse. This happens hundreds of
times each second, making the cursor appear to move very
smoothly.

Optical mice have several benefits over track-ball mice:

* No moving parts means less wear and a lower chance of
failure.
* There's no way for dirt to get inside the mouse and
interfere with the tracking sensors.
* Increased tracking resolution means a smoother
response.
* They don't require a special surface, such as a mouse
pad.

Optical Mouse Accuracy

A number of factors affect the accuracy of an optical mouse.
One of the most important aspects is resolution. The
resolution is the number of pixels per inch that the optical
sensor and focusing lens "see" when you move the mouse.
Resolution is expressed as dots per inch (dpi). The higher
the resolution, the more sensitive the mouse is and the less
you need to move it to obtain a respon­se.

Most mice have a resolution of 400 or 800 dpi. However, mice
designed for playing electronic games can offer as much as
1600 dpi resolution. Some gaming mice also allow you to
decrease the dpi on the fly to make the mouse less sensitive
in situations when you need to make smaller, slower
movements.

Historically, corded mice have been more responsive than
wireless mice. This fact is changing, however, with the
advent of improvements in wireless technologies and optical
sensors. Other factors that affect quality include:

* Size of the optical sensor -- larger is generally
better, assuming the other mouse components can handle the
larger size. Sizes range from 16 x 16 pixels to 30 x 30
pixels.
* Refresh rate -- it is how often the sensor samples
images as you move the mouse. Faster is generally better,
assuming the other mouse components can process them. Rates
range from 1500 to 6000 samples per second.
* Image processing rate -- is a combination of the size
of the optical sensor and the refresh rate. Again, faster is
better and rates range from 0.486 to 5.8 megapixels per
second.
* Maximum speed -- is the maximum speed that you can move
the mouse and obtain accurate tracking. Faster is better and
rates range from 16 to 40 inches per second.