Mouse buyer's guide

Introduction

The performance of an optical mouse is difficult to analyze because numerous parameters come into play, and the results are always a compromise. Improving one performance factor doesn't necessarily lead to a better overall result. For an optical mouse, end performance is the result of a long, complex process that includes analysis of the surface, calculation of coordinates and transmission to the computer.

LED/Laser function in mouse operation

A mouse's sensor takes a continuous series of "photographs" of the surface over which the mouse is moving. By comparing these pictures, the mouse's processor calculates coordinates. Obviously, for optimum measurement, the images have to be good. Thus the first task is to illuminate the surface. Until recently, red LEDs were used to do that. The surface reflects back the light, which is focused by lenses before it hits the sensor. A recent innovation replaced the LED with a small laser. This laser creates a more concentrated beam and its light is more stable, producing a more detailed image. As in a CD or DVD player, lasers are particularly effective for detecting surface irregularities.

LED

Laser

What LED can see

What Laser can see

How the lens & electronic components affects surface image improvements
The lenses that concentrate the image on the sensor also have an influence since. The quality of the optics contributes to the sharpness of the picture by avoiding distortion of the original image. The sensor itself is what takes the picture, so it too has its importance. The more sensitive it is, the more pixels it exposes to the image and the better the picture will be. Of course, when we talk about "photos" or "images," we're not talking about making a high-resolution color print. We simply mean reading the specificities of the surface over which the mouse is moving to determine its movement by comparing the successive images.

Sensor

Lens

Joint effort
This cooperation of a group of components results in a "photograph" that above all must reflect the structure of the surface under the mouse by pointing out its irregularities. Obviously higher-quality components will produce a better image, which will result in a better interpretation of that surface. So keep in mind that laser is more precise than an LED, that quality lenses won't distort the image and that a more sensitive sensor will create a better image.

Processing images
Now things get more complicated as we get into the area of processing the image that the sensor transmits. The first factor is the number of pictures taken within a given time span. It should be evident that the more pictures there are, the more precise the calculation can be. But these images have to be processed in real time and the result has to be put to use.

Resolution
Another measurement now enters the picture to make things more complicated - resolution. We're talking here about the number of measurements taken by the mouse for a given distance traveled. This is measured in Counts Per Inch (cpi) - the number of measurements taken per inch (2.54 cm).
Manufacturers generally use the term "dpi," which is inappropriate here because we're not talking about dots per inch. Instead, it's the number of measurements the mouse can register over a given distance that counts. The more measurements you take, the more precise the instantaneous positioning will be. But at the same time, the speed of the mouse increases. This has several repercussions in terms of use. First of all, you go to the spot you want to go to faster by moving the mouse less. The trade-off is that any movement, however infinitesimal, will be detected, which can actually work against preciseness. And to make things just a little more complicated, the resolution of the mouse also depends on the resolution of the monitor. If you increase screen resolution for a given mouse resolution, the movement will be longer.
So resolution is an ambiguous factor. Preciseness increases in absolute terms, but since the mouse reacts faster, controlling it becomes more complicated. It's also possible to change the resolution via software - either the mouse's driver or the Windows mouse controls.

Important factors
Thus, a balance needs to be found between mouse speed and the cursor positioning precision, for every given screen resolution. However, the intrinsic preciseness of the mouse plays a primordial role in resolution. The more precise the mouse sensor and the calculation of coordinates, the more the resolution can be increased, because you'll lose less preciseness of control. Still, there are limits imposed by hand movement. With the improvement in sensor precision, it's become possible to use higher resolutions. As long as you don't lose preciseness, greater speed is an advantage for better reactivity. That's evident above all with games, and to a lesser degree with graphics work.
The resolution can also be modified by adjusting the mouse-speed cursor in your mouse properties. Each manufacturer may also index its mouse differently. And you may decide that with the cursor in the middle, you're mouse is operating at its maximum physical resolution and any further acceleration will be via interpolation, with a loss of precision. In conclusion, resolution is a complex issue and its effects on mouse performance are contradictory.

Transmitting data from mouse to computer
Finally, to make things even more complicated, transmission of data from the mouse to the computer is also a limiting factor. USB theoretically limits the number of exchanges to 125 per second. If you increase the resolution, only the X-axis measurement will actually be transmitted. Here's an example: You cover a wide distance with 1,000 counts in two seconds, or 500 in one second. But the USB port can only transmit 125 counts, or four times fewer. The result is that the measurements sent won't be any less precise and the mouse will be in the right place, but the movement from one place to another won't be as fluid as it could be, because positions have been skipped.

User Friendly and Conformability
Finally, each individual has his or her own feel and may or may not be comfortable with various mouse speeds. Some of our test subjects can't play games at all with a mouse that moves too fast, while others are immediately at ease, and others gradually get used to it.
So only actual use will let you judge a mouse's real performance. And as usual, use depends on needs.
The sensors on all true second-generation mice (2,000 images/s and 800 dpi) are amply sufficient for the majority of day-to-day applications. Provided the build quality of the mouse is sufficient, speed and reactivity will be plenty enough for office applications, web browsing or video editing. Going beyond that only makes sense for two types of applications: games and graphics. For gaming, mouse preciseness is most important for FPS (First-Person Shooter) games, but also to a lesser degree for Real-Time Strategy (RTS) games, because you need to be rapid and precise in selecting units. For graphics, photo retouching, CAD and 3D creation; the mouse also plays an essential role. Generally, vendors' high-performance mice marketing campaigns are targeted for FPS players, while the devices are just as suitable for graphics work. One corollary to keep in mind, however, is that once you've gotten used to a high-performance mouse, it's hard to go back to another mouse for just about any application.