Help me understand how optical mouse works.

[ZUnit]

Can someone help me understand what means DPI in mouse specification?
I read toms hardware and still cant understand it.
I understand it like count of images taken for distance of 1 inch, like 800 images is taken for 1 inch, but with which movement speed they are taken or it is density of how much images is needed to cover 1 inch?
Or its about square inch?

 

[dc5]

text

i think you'll find this more helpful than someone trying to explain it over the forum.

 

[Delorian]

that's quite an interesting read dc5, I never realized how much there was to them!

 

[Mark R]

Just to clarify a few points in that article:

1) The key component is a miniature camera sensor (similar to those used in digicams) in the mouse which takes pictures of the surface. These cameras are very low resolution (14x14 pixels for low-end mice to 30x30 pixels for state of the art mice) but very high speed (up to 6000 fps).

2) A CPU in the mouse compares each picture with the one before it looking for movement.

3) dpi stands for 'dots per inch', although in this case 'pixels per inch' would be more correct. Essentially 800 dpi means that each pixel is 1/800 of an inch on each side. Combine this with the resolution of the sensor, and you can workout that a top-end mouse can only 'see' an area less than 1mm x 1mm. A higher dpi rating means that the mouse can detect smaller movements.

 

[ZUnit]

Mark R sry but 3) songs like BS.

 

[Mark R]

Why do you say that?

 

[HondaF1]

so it looks for movements? Does that mean an optical mouse would not work in a perfectly smooth and frictionless surface?

 

[Mark R]

Yes, that's right. The mouse has to be able to see the surface it is being moved on.

The lens on the camera is designed to focus at the level of the surface when the mouse is resting flat. If you lift the mouse up, you move the surface out of focus, and the mouse is unable to see clearly enough to track movements.

Friction has nothing to do with the performance of an optical mouse - it is purely whether the mouse is able to see movement. If the surface is perfectly smooth, or transparent (like glass) then it will not be able to track. However, because the mouse takes a highly magnified view (it's field of view is less than 1mm x 1mm) microscopic defects in the surface may give enough of an image for the mouse to work, at least some of the time.

Laser light provides much more precise illumination than an LED, and this shows up microscopic defects in the surface much more clearly (try illuminating something with a laser pointer - see how it sparkles as the microscopic roughness of the surface is shown up). Even though the logitech MX1000 uses the exact same sensor as the MX510, the MX1000 has far better performance on glass or polished surfaces because of the high-constrast laser illumination.

 

[ZUnit]

Originally posted by: Mark R
Why do you say that?

Sry for my english, but i was thinking u trying to say that image resolution cant be more than 1mm x 1mm. :

Originally posted by: Mark R
Combine this with the resolution of the sensor, and you can workout that a top-end mouse can only 'see' an area less than 1mm x 1mm.