Apparatus for controlling the position of a screen pointer with low sensitivity to particle contamination

A method of generating movement data with an optical pointing device, the method comprising:

• illuminating an imaging surface with an at least partially coherent light source, thereby generating reflected images;
• sensing reflected images from the imaging surface;
• performing analog-to-digital conversion on the sensed reflected images to generate digital images;
• performing a movement computation based on the digital images;
• and
• generating movement data based on the movement computation that is indicative of relative motion between the imaging surface and the optical pointing device,
• wherein the movement computation comprises summing only pixels values from a first one of the digital images, thereby generating a first plurality of sums, and summing only pixel values from a second one of the digital images, thereby generating a second plurality of sums.

A navigation sensor comprising:

• a sensor array configured to sense reflected images from an imaging surface produced by an at least partially coherent light source;
• an analog to digital converter for generating digital images based on outputs of the sensor array;
• and
• a processor for generating movement data based on the digital images, wherein the movement data is generated based on a movement computation,
• wherein the movement computation comprises summing only pixels values from a first one of the digital images, thereby generating a first plurality of sums, and summing only pixel values from a second one of the digital images, thereby generating a second plurality of sums.