Method for detecting sub-pixel motion for optical navigation device

A method for detecting sub-pixel motion of a navigation device, comprising:

• capturing a first image frame by an array of sensing elements of the navigation device;
• capturing a second image frame by the array of sensing elements after a period of time has elapsed since the first image frame was captured, wherein each of the first and second image frames comprises a plurality of image pixels;
• obtaining one or more brightness curve equations of the first image frame and the second image frame, wherein each of the brightness curve equations is represented as a function of positional coordinates (x, y), and wherein the brightness of pixels of the second image frame remains the same as that of the first image frame but the pixels have shifted in at least one of the x and y directions, and
• calculating a displacement of the image pixels in the second image frame relative to the first image frame according to the one or more brightness curve equations represented as a function of positional coordinates x and y.

A sensing device, comprising:

• a sensor array for capturing images reflected on the sensing device;
• and
• a processor for determining a sub-pixel motion of the sense device,
• wherein the sensor array is configured to capture a first image frame at a first time point in which a plurality of image pixels are selected as reference pixels and a second image frame at a second time point, and to track positions of the reference pixels in the first image frame and the second image frame, wherein the first and second images and the reference pixels are represented by functions of sub-pixel positional coordinates x and y,
• wherein the processor is configured to calculate a displacement of the reference image pixels in the second image frame relative to the first image frame according to one or more brightness curve equations represented as a function of positional coordinates (x, y).