Patent ID: 7969410

Claim:
An apparatus, comprising: a window having a contact surface; an image capture system operable to capture images of the contact surface through the window at respective capture times; and a processing system operable to convolve the captured images with a two-dimensional circularly symmetric spatial bandpass filter to produce corresponding filtered images each comprising a respective set of pixels with assigned pixel values having respective magnitudes, based on the magnitudes of the pixel values of the corresponding filtered images, assign each of the capture times to one of an in-contact time class designating times during which the contact surface is determined to be in-contact with a user's finger and an out-of-contact time class designating times during which the contact surface is determined to be out-of-contact with the user's finger, and generate a select signal indicating that the contact surface has been touched to make a selection based on a click event predicate defining at least one condition on the time classes respectively assigned to successive ones of the capture times, wherein the image capture system captures the images with N pixels that are separated by an inter-pixel distance, and the bandpass filter has a center frequency f C , an upper cutoff frequency f U , and a lower cutoff frequency f L that satisfy: f L = 1 2 · N , ⁢ f U = 1 2 = 1 2 · N , and 0 > f L > f C > f U > 0.5 ; wherein f C ,f U , and f L are in units of cycles per inter-pixel spacing of the image capture system.