Image sensor, which includes the following: a
pixel array including multiple pixels configured and functional to detect light from a scene, wherein the scene includes an object to be detected and a
background image, wherein each pixel of the multiple pixels is configured to generate a new
voltage signal in response to the intensity of light received by the pixel; a memory for storing digital values corresponding to a predetermined
voltage bandwidth around a prior
voltage signal R of at least some of the multiple pixels corresponding to the light detected from the
background image, wherein the voltage bandwidth defines a positive
delta voltage +Δ and a negative
delta voltage -Δ relative to the background voltage
signal R; a sample-and-hold or track-and-hold module capable of sampling the new voltage signal corresponding to one of the several pixels selected; a digital-to-analog converter that generates a reference voltage R+Δ or R-Δ from the digital values stored in the memory; a
comparator that receives the new voltage signal sample value from the hold module and receives one of the reference voltages R+Δ or R-Δ for the selected pixel to compare it with the voltage signal sample value, wherein the
comparator is configured to produce a high-voltage output signal if the voltage signal sample value is greater than the reference voltages R+Δ or R-Δ, and to produce a low- or zero-voltage output if the voltage signal sample value is less than the reference voltages R+Δ or R-Δ; a two-bit register containing a most significant bit (MSB) and a
least significant bit (LSB), wherein the two-bit register provides a two-bit output signal; and a
logic module that receives the voltage output from the
comparator, wherein the
logic module is configured and functional as follows: Selecting the reference voltage R+Δ to be supplied to the comparator, and setting the MSB to a logic "0" in response to a low-voltage output signal from the comparator or to a logic "1" in response to a high-voltage output signal from the comparator; and then Selecting the reference voltage R-Δ to be supplied to the comparator and setting the LSB to a logic "0" in response to a low-voltage output signal from the comparator or to a logic "1" in response to a high-voltage output signal from the comparator; a
background subtraction module configured and functional to receive the two-bit output signal from the two-bit register for the selected pixel and, based on the two-bit output signal, to identify the selected pixel as detecting light from a scene that is different from the light detected by the same pixel in the
background image; and a
processing module for generating an output image that includes the selected pixel identified by the
background subtraction module.