1. A digital integrated circuit for extracting features out of an input image, the integrated circuit comprising: at least one input/output data bus; and a plurality of cellular neural networks (CNN) processing engines operatively coupled to the at least one input/output data bus, the plurality of CNN processing engines being connected in a loop with a clock-skew circuit, each CNN processing engine comprising: a CNN processing block configured for simultaneously obtaining M×M convolution operations results by performing 3×3 convolutions at M×M pixel locations using received imagery data and filter coefficients, the received imagery data representing a (M+2)-pixel by (M+2)-pixel region with the M×M pixel locations being a M×M central portion of the (M+2)-pixel by (M+2)-pixel region, where M is a positive integer; a first set of memory buffers operatively coupling to the CNN processing block for storing the imagery data to be fed into the CNN block via a first multiplexer; and a second set of memory buffers operative coupling to the CNN processing block for storing the filter coefficients to be fed into the CNN processing block.