A method of an image sensor device includes: providing a pixel array having a plurality of pixel units; using a pixel pre-processing circuit for receiving a plurality of analog pixel signals respectively from the plurality of pixel units to perform a low-pass filter operation upon the plurality of analog pixel signals in analog domain to generate a plurality of analog processed signals, a number of the plurality of analog processed signals being smaller than a number of the plurality of analog pixel signals; using an analog-to-digital converter for converting the plurality of analog processed signals in the analog domain into a plurality of digital processed signals in digital domain; and, transmitting the plurality of digital processed signals in digital domain into a digital processing circuit coupled to the analog-to-digital converter.