A front end signal processing method and apparatus for processing a signal from an image sensor are provided for readily clamping a black level, improving the manufacturing yield, and reducing the power consumption. A luminance detector/digitizer receives a sensor output signal from an image sensor, detects luminance information included in the sensor output signal, and generates a digital luminance signal representative of the detected luminance information. A digital processor receives the digital luminance signal, and multiplies the digital luminance signal by a predetermined gain code to generate the multiplication result as a front end processed signal output. An optical black clamp receives the digital luminance signal from the luminance signal detector/digitizer and supplies a feedback signal produced from the digital luminance signal to the luminance signal detector/digitizer to clamp a black level of the luminance signal to a constant value.