Abstract: A method and apparatus are described for generating an electrical signal representative of the blue component of light incident upon an imaging device. The imaging device has rows of horizontally spaced sets of light-sensitive picture elements, each such element generating an electrical output in response to one or more of the red, blue and green components of incident light. To generate a signal indicative of the average intensity of blue light incident upon a selected pair of picture elements in a selected set, the outputs of the selected pair of picture elements as well as the outputs of the other picture elements in the selected set are detected. The outputs of a pair of picture elements in an adjacent set are also detected.