Conventionally, to code a digitized image signal, a corresponding
quantity of information is allocated to an edge part for carrying out coding, and
therefore reduction in the quantity of information is limited, deteriorating the
coding efficiency.
Thus, an evaluation section of an encoder evaluates the characteristics (strength
of correlation between pixels) of an image using a predetermined evaluation function,
and decides a transmission pixel in accordance with the characteristics, consequently
deciding a random scan order. A differential coding section differentially codes
the image on the basis of the scan order decided by the evaluation section. A multiplexing
section multiplexes the differential coding output from the differential coding section.
