1. An image processing apparatus for processing the image constituted by a group of pixels, comprising: an input section inputting information of an image; a conversion section converting the information of the image inputted by said input section into information suitable for edge detection; and an image processing section calculating a difference value of adjacent pixels of the image based on the converted information of the image, and adding an absolute value of the difference value to the calculated difference value of the pixels corresponding to the adjacent pixels if the difference value is negative, to generate an edge image.