1. An image processing apparatus comprising: input means for inputting binary image data indicative of an on or off state of a dot; first edge determining means for determining an edge corner in the inputted binary image data; second edge determining means for determining a number, x, of consecutive black dots in the horizontal direction and a number, y, of consecutive black dots in the vertical direction of the edge corner determined by said first edge determining means; and smoothing means for performing smoothing correction on stair-like notches formed by edge portions of the inputted binary image data in accordance with a shape of the edge corner determined by the numbers x and y which are determined by said second edge determining means, wherein said first edge determining means determines the edge corner by performing a logic operation employing the inputted binary image data.