An image forming apparatus that is capable of saving developing agents such as toner and ink by reducing the number of dots in an image while ensuring that the characters and figures in the image are nonetheless represented distinctly. Bit map data is read out from buffer 23 and a set of three-pixel bits are held in both a vertical and a horizontal direction, with the pixel of interest being located in the center. On the basis of this set of bits, upper/lower edge detector circuit 59 and right/left edge detector circuit 61 determine whether the pixel of interest is positioned in any one of the edges of the pattern in the image to be printed. Additionally, dot-saved pattern generator circuit 67 performs dot reduction on the bit for the pixel of interest. The edge detection signals from the edge detector circuits 59 and 61 are supplied to OR gate 65, where they are ORed with the bit for the pixel of interest that is supplied from the dot-saved pattern generator circuit 67 after dot reduction. The logic sum signal from OR gate 65 represents bit map data which, as compared with the initial bit map data, has the edges of the pattern left intact and has the internal region of the pattern subjected to dot reduction. Printing is executed using this logic sum signal.