In an image processing system, whether relevant pixels in the character image information obtained by reading an original on which characters have been recorded are object pixels to be subjected to enhancement processing is determined. The relevant pixel is determined to be an object pixel when the density of the relevant pixel is not lower than a first threshold value higher than the density of the background of the border of the original and not higher than the density of a thinnest line in lines which form the characters and is not higher than a second threshold value not lower than the density of a thinnest line in lines which form the characters and the relevant pixel is determined to be a thin line pixel forming a part of a thin line image.