An image reading system provided with an image sensing means to convert the image of an open-faced document to electronic signals in fine division in the viewing direction and a vertical direction intersecting said viewing direction to reduce reading time and regularize the image quality of a read pen-faced document, wherein the pixels having a binarized value of pixel value D(n) among pixels g of an image read by said image sensing means different from the pixels having a binarized value of pixel value D(n+1) of adjacent pixels on one side in a vertical direction are counted as border pixels, the difference &Dgr;D of pixel values is calculated between said border pixels and adjacent pixels on one side thereof, and correction of the pixel values of a pixel array is corrected in accordance with the sharpness of an image quality specified by the sum of said difference and the number of border pixels in a pixel array in a vertical direction for each pixel position in a viewing direction.