The present invention relates to an image pre-processing method for a pattern detection system, such as a bar code detection system. The method comprises the steps of: detecting a start point and an end point of a pattern on the basis of image data of at least a portion of a captured image, estimating a point spread function from the image data or a modified image data on the basis of the detected start point and the end point, and restoring the image data or the modified image data using the estimated point spread function.