An image correction method able to avoid error image. According to opposite properties of black and white, only the last few bits of the scanned digital signal are extracted for black correction, while only the first few bits of the scanned digital signal are extracted for white correction. Further, the most significant bit of the digital signal is 1 for white correction. Therefore, the unwanted LBB effect on the scanned image caused by dust or spot on the correction document is avoided. In addition, as only a few bits of the scanned digital signal are extracted, the requirement in memory capacity is reduced.