1. An apparatus comprising: means for scanning a document and a calibration pattern at the same time along a scanning path, wherein the means for scanning comprises one or more scan lines; a top; a scanning chassis configured to be movable under the top along the scanning path, wherein the scanning chassis comprises the scanning element: a scanning platform disposed at the top, wherein the scanning platform is configured to support the document above the scanning chassis, wherein the calibration pattern is positioned on the top along a lateral side of the scanning platform and extends continuously along substantially an entire length of the scanning path; means for obtaining actual gray level values from the scanned document and obtaining a correctional gray level value for white and a correctional gray level value for black from the scanned calibration pattern, wherein the actual gray level values and the correctional gray level values are obtained along the one or more scan lines; means for determining a compensational gray level value for pixels of the scanned document based on an actual gray level value for each of the pixels and the correctional gray level values, wherein determining the compensational gray level value for each of the pixels comprises calculating [(each of the actual gray level values with respect to each of the pixels−the correctional gray level value for black)÷(the correctional gray level value for white−the correctional gray level value for black) * (a theoretical gray level value for white−a theoretical gray level value for black)]; and means for compensating a gray level of the scanned document using the compensational gray level value.