Intensity correction in an optical scanner

A method of compensating for pixel variations in an optical scanner that comprises a light source and a line detector detecting pixel intensity information, comprising the steps of:

• initially scanning a reference and a background in order to generate line profile data and first smooth line profile data respectively, wherein the first line profile data represents intensities along a line on the background at a first point in time;
• compensating detected pixel intensities during scanning of a document by means of said line profile data;
• when required, scanning the background in order to obtain second smooth line profile data that represents intensities along a line on the background at a second point in time;
• further compensating detected pixel intensities during scanning of a document for along-line changes in said second smooth line profile data relative to said first smooth line profile data.

An optical scanner comprising:

• a light source;
• a line detector detecting pixel intensity information;
• a computer having a memory wherein the computer is capable of controlling the optical scanner such that the detected pixel intensity can be adjusted and wherein the memory holds a procedure comprising the steps of:
• initially generating line profile data that comprises pixel intensity information by scanning a reference, and storing the line profile data;
• initially generating first smoothed line profile data that comprises pixel intensity information by scanning a background, and storing the first line profile data to represent intensities along a line at a first point in time;
• whenever required generating second smoothed line profile data that comprises pixel intensity information by scanning the background, and storing the second line profile data to represent intensities along the line at a second point in time;
• generating the difference between said first smoothed line profile data and said second smoothed line profile data to represent changes in the intensities along the line;
• generating a combination of said difference and said line profile data;
• adjusting the detected pixel intensity to compensate for temporal and along-line changes in pixel intensities in the optical scanner.