Document reading apparatus that reads a document image with a CCD image sensor

An image forming apparatus, comprising:

• a light source configured to irradiate the surface of a document with light;
• an optical system configured to lead the light reflected by the document to a predetermined position;
• a photoelectric converter array configured to photoelectrically convert the light led by the optical system, pixel outputs of the photoelectric converter array being allocated to a plurality of terminals and then being output;
• an A/D converter unit configured to analog-to-digital convert each pixel output from the photoelectric converter array to produce digital outputs that are integers;
• an average output value detecting unit configured to detect the average value of the integer digital outputs of each terminal converted by the A/D converter unit;
• and
• a terminal difference correcting unit configured to correct the integer digital outputs of a first one of the terminals in response to a difference between the average value of the first one of the terminals and the average value of a second one of the terminals, a decimal being distributed to the integer digital outputs of the first one of the terminals when the difference includes the decimal, wherein the terminal difference correcting unit includes at least one random value generating adder/subtractor unit configured to perform an arithmetic operation on an integer digital output of the integer digital outputs, using the equation:
• Dout=ROUND(Din−0.5+RAND+a), wherein
• “ROUND” is a round-off function for rounding off a decimal, “Din” is the integer digital output, “RAND” is a random value between 0 and 1, “a” is the difference in average values, and “Dout” is the corrected integer digital output.

A method of reading a document, comprising:

• irradiating the surface of a document with light;
• leading the light reflected by the document to a predetermined position;
• photoelectrically converting the light, and allocating pixel outputs of the converted light to a plurality of terminals;
• analog-to-digital converting each of the pixel outputs to produce digital outputs that are integers;
• detecting the average value of the integer digital outputs of each of the terminals;
• correcting the integer digital outputs of a first one of the terminals in response to a difference between the average value of the first one of the terminals and the average value of a second one of the terminals, a decimal being distributed to the integer digital outputs of the first one of the terminals when the difference includes the decimal;
• and
• performing an arithmetic operation on an integer digital output of the integer digital outputs, using the equation:
• Dout=ROUND(Din−0.5+RAND+a), wherein
• “ROUND” is a round-off function for rounding off a decimal, “Din” is the integer digital output, “RAND” is a random value between 0 and 1, “a” is the difference in average values, and “Dout” is the corrected integer digital output.