Patent ID: 6445469
Filing Date: 2002-09-03
Classification: H04N

Abstract:
A document-image reading device comprising a document image reading means for reading image data from a document at a specified time-interval based on a reference clock by moving said document image reading means or the document in a feed direction, wherein said document-image reading means is provided with a reference-chart reading means for reading a reference chart representing alternations of a low-density or high-density division with a width equal to a least readable pitch and a high-density or low-density division with a width equal to an integer-multiple of the least readable pitch along the feed direction and an image-data processing means for processing the image data read from the reference chart by using a comb filter, performing integration calculations on the filtered data, extracting continuous detection of the substantially same integrated value by the integer-number of times and determining an integrated value at the extracted position by reducing the extracted integrated value by an integrated value of a upstream point along the feed direction at the distance of the integer-multiple of the least-readable pitch.