Method of correcting shading phenomenon in optical character reader

摘要

An optical character reader apparatus includes an image sensor, and a background reflection plate having such reflectivity which allows the image sensor to detect the entry of a document carrying thereon image information such as characters, graphics or the like within the field of view of the image sensor. A method of correcting a shading phenomenon comprises steps of setting a scan timing period of the image sensor at a first scan period, reading the reflection plate with the first scan period, setting the scan timing period of image sensor at a second scan period which is shorter than the first scan period, transporting the document in the field of view of the image sensor, detecting periphery of the document under the timing corresponding to the second scan period, cutting out image information on the document on the basis of the detected periphery thereof, correcting the cut out image information with respect to the shading with reference to the image sensor output derived through reading operation under the timing corresponding to the first scan period, and recognizing the image data undergone the correction of the shading.