The present invention relates to an image forming apparatus and method for forming images of documents, utilizing a function for detecting particular documents.
In accordance with recent enhancement of the performance of color image forming apparatuses such as color copy machines, unauthorized use of these apparatuses has become problematic. For example, color image forming apparatuses have come to be used to counterfeit particular documents, such as bank notes, securities, etc. To overcome this, techniques for detecting particular documents have come to be developed.
Jpn. Pat. Appln. KOKAI Publication No. 7-264419 discloses a technique for prestoring color distribution information concerning particular documents to determine the degree of similarity.
Further, Jpn. Pat. Appln. KOKAI Publication No. 7-123254 discloses an apparatus for determining whether or not the copying of an input document image is prohibited, this apparatus utilizing a repetition pattern dictionary that stores a characteristic amount indicative of a repeated pattern.
For reading a document, image forming apparatuses use a flat-bed system in which a document is read on a platen (document table), or a through-read system in which documents fed by an auto-feed unit are read.
In the flat-bed system, documents are stopped on the platen, and still image reading is performed. On the other hand, in the through-read system, moving documents are read, i.e., moving-image reading is performed.
Between the flat-bed system and through-read system, the start position of document reading is opposite in the horizontal direction. Therefore, the image read by the flat-bed system is a normal copy image, while the image read by the through-read system is a mirror copy image.
If an image forming apparatus employs both systems, it must have two types of dictionary for normal copy and mirror copy images, similar to the above-mentioned particular-document detecting dictionary, in order to detect particular documents.
Therefore, in the prior art, when the images read using the platen (still document reading) and document auto-feeder (moving document reading) are normal copy and mirror copy images, respectively, either a normal copy image dictionary or a mirror copy image dictionary is loaded to a particular document detection unit for detecting particular documents, according to circumstances.
Alternatively, in the prior art, hardware is provided, in which only one dictionary is used, and a normal copy or mirror copy image is always input to a particular-document detecting apparatus, regardless of whether a platen is used (still image reading) or a document auto-feeder is used (moving image reading).
In the image forming apparatus using two types of dictionary for normal copy and mirror copy images, if a normal copy image dictionary has been wrongly loaded, instead of a mirror copy image dictionary, into a particular document detection unit, a checksum corresponding to the dictionary (dictionary data) loaded in the particular document detection unit is referred to for determining whether the dictionary loaded is an appropriate one.
However, if software for performing such a determination has malfunctioned and a wrong dictionary has been loaded, particular documents may not be detected and hence their images may be formed (counterfeited).
Further, in the case of employing the hardware for enabling normal copy or mirror copy image data to be always input to the particular document detection unit, a line memory of a capacity corresponding to at least six lines is required, thereby increasing the cost, the six lines being the sum of one main-scanning directional line and one line as a buffer for each of colors R, G and B.
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