Image forming apparatus and density adjusting method

Abstract

The present invention provides an image forming apparatus and a density adjustment method for forming a latent image portion and a background portion on an original that cannot be known to exist, and when copying, display characters for preventing illegal output, etc. Furthermore, it is possible to reliably detect the special dot pattern formed on the background portion, so that unauthorized copying can be prohibited. The control unit detects a plurality of background part densities and a plurality of latent image part densities from an image obtained by an image reading operation on the paper on which a sample image is formed, and selects only one of the detected background part densities. When copying an original image with a dot pattern in the background, the density of the background portion of the dot pattern can be detected, and from the detected densities of the latent image portion, only the original image with the latent image portion can be extracted. The latent image density of the dot image corresponding to the dots constituting the latent image portion is formed on the copy, and the extracted background portion density and the latent image portion density matching the background portion density are derived.

Description

technical field [0001] The present invention relates to a technology for preventing important materials such as confidential documents from being leaked or falsified due to unauthorized copying. Background technique [0002] Conventionally, image forming apparatuses such as digital multi-function peripherals and copiers and image reading apparatuses have been required to have functions such as preventing unauthorized reading or outputting. In particular, leakage of confidential information to the outside due to unauthorized reading of confidential documents has become a serious problem in companies, and technology that can reliably prevent and limit reading of confidential documents has been urgently desired. [0003] In response to such requirements and wishes, for example, Japanese Patent Laying-Open No. 2005-094327 and Japanese Patent Laid-Open No. 2005-236954 disclose using the characteristics of scanners and printers to make text appear on the background when copying or...

AI Technical Summary

Problems solved by technology

However, if only the difference between the density of the latent image portion and the density of the background portion is reduced, for example, if the densities of both the background portion and the latent image portion are too high, the dots constituting the latent image portion will not disappear during copying. , the problem that the text cannot appear, on the contrary, when the density of the background part and the latent image part are too low, it is possible that the special dot pattern belonging to the background part cannot be detected during copying, so that it is impossible to prohibit illegal copy

Images