Watermark Spatial Frequency Control for Copy Detection
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Solution Overview
Problem
Existing image processing technologies face challenges in distinguishing between original documents and copies, particularly in recognizing watermarks due to differences in image quality between chromatic and achromatic foregrounds, and the difficulty in making watermarks visible only in copies.
Innovation Solution
An image processing apparatus that generates chromatic and achromatic watermarks with varying spatial frequencies, where the chromatic watermark has a lower spatial frequency than the achromatic, making it harder to recognize in original documents while ensuring clear visibility in copies, and storing associated patterns to maintain image quality consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the same spatial frequency is used for both chromatic and achromatic watermarks, then the watermark pattern consistency is maintained, but the visibility difference between chromatic and achromatic watermarks in original documents and copies cannot be optimized
Solution Approach 1:
The patent applies different spatial frequencies to chromatic and achromatic watermark patterns locally. Specifically, the achromatic watermark uses a first spatial frequency while the chromatic watermark uses a second spatial frequency that is higher than the first. This local differentiation allows the achromatic watermark to remain less visible in original documents while the chromatic watermark maintains appropriate visibility, resolving the contradiction between watermark visibility control and image quality consistency.
2Reliability
If a high spatial frequency is used for the achromatic watermark, then the watermark becomes more visible in copies, but the watermark may become visible in the original document as well
Solution Approach 1:
The patent changes the spatial frequency parameter differently for chromatic and achromatic watermarks. The achromatic watermark uses a lower first spatial frequency to prevent visibility in original documents, while the chromatic watermark uses a higher second spatial frequency to ensure visibility in copies. This parameter differentiation based on color characteristics resolves the contradiction between reliable copy detection and maintaining original document clarity.
3Device complexity
If the same image pattern is used for both chromatic and achromatic watermarks, then the system complexity is reduced, but the quality difference between chromatic and achromatic duplications cannot be minimized
Solution Approach 1:
The patent applies different spatial frequency characteristics to chromatic and achromatic watermark patterns. The achromatic watermark pattern uses a first spatial frequency while the chromatic watermark pattern uses a second spatial frequency. This local quality differentiation ensures that both chromatic and achromatic duplications maintain consistent and appropriate image quality, resolving the contradiction between system complexity and duplication quality consistency.
Data Source
AI summary
Original image data obtained by reading an original is joined with watermark data associated with a watermark for copy control, which appears as a result of making a copy. The watermark generating section sets the spatial frequency of a chromatic halftone pattern of a foreground, which appears as a result of making a copy, lower than the spatial frequency of an achromatic halftone pattern of a foreground, which appears as a result of making a copy. Accordingly, it becomes more difficult to recognize a foreground in an original document when the foreground is generated using an achromatic color, while a foreground in the duplication is recognized clearly when the foreground is generated using a chromatic color.