Multi-Layer Digital Watermarking Using Rotated Halftone Screens
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Solution Overview
Problem
Existing digital watermarking methods for color images embed watermarks in all color channels simultaneously, leading to color instability and moiré patterns, and do not allow for independent retrieval of watermarks from different layers.
Innovation Solution
The method generates distinct correlation-based digital watermarks for each color layer or channel, using rotated halftone screens with different frequencies and angles to embed and retrieve watermarks independently, enabling multiple encoded images within a single image while avoiding moiré patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If watermarks are embedded into all color channels simultaneously using dot-on-dot arrangement, then multiple watermarks can be encoded in a single image, but color instability and moiré patterns occur
Solution Approach 1:
The patent divides the color image into separate color channels (cyan, magenta, yellow, black) and embeds watermarks independently into each channel using rotated halftone screens. This segmentation allows each watermark to be embedded without interfering with others, eliminating moiré patterns while maintaining the ability to encode multiple watermarks in a single image.
Solution Approach 2:
The patent employs rotated halftone screens with different angles for different color channels. By using asymmetric rotation angles (e.g., 0°, 45°, 90°, 135°) for different colors, the system avoids the formation of moiré patterns that occur with parallel screens, while still enabling multiple watermarks to be encoded simultaneously.
2Productivity
If watermarks are embedded into all color channels simultaneously, then multiple watermarks can be encoded in a single image, but independent retrieval of watermarks from different layers is not enabled
Solution Approach 1:
By segmenting the watermark embedding process into separate color channels with independent halftone screens, the patent enables independent retrieval of watermarks. Each color channel contains a specific watermark that can be retrieved independently using the corresponding public key, without affecting other watermarks embedded in different channels.
Solution Approach 2:
The patent adds the dimension of color channel separation to the watermark embedding process. By embedding watermarks in different color channels with different orientations, the system creates multiple independent retrieval paths, allowing different users with different public keys to retrieve different watermarks from the same image.
3Ease of manufacture
If dot-on-dot rendering approach is used to embed watermarks, then watermarks can be embedded in color images, but color instability arises
Solution Approach 1:
The patent uses dynamic rotation of halftone screens for different color channels instead of a fixed dot-on-dot arrangement. This dynamic approach, where each color channel has a uniquely rotated screen pattern, maintains color stability by preventing the formation of moiré patterns while still enabling effective watermark embedding.
Data Source
AI summary
Disclosed are systems and methods directed to the generation of multi-layer digital watermarks, including the generation of distinct watermarks on each of at least two color layers or channels within an image such that each may be retrieved or viewed independently of the other in the output image.