3D Threshold Array Phase Shift for Halftone Watermarking
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Solution Overview
Problem
Existing digital watermarking methods for halftone images face limitations in embedding small watermark patterns due to the need for large stoclustic screens, which result in visible seams and limited information capacity, especially for multi-bit gray scale images, and are not suitable for run-time embedding of variable data.
Innovation Solution
The use of a three-dimensional threshold array that incorporates a phase shift value during the halftone process, allowing for the embedding of smaller watermark patterns with a smooth phase transition, thereby reducing seam visibility and increasing information capacity, by modifying the halftone threshold value based on spatial coordinates and phase shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large stoclustic screens are used for embedding watermarks in halftone images, then watermark visibility is reduced, but information capacity is limited and seam artifacts become visible
Solution Approach 1:
The patent transitions from traditional 2D stoclustic screens to a 3D threshold array that incorporates phase shift values as a third dimension. This allows watermark embedding by modulating the phase of halftone dots rather than relying solely on spatial distribution, thereby increasing information capacity while maintaining screen size and reducing visible seams
Solution Approach 2:
The patent changes the fundamental parameter used for watermark embedding from spatial position alone to phase shift values. By modifying the phase parameter of halftone dots according to the watermark data, the system achieves higher information capacity without increasing screen dimensions, and the phase modulation creates smoother transitions that reduce visible seams
2Object-affected harmful factors
If large stoclustic screens are used for watermark embedding, then seam visibility is reduced, but the process is not suitable for run-time embedding of variable data
Solution Approach 1:
The patent makes the watermark embedding process dynamic by allowing phase shift values to be calculated and applied in real-time based on variable data inputs. The 3D threshold array can be dynamically generated or modified during run-time operations, enabling flexible embedding of different watermark patterns without requiring pre-computed large screens, thus improving productivity while maintaining smooth transitions
3Reliability
If traditional phase-shift watermarking is used, then watermark embedding is achieved, but the process requires large screens that are not suitable for multi-bit gray scale images
Solution Approach 1:
The patent extends the phase shift parameter concept to work effectively with multi-bit gray scale images by mapping different gray levels to different phase shift values. The 3D threshold array structure allows each pixel's gray level to influence the phase modulation, enabling reliable watermark embedding across the full range of gray scale values without requiring large screens, thus improving both reliability and adaptability
Data Source
AI summary
Disclosed are systems and methods directed to digital watermarks, and more particularly, the generation of invisible correlation-based digital watermarks embedded in halftone images.