Digital Watermark Encoding on Low Reflectivity Inks
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Solution Overview
Problem
Current digital watermarking technologies face challenges in encoding and decoding signals on physical objects with low reflectivity, particularly spot colors like Pantone Green, which are difficult to encode without visibility errors and color match errors, especially under red LED Point of Sale scanners.
Innovation Solution
The use of sparse mark patterns with holes in the background color, filled with an ink color that has higher reflectivity at 660 nm, allowing red LED scanners to detect the signal while minimizing human visibility, and selecting hole fill colors using algorithms to optimize reflectance differences and reduce visibility errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital watermarking is applied to inks with low reflectivity (e.g., Pantone Green), then the encoded signal can be embedded in the ink, but the signal becomes difficult to detect by red LED scanners and exhibits high visibility errors and color match errors
Solution Approach 1:
The patent introduces a reflective barrier layer as an intermediary between the low-reflectivity ink and the red LED scanner. This barrier layer has high reflectivity at red wavelengths (660 nm) and redirects the scanner's light source back through the ink, enabling detection without requiring the ink itself to be highly reflective. The barrier layer mediates the interaction between the ink and scanner, solving the detectability problem while preserving the ink's color properties.
Solution Approach 2:
The patent employs a reflective barrier layer with specific optical properties that change or enhance reflectivity at red wavelengths (660 nm). The barrier layer is designed to be transparent or translucent at other wavelengths, allowing it to selectively enhance red light reflection while maintaining overall visual appearance. This color-selective reflectivity enables reliable detection by red LED scanners while minimizing visibility errors and color match errors.
2Reliability
If holes are added to the background color to create sparse mark patterns for encoding, then signal detection is enabled, but human visibility of the encoded signal increases
Solution Approach 1:
The patent applies different properties to different parts of the printed object: the background color areas have one set of optical properties (absorbing red light), while the hole fill areas have different properties (reflecting red light). This local differentiation enables the sparse mark pattern to encode signals detectably by red LED scanners while the overall visual appearance remains consistent with the original design, minimizing human visibility of the encoding.
Solution Approach 2:
The hole fill color is specifically selected to have high reflectivity at red wavelengths (660 nm) while maintaining appropriate visual properties. The algorithm optimizes the hole fill color to create sufficient contrast for machine detection while minimizing perceptibility to human eyes under normal viewing conditions. This color optimization allows the sparse mark pattern to be detectable without being obviously visible.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables robust signal detection with reduced visibility and color errors, ensuring efficient encoding and decoding of digital watermarks on objects with low reflectivity, even under typical retail scanning conditions.
Implementation Method 1
filled with an ink color that has higher reflectivity at 660 nm, allowing red LED scanners to detect the signal
Data Source
AI summary
This disclosure relates to advanced image signal processing technology including encoded signals and digital watermarking. The technology may be applied to retail packages and other printed objects, e.g., such as hang tags, labels and receipts.