Visible Watermarking Using Darkness Modulation and Error Correction
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Solution Overview
Problem
Existing visible watermarking techniques face challenges in effectively encoding and decoding messages in scanned images, particularly due to issues with message visibility, distortion, and skew errors during the print-and-scan cycles, which affect the reliability and readability of the watermark.
Innovation Solution
The method involves defining new printable pattern symbols to represent data bits, formatting the input text string into a bit-string with specific markers, and using error correction codes to ensure the watermark message can be reliably overlaid and extracted from images, even after print-and-scan cycles, while compensating for skew errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ASCII code is used to encode the watermark message as a series of 0's and 1's, then the message can be hidden from casual viewers, but the output image becomes cluttered and detectable by the human eye
Solution Approach 1:
The patent applies color changes by modulating the darkness levels of upper and lower regions of text characters to represent binary data. Instead of using visible 0's and 1's, the encoding uses relative darkness (shading) of character regions, making the watermark invisible to casual viewers while remaining extractable through scanning and processing.
Solution Approach 2:
The patent changes the encoding parameter from visible binary digits to invisible darkness modulation. By varying the darkness level of character regions rather than displaying binary symbols, the system transforms the message representation into a form that is imperceptible to human eyes but recoverable through optical scanning and digital processing.
2Reliability
If text character darkness regions are modulated to inscribe the encoded watermark message, then the message becomes hidden from casual readers, but the quality of scanning and printing equipment becomes critical for successful inscription and extraction
Solution Approach 1:
The patent applies preliminary action by pre-processing the input image to enhance contrast and compensate for potential printing and scanning degradations before the watermark is embedded. This includes adjusting image parameters and optimizing the encoding process to account for the print-scan cycle, ensuring the watermark remains extractable even with equipment limitations.
Solution Approach 2:
The patent implements beforehand cushioning by incorporating error correction codes and redundancy in the watermark encoding. This allows the system to tolerate degradation from printing and scanning processes, compensating for potential loss of information and ensuring reliable message extraction even when scanning or printing quality is suboptimal.
3Ease of operation
If the watermark message is made visible as text characters, then it can be easily read, but it becomes a distraction to casual viewers and moves their attention away from the output image
Solution Approach 1:
The patent uses color changes (darkness modulation) to encode the message within existing text characters, making the watermark invisible to casual viewers. The message is embedded through subtle variations in character shading rather than visible text, eliminating distraction while maintaining extractability through scanning and digital processing.
Data Source
AI summary
A watermarking system uses distinct bit patterns to identify a logic 0, a logic 1, and a marker bit, which demarcates segments of logic bit information. Marker bits, which are printed on both foreground and background areas of an image, outline message blocks. In message extraction, a preprocessing step removes any white boarders, identifies the best defined corner of a message block, crops the image, and rotates the image to place the identified corner at the top-left corner. Message extraction scans the rotated image in window segments of increasing size during multiple cycles. During each cycle, if a bit pattern cannot be identified as a data bit, then the size of the examined bit area is increased and rechecked to see it specifically is a marker bit. If no bit information can be definitively identified, then it is assigned a logic bit value based on a 50% random assignment.