Binary Image Watermarking via Local Pixel Classification

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Solution Overview

Problem

Existing methods for embedding watermarks in binary images face challenges such as noticeable changes, limited capacity, and poor visual quality, especially when dealing with small or large block sizes, and require secure and efficient techniques for copyright protection and authentication.

Innovation Solution

A method that identifies invertible pixels in binary images by checking specific color differences and uses transforms to assess candidate pixels for embedding data, ensuring minimal visual distortion and maintaining image quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If pixels are arbitrarily changed to embed watermark data, then data embedding capacity is improved, but visual quality deteriorates with noticeable changes

Engineering Contradiction:

Improvedata embedding capacityVSAvoidvisual distortion

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by classifying pixels into different types (corner, edge, interior) based on their local neighborhood characteristics, and selectively modifying only suitable pixels (Type A and Type B) while preserving others, thereby embedding data without causing noticeable visual changes in critical regions

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses run-length encoding to compress and store the modification map that records which pixels are inverted, allowing the watermark data to be embedded while the original image structure is preserved through the copying mechanism of the encoding scheme

Inventive Principle:

Principle #26Copying

2Measurement precision

If small block sizes are used for embedding, then localization precision is improved, but data embedding capacity deteriorates due to limited flippable pixels

Engineering Contradiction:

Improvelocalization precisionVSAvoiddata embedding capacity

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent segments the image into non-overlapping blocks and further classifies pixels within each block by their positional characteristics (corner, edge, interior), allowing different embedding strategies to be applied to different pixel types within the same block, thus maximizing capacity while maintaining precision

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent creates a universal classification system that works across all block sizes by defining pixel types based on their relative positions and neighborhood properties, making the method adaptable to any block dimension while maintaining consistent performance characteristics

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Quantity of substance

If large block sizes are used for embedding, then data embedding capacity is improved, but localization precision deteriorates and visual quality worsens

Engineering Contradiction:

Improvedata embedding capacityVSAvoidlocalization precision

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent divides large blocks into smaller conceptual units by classifying pixels into corner, edge, and interior types, allowing precise local control within each block while maintaining the benefits of large block processing for overall capacity

Inventive Principle:

Principle #1Segmentation

4Quantity of substance

If multiple pixels are inverted in a block, then data embedding capacity is improved, but visual quality deteriorates with salt-and-pepper noise

Engineering Contradiction:

Improvedata embedding capacityVSAvoidsalt-and-pepper noise

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The patent applies different modification rules to different pixel types within the same block, allowing multiple pixels to be modified strategically (Type A and Type B pixels) while preserving visually critical pixels (Type C corner pixels), thus embedding data without creating salt-and-pepper noise patterns

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent inverts the conventional approach by not modifying all suitable pixels but rather selectively preserving certain pixel types (Type C corner pixels) and only modifying specific types (Type A and Type B), reversing the traditional mindset of maximizing modifications

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS7688993B2Software and method for embedding data in two color images

Publication Date: 2010.03.30 NANYANG TECH UNIV

AI summary

A method of embedding watermark data in a two-color image includes assessing the suitability of each of several candidate pixels to embed a bit of watermark data. Candidate pixels for which one pixel directly above, directly below, and immediately to the left and right of the candidate pixel have different colors, are identified. In one embodiment, only a single candidate pixel in each 2×2 block is identified. Suitability of each candidate pixel may be determined based on a relationship of coefficients computed from a binary wavelet or binary lifting transform formed from the image. Data is embedded by inverting suitable pixels. A recipient of the image may assess which blocks contain watermark data, by assessing the suitability of each 2×2 block in the image to embed data and extract data without further information about the data's location.