Document Image Tilt Correction Using Segmented Line Analysis
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Solution Overview
Problem
Existing image processing technologies face challenges in accurately performing tilt correction on document images containing mixed handwritten and typed characters, especially when handwritten characters have uneven line spacing and pitch, or when there is no ruled line information or non-rectangular document layouts.
Innovation Solution
An image processing system that separates document images into components with and without handwritten characters, estimates the tilt angle using the image without handwritten characters, and performs correction based on this estimation to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If variance of pixels is measured as a function of rotation angle for tilt correction, then tilt correction can be performed, but accurate tilt angle estimation becomes difficult when many handwritten characters with uneven line spacing and angles are mixed together
Solution Approach 1:
The patent segments the document image into multiple line regions and analyzes each line separately to determine its tilt angle. By dividing the overall document into individual line segments, the system can accurately measure tilt angles even when handwritten characters with varying orientations are present, as each line's tilt can be independently calculated without being affected by other lines' variations.
Solution Approach 2:
The patent introduces an intermediary process of detecting ruled lines and using them as reference elements for tilt angle measurement. The ruled lines serve as a mediator between the raw image data and the final tilt correction, providing stable reference structures that are less affected by handwritten character variations. This intermediary reference system enables more reliable tilt angle estimation.
2Measurement precision
If tilt correction is performed based on ruled line detection, then accurate tilt correction can be achieved, but tilt correction cannot be performed when there is no ruled line information in the manuscript image
Solution Approach 1:
The patent creates a universal tilt correction system that can handle multiple document types by implementing multiple detection methods. The system first attempts to detect ruled lines for tilt correction, but if no ruled lines are found, it automatically switches to detecting handwritten character lines as an alternative reference. This multi-functional approach ensures the system works with both ruled-line documents and handwritten documents without requiring manual configuration.
Solution Approach 2:
The patent implements a dynamic detection strategy where the system adaptively switches between different tilt detection methods based on the document content. The detection process is not static but dynamically adjusts its approach: it prioritizes ruled line detection when available, and transitions to handwritten character line detection when ruled lines are absent. This dynamic behavior enables the system to maintain high precision across diverse document types.
3Ease of operation
If tilt correction is performed by detecting edges of the document image, then tilt correction can be performed without checking document content, but accurate tilt correction cannot be performed if an edge cannot be detected or the document manuscript is not rectangular
Solution Approach 1:
The patent replaces the mechanical edge-detection approach with a content-based line detection approach. Instead of relying on the physical edges of the document sheet, the system detects lines formed by text content (both ruled lines and handwritten characters) within the document. This substitution transforms the tilt measurement from a geometric edge-based method to a content-based method, which is more robust to document format variations and achieves higher precision by using actual text line orientations as reference.
Data Source
AI summary
An image processing system performs tilt correction with respect to a document image having handwritten characters and typed letters mixed with each other. The image processing system separates the document image into an image with handwritten characters determined as handwritten characters and an image without handwritten characters not determined as handwritten characters, estimates a tilt angle of the image without handwritten characters, and corrects the document image on the basis of the tilt angle.