Document Soiling Detection via Color Coordinate Reference Comparison
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Solution Overview
Problem
Existing methods for detecting soiling and color wear in documents of value, particularly banknotes, face challenges due to color transitions that resemble the normal design or are partial, making it difficult to distinguish authenticity without technical aids, especially at high speeds and over large document surfaces.
Innovation Solution
A method that processes color coordinate values in a color space to determine if they correspond to a specified color reference distribution, using a closed reference area defined by linear segments and distances, allowing for quick detection of soiling and color wear by comparing image elements' positions and values with predetermined reference positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If color transitions are used in document design for aesthetic purposes and authentication, then the document's distinguishability and security features are improved, but the difficulty of detecting soiling and color wear increases due to the complexity of color variations
Solution Approach 1:
The detection method divides the document into multiple evaluation regions, each with predefined reference color values. Instead of analyzing the entire document as one complex whole, the system segments the analysis into manageable zones, comparing each region's color coordinates against its specific reference values. This segmentation approach simplifies the detection process while maintaining high authentication reliability.
Solution Approach 2:
Different regions of the document are assigned different reference color values and evaluation criteria according to their specific design characteristics. The system applies local quality control by tailoring the detection parameters to each region's unique color transition patterns, rather than using a uniform approach across the entire document. This enables accurate detection of soiling and wear while preserving the document's complex color design.
2Productivity
If machine-based automatic detection is implemented for high-speed processing of valuable documents, then productivity is improved, but the complexity of the detection system increases due to the need for sophisticated color analysis algorithms
Solution Approach 1:
The method extracts only the essential color coordinate information from each evaluation region and compares it directly against predefined reference values. By taking out only the critical color data needed for authentication and ignoring unnecessary details, the system achieves high-speed processing without requiring overly complex analysis algorithms. The extraction focuses on color coordinates within specific regions rather than comprehensive image analysis.
Solution Approach 2:
The system transforms the detection problem into a parameter comparison task by converting color information into standardized color coordinates (such as L*a*b* values). This parameter transformation simplifies the detection process to a matter of comparing numerical values against reference ranges, enabling rapid automated processing while reducing algorithmic complexity. The parameter change from visual color assessment to numerical coordinate comparison streamlines the entire detection workflow.
Data Source
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AI summary
In a method for identifying colour transitions which are caused by soiling and/or colour fading in at least one section of a document of value (12) of a prescribed document-of-value type on the basis of processing data, which reproduce colour coordinate values for picture elements in a colour space on the basis of the position of the respective regions corresponding to the picture elements in the section of the document of value (12), and of reference data, which reproduce a colour reference distribution, prescribed for a type of documents of value (12), for colour coordinate values in the colour space on the basis of reference positions on a document of value (12) of the document-of-value type, it is ascertained for each of the picture elements whether the colour coordinate values associated with the picture element in the colour space correspond to the colour reference distribution, the colour reference distribution being provided by at least one prescribed, enclosed reference face in the colour space which is provided by at least one linear path, prescribed for the document-of-value type, and a prescribed distance between the points of the reference face and the at least one linear path. The positions of the picture elements whose colour coordinate values are inside or not outside the reference face are compared with prescribed reference positions on the document of value (12), and the result of the comparison is taken as a basis for establishing whether a colour transition caused by soiling or colour fading is present or absent.