Digital Watermark Decoding Contrast Enhancement
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Solution Overview
Problem
Point of sale (POS) camera systems face challenges in decoding digital watermarks due to non-linearities in image sensors, which compress small luminance variations, and down-sampling further diminishes these variations, making watermark detection difficult, especially in under-exposed areas and high-resolution images.
Innovation Solution
Applying contrast enhancement to POS camera imagery to enlarge pixel value variations, including those representing watermark data, which helps in reliable decoding even with dark exposures, sensor compression, and downsampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If down-sampling is applied to convert high-resolution barcode imagery to watermark-decoding resolution, then the resolution becomes suitable for watermark decoding, but the small luminance variations representing watermark data are further diminished
Solution Approach 1:
The patent applies contrast enhancement to the high-resolution image before down-sampling occurs. This preliminary action amplifies the small luminance variations that represent watermark data, ensuring that when down-sampling subsequently reduces resolution, the watermark signal remains detectable despite the loss of fine detail inherent in down-sampling operations.
2Productivity
If image sensors with non-linear response are used for barcode reading, then barcode decoding performance is optimized, but small luminance variations representing watermark data are compressed and difficult to detect
Solution Approach 1:
The patent transforms the non-linear sensor response into a linear representation through contrast enhancement processing. By applying contrast enhancement to the captured image, the system compensates for the sensor's non-linear compression of luminance variations, converting the compressed signal back into a form where the watermark data's luminance variations are sufficiently amplified for accurate detection.
3Measurement precision
If contrast enhancement is applied to amplify watermark signal variations, then watermark detection accuracy improves, but information in shadow and highlight regions may be lost
Solution Approach 1:
The patent performs contrast enhancement as a preliminary step before down-sampling and watermark decoding. By enhancing contrast first, the watermark signal is amplified in the high-resolution data structure, allowing subsequent down-sampling to occur without further degrading the already-amplified watermark variations. This sequencing minimizes information loss in critical regions.
Data Source
AI summary
Imagery captured by a point-of-sale scanner (e.g., in a supermarket) for purposes of barcode decoding, is contrast-enhanced preparatory to use for watermark decoding—despite the fact that such operation may sometimes result in contrast between certain pixels being diminished. A great variety of other features and arrangements are also detailed.