Bilateral High Pass Filter for Edge Sharpening Without Noise Amplification
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Solution Overview
Problem
Existing digital image filtering technologies, such as low-pass filters, often blur edges in images due to their noise reduction methods, and there is a need for techniques that can enhance edges without amplifying noise, especially in low-quality camera systems like those found in cellular telephones.
Innovation Solution
A bilateral high pass filter is introduced, which calculates a kernel based on Euclidean distances and thresholding operations to selectively weight pixels for edge sharpening, potentially combined with a bilateral low pass filter for noise reduction, using a 2D convolution process to produce filtered pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-pass filter is used for noise reduction, then noise is averaged away, but edges are blurred
Solution Approach 1:
The filter is segmented into two distinct components: a spatial low-pass filter for noise reduction and a photometric low-pass filter for edge preservation. Each component operates independently with its own kernel, allowing noise averaging while preserving edges through selective pixel weighting based on color similarity.
Solution Approach 2:
The photometric filter applies local quality by weighting pixels differently based on their color similarity to the target pixel. Pixels with similar colors receive higher weights, while pixels with dissimilar colors (edges) receive lower weights, thereby preserving edge sharpness while reducing noise in homogeneous regions.
2Manufacturing precision
If a bilateral filter is used to preserve edges, then edge blurring is reduced, but edge sharpening is not achieved
Solution Approach 1:
Instead of only preserving edges through smoothing, the invention inverts the approach by using a high-pass filter component that enhances edge sharpness. The high-pass spatial filter kernel emphasizes differences between neighboring pixels, actively sharpening edges while the photometric component maintains color consistency.
3Manufacturing precision
If edge sharpening is applied to enhance edges, then edge sharpness is improved, but noise is amplified
Solution Approach 1:
The invention merges a high-pass spatial filter for edge sharpening with a photometric filter for noise control. The combined bilateral high-pass filter applies both operations simultaneously: the spatial component sharpens edges by emphasizing high-frequency content, while the photometric component suppresses noise by weighting pixels based on color similarity, thereby achieving edge enhancement without noise amplification.
Data Source
AI summary
A target pixel and surrounding pixels corresponding to the target pixel are obtained from a digitally represented image. A bilateral high pass filtering kernel is determined based at least in part upon the target pixel and the surrounding pixels. A high pass spatial filtering kernel is provided and multiplied with the high pass photometric filtering kernel to provide a bilateral high pass filtering kernel. The resulting bilateral high pass filtering kernel is thereafter applied to the target pixel and the surrounding pixels to provide a filtered pixel. When it is desirable to combine noise filtering capabilities with sharpening capabilities, the bilateral high pass filter of the present invention may be combined with a bilateral low pass filtering kernel to provide a combined noise reduction and edge sharpening filter. The present invention may be advantageously applied to a variety of devices, including cellular telephones that employ image sensing technology.