Image Restoration Filter Frequency Selective Amplification
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Solution Overview
Problem
Image restoration processes amplify noise and alias signals, leading to image deterioration and artifacts like moire and coloring, especially when correcting for optical system diffraction and aberration.
Innovation Solution
An image processing apparatus and method that generates an image restoration filter with tailored amplification factors for frequency components based on the optical transfer function and sampling frequency, specifically addressing alias signals to reduce noise amplification and improve resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an image restoration process is performed to correct optical system deterioration, then image resolution is improved, but noise and alias signals are amplified causing artifacts
Solution Approach 1:
The patent applies different amplification factors to different frequency components in the frequency space. Specifically, it identifies alias signal frequencies (above Nyquist frequency) and applies suppression to those specific frequency regions while maintaining or enhancing amplification for valid frequency components below the Nyquist frequency. This local differentiation of quality (amplification factor) allows resolution improvement in valid bands while preventing artifact generation in alias bands.
Solution Approach 2:
The patent dynamically adjusts the amplification factor parameter based on frequency characteristics. By calculating the amplification factor as a function of frequency (considering the optical transfer function and noise characteristics at different frequencies), it transforms the restoration process from uniform amplification to frequency-selective amplification. This parameter change enables selective enhancement of useful high-frequency components while suppressing alias signals and noise.
2Measurement precision
If high frequency components are amplified in the image restoration process, then image resolution is improved, but alias signals above Nyquist frequency are also amplified generating moire and coloring
Solution Approach 1:
The patent implements frequency-selective quality control by applying different amplification factors to different frequency regions. Valid frequency components (0 to Nyquist frequency) receive amplification factors that enhance resolution, while alias frequency components (above Nyquist frequency) receive amplification factors that suppress or eliminate artifact generation. This local quality differentiation resolves the contradiction between resolution improvement and alias signal suppression.
Solution Approach 2:
The patent converts the harmful effect of alias signal amplification into a beneficial filtering mechanism. By intentionally designing the amplification factor to be less than 1 for frequencies above the Nyquist frequency, it transforms what would normally be harmful alias signal enhancement into a useful alias signal suppression mechanism, while still achieving resolution improvement in the valid frequency range.
Data Source
AI summary
The image processing apparatus includes an image inputting part configured to acquire a captured image produced by an image pickup system including an optical system and an image sensor, a filter producing part configured to produce an image restoration filter, and a restoration processing part configured to perform an image restoration process on the captured image by using the image restoration filter to produce a restored image. The filter producing part is configured to set amplification factors for respective frequency components in the image restoration filter according to a frequency characteristic of an alias signal that may be generated in the image sensor.