Wide-Angle Optical System Peripheral Light and Resolution Balance
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Solution Overview
Problem
It is challenging to manufacture a small, inexpensive optical system for surveillance cameras that can capture wide-angle images with high resolution while maintaining a sufficient amount of peripheral light, as there is a trade-off between peripheral light and aberration, and existing restoration processes based on optical transfer functions are not effective in all situations.
Innovation Solution
An imaging device with an optical system that includes an imaging element and a restoration processing unit, where the optical system has a balanced performance between peripheral light and resolution, with specific conditions such as an angle of view greater than 90 degrees, a light amount evaluation region with a ratio of 25% or more at a certain wavelength, and a modulation transfer function (MTF) value of 15% or higher at half of the Nyquist frequency, to improve image quality through restoration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a small and inexpensive optical system is used, then the size and cost are reduced, but the resolution performance and peripheral light amount deteriorate
Solution Approach 1:
The patent applies parameter changes by establishing specific quantitative criteria for optical system parameters (angle of view greater than 90 degrees, light amount ratio of 25% or more at evaluation wavelength, MTF value of 15% or more at half Nyquist frequency). These parameter specifications enable the optical system to achieve wide-angle coverage while maintaining sufficient peripheral light and resolution performance, resolving the contradiction between cost-effective design and performance requirements.
2Length of moving object
If a small and inexpensive optical system is used, then the size is reduced, but the peripheral light amount deteriorates
Solution Approach 1:
The patent addresses this contradiction by specifying parameter ranges that balance optical system compactness with peripheral illumination. The light amount evaluation region is defined as 80% or more of half the diagonal length of the imaging surface, with a minimum light amount ratio of 25% at the first evaluation wavelength. These parameter specifications ensure that even in compact wide-angle optical systems, sufficient peripheral light reaches the imaging element.
3Manufacturing precision
If a large and expensive optical system is used, then the resolution performance is improved, but the size and cost increase
Solution Approach 1:
The patent establishes minimum performance thresholds (MTF value of 15% or more at half Nyquist frequency, light amount ratio of 25% or more) that define the boundary between acceptable and unacceptable performance. This allows selection of cost-effective optical systems that meet the required performance level without unnecessarily specifying higher-performance, more expensive alternatives. The angle of view requirement of greater than 90 degrees further guides the selection toward appropriate wide-angle optical designs.
4Manufacturing precision
If restoration process based on optical transfer function is applied, then the resolution is improved, but the image quality may be degraded when SN ratio is low
Solution Approach 1:
The patent applies preliminary action by establishing optimal optical system parameters before image capture. By designing the optical system to meet specific criteria (angle of view >90 degrees, sufficient peripheral light distribution, adequate MTF values), the system ensures high signal quality at the source. This preliminary optimization of the optical path reduces the need for aggressive restoration processing, thereby preventing noise amplification while still achieving resolution improvement when restoration is applied.
Data Source
AI summary
A restoration processing unit performs a restoration process based on an optical transfer function of an optical system for a target image. The entire angle of view of the optical system is greater than 90 degrees. A light amount evaluation region of the optical system is a region in which a distance from the center of an image formation plane is not less than 80% of half of the length of a diagonal line of an imaging surface of an imaging element. When a first evaluation wavelength is used, the ratio of the amount of light in the light amount evaluation region to the amount of light in a region of the optical system corresponding to the center of the image formation plane is not less than 25%. When a second evaluation wavelength is used, the value of the MTF of the optical system acquired at half of the Nyquist frequency of the imaging element is not less than 15%.