TOF Camera Focal Distance Calculation With Lens Thickness Correction
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Solution Overview
Problem
Existing TOF cameras inaccurately convert ranging values to three-dimensional point cloud data due to neglecting lens thickness, leading to significant errors in focal distance calculations, and existing calibration methods are cumbersome and prone to lighting and noise issues.
Innovation Solution
The method involves calculating the horizontal and vertical focal distances based on ranging values from the central and end portions of the lens's angle of view, considering the optical path length and lens thickness, using a TOF sensor to acquire ranging values, and applying distortion correction to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If focal distance is set without considering lens thickness, then device complexity is reduced, but measurement precision deteriorates due to large errors in focal distance calculation
Solution Approach 1:
The patent changes the parameters used in focal distance calculation from simple pinhole model parameters to parameters that account for lens thickness, including the distance from light receiving surface to rear principal surface and distance to entrance pupil. This parameter change resolves the contradiction by improving measurement precision while maintaining reasonable calculation complexity through the use of distortion correction data.
Solution Approach 2:
The patent performs preliminary distortion correction on the distance image before calculating focal distance. This preliminary action removes optical distortions that would otherwise affect measurement precision, allowing for accurate focal distance calculation that accounts for lens thickness without excessively increasing device complexity.
2Ease of manufacture
If conventional pinhole lens model is used, then ease of manufacture is improved, but manufacturing precision deteriorates due to inaccurate three-dimensional coordinate conversion
Solution Approach 1:
The patent modifies the conversion parameters from the simple pinhole model to parameters that incorporate lens thickness effects. By using the distance to rear principal surface and distance to entrance pupil as conversion parameters, the system achieves accurate three-dimensional coordinate conversion while maintaining ease of manufacture through the use of distortion correction technology.
Solution Approach 2:
The patent replaces the mechanical pinhole lens model with an optical system that accounts for actual lens properties. By substituting the simplified mechanical model with an optical model that considers lens thickness and distortion characteristics, the system improves manufacturing precision while maintaining ease of manufacture through software-based correction.
3Device complexity
If lens thickness is neglected in focal distance calculation, then device complexity is reduced, but reliability deteriorates due to significant errors in distance measurement
Solution Approach 1:
The patent changes the optical system modeling parameters to include lens thickness effects by using the distance from light receiving surface to rear principal surface and distance to entrance pupil. This parameter change improves reliability of distance measurement while controlling device complexity through the application of distortion correction algorithms.
Solution Approach 2:
The patent uses distortion correction as a feedback mechanism to improve measurement reliability. By correcting optical distortions based on the distance image and using the corrected data for focal distance calculation, the system achieves reliable distance measurements without excessively increasing device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise determination of focal distances, reducing the need for complex calibration procedures and enhancing the accuracy of three-dimensional point cloud data generation.
Implementation Method 1
a TOF sensor that generates a distance image comprised of a plurality of ranging values corresponding to a time of flight for light elapsed until a projected light is reflected by a subject, passes through an optical system, and is received by a light receiving surface
Data Source
AI summary
In an information processing apparatus, an acquisition unit acquires ranging values of a TOF sensor. A calculation unit calculates a focal distance of an optical system, based on at least one of a horizontal ranging value of an observation point of a subject or a vertical ranging value of an observation point of the subject, a central ranging value of an observation point of the subject, a distance from the light receiving surface to a rear principal surface of the optical system, a distance from the light receiving surface to a position of an entrance pupil of the optical system, and an effective size of the TOF sensor.