White-Light Interferometer Image Calibration for Fringeless 3D Measurement
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Solution Overview
Problem
White-light interferometric systems are limited in performing lateral measurement and defect detection due to interference fringes in the image formed at the objective focal point, and existing phase shift methods result in a limited imaging range and longer processing times for fringeless images.
Innovation Solution
A method and apparatus for image calibration that involves acquiring a sequence of interference images, calculating sharpness and contrast focusing index curves, and adjusting the image formation position to align the peaks of these curves, allowing for the acquisition of clear images free of interference fringes, enabling real-time two-dimensional and three-dimensional measurements without additional processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a white-light interferometric system is used for lateral measurement and defect detection, then three-dimensional profile measurement is enabled, but interference fringes appear in the image formed at the objective focal point
Solution Approach 1:
The patent extracts the harmful interference fringes from the image by acquiring images at multiple defocus positions and processing them to obtain fringeless images, thereby separating the useful measurement information from the harmful visual artifacts
Solution Approach 2:
The patent introduces an intermediary processing step using phase shift method and image combining operations to transform the interferometric images into fringeless images, serving as a mediator between the raw interferometric data and the final measurement output
2Object-affected harmful factors
If phase shift method is used to calculate three-dimensional profile, then interference fringes are eliminated, but imaging range is limited and processing time increases
Solution Approach 1:
The patent performs preliminary image acquisition at multiple defocus positions before the final measurement, acquiring a sequence of images that are then processed to obtain the three-dimensional profile, thereby preparing data in advance to reduce overall processing time
Solution Approach 2:
The patent maintains continuous image acquisition and processing operations, acquiring images at multiple positions and continuously processing them through phase shift method and image combining operations to obtain the final three-dimensional profile measurement
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 enhances precision in auto-focusing and allows for high-contrast image acquisition within the coherent range, facilitating both two-dimensional and three-dimensional surface profile measurements without changing the objective lens, thereby improving imaging quality and efficiency.
Implementation Method 1
an interferoscope set, capable of transforming the reflected light beam into a reference light beam and a measurement light beam incident on an object to be tested and reflected to the interferoscope set so as to combine with the reference light beam to form an interfered light beam
Implementation Method 2
a beam splitting unit, capable of reflecting the light beam to generate a reflected light beam
Data Source
AI summary
The present invention relates to a method for image calibration and an apparatus for image acquiring. In the method for image calibration, the image formation position for an image acquiring unit of the apparatus is calibrated according to the relative location of the image acquiring unit to a objective lens of the apparatus, wherein the relative location is determined by calculating the focus index of the image acquired by the image acquiring unit so that a clear and sharp interferogram can be obtained for three dimensional surface profile measuring. In addition, it is possible to obtain a clear and sharp image without any interference fringe outside the coherent range by adjusting the image formation position, which is capable of being utilized for two dimensional defect detection and dimension measurement.