Surface Map Determination Using Defocused Imaging Under Mixed Reflectivity
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Solution Overview
Problem
Existing imaging systems have a limited dynamic range, leading to saturation issues when measuring surfaces with regions of varying reflectivities, resulting in either overexposed or underexposed image regions, which compromises the ability to accurately determine surface maps.
Innovation Solution
The method involves positioning the sample surface at a defocused distance Z from the focal measurement plane to obtain a defocused image, followed by applying a backpropagation algorithm to convert the defocused image into an in-focus image with an expanded dynamic range, using an interferometer or similar imaging system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the imaging system uses a limited dynamic range to capture the sample surface, then the measurement process is simple, but regions with varying reflectivities become saturated or too dark, compromising measurement accuracy
Solution Approach 1:
The method performs a preliminary defocused measurement before the final focused measurement. By first capturing a defocused image, the system determines appropriate measurement parameters (integration time, light intensity) that prevent saturation in high-reflectivity regions. This preliminary action enables the subsequent focused measurement to accurately capture both high and low reflectivity regions without saturation.
Solution Approach 2:
The system dynamically adjusts measurement parameters based on the defocused measurement results. The integration time and light intensity are modified according to the reflectivity characteristics observed in the defocused image, allowing the imaging system to adapt to the specific sample being measured and handle varying reflectivities effectively.
2Measurement precision
If the overall light intensity is increased to properly measure low reflectivity regions, then dark regions are captured adequately, but high reflectivity regions become saturated
Solution Approach 1:
The defocused measurement serves as a preliminary step to assess the reflectivity distribution across the sample surface. Based on this assessment, the system determines optimal light intensity and integration time settings that prevent saturation while ensuring adequate illumination of low reflectivity regions.
Solution Approach 2:
The system changes the measurement parameters (light intensity, integration time) based on the defocused measurement results. By adjusting these parameters according to the observed reflectivity characteristics, the system achieves proper exposure for both high and low reflectivity regions in the final focused measurement.
3Reliability
If the overall light intensity is reduced to prevent saturation of high reflectivity regions, then saturation is avoided, but low reflectivity regions become too dark to measure properly
Solution Approach 1:
The defocused measurement provides advance information about the reflectivity distribution, enabling the system to select measurement parameters that prevent saturation while maintaining adequate signal levels in low reflectivity regions.
Solution Approach 2:
Based on the defocused measurement, the system optimizes parameters such as integration time and light intensity to achieve a balance where neither saturation nor excessive darkness occurs in the final focused measurement of regions with varying reflectivities.
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 the determination of surface maps with a wider effective dynamic range, effectively capturing and processing both high and low reflectivity regions, thereby improving the accuracy of surface mapping.
Implementation Method 1
the sample surface may be illuminated, e.g. using a dedicated light source in an interferometer or using background light, which light may be reflected by the sample surface and captured by an imaging system
Implementation Method 2
using a dedicated light source in an interferometer
Data Source
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AI summary
The invention relates to a method for determining a surface map, such as a height map, of a sample surface having a first region with a first reflectivity and a second region with a different reflectivity, wherein use is made of an imaging system for determining an image of the sample surface, wherein the imaging system has a focal measurement plane. The method comprises determining that an image of the sample surface obtained with the imaging system is saturated when the sample surface is arranged in the focal measurement plane of the imaging system; arranging the sample surface in a defocused position at a distance Z from the focal measurement plane of the imaging system along an axis perpendicular to the focal measurement plane such that the image of the sample surface obtained with the imaging system is no longer saturated; obtaining a defocused image of the sample surface arranged in the defocused position with the imaging system; determining an infocus image by backpropagating the defocused image the distance Z by applying a backpropagation algorithm to the defocused image; and determining the surface map of the sample surface based on the infocus image. The invention further relates to an imaging system for determining a surface map of a sample surface having a first region with a first reflectivity and a second region having a second reflectivity. The invention is further related to a digital data carrier comprising a computer program which, when run on a processor of an imaging system according to the invention, causes the imaging system to perform the method according to the invention.