Surface Map Imaging Using Defocused Capture for Wide Reflectivity
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Solution Overview
Problem
Existing imaging systems have a limited dynamic range, leading to saturation issues when measuring surfaces with varying reflectivities, resulting in either overly bright or too dark regions that cannot be accurately imaged.
Innovation Solution
The method involves positioning the sample surface at a defocused distance Z from the focal measurement plane to obtain a defocused image, which is then backpropagated using an algorithm to generate an in-focus image with an expanded dynamic range, allowing for accurate imaging of surfaces with wide reflectivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light intensity projected on the sample surface is reduced to prevent saturation, then the imaging system can avoid saturation in high-reflectivity regions, but regions with lower reflectivities may not reflect enough light to allow proper measurement
Solution Approach 1:
The patent applies preliminary action by capturing a defocused image first, where the sample surface is intentionally positioned out of the focal plane. This preliminary defocused capture allows all regions to be recorded within the dynamic range without saturation, and then a backpropagation algorithm is applied to computationally generate the focused image. This preliminary defocused state enables the system to handle the full dynamic range of reflectivity variations before the final measurement is computed.
Solution Approach 2:
The patent replaces the mechanical approach of adjusting light intensity or integration time with a computational method. Instead of mechanically reducing light intensity to prevent saturation, the system uses a backpropagation algorithm to computationally reconstruct the focused image from a defocused capture. This substitution allows the imaging system to maintain high light intensity for better signal-to-noise ratio while avoiding saturation through computational processing rather than physical adjustment.
2Reliability
If the overall integration time of the imaging system is reduced to prevent saturation, then high-reflectivity regions can be measured without saturation, but low-reflectivity regions may not reflect enough light for proper measurement
Solution Approach 1:
The patent uses preliminary action by first capturing a defocused image with extended integration time to ensure sufficient light collection from all regions, then applying backpropagation to generate the focused image. This preliminary defocused capture allows the system to integrate light longer without causing saturation in the final focused image, because the defocused state naturally distributes light intensity across the sensor array.
Solution Approach 2:
The patent substitutes the mechanical adjustment of integration time with a computational backpropagation process. Instead of reducing integration time to prevent saturation, the system extends integration time during the defocused capture and then uses algorithms to computationally reconstruct the focused image, effectively decoupling the integration time parameter from the final image brightness and saturation characteristics.
3Measurement precision
If the sample surface is positioned in the focal measurement plane to obtain a focused image, then sharp imaging is achieved, but saturation occurs in high-reflectivity regions
Solution Approach 1:
The patent applies preliminary action by capturing a defocused image first, where the sample surface is intentionally positioned out of the focal plane. This preliminary defocused capture records light intensity information from all regions within the dynamic range without saturation, and then a backpropagation algorithm is applied to computationally generate the focused image. This preliminary defocused state enables the system to handle the full dynamic range of reflectivity variations before the final focused measurement is computed.
Solution Approach 2:
The patent replaces the mechanical positioning of the sample surface with a computational approach. Instead of physically positioning the sample at the focal plane to achieve focus, the system captures a defocused image and then uses a backpropagation algorithm to computationally reconstruct the focused image. This substitution allows the system to achieve focus quality without being constrained by the physical focal plane, thereby avoiding saturation in high-reflectivity regions.
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 effectively increases the imaging system's dynamic range, enabling clear imaging of both bright and dark regions by mixing light intensities, thus overcoming saturation issues and providing a more detailed surface map.
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
an infocus image is determined by backpropagating the defocused image the distance Z by applying a backpropagation algorithm to the defocused image
Data Source
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 second reflectivity. 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 including 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.