Time-of-flight eyeglass fitting using depth map segmentation
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Solution Overview
Problem
Existing systems for generating 3D models of faces for eyeglass fitting using time-of-flight technology face challenges in accurately calculating distances, especially when points shadow each other, and require external scales for precise measurements, making it impractical for handheld devices like smartphones.
Innovation Solution
A system that uses a time-of-flight scanner integrated with a handheld device to capture depth maps of a person wearing eyeglass frames, allowing for the calculation of three-dimensional coordinates without the need for an external scale, by identifying common measurement points and using known scan distances to determine fabrication measurements for prescription lenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a time-of-flight system is used to generate a three-dimensional mapping of space, then depth information can be obtained, but accurate calculation of distances between points is compromised when points shadow each other during scanning
Solution Approach 1:
The patent divides the scanning process into multiple segments by capturing images from multiple different positions. Instead of relying on a single time-of-flight scan that may have shadowed areas, the system segments the measurement task into multiple partial observations from different angles, then combines them to achieve complete and accurate measurement of all facial points.
Solution Approach 2:
The patent introduces an intermediary computational process that uses known distances between camera positions and the measured points to calculate and correct depth information. This intermediary calculation layer reconciles the incomplete data from individual scans by using geometric relationships and known reference distances to infer accurate positions of shadowed points.
2Measurement precision
If an external scale is used to apply sense of scale to time-of-flight mapping, then measurement precision is improved, but device complexity and ease of operation are worsened due to requiring additional equipment
Solution Approach 1:
The system performs self-service by using its own internal resources (the handheld device itself) as the measurement scale. Instead of requiring an external scale object, the device uses its known physical dimensions and pre-stored distance information about its own camera positions to establish the measurement scale automatically during the scanning process.
Solution Approach 2:
The handheld device serves multiple functions: it acts as both the scanning instrument and the measurement scale reference. The device's camera system is used for capturing depth information, while simultaneously its known geometric properties and stored distance data serve as the reference scale for all measurements, eliminating the need for separate scaling equipment.
3Loss of information
If multiple images are captured from different positions to eliminate shadowing, then measurement completeness is improved, but time consumption increases
Solution Approach 1:
The system performs preliminary action by pre-storing distance information about camera positions and pre-identifying key facial landmark points. This preparation allows the multiple images to be processed more efficiently, as the computational burden is reduced by having reference data already available, thus minimizing the time penalty of taking multiple images.
Solution Approach 2:
The system uses feedback by analyzing the captured images to identify which points were successfully measured and which remain shadowed. This feedback information guides the selection of subsequent camera positions, allowing the system to intelligently target areas that need additional observation, thereby reducing the total number of images required compared to a fixed multi-position approach.
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
Enables accurate and practical measurement of eyeglass frame dimensions and anatomical variables for proper lens fabrication, ensuring precise fitting and customization without the need for external scales, suitable for use in various situations, including selfies and everyday activities.
Implementation Method 1
The time difference between the emission of the light and receiving the reflected light can be used to determine distance
Implementation Method 2
The laser beam reflects off the various surfaces of the object. The lidar system analyzes the reflected laser light to determine the distance and size of the various surfaces
Data Source
AI summary
A system and method for determining the measurements needed to fabricate prescription eyeglasses. A person is scanned with a time-of-flight scanner while wearing the eyeglass frames. This produces depth maps from known distances. Common measurement points are identified within at least some of the scans. The positional changes of the common measurement points and the known distance to the imaging camera are utilized to map three dimensional coordinates for the measurement points using an actual measurement scale. Fabrication measurements are calculated between the various three-dimensional coordinates in the same scale.