TOF Image Processing for Shadow-Compensated Distance Sensing
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Solution Overview
Problem
Interfering objects between a TOF camera's light sources and the object of interest can cause accuracy issues in measuring distances, such as when a teat cup obstructs light from reaching a teat in a milking robot scenario.
Innovation Solution
An image processor adjusts distance data by compensating for shadow effects using a lookup table that determines adaptation amounts based on which light sources are obstructed, employing reverse ray-tracing and extrapolation to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a TOF camera uses multiple light sources to illuminate the scene, then the coverage and illumination intensity are improved, but shadow effects occur when objects block light from reaching other objects
Solution Approach 1:
The system performs preliminary ray-tracing calculations to predict which light sources will be blocked by which objects before actual measurement. This allows the system to pre-identify shadow regions and compensate for them in advance, rather than reacting to shadow effects after they occur.
Solution Approach 2:
The patent introduces an intermediary computational model (ray-tracing algorithm) that simulates light propagation and identifies shadow regions. This intermediary model acts as a mediator between the physical light sources and the measurement process, allowing the system to understand and compensate for shadow effects without changing the physical illumination setup.
2Measurement precision
If the system compensates for shadow effects by adjusting distance data, then measurement precision is improved, but device complexity increases due to ray-tracing calculations
Solution Approach 1:
The system applies shadow compensation selectively only to regions identified as shadowed through ray-tracing, rather than processing the entire scene uniformly. This partial action approach reduces computational overhead while maintaining measurement precision where it is most needed - in shadowed regions.
Solution Approach 2:
The ray-tracing algorithm uses the same geometric and optical parameters that are already present in the TOF system (light source positions, object positions from preliminary scans). The system serves itself by utilizing its own existing data to perform shadow analysis, avoiding the need for external or additional complex measurement systems.
3Measurement precision
If real-time shadow compensation is performed, then distance measurement accuracy is improved, but processing time increases
Solution Approach 1:
The system performs ray-tracing and shadow identification in advance, before the actual distance measurement is needed. This preliminary action allows the compensation factors to be pre-calculated and stored, so that during real-time operation, only simple lookups and adjustments are required, minimizing processing time.
Solution Approach 2:
The shadow compensation is performed periodically or at predetermined intervals rather than continuously for every measurement. The system updates shadow maps at appropriate intervals and holds them between updates, reducing the frequency of computationally intensive ray-tracing operations while maintaining accurate compensation during measurements.
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
The solution provides high-accuracy distance data even in scenarios where light is partially blocked, enabling precise attachment of teat cups by a milking robot.
Implementation Method 1
A TOF camera is a range imaging system that employs time-of-flight techniques to resolve distance between the camera and imaged objects for each point of the image. The TOF camera measures the round trip time of an artificial light signal provided by a laser or a light emitting diode (LED).
Implementation Method 2
The TOF camera measures the round trip time of an artificial light signal provided by a laser or a light emitting diode (LED).
Data Source
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AI summary
An image processor (140) obtains image data (Dimg) registered by a time-of-flight, TOF, imaging system (110). The image data (Dimg) represents a scene (100) illuminated by at least two light sources (121, 122, 123, 124) calibrated to enable the image processor (140) to include distance data in the image data (Dimg). The image processor (140) determines if a shadow effect exists by which at least one first object (TC) in the scene (100) obstructs light from at least one light source (121, 122, 123, 124) from reaching at least one part of at least one second object in the scene (100). The at least one first object (TC) has a known position and spatial extension relative to the TOF imaging system (110) and the at least two light sources (121, 122, 123, 124). If it is determined that the shadow effect exists, the image processor (140) adjusts the distance data to compensate for the at least one light source (121, 122, 123, 124) whose light did not reach the at least one part of the at least one second object by obtaining an adaptation amount (dΔ) from a lookup table (1450).