Depth Map Calibration Using Two-Distance Parallax Correction
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Solution Overview
Problem
The spatial positions of dots of light in a depth map generating system change due to parallax caused by the non-coaxial arrangement of the projection and imaging systems, leading to undesirable distortion in the depth map, which varies across different devices due to manufacturing tolerances.
Innovation Solution
A calibration method that calculates three-dimensional positions of dots at two known distances, associates these dots to determine the optical center of the projection system, and uses convergence of lines to predict the spatial position of dots for different distances, incorporating intrinsic properties of the imaging system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an array of dots of light is used instead of flood illumination, then power consumption is reduced and noise is reduced, but spatial distortion occurs due to parallax
Solution Approach 1:
The calibration process performs preliminary measurements at two different known distances to determine the optical center position and parallax characteristics before actual depth map generation. This preliminary characterization of the system geometry allows the parallax effect to be compensated for in subsequent operations, enabling the use of power-efficient dot illumination without sacrificing spatial accuracy
Solution Approach 2:
The system changes operational parameters by measuring at two different distances (z1 and z2) to characterize the parallax effect. By determining how dot positions change with distance, the system calculates correction parameters (optical center position and separation distance) that are then applied to compensate for parallax-induced spatial distortion in the final depth maps
2Device complexity
If manufacturing tolerances are not accounted for, then device complexity is reduced, but each device experiences different parallax distortion
Solution Approach 1:
Each depth map generating system performs its own calibration procedure to determine its specific optical center position and parallax characteristics. The system uses its own projected dots and imaging system to self-characterize its geometry, storing the results for use in compensating its own parallax effects. This self-service approach allows each device to be optimized for its specific manufacturing tolerances without requiring complex external calibration equipment or procedures
3Measurement precision
If traditional calibration methods are used, then accurate calibration is achieved, but calibration time is long and space requirements are large
Solution Approach 1:
The calibration method transitions from requiring physical movement of the system through space to a computational approach that uses measurements at two fixed positions. By measuring dot positions at two different known distances and using geometric convergence calculations, the method determines the optical center and parallax parameters without requiring extensive physical calibration space or time-consuming mechanical adjustments
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 faster and more space-efficient calibration of the depth map generating system, reducing distortion and improving the accuracy of depth maps by aligning the projection and imaging systems.
Implementation Method 1
using the projection system to project an array of dots onto a planar surface located at a first known distance from the projection system
Implementation Method 2
obtaining a first image of the projected dots using the imaging system
Implementation Method 3
The spatial positions of the dots of light, as seen by an imaging system, will change depending upon the distance from the system. This is due to parallax arising from the fact that the imaging system is not coaxial with the sources of the pulses of light
Implementation Method 4
Depth map generation may be via a time-of-flight system in which pulses of light are emitted at known times, and the elapsed time until the pulses of light are detected is measured
Data Source
AI summary
Disclosed herein is a calibration method for a depth map generating system. A projection system and imaging system thereof projects an array of dots onto a planar surface located at a first known distance, obtains a first image of the projected dots, and determines a first set of three-dimensional positions of the projected dots at the planar surface; projects an array of dots onto a planar surface located at a second known distance, obtains a second image of the projected dots, and determines a second set of three-dimensional positions of the projected dots at the planar surface. Projected dots of the first set are associated with projected dots of the second set. Convergence of the lines is used to calculate a center position. The center position is used with the projected dots and intrinsic properties to predict the spatial position of dots of light for different distances of an object.