3D Shape Measuring Apparatus Using Phase Unwrapping for Wide Density Objects
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Solution Overview
Problem
Conventional three-dimensional shape measurement techniques, such as the stereo phase-shift method, face challenges when measuring objects with wide density ranges, as they require multiple images and increased exposure conditions to reduce noise, which can damage sensitive objects like cultural artifacts and prolong image capture time.
Innovation Solution
A three-dimensional shape measuring apparatus that projects a stripe pattern and a reference position pattern, allowing for simultaneous image capture from multiple directions under varying exposure conditions, reducing the number of captured images needed while maintaining high accuracy through High Dynamic Range (HDR) combination and phase unwrapping techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple images are captured under different exposure conditions to reduce noise influence, then measurement accuracy is improved, but the number of captured images increases and image capturing time lengthens
Solution Approach 1:
The patent applies preliminary action by projecting gray code patterns before stripe patterns to pre-identify the period number of each pixel. This preliminary period identification allows the subsequent phase calculation to be performed more efficiently, reducing the need for multiple repeated measurements and thereby shortening the overall image capturing time while maintaining measurement accuracy.
2Measurement precision
If multiple gray codes are projected to specify phase period, then measurement accuracy is improved, but the number of captured images increases
Solution Approach 1:
The patent extracts the period identification function from the stripe pattern phase calculation process by using separate gray code patterns. This extraction allows the period number to be determined independently before phase calculation, eliminating the need to capture multiple images for both period identification and phase measurement, thereby reducing the total number of captured images while maintaining accuracy.
3Measurement precision
If light exposure is increased to improve image quality, then measurement accuracy is improved, but damage to cultural properties increases
Solution Approach 1:
The patent uses preliminary gray code projection to establish period information before stripe pattern projection. This preliminary action enables more efficient phase calculation that requires fewer repeated exposures, thereby reducing the cumulative light exposure to cultural properties while maintaining image quality and measurement accuracy through the pre-established period data.
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 three-dimensional shape measurement of objects with wide density ranges using fewer images, minimizing light exposure and image capture time, thus preserving sensitive objects and improving measurement efficiency.
Implementation Method 1
a projection unit that projects a stripe pattern having a luminance that changes periodically, and a reference position pattern indicating a position of at least one period, of a plurality of periods of the stripe pattern, as a reference position
Implementation Method 2
an image capturing unit that captures images of the measurement-target object from a plurality of directions
Data Source
AI summary
A control apparatus acquires a group of images, including an image acquired by capturing an image of an object irradiated with first pattern light, an amount of the first pattern light changing periodically, in a predetermined direction, and an image acquired by capturing images of the object irradiated with second pattern light, an amount of the second pattern light changing periodically, in the predetermined direction, and having a phase difference from the first pattern light. The control apparatus also acquires one image by capturing an image of the object irradiated with third pattern light, that provides for identification of a position of at least one period, of a plurality of periods, included in one of the first pattern light and the second pattern light, and calculates a three-dimensional shape of the object based on the group of images and the one image, for each of a plurality of directions.