# US 11,441,896 B2 · Inter-reflection detection apparatus and inter-reflection detection method

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- Number: US 11,441,896 B2
- Document ID: US11441896B2
- Status: Granted
- Kind: B2
- Application number: 16/483,461
- Filed: 2017-11-28
- Published: 2020-01-30
- Granted: 2022-09-13
- Earliest claimed: 2017-03-08
- Assignees: OMRON Corporation
- Applicants: OMRON Corporation
- Inventors: Yasuhiro Ohnishi
- Web page: https://patentgrep.com/patent/US11441896B2

## CPC

- G01B 11/2527: {with phase change by in-plane movement of the patern}
- G01B 11/2536: {using several gratings with variable grating pitch, projected on the object with the same angle of incidence}
- G01B 11/25: by projecting a pattern, e.g. {one or more lines,} moiré fringes on the object (G01B11/255 takes precedence {; image analysis for depth or shape recovery G06T7/50})
- G06T 7/521: from laser ranging, e.g. using interferometry; from the projection of structured light
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL

## Abstract

Provided is an inter-reflection detection apparatus including: an irradiation unit configured to emit light having variable-frequency sinusoidal patterns; an image acquisition unit configured to acquire an image of an object irradiated with the light from the irradiation unit; a phase determination unit configured to determine a phase at each position in the image; and a detection unit configured to detect a region in which inter-reflection occurs. The detection unit is configured to determine a phase difference between a phase acquired from an image generated by irradiation of a low-frequency sinusoidal pattern and a phase acquired from an image generated by irradiation of a high-frequency sinusoidal pattern for a plurality of combinations of low-frequency waves and high-frequency waves, and determine that inter-reflection occurs in a region in which the phase difference for any one of the plurality of combinations is equal or more than a threshold.

## Claims

### Claim 1

An inter-reflection detection apparatus, comprising:
a light source configured to emit light having variable-frequency sinusoidal patterns;
a camera configured to acquire an image of an object irradiated with the light from the irradiation unit; and
a processor configured to determine a phase at each position in the image, and detect a region in which inter-reflection occurs,
wherein the processor is configured to:
for each of a plurality of combinations of low-frequency sinusoidal patterns and high-frequency sinusoidal patterns, determine a phase difference between:
a first phase acquired by estimation from an image generated by irradiation of the low-frequency sinusoidal pattern; and
a second phase acquired by phase connection from: an image generated by irradiation of the high-frequency sinusoidal pattern; and the acquired first phase, the phase connection comprising converting an estimated phase from the image generated by the irradiation of the high frequency sinusoid pattern into a continuous variable; and
determine that inter-reflection occurs in a region in which the determined phase difference for any one of the plurality of combinations is equal to or more than a threshold.

### Claim 2 (depends on 1)

The inter-reflection detection apparatus according to claim 1,
wherein respective cycles of the high-frequency sinusoidal patterns in the plurality of combinations are all the same, and
respective cycles of the low-frequency sinusoidal patterns in the plurality of combinations are integral multiples of the cycle of the high-frequency sinusoidal patterns.

### Claim 3 (depends on 1)

The inter-reflection detection apparatus according to claim 1, wherein the cycles of the low-frequency sinusoidal patterns in the plurality of combinations are mutually different, and are integral multiples of a shortest cycle.

### Claim 4 (depends on 3)

The inter-reflection detection apparatus according to claim 3, wherein the cycles of the low-frequency sinusoidal patterns in the plurality of combinations are prime-number multiples of a shortest cycle.

### Claim 5

An inter-reflection detection method, comprising:
acquiring images of an object irradiated with light of a plurality of low-frequency sinusoidal patterns and high-frequency sinusoidal patterns for each of a plurality of combinations of low-frequency sinusoidal patterns and high-frequency sinusoidal patterns:
determining a phase difference between:
a first phase acquired by estimation from an image generated by irradiation of the low-frequency sinusoidal pattern; and
a second phase acquired by phase connection from:
an image generated by irradiation of the high-frequency sinusoidal pattern; and
the acquired first phase, wherein the phase connection comprises converting an estimated phase from the image generated by the irradiation of the high frequency sinusoid pattern, into a continuous variable; and
determining that inter-reflection occurs in a region in which the phase difference for any one of the plurality of combinations is equal to or more than a threshold.

### Claim 6 (depends on 5)

A non-transitory computer-readable storage medium storing a program that causes a computer to execute each step of the method according to claim 5.