# US 2018/0128602 A1 · Measurement method, measurement apparatus, measurement program and computer readable recording medium in which measurement program has been recorded

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- Number: US 2018/0128602 A1
- Document ID: US20180128602A1
- Status: Published application
- Kind: A1
- Application number: 14/906,987
- Filed: 2014-06-30
- Published: 2018-05-10
- Earliest claimed: 2014-06-30
- Assignees: 4D Sensor Inc.
- Applicants: 4D Sensor Inc.
- Inventors: Yoshiharu MORIMOTO; Akihiro MASAYA; Akifumi TAKAGI
- Web page: https://patentgrep.com/patent/US20180128602A1

## CPC

- G01B 11/2513: {with several lines being projected in more than one direction, e.g. grids, patterns}
- 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})
- G01B 11/254: {Projection of a pattern, viewing through a pattern, e.g. moiré}
- 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

A phase of a specific frequency component of an image of a grid image on the surface of an object taken by a camera is found, and the location of the surface of the object is found from the phase. As a result, measurement that is strong against noise can be carried out without projecting a grid having a brightness distribution of precise cosine waves. In addition, the process is simple and can be used for the surface of a moving object. The number of pixels used for the measurement is smaller than that in the sampling moire method.

## Claims

### Claim 1

A measurement method for measuring the location of a surface of an object from an image of a grid image on the surface of the object taken by a camera, comprising the steps of:
inputting an image taken by a camera in an adjusted state where one grid period of said grid image consists of N pixels where N is an integer greater than 2;
sampling a number of sequential pixels from the inputted image;
finding a phase of a frequency component where one period consists of N pixels from the image of the sampled sequential pixels; and
finding the location of the surface of the object from said phase.

### Claim 2 (depends on 1)

The measurement method according to claim 1, further comprising the steps of:
finding a phase on a reference plane; and
finding the form of the surface of the object through phase unwrapping (phase connection) that is carried out on phases in the reference plane and phases on the surface of the object.

### Claim 3 (depends on 2)

The measurement method according to claim 2, wherein the location of the surface of the object is a height, said grid image is projected onto the surface of the object via a grid with light from a light source, and the form of the surface of the object is gained by finding the height of the surface of the object.

### Claim 4 (depends on 3)

The measurement method according to claim 3, wherein the height of the center of the camera lens and the height of the light source are the same relative to the reference plane, and images of the surface of the object and the surface of said grid are taken by said camera in such a state as to be parallel to said reference plane.

### Claim 5 (depends on 1)

A measurement apparatus with which the measurement method according to claim 1 can be implemented.

### Claim 6

A measurement program for allowing a computer to run the steps of:
inputting a camera image that is gained by taking an image of a one-dimensional grid on a surface of an object;
gaining a phase of image data with N pixels that correspond to one period of the image; and
calculating the location of the surface of the object from said phase.

### Claim 7 (depends on 6)

A computer readable recording medium in which the measurement program according to claim 6 has been recorded.

### Claim 8 (depends on 2)

A measurement apparatus with which the measurement method according to claim 2 can be implemented.

### Claim 9 (depends on 3)

A measurement apparatus with which the measurement method according to claim 3 can be implemented.

### Claim 10 (depends on 4)

A measurement apparatus with which the measurement method according to claim 4 can be implemented.