# US 2017/0102228 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 2017/0102228 A1
- Document ID: US20170102228A1
- Status: Published application
- Kind: A1
- Application number: 14/907,009
- Filed: 2014-06-30
- Published: 2017-04-13
- 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/US20170102228A1

## CPC

- G01B 11/16: for measuring the deformation in a solid, e.g. optical strain gauge
- G01B 11/165: {by means of a grating deformed by the object}
- G06T 7/0004: {Industrial image inspection}
- G06T 7/246: using feature-based methods, e.g. the tracking of corners or segments
- G06T 2207/20056: Discrete and fast Fourier transform, [DFT, FFT]
- G06T 2207/20132: Image cropping
- 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 is found by carrying out a two-dimensional Fourier transformation on an image of a two-dimensional grid image on the surface of an object taken by a camera, and the displacement of the surface of the object is measured 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 the number of pixels used for the measurement is smaller than that in the sampling moire method. The displacement can be found at a high speed.

## Claims

### Claim 1

A measurement method for measuring a displacement of a surface of an object from an image of a two-dimensional grid image on the surface of the object taken by a camera, comprising the steps of:
taking an image of a two-dimensional grid image on a surface of an object with a camera in such a state that the direction of camera pixels is adjusted towards said image of the two-dimensional grid image before displacement, and at the same time one period of said image of the two-dimensional grid image in the x direction is adjusted to Nx pixels of the camera and one period in the y direction is adjusted to Ny pixels of the camera, where Nx and Ny are integers greater than 2;
obtaining a phase from said image of the two-dimensional grid image for the frequencies in the x direction and the y direction that correspond to one period of said grid in said image of the two-dimensional grid image; and
finding a displacement of the surface of the object from the phase.

### Claim 2 (depends on 1)

The measurement method according to claim 1, further comprising the steps of:
smoothing said image of the two-dimensional grid image in the x direction by Nx pixels or smoothing said image of the two-dimensional grid image in the y direction by Ny pixels so that any one of the grid lines in the x direction or the y direction disappears.

### Claim 3 (depends on 1)

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

### Claim 4

A measurement program for measuring a displacement on a surface of an object from an image of a two-dimensional grid image on the surface of the object taken by a camera and allowing a computer to run the steps of:
inputting an image of a two-dimensional grid image before displacement;
obtaining a phase from the image data of Nx×Ny pixels that correspond to one period of the grid in the x direction and the y direction in said image of the two-dimensional grid image for the frequencies in the x direction and the y direction that correspond to one period of said grid in said image of the two-dimensional grid image; and
finding a displacement on the surface of the object from the phase.

### Claim 5 (depends on 4)

A computer readable recording medium in which the measurement program according to claim 4 has been recorded.

### Claim 6 (depends on 2)

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