# US 9,753,128 B2 · Multi-path compensation using multiple modulation frequencies in time of flight sensor

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 9,753,128 B2
- Document ID: US9753128B2
- Status: Granted
- Kind: B2
- Application number: 13/189,903
- Filed: 2011-07-25
- Published: 2012-02-09
- Granted: 2017-09-05
- Earliest claimed: 2010-07-23
- Assignees: Heptagon Micro Optics Pte. Ltd.
- Applicants: Matthias Schweizer; Thierry Oggier; Bernhard Buettgen
- Inventors: Matthias Schweizer; Thierry Oggier; Bernhard Buettgen
- Web page: https://patentgrep.com/patent/US9753128B2

## CPC

- G01S 7/4912: Receivers
- G01S 17/36: with phase comparison between the received signal and the contemporaneously transmitted signal
- G01S 17/894: Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar
- H04N 13/207: using a single two-dimensional [2D] image sensor
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A method to compensate for multi-path in time-of-flight (TOF) three dimensional (3D) cameras applies different modulation frequencies in order to calculate/estimate the error vector. Multi-path in 3D TOF cameras might be caused by one of the two following sources: stray light artifacts in the TOF camera systems and multiple reflections in the scene. The proposed method compensates for the errors caused by both sources by implementing multiple modulation frequencies.

## Claims

### Claim 1

A time of flight three dimensional imaging system, comprising:
an illumination module that generates modulated light that is intensity modulated at a first frequency and at a second frequency;
a sensor that detects the modulated light at the first frequency and at the second frequency; and
a controller that generates a three dimensional image from the detected modulated light at the first frequency and at the second frequency and compensates for multipath error in the three dimensional image arising from the modulated light traveling an indirect path before detection based, at least in part, on a relationship between (i) a ratio of the generated modulated light at the first frequency and the generated modulated light at the second frequency, and (ii) a ratio of the detected modulated light at the first frequency and the detected modulated light at the second frequency.

### Claim 2 (depends on 1)

A system as claimed in claim 1, wherein the controller determines a vector associated with the multipath error by estimating a phase and an amplitude of the modulated light that traveled the indirect path and corrects a depth measured by the controller based on the vector.

### Claim 3 (depends on 2)

A system as claimed in claim 2, wherein the controller uses iterative approximations to determine the vector.

### Claim 4

A time of flight three dimensional imaging method, comprising:
generating modulated light that is intensity modulated at a first frequency and at a second frequency;
detecting the modulated light at the first frequency and at the second frequency;
generating a three dimensional image from the detected modulated light; and
compensating the three dimensional image for multipath error arising from the modulated light traveling an indirect path before detection based, at least in part, on a relationship between (i) a ratio of the generated modulated light at the first frequency and the generated modulated light at the second frequency, and (ii) a ratio of the detected modulated light at the first frequency and the detected modulated light at the second frequency.

### Claim 5 (depends on 4)

A method as claimed in claim 4, further comprising determining a vector associated with the multipath error by estimating a phase and an amplitude of the modulated light that traveled the indirect path and correcting a depth based on the vector.

### Claim 6 (depends on 5)

A method as claimed in claim 5, further comprising using iterative approximations to determine the vector.

### Claim 7 (depends on 1)

A system as claimed in claim 1, wherein the illumination module generates the modulated light at the first frequency and the second frequency serially in time.

### Claim 8 (depends on 1)

A system as claimed in claim 1, wherein the illumination module generates the modulated light at the first frequency and the second frequency simultaneously but at different optical wavelengths.

### Claim 9 (depends on 4)

A method as claimed in claim 4, further comprising generating modulated light at the first frequency and the second frequency serially in time.

### Claim 10 (depends on 4)

A method as claimed in claim 4, further comprising generating the modulated light at the first frequency and the second frequency simultaneously but at different optical wavelengths.