Calibration method, calibration device, and calibration system including the device

• US 8,400,505 B2
• Filed: 05/19/2009
• Issued: 03/19/2013
• Est. Priority Date: 05/19/2008
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Oyama, Ichiro, Imamura, Norihiro
• Primary Examiner(s): LIN, WEN TAI
• Application Number:
  US12/668,915
• Publication Number:
  US 20100201809A1
• Time in Patent Office: 1,400 Days
• Field of Search: None
• US Class Current: 348/135
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: G01C 3/14 with binocular observation at a single point, e.g. stereoscopic type G01C3/20 takes precedence
• CPC Class Codes: H04N 13/239 using two 2D image sensors having a relative position equal to or related to the interocular distance H04N13/243 takes precedence
• CPC Class Codes: H04N 13/246 Calibration of cameras
• CPC Class Codes: H04N 2013/0081 Depth or disparity estimation from stereoscopic image signals
• CPC Class Codes: H04N 25/61 the noise originating only from the lens unit, e.g. flare, shading, vignetting or "cos4"

Abstract

A calibration device and method calibrates a distance measuring device which provides captured images with significant lens aberration. The calibration device and method estimate a camera parameter representing a characteristic of each imaging system of a distance measuring device, and perform the following: capture, using the distance measuring device, an image of a reference chart which (i) represents a geometric pattern in which elements are arranged and (ii) is positioned to have a predetermined positional relationship with the distance measuring device; modify a luminance distribution affected by aberration of the lens in the captured image of the reference chart; calculate, as a feature point position, a gravity center position of each element in the captured image whose luminance distribution is modified; and estimate the camera parameter using the feature point position calculated in the calculating and an approximate actual gravity center position in the reference chart.

Claims

1. A calibration method for estimating a camera parameter representing a characteristic of imaging systems of a distance measuring device, each imaging system including a lens and an imaging area corresponding to the lens, and the calibration method comprising:

capturing, using the distance measuring device, an image of a reference chart which (i) represents a geometric pattern in which elements are arranged and (ii) is positioned to have a predetermined positional relationship with the distance measuring device;

modifying a luminance distribution affected by aberration of the lens in the captured image of the reference chart;

calculating, as a feature point position, a gravity center position of each element in the captured image whose luminance distribution is modified;

estimating the camera parameter using the feature point position calculated and an approximate actual gravity center position in the reference chart; and

subtracting from a luminance value of each of the pixels, a removal value that is a value obtained by adding a predetermined offset value to a minimum luminance value within a corresponding one of calculation areas segmented for respective elements within the captured image,

wherein the luminance distribution affected by the aberration of the lens is modified by subtracting the removal value from the luminance value of each pixel.

2. The calibration method according to claim 1,

wherein the removal value is subtracted from the luminance value of each pixel such that the offset value is between 2.5% and 40% inclusive of a difference value between a maximum luminance value and the minimum luminance value within the calculation area.

3. The calibration method according to claim 1, further comprising:

correcting a luminance distribution affected by (i) variation in sensitivity within the imaging area and (ii) variation in illuminance of a light source which projects light on the reference chart, and

the removal value is subtracted from the luminance value of the captured image whose luminance is corrected.

4. The calibration method according to claim 3,

wherein, the luminance distribution affected by (i) the variation in sensitivity within the imaging area and (ii) the variation in illuminance of the light source which projects light on the reference chart is corrected using a luminance distribution in a captured image of a illuminance distribution correction chart with a uniform color, the captured image being captured under approximately the same imaging condition for the reference chart.

5. The calibration method according to claim 1,

wherein the geometric pattern of the reference chart is a dot pattern in which approximately circular elements are arranged, and

the captured image of the reference chart is captured by the distance measuring device such that a diameter of each of the approximately circular elements corresponds to 25 pixels or more in the captured image.

6. A calibration device which estimates a camera parameter representing a characteristic of imaging systems of a distance measuring device using a captured image of a reference chart representing a geometric pattern, each imaging system including a lens and an imaging area corresponding to the lens, and the calibration device comprising:

an aberration luminance modification unit configured to modify a luminance distribution affected by aberration of the lens in the captured image;

a feature point position calculation unit configured to calculate, as a feature point position, a gravity center position of each of elements in the captured image whose luminance distribution is modified by the aberration luminance modification unit;

a camera parameter estimation calculation unit configured to estimate the camera parameter using the feature point position calculated by the feature point position calculation unit and an approximate actual gravity center position in the reference chart; and

an offset removal unit configured to subtract, from a luminance value of each of the pixels, a removal value that is a value obtained by adding a predetermined offset value to a minimum luminance value within a corresponding one of calculation areas segmented for respective elements within the captured image,

wherein the luminance distribution affected by he aberration of the lens is modified by subtracting the removal value from the luminance value of each pixel.

7. A calibration system, comprising:

a reference chart representing a geometric pattern;

a distance measuring device including imaging systems each including a lens and an imaging area corresponding to the lens; and

a calibration device which estimates a camera parameter representing a characteristic of each imaging system, using a captured image of the reference chart captured by the distance measuring device,

wherein the calibration device includes;

an aberration luminance modification unit configured to modify a luminance distribution affected by an aberration of the lens;

a feature point position calculation unit configured to calculate, as a feature point position, a gravity center position of each of elements in the captured image whose luminance distribution is modified by the aberration luminance modification unit;

a camera parameter estimation calculation unit which estimates the camera parameter using the feature point position calculated by the feature point position calculation unit and an approximate actual gravity center position in the reference chart; and

an offset removal unit configured to subtract, from a luminance value of each of the pixels, a removal value that is a value obtained by adding a predetermined offset value to a minimum luminance value within a corresponding one of calculation areas segmented for respective elements within the captured image,

wherein the luminance distribution affected by he aberration of the lens is modified by subtracting the removal value from the luminance value of each pixel.

8. The calibration system according to claim 7,

wherein the reference chart represents a dot pattern in which approximately circular elements are arranged, and

a color of each approximately circular element has a tone brighter than a tone of a background color.

9. A non-transitory computer-readable recording medium storing a program causing a distance measuring device to estimate a camera parameter representing a characteristic of image systems, using a captured image of a reference chart representing a geometric pattern, each imaging system including a lens and an imaging area corresponding to the lens, and the program causing a computer to perform steps comprising:

capturing, using the distance measuring device, an image of a reference chart which (i) represents a geometric pattern in which elements are arranged and (ii) is positioned to have a predetermined positional relationship with the distance measuring device;

modifying a luminance distribution affected by aberration of the lens in the captured image of the reference chart;

calculating, as a feature point position, a gravity center position of each element in the captured image whose luminance distribution is modified;

estimating the camera parameter using the feature point position calculated and an approximate actual gravity center position in the reference chart; and

subtracting, from a luminance value of each of the pixels, a removal value that is a value obtained by adding a predetermined offset value to a minimum luminance value within a corresponding one of calculation areas segmented for respective elements within the captured image,

wherein the luminance distribution affected by the aberration of the lens is modified by subtracting the removal value from the luminance value of each pixel.