Crossing point detector, camera calibration system, crossing point detection method, camera calibration method, and recording medium

• US 10,388,030 B2
• Filed: 11/05/2017
• Issued: 08/20/2019
• Est. Priority Date: 11/18/2016
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Inventors: Wakai, Nobuhiko, Azuma, Takeo, Nobori, Kunio, Sato, Satoshi, Maruyama, Ayako
• Primary Examiner(s): Harold, Jefferey F
• Assistant Examiner(s): Khalid, Omer
• Application Number:
  US15/803,784
• Publication Number:
  US 20180144502A1
• Time in Patent Office: 653 Days
• Field of Search: 348179
• CPC Class Codes: G06T 2207/20164 Salient point detection; Corner detection
• CPC Class Codes: G06T 2207/30208 Marker matrix
• CPC Class Codes: G06T 2207/30244 Camera pose
• CPC Class Codes: G06T 7/13 Edge detection
• CPC Class Codes: G06T 7/75 involving models
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/63 by using electronic viewfinders

Abstract

A crossing point detector includes memory and a crossing point detection unit that reads out a square image from a captured image in the memory, and detects a crossing point of two boundary lines in a checker pattern depicted in the square image. The crossing point detection unit decides multiple parameters of a function model treating two-dimensional image coordinates as variables, the parameters optimizing an evaluation value based on a difference between corresponding pixel values represented by the function model and the square image, respectively, and computes the position of a crossing point of two straight lines expressed by the decided multiple parameters to thereby detect the crossing point with subpixel precision. The function model uses a curved surface that is at least first-order differentiable to express pixel values at respective positions in a two-dimensional coordinate system at the boundary between black and white regions.

Claims

1. A crossing point detector, comprising:

a memory that stores a first image, a camera imaging a checker pattern to obtain the first image, the first image including an imaged checker pattern; and

a processor that reads out an image included in the first image from the memory, and detects a crossing point of two boundary lines in the image, wherein

each of the two boundary lines is a boundary line between a first region made up of pixels having first pixel values and a second region made up of pixels having second pixel values, the second pixel values being greater than the first pixel values, the image including the first region and the second regions,

the processor

decides first parameters of a numerical model, the first parameters being parameters for optimizing a first evaluation value based on differences, each of the differences being provided between a pixel value given by the numerical function model and a pixel value in the image, and

computes a position of a crossing point of two straight lines expressed by using the first parameters, and thereby detects with subpixel precision the crossing point of the two boundary lines,

the numerical model is a model that, when a step edge is imaged, simulates a pixel integration effect by assigning pixel values to respective regions inside a pixel divided by a straight line, and deciding a pixel value of the overall pixel,

an input to the numerical model is a pair of two-dimensional image coordinates,

an output value from the model is a pixel value at the pair of two-dimensional image coordinates, and

the function model uses a curved surface that is at least first-order differentiable to express pixel values at pairs of two-dimensional image coordinates on a boundary between the first region and the second region.

2. The crossing point detector according to claim 1, wherein

the processor, when deciding the first parameters,

generates subpixels by oversampling a pixel,

divides the pixel into regions with a straight line expressed by using the first parameters,

assigns a subpixel value expressed by using the first parameters to each subpixel included in each of the regions, and

computes a pixel value expressed by the numerical model by numerically integrating the subpixel values over the range of the pixel.

3. A crossing point detection method, comprising:

reading out, from a memory storing a first image, an image included in the first image, a camera imaging a checker pattern to obtain the first image, the first image including an imaged checker pattern; and

detecting a crossing point of two boundary lines in the checker pattern in the image, wherein

each of the two boundary lines is a boundary line between a first region made up of pixels having first pixel values and a second region made up of pixels having second pixel values, the second pixel values being greater than the first pixel values, the image including the first region and the second region,

the detecting of the crossing point includes

deciding first parameters of a numerical model, the first parameters being parameters for optimizing a first evaluation value based on differences, each of the differences being provided between a pixel value given by the numerical function model and a pixel value in the image, and

computing a position of a crossing point of two straight lines expressed by using the first parameters, and thereby detects with subpixel precision the crossing point of the two boundary lines,

the numerical model is a model that, when a step edge is imaged, simulates a pixel integration effect by assigning pixel values to respective regions inside a pixel divided by a straight line, and deciding a pixel value of the overall pixel,

the crossing point detection method further comprising;

inputting, to the numerical model, a pair of two-dimensional image coordinates; and

outputting, from the numerical model, a pixel value at the pair of the two-dimensional image coordinates, and

the function model uses a curved surface that is at least first-order differentiable to express pixel values at pairs of two-dimensional image coordinates on a boundary between the first region and the second region.

4. The crossing point detection method according to claim 3, wherein

the deciding of the first parameters includes

generating subpixels by oversampling a pixel,

dividing the pixel into regions with a straight line expressed by using the parameters,

assigning a subpixel value expressed by using the parameters to each subpixel included in each of the regions, and

computing a pixel value expressed by the numerical model by numerically integrating the subpixel values over the range of the pixel.