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

Patent metadata

Field	Value
Publication number	US-11615552-B2
Application number	US-202017113425-A
Country	US
Kind code	B2
Filing date	Dec 7, 2020
Priority date	Nov 18, 2016
Publication date	Mar 28, 2023
Grant date	Mar 28, 2023

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.

First claim

What is claimed is:

1. A crossing point detector, comprising:
a memory that stores a captured image obtained by imaging a checker pattern; and
a processor that reads out at least a partial image of the captured image from the memory as an image to process, and detects a crossing point of two boundary lines in the checker pattern depicted in the image to process, wherein
each of the two boundary lines is a boundary line between a first region made up of multiple pixels having a first pixel value and a second region made up of multiple pixels having a second pixel value greater than the first pixel value in the image to process,
the processor
decides multiple parameters of a function model that treats two-dimensional image coordinates as variables, the parameters being parameters for optimizing an evaluation value based on a difference between respective pixel values represented by the function model and respective pixel values in the image to process, and
computes a position of a crossing point of two straight lines expressed by the decided multiple parameters, and thereby detects with subpixel precision the crossing point of the two boundary lines in the image to process, and

the function model uses a curved surface that is at least first-order differentiable to express the first region and the second region in a two-dimensional coordinate system, and also pixel values at respective positions in the two-dimensional coordinate system at a boundary between the first region and the second region.

2. The crossing point detector according to claim 1 , wherein
the function model is made up of a logistic function expanded in two dimensions.

3. The crossing point detector according to claim 2 , wherein
the multiple parameters of the function model include angles θ and φ, pixel values a and d, distances b and c, and a degree of image blur σ, and
the function model uses the two straight lines in the two-dimensional coordinate system made from an x-axis and a y-axis, namely (x cos θ+y sin θ+b)=0 and (x sin φ−y cos φ+c)=0, to express a pixel value M(x, y) at a position (x, y) in the two-dimensional coordinate system according to the following formula:

M
⁡
(

x
,
y

)

=

a

1
+

exp
⁡
(

(

x
⁢
cos
⁢
θ

+

y
⁢
sin
⁢
θ

+
b

)

⁢

(

x
⁢
sin
⁢
ϕ

-

y
⁢
cos
⁢
ϕ

+
c

)

σ

)

+
d

.

4. The crossing point detector according to claim 1 , further comprising:
a display that displays the captured image, wherein
the processor
acquires a position on the displayed captured image in accordance with an operation performed by an operator as a second initial position, and
reads out, from the memory, a region including the second initial position from the captured image as the image to process.

5. The crossing point detector according to claim 1 , wherein
the processor additionally
generates multiple predetermined initial crossing points,
sequentially selects one of the multiple initial crossing points as a selected initial crossing point, and

in the reading out of the image to process,
every time the selected initial crossing point is selected, the processor reads out an image to process that includes the position of the selected initial crossing point, and
in the detecting of the crossing point with subpixel precision,
in a case in which the optimized evaluation value is less than a threshold value, the processor detects with subpixel precision the crossing point of the two boundary lines inside the image to process on a basis of the multiple parameters.

6. A camera calibration system, comprising:
the crossing point detector according to claim 1 ; and
a calculator that uses a crossing point detected by the crossing point detector to compute camera parameters of a camera used to image the checker pattern.

7. A crossing point detection method, comprising:
reading out, from a memory storing a captured image obtained by imaging a checker pattern, at least a partial image of the captured image as an image to process; and
detecting a crossing point of two boundary lines in the checker pattern depicted in the image to process, wherein
each of the two boundary lines is a boundary line between a first region made up of multiple pixels having a first pixel value and a second region made up of multiple pixels having a second pixel value greater than the first pixel value in the image to process,
the detecting of the crossing point includes
deciding multiple parameters of a function model that treats two-dimensional image coordinates as variables, the parameters being parameters for optimizing an evaluation value based on a difference between respective pixel values represented by the function model and respective pixel values in the image to process, and
computing a position of a crossing point of two straight lines expressed by the decided multiple parameters, and thereby detects with subpixel precision the crossing point of the two boundary lines in the image to process, and

the function model uses a curved surface that is at least first-order differentiable to express the first region and the second region in a two-dimensional coordinate system, and also pixel values at respective positions in the two-dimensional coordinate system at a boundary between the first region and the second region.

8. The crossing point detection method

Assignees

• Panasonic Ip Man Co Ltd

Inventors

• Wakai Nobuhiko
• Azuma Takeo
• Nobori Kunio
• Sato Satoshi
• Maruyama Ayako

Classifications

• G06T2207/20164

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• H04N17/002

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• G06T7/80 Primary

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• H04N23/63

  by using electronic viewfinders · CPC title

• G06T2207/30208

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