Measuring method and apparatus of photographic parameter and computer memory product

• US 6,097,850 A
• Filed: 04/29/1997
• Issued: 08/01/2000
• Est. Priority Date: 11/27/1996
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Shiitani, Shuichi, Watanabe, Masaki
• Primary Examiner(s): COUSO, YON JUNG
• Application Number:
  US08/848,178
• Time in Patent Office: 1,190 Days
• Field of Search: 382/286, 382/289, 382/291, 382/255, 382/225, 382/107, 382/100, 382/275, 354/432
• US Class Current: 382/275
• CPC Class Codes: G06T 7/60 Analysis of geometric attributes

Abstract

A method of measuring an unknown photographic parameter (distortion coefficient or focal length) from an image taken by a camera of which photographic parameter is unknown. An image to be measured is entered, the photographic parameter to be measured (distortion coefficient or focal length) is designated, an image region necessary for measuring the photographic parameter in the image to be measured is designated, a characteristic relating to the photographic parameter to be measured is extracted from the designated image region, and the photographic parameter is calculated according to a specified operation processing on the basis of the quantity and position of the extracted characteristic.

Claims

1. A method for measuring a distortion coefficient, a focal length or any other photographic parameter of a camera from a single image taken by the camera, the method comprising the steps of:

deciding the kind of photographic parameter for measurement;

selecting an object image region in the single image so as to extract characteristics of the photographic parameter therefrom;

executing the extraction of the characteristics from the selected image region in the single image; and

calculating the photographic parameter in accordance with the extracted characteristics.

2. The method for measuring according to claim 1, wherein the photographic parameter is a parameter selected from a group consisting of the distortion coefficient and the focal length used in taking the image.

3. The method for measuring according to claim 1, wherein selection of an object image region includes the step of selecting an image region containing a linear portion when no distortion is present, and the extraction of characteristics of the photographic parameter includes the steps of extracting one or more edge elements from the object image region, determining the coordinates of the extracted edge elements on the image, and calculating a distortion coefficient by reference to the coordinates.

4. The method for measuring according to claim 3, wherein the distortion coefficient κ

to be measured is calculated by solving the simultaneous equations of (1) through (3), supposing the coordinates of the edge element on the image to be (x'"'"', y'"'"') and the coordinates of the edge element being corrected of distortion to be (x, y),

space="preserve" listing-type="equation">x'"'"'=x{1-κ

(X.sup.2 +y.sup.2)} (1)

space="preserve" listing-type="equation">x'"'"'=y{1-κ

(X.sup.2 +y.sup.2)} (2)

space="preserve" listing-type="equation">-x sin θ

+Y cos θ

=ρ

(3)

where equation (3) is an equation of a straight line composed by each edge element being free from distortion, and

θ

is the angle formed between perpendicular lines drawn from the origin and the x-axis, and

ρ

is the distance from the origin of the xy coordinate system to the straight line of equation (3).

5. The method for measuring according to claim 1, wherein the photographic parameter is the focal length of the camera used in taking the image, said step of selecting the image region includes a step of selecting four image regions having four straight lines originally composing a rectangle, and said step of determining the characteristic includes a step of extracting plural edge elements from each selected image region, a step of determining the coordinates of the extracted edge elements on the image, a step of obtaining a straight line in each image region on the basis of the determined coordinates of the edge elements, a step of determining the coordinates on the image of the vertices of the rectangle having the obtained four straight lines as the sides, and a step of calculating the focal length on the basis of the determined coordinates of four vertices.

6. The method for measuring according to claim 5, wherein supposing the determined coordinates of the four vertices on the image to be (x_i, y_i) (i=0, . . . , 3), the provisional focal length as an arbitrary value to be f'"'"', and the focal length to be measured to be f, the focal length f is calculated in the following formula (4):

##EQU4## in formula (4), however, m_0x, m_0y, m_0f are vector elements of m₀ (m₀ =(m_0x, m_0y, m_0f)^T), and m_1x, m_1y, m_1f are vector elements of m₁ (m₁ =(m_1x, m_1y, m_1f)^T); and

m₀, m₁ are expressed in the following formulas (5) and (6), ##EQU5## further, in formulas (5) and (6), n₀, n₁, n₂, n₃ are expressed respectively in the following formulas (7) through (10);

##EQU6##

7. A measuring apparatus for measuring a photographic parameter when taking an image on the basis of the taken image, comprising:

means for selecting a part of an image region from a single image;

means for determining a characteristic relating to the photographic parameter to be measured from the selected image region in the single image; and

means for calculating the photographic parameter according to a specified operation processing on the basis of the determined characteristic.

8. The measuring apparatus according to claim 7, wherein the photographic parameter is a parameter selected from a group consisting of the distortion coefficient and the focal length of the photographic means used in taking the image.

9. The measuring apparatus according to claim 7, further comprising means for designating the kind of photographic parameter to be measured.

10. The measuring apparatus according to claim 8, further comprising means for designating the kind of photographic parameter to be measured.

calculating the photographic parameter according to a specified operation processing on the basis of the acquired characteristics.

11. A computer memory product storing a computer program for measuring a photographic parameter at the time of taking a single image on the basis of the single taken image incorporated into a computer, said computer program comprising the steps of:

extracting a part of an image region from the incorporated single taken image according to an external input;

acquiring a characteristic relating to the photographic parameter to be measured from the extracted image region of the single taken image; and

calculating the photographic parameter according to a specified operation processing on the basis of the acquired characteristics.

12. The computer memory product according to claim 11, wherein the photographic parameter is a parameter selected from a group consisting of the distortion coefficient and the focal length of the photographic means used in taking the image.

13. A computer memory product having computer readable program code means capable of being read by a computer for measuring a photographic parameter at the time of taking a single image on the basis of the single taken image incorporated into the computer, said computer readable program code means comprising:

program code means for causing the computer to extract a part of an image region from the incorporated single taken image according to an external input;

program code means for causing the computer to acquire a characteristic relating to the photographic parameter to be measured from the extracted image region of the single taken image; and

program code means for causing the computer to calculate the photographic parameter according to a specified operation processing on the basis of the acquired characteristic.

14. The computer memory product according to claim 13, wherein the photographic parameter is a parameter selected from a group consisting of the distortion coefficient and the focal length of the photographic means used in taking the image.

15. A method for measuring a distortion coefficient, a focal length or any other photographic parameter of a camera through an image taken by the camera, the method comprising the steps of:

deciding the kind of a photographic parameter for measurement;

selecting an object image region containing a linear portion when no distortion is present to extract characteristics of the photographic parameter;

extracting one or more edge elements from the object image region and determining the coordinates of the extracted edge elements on the image; and

calculating a distortion coefficient by reference to the coordinates.

16. The method for measuring according to claim 15, wherein the distortion coefficient κ

to be measured is calculated by solving the simultaneous equations of (1) through (3), supposing the coordinates of the edge element on the image to be (x'"'"', y'"'"') and the coordinates of the edge element being corrected of distortion to be (x, y),

space="preserve" listing-type="equation">x'"'"'=x{1-κ

(X.sup.2 +y.sup.2)} (1)

space="preserve" listing-type="equation">x'"'"'=y{1-κ

(X.sup.2 +y.sup.2)} (2)

space="preserve" listing-type="equation">-x sin θ

+Y cos θ

=ρ

(3)

where equation (3) is an equation of a straight line composed by each edge element being free from distortion, and

θ

is the angle formed between perpendicular lines drawn from the origin and the x-axis, and

ρ

is the distance from the origin of the xy coordinate system to the straight line of equation (3).

17. The method for measuring according to claim 15, wherein

the photographic parameter is the focal length of the camera used in taking the image,

said step of selecting the image region includes selecting four image regions having four straight lines originally composing a rectangle, and

said step of extracting includes extracting plural edge elements from each selected image region, determining the coordinates of the extracted edge elements on the image, obtaining a straight line in each image region on the basis of the determined coordinates of the edge elements, determining the coordinates on the image of the vertices of the rectangle having the obtained four straight lines as the sides, and calculating the focal length on the basis of the determined coordinates of four vertices.

18. The method for measuring according to claim 17, wherein supposing the determined coordinates of the four vertices on the image to be (x_i, y_i) (i=0, . . . , 3), the provisional focal length as an arbitrary value to be f'"'"', and the focal length to be measured to be f, the focal length f is calculated in the following formula (4):

##EQU7## in formula (4), however, m_0x, m_0y, m_0f are vector elements of m₀ (m₀ =(m_0x, m_0y, m_0f)^T), and m_1x, m_1y, m_1f are vector elements of m₁ (m₁ =(m_1x, m_1y, m_1f)^T); and

m₀, m₁ are expressed in formulas (5) and (6) ##EQU8## further, in formulas (5) and (6), n₀, n₁, n₂, n₃ are expressed respectively in the following formulas (7) through (10);

##EQU9##