KR20110068375A - Parameter adjustment method for distortion correction of an image obtained by a camera module having a fisheye lens - Google Patents

Abstract

The present invention relates to a parameter correction method for distortion correction of an image obtained by a camera module having a fisheye lens. According to an aspect of the present invention, distortion correction of an image obtained by a camera module having a fisheye lens is provided. A method for adjusting a parameter, the method comprising: a first step of capturing and acquiring at least one sample image by a camera module including a fisheye lens; A second step of dividing the housing area and the image area of the camera module based on the obtained sample image and extracting the outermost line of the image area; And a third step of determining an adjustment light center coordinate value for the image area based on the outermost line of the extracted image area. 2. Parameter adjustment for distortion correction of an image obtained by a camera module having a fisheye lens. Provide a method. According to the present invention, it is possible to provide a method capable of efficiently adjusting parameters such as the optical center position and the focal length, which are used when distortion correction is performed on an image obtained by a camera module of a fisheye lens having a wide viewing angle. have.

Fisheye Lens, Distortion Correction, Light Center, Focal Length

Description

METHODS FOR ADJUSTING PARAMETERS IN DISTORTION CALIBRATION OF IMAGE ACQUIRED BY CAMERA HAVING FISH EYE LENS}

The present invention relates to a parameter correction method for distortion correction of an image obtained by a camera module having a fisheye lens, and more particularly to distortion correction for an image obtained by a camera module of a fisheye lens providing a wide viewing angle. The present invention relates to a method for more precisely and precisely correcting image distortion by efficiently adjusting parameters such as a light center position and a focal length used when performing the operation.

A fish eye lens generally refers to a lens having a wide field of view of about 180 °, and such a fish eye lens is mainly used in a field requiring a wide field of view. Instead of providing a wide viewing angle, an image generated using a fisheye lens becomes more distorted toward the edge of the image, resulting in a very distorted image. In some cases, the distorted image may be used as it is. However, in some fields, it is necessary to correct and use the distorted image. This correction of the distorted shape formed by the fisheye lens is commonly referred to as "distortion calibration," which is based on the focal length or light center position of the fisheye lens, depending on the projection method used in the fisheye lens. Using a parameter such as this is done through the appropriate formula.

1 and 2 are diagrams for explaining a distortion correction process used in the prior art, Figure 1 is an image obtained by the camera module having a fisheye lens before the distortion correction, Figure 2 is an image after the distortion correction It is shown.

As shown in FIG. 1, an image acquired by a camera module having a fisheye lens exhibits a form in which distortion is increased toward the edge. There may be a number of equations for correcting such a distorted image, but the equations widely used in the prior art are as follows.

[Equation 1]

는 카메라의 촛점 거리,

는 카메라의 광중심에서 입력 영상의 (x,y) 좌표 즉,

까지의 거리,

및

은 입력 영상의 (x,y) 좌표값이고,

및

은 왜곡 보정 영상의 (x,y) 좌표값이다.From here,

The focal length of the camera,

Is the (x, y) coordinate of the input image at the camera's optical center,

Distance to,

And

Is the (x, y) coordinate value of the input image,

And

Is the (x, y) coordinate value of the distortion corrected image.

)와 광중심 까지의 거리(

)를 알아야 상기 수식을 적용해서 왜곡 보정 영상을 얻을 수 있다. 따라서, 어안 렌즈에 의해 형성되는 영상의 왜곡 보정에는 촛점 거리나 광중심 위치 등과 같은 파라미터가 매우 중요한 의미를 갖게 된다. 한편, 어안 렌즈를 사용하기 위해서는 어안 렌즈를 이미지 센서를 포함하는 카메라 모듈에 장착 및 조립해서 사용하게 되는데, 카메라 모듈에 어안 렌즈를 장착 및 조립하는 경우 장착 및 조립시의 오차나 사용되는 부품의 위치, 크기, 두께 등의 차이로 인하여 어안 렌즈의 촛점 거리나 광중심의 위치가 변형되는 경우가 발생한다. 이러한 경우, 어안 렌즈 자체의 고유한 촛점 거리나 광중심 위치의 파라미터를 그대로 사용하여 왜곡 보정을 수행하게 되면 변형된 촛점 거리나 광중심 위치가 반영되지 않아서 정밀하고 정교한 왜곡 보정이 이루어지지 않는다는 문제점이 있다.If the above formula is applied to the input image, that is, the image before distortion correction, the image as shown in FIG. 2 can be obtained.

) And the distance to the light center (

), The distortion correction image can be obtained by applying the above equation. Therefore, parameters such as focal length and optical center position have a very important meaning in distortion correction of an image formed by a fisheye lens. Meanwhile, in order to use a fisheye lens, the fisheye lens is mounted and assembled to a camera module including an image sensor.In the case of mounting and assembling the fisheye lens on the camera module, errors in mounting and assembly or positions of parts used Due to differences in size, thickness, etc., the focal length of the fisheye lens or the position of the optical center may be deformed. In this case, if the distortion correction is performed using the parameters of the focal length or the optical center of the fisheye lens itself, the modified focal length or the optical center position is not reflected so that precise and precise distortion correction is not performed. have.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and includes parameters such as optical center position and focal length, which are used when distortion correction is performed on an image obtained by a camera module that provides a wide viewing angle. It is an object to provide a method that can be efficiently adjusted.

In addition, the present invention provides a more accurate and precise correction of distortion of the distorted image generated by the camera module using the fisheye lens by accurately correcting the focal length and the optical center position of the camera module including the fisheye lens. Another way is to provide a way to do this.

According to an aspect of the present invention, there is provided a parameter adjusting method for correcting distortion of an image obtained by a camera module including a fisheye lens, wherein at least one sample image is selected by a camera module including a fisheye lens. A first step of photographing and obtaining abnormalities; A second step of dividing the housing area and the image area of the camera module based on the obtained sample image and extracting the outermost line of the image area; And a third step of determining an adjustment light center coordinate value for the image area based on the outermost line of the extracted image area. 2. Parameter adjustment for distortion correction of an image obtained by a camera module having a fisheye lens. Provide a method.

Here, the second step may use a difference between pixel values of at least one sample image photographed in the first step.

In addition, the third step may include a plurality of coordinate values constituting the outermost line.

의 수식에 대입하여

를 구하고,

를 조정 광중심 좌표로 결정하도록 구성할 수도 있다.

By substituting in the formula of

Obtaining

May be configured to determine the coordinates of the adjusted light center.

According to another aspect of the present invention, a parameter adjusting method for distortion correction of an image obtained by a camera module having a fisheye lens, the method comprising: a first step of obtaining a sample image by the camera module having a fisheye lens; And a second step of acquiring a corrected image while changing a focal length value with respect to the obtained sample image, determining straight lines appearing in each corrected image, and determining an adjusted focal length based on the determined straight lines. A parameter adjusting method for distortion correction of an image obtained by a camera module having a lens is provided.

Here, in the first step, the sample image may be configured to be obtained by photographing a straight line pattern crossing in the horizontal and vertical directions.

Further, in the second step, it may be configured to determine the adjustment focus distance based on the length of the continuous unit straight lines of the determined straight lines.

The focal length value in the case where the square root of the sum of the squares of the respective lengths of the continuous unit straight lines is the largest may also be configured to determine the focal length as the adjustment focal length.

According to another aspect of the present invention, in the parameter adjustment method for distortion correction of the image obtained by the camera module having a fisheye lens, at least one sample image is taken by the camera module having a fisheye lens A first step of doing; A second step of dividing the housing area and the image area of the camera module based on the obtained sample image and extracting the outermost line of the image area; Determining an adjusted optical center coordinate value for the image region based on the extracted outermost line of the image region; And acquiring a corrected image by using the adjusted optical center coordinate value while changing a focal length value with respect to the obtained sample image, determining straight lines appearing in each corrected image, and adjusting the adjusted focal length based on the determined straight lines. A method of adjusting a parameter for correcting distortion of an image acquired by a camera module including a fisheye lens including a fourth step of determining may be provided.

According to the present invention, it is possible to provide a method capable of efficiently adjusting parameters such as the optical center position and the focal length, which are used when distortion correction is performed on an image obtained by a camera module of a fisheye lens having a wide viewing angle. have.

In addition, according to the present invention, by accurately correcting the focal length and the optical center position of the camera module having a fisheye lens, it is possible to precisely and precisely correct distortion of an image of a distorted form generated by a camera module using a fisheye lens. There is an effect that can be done.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a flowchart showing an embodiment of a parameter adjusting method for distortion correction of an image obtained by a camera module having a fisheye lens according to the present invention, and an optical center position is adjusted among parameters used for distortion correction. For example.

Referring to FIG. 3, first, at least one sample image is captured by a camera module including a fisheye lens (S100). Although only one sample image may be photographed and used, in order to adjust a more precise optical center position, it is also preferable to photograph two or three sample images and perform a process described below based on these sample images. On the other hand, since the image obtained by the camera module is generally configured to have a long horizontal axis compared to the vertical axis, it is preferable to obtain a sample image so that the maximum viewing angle that can be provided by the fisheye lens is aligned with the horizontal axis. An example of the sample image acquired as above is illustrated in FIG. 4. In FIG. 4, an object having a grid pattern is photographed, but it is not necessary to use the grid pattern. In this embodiment of adjusting the optical center position, there is no particular limitation on the sample image, and a sample image is captured by photographing an arbitrary object. You may acquire it.

Next, when the sample image is obtained, the housing region of the camera module and the image region are divided based on the obtained sample image, and the outermost line of the image region is extracted (S110). Referring to FIG. 4, a portion displayed in red corresponds to the outermost line of the image area as a boundary between the housing area and the image area. Here, the housing region corresponds to the inner circumferential surface of the housing of the camera module, which is typically configured in a barrel shape as an area indicated by the black portion of the edge in FIG. 4. In addition, the image area refers to an area where an image is normally formed by a fisheye lens. In FIG. 4, the image area corresponds to a white lattice pattern of a central portion.

Since the housing area and the image area are generally different in color, as contrasted with black and white color, the distinction between the housing area and the image area may use, for example, an edge detection method. As a method for detecting an edge from an image, various methods known by the prior art may be used. In the present invention, there is no particular limitation on the edge detection method, and any method used in the prior art may be used. In this case, when at least one sample image is acquired in step S100, the housing region and the image region may be distinguished by detecting an edge by using a difference between pixel values of pixels constituting the sample images. . When the housing area and the image area are separated as described above, the boundary line to be divided constitutes the outermost line of the image area, and the outermost line may be displayed as a set of coordinate values.

 Next, when the outermost line of the image area is extracted, an adjusted light center coordinate value for the image area is determined based on the extracted outermost line of the image area (S130). Determination of the adjusted light center coordinate value may be performed by the following process.

The equation of an ellipse consisting of the outermost line of the image region may be defined as follows.

[Equation 2]

이다. In this elliptic equation, the center coordinates of this ellipse

to be.

Expanding this expression, it is as follows.

[Equation 3]

If this is expressed as determinant, it is as follows.

[Equation 4]

값들을 각각 구할 수 있 게 된다. 이에 의하여,

값을 알 수 있으므로, 상기 타원의 방정식의 중심 좌표인

를 결정할 수 있고, 이를 조정 광중심 위치로 결정할 수 있게 된다.Substituting five of the coordinate values constituting the outermost line, each coefficient can be obtained by the undecided coefficient method.

Each value can be obtained. By this,

Since the value is known, the center coordinate of the equation of the ellipse

Can be determined, and this can be determined as the adjustment light center position.

FIG. 5 is a flowchart illustrating another embodiment of a parameter adjusting method for distortion correction of an image obtained by a camera module having a fisheye lens according to the present invention, and adjusting focus distance among parameters used for distortion correction. An example is shown.

Referring to FIG. 5, first, a sample image is acquired by a camera module having a fisheye lens (S200). In the present exemplary embodiment, the object to be photographed in the sample image is not particularly limited, but as described later, horizontal lines are determined based on the corrected image and the focal length is adjusted based on the determined straight lines. And photographing a straight line pattern crossing in the vertical direction to obtain a sample image.

When the sample image is obtained, a corrected image is obtained by changing a focal length value with respect to the obtained sample image, the straight lines appearing in each corrected image are determined, and an adjustment focal length is determined based on the determined straight lines (S210). . Here, the corrected image means a "distortion corrected image" obtained by using the equation as in [Equation 1] as described above.

The step S210 will be described in more detail with reference to FIGS. 6 to 8 as follows.

6 to 8 illustrate correction images for respective focal length values. First, FIG. 6 illustrates a case in which the focal length f is 280. Two unit straight lines (red) are shown at the upper and lower portions of the correction image. It can be seen that this exists. FIG. 7 shows that there are three unit lines in the horizontal direction as the focal length f = 250, and FIG. 8 shows that there are eight unit straight lines as the focal length f = 228. 6 to 7 can be intuitively confirmed that the continuous unit straight lines are the most in FIG. 8 and the best in the case of FIG. 8.

As described above, when the correction image is acquired while the focal length is changed, continuous unit straight lines included in the corrected images are determined, and the determined unit straight lines are used with values such as the length, distortion correction is best performed. Image, and the focal length used to obtain this image is determined as the adjusted focal length.

Here, the determination of successive unit straight lines included in the corrected image may use a conventional technique. For example, a method such as a canny edge detection method and a hough transform can be used in combination. An edge detected by the canny edge detection method, that is, a straight line, is shown in FIG. The form converted to the unit straight line is shown in FIG. The present invention is not intended for the unit straight line discrimination method itself, and any straight line discrimination method provided by the prior art can be used, and thus detailed description thereof will be omitted. As shown in FIGS. 9 and 10, when a unit line is detected, the following equation may be applied using the detected line.

[Equation 5]

By applying Equation 5, the square root of the sum of the squares of the lengths of the unit lines included in the corrected image for each focal length can be obtained, and the focal length corresponding to the largest value can be determined as the adjusted focal length. .

Meanwhile, in the embodiments described with reference to FIGS. 5 to 8, the unit straight lines are determined and the focal length values are adjusted based on the straight lines, but for this purpose, a grid pattern including a straight line is not necessarily used as the sample image. . For example, even when photographing a general landscape, straight lines included in the general landscape can be extracted using a process of extracting straight lines included in them, that is, a canny edge detection method and a Hough transform. There is no need to use it as an image.

In addition, the present invention can be used in combination with the above-described embodiments. That is, the important parameters in performing the distortion correction are the focal length f and the optical center position R as described above. The above-described embodiments are related to the case of adjusting the focal length and the optical center position, respectively. By combining these embodiments, first, the optical center position may be adjusted, and when the optical center position is adjusted, the focal length may be adjusted to reflect the adjusted optical center position. As described above, the focal length is not used to adjust the optical center position, but the optical center position value should be used since [Equation 1] should be used to adjust the focal length. Therefore, in order to calculate more sophisticated parameters, the above-described embodiments may be combined to adjust the optical center position first, and if the focal length value is adjusted while reflecting the adjusted optical center position, more precise and precise parameters may be calculated. By using these parameters, distortion correction can be performed more precisely.

In the above, the present invention has been described with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains may make various modifications and variations from such descriptions. will be. For example, the above-described formulas are exemplary and may use other formulas than these formulas. Therefore, the present invention should be construed with reference to the overall description of the appended claims and drawings, and all equivalent or equivalent modifications thereof will belong to the scope of the present invention.

1 and 2 are diagrams for explaining the distortion correction process used in the prior art.

3 is a flowchart illustrating an embodiment of a parameter adjusting method for distortion correction of an image obtained by a camera module having a fisheye lens according to the present invention.

4 is a diagram illustrating an example of a sample image.

5 is a flowchart illustrating another embodiment of a parameter adjusting method for correcting distortion of an image obtained by a camera module having a fisheye lens according to the present invention.

6 to 8 illustrate correction images for respective focal length values.

9 and 10 are diagrams for describing a method for detecting a unit line.

Claims (8)

In the parameter adjustment method for distortion correction of an image obtained by a camera module having a fisheye lens, A first step of capturing and acquiring at least one sample image by a camera module having a fisheye lens; A second step of dividing the housing area and the image area of the camera module based on the obtained sample image and extracting the outermost line of the image area; And A third step of determining an adjusted optical center coordinate value for the image region based on the extracted outermost line of the image region; A parameter adjusting method for distortion correction of an image obtained by a camera module having a fisheye lens comprising a. The method of claim 1, The second step is a parameter adjustment method for distortion correction of an image obtained by a camera module having a fisheye lens, characterized in that the difference in the pixel value of at least one sample image taken in the first step. The method of claim 1, In the third step, a plurality of coordinate values constituting the outermost line may be used.

By substituting in the formula of

Obtaining

A method for adjusting the parameter for distortion correction of an image obtained by a camera module having a fisheye lens, characterized in that for determining the adjusted light center coordinates. In the parameter adjustment method for distortion correction of an image obtained by a camera module having a fisheye lens, A first step of acquiring a sample image by a camera module having a fisheye lens; And A second step of acquiring a corrected image while changing a focal length value with respect to the obtained sample image, determining straight lines appearing in each corrected image, and determining an adjusted focus distance based on the determined straight lines A parameter adjusting method for distortion correction of an image obtained by a camera module having a fisheye lens comprising a. 5. The method of claim 4, And in the first step, the sample image is obtained by photographing a straight line pattern crossing in the horizontal and vertical directions. The method of adjusting a parameter for distortion correction of an image obtained by a camera module having a fisheye lens. 5. The method of claim 4, In the second step, the parameter for adjusting the distortion of the image obtained by the camera module having a fish-eye lens, characterized in that for determining the adjustment focus distance based on the length of the continuous unit straight line of the determined straight line. Way. The method of claim 6, The focal length value of the case where the square root of the sum of the squares of the lengths of the continuous unit lines is the largest is determined as the adjustment focal length for the distortion correction of the image obtained by the camera module having a fisheye lens. How to adjust parameters. In the parameter adjustment method for distortion correction of an image obtained by a camera module having a fisheye lens, A first step of capturing and acquiring at least one sample image by a camera module having a fisheye lens; A second step of dividing the housing area and the image area of the camera module based on the obtained sample image and extracting the outermost line of the image area; Determining an adjusted optical center coordinate value for the image region based on the extracted outermost line of the image region; And Acquire a corrected image using the adjusted optical center coordinate value while changing a focal length value with respect to the obtained sample image, determine straight lines appearing in each corrected image, and determine the adjusted focal length based on the determined straight lines. 4th step A parameter adjusting method for distortion correction of an image obtained by a camera module having a fisheye lens comprising a.

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