JP4664259B2 - Image correction apparatus and image correction method - Google Patents

Description

  The present invention relates to an image correction technique for correcting distortion (distortion) due to a lens used for imaging of a video signal obtained by an imaging apparatus.

In an imaging apparatus including a lens and an imaging unit, a phenomenon is known in which an image is geometrically distorted due to the influence of lens aberration. This is because the imaging position is shifted due to the influence of aberration.
In order to correct the distortion (distortion) of the image, generally, the image is corrected based on the distortion characteristics corresponding to the image height at each pixel position.
For example, in the distortion correction apparatus disclosed in Japanese Patent Laid-Open No. 2005-286482, distortion characteristic data is held in a distortion memory, and four points near the image height of the pixel of interest are approximated by a cubic equation to obtain distortion. The characteristics are calculated. At this time, the distortion memory holds a plurality of characteristics depending on the zoom position or focus position of the lens.

In the aberration correction method disclosed in Japanese Patent Application Laid-Open No. 2004-336106, a correction vector is calculated for each pixel position based on chromatic aberration and distortion data, and enlargement or reduction processing is performed.
Moreover, in the distortion correction apparatus disclosed in Japanese Patent Laid-Open No. 2003-37769, the correction ratio in the horizontal direction is changed using the distortion characteristics in the vertical direction to eliminate unnatural distortion.

JP 2005-286482 A JP 2004-336106 A JP 2003-37769 A

However, in such a conventional distortion correction method, as shown in FIG. 2 and FIG. 3, by enlarging and reducing the image based on the distortion characteristics, There are pixels that refer to non-existing pixels. For this reason, when the image is enlarged and corrected, there is a problem that the angle of view of the image is changed. On the other hand, when the image is reduced and corrected, there are pixels that cannot be corrected.
Therefore, an object of the present invention is to provide an image correction method and an image correction apparatus that maintain an angle of view when an image is enlarged or reduced using distortion characteristics.

An image correction apparatus according to the present invention is as follows.
In an image correction apparatus that corrects distortion caused by lens aberration when an image formed on an image sensor through a lens is taken out as an image data signal, a horizontal synchronization signal and a vertical synchronization signal included in the image data signal are also included. And a pixel count unit that calculates the coordinate position of each pixel, calculates the distance between the coordinate position of each pixel and the optical axis center position, and at least according to any one of the zoom position, focus position, and aperture amount of the lens The amount of distortion for calculating the amount of distortion due to lens aberration based on the converted distance between each pixel and the optical axis center, a distance calculation unit for converting the calculated distance, an image memory for holding image data A calculation unit; and a distortion correction unit that corrects image distortion based on the distortion amount.

The image correction method according to the present invention includes:
A pixel counting step for calculating a coordinate position of each pixel based on a horizontal synchronization signal and a vertical synchronization signal included in an image data signal of an image formed on an image sensor through a lens; and a coordinate position and light of each pixel A distance calculating step for calculating the distance from the axial center position and converting the calculated distance according to at least one of the zoom position, the focus position, and the aperture amount of the lens, and holding the image data in the image memory A distortion amount calculating step for calculating a distortion amount due to lens aberration based on the converted distance between each pixel and the optical axis center; reading out image data stored in an image memory; and And a distortion correction step of correcting image distortion.

  In the image correction method or the image correction apparatus according to the present invention, the distance between the coordinate position of the target pixel and the optical axis center position is calculated, and the distortion characteristic due to the aberration of the lens calculated based on this distance is used to calculate the distance at the target pixel. By performing distortion correction by calculating the actual image formation position, there is an effect that the angle of view of the image is not changed and pixels that cannot be corrected even in the case of correction by image reduction can be eliminated.

Embodiment 1 FIG.
1 is a block diagram showing an image correction apparatus according to Embodiment 1 of the present invention. In FIG. 1, the image correction apparatus includes a pixel count unit 1, a distance calculation unit 2, a distortion amount calculation table 3, a distortion amount calculation unit 4, an image buffer unit 5, and a distortion correction unit 6.
Next, the operation will be described.
The pixel count unit 1 calculates the horizontal coordinate X and the vertical coordinate Y of the image signal by counting the horizontal synchronization signal and the vertical synchronization signal output from the image sensor.
The distance calculation unit 2 calculates the distance R between the coordinate value (X, Y) of the image signal and the optical axis center coordinate (Xc, Yc) in the captured image, using Expression (1).

  The distortion amount calculation table 3 discretely holds the distortion characteristic α expressed by the following equation (2) using the ideal imaging position distance r without distortion and the actual imaging position distance R. is doing.

In the case of barrel-type strain as shown in FIG. 2, this strain characteristic is a characteristic value of 1.0 or less as shown in FIG. 4, while in the case of pincushion-type strain as shown in FIG. 3, as shown in FIG. The characteristic value is 1.0 or more.
The distortion amount calculation unit 4 uses the distortion amount calculation table 3 to calculate the distortion amount α at the distance R from the optical axis center of the target pixel. Since the distortion amount calculation table 3 is discrete data with respect to the distance R, using the distortion characteristics α _n and α _{n + 1} at the two neighboring points R _n and R _{n + 1} , the following equation (3) Calculate from

The image buffer unit 5 temporarily stores image data signals and receives data reference from the distortion correction unit 6.
The distortion correction unit 6 corrects the image data signal temporarily stored in the image buffer unit 5 based on the distortion characteristic α calculated by the distortion amount calculation unit 4. As shown in FIG. 6, the image of the pixel of interest is imaged at a position where the distance from the center is αR. Therefore, the corrected image formation position (X ′, Y ′) is expressed by the following equation (4). Is done.

Since the image data is distributed discretely, the image data at the imaging position (X ′, Y ′) is obtained using the four neighboring points. The image data of the four neighboring points are I (x _n , y _n ), I (x _n , y _{n + 1} ), I (x _n , y _{n + 1} ), I (x _{n + 1} , y _{n + 1} ) Then, using the weight of distance, it is expressed as the following equation (5).

  Further, the distance calculation unit 2 converts the calculated distance using an Nth order polynomial according to the zoom position, focus position, and aperture amount of the lens, thereby correcting the distortion amount without changing the distortion amount calculation table 3. It can be carried out.

  As described above, in the image correction method according to the first embodiment of the present invention, the distance between the coordinate position of the target pixel and the optical axis center position is calculated, and the distortion characteristic due to the aberration of the lens calculated based on this distance is calculated. There is an effect that distortion correction can be performed by performing distortion correction by calculating an actual image formation position in the target pixel.

Embodiment 2. FIG.
In the second embodiment, a method of correcting barrel distortion when the distortion characteristic is barrel distortion as shown in FIG. 2 will be described. In the second embodiment, the operation of the distortion correction unit 6 is different from that of the first embodiment.
In the case of barrel distortion, since the distortion characteristic value is 1.0 or less, the normal correction is an enlargement process. Therefore, the distortion correction unit 6 performs distortion correction so as to maintain the horizontal and vertical field angles passing through the center of the optical axis. In other words, the distortion characteristic at the distance Rx (= XX _c ) is α _x , the distortion characteristic at the distance R _y (= YY _c ) is α _y , and the corrected imaging position (X ′, Y ′) is expressed by the following formula ( Find in 6).

  Therefore, as in the first embodiment, image data at the imaging position (X ′, Y ′) is obtained using the four neighboring points, and distortion correction is performed.

  As described above, in the image correction method according to the second embodiment of the present invention, the distortion characteristics of the target pixel can be obtained with the horizontal and vertical distortion characteristics passing through the center of the optical axis without changing the configuration shown in the first embodiment. By correcting this, there is an effect that the angle of view in the horizontal and vertical directions can be maintained and distortion correction can be performed.

Embodiment 3 FIG.
In the third embodiment, a method for correcting the pincushion distortion when the distortion characteristic is the pincushion distortion as shown in FIG. 3 will be described. In the third embodiment, the operation of the distortion correction unit 6 is different from that of the first embodiment.
In the case of pincushion type distortion, since the distortion characteristic value is 1.0 or more, the normal correction is a reduction process. However, in the peripheral portion of the image, the image data cannot be calculated because the pixel to be referenced is outside the image area. In addition, the distortion characteristic is maximized in a pixel having the longest distance in the diagonal direction from the optical axis center.
Therefore, the distortion correction unit 6 performs distortion correction with reference to the angle of view in the diagonal direction. In other words, when the maximum value of the distance from the optical axis center in the image is R _max , conversion is performed using the following equation (7) so that the distortion correction amount α ′ is 1 or less.

  Using this distortion correction amount α ′, the corrected imaging position (X ′, Y ′) is obtained by the following equation (8).

Therefore, as in the first embodiment, image data at the imaging position (X ′, Y ′) is obtained using the four neighboring points, and distortion correction is performed.
As described above, in the image correction method according to the third embodiment of the present invention, the distortion correction amount of the pixel having the largest distance from the optical axis center is set to 1 without changing the configuration shown in the first embodiment. By converting the distortion characteristics, there is an effect that distortion correction can be performed from the pixels in the captured image.

Embodiment 4 FIG.
In the fourth embodiment, a case will be described in which the distortion amount is calculated by approximating the distortion amount by an Nth order polynomial without using the distortion amount calculation table 3 described in the first to third embodiments.
Hereinafter, the approximate expression will be described as a second order polynomial.
FIG. 7 is a block diagram showing an image correction apparatus according to Embodiment 4 of the present invention. In FIG. 7, the image correction apparatus includes a pixel count unit 1, a distance calculation unit 2, a distortion amount calculation unit 4, an image buffer unit 5, and a distortion correction unit 6.
In the fourth embodiment, the operation of the distortion amount calculation unit 4 is different from that of the first embodiment.
The distortion amount calculation unit 4 calculates the distortion characteristic α of the pixel at the distance R from the optical axis center using a quadratic expression shown in the following expression (9).

Therefore, as in the first embodiment, the imaging position (X ′, Y ′) is obtained, and image data at the imaging position (X ′, Y ′) is obtained using the four neighboring points, and distortion correction is performed.
As described above, the image correction method according to the fourth embodiment of the present invention has an effect that memory can be reduced by performing distortion correction using an approximate expression without using a distortion amount calculation table. . Further, there is an effect that distortion correction can be performed by changing the coefficient of the approximate expression according to the zoom position, focus position, and aperture amount of the lens.

Embodiment 5. FIG.
FIG. 8 is a block diagram showing an image correction apparatus according to Embodiment 5 of the present invention. In FIG. 8, the image correction apparatus includes a pixel count unit 1, a distance calculation unit 2, a distortion amount calculation unit 4, an image buffer unit 5, a distortion correction unit 6, an image division unit 7, and an image memory unit 8.
In the fifth embodiment, the operations of the image memory unit 8 and the image dividing unit 7 are different from those of the first embodiment.
The image memory unit 8 is a component that stores image data obtained from the imaging apparatus.
The image dividing unit 7 cuts out the image data from the image memory unit 8 and outputs the image data to the image buffer unit 5 and the horizontal and vertical synchronization signals of the image data to the pixel count unit 1. At that time, the image dividing unit 7 divides the image based on the distortion characteristics. Pixels farther away from the optical axis center in the vertical direction have greater vertical distortion, and pixels farther in the horizontal direction have greater horizontal distortion. For this reason, as shown in FIG. 9, the image is divided in the vertical direction in a block having a large vertical distortion, and in the horizontal direction in a block having a large horizontal distortion.

  As described above, the image correction apparatus according to the fifth embodiment of the present invention has an effect that the capacity of the image buffer unit 5 can be reduced by adaptively dividing the image data based on the distortion amount.

  The image correction method and the image correction apparatus according to the present invention can be applied to an image pickup apparatus that picks up a still image or a moving image, an apparatus that records a video signal obtained by the image pickup apparatus as a digital signal, and the like.

It is a block diagram which shows the image correction apparatus by Embodiment 1 of this invention. It is explanatory drawing of the distortion correction method by the image expansion in the case of a barrel type distortion characteristic. It is explanatory drawing of the distortion correction method by the image reduction in the case of a pincushion type distortion characteristic. It is a distortion characteristic figure in the case of barrel type distortion. It is a distortion characteristic figure in the case of pincushion type distortion. It is explanatory drawing of the distortion correction in the distortion correction part by a distortion characteristic. FIG. 6 is a block diagram showing an image correction apparatus according to Embodiment 4 of the present invention. FIG. 10 is a block diagram showing an image correction apparatus according to Embodiment 5 of the present invention. FIG. 10 is an explanatory diagram of an image dividing method of an image dividing unit in a fifth embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1; Pixel count part, 2; Distance calculation part, 3; Distortion amount calculation table, 4; Distortion amount calculation part, 5; Image buffer part, 6; Distortion correction part, 7: Image division part, 8;

Claims (7)

In an image correction apparatus that corrects distortion caused by lens aberration when an image formed on an image sensor through a lens is taken out as an image data signal, a horizontal synchronization signal and a vertical synchronization signal included in the image data signal are also included. And a pixel count unit that calculates the coordinate position of each pixel, calculates the distance between the coordinate position of each pixel and the optical axis center position, and at least according to any one of the zoom position, focus position, and aperture amount of the lens The distance calculation unit that converts the calculated distance, the image buffer unit that holds the image data, and the distortion that calculates the distortion amount due to the lens aberration based on the converted distance between each pixel and the optical axis center An image correction apparatus comprising: an amount calculation unit; and a distortion correction unit that corrects image distortion based on a distortion amount.   The image correction apparatus according to claim 1, wherein the distortion amount calculation unit is configured to calculate a distortion amount based on an expression that approximates a distortion amount for each distance as a polynomial.   The image correction apparatus according to claim 1, wherein the distortion amount calculation unit is configured to calculate a distortion amount based on a distortion amount calculation table in which a distortion amount for each distance is recorded.   The distortion correction unit corrects distortion of an image by correcting a distortion amount of each pixel based on a distortion amount in a horizontal direction and a vertical direction passing through the optical axis center of each pixel. The image correction apparatus according to any one of 1 to 3.   2. The distortion correcting unit is configured to correct a distortion amount of each pixel by correcting a distortion amount of each pixel based on a distortion amount in a pixel having the longest distance from the optical axis center. The image correction apparatus according to any one of?   An image memory unit that stores image data of an image formed on the image sensor via the lens, and the image data is extracted from the image memory unit with reference to the amount of distortion, and the image data is stored in the image buffer unit. The image correction apparatus according to claim 1, further comprising an image dividing unit that outputs a vertical synchronization signal to the pixel count unit. In an image correction method for correcting distortion caused by lens aberration when an image formed on an image sensor through a lens is extracted as an image data signal, the horizontal synchronization signal and the vertical synchronization signal included in the image data signal are also included. And a pixel counting step for calculating the coordinate position of each pixel, the distance between the coordinate position of each pixel and the optical axis center position is calculated, and at least according to any one of the zoom position, focus position, and aperture amount of the lens The distance calculation step for converting the calculated distance, the holding step for holding the image data in the image buffer unit, and the distortion amount due to the lens aberration based on the converted distance between each pixel and the optical axis center. An image comprising: a distortion amount calculation step for calculating; and a distortion correction step of reading out image data held in the image buffer unit and correcting image distortion based on the distortion amount Positive way.

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