JP2010041403A - Device and method for correcting image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for correcting an image, which compensate a chromatic aberration without using a special-purpose lens. <P>SOLUTION: There are provided a distance calculation part 12 for calculating a distance R between a position of each pixel constituting a photographic image formed in an imaging element 2 through a lens 1 and a center on an optical axis, and a chromatic aberration characteristic calculation part 14 for calculating a chromatic aberration characteristic α of the lens aberration corresponding to the distance R calculated by the distance calculation part 12. The chromatic aberration compensating part 16 compensates the image data of the photographic image with the use of the chromatic aberration characteristic α calculated by the chromatic aberration characteristic calculation part 14. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image correction apparatus and an image correction method for compensating for chromatic aberration of lens aberration.

In an image pickup apparatus including a lens and an image pickup element, since the refractive index of the lens differs depending on the wavelength, chromatic aberration that causes a difference in image size and position depending on the color occurs.
This creates a situation in which color blur occurs at the edge portion of the captured image formed on the image sensor.
In a conventional imaging apparatus, in order to compensate for chromatic aberration of the captured image, the influence of chromatic aberration is reduced by combining a plurality of lenses having different refractive indexes.
However, when combining a plurality of lenses, the number and types of lenses increase, leading to an increase in cost.
In addition, since the digital still camera has been downsized and the lens has also been downsized, it is difficult to compensate for chromatic aberration by the lens.

  Therefore, instead of combining a plurality of lenses, an image correction apparatus that uses a special lens such as an aspheric lens or an anomalous dispersion lens and compensates for chromatic aberration using the special lens has been developed (for example, (See Patent Document 1).

JP-A-10-66097 (paragraph numbers [0011] to [0017], FIG. 1)

  Since conventional image correction devices are configured as described above, chromatic aberration can be compensated for by using special lenses such as aspherical lenses and anomalous dispersion lenses. Since a special design technique and processing technique are necessary, there are problems such as high costs.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an image correction apparatus and an image correction method capable of compensating for chromatic aberration without using a special lens.

  The image correction apparatus according to the present invention includes a distance calculation unit that calculates a distance between the position of each pixel constituting the captured image formed on the image sensor via the lens and the center position of the optical axis, and a distance calculation unit. Chromatic aberration characteristic calculating means for calculating the chromatic aberration characteristic of the lens aberration corresponding to the calculated distance is provided, and the image data correcting means corrects the image data of the captured image using the chromatic aberration characteristic calculated by the chromatic aberration characteristic calculating means. It is what I did.

  According to this invention, the distance calculation means for calculating the distance between the position of each pixel constituting the captured image formed on the image sensor via the lens and the center position of the optical axis, and the distance calculation means And a chromatic aberration characteristic calculating unit that calculates a chromatic aberration characteristic of the lens aberration corresponding to the distance, and the image data correcting unit corrects the image data of the captured image using the chromatic aberration characteristic calculated by the chromatic aberration characteristic calculating unit. Therefore, there is an effect that chromatic aberration can be compensated without using a special lens.

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 pickup device 2 is installed in the front stage of the image correction device 3, forms a picked-up image through the lens 1, outputs image data of the picked-up image to the image correction device 3, and In order to specify the pixels constituting the captured image, a horizontal synchronization signal and a vertical synchronization signal are output to the image correction device 3.
The image correction device 3 is a device that corrects image data output from the image sensor 2 and compensates for chromatic aberration of lens aberration.

The pixel count unit 11 of the image correction device 3 counts the horizontal synchronization signal and the vertical synchronization signal output from the image sensor 2 and indicates the position of each pixel constituting the captured image formed on the image sensor 2. A process of calculating X and vertical coordinate Y is performed. Hereinafter, the coordinates indicating the position of each pixel are represented by (X, Y).
The distance calculation unit 12 calculates a distance R between coordinates (X, Y) indicating the position of each pixel calculated by the pixel count unit 11 and coordinates (Xc, Yc) indicating the center position of the optical axis in the captured image. Perform the process.
The pixel count unit 11 and the distance calculation unit 12 constitute a distance calculation unit.

The chromatic aberration characteristic calculation table storage unit 13 is a memory that stores a chromatic aberration characteristic calculation table in which the correspondence between the distance R and the chromatic aberration characteristic α is shown.
The chromatic aberration characteristic calculation unit 14 refers to the chromatic aberration characteristic calculation table stored in the chromatic aberration characteristic calculation table storage unit 13 and specifies the chromatic aberration characteristic α of the lens aberration corresponding to the distance R calculated by the distance calculation unit 12. To implement.
The chromatic aberration characteristic calculation table storage unit 13 and the chromatic aberration characteristic calculation unit 14 constitute chromatic aberration characteristic calculation means.

The image buffer unit 15 is a memory that temporarily holds image data of a captured image output from the image sensor 2.
In addition, the image data of a captured image shall have all the color information of R, G, B as color information of each pixel. That is, color interpolation processing is performed using Raw data (data having only one single color information among R, G, and B color information as image data per pixel). Thus, it is assumed that image data having all color information of R, G, and B is obtained from the image sensor 2.

The chromatic aberration compensation unit 16 corrects the image data of the captured image held in the image buffer unit 15 using the chromatic aberration characteristic α specified by the chromatic aberration characteristic calculation unit 14 and performs processing for compensating for chromatic aberration of lens aberration. To do. The chromatic aberration compensator 16 constitutes image data correction means.
FIG. 2 is a flowchart showing the processing contents of the image correction apparatus according to Embodiment 1 of the present invention.

Next, the operation will be described.
When the image pickup device 2 forms a picked-up image via the lens 1, the image pickup device 2 outputs image data of the picked-up image to the image correction device 3 and outputs a horizontal synchronization signal and a vertical synchronization signal to the image correction device 3.

  When the pixel count unit 11 of the image correction device 3 receives the horizontal synchronization signal and the vertical synchronization signal from the image sensor 2, the pixel count unit 11 counts the horizontal synchronization signal and the vertical synchronization signal to thereby form a captured image formed on the image sensor 2. (X, Y) is calculated as the coordinates indicating the position of each pixel that constitutes (step ST1).

When the pixel count unit 11 calculates the coordinates (X, Y) indicating the position of each pixel, the distance calculation unit 12 indicates the coordinates (X, Y) indicating the position of each pixel as shown in the following equation (1). And a distance R between the coordinates (Xc, Yc) indicating the center position of the optical axis in the captured image is calculated (step ST2).

Here, the chromatic aberration characteristic calculation table storage unit 13 stores a chromatic aberration characteristic calculation table in which the correspondence between the distance R and the chromatic aberration characteristic α is shown.
The chromatic aberration characteristic calculation table is a chromatic aberration characteristic α (referred to below) expressed by using a distance R from the center position of the optical axis to an ideal imaging position without chromatic aberration and a distance r to the actual imaging position. The equation (chromatic aberration characteristic α expressed by 2) is held discretely.

  When the distance calculation unit 12 calculates the distance R, the chromatic aberration characteristic calculation unit 14 refers to the chromatic aberration characteristic calculation table stored in the chromatic aberration characteristic calculation table storage unit 13 and sets the distance R calculated by the distance calculation unit 12. The corresponding chromatic aberration characteristic α of the lens aberration is specified (step ST3).

However, since the chromatic aberration characteristic calculation table stored in the chromatic aberration characteristic calculation table storage unit 13 holds the chromatic aberration characteristic α discretely with respect to the distance R, the distance R calculated by the distance calculation unit 12 and When the matching distance is not recorded in the chromatic aberration characteristic calculation table, two points R _n and R _{n + 1} that are close to the distance R calculated by the distance calculation unit 12 are respectively shown in the following equation (3). A chromatic aberration characteristic α corresponding to the distance R is calculated using corresponding α _n and α _{n + 1} .

The image buffer unit 15 temporarily holds image data of a captured image output from the image sensor 2.
When the chromatic aberration characteristic calculation unit 14 specifies the chromatic aberration characteristic α, the chromatic aberration compensation unit 16 corrects the image data of the captured image held in the image buffer unit 15 using the chromatic aberration characteristic α, and the chromatic aberration of lens aberration. Is compensated (step ST4).

Hereinafter, the image data correction processing by the chromatic aberration compensator 16 will be specifically described.
For example, as shown in FIG. 3, an image of a pixel at the position of coordinates (X, Y) is imaged at a position where the distance from the center position of the optical axis whose coordinates are (Xc, Yc) is αR. .
The coordinates (X ′, Y ′) of the imaging position are expressed by the following formula (4).
X ′ = α (X−Xc) + Xc
Y ′ = α (Y−Yc) + Yc
(4)

Since the image data of the captured image is distributed discretely, the image data I (X ′, Y ′) of the imaging position is calculated using the image data of the four points in the vicinity of the imaging position, and the imaging is performed. The position image data I (X ′, Y ′) is output as corrected image data.
Here, the image data of four neighboring points _{I (X n, Y n)} , I (X n + 1, Y n), I (X n, Y n + 1), I (X n + 1, Y n ₊₁ ), the image data I (X ′, Y ′) at the imaging position is expressed by the following formula (5) using distance weighting.
s = X′−X _n
t = Y′−Y _n
I (X ', Y')
= (1-t) {( 1-s) I (X n, Y n) + sI (X n + 1, Y n)}
+ T {(1-s) I ( _Xn , Yn _{+ 1} ) + sI ( _{Xn + 1} , Yn _{+ 1} )}
(5)

  As apparent from the above, according to the first embodiment, the distance R between the position of each pixel constituting the captured image formed on the image sensor 2 via the lens 1 and the center position of the optical axis is calculated. And a chromatic aberration characteristic calculator 14 for calculating a chromatic aberration characteristic α of the lens aberration corresponding to the distance R calculated by the distance calculator 12, and the chromatic aberration compensator 16 is calculated by the chromatic aberration characteristic calculator 14. Since the image data of the captured image is corrected using the chromatic aberration characteristic α, the chromatic aberration can be compensated without using a special lens.

  Further, according to the first embodiment, the chromatic aberration characteristic of the lens aberration corresponding to the distance R calculated by the distance calculation unit 12 with reference to the chromatic aberration characteristic calculation table showing the correspondence between the distance and the chromatic aberration characteristic. Since α is specified, there is an effect that the chromatic aberration characteristic α of the lens aberration can be specified without performing complicated calculation.

  In the first embodiment, the distance calculation unit 12 calculates the distance R between the coordinates (X, Y) indicating the position of each pixel and the coordinates (Xc, Yc) indicating the center position of the optical axis. However, the distance R between the position of each pixel and the center position of the optical axis may be corrected according to the zoom position, focus position, and aperture amount of the lens 1.

That is, for example, when the distance calculation unit 12 holds a table that records the aperture amount corresponding to the zoom position and the focus position of the lens 1, the zoom position and focus of the lens 1 are referred to with reference to the table. The aperture amount corresponding to the position is specified. Here, the zoom position of the lens 1 is a, the focus position is b, and the aperture amount is c.
The distance calculation unit 12 is, for example, a conversion equation as shown in the following equation (6) (the equation (6) is a first order polynomial, but may be an Nth order polynomial (N is a second or higher order)). ) Is substituted for the zoom position a, the focus position b, and the aperture amount c of the lens 1, thereby correcting the distance R calculated by the equation (1). R ′ is the corrected distance R.
R ′ = aR + bR + cR (6)

Embodiment 2. FIG.
In the first embodiment, the chromatic aberration compensator 16 corrects image data having all the R, G, and B color information as the color information of each pixel. When the image data output and held in the image buffer unit 15 is Raw data, the Raw data may be corrected.

Specifically, it is as follows.
Raw data is data in which pixels of the same color as the R, G, and B pixels are arranged every other pixel.
For this reason, when correcting Raw data, it is necessary to select pixels of the same color when using four neighboring points.
Therefore, the color of the pixel located at the (X, Y) coordinate and the color of the reference pixel located at the (X _n , Y _n ) coordinate need to match.

Accordingly, in the second embodiment, the chromatic aberration compensation unit 16, if the odd-even the horizontal coordinate X and X _n match, select the X _n as the horizontal coordinate of the reference pixels, the odd-even the horizontal coordinate X and X _n match If not, X _n −1 is selected as the horizontal coordinate of the reference pixel.
Further, the chromatic aberration compensation unit 16, if the odd-even the vertical coordinate Y and Y _n match, select Y _n as the vertical coordinate of the reference pixel, if the parity of the vertical coordinate Y and Y _n do not match, the vertical reference pixel Select Y _n −1 as coordinates.

That is, the chromatic aberration compensator 16 determines that I (X _n , Y _n) as the image data of four neighboring points when the odd and even numbers of the horizontal coordinates X and X _n match and the odd and even numbers of the vertical coordinates Y and Y _n match. ), I (X _{n + 2} , Y _n ), I (X _n , Y _{n + 2} ), I (X _{n + 2} , Y _{n + 2} ), and as shown in the following formula (7) The image data I (X ′, Y ′) at the imaging position is corrected.
s = X′−X _n
t = Y′−Y _n
I (X ', Y')
= {(2-t) { (2-s) I (X n, Y n) + sI (X n + 2, Y n)}
+ T {(2-s) I ( _Xn , Yn _{+ 2} ) + sI ( _{Xn + 2} , Yn _{+ 2} )}} / 4
(7)

Expression (7) shows a case _where the odd and even numbers of the horizontal coordinates X and X _n match. However, when the odd and even numbers of the horizontal coordinates X and X _n do not match, “X _n ” in Expression (7) Is “X _n −1”, and the image data I (X ′, Y ′) at the imaging position is corrected.
Further, Expression (7) shows a case _where the odd-even numbers of the vertical coordinates Y and Y _n match, but when the odd-even numbers of the vertical coordinates Y and Y _n do not match, “Y” in Expression (7) The image data I (X ′, Y ′) at the imaging position is corrected with “ _n ” being “Y _n −1”.

  As is apparent from the above, according to the second embodiment, even when the image data held in the image buffer unit 15 is Raw data, as in the first embodiment, a special lens is not used. The chromatic aberration can be compensated.

Embodiment 3 FIG.
In the first and second embodiments, the chromatic aberration characteristic is applied to a symmetrical characteristic. However, in the third embodiment, the chromatic aberration characteristic is asymmetrical so that it can be applied. Yes.
Specifically, it is as follows.

FIG. 4 is an explanatory diagram showing chromatic aberration characteristics (asymmetric chromatic aberration characteristics) distributed concentrically.
When the pixel counting unit 11 calculates the coordinates (X, Y) indicating the position of each pixel, the distance calculation unit 12 calculates the coordinates (X, Y) indicating the position of each pixel and the center position of the optical axis in the captured image. In this Embodiment 3, as shown in the following equation (8), when calculating the distance R, coordinates indicating the center position of the optical axis are calculated. By performing a process of rotating the position of each pixel by θ with (Xc, Yc) as the origin and an enlargement / reduction process of P times and Q times, coordinates (X, Y) indicating the position of each pixel are represented by coordinates ( Xd, Yd).

The distance calculation unit 12 changes the set value of P in the positive direction and the negative direction in the A direction when performing the P / Q magnification process.
Also, the set value of Q is changed in the positive direction and the negative direction in the B direction.
By changing the set values of P and Q, applicable chromatic aberration characteristics (asymmetric chromatic aberration characteristics) can be changed.

When the coordinate (X, Y) indicating the position of each pixel is converted into the coordinate (Xd, Yd), the distance calculation unit 12 uses the converted coordinate (Xd, Yd) as shown in the following equation (9). The distance R is calculated.

  As apparent from the above, according to the third embodiment, when calculating the distance R, the process of rotating the position of each pixel by θ with the coordinates (Xc, Yc) indicating the center position of the optical axis as the origin, and Since the P / Q magnification enlargement / reduction processing is performed, the chromatic aberration can be compensated even when the chromatic aberration characteristic is asymmetrical.

Embodiment 4 FIG.
FIG. 5 is a block diagram showing an image correction apparatus according to Embodiment 4 of the present invention. In the figure, the same reference numerals as those in FIG.
The chromatic aberration characteristic calculation unit 17 substitutes the distance R calculated by the distance calculation unit 12 into the approximate expression, and performs processing for calculating the chromatic aberration characteristic α of the lens aberration.
The chromatic aberration characteristic calculation unit 17 constitutes chromatic aberration characteristic calculation means.

  In the first embodiment, the chromatic aberration characteristic calculation unit 14 refers to the chromatic aberration characteristic calculation table stored in the chromatic aberration characteristic calculation table storage unit 13, and the lens aberration corresponding to the distance R calculated by the distance calculation unit 12. Although the chromatic aberration characteristic α is specified, the chromatic aberration characteristic calculation unit 17 may substitute the distance R calculated by the distance calculation unit 12 into the approximate expression to calculate the chromatic aberration characteristic α of the lens aberration. .

That is, the chromatic aberration characteristic calculation unit 17 shows an example in which the approximate expression is a quadratic polynomial as shown in the following expression (10) when the distance calculation unit 12 calculates the distance R. However, a chromatic aberration characteristic α of the lens aberration is calculated by substituting the distance R into a polynomial of a third or higher order.
α = fR ² + gR + h (10)
However, f, g, and h are polynomial coefficients.

As apparent from the above, according to the fourth embodiment, the chromatic aberration characteristic calculation unit 17 substitutes the distance R calculated by the distance calculation unit 12 into the approximate expression to calculate the chromatic aberration characteristic α of the lens aberration. Thus, the chromatic aberration characteristic calculation table storage unit 13 for storing the chromatic aberration characteristic calculation table becomes unnecessary, and the memory amount can be reduced.
Further, chromatic aberration correction can be performed by changing the coefficients f, g, and h of the approximate expression according to the zoom position, focus position, and aperture amount of the lens 1.

It is a block diagram which shows the image correction apparatus by Embodiment 1 of this invention. It is a flowchart which shows the processing content of the image correction apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the position where the image of the pixel in the position of a coordinate (X, Y) is formed. It is explanatory drawing which shows the chromatic aberration characteristic (asymmetrical chromatic aberration characteristic) distributed to concentric ellipse. It is a block diagram which shows the image correction apparatus by Embodiment 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Lens, 2 Image pick-up element, 3 Image correction apparatus, 11 Pixel count part (distance calculation means), 12 Distance calculation part (distance calculation means), 13 Chromatic aberration characteristic calculation table storage part (chromatic aberration characteristic calculation means), 14 Chromatic aberration characteristic calculation Section (chromatic aberration characteristic calculating means), 15 image buffer section, 16 chromatic aberration compensating section (image data correcting means), 17 chromatic aberration characteristic calculating section (chromatic aberration characteristic calculating means).

Claims (6)

  Distance calculating means for calculating the distance between the position of each pixel constituting the picked-up image formed on the image pickup device via the lens and the center position of the optical axis, and a lens corresponding to the distance calculated by the distance calculating means An image correction apparatus comprising: chromatic aberration characteristic calculation means for calculating chromatic aberration characteristics of aberration; and image data correction means for correcting image data of the captured image using the chromatic aberration characteristics calculated by the chromatic aberration characteristic calculation means.   2. The image correction apparatus according to claim 1, wherein the distance calculation unit corrects the distance between the position of each pixel and the center position of the optical axis in accordance with the zoom position, the focus position, and the aperture amount of the lens.   The distance calculation means, when calculating the distance between the position of each pixel and the center position of the optical axis, rotates and scales the position of each pixel with respect to the center position of the optical axis. The image correction apparatus according to 1.   The chromatic aberration characteristic calculating means specifies a chromatic aberration characteristic of a lens aberration corresponding to the distance calculated by the distance calculating means with reference to a chromatic aberration characteristic calculation table showing a correspondence relationship between the distance and the chromatic aberration characteristic. The image correction apparatus according to any one of claims 1 to 3.   4. The chromatic aberration characteristic calculating unit calculates a chromatic aberration characteristic of lens aberration by substituting the distance calculated by the distance calculating unit into an approximate expression. 5. Image correction device.   A distance calculating step in which the distance calculating means calculates a distance between the position of each pixel constituting the captured image formed on the image sensor through the lens and the center position of the optical axis; and a chromatic aberration characteristic calculating means is the distance calculating means The chromatic aberration characteristic calculating step for calculating the chromatic aberration characteristic of the lens aberration corresponding to the distance calculated by the above, and the image data correcting unit corrects the image data of the captured image using the chromatic aberration characteristic calculated by the chromatic aberration characteristic calculating unit. An image correction method comprising: an image data correction step.

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