JP2009010674A - Chromatic-aberration measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, when executing measurement of a chromatic aberration amount of lens magnification by using an image photographed by an image pickup device, it is required to prepare a plurality of chromatic-aberration measurement charts respectively having different fineness in accordance with a photographing area since the photographing area is variously changed if a lens position is variously changed. <P>SOLUTION: A chromatic-aberration measurement chart has a characteristic that a distance from a reference position taken on the lens optical-axis and a striped frequency are inversely proportional to each other. When the chromatic-aberration measurement chart is used, an apparent frequency of the chromatic-aberration measurement chart to be photographed is not changed even when a lens position is changed. Therefore, it is possible to execute measurement of a chromatic aberration amount in various positions by one type of chromatic-aberration measurement chart. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a chromatic aberration measuring method for measuring a chromatic aberration amount necessary for correcting chromatic aberration of an image captured by an imaging device such as a television camera.

  In recent years, the HD (high definition, high definition) of TV cameras has progressed, and displays that use liquid crystal panels and plasma panels, commonly called FPDs (flat panel displays), have become mainstream. It is coming. Along with this, color misregistration at the periphery of the screen of video shot with a television camera has become a problem. This is because the convergence deviation inherent to the conventional CRT does not occur in the FPD, and image distortion called chromatic aberration that occurs in the lens of the TV camera is easily visible. In particular, image quality deterioration due to lateral chromatic aberration (hereinafter referred to as chromatic aberration), which appears as a difference in light wavelength, becomes a difference in image magnification, has become apparent. Conventionally, a chromatic aberration correction function that electrically corrects chromatic aberration optically generated by a lens on the TV camera side has been proposed, and a method for measuring an aberration amount that is information necessary for this correction has also been proposed. .

  A conventional chromatic aberration measuring method will be described below.

Conventionally, the chromatic aberration measuring method described in Patent Document 1 is known. FIG. 7 is a block diagram of a conventional chromatic aberration measuring method. In FIG. 7, the optical image of the chromatic aberration measurement diagram 201 that is incident from the interchangeable lens 202 and is imaged on the imaging surfaces of the imaging elements 204R, 204G, and 204B by the spectral prism 203 for each color component is an electrical video signal. And stored in the line memories 212R, 212G, and 212B. The chromatic aberration measurement diagram 201 is as shown in FIG. 8, and the fringes are inclined so as to be orthogonal to one of the diagonal lines of the imaging surfaces of the imaging elements 204R, 204G, and 204B, and the line memories 212R, 212G, and 212B are shown in FIG. The value of the pixel along the diagonal line of the imaging region as indicated by the square of 9 is selectively stored. Chromatic aberration measurement is performed by detecting a shift between the channels of the one-dimensional images of the R, G, and B channels stored in the line memories 212R, 212G, and 212B by the chromatic aberration detection circuit 213.
JP-A-3-169190

  However, in the above-described conventional configuration, when measuring the amount of chromatic aberration that varies depending on the lens position, if the fringe frequency of the chart used for measuring the amount of aberration is constant, the distance from the lens to the subject (subject distance), When trying to measure the amount of aberration by changing the angle of view (zoom) of the lens, the accuracy of the measurement will not be constant due to the change in the spacing of the striped pattern. There was a problem that it was necessary to prepare a plurality.

  The present invention solves the above-mentioned conventional problems, and even when the photographing range changes by changing the lens position such as the object distance and the angle of view of the lens, the measurement accuracy is kept constant without changing the measurement chart. It is an object of the present invention to provide a chromatic aberration measuring method for measuring a chromatic aberration amount.

In order to solve the above-mentioned problem, the chromatic aberration measuring method of the present invention is expressed by the following equation with respect to the distance r from the reference position: L (r) = A · cos (B · log (| r |) + C) (A, B, C: constant)
A chromatic aberration measurement diagram having a figure obtained by binarizing the luminance L (r) obtained by the above equation is used, and in the camera, the intersection of the optical axis of the lens and the imaging surface is set as a reference position of the two-dimensional imaging region, and the chromatic aberration measurement diagram. A photographic aberration for detecting a relative color shift in the radial direction of each color with reference to the reference position of the two-dimensional image photographed by the camera, and a photographing step for photographing in accordance with the reference position of the two-dimensional photographing region of the camera. A chromatic aberration measurement method comprising: a detecting step, wherein the chromatic aberration measurement can be performed using the same chromatic aberration measurement diagram even when the photographing range is changed by changing the lens position. Have.

  According to the chromatic aberration measurement method of the present invention, when performing chromatic aberration measurement by changing the lens position such as the object distance and the angle of view of the lens in chromatic aberration measurement, the measurement chart is exchanged even if the shooting range changes. Thus, an excellent effect is obtained that the amount of chromatic aberration can be measured while maintaining measurement accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

(Embodiment 1)
FIG. 1 is a block diagram of an imaging apparatus to which the chromatic aberration measuring method of the present invention is applied.

In FIG. 1, the optical image of the chromatic aberration measurement diagram 101 incident from the interchangeable lens 102 and imaged on the imaging surfaces of the imaging elements 104R, 104G, and 104B after being divided into color components by the spectral prism 103 is an electrical video signal. And stored in the frame memories 112R, 112G, and 112B. The chromatic aberration measurement diagram 101 is as shown in FIG. 2A, and the expression L (r) = A · cos (B · log (| r |) + C) in the figure with respect to the distance r from the reference position. (A, B, C: constant) (Formula 1)
The luminance L (r) obtained from the above is binarized into black and white. As a method for binarizing the luminance L (r), for example, there is a method in which white is used if the sign of L (r) is positive and black is used if it is negative.

  In Equation 1, since the change rate (slope, first derivative) of the cos parameter is inversely proportional to the distance r from the reference position, the apparent fringe frequency is inversely proportional to the distance r from the reference position. The constant B gives the overall frequency of the chromatic aberration measurement diagram 101, that is, the fineness of the fringes, and is determined by the relationship with the number of pixels of the image sensor of the camera used for chromatic aberration measurement. That is, if the constant B is small, the fringes become coarse and the measurement accuracy decreases, and if the constant B is large, the fringes become fine and cannot be resolved near the center. Therefore, the constant B is determined by balancing these.

  Considering the case where such a chromatic aberration measurement diagram is taken with a camera through a lens, the concentric fringe has an apparent frequency of ½ when the radius is doubled. However, the zoom magnification can be increased by changing the lens position. If the shooting range is doubled by doubling the angle of view by changing the distance to the subject or by doubling the distance to the subject, the image will be halved and the frequency will be doubled. Conversely, when the radius is halved, the apparent frequency is doubled, but when the lens is zoomed twice or the distance to the subject is halved, it is twice as large. The frequency is half of the original.

  In other words, even if the shooting range changes, if the chromatic aberration measurement diagram as shown in FIG. 2A is used, the apparent pattern (the relationship between the distance from the reference position and the frequency) does not change. Suitable for measuring the amount of chromatic aberration required. For example, there are a state where the subject distance (focus position) is short as shown in FIG. 3A, a state where the subject is far away from the subject as shown in FIG. 3B, and a state where the angle of view (zoom position) is different.

  The frame memories 112R, 112G, and 112B are taken in such a manner that the reference position in the chromatic aberration measurement diagram 101 coincides with the optical center of the image sensors 104R, 104G, and 104B (intersection with the optical axis of the interchangeable lens 102). The chromatic aberration amount detection circuit 113 detects the chromatic aberration amount.

  That is, a shift between the R, G, and B channels on a straight line passing through the reference position is detected for each image height (distance from the optical axis). Specifically, the following processing is performed. As shown in FIG. 4, it is assumed that there are pixels of the image sensor at the positions of circle marks arranged in a grid at a constant pixel pitch, and the pixel values are stored in the frame memory as they are. Pixel values at positions of triangular marks arranged at equal intervals on a line having an arbitrary inclination passing through the reference position are obtained for each of the R, G, and B channels by two-dimensional interpolation calculation. At this time, the cross-correlation value between the G-R channels in the vicinity of the image height at which the chromatic aberration amount is to be detected by shifting the R-channel interpolation pixel position as a whole with respect to the reference G-channel interpolation pixel position. The shift amount of the interpolated pixel position of the R channel that maximizes is obtained. The shift amount that maximizes the cross-correlation value between the GR channels for each image height is the chromatic aberration amount of the R channel. Similarly, the amount of chromatic aberration for each image height can be obtained for the B channel.

  As described above, according to this embodiment, chromatic aberration measurement at various lens positions can be performed with one type of chromatic aberration measurement diagram by using a chromatic aberration measurement diagram in which an apparent pattern does not change due to enlargement / reduction of an image. it can.

  In the above example, the R and B channels are shifted with reference to the G channel as a method for obtaining the chromatic aberration amount for each image height. Conversely, the G channel can be shifted with reference to the R and B channels. Good. Alternatively, the shift amount that maximizes the cross-correlation may be searched after the signals of all channels are smoothly interpolated by increasing the number of data by so-called oversampling processing.

  In addition to the method using the cross-correlation calculation, the detection of the chromatic aberration amount may be performed by another method such as obtaining and comparing the position where the luminance change in the contour portion of the pattern is maximized for each channel.

  As a two-dimensional interpolation calculation method, bicubic interpolation is performed in addition to bilinear interpolation in which weighted addition is performed based on the distance between the target pixel (black triangle mark) and the four pixels (black circle mark) surrounding it in FIG. Although there is a more accurate interpolation method, a more accurate calculation method is preferable.

(Embodiment 2)
FIG. 5 is a chromatic aberration measurement diagram used in the chromatic aberration measurement of the present invention.

The method and block diagram for chromatic aberration measurement are the same as those in FIG. 1 in the first embodiment, except that the chromatic aberration measurement diagram 101 in FIG. 1 is the distance from the reference position in FIG. 2 in the first embodiment. In contrast to the concentric chromatic aberration measurement diagram in which the luminance L (r) is determined by r, in the second embodiment, the luminance L (x) is determined by the distance from the origin on the one-dimensional coordinate axis X as shown in FIG. This is a point using a belt-like chromatic aberration measurement diagram. The chromatic aberration measurement diagram shown in FIG. 5 shows the expression L (x) = A · cos (B · log (| x |) + C) (A, B) in FIG. 5 with respect to the coordinate x on the one-dimensional coordinate axis X. , C: constant) (Formula 2)
The luminance L (x) obtained from the above is binarized into black and white. In Equation 2, since the change rate (slope, first derivative) of the parameter of cos is inversely proportional to the distance | x | from the origin of the point x on the coordinate axis X, the apparent fringe frequency becomes the distance | x | from the origin. It will be inversely proportional. Therefore, as in the case of the first embodiment, the chromatic aberration measurement diagram shown in FIG. 5 does not change the apparent pattern (the relationship between the distance from the origin and the frequency) even if the photographing range changes.

  The frame memory 112R is obtained by photographing so that the position of x = 0 in the chromatic aberration measurement diagram shown in FIG. 5 coincides with the optical center of the image sensors 104R, 104G, 104B (intersection with the optical axis of the interchangeable lens 102). , 112G, 112B, and the chromatic aberration amount detection circuit 113 detects the chromatic aberration amount.

  The amount of chromatic aberration at which the image formation position is displaced with respect to the image height is rotationally symmetric about the optical axis of the lens. Therefore, the position of x = 0 in the chromatic aberration measurement diagram is aligned with the optical axis position of the lens. The color shift amount for each image height may be measured on a straight line passing through the optical axis of the lens parallel to the coordinate axis X of the chromatic aberration measurement diagram. At this time, if a chromatic aberration measurement diagram is taken so that the diagonal direction including the maximum image height and the coordinate axis X are parallel to each other in the shooting region of the camera indicated by the dotted line in FIG. . In order to capture the image as shown in FIG. 6, the chromatic aberration measurement diagram may be installed diagonally in the diagonal direction of the shooting area of the camera. However, the chromatic aberration measurement diagram is installed horizontally and the camera side is tilted to the right to adjust the angle. Also good.

  The chromatic aberration measurement diagram used in this embodiment only needs to be on the diagonal line of the camera imaging area necessary for chromatic aberration measurement, so the lens position state with a wide imaging range such as a long subject distance and a wide angle of view. However, it is only necessary to prepare a belt-like chromatic aberration measurement chart, so that it can be handled relatively easily.

  As described above, according to the present embodiment, chromatic aberration measurement at various lens positions is performed with one type of chromatic aberration measurement diagram by using a belt-like chromatic aberration measurement diagram whose apparent pattern does not change due to enlargement / reduction of the image. be able to.

  Note that the method of copying the belt-like chromatic aberration measurement diagram is not limited to the upward direction as shown in FIG. 6, but may be the upward direction, and the final measurement is performed by combining the measurement results for each method. As a result.

  The method for measuring chromatic aberration according to the present invention can efficiently measure the amount of chromatic aberration at various lens positions, and is useful for improving the image quality by using the measurement result with a camera having a chromatic aberration correction function. .

Block diagram in Embodiment 1 of the present invention Chromatic aberration measurement diagram in the first embodiment Illustration of lens position and shooting range Illustration of two-dimensional interpolation operation Chromatic aberration measurement diagram in Embodiment 2 of the present invention The figure which shows the example of a imaging | photography screen in the same Embodiment 2. Block diagram of a conventional chromatic aberration measurement method Chromatic aberration measurement diagram of conventional chromatic aberration measurement method Explanatory diagram of line memory operation in conventional chromatic aberration measurement method

Explanation of symbols

101 Chromatic aberration measurement diagram 102 Interchangeable lens 104 Image sensor 112 Frame memory 113 Chromatic aberration detection circuit 201 Chromatic aberration measurement diagram 202 Interchangeable lens 204 Image sensor 212 Frame memory 213 Chromatic aberration detection circuit

Claims (4)

A chromatic aberration measurement method for detecting chromatic aberration by photographing a chromatic aberration measurement diagram with a camera mounted on the front surface of an interchangeable lens having a variable lens position,
The chromatic aberration measurement diagram shows the following equation for the distance r from the reference position: L (r) = A · cos (B · log (| r |) + C) (A, B, C: constant)
A figure obtained by binarizing the luminance L (r) determined by
In the camera, an intersection between the optical axis of the lens and the imaging surface is set as a reference position of the two-dimensional imaging region,
A shooting step of shooting in accordance with a reference position of the two-dimensional shooting area of the camera;
A chromatic aberration detection step of detecting a relative color shift in the radial direction of each color with reference to a reference position of a two-dimensional image taken by the camera;
A chromatic aberration measuring method comprising: A chromatic aberration measurement method for detecting chromatic aberration by photographing a chromatic aberration measurement diagram with a camera mounted on the front surface of an interchangeable lens having a variable lens position,
In the chromatic aberration measurement diagram, a coordinate axis X having a reference position as an origin is provided, and the following formula L (x) = A · cos (B · log) is obtained for a line region passing through the coordinate x on the coordinate axis X and orthogonal to the coordinate axis X. (| X |) + C) (A, B, C: constant)
And a figure obtained by converting the luminance L (x) obtained by
In the camera, an intersection between the optical axis of the lens and the imaging surface is set as a reference position of the two-dimensional imaging region,
An imaging step of aligning the reference position of the chromatic aberration measurement diagram with the reference position of the two-dimensional imaging region of the camera and imaging the coordinate axis X of the chromatic aberration measurement diagram parallel to the diagonal direction of the two-dimensional imaging region of the camera;
A chromatic aberration detecting step of detecting a relative color shift in the diagonal direction of each color of the two-dimensional image photographed by the camera;
A chromatic aberration measuring method comprising: L (r) = A · cos (B · log (| r |) + C) (A, B, C: constant) with respect to the distance r from the reference position
A chromatic aberration measurement diagram in which the luminance L (r) obtained by
An interchangeable lens with variable lens position;
A camera having the lens mounted on the front surface and having the intersection of the optical axis of the lens and the imaging surface as a reference position of a two-dimensional imaging area;
Chromatic aberration detection means for detecting a relative color shift in the radial direction of each color with reference to a reference position of a two-dimensional image taken by the camera,
An apparatus for measuring chromatic aberration, wherein the chromatic aberration measurement device is used for imaging in accordance with a reference position of a two-dimensional imaging region of the camera. A coordinate axis X having a reference position as an origin is provided, and the following formula L (x) = A · cos (B · log (| x |) + C for a line region orthogonal to the coordinate axis X through the coordinate x on the coordinate axis X (A, B, C: constant)
A chromatic aberration measurement diagram in which the luminance L (x) obtained by
An interchangeable lens with variable lens position;
A camera having the lens mounted on the front surface and having the intersection of the optical axis of the lens and the imaging surface as a reference position of a two-dimensional imaging area;
Chromatic aberration detecting means for detecting a relative color shift in the diagonal direction of each color of the two-dimensional image photographed by the camera,
The reference position of the chromatic aberration measurement diagram is matched with the reference position of the two-dimensional imaging region of the camera,
An apparatus for measuring chromatic aberration, wherein the coordinate axis X of the chromatic aberration measurement diagram is imaged in parallel with a diagonal direction of a two-dimensional imaging region of the camera.