JPH0879773A - Shading correction device - Google Patents

Abstract

PURPOSE: To obtain a shading correction device in which correction suitable for mass-production is attained and shading caused usually is almost completely corrected. CONSTITUTION: Color signals R, B are fed to a matrix circuit 4 via correction blocks 1R, 1B, amplifiers 2R, 2B and gamma correction circuits 3R, 3B, and a color signal G is fed to the matrix circuit 4 via an amplifier 2G and a gamma correction circuit 3G, and the matrix circuit 4 provides the output of a luminance signal Y and color difference signals R-Y, B-Y. Correction blocks 1R, 1B apply a correction coefficient COE obtained through approximation by a quadratic curved face function to the color signals R, B to conduct shading, correction in a way that the shading of image pickup elements for a red image and a blue image is almost coincident with shading for an image pickup element for a green image. Since electric shading correction is made, the correction suitable for mass-production is conducted. Since the coefficient COE obtained through approximation by a quadratic curved face function is in use, the high shading correction capability is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shading correction device for correcting shading caused by uneven sensitivity of an image pickup device.

[0002]

2. Description of the Related Art In a multi-plate color video camera, chroma shading (color unevenness) and luminance shading (luminance unevenness) occur due to shading that occurs due to uneven sensitivity of image pickup devices (for example, CCD solid-state image pickup devices).

Conventionally, in order to correct these shadings, a method of measuring the sensitivity of each image pickup device at a plurality of points on the image pickup surface and using image pickup devices having the same tendency (trioring).
Alternatively, a method of electrically correcting shading with a vertical or horizontal parabolic waveform signal has been proposed.

[0004]

The trio ring is used to select and use imagers having the same shading tendency, and it is not suitable for mass production because it requires much labor for selection.
Further, according to the one in which the shading is corrected by the parabolic waveform signal or the like, the degree of freedom in correction is small, and it is not possible to correct any shading.

Therefore, the present invention provides a shading correction apparatus capable of correction suitable for mass production and capable of almost completely correcting shading that normally occurs.

[0006]

A shading correction apparatus according to the invention of claim 1 outputs a shading correction coefficient approximated by an N-order curved surface function (N is an integer of 2 or more).
It comprises a quadric surface function generating means and a shading correction means for performing shading correction by multiplying an image pickup signal output from the image pickup element by a shading correction coefficient output from the Nth order curved surface function generation means.

According to a second aspect of the present invention, there is provided a shading correction apparatus according to the first aspect of the present invention, which includes image pickup elements for red images, green images and blue images as image pickup elements and a red image for shading correction means. A first shading correction unit that corrects the shading of the image pickup device for the blue image;
The second shading correction unit performs shading correction so that the shading of the image pickup element for the red image and the shading of the image pickup element for the blue image substantially match the shading of the image pickup element for the green image.

According to a third aspect of the present invention, there is provided a shading correction device according to the first aspect of the present invention, which includes image pickup elements for red image, green image and blue image as image pickup elements, and red image as shading correction means. It has first, second and third shading correction units for respectively correcting the shading of the image pickup device for the green image and the blue image, and the first, second and third shading correction units respectively for the red image. The shading correction is performed so that the shading of the image pickup elements for the green image and the blue image becomes almost zero.

[0009]

According to the first aspect of the invention, the shading correction is performed by multiplying the image pickup signal output from the image pickup element by the correction coefficient, and the shading correction is electrically performed. Different from the above, it becomes possible to perform correction suitable for mass production. Further, since the correction coefficient approximated by the N-order curved surface function is used, the shading correction capability is high, and the shading that normally occurs can be corrected almost completely.

According to the second aspect of the present invention, since the shading correction is performed so that the shading of the image pickup device for the red image and the shading of the image pickup device for the blue image substantially coincide with the shading of the image pickup device for the green image, the chroma shading is corrected. It will be possible.

According to the invention of claim 3, for a red image,
Since the shading correction is performed so that the shading of the image pickup elements for the green image and the blue image is substantially zero, both the chroma shading and the luminance shading can be corrected.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the present invention will be described below with reference to FIG.
Examples will be described. This example is an example applied to a three-plate color video camera having CCD solid-state image pickup devices for red image, green image and blue image, and is adapted to correct chroma shading.

In the figure, C for red image and C for blue image
A red primary color signal R and a blue primary color signal B obtained from a CD solid-state image pickup device (not shown) are respectively provided in a matrix circuit via shading correction blocks 1R and 1B, white balance control amplifiers 2R and 2B, and gamma correction circuits 3R and 3B. 4 is supplied. Also, a CCD for green images
Green primary color signal G obtained from a solid-state image sensor (not shown)
Is supplied to the matrix circuit 4 via the white balance control amplifier 2G and the gamma correction circuit 3G. Then, in the matrix circuit 4, the color signals R, G, B
Are subjected to matrix processing to obtain a luminance signal Y and a red color difference signal R-
Y and a blue color difference signal BY are output.

FIG. 2 shows a shading correction block 1R.
Is shown. In the figure, reference numeral 11 is a quadratic surface function generator, which is composed of a coordinate value generating unit 12 and a quadratic surface function calculating unit 13 which are counters. The coordinate value generator 12 is supplied with the clock signal CK, the horizontal synchronizing signal HD and the vertical synchronizing signal VD. This coordinate value generator 12
Then, the horizontal coordinate signal X is obtained by counting the clock signal CK using the horizontal synchronizing signal HD as a reset signal, and the vertical coordinate is obtained by counting the horizontal synchronizing signal HD using the horizontal synchronizing signal VD as a reset signal. Table Y
Is obtained.

The coordinate value (X,
Y) is supplied to the quadratic surface function calculation unit 13. The quadratic surface function calculation unit 13 calculates the quadratic surface function fR as follows.
The correction coefficient COE corresponding to the coordinate value (X, Y) is calculated by (X, Y).

FR (X, Y) = a ₀₀ + a ₀₁ Y + a ₀₂ Y ² + a ₁₀ X + a ₁₁ XY + a ₁₂ XY ² + a ₂₀ X + a ₂₁ X ² Y + a ₂₂ X ² Y ² (1) where (1) The coefficients a _{00 to} a ₂₂ of the equation) are supplied from a microcomputer (not shown) that constitutes the system controller.
The coefficients a _{00 to} a ₂₂ are set so that the shading of the image pickup element for the red image substantially matches the shading of the image pickup element for the green image when the red primary color signal R is multiplied by the correction coefficient COE in the correction amplifier 14 described later. In addition, the sensitivities of a plurality of points of the image pickup elements for the red image and the green image are measured in advance, are calculated based on the sensitivities of the measurement points, and are stored in a nonvolatile memory (not shown).

The correction coefficient COE output from the calculation unit 13 corresponding to the coordinate value (X, Y) is supplied to the multiplier 15 forming the correction amplifier 14. A digital red primary color signal R is supplied to the multiplier 15, and the red primary color signal R is multiplied by a correction coefficient COE to perform shading correction and output. As a result, shading correction is performed so that the shading of the image pickup element for the red image substantially matches the shading of the image pickup element for the green image.

The signal input is an analog red primary color signal R.
Then, the correction amplifier 14 is configured as shown in FIG. 3, for example. That is, the red primary color signal R is the correction amplifier 1
The gain of the gain control amplifier 16 is controlled by the correction coefficient COE converted into an analog signal by the D / A converter 17.

Although FIG. 2 shows the configuration of the shading correction block 1R, the shading correction block 1B is shown.
The shading correction block 1B performs shading correction so that the shading of the image pickup element for the blue image is substantially the same as the shading of the image pickup element for the green image.

As described above, in this example, shading correction is performed in the shading correction blocks 1R and 1B so that the shading of the image pickup elements for the red image and the blue image substantially coincides with the shading of the image pickup element for the green image. Therefore, the chroma shading can be satisfactorily corrected. Further, the red primary color signal R and the blue primary color signal B obtained from the image sensor are multiplied by a correction coefficient COE to perform shading correction.
Since shading correction is performed electrically, unlike conventional trio rings, correction suitable for mass production can be performed. Further, since the correction coefficient COE approximated by the quadric surface function is used, the shading correction capability is high, and the chroma shading can be almost completely corrected.

Next, a second embodiment of the present invention will be described with reference to FIG. This example includes CCD solid-state image pickup devices for red image, green image and blue image.
This is an example applied to a plate type color video camera, in which both chroma shading and luminance shading are corrected. In this FIG.
The parts corresponding to those in FIG. 1 are designated by the same reference numerals.

In the figure, a red primary color signal R, a green primary color signal G, and a blue primary color signal B obtained from CCD solid-state image pickup devices (not shown) for red image, green image and blue image are respectively shading correction blocks. 5R, 5G, 5B, white balance control amplifiers 2R, 2G, 2B,
It is supplied to the matrix circuit 4 through the gamma correction circuits 3R, 3G, 3B. Then, in the matrix circuit 4, the color signals R, G, B are subjected to matrix processing, and a luminance signal Y, a red color difference signal RY and a blue color difference signal BY are output.

The shading correction block 5R is shown in FIG.
The shading correction block 1R is configured in the same manner as the shading correction block 1R shown in FIG. 1, and shading correction is performed in the shading correction block 5R so that the shading of the image pickup element for the red image becomes substantially zero. In this case, the coefficients a _{00 to} a ₂₂ supplied from the microcomputer are such that when the correction amplifier 14 multiplies the red primary color signal R by the correction coefficient COE, the shading of the image pickup device for the red image becomes almost zero.
The sensitivity of multiple points of the image sensor for the red image is measured in advance,
It is calculated based on the sensitivity of the measurement point and stored in the non-volatile memory.

The shading correction block 5G,
5B has the same configuration as the shading correction block 1R shown in FIG.
Then, shading correction is performed so that the shading of the image pickup device for green image and the shading of the image pickup device for blue image are substantially zero.

As described above, in this example, the shading correction blocks 5R, 5G, and 5B perform shading correction so that the shading of the image pickup elements for the red image, the green image, and the blue image becomes substantially zero, respectively. It is possible to favorably correct both chroma shading and luminance shading. In addition, the red primary color signal R, the green primary color signal G, and the blue primary color signal B obtained from the image pickup device are multiplied by a correction coefficient COE to perform shading correction. Unlike the trio ring, the correction suitable for mass production can be performed. Further, since the correction coefficient COE approximated by the quadric surface function is used, the shading correction capability is high, and the chroma shading and the luminance shading can be almost completely corrected.

In the above embodiment, the quadratic surface function operation unit 13 calculates the correction coefficient COE by using the quadratic surface function, but the correction coefficient COE is calculated by using a surface function of cubic or higher. You can also However, the shading generated in the current CCD solid-state image pickup device is not so complicated in its spatial distribution, and the approximation by the quadric surface function has sufficient accuracy for the purpose of shading correction.
Further, in the above-described embodiment, an example in which the invention is applied to a three-plate color video camera is shown, but the present invention is also applicable to other multi-plate color video cameras, single-plate color video cameras, and monochrome video cameras. Of course, it can be applied to.

[0027]

According to the first aspect of the present invention, the shading correction is performed by multiplying the image pickup signal output from the image pickup device by the correction coefficient, and the shading correction is performed electrically. Unlike the trio ring of, the correction suitable for mass production becomes possible. Further, since the correction coefficient approximated by the N-order curved surface function is used, the shading correction capability is high, and the shading that normally occurs can be corrected almost completely.

According to the second aspect of the present invention, since the shading correction is performed so that the shading of the image pickup device for the red image and the shading of the image pickup device for the blue image substantially match the shading of the image pickup device for the green image, the chroma shading correction is performed. It can be performed.

According to the third aspect of the invention, since the shading correction is performed so that the shading of the image pickup elements for the red image, the green image and the blue image becomes almost zero, both the chroma shading and the luminance shading are performed. Corrections can be made.

[Brief description of drawings]

FIG. 1 is a first shading correction device according to the present invention.
It is a block diagram which shows an Example.

FIG. 2 is a configuration diagram showing a shading correction block.

FIG. 3 is a configuration diagram showing another example of a correction amplifier.

FIG. 4 is a second shading correction device according to the present invention.
It is a block diagram which shows an Example.

[Explanation of symbols]

 1R, 1B, 5R to 5B Shading correction block 4 Matrix circuit 11 Quadratic surface function generator 12 Coordinate value generation unit 13 Quadratic surface function operation unit 14 Correction amplifier 15 Multiplier 16 Gain control amplifier 17 D / A converter

Claims (3)

[Claims] 1. An N-order curved surface function generating means for outputting a shading correction coefficient approximated by an N-order curved surface function (N is an integer of 2 or more), and the N-order curved surface function generating means for an imaging signal output from an image sensor. A shading correction device, comprising: a shading correction unit that performs shading correction by multiplying the output shading correction coefficient. 2. A first image pickup device for a red image, a green image and a blue image is provided as the image pickup device, and a shading correction device is provided for correcting shading of the red image image pickup device and the blue image pickup device, respectively. And a second shading correction unit. In the first and second shading correction units, the shading of the image pickup device for the red image and the shading of the image pickup device for the blue image are substantially the same as the shading of the image pickup device for the green image. The shading correction apparatus according to claim 1, wherein the shading correction is performed as described above. 3. An image pickup device for red image, green image and blue image is provided as the image pickup device, and shading of the image pickup device for red image, green image and blue image is respectively provided as the shading correction means. It has first, second, and third shading correction units for correction, and in the first, second, and third shading correction units, the red, green, and blue image pickup elements are respectively The shading correction apparatus according to claim 1, wherein the shading correction is performed so that the shading becomes substantially zero.