JPH11168740A - Luminance signal processing circuit for color video camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminance signal processing circuit for color video camera with which a false signal produced in the luminance signal processing for the color video camera is suppressed greatly. SOLUTION: In a moire signal processing circuit 9 of a solid-state image- pickup element provided with color filters and receiving plural lines consisting of repetition of a couple of pixels, a conversion of T1'=T1.(T1L+T2L)/(2.T2L), and a conversion of T2'=T2.(T1L+T2L)/(2.T1L) are conducted, where T1 is an output signal of either of the couple of pixels, T2 is an output signal of the other, and T1L, T2L are low-frequency components of the output signals T1, T2. The signals after the conversion are made to go through low-pass filters, from which a luminance signal whose false signal has been eliminated is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for a color video camera, and more particularly to a luminance signal processing circuit including luminance correction.

[0002]

2. Description of the Related Art A color video camera is a solid-state image sensor,
In particular, those using a CCD solid-state imaging device have become mainstream. The basic processing process is a process of detecting an image image as a charge stored in a photoelectric conversion element by a solid-state imaging device, and converting a digital signal obtained by quantizing a charge amount into an analog image signal by a low-pass filter or the like. Is included.

On the other hand, the substantial resolution is determined by the number of pixels of the CCD solid-state imaging device, but after sampling and restoring processes, generation of a false signal due to an essentially high spatial frequency component is inevitable.

[0004]

FIG. 3 shows an example of a conventional color filter array. Here, W (white), G
A color array composed of r (green), Cy (cyan), and Ye (yellow) is used, and these four pixels are used as a basic unit. FIG.
, Px represents the pixel pitch in the horizontal direction, and Py represents the pixel pitch in the vertical direction.

In the horizontal direction, a luminance resolution corresponding to a spatial frequency of 1 / Px can be expected. However, for example, due to the difference in the intensity of W and Gr, the following false signal is generated with fs as the carrier frequency.

(Π / 2) · (W−Gr) sin (2π · fs · t) An object of the present invention is to reduce such a false signal.

[0007]

In order to achieve the above-mentioned object, the present invention (claim 1) provides an image forming apparatus having a color filter.
In a circuit for generating a luminance signal from an output signal of a solid-state imaging device having a plurality of lines formed by repeating a pair of pixels, one output signal of the pair of pixels is defined as T1 and the other output signal is defined as T2. The low frequency components of the signals T1 and T2 are T1L and T2L, and for each pixel of each line, T1 ′ = T1 · (T1L + T2L) / (2 · T2L) T2 ′ = T2 · (T1L + T2L) / (2 · T1L) And a luminance signal processing circuit for a color video camera, wherein the luminance signal is generated.

According to a second aspect of the present invention, there is provided a circuit for generating a luminance signal from an output signal of a solid-state imaging device having a plurality of lines formed by repeating a pair of pixels having a color filter. The output signal of one of the pixels
1, the other output signal is T2, and these output signals T1,
The low frequency components of T2 are defined as T1L and T2L, and for each pixel of each line, the following conversion is performed: T1 ′ = 2 · T1 · T2L / (T1L + T2L) T2 ′ = 2 · T2 · T1L / (T1L + T2L) Provided is a luminance signal processing circuit for a color video camera, which generates a luminance signal.

Further, according to the present invention (claim 3), in the above-mentioned claim 1 or claim 2, the solid-state imaging device comprises a CCD.
The present invention provides a luminance signal processing circuit for a color video camera, which is a solid-state imaging device.

Further, the present invention (claim 4) is characterized in that, in the above-mentioned claim 3, the combination of the color filters is a combination of a filter having a transparent or nearly transparent spectrum and a green filter. Provided is a luminance signal processing circuit for a video camera.

According to a fifth aspect of the present invention, in the third aspect, the combination of the color filters is a combination of a magenta filter and a green filter. A signal processing circuit is provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram of an embodiment in which the circuit of the present invention is applied to a color video camera. In FIG. 1, for the sake of simplicity, components generally provided in a color video camera such as a lens optical system, a recording system on a recording medium, various signal processing systems, and an operation system are omitted. ing.

First, an overall schematic configuration will be described.

In FIG. 1, a solid-state image sensor (hereinafter referred to as C)
Light from a subject or the like through a lens optical system (not shown) and further through a color filter of a complementary color system enters and forms an image on the CD1). In the CCD 1, incident light is photoelectrically converted, and the obtained image signal is supplied to a correlated double sampling (CDS) 2.

In this correlated double sampling circuit 2, C
This is a circuit for performing a so-called correlated double sampling process, which is one of noise reduction techniques for removing random noise (shot noise of a signal and dark current) from a CD. Processing for suppressing the reset noise by subtracting the level is performed. The output of the correlated double sampling circuit 2 is sent to an analog / digital (A / D) converter 3.

The analog / digital converter 3 includes a sample and hold circuit on the input side. The analog / digital converter 3 converts the analog image signal sampled and held by the sample and hold circuit through the correlated double sampling circuit 2 into a predetermined sample frequency. Digital signal (hereinafter, referred to as
Digital video signal). The digital video signal output from the analog / digital converter 3 is sent to a vertical filter circuit 4, a main signal processing circuit 6, and a pixel separation circuit 8.

The vertical filter circuit 4 includes a vertical band-pass filter (V-BPF) for extracting a predetermined vertical frequency band component from the digital video signal, and a vertical high-pass filter for extracting a vertical high frequency band component from the digital video signal. And a filter (V-HPF) for extracting a contour component in the vertical direction from the digital video signal. The vertical bandpass filter and the vertical highpass filter are both cyclic (IIR) or non-cyclic (F
IR) digital filter, a vertical high-pass filter is set with a 5-tap filter coefficient in Example 2, and a vertical band-pass filter is set with a 3-tap filter coefficient, for example. An output signal from the vertical filter circuit 4,
That is, the vertical contour components extracted from the digital video signal are sent to the coring processing circuit 5.

The coring processing circuit 5 suppresses a noise component included in the contour component of the image and generates a signal-to-noise ratio (S / N).
That is, a so-called coring process is performed to improve the above. The signal subjected to the coring processing by the coring processing circuit 5 is sent to a γ (gamma) front contour compensation circuit 12 and a γ rear contour compensation circuit 14 described later.

On the other hand, a digital video signal (hereinafter, referred to as a main signal) from which a false signal has been removed in a main signal processing circuit 6 described later is supplied to a vertical low-pass filter (V-LP).
F) 7a and horizontal low-pass filter (H-LPF) 7b
Are supplied sequentially.

The vertical low-pass filter 7a and the horizontal low-pass filter 7b add a contour component, that is, a high-frequency component to the main signal in the γ front contour compensating circuit 12 in the subsequent stage. Remove high frequency components. The vertical low-pass filter 7a is a recursive or non-recursive digital filter, for example, a filter for which a 5-tap filter coefficient is set. The main signal from which the high frequency component has been removed by the vertical low-pass filter 7a and the horizontal low-pass filter 7b is supplied to the γ front contour compensation circuit 12.

Next, the pixel separation circuit 8 converts the digital video signal supplied from the analog / digital converter 3 into a W signal.
(White), Gr (Green), Cy (Cyan), and Ye (Yellow) are signals sequentially supplied in accordance with the arrangement of the complementary color filters.
, And separates the signals of the pixels respectively corresponding to Further, in the pixel separation circuit 8, in order to interpolate a portion corresponding to a pixel which has been omitted by performing the pixel separation (that is, a complementary color signal exists in the omitted portion).
Alternatively, for example, horizontal pixel interpolation can be performed. The signal output from the pixel separating circuit 8 and the signal from which the high frequency component has been removed through the horizontal low-pass filter 8a are supplied to the moiré processing circuit 9 to the moiré processing circuit 9.

The moiré processing circuit 9 includes a pixel separation circuit 8
The moiré processing is performed to suppress the moiré by balancing the respective levels of the complementary haiku of W, G, Cy and Ye supplied from. An output signal from the moiré processing circuit 9 is supplied to a horizontal high-pass filter (H-HPF) 10. The moiré processing circuit 9 also outputs the above-described control signal yf1 used in the coring processing circuit 5.

The horizontal high-pass filter 10 extracts a high frequency band component from the supplied signal. That is, the horizontal high-pass filter 10 outputs a high-frequency component in the horizontal direction after the moiré processing. An output signal from the horizontal high-pass filter 10 is supplied to a coring processing circuit 11.

The coring processing circuit 11 has substantially the same configuration as the coring processing circuit 5, and removes noise components included in the high-frequency components of the signal supplied from the horizontal high-pass filter 10. A coring process for suppressing and improving a signal-to-noise ratio (S / N) is performed. The high frequency component in the horizontal direction after the moiré processing subjected to the coring processing by the coring processing circuit 11 is sent to the γ front contour compensation circuit 12.

The γ front contour compensating circuit 12 includes a vertical contour component obtained by the vertical filter circuit 4 and the coring processing circuit 5, and a main signal processing circuit 6, a vertical low-pass filter 7a, and a horizontal low-pass filter 7b. The obtained main signal from which the high frequency component has been removed, and the pixel separation circuit 8
And a high-frequency component in the horizontal direction after the moiré processing and the coring processing obtained by the configuration from to the coring processing circuit 11, to form a luminance signal and to perform contour compensation of the luminance signal. The video signal subjected to the contour compensation by the γ front contour compensation circuit 12 is supplied to a gamma processing circuit 13.

The gamma processing circuit 13 is supplied with γ (gamma) correction processing for correcting gamma characteristics of a CRT (cathode ray tube) to be used as a display device from the γ front contour compensation circuit 12. Apply to digital video signals. The video signal that has been subjected to the gamma correction processing by the gamma processing circuit 13 is sent to the γ rear contour compensation circuit 14 and the horizontal aperture control circuit 16.

The horizontal aperture control circuit 16 performs horizontal (and vertical) aperture correction on the video signal that has been gamma-corrected by the gamma processing circuit 13, and performs coring processing on the video signal after the aperture correction. Supply to circuit 15.

The coring processing circuit 15 has substantially the same configuration as the coring processing circuit 11 and the coring processing circuit 5, and suppresses a noise component included in a high frequency band component of the video signal. A coring process for improving a signal-to-noise ratio (S / N) is performed. The output signal of the coring processing circuit 5 is sent to the post-γ contour compensation circuit 14.

The post-gamma contour compensating circuit 14 includes a vertical contour component obtained by the vertical filter circuit 4 and the coring process, a video signal after the gamma correction process from the gamma processing circuit 13, and a horizontal aperture component. -Mix the signal after the cha correction and perform contour compensation of the luminance signal after the gamma correction processing.

The output signal of the post-γ contour compensating circuit 14 is
The digital video signal of the present embodiment is output as a digital video signal or recorded on a recording medium. The video camera according to the present embodiment has the above configuration.

Next, processing of digital video signals sequentially supplied from the pixel separating circuit 8 will be described. Here, the essential features of the present invention are included.

As shown in FIG. 3, the color filter array of the CCD 1 used in this camera is composed of W, Gr,
A color arrangement having four pixels of Cy and Ye as one unit is used. In FIG. 2, Px represents the pixel pitch in the horizontal direction, and Py represents the pixel pitch in the vertical direction.

In the CCD 1, as shown in FIG.
The electric charges stored in the photoelectric conversion elements 18 provided for each pixel are transferred to the vertical CCD 19 for all pixels, and are read out by the horizontal CCD 20 line by line. In addition, there are an interleaving method for reading out every other row, a method using two horizontal CCDs, and the like, and all of them can perform exactly the same processing.

Therefore, signals of a series of W, Gr, W, Gr... And a series of Cy, Ye, Cy, Ye.

Here, in the horizontal direction, generally, 1 /
A luminance resolution corresponding to the spatial frequency of Px can be expected.
However, after passing through the low-pass filter, the signal S on the WGr line includes a false signal due to the difference between the intensities of the W signal and the Gr signal, and fs is the carrier frequency as follows.

[0037]

S = (W + Gr) / 2 + (π / 2) · (W−Gr) sin (2π · fs · t) (1) where the first term is the original luminance The second term is a false signal due to a folded component. Then, the following conversion is performed for each pixel of each input line.

W '= 2.W.GrL / (WL + GrL) Gr' = 2.Gr.WL / (WL + GrL) Cy '= 2.Cy.YeL / (CyL + YeL) Ye' = 2.Ye.CyL / (CyL + YeL) Here, WL, GrL, CyL and YeL are CCDs, respectively.
Are the low frequency components of the output signals W, Gr, Cy, and Ye. Specifically, it is obtained from several pixels before and after the target pixel, for example, 5-15 pixels, via the horizontal low-pass filter 8a. This conversion is performed inside the moiré processing circuit 9.

By performing such a conversion, the low-frequency component SwL and the high-frequency component SwH of W of the WGr line signal obtained from the converted W ′, Gr ′, Cy ′, and Ye ′ are , As follows.

SwL = 2 · W · GrL / (WL + GrL) SwH = 2 · W · GrL / (WL−GrL) On the other hand, the component S of the signal of the WGr line in the low frequency region of W
gL and the component SgH in the high frequency region are as follows.

SgL = 2 · Gr · WL / (WL + GrL) SgH = −2 · Gr · WL / (WL−GrL) Similarly, the low-frequency component ScyL and the high-frequency component of the Cy signal on the CyYe line ScyH is as follows.

ScL = 2 · Cy · YeL / (CyL + YeL) ScH = 2 · Cy · YeL / (CyL−YeL) The component ScyL in the low frequency region and the component ScyH in the high frequency region of the Ye signal of the CyYe line are , As follows.

SyL = 2 · Ye · CyL / (CyL + YeL) SyH = −2 · Ye · CyL / (CyL−YeL) Therefore, it can be seen that the aliasing component in the high frequency region has the same level in each pixel. Conventionally, the luminance component is
Although the averaging was performed by the low-pass filter, the present invention performs the above calculation without adding in the horizontal direction.

The spectral effect obtained by the above calculation is equivalent to a common spectral component of each pixel, that is, Gr spectral.
The above calculation results are processed in a frequency band (luminance band) that does not affect color reproduction.

The above effect is the same even when the following conversion is used.

W ′ = W · (WL + GrL) / (2 · WL) Gr ′ = Gr · (WL + GrL) / (2 · GrL) Cy ′ = Cy · (CyL + YeL) / (2 · CyL) Ye ′ = Ye · (CyL + YeL) / (2 · YeL) The same conversion as the above conversion may be performed in the vertical direction. That is, the difference in the vertical direction is equivalent to the difference in the horizontal direction.
The following conversion may be performed with the luminance of the line, Yc, as the luminance of the CyYe line.

Yw '= Yw / (YwL + YcL) Yc' = Yc / (YwL + YcL) Here, a letter L is added to indicate a component in the low frequency region.

As described above, four pixels W, Gr, Cy, and Ye are
Although the color arrangement as a unit has been described, the present invention is not limited to this, and the conversion is effective even with another type of filter. For example, the same processing is effective for a CCD solid-state imaging device having a color arrangement in which four pixels of Mg (magenta), Gr, Cy, and Ye as one unit as shown in FIG. In this case, the conversion process is as follows.

Mg ′ = 2 · Mg · GrL / (MgL + GrL) Gr ′ = 2 · Gr · MgL / (MgL + GrL) Cy ′ = 2 · Cy · YeL / (CyL + YeL) Ye ′ = 2 · Ye · CyL / (CyL + YeL) ) Or Mg ′ = Mg · (MgL + GrL) / (2 · MgL) Gr ′ = Gr · (MgL + GrL) / (2 · GrL) Cy ′ = Cy · (CyL + YeL) / (2 · CyL) Ye ′ = Ye · ( CyL + YeL) / (2 · YeL)

[0050]

As described above, according to the present invention, it is possible to greatly suppress a false signal generated in the luminance signal processing for a color video camera.

[Brief description of the drawings]

FIG. 1 is a block diagram of a system using a luminance signal processing circuit for a color video camera according to an embodiment of the present invention.

FIG. 2 is a CCD of a color video camera including a luminance signal processing circuit for a color video camera according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating transfer of electric charge in a solid-state imaging device.

FIG. 3 is a color video camera CCD including a color video camera luminance signal processing circuit according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating a color filter array of a solid-state imaging device.

FIG. 4 is a diagram showing another example of the color filter array used in the CCD solid-state imaging device of the color video camera according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 solid-state imaging device 2 correlated double sampling circuit 3 digital converter 4 vertical filter circuit 5 coring processing circuit 6 main signal processing circuit 7a vertical low-pass filter 7b horizontal low-pass filter 8 pixel separation circuit 8a horizontal low-pass filter 9 moire processing circuit 10 horizontal High pass filter 11 Coring processing circuit 12 Front contour compensation circuit 13 Gamma processing circuit 14 Rear contour compensation circuit 15 Coring processing circuit 16 Horizontal aperture control circuit 18 Photoelectric conversion element 19 Vertical CCD 20 Horizontal CCD

Claims (5)

[Claims] 1. A circuit for generating a luminance signal from an output signal of a solid-state imaging device having a plurality of lines formed by repeating a pair of pixels having a color filter, wherein one output signal of the pair of pixels is set to T1. , The other output signal is T2, and the low frequency components of these output signals T1, T2 are T1.
L, T2L, and for each pixel of each line, the following conversion is performed: T1 ′ = T1 · (T1L + T2L) / (2 · T2L) T2 ′ = T2 · (T1L + T2L) / (2 · T1L) And a luminance signal processing circuit for a color video camera. 2. A circuit for generating a luminance signal from an output signal of a solid-state imaging device having a plurality of lines formed by repeating a pair of pixels having a color filter, wherein one output signal of the pair of pixels is represented by T1. , The other output signal is T2, and the low frequency components of these output signals T1, T2 are T1.
L, T2L, and for each pixel on each line, perform the conversion of T1 '= 2T1T2L / (T1L + T2L) T2' = 2T2T1L / (T1L + T2L) to generate the luminance signal. A luminance signal processing circuit for a color video camera. 3. The luminance signal processing circuit for a color video camera according to claim 1, wherein said solid-state imaging device is a CCD solid-state imaging device. 4. The luminance signal processing circuit for a color video camera according to claim 3, wherein the combination of the color filters is a combination of a filter having a transparent or nearly transparent spectrum and a green filter. 5. The luminance signal processing circuit for a color video camera according to claim 3, wherein the combination of the color filters is a combination of a magenta filter and a green filter.