JPH0723411A - Video camera - Google Patents

Abstract

PURPOSE:To prevent color jump of a reproduced picture at a low illuminance state. CONSTITUTION:The video camera 1 is provided with a color correction circuit 8 correcting a color of a Y signal, (R-Y) signal and (B-Y) signal in response to a picked up optical image by a matrix depending on the illuminance state, a low illuminance discrimination circuit 11 discriminating a low illuminance state based on each level of an iris position detection signal A outputted from an iris position sensor 10 and an illuminance detection signal B in response to a luminance of an optical image outputted from an AGC detection circuit 5 to output a low illuminance discrimination signal C, and a control circuit 12 outputting a low illuminance corresponding color correction signal D to the color correction circuit 8 based on the discrimination signal C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera.

[0002]

2. Description of the Related Art A luminance correction signal (Y signal) and color difference signals (RY), (BY) corresponding to an optical image to be picked up are color-corrected by a color correction circuit by a matrix, and then the color correction signal is obtained. (Y 'signal, (RY)' signal, (BY) 'signal)
There is a video camera having a well-known configuration that encodes a signal with an encoder and outputs a Y signal and a color signal (C signal).

[0003]

However, in the conventional video camera, in the color correction by the matrix performed in the color correction circuit, the coefficients of a large number of coefficient units constituting the color correction circuit are irrelevant to the illuminance of the optical image. Since it was a constant value,
When a low light condition subject with insufficient light is captured,
Since the level of the color correction signal is significantly reduced, the level of the C signal output from the encoder is consequently low, and therefore, there is a problem in that color reproduction is poor such that a dark reproduced image is not sufficiently colored. .

[0004]

In order to solve the above problems, the present invention provides a video camera having the following configuration.

A color correction circuit for color-correcting an image signal corresponding to an optical image to be picked up according to the illuminance state, a low illuminance discrimination circuit for discriminating the low illuminance state of the optical image and outputting a low illuminance discrimination signal, A video camera, comprising: a control circuit that outputs a color correction signal corresponding to low illuminance to the color correction circuit based on a low illuminance determination signal.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A video camera according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of an embodiment of a video camera according to the present invention, and FIGS. 2 and 3 are block diagrams similar to the color correction circuit disclosed in Japanese Patent Application No. 4-210870 "Color Correction Method".

As will be described later, the video camera according to the present invention generally provides an image signal (luminance signal, color difference signals (RY), (BY)) corresponding to an optical image to be picked up according to the illuminance state. Color correction circuit 8 for performing color correction (color correction by matrix) and a low illuminance state of the captured optical image (iris position detection signals A and AG output from the iris position sensor 10).
A low illuminance discriminating circuit which discriminates a low illuminance state in which the light amount is insufficient based on each level of the illuminance detection signal B corresponding to the brightness of the subject outputted from the C detecting circuit 5 and outputs a low illuminance discriminating signal C. 11 and a control circuit 12 for outputting a low illuminance corresponding color correction signal D to the color correction circuit 8 based on the low illuminance determination signal C.

That is, as shown in FIG. 1, the video camera 1 is an optical image radiated on its image pickup surface via an image pickup lens system (not shown) having various iris / focus / zoom variable mechanisms. CCD 2 which is a solid-state image sensor that sequentially scans and transfers a charge image obtained by photoelectric conversion according to the amount of light and outputs it as an image signal, and outputs an image signal from which noise components in the image signal output from this CCD 2 are removed A sample hold circuit 3 that is a correlated double sampling (CDS) circuit, an AGC circuit 4 that automatically adjusts the image signal level output from the sample hold circuit 3 to a predetermined value, and the output level is variable according to the brightness of the subject. The illuminance detection signal B is turned on (it becomes the minimum level in the open state)
Luminance signal process for generating and outputting a Y signal by separating the image signal of a predetermined level output from the AGC circuit 4 and the AGC circuit 4 to be described later as a C detection signal to the AGC detection circuit 5 and the low illuminance determination circuit 11 described below. Circuit 6, above A
A color signal process circuit 7 that separates image signals of a constant level output from the GC circuit 4 to generate and output color difference signals (RY) and (BY), respectively, the luminance signal process circuit 6 and the color signal process. Y signals output from the circuit 7,
The color difference signals (RY) and (BY) are color-corrected by a matrix to generate and output color correction signals (Y 'signal, (RY)' signal, (BY) 'signal). A color correction circuit 8, an encoder 9 that encodes the above-described color correction signal output from the color correction circuit 8 and outputs a Y signal and a C signal to a video signal recording system (not shown), and an iris according to the brightness of the subject. The iris position detection signal according to the iris scale position adjusted by the mechanism for automatically opening and closing the iris control circuit (not shown) and the low illuminance determination circuit 1 described later.
When the optical image taken by the iris position sensor 10 which outputs 1 to 1, the iris position detection signal A from the iris position sensor 10 and the illuminance detection signal B from the AGC detection circuit 5 is in the low illuminance state, the low illuminance determination signal Low illuminance discrimination circuit 11 for outputting C, and this low illuminance discrimination circuit 11
The low illuminance-corresponding color correction signal D is output to the color correction circuit 8 on the basis of the low illuminance discrimination signal from, and the coefficients of the large number of coefficient units 8g to 8p constituting the color correction circuit 8 are switched to the low illuminance compatible coefficients. A control circuit 12 for controlling color correction is provided.

The color correction method carried out by the color correction circuit 8 described above is based on the Y signal and the color difference signal (R) output from the luminance signal process circuit 6 and the color signal process circuit 7.
-Y) and (BY) are corrected by an operation (multiplication) including a square term, and a Y signal and a color difference signal (R -Y), (BY), the color correction signal (Y 'signal,
(R−Y) ′ signal, (B−Y) ′ signal).

[0010]

[Equation 1] First, obtaining the color correction signal (Y ′ signal) using this equation (Formula 1) will be described. Here, the case where the control circuit 12 does not output the low illuminance compatible color correction signal D will be described first.

As shown in FIG. 2, the color correction circuit 8 includes a squaring circuit 8a for squaring a Y signal, a squaring circuit 8b for squaring a color difference signal (RY), and a squaring circuit for squaring a color difference signal (BY). The circuit 8c includes a multiplier 8d that multiplies the Y signal and the color difference signal (RY), a multiplier 8e that multiplies the color difference signal (RY) and the color difference signal (BY), and a color difference signal (BY). A multiplier 8f for multiplying the Y signal, and a coefficient unit 8 for multiplying the Y signal by the coefficient a _11.
g, a coefficient unit 8 for multiplying the color difference signal (RY) by the coefficient a _12.
h, a coefficient unit 8 for multiplying the color difference signal (BY) by the coefficient a _13.
i, a coefficient unit 8j that multiplies the output signal Y ² of the squaring circuit 8a by a coefficient a ₁₄ , a coefficient unit 8k that multiplies the output signal (RY) ² of the squaring circuit 8b by a coefficient a _15, and an output signal of the squaring circuit 8c. The coefficient unit 8l for multiplying (BY) ² by the coefficient a ₁₆ , the coefficient unit 8m for multiplying the output signal Y × (RY) of the multiplier 8d by the coefficient a _17, and the output signal (R-R of the multiplier 8e Y) x (B-
The coefficient unit 8n for multiplying Y) by the coefficient a ₁₈ and the coefficient unit 8 for multiplying the output signal Y × (B−Y) of the multiplier 8f by the coefficient a _19.
and a coefficient unit 8o having coefficients a ₁ and a _10, and an adder 8q for adding all output signals of the coefficient units 8g to 8o and outputting a color correction signal (Y 'signal). The squaring circuits 8a to 8c and the multipliers 8d to 8f can be realized by a ROM by treating the above Y signal, color difference signals (RY) and (BY) as digital signals.

In this way, the color correction circuit 8 having the above-mentioned configuration can obtain the color correction signal (Y 'signal) from the Y signal and the color difference signals (RY) and (BY) described above.

Next, when the color correction signal ((RY) 'signal) is obtained by using the equation (1), the coefficient of the coefficient unit 8g in the configuration of the color correction circuit 8 described above. a ₁₁ is changed to a coefficient a ₂₁ , and similarly, the coefficient a ₁₂ of the coefficient unit 8h is the coefficient a ₂₂ , the coefficient a ₁₃ of the coefficient unit 8i is the coefficient a ₂₃ , and the coefficient unit 8j is the same.
Coefficient a ₁₄ of coefficient a ₂₄ and coefficient a ₁₅ of coefficient multiplier 8k are coefficient a _24
25 , coefficient a ₁₆ of coefficient unit 8l is coefficient a ₂₆ , coefficient a ₁₇ of coefficient unit 8m is coefficient a ₂₇ , coefficient a ₁₈ of coefficient unit 8n is coefficient a ₂₈ ,
The coefficient a ₁₉ of the coefficient unit 8o is the coefficient a ₂₉ , and the coefficient a of the coefficient unit 8p is
_It suffices to use ₁ and a ₁₀ as coefficients a ₂ and a ₁₀ (the other square circuits 8a to 8c and multipliers 8d to 8f need not be changed).

In this way, the color correction circuit 8 performs the same calculation as that for obtaining the above-mentioned color correction signal (Y 'signal) although the coefficients are different, whereby the color correction circuit 8 outputs the Y signal, the color difference signal (RY),
The color correction signal ((RY) 'signal) can be obtained from (BY).

Further, when the color correction signal ((BY) 'signal) is obtained by using the equation (1), the coefficient a of the coefficient unit 8g in the configuration of the color correction circuit 8 described above. ₁₁ is changed to a coefficient a ₃₁ , and similarly, the coefficient a ₁₂ of the coefficient unit 8h is the coefficient a ₃₂ , the coefficient a ₁₃ of the coefficient unit 8i is the coefficient a ₃₃ , and the coefficient unit 8 is the same.
The coefficient a ₁₄ of j is the coefficient a ₃₄ , the coefficient a ₁₅ of the coefficient unit 8k is the coefficient a ₃₅ , the coefficient a ₁₆ of the coefficient unit 8l is the coefficient a ₃₆ , the coefficient a ₁₇ of the coefficient unit 8m is the coefficient a ₃₇ , and the coefficient unit 8n is the coefficient a ₃₇ . The coefficient a ₁₈ may be the coefficient a ₃₈ , the coefficient a ₁₉ of the coefficient unit 8o may be the coefficient a ₃₉ , and the coefficients a ₁ and a ₁₀ of the coefficient unit 8p may be the coefficients a ₃ and a ₁₀ (other square circuits 8a to 8c). And it is not necessary to change the multipliers 8d to 8f).

Therefore, although the coefficients are different, the color correction circuit 8 performs the same calculation as that for obtaining the color correction signal (Y 'signal) described above, whereby the color correction circuit 8 outputs the Y signal, the color difference signal (RY),
A color correction signal ((BY) 'signal) can be obtained from (BY). Coefficients of the above-mentioned coefficient units 8g to 8p {a
_ij } (i = 1,2,3; j = 1,2,3, ..., 10) is determined by the least squares method based on a large number of samples.

When the control circuit 12 outputs the low illuminance-corresponding color correction signal D, the coefficient unit 8g described above is output.
The coefficients {a _ij } of ~ 8p are all switched to the coefficients corresponding to low illuminance. That is, the coefficient corresponding to the low illuminance is replaced with a larger value as compared with the coefficient corresponding to the normal illuminance in which the low illuminance determination signal C is not output. As a result, the respective levels of the color correction signals (Y ′ signal, (RY) ′ signal, (BY) ′ signal) color-corrected in the low illuminance state are larger than those in the normal illuminance state. It is possible to output at a certain level, which makes it possible to make the level of the C signal, of the Y and C signals encoded and output by the encoder 9 described above, higher than in the past, so that a dark reproduced image can be reproduced. Also in the case of (1), an effect that good color reproducibility and good color reproduction can be obtained.

Next, the color correction circuit 8 shown in FIG.
A color correction circuit 8'having a simplified configuration will be described.
The color correction method performed by the color correction circuit 8'is the Y signal output from the luminance signal process circuit 6 and the color signal process circuit 7 and the color difference signals (RY) and (BY).
Is corrected by an operation including a squared term. From the Y signal, the color difference signals (RY) and (BY), the 3 × 6 matrix operation shown in the following (Equation 2) is performed. Color correction signal (Y 'signal, color difference signal (RY)', (B
-Y) '). The same components as those described above are designated by the same reference numerals and the description thereof will be omitted.

[0019]

[Equation 2] First, obtaining the color correction signal (Y ′ signal) using this equation (Formula 2) will be described. Here, the case where the control circuit 12 does not output the low illuminance compatible color correction signal D will be described first.

The color correction circuit 8'is, as shown in FIG.
Squaring circuit 8a squaring a signal, squaring circuit 8b, the squaring circuit 8c, the coefficient unit 8g for multiplying the coefficients a ₁₁ to Y signal squaring the color difference signals (B-Y) for squaring the color difference signals (R-Y),
Coefficient multiplier 8h for multiplying the coefficients a ₁₂ color difference signals (R-Y),
Coefficient multiplier 8i for multiplying the coefficients a ₁₃ color difference signals (B-Y),
A coefficient multiplier 8j for multiplying the output signal Y ² of the squaring circuit 8a by a coefficient a _14, and a coefficient a of the output signal (RY) ² of the squaring circuit 8b.
Coefficient multiplier 8k that multiplies ₁₅ and output signal (B
-Y) ² is composed of a coefficient unit 8l for multiplying the coefficient a ₁₆ and an adder 8q for adding all output signals of the coefficient units 8g to 8l and outputting a color correction signal (Y 'signal).

The squaring circuits 8a to 8c described above are connected to the Y circuit described above.
If the signals and the color difference signals (RY) and (BY) are treated as digital signals, they can be realized by a ROM (Read Only Memory). In this way, the color correction circuit 8'having the above configuration can obtain a color correction signal (Y 'signal) from the Y signal, color difference signals (RY), (BY).

Next, when the color correction signal ((RY) 'signal) is obtained by using the above equation (2), the coefficient unit 8g in the color correction circuit 8'is configured. The coefficient a ₁₁ is changed to the coefficient a ₂₁ , and similarly, the coefficient a ₁₂ of the coefficient unit 8h is the coefficient a ₂₂ , the coefficient a ₁₃ of the coefficient unit 8i is the coefficient a ₂₃ , and the coefficient unit 8 is the same.
The coefficient a ₁₄ of j is the coefficient a ₂₄ , the coefficient a ₁₅ of the coefficient unit 8k is the coefficient a ₂₅ , and the coefficient a ₁₆ of the coefficient unit 8l is the coefficient a ₂₆ (other square circuits 8a to 8c can be changed). Unnecessary).

In this way, the color correction circuit 8'has the Y signal and the color difference signal (R- by performing the same calculation as that for obtaining the color correction signal (Y 'signal) described above, although the coefficients are different.
Y), (B-Y) to color correction signal ((R-Y) 'signal)
Can be asked.

Further, when the color correction signal ((BY) 'signal) is obtained by using the equation (2), the coefficient of the coefficient unit 8g in the configuration of the color correction circuit 8'is set. The coefficient a ₁₂ is changed to the coefficient a ₃₁ by changing the coefficient a ₁₁ to the coefficient a _31.
Is the coefficient a ₃₂ , the coefficient a ₁₃ of the coefficient unit 8i is the coefficient a ₃₃ , the coefficient a ₁₄ of the coefficient unit 8j is the coefficient a ₃₄ , the coefficient a ₁₅ of the coefficient unit 8k is the coefficient a ₃₅ , and the coefficient a ₁₆ of the coefficient unit 8l is the coefficient a ₁₆ . It should be a ₃₆ (the other square circuits 8a to 8c need not be changed).

Therefore, although the coefficients are different, the color correction circuit 8'has the Y signal, the color difference signal (RY), by performing the same calculation as that for obtaining the color correction signal (Y 'signal) described above.
A color correction signal ((BY) 'signal) can be obtained from (BY). Coefficients of the above-mentioned coefficient units 8g to 8l {a
_ij } (i = 1,2,3; j = 1,2,3, ..., 6) is determined by the least squares method based on a large number of samples.

When the control circuit 12 outputs the low illuminance-corresponding color correction signal D, the coefficient unit 8g described above is output.
The coefficients {a _ij } of ˜8l are all switched to the coefficients corresponding to low illuminance. That is, the coefficient corresponding to the low illuminance is replaced with a larger value as compared with the coefficient corresponding to the normal illuminance in which the low illuminance determination signal C is not output. As a result, the respective levels of the color correction signals (Y ′ signal, (RY) ′ signal, (BY) ′ signal) color-corrected in the low illuminance state are larger than those in the normal illuminance state. It is possible to output at a certain level, which makes it possible to make the level of the C signal, of the Y and C signals encoded and output by the encoder 9 described above, higher than in the past, so that a dark reproduced image can be reproduced. Also in the case of (1), an effect that good color reproducibility and good color reproduction can be obtained.

[0027]

The video camera according to the present invention includes a color correction circuit for color-correcting an image signal corresponding to an optical image to be picked up according to the illuminance state, and a low illuminance determination signal for determining the low illuminance state of the optical image. And a control circuit for outputting a color correction signal corresponding to the low illuminance to the color correction circuit based on the low illuminance determination signal. Therefore, the control circuit outputs the color correction signal for the low illuminance. Then, the color correction circuit performs fine color correction according to each hue in the low illuminance state. In addition, because of the above-described configuration, it is possible to output the color correction signal at a large level, for example, in relation to the case where the low illuminance-corresponding color correction signal is not output, for example, the hue related to the large occurrence of color skipping. In addition, even in a dark reproduced image reproduced based on a luminance signal and a color signal obtained by encoding the color correction signal, a sufficient color can be obtained, and an effect of good color reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a video camera according to the present invention.

FIG. 2 is a block diagram of a color correction circuit.

FIG. 3 is a block diagram of a color correction circuit.

[Explanation of symbols]

 1 Video Camera 5 AGC Detection Circuit 8 Color Correction Circuit 10 Iris Position Sensor 11 Low Illumination Discrimination Circuit 12 Control Circuit A Iris Position Detection Signal B Illuminance Detection Signal C Low Illumination Discrimination Signal D Low Illumination Corresponding Color Correction Signal

Claims (1)

[Claims] 1. A color correction circuit for color-correcting an image signal corresponding to an optical image to be picked up according to an illuminance state, and a low illuminance determination circuit for determining a low illuminance state of an optical image and outputting a low illuminance determination signal. And a control circuit that outputs a color correction signal corresponding to low illuminance to the color correction circuit based on the low illuminance determination signal.