JP3287833B2 - Blooming reduction circuit of color television receiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a blooming reduction circuit of a color television receiver.

[Summary of the Invention]

The present invention relates to a blooming reduction circuit for a color television receiver, wherein both a luminance signal and a chrominance signal are supplied as input signals, and the luminance signal and the chrominance signal are controlled in conjunction with each other in response to a first control signal. Contrast and color density control means for adjusting the contrast and color density of an image projected on the screen of a color picture tube in a coordinated manner, and a signal path of a luminance signal for compensating for the gamma characteristic of the color picture tube Gamma correction means for changing the gamma characteristic in response to the second control signal, and control signal generation means for generating the first control signal and the second control signal. A blooming detecting means for detecting a color level of the luminance signal, and detecting whether or not the white level of the detected luminance signal becomes a predetermined level in the color picture tube to cause blooming. When the level of the luminance signal detected by the blooming detecting means is equal to or higher than a predetermined level, the second control signal is changed so that the input / output characteristic of the gamma characteristic of the gamma correction circuit becomes gentle. If the control signal generating means determines that the contrast and color density of the image are not suppressed to a low level, the first control signal is controlled so as to reduce the adjustment voltage of the contrast and color density control means. If it is determined by the control signal generation means that the contrast and color density of the image have been suppressed to a low level, the first control signal is controlled so that the adjustment voltage of the contrast and color density control means remains unchanged. This is a circuit for reducing blooming of a color television receiver.

[Conventional technology]

In a conventional color television receiver, when an image is received with an increased contrast, when bright white characters or the like appear in a part of an image, blooming occurs in which the periphery of the white characters is blurred. The simplest method of suppressing the occurrence of such blooming is to view the image while keeping the contrast low. However, in an image without bright white characters or the like, there is a problem that the contrast cannot be sufficiently obtained. A conventional example which solves such a problem will be described with reference to FIGS. To the input terminal T ₁ in FIG. 8 is supplied composite color signal from the VIF (video intermediate frequency) circuit, is separated into Y and C signals by the Y / C (luminance / chroma) signal separating circuit (2), Y
The signal is supplied to the clip circuit (3) through a delay circuit (not shown) for compensating a time difference from the C signal. In the clipping circuit (3), as shown in FIG. 9, a video signal (Y signal)
(4) A white character signal (5) component causing blooming contained therein is clipped at a predetermined clip level _CL , and a video signal is not shown, but a sharpness control (not shown) constituting a video signal processing circuit (1) is performed. It is supplied to the contrast control circuit (6) through the circuit. The contrast control circuit (6) adjusts the degree of lightness and darkness of the color image of the video signal (4). The pedestal clamp circuit (7) reproduces the DC component and adjusts the luminance. 8). The chroma signal C separated by the Y / C separation circuit (2) is supplied to a color signal reproduction circuit (8). The color signal reproducing circuit (8) includes a carrier chrominance signal amplifying circuit, a color synchronizing circuit for extracting a continuous wave of 3.58 MHz from the color bust signal, and a 3.58 MHz carrier chrominance signal from the carrier chrominance signal amplifying circuit.
A demodulation circuit for demodulating the chrominance signal with the reference subcarrier of MHz, and a matrix circuit to which the output of the demodulation circuit is supplied.
The R, G, and B signals are supplied to the color picture tube (9) via the (red), G (green), and B (blue) output circuits. ACC (Automatic Color) is used for the carrier color signal amplification circuit of the color signal reproduction circuit (8).
Control) an amplifier, a color control color amplifier, a color killer circuit, a burst amplifier, and a color density (picture) control circuit (10). This color depth control circuit (1
0) similarly carrier chrominance signal when changing the level of the luminance signal by changing the contrast of the black and white image level, ie, to control the contrast input terminal T ₂ to change the color depth at the same rate voltage and color The voltage for adjusting the density is supplied as a picture adjustment voltage to the contrast and color density control circuits (6) and (10) so that the gain of each amplifier in each control circuit is simultaneously adjusted.

In order to prevent a large anode current from flowing through the color picture tube (9) when the brightness increases, the ABL (Automatic
A Brightness Control) circuit is used, and as the ABL circuit, an average value type ABL circuit and a peak value type ABL circuit are known. These are arranged side by side in a normal color television receiver, but FIG. 8 shows a peak value type ABL circuit. If blooming occurs due to a white character or the like in a part of the image, the average value ABL does not follow the anode current below the limit value, but the peak value ABL circuit can suppress such an excessive beam. That is, the peak levels of the R, G, B primary color signals output from the color signal reproduction circuit (8) are supplied to the level control circuit (11). This level control circuit is turned “ON” at a predetermined threshold value or more, and the ABL control voltage generation circuit (1
2) The control signal is output to the ABL control voltage generation circuit (12).
Generates ABL control voltage. This ABL control voltage is supplied to a color density (picture) control circuit (10) and a contrast control circuit (6) to reduce both video signals and color signals to 3
The primary color signals R, G, B are kept below a predetermined threshold.

[Problems to be solved by the invention]

Like the conventional configuration described with reference to FIGS. 8 and 9 described above,
With clipping circuit (3) in order to reduce the blooming white characters and the like issued movies in a part of the image, and clip level C _L bright parts of above white character signal (5) is clipped, white "Bleeding" around a character, that is, blooming, is reduced. However, there is a problem that the color is different from the transmitted video signal because the bright portion is clipped.

Further, a gamma correction circuit is provided at the position where the above-mentioned clip circuit (3) is provided, and when the blooming occurs, the gamma correction circuit having the determined gamma characteristic is manually turned on to perform the gamma correction. Some are known. However, even in the case where such a gamma correction circuit is inserted, the level of a bright portion such as a white character is gently suppressed by the gamma correction as shown by a curve (13) shown by a broken line in FIG.
For example, when a flesh-colored face or the like is projected on the screen, there is a defect that the color changes due to the nose head or the like having many luminance signal components in the face and the image becomes a feeling that the nose head is crushed.

The present invention has been made in view of the above-mentioned drawbacks, and its purpose is to automatically detect blooming and control the gamma correction circuit to reduce blooming so that a color tone faithful to a transmitted image can be obtained. An image is obtained.

[Means for solving the problem]

As shown in FIG. 1 and FIG. 8, the blooming reduction circuit of the color television receiver of the present invention is supplied with both the luminance signal Y and the chrominance signal C as input signals. A luminance signal Y and a chrominance signal C in response to a control signal;
Control means for controlling the contrast and color density of the image projected on the screen of the color picture tube 9 in conjunction with each other by controlling A gamma correction means 20 provided in the signal path of the luminance signal Y for compensating for the gamma characteristic of the luminance signal Y, and capable of changing the gamma characteristic in response to the second control signal; And a control signal generating means 22 for generating a second control signal, a white level of the luminance signal Y is detected, and the white level of the detected luminance signal Y becomes a predetermined level in the color picture tube 9 to perform blooming. comprising a blooming detecting means ST ₁ for detecting whether or not to generate the gamma of the second control signal to the gamma correction circuit 20 when the level of the luminance signal Y detected by the blooming detecting means ST ₁ is equal to or higher than a predetermined level Characteristic Form so as to vary in a direction becomes smooth the input and output characteristics, and control signal generating means 22
If it is determined that the contrast and the color density of the image are not suppressed low, the first control signal is controlled so as to reduce the adjustment voltage of the contrast and color density control means 6 and 10, and the control is performed. If it is determined by the signal generation means 22 that the contrast and color density of the image have been suppressed to a low level, the first control signal is set so that the adjustment voltages of the contrast and color density control means 6 and 10 remain unchanged. This is a circuit for controlling blooming of a color television receiver characterized by being controlled.

[Action]

According to the blooming reduction circuit of the color television receiver of the present invention, even when the level of the luminance signal is likely to cause blooming, when the contrast and color density of the image are suppressed low. Does not reduce the contrast of the image or the color density. As a result, the white peak of the luminance signal is not unnecessarily suppressed and the image does not become unnatural, and an image having a color tone faithful to the transmission image can be obtained.

〔Example〕

An embodiment of a blooming reduction circuit of a color television receiver according to the present invention will be described below with reference to FIGS.

In the system diagram of FIG. 1, a television broadcast signal caught by an antenna (14) is supplied to a tuner (15), and a desired signal is selected by a tuner (16) by a tuner (15). After amplification, it is converted to a video intermediate frequency (VIF) signal,
The VIF signal is supplied to the amplifier circuit (17), and the VIF signal is amplified and further detected to obtain a composite signal. At the same time, an audio intermediate frequency (SIF) signal is created from the VIF signal, and the SIF signal is amplified and FM detected. An audio signal is emitted from a speaker (19) via an audio processing circuit (18) for obtaining and outputting an audio signal.

The output of the video receiving circuit including the VIF amplifying circuit and the video detecting circuit is supplied to a Y / C separating circuit (2) to be separated into a Y signal and a chroma signal C, and the chroma signal C is subjected to the video signal processing described in FIG. The Y signal is supplied to a circuit (1), and the Y signal is supplied to a gamma correction circuit (20) and an analog-to-digital
Supplied to 1).

The chroma signal C separated by the Y / C separation circuit (2) is supplied to a color signal reproduction circuit (8) (see FIG. 8) in the video signal processing circuit (1), and is supplied to a color density control circuit (10). ) (See FIG. 8) and the like, the Y signal supplied from the RGB output circuit to the color picture tube (9) and passed through the gamma correction circuit (20)
The signal is supplied to a color signal reproducing circuit (8) via a contrast / control circuit (6) and a pedestal clamp circuit (7) as shown. Although not shown, a high voltage is supplied to the anode of the color picture tube (9) from a high voltage generating circuit, and an ABL signal is transmitted from the high voltage generating circuit via an ABL circuit via a line (24) to a video signal processing circuit (1). Of the pedestal clamp circuit (7) (see FIG. 8) and the CPU (22).

The Y signal separated by the Y / C separation circuit (2) is A / D (2
It is converted to digital data in 1). That is, each scanning line (26) in the image (25) shown in FIG. 2 for each field or frame is finely divided into n pixels (27), sampled, and stored in the CPU (22). , Field or frame memory. (For example, one frame is sampled to about 250 pixels) Here, CPU (22)
Detects the condition under which each pixel stored in the memory blooms. For example, if an image (25) shown in FIG. 2A has a bright portion such as a white character (28) that causes blooming, as shown in FIG. 3A, for example, a video signal generated during one horizontal scanning period is generated. IR with high amplitude of white character signal (5) in (29)
E, for example, when a device having a 90-110 IRE unit (1 IRE = 1/140 V) is detected, the CPU (2
2) controls the gamma correction circuit (20). That is, control for lowering the white peak of the Y signal is performed. The gamma correction circuit (20) can be configured, for example, as shown in FIG. 4A. In FIG. 4, the input terminal T ₄
And the current source I ₁ is inserted between the T _5, the input terminal T ₄ and
With parallel connection of the resistor R ₀ between T _5, the diode and the bias source parallel to a resistor _{(D 1, E 1, R} 1) (D 2, E 2, R 2) (D 3, E 3,
R ₃ ), the output voltage V ₂ is compressed by the bias sources E ₁ , E ₂ , E ₃ ‥‥ or more of each series circuit. That is, θ ₁ = tan ⁻¹ R ₀ , θ ₂ = ta shown in FIG.
n ^-1 R ₀ / R ₁ , θ ₃ = tan ^-1 R ₀ / R ₁ / R ₂ ‥‥
A gamma correction characteristic curve (30) corresponding to the number of polygonal lines of the non-linear function based on D ₁ , D ₂ , D ₃得 is obtained. In this case, the bias voltages of the bias sources E ₁ , E ₂ , E ₃可 変 are varied based on the high IRE unit value detected by the CPU (22), for example,
The gamma correction may be controlled so as to increase the gamma correction as indicated by the gamma correction characteristic curve (31) in FIG.

That is, in this example, as shown in the flowchart of FIG.
U (22) detects the white level peak value of the first step ST ₁ the Y signal, the second step is not detected peak value
ST ₂ the gamma correction circuit (20) forms the "off" state (state of the gamma 1) When the white level peak value is detected gamma correction circuit (20) as shown in the fourth step ST ₄ "on By controlling the state, that is, to increase the gamma correction, the peak value of white characters can be reduced to, for example, about 80 IRE units as shown in the video waveform of FIG. 3B. Further as shown in the fifth step ST ₅ after the fourth step ST ₄ terminates example, CPU (22) Digital after the white level peak detection - analog converter (D / A) video signal processing circuit via (23) ( The control is performed to lower the picture adjustment voltage to the color density control circuit (10) and the contrast control circuit (6) in 1), and the process ends. Also, the second
Step ST after ₂ End CPU as shown in the third step ST ₃
In (22), control is performed to increase the picture adjustment voltage, and the process ends.

When the CPU (22) performs the control for lowering the voltage of the color density control circuit (10) and the contrast control circuit (6), if the picture adjustment voltage is sufficiently reduced,
The CPU (22) detects this and does not perform such control. The same applies when the picture adjustment voltage supplied to the contrast control circuit (6) and the color density control circuit (10) through the ABL control voltage generation circuit (12) described in FIG. 8 is sufficiently reduced. CPU (22) is this ABL
By detecting the value, it does not perform the operations shown in the fifth step ST _5.

In the present example, the configuration and operation are performed in this manner, so even when the level of the luminance signal is likely to cause blooming, if the contrast and color density of the image are kept low, the image There is no decrease in contrast or color depth. As a result, the white peak of the luminance signal is not unnecessarily suppressed, and the image does not become unnatural. Blooming can be effectively prevented, and an image having a color tone faithful to the transmission image can be obtained.

Another embodiment of the present invention will be described with reference to FIGS.

FIG. 6 shows another embodiment of the blooming reduction circuit of the color television receiver according to the present invention, in which parts corresponding to those in FIG.

In this example, the Y signal is supplied to the peak hold circuit (32), the white peak value of each line is held, the peak value is supplied to the A / D (22), and the gamma correction circuit is supplied via the CPU (23). The contrast and picture of the gamma characteristic and control control circuit (6) and the color density control circuit (10) of (20) are controlled. FIG. 7 shows the RGB output signal from the video signal processing circuit (1) as an R white peak detection circuit (33R) and a G white peak detection circuit (33G), and a B white peak detection circuit (33).
B) to detect each white peak value,
The gamma correction circuit (20) is controlled when the GB white peak value approaches the maximum driving current of the color picture tube (9), and the contrast and picture are controlled from the D / A (23). Controlled by a signal.
Even in such a configuration, the amount of correction of gamma and picture (contrast and color density) can be reduced as compared with the prior art, so that it is possible to prevent the display of an image in which a part of the skin color is stained, and to reduce the transmission signal. A faithful screen can be reproduced. It should be noted that the present invention is not limited to the above-described embodiments, but can be variously modified without departing from the gist of the present invention.

〔The invention's effect〕

According to the blooming reduction circuit of the color television receiver of the present invention, even when the level of the luminance signal is likely to cause blooming, the contrast and color density of the image are kept low. In this case, the contrast of the image does not decrease and the color density does not decrease. As a result, the white peak of the luminance signal is not unnecessarily suppressed, and the image does not become unnatural. This has the effect that blooming can be effectively reduced and an image faithful to the transmitted image can be obtained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a blooming reduction circuit of a color television receiver of the present invention, FIG. 2 is an explanatory diagram of a screen of the present invention, FIG. 3 is an explanatory diagram of a waveform of the present invention, FIG. Is an explanatory diagram of a gamma correction circuit used in the present invention, FIG. 5 is a diagram showing a flowchart of the present invention, and FIGS. 6 and 7 are other embodiments of a blooming reduction circuit of a color television receiver of the present invention. FIG. 8 is a system diagram of a blooming reduction circuit of a conventional color television receiver, and FIG. 9 is a waveform explanatory diagram of FIG. (1) is a video signal processing circuit, (2) is a Y / C separation circuit,
(3) is a clip circuit, (6) is a contrast control circuit, (10) is a color density control circuit, (20) is a gamma correction circuit, (21) is A / D, (22) is a CPU, (23) ) Is D / A, (32)
Is the peak hold circuit, (33R) (33G) (33B) is R, G, B
Is a white peak detection circuit.

Continuation of the front page (56) References JP-A-64-73887 (JP, A) JP-A-62-166690 (JP, A) JP-A-1-129673 (JP, A) JP-A-61-206375 (JP) JP-A-60-223383 (JP, A) JP-A-62-183471 (JP, U) JP-A-55-138872 (JP, U) JP-A-57-23669 (JP, U)

Claims (1)

(57) [Claims] 1. A color picture tube according to claim 1, wherein both the luminance signal and the color signal are supplied as input signals, and the luminance signal and the color signal are controlled in conjunction with each other in response to a first control signal. Contrast and color density control means for adjusting the contrast and color density of an output image in conjunction with each other, and provided in a signal path of the luminance signal to compensate for the gamma characteristic of the color picture tube. Gamma correction means capable of changing a gamma characteristic in response to a second control signal; control signal generation means for generating the first control signal and the second control signal; and the luminance signal A blooming detecting means for detecting whether or not the detected white level of the luminance signal becomes a predetermined level in the color picture tube to cause blooming; When the level of the luminance signal detected by the zooming detection means is equal to or higher than a predetermined level, the second control signal is changed so that the input / output characteristic of the gamma characteristic of the gamma correction circuit becomes gentle, If the control signal generation means determines that the contrast and color density of the image are not suppressed low, the first control is performed so as to reduce the adjustment voltage of the contrast and color density control means. Controlling the signal, and when it is determined by the control signal generating means that the contrast and color density of the image have been suppressed to a low level, the adjustment voltage of the contrast and color density control means is maintained as it is. A blooming reduction circuit for a color television receiver, wherein the first control signal is controlled.