JPH06189221A - Black level reproducing device of video - Google Patents

Abstract

PURPOSE:To make only the original video part the object of the detection of a black peak level by suppressing the level of the frame part of the right and left of a screen to be detected as the black peak level when a video having an aspect ratio of 4:3 on a wide aspect screen is displayed. CONSTITUTION:This device is provided with an aspect conversion circuit 11, a black detection circuit 2, a pedestal clamp circuit 3, a black peak hold circuit 4 capable of suppressing the detection of a black peak by a suppression signal and a black elongation circuit 5, takes out a signal where the frame is outputted from the aspect conversion circuit 1 and makes this the suppression signal of the black peak hold circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video reproducing apparatus having a video screen having a wide aspect ratio (for example, an aspect ratio of 16: 9) having a second aspect ratio which is longer than the first aspect ratio, and more particularly, The present invention relates to a video black level reproducing device in a video reproducing device which can also display software having a first aspect ratio (for example, 4: 3) with frames on the left and right sides of the screen.

[0002]

2. Description of the Related Art In high-definition broadcasting, which is expected as a next-generation television broadcasting, an experimental broadcasting from a broadcasting satellite (BS) is upgraded to a test broadcasting, and the broadcasting time is extended to 8 hours a day. This HD (High Definition TV:
HDTV is an abbreviation for the Japanese system), which has about twice the horizontal and vertical resolution of the current TV, and has a horizontal aspect ratio of 16: 9 with a screen aspect ratio (horizontal to vertical). Wave (VHF, UHF) TV Broadcast 4:
It is wider than 3.

Wide-aspect television receivers currently on the market have a genuine high-definition television that reproduces this high-definition broadcast at the original resolution and the same number of scanning lines as high-definition 1125, but a simplified MUSE decoder. Type HDTV and a horizontal screen television with 525 scanning lines, which is equipped with a MUSE-NTSC converter and has the same number of scanning lines.

Further, conventionally, a television receiver has been provided with a black level reproducing circuit in order to correct a variation in black level due to a video source to form an image with a sense of depth. As an example of a conventional black level reproducing circuit, Japanese Patent Laid-Open No. 60-04397.
There is No. 2 "Video black level reproduction circuit". In this, the amplitude of a black signal below a certain level of the video signal is variably amplified, and feedback control is performed so that the black peak matches the pedestal level.

A block diagram of this conventional example is shown in FIG.
According to the above specification, the processing of the video signal is as follows. First, the video signal is input to the black detection circuit and the pedestal clamp circuit. The black detection circuit detects the black signal of the video signal. The detected black signal is sent to the black expansion circuit whose amplitude is controlled by the gain control amplifier.

On the other hand, the pedestal clamp circuit detects the pedestal level, and controls the gain of the black expansion circuit based on the difference from the black peak level detected by the next black peak hold circuit. As a result, the black level is extended to match the black peak level with the pedestal clamp level.

[0007]

When a conventional aspect ratio 4: 3 software is projected on the above-described wide aspect television image reproducing apparatus, a no-signal frame is formed on the left and right sides of the screen. In general, this frame has a lower brightness level to make the screen easier to see. This state is shown in FIG. In the conventional black level reproduction circuit, since the level of this frame is detected as a black peak, the level of the frame is held at the black peak, and there is a problem that the original black expansion of the video signal cannot be performed. .

In view of the above problems, an object of the present invention is to provide a wide aspect video reproducing apparatus, when displaying conventional software having an aspect ratio of 4: 3, the level of a non-signal portion corresponding to the left and right frames of the screen is An object of the present invention is to provide a video reproducing apparatus capable of preventing the black peak from being erroneously held as the black level, holding the black peak from the original black level of the video signal portion, and correctly expanding the black to correct the black level.

[0009]

In a video reproducing apparatus having a wide aspect screen having a second aspect ratio which is horizontally longer than the first aspect ratio, when displaying video software having the first aspect ratio, it is displayed on the left and right sides of the screen. Display a frame, and
An aspect conversion circuit that converts a video signal of the software so that the software is displayed in the video section in the first aspect as it is, a circuit that detects black of a brightness level, and a gain control of a black part of the detected brightness are provided. Black stretch circuit to do,
A pedestal clamp circuit that determines and holds the pedestal level, and detects and holds the black level peak of luminance,
A black peak hold circuit capable of suppressing black peak detection while a suppression signal is present is provided, and when a frame is displayed on the left and right of the screen, a signal indicating that the frame is being output from the aspect conversion circuit is extracted, By using the signal as a masking signal for the black peak hold circuit, the above problem is solved by operating the black peak hold circuit only in the video section.

[0010]

When the software having the aspect ratio of 4: 3 is projected, the signal indicating that the frame is being output is taken out from the aspect conversion circuit, and the black peak hold circuit is not operated while this signal is being output. To As a result, the black peak hold circuit holds the black peak only for the original video signal part, and the black level can be properly expanded to reproduce the black level so that the black peak level matches the pedestal level. Can be done correctly.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of a black level reproducing circuit according to the embodiment. The aspect conversion circuit 1 aspect-converts the input video signal. The aspect-converted video signal is input to the black detection circuit 2 and the pedestal clamp circuit 3. The black detection circuit 2 detects a black level equal to or lower than a certain threshold and sends it to the black expansion circuit 5. The pedestal clamp circuit 3 clamps the pedestal level of the aspect-converted video signal to the pedestal clamp potential and outputs it.

The black peak hold circuit 4 receives the signal from the pedestal clamp circuit 3 and the frame signal from the aspect conversion circuit 1, and outputs the black peak level from the pedestal clamped signal only while there is no frame signal. To detect.
The black decompression circuit 5 performs black decompression on the signal of the amplitude range in which black is detected, based on the amplifier gain given from the black peak hold circuit 4. The black-expanded video signal is sent to the cathode ray tube through the transmission rate correction circuit 6. FIG. 2 is a waveform diagram of a video signal showing the operation of the embodiment.

Next, the operation of the embodiment will be described in detail with reference to FIGS. An image signal obtained by tuning, amplifying, and detecting a television signal in an RF unit IF unit (not shown) is input to the aspect conversion circuit 1. The waveform of this input signal is schematically shown in FIG. In FIG. 2, one horizontal period is indicated by H, and the horizontal synchronizing signal is indicated by a negative pulse.

When displaying software of a conventional aspect ratio of 4: 3 (= 12: 9) on a screen of a television receiver having a wide aspect (16: 9) CRT to which the present invention is applied, the screen is displayed. The vertical length of the software should be displayed together with the vertical length of the software. At this time, there are 4 (= 16−12) video signal-free portions with respect to a horizontal screen length of 16. In order to make the screen easy to see, the part without the video signal is equally divided into left and right and displayed as two frames.

For this screen display, the aspect conversion circuit 1 makes the video signal portion within one horizontal period approximately 3/4.
It is output after time compression (aspect conversion). This compressed signal is shown in FIG. In addition, the part of the frame is slightly higher than the pedestal level in order to avoid "burn" of the CRT.

The aspect-converted video signal is input to the black detection circuit 2 and the pedestal clamp circuit 3. The black detection circuit 2 detects a black level below a certain threshold. A signal whose amplitude level is higher than this threshold value, that is, a bright signal does not change in the next black expansion circuit 5. A signal whose amplitude level is lower than this threshold, that is, a dark signal is a processing target of the black expansion circuit 5. A blanking pulse (not shown) is applied to the black detection circuit 2 so that the detected black signal does not include a synchronization signal.

In the pedestal clamp circuit 3, the pedestal level is clamped to the reference clamp potential during a clamp pulse section (not shown). This pedestal clamped video signal is input to the next black peak hold circuit 4. Further, from the aspect conversion circuit 1, a frame signal (c) indicating that the frame portion of the video signal is output is
It is output to the black peak hold circuit 4.

The black peak hold circuit 4 detects the black peak level from the pedestal clamped video signal only while the frame signal (c) does not indicate the frame. Next, the black peak hold circuit 4 outputs an amplifier gain for black expansion based on the difference between the pedestal clamp level of the pedestal clamped video signal and the detected black peak level.

Next, the black expansion circuit 5 expands the amplitude of the black signal portion below the threshold value of the black detected video signal by the amplifier gain output from the black peak hold circuit 4. In this way, an image signal whose black peak level matches the pedestal level is obtained, and becomes a luminance signal of a cathode ray tube (not shown) through the next transmission rate correction circuit 6.

In the above-mentioned embodiment, the case where the image of the screen of 4: 3 and 16: 9 as the first and second aspect ratios is processed is shown, but the scope of the present invention is not limited to this.
The point is that the second aspect ratio is longer than the first aspect ratio, and it is applicable to all devices that reproduce the video signal of the first aspect ratio on the horizontally long screen of the second aspect ratio. .

[0021]

As described above, according to the present invention, when the video signal is in the frame portion, the operation of the black peak hold circuit is suppressed to correctly detect the original black peak level of the video portion, There is an effect that proper black expansion can be performed, fluctuation of the brightness level can be prevented, and an image with a sense of depth can be reproduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the present invention.

[Fig. 3] Wide aspect ratio screen has an aspect ratio of 4: 3
FIG. 7 is an explanatory diagram of a video signal when displaying the video of FIG.

FIG. 4 is a block diagram showing an example of a conventional technique.

[Explanation of symbols]

 1 Aspect conversion circuit 2 Black detection circuit 3 Pedestal clamp circuit 4 Black peak hold circuit 5 Black expansion circuit 6 Transmission rate correction circuit 8 Conventional black peak hold circuit

Claims (1)

[Claims] 1. A video reproducing apparatus having a wide aspect screen having a second aspect ratio which is horizontally longer than the screen having the first aspect ratio, and when displaying video software having the first aspect ratio, a frame is provided on the left and right sides of the screen. An aspect conversion circuit for displaying the software and for converting the video signal of the software so as to display the software in the video section at the first aspect ratio, a circuit for detecting black of the brightness level, and a circuit for detecting the brightness of the detected brightness. A black expansion circuit that controls the gain of the black part, a pedestal clamp circuit that determines and holds the pedestal level, and a black level peak of luminance that is detected and held, and a black signal that can suppress black peak detection while there is a suppression signal. A peak hold circuit is provided, and when a frame is displayed on the left and right of the screen, the signal indicating that the frame is being output from the aspect conversion circuit is extracted. Then, by using this signal as a suppression signal for the black peak hold circuit,
An image black level reproducing device characterized in that a black peak hold circuit is operated only in an image part.