JPH06225240A - Wide aspect television receiver - Google Patents

Abstract

PURPOSE:To prevent picture quality from changing even if the display size of a picture is switched in a wide aspect television receiver. CONSTITUTION:An aspect conversion circuit converting the aspect ratio of a video signal into a desired value based on a control signal from an aspect conversion control circuit 3 is provided. A DC transmission rate gain correction circuit 9 controlling the correction gain of a DC transmission rate by the control signal derived from the aspect conversion control circuit 3 in accordance with the fluctuation of an average video level based on the conversion of the aspect ratio is provided. The fluctuation of the correction amount of the DC transmission rate by the fluctuation of the average video level on account of the switching of the display size of the picture is compensated, and the correction amount of the DC transmission rate is held constant in spite of the fluctuation of the average video level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide aspect television receiver capable of displaying images of various aspect ratios, and in particular, a constant DC transmission rate can be obtained regardless of the image display size. The present invention relates to a wide aspect television receiver.

[0002]

2. Description of the Related Art Conventionally, in a television receiver, direct-current component reproduction is performed in which the pedestal level of a video signal is fixed to a predetermined direct-current voltage value.
There is the following problem if the above-mentioned direct current component regeneration is performed regardless of the "L").

The television receiver is provided with an automatic beam limiting (hereinafter referred to as "ABL") circuit, which narrows the electron beam amount of the cathode ray tube when the APL is high. This is done by narrowing the brightness. If you reduce the brightness, the level of the black part will also be suppressed, and the black part will be crushed and the image will be difficult to see. That is, when there is a black portion on the screen where the whole is bright, the black portion becomes blacker and becomes sticky black, and in the case of hair etc., each one becomes unclear.

In order to solve such a problem, Japanese Patent Laid-Open No. Sho 60
A DC signal transmission rate correction circuit for video signals as disclosed in Japanese Patent No. 48675 is known. This circuit controls the clamp portion of the pedestal level of the video signal by the APL and superimposes a negative pulse having a large peak value as the APL is higher, and lowers the clamp portion by the peak value of the negative pulse. When performing direct current component regeneration,
The pedestal level and the video signal portion are increased by the peak value of the negative pulse, and the black portion is also lifted. Therefore, even if the black level is lowered due to the high APL by the ABL circuit, the black portion is compensated by the amount of lift by the negative pulse, and the black portion of the screen is not crushed.

FIG. 5 is a block diagram of a main part when the above DC transmission rate correction circuit is used in a wide aspect television receiver. In FIG. 5, the video signal separated into the luminance signal Y and the color signal C is subjected to synchronous slicing and chroma demodulation in the video / chroma processing circuit 1 to become the luminance signal Y and the color difference signals RY and BY, and the aspect conversion is performed. It is input to the circuit 2. The aspect conversion circuit 2 performs time axis conversion processing according to the aspect ratio to be converted according to the command of the aspect conversion control circuit 3 and outputs it.

The luminance signal Y output from the aspect conversion circuit 2 is guided to the DC transmission rate correction circuit 4, and the DC transmission rate correction circuit 4 superimposes the transmission rate correction signal on the pedestal portion. That is, the DC transmission rate correction circuit 4 averages the input video signal by the time constant circuit 5 including the capacitor C and the resistor R, and outputs a wave proportional to the averaged video signal level (average video level: APL). A negative pulse with a high value is superimposed on the pedestal part.

Then, the luminance signal Y in which the transmission rate correction signal corresponding to the APL is superimposed on the pedestal portion is input to the matrix circuit 7 in the next stage. On the other hand, the color difference signals RY and BY from the aspect conversion circuit 2 are input to the matrix circuit 7 via the color / tint adjustment circuit 6. In the matrix circuit 7, the luminance signal Y and the color difference signals RY, B-
Y is calculated and converted into R, G, and B signals of primary colors. The R, G, and B signals of the primary colors are guided to the contrast / brightness adjustment circuit 8 and the contrast and brightness are adjusted.

On the other hand, in the contrast / bright adjustment circuit 8, the above-mentioned ABL circuit adjusts so that the black level is lowered according to the APL when the APL is high. Since the transmission rate correction signal is superimposed in advance by the correction circuit 4, it is compensated for the decrease in the black level due to the ABL circuit.

Then, the contrast / brightness adjustment circuit 8 adjusts the contrast and brightness, and the R, G, and B signals of the primary colors whose lowering of the black level by the ABL circuit is compensated by the transmission rate correction signal are driven by a cathode ray tube. A CRT is driven by a circuit (not shown).
An image without blackout by the BL circuit is displayed.

[0010]

By the way, when displaying a current television signal having an aspect ratio of 4: 3, a wide aspect television receiver may perform display in various display modes. FIG. 2 shows an example of various display modes. FIG. 2A shows a mode in which all video signals with an aspect ratio of 4: 3 are displayed on a cathode ray tube with an aspect ratio of 16: 9. It is called "full mode". The full mode is a mode suitable for reproducing a "full mode signal or squeeze signal" in which a video signal having an aspect ratio of 16: 9 is time-axis compressed to an aspect ratio of 4: 3. Since FIG. 2A shows a case where the current television signal is reproduced, the image becomes a horizontally long image and the roundness is 1.33.

FIG. 2B shows a mode in which the current television signal is subjected to time-axis compression processing so that it is displayed on a CRT having an aspect ratio of 16: 9 with an aspect ratio of 4: 3. Here is the "normal mode"
I call it. In this normal mode, portions other than the area displayed with the aspect ratio of 4: 3 are replaced with specific signals such as those corresponding to the pedestal level, so that black frames are displayed on both sides of the image. The roundness at this time is 1.

In FIG. 2C, the upper and lower parts of a video signal having an aspect ratio of 4: 3 are cut by 30%, respectively, and the aspect ratio is 1
It is a mode displayed on the whole surface of a 6: 9 CRT.
This mode is referred to herein as the 16: 9 mode. In this case, the roundness is 1.

In a wide aspect television receiver, the time axis is converted by the aspect conversion circuit according to the aspect ratio of the input video signal and the display mode to be displayed. Specifically, the video signal is stored in the memory by the write clock, and the time axis is expanded / compressed by changing the rate of the read clock.

The writing / reading clock rate is 1: 1 in the full mode, but the writing / reading clock rate is 1: 1.33 in the normal mode. Therefore, the time axis in the normal mode is about 75. Compressed to%. Then, outside the video period, it is replaced with a specific signal corresponding to the pedestal level. The video signal at this time is viewed in a horizontal cycle as shown in FIG. FIG. 3C shows a case where the pedestal level outside the video period is replaced in the normal mode.
APL will be 75%.

Now, when a video signal of APL 100% (all white signal) is input as a receiver input in the DC transmission rate correction circuit, the DC transmission rate correction is performed because the time axis is the same as the input when the display size is set to full mode. The signal input to the circuit has an APL of 100%, but when the normal mode is selected, the APL becomes 75% due to the effect of aspect conversion.

As described above, the DC transmission rate correction circuit has the AP
Since the pulse corresponding to L is superimposed on the clamp part, the correction amount of the transmission rate varies depending on the display size of the image, even though the input signal to the television receiver is the same. FIG. 6 shows the characteristics of the input signal APL versus the transmission rate correction amount in the full mode and the normal mode. As described above, since the correction amount of the DC transmission rate changes depending on the display mode, there is a problem that stable DC transmission rate correction cannot be performed if the APL changes.

If the DC transmission rate correction circuit is inserted before the aspect conversion circuit, there is no aspect ratio conversion, so there is no change in APL due to the aspect ratio conversion, and correction of the DC transmission rate due to such APL change. The problem of changing the quantity disappears. However, since the aspect conversion circuit is processed by a digital signal, it is more advantageous for quantization noise to use the dynamic range as much as possible while keeping the input signal level constant. Therefore, in general, the DC transmission rate correction circuit is often arranged behind the aspect conversion circuit as shown in the drawing.

[0018]

In order to solve the above problems, the present invention solves the above problems by an aspect conversion circuit for switching the display size of an image, an aspect conversion control circuit for controlling the aspect conversion circuit, and an average video level of a video signal. In a wide aspect television receiver provided with a DC transmission rate correction circuit for correcting the DC transmission rate of the video signal according to
A DC transmission rate gain correction circuit for varying the gain of the DC transmission rate correction circuit according to a control signal for switching the display size of an image from the aspect conversion control circuit to make the DC transmission rate constant regardless of the display size of the image. Is provided.

In addition, the aspect conversion circuit, the aspect conversion control circuit, the average video level of the video signal and the pedestal level are compared, and a DC pulse having an amplitude corresponding to the comparison result is superimposed on the clamp portion of the pedestal level. In a wide aspect television receiver provided with a transmission rate correction circuit and a time constant circuit for determining a correction gain of the DC transmission rate correction circuit, in response to a control signal for switching the image display size from the aspect conversion control circuit. The time constant of the time constant circuit is varied, and a DC transmission rate gain correction circuit is provided which changes the correction gain so as to suppress the variation of the DC transmission rate due to the switching of the image display size.

[0020]

According to the above construction, when the control signal for converting the aspect ratio of the image is given from the aspect conversion control circuit to the aspect conversion circuit, the aspect conversion circuit changes the aspect ratio of the video signal according to the control signal. Convert to the desired value. Then, the video signal whose aspect ratio has been converted to a desired value is supplied to the DC transmission rate correction circuit, where the amplitude and the time constant circuit are used according to the comparison result between the average video level of the video signal and the pedestal level. A DC transmission rate correction pulse having an amplitude corresponding to the correction gain determined by a constant is superimposed on the clamp portion of the video signal to correct the DC transmission rate according to the average video level.

On the other hand, at the same time, a control signal corresponding to the display size of the image is supplied from the aspect conversion control circuit to the DC transmission rate gain correction circuit to change the time constant of the time constant circuit according to the display size of the image. Change the correction gain of DC transmission rate. As a result, the change of the correction pulse of the DC transmission rate correction circuit due to the change of the APL due to the change of the display size of the image is compensated by changing the above correction gain, and the change of the APL due to the change of the display size of the image is corrected. Regardless, the correction amount of the DC transmission rate should be kept constant.

That is, when the display mode is, for example, the full mode, the APL does not change between the input and output signals of the aspect conversion circuit, so the DC transmission rate gain correction circuit does not operate, and the predetermined time constant of the time constant circuit is used. A DC transmission rate correction pulse having an amplitude according to the determined correction gain is superimposed. However, when the display mode becomes, for example, the normal mode, the APL of the output signal is 75% with respect to the input signal of the aspect conversion circuit.
Go down to. Therefore, in this case, the DC transmission rate gain correction circuit operates, the time constant of the time constant circuit is reduced to increase the correction gain, and the drop in the peak value due to the decrease in the APL of the DC transmission rate correction pulse is compensated for. Make sure that the DC transmission rate correction amount does not change.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of an embodiment of the present invention. Parts corresponding to those of the conventional example shown in FIG. In FIG. 1, reference numeral 9 indicated by a dotted frame is a DC transmission rate gain correction circuit which forms an essential part of the present invention. The DC transmission rate gain correction circuit 9 is a time constant circuit for determining the correction gain of the DC transmission rate correction circuit 4. A resistor R ₂ provided in parallel with the resistor R _{1 of} 5 and a DC circuit of a transistor Q ₁ , an output terminal A of an aspect conversion control circuit 3 for deriving a control signal according to an image display size, and control of the transistor Q ₁ . It consists of a resistor R ₃ provided between the terminals. Each block shown by 1 to 8 has basically the same configuration as the corresponding block of the conventional example shown in FIG.

In the present embodiment, the correction amount of the direct current transmission rate is adapted to be determined by the time constant determined by the resistance R ₂ of the capacitor C and a resistor R ₁ and a DC transmission rate gain correcting circuit 9 of the time constant circuit 5 The correction amount increases with a decrease in the time constant, that is, when the resistance value decreases, the correction gain increases.

Now, when a video signal having an aspect ratio of 4: 3 is input, if the image display mode is set to the full mode as shown in FIG. 2A by the aspect conversion control circuit 3, the aspect conversion is performed. The circuit 2 converts the aspect ratio of the input video signal having an aspect ratio of 4: 3 into 16: 9, while the output terminal A of the aspect conversion control circuit 3
A control signal is further derived according to the display size of the image. In the case of this full mode, the APL of the output signal with respect to the input signal of the aspect conversion circuit 2 is 100%.
Does not cause a change in the correction amount in the DC transmission rate correction circuit 4, so that the control signal becomes "L" level. The "L" level control signal is applied to the transistor Q ₁
Is supplied to the control terminal to turn off the transistor Q _{1 so} that the resistor R ₂ does not affect the time constant of the time constant circuit 5. Therefore, the correction amount of the DC transmission rate in this case is determined by the correction gain determined by the capacitor C and the resistance R ₁ of the time constant circuit 5, and is superimposed on the clamp portion of the video signal by the DC transmission rate correction circuit 4.

Next, when the display mode is set to the normal mode shown in FIG. 2B by the aspect conversion control circuit 3, a command is given to the aspect conversion circuit 2 to compress the time axis of the video signal and the aspect conversion control circuit. A control signal corresponding to the display size of the image is derived from the output terminal A of No. 3. In the normal mode, this control signal has an APL of 7 as an output signal with respect to an input signal of the aspect conversion circuit 2.
Because of 5% becomes the "H" level signal, connected in parallel to resistor R ₂ of the DC transmission rate gain correcting circuit 9 to the transistors Q ₁ in the ON state to the resistance R ₁ of the time constant circuit 5. As a result, the resistance of the time constant circuit 5 decreases, the time constant decreases, the correction gain increases, and the DC transmission rate correction circuit 4 increases.
By compensating for the decrease in the amplitude of the correction pulse caused by the decrease of APL to 75%, the correction pulse whose correction amount is kept constant is superimposed on the clamp portion of the video signal, and the DC transmission rate equivalent to that in the full mode is obtained. Correction is performed.

FIG. 4 is a graph showing the change in the DC transmission rate correction amount depending on the presence or absence of the DC transmission rate gain correction circuit 9 in the normal mode. Comparing with the graph showing the change in the DC transmission rate correction amount in the full mode and the normal mode in the conventional example shown in FIG.
It can be seen that the correction amount of the DC transmission rate equivalent to that in the case of the full mode can be obtained even if is decreased.

Although the above embodiment shows the case of the normal mode as opposed to the full mode, a plurality of DC transmission rate gain correction circuits 9 are provided in order to perform control according to various screen display sizes, and depending on the mode. If the correction gain is set by setting the correction gain, the DC transmission rate in each mode can be kept constant. Further, in the above-described embodiment, the correction gain is varied so that the DC transmission rate is constant regardless of the screen display size, but it is also possible to set the DC transmission rate suitable for the screen display size. is there.

[0029]

As described above, the present invention has the above-described structure. Therefore, in a wide aspect television receiver, even if the display size of an image is variously changed, the DC transmission rate can be changed by changing the correction gain of the DC transmission rate according to the display size. Can be kept constant, and the change in image quality due to the switching of the image display size can be suppressed.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining a display mode of a wide aspect television receiver.

FIG. 3 is an input / output signal waveform diagram of the aspect conversion circuit.

FIG. 4 is an operation explanatory diagram of the present invention.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is an operation explanatory view of a conventional example.

[Explanation of symbols]

 2 Aspect conversion circuit 3 Aspect conversion control circuit 4 DC transmission rate correction circuit 5 Time constant circuit 9 DC transmission rate gain correction circuit

Claims (2)

[Claims] 1. An aspect conversion circuit for switching a display size of an image, an aspect conversion control circuit for controlling the aspect conversion circuit, and a DC transmission rate for correcting the DC transmission rate of the video signal according to an average video level of the video signal. In a wide aspect television receiver provided with a correction circuit, the gain of the DC transmission rate correction circuit is varied according to a control signal for switching the image display size from the aspect conversion control circuit, regardless of the image display size. A wide aspect television receiver characterized by being provided with a DC transmission rate gain correction circuit for making the DC transmission rate constant. 2. An aspect conversion circuit for switching a display size of an image, an aspect conversion control circuit for controlling the aspect conversion circuit, an average video level of a video signal and a pedestal level are compared, and an amplitude according to the comparison result is compared. In a wide aspect television receiver provided with a DC transmission rate correction circuit that superimposes a pulse on a pedestal level clamp portion, and a time constant circuit that determines a correction gain of the DC transmission rate correction circuit, from the aspect conversion control circuit A DC transmission rate gain correction circuit that changes the time constant of the time constant circuit according to a control signal for switching the display size of the image and changes the correction gain so as to suppress the fluctuation of the DC transmission rate due to the switching of the display size of the image. Wide aspect television receiver characterized by the provision of.