JPH07322093A - Picture display device - Google Patents

Abstract

PURPOSE:To prevent the tone collapse especially on the low luminance side of a bright screen. CONSTITUTION:The luminance signal inputted to an input terminal 2 is inputted to a black level correction circuit 4. The output of the circuit 4 is inputted to an amplifier 5. The output and the clamp pulse inputted to the input terminal are inputted to a synchronizing signal eliminating circuit 7 and an adder 12. The output of the circuit 7 is inputted to a luminance detection circuit 9 and the output is inputted to a correction signal preparing circuit 10. A bias circuit 8 supplies the reference voltage to a clamp circuit 6, the circuit 7 and the circuit 9. The output voltage of the ABL inputted to the input terminal 3 is inputted to a correction signal control circuit 11. The output is inputted to the circuit 10. The output of the circuit 10 is inputted to the adder 12. It is outputted from the adder 12 to the output terminal 13. Thus, the tone collapse in the bright screen is eliminated and the inputted luminance signal is outputted as it is in the dark screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation correction circuit for controlling gradation of an image display device to prevent gradation of a displayed image, especially gradation collapse on a low luminance side.

[0002]

2. Description of the Related Art Generally, in an image display device, a luminance signal has a level higher than a level (hereinafter, referred to as a pedestal level) in which a black portion in the display period other than the blanking period indicates the blackest. (Hereinafter, this state is referred to as a state in which black is floating) is supplied. The difference between the level of the black portion and the pedestal level within this display period is called setup. This setup differs depending on the broadcasting station or signal source, and when the setup is large, the black portion of the displayed image will appear to float.

In order to reduce such a black floating phenomenon,
For example, as disclosed in Japanese Patent Laid-Open No. 1-265788, a black level correction circuit is used. As shown in FIG. 15A, this black level correction circuit detects the black peak portion when a luminance signal having a black peak is input during the display period, and the black peak level becomes the pedestal level. 15B, the luminance signal is level-shifted in the pedestal level direction to obtain a luminance signal having a waveform as shown in FIG.
The luminance signal has a waveform as shown in.

As described above, the black level correction circuit reduces the black floating phenomenon by correcting the black peak level during the display period of the luminance signal to the pedestal level. Therefore, the input / output characteristics of the black level correction circuit are as shown in FIG.

[0005]

However, in an image display device having an optical system including a projection lens such as a projection television receiver, for example, a bright portion of an image displayed on the display surface of the projection tube is used. Light is reflected and scattered by the optical system, and may become so-called stray light, which may leak into all parts of the image. In such cases,
When the black floating phenomenon of the display image is suppressed as in the above-described conventional technique, the brightness is originally high in the bright part of the display image, so that it is not affected by stray light so much, but in the low brightness part, the gradation is masked by stray light. And the gradation on the low-luminance side appears to have collapsed. For example,
When considering a screen displaying black, there arises a problem that it is not possible to display a screen in which each hair can be identified.

Further, the conventional black level correction circuit described above has a problem that it operates only when the area of the display image on the low luminance side is small.

An object of the present invention is to solve this problem, and not only in an optical television receiver but also in an image displayed on the screen of various image display devices, gradation collapse on a bright display screen, particularly, An object of the present invention is to provide an image display device capable of preventing gradation deterioration on the low luminance side and enhancing the gradation.

[0008]

In order to achieve the above object, the image display device of the present invention detects a signal having a level lower than an arbitrary level of an input luminance signal, and further, the arbitrary value of the input luminance signal is determined. Is provided with a gradation correction circuit that detects a signal of a level equal to or lower than the level of 1 and outputs a gradation correction signal based on the difference between the two signals.

Specifically, a signal (signal 1) below the arbitrary level of the input luminance signal is detected, and a signal (signal 2) below the arbitrary level of the input luminance signal is detected. It is detected and amplified or compressed so that the two signals have the same amplitude (signal 1A and signal 2).
A). A gradation correction circuit that outputs a gradation correction signal by subtracting the signal 2A from the signal 1A and amplifying the signal 2A is provided.

Further, when the present invention is applied to an image display device having an automatic brightness limiting circuit (hereinafter referred to as ABL), the output signal of the correction signal generating circuit is output as it is when a bright display screen is displayed, and the gray scale is output. In order to perform the correction and to suppress the gradation correction in the dark display screen, the ABL
It is possible to provide the gradation correction circuit with a correction signal control circuit for controlling the gradation correction of the luminance signal according to the output signal of.

On the other hand, when the present invention is applied to an image display device not equipped with an ABL, an automatic brightness detection circuit (hereinafter referred to as an APL detection circuit) for detecting the average brightness of the brightness signal output from the clamp circuit and an APL. The gradation correction circuit can be replaced by providing a correction signal control circuit for controlling the gradation correction of the luminance signal according to the output signal of the detection circuit.

Furthermore, when the gradation correction circuit is provided in an image display device having a black level correction circuit, a luminance signal is input to the black level correction circuit and then to the clamp circuit. Configure

[0013]

Since the image display device of the present invention is provided with the first brightness detection circuit and the second brightness detection circuit, it is possible to enhance the gradation of the brightness signal, especially the gradation on the low brightness side. It is possible to display a high-definition image.

Further, when a limiting circuit for limiting the gradation correction of the luminance signal according to the output signal of the ABL or APL detection circuit is provided, when the display screen is a bright screen, for example, when the influence of stray light is great. When the display screen becomes bright as shown in, the brightness signal gradation correction is performed.When the display screen is dark, that is, when stray light is small and blackout is less likely to occur, brightness signal gradation correction is performed. It becomes possible to suppress.

Further, when the gradation correction circuit is provided in the image display device having the black level correction circuit, it is possible to correct the gradation of the luminance signal and reduce the black floating phenomenon. .

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first image display device according to the present invention.
FIG. 3 is a block diagram showing a gradation correction circuit provided in an image display device having an ABL and black level correction circuit according to the embodiment of FIG. 1 is an input terminal for a clamp pulse, 2 is an input terminal for inputting a luminance signal, 3 is an input terminal for inputting an output signal of ABL, 4 is a black level correction circuit, 5 is an amplifier circuit, 6 is a clamp circuit, 7 Is a sync signal removal circuit, 8 is a bias circuit, 9 is a luminance detection circuit, 10 is a correction signal creation circuit, 11 is a correction signal control circuit, 12 is an addition circuit, and 13 is an output terminal. The operation will be described below.

The black level correction circuit 4 lowers the black peak of the luminance signal input to the input terminal 2 to the pedestal level, and then inputs it to the amplification circuit 5. The amplifier circuit 5 amplifies the brightness signal after black level correction and inputs it to the clamp circuit 6. FIG. 2 shows a configuration example of the clamp circuit 6, the synchronization signal removal circuit 7, the brightness detection circuit 9, and the bias circuit 8, and their operations will be described.

In FIG. 2, reference numeral 61 is an input terminal to which the luminance signal output from the amplifier circuit 5 is input, 62 is an input terminal of a clamp pulse, 63 is a capacitor, and 64, 65 and 6 are shown.
8, 71, 72, 74, 92, 93, 95 and 96 are transistors, 66, 67, 73, 75, 81, 82, 8
3, 84, 91, 97 and 98 are resistors, and 14 is a voltage source.

The bias circuit 8 includes resistors 81, 82 and 83.
And 84, and supplies a voltage (hereinafter abbreviated as V1) at the connection point between the resistors 83 and 84 to the clamp circuit 6 and the synchronization signal removing circuit 7, and the resistor 8
2 and the voltage at the connection point of the resistor 83 (hereinafter abbreviated as V2).
And the voltage at the connection point between the resistors 81 and 82 (hereinafter, V3
Abbreviated. ) And are supplied to the luminance detection circuit 9.

The clamp circuit 6 is composed of a capacitor 63, transistors 64, 65 and 68, and resistors 66 and 67. The luminance signal input to the input terminal 61 is clamped by the capacitor 63, the transistors 64 and 65, and the resistor 66. However, it is output through a buffer including a resistor 67 and a transistor 68. The operation will be described in detail below.

The luminance signal input to the input terminal 61 appears in the collector of the transistor 64 after the direct current component is removed by the capacitor 63. On the other hand, the transistor 6
Since 5 has the base set to V1, the emitter voltage is a voltage reduced by the base-emitter voltage (hereinafter, abbreviated as V _BE ) of the transistor.

The transistors 64 and 65 are
Since the emitters are connected to each other, the transistor 64
When a clamp pulse is input to the base of, the clamp pulse is in the conductive state only during the period (Hi), and the collector voltage becomes substantially equal to the emitter voltage. Therefore, the pedestal level of the input luminance signal can be fixed to V1- _VBE . Then, the transistor 68 and the resistor 6
It outputs to the synchronizing signal removing circuit 7 and the adding circuit 12 through the buffer constituted by 7.

Since the transistor 68 is a PNP type transistor, the emitter voltage is higher than the base voltage by V _{BE of the} transistor 68.
Therefore, V _{BE of} transistor 68 and transistor 64,
Considering that the V _{BE of} 65 is almost equal, the transistor 68
When a luminance signal whose pedestal level is fixed to V1−V _BE is input to the base of, the pedestal level of the luminance signal output to the emitter of the transistor 68 becomes V1 because it is higher than the base by V _BE .

From the above, the clamp circuit 6 can fix the pedestal level to the constant value V1 without being affected by the change in V _BE due to the temperature change.

The sync signal removing circuit 7 includes a transistor 7
1, 72 and 74 and resistors 73 and 75, the sync signal portion below the pedestal level of the luminance signal clamped by the clip circuit composed of the transistors 71 and 72 and the resistor 73 is deleted, and the transistor 74 and the resistor 75 are used. Output through the buffer. The waveform of each part of the circuit is shown in FIG. 3 and the operation will be described in detail with reference to them.

First, the base of the transistor 72 is fixed to V1 by the bias circuit 8, and the emitter of the transistor 72 is commonly connected to the emitter of the transistor 71. The emitters of the transistor 71 and the transistor 72 are set to V1-V _BE or less. It is set so that the transistor 72 becomes active when it becomes.

As a result, the input terminal 61 shown in FIG.
When the ramp waveform shown in is input, it is input to the base of the transistor 71 after fixing the pedestal level to V1 by the clamp circuit 6. Since the emitter voltage of the transistor 71 drops by V _{BE of} the transistor 71, the pedestal level of the ramp waveform becomes V1−V _BE . Therefore, the transistor 72 becomes active in the synchronizing signal portion below the pedestal level of the ramp waveform, and that portion is fixed to V1-V _BE . Therefore, the transistor 7
1 and the common emitter of the transistor 72 have a waveform obtained by removing the synchronizing signal portion.

Then, the signal is output through a buffer composed of the transistor 74 and the resistor 75. The transistor 74 is
Since it is a PNP type transistor, the emitter voltage is V _BE higher than the base voltage. Therefore, the pedestal level of the ramp waveform from which the sync signal portion is removed becomes V1 and is not affected by the change in V _BE due to the temperature change. The emitter waveform of the transistor 74 is shown in FIG.

Next, the brightness detecting circuit 9 includes a first brightness detecting circuit including a resistor 91 and transistors 92 and 93, and a second brightness detecting circuit including a resistor 97, a resistor 98, and transistors 95 and 96.
It is composed of a brightness detection circuit. In addition, the transistor 93
The base voltage of the transistor 93 is connected to the connection point of the resistors 82 and 83, and the base of the transistor 96 is connected to the connection point of the resistors 81 and 82.
2. The base voltage of the transistor 96 is set to V3. Hereinafter, the operation will be described in detail with reference to FIG.

To the base of the transistor 92 of the first luminance detection circuit, the ramp waveform from which the sync signal portion has been removed by the sync signal removal circuit 7 is input. On the other hand, the transistor 93 fixes the base voltage to V2 by the bias circuit 8, and the emitter of the transistor 93 is commonly connected to the emitter of the transistor 92. Therefore, the ramp waveform output from the synchronization signal removal circuit 7 is V2 + V _BE. Clip with. Therefore, the output terminal 94 outputs a waveform in which the pedestal level is V1 + V _BE and the upper limit is V2 + V _BE as shown in FIG. 3C.

In the second luminance detection circuit, the ramp waveform from which the above-mentioned sync signal portion has been removed is input to the base of the transistor 95. Since the base of the transistor 96 is fixed to V3, the pedestal level shown in FIG. 3D is V1 + V _BE and the upper limit is V3 (> V2) + in the common emitter of the transistor 95 and the transistor 96.
The waveform clipped by V _BE is output. Also, the resistance 9
7 and the resistor 98 are set such that the amplitude of the waveform output to the connection point of the resistors 97 and 98 is equal to the amplitude of the output waveform of the first luminance detection circuit. As shown in FIG. 3E, a waveform having a different clipping voltage from that of the first luminance detection circuit but having the same amplitude is output.

Next, the operation of the correction signal generating circuit 10, the correction signal control circuit 11, and the adding circuit 12 will be described with reference to FIG. 3 is an input terminal to which the output voltage of the ABL is input, 15 is an input terminal to which a luminance signal whose pedestal level is fixed to V1 by the clamp circuit 6 is input, 101, 114 and 116 are capacitors, 102,
103, 104, 107, 108, 109, 111, 1
13, 117, 118, 1011, 121, 123 and 125 are resistors, 105, 106, 1010, 124, 1
Reference numerals 12 and 115 are transistors, and the portions corresponding to those in FIG.

Generally, the output voltage of the ABL is low when the screen is bright and is high when the screen is dark.

Capacitor 101 and resistors 102, 103,
The correction signal generating circuit 10 is composed of the transistors 104, 107, 108, 109 and 1011 and the transistors 105, 106 and 1010. Output terminal 9 from the first luminance detection circuit
The signal output to 4 is input to the base of the transistor 106. Further, the waveform output from the second detection circuit to the output terminal 99 has a direct current component removed by the capacitor 101, a bias equal to the output signal of the first brightness detection circuit is applied by the resistors 102 and 103, and then the transistor Input to the base of 105.

Transistor 105 and transistor 106
The differential amplifier circuit is composed of
And the ratio of the resistance 104. That is, the signal input from the output terminal 94 and the signal input from the input terminal 99 are subtracted and amplified. Therefore, in the collector of the transistor 105, the waveform of the output signal of the second luminance detection circuit is subtracted and amplified from the waveform of the output signal of the first luminance detection circuit as shown in FIG. The waveform as shown in () is output.

Here, the output signal of the correction signal generating circuit 10 is a difference signal between the output signal of the first brightness detecting circuit and the output signal of the second brightness detecting circuit, and the original brightness signal, that is, the output from the clamp circuit 6. Since it is a signal generated from the generated luminance signal, the output signal of the correction signal generating circuit 10 can be used as a gradation correction signal in the low luminance range of the original luminance signal.

By the way, as described above, it is when the screen is bright that the gradation on the low luminance side of the display image is destroyed by the stray light of the optical system. However, in the case of a dark screen, there is almost no effect of stray light, and when the gradation of the screen, especially the gradation on the low luminance side is corrected in such a case, the displayed image becomes rather unnatural. In this embodiment, the amplitude of the gradation correction signal is changed according to the brightness of the screen,
When the screen is dark, it has a correction signal control circuit 11 that suppresses gradation correction. Hereinafter, the correction signal control circuit 1 of FIG.
The part 1 will be described.

Resistors 111, 113, 117 and 118, transistors 112, 115 and capacitors 114, 11
Reference numeral 6 is a correction signal control circuit 1 for suppressing correction on a dark screen.
Make up one. The operation of the circuit will be described below.

The output voltage of the ABL input to the input terminal 3 is input to the base of the transistor 115 through the buffer including the resistor 111 and the transistor 112 and the low pass filter including the resistor 113 and the capacitor 114. The emitter voltage is set by the resistors 117 and 118 such that the base voltage of the transistor 115 is low when the screen is bright, that is, the cut-off state is set, and when the base voltage of the transistor 115 is high, that is, the screen is dark when the transistor 115 is active.

With this configuration, the transistor 115
In the case of a bright screen, since the output voltage of the ABL is low, it is in a cut-off state and does not affect the gradation correction signal created by the correction signal creation circuit 10. On the other hand, when the screen is dark, the output voltage of ABL is high, so that the transistor 115 is activated. Since the collector of the transistor 115 is connected to the collector of the transistor 105, the gradation correction signal appearing at the collector of the transistor 105 is attenuated and the amplitude is made almost zero. As described above, the correction signal control circuit 11 suppresses gradation correction on a dark screen.

In FIG. 4, resistors 121, 123 and 12 are shown.
5, the capacitor 122, and the transistor 124 form an adding circuit 12 that adds the gradation correction signal created by the correction signal creating circuit 10 to the original luminance signal. The luminance signal input from the clamp circuit 6 to the input terminal 15 is the resistance 12
3 appears at the connection point between the resistor 123 and the capacitor 122. On the other hand, the gradation correction signal output from the emitter of the transistor 1010 is also the resistor 121 and the capacitor 122.
Through the resistor 123 and the capacitor 122. Since the DC component of the gradation correction signal is removed by the capacitor 122, only the gradation correction signal which is an AC component is added to the original luminance signal.

Therefore, at the connection point between the resistor 123 and the capacitor 122, as shown in FIG. 5 (c), a luminance signal that emphasizes gradation can be obtained. And transistor 1
By outputting to the output terminal 13 through the buffer composed of 24 and the resistor 125, as shown in FIG. 6, gradation correction on the low luminance side of the luminance signal, that is, about 30 [IRE] or less becomes possible. Further, when the screen is dark, the correction signal control circuit 11 attenuates the gradation correction signal so that the amplitude is almost 0, so that the gradation correction can be suppressed.

As described above, in the present embodiment, in the case of an entirely bright screen, even if stray light of the optical system leaks into the black portion of the image, the gradation on the low luminance side is emphasized, and the floor on the low luminance side is emphasized. It is possible to display an image with no adjustment, and it is possible to obtain a luminance signal in which this correction is suppressed on a screen that is dark as a whole and is hardly affected by stray light.

In this embodiment, the gradation correction circuit of the present invention is used as an example to correct only the gradation on the low luminance side. However, according to the gradation correction circuit of the present invention, the low luminance side is corrected. Without being limited to the above, gradation correction can be performed from the low luminance side to the luminance of any level. Hereinafter, an example in which the gradation correction circuit according to the present invention is used to perform gradation correction from a low brightness side to an arbitrary brightness will be described with reference to FIG. 7.

In the first brightness detecting circuit consisting of the resistor 91 and the transistors 92 and 93 of the brightness detecting circuit 9 shown in FIG. 2, the input brightness signal is clipped by V4, and further the resistors 97 and 98 and the transistors 95 and 96 are clipped. The second consisting of
In the brightness detection circuit, the input brightness signal is changed to V5 (>
The reference voltage of the brightness detection circuit 9 supplied from the bias circuit 8 is set so as to clip at V4). As a result, if the reference voltage of the first brightness detection circuit is V4, the output terminal 94 has a ramp waveform of V as shown in FIG.
A waveform in which the luminance component of 4 + V _BE or more is deleted is obtained.

Further, in the second brightness detection circuit, the common emitter of the transistors 95 and 96 has a waveform in which the brightness component of V5 + V _BE or more of the ramp waveform is deleted as shown in FIG. 7B. Here, as described above, since the waveform of the common emitter of the transistors 95 and 96 is divided by the resistors 97 and 98 so that the amplitude becomes equal to the output signal of the first brightness detection circuit, the output terminal 99 is divided. In Figure 7
As shown in (c), a waveform different from the output signal of the first luminance detection circuit but having the same amplitude is obtained.

After that, the correction signal generating circuit 10 subtracts and amplifies the waveforms output from the respective detecting circuits, thereby amplifying the waveforms from low luminance to arbitrary luminance as shown in FIG. 7 (d). By creating a tonal correction signal, adding it to the original luminance signal and outputting it, it is possible to perform gradation correction from the low luminance side to any luminance as shown in FIG. 7 (e). The input / output characteristic at the output terminal 13 at this time is shown in FIG.

In this embodiment, as shown in FIG.
The gradation around 50 [IRE] is emphasized most strongly, but by appropriately setting V4 and V5, 0 to 10 can be obtained.
It is obvious that any part of 0 [IRE] can be emphasized.

FIG. 9 shows a second image display device according to the present invention.
FIG. 3 is a block diagram showing a gradation correction circuit provided in an embodiment of the present invention, particularly in an image display device that does not include an ABL, and is an example in the case of performing gradation correction on the low luminance side. In FIG. 9, reference numeral 16 is an APL (average luminance level) of the luminance signal from which the synchronizing signal portion output from the synchronizing signal removing circuit 7 is removed.
Is a APL detection circuit for detecting the same, and the portions corresponding to those in FIG.

In the embodiment shown in FIG. 1, the correction signal control circuit 11 is operated by the output voltage of the ABL, but in the embodiment shown in FIG. 9, the APL detection circuit 1 is operated as shown in the figure.
The output voltage of 6 operates the correction signal control circuit 11. The other points are the same as in the embodiment shown in FIG.

In FIG. 9, the APL detection circuit 16 integrates the luminance signal output from the synchronization signal removal circuit 7, for example, and outputs a voltage (APL voltage) indicating the average level of this luminance signal. Therefore, when the luminance signal output from the synchronization signal removal circuit 7 is a window signal having a large maximum amplitude but a small bright portion area as shown in FIG. 10A, the output voltage of the APL detection circuit 16 is: When the luminance signal is low as shown in FIG. 10B and the maximum amplitude is large and the area of the bright portion is also large as shown in FIG.
The output voltage of the L detection circuit 16 becomes high as shown in FIG.

Unlike the output voltage of the ABL in the embodiment shown in FIG. 1, the output voltage of the APL detection circuit 16 is high when the screen is totally bright and is low when the screen is totally dark. Therefore, the correction signal control circuit 11
It is necessary to suppress gradation correction when the output voltage of the L detection circuit 16 is low. This is the correction signal control circuit 1 shown in FIG.
The transistors 112 and 115 in 1 are PN
This can be dealt with by changing to a P type transistor.
Since the operation is similar to that of the first embodiment, the description is omitted.

In the first and second embodiments, the signal detected by the second luminance detection circuit is divided from the output signal of the first luminance detection circuit by the resistor and the signal detected by the first luminance detection circuit. The signal shown in FIG. 5B is obtained by subtracting and amplifying the signal having the same amplitude as that of the luminance signal, and the gradation correction of the luminance signal is performed.

However, although not shown, the signal detected by the first luminance detection circuit is amplified by an amplifier circuit so as to have the same amplitude as the signal detected by the second luminance detection circuit. The output signal of the brightness detection circuit may be subtracted and amplified, and even in this case, a signal as shown in FIG. 5B is obtained, and gradation correction of the brightness signal can be performed. Absent.

FIG. 11 shows a third embodiment of the image display device according to the present invention.
2 is a block diagram showing a gradation correction circuit thereof, in which 17 and 18 are clip circuits, 19 and 21 are inverting amplifier circuits, and 20 is an adder circuit. , And duplicate description is omitted. The embodiment shown in FIG. 1 is different from the brightness detection circuit 9 and the correction signal generation circuit 1 in FIG.
It differs from the configuration of 0 in that an inverting amplifier circuit 21 is provided. Hereinafter, these different points will be described.

The second brightness detecting circuit of the brightness detecting circuit 9 of the embodiment shown in FIG. 1 outputs the brightness signal appearing at the common emitter of the transistors 95 and 96 to the output signal of the first brightness detecting circuit by the resistors 97 and 98. And the voltage was output so that the amplitude would be equal. On the other hand, the brightness detection circuit 9 of this embodiment directly outputs from the common emitter of the transistors 95 and 96 of the second brightness detection circuit as shown in FIG.

Further, the correction signal generating circuit 10 of the embodiment shown in FIG. 1 adds the output signal of the first brightness detecting circuit and the output signal of the second brightness detecting circuit and at the same time amplifies them, while the correction signal creating circuit 10 of this embodiment The correction signal generating circuit 10 of FIG. 1 inversely amplifies the output signal of the first luminance detection circuit by the inverting amplification circuit 19 so that the amplitude becomes equal to the output signal of the second luminance detection circuit, and then adds the second luminance by the addition circuit 20. The gradation correction signal is created by adding it to the output signal of the detection circuit. The above operation will be described below with reference to the waveform diagrams of the respective parts shown in FIG.

The output signal of the first luminance detection circuit is shown in FIG.
When the amplitude shown in (a) is a ramp waveform of a and the output signal of the second luminance detection circuit is a ramp waveform of b shown in FIG. 13 (b), the inverting amplifier circuit 19 operates as shown in FIG.
Since the waveform of (a) is inverted and amplified so that the amplitude becomes b, it is possible to obtain a waveform in which the amplitude is b and the polarity is inverted as shown in FIG.

Next, by the adder circuit 20, FIG.
The output signal of the second luminance detection circuit shown in FIG.
By adding the output signals of the inverting amplifier circuit 19 shown in (c), the difference signal of the two waveforms shown in FIG. 13D, that is, the gradation correction signal on the low luminance side can be obtained. As can be seen from FIG. 13D, since the gradation correction signal here is a negative signal, the polarity is inverted by the inverting amplifier circuit 21 to be converted into a positive signal, and as a result, FIG. A signal as shown in (e) is obtained. Further, by adjusting the gain of the inverting amplifier circuit 21, the strength of gradation correction can be controlled.

Also in this embodiment, for example, FIG.
It goes without saying that the gradation correction can be performed from the low brightness side to the brightness of any level as shown in (e).

FIG. 14 is a block diagram showing a fourth embodiment of the image display device according to the present invention, particularly a gradation correction circuit thereof, in which the correction signal control circuit 11 is controlled by the output voltage of the APL detection circuit 16. To do. 9 and 11
The same symbols are attached to the portions corresponding to. The configuration and operation of the APL detection circuit 16 are the same as those of the embodiment shown in FIG. 9, and the other points are the same as those of the embodiment shown in FIG.

In the third and fourth embodiments, the output signal of the second brightness detecting circuit and the output signal of the first brightness detecting circuit are made equal to the amplitude of the output signal of the second brightness detecting circuit by the inverting amplifier circuit. 13 and the inverted signal is added, and the added signal is inverted and amplified.
The signal as shown in (c) was obtained.

However, although not shown, a signal obtained by amplifying the output signal of the first luminance detection circuit so that its amplitude becomes equal to that of the output signal of the second luminance detection circuit by using an amplification circuit, and the second luminance. It goes without saying that even if the output signal of the detection circuit is added to the signal inverted by the inversion circuit, a signal as shown in FIG. 13C is obtained in the same manner, and gradation correction of the luminance signal can be performed. .

Although the second, third and fourth embodiments describe the case where the gradation correction circuit of the present invention corrects the gradation on the low luminance side, the gradation correction circuit of the present invention. Is
Similar to the first embodiment, the gradation correction is not limited to the gradation on the low luminance side, and gradation correction can be performed from the low luminance side to any level of luminance.

Further, in all of the embodiments, the case where the present invention is applied to the image display device having the black level correction circuit has been described, but the present invention is applied to the image display device which does not have the black level correction circuit. Even in this case, it is obvious that the gradation correction of the image, especially the gradation correction on the low luminance side can be performed.

[0067]

As described above, according to the present invention,
It is possible to emphasize the gradation of the image displayed on the image display device, particularly the gradation on the low luminance side. Furthermore, by differentiating the degree of image gradation enhancement between a bright screen and a dark screen, for example, due to stray light from the optical system leaking into the black portion of the image on a bright screen, the gradation on the low-luminance side is destroyed. Even if occurs, by emphasizing the gradation on the low luminance side, it is possible to prevent the gradation from being collapsed on the low luminance side. Moreover, since the degree of emphasis of the gradation of the luminance signal is reduced in the case of a dark screen where gradation collapse on the low luminance side is unlikely to occur, there is almost no effect on the gradation. Therefore, compared to the conventional image display device,
It is possible to more clearly express the gradation of an image, especially the gradation on the low luminance side.

Further, when the present invention is applied to the image display device having the black level correction circuit, it is possible to correct the gradation of the image and at the same time reduce the black floating phenomenon of the image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an image display device according to the present invention, particularly a gradation correction circuit thereof.

FIG. 2 is a circuit diagram showing a clamp circuit of the embodiment, a sync signal removing circuit,
It is a circuit diagram which shows the specific structural example of a brightness | luminance detection circuit and a bias circuit.

FIG. 3 is a waveform diagram showing signals of respective parts in FIG.

FIG. 4 is a circuit diagram showing a specific configuration example of a correction signal generation circuit, a correction signal control circuit, and an addition circuit of the same embodiment.
FIG. 4 is a waveform diagram showing signals of respective parts in FIG. 3.

FIG. 5 is a waveform diagram showing signals of respective parts in FIG.

FIG. 6 is a graph showing the input / output characteristics of the same example.

FIG. 7 is a waveform diagram showing signals of respective parts in FIG.

FIG. 8 is a graph showing the input / output characteristics of the same example.

FIG. 9 is a block diagram showing a second embodiment of an image display device according to the present invention, particularly a gradation correction circuit thereof.

FIG. 10 is an explanatory diagram showing an operation of the APL detection circuit of the same embodiment.

FIG. 11 is a third embodiment of the image display device according to the present invention,
In particular, it is a block diagram showing the gradation correction circuit.

FIG. 12 is a circuit diagram showing a specific configuration example of the luminance detection circuit of the same embodiment.

FIG. 13 is a waveform diagram showing signals of respective parts in FIG.

FIG. 14 is a fourth embodiment of the image display device according to the present invention,
In particular, it is a block diagram showing the gradation correction circuit.

FIG. 15 is a waveform diagram showing the operation of the black level correction circuit.

FIG. 16 is a graph showing the input / output characteristics of the black level correction circuit.

[Explanation of symbols]

 1, 2, 3, 15, 61, 62, 90 ... Input terminal 4 ... Black level correction circuit 5 ... Amplification circuit 6 ... Clamp circuit 7 ... Sync signal removal circuit 8 ... Bias circuit 9 ... Luminance detection circuit 10 ... Correction signal creation Circuit 11 ... Correction signal control circuit 12, 20 ... Addition circuit 13, 94, 99 ... Output terminal 14 ... Voltage source 16 ... APL detection circuit 17 ... Second clipping circuit 18 ... First clipping circuit 19, 21 ... Inversion amplification circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Okada 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Stock company Hitachi Image Information Systems (72) Inventor Masahiko Umeda 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Hitachi, Ltd. AV Equipment Division (72) Inventor Takaaki Nishiseto 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock Company Hitachi Ltd. AV Equipment Division

Claims (9)

[Claims] 1. An image display device, which receives at least a luminance signal and displays an image corresponding to the luminance signal, detects a signal equal to or lower than an arbitrary level of the luminance signal, and detects the signal of the arbitrary level of the luminance signal. Is an image display device comprising a gradation correction circuit for detecting a signal having a different level or less and outputting a gradation correction signal based on a difference between the two signals. 2. An image display device which receives at least a luminance signal and displays an image corresponding to the luminance signal, detects a signal equal to or lower than an arbitrary level of the luminance signal, and detects from the arbitrary level of the luminance signal. A signal below a high level is detected and amplified or compressed so that the amplitudes of the two signals become equal. Of the two amplified or compressed signals, the signal before being amplified or compressed is the luminance signal. An image display device comprising: a gradation correction circuit that subtracts the other signal from a signal having an arbitrary level or lower and outputs the subtracted signal as a gradation correction signal. 3. An image display device which receives at least a luminance signal and displays an image according to the luminance signal, wherein a clamp circuit for fixing the pedestal level of the luminance signal to a constant value, and a signal output from the clamp circuit. Among these, a sync signal removing circuit for removing a sync signal, a first luminance detecting circuit for detecting a signal below an arbitrary level of the signal output from the sync signal removing circuit, and an output from the sync signal removing circuit. A second luminance detection circuit that detects a signal having a level equal to or lower than the arbitrary level and that compresses the detected signal so as to be equal to the amplitude of the signal detected by the first luminance detection circuit; Clamp circuit, the first luminance detection circuit, and the second
A bias circuit for generating a reference voltage of a brightness detection circuit; a correction signal generation circuit for subtracting an output signal of the second brightness detection circuit from an output signal of the first brightness detection circuit, amplifying the output signal, and outputting the correction signal; An image display device, comprising: a gradation correction circuit having an addition circuit for adding and outputting an output signal of a creation circuit and an output signal of the clamp circuit. 4. An image display device which receives at least a luminance signal and displays an image according to the luminance signal, wherein a clamp circuit for fixing the pedestal level of the luminance signal to a constant value, and a signal output from the clamp circuit. Among these, a sync signal removing circuit for removing a sync signal, a first luminance detecting circuit for detecting a signal below an arbitrary level of the signal output from the sync signal removing circuit, and an output from the sync signal removing circuit. A second brightness detection circuit for detecting a signal having a level lower than the arbitrary level and a signal amplitude of the output signal of the first brightness detection circuit equal to that of the output signal of the second brightness detection circuit; An amplifying circuit for amplifying the light into a plurality of lines, the clamp circuit, the first luminance detecting circuit, and the second
A bias circuit that generates a reference voltage for the brightness detection circuit; a correction signal creation circuit that subtracts the output signal of the second brightness detection circuit from the output signal of the amplification circuit; An image display device comprising: a gradation correction circuit having an adder circuit for adding and outputting an output signal and an output signal of the clamp circuit. 5. An image display device which receives at least a luminance signal and displays an image according to the luminance signal, wherein a clamp circuit for fixing the pedestal level of the luminance signal to a constant value, and a signal output from the clamp circuit. Of these, a sync signal removing circuit for removing a sync signal, a first brightness detection circuit for detecting a signal below an arbitrary level of an output signal of the sync signal removing circuit, and a brightness signal output from the sync signal removing circuit A second signal for detecting a signal below a level higher than the arbitrary level
A luminance detection circuit, the clamp circuit, the first luminance detection circuit, and the second
A bias circuit for generating a reference voltage for the brightness detection circuit; and an output signal from the first brightness detection circuit for inversion,
An inverting amplifier circuit that amplifies the output signal of the brightness detection circuit so as to have the same amplitude as that of the output signal, and a correction signal creation circuit that adds the output signal of the first brightness detection circuit and the output signal of the inverting amplifier circuit to perform inverting amplification And a second adder circuit for adding the output signal of the correction signal creation circuit and the luminance signal output from the clamp circuit,
An image display device comprising: 6. An image display device which receives at least a luminance signal and displays an image according to the luminance signal, wherein a clamp circuit for fixing the pedestal level of the luminance signal to a constant value, and a signal output from the clamp circuit. Of these, a sync signal removing circuit for removing a sync signal, a first brightness detection circuit for detecting a signal below an arbitrary level of an output signal of the sync signal removing circuit, and a brightness signal output from the sync signal removing circuit A second signal for detecting a signal below a level higher than the arbitrary level
A luminance detection circuit, the clamp circuit, the first luminance detection circuit, and the second
A bias circuit for generating a reference voltage for the brightness detection circuit; an amplification circuit for amplifying the amplitude of the output signal of the first brightness detection circuit to be equal to the amplitude of the output signal of the second brightness detection circuit; An inverting circuit that inverts the output signal of the luminance detection circuit, a correction signal creating circuit that adds the output signal of the amplifier circuit and the output signal of the inverting circuit, an output signal of the correction signal creating circuit, and an output from the clamp circuit A second adder circuit for adding the generated luminance signal,
An image display device comprising: 7. An image display device comprising the gradation correction circuit according to claim 2 and an automatic brightness limiting circuit, wherein the gradation correction circuit outputs an output signal of the automatic brightness limiting circuit. An image display device comprising a correction signal control circuit for changing the amplitude of an output signal of the correction signal generating circuit according to the above. 8. An image display device including the gradation correction circuit according to claim 2, wherein the gradation correction circuit detects an average brightness level of a brightness signal output from the clamp circuit. And outputs a voltage corresponding to the detected voltage A
An image display device comprising: a PL detection circuit; and a correction signal control circuit that changes the amplitude of the output signal of the correction signal generation circuit according to the output signal of the APL detection circuit. 9. An image display device including the gradation correction circuit according to claim 2, wherein a luminance signal is input, a black peak of the input luminance signal is detected, and a pedestal level direction is detected. 2. An image display device, comprising: a black level correction circuit for lowering the black peak of the luminance signal to a pedestal level for output by performing level shift or black expansion.