JP3524115B2 - Contour correction device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction device used in a television system.

[0002]

2. Description of the Related Art Conventionally, as a display device for video signals,
A CRT is generally used, which has a light emission characteristic as shown in FIG. 9 with respect to an input voltage. This light emission characteristic can be expressed by the following equation, where V is an input voltage, L is a light emission luminance, and k is a proportional constant.

[0003] L = kV raised to the power of γ (γ is about 2.2) (1)

Therefore, in a television system, a process called gamma correction is performed to correct this at the time of image pickup. Gamma correction can be expressed by the following equation, where E is the brightness level and V is the level after gamma correction.

V = E to the power of 1 / γ (2)

FIG. 10 shows the gamma correction characteristic according to the above equation (2).

FIG. 11 shows a gamma correction circuit used in a conventional video camera or the like for performing the above-mentioned gamma correction. In the figure, 1 is an input terminal to which an input signal (negative polarity) is supplied and 2 is impedance converting transistor, 3 emitter resistor for determining the emitter current of the transistor 2, 4 ₁ to 4 _n diodes, 5, 6 ₁ to 6 _n is divided resistor for determining the amplitude voltage of the output signal, E ₁ to E _n is input A power supply voltage that sets a break point of the output characteristic, and 7 is an output terminal.

Next, the operation will be described. For example, in FIG.
When an input signal such as that shown in FIG. 2 is supplied to the input terminal 1, this signal is output to the output terminal 7 through the impedance conversion transistor 2 and the dividing resistor 5 connected to its emitter.
Is output from. At this time setting the folding point of the potential of the output terminal 7 is input-output characteristic voltage E ₁ to E _n than V _D (diode 4
_{When the} voltage applied to ₁ to 4 _n is lower than a potential lower by 0.6 V, the diodes 4 ₁ to 4 _n become conductive, and the output voltage of the emitter is divided by the dividing resistors 5 and 6 _{1 to} 6 _n . Is pressed.

In this case, the diodes 4 ₁ to 4 _n and the resistor 6
₁ to 6 _n, if the combination of the voltage E ₁ to E _n is one set,
Regarding the input / output characteristics of this circuit, one broken line characteristic due to voltage division has one broken line characteristic, and if there are n sets, there will be n broken line characteristic.

FIG. 13 shows the input / output characteristics when there are three break points, and gamma correction characteristics similar to those shown in FIGS. 10 and (2) are obtained. . Incidentally, in FIG. 13, the input signal and the output signal are shown by relative values.

Accordingly, the number of in order to increase the accuracy of the gamma correction, the diode 4 ₁ to 4 _n, the dividing resistors 6 ₁ to 6 _n, break points set voltage breakpoint by increasing the number of E ₁ to E _n Need to increase.

Next, in the television system, a contour correction device is used to enhance the contour of the displayed image. FIG. 14 shows a conventional contour correction device.

In FIG. 14, reference numeral 31 is a video signal input terminal, 32 is a delay circuit for matching the phases of the video signal and the contour signal, and 34 is a contour for extracting a contour signal from the video signal input from the input terminal 31. A signal extraction circuit, 36 is a gain adjustment circuit that adjusts the gain of the contour signal to adjust the amount of the contour added to the video signal, 37 is an adder for adding the contour signal to the video signal, and 38 is the contour-corrected image This is a signal output terminal.

Next, the operation will be described. Input terminal 31
When a video signal as shown in FIG.
The contour signal extraction circuit 34 extracts a contour signal as shown in FIG. This contour signal is a gain adjustment circuit 36.
Is adjusted to an appropriate level by the adder 37 and added to the original video signal. For example, as shown in FIG. 15C, this addition output has a waveform whose contour is emphasized by the overshoot portion and the undershoot portion, and this waveform signal is output from the output terminal 38.

[0015]

Since the conventional gamma correction circuit is constructed as shown in FIG. 11, it has the following problems.

(1) It is not possible to automatically adjust the state of whiteout on the screen or remotely control from the outside.

(2) It is not possible to automatically adjust the input / output characteristics of gamma correction or to remotely control from outside.

[0018] (3) In order to perform accurate gamma correction, it is necessary to use more diodes 4 ₁ to 4 _n, Therefore, the junction capacitance of the diode becomes a load of the circuit, the input signal The frequency characteristics are deteriorated by the AC and DC levels.

Further, since the conventional contour correction device is constructed as shown in FIG. 14, there is no problem when performing the gamma correction after the contour correction, but the following problem occurs when the contour correction is performed after the gamma correction. was there.

The contour correction can be obtained by adding an equal amplitude overshoot portion and an undershoot portion to the edge portion of the image as shown in FIG. 15C, and this signal is output on the CRT for display. In this case, due to the light emission characteristics of the CRT shown in FIG. 9, the amplitudes of the undershoot portion and the overshoot portion are significantly different as shown in FIG. 16, and the undershoot portion is particularly small. As a result, the image has an uplifted impression, and the image lacks a natural feeling and a three-dimensional effect.

The present invention has been made in order to solve the above problems, and it is possible to obtain a highly accurate gamma correction circuit which can improve white crushing, can be remotely operated, and has a good frequency characteristic. It is an object of the present invention to obtain a contour correction device capable of performing contour correction with a well-balanced chute and undershoot.

[0022]

According to a first aspect of the present invention, there is provided an extracting means for extracting a contour signal from an input video signal, and a gain on the negative polarity side of the contour signal extracted by the extracting means.
The control means includes a control means for controlling based on the signal level of the video signal, and an adding means for adding the contour signal controlled by the control means and the video signal. The control means increases the signal level of the video signal. Accordingly, the gain of the contour signal on the negative polarity side is controlled to be small. According to a second aspect of the present invention, a extracting means for extracting a contour signal from the input video signal, and a gain on the positive side of the contour signal extracted by the extracting means are controlled based on a signal level of the video signal. And a second control means for controlling the gain on the negative polarity side of the contour signal extracted by the extraction means based on the signal level of the video signal.
Control means, and an adding means for adding the contour signal controlled by each of the first and second control means and the video signal, wherein the second control means increases the signal level of the video signal. Accordingly, the gain of the contour signal on the negative polarity side is controlled to be small.

[0023]

[0024]

According to the contour correction apparatus of the present invention, even if contour correction is performed after gamma correction, contour correction in which the positive polarity side (overshoot portion) and the negative polarity side (undershoot portion) of the image are well balanced is performed. Done.

[0025]

[0026]

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the first invention will be described below with reference to the drawings. In FIG. 1, 13 _{1 to} 13 _n are clip levels
A clip circuit capable of controlling (clip characteristics) , to which an input signal (video signal) from the input terminal 1 is added. Reference numeral 14 denotes a knee circuit, which includes emitter follower transistors 15 and 16 for impedance conversion and their emitter resistors 1
7 and 18, knee slope switching resistors R _A , R ₁₁ and R ₁₂ and knee slope switching transistors 19 and 20.

[0028] 21, the clip circuit 13 ₁ to 13 _n summing amplifier which is an operational amplifier for adding the outputs of the output and the knee circuit 14, R ₁ ~R _n, R _B is the summing resistor, R _f is It is the feedback resistance of the operational amplifier.

22 is a D / A converter (control signal generator)
A stage), the transistor 1 for switching the voltage E ₁ to E _n as a control signal for controlling the clipping level of the clipping circuit 13 ₁ to 13 _n, the connection of the resistor R _11, R ₁₂
It outputs voltages V ₁ and V ₂ as control signals for controlling 9 and 20.

[0030] 23 the voltage E ₁ to E _n, the digital data (clip characteristic control data for V _1, V _2,
A CPU as a control means for giving the voltage division ratio control data) to the D / A converter 22 and a memory 24 (control data holding means) for storing the digital data.

FIG. 2 shows the structure of the clip circuits 13 _{1 to} 13 _n , which is composed of transistors 8 and 9 forming a differential amplifier, a transistor 10 to which the emitter follower output is added, and emitter resistors 11 and 12. ,
The output of the emitter follower of the transistor 10 is divided by the resistance ratio and added to the adding amplifier 21 (adding means) via the resistor R _i .

Next, the operation of the above configuration will be described. When the input signal shown in FIG. 12 is applied from the input terminal 1 to one of the clip circuits 13 _{1 to} 13 _n , the clip characteristic of this clip circuit becomes, for example, the characteristic a of FIG. Similarly, the respective clip characteristics of the other two clip circuits are, for example, the characteristics b and c of FIG. At this time, the inclinations of the clip characteristics a, b, and c are determined by the gain of the summing amplifier 21 | −R _f / R _i | (i =
1, 2, ... N).

Further, in the knee circuit 14, when both the transistors 19 and 20 are OFF, the input / output characteristic of the knee circuit 14 has the maximum ratio of the addition resistance R _A + R _B to the feedback resistance R _f. | −R _f / (R _A + R _B ) |, which is as the characteristic d in FIG. Therefore, the input / output characteristics of the entire gamma correction circuit at this time are the characteristics a, b, and
The characteristic e is obtained by adding c and d.

In this state, only the transistor 19 is turned on.
If the resistor R ₁₁ is connected to the input terminal and the absolute value of the input signal is V ₁
When −V _BE1 (V _BE1 : the base-emitter voltage of the transistor 19) is exceeded, the slope of the input / output characteristics is | −
R _f / (R _A + R _B ) × R ₁₁ / (R _A + R ₁₁ ) | At this time, the characteristic f of FIG. 3 is obtained.

Similarly, when only the transistor 20 is turned on and the resistor R ₁₂ is connected, the absolute value of the input signal becomes │V ₂ -V
When it is larger than _BE2 |, the slope has the characteristic g.

In this case, each V _i -V _BEi needs to have the same voltage, and this voltage is taken as a knee characteristic switching voltage (knee point). Then, the knee point can be changed like the characteristics h and j by changing the values of V ₁ and V ₂ .

Therefore, according to this embodiment, the gain (knee slope) and the knee point of the high-luminance portion can be changed independently, so that in the case of an image signal in which the high-luminance portion and the low-luminance portion are mixed. The CPU 23 can be used to control the improvement of the whiteout.

Further, the clipping circuits 13 _{1 to} 13 _n using the differential amplifier by the emitter follower are the transistors 8
Is off, the transistor 9 is on and the emitter resistance is small, so that the field through due to the base-emitter capacitance of the transistor 8 is negligibly small. Therefore, good high frequency characteristics can be obtained, and changes in the frequency characteristics due to the AC and DC levels of the input signal can be reduced.

If the characteristics of the transistors 8 and 9 are matched, the precision of the break point of the input / output characteristics is high, and therefore the luminance of gamma correction can be made relatively high.

FIG. 4 is a block diagram showing an embodiment of the second invention. The parts corresponding to those in FIG. 14 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 4, reference numeral 33 denotes a negative polarity amplitude expansion control circuit (control means) for controlling the degree of amplitude expansion on the negative polarity side of the contour signal according to the level of the input video signal.
Reference numeral 5 denotes a negative-polarity amplitude expansion circuit which is controlled by the negative-polarity amplitude expansion control circuit 33 to expand the negative-polarity-side amplitude of the contour signal and add it to the gain adjustment circuit 36.

Next, the operation will be described. Input terminal 31
When a signal as shown in FIG. 5 (a) is input to the contour signal extraction circuit 34, the contour signal extraction circuit 34 extracts the contour signal as shown in FIG. 5 (b) as in the conventional case. Thereafter, the negative polarity amplitude expansion control circuit 33 and the negative polarity amplitude expansion circuit 35 expand the amplitude of the contour signal on the negative polarity side by the method shown in FIG. 6 according to the level of the video signal. As a result, a contour signal as shown in FIG. 5 (c) is obtained.

Next, after adjusting the contour correction amount by the gain adjusting circuit 36, the contour signal is added to the video signal by the adder 37 (adding means) and output from the output terminal 38. As shown in FIG. 5D, this addition output has a waveform in which the undershoot portion becomes smaller as the level of the video signal increases. When the video signal having the above waveform is output to the CRT having the light emission characteristic shown in FIG. 9, the undershoot portion is compressed according to the light emission characteristic, and a balanced image of the contour overshoot portion and the undershoot portion is obtained. .

In this embodiment, only the case where the amplitude of the contour signal on the negative polarity side is expanded according to the video level has been described, but the positive polarity side and the negative polarity side of the contour signal are dependent on the video signal level. It is also possible to change the amplitude gain of each independently. An example in that case is shown in FIG.

In FIG. 7, reference numerals 31, 32, 34 to 38 are the same as those in FIG. Gain control circuit 39 (first and second control
The control means) controls the gain on the negative polarity side and the gain on the positive polarity side of the contour signal in accordance with the level of the video signal. The positive polarity amplitude compression circuit 40 controlled by the gain control circuit 39 compresses the amplitude of the contour signal on the positive polarity side.

The outputs of the negative polarity amplitude expansion circuit 35 and the positive polarity amplitude compression circuit 40 are added by the adder 41 (adding means) , and then added to the video signal by the adder 37 via the gain adjusting circuit 36. Is output.

When the video signal shown in FIG. 8A is input to the input terminal 31, the contour signal extraction circuit 34 extracts the contour signal shown in FIG. 8B. The negative polarity amplitude expansion circuit 35 and the positive polarity amplitude compression circuit 40 independently compress and expand the amplitude of the contour signal according to the level of the video signal, and add these by the adder 41, as shown in FIG. A contour signal is obtained.

After that, after adjusting the contour correction amount by the gain adjusting circuit 36 and adding it to the video signal by the adder 37,
The added output has a waveform as shown in FIG. When the video signal of this waveform is output to a CRT having a light emission characteristic as shown in FIG. 9, a well-balanced image of the contour overshoot portion and undershoot portion can be obtained.

[0049]

As described above, according to the contour correcting apparatus of the present invention, the amplitude of at least one of the positive polarity side and the negative polarity side of the contour signal is controlled according to the level of the video signal. As a result, even when the contour-corrected video signal after gamma correction is output to the CRT, a high-quality image with a well-balanced contour portion can be obtained with a simple circuit configuration.

[0050]

[0051]

[0052]

[0053]

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a signal correction circuit.

FIG. 2 is a circuit diagram showing an embodiment of a clip circuit.

FIG. 3 is a characteristic diagram showing clip characteristics, input / output characteristics, and the like.

FIG. 4 is a block diagram showing an embodiment of a contour correction device of the present invention .

FIG. 5 is a waveform diagram showing an operation.

FIG. 6 is a characteristic diagram showing an operation.

FIG. 7 is a block diagram showing another embodiment of the contour correction device .

FIG. 8 is a waveform diagram showing an operation.

FIG. 9 is a characteristic diagram showing a light emission characteristic of a CRT.

FIG. 10 is a characteristic diagram showing gamma correction characteristics.

FIG. 11 is a circuit diagram of a conventional gamma correction circuit.

FIG. 12 is a waveform chart showing an example of an input signal.

FIG. 13 is a characteristic diagram showing an example of input / output of a conventional gamma correction circuit.

FIG. 14 is a block diagram showing a conventional contour correction device.

FIG. 15 is a waveform diagram showing an operation.

FIG. 16 is a characteristic diagram showing an operation.

[Explanation of symbols]

13 _{1 to} 13 _n Clip circuit 14 Knee circuit 19, 20 Knee slope switching transistor 21 Summing amplifier 22 D / A converter 23 CPU _RA , R ₁₁ , R ₁₂ Knee slope switching resistor 33 Negative polarity amplitude expansion control circuit 34 Contour signal extraction circuit 35 Negative polarity amplitude expansion circuit 36 Gain adjustment circuit 37 Adder 39 Gain control circuit 40 Positive polarity amplitude compression circuit 41 Adder

Continuation of front page (56) Reference JP-A-3-36884 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 5/208 H04N 5/202

Claims (2)

(57) [Claims] 1. Extraction means for extracting a contour signal from an input video signal, and control means for controlling the negative gain of the contour signal extracted by the extraction means based on the signal level of the video signal. And an adding means for adding the contour signal controlled by the control means and the video signal, wherein the control means has a gain on the negative side of the contour signal as the signal level of the video signal increases. A contour correction device characterized in that it is controlled so as to be smaller. 2. A first extracting means for extracting a contour signal from an inputted video signal, and a first gain controlling means for controlling a gain on the positive side of the contour signal extracted by the extracting means based on a signal level of the video signal. The control means, the second control means for controlling the gain on the negative polarity side of the contour signal extracted by the extraction means based on the signal level of the video signal, and the first and second control means. The second control means reduces the gain on the negative polarity side of the contour signal as the signal level of the video signal increases. A contour correction device characterized in that it is controlled to