JPH07105902B2 - Video signal processing circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit used in a video camera, and more particularly to a white level compression circuit for reproducing high level gradation of a luminance signal, that is, The present invention relates to a video signal processing circuit including a white knee circuit.

[Background of the Invention]

2. Description of the Related Art Conventionally, in a video processing circuit used for a video camera, a white clip circuit is provided for the purpose of preventing overmodulation. This is to set a level of, for example, 115% of a specified white level as a clip level, and limit the level of a portion of the video signal equal to or higher than this white clip level to this white clip level. For this reason, the dynamic range of the video processing circuit of the video camera is limited, and for example, when the level of the video signal obtained from the subject is equal to or higher than the white clip level, such as a pattern on a white background, this pattern is It cannot be reproduced because it is removed. Therefore, in the video processing circuit, a white knee circuit is further provided in order to reproduce the gradation over a wide range of the input level within the finite dynamic level.

As shown in FIG. 11, the input / output characteristic is not represented by a straight line a having a constant inclination, but is bent at a prescribed white level (this bending point n is called a knee point), and this knee point n Is a straight line b having a gentler inclination than the straight line a, and the output level becomes constant at the white clip level or higher. The straight line b from the knee point n to a point (white clip point) that coincides with the white clip level is called a knee slope. As a result, the dynamic range of the video processing circuit was originally set to V _a up to the white clip level by the white clip circuit, but it is equivalent to the level V _w corresponding to the specified white level to the white clip level. The level up to level V _b higher than the level V _a is compressed between the specified white level and the white clip level, and the dynamic range is expanded to level V _b .
Therefore, the pattern in the white background can be reproduced even if the level of the video signal representing the white background is equal to or higher than the white clip of the white clip circuit and is below the white clip point of the white knee circuit.

Conventionally, as a specific example of such a white knee circuit, for example, as disclosed in Japanese Patent Laid-Open No. 57-148476, two slice circuits to which video signals are respectively supplied and outputs of these slice circuits are set to a predetermined value. The slice point of one of these slice circuits is made constant and the other slice level is made variable, and the knee point is defined by this slice level and the addition ratio of the adder circuit. It is known that the knee slope and the white clip point can be independently adjusted while being fixed at the white level.

However, even if they can be adjusted independently, if the slice levels of the two slice circuits are fixed, the white clip point changes at the same time as the knee slope is adjusted, and this change makes the compression range of the input level constant. It becomes something like. That is, when the slice level of the slice circuit is determined, the compression range of the input level is uniquely determined. As described above, if the compression range of the input level is set to a predetermined value, one of the slice level of the slice level circuit and the addition ratio of the addition circuit must be adjusted while the other is adjusted, which is very troublesome. Will be things.

On the other hand, a white knee circuit having a fixed knee slope in which the knee point can be variably set is well known, and the knee point is fixedly used. Therefore, although the gradation is reproduced within the range of the set input signal level, the gradation is white and the gradation is not reproduced outside the range. Further, since the knee slope is fixed, there is only a method of setting the knee point low in order to expand the gradation reproduction range.

However, in general, we do not want to perform level compression on an input signal of a certain specified level, so there is a limit to lowering the knee point setting, and naturally there is a limit to expanding the gradation reproducible range of the input signal. There was a problem that there was.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned problems of the prior art, and the level range in which the input signal is compressed is always a specified level or higher, and it is possible to set an arbitrary gradation reproducible level range easily and in the dynamic range. To provide a video signal processing circuit.

[Outline of Invention]

To achieve this object, the present invention makes it possible to change the knee point of a white knee circuit, and by changing the knee point according to the level of an input signal, the knee slope of each knee point is equivalently changed. The feature is that the required knee slope is obtained.

Example of Invention

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

FIG. 1 is a block diagram showing an embodiment of a video signal processing circuit according to the present invention, in which 1 is an input terminal of a video signal, 2 is a clamp circuit, 4 is a comparator, 5 is a variable resistor, and 6 is a phase. An inverting circuit, 7 a white knee circuit, 8 a control input terminal,
Reference numeral 9 is a variable resistor, and 10 is an output terminal.

In the figure, the video signal is input to the input terminal 1, and the black level is clamped by the clamp circuit 2. The clamp signal is input to the comparator 4 and the white knee circuit 7.

The white knee circuit has a fixed knee slope, but the knee point can be arbitrarily set by the DC voltage input to the control input terminal 8.

In the comparator 4, the control of the knee point is started when the input clamp video signal is equal to or higher than the DC voltage determined by the sliding position of the variable resistor 5. The output of the comparator 4 is input to the phase inverter 6 and inverted. The variable resistor 9 mixes its inverted signal with the normal signal of the comparator 4. This mixing ratio is determined by the sliding position of the variable resistor 9. The output of the variable resistor 9 is input as a control signal from the control input terminal 8 to the white knee circuit 7 and changes the knee point in response to the voltage thereof.

As a result of the above operation, the input / output characteristics of the input terminal 1 and the output terminal 10 are shown in FIG. 2 or 3 depending on the sliding position of the variable resistor 9.
It becomes a figure.

2 and 3 are input / output characteristic diagrams for explaining the operation.

The characteristic of FIG. 2 is when the sliding position of the variable resistor 9 is the upper side in FIG. 1, that is, when the mixing ratio of the inverted signal is large, and the input level is large as V ₁ , V ₂ , V ₃ and V _4. As it gets closer, the unique knee point is controlled in the lower direction. The unique knee slope for each knee point n ₁ , n ₂ , n ₃ , n ₄ is shown by a thin line that slopes upward from each knee point,
The knee points for the input levels V ₁ , V ₂ , V ₃ , V ₄ are n ₁ ,
Assuming that n ₂ , n ₃ and n ₄ , the intersections n ₁ , a, b, from the input levels V ₁ , V ₂ , V ₃ and V ₄ with the unique knee slopes corresponding to the broken lines parallel to the vertical axis, respectively. c is the output level for each input level. Therefore, the solid line connecting the intersection points n ₁ , a, b, and c is a nice slope. Therefore, the input level is V ₁ ,
When changing to V ₂ , V ₃ and V ₄ , the knee point changes to n ₁ , n ₂ , n ₃ and n ₄ , the knee slope becomes gentle and the effective range of the input level expands.

On the other hand, the characteristic of FIG. 3 is that the sliding position of the variable resistor 9 is the first.
In the figure, the lower side, that is, the case where the mixing ratio of the normal rotation signals is large, and the unique knee point is controlled to increase in accordance with the increase of the input level to V ₅ , V ₆ , V ₇ , and V ₈ , _{n 5, n 6, n 7} , n 8 and knee-point to be moved, can be steeper knee slope.

FIG. 4 is a circuit diagram showing a specific main part of the circuit configuration of FIG. 1, in which 11 is an input terminal of a video signal, 12, 15, 17 to 19, 21,
23,24,26 to 28,30,31 are transistors, 13 is a capacitor,
Reference numeral 16 is an input terminal for a clamp pulse, 20 is an output terminal, 22 is an input terminal for a knee point control voltage, and 25 and 29 are variable resistors.

In the figure, the video signal is input from the input terminal 11 to the transistor.
The output signal of the emitter supplied to the base of 12 is a transistor by the clamp pulse supplied to the input terminal 16.
15 switches and black level is clamped.
Transistors 17, 18 and 19 form a differential amplifier, amplify the clamp signal, and output it from output terminal 20. The transistor 21 conducts when the difference between the base potential of the transistor 21 and the collector potential of the transistor 19 is equal to or higher than the forward voltage, and forms a knee point. This knee point changes depending on the DC voltage at the input terminal 22. The transistors 30 and 31 form a comparator, compare the above clamp signal with the DC potential determined by the sliding position of the variable resistor 29, and output the larger potential of both to the base of the transistor 24. The variable resistor 29 causes the voltage V _{1 in} FIG. 2 and V _{5 in} FIG.
give. Transistors 24, 26 and 27 form a differential amplifier, which inverts and forward-amplifies the output signal of the comparator. The variable resistor 25 mixes the inverted and forward rotation signals and gives a signal of a mixing ratio determined by the sliding position to the knee point control input terminal 22 via the transistor 23. As described above, depending on the sliding position of this variable resistor, the characteristic shown in FIG. 2 or 3 can be obtained.

Next, another embodiment of the present invention will be described with reference to FIGS.

FIG. 5 is a block diagram showing another embodiment of the video signal processing circuit according to the present invention, and FIG. 6 is an input / output characteristic diagram for explaining the operation thereof, wherein 1 is an input terminal of a video signal and 2 clamps. Reference numeral 4 is a comparator, 5 and 9 are variable resistors, 6 is a phase inversion circuit, 7 is a white knee circuit, 8 is an input terminal of a knee point control voltage, 10 is an output terminal, and 32 is a peak detector.

In FIG. 5, the video signal is input to the input terminal 1, and the clamp circuit 2 clamps the black level. The clamp signal is the peak detector 32 and the white knee circuit 7
Entered in.

The peak value of the clamp signal (for example, within one field) is detected by the peak detector 32, and its DC voltage is input to the comparator 4. This comparator compares the DC potential determined by the sliding position of the variable resistor 5 with the output voltage of the peak detector, and the larger voltage is output to the phase inverter 6. Then, the signal inverted by the phase inverter is input to the knee point control input terminal 8 via the variable resistor 9, and responds to the input voltage to control the knee point.

With the above operation, the input / output characteristics of the input terminal 1 and the output terminal 10 are as shown in FIG.

In FIG. 6, the starting voltage at which the knee point is controlled by the peak value of the input video signal level is V _5, which is set by the variable resistor 5. Further, the knee point is set to n ₆ when the peak value is V ₆ , similarly to n ₇ when V ₇ and n ₈ when V ₈ is set by the variable resistor 9.
In this way, by controlling the knee point from the peak value of a predetermined level or higher of the input video signal to the direction in which the value becomes higher, the gradation of the highlight part of the video signal is made finer when the peak value is small. (Precisely) When the peak value is large, the gradation is roughly expressed. As a result, it is possible to express the gradation of the video signal at all levels within the white clip level.

FIG. 7 is a circuit diagram showing a specific main part of the circuit configuration of FIG. 5, in which 33 and 35 are variable resistors, 34, 36 and 37 to 39 are transistors, and the same reference numerals in FIG. The same part is shown.

In the figure, the clamp circuit and the white knee circuit are the fourth.
The circuits are the same as those in the figure, and the description of their operation is omitted.
The clamped video signal is applied to the base of transistor 39 to charge capacitor 38 to the peak voltage of its emitter output voltage. The DC potential determined by the sliding position of the variable resistor 35 is compared with the peak voltage by the comparator composed of the transistors 36 and 37, and the larger one is output. Then, the phase is inverted by the transistor 34 and supplied to the knee point control input terminal 22 via the transistor 23 and the variable resistor 33.

By the above operation, the knee point is changed according to the peak value of the video signal which is determined by the sliding position of the variable resistor 35 or more, and the input / output characteristic shown in FIG. 6 is realized.

Next, still another embodiment of the present invention will be described with reference to FIGS.

FIG. 8 is a block diagram showing still another embodiment of the video signal processing circuit according to the present invention, and FIG. 9 is an input / output characteristic diagram for explaining the operation thereof, in which 1 is a video signal input terminal, 2 is a clamp circuit, 4 is a comparator, 5 is a variable resistor,
6 is a phase inversion circuit, 7 is a white knee circuit, 8 is a knee point control input terminal, 10 is an output terminal, 32 is a peak detector, and 40 is a multiplier.

In FIG. 8, 1, 2, and 3 are the same as in FIG. The clamped video signal is supplied to the white knee circuit 7, the comparator 4 and the peak detector 32.

The comparator 4 compares the DC potential determined by the sliding position of the variable resistor 5 with the DC potential of the video signal, and outputs the larger one. Then, the signal inverted by the phase inverter 6 and the normal signal are supplied to different multipliers 40. The peak detector 32 detects the peak of the clamp signal,
It is supplied to the multiplier 40. When the peak value is large, an inverted signal of the clamp signal is mainly supplied to the knee point control input terminal 8 and the input / output characteristic of l ₃ shown in FIG. 9 is obtained.
On the contrary, when the peak value is small, the normal signal of the clamp signal is mainly supplied to 8, and the input / output characteristic of l ₂ shown in FIG. 9 is obtained.

With the above operation, when the peak of the input video signal is small, the knee slope becomes steep so that the white part is reproduced finely, and when the peak of the input video signal is large, the knee slope becomes gentle. As a result, the range of input levels in which gradation can be reproduced is expanded.

FIG. 10 is a circuit diagram showing a specific main part of the circuit configuration of FIG. 8, 41 and 42 are variable resistors, 43 to 46 are transistors, and 4
Reference numeral 7 is a capacitor, and the same symbols as those in FIG. 4 indicate the same portions.

In the figure, the clamp circuit and the white knee circuit are the fourth
The description is omitted because it is similar to the figure.

The clamped video signal is supplied to the base of the transistor 48, and its peak value is detected by the capacitor 47. The transistors 43 and 44 form a comparator, and the collector current of the transistor 44 is based on the base potential of the transistor 43 determined by the sliding position of the variable resistor 41.
Flows when the clamp signal supplied to the base of
The multiplier of transistors 45 and 46 limits the peak value supplied to the base of transistor 46. The collector voltage of the transistor 45 is supplied to the knee point control input terminal 22 via the transistor 23.

With the above operation, the control amount of the knee point by the video signal changes according to the peak value of the video signal, and the input / output characteristic of FIG. 9 is obtained.

〔The invention's effect〕

As described above, according to the present invention, as the characteristics of the white knee circuit, the knee point and the white clip level can be fixed and the knee slope with an arbitrary inclination can be set. It is possible to arbitrarily set the level range in which the gradation of the video signal can be reproduced without compressing the following part, and it is possible to express without impairing the gradation in the highlight part of the video signal. It is possible to provide a video signal processing circuit having an excellent function by solving the above-mentioned problems of the prior art.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a video signal processing circuit according to the present invention, FIGS. 2 and 3 are input / output characteristic diagrams for explaining the operation of the embodiment shown in FIG. 1, and FIG. FIG. 5 is a circuit diagram showing a specific main part of the circuit configuration of FIG. 1, FIG. 5 is a block diagram showing another embodiment of a video signal processing circuit according to the present invention, and FIG. 6 is an implementation shown in FIG. FIG. 7 is an input / output characteristic diagram for explaining the operation of the example, FIG. 7 is a circuit diagram showing a specific main part of the circuit configuration of FIG. 5, and FIG. FIG. 9 is an input / output characteristic diagram for explaining the operation of the embodiment shown in FIG. 8. FIG. 10 is a circuit diagram showing a specific main part of the circuit configuration of FIG. FIG. 11 is an input / output characteristic diagram of the white knee circuit in the conventional video signal processing circuit. 1 ... input terminal, 2 ... clamp circuit, 4 ... comparator,
5,9 ... Variable resistor, 6 ... Phase inversion circuit, 7 ... White knee circuit, 10 ... Output terminal, 32 ... Peak detection circuit, 40 ... Multiplier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-61-251375 (JP, A) JP-A-57-148476 (JP, A) Actually open 57-111119 (JP, U) Actual-open Sho-56- 37575 (JP, U)

Claims (1)

[Claims] 1. A video signal processing circuit comprising a white clip circuit for clipping a video signal at a predetermined white clip level exceeding a specified white level of the video signal, wherein a DC level of an input video signal is a predetermined level. A clamp circuit for clamping the input video signal, a detection circuit for detecting a level in the output video signal of the clamp circuit that exceeds a predetermined reference level equal to or higher than the specified white level, and a detection level by the detection circuit. And a control signal forming circuit for forming a control signal according to the adjusted detection level, and an output video signal of the clamp circuit are supplied. , A constant gain is set, and in the part of the output video signal above the constant reference level, the level of the control signal is A white knee circuit whose gain changes in accordance with the characteristics of the white knee circuit has a knee point at the constant reference level, and a portion of the output video signal of the clamp circuit above the constant reference level. The present invention is characterized in that a knee slope whose slope is variable according to the adjustment of the detection level by the detection circuit in the control signal forming circuit is presented, and the output video signal of the white knee circuit is supplied to the white clip circuit. Video signal processing circuit.