JPH089198A - Gamma correction circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] Providing a gamma correction circuit that can improve accuracy. [Structure] The non-linear amplifier 2 non-linearly amplifies the input signal from the input terminal 1 and supplies it to the adder 4, and the linear amplifier 3 linearly amplifies the input signal from the input terminal 1 to the adder 4. Supply. The adder 4 is a non-linear amplifier 2
And the output of the linear amplifier 3 are added and output via the output terminal 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction circuit for gamma-correcting a video signal, and more particularly to a gamma correction circuit having a linear amplification means and a non-linear amplification means.

[0002]

2. Description of the Related Art Conventionally, as an image display device, there is a monitor device using a cathode ray tube that displays an image by scanning an accelerated voltage to irradiate a phosphor formed on a cathode and causing a light emitter to emit light. in use. In these monitor devices, the level of the luminance signal of the input image signal and the luminance of the light emission of the phosphor on the cathode ray tube are not in a proportional relationship,

Therefore, in video equipment such as a video tape recorder for recording and reproducing images, a gamma correction circuit for performing gamma correction of a video signal is used in order to improve reproducibility of an image displayed on a cathode ray tube. ing. In this gamma correction circuit, gamma correction is performed on the supplied video signal according to the non-linear gamma characteristic.

The gamma characteristic is a continuous function, but in general, a characteristic obtained by polygonal approximation of the gamma characteristic is used.
For example, as shown in FIG. 7, the gamma correction circuit that realizes the gamma characteristic approximated to the broken line includes a transistor Q41 to which a video signal is supplied via an input terminal 31, three diodes D1, D2 and D3, and an output transistor. Equipped with Q42 etc.

In this gamma correction circuit, the diodes D1, D2 and D3 are sequentially turned on according to the voltage of the input video signal, whereby the gain for the input video signal changes, and as shown in FIG. In addition, it has a linear input / output characteristic.

Specifically, in this gamma correction circuit, the diode D1 is turned on at the point a shown in FIG.
The diode D2 is turned on at the point b, and the diode D3 is turned on at the point c. The input voltage at the points a to c at which the diodes D1 to D3 turn on are the variable resistors R55 and R5.
It can be set by adjusting the values of R6 and R57.

The slope of the input / output characteristics after the diodes D1 to D3 are turned on is determined by the ratio of the currents Ia, Ib and Ic flowing into the diodes D1 to D3 and the current Id flowing into the resistor R51. That is, the diodes D1 to
When D3 is turned on, the emitter resistance of the transistor Q41 changes, and this change in emitter resistance changes the voltage supplied to the base of the transistor Q42.

A current I flowing into the diodes D1 to D3
Since the ratio of a, Ib, Ic and the current Id flowing into the resistor R51 is determined according to the values of the resistor 51 and the variable resistors R52, R53, R54, this gamma correction circuit adjusts the values of the variable resistors R52 to R54. Then, the slope of the input / output characteristic can be changed.

[0009]

However, since the gamma correction circuit shown in FIG. 7 described above approximates the gamma characteristic with three inflection points of points a to c, the correction accuracy is insufficient. In addition, there is a problem in that the accuracy of the correction is reduced because the video signal with a small change in shading is corrected substantially linearly.

As another gamma correction circuit, a correction circuit using the non-linearity of the transistor base-emitter voltage and the emitter current is known. In this gamma correction circuit, a signal based on a video signal is input to the base of a transistor, an emitter current based on this base voltage is taken out as a voltage, and is output as an output signal.

In this gamma correction circuit, the maximum value of the base-emitter voltage of the transistor is 0.7 to 0.8V.
However, since its dynamic range is small, its output is amplified by an amplifier. Further, since the non-linearity of the transistor is used to obtain the gamma characteristic, the signal-to-noise ratio (hereinafter referred to as S / N) is poor, and there is a problem that the S / N is further deteriorated by amplification by the amplifier.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a gamma correction circuit which can perform gamma correction with high accuracy without lowering the signal-to-noise ratio.

[0013]

A gamma correction circuit according to the present invention comprises a linear amplification means for linearly amplifying a supplied video signal, a non-linear amplification means for non-linearly amplifying the supplied video signal, and a linear amplification. Means and an adding means for adding the outputs of the non-linear amplifying means.

Further, the gamma correction circuit according to the present invention is characterized in that the linear amplification means has an adjustment means for adjusting the amplification factor.

Further, the gamma correction circuit according to the present invention is characterized in that the non-linear amplification means has an adjustment means for adjusting the amplification factor.

Further, the gamma correction circuit according to the present invention is characterized in that the non-linear amplification means non-linearly amplifies the video signal supplied by the non-linear characteristics of the base-emitter voltage and the emitter current of the transistor.

[0017]

In the gamma correction circuit according to the present invention, the linear amplification means linearly amplifies and outputs the supplied video signal, and the non-linear amplification means non-linearly amplifies and outputs the supplied video signal. The adding means adds the outputs of the linear amplifying means and the non-linear amplifying means and outputs the result.

Further, in the gamma correction circuit according to the present invention,
The adjusting means of the linear amplifying means adjusts the amplification factor of the linear amplifying means, the linear amplifying means linearly amplifies the supplied video signal and supplies it to the adding means, and the adjusting means of the non-linear amplifying means amplifies the non-linear amplifying means. The rate is adjusted, and the non-linear amplification means non-linearly amplifies the supplied video signal and supplies it to the addition means.

The addition means adds the outputs of the linear amplification means and the non-linear amplification means and outputs the result. As a result, this gamma correction circuit performs gamma correction on the supplied video signal.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the gamma correction circuit according to the present invention will be described in detail below with reference to the drawings.

A first gamma correction circuit to which the present invention is applied is, for example, as shown in FIG. 1, a non-linear amplifier (hereinafter referred to as a non-linear amplifier) that non-linearly amplifies an input signal (video signal) supplied from an input terminal 1. ) 2 and input terminal 1
A linear amplifier (hereinafter, referred to as a linear amplifier) 3 that linearly amplifies a video signal supplied from the adder 4, and an adder 4 that adds and outputs the outputs of the non-linear amplifier 2 and the linear amplifier 3
It has and.

The non-linear amplifier 2 non-linearly amplifies the video signal supplied from the input terminal 1 to add it to the adder 4
The linear amplifier 3 linearly amplifies the video signal supplied from the input terminal 1 and supplies it to the adder 4.

The adder 4 adds the outputs of the non-linear amplifier 2 and the linear amplifier 3 and outputs the result via the output terminal 5.

As a result, this gamma correction circuit performs gamma correction on the supplied video signal.

Next, the second gamma correction circuit to which the present invention is applied will be described. This gamma correction circuit is shown in FIG.
As shown in its concrete configuration, a non-linear amplifier 12 that non-linearly amplifies the video signal supplied from the input terminal 11, a linear amplifier 13 that linearly amplifies the video signal supplied from the input terminal 11, and a non-linear amplifier Adder 14 that adds the outputs of amplifier 12 and linear amplifier 13 and outputs
It has and.

In this gamma correction circuit, a resistor R4 to which the outputs of the non-linear amplifier 12 and the linear amplifier 13 are connected instead of the adder 4 of the gamma correction circuit shown in FIG.
It has an adding unit 14 consisting of. Then, the addition unit 14
Output current from the non-linear amplifier 12 and the linear amplifier 13 and is converted into a voltage while being added to the output terminal 1
5 is output.

The non-linear amplifier 12 inverts the input signal and compresses the output of the inverting compression unit 111 and the inverting compression unit 111 in a non-linear manner to add the output signal to the addition unit 1.
4 is provided with a non-linear amplification unit 112 and the like.

The inverting compression section 111 is a differential amplifier including a transistor Q1 supplied with an input signal, a transistor Q2 supplied with a bias voltage V1, and a resistor R1 connected between the emitters of the transistors Q1 and Q2. The input signal is inverted and compressed by outputting the collector voltage corresponding to the voltage supplied to the bases of the transistors Q1 and Q2 as the voltage via the resistors R2 and R3.

The non-linear amplification section 112 includes a transistor Q3 to which the output of the transistor Q2 is supplied, a transistor Q4 to which the output of the transistor Q1 is supplied, and the like, which non-linearly amplifies the difference between the output voltages of the transistor Q1 and the transistor Q2. And output it.

The linear amplifier 13 includes a differential amplifier composed of a transistor Q5 to which an input signal is supplied, a transistor Q6 to which a bias voltage V2 is supplied, and the like, and amplifies a difference between the input signal and the bias voltage V2. Has become.

The operation of this gamma correction circuit will be described. The inverting compression unit 111 inverts the supplied input signal, compresses the input signal, and supplies the compressed signal to the nonlinear amplification unit 112. Specifically, since the resistor R2 connected to the collector of the transistor Q1 and the resistor R3 connected to the collector of the transistor Q2 have the same value (R2 = R3), the input supplied to the inverting compression unit 111. Signal is R2 / R
It is compressed at a ratio of 1.

The transistor Q1 converts the collector current I1 corresponding to the input signal supplied to its base into a voltage by the resistor R2 and supplies the voltage to the base of the transistor Q4, and the transistor Q2 receives the input signal supplied to its base. Is converted into a voltage by the resistor R3 and supplied to the base of the transistor Q3.

The non-linear amplification section 112 includes an inverting compression section 1
A non-linear amplification of the difference between the output voltages from the adder 11 and the adder 14
Supply to. Specifically, when the voltage supplied to the base of the transistor Q3 is V _R3 and the voltage supplied to the base of the transistor Q4 is V _R2 , the collector current I3 of the transistor Q3 and the collector current I of the transistor Q4 are given.
The ratio of 4 is expressed by the following equation from Shockley's equation.

[0034]

[Equation 1]

In equation 1, these transistors Q3 and Q
Since the base potential difference (V _R3 −V _R2 ) of 4 is obtained by inverting and compressing the input signal by the inverting compression unit 111 as described above, it increases as the level of the input signal increases. Therefore, if the sum of the emitter currents of the transistors Q3 and Q4 is constant, the collector current I4 of the transistor Q4 has an exponential change curve with respect to the potential difference (V _R3 −V _R2 ) of the base. In this non-linear amplification section 112, the collector current I4 is supplied to the addition section 14 and converted into a voltage.

On the other hand, the linear amplifier 13 linearly amplifies the supplied input signal and supplies it to the current amplifier 14.

Specifically, when the input signal and the bias voltage V2 are supplied to the bases of the transistors Q5 and Q6, the collectors of the transistors Q5 and Q6 are supplied with the input signal and the bias voltage V2, respectively. Collector currents I5 and I6 based on The linear amplifier 13 supplies the collector current of the transistor Q6 as an output current to the current adder 14.
The gain of the differential amplifier including the transistor Q5 and the transistor Q6 is R4 / R5.

The adder 14 adds the collector current I4 of the transistor Q4 and the collector current I6 of the transistor Q6 and outputs the result as a voltage. Specifically, the output terminal 15
The voltage Vout of the output signal output from Vout = Vcc-R4 (I4 + I6)

As a result, this gamma correction circuit has, for example, the input / output characteristic (gamma characteristic) shown in FIG. The gamma characteristic shown in FIG. 3 has an input signal voltage of about 2.3V.
In the region where the input voltage and the output voltage have a non-linear relationship (hereinafter referred to as the non-linear region), the output voltage changes non-linearly with respect to the input signal, and the voltage of the input signal is about 2.3 V or more. The output voltage changes linearly with respect to the input signal in a region where the voltages have a linear relationship (hereinafter referred to as a linear region).

As a result, this gamma correction circuit has a smooth input / output characteristic (gamma characteristic) that continuously changes and has a higher accuracy than a gamma correction circuit that performs conventional polygonal line approximation. Corrections can be made.

Next, a third gamma correction circuit to which the present invention is applied will be described. The second gamma correction circuit described above has a constant gamma characteristic, but the third gamma correction circuit can change the gamma characteristic according to an adjustment voltage supplied from the outside.

This gamma correction circuit, as shown in FIG. 4, for example, nonlinearly amplifies the input signal (video signal) supplied from the input terminal 21, and the input signal supplied from the input terminal 21. A linear amplifier 23 that linearly amplifies, and an addition unit 24 that adds and outputs the outputs of the non-linear amplifier 22 and the linear amplifier 23 are provided.

The non-linear amplifier 22 includes an inverting compression section 221 for inverting and compressing the input signal, a correction control section 222 for adjusting the compression ratio of the inverting compression section 221, and an inverting compression section 221 for which the compression ratio is adjusted. A non-linear amplification unit 223 that amplifies the output nonlinearly and supplies the output signal to the addition unit 24 is provided.

The inverting compression section 221 is a differential amplifier including a transistor Q11 supplied with an input signal, a transistor Q12 supplied with a bias voltage V3, and a resistor R11 connected between the emitters of the transistors Q11 and Q12. A collector voltage corresponding to the voltage supplied to the bases of the transistors Q11 and Q12,
By outputting as a voltage via R13, the input signal is inverted and compressed.

The correction control section 222 is composed of two sets of transistors Q13, Q14, Q15 and Q16, which are so-called balanced modulation circuits and each of which is emitter-coupled.
One differential amplifier is provided, and the compression ratio of the inverting compression unit 221 is adjusted according to the adjustment voltage supplied to the non-linear adjustment terminals 26 and 27.

The non-linear amplifier 223 includes a transistor Q17 to which the output of the transistor Q15 is supplied and a transistor Q18 to which the output of the transistor Q14 is supplied.
And the like, and transistor Q14 and transistor Q15
The difference in the output voltage from is amplified non-linearly and output.

The linear amplifier 23 adjusts the amplification factor (hereinafter referred to as gain) of the output signal in accordance with the differential amplifier 231 for amplifying the difference between the input signal and the bias voltage V4 and the adjustment voltage supplied from the outside. It has a correction control unit 232 and the like.

The differential amplifier 231 is composed of a transistor Q19 to which an input signal is supplied, a transistor Q20 to which a bias voltage V4 is supplied, and the like, and amplifies the difference between the input signal and the bias voltage V4. .

The correction controller 232 is composed of a transistor Q21 and a transistor Q22 which are emitter-junctioned,
The gain of the linear amplifier 23 is adjusted according to the adjustment voltage supplied to the linear adjustment terminals 28 and 29.

The adder 24 comprises a resistor R14 connected to the collectors of the transistor Q18 and the transistor Q21, adds the collector current I18 of the transistor Q18 and the collector current I21 of the transistor Q21, and outputs it as a voltage to the output terminal 25. It has become.

The operation of this gamma correction circuit will be described. The inverting compression unit 221 inverts and compresses the supplied input signal. Specifically, the transistor Q1
Resistor R12 and transistor Q connected to the collector of 4
The same value as the resistor R13 connected to the collector of 15 (R
Since 12 = R13), the input signal supplied to the inverting compression unit 221 is compressed at the ratio of R12 / R11.

The correction control unit 222, in accordance with the potential supplied to the non-linear adjustment terminals 26 and 27, the inverting compression unit 22.
The compression ratio of 1 is adjusted, and the input signal with the adjusted compression ratio is supplied to the non-linear amplification unit 223.

Specifically, assuming that the voltage supplied to the non-linear adjustment terminal 26 is VN1 and the adjustment voltage supplied to the non-linear adjustment terminal 27 is VN2, the transistor Q1
3, the ratio of collector currents I13 and I14 of Q14 and the collector currents I15 and I16 of transistors Q15 and Q16.
The ratio of is expressed by the following equation from Shockley's equation.

[0054]

[Equation 2]

As shown in the equations 3 and 4, the adjustment voltages VN1 and VN2 supplied to the non-linear adjustment terminals 26 and 27, respectively.
According to the ratio of collector current I14 to collector current I13 and collector current I15 of collector current I16.
The ratio to changes.

Here, the collector current I11 of the transistor Q11 is the sum of the collector currents I13 and I14 of the transistors Q13 and Q14, and the transistor Q1
The collector current I12 of 2 is the transistor Q15, Q1.
It is the sum of the collector currents I15 and I16 of 6. As a result, the collector current I1 is changed according to the voltages VN1 and VN2.
1 and collector current I14, or collector current I
When the ratio between 12 and the collector current I15 changes, the compression ratio in the inverting compression unit 221 is adjusted.

The non-linear amplification section 223 is the inverting compression section 2
A non-linear amplification of the difference between the output voltages from the adder 21 and the adder 24
Supply to. Specifically, if the voltage supplied to the base of the transistor Q17 is VR13 and the voltage supplied to the base of the transistor Q18 is VR12, the ratio of the collector current I17 of the transistor Q17 and the collector current I18 of the transistor Q18 is It is expressed by the following equation from the Ray's equation.

[0058]

[Equation 3]

In equation 5, this transistor Q17,
Since the base potential difference (VR13-VR12) of Q18 is obtained by inverting and compressing the input signal by the inverting compression unit 221, as described above, it increases as the level of the input signal increases. Therefore, assuming that the sum of the emitter currents of the transistors Q17 and Q18 is constant, the transistor Q18
Collector current I18 of the base is the potential difference of the base (VR13-VR
It has an index change curve for 12). In this non-linear amplification section 223, the collector current I18 is added to the addition section 24.
It is supplied to and converted into voltage.

On the other hand, the differential amplifier 231 amplifies the difference between the input signal and the bias voltage V4. Specifically, when the input signal and the bias voltage V4 are supplied to the bases of the transistors Q19 and Q20, the transistor Q1
Collector currents I19 and I20 based on the input signal supplied to the base and the bias voltage V4 respectively flow into the collector of the transistor 9 and the collector of the transistor Q20. The linear amplifier 23 supplies the collector current of the transistor Q20 as an output current to the current adder 24 via the correction controller 232.

The correction controller 232 uses the linear adjustment terminal 2
The gain is adjusted in accordance with the adjustment voltage supplied to 8 and 29. Specifically, assuming that the voltage supplied to the linear adjustment terminal 28 is VL1 and the adjustment voltage supplied to the linear adjustment terminal 29 is VL2, the collector currents I22 and I23 of the transistors Q21 and Q22 are calculated from the Shockley equation. It is expressed by the following equation.

[0062]

[Equation 4]

As shown in Equation 6, the linear adjustment terminal 2
The ratio of the collector current I21 to the collector current I20 changes according to the adjustment voltages VL1 and VL2 supplied to the output terminals 8 and 29. Since the emitters of the transistors Q21 and Q22 are connected to the collector of the transistor Q20, the collector current I20 of the transistor Q20 is the collector currents I21 and I22 of the transistors Q21 and Q22.
Is the sum of

From the above equation 6, since I21 = εI22, I21 = I20 / (1 + ε), and the gain G for the input signal is expressed by the following equation.

[0065]

[Equation 5]

Since ε in the equation 7 changes according to the adjustment voltages VL1 and VL2 supplied to the linear adjustment terminals 28 and 29 as described above, the gain of the linear amplifier 23 is adjusted by the adjustment voltage. .

The adder 24 adds the collector current I18 of the transistor Q18 of the non-linear amplifier 22 and the collector current I21 of the transistor Q21 of the linear amplifier 23, and outputs it as a voltage. Specifically, the voltage Vout of the output signal output from the output terminal 25 is as follows: Vout = Vcc-R14 (I18 + I21).

As a result, this gamma correction circuit has a gamma characteristic indicated by the symbol Y in FIG. 5 for the input signal and the output signal.

Here, when the voltage between the non-linear adjustment terminals 26 and 27 is changed, the input / output voltage characteristic of this gamma correction circuit changes the gain in the above non-linear region as shown in FIG. . Also, the linear adjustment terminal 2
When the voltage between 8 and 29 is changed, in the input / output voltage characteristic of this gamma correction circuit, the gain in the above-mentioned linear region changes as shown in FIG.

Specifically, the non-linear adjustment terminals 26, 2
The voltage between 7 is set to ΔVA (ΔVA = VN1−VN2), and the voltage between the linear adjustment terminals 28 and 29 is set to ΔVB (ΔVB = VL1).
-VL2), the input / output voltage characteristic when ΔVA = 0 and ΔVB = 0 is indicated by the symbol Y in FIG. 5, and when ΔVA is increased to ΔVA = 0.03V, the symbol Z in FIG. As shown, when the gain in the non-linear region increases and ΔVA is decreased to ΔVA = −0.03V, the gain in the non-linear region decreases as indicated by the symbol X in FIG.

Further, by increasing ΔVB, ΔVB = 0.0
If it is set to 3 V, the gain in the linear region increases as indicated by the symbol X in FIG. 5, and ΔVB is decreased to ΔVB = −
When it is set to 0.03V, the gain in the linear region decreases as indicated by the symbol Z in FIG.

As a result, the gamma correction circuit can adjust the gamma characteristic according to the voltage from the outside, and when it is used in an image display device having different reproducibility or an image pickup device having different sensitivity, for example. The gamma characteristic can be adjusted to match the characteristic of the target device, and gamma correction with improved accuracy can be performed.

In the third gamma correction circuit described above, the correction control units 222 and 232, the non-linear amplification unit 223, and the like are described as being configured by transistor pairs that are emitter-coupled, but this transistor pair has a signal-to-noise ratio ( Hereinafter, it will be referred to as S / N).

That is, the actual transistor has an output resistance at the emitter, and this output resistance is equivalently expressed as an emitter resistance connected to the emitter. In particular,
In the case of an emitter-coupled transistor pair, the emitter currents from the two transistors flow to the emitter resistance of each transistor, so the thermal noise due to this emitter resistance reduces the S / N.

Therefore, in order to improve the S / N, the non-linear amplification section 223 of the gamma correction circuit shown in FIG. 4 described above.
For example, as shown in FIG. 6, a transistor Q30 to which the output of the transistor Q15 shown in FIG. 4 is supplied.
And three so-called diode-connected transistors Q connected in series to the emitter of the transistor Q30
31, Q32, Q33, the transistor Q40 to which the output of the transistor Q14 shown in FIG. 4 is supplied, and three diode-connected transistors Q41, Q42 connected in series to the emitter of the transistor Q40.
It may be configured to include Q43.

By the way, when the output voltage Vout when the input voltage Vin is supplied to the differential amplifier composed of the emitter-coupled transistor pair is expressed by the following equation, where R is the output resistance and Re is the emitter resistance of each transistor. Like

[0077]

[Equation 6]

Here, assuming that the noise voltage generated inside the transistor is Vnb, the noise output voltage Vn is similarly obtained.
Is as follows.

[0079]

(Equation 7)

Here, the output resistance R is set to 6.67 kΩ,
If the emitter resistance Re is 260Ω, the noise output voltage Vn = 12.8Vnb, and the noise is amplified with a gain of about 22 dB.

The non-linear amplification section 223 shown in FIG.
Are transistors Q31 to Q3 which are diode-connected to the emitters of the transistors Q30 and Q40.
3 and transistors Q41 to Q43,
Equivalently, the emitter resistance Re is quadrupled. That is, in the above expression 10, Vn = 3.2Vnb, the gain for noise is about 10 dB, and the noise gain can be reduced by about 12 dB.

On the other hand, since the gain for the input signal Vin is the gain of the differential amplifier, there is almost no change from the equation 9 even if the emitter-coupled transistors are multistage. As a result, the non-linear amplification unit 223 can improve the S / N as compared with the conventional one.

Similarly, by making the emitter-coupled transistors of the correction control units 222 and 232 multistage, the S / N ratio can be improved similarly to the non-linear amplification unit 223.

The present invention is not limited to the above-described embodiments, but, for example, in the above-described embodiments, the non-linear amplifier 22 and the linear amplifier 23 are described as having a correction control section for adjusting the gain, respectively. Needless to say, one of the non-linear amplifier 22 and the linear amplifier 23 may have a configuration having a correction control unit, and various changes can be made.

Further, in the above-described embodiment, an example in which the non-linear amplifier amplifies the input signal non-linearly due to the non-linear characteristic of the base-emitter voltage of the transistor and the emitter current has been described. If it can be amplified to, a logarithmic amplifier using a so-called operational amplifier or the like may be used, and the same effect as described above can be obtained.

[0086]

In the gamma correction circuit according to the present invention, the adjusting means of the linear amplifying means adjusts the amplification factor of the linear amplifying means, and the linear amplifying means linearly amplifies the supplied video signal and supplies it to the adding means. Then, the adjusting means of the non-linear amplifying means adjusts the amplification factor of the non-linear amplifying means, and the non-linear amplifying means non-linearly amplifies the supplied video signal and supplies it to the adding means, so that a smooth gamma which continuously changes. It is possible to perform gamma correction which has characteristics and is improved in accuracy.

In the present invention, the adjusting means of the linear amplifying means adjusts the amplification factor of the linear amplifying means, and the linear amplifying means linearly amplifies the supplied video signal and supplies it to the adding means. When used in image display devices with different reproducibility or image pickup devices with different sensitivities, the gamma characteristics can be adjusted to match the characteristics of the target device, and gamma correction with improved accuracy is performed. be able to.

According to the present invention, the adjusting means of the non-linear amplifying means adjusts the amplification factor of the non-linear amplifying means, and the non-linear amplifying means non-linearly amplifies the supplied video signal and supplies it to the adding means. When used in image display devices with different reproducibility or imaging devices with different sensitivities,
The gamma characteristic can be adjusted to match the characteristic of the target device, and gamma correction with improved accuracy can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a gamma correction circuit to which the present invention is applied.

FIG. 2 is a block diagram showing a detailed configuration of a gamma correction circuit to which the present invention is applied.

FIG. 3 is a diagram showing input / output characteristics of the gamma correction circuit.

FIG. 4 is a block diagram showing a detailed configuration of another gamma correction circuit to which the present invention is applied.

FIG. 5 is a diagram showing input / output characteristics of the gamma correction circuit.

FIG. 6 is a circuit diagram showing another configuration of a non-linear amplification section which constitutes the gamma correction circuit.

FIG. 7 is a block diagram showing a configuration of a conventional gamma correction circuit.

FIG. 8 is a diagram showing input / output characteristics of the conventional gamma correction circuit.

[Explanation of symbols]

 1,11,21 Input terminal 2,12,22 Non-linear amplifier 3,13,23 Linear amplifier 4 Adder 5,15,25 Output terminal 14,24 Adder section 26,27 Non-linear adjustment terminal 28,29 Linear adjustment terminal 111, 221 Inversion compression unit 112,223 Non-linear amplification unit 222,232 Correction control unit 231 Differential amplification unit

Claims (4)

[Claims] 1. A gamma correction circuit for gamma-correcting a video signal, comprising: a linear amplification means for linearly amplifying the supplied video signal; and a non-linear amplification means for non-linearly amplifying the supplied video signal, A gamma correction circuit comprising: a linear amplification means and an addition means for adding the outputs of the non-linear amplification means. 2. The gamma correction circuit according to claim 1, wherein the linear amplification means has an adjustment means for adjusting an amplification factor. 3. The gamma correction circuit according to claim 1, wherein the non-linear amplification means has an adjustment means for adjusting an amplification factor. 4. The gamma correction circuit according to claim 3, wherein the non-linear amplification means non-linearly amplifies the video signal supplied by the non-linear characteristic of the base-emitter voltage and the emitter current of the transistor.