JPH10276348A - Video signal processing circuit, camera employing it and gamma correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the video signal processing circuit that realizes both gradation emphasis in the vicinity of a black level and emphasized S/N functions by means of same signal processing while making the circuit scale small, to provide the camera employing the circuit and to provide the gamma correction method. SOLUTION: The gamma correction circuit is formed to be a ROM table system gamma correction circuit provided with a gamma ROM 11 that generates data of a standard gamma curve characteristic with respect to a received correction object Y signal, with a correction data generating section 12 that generates correction data to correct a characteristic of an area around a black level of a standard gamma curve characteristic and with a subtractor 13 that subtracts the correction data from data of the standard gamma curve characteristic. Then both gradation emphasis in the vicinity of a black level and emphasized S/N functions are realized by means of same signal processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit, a camera using the same, and a gamma correction method, and more particularly to a video signal processing circuit including a circuit for gamma (γ) correction of a video signal and using the same. The present invention relates to a camera and a gamma correction method.

[0002]

2. Description of the Related Art In order to correctly express the gradation of a subject, the gamma of the entire system from the video camera to the monitor must be set to 1. Therefore, for example, C
A gamma correction circuit is provided in a video signal processing circuit that processes a video signal output from a CD (Charge Coupled Device) image pickup device so that the overall gamma characteristic becomes 1.
In this gamma correction circuit, a ROM (read-only memory) table method and a linear approximation method are known as methods for generating data having a standard gamma curve characteristic for an input video signal to be corrected.

FIG. 12 shows a conventional example of a ROM table type gamma correction circuit. The gamma correction circuit according to this conventional example has a luminance (Y) output from a CCD image sensor, for example.
A signal to be corrected is used to perform gamma correction on the input Y signal. A gamma RO having standard gamma curve characteristic data for the Y signal as a table is provided.
M101; a knee generator 102 for generating data having knee characteristics with respect to the Y signal; a standard level detection circuit 103 for detecting that the level of the Y signal has exceeded a predetermined standard level; And a selector 104 for selecting output data of the gamma ROM 101 and selecting and outputting output data of the knee generating unit 102 based on the output of the standard level detection circuit 103 when the level of the input Y signal is higher than the standard level. ing.

[0004] By the way, in the gamma correction circuit at present, a gamma curve characteristic having a characteristic shape is drawn depending on an application to be used. In the gamma curve characteristic, the curve characteristic of the low level region of the gamma curve characteristic depends on whether the gradation is emphasized for the data in the low level area, that is, the data near black, or the S / N is emphasized while suppressing the noise level. Will change. That is, as shown in FIG. 13, when the tone near black is emphasized, the low-level region has a steep gamma curve characteristic, and when the noise near black is reduced (S / N is emphasized), , FIG.
As shown in (1), the low-level region has a gentle gamma curve characteristic.

Therefore, in order to realize a gamma correction circuit which emphasizes the gradation near black, data having a standard gamma curve characteristic as shown in FIG.
1, and when a gamma correction circuit that emphasizes S / N near black is realized, data having a gamma curve characteristic as a standard as shown in FIG.
It should have been stored in M101.

[0006]

However, in the above-described gamma correction circuit according to the conventional example, if both functions of emphasizing gradation near black and emphasizing S / N are to be satisfied at the same time, two systems of gamma ROM 101 are required. Since the data of the gamma curve characteristic shown in FIG. 13 and the data of the gamma curve characteristic shown in FIG. 14 are stored respectively,
The circuit scale is increased accordingly. In addition, in order to change the gray scale and S / N in the vicinity of black in multiple stages, it is necessary to provide the gamma ROM 101 correspondingly, and the circuit scale is further increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to realize both functions of emphasizing gradation near black and emphasizing S / N while maintaining a small circuit scale. An object of the present invention is to provide a video signal processing circuit which can be realized by signal processing, a camera using the same, and a gamma correction method.

[0008]

A video signal processing circuit according to the present invention comprises a gamma curve data generating means for generating standard gamma curve characteristic data for an input video signal to be corrected, and a standard gamma curve. Correction data generating means for generating correction data for correcting the characteristic in the low-level region of the characteristic; and standard gamma curve characteristic data generated by the gamma curve data generating means and correction data generated by the correction data generating means. And an operation means for performing an operation.

In the video signal processing circuit having the above configuration, the gamma curve data generating means is for generating data of standard gamma curve characteristics for an input video signal. Here, in the case of the ROM table system, a gamma ROM having data of standard gamma curve characteristics as a table with respect to an input video signal corresponds to the gamma curve data generation means. A linear approximation circuit that outputs linear approximation data for a video signal corresponds to gamma curve data generation means.
Based on the data of the standard gamma curve characteristics, gamma correction based on the standard gamma curve characteristics with emphasis on the gradation near black is performed.

On the other hand, the correction data generating means applies correction data for correcting the characteristic of the low-level region of the standard gamma curve characteristic generated by the gamma curve data generating means, that is, the characteristic near black, to the input video signal. Generate based on
Then, the calculating means calculates the correction data generated by the correction data generating means with respect to the data of the standard gamma curve characteristics generated by the gamma curve data generating means. As a result, the characteristic near the black of the standard gamma curve characteristic is corrected. That is, in the case of subtraction processing, gamma correction is performed with emphasis on S / N near black, and in the case of addition processing, gamma correction is performed with emphasis on gradation near black.

[0011]

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

FIG. 1 is a block diagram showing an example of a basic configuration of a camera system to which the present invention is applied. Image light from a subject (not shown) is incident on an imaging surface of a solid-state imaging device, for example, a CCD imaging device 1 via an optical system including a lens 2. The CCD image pickup device 1 controls the exposure time (shutter speed), signal charge readout, vertical transfer, horizontal transfer, and the like according to various timing signals generated from a timing generator (not shown), so that incident light is controlled. Is converted into an electric signal in pixel units and output.

The analog video signal output from the CCD image pickup device 1 is supplied to a preamplifier 3 where the signal component is sampled and held, and a gain control (AGC) process is performed to adjust the signal component to an appropriate level. The analog video signal that has passed through the preamplifier 3 is digitized by an A / D converter 4 and then supplied to a delay line 5. From the delay line 5, digital video signals H1D and H2D delayed by a period corresponding to 1H (H is a horizontal scanning period) and a period corresponding to 2H are output. Then, the digital video signal H1D is supplied to both the Y (luminance) signal processing circuit 6 and the C (chroma) signal processing circuit 7, and the digital video signal H2D is supplied only to the C signal processing circuit 7.

In the Y signal processing circuit 6, the input digital video signal H 1 D is converted into an LPF (low-pass filter) 6.
1, the C signal component is cut by passing through Y
It becomes signal data. The Y signal data is subjected to gamma correction by the gamma correction circuit 62, and then the Y signal level equal to or higher than a certain level is clipped to the white clip level by the white clip circuit 63. Then, a blanking signal is added by a blanking (BLK) adding circuit 64, a synchronizing signal is added by a sync (SYNC) adding circuit 65, and a phase adjustment is performed by a phase adjusting circuit 66.

In the C signal processing circuit 7, the input digital video signals H1D and H2D are converted by an RGB conversion circuit 71 into three primary color signal data of R (red), G (green) and B (blue). The R, G, and B signal data are white-balanced by a white balance circuit 72, gamma-corrected by a gamma correction circuit 73, and then subjected to a hue (HUE) gain circuit 74 to obtain the RY, BY color difference. It is converted to signal data. Then, a blanking signal is added by a blanking / burst circuit 75, subsequently, a burst signal is added, modulated by an encoder 76, and further subjected to phase adjustment by a phase adjustment circuit 77.

The Y signal data subjected to signal processing such as gamma correction and phase adjustment in the Y signal processing circuit 6 is converted into an analog Y signal by a D / A converter 8 and supplied to a subsequent circuit. The C signal data on which signal processing such as white balance and gamma correction has been performed by the C signal
The signal is converted into an analog C signal by the A converter 9 and supplied to a subsequent circuit. The setting of various parameters for signal processing in the Y signal processing circuit 6 and the C signal processing circuit 7 is performed by a microcomputer (hereinafter abbreviated as a microcomputer) 10.

In the camera system having the above configuration, as an example, the gamma correction circuit 62 in the Y signal processing circuit 6
The present invention is applied to: FIG. 2 is a block diagram showing one embodiment of the gamma correction circuit according to the present invention. In this embodiment, a case where the present invention is applied to, for example, a ROM table type gamma correction circuit will be described as an example.

The gamma correction circuit according to this embodiment includes a gamma ROM 11 as gamma curve data generation means,
Black correction data generation unit 12 as correction data generation means
And a subtractor 13 as a calculating means, and a knee generating unit 14
, A standard level detection circuit 15 and a selector 16.

The gamma ROM 11 has, as a table, data of characteristics below the standard level among the standard gamma curve characteristics shown in FIG. 13 for the input Y signal data to be corrected. The black correction data generation unit 12 converts the low-frequency data of the input Y signal data into a low-level region having a standard gamma curve characteristic, Correction data for correcting characteristics is generated. The specific configuration of the black compressed data generation unit 12 will be described later.

The subtractor 13 subtracts the correction data output from the black correction data generator 12 according to the input Y signal data from the gamma curve characteristic data output from the gamma ROM 11 according to the input Y signal data. The processing is performed, and the subtracted data is used as one input of the selector 16. The knee generating unit 14 generates, for the input Y signal data, data having characteristics exceeding the standard level among the standard gamma curve characteristics shown in FIG. And

The standard level detection circuit 15 is composed of, for example, a comparator that uses the standard level as a comparison reference level and uses the input Y signal data as a comparison input, and the level of the input Y signal data becomes higher than the standard level. When this is detected, the selector 16 is switched according to the detection output. The selector 16 normally selects the subtraction data of the subtractor 13, and selects and outputs the output data of the knee generation unit 14 based on the output of the standard level detection circuit 15 when the level of the input luminance signal is equal to or higher than the standard level. It has a configuration.

FIG. 3 is a block diagram showing an example of the circuit configuration of the black correction data generation unit 12. In this example, n
It is assumed that bit Y signal data is input to the black correction data generation unit 12. Black correction data generation unit 12 according to this example
Is, for example, a black correction decoder 21 as data generation means.
, A NOR circuit 22, an AND circuit 23, and a bit shift circuit 24 as a characteristic conversion means.

The black correction decoder 21 outputs low-frequency data of n-bit Y signal data, that is, lower a bits (a <
The data of (n) is input, the data is decoded into data having predetermined characteristics, and the decoded data is input to one input of the AND circuit 23. The NOR circuit 22 receives (na) bits of the n-bit Y signal data as input, and when the Y signal data is a bit or less, it is at a high level (logic "1") and when the Y signal data exceeds a bit. An output of low level (logic “0”) is generated and used as the other input of the AND circuit 23.

The AND circuit 23 controls passing / blocking of the decoded data of the black correction decoder 21 based on the logic of the output of the NOR circuit 22. That is, the NOR circuit 2
When the output of the NOR circuit 22 is logic "1", the decode data of the black correction decoder 21 is passed as it is, and when the output of the NOR circuit 22 is logic "0", the decode data of the black correction decoder 21 is cut off. The bit shift circuit 24 shifts the data that has passed through the AND circuit 23 by the number of bits set according to the correction amount setting information of m (m <a) bits given from the microcomputer 10 to thereby provide a black correction decoder. 21 converts the characteristics of the decoded data.

In this embodiment, an example is shown in which a bit shift circuit 24 is used as a characteristic conversion means for converting the characteristics of data decoded by the black correction decoder 21 based on correction amount setting information given from the microcomputer 10. However, it is not limited to this. As another example, for example,
The data that has passed through the AND circuit 23 is
A multiplier that multiplies a coefficient corresponding to the correction amount setting information given from 0, a subtractor that subtracts a decode value based on the correction amount setting information given from the microcomputer 10 from data passed through the AND circuit 23, or the like may be used. It is possible.

Next, the processing procedure for performing gamma correction in the gamma correction circuit according to one embodiment of the above configuration will be described with reference to the input / output characteristic diagram of FIG. 4 and the flowchart of FIG. In FIG. 4, (A)
Is the output characteristic of the gamma ROM 11 for the input Y signal data, (B) is the output characteristic of the black correction data generation unit 12 for the input Y signal data, and (C) is the output characteristic of the subtractor 13 for the input Y signal data. (D) is the input Y
The output characteristics of the gamma correction circuit with respect to the signal data are shown respectively.

When the Y signal data is input (step S
11), receiving the input Y signal data, the gamma ROM 1
1 outputs standard gamma curve characteristic data as shown in FIG. 4A (step S12), and the black correction data generator 12 outputs correction data as shown in FIG. 4B. (Step S13). Here, the characteristics of the correction data output from the black correction data generation unit 12 are as follows:
It is variable according to the correction amount setting information given from the microcomputer 10. For example, in the case of the circuit example shown in FIG. 3, in the characteristic diagram of FIG. 4B, the characteristic x1 having the largest bulge is set as a reference characteristic, and the bulge increases as the shift amount in the bit shift circuit 24 increases. Characteristics x that become smaller
2, x3, ...

The correction data generated by the black correction data generation unit 12 is subjected to a subtraction process by the subtractor 13 from the standard gamma curve characteristic data output from the gamma ROM 11 (step S14). Thereby, the subtracter 1
As shown in FIG. 4C, when the correction data is 0 as the subtraction data of 3, the data of the standard gamma curve characteristic output from the gamma ROM 11 is obtained as it is.
When the correction data has the maximum characteristic x1, data of a characteristic y1 in which the vicinity of black of the standard gamma curve characteristic is gentle is obtained.

Then, it is determined whether or not the input Y signal data is in a region below the standard level (step S15). If it is in the region below the standard level, the subtraction data of the subtractor 13 is selected by the selector 16 (step S15). Step S16) If the input Y signal data exceeds the standard level, the selector 16 selects the data having the knee characteristic generated by the knee generating section 14 (step S17). Input Y
Whether or not the signal data is below the standard level is determined by the standard level detection circuit 15, and the output of the standard level detection circuit 15 controls switching of the selector 16.

As described above, the input Y to be corrected is
In addition to generating standard gamma curve characteristic data for the signal data, it also generates correction data for correcting the low-level characteristic of the standard gamma curve characteristic, and converts this correction data from the standard gamma curve characteristic data. By performing the subtraction processing, it is possible to realize both the functions of emphasizing gradation near black and emphasis on S / N based on the data of the standard gamma curve characteristics.

Thus, both the data for emphasizing gradation near black and the data for emphasizing S / N can be stored in the gamma ROM.
Therefore, the gate scale (circuit scale) of the gamma ROM can be greatly reduced as compared with the case where both data are provided when forming an LSI. In addition, the characteristics of the correction data are made variable, and the characteristics are changed from the microcomputer 10 according to the conditions of the subject, for example, the brightness of the subject, and the noise level is suppressed. Obtainable.

In the black correction data generator 12, the black correction data (black compressed data) is composed of decoded data of several bits of the input Y signal data, and the conversion of the characteristics of the decoded data is performed by a bit shift circuit 24. , The circuit scale can be reduced. As an example, it is possible to reduce the circuit size by about 90% under the condition of compressing 9 bits of input data by 4 bits, as compared with the case of storing data for 2 systems.

FIG. 6 is a block diagram showing another embodiment of the gamma correction circuit according to the present invention. In this embodiment, a case where the present invention is applied to a ROM table type gamma correction circuit will be described as an example. And

The gamma correction circuit according to this embodiment includes a gamma ROM 31 as gamma curve data generating means,
Black correction data generation unit 32 as correction data generation means
And an adder 33 as a calculating means, and a knee generating unit 34
, A standard level detection circuit 35, and a selector 36.

The gamma ROM 31 has, as a table, data of characteristics below the standard level among the standard gamma curve characteristics shown in FIG. 13 for the input Y signal data to be corrected. The black correction data generation unit 32, based on the correction amount setting information given from the microcomputer 10 in FIG. Correction data for correcting characteristics is generated. As the black compressed data generation unit 32, one having a circuit configuration shown in FIG. 3 is used.

The adder 33 converts the correction data output from the black correction data generator 32 according to the input Y signal data with respect to the gamma curve characteristic data output from the gamma ROM 31 according to the input Y signal data. The adding process is performed, and the added data is used as one input of the selector 36. The knee generating unit 34 generates data having characteristics exceeding the standard level, that is, data having knee characteristics, out of the standard gamma curve characteristics shown in FIG. And

The standard level detection circuit 35 is composed of, for example, a comparator using the standard level as a comparison reference level and using the input Y signal data as a comparison input, and the level of the input Y signal data becomes higher than the standard level. When this is detected, the selector 36 is switched according to the detection output. The selector 36 normally selects the added data of the adder 33, and when the level of the input luminance signal is equal to or higher than the standard level, selects and outputs the output data of the knee generating section 34 based on the output of the standard level detection circuit 35. It has a configuration.

As described above, the input Y to be corrected is
In addition to generating standard gamma curve characteristic data for the signal data, it also generates correction data for correcting the low-level characteristic of the standard gamma curve characteristic, and converts the correction data into standard gamma curve characteristic data. By performing the addition, as shown in FIG. 7, the characteristics in the low-level region become steep, and a gamma curve characteristic that places more importance on the gradation near black can be obtained. Further, the characteristics of the low-level region can be arbitrarily set in accordance with the correction amount setting information provided from the microcomputer 10 as in the case of the above embodiment.

In the above embodiments, the case where the subtractor 13 or the adder 33 is used as means for calculating the data of the standard gamma curve characteristic and the correction data has been described. It is also possible to adopt a configuration in which the subtraction and the addition of the correction data are selectively performed on the data of the standard gamma curve characteristics by using both of them. According to this, both the gamma curve characteristic that places more importance on the gradation near black and the gamma curve characteristic that places importance on the S / N can be realized by the same signal processing.

Further, each of the above embodiments can be applied to a gamma correction circuit of a variable gamma system in which a standard gamma curve characteristic can be arbitrarily set. In the gamma correction circuit of the variable gamma system, gamma curve characteristics are set according to the dynamic range for the purpose of expanding the dynamic range. FIG. 8 is a block diagram showing an example of application to a gamma correction circuit of a variable gamma method.

In the gamma correction circuit according to this application example, the ROM 41 is used as gamma curve data generation means.
A multiplier 42, an adder 43, and a straight line data generator 44 are provided. The ROM 41 stores, as a table, data of gamma curve characteristics as indicated by a solid line in FIG. 9A for input Y signal data up to the standard level. The multiplier 42 is provided for the data output from the ROM 41 to the ROM provided from the microcomputer 10 in FIG.
By multiplying the decode data based on the curve selection information, data of various gamma curve characteristics indicated by dotted lines with respect to the gamma curve characteristics indicated by solid lines in FIG. 9A is generated.

On the other hand, the straight line data generator 44 stores, as a table, straight line data having a certain inclination angle with respect to the input Y signal data up to the standard level, as shown in FIG. 9B. . The straight line data output from the straight line data generation unit 44 is added to the data output from the multiplier 42 by the adder 43, so that data having a gamma curve characteristic as shown by a solid line in FIG. Generated.
Then, the gamma curve characteristic of the output data of the multiplier 42 changes as indicated by the dotted line in FIG. 9A according to the ROM curve selection information given from the microcomputer 10, whereby the gamma curve of the output data of the adder 43 is changed. The characteristics are also shown in FIG.
(C) changes as shown by the dotted line.

The above configuration is a circuit portion unique to the variable gamma gamma correction circuit. In this application example, for example, a circuit according to the embodiment of FIG. 2 is added to this circuit portion. In other words, the black correction data generation unit 45 converts the low-frequency data of the input Y signal data into a low-level region having a standard gamma curve characteristic, that is, a black level, according to the correction amount setting information given from the microcomputer 10 in FIG. Correction data for correcting nearby characteristics is generated.

The subtractor 46 converts the gamma curve characteristic data output from the adder 43 in accordance with the input Y signal data into a black correction data generator 45 in accordance with the input Y signal data.
Is performed, and the subtracted data is used as one input of the selector 47. The variable knee generator 48 generates data having characteristics exceeding the standard level, that is, data having knee characteristics, with respect to the input Y signal data, and uses the data as the other input of the selector 47. The variable knee generator 48 has a configuration in which the knee characteristic is variable based on the knee characteristic selection information given from the microcomputer 10 in FIG. 1 corresponding to the selection information when the ROM curve is selected.

The standard level detection circuit 49 monitors the level of the input Y signal data and, when detecting that the level has exceeded the standard level, switches the selector 47 according to the detection output. The selector 47 usually has the subtractor 4
6 is selected, and when the level of the input luminance signal is equal to or higher than the standard level, the output data of the variable knee generator 48 is selected and output based on the output of the standard level detection circuit 49. .

As described above, the present invention can be applied to a gamma correction circuit of a variable gamma system. As a result, for the purpose of expanding the dynamic range, etc., it is possible to set a gamma curve characteristic according to the dynamic range, and to arbitrarily set the S / N according to the condition of the subject. In the present application example described above, the embodiment using the subtractor as the calculating means is applied to the gamma correction circuit of the variable gamma method. However, the embodiment using the adder as the calculating means, and further the subtractor as the calculating means. An embodiment using an adder is also applicable.

In each embodiment and application example of the present invention described above, a case where the present invention is applied to a ROM table type gamma correction circuit is described. However, the present invention is not limited to this. It is equally applicable to circuits. Here, the gamma ROM is used in the ROM table method, whereas the linear approximation circuit is used in the linear approximation method. That is, when applied to a linear approximation type gamma correction circuit, in FIGS.
The gamma ROMs 11 and 31 are replaced with linear approximation circuits.

FIG. 10 shows an example of the gamma curve characteristic in the case of the linear approximation method. FIG. 11 shows an example of a circuit configuration of the linear approximation circuit in this case. The straight line approximation circuit of this example includes, for example, three coefficient units 51, 52, and 53 for obtaining data of lines A, B, and C according to input Y signal data, and outputs of the coefficient units 51, 52, and 53, respectively. A selector 54 for selectively outputting one of the data and a decoder for switching and controlling the selector 54 to select one of the data of the straight lines A, B and C based on the input Y signal data (Comparator) 55.

As described above, when the present invention is applied to the gamma correction circuit of the linear approximation method, the low-level region (region near black) of the standard gamma curve characteristic, for example, the characteristic of the straight line A in FIG. As in the case of the above-described embodiment or another embodiment, the S / N is reduced by emphasizing the noise level, or the gamma correction is performed by emphasizing the gradation near black as in the case of the above-described embodiment or other embodiments. It can be performed as appropriate.

In the embodiments and application examples of the present invention described above, in the camera system shown in FIG. 1, when applied to the gamma correction circuit 62 of the Y signal processing circuit 6, that is, the gamma correction processing is performed on the Y signal. Although the description has been given of the case where the gamma correction is performed, the gamma correction circuit 73 of the C signal processing circuit 7, that is, the case where the gamma correction is performed on the C signal can be similarly applied. it can.

[0051]

As described above, according to the present invention,
Generates standard gamma curve characteristics data for the input video signal to be corrected, and generates correction data for correcting the low-level region characteristics of the standard gamma curve characteristics. Gamma correction by calculating the gamma curve characteristics and the correction data allows gamma correction based on multiple types of gamma curve characteristics to be performed in the same signal Therefore, the gradation and S / N near black can be switched in multiple stages while the circuit scale is kept small.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a basic configuration of a camera system according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a gamma correction circuit according to the present invention.

FIG. 3 is a block diagram illustrating an example of a circuit configuration of a black correction data generation unit.

FIG. 4 is an input / output characteristic diagram according to an embodiment of the present invention.

FIG. 5 is a flowchart illustrating a procedure of a gamma correction method according to the present invention.

FIG. 6 is a block diagram showing another embodiment of the gamma correction circuit according to the present invention.

FIG. 7 is an input / output characteristic diagram according to another embodiment of the present invention.

FIG. 8 is a block diagram showing an application example of the present invention.

FIG. 9 is an input / output characteristic diagram according to an application example of the present invention.

FIG. 10 is a gamma curve characteristic diagram of a linear approximation method.

FIG. 11 is a block diagram illustrating an example of a linear approximation circuit.

FIG. 12 is a block diagram showing a conventional example.

FIG. 13 is a gamma curve characteristic diagram in the case where priority is given to gradation near black.

FIG. 14 is a gamma curve characteristic diagram in the case where importance is placed on S / N near black.

[Explanation of symbols]

1 CCD imaging device 4 A / D converter 6
Y signal processing circuit 7 C signal processing circuit 8,9 D / A converter 10 Microcomputer 11,31 Gamma R
OM 12, 32, 45 Black correction data generation unit 13, 46
Subtractors 14, 34 Knee generators 15, 35, 49 Standard level detector 16, 36, 47 Selector 21 Black correction decoder 24 Bit shift circuit 33, 43 Adder 4
8 Variable knee generator

Claims (9)

[Claims] 1. A gamma curve data generating means for generating standard gamma curve characteristic data for an input video signal to be corrected, and correction data for correcting a characteristic of the standard gamma curve characteristic in a low level region. Correction data generating means for generating the data, and calculating means for calculating the data of the standard gamma curve characteristics generated by the gamma curve data generating means and the correction data generated by the correction data generating means. Characteristic video signal processing circuit. 2. The method according to claim 1, wherein said calculating means is a subtractor for subtracting the correction data generated by said correction data generating means from the data of the standard gamma curve characteristics generated by said gamma curve data generating means. The video signal processing circuit according to claim 1. 3. The arithmetic unit is an adder that adds correction data generated by the correction data generation unit to data of standard gamma curve characteristics generated by the gamma curve data generation unit. The video signal processing circuit according to claim 1, wherein: 4. The video signal processing circuit according to claim 1, wherein standard gamma curve characteristics generated by said gamma curve data generation means are variable. 5. The correction data generation unit includes: a data generation unit configured to generate data having predetermined characteristics with respect to low-frequency data of the video signal; 2. The video signal processing circuit according to claim 1, further comprising: a characteristic conversion unit configured to perform conversion based on provided information. 6. The video signal processing circuit according to claim 5, wherein said data generation means comprises a decoder for decoding low-frequency data of said video signal into data having said predetermined characteristic. 7. The characteristic conversion means comprises a bit shift circuit for shifting data generated by the data generation means by the number of bits according to the information provided from the outside. Video signal processing circuit. 8. An image pickup device for converting incident light into an electric signal and outputting the electric signal, an optical system for guiding incident light from a subject on an image pickup surface of the image pickup device, and processing a video signal output from the image pickup device. A video signal processing circuit comprising: a gamma curve data generating unit configured to generate data of a standard gamma curve characteristic for a video signal output from the imaging device; Correction data generating means for generating correction data for correcting the characteristic of the low-level region of the standard gamma curve characteristic; and standard gamma curve characteristic data generated by the gamma curve data generating means and the correction data generating means. A calculating means for calculating the generated correction data. 9. Generating standard gamma curve characteristic data for an input video signal to be corrected,
A gamma correction method, comprising: generating correction data for correcting characteristics of a low-level region of the standard gamma curve characteristics; and calculating data of the standard gamma curve characteristics and the correction data.