JP3934363B2 - Gamma correction circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gamma correction circuit, and more particularly, to a gamma correction circuit that can be adapted to an average video level (hereinafter, abbreviated as APL) of a video signal and corresponds to gradation reproducibility of the video signal.
[0002]
[Prior art]
In recent years, with the increase in the size of television receivers, a technique for maximizing the dynamic range of a cathode ray tube used in a television receiver has attracted attention. It is well known that among these prior arts, improvement in visual brightness and contrast ratio is a factor in improving image quality.
[0003]
In general, gamma correction is often used as an improvement in gradation reproducibility of video signals. Further, gamma correction for correcting only a luminance signal is known as a circuit that can be easily configured on a small scale.
[0004]
In the video signal, the gradation of the white part is limited to improve the intermediate brightness gradation and improve the visual brightness. It is possible to prevent blooming and to improve the visual contrast ratio.
[0005]
However, when APL (Average Picture Level: average video level) is low, for example, the above-described improvement is made for a signal that has a little white while there is a lot of black as a whole, but when APL is high, For example, in a signal with a lot of white as a whole, white-out is visible, which is detrimental. That is, gamma correction also becomes a factor that deteriorates image quality. In recent years, it has been required to improve the white-out.
[0006]
In order to solve this problem, conventionally, the operating point of gamma correction is changed by APL. That is, for a signal with a low APL, the operating point remains fixed at a certain position, and when the signal has a high APL, the operating point is shifted to the white side. As a result, the limitation of gradation on the white side can be reduced, so that whiteout can be improved.
[0007]
Such a prior art is disclosed in, for example, Japanese Patent Laid-Open No. 7-303222. FIG. 6 shows the configuration of this prior art.
[0008]
Referring to FIG. 6, this prior art uses a differential amplifier at the output of the video signal amplitude limiter circuit to detect APL from the video signal, and uses the detection result as a differential signal as an amplitude limit start point. The video signal is input to one input of the amplifier and the video signal is input to the other input, and the white-side amplitude of the video signal is limited from the amplitude limit start point.
[0009]
That is, gamma correction is performed using a broken line. Thus, a technique for changing the starting point of the video signal amplitude limiting circuit by APL is described.
[0010]
As described above, the conventional gamma correction circuit uses the APL as it is to perform correction by changing the operating point of gamma correction.
[0011]
[Problems to be solved by the invention]
However, the conventional gamma correction circuit has the following drawbacks.
[0012]
That is, as a first problem, even if the adaptation amount for APL is the same, depending on the setting of the operating point initial value (operating point when APL is 0%), a signal with no gamma correction above a predetermined APL can be generated.
[0013]
As a result, as shown in FIG. 5A, when the APL increases, a part where the operating point exceeds the maximum value of the video signal is generated, and an area where no gamma correction is applied occurs beyond a certain APL.
[0014]
Depending on the initial value of the operating point, the signal range where no gamma correction is applied varies. If the gamma correction is not applied at all, the tone reproducibility, which is the original purpose of the gamma correction, is not improved.
[0015]
As a second problem, even if the operating point initial value is the same, if the adaptation amount for APL is increased, a signal which is not subjected to gamma correction at a certain APL or higher can be generated.
[0016]
As a result, as shown in FIG. 5B, when the change of the operating point is increased with respect to the change of APL (the slope of the operating point characteristic is steep), the operating point exceeds the maximum value of the video signal. This causes a region where no gamma correction is applied at a certain APL or higher.
[0017]
The larger the adaptation amount, the more areas where this gamma correction is not applied. As in the first problem, if the gamma correction is not performed at all, the gradation reproducibility is not improved.
[0018]
Accordingly, in view of the above problems, the object of the present invention is to improve the gradation reproducibility by always applying gamma correction in all areas of the APL, and to improve the gamma correction operating point in conformity with the APL. It is an object of the present invention to provide a gamma correction circuit that can improve the whiteout when the APL is high.
[0019]
[Means for Solving the Problems]
A gamma correction circuit of the present invention is a gamma correction circuit configured to be a video signal processing circuit for processing a video signal, and performs processing according to an average video level of the video signal,
An operating point control unit for outputting an operating point adapted to the average video level from the input of the average video level and the input of the operating point initial setting;
A gamma correction unit that performs gamma correction on the input luminance signal on the white side from the operating point ,
The operating point control unit includes a subtracting means for subtracting the input of the operating point initial setting from a fixed value that is a maximum value of a signal to be corrected,
Normalizing means for normalizing the average video level input to a value between 0 and 1;
Multiplying means for multiplying the result of the subtracting means by the normalized average video level signal of the normalizing means;
An average video level adaptive amount control means for amplifying the multiplication result with a gain of 1 or less by external control and controlling the average video level adaptive amount;
And an addition means for adding the result of controlling the adaptation amount to the input of the operating point initial setting .
[0021]
Further, the subtracting means of the gamma correction circuit of the present invention has a variable maximum width in which the subtraction result does not exceed the maximum value of the signal to be corrected when the operating point is changed according to the average video level. It is a configuration.
[0022]
Furthermore, the multiplication means of the gamma correction circuit of the present invention calculates the correction amount of the operating point adapted to the average video level by multiplying the normalized input of the average video level by the subtraction result. The average video level adaptive amount control means of the gamma correction circuit of the present invention is configured to amplify the gain with a gain of 1 or less by an external adaptive amount control signal and output it to the adder.
[0023]
Further, the gamma correction unit of the gamma correction circuit of the present invention has a configuration in which the gamma correction characteristic is a non-linear characteristic in which the level on the white side from the operating point is compressed.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
A gamma correction circuit according to an embodiment of the present invention will be described with reference to the drawings.
[0025]
FIG. 1 is a configuration diagram of a gamma correction circuit according to the first embodiment of the present invention, and FIG. 2 is a configuration diagram of an operating point control unit of the gamma correction circuit according to the first embodiment of the present invention. 3 is an operating point output characteristic diagram of the operating point control unit of the gamma correction circuit according to the first embodiment of the present invention, and FIG. 4 is a gamma correction of the gamma correction circuit according to the first embodiment of the present invention. It is a characteristic (input / output relation characteristic) figure.
[0026]
Referring to FIG. 1, a luminance signal is input to the input unit 1 of the gamma correction circuit 101 according to the first embodiment of the present invention. The gamma correction unit 5 is connected to the input unit 1 and an operating point control unit 6 to be described later, and with respect to the luminance signal from the input unit 1 at a level on the white side of the operating point output 9 from the operating point control unit 6, Gamma correction is performed with a correction amount based on an external correction amount control signal 4, and the corrected luminance signal is output to the output unit 8.
[0027]
Although not shown, the input unit 2 receives a signal obtained by integrating the luminance signal outside as an APL input. An arbitrary operating point for gamma correction when the APL is 0% is input to the input unit 3 as an initial operating point setting. The operating point control unit 6 is connected to the input units 2 and 3 and outputs an operating point output 9 adapted to APL to the gamma correction unit 5.
[0028]
Next, referring to FIG. 2, the input unit 2 (APL input) of the operating point control unit 6 of the gamma correction circuit 101 according to the first embodiment of the present invention is connected to the normalization unit 61. The normalizing unit 61 sets the APL input to a value between 0 and 1 and outputs it to the multiplier 63.
[0029]
The input unit 3 (operation point initial setting) is connected to a subtracter 64 and an adder 66. The subtractor 64 subtracts the operating point initial setting from a fixed value (maximum corrected signal value) that is the maximum value of the signal to be corrected, and outputs the result to the multiplier 63.
[0030]
The multiplier 63 multiplies the output of the normalization unit 61 and the output of the subtractor 64 and outputs the result to the adaptation amount control unit 65.
[0031]
The adaptive amount control unit 65 amplifies the gain with a gain of 1 or less by the external adaptive amount control signal 7 and outputs the amplified signal to the adder 66. The adder 66 adds the output of the adder 66 which is an APL adaptive amount to the input unit 3 (operation point initial setting), and outputs the operation point output 9 to the gamma correction circuit 5.
[0032]
Next, the operation of the gamma correction circuit 101 according to the first embodiment of this invention will be described.
[0033]
Referring again to FIG. 1, the APL input from the input unit 2 and the operating point initial setting from the input unit 3 are input to the operating point control unit 6. Although not shown, the APL input is a signal that changes with respect to APL 0% to 100% obtained by integrating the luminance signal externally.
[0034]
The operating point initial setting is a value of an arbitrary operating point for gamma correction when the APL is 0%. The operating point control unit 6 outputs an operating point adapted to APL to the gamma correction unit 5 as an operating point output 9 from these two inputs (APL input and operating point initial setting).
[0035]
The gamma correction unit 5 applies gamma correction to a portion on the white side of the operating point output 9 of the luminance signal input from the input unit 1 (input level> operating point). The correction at this time is corrected with the intensity of the correction amount determined by the correction amount control signal 4 from the outside.
[0036]
The gamma correction characteristic at this time is a non-linear characteristic in which the level on the white side from the operating point is compressed as shown in FIG. Thereafter, the corrected result is output to the output unit 8 as a corrected luminance signal.
[0037]
In FIG. 4, the gamma correction by the one-point broken line has been described, but it is also possible to divide the level on the white side from the operating point and correct by a multi-line broken line or curve.
[0038]
Referring to FIG. 2 again, in the operating point control unit 6 of the gamma correction circuit 101 according to the first embodiment of the present invention, the APL input input from the input unit 2 is input to the normalization unit 61.
[0039]
The normalizing unit 61 normalizes the APL input so that the value is 0 or more and 1 or less, that is, 0 when APL is 0%, and 1 when APL is 100%, and outputs the normalized value to the multiplier 63.
[0040]
The operating point initial setting input from the input unit 3 is input to the subtracter 64 and the adder 66. The subtractor 64 subtracts the operating point initial setting from a fixed value (maximum corrected signal value) that is the maximum value of the signal to be corrected, and outputs the result to the multiplier 63.
[0041]
(Maximum value of corrected signal-Initial setting of operating point)
This fixed value is a constant that is inevitably determined when the entire system including the present invention is considered (the maximum value of the luminance signal for performing signal processing). This subtraction result has a maximum changeable width that does not exceed the maximum value of the signal to be corrected even if the operating point is changed by APL.
[0042]
The multiplier 63 multiplies the normalized APL input by the subtraction result, thereby calculating an operating point correction amount 67 adapted to the APL.
[0043]
(Correction amount = normalized APL input * subtraction result)
That is, when the APL is 0%, the correction amount 67 is 0, and when the APL is 100%, the changeable maximum value is obtained. Thereafter, the correction amount 67 is amplified with an gain of 1 or less by an external adaptation amount control signal 7 and is output to the adder 66 as an adaptation amount 68. By setting the gain to 1 or less, the operating point does not exceed the maximum value of the signal to be corrected.
[0044]
The adder 66 adds the adaptive amount 68 to the initial setting of the operating point from the input unit 3 that is the operating point of APL 0%, and outputs the operating point output 9 to the gamma correction unit 5.
[0045]
(Operating point output = Operating point initial setting + Adaptation amount)
The characteristics of the operating point output 9 of the operating point control unit 6 are as shown in FIG. As described above, in the present invention, there is no region where the gamma correction is not applied at all, and tone reproducibility can be improved with any APL, and whiteout can be improved.
[0046]
The amplitude of the luminance output increases as the APL increases as shown in FIG. 4, but this is not shown, but an AGC (auto gain control) circuit, an ACL (automatic contrast limiter) circuit, etc. are provided after the circuit of the present invention. By connecting a circuit for controlling the amplitude, a signal having an arbitrary and constant amplitude or a signal whose amplitude is changed by APL can be obtained.
[0047]
【The invention's effect】
As described above, by adopting the gamma correction circuit of the present invention, the operating point of gamma correction changes from the initial setting value (operating point of APL 0%) to the maximum value of the signal to be corrected to adapt to APL. The adaptation amount can also be changed. The operating point does not exceed the maximum value of the signal to be corrected. As a result, there is no signal that is not subjected to gamma correction at all, and any APL impairs the improvement of gradation reproducibility such as improvement of visual brightness and contrast ratio, prevention of blooming, etc., which is the original purpose of gamma correction. Therefore, it is possible to improve the problem of whiteout when the APL is high.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a gamma correction circuit according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of an operating point controller of the gamma correction circuit according to the first embodiment of this invention.
FIG. 3 is an operating point output characteristic diagram of an operating point control unit of the gamma correction circuit according to the first embodiment of the present invention.
FIG. 4 is a gamma correction characteristic diagram (input / output relation characteristic diagram) of the gamma correction circuit according to the first embodiment of the present invention;
FIG. 5 is an operating point characteristic diagram of a conventional gamma correction circuit.
FIG. 6 is a configuration diagram of a conventional gamma correction circuit.
[Explanation of symbols]
1 Input section (luminance signal input)
2 Input section (APL input)
3 Input section (initial setting of operating point)
4 Correction amount control signal 5 Gamma correction unit 6 Operating point control unit 7 Adaptive amount control signal 8 Output unit (luminance signal output)
9 Operating point output of the operating point control unit 61 Normalizing unit 62 Corrected signal maximum value 63 Multiplier 64 Subtractor 65 Adaptive amount control unit 66 Adder 67 Correction amount 68 output from the multiplier 63 of the adaptive amount control unit 65 Adaptive amount 101 as output gamma correction circuit

Claims (9)

A video signal processing circuit configured to process a video signal , a gamma correction circuit that performs processing according to an average video level of the video signal,
An operating point control unit for outputting an operating point adapted to the average video level from the input of the average video level and the input of the operating point initial setting;
A gamma correction unit that performs gamma correction on the input luminance signal on the white side from the operating point ,
The operating point control unit includes a subtracting means for subtracting the input of the operating point initial setting from a fixed value that is a maximum value of a signal to be corrected,
Normalizing means for normalizing the average video level input to a value between 0 and 1;
Multiplying means for multiplying the result of the subtracting means by the normalized average video level signal of the normalizing means;
An average video level adaptive amount control means for amplifying the multiplication result with a gain of 1 or less by external control and controlling the average video level adaptive amount;
A gamma correction circuit comprising: addition means for adding the result of controlling the adaptation amount to the input of the operating point initial setting . 2. The gamma correction circuit according to claim 1 , wherein when the operating point is changed according to the average video level, the subtraction means has a variable maximum width that does not exceed a maximum value of a signal to be corrected. 3. The gamma correction circuit according to claim 1 , wherein the multiplication unit calculates a correction amount of an operating point adapted to the average video level by multiplying the normalized input of the average video level by the subtraction result. . 4. The gamma correction circuit according to claim 1, wherein the average video level adaptive amount control means amplifies the gain with a gain of 1 or less by an external adaptive amount control signal and outputs the amplified signal to the adder. The gamma correction unit, the characteristics of the gamma correction, the gamma correction circuit according to claim 1, 2, 3 or 4, wherein the level of the white side was set to non-linear characteristics that has been compressed from the operating point. The gamma correction circuit according to claim 5 , wherein the gamma correction unit outputs the corrected result to the output unit as a corrected luminance signal. The gamma correction circuit according to claim 6 , wherein the gamma correction unit performs gamma correction using a one-point broken line by dividing a white level from an operating point. The gamma correction circuit according to claim 6 , wherein the gamma correction unit uses gamma correction by dividing a level on the white side of the operating point and performing gamma correction based on a multipoint broken line. The gamma correction circuit according to claim 6 , wherein the gamma correction unit is configured to perform gamma correction by a curve by dividing a white side level from an operating point.

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