JPH04282689A - Gradation correction device - Google Patents

Abstract

PURPOSE:To offer the gradation correction device which has small deterioration in an SN ratio due to the gradation correction of a video brightness signal. CONSTITUTION:The high frequency component and low frequency component of an input brightness signal are separated through an HPF 3 and an LPF 2; and the low frequency component is supplied to a gradation correcting circuit 11 for (r) correction and the high frequency component which contains many noise components is supplied to an adding circuit 8 as it is or after being reduced by a gain control circuit 5 relatively to the low frequency component amplitude, so that the adding circuit puts both low frequency components together into one.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation correction device for correcting the gradation of a video luminance signal in video equipment such as a television receiver or a video tape recorder.

0002

[Prior Art] In recent years, as color television receivers have become larger, the gradation of the video signal is corrected by passing the video signal through a non-linear amplifier in order to make the image appear clearer. Gradation correction devices that expand the dynamic range of images are becoming increasingly important.

An example of the above-mentioned conventional gradation correction device will be described below with reference to the drawings.

FIG. 7 shows a block diagram and main waveforms of a conventional tone correction device. In FIG. 7, reference numeral 1 denotes a gradation correction device, which corrects the gradation of a video luminance signal.

The operation of this gradation correction device will be explained below. First, an input luminance signal a as shown in FIG. 7(a) is input to the gradation correction circuit 1. When the input luminance signal a is as shown in FIG. 7(a), the luminance conversion characteristic of the gradation correction circuit 1 is as shown in FIG. 7(b), and the output luminance signal b in this case is as shown in FIG. 7(c). A higher contrast video signal with expanded gradation can be obtained. However, the result is that the amplitude of the noise component on the flat portion is also expanded at the same time.

[0006]

[Problems to be Solved by the Invention] However, in the above configuration, the gradation is certainly expanded as shown in FIG. 7(c), but at the same time, the amplitude of the noise component on the flat part is also Since the image is enlarged, the S/N ratio of the output signal deteriorates, resulting in a grainy image.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a gradation correction device that can reduce deterioration of the S/N ratio when gradation correction is performed on a video luminance signal.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a decompression means (gradation correction circuit) for decompressing the gradation characteristics of the main component of an input video signal; A means for reducing the noise component relative to the main component is provided.

Furthermore, in order to separate the main component (low-frequency component) and the noise component, a low-pass filter and a high-pass filter are used, and a delay circuit is used to correct the delay time difference between the two.

Furthermore, the amplitude of the noise component is controlled by a signal corresponding to the expansion characteristic. Furthermore, the signal is passed through a coring circuit before noise component amplitude control.

[0011] Furthermore, the signal is passed through a limiter circuit before noise component amplitude control. Note that when using coring, the noise component is added to the main component, and when using a limiter, it is subtracted.

0012

[Function] With the above configuration, the present invention allows the high frequency components containing noise to be expanded in the same way as the low frequency components even in the part where the low frequency components, which are the main components of the input video signal, have been expanded (gradation correction). Since there is no noise, deterioration of S/N can be suppressed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A tone correction apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a tone correction device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a gradation correction circuit, which has the same configuration as the conventional one. A low-pass filter 2 separates and outputs a low-pass video signal c from the input video signal a. A high-pass filter 3 separates and outputs a high-frequency video signal d from the input video signal a. 4 is a delay circuit which eliminates the time difference between the low frequency gradation correction signal e and the delayed high frequency video signal f which is the output of this circuit. Reference numeral 8 denotes an adder circuit which adds the low-frequency gradation correction signal e and the delayed high-frequency video signal f, and outputs an output video signal d.

The operation of the tone correction device of the above-described constituent blocks will be explained below.

First, among the input video signals, high-frequency video signal components (1 to 2 MHz or more) that generally contain a lot of visual noise and low-frequency video signal components (1 to 2 MHz or less) are filtered through a high-pass filter 3. The signals are separated by a low-pass filter 2, and a high-frequency video signal d and a low-frequency video signal c are obtained as outputs, respectively. The low frequency video signal c is gradation corrected in the same manner as in the past to become the low frequency gradation correction signal e.The high frequency video signal d is passed through the delay circuit 4 and outputs the delayed high frequency video signal f and the low frequency After the timing is matched with the gradation correction signal e, the signals e and f are added together in an adder circuit 8 to obtain an output video signal b.

As described above, according to this embodiment, by combining a low-pass filter, a high-pass filter, a delay circuit, and an adder circuit with a conventional gradation correction circuit, emphasis on high-frequency components can be suppressed and gradation correction can be performed. Even if you do so, there will be little increase in noise.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows a block diagram of a tone correction device according to a second embodiment of the present invention. In FIG. 2, 2 is a low-pass filter, 3 is a high-pass filter, and 8 is an adder circuit, which are the same as those in the first embodiment. Reference numeral 11 denotes a gradation correction circuit, which differs from the conventional gradation correction circuit 1 in that it outputs a gradation correction amount detection signal g representing the magnitude of the correction amount of the gradation correction circuit. be. A gain control and delay circuit 5 controls the amplitude of the high frequency video signal d according to the gradation correction amount detection signal g, also performs a signal delay operation, and outputs a delayed high frequency video signal f.

The operation of the gradation correction device of the above-described structural blocks will be explained below with reference to FIGS. 2 and 3. FIG. 3 is a block diagram showing one means for obtaining the gradation correction amount detection signal g and its operation diagram.

First, the input video signal a is separated by a low-pass filter 2 and a high-pass filter 3, as in the first embodiment. In the first embodiment, the high frequency video signal d is delayed by the delay circuit 4 and then added to the low frequency gradation correction signal e to obtain the output video signal b. However, in this embodiment, the high frequency video signal d is The gain control and delay circuit 5 changes the amplitude according to the gradation correction amount detection signal g representing the gradation correction amount, and then the addition circuit 8 adds it to the low-frequency gradation correction signal e to obtain the output video signal b. It has gained. FIG. 3 shows one means for obtaining this tone correction amount detection signal g, and the tone correction circuit 11 used in this embodiment has a configuration as shown in FIG. 3(c). There is a gradation correction amount control unit 21 that determines the gradation correction amount according to the properties of the range video signal c;
) A gradation correction lookup table section 22 as shown in the figure.
(generally composed of random access memory) is set, the horizontal axis (memory address) is the level of the input low-frequency video signal c, and the vertical axis (memory data) is the output low-frequency video signal c. This becomes the level of the gradation correction signal e. The above configuration was used in the conventional example and the first example, but in the case of this example, this gradation correction lookup table section 2
By differentiating 2, the gradient is calculated by the gradation correction control section 21, and as shown in FIG. Depending on the level of the video signal, a gradation correction amount detection signal g corresponding to the gradation correction amount of that portion can be output. For example, in the case of Figure 3 (a), the solid line in the figure shows the conversion table when gradation is corrected, and the broken line shows the conversion table in the linear case without gradation correction, and when differentiated, (b) As shown in the figure, the value is 1 or more in the part where the gradation is expanded, and the value is 1 or less in the part where the gradation is collapsed. The dashed line is the differentiation of the dashed line in figure (a) and is 1
It is.

[0021] Actually, if the differential result is used as the correction amount as it is, the output video signal will be the same as in the conventional example, so the signal g is obtained by multiplying the differential result by a coefficient of 1 or less, or by subtracting a constant value from the differential result. Alternatively, only for parts where the differential result is 1 or more, the differential value is converted by multiplication or subtraction as described above.

According to this embodiment, the tone correction amount detection signal g
By controlling the amplitude of the high frequency video signal d to below the conventional example by the gain control circuit 5 in a portion where the gradation is large (a portion where the gradation is extended), the S/
In addition to improving the N ratio, it is possible to obtain a more natural output video signal b compared to the first embodiment.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 4 shows a block diagram of a tone correction device according to a third embodiment of the present invention. In FIG. 4, 2 is a low-pass filter, 3 is a high-pass filter, 5 is a gain control and delay circuit, 8 is an addition circuit, and 11 is a gradation correction circuit, which are the same as in the second embodiment. A coring circuit 9 clips a small amplitude component of the high frequency video signal d and outputs a coring high frequency video signal k.

The operation of the gradation correction device of the above-described structural blocks will be explained below with reference to FIG.

First, the input video signal a is separated into low-frequency and high-frequency video signals by the low-pass filter 2 and high-pass filter 3, and the low-frequency video signal c is subjected to gradation correction as in the second embodiment. Then, a gradation-corrected low-frequency video signal e and a gradation correction amount detection signal g are obtained. In this embodiment, a coring circuit 9 is provided for the high frequency video signal d, and after first clipping a small amplitude portion containing many noise components of the high frequency video signal d, the signal is input to the gain control circuit 5. The feature is that it performs gain control. The gradation correction amount detection signal g in this embodiment is not only a signal obtained by differentiating and then undergoing conversion as in the second embodiment, but also a noise component of the differentiated signal itself has already been removed by the coring circuit 9. It is possible to use it because it is.

As described above, according to this embodiment, after inserting the coring circuit into the high-frequency video signal, the gain control and delay circuit perform control according to the gradation correction amount detection signal. Remove the noise of S/
In addition to improving the N ratio, it is possible to perform gradation correction on parts other than noise in the high-frequency video signal in the same manner as in the low-frequency range, and it is possible to obtain a more faithful output video signal b.

Next, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows a block diagram of a tone correction device according to a fourth embodiment of the present invention. In FIG. 5, 3 is a high-pass filter, 5 is a gain control and delay circuit, and 11 is a gradation correction circuit.
The above is similar to the second and third embodiments. A limiter circuit 7 limits the amplitude of the high frequency video signal d and outputs a limited high frequency video signal i. This level of restriction is
Settings are made so that small amplitude components containing many noise components are passed through, and other relatively large amplitude components are subjected to amplitude limitation. 12 is a subtraction circuit that subtracts the high frequency correction signal j from the gradation correction video signal e and outputs an output video signal b.

The operation of the tone correction device of the above-described constituent blocks will be explained below.

First, the input video signal a is sent to the gradation correction circuit 11.
is input to the high-pass filter 3. The present embodiment is characterized in that the input video signal a is input to the gradation correction circuit 11 without passing through a low-pass filter. The gradation correction circuit 11 corrects the gradation of the input video signal as in the second and third embodiments, and outputs a gradation correction signal e and a gradation correction amount detection signal g. Further, the high-pass filter 3 is also similar to those in the second and third embodiments, and separates the high-frequency component of the input video signal a, and outputs a high-frequency video signal d. This signal d is the limiter circuit 7
, the amplitude is limited to the amplitude of a small amplitude component containing a lot of noise, and as a result, a limited high frequency video signal i is output. This signal i is input to a gain control and delay circuit 5, and its amplitude is controlled according to the gradation correction amount detection signal g, and is output as a high frequency correction signal j. In other words, the part where the gradation has been extended due to gradation correction is the signal i.
The amplitude of the signal i is increased, and conversely, the amplitude of the signal i is controlled to be decreased in the portion where the amplitude has been reduced by the gradation correction. Then, the subtraction circuit 12 subtracts the high frequency correction signal j from the gradation correction signal e to obtain the output video signal b. That is, by subtracting the noise component j included in the signal e by the noise component j by the subtraction circuit 12, an output signal b with a good S/N ratio and less noise can be obtained.

As described above, according to this embodiment, after providing a limiter circuit after the high-pass filter, gain control is performed according to the amount of gradation correction, and subtraction is performed from the gradation-corrected signal. It has a simpler configuration than the third embodiment, suppresses the increase in noise components due to gradation correction, and improves S/
A gradation correction device with a good N ratio and less noise can be constructed.

Next, a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 6 shows a block diagram of a tone correction device according to a fifth embodiment of the present invention. In FIG. 6, 3 is a high-pass filter, 7 is a delay circuit, and 7 is a high-pass filter.
11 is a limiter circuit, 11 is a gradation correction circuit, and 12 is a subtraction circuit, and their respective operations are similar to those in the second, third, and fourth embodiments.

The operation of the gradation correction device of the above-described constituent blocks will be explained below. First, input video signal a
is input to the gradation correction circuit 11 and becomes the gradation correction signal e, which undergoes gradation correction. At the same time, a gradation correction amount detection signal g representing the magnitude of the gradation correction amount is output. Next, the tone correction signal e is input to the delay circuit 4 and the high-pass filter 3. The delay circuit 4 is provided at the input of the subtraction circuit 12 in order to match the timing of the signal m and the signal p. The high-pass filter 3 separates the high frequency component of the gradation correction signal e and outputs it as a high-frequency gradation correction signal n to the limiter circuit 7.
Output to. The limiter circuit 7 functions to limit the amplitude of this high frequency gradation signal n to a certain amplitude or less and output a limited high frequency gradation correction signal p. This amplitude limit level is changed according to the gradation correction amount detection signal g. In other words, the way of thinking is the fourth
This is similar to the example in , but in order to separate components containing a lot of noise from the signal after tone correction, the amplitude of the noise component is also increased in the part where the tone is stretched. Therefore, increase the amplitude limit level and conversely,
For the portion where the gradation is reduced, the level of amplitude restriction is made smaller. Next, the limited high-frequency gradation correction signal p is subtracted from the delayed gradation correction signal m by the subtraction circuit 12, and an output video signal b is obtained. This operation is similar to the fourth embodiment.

As described above, according to this embodiment, a delay circuit, a hyper filter, a limiter circuit, and a subtraction circuit are provided after the gradation correction circuit 11, and by varying the limiter level according to the amount of gradation correction, It is possible to provide a gradation correction device with less noise increase and less deterioration of S/N ratio.

In the second embodiment, one means for obtaining the gradation correction amount detection signal has been described, but this is a strict method, and in reality, the amount of correction is determined by taking the difference between the input and output of the gradation correction circuit. Any method may be used as long as it can be detected.

Further, although a coring circuit is used in the third embodiment, a base clip circuit may be used instead.

[0036]

As is clear from the above embodiments, the present invention provides a low-pass filter, a high-pass filter, a coring circuit, a gain control and delay circuit, and an adder circuit in addition to the conventional configuration.
A limiter circuit, a gain control and delay circuit, a subtraction circuit, or a delay circuit, high-pass filter,
By providing a limit circuit, a subtraction circuit, etc., it is possible to provide a gradation correction device that reduces deterioration of the S/N ratio (increase in noise components) of an input video signal due to gradation correction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tone correction device in a first embodiment of the present invention.

FIG. 2 is a block diagram of a tone correction device in a second embodiment of the present invention.

[Figure 3] Block diagram and characteristic diagram for explaining the operation of the gradation correction circuit in Figure 2

FIG. 4 is a block diagram of a tone correction device in a third embodiment of the present invention.

FIG. 5 is a block diagram of a tone correction device in a fourth embodiment of the present invention.

FIG. 6 is a block diagram of a tone correction device in a fifth embodiment of the present invention.

[Figure 7] Block diagram and main waveform diagram of a conventional gradation correction device

[Explanation of symbols]

1 Gradation correction circuit 2 Low pass filter 3 High pass filter 4 Delay circuit 5 Gain control and delay circuit 7
Limiter circuit 8 Addition circuit 9 Coring circuit 11 Gradation correction circuit (expansion means) 12 Subtraction circuit

Claims (6)

[Claims] 1. A gradation system comprising: expansion means for expanding the gradation characteristics of a main component of an input video luminance signal; and means for reducing a noise component relative to the main component when the expansion means expands the main component. Key correction device. 2. A high-pass filter that passes a high-frequency component of an input video luminance signal, a low-pass filter that passes a low-frequency component of the input video luminance signal, and corrects the gradation of an output signal of the low-pass filter. A gradation correction device comprising: a gradation correction circuit that delays an output signal of the high-pass filter for a certain period of time; and an addition circuit that adds an output signal of the gradation correction circuit and an output signal of the delay circuit. 3. A high-pass filter that passes high-frequency components of the input video luminance signal, a low-pass filter that passes the low-frequency components of the input video luminance signal, and corrects the gradation of the output signal of the low-pass filter. a gradation correction circuit for controlling the amplitude of the output signal of the high-pass filter; a gain control and delay circuit for controlling the amplitude of the output signal of the high-pass filter; and an addition circuit for adding the output signal of the gradation correction circuit and the output signal of the gain control circuit; A gradation correction device that determines a gain control amount of the gain control and delay circuit based on a signal representing a correction amount output from a gradation correction circuit. 4. A high-pass filter that passes high-frequency components of the input video luminance signal, a low-pass filter that passes the low-frequency components of the input video luminance signal, and correcting the gradation of the output signal of the low-pass filter. a coring circuit that attenuates or removes a small amplitude component of the output signal of the high-pass filter; a gain control and delay circuit that controls the amplitude of the output signal of the coring circuit; A gradation comprising an adding circuit that adds an output signal of a gradation correction circuit and an output signal of a gain control circuit, and determining a gain control amount of the gain control circuit based on a voltage representing a correction amount output from the gradation correction circuit. correction device. 5. A gradation correction circuit that corrects the gradation of an input video luminance signal, a high-pass filter that passes a high frequency component of the input video luminance signal, and an amplitude of an output signal of the high-pass filter that is set to a predetermined value or less. a gain control and delay circuit that controls the amplitude of the output signal of the limiter circuit by a voltage according to the amount of gradation correction provided by the gradation correction circuit; A gradation correction device comprising a subtraction circuit that subtracts an output signal of a gain control and delay circuit, and determining a gain control amount of the gain control and delay circuit based on a voltage representing a correction amount output from the gradation correction circuit. 6. A gradation correction circuit for correcting the gradation of an input video luminance signal; a high-pass filter for passing a high frequency component of an output signal of the correction circuit; a limiter circuit that limits the limit value to the following and controls the limit value by a voltage according to the amount of gradation correction given by the gradation correction circuit; and a subtraction circuit that subtracts the output of the limiter circuit from the output signal of the gradation correction circuit. A gradation correction device comprising a delay circuit between a circuit, the gradation correction circuit, and the subtraction circuit.