KR100197610B1 - Gamma correction apparatus - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction apparatus used for processing a luminance signal of a camera or the like, and more particularly to a gamma correction apparatus capable of suppressing an increase in noise in a blank period of a video signal by gamma processing and adjusting a black level more easily. will be. The gamma correction device of the present invention comprises a clamp unit for setting a black level of an input luminance signal to a voltage suitable for gamma correction, a first synthesizer for synthesizing a blank signal representing a blank period of the output signal and the luminance signal of the clamp unit, and a first synthesizer. A nonlinear amplifier for amplifying a signal synthesized by a synthesizer according to a variable amplification degree, an inverter for inverting a blank signal, and a second synthesizer for synthesizing an inverted blank signal and an output signal of the nonlinear amplifier. Accordingly, the present invention has the effect of suppressing the increase in the noise of the blank period while maintaining the correlation between the blank level and the black level to more accurately represent the luminance.

Description

Gamma Correction Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction apparatus used for luminance signal processing such as a camera, and more particularly, to suppress an increase in noise in a blank period of a video signal by gamma processing and to view a black level. It relates to a gamma correction device that can be easily adjusted.

In general, video signals output from television cameras require gamma correction due to the characteristics of the CRT at the receiver. In a typical CRT, the luminance signal voltage is not linearly proportional to the brightness of the screen, that is, the luminance. When the luminance signal voltage is small, the change in the luminance with respect to the unit voltage change is small, and when the luminance signal voltage is high, the change in the luminance with respect to the unit voltage change becomes large, indicating a form of an exponential curve. That is, the amount of light exiting the CRT is not proportional to the voltage driving the CRT. Therefore, when the television camera sends the luminance signal proportional to the luminance of the image to the television without any additional correction, the luminance shown in the CRT is displayed differently from the actual luminance.

In order to solve this problem, the camera compensates the luminance signal with the characteristics opposite to that of the CRT and sends it to the television. A device for performing such correction is generally called a gamma correction device. This conventional gamma correction device is shown in FIG.

1 is a block diagram showing a conventional gamma correction device. As illustrated, the clamp unit 11 receiving the input luminance signal Sin, the nonlinear amplifier 12 which receives the signal output from the clamp unit 11 and non-linearly amplifies and outputs the blank, and generates a blank level. The switching unit for switching the blank level generator 13 and the non-linear amplifier 12 from the signal input to the first input terminal, the blank level to the second input terminal and the blank signal P ₁ as a control signal for switching. It consists of 14.

FIG. 2 is an input / output waveform diagram of each part shown in FIG. 1.

The operation of the conventional gamma correction device configured as described above will be described with reference to FIG. 2.

First, the clamp unit 11 receives the input luminance signal Sin as shown in FIG. 2A, detects the black reference level included in the blank period of the input luminance signal, and compares the difference with the voltage set for gamma correction. Adjust the level of the luminance signal by adding or subtracting. The level-adjusted luminance signal is applied to the nonlinear amplifier 12, and the nonlinear amplifier 12 responds to the unit voltage change when the luminance signal voltage is small and the voltage of the output luminance signal is large when the luminance signal voltage is high. The amplification degree is varied so that the variation of the output luminance signal with respect to the output signal is output as shown in FIG. 2B. The blank level generator 13 generates and outputs a blank level. The switching unit 14 receives the output signal of the nonlinear amplifier 12 to the first input terminal a and the blank level to the second input terminal b, respectively, and the blank signal P ₁ as shown in FIG. 2C. Is applied as a control signal. At this time, the blank signal P ₁ represents a blank period. Therefore, the switching unit 14 outputs a blank level input to the second input terminal b when the blank signal P ₁ is in a high state, and when the blank signal P ₁ is in a low state. The signal of FIG. 2B input to the first input terminal a is output to finally output a gamma corrected signal Sout as shown in FIG. 2D.

However, in the conventional gamma corrected device as shown in FIG. 2B, the amplification degree is increased at the black level (low state), and the amplification degree is 1 at the 100% white level (high state), and the noise in the black level portion is shown. If is included there is a problem that the noise signal is greatly increased. In particular, the blank period of the luminance signal includes the black reference level, so that the noise of the blank period is amplified most. Although the noise is removed to some extent by the switching unit 14, in the case of the conventional gamma correction apparatus, the blank level output from the blank level generating unit 14 has no correlation with the black level of the luminance signal. If this is not correct, a level difference occurs between the blank level and the black level of the luminance signal, so that the luminance cannot be represented correctly. In addition, since the blank level generator 14 must always generate a constant voltage, a highly stable circuit is required, and the switching unit is also required to have low crosstalk.

1 is a block diagram showing a conventional gamma correction device,

2 is an input / output waveform diagram of each part shown in FIG. 1;

3 is a block diagram showing a gamma correction device according to a preferred embodiment of the present invention,

4 is an input / output waveform diagram of each part shown in FIG. 3;

* Explanation of symbols for main parts of the drawings

21: clamp portion 22: first synthesizer

23 nonlinear amplifier 24 second synthesizer

INV: Inverter

Accordingly, the gamma correction device of the present invention is a device for gamma correcting an input luminance signal, comprising: a clamp portion for setting a black level of the luminance signal to an appropriate voltage, a blank period between the signal output from the clamp portion and the luminance signal; A first synthesizer for synthesizing a blank signal representing a nonlinear amplifier, a nonlinear amplifier for amplifying the signal synthesized by the first synthesizer according to a variable amplification degree, and a synthesized output signal of the nonlinear amplifier and an inverted signal of the blank signal And a second synthesizer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram showing a gamma correction device according to the present invention. As shown, the gamma correction device of the present invention is applied to the clamp unit 21 for applying the luminance signal Sin to adjust the level, and outputs the output signal of the clamp unit 21 and the blank signal P ₁ inputted. A first synthesizer 22 is synthesized and output. The output terminal of the first synthesizer 22 is connected with a nonlinear amplifier 23 for nonlinearly amplifying and outputting the signal output from the first synthesizer 22. The blank signal P ₁ is inverted through the inverter INV, and a second synthesizer for synthesizing the inverted blank signal with the output signal of the nonlinear amplifier 23 at the output terminals of the nonlinear amplifier 23 and the inverter INV. 24) is configured to be connected.

FIG. 4 is a waveform diagram illustrating the operation of the gamma correction device of FIG. 3.

The operation of the gamma correction device of the present invention configured as described above will be described in more detail with reference to FIG. 4.

As shown in FIG. 4A, when a luminance signal Sin that is proportional to the luminance of the subject is applied to the input terminal, the clamp unit 21 detects and gamma detects the black reference level included in the blank period of the input luminance signal Sin. The level of the luminance signal is adjusted by the action of adding or subtracting the difference compared to the voltage set for correction. The first synthesizer 22 receives and synthesizes the luminance signal level adjusted by the clamp unit 21 and the blank signal P ₁ as shown in FIG. 4B. At this time, the blank signal P ₁ indicates a blank period including a synchronization signal, a black reference level, a color burst, and the like. The blank signal P ₁ is maintained at a high state in a blank period and at a low state in a valid period of a video signal. do. In addition, the first combiner 22 includes a second resistance in series with the stage in which the first resistance (R ₁₎ is connected in series to the stage where the level of the adjusted luminance signal input and the blank signal (P ₁₎ is entered (R ₂ ) Is connected so as to increase the blank level of the luminance signal to 100% white level as shown in FIG. 4C by the ratio of the first resistor R ₁ and the second resistor R ₂ . The nonlinear amplifier 23 receives the signal synthesized by the first synthesizer 22 (shown in FIG. 4C), and when the input luminance signal voltage is small, the variation of the output luminance signal with respect to the unit voltage change is large, and the input luminance signal When the voltage is high, the amplification degree is variable and amplified so that the change of the output luminance signal with respect to the unit voltage change is small, and the signal as shown in FIG. 4D is output. The blank signal P ₁ is inverted as shown in FIG. 4E through the inverter INV, and the second synthesizer 24 synthesizes the output signal of the nonlinear amplifier 23 and the inverted signal of the blank signal to FIG. 4F. A gamma corrected luminance signal Sout as shown in Fig. Is output. At this time, the second synthesizer 24 is connected to the third resistor (R ₃ ) in series with the stage where the output signal of the nonlinear amplifier 23 is input and the fourth resistor (in series) with the stage where the inverted signal of the blank signal is input. R ₄ ) is configured to be connected to return the level up to 100% white level to the original blank level by the ratio of the third resistor R ₃ and the fourth resistor R ₄ . By raising the blank level to 100% white level with amplification degree 1 as shown in FIG. 2C, the noise included in the blank period does not increase, and lowering the raised blank level back to the original blank level as shown in FIG. 4F. It can be seen that the noise increase in the blank period is reduced compared to the conventional gamma correction device.

As described above, the present invention is 100% with a blank level amplification degree of 1, compared to the conventional method in which the gamma correction up to the blank level greatly increases the noise signal in the blank period and a level difference occurs between the blank level and the black level of the luminance signal. By raising the white level and performing gamma correction and lowering it back to the original blank level, it is possible to suppress the increase of the noise during the blank period while maintaining the correlation between the blank level and the black level to more accurately represent the luminance.

An object of the present invention is to suppress the increase in noise in the blank period after gamma correction by raising the blank level to the white level during the blank period and after gamma correcting again to reduce the noise level between the blank level and the black level. The present invention provides a gamma correction device capable of accurately displaying luminance by maintaining correlation.

Claims (6)

A device for gamma correcting an input luminance signal, comprising: a clamp unit for setting a black level of the luminance signal to an appropriate voltage; A first synthesizer for synthesizing a blank signal representing a blank period of the signal output from the clamp unit and the luminance signal; A nonlinear amplifier for amplifying the signal synthesized by the first synthesizer according to a variable amplification degree; And a second synthesizer for synthesizing the output signal of the nonlinear amplifier and the inverted signal of the blank signal. The gamma correction device of claim 1, wherein the first synthesizer comprises a first resistor connected to an output terminal of the clamp unit and a second resistor connected to the blank signal input terminal. The gamma correction device of claim 2, wherein the first synthesizer adjusts the level of the output signal by a ratio of the two resistance values. The nonlinear amplifier of claim 1, wherein the change of the output luminance signal with respect to the unit voltage change is large when the input luminance signal voltage is small, and the change of the output luminance signal with respect to the unit voltage change is small when the input luminance signal voltage is large. A gamma correction device characterized in that the amplification by varying the degree of amplification. The gamma correction device of claim 1, wherein the second synthesizer comprises a third resistor connected to an output terminal of the nonlinear amplifier and a fourth resistor receiving an inverted signal output of the blank signal. The gamma correction device of claim 5, wherein the second synthesizer adjusts the level of the output signal by a ratio of the two resistance values.