KR20070028158A - Apparatus and method for controlling dynamic contrast ratio using peak level - Google Patents

Abstract

An apparatus and a method for controlling a dynamic contrast ratio using an autocorrelation function are provided to adaptively process a backlight brightness control rate and a response time according to a current image to achieve an effective AI(Adaptive Intensify) function. An apparatus for controlling a dynamic contract ratio using an autocorrelation function includes a gamma corrector(120), a mean calculator(140), a PWM(Pulse Width Modulation) unit(150), a video frame variation state detector(200), an inverter(160), and a backlight(170). The gamma corrector compensates for non-linearity with respect to a brightness recognition degree of the human eye for a video signal output from a scaler. The mean calculator calculates a mean brightness value of a video frame output from the scaler. The PWM unit outputs a pulse-width-modulated signal corresponding to the output signal of the mean calculator. The video frame variation state detector analyzes a variation in the video frame output from the scaler. The inverter controls the voltage of a frequency synchronized with the output signal of the PWM unit according to the output signal of the video frame variation state detector. The backlight outputs light with brightness corresponding to the output signal of the inverter to an LCD(Liquid Crystal Display) panel.

Description

Apparatus and Method for controlling dynamic contrast ratio using peak level}

1 is a diagram illustrating a configuration of an image display device for controlling dynamic contrast ratio according to the related art.

2 is a view for explaining a dynamic contrast ratio control apparatus using an autocorrelation function according to the present invention;

3 is a flowchart illustrating a process of detecting characteristic information of a before and after image changed in a dynamic contrast ratio control method using an autocorrelation function according to the present invention.

<Explanation of symbols for the main parts of the drawings>

110: scaler 120: gamma compensation

130: LCD panel 140: average calculation unit

150: PWM converter 160: inverter

170: backlight 200: image frame change state detection unit

The present invention relates to an apparatus and method for controlling dynamic contrast ratio using an autocorrelation function using an autocorrelation function.

The environment in which the viewer views the video display device changes according to the video being viewed. Therefore, in order to enjoy the optimal video, each image that composes the image quality of color temperature, color density, color, sharpness, brightness, contrast, etc. according to the changed environment is viewed. There is a need to change the quality setting information for the status. However, whenever the viewing environment changes, it is very inconvenient for the user to change the image quality setting information accordingly.

Contrast ratio expresses the difference between the lightest and darkest parts of the image. The sharpness perceived by the human eye depends on how bright and dark areas of the same screen represent dark areas, allowing the image display device to automatically adjust the contrast ratio according to the image state. This function is called Dynamic Contrast Ratio control or Adaptive Intensify (AI).

1 is a diagram illustrating a configuration of a video display device for controlling dynamic contrast ratio according to the prior art.

Referring to FIG. 1, the image display apparatus for controlling the dynamic contrast ratio according to the related art includes a scaler 110 for converting a magnitude of an image signal into an image signal having a size suitable for displaying on a display device, and outputting the image signal to the image signal. A gamma correction unit 120 for compensating and outputting nonlinearity with respect to brightness of a human eye, an average calculator 140 for calculating and outputting an average brightness value of an image frame, and a pulse width modulation corresponding to an input signal PWM converter 150 for outputting the signal and the inverter 160 for outputting a signal having a voltage and frequency in synchronization with the input signal, the backlight 170 for outputting light of the brightness corresponding to the output of the inverter, And an LCD panel 130 for displaying an image.

An operation of the video display device for controlling the dynamic contrast ratio according to the prior art configured as described above will be described.

The scaler 110 converts an input image signal into an image signal having a size suitable for display on a display device and outputs the converted image signal.

The average calculating unit 140 receives the output image signal of the scaler 110, detects the brightness of each pixel of the image frame for each block, calculates an average brightness value thereof, and converts the calculation result into a DC voltage value DC. Output

The PWM converter 150 receives the output of the average calculator 140 and outputs a pulse width modulated signal PWM according to the output level.

The gamma correction unit 120 receives an output image signal of the average calculating unit 140 and an output voltage of the average calculating unit 140 and compensates for the nonlinearity of the brightness recognition degree of the human eye with respect to the image signal. Data is output to the LCD panel 130.

The inverter 160 generates an output having a voltage and a frequency synchronized with a PWM input output from the PWM converter 150 and outputs the output to the backlight 170.

The LCD panel 130 actively adjusts the brightness of the finally displayed image by outputting the corrected image output of the gamma correction unit 120 and the image corresponding to the output level of the inverter 160.

The dynamic contrast ratio control, that is, AI, is a technology for dynamically improving C / R by analyzing brightness information of an input image and performing backlight modulation and data stretch. The AI function, a technology designed to improve the contrast ratio of TFT-LCD televisions, obtains a histogram of the digital signal of the current image, calculates brightness information of the image, and drives the TFT-LCD through the information. It is to adjust the brightness of the backlight of the inverter.

Through this series of processes, adaptive optical enhancement is provided by providing bright optical illumination in high luminance images and dark optical illumination in low luminance image signals. In addition, the TFT-LCD using the transmissive element using the light of the backlight adjusts the brightness of the light in addition to the effect of the image generated on the LCD, thereby enabling an effective image implementation on a particularly dark screen.

In the above-described AI function, in case of an image having a small change in scene and a low rate of change in the light, the backlight light is gradually adjusted so that the viewer can be naturally provided with an improved performance, but in a case where the change rate of the image is high It can have unnatural consequences.

This drawback is particularly problematic due to the histogram calculation block for AI processing and the delay time that occurs during processing. That is, in the case of an image having a high frequency of the lighting change that occurs clearly, a problem of suddenly changing the brightness of the backlight after the lighting change occurs.

Therefore, implementing the AI function by analyzing the luminance information of the image using a histogram based on an integration technique and calculating brightness information of the entire image represents a performance limitation due to problems occurring in the implementation process.

In order to solve the above problem, the present invention simply changes the illumination in a similar scene together with the brightness information of the current image, the transition state of a complete scene, and an image state such as a gradual change of the image. An object of the present invention is to provide an apparatus and method for controlling dynamic contrast ratio using an autocorrelation function using an autocorrelation function that can implement adaptive image reinforcement by reflecting additional information.

In addition, the present invention prevents an unnatural backlight change in case of a sudden change in illumination, and minimizes the waiting time to improve the reliability of the backlight change at the time of a complete scene change, thereby implementing immediate backlight adjustment. In the case of image change, an object of the present invention is to provide an apparatus and method for controlling dynamic contrast ratio using an autocorrelation function using an autocorrelation function capable of implementing adaptive image reinforcement based on an existing processing process.

A dynamic contrast ratio control apparatus using an autocorrelation function according to the present invention for achieving the above object comprises: a gamma correction unit for compensating and outputting nonlinearity of brightness perception of a human eye with respect to an image signal output from a scaler; An average calculator for calculating and outputting an average brightness value of a scaler output image frame, a PWM converter for outputting a pulse width modulated signal corresponding to the output signal of the average calculator, and a change before and after the image frame output from the scaler An image frame change state detector for analyzing and outputting a state, an inverter for adjusting and outputting a voltage at a frequency synchronized with the output of the PWM converter according to the output of the image frame change state detector, and a brightness corresponding to the output of the inverter It is configured to include a backlight for outputting light to the LCD panel It shall be.

In accordance with another aspect of the present invention, a dynamic contrast ratio control method using an autocorrelation function includes performing adaptive image reinforcement using a combination of brightness information of a current image and characteristic information of a changing front and rear image. It features.

The changing characteristic information of the before and after image may include an image state in which only a sudden change in illumination occurs in a similar scene, an image state at a time of switching a complete scene, and gradually change state information of an image.

A dynamic contrast ratio control method using an autocorrelation function according to the present invention for achieving the above object comprises a first determination step of determining whether the scene transition state by comparing the histogram difference of the luminance component between the image frame and the auto-correlation coefficient; A second determination step of determining whether the scene is in a gradual scene change state using entropy differences between successive frames when the scene is not a scene change; and a difference in the histogram change amount when the result is not a gradual scene change. And a third determination step of determining whether the lighting change state is sudden and controlling an output method of the inverter controlling the output of the backlight according to each image state according to the determination result.

In the third determination step, when it is not a sudden lighting change state, it is determined as a general video screen, and a general dynamic contrast ratio control method is applied.

Preferably, when it is determined that the scene change, the instantaneous VBR output is generated with respect to the current histogram value to apply the changed backlight driving voltage to the inverter circuit immediately.

Preferably, when it is determined that the scene is gradually changed, the circuit is operated according to the AI reliability guarantee algorithm, and the response speed of the VBR output is set to be slow.

Preferably, the interpolation response coefficient is set to the maximum so as to gradually change the VBR output level by the dynamic contrast ratio control function when it is determined that the rapid lighting change continues.

According to the apparatus and method for controlling the dynamic contrast ratio using the autocorrelation function according to the present invention configured as described above, an effective AI function is provided by adaptively processing the speed and response time of brightness adjustment of the backlight according to the current image. Can be implemented. As a result, the AI function with improved performance can achieve the advantages of the dynamic contrast ratio and the natural image processing effect.

Hereinafter, an apparatus and method for controlling a dynamic contrast ratio using an autocorrelation function according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a diagram illustrating an apparatus for controlling dynamic contrast ratio using an autocorrelation function according to the present invention, and FIG. 3 illustrates characteristic information of a before and after image changed in the method for controlling dynamic contrast ratio using an autocorrelation function according to the present invention. It is a flowchart which shows a process of detecting.

Referring to FIG. 2, the apparatus for controlling the dynamic contrast ratio using the autocorrelation function according to the present invention includes a gamma correction unit for compensating and outputting nonlinearity of brightness recognition degree of a human eye with respect to an image signal output from the scaler 110. 120, an average calculator 140 for calculating and outputting an average brightness value of the scaler 110 output image frame, and a pulse width modulated signal corresponding to the output signal of the average calculator 140. The PWM converter 150, the image frame change state detector 200 for analyzing and outputting the change state before and after the image frame output from the scaler 110, and the voltage of the frequency synchronized with the output of the PWM converter Inverter 160 for adjusting and outputting the image frame change state detector 200 and a backlight for outputting light having a brightness corresponding to the output of the inverter 160 to the LCD panel. It is configured to include the 170.

The scaler 110 converts the magnitude of the input digital image signal into an image signal of a size suitable for display on the LCD panel 130 as a display device and outputs the converted image signal. The LCD panel 130 used as the display device is just one example, and it is also possible to use another image display device such as a plasma display panel (PDP).

The average calculator 140 detects the output image frame of the scaler 110 for each block divided into local regions, detects an average brightness value of the image frame, and outputs a signal for adjusting the image brightness.

The PWM converter 150 receives the output of the average calculator 140 and outputs a pulse width modulated signal PWM according to the input level.

The gamma correction unit 120 receives the output of the average calculator 140 and compensates for the nonlinearity of the brightness recognition degree of the human eye with respect to the image signal output from the scaler 110. 130).

The image frame change state detector 200 analyzes the change state before and after the frame of the image signal output from the scaler 110 and outputs a signal for controlling the output of the inverter according to the image frame change state.

The inverter 160 outputs a voltage having a constant frequency corresponding to the output of the PWM converter 150 under the control of the image frame change state detector 200 to adjust the brightness of the LCD panel 130 to thereby output the final output. The image is augmented adaptively to the image frame change state and output as a natural screen.

An embodiment in which the dynamic contrast ratio control method using the autocorrelation function according to the present invention is applied to the dynamic contrast ratio control apparatus using the autocorrelation function according to the present invention will be described with reference to FIG. 3. .

As shown in FIG. 3, when the image display apparatus starts to operate, in order to perform the dynamic contrast ratio control method using the autocorrelation function according to the present invention, the histogram difference and the autocorrelation coefficient of the luminance component between image frames are first compared. It is determined whether the scene transition state.

To this end, the R, G, B format video signals are converted into YCbCr format video signals (S311). Subsequently, the histogram of the luminance (Y) component is compared among the video signals converted into the YCbCr format (S312) to obtain an autocorrelation (Self-correlation) (S313). Thereafter, the difference between the current histogram (TAC) and Ac (Autocorrelation) is compared (S314).

The autocorrelation is calculated by applying a window to the autocorrelation function that represents the correlation between the signal value at one time and the signal value at another time. Since a method of obtaining autocorrelation for an image frame is generally known, a detailed description thereof will be omitted.

As described above, in the present invention, autocorrelation is used to determine whether the scene is changed by using the difference in the histogram. If there is no change in the image, the difference in the histogram is almost unchanged. That is, in the same scene, the histogram of the image of the image frame before and after is not changed. In this case, the autocorrelation value is similar to the current histogram difference.

However, if the image suddenly changes, the value changes significantly compared to the value obtained from autocorrelation and the current histogram difference. If the image becomes clear as it gradually becomes brighter than the black image, the histogram difference greatly increases and then gradually falls.

Likewise, when the image changes, such as zoom in / out, the histogram difference gradually increases. The autocorrelation value at that time also increases. Comparing the two values does not make much difference, so you can distinguish between zoom in / out and scene transition.

As a result of the comparison (S315), if the TAC is larger than Ac, it is determined that the scene change state (S320). In this case, when it is determined that the scene change, the instantaneous VBR output is generated with respect to the current histogram value to immediately apply the changed backlight driving voltage to the inverter circuit.

However, if the comparison result (S315), the total autocorrelation (TAC) is not greater than the self image (Ac), that is, if not in the scene transition state, it is determined whether the progressive scene change state by using the entropy difference between successive frames Done.

To this end, first, the entropy of the image frame is analyzed (S331). Since a method of obtaining entropy of an image frame is generally known, a detailed description thereof will be omitted.

When the entropy of the image frame is obtained according to a conventional method, the current entropy value and the previous entropy value are compared with each other in order to calculate the complexity of the current image (S332).

In the video, the frame difference is determined by measuring an entropy difference between two consecutive frames. The distribution of color histograms differs significantly when there are sudden changes in lighting. However, even if the brightness of the object, the background, or the entire image changes, the complexity of the image does not change significantly, so the entropy value does not change significantly. Therefore, by using the entropy difference between two consecutive frames, it is possible to distinguish between a change in an image and a scene change caused by a change in lighting.

However, while there is a distinction between sudden lighting changes, there is no distinction between scene transitions and darker or brighter screens such as fade. Therefore, when the amount of change of entropy D_total exceeds the threshold, it is a case of a scene change point or fade and the sudden change of lighting is not checked.

That is, when the comparison result (S232), the total entropy change amount (TDE) is greater than the entropy change amount (DE), it is determined as a progressive scene change (Fade / Zoom) state (S340).

In this case, if it is determined that the progressive scene change (Fade / Zoom) state, that is, the fade in / out or zoom in / out state, the circuit operates according to the AI reliability guarantee algorithm, and the response speed of the VBR output is set to be slow and in some cases Set to inversely proportional to the Fade / Zoom speed.

However, if the comparison result (S232) is not a gradual scene change, that is, if the TDE is not greater than DE, it is again determined whether the state of sudden illumination changes by using the difference in the histogram change amount. For this purpose, the histogram change amount is calculated (S351).

When the result of the comparison between the histogram change amount DH and the total histogram change amount TDH obtained as a result of the calculation (S352) and the histogram change amount DH is greater than the total histogram change amount TDH (S360), it is determined as a sudden lighting change.

If a sudden change in illumination continues, it will hold back the drive voltage change in the backlight to prevent unnatural AI behavior. In this case, the interpolation response coefficient is set to the maximum so that the VBR output level of the dynamic contrast ratio control (AI) function is gradually changed.

However, if the histogram change amount DH is not greater than the total histogram change amount TDH as a result of the comparison (S352), it is determined as a normal video (S370).

In the case of a normal video as described above, since the histogram change of the image is small and only motion exists, the AI function of a normal mode to which a general dynamic contrast ratio control method is applied is implemented.

As such, by controlling the output method of the inverter for controlling the output of the backlight according to each image state according to the determination result, the final output image is adaptively reinforced to the image frame change state and is output as a natural state screen. .

In the above, the apparatus and method for controlling the dynamic contrast ratio using the autocorrelation function according to the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and many variations are possible by those skilled in the art within the spirit of the present invention. Therefore, changes and modifications are included in the present invention without departing from the spirit of the invention, such facts will be apparent to those skilled in the art.

According to the apparatus and method for controlling the dynamic contrast ratio using the autocorrelation function according to the present invention, an effective AI function can be realized by adaptively processing the speed and response time of brightness adjustment of the backlight according to the current image. .

Accordingly, there is an advantage that a natural image processing effect can be obtained while gaining an advantage of improving dynamic contrast ratio by implementing AI function with improved performance.

Claims (8)

A gamma correction unit for compensating and outputting the nonlinearity of the brightness recognition degree of the human eye with respect to the image signal output from the scaler; An average calculator configured to calculate and output an average brightness value of the scaler output image frame; A PWM converter for outputting a pulse width modulated signal corresponding to the output signal of the average calculator; An image frame change state detector for analyzing and outputting change states before and after the image frame output from the scaler; An inverter for adjusting and outputting a voltage having a frequency synchronized with the output of the PWM converter according to the output of the image frame change state detector; And And a backlight for outputting light having a brightness corresponding to the output of the inverter to the LCD panel. A method for controlling dynamic contrast ratio using an autocorrelation function characterized by performing adaptive image reinforcement using both brightness information of a current image and characteristic information of a changing front and rear image. The method of claim 2, wherein the characteristic information of the before and after the changing image, A dynamic contrast ratio control method using an autocorrelation function, which includes an image state in which only a sudden change in illumination occurs in a similar scene, an image state at the time of a complete scene change, and a progressive state change state of the image. The method of claim 2, wherein the dynamic contrast ratio control method using the autocorrelation function includes: A first judging step of judging whether the scene transition state is made by comparing the histogram difference of the luminance component between the image frames and the autocorrelation coefficient; A second determination step of determining whether the scene is gradually changed using entropy differences between successive frames when the determination result is not a scene change; A third determination step of determining whether the lighting state is suddenly changed by using the difference in the histogram change amount when the change is not a gradual scene change; Controlling an output method of an inverter controlling an output of a backlight according to each image state according to the determination result; Dynamic contrast ratio control method using an autocorrelation function characterized in that it comprises a. 5. The method of claim 4, wherein when the lighting state is not suddenly changed in the third determination step, a general video screen is determined and a general dynamic contrast ratio control method is applied. 6. The method of claim 4, wherein the controlling of the output method of the inverter controlling the output of the backlight according to each image state according to the determination result comprises: And when the scene change is determined in the first determination step, an instantaneous VBR output is generated with respect to a current histogram value, and the backlight driving voltage immediately changed is applied to the inverter circuit. The method of claim 4, wherein the controlling of the output method of the inverter controlling the output of the backlight according to each image state according to the determination result comprises: And determining the response speed of the VBR output by operating the circuit according to an AI reliability guarantee algorithm when it is determined that the scene is gradually changed in the second determination step. The method of claim 4, wherein the controlling of the output method of the inverter controlling the output of the backlight according to each image state according to the determination result comprises: In the third determination step, when it is determined that the abrupt lighting change continues, the interpolation response coefficient is set to the maximum so as to gradually change the VBR output level by the dynamic contrast ratio control function. The dynamic contrast using the autocorrelation function Non-control way.

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