KR20110113090A - Circuit and method for gray-level error control for low power image displays - Google Patents

Abstract

The present invention relates to a gray level error control method and apparatus for a low power image display device capable of reducing the power consumption of a video display device as much as possible while maintaining the image quality of the display image at a desired level or more corresponding to the displayed image. Detecting a reference target value for measuring an image quality of a display image based on a peak signal to noise ratio (PSNR) target; Analyzing red, green, and blue image data input from the outside to generate histograms of red, green, and blue; Analyzing each histogram to detect a maximum gradation level of each of red green and blue; Detecting an error threshold by gradually decreasing the level from the largest gradation level among the detected red, green, and blue maximum gradation levels; Comparing the detected reference target value with an error threshold value; And setting a gray-level clipped point according to the comparison result.

Description

Gradation level error control method and device for low power video display device {CIRCUIT AND METHOD FOR GRAY-LEVEL ERROR CONTROL FOR LOW POWER IMAGE DISPLAYS}

The present invention relates to a method and a device for driving an image display device. In particular, a low power image display device capable of reducing power consumption of an image display device as much as possible while maintaining image quality of a display image at or above a desired level in response to the displayed image. The present invention relates to a gray level error control method and apparatus.

Background Art In recent years, lightweight thin flat panel displays have been mainly used as video display devices used for personal computers, portable terminals, monitors of various information apparatuses, and the like. Such flat panel displays include liquid crystal displays, light emitting displays, plasma display panels, field emission displays, and the like.

Among the flat panel displays, liquid crystal displays are actively applied to notebooks, desktop monitors, and mobile terminals due to their excellent resolution, color display, and image quality.

Such a liquid crystal display device displays an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display includes a liquid crystal panel having a plurality of liquid crystal cells for displaying an image, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light to the liquid crystal panel.

The liquid crystal panel displays a desired image by adjusting a transmittance of light emitted from the backlight unit according to the image signal. In this case, the backlight unit supplies light to the liquid crystal panel by driving a plurality of lamps provided in the backlight unit according to the lamp driving control signal supplied from the driving circuit.

However, the backlight unit driven as described above has a problem in that power consumption increases because light is always generated at a constant brightness regardless of an image signal of a liquid crystal panel. Thus, conventionally, a method of compensating the brightness of the backlight by reducing the brightness of the backlight unit so as to reduce the power consumption of the backlight unit and changing the light transmittance in response to the backlight brightness change rate has been used. However, when the brightness change rate of the backlight unit is changed so that the light transmittance cannot be adjusted, gray level error occurs due to maintaining the maximum brightness for image data beyond the expressible brightness.

In order to solve this problem, the maximum brightness of the backlight unit is fixed by using a fixed ratio of the number of gray levels, ie, gray-level clipped rate, which is excluded by saturation of the gray level with respect to the total number of grays of the image data. Was also determined in advance. However, in the case of the prior art, the image quality is greatly deteriorated according to the characteristics of the specific images that have not been considered in advance, or the brightness of the backlight unit is greatly reduced, resulting in a problem that the image quality is greatly reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The present invention provides a gray level for a low-power video display device capable of reducing the power consumption of the video display device as much as possible while maintaining the image quality of the display image above a desired level in response to the displayed image. It is an object of the present invention to provide a level error control method and apparatus.

The gray level error control method for a low power image display device according to an embodiment of the present invention for achieving the above object is a reference target value for measuring the image quality of the display image based on the PSNR (Peak signal to noise ratio) target Detecting; Analyzing red, green, and blue image data input from the outside to generate histograms of red, green, and blue; Analyzing each histogram to detect a maximum gradation level of each of red green and blue; Detecting an error threshold by gradually decreasing the level from the largest gradation level among the detected red, green, and blue maximum gradation levels; Comparing the detected reference target value with an error threshold value; And setting a gray-level clipped point according to the comparison result.

In the detecting of the reference target value, PSNR is first detected using the following equations,

Using the following equations,

(여기서, λ_r, λ_c, λ_co는 각각 입력 영상의 가로와 세로 화소 수 및 R,G,B 컬러의 수)

(Where λ _r , λ _c , and λ _co are the number of horizontal and vertical pixels and the number of R, G, B colors of the input image, respectively)

The reference target value is calculated.

The detecting of the error threshold may include detecting the error threshold of each of the red, green, and blue colors by gradually decreasing the level from the largest gradation level among the detected maximum gradation levels of red, green, and blue. The red, green, and blue error thresholds are detected using the following equations.

The detecting of the error threshold value may include detecting the error threshold value summed up by using an equation of each of the error threshold values of red, green, and blue which are sequentially detected to be updated.

In addition, a gray level error control apparatus for a low power image display device according to an embodiment of the present invention for achieving the above object is a target value detector for detecting a reference target value for measuring the image quality of the display image based on the PSNR target ; A histogram generator for generating red, green, and blue histograms by analyzing red, green, and blue image data input from the outside, and detecting maximum gray levels of red, green, and blue by analyzing the histograms; Error threshold detection units of red, green, and blue for detecting error threshold values of each of the red, green, and blue colors by gradually decreasing the level from the largest gradation level among the detected maximum gradation levels of red, green, and blue. ; An error threshold detector for detecting a final error threshold value by summing error threshold values of each of the red, green, and blue colors; And a comparison unit configured to sequentially compare the detected reference target value with a final error threshold value and to set a gray scale exclusion point according to the comparison result.

The target value detector first detects a PSNR using the following equations,

Using the following equations,

(여기서, λ_r, λ_c, λ_co는 각각 입력 영상의 가로와 세로 화소 수 및 R,G,B 컬러의 수) 상기 기준 타겟 값을 계산하는 것을 특징으로 한다.

(Where λ _r , λ _c , and λ _co are the horizontal and vertical pixels and the number of R, G, and B colors of the input image, respectively). The reference target value is calculated.

The error threshold detection unit detects the error threshold values of each of the red, green, and blue levels by gradually decreasing the level from the largest gradation level among the detected maximum gradation levels of red, green, and blue. The blue error threshold value may be detected using the following equations.

The error threshold detection unit may detect the error threshold summed up by using an equation for each of the error thresholds of red, green, and blue which are sequentially detected to be updated.

The comparison unit continuously compares the reference target value that was previously detected with the value sequentially and inputs an error threshold value, and when the error threshold value is smaller than the reference target value that was previously detected, the maximum gray level is 1 level. The error threshold is recalculated after decreasing by a value, and when the error threshold is larger than the detected reference target value, the maximum gray level previously calculated is set as the final gray exclusion point of the gray level. do.

The gray level error control method and apparatus for a low power image display device according to an embodiment of the present invention having the above-described features can be performed while maintaining the image quality of the display image at a desired level or higher in response to the displayed image. Can be reduced as much as possible.

1 is a flowchart illustrating a gray level error control method for a low power image display device according to an exemplary embodiment of the present invention.
2 is a histogram generated according to grayscale values of red image data.
3 is a histogram generated according to grayscale values of green image data.
4 is a histogram generated according to grayscale values of blue image data.
5 is a block diagram illustrating a gray level error control apparatus for a low power image display device according to an exemplary embodiment of the present invention.
FIG. 6 is a block diagram illustrating the gray scale exclusion controller shown in FIG. 5 in more detail.

The present invention is described in IEEE Transactions on Consumer Electronics, Vol. 55, No. 4, which is filed on the basis of NOVEMBER 2009 (name: Image Integrity-based Gray-Level Error Control for Low Power Liquid Crystal Displays), is a method of controlling gray scale level error for a low power image display device according to an embodiment of the present invention. And a description with reference to the accompanying drawings as follows.

1 is a flowchart illustrating a gray level error control method for a low power image display device according to an exemplary embodiment of the present invention.

The gray level error control method illustrated in FIG. 1 includes detecting a reference target value TSE _T for measuring an image quality of a display image based on a peak signal to noise ratio (PSNR) target (T1); Generating a histogram of red, green, and blue colors by analyzing red, green, and blue image data (RGB) input from the outside (T2); Analyzing each histogram to detect a maximum gradation level of each of red green blue (T3); Detecting (T4) an error threshold value TSE _C by gradually decreasing the level from the largest gradation level among the detected red, green, and blue maximum gradation levels; Comparing (T5) the detected reference target value TSE _T with an error threshold value TSE _C ; And setting a gray-level clipped point according to the comparison result (T6).

The reference target value TSE _T in the detection target reference value TSE _T is a reference value detected to measure the image quality of the display image based on the PSNR target, and the reference target value TSE _T is detected. In order to detect the underlying PSNR first. Here, the PSNR can be obtained by using Equations 1 and 2 below.

Here, N for obtaining a mean square error (MSE) is the total number of pixels of the input image data, and x _i and y _i may be the gradation level of the i-th pixel of the input original image data and the processed image data, respectively. have.

Since the image data size for one pixel may be 24 bits, each of the red, green, and blue image data is allocated 8 bits. Thus, the maximum gradation level is 255 gradation levels. In addition, when the PSNR is 30dB or more, generally acceptable image quality may be set, so the target PSNR of the present invention is set to 30dB.

The reference target value TSE _T based on the target PSNR and the MSE set as described above may be calculated using Equations 3 and 4 below.

Here, λ _r , λ _c , and λ _co may be the number of horizontal and vertical pixels and the number 3 of R, G, and B colors of the input image, respectively.

As described above, the reference target value TSE _T detection step T1 detects and stores the reference target value TSE _T to measure the image quality of the display image based on the PSNR target.

Next, in the step T2 of generating the histogram, the histograms of the red, green, and blue colors are generated by analyzing the red, green, and blue image data RGB input from the outside. Specifically, in the histogram generation step T2, as illustrated in FIGS. 2 to 4, the histograms of red, green, and blue colors are analyzed by analyzing grayscale values of image data RGB input from the outside in at least one frame unit. Create 2 is a histogram generated according to grayscale values of red image data, FIG. 3 is a histogram generated according to grayscale values of green image data, and FIG. 4 is a histogram generated according to grayscale values of blue image data. .

In the detecting of the maximum gray level (T3), the respective histograms are analyzed to detect the maximum gray level I _ccp of each of the red, green, and blue colors.

The next step is to set the grayscale exclusion point to generate the converted image data having the PSNR closest to the reference target PSNR of 30dB or more. This may be applied by varying the ratio of the number of gray levels to which the gray level is saturated relative to the total number of grays of the image data, that is, the gray-level clipped rate, according to the brightness characteristics of the input image without fixing in advance. To make it work.

To this end, in the error threshold value TSE _C detection step T4, the largest gray level among the detected maximum gray levels of red, green, and blue, for example, the maximum gray level I detected in the red histogram of FIG. 2. _ccp ) to decrease the level step by step to detect the error threshold values TSE _{R _C} , TSE _{G _ C} and TSE _{B _ C for} each of the red, green, and blue colors. Here, the red, green, and blue error threshold values TSE _{R _ C} , TSE _{G _ C} , and TSE _{B _C} are detected using Equations 5 to 7 below.

In this case, the maximum gray level I _CCP is a candidate for the maximum gray-level clipped point among all gray levels, and if the given maximum gray level does not satisfy the condition, the operation is reduced by one gray level. .

Here, I _MAX represents the highest gray level in the input data of red, green, and blue, respectively. The starting point of the maximum gradation level is I _MAX -1, and H _R (i), H _G (i), and H _B (i) respectively represent the number of pixels of the red, green, and blue input data at the i th gradation level. Indicates.

In this way, the maximum gray level is detected from the input data of each of the input red, green, and blue, and error threshold values TSE _{R _ C} , TSE _{G _ C} , and TSE _{B _ C of} each of the red, green, and blue colors sequentially from the maximum gray level. In case of detecting the error, the complicated calculation process of repeatedly comparing the gradation levels of the conventional input image data with each other is omitted, so that the error threshold values of TSE _{R _C} , TSE _{G _C} , TSE _{B _C} ) can be detected.

As described above, when the error threshold values TSE _{R _ C} , TSE _{G _ C} , and TSE _{B _ C of} each of the red, green, and blue colors are sequentially detected, the error threshold values TSE _C summed up using Equation 8 below are used. Is detected (T4).

The summation values TSE _C detected in the sum are sequentially increased in response to the error threshold values TSE _{R _ C} , TSE _{G _ C} , and TSE _{B _ C of} red, green, and blue which are sequentially increased. .

In the step (T5) of comparing the detected reference target value TSE _T with the error threshold value TSE _C , the value is sequentially changed with the previously detected reference target value TSE _T and an input error threshold value ( TSE _C ) will be compared continuously. At this time, if the error threshold value TSE _C is smaller than the reference target value TSE _T previously detected, the error threshold value TSE _C is recalculated after decreasing the maximum gradation level by one level.

In the step of setting the gray level exclusion point T6, when the error threshold value TSE _C is larger than the reference target value TSE _T , which was previously detected in the comparison step T5, the previously calculated maximum gray level is determined as the gray level. The final gradation exclusion point is set.

The gradation exclusion points sequentially detected in at least one frame unit through the above-described process are sequentially supplied to the driving circuit and the backlight control circuit of the image display device and used to set the brightness change rate of the backlight unit and the brightness conversion rate of the image. do.

Thus, the gray level error control method for the low power image display device according to the embodiment of the present invention can reduce the power consumption of the image display device as much as possible while maintaining the image quality of the display image at or above a desired level corresponding to the displayed image. A gray exclusion point is set and supplied to the driving circuit of each image display device.

5 is a block diagram illustrating a gray level error control apparatus for a low power image display device according to an exemplary embodiment of the present invention.

The gradation level error control apparatus shown in Figure 5 is based on a target value of the PSNR target based (TSE _T) and the error threshold (TSE _C) detected by the detected based on the target value of (TSE _T) and the error threshold (TSE _And a gray exclusion controller 2 for setting a gray scale exclusion point according to the comparison result by comparing _C ), and converting the gray scale level of the image data RGB input from the outside using the set gray exclusion point. It may further include a backlight brightness conversion control unit 6 for controlling the brightness of the backlight unit by using the conversion unit 4 and the set gray scale exclusion point.

Here, the gray scale exclusion controller 2 includes a target value detector 21 for detecting a reference target value TSE _T for measuring the quality of the display image based on the PSNR target; A histogram generator for generating red, green, and blue histograms by analyzing red, green, and blue image data (RGB) input from the outside, and detecting the maximum gray level of each of red, green, and blue by analyzing the histograms ( 22); The error threshold values TSE _{R _C} , TSE _{G _C} , and TSE _{B _C for} each of the red, green, and blue colors are gradually decreased by decreasing the level from the largest gradation level among the detected maximum gradation levels of red, green, and blue. Error threshold detection units 23, 24, and 25 for detecting red, green, and blue, respectively; An error threshold detection unit 26 for detecting a final error threshold value TSE _C by summing error threshold values TSE _{R _ C} , TSE _{G _ C} , and TSE _{B _ C for} each of the red, green, and blue colors; And a comparison unit 27 for sequentially comparing the detected reference target value TSE _T and the final error threshold value TSE _C and setting a gray scale exclusion point according to the comparison result.

The target value detector 21 detects the reference target value TSE _T for measuring the image quality of the display image based on the PSNR target. To detect the reference target value TSE _T , the target PSNR is first determined. Detection is performed according to equations (1) and (2). The reference target value TSE _T based on the target PSNR and the MSE set as described above may be calculated using Equations 3 and 4 above. As described above, the target value detector 21 detects and stores the reference target value TSE _T to measure the image quality of the display image based on the PSNR target.

As shown in FIGS. 2 to 4, the histogram generator 22 analyzes grayscale values of image data RGB input from the outside in at least one frame unit to generate histograms of red, green, and blue. Each histogram is analyzed to detect the maximum gray level of each of the red, green, and blue colors.

The red, green, and blue error threshold detection units 23, 24, and 25 respectively decrease the levels gradually from the largest gray level among the detected maximum gray level levels of the red, green, and blue colors. Detects each error threshold value TSE _{R _ C} , TSE _{G _ C} , TSE _{B _ C.} The red, green, and blue error thresholds TSE _{R _ C} , TSE _{G _ C} , and TSE _{B _ C} are detected using Equations 5 to 7, respectively.

As shown in Equation 8, the error threshold detection unit 26 sums the error threshold values TSE _{R _C} , TSE _{G _ C} , and TSE _{B _ C of the} red, green, and blue colors, respectively, to obtain a final error threshold value ( TSE _C ) is detected. The comparison unit 27 sequentially compares the detected reference target value TSE _T with the final error threshold value TSE _C and sets a gray-level clipped point according to the comparison result.

The gradation exclusion points sequentially detected in at least one frame unit through the above-described process are sequentially supplied to the driving circuit and the backlight control circuit of the image display device and used to set the brightness change rate of the backlight unit and the brightness conversion rate of the image. do.

Thus, the gray level error control method for the low power image display device according to the embodiment of the present invention can reduce the power consumption of the image display device as much as possible while maintaining the image quality of the display image at or above a desired level corresponding to the displayed image. A gray exclusion point is set and supplied to the driving circuit of each image display device.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention It will be apparent to those skilled in the art.

2: gradation controller 4: image converter
6: backlight brightness conversion control unit 21: target value detection unit
22: histogram generator 23: red error threshold detection unit
24: green error threshold detection unit 25: blue error threshold detection unit
26: error threshold detection unit 27: comparison unit

Claims (10)

Detecting a reference target value for measuring an image quality of a display image based on a peak signal to noise ratio (PSNR) target;
Analyzing red, green, and blue image data input from the outside to generate histograms of red, green, and blue;
Analyzing each histogram to detect a maximum gradation level of each of red green and blue;
Detecting an error threshold by gradually decreasing the level from the largest gradation level among the detected red, green, and blue maximum gradation levels;
Comparing the detected reference target value with an error threshold value; And
And setting a gray-level clipped point according to the comparison result. The method of claim 1,
The reference target value detection step
PSNR is first detected using the following equations,

Using the following equations,

(Where λ _r , λ _c , and λ _co are the number of horizontal and vertical pixels and the number of R, G, B colors of the input image, respectively)
A gray level error control method for a low power image display device, characterized by calculating a reference target value. The method of claim 2,
The error threshold detection step
Detecting an error threshold value of each of the red, green, and blue colors by gradually decreasing the level from the largest gradation level among the detected maximum gradation levels of the red, green, and blue colors; The error threshold value is detected using the following equations. Gray level error control method for a low power image display device.

The method of claim 3, wherein
The error threshold detection step
Detecting the error threshold summed by using an equation of the error threshold values of red, green, and blue which are sequentially detected to update their values, and the gray level for the low power image display device. Error control method.

The method of claim 4, wherein
Comparing the detected reference target value and the error threshold value is
The reference target value, which has been detected in advance, is sequentially reduced, and the error threshold value which is input is continuously compared. Recalculate the error threshold later;
In the gradation exclusion point setting step
And setting the final gray level exclusion point of the gray level as the previously calculated maximum gray level when the error threshold value is larger than the detected reference target value. A target value detector for detecting a reference target value for measuring an image quality of a display image based on the PSNR target;
A histogram generator for generating red, green, and blue histograms by analyzing red, green, and blue image data input from the outside, and detecting maximum gray levels of red, green, and blue by analyzing the histograms;
Error threshold detection units of red, green, and blue for detecting error threshold values of each of the red, green, and blue colors by gradually decreasing the level from the largest gradation level among the detected maximum gradation levels of red, green, and blue. ;
An error threshold detector for detecting a final error threshold value by summing error threshold values of each of the red, green, and blue colors; And
And a comparator configured to sequentially compare the detected reference target value with a final error threshold value and to set a gray scale exclusion point according to the comparison result. The method according to claim 6,
The target value detector
PSNR is first detected using the following equations,

Using the following equations,

(Where λ _r , λ _c , and λ _co are the number of horizontal and vertical pixels and the number of R, G, B colors of the input image, respectively)
Gray level error control device for a low-power video display, characterized in that for calculating a reference target value. The method of claim 7, wherein
The error threshold detection unit
The error threshold value of each of the red, green, and blue colors is detected by gradually decreasing the level from the largest gray level among the detected maximum gray level levels, and the red, green, and blue error threshold values are Gray level error control device for a low power image display device characterized in that the detection using the following equation.

The method of claim 8,
The error threshold detection unit
The gray level error control device for the low power image display device, wherein the error threshold values are detected by adding the error threshold values of red, green, and blue which are detected to be sequentially updated. .

The method of claim 9,
The comparison unit
The value is sequentially reduced with the reference target value which has been detected in advance, and the error threshold value which is input is continuously compared. When the error threshold value is smaller than the reference target value which has been detected beforehand, the maximum gray level is decreased by one level. After calculating the error threshold value,
And a gray level level error control device for a low power image display device, wherein, when the error threshold value is larger than the detected reference target value, a previously calculated maximum gray level is set as a final gray level exclusion point of the gray level.

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