KR100847241B1 - Method for preventing image sticking in advance - Google Patents

Abstract

Disclosed are an afterimage prevention apparatus and method, and an image display apparatus using the same. An afterimage preventing apparatus according to the present invention includes a memory for storing an input video signal in units of frames; An image processor for changing the luminance value of each pixel of the image signal stored in the memory by N steps; And a display unit which displays the image signal changed by the image processor. According to the present invention, it is possible to prevent the afterimage caused by the long time display of the still image by the effect of continuously displaying the moving image instead of displaying the still image by continuously changing the luminance value of the pixel.

LCD, afterimage prevention, pixel capturing

Description

Method for preventing image sticking in advance}

1 is a view for explaining the principle of the afterimage occurs in a typical video display device.

2 is a block diagram of a video display device having an afterimage prevention function according to the present invention;

3 is a flowchart illustrating an image display method for performing after-image prevention in accordance with the present invention.

4A and 4B are flowcharts showing in detail the steps of displaying by changing the luminance value of the pixel of FIG.

5 is a diagram illustrating a change in luminance value of the pixel of FIG. 3 step by step;

FIG. 6 is a diagram illustrating a pixel capturing position shift in FIG. 3. FIG.

The present invention relates to an image display, and more particularly, to an afterimage prevention apparatus and method for preventing afterimages generated when continuously displaying a still image on a screen for a long time, and an image display apparatus and method using the same. .

In an image display device, for example, a liquid crystal display (LCD), a voltage applied to a liquid crystal cell is symmetrically changed due to a parasitic capacitance of a thin film transistor (TFT). The image deteriorates. That is, afterimages appear on the LCD. Various technical approaches, such as a common voltage modulation method, have been attempted in LCDs to solve such deterioration of images. However, when the same image is displayed for a long time and another image is displayed, afterimage remains. This is due to the accumulation of a certain amount of direct current components in the liquid crystal cell for each frame when the same image is displayed on the liquid crystal display panel.

This phenomenon will be described in more detail with reference to FIG. 1.

Referring to FIG. 1, a TFT having a gate connected to a scan line V _line and a source connected to a data line V _data , and a liquid crystal cell connected in parallel between a drain of the TFT and a common voltage source V _com . An LCD consisting of L _c and an auxiliary capacitor C _sto is shown. The liquid crystal cell L _c includes a liquid crystal internal resistor R _lc and a liquid crystal internal capacitor C _lc . The TFT is selectively turned on by the pulsed scan control signal to connect the data line V _data to the liquid crystal cell L _c and the auxiliary capacitor C _sto . When the TFT is turned on, the liquid crystal cell L _c and the auxiliary capacitor C _sto accumulate the voltage of the image signal from the data line V _data and hold it until the TFT is turned on again. However, the voltage accumulated in the liquid crystal cell L _c and the auxiliary capacitor C _sto is up to the same voltage as the voltage on the data line when the TFT is turned on due to the TFT's stray capacitors C _gd and C _gs . When the TFT is turned off (Turn-Off) after a sharp change, it is lower than the voltage on the data. In addition, the positive voltage and the negative voltage applied to the liquid crystal cell L _c have different absolute values. Thus, when the same image is displayed on the LCD for a predetermined period of time, the DC voltage component accumulates by a predetermined amount as the frame progresses in the liquid crystal cell L _c . The DC voltage component accumulated in the liquid crystal cell L _c causes an afterimage to appear on the LCD when the image is changed.

Various technical approaches have been taken by LCD manufacturers to solve such structural afterimage problems, and technical achievements have been made considerably.

In general, the related art of afterimage removal can be divided into two types, one of which is a technique for improving the properties of physical properties when manufacturing an LCD, and the other is a signal processing technique applied to an LCD in a display device using the LCD.

Since the technique to be dealt with in the present invention is an afterimage prevention and removal technique in a display device such as an LCD, the technique by signal processing applied to the latter liquid crystal panel will be described.

According to the related art, when a still image is input for a long time by using a method of making an OSD (On Screen Display) signal into a black / white signal in units of pixels and mixing with an image image and then transmitting it to the display unit. The effect is similar to that displayed in the pixel-by-pixel video signal. However, this technology has a disadvantage in that it is not possible to effectively respond to the input video signal by replacing the black / white signal by the OSD with the image pixel irrespective of the image value of the video signal.

In other words, the technique of changing the video signal using the OSD signal is different effects according to the type of the input signal, it is difficult to expect the effect in the actual environment. In addition, since the black / white signal is used as the afterimage prevention signal, there is a disadvantage in that the display of the black / white signal on the screen can be easily detected by the general user.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an afterimage preventing apparatus and method for preventing an afterimage occurring in an image display device in advance by a circuit technology in an image display device without the help of an external device.

In addition, another technical problem to be achieved by the present invention is an image display apparatus having an afterimage prevention function that prevents afterimages occurring in the image display apparatus in advance by the circuit technology in the image display apparatus without the help of an external device. To provide.

According to an aspect of the present invention, there is provided a afterimage dictionary apparatus including a memory configured to store an input image signal in units of frames; An image processor for changing the luminance value of each pixel of the image signal stored in the memory by N steps; And a display unit which displays the image signal changed by the image processor.

According to an aspect of the present invention, there is provided a video display device including: an analog-digital converter for converting an input analog video signal into a digital video signal; A memory for storing the digital video signal in units of frames; An image processor for changing the luminance value of each pixel of the digital image signal stored in the memory by N steps; And a display unit which displays the image signal changed by the image processor.

According to an aspect of the present invention, there is provided a method of preventing afterimages, which includes: (a) storing an input image signal in units of frames; And (b) changing the luminance value of each pixel of the stored video signal by N steps and displaying the same.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the accompanying drawings.

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

2 is a block diagram illustrating an image display apparatus having an afterimage prevention function according to an exemplary embodiment of the present invention, and the image display apparatus 200 includes an analog to digital (A / D) converter 210 and an image processor. 220, a main controller 230, a memory controller 240, a synchronous dynamic random access memory (SDRAM), and a display unit 260.

Referring to FIG. 2, the A / D converter 210 converts an input analog video signal into a digital signal and outputs the digital signal.

The image processor 220 converts the digital image signal output from the A / D converter 210 to match the resolution of the display unit 260 and outputs the digital image signal to the display unit 260. In addition, the image processor 220 stores the digital image signal in the SDRAM 250 through the memory controller 240 in accordance with a vertical synchronizing signal (V _sync ). The image processor 220 changes the luminance value of each pixel of the image signal stored in the SDRAM 250 by N levels, and stores the changed luminance value of the pixel in the SDRAM 250. When the image processor 220 changes the luminance value of the pixel, the image processing unit 220 captures one pixel of the image signal stored in the SDRAM 250 and captures and displays until the luminance value is changed for all pixels. Execute repeatedly. The image processor 220 randomly moves the position capturing one pixel, for example, in a zigzag manner.

The main controller 230 performs an overall control operation of the image display apparatus 200.

The memory controller 240 generates input / output addressing and a write / read command signal of the SDRAM 250.

The SDRAM 250 stores the input video signal in the form of 24-bit RGB data. The SDRAM 250 stores digital video signals in frame units.

The display unit 260 displays an image signal output from the image processor 220.

FIG. 3 is a flowchart illustrating an image display method for performing afterimage prevention according to the present invention, and will be described with reference to the components of FIG. 2.

2 and 3, the A / D converter 210 converts an input analog image signal into a digital signal and outputs the converted digital signal (S300).

The image processor 220 stores the digital image signal in the SDRAM 250 through the memory controller 240 in synchronization with the vertical synchronization signal V _sync (S310). In addition, the image processor 220 converts the digital image signal output from the A / D converter 210 to match the resolution of the display unit 260 and outputs the digital image signal to the display unit 260.

When the image processor 220 changes the luminance value of the pixel, the image processor 220 captures one pixel of the image signal stored in the SDRAM 250 (S320).

The image processor 220 changes the luminance value of each pixel of the image signal stored in the SDRAM 250 by N levels, and outputs the changed luminance value of the pixel to the display unit 260 (step S330). The display unit 260 displays an image signal according to the luminance value of the pixel changed in the image processor 220. A detailed description of the step S330 will be described later with reference to FIGS. 4A and 4B.

The image processor 220 determines whether the luminance value is changed for all pixels (step S340). If the luminance value is not changed for all pixels, the image processor 220 randomly moves the pixel capturing position, for example, in a zigzag manner (S350). The process of moving the pixel capturing position in a zigzag manner is illustrated in FIG. 6. After moving the pixel capturing position, steps S320, S330, and S350 are repeatedly executed until the process returns to step S320 to change luminance values for all pixels.

4A and 4B show flowcharts showing the operation S330 in detail in FIG. 3.

4A and 4B, the luminance value of the captured pixel is reduced (S400). The reduced luminance value is stored and an image signal is displayed according to the reduced luminance value (S405). After waiting for the next vertical synchronizing signal (step S410), it is determined whether or not the luminance value is lower than or equal to the lower limit value (step S415). If the luminance value is larger than the lower limit value, the process returns to step S400. If the luminance value is less than or equal to the lower limit, the flow proceeds to step S420. If the luminance value is smaller than the lower limit value, the luminance value is set to the lower limit value (step S420).

The luminance value of the captured pixel is increased (S425). The increased brightness value is stored and an image signal is displayed according to the increased brightness value (S430). After waiting for the next vertical synchronizing signal (step S435), it is determined whether the luminance value is equal to or greater than the upper limit value (step S440). If the luminance value is smaller than the upper limit value, the flow returns to step S425. If the luminance value is greater than or equal to the upper limit, the process proceeds to step S445. If the luminance value is larger than the upper limit value, the luminance value is set to an upper limit value (step S445).

The luminance value of the captured pixel is reduced (S450). The reduced luminance value is stored and an image signal is displayed according to the reduced luminance value (S455). After waiting for the next vertical synchronizing signal (step S460), it is determined whether the brightness value is equal to or less than the original brightness value (step S465). If the luminance value is larger than the original luminance value, the flow returns to step S450. If the luminance value is less than or equal to the original luminance value, the flow proceeds to step S465. If the luminance value is smaller than the original luminance value, the luminance value is set to the original luminance value (step S470).

5 is a view for explaining the step-by-step change of the luminance value of FIGS. 4A and 4B.

Referring to FIG. 5, the luminance value of each pixel of the image signal stored in the frame unit is increased / decreased by a given value α according to the magnitude of the absolute value of the luminance value. That is, if the increase / decrease step S is given in N steps, one cycle becomes 2 × S = N, so S = N / 2, and α = 256 / S. Therefore, one pixel increases / decreases one cycle within the range of the given upper limit value and lower limit value based on this value. It shows the change of the S value when the N-level change of the pixel. That is, an arbitrary pixel moves one cycle between the upper limit Du and the lower limit Dn. For convenience, the upper limit Du and 255 and the lower limit Dn = 0 are set for convenience. If the absolute value is 100, the first changed value by the algorithm is changed to a 100-α value, and then after a predetermined time it is changed to a 100-2α value. That is, 100-α → 100-2α → 100-3α →. It is changed in order of, and after each change, it waits for a certain time and then changes according to the vertical synchronization signal.

After a period of luminance changes, the pixel is returned to its original value, and then the pixel is captured to change the next value. When capturing adjacent pixels, a change in data may be detected. Therefore, in order to avoid such an error, capturing pixels is performed using a zigzag method.

Based on this principle, if the afterimage elimination algorithm is applied to a signal with an input resolution of 800 x 600 x 60 Hz (SVGA), the parameter values are set to H _active = 800 pixels, V _active = 600 lines, and N = 10 The total number of pixels stored in the SDRAM is 1,440,000 (= 800 × 600 × 3).

Therefore, when the individual pixels are changed in 10 steps for 200 msec and all the image data values of one frame are changed, 288,000 (= 1,440,000 × 0.2) seconds are required. Therefore, calculating this as a period takes about three days.

Therefore, in the still picture, the pixel at any position changes the data value of the pixel in about 10 days every three days, so that after-image phenomenon caused by long-term display of the still picture can be solved in advance.

Although the present invention has been described with reference to the embodiments illustrated in the drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

According to the present invention, it is possible to prevent the afterimage caused by the long time display of the still image by the effect of continuously displaying the moving image instead of displaying the still image by continuously changing the luminance value of the pixel. Also, by changing the luminance value of the pixel after zigzag capturing, the user cannot easily detect the change in the pixel luminance value.

Claims (15)

delete delete delete delete delete delete delete delete delete delete delete delete delete In the method for preventing afterimages in the image display device in advance, (a) storing the input video signal in units of frames; (b) randomly moving a location capturing one pixel; (c) capturing one pixel of the stored video signal; And (d) changing the luminance value of each pixel of the stored video signal by N steps and displaying the same; Steps (c) and (d) are repeated until all luminance values are changed. In step (d), (d1) storing the reduced luminance value by decreasing the luminance value of the one pixel; (d2) repeating step (d1) until the luminance value is less than or equal to the lower limit value, and storing the lower limit value when the luminance value is less than or equal to the lower limit value; (d3) increasing the luminance value of the one pixel to store the increased luminance value; (d4) repeating step (d3) until the luminance value is equal to or greater than an upper limit value, and storing the upper limit value when the luminance value is equal to or greater than an upper limit value; (d5) storing the reduced luminance value by reducing the luminance value of the one pixel; And (d6) repeating step (d5) until the luminance value is less than or equal to the original luminance value of the one pixel, and storing the original luminance value when the luminance value is less than or equal to the original luminance value. How to prevent afterimages The method of claim 14, wherein (d1), (d3) and (d5) step And storing the luminance values in accordance with a vertical synchronization signal.

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