KR100573123B1 - Image processing apparatus for display panel - Google Patents

Abstract

An image processing apparatus according to the present invention includes: a pseudo contour detection unit detecting a pseudo contour area using an image of a current frame and an image of a previous frame, and outputting a detection result as first data; And a flat region detector for detecting a flat region from an image of the current frame and outputting the detection result as second data, and performing pseudo contour correction on the region except for the second data in the first data. Therefore, the pseudo contour of the general video is removed, and at the same time, the deterioration of the image quality can be prevented in a special video part such as letters, figures, and graphs.

Description

Image processing apparatus for display panel

1 is a view showing the structure of a conventional three-electrode surface discharge plasma display panel.

FIG. 2 shows a typical driving apparatus of the plasma display panel shown in FIG. 1.

FIG. 3 shows a conventional address-display separation driving method for Y electrode lines of the plasma display panel of FIG. 1.

4 illustrates an example of generating a pseudo pseudo contour.

5 is a block diagram illustrating an image processing apparatus according to an exemplary embodiment of the present invention.

FIG. 6 is a block diagram illustrating the detector illustrated in FIG. 5.

FIG. 7 is a diagram for describing gradation conversion as a preferred embodiment of an algorithm that may be implemented in the correction unit illustrated in FIG. 5.

8A to 8D illustrate a distortion of an image generated when the flat area is corrected by an example in which the rectangular figure moves to the right.

9 illustrates an example of a region considered for detecting a flat region.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image processing of a display panel (PDP), and more particularly to an image processing apparatus for reducing video pseudo contours.

1 is a view showing the structure of a conventional three-electrode surface discharge plasma display panel.

Referring to FIG. 1, between the front and rear glass substrates 100 and 106 of a conventional surface discharge plasma display panel 1, address electrode lines A ₁ , A ₂ ,..., A _m , Dielectric layers 102 and 110, Y electrode lines Y ₁ , ..., Y _n , X electrode lines X ₁ , ..., X _n , fluorescent layer 112, barrier rib 114, and As a protective layer, the magnesium monoxide (MgO) layer 104 is provided, for example.

The address electrode lines A ₁ , A ₂ ,..., A _m are formed in a predetermined pattern on the front side of the rear glass substrate 106. The lower dielectric layer 110 is applied in front of the address electrode lines A ₁ , A ₂ ,..., A _m . In front of the lower dielectric layer 110, barrier ribs 114 are formed in a direction parallel to the address electrode lines A ₁ , A ₂ ,..., A _m . The partition walls 114 function to partition the discharge area of each display cell and to prevent optical interference between the display cells. The fluorescent layer 112 is formed between the partition walls 114.

The X electrode lines X ₁ , ..., X _n and the Y electrode lines Y ₁ , ..., Y _n are address electrode lines A ₁ , A ₂ , ..., A _m . It is formed in a predetermined pattern on the back of the front glass substrate 100 to be orthogonal to the. Each intersection sets a corresponding display cell. Each X electrode line (X ₁ , ..., X _n ) and each Y electrode line (Y ₁ , ..., Y _n ) are transparent electrode lines (X _na ) made of a transparent conductive material such as indium tin oxide (ITO). , Y _na ) and metal electrode lines X _nb and Y _nb for increasing conductivity may be formed. The front dielectric layer 102 is formed by applying the entire surface to the rear of the X electrode lines (X ₁ ,..., X _n ) and the Y electrode lines (Y ₁ ,..., Y _n ). A protective layer 104 for protecting the panel 1 from a strong electric field, for example, a magnesium monoxide (MgO) layer, is formed by applying a front surface to the back of the front dielectric layer 102. The plasma forming gas is sealed in the discharge space 108.

A driving scheme generally applied to such a plasma display panel is a method in which initialization, address, and display holding steps are sequentially performed in a unit sub-field. In the initialization step, the charge states of the display cells to be driven are made uniform. In the address step, the charge state of display cells to be selected and the charge state of display cells not to be selected are set. In the display holding step, display discharge is performed in the display cells to be selected. At this time, a plasma is formed from the plasma forming gas of the display cells performing display discharge, and the fluorescent layer 112 of the display cells is excited by ultraviolet radiation from the plasma to generate light.

2 illustrates a general driving device of the plasma display panel of FIG. 1.

Referring to the drawings, a typical driving device of the plasma display panel 1 includes an image processor 200, a controller 202, an address driver 206, an X driver 208, and a Y driver 204. The image processing unit 200 converts an external analog image signal into a digital signal, and internal image signals, for example, 8-bit red (R), green (G) and blue (B) image data, clock signals, vertical and horizontal, respectively. Generate synchronization signals. The controller 202 generates the driving control signals SA, SY, and SX according to the internal image signal from the image processor 200. The address driver 206 processes the address signal SA among the drive control signals SA, SY, and SX from the controller 202 to generate a display data signal, and generates the display data signal through the address electrode lines. To apply. The X driver 208 processes the X driving control signal SX among the driving control signals SA, SY, and SX from the controller 202 and applies the X driving control signal SX to the X electrode lines. The Y driver 204 processes the Y driving control signal SY among the driving control signals SA, SY, and SX from the controller 202 and applies the Y driving control signal SY to the Y electrode lines.

As a driving method of the plasma display panel 1 having the structure described above, an address-display separation driving method which is mainly used is disclosed in US Pat.

FIG. 3 illustrates a conventional address-display separation driving method for Y electrode lines of the plasma display panel of FIG. 1.

Referring to the drawings, a unit frame may be divided into a predetermined number, for example, eight subfields SF1, ..., SF8 to realize time division gray scale display. Each subfield SF1, ..., SF8 is divided into a reset section (not shown), an address section A1, ..., A8, and a sustain discharge section S1, ..., S8. do.

In each address section A1, ..., A8, a display data signal is applied to the address electrode lines AR1, AG1, ..., AGm, ABm in FIG. Scan pulses corresponding to..., Yn) are sequentially applied.

In each sustain discharge section S1, ..., S8, pulses for display discharge alternately in the Y electrode lines Y1, ..., Yn and the X electrode lines X1, ..., Xn. Is applied to cause display discharge in discharge cells in which wall charges are formed in the address periods A1, ..., A8.

The luminance of the plasma display panel is proportional to the number of sustain discharge pulses in the sustain discharge sections S1, ..., S8 occupied in the unit frame. When one frame forming one image is represented by eight subfields and 256 gray levels, each subfield is sequentially held at a ratio of 1, 2, 4, 8, 16, 32, 64, and 128 in order. The number of pulses can be assigned. In order to obtain luminance of 133 gray levels, cells may be addressed and sustained and discharged during the subfield 1 period, the subfield 3 period, and the subfield 8 period.

The number of sustain discharges allocated to each subfield may be variably determined according to the weights of the subfields according to the APC (Automatic Power Control) step. In addition, the number of sustain discharges allocated to each subfield is. Various modifications are possible by considering gamma characteristics or panel characteristics. For example, the gradation level assigned to subfield 4 may be lowered from 8 to 6, and the gradation level assigned to subfield 6 may be increased from 32 to 34. In addition, the number of subfields forming one frame can be variously modified according to design specifications.

Unlike the CRT (Cathode Ray Tube) which adjusts the brightness by adjusting the intensity of the electron beam, the PDP expresses the brightness through the pulse number control method in the sustain discharge section as described with reference to FIG. 3.

4 illustrates an example of generating a pseudo pseudo contour.

Pseudo contouring is caused by human visual characteristics when displaying an image by a combination of subfields as shown in FIG. 3. Referring to FIG. 4, when the image having the gradations 127 and 128 side by side moves at a speed of 1 to the right, the image is displayed as shown in FIG. 4 by the subfield arrangement of FIG. Gradation is recognized by. Therefore, a pseudo contour such as 255 occurs between the grayscales 127 and 128.

However, when a pseudo contour reduction technique is applied when a character, a figure, a graph, or the like with little gradation change, which is not a general moving picture such as a movie or a TV, moves, the image quality deteriorates.

The present invention has been made in an effort to provide an image processing apparatus capable of preventing deterioration of image quality in a special moving picture portion such as letters, figures, and graphs while removing pseudo contours of a general moving picture.

According to an aspect of the present invention, there is provided an image processing apparatus including: a pseudo contour detection unit detecting a pseudo contour region using an image of a current frame and an image of a previous frame, and outputting a detection result as first data; And a flat region detector for detecting a flat region from an image of the current frame and outputting a detection result as second data, and performing pseudo contour correction on an area excluding the second data from the first data. do.

The pseudo contour detector may detect a pseudo contour area by motion detection.

In addition, the pseudo contour detector may detect an edge of the image and exclude the detected edge from the pseudo contour area.

The flat area may be an area where a system with a peripheral pixel is equal to or less than a predetermined value.

Hereinafter, the configuration and operation of an image processing apparatus according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a block diagram illustrating an image processing apparatus according to an exemplary embodiment of the present invention, and includes a storage unit 500, a detector 502, and a correction unit 504.

The storage unit 500 outputs the current input image IN1 by delaying at least one frame.

The detector 502 detects the pseudo contour area using the image frame IN1 currently input and the image IN2 delayed by at least one frame output through the storage 500 such as a frame memory.

The correction unit 504 corrects the detected pseudo contour area by a pseudo contour correction algorithm. The pseudo contour correction algorithm may include gray scale transformation, error diffusion, and the like.

FIG. 6 is a block diagram illustrating the detector illustrated in FIG. 5, and includes a pseudo contour detector 600 and a flat region detector 602.

The pseudo contour detection unit 602 may detect the pseudo contour area by motion detection. Pseudocontours usually occur on so-called smooth images with large movements and slow changes. The pseudo contour detection unit 602 compares the current frame IN1 with the previous frame IN2 to calculate the magnitude of the motion, and detects the pseudo contour area when the magnitude of the motion is equal to or larger than a predetermined value. Here, the magnitude of the movement can be determined, for example, by calculating even the system of pixels at the same position of the current frame IN1 and the previous frame IN2.

In addition, the pseudo contour detection unit 602 detects an edge of the image and excludes the edge portion of the detected image from the pseudo contour area, thereby preventing the sharpness degradation caused by the pseudo contour correction algorithm. The edge detection may be performed by, for example, comparing the image of the current frame IN1 with a predetermined pixel and a predetermined line shifted image of the current frame IN1.

The flat area detection unit 600 detects and outputs a flat area from the input image. In the present invention, the flat area is a specific image such as a character, a figure, or a graph, which is not a general moving image, and the inside of the specific image is an area in which there is little change of the image. For example, the flat area may be an area in which the system with the surrounding pixel is equal to or less than a predetermined value. If the pseudo contour correction algorithm is applied to the flat region, image distortion may be severe. Therefore, in the image processing apparatus according to the present invention, only the area IN3 excluding the output of the flat area detection unit 600 from the output of the pseudo contour detection unit 602 is output to the correction unit 504 shown in FIG. Calibration will be performed.

FIG. 7 is a diagram for describing gradation conversion as a preferred embodiment of an algorithm that may be implemented in the correction unit 504 shown in FIG. 5.

Generally, pseudo contours do not occur when the light emission pattern is uniform. By using this concept, a method of converting an image in which pseudo contours are generated into a uniform gray scale with a light emission pattern may be used. If the input is 256 gray levels and the subfield array for expressing it is [1,2,4,8,16,32,42,44,52,54], the pseudo contour detection unit 602 detects the area. For this, pseudo contours can be corrected by converting the light emission pattern shown in FIG. 7 into uniform gradations. At this time, the pseudo contour is removed by the gray level conversion, but distortion of the gray level may occur by this. Such gray level distortion can be corrected through an error diffusion method.

However, if a flat area is detected as a pseudo contour area by motion detection, and a gray scale transformation is applied thereto as a pseudo contour correction algorithm, an afterimage may occur.

8A to 8D, the distortion of an image generated when the flat area is corrected will be described by an example in which the rectangular figure moves in the right direction.

When the rectangle of the previous frame IN2 of FIG. 8A is moved to the right direction from the current frame IN1 of FIG. 8B, when the motion is calculated by the motion detector 602, the previous frame rectangle as shown in FIG. 8C. And the position of the rectangle of the current frame is detected as the movement area in the current frame. When a pseudo contour correction algorithm such as gradation transformation and error diffusion is applied to the motion detection region of FIG. 8C, a noise image such as an afterimage is generated at a position where a rectangle of a previous frame is located on the left side of the current frame. In addition, the square of the current frame may be distorted with a completely different gray scale by the gray scale conversion. However, in this flat region, virtually no outline is generated except for some boundary regions. Therefore, by applying the pseudo contour algorithm to the flat region where the pseudo contour does not substantially occur, the image is severely distorted.

In the present invention, the flat area is a specific image such as a character, a figure, or a graph, which is not a general moving image, and the inside of the specific image is an area in which the gray level is hardly changed.

The flat area detection unit 600 is a component provided to detect an area of a predetermined size with little change in gradation. The flat area detector 600 may detect, for example, a pixel having a predetermined value TH or less as a flat area even with a neighboring pixel.

An algorithm that may be implemented in the flat area detection unit 600 is, for example, Equation 1 below.

The target pixel x (i, j) and the pixel of interest x (i, j) even flat _L (i, j) based on the left peripheral pixels in the example can be determined as in the following equation (2).

In addition, even based on the target pixel x (i, j) and the pixel of interest of the right neighboring pixel _{x (i, j) flat R} (i, j) may be determined, for example, as shown in the following equation (3).

At this time, the threshold value TH represents a reference of the gradation change for determining the flat area. If you want to detect a completely flat area without gray level change in any figure, you can set TH = 0. However, in consideration of noise components and the like of the input image, the TH value may be set to an appropriate value close to zero.

In Equations 3 and 4, Q represents the size of the area considered by the flat area detection unit. For example, when Q = 2, the planar region can be detected by applying to Equations 1 to 3 in consideration of the region shown in FIG. 9 based on the pixel of interest x (i, j) .

In addition, the area considered in detecting the planar area illustrated in FIG. 9 may be equally extended to the upper and lower lines of the current line. For example, as shown in Equations 4 and 5, even the system with surrounding pixels above and below the pixel of interest may be determined to detect the flat portion.

The image processing apparatus according to the present invention is prepared by a schematic or ultra high-speed integrated circuit hardware description language (VHDL) or the like on a computer, and is connected to a computer and programmed by an integrated circuit, for example, a field programmable gate array (FPGA). It can be implemented as a circuit.

In addition, the image processing apparatus according to the present invention may be implemented by being included in, for example, the image processing unit 200 illustrated in FIG. 2 when applied to a plasma display panel. Accordingly, by the image processing apparatus according to the present invention, the image from which the pseudo contour is removed may be output to the panel 1 via the logic controller 202 shown in FIG. 2.

The best embodiments have been disclosed in the drawings and specification above. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, according to the image processing apparatus of the present invention, it is possible to remove pseudo contours of a general video and to prevent deterioration of image quality in a special video part such as letters, figures, and graphs.

The invention is not limited to the examples described above and represented in the drawings. Those skilled in the art taught by the above-described embodiments, many modifications to the above-described embodiments are possible by substitution, erasure, merging, etc. within the scope and object of the present invention described in the following claims.

Claims (4)

A pseudo contour detection unit detecting a pseudo contour area by using an image of a current frame and an image of a previous frame and outputting a detection result as first data; And A flat area detection unit for detecting a flat area from an image of the current frame and outputting a detection result as second data; And an outline contour correction is performed on an area excluding the second data from the first data. The method of claim 1, wherein the pseudo contour detection unit, An image processing apparatus comprising detecting a pseudo contour area by motion detection. The method of claim 1, wherein the pseudo contour detection unit, And detecting the edge of the image and excluding the detected edge from the pseudo contour area. The method of claim 1, wherein the flat region, An image processing apparatus according to claim 1, wherein even a system with a neighboring pixel is an area of less than a predetermined value.

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