KR20050105922A - Display apparatus - Google Patents

Abstract

The present invention relates to a display device. The present invention provides a display apparatus for processing a frame of an image into a plurality of subfields for time division; A gradation converter for converting an image signal into a predetermined moving image gradation; The moving picture gradation includes a linear gradation having at least one continuous light emitting subfield and at least one non-emitting subfield contiguous, and one subfield not contiguous with the non-emitting subfield among the light emitting subfields of the linear gradation. Is characterized in that it comprises a halftone which is a non-emitting subfield. As a result, detailed expression of the video signal can be performed, and at the same time, the pseudo contour can be effectively reduced.

Description

Display apparatus

The present invention relates to a display apparatus, and more particularly, to a display apparatus for processing a frame of an image into a plurality of subfields which are time-divided.

In a display device such as a plasma display panel (PDP) or a digital mirror device (DMD) that displays gray levels using a time division method, a false contour may occur in an image of a moving object. In this case, pseudo contour means that even the system with the surrounding area is visually accumulated in the moving area and appears as an afterimage like a contour line.

1 is a schematic control block diagram of a PDP for reducing video pseudo contours.

As shown in FIG. 1, the PDP includes an inverse gamma correction unit 101, a gray scale limit and error diffusion unit 102, a dither circuit 103, a motion detector 104, a selector 105, and a panel controller 106. Has

The inverse gamma correction unit 101 converts and outputs an input video signal by the following equation (1). The video signal input here has luminance level information of each of R, G, and B. When the input / output luminance level is expressed by an integer, luminance information below the decimal point becomes an error.

Y = X ^2.2 Equation (1)

(Where X represents an input video signal and Y represents an output signal.)

The gray scale and error diffusion unit 102 allows this error to be reflected in the luminance of the surrounding pixels. That is, the generated error is added to the luminance of the peripheral pixels, and the error of the peripheral pixels is reflected in the luminance information input from the inverse gamma correction unit 101.

A more important function of the gradation limit and error diffusion unit 102 is to express the output of the inverse gamma correction unit 101 in an appropriate gradation for reducing the pseudo contour of the video.

FIG. 2 shows <Table 1> in which some of the gradations that can be displayed by each weighted subfield are listed.

Hereinafter, with reference to <Table 1>, the configuration of the gradation will be described in detail.

One frame is divided into eight subfields sf1 to sf8, and (1, 2, 4, 8, 16, 32, 64, 128) sustain pulses are sequentially weighted to each subfield. Each gradation is determined by a combination of the light emission states of each subfield, which is represented by a codeword in which the light emission state is 1 and the non-light emission state is 0. For example, the codeword of gradation [3] is represented by (11000000), and it can be seen that the gradation coincides with the total number of sustain pulses emitted during one frame by selection of the codeword.

'Used gradation' in the right column of <Table 1> is a selected gradation to reduce pseudo contour of the video signal. Dither gradation is a gradation used as a gradation for displaying still images together with a gradation used. 'Dither value' is an inherent value of dither gradation and is like a gradation with adjacent use gradation. As described above, the range of gradations that can be displayed by the subfields shown in Table 1 is [0 to 255] gradations, but only gradations of specific codewords are selectively used.

In summary, the gradation limit and error diffusion unit 102 limits the output of the inverse gamma correction unit 101 to a series of gradation groups ('use gradation' + 'dither gradation') for displaying still images, Spread all errors to the surrounding pixels.

The dither circuit 103 outputs a corresponding dither value when the input grayscale is a dither grayscale, and the motion detector 104 detects the movement of the image represented by the video signal and outputs the detection result to the selector 105.

When the selection unit 105 detects that the video signal is a still image from the motion detection unit 104, the selection unit 105 outputs the gradation input from the dither circuit 103 to the rear panel control unit 106 as it is. On the other hand, if it is detected as a moving picture, the selection unit 105 converts the gray level input from the dither circuit 103 into a use gray level for displaying the moving picture and outputs the gray level.

For example, when the luminance level of the video signal is [44], the gray scale limit and error diffusion unit 102 converts it to dither grayscale [47] and spreads the error by [3] to the surrounding pixels. When it is detected as a moving picture from the motion detector 104, the selector 105 converts the dither value to a dither gradation level and converts it into an adjacent use gradation level. Specifically, in even frames, dither values are added to convert to [47] + [16] = [63] used gradation, and in odd frames, [47]-[16] = [32] used for subtraction. Convert to gradation. As a result, an image close to the original image is obtained by having an average [47] gradation in time.

3 shows a subfield codeword of moving picture gradation for representing a conventional moving picture.

As shown in Fig. 3, in the conventional moving image gradation, a 1-bit transition occurs linearly between adjacent gradations. Such gradation is known to be effective in reducing pseudo contours of moving images. However, such linear moving picture gradation is limited to 9 display gradations when there are 8 subfields. Since the number of gray scales that can be displayed is limited, there is a problem in that the image cannot be displayed fine when the motion of the video is slow.

Accordingly, an object of the present invention is to provide a display device capable of reducing image pseudo contours and expressing images in detail.

According to the present invention, there is provided a display apparatus for processing a frame of an image into a plurality of subfields for time division; A gradation converter for converting an image signal into a predetermined moving image gradation; The moving picture gradation includes a linear gradation having at least one continuous light emitting subfield and at least one non-emitting subfield contiguous, and one subfield not contiguous with the non-emitting subfield among the light emitting subfields of the linear gradation. Can be achieved by a display device characterized by including a halftone which is a non-emitting subfield.

It is effective to reduce pseudo contours by increasing the frequency of converting the image signal to the linear gray level rather than the intermediate gray level.

The display apparatus further includes a motion measuring unit for measuring a degree of motion of the video signal, wherein the gradation converter is a gray level between the gradation adjacent to each of the intermediate gradations and the gradation between the intermediate gradations according to the measurement result of the motion measuring unit. The image may be converted into any one of predetermined virtual gradations having a level, and converted into any one of the video gradations adjacent to the virtual gradations.

Here, the video gray scale may be limited to having the intermediate gray scale having a predetermined reference number or less between adjacent linear gray scales, thereby reducing the occurrence of pseudo contours. Therefore, the moving picture gradation may be limited to having one of the intermediate gradations between adjacent linear gradations.

At this time, the gradation converter; A predetermined high gray level and a low gray level between the two linear gray levels and the half gray level adjacent to the half gray level, and a video signal having a gray level level between the high gray level and the low gray level; A first gradation complementary unit which converts into one; And a second gray level correction unit for converting the upper gray level and the lower gray level into one of a linear gray level and an intermediate gray level adjacent to each other. The second gray level correction unit converts a video signal having a gradation level between the upper gradation and the lower gradation and a linear gradation adjacent to each one into the adjacent linear gradation and the intermediate gradation. Of course, the gray level conversion may be processed by any one of a dithering method and an error diffusion method.

The display apparatus may further include a moving picture detection unit for detecting whether an input video signal is a moving picture signal, and the gradation conversion unit converts the video signal to the moving picture gradation when it is detected as a moving picture signal from the moving picture detection unit. .

The above object is also directed to a display apparatus according to the present invention for processing a frame of an image into a plurality of subfields for time division; A gradation converter for converting an image signal into a predetermined moving image gradation; The moving picture grayscale includes a grayscale having a series of subfields in which a plurality of light emitting subfields and one non-light emitting subfield are continuous, and at least one non-light emitting subfield consecutive to the light emitting subfield among the series of subfields. It can also be achieved by a display device characterized in that.

The display apparatus further includes a motion measuring unit for measuring a degree of motion of the video signal, wherein the gradation converting unit converts the video signal to a first adjacent gray level adjacent to the gray level of the video signal according to a measurement result of the motion measuring unit. The conversion to either the second adjacent gradation adjacent to the first adjacent gradation or the third adjacent gradation adjacent to the second adjacent gradation is effective for adapting to the degree of motion of the video signal.

Wherein the gradation converter; A first gradation compensator for converting the video signal into one of virtual gradations between the adjacent gradations according to a measurement result of the motion measuring unit; And a second gray level correction unit for converting the converted gray level from the first gray level correction unit into any one of the adjacent gray levels adjacent to the virtual gray level. The gray level converter may determine the gray level to be converted based on the gray level of the video signal, thereby preventing the difference between the gray level of the converted gray level and the original video signal from being apparent.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

4 is a control block diagram of a display apparatus according to an exemplary embodiment of the present invention.

As shown in FIG. 4, the display apparatus includes a video detecting unit 10, a gradation converting unit 20, and a panel driving unit 30.

The video detecting unit 10 detects whether the input video signal is a video signal. As a detection method, a motion estimation method of extracting motion vectors of a previous frame and a current frame in a block unit of a predetermined size, a motion detection method of estimating a change in an image value of a pixel, and the like are used.

The gray level converting unit 20 converts the video signal into either the video gray level or the still image gray level according to the detection result of the video detecting unit 10 and outputs the image signal to the panel driver 30.

The gray level converter 20 may include an inverse gamma correction unit 21, a gray limit and an error diffusion unit 22, and the like. The inverse gamma correction unit 21 performs gamma correction on the input image signal, and the gray scale limit and error diffusion unit 22 spreads an error generated in the gamma correction process. The gradation converting unit 20 may further include a first gradation compensator 23 and a second gradation compensator 24. These gradation corrections will be described later in detail together with a method for reducing pseudo contours.

The panel driver 30 emits the corresponding pixel of the panel according to the gray level input for each pixel unit.

The gray level converting unit 20 converts the input image signal into a video gray level or a still image gray level according to the detection result of the video detecting unit 10, thereby reducing the pseudo contour of the video and finely adjusting the gray level for the still image. I can express it.

The display device of the present embodiment may further include a motion measuring unit 40 for measuring the degree of motion of the input image signal. As a result of the measurement of the motion measuring unit 40, the gray scale converter 20 greatly reduces the pseudo contour, and converts the gray scale to display the image more precisely when the motion is slow.

Hereinafter, a method for reducing video gradation and video pseudo contour which can express fine images according to an embodiment of the present invention will be described in detail.

First, in the exemplary embodiment of the present invention, the video gray scale is composed of a linear gray scale and an intermediate gray scale.

The linear gradation has a continuous light emitting subfield and a continuous non-light emitting subfield. As described above, each bit of the subfield codeword indicates whether or not each subfield emits light. Specifically, a bit '1' indicates light emission and a bit '0' indicates a non-light emission subfield. In the embodiment of the present invention, the subfields are composed of a predetermined number (for example, 12) and are weighted in increasing order of the number of sustaining pulses from the first subfield to the last subfield, compared to the case of 8 subfields. The increase in the number of sustain pulses between fields can be allocated differently and weighted. For example, in the case of a total of 12 subfields, a linear gray scale may be expressed as a codeword (111100000000).

The intermediate gradation includes gradation in which one subfield which is not continuous with the non-emission subfield among the light emission subfields of the linear gradation is the non-emission subfield. For example, in the case of a total of 12 subfields, the halftone may be expressed as a codeword (110100000000). The non-light emitting subfields of the halftone may be arbitrarily selected from among the light emitting subfields unless they are adjacent to successive non-light emitting subfields. In this case, however, for the display of fine gray scales, it is preferable that the intermediate gray scales are selected to be close to the arithmetic mean level of the adjacent linear gray scales.

Such video gradation has more display gradations than the display subdivisions of one plus the number of conventional subfields (e.g., 24 display gradations can be implemented in the case of 12 subfields). The likelihood of contouring also increases. Therefore, increasing the frequency of image signal conversion to linear gradation rather than intermediate gradation may be an effective way to reduce pseudo contours. Such frequency adjustment may be performed by error diffusion processing or dithering.

5 is a gradation distribution diagram for explaining a method of adjusting the frequency of gradation transformation using a dithering technique.

As shown in Fig. 5, the case where there is an intermediate gradation [M1] between the linear gradations [X1] and [X2] is described as an example (where [X1] <[X2] is a relationship).

The gradation converting section 20 is a predetermined higher gradation [U1] and lower gradation [L1] between the intermediate gradation and the linear gradation, that is, between [M1] and [X2], and between [M1] and [X1] for dithering. ] Is set. Here, the upper and lower gray scales are preferably adjusted close to the arithmetic mean gray level of the adjacent gray scales.

The gradation converting section 20 processes the video signal having the gradation level between the linear gradations according to the magnitude of the gradation level.

First, when the image signal having the gradation level between the upper gradation level [U1] and the lower gradation level [L1] is input, the gradation conversion unit 20 converts the image signal into one of the upper and lower gradations.

In this case, the following dynamic dithering technique may be used as the converter method. The dynamic dithering technique converts an image signal to an adjacent gray level by reflecting the relative magnitude between the gray level and the adjacent gray level of the video signal, the weight of the pixel position, and the like. Equation (2) reflects this relationship.

Threshold = S` TIMES {(EDx-lower)} over {(upper-lower)} expression (2)

(Where S is an arbitrary proportional constant, EDx is the gradation of the video signal, upper is the upper neighbor gradation, lower is the lower neighbor gradation, and the threshold is even relative).

According to equation (2), when EDx is lower, the threshold is 0, and when it is upper, the threshold is S. As such, the threshold is a numerical representation of the relative gray level of the video signal and the adjacent gray levels. The adjacent gradation to be converted and output is selected according to the magnitude of the threshold. Alternatively, the weight may be added to the threshold value according to the position of the pixel, and the adjacent gray level to be converted may be selected according to the addition result.

Referring back to FIG. 5, dynamic dithering is applied using the upper gradation [U1] and the lower gradation [L1] as upper and lower gradations (hereinafter, referred to as "first dithering").

The video signal converted into any one of the upper gradation [U1] and the lower gradation [L1] is subjected to dithering using any one of adjacent linear gradation [X2] and [X1] and middle gradation [M1] as upper / lower adjacent gradation. The image is converted into the final moving image gradation (hereinafter referred to as "second dithering"). As a result, the frequency of the image signal is converted to linear gradation rather than intermediate gradation.

On the other hand, for a video signal having no gray level between the upper gray level and the lower gray level, that is, between the upper gray level [U1] and the linear gray level [X2] or between the lower gray level [L1] and the linear gray level [X1] Only dithering is applied.

In summary, in the exemplary embodiment of the present invention, the video gradation may allow two-bit transition of codewords between adjacent display gradations to increase the number of display gradations, and reduce the pseudo contour of the video by adjusting the conversion frequency accordingly. .

Meanwhile, according to another exemplary embodiment of the present invention, the number of intermediate grays may be further increased.

That is, the video gradation uses a plurality of intermediate gradations as display gradations between the linear gradations. For example, it is possible to have seven intermediate gradations [M1] to [M7] between the linear gradations [X1] and [X2], and the number of intermediate gradations is appropriately adjustable.

Accordingly, the number of display gradations is much increased than in the previous embodiment, so that the image can be displayed more precisely. As in the previous embodiment, the added grayscale may have a bit transition of 2 bits with the adjacent grayscale. In this case, the possibility of pseudo contours still increases.

In order to reduce pseudo contours, the first and second dithering as in the case of FIG. 5 may be applied.

First, in order to apply the first dithering, an upper gray level and a lower gray level are set between the middle grays. When the gray level of the input video signal is located between the upper gray level and the lower gray level, dithering is applied to the gray level to convert one of the adjacent upper gray levels and the lower gray levels. Next, second dithering is performed on the transformed upper and lower grayscales to either adjacent intermediate or linear grayscales.

Here, the display device preferably further includes a motion measuring unit 40. The motion measuring unit 40 measures the degree of motion of the video. This can be measured through the detection method of the moving picture detector, and the degree of movement / speed is measured.

If the motion is fast, pseudo contours are likely to occur, so it is necessary to correct dithering for the video grayscale having a 2-bit transition.

Referring to Fig. 6, there are seven intermediate gradations [M1] to [M7] between the linear gradations [X1] and [X2], and the predetermined virtual gradations [H1] to [H8] are set for each of the gradations. Illustrate illustratively. Here, the halftones [M1] of FIG. 6 and the halftones [M1] of FIG. 5 are separate values.

Each virtual gradation is used as the upper gradation and the lower gradation according to the gradation level of the video signal. In this case, in applying the first dithering, the image is not converted into any one of the adjacent upper and lower grayscales, but is converted into an arbitrary virtual grayscale located between the linear grayscales according to the degree of movement.

For example, if the gradation level [S1] of the video signal has a value near the intermediate gradation [M4], when the movement is small, it is converted to any one of the adjacent virtual gradations [H4] and [H5] as indicated by '1 step'. do. However, if the movement is fast, it is converted to either virtual gradation [H3] or [H6], as indicated by '2step'. In addition, when a faster motion is measured, the video signal is converted into one of virtual gradation [H2] and [H7] as in '3step'. The converted virtual gradations are converted to either adjacent gray scales or linear gray scales by the second dithering.

Accordingly, the pseudo contour can be adjusted adaptively according to the degree of motion of the video. However, if the motion is fast, there is a problem in that the difference between the converted original video signal and the converted gray scale becomes large. Therefore, it is preferable not to allow large-scale conversion, for example, '3step', '4step', etc., for the dark gradation region that is visually sensitive, and to allow large-scale conversion for the bright gradation region. Here, in order to reduce the occurrence of pseudo contours, it is also preferable to limit the number of intermediate gradations between each linear gradation to be less than or equal to a predetermined reference number.

As in the present embodiment, if the pseudo contour is adaptively adjusted according to the degree of movement of an image, various codewords having a 2-bit transition can be used as video gradation.

Reflecting this, in another embodiment of the present invention, it is possible to express the video gray level consisting of only the half gray level.

In this case, the linear gradation is excluded from the moving image gradation, and the moving image gradation is used to display the image with more display gradation than in the above embodiments. Since the video gradation here does not have a linear gradation, it measures motion and adapts it to convert the gradation.

That is, according to the degree of motion, the video signal is first adjacent gradation adjacent to the gradation level of the video signal, ie, second adjacent gradation adjacent to the second adjacent gradation, third adjacent gradation, fourth adjacent gradation. Is converted to any of. However, as described above, when the motion is large, there is a problem that a large error occurs between the gray level of the video signal and the converted adjacent gray level. Therefore, in consideration of the gradation level of the video signal, it is desirable to limit the conversion difference for the level where the human eye is sensitive.

Of course, the process of converting to any of the adjacent gradations may be controlled by converting to virtual upper / low gradations between each gradation according to the first dithering and converting to each gradation according to the second dithering.

In the above-described embodiments, the case of having a linear gradation or an intermediate gradation is exemplified, but it is a matter of course that other forms of gradation may be included in addition to these gradations. The first gradation correction section 23 and the second gradation correction section 24 of FIG. 4 are used as blocks for performing the first dithering and the second dithering in the above-described embodiment, respectively.

Although some embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that the embodiments may be modified without departing from the spirit or spirit of the invention. . It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

According to the present invention, it is possible to precisely express the moving picture signal and to effectively reduce pseudo contours.

1 is a schematic control block diagram of a PDP for reducing video pseudo contour;

FIG. 2 shows <Table 1> in which some of the gradations that can be displayed by each weighted subfield are listed;

3 shows a subfield codeword of moving picture gradation for representing a conventional moving picture;

4 is a control block diagram of a display device according to an embodiment of the present invention;

5 is a gradation distribution diagram for explaining a method of adjusting the frequency of gradation conversion using a dithering technique;

6 is a gradation distribution diagram for explaining a gradation conversion method when there are a plurality of intermediate gradations.

* Explanation of symbols for main parts of the drawings

10: video detection unit 20: gradation conversion unit

21: Reverse Gamma Compensation Government 22: Gradation Limit and Error Diffusion Department

23: First Gradient Supplementary Government 24: Second Gradient Supplementary Government

30: panel driver 40: motion measuring unit

Claims (13)

A display apparatus for processing a frame of an image into a plurality of subfields for time division; A gradation converter for converting an image signal into a predetermined moving image gradation; The moving picture gradation includes a linear gradation having at least one continuous light emitting subfield and at least one non-emitting subfield contiguous, and one subfield not contiguous with the non-emitting subfield among the light emitting subfields of the linear gradation. A display device comprising a halftone that is a non-emitting subfield. The method of claim 1, And the gray level converter converts the video signal to the linear gray level more than the intermediate gray level. The method of claim 1, Further comprising a motion measuring unit for measuring the degree of movement of the video signal, The gray level converter converts the image signal into one of grayscales adjacent to each of the intermediate grayscales and a predetermined virtual grayscale having each of the grayscale levels between the grayscales according to the measurement result of the motion measuring unit, and the video grayscale adjacent to the virtual grayscales. Display device characterized in that the conversion to any one of. The method of claim 1, And the moving image gray scale has the intermediate gray scale equal to or less than a predetermined reference number between adjacent linear gray scales. The method of claim 1, And the video grayscale has one of the intermediate grayscales between adjacent linear grayscales. The apparatus of claim 5, wherein the gray level converter;  The upper gray level and the lower gray level constitute a predetermined upper gray level and lower gray level between the two linear gray levels adjacent to the intermediate gray levels, and the image signal having the gray level level between the upper gray level and the lower gray level. A first gradation complementary unit for converting to any one of; And a second gray level correction unit for converting the upper gray level and the lower gray level into one of adjacent linear gray levels and the intermediate gray levels. The method of claim 6, And the second gradation compensator converts an image signal having a gradation level between the upper gradation and the lower gradation and a linear gradation adjacent to each of the adjacent gradation and the intermediate gradation. The method according to claim 3 or 7, The gray level conversion is processed by any one of a dithering method and an error diffusion method. The method of claim 1, And a video detecting unit detecting whether the input video signal is a video signal. And the gray level converter converts the video signal to the video gray level when it is detected as a video signal from the video detector. A display apparatus for processing a frame of an image into a plurality of subfields for time division; A gradation converter for converting an image signal into a predetermined moving image gradation; The moving picture grayscale includes a grayscale having a series of subfields in which a plurality of light emitting subfields and one non-light emitting subfield are continuous, and at least one non-light emitting subfield consecutive to the light emitting subfield among the series of subfields. Display device, characterized in that. The method of claim 10, Further comprising a motion measuring unit for measuring the degree of movement of the video signal, The gray level converting unit converts the video signal into a first adjacent gray level adjacent to the gray level of the video signal, a second adjacent gray level adjacent to the first adjacent gray level, and a third adjacent gray level adjacent to the second adjacent gray level. Display device, characterized in that for converting to any one of the adjacent gradations. The apparatus of claim 11, wherein the gray scale conversion unit; A first gradation compensator for converting the video signal into one of virtual gradations between the adjacent gradations according to a measurement result of the motion measuring unit; And a second gray level correction unit for converting the converted gray level from the first gray level correction unit into any one of the adjacent gray levels adjacent to the virtual gray level. The method according to claim 11 or 12, wherein And the gradation converter determines the gradation to be converted based on the gradation level of the video signal.