JP3314556B2 - Image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides means suitable for improving a gradation display method used in an image display device, particularly a plasma display.

[0002]

2. Description of the Related Art In a conventional plasma display device, a driving method called a subfield method disclosed in Japanese Patent Application Laid-Open No. H4-195087 is used. The concept of this method is briefly described below.

If one field is divided into, for example, eight sub-fields and the image signal is an 8-bit digital signal, each bit of the image signal is assigned to each of the eight sub-fields, and a halftone display of 256 gradations is performed. I have. In other words, in the first subfield, of all the pixels, the digital value of the image signal represented by 8 bits is 128 or more, that is, the image whose most significant bit is 1 is 128.
Light emission is performed twice.

Similarly, in the next subfield, of all the pixels, an image in which the second bit from the high order of the digital value of the image signal represented by 8 bits is 1 emits light 64 times more. By performing the same operation for the remaining six subfields, a total of 128 + 64 + 32 + 16 +
8 + 4 + 2 + 1 = 255 times of light emission are obtained, and the pixel with the lowest luminance does not emit light once, indicating the lowest luminance.

[0005] As described above, the total number of times of light emission in the eight subfields of each pixel ranges from 0 to 255 times depending on the value of the digital signal, and the luminance corresponding to the digital signal is observed. Will be. By adopting such a driving method, the entire screen can be made to emit light almost at the same time, so that the ratio of light emission time per pixel can be increased, and high luminance can be secured.

[0006]

As described above, in the conventional method, the luminance of each pixel is determined by the sum of eight sub-fields. In the case of an image having a field frequency of 60 Hz, it takes 1/480 seconds per pixel. The gradation display of the pixel becomes possible. This does not hinder the display of a still image. However, when displaying a moving image, depending on the image, unnaturalness may be remarkably perceived for the following reasons.

[0007] Consider a moving image in which an image includes an object of interest and an observer tracks the object on a screen. In the case of observing a fast-moving object, for example, in the case of a high-definition image, when observing an object moving right and left over the entire screen in one second on the screen, the movement is about 1000 pixels per second. Equivalent to. In other words, the observation time per pixel is only 1/1000 second, which is less than 1/480 seconds required for one subfield length.
This indicates that gradation display cannot be performed completely. Also, even when a relatively slow-moving object is tracked and observed on the screen, unnaturalness may be perceived in the following cases. This will be described with reference to FIG.

FIG. 4 shows that the luminances are level 9, level 8 and level 7 (1001, 100
0, 0111), three pixels (P1), (P2),
It is a figure which shows typically the mode of light emission in the subfield in (P3). Suppose, for example, points P1, P2, and P3 are sequentially observed in a short time in accordance with the movement of the line of sight on the screen. The number of times these points emit light per field,
That is, the average luminance is level 9 to level 7, and the difference is small. However, if there is a line-of-sight movement from P2 to P3 (corresponding to A) at a time corresponding to t1 in the figure, P
In the pixel position of 2, the number of times of light emission immediately before was as large as 8 times, whereas in the pixel position of P3, the number of times of light emission immediately before was 0, and even if the afterglow characteristics of the eyes were taken into account, the original luminance difference was small. Despite being 1, it is observed that there is a considerable luminance difference.

As described above, the gradation display by the subfield method is not suitable for observing a screen following the movement of an image, in which there is a considerable luminance difference between pixels having almost no original luminance difference. There was a problem that naturalness might be perceived.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a driving type image display device capable of obtaining a natural gradation expression even in a moving image.

[0011]

SUMMARY OF THE INVENTION The present invention divides one field into a plurality of subfields and associates each of the subfields with each bit of an image signal represented by a digital signal to perform gradation display. a display apparatus, a motion detection means for detecting a motion of the image signal, and a noise reduction means for reducing the noise contained in the image signal, noise reduction in the noise reducing means by the output of said motion detecting means The direction of noise reduction and the degree of noise reduction
It is characterized by the following.

[0012]

According to the present invention, a so-called subfield method is used in which one field is divided into a plurality of subfields, and each of the subfields corresponds to each bit of an image signal represented by a digital signal and performs gradation display. In the image display device, by providing the above configuration, the motion of the image signal is detected, and the noise reduction direction and noise in the noise reduction unit are reduced based on the motion detection result.
Since the degree of noise is changed, noise included in the image signal can be selectively reduced according to the motion of the image. In particular, by detecting noise only in the moving part of the image by the motion detecting means ,
In addition, by detecting only a portion where unnaturalness is perceived, it is possible to minimize the image area to be subjected to noise reduction processing, and the processing for removing unnaturalness becomes easy and effective. Things.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration example of an image display device according to an embodiment of the present invention. 1 is a motion vector detection circuit, 2 is an edge detection circuit, 3 is a directional LPF for smoothing an input signal, 4 is a hysteresis circuit, 5 is a mixing circuit,
Reference numeral 6 denotes a subfield image display device that performs gradation display by the subfield method.

The operation of the image display apparatus according to the embodiment of the present invention configured as described above will be described. The motion vector detection circuit 1 detects the direction 11 of the motion vector and the size 12 of the motion vector for each pixel of the input image signal. The edge detection circuit 2 detects an edge of the input image signal and supplies the edge to the directional LPF 3. The directional LPF 3 is a two-dimensional filter for smoothing the input image signal. The smoothing direction is determined by using the output 11 of the motion vector detection circuit 1 as shown in FIG.
To four directions shown in FIG. 2D can be selected. FIG. 2 shows the smoothing of the pixel of interest and its surrounding eight pixels.
This is a two-dimensional filter having coefficients to achieve this. Fig. 2
Each of them has a characteristic of performing smoothing in a specific direction.
(A) is a horizontal direction with respect to the center pixel of interest, FIG.
(B) is a vertical direction, and FIGS. 2 (c) and 2 (d) are oblique.
The direction is smoothed. These characteristics are
The selection is made according to the output of the vector detection circuit 1. The operation of the directional LPF 3 can be controlled based on the output of the edge detection circuit 2. For example, in order to suppress signal smoothing in an edge portion, as shown in FIGS. Characteristics. That is, the output of the motion vector detection circuit 1 is
The motion, that is, a portion that the observer's line of sight may follow, is detected by the motion detection circuit 1, and the signal is smoothed along the direction of motion, thereby removing a small change portion of the signal and removing the portion between adjacent pixels. Remove noise.

Further, a hysteresis circuit 4 having a hysteresis characteristic shown in FIG. 3 suppresses the change of the most significant bit. Therefore, the output of the hysteresis circuit 4 is smoothed along the direction in which the line of sight of the observer follows, and the minute noise is reduced. Further, since the movement of the most significant bit due to a small signal fluctuation is suppressed to a minimum by the hysteresis characteristic, unnaturalness is hardly observed even when an image is displayed using the subfield method. The image portion having no motion outputs the input image signal as it is. However, in order to realize smooth control, the image portion having motion has a signal 52 with noise removed by the mixing circuit 5 according to the degree of motion. The input image signal 51 is mixed and supplied to the sub-field image display device 6.

As described above, according to this embodiment, noise is removed in accordance with the movement of an image, and unnecessary fluctuation of the most significant bit is minimized. The present invention realizes means for enabling suitable moving image display in an image display device.

The motion vector detecting circuit 1 of the present embodiment
However, when a horizontal motion vector detection circuit is used, the configuration of the motion vector detection circuit 1 is only one-dimensional processing, and the circuit scale can be significantly reduced. In an image display using a normal subfield method, unnaturalness is relatively rarely perceived for an image having a vertical movement, and a good moving image display can be realized with a small circuit scale. .

In this embodiment, the motion vector detecting circuit 1 has been described as a means for detecting the motion of the image signal. However, the means for detecting the motion that the observer tracks on the screen includes the color and the object. It goes without saying that various modifications and limitations can be considered, such as performing processing focusing on the size and the like.

In this embodiment, the means for reducing noise contained in the image signal has been described by using the hysteresis characteristic. However, the low-pass filter may be used, or a non-linear processing of a high frequency component called noise coring may be performed. It goes without saying that various methods such as a noise removing method are possible.

[0021]

As described above, the conventional image display using the subfield method has a drawback that when noise is present in an image, unnaturalness is observed depending on the motion of the image. According to the present invention, the following effects can be obtained.

(1) In the configuration of the present invention, the motion of an image is detected, and noise contained in the image signal is reduced and removed based on the detection result. An image portion having no motion can be distinguished and processed, and perceived unnaturalness can be reduced when a moving image is displayed on an image display device using the subfield method.

(2) In the configuration of the present invention, since a horizontal motion vector detection circuit is used as the motion detection means, the configuration of the motion detection circuit can be realized by one-dimensional processing, and the circuit scale can be significantly reduced. . In addition, in the image display using the normal subfield method, since it is relatively rare to perceive unnaturalness in the vertical movement as compared with the horizontal movement, a good moving image can be obtained even with such a configuration. Display becomes possible.

(3) In the configuration of the present invention, when a small change portion included in an image signal is removed as noise reduction processing,
By providing a means for controlling the degree of removing the minutely changed portion according to the size of the edge component included in the image signal, the fluctuation of the image which is likely to occur at the edge portion is suppressed, and the image is output as natural as possible. be able to.

(4) In the configuration of the present invention, the element having the hysteresis characteristic can be easily configured by using a non-linear circuit element or the like, and has a high noise reduction effect.

(5) In the configuration of the present invention, attention is paid to the bit representation of a digital signal. In particular, only noise that is easily perceived as unnatural is selectively reduced, thereby changing the image signal due to higher-order bit noise. Can be suppressed as much as possible, and noise reduction processing can be effectively introduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image display device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of a directional LPF according to an embodiment of the present invention.

FIG. 3 is a diagram showing hysteresis characteristics in one embodiment of the present invention.

FIG. 4 is a diagram schematically showing a state of light emission at a specific pixel of an image display device using a driving method based on a subfield method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 motion vector detection circuit 2 edge detection circuit 3 directional LPF 4 hysteresis circuit 5 mixing circuit 6 subfield image display device 11 direction of motion vector 12 magnitude of motion vector 51 input image signal 52 signal from which noise has been removed

Claims (5)

(57) [Claims] 1. An image display device which divides one field into a plurality of sub-fields and performs gradation display by associating each bit of an image signal represented by a digital signal with each of the sub-fields. A motion detection unit that detects a motion, and a noise reduction unit that reduces noise included in the image signal; and a direction in which noise is reduced in the noise reduction unit by an output of the motion detection unit.
An image display device wherein the degree of reducing noise is changed . 2. The image display device according to claim 1, wherein the motion detecting means is means for detecting a motion vector at each pixel of the image signal. 3. The image display device according to claim 1, wherein said motion detecting means is means for detecting a horizontal motion vector in each pixel of the image signal. 4. The image display device according to claim 1, wherein said noise reduction means is constituted by a circuit whose input / output characteristics are hysteresis characteristics. 5. The image display device according to claim 1, wherein the noise reduction unit suppresses a change in upper bits of the image signal represented by a digital signal.