JPH0886998A - Drive method for display device - Google Patents

Abstract

PURPOSE: To hardly visually recognize turn distortion and horizontal stripes flow in a display device displaying an image by plural pixels having switching elements or a scanning line. CONSTITUTION: In an active matrix liquid crystal display device provided with A pieces of pixels respectively having selecting switches, a sheet of frame image is divided to n pieces of sub-fields SF11, SF12, SF13 successively displaying along a time base, and they are constituted of the pixels of A÷n×m (where, A is a positive integer, n is 3 <= the positive interger<=A, m is the positive integer <=n) pieces basically. This method is constituted so that the pixel interval differs at every sub-fields SF11, SF12, SF13, and the pixel interval is changed irregularly along the time base.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a display device in which a switching element for selection is provided for each pixel or scanning line, and more particularly to a method of driving a liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device is thin and lightweight and can be driven at a low voltage, so that it can be used in wrist watches, calculators, word processors, personal computers,
It is widely used in small game machines and the like. Further, the demand for a pen input electronic notebook is increasing, and the demand for a portable terminal (PDA) is expanding.

On the other hand, with the progress of multimedia, a plurality of displays are to be displayed on the same screen, and if a large screen and high definition are required, the amount of information increases and the driving frequency increases. An increase in power consumption due to this becomes a problem, and a driving method for reducing power consumption (for example, Japanese Patent Application No. 2-69706).
Is proposed. This method is named here as a multi-field driving method. This multi-field drive method
The surface flicker is a very effective means, but since the holding period is significantly increased, the flicker component for each pixel (usually for each line) becomes large. Therefore, there is a problem that horizontal stripes (line interference) generated in each field are visually recognized and cause deterioration of image quality of a still image.

Further, in a high-definition image in which the images have no correlation, each flicker component is not compensated, and among the flicker components, new carriers generated by the difference between the positive polarity and the negative polarity are spatial frequency axes. It has been clarified from the experiment that it occurs on the upper side and causes the folding distortion. Since this aliasing distortion is not stationary but moving, when it enters the region visually recognized by the spatiotemporal frequency characteristic of vision, the image quality is significantly deteriorated.

As described above, in the multi-field driving method, the line disturbance and the aliasing distortion caused thereby deteriorate the image quality. Usually, as a means for correcting this, correction is performed during the blanking period (retrace line period), but this was not sufficient.

As for the moving image, as another problem, the driving frequency is lowered, so that the signal cannot be rewritten sufficiently and the afterimage phenomenon occurs. Therefore, with regard to moving images, a signal processing system means is additionally required.

[0007]

Therefore, according to the present invention, among the flicker components that cannot be sufficiently compensated by each flicker component, the aliasing distortion of the carrier caused by the difference between the positive polarity and the negative polarity is regarded as a visual spatiotemporal space. The purpose is to make the region invisible to the frequency characteristics.

It is another object of the present invention to perform random driving in accordance with a signal in order to suppress the occurrence of an afterimage phenomenon for a moving image such as a moving picture whose frequency is higher than the driving frequency.

[0009]

In the driving method according to the present invention, the switching device for selection A
In a display device that displays an image with a plurality of pixels or scanning lines, one frame image is divided into n subfields that are sequentially displayed along the time axis, and the subfield is divided into a plurality of pixels or scanning lines. Of A ÷ n × m
(Here, A is a positive integer, n is a positive integer not less than 3 and not more than A, and m is a positive integer not more than n).

In order to improve the image quality, it is preferable that flicker can be compensated between a pixel or a scanning line to be written and a pixel or a scanning line in the vicinity thereof.

When an image is displayed by scanning lines, the image signal of one frame image can be interlaced to n: m, and the switch element can be selectively driven according to the processed image signal.

A first aspect of the present invention is characterized in that the intervals of the pixels or the scanning lines are made different for each subfield, and the intervals are irregularly changed along the time axis.

A second aspect of the present invention is characterized in that the value of m / n is changed depending on the image signal.

A third aspect of the present invention is characterized in that the subfields are grouped along the time axis, and the value of m / n is made different for each group.

In order to compensate for a change in the screen brightness caused by switching the value of m / n, the screen brightness of the previous subfield at the time of switching is detected, and the screen brightness of the next subfield is fed back. Can be

A fourth aspect of the present invention is characterized in that among the pixels or scanning lines which do not belong to the pixels or scanning lines of the displayed sub-field, displacement pixels or scanning lines are selectively written. To do.

When writing is not performed in a certain pixel or scanning line for several frames, a function of performing writing again may be provided in order to compensate luminance unevenness in the screen.

Also in the second to fourth aspects of the present invention,
Desirably, the intervals of pixels or scanning lines are made different for each subfield.

[0019]

According to the first aspect of the present invention, the switching elements are periodically turned on and off spatially and temporally so that the intervals of pixels or scanning lines vary irregularly for each subfield. I don't know. As a result, for example, the change in the luminance of the pixel due to the holding characteristic of the liquid crystal does not have a spatial or temporal periodicity within the panel surface, so that it does not fit into the visually perceptible area or becomes difficult to visually perceive. .

For example, when an image signal is interlaced to n: m in order to display an image with scanning lines, the intervals between selected scanning lines change irregularly during one frame. Therefore,
Since the scanning lines that are turned on during the field period do not have spatial periodicity within the panel surface, for example, a change in pixel brightness (line interference) due to the liquid crystal retention characteristics is visible in the area that is visually recognized. It does not apply, or it becomes difficult to be visually recognized, and the deterioration of image quality can be greatly improved.

Further, in a high-definition image having no correlation between images, when a new carrier is generated on the spatial frequency axis due to the difference between the positive and negative flicker components, and aliasing distortion is caused, This aliasing distortion also has no spatial periodicity, so it does not apply to the spatiotemporal frequency characteristics of vision, or can be made difficult to be visually recognized, and the deterioration of image quality can be greatly improved.

According to the second aspect of the present invention, for example, the value of m / n can be appropriately changed between a moving image and a still image. According to a third aspect of the present invention, a certain constant m / n
Even if an image signal in which flicker is likely to occur is input by driving with the value of, since this is switched for each subfield group, the flicker generation pattern is different for each group and is difficult to be visually recognized.

In the second and third viewpoints, when the screen brightness of the previous subfield at the time of switching is detected and the screen brightness of the next subfield is fed back, the screen can be changed by changing the value of m / n. The brightness change can be compensated.

According to the fourth aspect of the present invention, it is possible to eliminate an afterimage caused by, for example, a brightness difference. For information such as a moving image having a higher information frequency than the driving frequency, one frame of the image signal is subsampled and displayed, so that the one frame of the image signal is divided into a plurality of subfields. Therefore, for a pixel that has been once written, the image at the time of writing is retained during the non-selection period until the pixel is written again, and a signal extremely different from the luminance at the time of writing was input during the non-selection period. However, since it is not written, an afterimage phenomenon appears. Therefore, a signal having a different brightness level between the previous frame and the next frame is selectively driven so as not to cause an afterimage.

[0025]

EXAMPLES The present invention will be described in detail below with reference to examples. (First Embodiment) In the first embodiment, a multi-field driving method is applied in which one frame (one frame image) is divided into a plurality of sub-fields (sub-images) to reduce the driving frequency. . Since the multi-field driving method is well known, its detailed description is omitted.

FIG. 1 shows the configuration of the main part of a liquid crystal display device according to the first embodiment of the present invention. The liquid crystal display device of this embodiment is
As shown in FIG. 1A, a liquid crystal display panel 12, a subfield division processing unit 14, a signal line driver 16,
The pixel or scanning line selection signal generating circuit 18 and the gate line driving circuit 22 are provided. Liquid crystal display cell 24
Has a configuration (for example, a segment type display) that can be selected for each pixel, as shown in FIG.
Even if the intervals of the pixels forming each subfield are irregular, that is, the intervals of the selected pixels are changed for each subfield, it is possible to deal with the problem.

The contents of processing performed by the subfield division processing unit 14 may be any contents, but in this embodiment, in order to improve the deterioration of the display image, which is a problem in the prior art. It is the processing content.

To facilitate understanding, as shown in FIG. 2, the driving method according to this embodiment will be described by taking as an example the case of selecting 3 pixels out of 9 pixels (the number of subfields is 9/3 = 3). Will be explained.

First, in the subfield division processing section 14, for example, the pixel 26 is selected as shown in FIG. 2 to form three subfields SF11 to SF13. Figure 2
The shaded portion is the selected pixel, and the white portion is the non-selected pixel. In this case, since the image signal to be read by the subfield division processing unit 14 is reduced to 1/3 of the conventional one, the drive frequency can be reduced as is well known in the multi-field drive method, and the drive circuit 22 and the panel 12 can be reduced. Also, the power consumption of the signal line driver 16 can be reduced.

When writing an image signal to each pixel in the panel 12, a signal indicating which pixel should be selected from the pixel selection signal generating circuit 18 is a gate line driving circuit 2.
2 and the gate line corresponding to each pixel is controlled to be turned on.

The purpose of the subfield division processing section 14 is to prevent line interference, which is a factor causing aliasing distortion, from occurring fundamentally, and set the spacing of selected pixels in a region where the visual spatiotemporal frequency is not visible. It can be most effective.

In this embodiment, the case has been described in which the same number of pixels is selected in each subfield so that the pixel interval changes irregularly along the time axis, but the number of selected pixels and the selection method are various. Can be changed in the following manner. Also, the present embodiment can be applied to a case where the scanning lines are selected in substantially the same number in each subfield so that the scanning line intervals vary irregularly along the time axis. (Second Embodiment) The second embodiment is a modification of the first embodiment, which is also driven by dividing one frame (one frame image) into a plurality of subfields (subimages). This is an application of the multi-field driving method that lowers the frequency. Since the multi-field driving method is well known, its detailed description is omitted.

FIG. 3 shows the structure of the main part of a liquid crystal display device according to the second embodiment of the present invention. The liquid crystal display device of this embodiment is
As shown in FIG. 3A, in particular, an n: m interlace processing circuit 34 and a scanning line selection signal generation circuit 38 are provided. In addition, the liquid crystal display device of this embodiment includes a liquid crystal display panel 32, a signal line driver 36, an n counter circuit 40, and a gate line drive circuit 42. The structure of the gate line drive circuit 42 is as shown in FIG.

The content of processing performed by the interlace processing circuit 34 may be any content, but in the present embodiment, the processing content for improving the deterioration of the display image, which is a problem in the prior art. It has become.

To facilitate understanding, as shown in FIG. 4, n = 6 and m = 2 (the number of subfields is 6/2 = 3).
The driving method according to the present embodiment will be described by taking the case as an example.

First, the n: m interlace processing circuit 34.
In FIG. 4, for example, as shown in FIG. 4, a pixel corresponding to the scanning line 46 is selected, and three subfields SF21 to SF21 are selected.
Make up 23. In FIG. 4, hatched portions are selected scanning lines, and white portions are non-selected scanning lines. In this case, since the image signal to be read by the interlace processing circuit 34 is reduced to 1/3 of the conventional one, the drive frequency can be reduced as is well known in the multi-field drive method, and the drive circuit 42 and the panel 32 can be reduced. Power consumption can be reduced.

When writing an image signal to each pixel in the panel 32, a signal (S1) indicating which pixel should be selected from the scanning line selection signal generating circuit 38 is sent to the gate line driving circuit 42. , And the signal obtained by shifting the signal (S2) from the n counter circuit 40 is processed by the AND circuit. As a result, the gate line corresponding to each pixel is controlled to be turned on.

FIG. 5 shows signal waveforms corresponding to the respective signal lines. In the figure, "input", "S3", "Gn", "Pn"
Indicates an input image signal, a signal from the signal line driver 36 to the panel 32, ON / OFF of each gate line, and a voltage of a pixel corresponding to each scanning line.

Even if the n: m interlacing process is performed, line interference, which is a factor of causing aliasing distortion, occurs. However, as shown in FIG. 6, since there is no line-interference interval or horizontal stripe flow that occurs when scanning lines are sequentially scanned from an upper line to a lower line, the spatio-temporal spectrum of line interference is dispersed and becomes difficult to be visually recognized. At the same time, it has been confirmed by experiments that it is also effective against aliasing. FIG. 6 shows a change in the luminance of the pixel corresponding to the scanning line when the method according to the present embodiment is used (a) and when the conventional multi-field driving method is used (b). In the figure, the brightness changes from light to dark and the pixel voltage changes from low to high in the order of white, diagonal, and halftone.

In the above description, the case where the input signal is interlaced at 6: 2 is exemplified, but the gist of the present invention can be applied to a normal n: 1 interlaced signal or an n: m (m <n) interlaced signal. It can be changed without departing.

In the first and second embodiments, as the pixel selection method for forming the subfield, it is preferable that flicker is compensated within one frame in order to improve the image quality. Since the line interference is caused by the holding characteristic of the pixel, the pixel or scanning line selection interval is such that a 10% level image signal in which crosstalk easily occurs or a 50% level image signal in which the transmittance changes abruptly. On the other hand, it is desirable to decide so that line interference and aliasing distortion do not occur. (Third Embodiment) In the present invention, an image is displayed by changing the intervals of the pixels or the scanning lines according to the input image signal, so that the processing in the image signal input section is required. Since the image signal of one frame is divided into a plurality of subfields, the pixel once written retains the image at the time of writing for a non-selection period until writing again. Therefore, in a signal such as a moving image that requires a sampling frequency in the time axis direction, even if a signal that is extremely different from the brightness during writing is input during the non-selection period, it will not be written, resulting in an afterimage phenomenon. come.

FIG. 7 shows an afterimage phenomenon when a cursor such as a mouse is moved in a 3: 1, 5: 2, 3: 2 interlace drive. When the 3: 1 interlace drive is used, there are many afterimages and almost no new image signal appears. In the 5: 2 interlace drive, a new image signal appears although there is an afterimage. In the 3: 2 interlace drive, afterimages are small and many new images appear. The change in the image signal due to the increase in the number of subfields in one frame is conspicuous.

FIG. 8 shows the structure of the main part of a liquid crystal display device according to the third embodiment of the present invention. The liquid crystal display device of this embodiment is
As a changed portion from the second embodiment shown in FIG. 3, a moving image / still image detection processing unit 52 and n: m = 3: connected to this are shown.
Three interlace processing circuits 5 of 1: 5: 2 and 3: 2
4a, 54b, 54c, a multi-field drive method selection processing unit 56, and interlace processing circuits 54a, 54
and a switch 58 for switching between b and 54c. The moving image / still image detection processing unit 52 discriminates an appropriate multi-field driving method for the next frame and switches 58.
Switch. In each n: m interlace drive, the scanning lines may have irregular intervals, as described in the second embodiment. (Fourth Embodiment) FIG. 9 shows a structure of a main part of a liquid crystal display device according to a fourth embodiment of the present invention. The device according to the present embodiment is premised on having a basic configuration for performing multi-field driving, but the configuration for multi-field driving is duplicated in the description with, for example, the first embodiment, It is omitted here.

The liquid crystal display device according to the present embodiment includes a liquid crystal display panel 62, a signal line driver 66, a pixel selection signal generating circuit 68, a gate line driving circuit 72, a displacement pixel detecting circuit 64 and a pixel signal generating circuit. 74 are provided. The cells of the liquid crystal display panel have a configuration (for example, a segment type display) that can be selected for each pixel.

The displacement pixel detection circuit 62 detects displacement pixels of signals different between the previous frame and the next frame. In response to this, the pixel signal generation circuit 74 outputs the changed image signal, and the pixel selection signal generation circuit 68 is output.
Selects a pixel. That is, only displacement pixels are selected and writing is performed. Therefore, the signal of the previous frame is temporarily recorded in the frame memory, and the selection or non-selection of the signal is determined by the correlation with the next frame.

Since the afterimage is caused by the brightness difference between the previous frame and the next frame, for example, only the high-order bit of the grayscale signal is
Alternatively, the pixels obtained by collecting the pixels may be subsampled and used as a selection criterion. This allows the signal processing system to have a simpler configuration. For example, for an image signal composed of a 4-bit gradation signal, the high-order 2 bits are used as the selection reference, and when H is input in the frame preceding this bit and all L is input in the next frame, The image signal is selected.

Further, in consideration of the retention characteristic of the pixel, for the pixel which is not written for several frames, a function of writing again may be provided in order to compensate the uneven brightness in the screen.

In the above description of the present embodiment, the description has been made assuming that a variant pixel is detected. For example, as in the first embodiment, the present invention is applied to a configuration in which a cell of a liquid crystal display panel can be selected for each pixel. be able to. If displacement scanning lines are detected instead of the mutated pixels, n: as in the second and third embodiments is detected.
It can be applied to m-interlaced driving. As described above, the fourth embodiment is applicable to all of the multi-field driving method (including the conventional method) in which the selected and non-selected pixels (scan lines) are generated. (Fifth Embodiment) In the liquid crystal display device of the fifth embodiment, in the configuration of the liquid crystal display device of FIG. 1 described in the first embodiment, n: m is changed for each group consisting of a plurality of subfields. Characterize.

For example, as shown in FIG. 10, in the first group G1 consisting of X subfields, one in three subfields.
(3: 1) scanning lines are driven, and in the second group G2 including the next Y subfields, 2 in 5 (5: 2) scanning lines are driven to drive the next Z scanning lines. In the third group G3 including subfields, one in every five lines (5: 1) is driven. Here, each of X, Y, and Z is a multiple of 3, 5, and 5 corresponding to n of n: m.

The number of subfields in one group may be different or the same. In each n: m interlace drive, as described in the second embodiment, the scanning lines may have irregular intervals,
Alternatively, it may be regularly changed like the conventional multi-field driving method. Further, although an example is shown here for each scanning line, it may be performed for each pixel.

According to the present embodiment, when an image signal which is likely to cause flicker when driven at a certain fixed pixel or scanning line interval is input, this interval is switched for each subfield group. The flicker generation pattern differs for each group, making it difficult to be visually recognized. In addition, switching this interval may cause surface flicker due to a change in screen brightness.However, this surface flicker causes a problem by reducing the temporal frequency and contrast below the unrecognized temporal and spatial characteristics. You can prevent it from happening.

In order to compensate for this surface flicker, the screen average brightness of the previous subfield at the time of switching is detected and the screen brightness of the next subfield is fed back. It is also possible not to generate. FIG. 11 shows a configuration of a main part of a liquid crystal display device for realizing this.

The liquid crystal display device of this embodiment comprises a liquid crystal display panel 82, a signal line driver 86, a scanning line selection signal generating circuit 88, and a gate line driving circuit 92. A subfield group division processing unit 94 for grouping subfields is connected to the signal line driver 86 via the image signal generation circuit 84. Further, a screen brightness detection circuit 96 is connected to the panel 82 to compensate for surface flicker. The screen brightness detection circuit 96 detects the voltage applied to the pixel in the previous subfield during the blanking period, and feeds the information back to the image signal in the next field through the surface flicker prevention processing unit 98.

In the above description of the fifth embodiment, subfield grouping is performed regardless of the frame image unit. However, the grouping of subfields may be combined with the unit of the frame image, and each group may be composed of one frame or a plurality of frames. The number of frames in each group may be the same or different. By doing so, when an image signal that is likely to cause flicker if driven at a certain fixed pixel or scanning line interval is input, this interval is switched for each frame group, so the flicker occurrence pattern is visually recognized. It becomes difficult to be done.

Although the present invention has been described with reference to the illustrated embodiments, the present invention is not limited to the embodiments, and various modifications can be made without departing from the scope of the invention. is there.

[0056]

According to the present invention, by changing the intervals of pixels or scanning lines for each sub-field and changing them irregularly along the time axis, changes in the luminance of pixels or scanning lines can be visually recognized. It will be difficult. Further, the aliasing distortion is less likely to be visually recognized, and the deterioration of image quality can be significantly improved.

Further, according to the present invention, the value of m / n, that is, the density of the pixels or the scanning lines in the subfield is changed depending on the image signal, so that the value can be changed depending on the image even if the driving frequency is lowered. The required image quality can be maintained.

Further, according to the present invention, by changing the value of m / n for each group divided along the time axis, the flicker generation pattern is different for each group, and is difficult to be visually recognized.

Further, according to the present invention, by selectively performing additional writing on the displaced pixel or the scanning line, it is possible to eliminate an afterimage caused by, for example, a brightness difference.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing subfields according to the driving method of the first embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a diagram showing subfields according to a driving method according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a drive signal voltage and a timing chart in the drive method according to the second embodiment of the present invention.

FIG. 6 is a diagram showing a comparison between a driving method according to a second embodiment of the present invention and a conventional multi-field driving method regarding a horizontal stripe flow phenomenon.

FIG. 7 is a diagram showing a display image when an image signal is switched in a moving image.

FIG. 8 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing subfields according to a driving method according to a fifth embodiment of the present invention.

FIG. 11 is a block diagram showing a configuration of a main part of a liquid crystal display device according to a fifth embodiment of the present invention.

[Explanation of symbols]

12, 32, 62, 82 ... Liquid crystal display panel, 14 ... Subfield division processing section, 16, 36, 66, 86 ... Signal line driver, 18, 38, 68, 88 ... Pixel or scanning line selection signal generating circuit, 22 , 42, 72, 92 ... Gate line driving circuit, 34, 54a, 54b, 54c ... N: m interlace processing circuit, 40 ... N counter circuit, 52
... moving image / still image detection circuit, 56 ... multi-field drive method selection processing unit, 58 ... switch, 64 ... displacement pixel detection circuit, 74,84 ... pixel signal generation circuit, 94 ... subfield group division processing unit, 96 ... screen Luminance detection circuit, 9
8 ... Surface flicker prevention processing section.

Claims (5)

[Claims] 1. A display device for displaying an image by A pixels or scanning lines, each of which is provided with a switching element for selection, wherein n frame images are sequentially displayed along a time axis. It is divided into sub-fields, and the sub-fields are divided by A / n × m (where A is a positive integer, n is a positive integer of 3 or more and A or less, of the pixels or scanning lines).
m is a positive integer less than or equal to n) basically consisting of a number of pixels or scanning lines. Further, the intervals of the pixels or scanning lines are made different for each subfield, and the intervals are irregular along the time axis. A driving method characterized by changing to. 2. A display device for displaying an image by A pixels or scanning lines, each of which is provided with a selection switch element, wherein n frame images are sequentially displayed along a time axis. It is divided into sub-fields, and the sub-fields are divided by A / n × m (where A is a positive integer, n is a positive integer of 3 or more and A or less, of the pixels or scanning lines).
(m is a positive integer equal to or less than n) basically consisting of pixels or scanning lines, and further, the value of m / n is changed depending on the image signal. 3. A display device for displaying an image by A pixels or scanning lines, each of which is provided with a switching element for selection, and n frame images for displaying one frame image in order along a time axis. It is divided into sub-fields, and the sub-fields are divided by A / n × m (where A is a positive integer, n is a positive integer of 3 or more and A or less, of the pixels or scanning lines).
m is a positive integer equal to or less than n) or pixels, or scanning lines, and the subfields are grouped along the time axis so that the value of m / n is different for each group. A driving method characterized by the above. 4. A display device for displaying an image by A pixels or scanning lines, each of which has a switching element for selection, displays n frame images in order along a time axis. It is divided into sub-fields, and the sub-fields are divided by A / n × m (where A is a positive integer, n is a positive integer of 3 or more and A or less, of the pixels or scanning lines).
m is a positive integer less than or equal to n) basically consisting of pixels or scanning lines, and further, of the pixels or scanning lines that do not belong to the pixels or scanning lines of the displayed sub-field, for displacement pixels or scanning lines Is a driving method characterized by selectively writing. 5. The pixel according to claim 2, wherein an interval between the pixels or the scanning lines is different for each subfield, and the interval is irregularly changed along a time axis. Driving method.