JPH05127614A - Half-tone image displaying method - Google Patents

Abstract

PURPOSE:To provide the method which displays half-tones of plural levels with a flicker less than before on a display device having a binary memory function. CONSTITUTION:The half-tones of plural levels are displayed by combining light emission times of plural respective subfields 21a-22c of 1st and 2nd successive fields 21 and 22 in one frame. At this time, the light emission times of the subfields 21b, 21c, 22d, and 22c for displaying bits less than normal bits are set so that the sums of the light emission times of the subfields for displaying the bits less than the normal bits in each of the 1st and 2nd fields among plural times (four times, e.g. 1/2, 1/4, 1/8, and 1/16) prescribed so as to obtain the half-tones of plural levels are averaged most between the 1st and 2nd fields.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of displaying a halftone image on a display device having a binary memory function, such as a plasma display panel (hereinafter sometimes abbreviated as "PDP"). It is about.

[0002]

2. Description of the Related Art PDPs, liquid crystal display devices and the like have been attracting attention as display devices replacing CRTs (Cathode Ray Tubes). This is because it is possible to realize a display device that cannot be obtained by a CRT, such as a flat panel display. However, in a PDP, for example, the display is performed depending on whether or not the light emitting point emits light, so that the display of an image of a halftone level is not so easy as that of a CRT. Therefore, various methods for displaying a halftone image on a PDP have been conventionally proposed.

As one of the typical methods, one field is divided into n (n is a positive integer of 2 or more) subfields, and the light emission time in each of these subfields is weighted. There has been a method of displaying 2 ⁿ steps of gradation by the visual afterimage combination time when the subfields are selectively made to emit light (Japanese Patent Publication No. 51-32051).
issue).

In this method, when one field is divided into four subfields, the following display is made. 9 (A) and 9 (B) are diagrams provided for the description. In particular, in FIG. 9A, one field has a bit I and a bit II corresponding to the most significant bit (hereinafter, MSB),
An address timetable for driving a matrix-like PDP having N rows is shown under the condition that the subfield is divided into a total of 4 bits of bit III and bit IV corresponding to the least significant bit (LSB). There is. Further, FIG. 9B shows a light emission waveform of the i-th row in this PDP. However, this light emission waveform is an example in which all bits from MSB to LSB are emitting light and an example in which it is assumed that there is no afterglow.

In FIG. 9A, Tf is a field period, which is normally set to 16 to 20 msec. Furthermore, the right diagonal solid line is the write timing, the right diagonal broken line is the erase timing, and T is the address scanning time. Except in special cases, the subfield period is set equal to this address scanning time T. Therefore, in the following description, the symbol T is also used for the subfield period unless otherwise specified. In this case, since the number of subfields is 4, the subfield period T is T = Tf / 4 = 4 to 5 mse
c. Also, the light emission time in each subfield is MS
Assuming that the light emission time in the B subfield is approximately T, bit II is T / 2, bit III is T / 2 ² , and LSB is T / 2.
It is said to be ³ . In the case of this configuration, it is possible to display 2 ⁴ gradation levels by selectively emitting light from the four subfields.

However, in the above-mentioned halftone image display method,
N subfields must be prepared for each field. For PDP and LCD, the row address time is T
If a and the subfield period are T, the number N of addressable rows is given by N = T / Ta. And Ta
Is a finite value depending on the nature of the display device, and the subfield period T is T =
Since Tf / n, the number of addressable rows N is N = T
It means f / nTa. Therefore, in the above method of preparing n subfields for each field,
Since the number of addressable rows N decreases as the number of bits n increases, there is a trade-off relationship between the panel size increase and the number of gradations.

As a method for reducing the inconvenience that the number of addressable lines is restricted by the number of subfields, a halftone image display method disclosed in, for example, Document a (Electronic Science (1973) pp.69-75) is available. there were.

This method has been one in which halftones are displayed by utilizing afterimages of a plurality of subfields of a plurality of consecutive fields in one frame. In addition, each of the plurality of fields includes one or more subfields that display a regular bit, including a subfield that displays an MSB, and 1 that displays a bit less than the regular bit.
The method is configured to include the above subfields.

Here, the subfield for displaying the regular bit is M in each of the following fields.
Each subfield from the subfield displaying SB to the place where the light emission time is set in the same array when the lower subfield is viewed (hereinafter, referred to as "regular bit subfield") is less than the regular bit. The subfield for displaying the bit is a subfield lower than the normal bit subfield (hereinafter referred to as “non-normal bit subfield”).
However, in each of a plurality of subsequent fields, when all subfields have the same arrangement and the emission time is set when the subfields lower than the subfield displaying the MSB are viewed, the plurality of subfields are displayed for the still image. The subfields that emit light together are called normal bit subfields, and the subfields that may emit light in only one of the fields are called non-normal bit subfields.

The display method and the normal bit subfield / non-normal bit subfield disclosed in Document a will be specifically described with reference to FIGS. 10 (A) and 10 (B).

In the example of FIG. 10, one frame is composed of two fields, a first field 11 and a second field 12, and the first field 11 is composed of a first subfield 11a and a second subfield 11b. The second field 12 includes the first subfield 12a and the second subfield 12a.
It is composed of the subfield 12b. And the first
And the emission time in each of the first subfields 11a and 12a of the second fields 11 and 12 is set to about T, respectively, and the second subfield 11b of the first field 11 is set.
Light emission time is set to T / 2, and the second field 12
The light emission time in the second subfield 12b is set to T / 4.

In the configuration of FIG. 10, each of the subfields 11a and 12a having the same light emission time T in the successive fields 11 and 12 in one frame is a subfield for displaying the MSB and has a regular bit. The sub-field for the normal bit and corresponds to the lowest sub-field of the sub-field for regular bits. The second subfields 11a and 12a of the first and second fields 11 and 12 correspond to subfields for non-regular bits.

The method disclosed in this document a is shown in FIG.
In the case of the condition (A), 0, 1/4, 2/4, 3/4, ...
..., 12 gradations of 11/4 were produced.

This display method has an advantage that a certain number of gradations can be secured although the number of subfields is smaller than that in the display method described with reference to FIG. Therefore, the influence of the number of subfields n on the number of drive rows N can be reduced.

[0015]

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention
According to the conventional halftone image display method disclosed in FIG. 10 (described with reference to FIG. 10), only 12 gradation levels can be obtained. Further, document a does not show a specific method for increasing the number of gradations. It is desired to further increase the number of gradations in order to improve the characteristics of the display device.

As a method of further increasing the number of gradations based on the conventional technique described with reference to FIGS. 9 and 10, FIG.
A method as shown in FIG. 11A or FIG. 11B can be easily considered. That is, this is a method of increasing the number of subfields.

In the case of the method of FIG. 11A, the maximum light emission time is 1 + 1/2 + 1/4 + 1 + 1/8 + 1/16 = 47.
/ 16, the minimum light emission time is 1/16, and since there are gradations corresponding to the black level, the gradation number is 47/16 ÷ 1.
/ 16 + 1 = 48. In the case of the method of FIG. 11B, the number of gradations is 28. As in the former case, the number of gradations can be increased in the configuration in which the subfield for non-regular bits is added (FIG. 11A).

However, in the method of FIG. 11A, the non-normal bit subfields whose light emission times are 1/2 and 1/4 are included in the same field. That is, of the four subfields having the light emission times of 1/2, 1/4, 1/8, and 1/16, the two non-regular bit subfields on the longer light emission time side are the first field 11a. It is in. Therefore, there is a first problem that the flicker becomes large at the gradation level at which the cells are illuminated in the two sub-fields for non-regular bits whose emission times are 1/2 and 1/4.

Here, the flicker amount is a period for displaying a halftone (3Tf in the case of FIG. 11 because one frame is composed of three fields. One frame is composed of k fields). If the reciprocal of kTf (k is a positive integer) is used as the fundamental frequency, the amount is proportional to the fundamental wave component (amplitude peak value) in the light emission waveform.

Further, in the display method of FIG. 11A, the light emission time Tn in the normal bit subfield 11a is 1, and the irregular bit subfields 11b, 11c,
The total light emission time Ts of 12b and 12c is 1/2 + 1 /
Since 4 + 1/8 + 1/16 = 15/16, Ts /
Tn = 15/16 <1. For this reason, when light emission of the same gray level corresponding to the normal bit is performed in subsequent frames (for example, when light emission is performed in emission time 1 in each of subsequent frames), in a specific subfield (FIG. 11A). Since the subfield (11a) is emitted in a state of being substantially synchronized with the frame period, there is a second problem that the fundamental wave component becomes remarkable and flicker is very noticeable. This is less problematic when the field period Tf is a normal value (16 to 20 msec), but is more problematic when the field period is longer than the normal value.

The present invention has been made in view of the above circumstances. Therefore, an object of the present invention is to provide a display device having a binary memory function with a plurality of levels of halftones in a plurality of consecutive fields in one frame. An object of the present invention is to provide a method capable of reducing flicker as compared with a conventional method in a method of displaying a plurality of subfields in combination.

[0022]

In order to achieve this object, a display device having a binary memory function is used to display halftones of a plurality of levels in a plurality of subfields of a plurality of successive fields in one frame. In the halftone image display method for displaying afterimages in combination, each of the plurality of fields includes one or more normal bit subfields for displaying normal bits including a subfield for displaying the most significant bit. , And at least two non-regular bit subfields for displaying bits less than the regular bits, and the display time in each non-regular bit subfield is to obtain the halftone of the plurality of levels. In the halftone image display method having a configuration in which it is assigned and set from a plurality of times defined in advance, Sum between the display time of at least two non-normal bit subfield of each of each field and performs so as to best averaged across multiple fields mentioned above.

In implementing the present invention, when the display time in the lowest subfield of the above-mentioned normal bit subfields is expressed as Tn, the display in all non-normal subfields is performed. Total time T
It is preferable to set the display time in each non-regular subfield so that s satisfies the following expression (1).

Here, the display device having a binary memory function is, for example, an AC type PDP or a DC type resistive PD.
P, DC type PD driven by pulse memory driving method
Examples include various PDPs such as P, those PDPs in which each cell has a memory function composed of a circuit such as a flip-flop, and those which are used by binarizing 1 and 0 by an analog memory. .. Further, a liquid crystal display device, a display device using a light emitting diode or electroluminescence, a display device using a Kerr effect, a Pockels effect, a Franz-Keldish effect, or the like can be given.

[0025]

According to the structure of the present invention, when a plurality of predetermined times for obtaining a plurality of levels of halftone are randomly assigned as the light emission time of each non-regular bit subfield of a plurality of successive fields. Compared with the above, since the basic frequency component serving as an index of flicker is reduced, flicker can be reduced.

When the display time in each non-regular subfield of a plurality of successive fields is set so that the condition of 1≤Ts / Tn is satisfied, for each of a plurality of successive fields in one frame, By combining the display in subfields for non-regular bits, the least significant bit of the regular bits can be displayed. Therefore, the display of the gradation level of the least significant bit of the regular bits can be performed by appropriately combining the subfields at each time position in one frame. Therefore, for example, in the case where a PDP is used to display a grayscale level corresponding to a regular bit in each subsequent frame, for example, a grayscale level corresponding to a light emission time “1”, in the conventional method, as shown in FIG. Field 1
Although 1a was made to emit light in a state of being substantially synchronized with the frame period, this can be avoided in the present invention. This means that it is possible to reduce the fundamental frequency component that is an index of flicker, which also reduces flicker.

[0027]

Embodiments of the halftone image display method of the present invention will be described below with reference to the drawings. It should be noted that the drawings used for the description are only schematically shown so that the present invention can be understood. Further, each of the following embodiments will be considered as an example of displaying a still image or a substantially still image, that is, an example of displaying an image in which signals are not substantially changed in a plurality of successive fields in one frame. This is because, in the case of a moving image, the signal between successive fields changes significantly and the halftone level also changes between successive fields. Since the image is a still image, the sampling of the image signal is performed in principle for each frame, but it is of course also possible to perform it for each field.

1. First Example As a first example, an example will be described in which the present invention is applied to the display method that can obtain 48 gradations described with reference to FIG.

FIG. 1 is a diagram which is used for the explanation.
Fields, subfields, and display times set in each subfield in the display method of the embodiment (hereinafter referred to as PD
Assuming P, it is called "light emission time". ) It is each explanatory drawing.

In the first embodiment, as shown in FIG. 1, one frame is composed of two fields, a first field 21 and a second field 22, and further, a first field 2
1 to the first to third three subfields 21a to 21c
The second field 22 is composed of three first to third subfields 22a to 22c. The number of fields, the number of subfields, which of the subfields are for normal bits and which are for non-normal bits, and the like are the same as those in FIG. 11A.

FIG. 11 of the display method of the first embodiment.
The difference from the case of (A) is how to allocate the light emission time in the subfield for non-regular bits.

In the first embodiment, a plurality of light emission times (in this case, 1 / in this case) which are predetermined as the light emission time in the non-normal bit subfield in order to obtain 48 gradations are obtained.
2 1/4, 1/8, 1/16) are assigned to the non-normal bit subfields of the first field and the second field.
1st and 2nd non-regular bit subfield 21
The sum of the display times of b and 21c and the second field 22
First and second irregular bit subfields 22 of
That is, the sum of the display times of b and 22c is averaged. Specifically, the light emission time in the second subfield 21b of the first field 21 is 1 /
2, the emission time in the third subfield 21c is 1/16
The light emission time in the second subfield 22b of the second field 22 is set to 1/4 and the light emission time in the third subfield 22c is set to 1/8.

When the light emission time in each sub-field for irregular bits is set as described above, the first field 21
The total of the light emission times in the second and third subfields 21b and 21c is 7/16, and the second field 22
The total sum of the light emission times in the first and second subfields 22b and 22c is 6/16. In the case of FIG. 11A, the second and third subfields 1 of the first field 11
Compared with the sum of the respective light emitting times in 1b and 11c being 12/16, and the sum of the respective light emitting times in the first and second subfields 12b and 12c of the second field 12 being 3/16. Then, it is understood that the above-mentioned averaging is achieved in the embodiment.

In the case of the first embodiment, it is necessary to illuminate both the subfield in which the emission time of 1/2 is set and the subfield in which the emission time of 1/4 is set. When displaying, these subfields belong to different fields, and only the difference (1/4) between the two emission times contributes to the flicker amount. However, in the case of FIG. 11 (A), 1/2 + 1/4
Considering that = 3/4 contributed to the amount of flicker,
The flicker amount in the first embodiment is 1 as compared with that in FIG.
It turns out that it becomes / 3.

Table 1 below shows a display method of 47 gradations excluding the black level according to the display method of the first embodiment. In Table 1, 1A represents a driving state of the first subfield of the first field, 1/2 represents a driving state of the second subfield of the first field, and 1/16 represents a driving state of the first field. A term indicating the driving state of the third subfield, 1B is a term indicating the driving state of the first subfield of the second field, 1/4 is a term indicating the driving state of the second subfield of the second field, 1/8 Is a term indicating the driving state of the third subfield of the second field. Furthermore, the circles in each section mean that the cell emits light in that subfield, and (◯) drives either the subfield of 1A or the subfield of 1B at that halftone level. It means that it is okay (the same applies to the corresponding table below). In addition, the subfields marked with A or B in Table 1 and the following tables are normal bit subfields.

Further, in Table 2 below, the display method according to the conventional display method described with reference to FIG. 11A is shown by the same notation method as in Table 1.

2. Second Embodiment FIG. 2 is an explanatory view similar to FIG. 1 for explaining the second embodiment.

In the second embodiment, the first field 21 is composed of four first to fourth subfields 21a to 21d, and the second field 21 is composed of four first to fourth subfields 22a to 21d. This is an example of a display method which is configured and which can obtain 192 gradations. The normal bit subfields are the first subfields 21a and 22a for both the first and second fields 21 and 22, and the remaining subfields are non-normal bit subfields.

In the second embodiment, in order to obtain 192 gradations, a plurality of light emission times (in this case, 1 / in this case, predetermined as the light emission time in the subfield for irregular bits) are used.
(6 emission times of 2, 1/4, 1/8, 1/16, 1/32, 1/64) are assigned to each non-regular bit subfield of the first field and the second field. , The second subfield 21 of the first field 21
The light emission time in b is set to 1/2, the light emission time in the third subfield 21c is set to 1/32, and the light emission time in the fourth subfield 21d is set to 1/64. Light emission time in subfield 22b is 1 /
4, the emission time in the third subfield 22c is 1/8,
The light emission time in the fourth subfield 22d is set to 1/16.

As a result, the sum of the display times of all the non-regular bit subfields 21b to 21d of the first field 21 and the sum of the display times of all the non-regular bit subfields 22b to 22d of the second field 22. And are most averaged.

3. Third Embodiment FIG. 3 is an explanatory view similar to FIG. 1 for explaining the third embodiment.

In the third embodiment, one frame is divided into first to third frames.
Of the three fields 21 to 23 and each of the fields 21 to 23 is composed of three first to third subfields 21a to 21c (22a to 22c, 23a to 23c), and 256 gradations It is an example of the obtained display method. The normal bit subfields include the first subfields 21a and 22 together with the first to third fields 21 to 23.
a and 23a, and the remaining subfields are non-normal bit subfields.

In the third embodiment, a plurality of light emission times (in this case, 1 / in this case) which are predetermined as the light emission time in the non-normal bit subfield in order to obtain 256 gradations are obtained.
(6 emission times of 2, 1/4, 1/8, 1/16, 1/32, 1/64) are assigned to the subfields for irregular bits of the first to third fields. The emission time in the second subfield 21b of the first field 21 is 1/2, and the emission time in the third subfield 21c is 1
/ 64 respectively, the second field 22 second
The light emission time in the subfield 22b is set to 1/4 and the light emission time in the third subfield 22c is set to 1/32, respectively, and the second subfield 23 of the third field 23 is set.
The light emission time in b is set to 1/8, and the light emission time in the third subfield 23c is set to 1/16.

As a result, the sum of the display times of all the non-regular bit subfields 21b and 21c of the first field 21 and the sum of the display times of all the non-regular bit subfields 22b and 22c of the second field 22. And the third
Subfield 23 for all non-regular bits of field 23
The sum of the display times of b and 23c is most averaged.

4. Fourth Embodiment FIG. 4 is an explanatory view similar to FIG. 1 for explaining the fourth embodiment.

In the fourth embodiment, one frame is composed of two fields 21 and 22, each field is composed of four subfields, and the first and second subfields of each field are defined as normal bit subframes. It is an example. The number of gradations is 128 in this example.

In the fourth embodiment, a plurality of light emission times (in this case, 1 / in this case) which are previously defined as light emission times in the sub-field for non-regular bits in order to obtain 128 gradations are obtained.
(4, 1/8, 1/16, 1/32 4 emission time)
Is assigned to each subfield for non-regular bits of the first and second fields, the light emission time in the third subfield 21c of the first field 21 is set to 1/4,
The light emission time in the subfield 21d is set to 1/32, the light emission time in the third subfield 22c of the second field 22 is set to 1/8, and the fourth subfield 22 is set.
The light emission time at d is set to 1/16.

As a result, the sum of the display times of all the non-regular bit subfields 21c and 21d of the first field 21 and the sum of the display times of all the non-regular bit subfields 22c and 22d of the second field 22. And are most averaged.

5. Fifth Embodiment In each of the above-described first to fourth embodiments, the total sum of the light emission times in the non-normal bit subfields of each field is averaged between these fields. The emission time in the lowest subfield of the use subfields (first subfield in the first to third embodiments, second subfield in the fourth embodiment) is Tn, and all the succeeding fields are set. The total sum Ts of the light emission times in each sub-field for irregular bits (for example, 21b, 21c, 22b, 22 in the example of the first embodiment).
When the sum of the light emission times in the four subfields of c) is given, the relationship between them is Ts / Tn <1.

In the fifth embodiment, in addition to the fact that the sums of the light emission times in the sub-fields for non-regular bits in each field are averaged between these fields, 1 ≦ T
Each light emission time is set so that s / Tn <2 is satisfied.

FIG. 5 is used for the explanation, and is an example in the case of obtaining 46 gradations.

One frame corresponds to the first field 21 and the second
It consists of two fields, field 22,
The first field 21 is composed of three first to third subfields 21a to 21c, and the second field 22 is composed of the first subfield 21a to 21c.
~ It is constituted by the third three sub-fields 22a-22c. Each of the first subfields 21a and 22a of the fields 21 and 22 is a normal bit subfield and corresponds to the least significant bit subfield thereof.

Here, Tn is 1. Further, in order to satisfy the condition 1 ≦ Ts / Tn <2 so that 46 gradations can be obtained, the light emission time in the non-normal bit subfield is 1/15, 2/15, 4 / 15, 8 /
Four emission times of 15 are defined in advance. Therefore, Ts = 1/15 + 2/15 + 4/15 + 8/15 =
Since 15/15 = 1 and Tn = 1, Ts / T
n = 1.

The emission time in the second subfield 21b of the first field 21 is set to 8/15, and the emission time in the third subfield 21c is set to 1/15, respectively. 2 subfields 22b
The light-emission time in the sub-field 22c is set to 4/15, and the light-emission time in the third subfield 22c is set to 2/15.

Since the light emission time is set in this way in each sub-field for irregular bits, 1≤Ts / Tn <2
And the sum of the display times of all the non-regular bit subfields 21b and 21c of the first field 21 and the sum of the display times of all the non-regular bit subfields 22b and 22c of the second field 22. And are most averaged. Table 3 below shows a display method of 45 gradations excluding the black level according to the display method of the fifth embodiment.

In the fifth embodiment, when displaying the halftone level corresponding to the light emission time "1", the cells may be made to emit light in each of the irregular bit subfields 21b, 21c, 22b and 22c. .. In this way, 8/15 width light emission, 1/15 width light emission dispersed in one frame,
When the light emission time “1” is obtained by combining the light emission with the width of 4/15 and the light emission with the width of 2/15, when the halftone level corresponding to the light emission time “1” is displayed in the subsequent frame, FIG.
The fundamental wave component is smaller than that in the method of emitting light in the specific subfield 11a as shown in FIG. Therefore,
Flicker can be further reduced.

As another example to which the idea of the fifth embodiment is applied, for example, one frame is composed of two fields, a first field and a second field, and the first field and the second field are the first to third fields, respectively. And the light emission time in each subfield from the first subfield of the first field to the third subfield of the second field is 1, 8/12, 1/12 in this order. , 1,
Example set to 4/12, 2/12, or 1,7 /
Examples can be set to 12, 1/12, 1, 4/12, 2/12.

In the former example, in order to obtain 40 gradations, the light emission time of the sub-field for irregular bits is 1/12, 2 /
This is an example in which four times of 12, 4/12, and 8/12 are defined in advance and these are assigned so as to average the light emission time in each subfield. The latter example is 39
In order to obtain gradation, four times 1/12, 2/12, 4/12, and 7/12 are previously defined as the light-emission time of the sub-field for irregular bits, and these are defined as the light-emission time in each sub-field. Is an example of allocation so as to average. Furthermore, in the former example, Tn = 1, Ts = 8/12 +
This is an example of 1/12 + 4/12 + 2/12 = 15/12, which corresponds to an example of Ts / Tn = 5/4> 1. In the latter example, Tn = 1, Ts = 7/12 + 1/12 + 4 /
12 + 2/12 = 14/12, and Ts / Tn =
This corresponds to the example of 14/12> 1. Table 4 below shows a display method of 39 gradations excluding the black level according to the former display method of the other display methods of the fifth embodiment.

In both the former and latter cases, the same effect as the example described with reference to FIG. 5 can be obtained.

6. Sixth Embodiment As a method of compensating for the shortage of the light emission time, the light emission time of the subfield displaying the MSB is conventionally set to the address scanning time T (also called the subfield period in the fifth embodiment). The doubled method was adopted (see MSB subfield in FIG. 6). However, if this is done, the number of subfields is usually reduced, and thus the number of gradations is reduced. However, this can be prevented by using the display method of the present invention together with the above method for correcting the light emission time. This will be described. FIG. 6 is a diagram used for the explanation.

The example of FIG. 6 is an example in which the light emission time in the first subfield corresponding to the MSB is 2. Of course, 8
1/12, 2/12, 4 pre-specified as the light emission time in the sub-field for non-regular bits to obtain 8 gradations
This is an example in which four times of / 12 and 8/12 are assigned so as to average the light emission time in each subfield. Specifically, the third and fourth subfields 21c, which correspond to the subfields for non-regular bits of the first field 21,
The light emission time at 21d is set to 8/12 and 1/12, respectively, and the third and fourth subfields 22c and 2 corresponding to the non-normal bit subfield of the second field 22 are set.
The light emission time in 2d is set to 4/12 and 2/12, respectively. In this way, the conventional method described with reference to FIG. 9 can obtain only 2 ⁴ = 16 gradations.
12 ÷ 1/12 + 1 = 88 gradations can be obtained.
In this case, one frame has a width of 10T and the total light emission time when all the subfields emit light is 7 + 3/12.
Therefore, the maximum emission time rate is (7 + 3).
/ 12) T / 10T≈3 / 4.

7. Seventh Embodiment The halftone image display method of the present invention can also be applied to a display method having a configuration in which each of a plurality of subsequent fields has two subfields for displaying MSBs. This 7th
The example is this example. FIG. 7 is a diagram used for the explanation and shows the light emission time in each subfield.

The seventh embodiment is similar to the sixth embodiment, but has an advantage that two subfields displaying the MSB can be independently addressed and the flicker can be reduced more than before. When color display is performed on a PDP and the number of cells of each color is different, for example, when the number of green cells (G cells): the number of red cells (R cells): the number of blue cells (B cells) = 2: 1: 1 On the contrary, when the luminous efficiency of each color cell is almost the same, it is necessary to set the luminous time ratio to a ratio of about 1: 2: 2. This is convenient in such cases. In this case,
The light emission time is set as shown in FIG. 7 and the G cell is not made to emit light in the subfield M ₁ of FIG. Moreover, sufficient gradation can be obtained and flicker can be reduced as compared with the conventional case.

In the configuration of FIG. 7, green has 128 gradations, and red and blue each have 192 gradations.

8. Eighth Embodiment In each of the above-described embodiments, the present invention is applied to an example in which the writing of the second subfield of every row is completed after the writing of the first subfield of every row of the PDP. .. However, as shown in FIG. 8, a modified panel driving method in which writing of the second subfield of every row is started in the middle of writing of the first subfield of every row of the PDP (see, for example, Literature: IEICE). Image Technology Research Institute IT-
72-45 (1973)).

Also in this case, as shown in FIG. 8, the light emission times at the subfields 21c, 21d, 22c, 22d for the non-regular bits are set in advance to obtain a plurality of levels of halftone. Time (8/1 in the case of FIG. 8)
5/15, 4/15, 2/15), the sum of the light emission time in each non-normal bit subfield 21c, 21d of the first field 21 and each non-normal bit of the second field 22. Normal bit subfields 22c, 2
Allocation is performed so that the sum of the light emission time in 2d and the sum of light emission time are most averaged. In addition, in the example of FIG. 8, more specifically, the total sum Ts of the light emission times in the subfields for the non-regular bits of the first field 21 and the second field 22 is 1 ≦ Ts / Tn <2, specifically, , Tn = 1 and Ts = 8 /
15 + 1/15 + 4/15 + 2/15 = 15/15 = 1
Therefore, Ts / Tn = 1 is set.

In the above, each embodiment of the halftone image display method of the present invention has been described. However, the present invention is not limited to the above embodiment.

For example, in each of the above-described embodiments, the second bit subfield of the normal bit subfield (for example, the second subfields 21b and 22b in FIG. 6) is set to M.
It was arranged to be positioned next to SB. However, it is not always necessary to position the second bit of the regular bit next to the MSB. Since it is well known that the second bit of the regular bit does not need to be located next to the MSB and the method in that case is well known, the description thereof will be omitted.

Further, in the above description, an example of displaying a halftone of a still image or an almost still image was considered. This is because, in the case of a moving image, the signal between successive fields changes significantly and the halftone level also changes between successive fields. However, the method of the present invention can of course be applied to a moving image, although the problem of whether or not the halftone of the original image can be displayed with good reproduction remains. For example, it is possible to display by using the signal of each bit as it is for each succeeding field. However, in this case, the halftones are the synthesized halftones of the respective halftones of the image for each succeeding field.
It is also possible to use a signal corrected to a value closest to the signal of the original image.

[0070]

As is apparent from the above description, according to the halftone image display method of the present invention, the display time in each subfield for non-regular bits of a plurality of successive fields is equal to a plurality of levels of halftone. A plurality of pre-specified times are set by allocating the sum of the display times of the sub-fields for non-normal bits for each of the plurality of fields so that they are averaged most among the plurality of fields. ing. For this reason, it becomes an index of flicker as compared with the case where a plurality of times defined in advance to obtain a plurality of levels of halftone are randomly assigned as the light emission time of each non-regular bit subfield of the following plurality of fields. Since the fundamental frequency component is reduced, flicker can be reduced.

Further, when the display time in each non-regular subfield of a plurality of successive fields is set so that the condition of 1≤Ts / Tn is satisfied, a plurality of fields of a plurality of successive fields in one frame are set. It is possible to display the least significant bit of the regular bits by combining subfields that display less than the regular bits of the subfields. Therefore, when displaying a gradation level corresponding to a regular bit in each succeeding frame, it is possible to appropriately combine the subfields in one frame, and to emit light in a state in which a specific subfield is substantially synchronized with the frame period. It can be done less frequently. For this reason, even in the case of this configuration, the fundamental wave component at the time of image display is reduced, so that flicker can be reduced as compared with the conventional case.

[Table 1]

[0072]

[0073]

[Table 2]

[0074]

[0075]

[Table 3]

[0076]

[0077]

[Table 4]

[0078]

[Brief description of drawings]

FIG. 1 is a diagram for explaining a first embodiment.

FIG. 2 is a diagram for explaining a second embodiment.

FIG. 3 is a diagram for explaining a third embodiment.

FIG. 4 is a diagram for explaining a fourth embodiment.

FIG. 5 is a diagram for explaining a fifth embodiment.

FIG. 6 is a diagram for explaining a sixth embodiment.

FIG. 7 is a diagram for explaining a seventh embodiment.

FIG. 8 is a diagram for explaining an eighth embodiment.

FIG. 9 is a diagram for explaining a conventional technique.

FIG. 10 is a diagram provided for explaining another conventional technique.

FIG. 11 is a diagram for explaining a technique inferred from a conventional technique.

[Explanation of symbols]

 21: first field 21a to 21d: first field subfield 22: second field 22a to 22d: second field subfield 23: third field 23a to 23c: third field subfield

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Takashi Komatsu, Inventor Takashi Komatsu 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (72) Hideo Sawai 1-7 Toranomon, Minato-ku, Tokyo 12 Oki Electric Industry Co., Ltd. (72) Inventor Kozo Fujii 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (2)

[Claims] 1. A halftone image display method for displaying halftones of a plurality of levels in a display device having a binary memory function by combining afterimages of a plurality of subfields of each of a plurality of consecutive fields in one frame. Wherein each of the plurality of fields includes one or more regular bit subfields for displaying regular bits including a subfield for displaying the most significant bit and at least two subfields for displaying bits less than the regular bits. Each sub-field for non-regular bits is configured to have a display time in each sub-field for non-regular bits, which is set by allocating from a plurality of pre-specified times to obtain the gray levels of the plurality of levels. In the halftone image display method having the above-mentioned configuration, the allocation is performed by at least two non-normal video for each of the plurality of fields. Halftone image display method sum between the display time of the subfield preparative is and performing as most averaging among the plurality of fields. 2. The halftone image display method according to claim 1, wherein when the display time in the least significant subfield of the normal bit subfields is represented by Tn, all of the plurality of fields are non-displayed. A halftone image display method characterized in that the display time in each non-regular subfield is set so that the total Ts of the display times in the regular subfield satisfies the following expression (1). 1 ≦ Ts / Tn <2 (1)