JPH11119724A - Display device, drive circuit, and gradation display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce disturbance in gradation display for moving picture and a high luminance image and to lengthen the light emission time in one field by arranging all six pieces or above of sub-fields in a nearly fixed partial period in the field by a prescribed sub-field arrangement information. SOLUTION: Six pieces or above of sub-fields are provided in the field as all sub-fields used for forming a gradation level, and all six pieces or above of sub-fields are arranged in the nearly fixed partial period in the field by the prescribed sub-field arrangement information. Without allocating all of the time of one field to the light emission time, the sub-field is arranged packing to one side of the field period. The interval Tm between the light emission start time point (display period start time point) of the sub-field b0 initially operating in one field and the light emission start time point (display period start time point) of the sub-field b7 finally light emitting in next field is made shorter than a critical fusion period of a visual sense characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a gradation display of an image, and relates to a field technique for controlling the gradation by a display time of a display element.

[0002]

2. Description of the Related Art Conventionally, techniques for controlling a display time of a display element to display an image with a gradation include, for example, (1) Kaji et al.
72-45 (1973-03) (1973.3.12)
"Display of halftone moving images with AC plasma display"
There is a technology about a memory type plasma display described in the above. This is because a fixed light emission time (for example, one field of a television signal) is time-distributed to the display period of each subfield of a binary code, and the presence or absence of operation of each subfield is controlled to thereby control the image floor. The key is controlled. In addition, as a television-related technique for performing gradation display by time division, (2) Murakami et al .: Journal of the Institute of Television Engineers of Japan, vol. 38, no. 9 (1984) "Color TV display using an 8-type pulse memory discharge panel" and (3) Kogami et al .: Technical Report of the Institute of Television Engineers of Japan, vo.
l. 13, No. 58 (1989) "Reactive power recovery of Townsend light emitting gas discharge television".

In the former case ((1)), as shown in FIG.
One field is divided into eight subfields b7 to b0, and each subfield is scanned and displayed in this subfield.

In the latter case ((2) and (3)), as shown in FIG. 8, one field is divided into eight time regions (b0 to b7) each having a length corresponding to each subfield of a binary code, and scanning is performed. Are shifted by 1H (horizontal scanning period) for each line, and the scanning pulse for the line address is slightly shifted in each subfield so that the selection of the line in each subfield does not become two lines at the same time.

[0005]

In the above prior art, image quality deterioration such as flicker may not be visually recognized depending on the device specification, but when the display screen becomes large or the luminance becomes high. At the time, or in the case of a moving image in which an image has a motion, it is visually recognized as gradation disturbance such as flicker. In the display technique of FIG. 7, the display screen is dark because the light emission time between one field is short.
No gradation disturbance is observed. Further, in the display technique of FIG. 8, since the number of scanning lines is small, details of an image cannot be visually recognized. Therefore, also in this case, no disturbance in the gradation is recognized. However, for example, in a 40-inch class large gas discharge television having a higher brightness and a larger display screen size than these, the maximum brightness of the image is set to 50 fL (# 171c).
d / m 2) or more, when an image is displayed by the same method as in the above-described conventional technique, a significant gradation disturbance occurs in a moving image. That is, for example, in displaying a person's face, when the face moves, a phenomenon occurs in which a white streak runs on the cheek. In other words, in a smooth gradation display, when a display image moves (a so-called moving image), a streak is generated in the screen, and it is as if a certain gradation subfield is missing. This is a phenomenon that cannot be seen in a conventional cathode ray tube or the like.

The disturbance of the gradation in the moving image is caused by the instantaneous flicker of a specific pattern in the time division gradation display. This will be described below using the conventional gradation display method of FIG.

FIG. 8 shows an example of a case of displaying 256 gradations (8 bits). For example, at 127 gradation levels,
Subfields b0 to b6 are activated, that is, the first half of one field emits light, and b7 is activated at a gradation level of 128 where the gradation of the next field is increased by one level, that is, the latter half of the field and a part thereof emit light. . That is, the light emission position (operating position) greatly changes in the first half and the second half of the field just by increasing the gradation by one level. The instantaneous light emission cycle at this time is from the light emission start time of b0 in the field to the light emission start time of b7 in the next field, and the time interval is 25 ms. This cycle of 25 ms causes flickering and causes disturbance of gradation. When the image is a moving image, the gradation is disturbed one after another in the cells of the screen, and appears as a streak that can be visually recognized clearly.

Next, the principle of the time-division gradation technology including the flicker will be described. As a human visual characteristic, luminance L1
It is known that the brightness sensation L is expressed as L = (t1L1 + t2L2) / (t1 + t2) when t1 seconds and luminance L2 are alternately displayed for t2 seconds (Talbot-Plateau). Law (TV Handbook, Volume 1, Section 3.4, 55
page)). However, this rule must be satisfied when flicker is not felt (called fusion).

FIG. 9 shows a measurement result of a critical fusion period of visual characteristics when a luminance is changed by changing a white display emission time width using a memory type gas discharge television. Here, the critical fusion cycle of the visual characteristics refers to a cycle in which flicker cannot be identified when the light emitting element is repeatedly turned on and off at a constant luminance with a constant cycle. In the figure, the upper broken line indicates the period from the start of the display period of the first subfield (b7) in the field by the gradation display technique of FIG. 7 to the start of the display period of the last subfield (b0) of the next field. 7 shows a time interval (in the example of FIG. 7, one field is equally divided into eight subfields). The lower broken line in FIG. 9 indicates the start of the display period of the first subfield (b0) in the field by the gradation display technique shown in FIG. 8 from the start of the display period of the last subfield (b7) of the next field. The time interval up to the time point is shown (in the example of FIG. 8, one field is divided into 8-bit subfields, and each subfield is weighted with a display period ratio of 1: 2: 4...: 128). As can be seen from FIG. 9, in the conventional gray scale display techniques of FIGS. 7 and 8, the time from the start of the display period of the first subfield in a field to the start of the display period of the last subfield of the next field is shown. The interval exceeds the critical fusion period when the luminance is several fL or more. Therefore, when the light emission of each subfield changes like a moving image,
Particularly on a bright screen, instantaneous flicker is felt, and gradation is disturbed. Usually, since the average luminance required for the display device is 50 fL or more, it is desirable that the critical fusion period of the above visual characteristics is 20 ms or less. Is done.

Further, in the above-mentioned prior art, the utilization rate of the time within one field as the light emission time is poor, that is, the light emission time is short, so that the screen brightness is reduced.

An object of the present invention is to improve the prior art in display technology for controlling the gradation of an image by the light emission time of a light emitting element, to reduce disturbance of gradation display even for a moving image or a high-luminance image, Another object of the present invention is to provide a technique capable of extending the light emission time within one field.

[0012]

In order to achieve the above object, according to the present invention, there is provided (1) a display device for displaying a gradation image on a display unit using a subfield, wherein a gradation level is formed in the field. 6 or more sub-fields are provided as all the sub-fields used for all the sub-fields, and all of the 6 or more sub-fields are arranged in a substantially constant partial period in the field by preset sub-field arrangement information. I do.

In the above, the configuration in which all of the six or more subfields are arranged within a partial period within the field is as follows:
In adjacent fields, the difference between the in-field position of the active subfield in the preceding field and the in-field position of the active subfield in the succeeding field is reduced. Thereby, the disturbance of the gradation of the image is suppressed.

[0014]

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

FIG. 1 is a diagram showing an embodiment of the present invention. In the case of this embodiment, the number of scanning electrodes is 240, and the signal to be displayed is 8 bits (8 subfields b0, b1, b2, b
3, b4, b5, b6, b7), each subfield is coded by a binary code, and 256 gray scales can be displayed.

In FIG. 1, the vertical axis indicates the horizontal scanning electrode 2.
Forty rows (the upper half of the display panel), the horizontal axis shows the time for two fields (1/30 second). Instead of allocating all of the time of one field to the emission time, the subfields are arranged on one side of the field period. With this configuration, the emission start time (display period start time) of the subfield b0 that operates first in one field
And the interval (T
m) is shorter than the critical fusion period of the visual characteristics (about 20 ms). The arrangement order of each subfield does not need to be limited to the illustrated order. The subfields may be padded on the right or left side of the field in the field. When the order of the sub-fields in FIG. 1 is reversed and the arrangement order of b7, b6, b5,. The time interval until the light emission start time (display time start time) is shorter than the critical fusion cycle (about 20 ms).

FIG. 2 is a diagram showing an example of a circuit configuration in a gas discharge television device as a display device according to the present invention.
The video signals G, B, and R separated into green (G), blue (B), and red (R) color signals of the television signal are A / D converters 1-1, 1-2, and 1-3, respectively. From the analog signal
Bit (8 subfields b0, b1, b2, b3, b
4, b5, b6, b7) digital signal (binary code)
And stored in the frame memory (or field memory) 2. On the other hand, reading out of the frame memory 2 is performed by using a dedicated read-out ROM 5 so as to make a timing suitable for the gradation sub-field. The read ROM 5 is operated by the counter 4 that counts the clock signal CLK. The reset of the counter 4 is performed using a V (vertical synchronization) signal of the television signal or an H (horizontal synchronization) signal as necessary. Frame memory 2
Are read from each subfield (b0, b2,...) Of FIG.
This is performed by accessing the address where the subfield signal of each scanning electrode is stored at the timing of b7). Each subfield signal read from the frame memory 2 is applied to shift registers 8 and 11 of a driver circuit for an auxiliary anode of the light emitting element, and further passes through drivers 9 and 10 to output signals of the light emitting element constituting the gas discharge panel 3. Are applied to the auxiliary anodes S1, S2, S3,..., S1 ', S2', S3 ',.

On the other hand, a cathode ROM 6 and an anode ROM 7
Respectively use the output of the counter 4 to convert the arrangement signals of the subfields into the shift registers 13, 14 and 17, 18.
Add to Further, shift registers 13, 14, and 1
The signals from 7 and 18 are applied to drivers 15, 16 and 19 and 20, respectively, where the driving signals for the anode and cathode of the light emitting element of the gas discharge panel 3 are generated. The anode of the light emitting element has anode lead wires A1, A2, A3.
A480 are provided, and the cathode is provided with cathode leads K1, K2, K3... K240 and K241. These ROM, shift register and driver constitute a drive circuit for selecting a light emitting element to be displayed. In this embodiment, since the gas discharge panel 3 is divided into upper and lower parts, two scanning electrodes can be driven simultaneously.

FIG. 3 is a partially enlarged view of the gas discharge panel 3 and shows the electrode wiring of the light emitting element. The gas discharge panel 3 has a plurality of light emitting elements 30 arranged in a matrix of rows and columns. The light emitting element 30 has three electrodes of a cathode, an anode, and an auxiliary anode, and has a memory function. A first electrode lead 32 (k1, k2,... Kl) and a third electrode lead 31 (A1, A2,... Al) are provided on the cathode and anode of each light emitting element 30 in the lateral direction, respectively. S has a vertical auxiliary electrode lead wire 33 (S1, S2,
…) Are provided. Assuming that the number of horizontal scanning electrodes 1 = 480, the gas discharge panel 3 is
When the rows are driven simultaneously, the auxiliary electrode lead wires 33 are separated at the center of the panel. The first electrode lead 32 (k1, k
2,... Kl), the third electrode lead wire 31 (A1, A2,.
1) and the auxiliary electrode lead wires 33 (S1, S2,...) respectively from the cathode driver 19 (or 20), anode driver 15 (or 16) and auxiliary anode driver 9 (or 10) in FIG. Are applied.

FIG. 4 is a diagram showing a cross section of the light emitting element 30. On a substrate 21, a first electrode (cathode) 22 is made of Ba, N
i, made of a material such as LaBa. On the other hand, face plate 2
In FIG. 8, a third electrode (display anode) 24 is formed by a printing technique. Further, the discharge space (display discharge space 25 and auxiliary discharge space 27) shown in the drawing is formed by, for example, stacking a number of spacers with holes, etc., and the second space shown in the drawing.
An electrode (auxiliary anode) 23 is provided. When a discharge (display discharge) occurs between the first electrode 22 and the third electrode 24, the gas (Xe or Ne-Xe, He-X) in the display discharge space 25 is generated.
(e.g., a mixed gas such as e) generates ultraviolet light, and the phosphor 26 emits light to perform display. A so-called pilot discharge (auxiliary discharge) is generated between the first electrode 22 and the second electrode 23, and this auxiliary discharge is transferred to a display discharge between the first electrode 22 and the third electrode 24. This is controlled by the presence or absence of a pulse applied to the second electrode 24. Since this auxiliary discharge does not excite the phosphor 26, it does not affect display light emission.

Next, a discharge state between the electrodes will be described with reference to FIG. In FIG. 5, Vk indicates a voltage waveform applied to the first electrode lead line, and 40 indicates a pulse for addressing one line of the gas discharge panel 3, which is referred to as a first electrode scanning pulse. In the example of FIG. 5, the pulse width of the first electrode pulse is
Time width Δ assigned to address one line
It is the same as For example, the scanning time of each line is 1H
When 240 lines are addressed in one field (the number of lines in the upper half of a panel driven simultaneously by two rows) and 8-bit gradation display is performed, Δ ≒ 8 μs. Vs indicates a pulse voltage waveform applied to the second electrode lead, and pulse 41 is a second electrode pulse, which has a smaller pulse width than the first electrode scanning pulse 40 and is located behind the time width Δ. The presence or absence of the second electrode pulse 41 changes depending on the content of the television signal, that is, “1” or “0” of the bit signal. VA is 3rd
The waveform of the pulse voltage applied to the electrode leads is shown in FIG.
In the figure, the narrow pulse 41 applied to the third electrode is changed to the number of gradation bits immediately after the first electrode scanning pulse 40 for the same electrode number of the electrode lead line and the third electrode lead line. It is applied continuously by the number of pulses corresponding to the number.

In a period III in the drawing, a pulse 42 having a narrow pulse width is first applied to the third electrode. Since a large number of charged particles are present in the display discharge space 25 due to the switching in the period II, the pulse 42 causes the first electrode and the third
A pulsating discharge occurs between the electrodes. Due to this pulse-like discharge, charged particles are further generated in the display discharge space 25, and the discharge is performed even in the next pulse 43. As described above, in the period III, the discharge continues while the pulse is continuously applied or until a new voltage for stopping the discharge is applied to the first electrode. This function is called a pulse memory function.
By this pulse discharge, the phosphor 26 of FIG. 4 is excited to perform display light emission.

When no display light emission is required, the pulse 41 of the second electrode shown in FIG. 5 is removed. In this case, switching is not performed, and no discharge occurs between the first electrode and the third electrode, so that the number of charged particles in the display discharge space 25 in FIG. 4 is small. Therefore, even if the pulses 42 and 43 are applied to the third electrode, no discharge occurs, and the phosphor 26 in FIG. 4 is not excited.

Therefore, the pulse 41 of the second electrode serves to control the discharge between the first electrode and the third electrode, and the display brightness is controlled by the presence or absence of this pulse.

FIG. 6 is an explanatory diagram for displaying an image in 256 gradations on the gas discharge panel 3 using an 8-bit binary code.
One field in FIG. 1 (about 1 in the case of an NTSC television signal)
/ 60 seconds = 16.7 ms). FIG. 3 shows a voltage waveform Vk applied to the first electrode and a voltage waveform VA applied to the third electrode. The first electrode has subfields b0, b1,... B6, b7 between one field.
Are applied. As shown in FIG. 5, the pulse 42 applied to the third electrode starts immediately after the application of the scan pulse 40 and ends before the next scan pulse 40 comes. The number of each pulse 42 is proportional to the display period of the subfields b0, b1,... B6, b7,
If the ratio is 1: 2: 4: 8...: 128, 256 gradations are realized by the combination. The control of whether or not to discharge the pulse train of each third electrode is performed based on the presence or absence of a pulse (41 in FIG. 5) of the second electrode corresponding to the scan pulse in the subfields b0, b1,... B6, b7.
In FIG. 5, when the light emission in the period II cannot be neglected, the number of pulses of the third electrode is distributed in consideration of the luminance due to the light emission. Here, the absolute value of the number of pulses of the third electrode is set such that the period from the beginning of the subfield b0 (start of the display period) to the end of b6 (end of the display period) in FIG. 6 is about 3.3 ms. Is determined, the above-described critical fusion period becomes 20 (= 3.3 + 16.7) ms, and the disturbance of the gradation for the moving image can be suppressed.

In the embodiment shown in FIGS. 1 and 6, the start of the display period of the first subfield of the subfield array in a certain field and the start of the display period of the last subfield in the next field are determined. In order to make the interval (Tm) shorter than the critical fusion period of the visual characteristics, the entire display period is made considerably short. However, in order to extend the light emission time, at least one of the subfields of the binary code configuration is used.
1 and 6, the divided sub-fields are operated in a time zone different from the sub-field operation time zone in the case of FIG. 1 and FIG. 6, for example, in a time zone vacant in FIG. 1 and FIG. The effect can be obtained.

Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to the above embodiments. For example, the present invention includes a case where the direction of the time axis in the subfield arrangement of FIGS. 1 and 6 is reversed. In addition, as a display device according to the present invention, a gas discharge television device using a gas discharge light emitting element is typical, but the present invention is not limited to this.

[0028]

According to the present invention, the disturbance of the gradation can be improved without lowering the brightness.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a circuit configuration for an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example of a gas discharge panel used in an embodiment of the present invention.

FIG. 4 is a sectional view of a light emitting device of a gas discharge panel used in an embodiment of the present invention.

FIG. 5 is a voltage waveform chart for explaining the operation of the light emitting device shown in FIG.

FIG. 6 is a diagram showing one embodiment of the present invention.

FIG. 7 is a diagram showing a conventional example of gradation display.

FIG. 8 is a diagram showing another conventional example of gradation display.

FIG. 9 is a diagram illustrating an example of a measurement result of a critical fusion period.

[Explanation of symbols]

 1: A / D converter, 2: Frame memory, 3: Gas discharge panel, 4: Counter, 5, 6, 7, ROM, 8, 11, 13, 14, 17, 18: Shift register, 9, 10, 15, 16, 19, 20: driver, 21: substrate, 22: cathode, 23: auxiliary anode, 24: display anode, 25: display discharge space, 26: phosphor, 27: auxiliary discharge space, 28: face plate, Reference numeral 30 denotes a discharge cell (light emitting element), 31 denotes a third electrode lead, 32 denotes a first electrode lead, and 33 denotes a second electrode lead.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mutsumi Suzuki 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (9)

[Claims] 1. A display device for displaying an image with gradation on a display unit using sub-fields, wherein six or more sub-fields are provided in the field as all sub-fields used for forming gradation levels. All of the above subfields have subfield arrangement information set in advance so as to be arranged in a substantially constant partial period in the field, and the display unit is driven by a display unit driving signal formed based on the arrangement information. A display device which is driven to display an image in which gradation disturbance is suppressed. 2. A display device for displaying an image with gradation on a display unit using subfields, wherein six or more subfields are provided in the field as all subfields used for forming a gradation level. Means for outputting a subfield arrangement information signal set in advance so that all of the above subfields are arranged in a substantially constant partial period in the field; and forming a display unit driving signal based on the arrangement information signal. And a driving signal forming unit, wherein the display unit is driven by the display unit driving signal in which all of the six or more subfields are arranged in a substantially constant partial period in the field to suppress gradation disturbance. A display device for displaying an image. 3. The display device according to claim 2, wherein said means for outputting said subfield arrangement information signal is configured to output information data corresponding to an electrode type of a display unit from a memory unit in a separate system. 4. A display device for displaying an image with gradation on a display unit using subfields, wherein six or more subfields are provided in the field as all subfields used for forming a gradation level. Means for outputting a subfield arrangement information signal set in advance so that all of the above subfields are arranged in a substantially constant partial period in the field; and forming a display unit driving signal based on the arrangement information signal. A driving signal forming unit, wherein the display unit is driven by the display unit driving signal in which all of the six or more subfields are arranged in a substantially constant partial period in the field, and the display of the subfield is performed. A display device, wherein an image of a gradation level corresponding to a period length is displayed in a state where gradation disturbance is suppressed. 5. The display device according to claim 4, wherein the subfields are arranged such that the subfield having the longest display period is arranged at the end. 6. A display device for displaying an image with gradation on a display unit using subfields, wherein six or more subfields are provided as all the subfields used for forming a gradation level in the field. Means for outputting a subfield arrangement information signal set in advance so that all of the above subfields are arranged in a substantially constant partial period in the field; and forming a display unit driving signal based on the arrangement information signal. And a drive signal forming unit. The display unit is driven by the display unit drive signal in which all of the six or more subfields are arranged in a substantially constant partial period in the field, and are assigned to the subfields. A display device characterized in that an image having a gradation level corresponding to the number of display pulses obtained is displayed in a state where gradation disturbance is suppressed. 7. The display device according to claim 6, wherein the arrangement of the subfields is an arrangement in which the subfield having the largest number of display pulses is arranged at the end. 8. A drive circuit of a display device for displaying a gradation image by causing a matrix panel to emit light in accordance with a display period of a subfield, wherein all of six or more subfields as all subfields used for forming a gradation level are provided. Means for outputting a subfield array information signal preset so as to be disposed for a substantially constant partial period in the field, and forming a drive signal for causing the matrix panel to emit light based on the array information signal; and an image signal. And a means for forming a setting signal for setting, for each subfield, whether or not the matrix panel is to be in a light emitting state by the drive signal, based on a signal from the memory means. Characteristic drive circuit. 9. A subfield arrangement information signal set in advance so that six or more subfields as all subfields used for forming a gradation level of an image are arranged in a substantially constant partial period in the field. Forming the drive signal,
A gray scale display method, characterized in that the matrix panel is caused to emit light by the drive signal, and an image with reduced gray scale disturbance is displayed.