JP4595524B2 - Driving method of image display device - Google Patents

Description

  The present invention is applied to liquid crystal image display devices such as transmission type and projection type displays, viewfinders, head mounted displays, plasma image display devices, digital mirror image display devices, electroluminescence image display devices, field emission image display devices, and the like. The present invention relates to a method for driving an image display device using a subfield method.

  In general, in a display device based on binary display, such as a liquid crystal image display device, a plasma image display device, or a digital mirror image display device, a subfield method (drive) is used as a drive method in order to obtain an intermediate gradation. Is used. In this method, the luminance of light emission is weighted according to a predetermined rule, that is, divided into a plurality of subfields having different luminance relative ratios, and the respective gradations are overlapped over one field. An intermediate gradation is displayed.

  However, it is known that by performing this subfield driving, a good display image can be obtained in the case of still image display, but a pseudo contour and flicker are generated in the case of moving image display. As a method for solving these problems, even if the image data (gradation) changes, in order not to cause the change in the center of gravity of light emission as much as possible, one field is a half field composed of the same plurality of subfields. Has been proposed (for example, see Patent Document 1).

For this purpose, lower bits are used as binary weighting subfields, and binary weighting subfields corresponding to upper bits are divided into a plurality of subfields. For example, assuming that 256 gradations are displayed by combining eight subfields having a weight of 1: 2: 4: 8: 16: 32: 64: 128, and a combination of these subfields, 1, 2, 4, The 8, 16, and 32 weight subfields are left as they are, the 64 weight subfield is divided into two 32 weight subfields, and the 128 weight subfield is divided into four 32 weight subfields. Then, by combining them, a predetermined gradation is displayed in a 1/2 field period.
JP-A-9-172589

  As shown in FIG. 5, one field is composed of a plurality of subfields, and the subfield is composed of an address period and a switching period. The address period corresponds to the driving period. Here, the drive period is a period during which display ON / OFF for each subfield can be controlled. If it is ON, all the periods are ON, and if it is OFF, all the periods are OFF. The address period is a period for transferring ON / OFF information of all the pixels of the display device for each subfield, and is determined by the total number of pixels, the transfer speed, etc. for each display device, and is a fixed period for every subfield. is required. For this reason, when the drive period is shorter than the address period as in the pattern A, a non-drive period occurs.

Here, when the 1/2 field driving method is used as the subfield method, although it is effective in suppressing flicker, it will be described in detail in a comparative example described later, but the binary weighting bit also needs to be divided into two. 5, the number of subfields of pattern A in FIG. 5 increases, and the ratio of the non-driving period in one field period increases, resulting in a problem that driving efficiency is lowered and display luminance is lowered.
At the same time, since the number of subfields assigned to equal weight bits is reduced, the number of drive gradations is reduced, and there is a problem that multi-gradation display is difficult.

  Accordingly, an object of the present invention is to solve the above-described problems, and to provide a driving method of an image display device capable of suppressing flicker and moving image pseudo contour, and having high driving efficiency and high gradation display.

The present invention provides a binary number for displaying a video signal having a halftone by displaying a plurality of sub-fields, each of which is a binary image weighted by a time width or a pulse width in one field period, overlaid in time. display portions corresponding to a plurality of upper bits of the halftone is represented in a plurality of subfields of equal weighting, a plurality of subfields weighted in accordance with the portion corresponding to the remaining lower bits to the binary a driving method of an image display device for displaying the portion be in one field, a plurality of sub-fields of a portion corresponding to the remaining lower bits to the central portion are arranged to correspond to a plurality of bits of the upper each of the plurality of sub-fields is divided into two, a set of a plurality of subfields of a portion corresponding to a plurality of bits of said two divided upper every gradation Dividing into a high gradation group, a medium gradation group, and a low gradation group, in front of a plurality of subfields corresponding to the remaining lower bits, one subfield of a plurality of sets belonging to the high gradation group, Arranged in the order of one subfield of a plurality of sets belonging to the middle gradation group and one subfield of the plurality of sets belonging to the low gradation group, a plurality of subfields corresponding to the remaining lower bits Behind the other subfields of the plurality of sets belonging to the middle gradation group, the other subfield of the plurality of sets belonging to the low gradation group, and the other subfield of the plurality of sets belonging to the high gradation group An image display apparatus driving method is provided, which is arranged and displayed.

  In the image display apparatus of the present invention, the driving method is in one field, in which a plurality of subfields corresponding to the remaining lower bits are arranged in the center, and a plurality of subfields corresponding to the upper bits are arranged. Since the field is divided into two and arranged and displayed on both sides of the plurality of subfields corresponding to the remaining lower bits, the generation of flicker and moving image pseudo contour is suppressed, and the driving efficiency is high. There is an effect that it is possible to provide a driving method of an image display device capable of high gradation display.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings by way of preferred examples.

FIG. 1 is a subfield pattern in an embodiment of a driving method of an image display apparatus according to the present invention.
FIG. 2 is a chart showing lighting (ON / OFF) of each subfield corresponding to each gradation level in the embodiment.
FIG. 3 is a diagram illustrating the flicker suppression effect in the embodiment.
FIG. 4 is a block diagram of the image display apparatus according to the embodiment.

The driving method of this example was applied to driving a reflective liquid crystal display element: LCOS (Liquid Crystal On Silicon) at 60 Hz.
As shown in FIG. 1, in this embodiment, in each field, a plurality of binary light emission groups weighted according to the time width or the number of light emission pulses are temporally overlapped to obtain an intermediate gradation. However, one field is divided into 24 subfields and 640 gradations are displayed.
Here, the nine light emitting groups having 64 weights corresponding to the upper 3 bits of the halftone expressed in binary notation are each divided into two and represented by 18 subfields having 32 weights, and The light emission group corresponding to the lower 6 bits of the halftone expressed in the binary system is represented by 6 subfields in the binary weight (1, 2, 4, 8, 16, 32).

The 64 weights are represented by a set of two subfields having 32 weights, and T1, T2, Numbering sets of T3, T4, T5, T6, T7, T8, and T9 and subfields are numbered.
The subfield set T1 is composed of 32 weighted subfields having a number T1a and a number T1b, and is displayed as [T1a, T1b]. Here, in the same set of subfields, symbol a represents low weighting and symbol b represents high weighting.

Hereinafter, similarly, the subfield set T2 is composed of 32 weighted subfields having a number T2a and a number T2b, and is represented as [T2a, T2b].
The subfield set T3 is composed of 32 weighted subfields having a number T3a and a number T3b, and is displayed as [T3a, T3b].
The subfield set T4 is composed of 32 weighted subfields having a number T4a and a number T4b, and is displayed as [T4a, T4b].
The subfield set T5 is composed of 32 weighted subfields of number T5a and number T5b, and is represented as [T5a, T5b].

The subfield set T6 includes 32 weighted subfields having a number T6a and a number T6b, and is represented as [T6a, T6b].
The subfield set T7 is composed of 32 weighted subfields having a number T7a and a number T7b, and is displayed as [T7a, T7b].
The subfield set T8 is composed of 32 weighted subfields having a number T8a and a number T8b, and is displayed as [T8a, T8b].
The subfield set T9 is composed of 32 weighted subfields having a number T9a and a number T9b, and is displayed as [T9a, T9b].
In the above, in the same set of subfields, symbol a represents low weighting and symbol b represents high weighting.

  Here, [T1a, T1b], [T2a, T2b], [T3a, T3b] are changed to a low gradation group, [T4a, T4b], [T5a, T5b] [T6a, T6b according to the appearing gradation level. ] Are divided into medium gradation groups, and [T7a, T7b], [T8a, T8b], and [T9a, T9b] are divided into high gradation groups.

  On the other hand, six subfields of binary weighting are assigned in the order of smaller weighting, B1 (weighting 1), B2 (weighting 2), B3 (weighting 4), B4 (weighting 8), B5 (weighting 16), B6. Numbering is performed as (weighting 32).

Subfields are arranged as follows.
First, B1 to B6 are arranged in the central subfield in the order of B6, B5, B4, B3, B2, and B1 from the earlier time.
Specifically, the subfield number B6 is assigned to the 10th subfield with respect to the 1st to 24th subfields constituting one field. Hereinafter, the subfield of number B5 is assigned to the eleventh subfield. A subfield of number B4 is assigned to the 12th subfield. A subfield of number B3 is assigned to the 13th subfield. A subfield of number B2 is assigned to the 14th subfield. A subfield of number B1 is assigned to the 15th subfield.

Next, T3a, T1a, and T2a are arranged in the order of T3a, T1a, and T2a from the earlier time in front of the subfields B1 to B6 in which T1a, T2a, and T3a having low weights in the low gradation group are arranged in the center.
Specifically, the subfield with the number T3a is assigned to the seventh subfield. A subfield of number T1a is assigned to the eighth subfield. A subfield of number T2a is assigned to the ninth subfield.

Next, T1b, T2b, and T3b having higher weights in the low gradation group are arranged in the order of T2b, T1b, and T3b from the earlier one by 1/2 field behind T1a, T2a, and T3a having lower weights. .
Specifically, a subfield of number T2b is assigned to the 19th (after the seventh ½ field) subfield. A subfield of number T1b is assigned to the 20th subfield (after the eighth half field). A subfield of number T3b is assigned to the 21st subfield (after the 9th 1/2 field).

Next, T4a, T5a, and T6a having low weights in the middle gradation group are arranged in front of the group having low weights T1a, T2a, and T3a in the low gradation group, and T4a, T5a, and T6a are earlier than the earlier one. Arrange each in order.
Specifically, a subfield with number T4a is assigned to the fourth subfield. A subfield of number T5a is assigned to the fifth subfield. A subfield of number T6a is assigned to the sixth subfield.

Next, T4b, T5b, and T6b with high weight in the middle gradation group are ½ field backward from T4a, T5a, and T6a with low weight, that is, T1b and T2b with high weight in the low gradation group. , T3b are arranged in the order of T6b, T5b, and T4b in the order from the earlier time.
Specifically, the subfield of number T6b is assigned to the 16th subfield. A subfield of number T5b is assigned to the 17th subfield. A subfield of number T4b is assigned to the 18th subfield.

Next, T7a, T8a, and T9a with lower weight in the high gradation group are arranged in the order of T9a, T8a, and T7a in the order of T9a, T8a, and T7a in front of the earlier one in the middle weight group. To place each. These are located at the beginning of the field.
Specifically, a subfield with number T9a is assigned to the first subfield. A subfield of number T8a is assigned to the second subfield. A subfield of number T7a is assigned to the third subfield.

Next, T7b, T8b, and T9b having higher weights in the high gradation group are arranged in the order of T7b, T8b, and T9b in the order of T7b, T8b, and T9b from the earlier ones in the lower weight group. Place each one. These are located at the end of the field.
Specifically, the subfield with the number T7b is allocated to the 22nd subfield. A subfield of number T8b is assigned to the 23rd subfield. A subfield of number T9b is assigned to the 24th subfield.

As described above, high-gradation, medium-gradation, low-gradation, and binary weighting subfields are allocated to each subfield.
Here, for example, when T2a is arranged in front of T1a, T2b determines the position in each group so that the arrangement directions of a and b are reversed as much as possible in the wind behind T1b. For example, from the front of the field, T9a, T8a, T7a, T4a, T5a, T6a, T3a, T1a, T2a, B6, B5, B4, B3, B2, B1, T6b, T5b, T4b, T2b, T1b , T3b, T7b, T8b, T9b.
Changing the position of the group greatly affects the display characteristics such as flicker. However, changing the position within the group has little influence on the display characteristics.

The reason why B1 to B6 having binary weighting are arranged as B6, B5, B4, B3, B2, and B1 in descending order of weighting is effective for flicker.
That is, B1 to B6 having binary weights are rearranged in this order in descending order, and these are separated by T1a, T2a, T3a and T1b, T2b, T3b separated by 1/2 subfield appearing in a low gradation. By arrange | positioning ahead, the influence on the brightness | luminance of T1b, T2b, and T3b arrange | positioned at the back by the brightness | luminance of B1-B6 is reduced, ie, it becomes difficult to recognize flicker.

As shown in FIG. 3, according to the driving method of this embodiment, in one field, binary weighted subfields are arranged in the center, and two sets of subfields for low gradation are 1 / Two sets of subfields for medium gradation are arranged two fields apart from each other, and two sets of subfields for high gradation are sandwiched outside by two fields.
Flicker and pseudo-moving image contours are inconspicuous at the gradation levels displayed in the binary weighting and high gradation subfields, and are conspicuous at the gradation levels displayed in the low gradation and intermediate gradation subfields. It is.

  As described above, in this embodiment, the change in the center of gravity of light emission is suppressed, and the subfields for low gradation and medium gradation are driven by 1/2 field. Can be suppressed.

Next, drive efficiency will be described.
The driving efficiency indicates the maximum rate at which light can be emitted in the address period in one field period. Accordingly, in the case of this embodiment, if there are 24 subfields in one field and the address period of each subfield is 32, the subfield structure shown in FIG. Until there are 18 subfields with a weight of 32 (9 weightings 64) and the binary weighting is a total of 63, the driving efficiency = (64 × 9 + 63) / (32 × 24) = 0.833. Extremely high drive efficiency.

Next, ON / OFF of each bit (subfield) for each gradation shown in FIG. 2 will be described.
In the figure, 0 indicates that the subfield is OFF, and 1 indicates that the subfield is ON (lit).
In the above-described subfield configuration, there are 640 gradations.
B1 to B6, which are binary weights, are determined ON / OFF for each gradation in the order according to the binary system. When all of B1 to B6 are ON and all of T1 to T9 which are equal weights are OFF, the gradation is 63/639.

In the case of 64/639, which is the next gradation, B1 to B6 and T2 to T9 are OFF, and only T1 is ON.
T1 is ON and gradations B1 to B6 are turned ON / OFF in the order according to the binary system for gradations from 65/639 to 127/639.
In the same manner, the gradation is determined. In the case of gradation 127/639, B1 to B6 and T1 are turned on, and T2 to T9 are turned off.
In the case of the next gradation 128/639, B1 to B6 and T3 to T9 are turned off, and T1 and T2 are turned on.
When all of B1 to B6 and T1 to T9 are ON, the highest luminance 639/639 gradation is expressed.

Next, with reference to FIG. 4, how the input Video Signal is converted into subfield data and output in the display device to which the present embodiment is applied will be described.
The input 8-bit Video Signal is converted into Subfield Data (subfield structure bit data) in the Color Lookup Table section. The subfield data is converted into frame data for each subfield by a plurality of subfield data in the shift register unit, and stored in the specified subfield frame buffer unit. The Frame Data stored in the Frame Buffer section is read out for each subfield by the Drive Control section and transferred to the Display section. At the same time, it is driven by performing the Voltage Control of the Display section, and the Video Signal is displayed.

(Comparative example)
Next, an example of a conventional 1/2 field driving method when one field is composed of 24 subfields will be described.
FIG. 6 is an example of a subfield pattern in the driving method of the image display device of the comparative example.
FIG. 7 is a chart showing lighting (ON / OFF) of each subfield corresponding to each gradation level in the comparative example.

As shown in FIG. 6, if one field is composed of 24 subfields, if this is driven by 1/2 field, it is necessary to perform gradation display by repeating 12 subfields.
Here, since it is necessary to divide all the weights into two, the number of bits allocated to the weight bits equal to the binary bits is 12, and the number of binary bits is set to 6, which is the same as in the embodiment. The number of bits allocated is 6.

  Subfields of binary weighting (1, 2, 4, 8, 16, 32) are assigned a number b1 with weighting 1 (a combination of b1a and b1b with weighting 0.5: [number b1a with weighting 0.5 and number b1b], the number is omitted, and so on.), weight 2 b2 [weight 2 b2a and b2b], weight 4 number b3 [weight 2 b3a, b3b], It is represented by subfields of weight 8 number b4 [weight 4 b4a and b4b], weight 16 b5 [weight 8 b5a and b5b], weight 32 b6 [weight 16 b6a and b6b].

  In order from the lower weighting with 64 weights, the five numbers t1 [t1a and t1b], t2 [t2a and t2b], t3 [t3a and t3b], t4 [t4a and t4b], t5 [t5a and t5b] and t6 [t6a and t6b]. Each subfield weighted by the number in square brackets is 32.

  When these subfields are arranged so that the light emission center of gravity is at the center with the 1/2 field driving method, the first 1/2 field is sequentially ordered from the first subfield to the 12th subfield. Number t5a (weighting 32), number t3a (weighting 32), number t1a (weighting 32), number b6a (weighting 16), number b5a (weighting 8), number b4a (weighting 4), number b3a (weighting 2), number Subfields b2a (weighting 1), number b1a (weighting 0.5), number t2a (weighting 32), number t4a (weighting 32), and number t6a (weighting 32) are arranged.

  In the subsequent 1/2 field, from the 13th subfield to the 24th subfield, number t5b (weight 32), number t3b (weight 32), number t1b (weight 32), number b6b (weight 16) ), Number b5b (weighting 8), number b4b (weighting 4), number b3b (weighting 2), number b2b (weighting 1), number b1b (weighting 0.5), number t2b (weighting 32), number t4b (weighting) 32), subfields of number t6b (weighting 32) are arranged.

The driving efficiency in this case is calculated.
In the comparative example, if there are 24 subfields in one field and the address period of each subfield is 32, the subfield configuration shown in FIG. 6 is weighted from high gradation to low gradation in the case of white display. There are 12 subfields (6 weightings 64) and binary weighting is 63 in total, so that drive efficiency = (64 × 6 + 63) / (32 × 24) = 0.582.

Next, the number of gradations that can be displayed will be described.
As shown in FIG. 7, the gradation that can be displayed by the arrangement of the subfields is 448 gradations.
For binary weighting b1 to b6, ON / OFF is determined for each gradation in the order according to the binary system. When all of b1 to b6 are ON and all of t1 to t6 which are equal weights are OFF, the gradation is 63/448.
In the case of 64/448, which is the next gradation, b1 to b6 and t2 to t6 are OFF, and only t1 is ON.

For gradations from 65/448 to 127/448, t1 is ON, and b1 to b6 are turned ON / OFF in the order according to the binary system.
In the same manner, gradation is determined, and in the case of gradation 127/448, b1 to b6 and t1 are turned on, and t2 to t6 are turned off.
In the case of the next gradation 128/448, b1 to b6 and t3 to t6 are turned off, and t1 and t2 are turned on.
When all b1 to b6 and t1 to t6 are turned on, the highest luminance 448/448 gradation is expressed.

  As described above, in the comparative example, since the half field drive is performed, the occurrence of flicker and moving image pseudo contour can be suppressed, but the drive efficiency is 0.582 and the number of displayable gradations is 448.

Here, when comparing the above-described embodiment with the comparative example, regarding the occurrence of flicker and dynamic pseudo contour, the embodiment is substantially in the low gradation and the middle gradation where the phenomenon becomes remarkable. Since the subfields are arranged so as to be ½ field driven, the occurrence of flicker and dynamic pseudo contour can be suppressed as in the comparative example.
Regarding the number of gradations that can be displayed, 640 gradations can be displayed in the embodiment, but only 448 gradations in the comparative example, and the ratio is 1.4 times. In the embodiment, high gradation display is possible. it can.
The driving efficiency is 0.832 in the embodiment, but is 0.582 in the comparative example, and the ratio is 1.4 times. In the embodiment, high-efficiency driving is possible.
That is, according to the driving method of the image display apparatus of the present invention, it is possible to realize high driving efficiency and high gradation display while suppressing the occurrence of flicker and moving image pseudo contour.

It is a subfield pattern in the Example of the drive method of the image display apparatus which concerns on this invention. In an Example, it is the chart showing lighting (ON / OFF) of each subfield corresponding to each gradation level. In an Example, it is the figure illustrated about the suppression effect of flicker. 1 is a block diagram of an image display device according to an embodiment. It is a figure for demonstrating a subfield structure. It is an example of the subfield pattern in the drive method of the image display apparatus of a comparative example. In a comparative example, it is a chart showing lighting (ON / OFF) of each subfield corresponding to each gradation level.

Explanation of symbols

B1, B2, B3, B4, B5, B6 ... Binary weighting subfield (number), T1a, T1b, T2a, T2b, T3a, T3b ... Subfield for low gradation (number), T4a, T4b, T5a, T5b, T6a , T6b... Medium gradation subfield (number), T7aT7bT8aT8bT9aT9b... High gradation subfield (number).

Claims (1)

When displaying a video signal having a halftone by displaying a plurality of sub-fields, each of which is a binary image weighted by a time width or a pulse width, over one time period, it is represented by a binary number. display portions corresponding to a plurality of upper bits of the halftone with a plurality of sub-fields equal weighting, an image display for displaying a plurality of subfields weighted in accordance with the portion corresponding to the remaining lower bits to the binary A method for driving an apparatus, comprising:
In one field, a plurality of subfields corresponding to the remaining lower bits are arranged in the center ,
Each of the plurality of subfields of a portion corresponding to a plurality of bits before Symbol upper two divided,
A set of a plurality of subfields corresponding to a plurality of upper bits divided into two is divided into a high gradation group, a medium gradation group, and a low gradation group for each gradation,
In front of the plurality of subfields corresponding to the remaining lower bits, one subfield of the plurality of sets belonging to the high gradation group, one subfield of the plurality of sets belonging to the medium gradation group, Arranged in the order of one subfield of the plurality of sets belonging to the low gradation group, and behind the plurality of subfields of the portion corresponding to the remaining lower bits, the other of the plurality of sets belonging to the middle gradation group An image display characterized by being arranged and displayed in the order of a subfield of the second subfield of the plurality of sets belonging to the low gradation group and the other subfield of the plurality of sets belonging to the high gradation group Device driving method.

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