JPH11119730A - Video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a pseudo contour and to decrease a black level without deteriorating gradation, in the expression of gradation by a sub-field method. SOLUTION: A digital video signal DV1 from an A/D conversion means 2 is supplied to a sub-field conversion means 6 through a field storage means 5, with each field divided into plural sub-fields and converted into a sub-field configuration. A matrix display device 9 is driven by the video signal converted to this sub-field configuration. Meantime, the digital video signal DV1 from the A/D conversion means 2 is supplied to a statistical means 3, with the luminance distribution (e.g. maximum luminance level) M detected for each field. A means 4 for deciding a sub-field emission period controls the sub-field conversion means 6, making the sub-field configuration in each field of the digital video signal DV2 correspond to the luminance distribution M, and constituting a configuration that reduces a pseudo contour or a black level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video display device which divides a video signal of one field into several subfields and controls the presence or absence of light emission in each subfield, thereby expressing a gradation of light emission luminance. In particular, the present invention relates to a video display device capable of displaying more gray scales while reducing the influence of the pseudo contour effect inherent to the device.

[0002]

2. Description of the Related Art An image display device using plasma emission (plasma display device) has been put to practical use as a means for realizing an image display device larger than a cathode ray tube type or liquid crystal type image display device.

[0003] In plasma emission, there are only two emission intensity states, emission and non-emission, and it is difficult to express an intermediate intensity. Although it is possible to express the intermediate intensity in a pseudo manner by adjusting the light emission time, it is difficult to adjust the light emission time for each pixel, and it is possible to set pixels that emit light and pixels that do not emit light. It is.

[0004] A subfield method is used as a technique for expressing gradation in such a plasma display device.

[0005] This is because a display period of one field is divided into a plurality of sub-field periods having various light-emission times, and a predetermined combination of sub-fields corresponding to the gradation is emitted for each pixel, whereby each pixel is emitted. This is a method of expressing the gradation of. For example, the period of one field is divided into eight subfields S7 to S0, and S7 = 128 and S7, respectively.
6 = 64, S5 = 32, S4 = 16, S3 = 8, S2 =
By setting the light emission time at a ratio of 4, S1 = 2, S0 = 1, and controlling which subfield emits light for each pixel, 256 gradations of luminance levels 0 to 255 can be expressed. It is possible.

[0006]

According to such a subfield emission method, the greater the number of subfields set per field, the more gradations can be expressed. However, a period (addressing period) for instructing which pixel emits light is required for each subfield. Therefore, if the number of subfields in one field is increased, the addressing period increases and the light emission period decreases. However, there is a problem that the luminance is reduced accordingly. Therefore, in the current technology, the number of subfield divisions set in one field is limited to about eight.

In the subfield display method, an illusion that there is a high-luminance pixel region or a low-luminance pixel region (so-called pseudo contour) that does not originally exist may occur due to a shift in light emission time between subfields. is there. For example, in the light emission pattern of the above eight subfields, a certain pixel emits light in subfields S1 to S6 in order to display the luminance of level 126, and a pixel close to this emits light in subfield S7 in order to display the luminance of level 128. In this case, the observer who paid attention to the pixel having the luminance of level 126 at the time when the sub-fields S1 to S6 emit light is changed to the pixel displaying the luminance at the level 128 at the time when the sub-field S7 emits light. Upon entering the eye, on the retina of the eye, the subfields S1 to S7 are projected and added to the same position (in this case, the position of the pixel displaying the luminance of level 126), and the luminance of level 254 is displayed at this position. Give the impression like. Therefore, an illusion that an area of level 254 exists in an area having only luminance near level 126 is generated. This is called a pseudo contour because the contour shape is formed by reflecting the luminance gradient of the video.

In order to reduce the false contour, various measures have been taken such as reducing the luminance difference between the subfields and providing the subfield having the highest luminance twice or more. For example, even if one field is divided into the same eight subfields, S7 = 64, S6 = 64, S5 = 64, S4 =
32, S3 = 16, S2 = 8, S1 = 4, S0 = 2, the light emission time of each subfield S7-S0 is set, and when displaying the luminance of level 126, the subfields S0-S5 Is displayed, and when the luminance of the level 128 is expressed, the subfields S5 to S6 are displayed.

Under these conditions, the observer who paid attention to the pixel having the luminance of level 126 at the time when the subfields S0 to S5 emit light has the pixel displaying the luminance at the level 128 at the time when the subfields S6 and S7 emit light. , The subfields S0 to S6 are only added on the retina to generate a pseudo contour having a luminance of level 190, and the influence of the pseudo contour is reduced as compared with the above example.

However, in this subfield configuration, 1
Since only 28 gradations can be expressed, there is a first problem that the number of gradations is reduced as compared with the above example in which 256 gradations can be expressed.

Further, in a plasma display device, even a pixel designated to emit no light emits a slight amount of light due to a process (reset discharge) for performing a light emission process on another pixel. Since the reset discharge is required by the number of subfields, even a pixel having the lowest luminance will emit light slightly. Therefore, when this image is observed in a dark environment, there is a second problem that a dark portion displayed at low luminance in the image looks bright, and the image has a sense of incongruity in visual characteristics.

An object of the present invention is to provide an image display device which solves such a problem and reduces the influence of a false contour and can increase the gradation.

Another object of the present invention is to provide a video display device which can prevent pseudo light emission of pixels in a dark portion of an image and can obtain an image having no unnatural feeling in visual characteristics.

[0014]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention adaptively changes the light emission period of each subfield and the set number of subfields per field according to the luminance distribution of an input image. It is to let.

When an input video signal is an 8-bit digital signal, its luminance level may change in the range of 0 to 255, but the input video in each field has 256 gradation levels. Is not always included.
When displaying an image with a low maximum luminance, it is possible to express all the gradations of the input image even if the light emission time of the longest subfield is shortened. In such a subfield configuration, since the light emission period of the maximum subfield is short, the pseudo contour is inconspicuous.

In order to achieve the other object, the present invention does not emit a subfield having a maximum light emission period indicating a luminance of level 128 when the maximum luminance is low and there is only a luminance of level 127 or less. In both cases, all gradations can be expressed. When such an image is input, by not performing the light emission processing for the maximum light emission period, it is possible to suppress an increase in the brightness of the dark part due to the reset discharge.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of an image display device according to the present invention.
1 is an input terminal of a video signal, 2 is an A / D converter, 3 is a statistic, and 4 is a luminous period of each subfield based on the statistic result. Subfield light emission period determining means, 5 is a field storage means for storing an input video signal while determining the subfield light emission period, 6 is a conversion means for converting the input video signal according to the determined subfield, and 7 is the required number of subfields. A storage means for temporarily storing for display, a driving means for controlling light emission of each pixel of the matrix display in accordance with the converted input video signal, and a matrix display device.

In a matrix display device such as a plasma display device, each field of an input video signal is divided into a predetermined number of subfields (an arrangement of a series of subfields in this case is referred to as a subfield configuration). In this first embodiment, gradation is displayed in each pixel by emitting light or not emitting light during a light emission period determined for each subfield in accordance with the luminance to be displayed. , The maximum amplitude is obtained for each field, and the emission period of each subfield is determined according to the maximum amplitude.

In FIG. 1, R from input terminal 1
An analog input video signal AV composed of (red), G (green) and B (blue) components is converted by an A / D converter 2 into a digital video signal DV1 having a predetermined bit width. It is stored and supplied to the statistical means 3. Here, it is assumed that A / D conversion is performed to an 8-bit width (256 tones from 0 to 255). The statistical means 3 statistically processes the luminance level distribution of the digital video signal DV1 for each field, and calculates the maximum luminance level M for each field of the supplied digital video signal DV1.

FIG. 2 is a block diagram showing a specific example of the statistical means 3 shown in FIG. 1, and 3a denotes a digital video signal DV.
1 is an input terminal, 3b is a comparison means, 3c is a maximum value storage means, and 3c is an output terminal.

In FIG. 1, a digital video signal DV1 supplied from an input terminal 3a is supplied to a comparison means 3b, and its amplitude value (digital value: luminance level) is stored in a maximum value storage means 3c. Value (luminance level).

The maximum value storage means 3c is reset at the beginning of each field, and when the amplitude value of the digital video signal DV1 from the input terminal 3a is larger than the amplitude value stored in the maximum value storage means 3c, Value storage means 3c
Is rewritten to the amplitude value of the digital video signal DV1. Therefore, the maximum value storage means 3c sets an amplitude value of zero at the beginning of the field, but when the amplitude value of this field becomes larger than zero, the amplitude value is rewritten to this amplitude value, Becomes larger than the rewritten amplitude value, the amplitude value is further rewritten. So, when this field ends,
The maximum amplitude value MA of this field (that is, the maximum luminance level M) is obtained in the maximum value storage means 3c. This maximum amplitude value MA is output from the output terminal 3d and supplied to the subfield light emission period determination means 4 in FIG.

This subfield light emission period determination means 4
Fetches the maximum luminance level M of this field from the maximum value storage means 3c at the end of the field, and according to the maximum luminance level M, the light emission period length (luminance level) of each subfield in the subfield configuration of this field To determine.

Next, a specific example of an algorithm of a method of determining a light emitting period length of each subfield in a subfield configuration according to the luminance distribution of the digital video signal DV1 will be described.

FIG. 3 is a diagram showing an example of the distribution of amplitude in one field. The horizontal axis represents the luminance level, and the vertical axis represents the frequency (the number of pixels for each luminance level). FIG.
FIG. 3A shows the distribution when one or more pixels corresponding to each of the luminance levels 0 to 255 exist (that is, the maximum luminance level M is 255), and FIG.
(B) shows a distribution in a case where one or more pixels of the corresponding luminance level exist for each of the luminance levels 0 to M (<255), but no pixel exceeding the maximum luminance level M exists. .

For a field as shown in FIG. 3A, it is necessary to express all gradations from 0 to 255 in a subfield configuration consisting of eight subfields, so that the luminance represented by each subfield The level ratio is determined by dividing the subfields into S in ascending order of the shared brightness level.
.., S7, S0 = 1, S1 = 2, S2 = 4, S3 = 8, S4 =
16, S5 = 32, S6 = 64, S7 = 128. This ratio is also a ratio of the light emitting period lengths of these subfields.

The sub-field which shares the highest-ranked luminance level among these sub-fields is called the maximum luminance sub-field. In the above example, the maximum luminance subfield is subfield S7.

On the other hand, for a field having a frequency distribution as shown in FIG. 3 (b), only the range of luminance levels 0 to M needs to be expressed. Need not be a power-of-two ratio.

For example, if 192 ≦ M <256, S7 = (M-127), S6 = 64, S5 = 32, S
Eight subfields S7, S having light emission periods at the ratio of 4 = 16, S3 = 8, S2 = 4, S1 = 2, S0 = 1
5, S4,..., S0 (the maximum luminance subfield in this case is the subfield S7, and the luminance level shared by the maximum luminance subfield S7 is (M− 127) Here, the luminance level when all the sub-fields S6 to S0 emit light is 127, and in order to obtain the maximum luminance level M, the maximum luminance sub-field S7 further has the level (M- It is necessary to emit light at a luminance level of 127)).

Therefore, in this case, the brightness level L is 0 ≦ L
When it is within the range of <128, all the luminance levels L can be expressed by combining the seven sub-fields S0 to S6.
When 8 ≦ L ≦ M, the subfield S7
(= (M-127)), and the subfields S0 to S6 are appropriately illuminated.
It is possible to represent a luminance level in the range of ~ M. In this case, the luminance level by subfields S0 to S6 is X
Then, since L = (M-127) + X, the luminance level X based on the subfields S0 to S6 is X = L + 127-M.

When M <192, the subfield emission period can be selected more freely. FIG. 4 is a diagram showing a specific example of a combination of light emitting periods of subfields according to various maximum luminance levels M.

In this specific example, each of the maximum luminance levels M
5 shows a subfield configuration calculated and obtained such that the period length of the maximum luminance subfield S7 is the shortest. However, division is rounded down.

For example, when the maximum luminance M = 128,
The second subfield configuration from the top in FIG.
S7 = 33, S6 = 32, S5 = 32, S4 = 16, S
3 = 8, S2 = 4, S1 = 2, S0 = 1, and by appropriately combining these subfields,
All 128 gradations can be displayed. In this case, since the maximum luminance subfield S7 having the maximum light emission period shares the luminance level 33, the influence of the pseudo contour becomes extremely small as compared with the luminance level 128 in the conventional maximum luminance subfield.

FIG. 4 is generalized as follows. Maximum luminance gradation to be represented in the sub-field (shared luminance level) Smax, the following ^{equation, Smax = (M- (2 U} -B + U)) / (B-U) ......... (1) where, B : Maximum number of subfields (B = 8 in FIG. 4) M: Maximum value of gradation to be expressed U: 2 ^(U-1) × (BU−2) ≦ M <2 ^U × (BU−1) ) Which satisfies 0 ≦ U <2 ^B −1 (2). If the gradation represented by the maximum luminance subfield S7 is equal to or greater than this value Smax, the maximum luminance level M can be represented.

For example, in FIG. 4, 128 ≦ M ≦ 19
Assuming that ¹ , B = 8. Therefore, according to the above equation (2), 2 ^(U−1) × (BU−2) ≦ 128 to 191 <2 ^U × (B−
U satisfying (U + 1) is U = 6. Therefore, this is expressed by equation (1)
Substituting the brightness level Smax of the maximum luminance subfield ^{S7,, Smax = (M- (2 6} -8 + 6)) / (8-6) = the (M-62) / 2.

The generalization including the subfields for other luminance levels is as follows.

Now, assuming that n = 0, 1, 2,..., 7,
Assuming that the luminance level of the n-th sub-field from the lower luminance level is Sn, n when U ≦ n
Th luminance level Sn ^{subfield, (M- (2 U + n} -U-1)) is / (U-B) ≦ Sn ≦ 2 n ...... (3), n when an n <U The luminance level Sn of the second subfield is as follows: Sn = 2 ⁿ (4)

Where Sn is the luminance level of a subfield representing the nth smallest luminance level (n = 0 is a subfield representing the minimum luminance level, and n = B-1 is a subfield representing the maximum luminance level) M: Expression Maximum luminance level of gradation to be performed U: 2 ^(U−1) × (BU−2) ≦ M <2 ^U × (BU−1)
0 ≦ U <2 ^B −1.

Therefore, 128 ≦ M ≦ 19 in FIG.
Taking 1 as an example, in this case, since U = 6, the luminance levels of the illustrated subfields S6 and S7 are obtained by the above equation (3), and the other S0, S1,. S
The luminance level of No. 5 is obtained by the above equation (4).

When the luminance level of each subfield is represented by the above equation, it is possible to represent all gradations below the maximum luminance level M. That is, a set of sums of the light emission amounts of any number of subfields of 0 or more is
It will include all values below the maximum value of the quantized luminance level for each field.

FIG. 5 shows a specific example of another combination of subfields. Here, the crosses indicate that no light is emitted.

In this specific example, the calculation is performed so that the required number of subfields is minimized for each maximum luminance level M. For example, when M = 63,
No light is emitted in subfields S7 and S6, and S5
= 32, S4 = 16, S3 = 8, S2 = 4, S1 = 2
Assuming that S0 = 1 (in this case, subfield S5 is the maximum luminance subfield), by appropriately combining these six subfields, level 0 is obtained.
It is possible to display all gradations of ~ 63. In this case, since the number of subfields in this field may be six, only six reset discharges are required to cause the subfields to emit light, and the black level must be lower than in the conventional eight discharges. Is possible. Therefore, a preferable image in terms of visual characteristics can be obtained.

In any of the above cases, the luminance level of the maximum luminance subfield is equal to or less than the maximum amplitude of the digital video signal DV2, and the sum of the luminance levels of all subfields is equal to or less than the maximum amplitude of the digital video signal DV2. It is. By limiting to such a value, without using a subfield having an unnecessarily long emission time,
All gradations of the digital video signal DV2 can be expressed.

In FIG. 1, the subfield conversion means 6
Is a digital video signal VD1 from the A / D conversion means 2.
Are expressed using the subfield configuration determined as described above. In this case, each field of the digital video signal VD1 has its subfield configuration determined after the entire field is input to the statistical means 3. Therefore, it is necessary to supply the field to the subfield converting means 6 after waiting for this determination. Must. For this purpose, the digital video signal VD1 is written and read out by the field storage means 5, is delayed by approximately one field period, and is supplied to the subfield conversion means 6 as a digital video signal DV2.

The conversion method by the subfield conversion means 6 is as follows.

An amplitude (luminance level: digital value) representing the gradation is set for each of the determined subfields (this amplitude is hereinafter referred to as a set amplitude).
First, the set amplitude of these subfields is compared with the amplitude (luminance level: digital value) of the digital signal DV2 from the field storage means 5. In this case, the amplitude of the digital video signal DV2 is compared with the set amplitude in the order of the subfield having a long light emission period (that is, in order from the maximum luminance subfield). When the set amplitude of a certain subfield is equal to or larger than the amplitude of the digital video signal DV2, the subfield is set to emit light, and the set amplitude of the subfield is subtracted from this amplitude of the digital video signal DV2. This is compared with the set amplitude of a subfield having a long light emission period. When the set amplitude of the subfield is smaller than the amplitude of the digital video signal DV2, the subfield is not illuminated. Compare with the set amplitude. Hereinafter, the same processing is sequentially repeated up to the subfield of the shortest light emitting period.

For example, the maximum luminance level M in a certain field of the digital video signal DV2 is 192, and the field is S7 = 65, S6 = 64, S5 = 32, S4 =
16, S3 = 8, S2 = 4, S1 = 2, S0 = 1, the digital video signal V
For a pixel having an amplitude L = 66 of D2, only the subfields S0 and S7 emit light, so that the gradation of the luminance level 66 can be obtained. This light emission pattern is not necessarily unique, and the subfields S2 and S6 may emit light.

In FIG. 1, a signal DV3 converted into a subfield configuration for each field in this manner (referred to as a subfield configuration signal) is temporarily stored in a subfield storage unit 7, read out by a driving unit 8, and read out by a driving unit 8. Light emission and non-light emission of each pixel in the matrix display device 9 are driven for each subfield. As a result, each pixel in the matrix display device 9 emits light at a gradation corresponding to the amplitude value of the corresponding pixel of the digital video signal DV2.

FIG. 6 is a block diagram showing another specific example of the statistic means 3 in FIG. 1. 3e is a classification means, 3f is a tally means, and parts corresponding to those in FIG. I have.

In the figure, a digital video signal DV1 input from an input terminal 3a is classified by an amplitude (luminance level) of each pixel by a classification means 3e.
The frequency of each classification for each field (that is,
The number of pixels for each amplitude is summed, and the sum is supplied from the output terminal 3d to the subfield light emission period determining means 4 (FIG. 1).

The subfield configuration is determined based on the tabulation result obtained from the statistical means 3 in such a manner that the frequency with respect to the luminance level at which a pseudo contour is generated is reduced.

Next, the above operation of the statistic means 3 shown in FIG. 6 is performed by setting the digital video signal DV2 to an 8-bit width (0 to 25).
5 (256 gradations) will be described below.

For each field of the digital video signal DV2, the classifying means 3e classifies the luminance level (amplitude) into several steps, and the frequency of each step is totalized by the totaling means 3f. The maximum luminance level M and the frequency at each luminance level are obtained. For example,
In the aggregation result shown in FIG. 7, the maximum luminance level is M,
The frequency at the maximum and minimum luminance levels N0 and N1 is Nf, respectively.
0, Nf1. Based on these values, the subfield emission period determining means 4 (FIG. 1) determines the subfield configuration of this field.

That is, the subfield emission period determining means 4 first determines the lower limit value of the brightness level range obtained when the maximum brightness subfield emits light, based on the detected maximum brightness level M. This determination method is the same as the method for determining the maximum luminance level described above. For example, if 191 <M, M-127 is the lower limit. In the tabulation result shown in FIG. 7, since M = 192, 65 ≦ the lower limit.

Next, in the subfield S7 in which the above lower limit value is in the above range, the luminance level at which the frequency of the false contour becomes the least is calculated. Subfield S7 in video
From the region of the luminance level in which
Since the pseudo contour is the largest when the transition to the region of the luminance level at which light emission occurs is made, the luminance level of the subfield S7 is set so that this luminance level becomes the least frequent.

For example, in the field of the digital video signal DV2 having a frequency distribution as shown in FIG. 7, since the frequency is locally small at the luminance level 96, the subfield S7 starts emitting light near this level. Then, the occurrence frequency of the false contour is reduced. That is, in order to make the subfield S7 emit light at this luminance level, S7 = 96 may be set.

As described above, the subfield structure is adaptively determined in consideration of not only the maximum luminance level M of the digital video signal DV2 but also a luminance level which is locally infrequent, so that an image with few pseudo contours can be obtained. Can be obtained.

FIG. 8 is a block diagram showing a second embodiment of the video display device according to the present invention. In FIG. 8, reference numeral 10 denotes a subfield configuration generating means, and 11 denotes a pseudo contour evaluation means. Are denoted by the same reference numerals, and redundant description is omitted.

In the second embodiment, pseudo contours in various subfield configurations are evaluated for each field of the digital video signal DV1, and a subfield configuration with little influence of the pseudo contour is selected. Thus, it is possible to obtain an image with little influence of the pseudo contour.

In FIG. 8, the digital video signal DV1 having a predetermined bit width is output from the A / D conversion means 2. Here, the bit width of the digital video signal DV1 is also 8 bits (256 floors from 0 to 255). Tones).

The subfield structure generating means 10 generates several subfield structures for each field of the digital video signal DV1. For example, S7 = 9
6, S6 = 64, S5 = 32, S4 = 32, S3 = 1
6, S2 = 8, S1 = 4, S0 = 2, a subfield configuration SF0, and S7 = 64, S6 = 64, S5 = 6
4, S4 = 32, S3 = 16, S2 = 8, S1 = 4, S
The subfield configuration SF1 of 0 = 2 is generated by the subfield configuration generation means 10, and the size of the pseudo contour in the input video when the field at that time is represented by each subfield configuration is determined by the pseudo contour evaluation means. 11 rate.

A specific example of this evaluation method is as follows. That is, a pseudo contour is likely to occur when a subfield having a large luminance level is inverted. In the above-described subfield configuration SF0, the luminance level equal to or lower than level 158 can be represented by subfields S6 to S0.
In order to express a luminance level of level 160 or higher, it is necessary to further emit light in the subfield S7. Therefore, if attention is paid to the area A representing the luminance level of the level 158 or less, and this area emits light in, for example, the subfield S6, and the area in which the subsequent field S7 emits light is noticed. , This area A
In addition, the subfield S7 appears to emit light, which may cause a pseudo contour having a level 96 size. Similarly, in order to obtain a luminance level of 96 or more, it is necessary to emit light in the subfield S6. Therefore, a pseudo contour having a luminance level of 64 may be generated in a region in which the subfield is not emitted.

On the other hand, in the above-described subfield structure SF1, similarly, the level 6
When the light emission of the subfield S5 representing the level 64 is noticeable in the area A in which the luminance level is 2 or less,
Further, when the light emission of the subfield S6 representing the level 64 is noticeable in the area A in which the luminance level of the level 126 or lower is represented in the subfields S0 to S5, furthermore,
If light emission of the subfield S7 representing the level 64 is noticeable in the area A in which the luminance level of the level 190 or less is represented in the subfields S0 to S6, there is a possibility that a pseudo contour having the luminance level 64 is generated. is there.

Therefore, for the subfield structure SF0, the level 158 or lower in the field is changed to the level 16 or lower.
The value obtained by multiplying the number of times the change to 0 or more and the reverse change occurs by 96 or the value obtained by multiplying the number of change from the level 95 or less to the level 96 or more and vice versa by 64 is a guideline of the pseudo contour. Similarly, for the subfield configuration SF1, a value obtained by multiplying the number of times a change from the level 63 or lower to the level 64 or higher and vice versa in the field occurs by 64 or a level 127 or lower. The value obtained by multiplying the number of times the change to level 128 or more and the reverse change occurs by 64 and the value obtained by multiplying the number of change from the level 191 or lower to the level 192 or more and the reverse change by 64 is a guideline of the pseudo contour. Can be

The pseudo-contour evaluation means 11 outputs the subfield structure S from the subfield configuration generation means 10 for each field of the supplied digital video signal DV2.
For each of F0 and SF1, an estimate of the pseudo contour is obtained,
By comparing the two, the subfield configuration in which the pseudo contour that may occur is smaller is instructed to the subfield emission period determination means 4. Thus, the subfield light emission period determining means 4 controls the subfield conversion means 6 to convert the field of the digital video signal DV2 read from the field storage means 5 using the designated subfield configuration. .

FIG. 9 is a block diagram showing a third embodiment of the video display apparatus according to the present invention. Numeral 12 denotes an image quality evaluation means, and portions corresponding to those in FIG. Is omitted.

In the third embodiment, the same pseudo contour evaluation as that of the second embodiment shown in FIG. 8 is performed on each field of the digital video signal DV1, and the image quality in various subfield configurations is obtained. Evaluation is also performed, and the subfield configuration is determined based on these evaluations. In this case, too, the effect of the pseudo contour is small, and a subfield configuration with good image quality can be obtained. Can be obtained with less influence of the image.

In FIG. 9, the digital video signal DV1 output from the A / D converter 2 has an 8-bit width (256 tones from 0 to 255). This digital video signal DV1 is supplied to a pseudo-contour evaluation unit 11 and a quality evaluation unit 12. In the pseudo-contour evaluation unit 11, as in the second embodiment shown in FIG. Pseudo contours are evaluated for a plurality of subfield configurations from the generator 10.

The subfield configuration generating means 10
Is, for example, S7 = 128, S6 = 64, S5 = 32,
S4 = 16, S3 = 8, S2 = 4, S1 = 2, S0 = 1
, And S7 = 64, S
6 = 64, S5 = 64, S4 = 32, S3 = 16, S2
= 8, S1 = 4, and S0 = 2.

For this reason, the pseudo contour evaluation means 11 calculates, for each subfield configuration SF2, a value obtained by multiplying the number of times the change from the level 158 or lower to the level 160 or higher and vice versa for each field by 96. And level 95
The value obtained by multiplying the number of times the change from the following to the level 96 or higher and the reverse change occurs by 64 is used as a guide of the pseudo contour. Similarly, for the subfield configuration SF1, the level is changed from the level 63 or lower for each field. A value obtained by multiplying the number of times the change to level 64 or more and the reverse change occurs by 64, a value obtained by multiplying the number of change from level 127 or less to level 128 or more and the opposite change by 64, level 191
A value obtained by multiplying the number of times the change from the following to the level 192 or more and vice versa occurs by 64 is used as a guide of the pseudo contour.
Then, these measures are compared, and the difference is evaluated as the evaluation result P1.
Is supplied to the subfield emission period determination means 4.

On the other hand, the image quality evaluation means 12 evaluates the display image quality when the image is displayed in each subfield configuration.

That is, in the above-described subfield configuration SF2, since all the gradations of 0 to 255 in the digital video signal DV1 can be expressed, there is no image quality deterioration accompanying the subfield conversion. However, in the above-described sub-field SF1, since the gradation can only be expressed as an even value such as 2, 4, 6,..., The image quality is not degraded with respect to the even-valued luminance level of the digital video signal DV1, but the odd value. Is represented as an even value closest to the luminance level, the image quality is degraded by a value of 1.

From this, the frequency of the supplied digital video signal DV1 with respect to the odd-numbered luminance level in the field is a measure of image quality deterioration. Then, this frequency is transmitted to the subfield light emission period determination means 4 as the evaluation result P2.

The subfield light emission period determining means 4 compares the evaluation result P1 as a measure of the pseudo contour with the evaluation result P2 as a measure of the image quality deterioration. If the frequency is low and the image quality degradation occurs frequently in the subfield configuration SF1, the subfield SF2 is selected. The pseudo contour occurs frequently in the subfield configuration SF2, and the image quality degradation occurs in the subfield configuration SF1. If the frequency is low, the subfield configuration SF1 is selected.

Thus, digital video signal DV2 is converted using the selected subfield configuration,
The matrix display device 9 is driven.

[0076]

As described above, according to the present invention,
By setting the luminance level of each subfield according to the luminance level of the local minimum frequency in the maximum luminance level of the video and the frequency distribution with respect to the luminance level, the pseudo contour can be reduced without reducing the number of expressible gradations. It is possible to express a video with little noise.

Further, according to the present invention, by controlling the number of subfields for each field in accordance with the maximum luminance level of an image, the black level of the image can be lowered, and a preferable image in terms of visual characteristics can be obtained. Can be.

Further, according to the present invention, an appropriate subfield configuration is selected from a plurality of subfield configurations in accordance with the evaluation result of the pseudo contour level and the image quality level. Therefore, it is possible to obtain a high-quality image with few false contours.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a video display device according to the present invention.

FIG. 2 is a block diagram showing a specific example of a statistical unit in FIG. 1;

FIG. 3 is a diagram illustrating an example of a frequency with respect to a luminance level of an image.

FIG. 4 is a diagram illustrating a specific example of a relationship between a maximum luminance level of a video signal and a subfield configuration in the first embodiment illustrated in FIG. 1;

FIG. 5 is a diagram showing another specific example of the relationship between the maximum luminance level of the video signal and the subfield configuration in the first embodiment shown in FIG. 1;

FIG. 6 is a block diagram showing another specific example of the statistical means in FIG. 1;

7 is a diagram illustrating an example of a frequency with respect to a luminance level of a video signal to be evaluated in the specific example illustrated in FIG. 6;

FIG. 8 is a block diagram showing a second embodiment of the video display device according to the present invention.

FIG. 9 is a block diagram showing a third embodiment of the video display device according to the present invention.

[Description of Signs] 1 Video signal input terminal 2 A / D conversion means 3 Statistical means 3b Comparison means 3c Maximum value storage means 3e Classification means 3f Totalization means 4 Subfield emission period determination means 5 Field storage means 6 Subfield conversion means 7 Sub-field storage means 8 Driving means 9 Matrix display device 10 Sub-field configuration generating means 11 Pseudo contour evaluation means 12 Image quality evaluation means

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroki Mizozoe 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Multimedia Systems Development Division of Hitachi, Ltd. (72) Inventor Keizo Suzuki Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa 292 Hitachi Electronics, Ltd.Household Appliances & Information Media Division (72) Inventor Michitaka Osawa 292 Yoshidacho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi Electronics Corporation Home Appliances & Information Media Division (72) Inventor Akihiko Kogami Kanagawa 292, Yoshida-cho, Totsuka-ku, Yokohama, Japan Home Appliances & Information Media Division, Hitachi, Ltd. (72) Inventor Naka Ichitaka 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi, Ltd. Home Appliances & Information Media Division

Claims (9)

[Claims] 1. A video display device which divides one field period of a video signal into a plurality of sub-field light emission periods and controls the presence or absence of light emission of each sub-field to perform gradation expression. An image display device comprising: first means for generating statistics; and second means for determining a light emission amount of each of the subfields according to the generated amplitude distribution statistics. 2. The video display device according to claim 1, wherein the amplitude distribution statistics generated by the first means is a maximum value of luminance of each field. 3. The video display according to claim 1, wherein the amplitude distribution statistics generated by the first means are a luminance value and a frequency at which the luminance frequency of each field has a local minimum value. apparatus. 4. A video display device which divides one field period of a video signal into a plurality of subfield light emission periods and controls the presence or absence of light emission of each subfield to perform gradation expression, wherein an amplitude distribution of an input video signal is provided. An image display apparatus comprising: third means for generating statistics; and fourth means for determining the number of subfields in a field according to the generated amplitude distribution statistics. 5. The video display device according to claim 4, wherein the amplitude distribution statistics generated by the first means is a maximum value of luminance of each field. 6. The video display according to claim 4, wherein the amplitude distribution statistics generated by the first means are a luminance value and a frequency at which the luminance frequency of each field has a local minimum value. apparatus. 7. The method according to claim 1, wherein a set of sums of light emission amounts of any number of zero or more subfields is a maximum value of quantized luminance of each field. A video display device comprising all of the following values: 8. A video display device which divides one field period of a video signal into a plurality of subfield light emission periods, and controls the presence or absence of light emission of each subfield to perform gradation expression. Fifth to evaluate contour relationship
And a sixth means for determining the light emission amount of each of the subfields according to the evaluation result of the fifth means. 9. The video display device according to claim 8, further comprising an evaluation unit that evaluates a relationship between a subfield configuration and image quality.