JPH10319894A - Picture image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture image display device which realizes a picture quality having practically sufficient gradations even within the limit of the number of subfields. SOLUTION: The purpose of the invention is embodied by adjusting the correspondence between the level of a picture image signal and the light-emitting subfield based on the results of a signal level detecting means 8 and furthermore adjusting the weight of the signal levelsubfield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device such as a plasma display using a so-called sub-field method for displaying a plurality of binary images each weighted with time in a superimposed manner.

[0002]

2. Description of the Related Art In recent years, a plasma display device has been demanded as a display device if a color CRT can be greatly reduced in thickness. This plasma display device has a
As shown in JP-A-195087 and the like, a so-called subfield method is used to display a halftone. The driving method requires a write period and a sustain period for display data. Here, the configuration of a conventional image display device will be described with reference to FIGS.

FIG. 8 is a diagram showing a configuration of a conventional image display device. In FIG. 8, reference numeral 1 denotes a video signal synchronization separation circuit. 2
Is a timing pulse generation circuit that generates a timing pulse from the synchronization signal separated by the synchronization separation circuit 1. Reference numeral 3 denotes A for converting a video signal into an 8-bit digital signal of 256 gradations.
/ D conversion circuit. 4 is a subfield processing circuit. Reference numeral 5 denotes a frame memory required for the subfield processing circuit. 6
Is a panel drive circuit of a plasma display panel. Reference numeral 7 denotes a plasma display panel.

[0004] In the image display device configured as described above, the video signal is converted into an 8-bit digital signal of 256 gradations by the A / D conversion circuit 3 and the synchronization separation circuit 1 is used.
Separates the synchronization signal. Timing pulse generation circuit 2
Generates a timing pulse necessary for the subfield processing circuit 4 and the A / D conversion circuit 3. The subfield processing circuit 4 controls the panel drive circuit 6 so as to control the frame memory 5 to divide the grayscale of the video signal converted into the digital signal into subfields and display the divided subfields.

FIG. 9 is a diagram showing an example of a subfield method in which higher-order 7-bit 128-gradation display of a digitized 8-bit video signal is performed while writing and maintaining are repeated. First, in the first subfield SF1, the LSB of the video signal is written and scanned on the panel in the order of the scanning line, and then a sustain pulse for a time corresponding to the weight “1” is applied. After this display is completed, the second sub-field SF2 writes and scans the second LSB to obtain the weight “2”.
Is applied. In this way, the bit weight and the length of the sustain pulse are made to correspond to each other, and the process is repeated until the eighth subfield SF8. In FIG. 9, SF7 and SF8 display the weight 64 of the most significant bit (MSB) divided into two subfields. By dividing the MSB subfield in this way, it is possible to reduce pseudo contours generated in a moving image.

[0006] By such an operation, light emission corresponding to video bits is generated for each pixel, and a total of 128 light emission levels can be displayed.

[0007]

However, in such a configuration, the number of subfields must be increased in order to improve the gradation of the image display device. When the number of subfields is increased, the writing time of the panel is inevitably shortened, and there is a problem that the display on the panel cannot be performed stably. That is, the number of displayable gradations of the image display device is limited by the number of subfields of the panel, and there is a problem that a sufficient gradation cannot be displayed as a video display device.

[0008] When displaying a video signal to which a CRT gamma is added on an image display device such as a plasma display having no gamma characteristic, the reverse gamma of the CRT is applied to the video signal. Must be appended to Such processing is to perform non-linear processing on the video signal, and particularly requires low-brightness gradation characteristics.
The conventional image display device in which the gradation is limited by the number of subfields has a problem that sufficient image quality cannot be expressed.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide an image display apparatus which realizes a practically sufficient image quality with sufficient gradation even within the limit of the number of subfields.

[0010]

An image display apparatus according to the present invention divides a video signal into a plurality of subfields weighted by a time width or the number of pulses for each field, and converts a plurality of binary images into time. What is claimed is: 1. An image display apparatus for performing gradation display by superimposedly displaying a signal level, comprising: signal level detection means for detecting a signal level of a video signal; Adjust the correspondence between the fields,
Signal level-subfield weight adjustment means for adjusting the weight of the subfield, characterized in that, based on the detection result of the signal level detection means, the signal level-subfield weight adjustment means,
By adjusting the correspondence between the signal level and the subfield to emit light and adjusting the weight of the subfield, it is possible to realize a practically sufficient image quality with gradation even within the limit of the number of subfields.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image display apparatus according to the present invention divides a video signal into a plurality of subfields weighted by a time width or a pulse number for each field,
What is claimed is: 1. An image display device which performs a gray scale display by superimposing a plurality of binary images temporally, wherein a signal level detecting means for detecting a signal level of said video signal; Adjusting the correspondence between the signal level and the subfield to emit light on the basis of the signal level, characterized by having a signal level-subfield weight adjustment means for adjusting the weight of the subfield,
Even within the limit of the number of subfields, it is possible to realize an image quality with sufficient gradation for practical use.

According to a second aspect of the present invention, when the detection result of the signal level is smaller than the specific value, the signal level-subfield weight adjusting means may adjust the weight of the plurality of subfields. Is reduced by a specific ratio, and the signal level is increased by a specific ratio to adjust the correspondence between the signal level and the subfields that emit light. Practically sufficient image quality with sufficient gradation can be realized in the low luminance portion of the signal.

According to a third aspect of the present invention, in the image display device, the signal level-subfield weight adjusting means corresponds to a plurality of sub-fields having a weight equivalent to a plurality of upper bits of the signal level. Let
A subfield configuration in which specific lower bits correspond to subfields of the minimum unit weight, and several subfields of a plurality of subfields having substantially the same weight corresponding to portions corresponding to the upper bits of the signal level. The fields are grouped into one subfield having the same total weight, and a subfield corresponding to a weight of 1/2 of the minimum unit is newly provided to correspond to a bit having a weight of 1/2 of the specific lower bit. It is characterized by switching between the field configuration and realizing a practically sufficient image quality with sufficient gradation without deteriorating the gradation in the high-luminance part even within the limit of the number of subfields. Can be.

According to a fourth aspect of the present invention, there is provided an image display apparatus according to the third aspect, wherein the newly provided subfield corresponding to 1/2 of the specific lower-order bit is provided for each field of the video signal. In addition, the mode is switched to a subfield having a weight of the minimum unit and a weight of 0, and as a result, the gradation can be improved.

According to a fifth aspect of the present invention, there is provided an image display apparatus according to the third aspect, wherein a subfield corresponding to a half of a specific lower-order bit newly provided in the image display apparatus according to the third aspect has a weight of the minimum unit. Is turned on with a probability of 1/2 in the field of the video signal. As a result,
Gradation can be improved.

According to a sixth aspect of the present invention, there is provided an image display apparatus comprising: the image display apparatus according to the first to fifth aspects;
Inverse gamma correction means for digitally inversely correcting the gamma characteristic of the signal level, the number of bits after the inverse gamma correction is larger than the number of bits before the correction, and the inverse gamma correction as an input to the signal level-subfield weight adjustment means. It is characterized by using the output signal of the means, and it is possible to realize practically sufficient image quality with sufficient gradation without increasing the number of bits of the A / D conversion means for the video signal.

According to a seventh aspect of the present invention, there is provided an image display apparatus according to the first to fifth aspects, further comprising an inverse gamma correction varying means for varying a characteristic for inversely correcting a gamma characteristic of the CRT. The characteristic of the inverse gamma correction is varied according to the detection result of the signal level, and the apparent gradation of a low luminance portion can be improved.

According to an eighth aspect of the present invention, there is provided the image display apparatus according to any one of the first to seventh aspects, further comprising an error diffusion unit, wherein the signal level-subfield weight adjustment unit includes a signal level and a light emission. Error diffusion is performed on the signal data after the correspondence of the subfields to be adjusted is performed.

According to a ninth aspect of the present invention, as the signal level detecting means for detecting the video signal level of the image display device according to the first to eighth aspects, the luminance distribution of the video signal is frequency-counted. , Signal level detection results are determined.

According to a tenth aspect of the present invention, as the signal level detecting means for detecting the video signal level of the image display device according to the first to eighth aspects, the signal levels of a plurality of previous fields are detected. It is characterized by adding the result.

(Embodiment 1) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of an image display device according to a first embodiment of the present invention. Here, components having the same purpose and operation as those in FIG. 8 showing the conventional example are denoted by the same reference numerals, and detailed description is omitted. In FIG. 1, 1 to 7 have the same purpose and configuration as those of FIG. 8 of the conventional example.

Reference numeral 8 denotes signal level detecting means for detecting the signal level of the video signal converted by the A / D conversion circuit 3 into a digital signal. Reference numeral 9 denotes a signal level-subfield weight adjusting means for adjusting the correspondence between the signal level and the subfield to be lit according to the signal level detected by the signal level detecting means 8 and adjusting the weight of the subfield.

The operation of the image display apparatus of the first embodiment configured as described above will be described below with reference to FIGS.

The A / D conversion circuit 3 converts the input video signal into a digital signal of 8 bits and 256 gradations, and the signal level detecting means 8 detects the level of the video signal. If the maximum signal level in one field detected by the signal level detecting means 8 is equal to or more than の of the full scale (128 gradations), the signal level-subfield weighting adjusting means 9 will be described with reference to FIG. As shown, the subfield processing circuit 4 is controlled so as to drive the plasma display panel with the same subfield configuration as the conventional example. When the maximum value of the signal level in one field detected by the signal level detecting means 8 is lower than フ ル of the full scale (128 gradations), the signal level-subfield weight adjusting means 9 respectively. Weight of the subfield of 1 /
2 and the video signal converted by the A / D conversion circuit 3 into a digital signal is doubled, and as shown in FIG.
The sub-field processing circuit 4 is controlled so as to correspond to SF1 ′ and SF2 ′ in order from B and to make the seventh bit from LSB correspond to SF7 ′ and SF8 ′.

According to the first embodiment configured as described above, when the maximum value of the video signal level in one field period is lower than フ ル of the full scale, the signal level subfield weight adjusting means is used. , To reduce the weight of the subfield to half and to double the signal level value to make the subfield correspond to the video signal bit,
There is no change in the luminance of the video signal, and the gradation can be doubled as compared with the related art.

Further, as a matter of course, the number of bits of the A / D conversion circuit may be further increased, and the threshold value of the video signal level to be detected may be increased to switch the subfield configuration more finely.

By adjusting the correspondence between the signal level and the subfield according to the input video signal level and adjusting the weight of the subfield, it is possible to provide an image which can provide image quality with a gradation sufficient for practical use. A display device can be provided.

(Embodiment 2) Next, a second embodiment of the present invention will be described. FIG. 3 is a diagram showing a subfield configuration for illustrating a second embodiment of the present invention. The configuration diagram of the image display device in this embodiment is the same as the configuration diagram of the image display device described in (Embodiment 1).

In the second embodiment, the A / D conversion circuit 3 converts the input video signal into a digital signal of 8 bits and 256 gradations, and the signal level detecting means 8 detects the level of the video signal. When the detection result of the signal level within one field detected by the signal level detection means 8 is equal to or more than a specific value, the signal level-subfield weight adjustment means 9 as shown in FIG. The sub-field processing circuit 4 is controlled so that the bits drive the plasma display panel 7 in the same sub-field configuration as in the conventional example.

When the signal level-subfield weight adjusting means 9 detects the signal level within one field detected by the signal level detecting means 8 is lower than the specific value, as shown in FIG. The subfields 7 and 8 having a weight of 32 of the prior art are combined into a subfield 7 'having a weight of 64, and a subfield 0' having a weight of 1/2 is newly provided so that 8 bits of the digital video signal correspond to the subfield. The subfield processing circuit 4 is controlled so as to drive the plasma display panel 7 with the configuration of the subfield to be performed.

According to the second embodiment configured as described above, when the detection result of the video signal level in one field period is lower than the specific value, the signal level-subfield weight adjustment means sets the The fields 7 and 8 are combined into a subfield 7 'having a weight of 64, and a subfield 0' having a weight of 1/2 is newly provided, so that the digital video signal has 8 bits corresponding to the subfield. Since the subfield processing circuit 4 is controlled to drive the display panel 7, it is possible to reduce the false contour of a moving image in an image with a high average luminance, and to double the gradation in an image with a low average luminance. Can be improved.

By switching the signal level and the configuration of the subfields in accordance with the input video signal in this manner, even if the number of subfields is limited, the gradation in a high-luminance portion is not deteriorated, and is practically sufficient. It is possible to provide an image display device which realizes image quality with gradation.

Further, in Embodiment 2 of the present invention,
If a subfield corresponding to / 2 cannot be provided, a subfield having a weight of 1 and a subfield having a weight of 0 are switched for each field of the video signal, or a subfield having a weight of 1 is halved in a field of the video signal. ON with probability
It can also be realized by doing.

In this way, it is possible to provide an image display device with improved gradation even when a subfield equivalent to 1/2 cannot be newly provided due to the restriction of driving the plasma display panel. it can.

(Embodiment 3) An example of a third embodiment of the present invention will be described.

FIG. 4 is a diagram showing a configuration of an image display device according to a third embodiment of the present invention. Here, components having the same purpose and operation as those in FIG. 1 showing the first embodiment are denoted by the same reference numerals, and detailed description is omitted. FIG.
1 to 9 have the same purpose and configuration as FIG. 1 of the first embodiment. Reference numeral 10 denotes an inverse gamma correction unit that performs inverse gamma correction on the video signal converted into a digital signal by the A / D conversion circuit 3. The inverse gamma correction unit 10 has a configuration in which the number of bits after correction is larger than the number of bits before correction.

FIG. 5 shows a correction curve of the inverse gamma correction means. FIG. 6 is a diagram illustrating characteristics of the inverse gamma processing in a low luminance portion when the number of output bits is 7 bits and 8 bits. The solid line indicates a 7-bit output, and the dotted line indicates an 8-bit output.

The operation of the image display apparatus according to the third embodiment having the above-described configuration will be described with reference to FIGS. 4, 5 and 6. The A / D conversion circuit 3 converts the input video signal into a digital signal, and the signal level detection means 8 detects the level of the video signal. The inverse gamma correction means 10 performs gamma correction processing shown in FIG. 5 on the video signal converted by the A / D conversion circuit 3 into a digital signal.

If the signal level-subfield weight adjusting means 9 detects the signal level within one field detected by the signal level detecting means 8 is equal to or more than a specific value, as shown in FIG. The sub-field processing circuit 4 is controlled so that the upper 7-bit video signal of the output signal of the correcting means 10 drives the plasma display panel 7 in the same sub-field configuration as in the conventional example. When the signal level-subfield weight adjusting means 9 detects the signal level within one field detected by the signal level detecting means 8 is lower than the specific value, as shown in FIG. Subfields 7 and 8 of weight 32
Are combined into a subfield 7 'having a weight of 64, and a subfield 0' having a weight of 1/2 is newly provided.
The subfield processing circuit 4 is controlled so as to drive the plasma display panel 7 in a subfield configuration in which the 8-bit video signal of the output signal of the inverse gamma correction unit 10 corresponds to the subfield.

According to the third embodiment configured as described above, the deteriorated gradation can be reproduced by the non-linear characteristic of the inverse gamma correction, so that the number of bits of the A / D converter It is possible to provide an image display device capable of realizing an image having practically sufficient gradation even at low luminance without increasing the luminance.

Further, in the third embodiment, the characteristics of the inverse gamma correction means 10 can be varied according to the detection result of the signal level detection means 8. By doing so, the apparent gradation can be further improved.

(Embodiment 4) An image display device according to a fourth embodiment of the present invention will be described below.

FIG. 7 is a diagram showing a configuration of an image display device according to a fourth embodiment of the present invention. Here, the same objects and operations as those in FIG. 4 showing the third embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. In FIG. 7, 1 to 10 have the same purpose and configuration as FIG. 4 of the third embodiment. An error diffusion unit 11 performs an error diffusion process on the output signal of the signal level-subfield weight adjustment unit 9.

The operation of the image display apparatus according to the fourth embodiment having the above-described configuration will be described. The A / D conversion circuit 3 converts the input video signal into a digital signal, and the signal level detection means 8 detects the level of the video signal. The inverse gamma correction unit 10 performs gamma correction on the video signal converted by the A / D conversion circuit 3 into a digital signal. The signal level-subfield weight adjusting means 9 adjusts the correspondence between the signal level and the subfield to be lit and the weight of the subfield based on the detection result of the signal level detecting means 8. The error diffusion means 11 outputs the signal level −
An error diffusion process is performed on the output signal of the subfield weight adjustment means 9. The subfield processing unit 4 controls the panel driving circuit 6 based on the output result of the error diffusion unit 11.

According to the fourth embodiment configured as described above, the error diffusion processing is performed on the signal whose gradation has been improved by the signal level-subfield weight adjusting means 9, so that it is possible to perform the error diffusion processing in the spatial domain. An image display device with further improved gradation can be provided.

In the first to fourth embodiments, the video signal level detecting means determines the signal level detection result by counting the frequency distribution of the luminance of the video signal and determining the signal level detection result. It is possible to provide an image display device in which a change in image quality when the weighting adjustment unit performs the adjustment operation is reduced and the stability is further improved.

In the first to fourth embodiments, the signal level detecting means for detecting the video signal level takes into account the signal level detection results of a plurality of previous fields. It is possible to provide an image display device in which a change in image quality when the signal level-subfield weight adjustment unit performs an adjustment operation is reduced, and stability is improved with a relatively simple configuration.

[0048]

As described above, according to the image display apparatus of the present invention, the signal level-subfield weight adjusting means can be adjusted according to the detection result of the signal level detecting means.
Since the correspondence between the signal level and the subfields that emit light is adjusted, in the case of a video input with a low average luminance, the number of subfields does not change, and the weighting of the subfields is reduced, thereby improving the gradation display. An apparatus can be provided.

Further, according to the image display apparatus of the present invention, the occurrence probability of the data having the weight 1 is temporally and spatially reduced to １ ／ by using the subfield having the weight 1 to thereby reduce the 1/2 of the minimum weight. A subfield with a weight of 2 can be realized. With this configuration, even when the weight of the subfield having the minimum weight cannot be further reduced due to the restriction of panel driving, a subfield having 1/2 weight can be provided equivalently, and the gradation at low luminance can be improved. An improved image display device can be provided.

Further, according to the image display apparatus of the present invention, the output signal of the inverse gamma correction means having an increased number of bits can be used as an input to the signal level-subfield weight adjustment means. An image display that can reproduce a deteriorated gradation due to the non-linearity characteristic, and can realize a practically sufficient gradation image even at a low luminance without increasing the number of bits of the A / D converter. An apparatus can be provided.

Further, according to the image display apparatus of the present invention, the error diffusion processing is performed on the signal whose gradation is improved by the signal level-subfield weight adjusting means.
An image display device with further improved gradation in a spatial region can be provided.

Further, according to the image display device of the present invention,
As the video signal level detection means, to count the frequency distribution of the luminance of the video signal and to use the signal level detection result, or the signal level detection results of a plurality of previous fields,
It is possible to provide an image display device in which a change in image quality when the signal level-subfield weight adjusting means performs an adjusting operation is reduced and stability is further improved.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a configuration example of a subfield used in the first embodiment of the present invention;

FIG. 3 is a diagram showing a configuration example of a subfield used in a second embodiment of the present invention;

FIG. 4 is a configuration diagram showing a third embodiment of the present invention.

FIG. 5 is a diagram showing characteristics of inverse gamma correction processing;

FIG. 6 is a diagram showing characteristics of inverse gamma correction used in a third embodiment of the present invention.

FIG. 7 is a configuration diagram showing a third embodiment of the present invention.

FIG. 8 is a configuration diagram showing a conventional example.

FIG. 9 is a diagram showing a configuration example of a subfield used in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synchronization separation circuit 2 Timing pulse generation circuit 3 A / D conversion circuit 4 Subfield processing circuit 5 Frame memory 6 Panel drive circuit 7 Plasma display panel 8 Signal level detection means 9 Signal level-subfield weight adjustment means 10 Inverse gamma correction means 11 Error diffusion means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshito Ota 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (10)

[Claims] An image signal is divided into a plurality of sub-fields weighted by a time width or the number of pulses for each field, and a plurality of binary images are temporally superimposed and displayed to perform gradation display. A signal level detecting means for detecting a signal level of the video signal, and adjusting a correspondence between a signal level and a subfield to emit light based on a detection result of the signal level detecting means. An image display device comprising signal level-subfield weight adjustment means for adjusting field weights. 2. The signal level-subfield weight adjusting means, when the detection result by the signal level detecting means is smaller than a specific value, reduces the weight of the plurality of subfields at a specific ratio and reduces the signal level at a specific ratio. 2. The image display device according to claim 1, wherein the correspondence between the signal level and the subfield that emits light is adjusted. 3. The signal level-subfield weight adjusting means associates a portion corresponding to a plurality of upper bits of a signal level with a plurality of subfields of substantially equal weight, and assigns a specific lower bit to a subfield of minimum unit weight. And a plurality of subfields having substantially the same weight corresponding to a portion corresponding to a plurality of high-order bits of the signal level. And 1/2 of the minimum unit
2. The image display device according to claim 1, wherein a subfield corresponding to the weighting of the second subfield is newly provided to switch between a subfield configuration in which a bit having a weight of 特定 of the specific lower bit corresponds. 4. A subfield corresponding to の of newly specified lower bits is switched to a subfield having a weight of the minimum unit and a weight of 0 for each field of a video signal. Item 3. The image display device according to Item 3. 5. The sub-field corresponding to 1/2 of a newly provided specific lower bit is turned on with a probability of 1/2 in a field of a video signal with the weight of the minimum unit. 3. The image display device according to 3. 6. A signal level-subfield weight adjusting means, wherein inverse gamma correction means for digitally inversely correcting the gamma characteristic of a CRT is provided, and the number of bits after inverse gamma correction is larger than the number of bits before correction. 6. The image display device according to claim 1, wherein an output signal of an inverse gamma correction unit is used as an input of the image display. 7. An apparatus according to claim 1, further comprising an inverse gamma correction varying means for varying a characteristic for inversely correcting a gamma characteristic of the CRT, wherein the characteristic of the inverse gamma correction is varied according to the detection result of the signal level. The image display device according to claim 5. 8. An error diffusion means, wherein the signal level-subfield weight adjustment means performs error diffusion on the signal data after adjusting the correspondence between the signal level and the light emitting subfield. The image display device according to claim 1. 9. The image display according to claim 1, wherein the signal level detecting means for detecting a video signal level counts a luminance distribution of the video signal and determines a signal level detection result. apparatus. 10. The apparatus according to claim 1, wherein said signal level detecting means for detecting a video signal level takes into account signal level detection results of a plurality of previous fields.
The image display device as described in the above.