JPH10171400A - Gradation display method for video signal and display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce picture quality deterioration due to false outline noise in gradation representation of a subfield system. SOLUTION: Digital data of an input video signal are supplied to a subfield converting circuit 2 and the respective bits of the data are assigned to subfields set in one field to generate subfield data. In this case, high-order bits having weights of a value obtained by equally dividing the total of the values of bits from the most significant bit are generated and assigned to different subfields. When gradations are low, the light emission period of pixels is determined by a combination of low-order bits of the subfield data, but when the gradations are high, the light emission period of the pixels is determined by a combination of the high-order and low-order bits of the subfield data, and consequently a gradational display is made, but high-order bits which contribute to the light emission of the same pixels are made different between adjacent pixels or in odd/even fields.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation expression method for displaying a video signal such as a television signal or a high vision signal, and more particularly, to a method of dividing one field of a video signal into several subfields. In addition, the present invention relates to a gray scale display method for expressing the gray scale of light emission luminance by controlling the presence or absence of light emission in these subfields, and a display device using this gray scale display method.

[0002]

2. Description of the Related Art As a conventional method for realizing gradation display in a display device in which it is difficult to perform gradation display between light emission and non-light emission with a single element, a method of controlling a light emission time width of a light emitting element is known. .

For example, Japanese Patent Application Laid-Open No. 4-195188 discloses a gradation driving method for a flat display device using a subfield method as shown in FIG. In this method, one field is divided into five subfields SF0 each including a pair of an address period and a light emitting period.
~ SF4, and controlling the presence / absence of light emission in each subfield, thereby expressing the gradation of luminance. The ratio of the light emission amount in the light emission period of each subfield is made to match the weight of the binary code, and each bit of the input digital data is made to correspond according to the light emission weight.

[0004]

In such a conventional gradation display method using the subfield method, an object having a gradual gradation change is displayed, and when the object moves, an outline is formed at a gradation change point. The disturbance referred to as "pseudo-contour noise" is perceived. Such pseudo contour noise causes noise on the contour to be superimposed on a face, skin, or the like when a person moves, resulting in remarkable image quality deterioration.

As a method of improving the quality of a moving image by reducing such pseudo contour noise, for example, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 211294 discloses a method of dividing and displaying several bits out of the most significant bit or the most significant bit of the gradation expression by the subfield method.

However, even if this method is used, the reduction of the pseudo contour noise is not sufficient, and there is a problem that the effect of improvement is small, especially for fast moving images.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problem, and to provide a method for displaying a gradation of a video signal for a moving image, which can greatly reduce the image quality deterioration due to the pseudo contour noise. The present invention is to provide a display device that has been used.

[0008]

In order to achieve the above-mentioned object, the present invention provides a method of expressing gradation by using a plurality of upper sub-fields having the largest emission weight and a lower sub-field having an emission weight ratio of a power of two. Is performed.

Further, when displaying a gray scale in which a part of a plurality of upper sub-fields having the same light emission weight emit light, 1
Two types of light emission patterns are provided: a light emission pattern A that allocates a subfield that emits light from a temporal first half of a field and a light emission pattern B that assigns a subfield that emits light from a second half of a field. Are alternately arranged so as not to be continuous with adjacent pixels in space and time.

The arrangement of the upper sub-fields having the same light-emission weight is equally divided so that the center of gravity of the light-emission is almost at the center when all the upper sub-fields emit light.
.. Are arranged in the first half of one field and the other half are arranged in the second half of one field, and when divided into an odd number of 1, 3, 5,. Are arranged almost at the center, and the remaining even numbers are divided into the first half and the second half of one field.

In addition, in the lower sub-field in which the equal division is not performed into a plurality of sub-fields, when all the gradations which can be expressed by the combination of the light emission in the lower sub-field are displayed, the temporal center of gravity of the light emission has little variation. It is arranged so that it becomes. Specifically, they are arranged so as to monotonously decrease before and after a subfield having a large emission weight. Alternatively, they are arranged so as to monotonously decrease before and after about one of the upper subfields divided into odd numbers.

Alternatively, the configuration of the upper subfield is
The configuration is such that the emission weights of subfields corresponding to the most significant bits or the most significant bits including the most significant bits are summed up and divided equally into a plurality of subfields.

Further, the arrangement of the lower subfields is temporally reversed for each field.

[0014]

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

FIG. 1 is a block diagram showing a first embodiment of a display device using a gradation display method of a video signal according to the present invention, wherein 1R, 1G and 1B are A / D (analog / digital) conversion. Circuit, 2 is a subfield conversion circuit, 3 is a subfield sequential conversion circuit, 3A is a frame memory,
4 is a drive circuit, 5 is a matrix display panel,
6 is a control circuit.

In FIG. 1, A / D conversion circuits 1R, 1R
G and 1B respectively convert each color signal of the input analog video signal, that is, R, G and B signals into digital signals. The subfield conversion circuit 2 includes A / D conversion circuits 1R, 1G,
The binary digital R, G, B signals output from 1B are converted into subfield data indicating the presence or absence of light emission in the subfield. The sub-field sequential conversion circuit 3 converts the sub-field data, which is expressed in pixel units from the sub-field conversion circuit 2, into a field-sequential format in sub-field units. The subfield sequential conversion circuit 3 is provided with a frame memory 3A for realizing frame sequential in bit units. The drive circuit 4 additionally inserts a pulse necessary for driving the display device into the signal converted into the field sequential format in the unit of subfield, and converts the signal into a voltage (or a current) for driving the display device. The matrix display panel 5 is driven by the drive circuit 4 and performs display by gradation expression by a subfield method. The control circuit 6 generates a control signal necessary for each block from the dot clock CK, the horizontal synchronization signal H, the vertical synchronization signal V, etc., which are timing information of the input video signal.

Next, the operation of the first embodiment will be described.

The input R, G, B signals are converted into digital signals by A / D conversion circuits 1R, 1G, 1B, respectively. These digital signals are based on general binary notation, and each bit has a power of two weight. Specifically, when quantizing into an 8-bit signal of b0, b1,..., B6, b7, the least significant bit b0 is 2 bits.
⁰ = 1 has a weight, the weight of the bit b1 is 2 ¹ = 2, the weight of the bit b2 is ² 2 = 4, the weight of the bit b3 is 2 ³ = 8, ..., bit b7 is 2 ⁷ = 128.

These digital signals are converted by the subfield conversion circuit 2 into subfield data indicating the presence or absence of light emission in the subfield. This subfield data is composed of information on the number of bits corresponding to the number of subfields to be displayed. When one field is displayed by nine subfields SF0, SF2, SF3,. Bit S in SF0
.., S7,..., S7, and S8 such that bit S1 corresponds to subfield SF1 and bit S8 corresponds to subfield SF8. The bit S0 indicates whether or not the pixel emits light during the light emission period of the first subfield SF0.
.. Correspond to the presence or absence of light emission in the subfields SF1, SF2,.

The subfield data is supplied to the subfield sequential conversion circuit 3, and is written in a frame memory 3A provided in the subfield sequential conversion circuit 3 in pixel units. Reading from the frame memory 3A is performed in a frame-sequential manner on a subfield basis. That is, the bit S0 indicating the presence or absence of light emission in the subfield SF0 is 1
After reading for the field, a bit S1 indicating whether or not light emission is performed in the subfield SF1 is read.
By reading the bits S2, S3,..., S8 in this order, a subfield is formed, and signal conversion and pulse insertion necessary for driving the display element by the drive circuit 4 are performed. The matrix display panel 5 is driven.

FIG. 3 is a diagram showing a subfield configuration in the first embodiment of the video signal gradation display method according to the present invention used in the display device shown in FIG. FIG. 8 shows a specific example of the arrangement order of fields and the assignment of emission weights in each subfield.
Here, a case is shown in which digital data of an input video signal quantized by 8 bits is expressed in gradations by 9 subfields.

In this figure, in this specific example, the emission weight of the subfield SF0 at the head of the field is 64, 2
The emission weight of the first subfield SF1 is 1, the emission weight of the third subfield SF2 is 4, the emission weight of the fourth subfield SF3 is 16, the emission weight of the fifth subfield SF4 is 64, and the sixth The emission weight of subfield SF5 is 32, and the seventh subfield SF
The emission weight of the sixth subfield SF8 is set to 8, the emission weight of the eighth subfield SF7 is set to 2, and the emission weight of the ninth subfield SF8 is set to 64.

In FIG. 3, S0, S1,...
S8 is each subfield SF0, SF of the subfield data obtained by the subfield conversion circuit 2 (FIG. 1).
,..., SF8, and these bits control whether or not each subfield emits light with the emission weight.

Next, the operation when signals of each gradation are input will be described.

Here, in order to make the description easy to understand, a plurality of subfields having the largest emission weight are called upper subfields, and the other subfields having an emission weight ratio of a power of 2 are called lower subfields. I will. In FIG. 3, the subfields SF0, SF
4 and SF8 are upper subfields, and the remaining six subfields SF1, SF2, SF3 and SF
5, SF6 and SF7 are lower subfields.

The gradation of the input video signal is 63 (= 2 ⁶ -1)
In the following case, the six lower subfields SF1, S
F2, SF3, SF5, SF6, and SF7 are controlled to emit light to perform gradation display. The light emission weights of these six lower subfields are formed by powers of two, and the lower bits of the digital data of the input video signal can be associated one-to-one.

The gradation of the input video signal is 64 (= 2 ⁶ ) to 1
27 (= 2 ⁷ -1), the upper subfield S
Any one of F0, SF4, SF8 and six lower subfields SF1, SF2, SF3, SF5, SF6
The gradation expression is performed in combination with SF7.
8 (= 2 ⁷ ) to 191 (= 2 ⁷ +2 ⁶ -1), any two of the upper subfields SF0, SF4, SF8 and the six lower subfields SF1, SF2, S
F3, SF5, SF6, and SF7 are combined to perform gradation expression, and 192 (= 2 ⁷ +2 ⁶ ) to 255 (=
In the gray scale of 2 ⁸ ), three upper sub-fields SF0, SF0,
SF4, SF8 and six lower subfields SF1, S
The gradation expression is performed in combination with F2, SF3, SF5, SF6, and SF7.

Further, upper subfields SF0, SF
When one or two of SF4 and SF8 emit light (grayscale is 128 to 191), a desired grayscale can be obtained by emitting any of the upper subfields. In order to make pseudo contour noise difficult to perceive,
Light emission pattern A that concentrates light emission in the first half of the field
And a light emission pattern B for concentrating light emission in the latter half of one field are arranged so as to be alternately arranged in the vertically and horizontally adjacent pixels in the screen and to be inverted in the field.

FIGS. 4A and 4B are diagrams showing the outline of the switching of the light emission pattern. FIG. 4A shows the switching of the light emission pattern of the odd field, and FIG. 4B shows the switching of the light emission pattern of the even field. A in the drawing indicates a light emitting pattern A, and B indicates a pixel that emits light in the light emitting pattern B.

As shown in the figure, the checker flag pattern in which the light emission patterns are switched between adjacent pixels in the vertical and horizontal directions is a switching pattern that is inverted for each field.

FIG. 5 is a light emission pattern list showing a specific example of the gradation display by the subfield structure shown in FIG. 3, and the left half of FIG. 5 shows the light emission pattern A shown in FIG.
The right half surface similarly shows the light emission pattern B, and the light emission of the subfield at each gradation is indicated by a circle.

In the figure, for gradations 1 to 63,
The upper subfield does not emit light. For the gradations 64-127, in the light emission pattern A, the first subfield SF0 emits light as the upper subfield, and in the light emission pattern B, the last subfield SF8 emits light as the upper subfield. Similarly, gradations 128 to 19
On the other hand, in the light emitting pattern A, the upper two subfields SF0 and SF4 emit light as the upper subfield, and in the light emitting pattern B, the upper two subfields SF8 and SF4 emit light as the upper subfield. I do.

The pseudo contour noise which is a problem in the gradation expression method by the subfield method is such that when the binary representation of the digital data of the video signal is output as a subfield from the least significant bit or the most significant bit as it is, the gradation is reduced. It is known that it occurs intensely at a transition point from 127 to gradation 128 (or vice versa). This is because the state in which one subfield having a weight of 128 emits light and the gradation 128 is displayed is switched from the state in which all seven subfields corresponding to the lower 7 bits emit light and the gradation 127 is displayed. It is considered that the temporal center of the light emission in one field is largely shifted.

[0034] In an image perceived when a line of sight is followed by a moving object, a subfield that emits light with a delay in time tends to be perceived as being shifted to a position in the opposite direction to the motion, even for the same pixel. is there. Since the temporal center of light emission by the subfield of the display pixel indicates the average delay time of pixel emission, if this delay time is the same as that of an adjacent pixel, the amount of displacement due to movement becomes almost constant, and the overall shift occurs. Doing so will not be a major hindrance. However, when a large shift occurs in the temporal centroid of light emission between adjacent pixels, a phenomenon occurs in which adjacent pixel data is mixed in units of bits (subfields), and gradation disturbance occurs as a pseudo contour.

When the emission weight of the subfield has a power-of-two ratio, in order to suppress the fluctuation of the emission center of gravity, a subfield corresponding to the upper bit having a large emission weight is arranged at the center of the field. The arrangement may be such that the light emission weight decreases as the distance from the center increases. Specifically, the arrangement of the subfields having the binary emission weights of 1: 2: 4: 8: 16 is 1: 4: 1.
6: 8: 2 or 1: 2: 16: 8: 4, 1: 8: 16:
4: 2, or these inverted arrangements,
By arranging them so as to monotonously decrease before and after the subfield having a large emission weight, fluctuations in the center of emission can be suppressed, and pseudo contour noise can be reduced.

Further, the magnitude of the pseudo contour noise is determined by the amount of light emission mixed with adjacent pixels. Specifically, assuming a process of generating the largest disturbance, this is caused by whether a bit (sub-field) having a large emission weight is mixed in or dropped out of an adjacent pixel, and the digital signal of a video signal quantized by 8 bits is generated. If the binary representation of the data is output as a subfield as it is, a maximum of 128
Level disturbance occurs. In other words, by reducing the light emission weight that emits light in one subfield, there is an effect of suppressing the interference amount of the pseudo contour noise.

According to the subfield configuration method of this embodiment shown in FIG. 3, gradations 0 to 63 and 192 to 25
In the case of No. 5, the variation of the light emission center of gravity is determined by the arrangement of the lower subfields depending on whether the upper subfield does not emit light at all or emits all light. As described above, the lower subfield is arranged such that the sub-yield having a large emission weight is the center of the field and the emission weight decreases as the distance from the center increases, so that the emission time is reduced. The variation can be reduced by aligning the center of gravity substantially at the center, and the occurrence of a false contour can be suppressed.

In gradations 64 to 191, the light emission center of gravity is largely changed by switching the light emission pattern of the upper subfield between adjacent pixels. In addition, one of the three upper sub-fields is arranged almost at the center, and the other two are arranged at the beginning and end of one field, so that the fluctuation due to the change of the light emission pattern of the light emission center of gravity can be almost covered. it can.

By this processing, the pseudo contour noise generated in the adjacent pixel and the next field is generated in a form in which the brightness is inverted in a well-balanced manner. Even when the horizontal and vertical spatial frequencies are high and the time frequency is inverted for each field,
A component having a high frequency is a signal in an area that is most difficult to perceive in terms of human visual characteristics, so that false contour noise can be made less noticeable, and image quality degradation can be reduced. further,
By equally dividing the upper subfield into a plurality,
The amount of light emission in one subfield can be reduced to 64 at the maximum, which has the effect of suppressing the magnitude of the generated pseudo contour noise.

Next, a specific example of a main part constituting this embodiment shown in FIG. 1 will be described.

FIG. 6 is a circuit diagram showing a part of a specific example of the control circuit 6 in FIG.
This is an XOR (exclusive OR) circuit.

In the figure, an EXOR circuit 601 is supplied with a field inversion signal FI which is inverted for each field and a line odd / even signal VL indicating an odd / even line number of an input video signal. Also, EXOR 602 is EXO
The output signal of the R circuit 601 and the dot odd / even signal HD indicating the odd / even number of the horizontal dot number of the input video signal are supplied, and the light emitting pattern selection signal ABSL is output.

Here, the field inversion signal FI is "H" (high level) for each field of the input video signal,
The line odd / even signal VL is a signal that repeats “L” (low level) and level inversion. The line odd / even signal VL is a signal that becomes “H” when the line number of the input video signal is odd and “L” when the line number is even. It consists of the least significant bit of the count value of the line counter provided in the control circuit 6 (FIG. 1). Also,
The dot odd / even signal HD is a signal that becomes “H” when the horizontal dot number of the input video signal is odd and “L” when the horizontal dot number is even, and is the lowest count value of the horizontal dot counter provided in the control circuit 6. It consists of bits. Further, the light emission pattern selection signal ABSL is one of the control signals output from the control circuit 6 to the subfield conversion circuit 2 (FIG. 1), and is “L” when the light emission pattern of the upper subfield is “A”. This is a logic signal which becomes "H" at this time.

Then, by the operation of the EXOR circuits 601 and 602, the inversion is carried out for each field and for each line.
Further, a light emitting pattern selection signal ABSL as shown in FIGS. 4A and 4B that is inverted for each dot is generated, and FIG.
Is supplied to the sub-field conversion circuit 2.

FIG. 7 is a circuit diagram showing a specific example of the subfield conversion circuit 2 in FIG. 1. In FIG. 7, reference numeral 201 denotes a combinational logic circuit, and b0, b1, b2, b3,. Bits constituting digital data supplied from the A / D conversion circuit 1R, 1G or 1B.
b0 is the least significant bit and b7 is the most significant bit.

In the figure, digital data is supplied from the above-described A / D conversion circuit, and a light emission pattern selection signal ABSL is supplied from the control circuit 6 shown in FIG. And the light-emission pattern selection signal ABSL are supplied.

The subfield conversion circuit 2 outputs subfield data consisting of bits S0, S1, S2,..., S8, and supplies it to the subfield sequential conversion circuit 3 in FIG. Here, bits S0, S1,
S2,..., S8 are subfields SF0, SF, respectively.
, SF8,..., SF8. Between the digital data and the subfield data of the input video signal, the lower 6 bits of the digital data are assigned to the subfield SF of the lower subfield.
1, SF2, SF3, SF5, SF6, SF7, b0-S1, b1-S7, b2-S2, b3-S
6, b4-S3, b5-S5, whereby the bits b0, b1, b2, b3, b4, b5 are directly set in the bits S1, S7,.
S2, S6, S3, and S5. The upper two bits b6 and b7 of the digital data and the light emitting pattern selection signal ABSL are supplied to the combinational logic circuit 201,
Subfields SF0, SF4 of the upper subfield
Bit S0 of the subfield data corresponding to SF8,
S4 and S8 are generated.

FIG. 8 shows a truth table of the operation of the combinational logic circuit 201, wherein the gradation of the input video signal is 6
From 4 to 127, {b6, b5} = {0, 1}, the bit S0 or S8 becomes “H”, and the gradation 128
~ 191, {b6, b5} = {1, 0}
It is confirmed that the light emission pattern is switched by the light emission pattern selection signal ABSL so that the bits S0 and S4 or the bits S4 and S8 become "H".

With such a configuration of the subfield conversion circuit 2, digital data from the A / D conversion circuits 1R, 1G, and 1B can be converted into subfield data by a simple combinational logic circuit 201.

It should be noted that the configuration shown in FIG.
Although only one of the system signals is shown, the subfield conversion circuit 2 of FIG. 1 has the same configuration for each of the three systems.

With the configuration described above, it is possible to reduce image quality deterioration due to pseudo contour noise, and to realize a display device with high image quality.

In the configuration shown in FIG. 1, each of the color signals R, G, and B of the input analog video signal is converted into digital data by the A / D conversion circuits 1R, 1G, and 1B, respectively. Each of the input color signals R, G, B may be a digital signal. In this case, of course, the A / D conversion circuits 1R, 1G, and 1B become unnecessary, and such digital signals input from the outside are directly supplied to the subfield conversion circuit 2.

In this embodiment, the subfield conversion circuit 2 is constituted by the combinational logic circuit 201 as shown in FIG. 7 in order to reduce the circuit scale. However, a ROM (read only memory) is used. May be configured to obtain subfield data from digital data of an input video signal. At this time, in the configuration shown in FIG. 7, only the part of the logic circuit 201 for generating the bits of the subfield data for the upper subfield may be realized by a look-up table. A configuration may be used in which the data is generated by a look-up table using a ROM, and is converted into subfield data simultaneously with the process of reversely correcting the gamma characteristic of the input video signal.

In the above embodiment, the input video signal is quantized by 8 bits, and the gradation is expressed by using 9 subfields. However, the present invention is not limited to this. When the number of subfields is one greater than the number of bits of digital data of the input video signal, a similar circuit and subfield configuration can realize a gradation display method in which pseudo contours are less noticeable. . For example, the number of quantization bits of the video signal may be 6, and the number of subfields may be 7. In this case,
Convert the lower subfield from 6 bits to 4 bits,
For the subfields corresponding to the least significant two bits that have been deleted, this time may be shortened to increase the time distribution within one field of each subfield. When displaying a video signal quantized to 9 bits in 10 subfields,
The lower sub-field is changed from 6 bits to 7 bits, and the sub-field corresponding to the added least significant 1 bit is changed to sub-fields SF7, S so that the time variation of light emission is reduced.
What is necessary is just to arrange between F8 and change the time distribution within one field of each subfield.

The gradation display method based on the subfield arrangement shown in FIG. 3 uses a number of subfields obtained by adding 1 to the number of quantization bits of the input video signal and a plurality of upper subfields having the largest light emission weight. The gray scale is expressed by lower subfields having a light-emitting weight ratio of a power of two. Next, without using all 256 gray scales represented by the input video signal quantized to 8 bits, ,
A second embodiment of the video signal gray scale display method according to the present invention in the case of performing gray scale expression in 9 subfields using only 160 gray scales of gray scales 0 to 159 will be described with reference to FIGS. I do.

FIG. 9 is a diagram showing the arrangement order of subfields in one field and the assignment of the emission weight of each subfield in the second embodiment.

In the figure, when image data (corresponding to 7.3 bits) of gradations 0 to 159 out of gradations 0 to 255 of a video signal quantized by 8 bits is expressed by 9 subfields, As shown in the figure, in one field, the emission weight of the first subfield SF0 is 32, 2
The emission weight of the third subfield SF1 is 32, the emission weight of the third subfield SF2 is 1, the emission weight of the fourth subfield SF3 is 4, and the emission weights are 16, 8, 2, 32, 32.

Also, S0, S1,..., S8 correspond to the bits of the subfield data converted by the subfield conversion circuit 2 in FIG. 1, and the bits emit light with the respective weights. Is controlled.

In this subfield arrangement, four subfields SF0, SF1, SF7,
SF8 is the upper subfield, and the remaining five subfields SF2, SF3, SF4, SF5, SF6
Is a lower subfield, and corresponds to the lower 5 bits of digital data of the input video signal on a one-to-one basis. Specifically, the lower bits b0, b of this digital data
B0-S2, b1-S for 1, b2, b3, b4
6, b2-S3, b3-S5, and b4-S4 are set by the subfield conversion circuit 2 in FIG.
Also, bits S0, S1, S7,
At S8, subfield conversion is performed by the combinational logic circuit having the input / output characteristics of the truth table shown in FIG. 10 from the upper three bits b7, b6, b5 of the digital data of the input video signal and the light emitting pattern selection signal ABSL. . The specific circuit configuration for converting the data into the subfield data is substantially the same as that shown in FIG. 7, and bits S2, S6, S3 of the lower subfield corresponding to the lower bits of the digital data of the input video signal on a one-to-one basis. , S5, and S4 are assigned the lower bits directly, and the bits S0, S1, S7, and S8 for the upper subfield are generated by a combinational logic circuit. Further, the light-emission pattern selection signal ABSL is generated by the control circuit 6 shown in FIG.

With the subfield configuration shown in FIG. 9, the emission weight of the subfield having the largest emission weight is 32, which is smaller than the maximum emission weight 64 of the subfield configuration shown in FIG. This has the effect of further suppressing the amount of interference.

Further, gradations 0 to 31 and gradations 128 to 159
In the case of, the center of gravity of the light emission is aligned substantially at the center, the fluctuation is reduced, and the occurrence of the false contour can be suppressed. In the gradations 32 to 127, the light emission center of the upper subfield arranged at the head of the field and the light emission pattern of the upper subfield arranged at the end of the field are switched between adjacent pixels, so that the light emission center of gravity becomes large and fluctuates. The pseudo contour noise generated in the adjacent pixel and the next field is generated in a well-balanced manner in which the brightness is inverted. This makes it possible to make the generated pseudo contour noise less noticeable.

In the subfield structure shown in FIG. 9, since the maximum luminance that can be expressed is 159 gradations, it is necessary to limit the level of the input video signal to 159 gradations. More specifically, the A / D conversion circuit 1R shown in FIG.
When an analog signal of the maximum luminance, which is assumed to be a digital output of 1G and 1B, is input, the number of gradations may be converted to 159, or FIG.
The digital outputs of the A / D conversion circuits 1R, 1G, and 1B shown in (1) are configured to convert up to an 8-bit full-scale gradation 255, and use a coefficient circuit that converts the data value to 0.625 (= 160/256) times. May be converted. Alternatively, the process of inversely correcting the gamma characteristic of the input video signal and the process of converting the subfield data, and further, all of the coefficient calculation process and the gradation upper limit process are performed by one.
A configuration realized by a conversion circuit using two lookup tables may be used.

Further, in the embodiment shown in FIG. 9, the input video signal is quantized by 8 bits and the gradation up to 159 is expressed by using 9 subfields. By omitting the lower bits, a gray scale display method in which pseudo contours are similarly inconspicuous can be realized even if the number of input bits and the total number of subfields are reduced. For example, when a video signal having a quantization bit number of 6 and a gradation up to 39 (full scale 63) is displayed with a subfield number of 7, the lower subfield is changed from 5 bits to 3 bits, and the least significant 2 bits are deleted. In the corresponding subfield, this time may be reduced to increase the time distribution within one field of each subfield. At this time, the emission weights are 8:
8: 1: 4: 2: 8: 8.

Next, a gradation according to the present invention in the case where gradation is expressed in 10 subfields using 192 gradations of gradations 0 to 191 of 256 gradations of an input video signal quantized by 8 bits. A third embodiment of the tone display method will be described with reference to FIGS.

FIG. 11 is a diagram showing the arrangement order of subfields in one field and the assignment of light emission weights in each subfield in the third embodiment, wherein 256 bits of an input video signal quantized by 8 bits. Gradation 0-1
This figure shows a case where image data of 91 (corresponding to 7.6 bits) is expressed in gradation by 10 subfields.

In this figure, the emission weight of the first subfield SF0 of one field is 32, the emission weight of the second subfield SF1 is 32, and the emission weight of the third subfield SF2 is 1st and 4th. It is assumed that the emission weight of the subfield SF3 is 4, and the emission weight is 16, 32, 8, 2, 32, and 32 in the following order, and one field is composed of 10 subfields.

Further, S added to each subfield
.., S9 are bits of subfield data converted by the subfield conversion circuit 2 of FIG. 1 corresponding to the subfield to which the subfields are attached. Whether or not to emit light is controlled by the emission weight.

In such a subfield arrangement, five subfields SF0, SF1, SF5,
SF8 and SF9 are upper subfields, and the remaining 5
Subfields SF2, SF3, SF4, SF6
SF7 is the lower subfield, and the lower 5 bits of the digital data of the input video signal correspond to the bits of the subfield data accompanying these lower subfields on a one-to-one basis. Specifically, the lower 5 bits b0, b1, b2, b3, b of the digital data of the input video signal
For b4 and b5, b0-S2, b1-S7, b2-S
3, b3−S6, b4−S4, so that the subfield conversion circuit 2 of FIG. 1 performs such conversion as described above. The bits S0, S1, S5, S8, S9 of the upper subfield are the upper three bits b7, b6, b5 of the digital data of the input video signal and the light emitting pattern selection signal A, as in the previous embodiments.
It is obtained from the BSL by a combinational logic circuit having the input / output characteristics of the truth table shown in FIG. The specific circuit configuration of the subfield conversion circuit 2 for converting the digital data of the input video signal into subfield data is substantially the same as that shown in FIG. 5 bits S of the subfield data for the corresponding lower subfield
2, S7, S3, S6, and S4 are directly obtained from the five lower bits of the digital data of the input video signal, and the five bits S0, S1, S5, S8, and S9 of the subfield data for the upper subfield are: Upper 3 bits b7, b6, b5 of digital data of input video signal
And a light emission pattern selection signal ABSL, which is generated by a combinational logic circuit. Also, the light emitting pattern selection signal ABS
L is generated by the control circuit 6 shown in FIG. 6, similarly to the above embodiment.

With the subfield configuration shown in FIG.
The light-emitting weight of the subfield having the largest light-emitting weight is 32, which has the effect of further suppressing the amount of false contour interference as in the embodiment shown in FIG.

Further, gradation 0 to 31 and gradation 160 to 191
In the case of, the center of gravity of the light emission is aligned substantially at the center, the fluctuation is reduced, and the occurrence of the false contour can be suppressed. In the gradations 32 to 159, the light emission center of the field is increased by switching the light emission pattern of the upper subfield arranged at the center of the field, two at the beginning of the field, and two at the end of the field between adjacent pixels. In addition, the pseudo contour noise generated in the adjacent pixel and the next field is generated in a well-balanced manner in which the light and shade are inverted with respect to each other. This makes it possible to make the generated pseudo contour noise less noticeable.

In the subfield configuration shown in FIG. 11, it is necessary to limit the level of the input video signal to gradation 191 as in the subfield configuration shown in FIG.

Further, in the embodiment shown in FIG. 11, the signal up to the gradation 191 obtained by quantizing the input video signal by 8 bits is expressed by using 10 subfields, but the lower sub By omitting the field and the corresponding lower-order bits, it is possible to realize a gradation display method in which the pseudo contour is similarly inconspicuous even if the number of input bits and the total number of subfields are reduced. For example, when displaying a video signal having a quantization bit number of 6 and a gradation of 47 (full scale 63) with a subfield number of 8, the lower subfield is changed from 5 bits to 3 bits, and the least significant 2 bits are deleted. In the corresponding subfield, this time may be reduced to increase the time distribution within one field of each subfield. At this time, the emission weights are 8: 8: 1: 4: 8: 2: 8: 8 in the order of the subfields.

Further, in the embodiment shown in FIG.
Although 0 subfields are used to represent 192 gradations of gradations 0 to 191 out of 256 gradations of the input video signal quantized by 8 bits, the upper subfields are further increased, and The number of expressible gradations may be increased. For example, the number of upper sub-fields may be 6, and gradation 0 to 224 (= 192 + 32) may be expressed. In this case, the arrangement of the sub-fields is as shown in FIG.

As described above, the number of upper subfields is even (SF0, SF1, SF2, SF8, SF9, SF
In the case of 10), the lower sub-field may be arranged substantially at the center, half of the upper sub-field may be arranged at the head of the field, and the other half of the upper sub-field may be arranged at the tail of the field. In this case, the lower subfields are arranged such that the emission weight decreases with increasing distance from the center, with the subfield having the largest emission weight among the lower subfields.

When the number of upper sub-fields is odd, one of the upper sub-fields is arranged substantially at the center of the field, and the emission weight decreases as the distance from the center upper sub-field increases. To
Place the lower subfield. Further, half of the remaining upper subfields are arranged at the head of the field, and the other half are arranged at the tail of the field.

With the above-described configuration, the variation of the light-emission centroid between the gray scale in which only the lower sub-field emits light without emitting light in the upper sub-field and the gray scale in which all upper sub-fields emit light is suppressed. Can be reduced. In a gray scale where a part of the upper sub-field emits light, the light emission center can be switched almost symmetrically for each adjacent pixel and field by switching the light emission pattern. As a result, it is possible to suppress the occurrence of pseudo contour noise or to make the pattern hard to be perceived, and to perform high-quality gradation expression.

In the third embodiment of the gradation display method shown in FIG. 11, 10 subfields are used for gradation display and 8 gradations are displayed.
Of the 256 gradations of the input video signal quantized by bits, 192 gradations of gradations 0 to 191 were expressed.
A fourth embodiment of the video signal gradation display method according to the present invention when up to 5 can be expressed will be described with reference to FIG.

FIG. 13 is a diagram showing the arrangement order of subfields in one field and the assignment of light emission weights in each subfield in the fourth embodiment, and shows the digital data of a video signal quantized to 8 bits. Is represented by 10 subfields.

The subfield configuration shown in FIG. 3 adds the weight 128 of the most significant bit b7 of the digital data of the video signal quantized to 8 bits and the emission weight of the weight 64 of the next bit b6 ( 128 + 64 = 192),
This is equally divided into three upper subfields (192/3
= 64), the subfield configuration shown in FIG. 13 has a weight 128 of the most significant bit b7 of the digital data of the video signal quantized by 8 bits and a weight 64 of the next bit b6. The light emission weights are added together (1
28 + 64 = 192), which can be regarded as being equally divided (192/4 = 48) into four upper subfields. By dividing the weights of the two bits b7 and b6 into four upper subfields, the number of subfields is increased by two with respect to the number of input bits.

In FIG. 13, in this embodiment, one field has a light emission weight of the first subfield SF0 of 48, a light emission weight of the second subfield SF1 of 48, and a light emission weight of the third subfield SF2. 1,
The light emission weight of the fourth subfield SF3 is set to 4, and the light emission weight is set to 16, 32, 8, 2, 48, and 48 in the following order, and is constituted by 10 subfields. Also, S
, S9 are subfields S of the subfield data obtained by the subfield conversion circuit 2 of FIG.
These bits correspond to F0, SF1,..., SF9,
This bit controls whether or not to emit light with each emission weight.

In the subfield arrangement shown in FIG.
Four subfields SF0, SF1,
SF8 and SF9 are upper subfields, and the remaining 6
Subfields SF2, SF3, SF4, SF5
SF6 and SF7 are lower subfields.

In all of the embodiments described above, the emission weights of the subfields have a power-of-two weight, and the lower subfields correspond to the lower bits of the digital data of the input video signal on a one-to-one basis. Figure 7 on the field
However, in the fourth embodiment shown in FIG. 13, the emission weight of the upper subfield is 48, which is not a power of two. In such a case, conversion into subfield data can be performed by the following method.

When the gradation of the input video signal is 191 or less,
The value of the digital data is divided by 48 to obtain its quotient Q and remainder R (0 ≦ Q ≦ 3, 0 ≦ R ≦ 47). The emission weight corresponding to the remainder R is emitted in the lower subfield, and the upper subfield is emitted according to the number of quotients Q. At this time, the subfields that emit light are allocated in the order of the subfields SF0, SF1, and SF8 if the light emitting pattern selection signal ABSL is “L”, and if the light emitting pattern selection signal ABSL is “H”, the subfields are allocated. The configuration may be such that fields SF9, SF8, and SF1 are performed in this order.

When the gradation of the input video signal is 192 or more,
A light emission weight corresponding to a value obtained by subtracting 192 from the value of the digital data is caused to emit light in the lower subfield, and light is emitted in all upper subfields.

According to the subfield structure shown in FIG.
The light-emitting weight of the subfield having the largest light-emitting weight is 48, which has an effect of suppressing the amount of false contour interference as compared with the conventional binary-weight light-emitting weight.

Further, gradations 0 to 47 and 192 to 255
In this case, the temporal center of the light emission is aligned substantially at the center of the field to reduce the fluctuation and suppress the generation of the false contour. In gradations 48 to 191, the light emission center of the upper subfield, which is arranged at the head of the field and two at the end of the field, is switched between adjacent pixels, so that the center of light emission is changed to a large value and a target. Pseudo-contour noise generated in adjacent pixels and in the next field is generated in a well-balanced manner in which light and dark are inverted from each other,
This makes it possible to make the generated pseudo contour noise less noticeable.

Further, in the subfield configuration shown in FIG. 13, since the gradation of all 8 bits of the input video signal can be expressed, the conversion of the level of the input video signal and the restriction processing are not required.

Further, in the embodiment shown in FIG.
Although the input video signal quantized by bits is used to express gradation using 10 subfields, the number of input bits and the total number of subfields can be reduced by omitting the lower subfields and the corresponding lower bits. Even if you reduce
Similarly, it is possible to realize a gradation display method in which a pseudo contour is less noticeable. For example, when a video signal having 6 quantization bits is displayed with 8 subfields, the lower subfield is changed from 6 bits to 4 bits, and the subfield corresponding to the deleted 2 least significant bits shortens the time. Thus, the time distribution within one field of each subfield may be increased. At this time, the emission weights are 12: 12: 1: 4: 8: 2: 12: 12 in the order of subfields. The subfield conversion method in this case is as follows.

That is, when the digital data of the input video signal has a gradation of 47 or less, the value of this digital data is set to 12
To obtain its quotient Q and remainder R (0 ≦ Q ≦ 3,
0 ≦ R ≦ 11). The emission weight corresponding to the remainder R is emitted in the lower subfield, and the upper subfield is emitted according to the number of quotients Q. At this time, the subfields that emit light are assigned to the subfields SF0, SF1, and SF if the light emission pattern selection signal ABSL is “L”.
8 and if the light emitting pattern selection signal ABSL is “H”, the subfields SF9, SF8, SF
1 may be performed in this order.

If the gradation of the input video signal is 48 or more, a light emission weight corresponding to a value obtained by subtracting 48 from the value of the digital data is caused to emit light in the lower subfield, and all upper subfields emit light. Good.

In the above configuration example, the light emission center of the upper subfield is changed by the light emission pattern selection signal ABSL. However, the arrangement of the subfields uses the same pattern in each field. This may be configured such that the temporal arrangement is inverted for each field only in the lower subfield. Specifically, the configuration is such that a subfield arrangement as shown in FIG. 15 in which the emission weight arrangement of the lower subfield is inverted in terms of weighting time with respect to the subfield arrangement shown in FIG.
For each field, the even field outputs the subfield configuration shown in FIG. 3, and the odd field outputs the subfield configuration shown in FIG. As described in the above embodiments, the light emission pattern of the upper subfield is switched in the same manner.

By the above-described processing, a change in the center of light emission due to light emission / non-light emission in the lower subfield substantially occurs in each field, and the remaining pseudo contour pattern can be flickered. As a result, the slightly remaining pseudo contour noise can be made less noticeable.

In the figures showing the embodiments described so far, each subfield has a time occupancy rate proportional to the light emission weight. However, in practice, the subfields are as shown in FIG. When the time occupancy of the address period is high, the light emission intervals of the subfields may be substantially equal. Alternatively, a display element that divides one field into a plurality of sub-fields and performs gradation expression, even if the display element does not control the light emission amount by changing the number of pulses having a constant light emission amount or the light emission time during the light emission period. If so, the gradation display method of the present invention can reduce image quality deterioration due to pseudo contour noise. Also, as shown in FIG. 1, in the driving method in which the address period and the light emission period are not separated and the light emission is sequentially performed by the subfield while performing the address processing, the subfield configuration is sequentially temporally shifted according to the vertical scanning. However, even such a display method is in accordance with the gist of the present invention.

[0094]

As described above, according to the present invention,
Even in a fast-moving image, image quality degradation due to pseudo contour noise can be reduced, and a high-quality image can be obtained.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram of a conventional gradation expression method using a subfield method.

FIG. 3 is a diagram showing a subfield configuration in a first embodiment of a video signal gradation display method according to the present invention.

FIG. 4 is a diagram for explaining light emission pattern switching in a video signal gradation display method according to the present invention.

FIG. 5 is a diagram showing a light emission pattern list at the time of gradation display by the subfield configuration shown in FIG. 3;

6 is a circuit configuration diagram showing a specific example of a light emission pattern selection signal ABSL generation circuit in the control circuit in FIG. 1;

FIG. 7 is a block diagram illustrating a specific example of a subfield conversion circuit in FIG. 1;

8 is a diagram showing a truth table of the combinational logic circuit in FIG. 7;

FIG. 9 is a diagram showing a subfield configuration in a second embodiment of the video signal gradation display method according to the present invention.

10 is a diagram showing a truth table of a combinational logic circuit when realizing the subfield configuration shown in FIG. 9;

FIG. 11 shows a third method of displaying a gradation of a video signal according to the present invention.
FIG. 10 is a diagram showing a subfield configuration in the embodiment.

12 is a diagram showing a truth table of a combinational logic circuit when realizing the subfield configuration shown in FIG. 11;

FIG. 13 shows a fourth method of displaying a gradation of a video signal according to the present invention.
FIG. 10 is a diagram showing a subfield configuration in the embodiment.

FIG. 14 is a fifth embodiment of the video signal gradation display method according to the present invention;
FIG. 10 is a diagram showing a subfield configuration in the embodiment.

FIG. 15 shows a sixth embodiment of the video signal gradation display method according to the present invention.
FIG. 10 is a diagram showing a subfield configuration in the embodiment.

[Explanation of symbols]

 1R, 1G, 1B A / D conversion circuit 2 Subfield conversion circuit 201 Combinational logic circuit 3 Subfield sequential conversion circuit 301 Frame memory 4 Drive circuit 5 Matrix display panel 6 Control circuit 601 and 602 EXOR circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Otaka 4-6 Kanda Surugadai, Chiyoda-ku, Tokyo Inside the Home Appliances and Information Media Business Division, Hitachi, Ltd.

Claims (10)

[Claims] 1. A gradation display of a video signal in which one field period of a video signal is divided into a plurality of subfields, and the presence or absence of light emission at a light emission amount determined in each subfield is controlled to perform gradation expression. In the method, an upper sub-field group including a plurality of sub-fields having the largest light emission amount and having the same light-emission amount, and a lower sub-field group including sub-fields having different light emission amounts having a light-emission amount ratio of a power of two. In the specific gray scale display, there are two different types of subfield light emission sequences for the same gray scale display, and pixels emitting light in the two types of subfield light emission sequences A gradation display method for a video signal, wherein three-dimensionally adjacent pixels are alternately arranged so as not to be continuous. 2. The light emission sequence according to claim 1, wherein the two types of subfield light emission sequences are a first light emission sequence in which the temporal position of the center of gravity of the light emission amount is located in the first half of one field, and a temporal position of the centroid of the light emission amount. Position 1
And a second light emission sequence located in the latter half of the field. 3. The method according to claim 1, wherein, when the number of subfields belonging to the upper subfield group is an even number, the lower subfield group is continuously arranged substantially at the center of one field. When the number of subfields belonging to the upper subfield group is an odd number, one subfield belonging to the upper subfield group is substantially divided into two groups. The lower sub-field group is arranged at the center, the lower sub-field group is arranged adjacent to the upper sub-field arranged substantially at the center, and the even number of upper sub-field groups excluding the upper sub field arranged at the substantially center are divided into two. A gradation display method for a video signal, wherein the video signal is arranged continuously at the beginning and end of one field. 4. The sub-field group according to claim 3, wherein the lower sub-field group arranged continuously at substantially the center of the one field or adjacent to the upper sub-field arranged at substantially the center is a sub-field group having a large light emission amount. Sub-fields before and after the field are
A gradation display method for a video signal, wherein the light emission amount is arranged to decrease as the distance from the center increases. 5. The sub-field group according to claim 3, wherein a lower sub-field group continuously arranged at substantially the center of the one field or arranged adjacent to an upper sub-field arranged at the substantially center is a time axis. A gradation display method of a video signal, wherein a sub-field arrangement is inverted. 6. The amount of light emission corresponding to the most significant bit or the most significant bits including the most significant amount of light emission represented by a power of two based on a digital representation of an input video signal in the upper subfield group. And a method for displaying the gradation of a video signal by dividing the sum into equal parts. 7. A video signal display device which divides one field period of a video signal into a plurality of subfields and controls the presence or absence of light emission at a light emission amount defined in each subfield to perform gradation expression. An upper subfield group consisting of a plurality of subfields having the largest light emission amount and having the same light emission amount, and a lower subfield group consisting of subfields having different light emission amounts and having a light emission ratio of a power of two. In a specific gradation display, there are two different types of subfield emission sequences for the same gradation display,
Subfield conversion means for alternately arranging pixels that emit light by the two types of subfield light emission sequences so as not to be continuous with adjacent pixels in three dimensions in space and time; Subfield sequential conversion means for converting into a field sequential format in subfield units, driving means for driving a display element based on the subfield display sequential signal, and display element driven by the driving means A video signal display device characterized by the above-mentioned. 8. The light emission sequence according to claim 7, wherein the two types of subfield light emission sequences are a first light emission sequence in which the temporal position of the center of gravity of the light emission amount is located in the first half of one field, and a temporal position of the centroid of the light emission amount. Position 1
And a second light emission sequence located in the latter half of the field. 9. The subfield conversion means according to claim 7, wherein, when the number of subfields belonging to said upper subfield group is an even number, said lower subfield group is set to one.
In the case where the upper subfield group is divided into two parts and arranged continuously at the beginning and end of one field, and the number of subfields belonging to the upper subfield group is odd. One subfield belonging to the upper subfield group is arranged substantially at the center, the lower subfield group is arranged adjacent to the upper subfield arranged at the center, and the upper subfield arranged at the substantially center is A video signal display device characterized in that an even number of upper sub-field groups excluding fields are divided into two and arranged continuously at the beginning and end of one field. 10. The subfield conversion means according to claim 7, wherein said upper subfield group is an uppermost number or an uppermost number including an uppermost one of a light emission amount expressed by a power of two based on a digital representation of an input video signal. A video signal display device characterized in that light emission amounts corresponding to bits are summed and equally divided.