BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the constitution of a liquid crystal display device;
FIG. 2 is gradation brightness characteristics of respective fields in an embodiment 1;
FIG. 3 is a conceptual view showing an example of the reduction of moving image blurring;
FIG. 4 is a conceptual view showing another example of reducing moving image blurring;
FIG. 5 is a conceptual view showing the reduction of moving image blurring in the embodiment 1;
FIG. 6 is an example of moving image blurring when 1 frame is divided into 2 fields;
FIG. 7 is a view showing a comparison example for the embodiment 1;
FIG. 8 is a conceptual view showing another mode of the embodiment 1;
FIG. 9 is a table which describes cases which are adopted when 1 frame is divided into 3 fields;
FIG. 10 is a graph showing gradation-brightness characteristics of an embodiment 2;
FIG. 11 is a view showing a comparison example for the embodiment 2;
FIG. 12 is a conceptual view showing the reduction of moving image blurring in the embodiment 2;
FIG. 13 is a graph showing gradation-brightness characteristics of an embodiment 4; and
FIG. 14 is a graph showing an example of gradation-brightness characteristics when 1 frame is divided into 2 fields.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is described in detail in conjunction with embodiments.
Embodiment 1
FIG. 1 is a block diagram showing the constitution of the liquid crystal display device. The display device corresponds to a display of 16,770,000 colors in total in which respective colors of R, G, B are constituted of 256 gradations. Numeral 101 indicates input display data formed of 24 bits in total in which respective colors of R, G, B are constituted of 8 bits, and numeral 102 indicates a group of input signals. The group of input signals 102 is constituted of a vertical synchronizing signal Vsync which defines 1 frame period (period in which 1 screen is displayed), a horizontal synchronizing signal Hsync which defines 1 horizontal period (period in which 1 line is displayed), a display timing signal DISP which defines an effective period of display data, and a reference clock signal DCLK which is synchronized with display data.
Numeral 103 indicates a drive selection signal. In response to the drive selection signal 103, either a conventional drive method or a drive method which reduces moving image blurring is selected. The input display data 101, a group of input signal 102, and the drive selection signal 103 are transferred from an external system (for example, a television receiver set, a PV set or a mobile phone set).
Numeral 104 indicates a timing signal generation circuit, numeral 105 indicates a group of memory control signals, numeral 106 indicates a table initializing signal, numeral 107 indicates a data selection signal, numeral 108 indicates a group of data driver control signals, and numeral 109 indicates a group of scanning driver control signals. The group of data driver control signals 108 is constituted of an output signal CL1 which defines output timing of a gradation voltage based on the display data, an AC signal M which determines polarity of a source voltage, and a clock signal PCLK which is synchronized with the display data. The group of scanning driver control signals 109 is constituted of a shift signal CL3 which defines a scanning period for 1 line, and a vertical start signal FLM which defines starting of scanning of a head line.
Numeral 110 indicates a frame memory having capacitance amounting at least 1 frame of the display data and performs reading and writing processing of display data based on the group of memory signals 105. Numeral 111 indicates memory read data which is read from the frame memory 110 in response to the group of the memory control signals 105. Numeral 112 indicates a ROM (ReadOnlyMemory) which outputs data stored in the inside thereof in response to the table initializing signal, numeral 113 indicates table data which is outputted from the ROM 112, numeral 114 indicates a first field conversion table, numeral 115 indicates a second field conversion table, and numeral 116 indicates a third field conversion table.
Values of respective tables are set based on the table data 113 at the time of supplying electricity, and the memory read data 111 read from the frame memory 110 is converted based on the values set in the respective tables. The first field conversion table 114 has a function of a data conversion circuit for the first field, the second field conversion table 115 has a function of a data conversion circuit for the second field, and the third field conversion table 116 has a function of a data conversion circuit for the third field.
Numeral 117 indicates first field display data acquired by conversion in the first field conversion table 114, numeral 118 indicates second field display data acquired by conversion in the second field conversion table 115, and numeral 119 indicates third field display data acquired by conversion in the third field conversion table 116. Numeral 120 indicates a display data selection circuit. The display data selection circuit 120 selects and outputs any one of the first field display data 117, the second field display data 118 and the third field display data 119 based on the data selection signal 107. Numeral 121 indicates field display data selected by the display data selection circuit 120.
Numeral 122 indicates a gradation voltage generation circuit, and numeral 123 indicates a gradation voltage. Numeral 124 indicates a data driver. The data driver 124 generates potentials of 512 levels in total consisting of 256 levels (28 (8 powers of 2)) for positive polarity and negative polarity respectively from the gradation voltage 123 and, at the same time, selects a potential of 1 level corresponding to the field display data 121 of 8 bits for respective colors and a polarity signal M, and applies the potential to a liquid crystal display panel 128 as a data voltage.
Numeral 125 indicates a data voltage generated by the data driver 124. Numeral 126 indicates a scanning driver, and numeral 127 indicates a scanning line selection signal. The scanning driver 126 generates a scanning line selection signal 127 in response to the group of scanning driver control signals 109, and outputs the scanning line selection signal 127 to scanning lines of the liquid crystal display panel 128.
In the liquid crystal display panel 128, 1 pixel of the liquid crystal display panel 128 is schematically indicated by numeral 129. 1 pixel of the liquid crystal display panel 128 is constituted of a TFT (Thin Film Transistor) which is formed of a source electrode, a gate electrode and a drain electrode, a liquid crystal layer and a counter electrode. The TFT performs a switching operation when the scanning signal is applied to the gate electrode thereof. The data voltage is written in the source electrode which is connected with one side of the liquid crystal layer via the drain electrode when the TFT is in an open state, and the voltage written in the source electrode is held when the TFT is in a closed state. Assume the voltage of the source electrode as Vs and a counter electrode voltage as Vcom. The liquid crystal layer changes the polarization direction based on the potential difference between the source electrode voltage Vs and the counter electrode voltage Vcom and, at the same time, a transmission light quantity from a backlight arranged on a back surface of the liquid crystal display panel 128 is changed via the polarizer arranged above and below the liquid crystal layer thus performing a gradation display.
In FIG. 1, for example, the first field is a brightest field, the second field is an intermediate brightness field, and the third field is the darkest field. FIG. 2 shows an example of a range of gradations which are allocated to the respective fields. In FIG. 2, the gradations are taken on an axis of abscissas and the relative brightness is taken on an axis of ordinates, wherein the maximum gradation is a 255th gradation which corresponds to 256 bits. When the gradation is relatively low, that is, when the gradation takes a value equal to or below a 171th gradation, only the field which is allocated to 1g contributes to the formation of images. When the gradation takes a value which exceeds the 171th gradation and equal to or below a 228th gradation, the field allocated to 1g and the field allocated to 2g contribute to the formation of images. When the gradation takes a value which exceeds the 228th gradation, all of the fields allocated to 1g, 2g, 3g contribute to the formation of images. Then, when the gradation assumes the maximum gradation which is a 256th gradation, all fields ranging from the first field to the third field assume the maximum brightness and hence, a white peak is displayed. For the sake of brevity, the relationship between the gradations and the brightness is set linearly in FIG. 2. However, this relationship can be changed depending on properties or the like of an actual liquid crystal display panel.
When the relationship between the gradations and the brightness shown in FIG. 2 is set, the conversion tables corresponding to the respective fields are written in the ROM shown in FIG. 1 based on the relationship, and the first field conversion table, the second field conversion table and the third field conversion table read the conversion tables each time the display device is turned on. Although the respective conversion tables include the number of data equal to the number of frame data of the input data, the respective conversion tables differ from each other in the relationship between the gradations and the brightness. Then, the field display data ranging from the first field to the third field is read by the display data selection circuit and is outputted to the data driver. A reading speed of the respective fields is three times as fast as the reading speed of the input data.
The relationships between the gradations and brightness (hereinafter, also referred to as gradation-brightness characteristics) 1g, 2g, 3g shown in FIG. 2 are candidates for tables allocated to respective fields. For example, when necessary, the relationship 1g may be allocated to the third field, the relationship 3g may be allocated to the first field, and the relationship 2g may be allocated to the second field. As will be explained later, this manner of allocation brings about effects for preventing moving image blurring which differ from each other.
In FIG. 2, when the gradation is the 100th gradation, for example, the brightness data is outputted only to the field which corresponds to 1g and data on other field is zero. Accordingly, in such a case, black is written within ⅔ of 1 frame period and hence, the moving image blurring can be remarkably reduced. One example of this case is shown in FIG. 3. FIG. 3 shows the case in which the gradation-brightness characteristic 1g shown in FIG. 2 is allocated to the first field. In FIG. 3, a lapse of time is taken on an axis of ordinates, wherein symbol 1F indicates 1 frame period, symbol if indicates a first field, symbol 2f indicates a second field, and symbol 3f indicates a third field. That is, FIG. 3 shows that 1 frame is constituted of 3 fields. The movement of an image within the corresponding time is taken on an axis of abscissas. In FIG. 3, 3 pixels are assumed to move within 1 frame period. Although a moving quantity of the pixel is set small for the sake of brevity, the same idea is fundamentally applicable even when the moving quantity of the pixel is increased.
In FIG. 3, an arrow J shows the movement of an image which human eyes predict when the image is moved. However, in this embodiment, the brightness of the pixel is fixed during 1 field and hence, an image indicated by an arrow K is also recognized by the human eyes and hence, the difference B between the arrow J and the arrow K is recognized as moving image blurring by the human eyes. Here, a quantity of moving image blurring which the human eyes recognize when the black insertion is not performed is expressed as the difference BB between the arrow J and an arrow L shown in FIG. 3. It is understood from FIG. 3 that the quantity of moving image blurring is largely reduced compared to the quantity of moving image blurring of the conventional example.
FIG. 4 shows a case in which the gradation-brightness characteristic 1g shown in FIG. 2 is made to correspond to the second field. Also in this case, a quantity of moving image blurring is substantially equal to the quantity of the moving image blurring in the case in which the gradation-brightness characteristic 1g is made to correspond to the first field shown in FIG. 2. Although not shown in the drawing, a quantity of moving image blurring is substantially equal to the quantity of the moving image blurring in the case in which the gradation-brightness characteristic 1g is made to correspond to the third field shown in FIG. 2.
Next, when the gradation shown in FIG. 2 is the 200th gradation, it is necessary to use 2 fields which possess the gradation-brightness characteristic 1g and the gradation-brightness characteristic 2g. In this case, unless the gradations and the brightness characteristics allocated to the respective fields are properly selected, it is impossible to obtain a sufficient moving image blurring effect even when the frame is expressed by 3 fields.
FIG. 5 shows a case in which the gradation-brightness characteristic 1g shown in FIG. 2 is made to correspond to the first field, the gradation-brightness characteristic 2g shown in FIG. 2 is made to correspond to the second field, and the gradation-brightness 3g shown in FIG. 2 is made to correspond to the third field. This case is referred to as a first mode. In this case, a value of B in FIG. 5 indicates a quantity of moving image blurring. FIG. 6 shows a case in which 1 frame is expressed by 2 fields for a comparison purpose. This case also corresponds to the case of the 200th gradation in FIG. 2. In FIG. 2, to generate the brightness of 200th gradation, it is necessary to use the gradation-brightness characteristic 1g and the gradation-brightness characteristic 2g and hence, complete black is not displayed in either one of two fields. Symbol B in FIG. 6 indicates a quantity of moving image blurring. As can be understood from a comparison of FIG. 5 and FIG. 6, the moving image blurring can be reduced more effectively in the case shown in FIG. 5 than the case shown in FIG. 6.
FIG. 7 shows a case in which the gradation-brightness characteristic 1g shown in FIG. 2 is made to correspond to the first field, the gradation-brightness characteristic 2g shown in FIG. 2 is made to correspond to the third field, and the gradation-brightness 3g shown in FIG. 2 is made to correspond to the second field. This case is referred to as a second mode. In this case, moving image blurring is expressed as a value B shown in FIG. 7. Compared to a case shown in FIG. 5, a quantity of moving image blurring is increased. Further, to compare the case shown in FIG. 7 and the case shown in FIG. 6, in spite of the fact that 1 frame is expressed by 3 fields by increasing frequency for writing data into the liquid crystal display panel in FIG. 7, the quantity of moving image blurring becomes substantially equal to the quantity of moving image blurring in the case in which 1 frame is expressed by 2 fields.
FIG. 8 shows a case in which the gradation-brightness characteristic 1g shown in FIG. 2 is made to correspond to the third field, the gradation-brightness characteristic 2g shown in FIG. 2 is made to correspond to the second field, and the gradation-brightness characteristic 3g shown in FIG. 2 is made to correspond to the first field. This case is referred to as a third mode. A quantity of moving image blurring in this case is expressed by symbol B shown in FIG. 8. In FIG. 8, the moving image blurring is reduced and a quantity of B is substantially equal to the quantity of B in the first mode.
To summarize advantageous effects against the moving image blurring in the above-mentioned modes, the blurring reduction effect becomes least when there is no black display immediately before the frame is changed or immediately after the frame is changed. That is, it is necessary to obviate these combinations. While it is possible to obtain a large moving image blurring reduction effect when the field of black display exists immediately before the frame is changed or immediately after the frame is changed, such an effect can be further increased by eliminating the brightest field immediately before the black field.
The number of methods for expressing 1 frame by 3 fields is 3!, that is, 6. All cases in allocating the respective gradation-brightness characteristics to respective fields are expressed in a Table shown in FIG. 9. FIG. 9 shows 6 cases for 2 frames. 1 frame is formed of 3 fields, wherein 1g, 2g, 3g respectively correspond to the gradation-brightness characteristics shown in FIG. 2. To classify the respective data based on the above-mentioned finding, the case 1 shown in FIG. 9 corresponds to the above-mentioned first mode and exhibits the largest moving image blurring reduction effect. The case 6 shown in FIG. 9 corresponds to the above-mentioned third mode and exhibits the moving image blurring reduction effect substantially equal to the moving image blurring reduction effect of the above-mentioned first mode. The cases which exhibit the least moving image blurring reduction effect are the case 2 and the case 4 which correspond to the above-mentioned second mode. These cases should be obviated from a viewpoint of the moving image blurring reduction. Although the case 3 and the case 5 do not belong to any modes, these cases exhibit the moving image blurring reduction effect substantially equal to the moving image blurring reduction effect of the above-mentioned first mode or third mode only under the condition that 3g is black. Here, the correspondence between the respective fields and the respective gradation-brightness characteristics may be written in the ROM 113 shown in FIG. 1.
As described above, while this embodiment reduces the moving image blurring by expressing 1 frame using 3 fields, this embodiment describes that the moving image blurring reduction effect largely differs depending on setting of the gradation-brightness characteristics of respective fields. Further, by setting the field exhibiting the lowest brightness (gradation-brightness characteristic 3g shown in FIG. 2) immediately before or immediately after the frame is changed, and by obviating the setting of the field exhibiting the maximum brightness (gradation-brightness characteristic 1g shown in FIG. 2) immediately before the field exhibiting the lowest brightness, it is possible to obtain a large moving image blurring reduction effect.
Embodiment 2
Although the embodiment 1 reduces the moving image blurring by expressing the image corresponding to 1 frame using 3 fields, in this embodiment, 1 frame is expressed by n pieces of fields for finely reducing the moving image blurring. FIG. 10 shows such an example in which 1 frame is expressed by 5 fields.
In FIG. 10, up to a gradation 1T, only the field corresponding to the gradation-brightness characteristic 1g expresses an image and other fields perform a black display. Up to a gradation 2T, the field corresponding to the gradation-brightness characteristic 1g and the field corresponding to the gradation-brightness characteristic 2g express an image, and other fields perform a black display. In this manner, by dividing 1 frame into the larger number of fields, chances of inserting black in various screens are increased and hence, the image blurring can be reduced correspondingly.
The system for this case is configured such that, in FIG. 1, the capacitance of the frame memory 110, the capacitance of ROM 113, and the number of conversion tables 114, 115, 116 and the like corresponding to the gradation-brightness characteristics are increased corresponding to the number of fields. Further, a speed for writing field display data into the data driver 124 becomes 5 times as fast as a corresponding speed of the input data 101.
When 1 frame is expressed by n fields, the number of combinations of the correspondence between the fields and the gradation-brightness characteristics becomes n!. Also in this case, depending on the correspondence between the field and the gradation-brightness characteristic, the moving image blurring reduction effect largely differs. When 1 frame is expressed by 5 fields as shown in FIG. 10, the number of combinations becomes 5!, that is, 120.
The combination which is considered first is a method which arranges the brightest gradation-brightness characteristic 1g in FIG. 10 at the center of the frame. In FIG. 11, the gradation-brightness characteristic 1g is allocated to the third field, the gradation-brightness characteristic 2g is allocated to the fourth field, the gradation-brightness characteristic 3g is allocated to the fifth field, the gradation-brightness characteristic 4g is allocated to the first field, and the gradation-brightness characteristic 5g is allocated to the second field. In this case, when the brightness is low, that is, when the gradation-brightness characteristics 1g, 2g or the like is used, there arises no problem. However, when the brightness is increased and the gradation-brightness characteristic up to 4g is used, it is difficult to acquire a sufficient moving image blurring reduction effect. In this case, the moving image blurring is expressed by symbol B in FIG. 11.
To the contrary, in FIG. 12, although the gradation-brightness characteristic 1g shown in FIG. 10 is allocated to the third field and the gradation-brightness characteristic 2g shown in FIG. 10 is allocated to the fourth field in the same manner as the case shown in FIG. 11, the gradation-brightness characteristic 5g is allocated to the fifth field and the gradation-brightness characteristic 4g is allocated to the first field. In this case, even when the gradation-brightness characteristic is used up to the gradation-brightness characteristic 4g, it is possible to acquire the moving image blurring reduction effect. The case shown in FIG. 12 is characterized by setting the minimum gradation-brightness characteristic 5g (black in this case) at the final field of 1 frame.
The similar advantageous effects can be also obtained by allocating the minimum gradation-brightness characteristic 5g to the initial field of 1 frame. Further, in FIG. 12, the next minimum gradation-brightness characteristic 4g is arranged in the initial field of the frame. By setting the gradation-brightness characteristics in this manner, it is possible to further increase a black insertion effect with respect to an image which uses the gradation-brightness characteristic 3g. Further, as can be understood from FIG. 12, by continuously arranging the fields which are allocated to the high gradation-brightness characteristics 1g, 2g, it is possible to cope with the moving image blurring more effectively.
It is needless to say that, besides the above-mentioned orders of gradation-brightness characteristics, it is possible to adopt the ascending order of 1g, 2g, . . . 5g or the descending order of 5g, 4g, . . . 1g. Also in these cases, the gradation-brightness characteristic 5g which has the highest probability of performing a black display is set in the initial or final field and hence, it is possible to acquire the substantially equal image blurring reduction effect.
Embodiment 3
The embodiment 1 and the embodiment 2 cope with the moving image blurring by forming 1 frame using 3 or more fields which differ from each other in the gradation-brightness characteristic. In these embodiments, as the brightness approximates the maximum brightness, an image display is performed in all fields and hence, the black display is not performed whereby the moving image blurring cannot be eliminated. In this embodiment, in forming 1 frame using 3 or more fields, no signal is written in 1 field and the field always performs a black display. A crucial point in this embodiment lies in that the field in which the black display is always performed is set to either an initial field or a last field of the frame.
In forming 1 frame using 3 fields, the combination of the fields and the gradation-brightness characteristics when the black display is always performed in 1 field does not essentially differ from the corresponding combination in the embodiment 1. That is, by using the field which always performs the black display in place of the gradation-brightness characteristic 3g in the embodiment 1, it is possible to acquire a moving image blurring reduction effect.
In forming 1 frame using 3 fields, when the black display is always performed in 1 field, an image is formed using 2 fields. Accordingly, compared to a case in which 1 frame is formed of only 1 field, a value of the peak brightness becomes ⅔. However, compared to a conventional case adopting the black insertion which forms 1 frame using 2 fields and exhibits the peak brightness value of ½, the lowering of the peak brightness is not large.
In forming 1 frame using n fields, the combination of the fields and the gradation-brightness characteristics when the black display is always performed in 1 field does not substantially differ from the corresponding combination in the embodiment 2. That is, with the use of the field in which the black is always displayed in place of the lowest gradation-brightness characteristic in the embodiment 2, it is possible to acquire the moving image blurring reduction effect.
In forming 1 frame using n fields, when the black display is always performed in 1 field, an image is formed using (n−1) fields. Accordingly, compared to a case in which 1 frame is formed of only 1 field, a value of the peak brightness becomes (n−1)/n. However, compared to a conventional case adopting the black insertion which forms 1 frame using 2 fields and exhibits the peak brightness value of ½, the lowering of the peak brightness becomes extremely small.
Embodiment 4
FIG. 13 shows a fourth embodiment. The embodiment 1 and the embodiment 2 display the maximum brightness in all fields at the maximum gradation and hence, there is no reduction of the moving image blurring due to black insertion. FIG. 13 shows a case in which 1 frame is formed of 3 fields. When the gradation becomes T2 or more, a region exhibiting the gradation-brightness characteristic 3g is used. In this embodiment, even at the maximum gradation, the gradation-brightness characteristic 3g is set smaller than the maximum brightness. Due to such setting, it is possible to acquire at least two following advantageous effects.
One advantageous effect is that the gradation T2 which moves from the gradation-brightness characteristic 2g to the gradation-brightness characteristic 3g can be increased. In the gradation-brightness characteristic 3g, to express the brightness change from the minimum brightness to the maximum brightness, it is necessary to ensure the gradations within a fixed range. However, in this embodiment, it is unnecessary to output the maximum brightness in the gradation-brightness characteristic 3g and hence, the gradation range of the gradation-brightness characteristic 3g can be reduced whereby the value of T2 in FIG. 13 can be increased correspondingly. Accordingly, chances that the region of the gradation-brightness characteristic 3g is used can be reduced thus enhancing the moving image blurring reduction effect attributed to black insertion. Another advantageous effect is that the maximum brightness at the gradation-brightness characteristic 3g can be lowered and hence, even when the region of the gradation-brightness characteristic 3g is used, it is possible to reduce an image retention effect on naked eyes corresponding to the lowering of the brightness.
In FIG. 13, although the maximum brightness in 1 frame is also lowered corresponding to the lowering of the maximum brightness in the gradation-brightness characteristic 3g, the lowered amount only contributes to the lowering of the maximum brightness for the 3g region and hence, the lowered amount is small.
Although FIG. 13 shows a case in which 1 frame is formed of 3 fields, the same advantageous effects can be acquired by forming 1 frame using n pieces of fields. Also in this case, the maximum brightness of the field which is allocated to the region of the highest gradation is set lower than the brightnesses of other fields. Also in this case, the moving image blurring can be reduced due to the substantially same reasons as the above-mentioned case in which 1 frame is formed using 3 fields. The advantageous effects acquired when this embodiment is applied to n pieces of fields are limited by an amount that the number of fields is increased. On the other hand, the case which forms 1 frame using n pieces of fields can further reduce the lowering of brightness than the case which forms 1 frame using 3 fields. The number of fields may be selected or determined based on properties of an image to be displayed.
Although the explanation has been made using the liquid crystal display device which adopts TFTs as the display device in the above-mentioned embodiments, the present invention is also applicable to an organic EL display device which adopts TFTs in the substantially same manner.
Patent Application
20080068395
