JP2008241975A - Display device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a storage capacity for storing a lookup table for sub-field data conversion. <P>SOLUTION: A compressed LUT 137 stored in an LUT code memory 131 is obtained by compressing a lookup table for converting an image signal into sub-field patterns composed of variable length portions all of which are ON, fixed length portions in which ON and OFF are mixed and variable length portions all of which are OFF. Since a sub-field pattern having such a format can be compressed at a high compression rate, the compression rate of the lookup table is also high and storage capacity for storing the lookup table can be reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a display device and an electronic apparatus that display gradation by a subfield driving method.

  A liquid crystal device that performs display by changing the transmittance of liquid crystal is widely used as a display device of an electronic device such as an information processing device, a television, or a mobile phone. In the liquid crystal device, pixel electrodes are formed corresponding to intersections between scanning lines extending in the row direction and data lines extending in the column direction. In addition, a pixel switch such as a thin film transistor (hereinafter referred to as a TFT: Thin Film Transistor) that is turned on and off according to a scanning signal supplied to the scanning line is interposed between the pixel electrode and the data line at the intersection. It is. Further, a counter electrode is provided so as to face the pixel electrode through the liquid crystal. When a voltage corresponding to the gradation of the image signal is applied between the pixel electrode and the counter electrode, the alignment state of the liquid crystal changes according to the applied voltage. As a result, the amount of transmitted light in the pixel changes, and a predetermined gradation display becomes possible.

  Conventionally, an image signal applied to a data line is a voltage corresponding to a gradation, that is, an analog signal. For this reason, a peripheral circuit of the liquid crystal device requires a D / A conversion circuit, an operational amplifier, and the like. This causes a problem that in addition to increasing the cost, it is difficult to perform uniform display. Therefore, in recent years, as a digital driving method for driving liquid crystal, one field is divided into a plurality of subfields on the time axis, and an on voltage or an off voltage is applied in each subfield according to the gradation of each pixel. A subfield driving method has been proposed.

  Patent Document 1 also discloses a technique for displaying with gradations smaller than the number of subfields in one field by finely controlling the change in transmittance in one subfield. According to this technique, when the number of subfields is n and simple pulse width control (a pattern in which ON subfields are continuous) is performed, only (n + 1) gradations can be obtained. By mixing off subfields, it is possible to express significantly more gradations than (n + 1) gradations.

Further, in Patent Document 2, in a display device that performs gradation display by a subfield driving method, in order to prevent a pseudo contour from being generated during reproduction of a moving image, a first that has a different lighting subfield according to a gradation level to be displayed. It is described that the subfield of the mode and the subfield of the second mode are appropriately set.
JP 2003-114661 A Japanese Unexamined Patent Publication No. 07-271325 (FIGS. 16 and 17)

  A lookup table is used as one method for converting the gradation of image data to be displayed into subfield data. The look-up table is created by correlating the gradation of the image to be displayed (for example, gradation represented by 8 bits) with the on / off pattern of the subfield (for example, a subfield obtained by dividing one field into 32). It is a table. For this reason, the look-up table needs to store as many corresponding patterns as the number of gradations. Note that the on / off pattern of the subfield is obtained theoretically and experimentally in advance in accordance with the characteristics of the liquid crystal and the like, suitable for expressing gradation.

By the way, in general, the characteristics of liquid crystal change with temperature. Therefore, in order to obtain uniform and low luminance characteristics, it is necessary to prepare a lookup table for each temperature. Further, as described in Patent Document 2, in order to prevent a pseudo contour during moving image display, it is necessary to further prepare different subfield patterns even at the same temperature.
Generally, the lookup table is stored in advance in a nonvolatile manner in a ROM or the like. However, if there are many types of lookup tables, a large amount of storage capacity is required to store the lookup tables.

  The present invention has been made in view of such circumstances, and an object of the present invention is to reduce the storage capacity for storing a lookup table for subfield data conversion.

In order to solve the above-described problem, a display device according to the present invention includes a display area in which a plurality of pixels are arranged, and each of the plurality of pixels is turned on or off for each of a plurality of subfields obtained by dividing one field. A plurality of compression tables are stored, and each of the plurality of compression tables is a compression obtained by compressing a gradation to be displayed and a code pattern instructing turning on or off for each of the plurality of subfields. Table storage means for storing code patterns in association with each other, compression table selection means for selecting a compression table stored in the table storage means, and decompressing the compression code pattern of the table selected by the table selection means Decompression means for generating a restoration table for associating the code pattern with the gradation to be displayed, and display Based on the image signal indicating the power gradation, referring to the restored table, the data conversion means for generating a code pattern corresponding to the gradation to be displayed, and the code pattern generated by the data conversion means And display control means for displaying an image in the display area.
According to the present invention, the table storage means stores a plurality of compression tables, and selects and decompresses them appropriately. As a result, the storage capacity of the table storage means can be greatly reduced, and the configuration can be simplified. A typical example of such a display device is a liquid crystal device, and the length of each subfield is preferably equal.

  As a specific aspect of the code pattern, lighting is designated for all of the corresponding subfields, and the first code part in which the number of corresponding subfields is variable and lighting or extinction of the corresponding subfields are mixed. The second code part is designated and the number of corresponding subfields is fixed, and the third code part is designated to turn off all the corresponding subfields and the number of corresponding subfields is variable. It is preferable. According to this code pattern, the first code part that designates lighting and the third code part that designates light-off are variable length, and the second code part that designates lighting or light-off is fixed. For this reason, by determining the number of subfields included in each of the first code portion and the third code portion, an approximate gradation can be designated, and a lighting pattern or a non-lighting pattern of the second code portion is designated. As a result, a more detailed gradation can be designated.

  Here, the compressed code pattern is turned on or off for a portion representing the number of subfields corresponding to the first code portion or the third code portion in binary and a subfield corresponding to the second code portion. Is preferably composed of a part represented by a binary number. In this case, since the number of subfields corresponding to the first code part or the third code part is represented by a binary number, the data amount can be compressed.

  Further, the display device described above includes temperature acquisition means for acquiring the temperature of the display area, each of the plurality of compression tables is associated with temperature, and the selection means is acquired by the temperature acquisition means. It is preferable to select a compression table according to the temperature. According to the present invention, since the compression table corresponding to the temperature is selected, the temperature characteristic can be corrected. In addition, since the compression table only needs to be stored, the storage capacity can be reduced.

  In the display device described above, the selection unit selects at least two compression tables, and the expansion unit generates at least two restoration tables by expanding the selected at least two compression tables. The data conversion means selects one of the at least two restoration tables according to a predetermined rule, displays the selected restoration table with reference to the selected restoration table based on the image signal indicating the gradation to be displayed. It is preferable to generate a code pattern corresponding to the gradation to be generated. According to this invention, one of a plurality of restoration tables is selected and a code pattern is generated, so that block noise can be reduced.

In the display device described above, it is preferable that the plurality of subfields are obtained by equally dividing the one field in time.
Next, an electronic apparatus according to the present invention includes the display device described above. Examples of such an electronic device include a personal computer, a mobile phone, a portable information terminal, and the like.

<1. Embodiment>
FIG. 1 shows a block diagram of a liquid crystal device according to the embodiment. The liquid crystal device 100 uses liquid crystal as an electro-optic material. The liquid crystal device 100 includes a liquid crystal panel 110 as a main part. In the liquid crystal panel 110, an element substrate on which a TFT is formed as a switching element and a counter substrate are pasted with their electrode formation surfaces facing each other with a certain gap therebetween, and liquid crystal is sandwiched in the gap. In the present embodiment, the liquid crystal device 100 employs a subfield driving method.

  The liquid crystal device 100 includes an image processing circuit 120, a digital signal subfield conversion circuit 130, a temperature correction circuit 140, a temperature sensor 150, and an A / D conversion circuit 160. On the element substrate of the liquid crystal panel 110, an image display area 111, a scanning driver 112, and a data driver 113 are formed.

  The image processing circuit 120 is supplied with an analog image signal and a control signal from an external device. The image processing circuit 120 converts an analog image signal into a digital signal, performs image processing such as gamma correction and liquid crystal panel unevenness / variation correction, and supplies the processed image signal to the digital signal subfield conversion circuit 130 as a corrected image signal. . The image processing circuit 120 outputs a control signal for controlling the scan driver 112 and the data driver 113. The control signal is, for example, a horizontal scanning signal or a vertical scanning signal.

  The temperature sensor 150 is disposed in the vicinity of the liquid crystal panel 110 and acquires the temperature of the image display area 111 of the liquid crystal panel 110 indirectly or directly. The analog temperature data acquired by the temperature sensor 150 is digitally converted by the A / D conversion circuit 160 and sent to the digital signal subfield conversion circuit 130. Note that the temperature sensor 150 may be incorporated in the liquid crystal panel 110.

  The digital signal subfield conversion circuit 130 includes a look-up table (LUT) code memory 131, an expansion circuit 132, a conversion circuit 133, a temperature characteristic LUT selection circuit 134, and a pseudo contour LUT selection circuit 135. The lookup code memory 131 is composed of, for example, a ROM, and a compressed lookup table 137 is stored in a nonvolatile manner. The compressed look-up table 137 stored in the look-up code memory 131 is prepared for each temperature, and a plurality of different code patterns (two in the present embodiment) are used as a set for pseudo contour correction. Stored. The compression lookup table 137 prepared for each temperature is selected by the temperature characteristic LUT selection circuit 134 according to the acquired temperature data, and is sent to the expansion circuit 132.

The decompression circuit 132 decompresses the compression lookup table 137 according to a predetermined algorithm, generates a restoration table, and stores it in a work memory such as a RAM. In the present embodiment, since two look-up tables having different code patterns are prepared for pseudo contour correction, the first LUT 138a and the second LUT 138b are stored as restoration tables in the working memory.
The conversion circuit 133 refers to the lookup table 138 stored in the working memory, converts the corrected image signal supplied from the image processing circuit 120 into subfield data, and supplies the subfield data to the data driver 113.

  The pseudo contour LUT selection circuit 135 determines which lookup table of the first LUT 138a and the second LUT 138b is used for the conversion in accordance with a predetermined algorithm. This algorithm can be random, alternating, etc., for example. Further, a single lookup table may be used in the case of a still image, and a plurality of lookup tables may be used properly only in the case of moving image display.

  FIG. 2 is a diagram showing the configuration of the image display area 111. In the image display area 111, m (m is a natural number of 2 or more) scanning lines 20 are formed in parallel along the X direction, while n (n is a natural number of 2 or more) data. Lines 10 are formed in parallel along the Y direction. Then, m × n pixel circuits P are arranged corresponding to the intersection of the data line 10 and the scanning line 20.

  As shown in the figure, the pixel circuit P includes a liquid crystal element 60 and a TFT 50. The liquid crystal element 60 is configured by sandwiching liquid crystal between a pixel electrode 61 and a counter electrode 62. A common potential Vcom is supplied to the counter electrode 62. The gate electrode of the TFT 50 is electrically connected to the scanning line 20, one of its drain electrode or source electrode is electrically connected to the data line 10, and the other is electrically connected to the pixel electrode 61.

The data driver 113 shown in FIG. 1 outputs data signals X1 to Xn to the n data lines 10. In the liquid crystal device, AC driving is generally performed, and in this embodiment, driving is performed by combining line-by-line inversion that inverts the voltage applied to the liquid crystal in units of lines and frame-by-frame inversion that inverts in units of frames. Shall. Note that either line-by-line inversion or frame-by-frame inversion, or another driving method may be used.
The scanning signals Y1, Y2,..., Ym are applied to each scanning line 20 from the scanning driver 112 in a line-sequential manner in a pulse manner. For this reason, when a scanning signal is supplied to a certain scanning line 20, the TFT 50 is turned on in the pixel circuit P of the row, and the data signal supplied via the data line 10 is written into the liquid crystal element 60. Since the orientation and order of liquid crystal molecules change according to the voltage applied to each pixel, gradation display by light modulation becomes possible.

For example, the amount of light passing through the liquid crystal is limited as the integral amount of the applied voltage increases in the normally white mode, while it is reduced as the integral amount of the applied voltage increases in the normally black mode. Therefore, in the entire liquid crystal device 100, light having contrast corresponding to the image signal is emitted for each pixel.
The liquid crystal device 100 in this example is normally white. For this reason, the transmittance increases and white is displayed in a state where no voltage is applied, and the transmittance decreases and black is displayed in a state where the integrated amount of the applied voltage is large. Note that a storage capacitor may be added in parallel with the liquid crystal capacitor formed between the pixel electrode 61 and the counter electrode 62 in order to prevent the stored image signal from leaking.

  Next, the subfield code pattern in this embodiment will be described. In general, the total number of subfield code patterns is determined according to the number of subfields. For example, if one field is composed of 40 subfields, there are 2 to 40 power code patterns. In practice, not all 2 40 patterns are used, but code patterns corresponding to gradations to be expressed are extracted and used.

For example, if the image signal is expressed by 8 bits (256 gradations), one code pattern that matches the ideal gradation-luminance (transmittance) characteristic is selected from 2 to the 40th power pattern. 256 are extracted per lookup table.
Here, when extracting the code pattern that matches the gradation-luminance (transmittance) characteristics, if the transmittance is calculated theoretically or experimentally for each of the 40 code patterns of 2, it takes a lot of trouble. It will take time. In addition, since the lookup table associates an image signal with a subfield code pattern, it can be expected that the compression rate of the lookup table increases as the format of the subfield code pattern is suitable for compression. .

Therefore, in this embodiment, it is assumed that subfields are handled as follows. FIG. 3 is a diagram for explaining an example of a field configuration in the present embodiment. As shown in the figure, one field is composed of a plurality of subfields, and is divided into three parts: a first code part, a second code part, and a third code part.
Here, the first code portion is composed of a variable number of subfields, and all are on (lighted) values. The second code part is composed of a fixed number of subfields, and an on subfield and an off subfield are mixed. The third code part is composed of a variable number of subfields, and all are off (extinguish) values.

  In the present embodiment, a code pattern adapted to such a format is extracted as a subfield pattern. A code pattern conforming to this format can be compressed at a high compression rate. Any method can be used as the compression algorithm. For example, when the total number of subfields is 40 and the number of subfields in the second code part is 8, the following compression algorithm can be considered.

  That is, since all the first code parts are on, it is sufficient to indicate a variable number of subfields. Since the total number of subfields is 40, and 32 is obtained by subtracting the number of 8 subfields in the second code portion, the maximum length is sufficient. If the value of each subfield is shown as it is, the second code part can be expressed by 8 bits. Since the third code part is all off in the remaining part, it need not be expressed. Therefore, 40 subfields can be expressed by 5 plus 8 13 bits.

  For example, since the length of the first code portion is 8, the subfield code pattern as shown in FIG. 4A can be expressed as “00100” in 5 bits, and the second code portion is “01010101”. For this reason, the code pattern compressed as a whole can be expressed as “0010001010101”. Similarly, the subfield code pattern shown in FIG. 4B can be expressed as “01010010101101” as a compressed code pattern, and the subfield code pattern shown in FIG. 01010010011 ".

  FIG. 4 (d) shows an example of a subfield code pattern that is paired with FIG. 4 (b) in order to prevent pseudo contours. In this example, a pattern in which the code of FIG. 4 (b) is reversed is shown. Used. In this way, all the first code portions may be turned off and all the third code portions may be turned off, or the positions of the first code portion and the second code portion may be switched. In short, it is sufficient that each subfield pattern is divided into variable length portions that are all on, fixed length portions that are a mixture of on and off, and variable length portions that are all off.

Thus, the following effects can be obtained by extracting a subfield code pattern that matches a format in which one field is divided into three parts.
First, the capacity of the lookup code memory can be reduced. That is, a format in which one field is divided into three parts can realize a high compression rate. For this reason, the compression rate of the lookup table can also be increased. In general, the look-up table is compressed and stored in a nonvolatile manner in a memory, but a plurality of types of look-up tables must be prepared in order to cope with temperature characteristics and prevent false contours. Therefore, if the compression rate of the lookup table is high, the overall capacity of the lookup code memory can be greatly reduced.

  Second, the efficiency in extracting a subfield code pattern that matches the gradation-luminance (transmittance) characteristics is improved. That is, since the code patterns for which the transmittance is theoretically or experimentally obtained can be narrowed down in advance, labor and time can be saved significantly compared to exhaustive investigation.

  Next, the flow of subfield conversion processing of the liquid crystal device 100 using the subfield code pattern according to the above format will be described again with reference to FIG. Here, each look-up table decompressed from each compression LUT 137 stored in the LUT code memory 131 includes an image signal, a variable length portion in which each subfield pattern is all on, and a combination of on and off. The subfield code pattern is divided into a fixed-length portion and a variable-length portion that is all off. However, a pattern that does not conform to this format may be included in some of the subfield code patterns due to the characteristics of the liquid crystal.

  First, the temperature characteristic LUT selection circuit 134 selects the compression LUT 137 corresponding to the temperature around the liquid crystal panel 110 acquired by the temperature sensor 150. The selected compression LUT 137 is sent to the decompression circuit 132. The compression LUT 137 can use the same data as long as the temperature of the liquid crystal panel 110 does not change. That is, it is not necessary to re-supply the expansion circuit 132 as long as the temperature of the liquid crystal panel 110 does not change.

  The decompression circuit 132 decompresses the compression LUT 137 according to the compression algorithm of the first code part and the second code part to obtain the first LUT 138a and the second LUT 138b. In the above example, the subfield code portion of the lookup table is expanded from 13-bit compressed data into a subfield code pattern of 40 subfields.

  When the conversion circuit 133 receives the 8-bit corrected image signal from the image processing circuit 120, the conversion circuit 133 converts it into subfield data with reference to the first LUT 138a or the second LUT 138b selected by the pseudo contour LUT selection circuit 135. The obtained subfield data is supplied to the data driver 113. When the liquid crystal panel 110 performs display based on the subfield data, a display result based on the input image signal can be obtained.

  At the look-up table stage, the subfield code portion may still be compressed 13 bits, and may be expanded into a subfield code pattern of 40 subfields when converted to output subfield data. . In this way, the capacity of the working memory for storing the lookup table can be saved.

<2. Electronic equipment>
Next, electronic equipment using the liquid crystal device 100 according to the present invention will be described. FIG. 5 is a perspective view showing the configuration of a mobile personal computer that employs the liquid crystal device 100 described above as a display device. The personal computer 2000 includes a liquid crystal device 100 as a display device and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002.

  FIG. 6 shows a configuration of a mobile phone to which the liquid crystal device 100 according to the embodiment is applied. A cellular phone 3000 includes a plurality of operation buttons 3001, scroll buttons 3002, and the liquid crystal device 100 as a display device. By operating the scroll button 3002, the screen displayed on the liquid crystal device 100 is scrolled.

  FIG. 7 shows a configuration of a personal digital assistant (PDA) to which the liquid crystal device 100 according to the embodiment is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and the liquid crystal device 100 as a display device. When the power switch 4002 is operated, various kinds of information such as an address book and a schedule book are displayed on the liquid crystal device 100.

  Electronic devices to which the liquid crystal device according to the present invention is applied include projectors, televisions, video cameras, car navigation devices, pagers, electronic notebooks, electronic papers, calculators, word processors in addition to those shown in FIGS. , Workstations, videophones, POS terminals, printers, scanners, copiers, video players, devices with touch panels, and the like.

1 is a block diagram of a liquid crystal device according to an embodiment of the present invention. It is a block diagram which shows the structure of the image display area of the same apparatus. It is a figure for demonstrating an example of a field structure. It is a figure which shows the example of a subfield code pattern. It is a perspective view of the personal computer which is an example of an electronic device. It is a perspective view of the mobile telephone which is an example of an electronic device. It is a perspective view of the portable information terminal which is an example of an electronic device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Data line, 20 ... Scan line, 60 ... Liquid crystal element, 61 ... Pixel electrode, 62 ... Counter electrode, 100 ... Liquid crystal device, 110 ... Liquid crystal panel, 111 ... Image display area, 112 ... Scan driver, 113 ... Data driver , 120 ... Image processing circuit, 130 ... Digital signal subfield conversion circuit, 131 ... LUT code memory, 132 ... Expansion circuit, 133 ... Conversion circuit, 134 ... Temperature characteristic LUT selection circuit, 135 ... Pseudo contour LUT selection circuit, 137 ... Compression LUT, 150 ... temperature sensor, 160 ... A / D conversion circuit, 2000 ... personal computer, 3000 ... mobile phone, 4000 ... information portable terminal

Claims (7)

A display device comprising a display area in which a plurality of pixels are arranged, and for controlling each of the plurality of pixels to be turned on or off for each of a plurality of subfields obtained by dividing one field,
A plurality of compression tables are stored, and each of the plurality of compression tables stores a gradation to be displayed and a compression code pattern obtained by compressing a code pattern instructing turning on or off for each of the plurality of subfields. Table storage means for
Compression table selection means for selecting a compression table stored in the table storage means;
Decompression means for decompressing the compressed code pattern of the table selected by the table selection means to generate a restoration table that associates the code pattern with a gradation to be displayed;
Data conversion means for generating a code pattern corresponding to the gradation to be displayed with reference to the restored table based on the image signal indicating the gradation to be displayed;
Display control means for displaying an image in the display area based on the code pattern generated by the data conversion means;
Provided display device.   The code pattern specifies lighting for all of the corresponding subfields, specifies the first code part in which the number of corresponding subfields is variable, and specifies whether the corresponding subfields are mixedly turned on or off, and corresponds. It is characterized by comprising a second code part in which the number of subfields is fixed, and a third code part in which turn-off is designated for all corresponding subfields and the number of corresponding subfields is variable. The display device according to claim 1.   The compressed code pattern is a binary number indicating that the number of subfields corresponding to the first code part or the third code part is expressed in binary and the subfield corresponding to the second code part is turned on or off. The display device according to claim 2, comprising: Temperature acquisition means for acquiring the temperature of the display area;
Each of the plurality of compression tables is associated with a temperature,
The selection means selects a compression table according to the temperature acquired by the temperature acquisition means;
The display device according to claim 1, wherein the display device is a display device. The selection means selects at least two compression tables;
The decompression means decompresses at least two selected compression tables to generate at least two restoration tables;
The data conversion means selects one of the at least two restoration tables according to a predetermined rule, displays the selected restoration table with reference to the selected restoration table based on an image signal indicating a gradation to be displayed. Generate a code pattern according to the power gradation,
The display device according to claim 1, wherein the display device is a display device.   The display device according to claim 1, wherein the plurality of subfields are obtained by equally dividing the one field in terms of time. An electronic apparatus comprising the display device according to claim 1.

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