JP2008107653A - Drive unit having gamma correction function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive unit which enables visual recognition of a plurality of kinds of images to be displayed on a display panel without feeling uncomfortable. <P>SOLUTION: A gamma correction circuit includes a first LUT (lookup table) 410 corresponding to a first sequence and a second LUT 420 corresponding to a second sequence. The first sequence corresponds to a natural image while the second sequence corresponds to a text image. In each LUT, gamma corrected data being the data indicating the selection of data voltage (source voltage) values corresponding to signal levels indicated by display data are set in accordance with the respective signal levels of 0 to 63. An image type deciding circuit decides whether an image to be displayed is a natural image or a text image on the basis of signal levels of the display data and outputs an enable signal corresponding to the decision result. Only a sequence data selection circuit receiving the enable signal out of the sequence data selection circuits 415, 425 passes the data outputted from the corresponding LUT. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a drive device for driving a display panel such as a liquid crystal display panel or an organic EL display panel, and in particular, a drive device having a gamma correction function for generating a drive voltage according to the transmittance characteristic or light emission characteristic of the display device. About.

  FIG. 13 is an explanatory diagram showing an example of applied voltage-light transmittance characteristics (hereinafter referred to as VT characteristics) of a normally black mode TFT (Thin Film Transistor) type liquid crystal display panel. The horizontal axis corresponds to the voltage value applied to the source wiring of the liquid crystal display panel. As shown in FIG. 13, the relationship between the voltage applied to the liquid crystal and the light transmittance (hereinafter referred to as transmittance) is non-linear. Further, the degree of change in transmittance when the applied voltage is low and when the applied voltage is high is smaller than the change in transmittance when the applied voltage is intermediate.

  In the case of performing gradation display, if the relationship between the gradation level and the transmittance shows such characteristics as shown in FIG. 14, the image displayed on the liquid crystal display panel can be visually recognized (for example, patents). Reference 1). In FIG. 14, the horizontal axis indicates the signal level. FIG. 14 shows an example in which 64-gradation display is performed. The signal levels from level 0 to 63 are set at equal intervals from level 0 to 63. The characteristics as shown in FIG. 14 are represented by T = V to the γ power, where T is the transmittance and V is the input level (signal level). FIG. 14 shows an example when γ = 2.2. In the liquid crystal display panel having the characteristics as shown in FIG. 13, in order to obtain the characteristics as shown in FIG. 14, it is necessary to correct the voltage value corresponding to the input level (signal level). That is, it is necessary to perform gamma correction.

  The types of images displayed on one liquid crystal display panel are diversified. For example, an image containing a lot of text (characters) at one point in time or an image containing only text (hereinafter referred to as a text image) is displayed. A still image (hereinafter referred to as a natural image) may be displayed. Note that the natural image may include text in a part (for example, an area of 30% or less of the entire display area). Generally, liquid crystal display devices are equipped with a gamma correction function that performs gamma correction for natural images. However, in liquid crystal display panels that need to display many types of images, gamma correction suitable for natural images can be performed. The characteristics are not always suitable for text images.

  There is a liquid crystal display device in which means for realizing a plurality of gamma correction functions is mounted on a drive circuit for driving a display panel (see, for example, Patent Document 2). However, in the liquid crystal display device described in Patent Document 2, a plurality of means for realizing the gamma correction function are means for performing gamma correction for R (red) data, and means for performing gamma correction for G (green) data. And B (blue) data for performing gamma correction. A plurality of means corresponding to the type of image are not provided. That is, considering the entire image, it has only one type of gamma correction function.

Japanese Patent Laying-Open No. 2006-171367 (paragraphs 0004-0006, FIGS. 3 to 5) JP 2001-238227 A (paragraphs 0014-0017, FIG. 1)

  As described above, when a liquid crystal display device including a drive circuit having a gamma correction function is used for displaying different types of images depending on the situation, a gamma correction function suitable for a certain type of image is Other types of images are not necessarily appropriate. In other words, even if a viewer can display a certain type of image so as to be visually recognized without a sense of incongruity, the viewer may not necessarily be able to display other types of images without a sense of incongruity. The sense of incongruity is, for example, that the color becomes lighter or the degree of gradation change becomes lower.

  Therefore, the present invention is suitable for driving a display panel that displays a plurality of types of images depending on the situation, and allows a plurality of types of images displayed on the display panel to be visually recognized without a sense of incongruity. An object of the present invention is to provide a drive device having a function.

  The driving apparatus having the gamma correction function according to the present invention includes a plurality of gamma correction units (for example, a gamma correction unit including the first LUT 410 and the first series data selection circuit 415, and a second LUT 420) that perform gamma correction on each of a plurality of types of images. And a gamma correction unit by the second series data selection circuit 425), and which type of image is displayed on the display panel is determined based on the signal level of the display data, and the gamma correction unit corresponding to the determination result has a gamma correction. And an image type determination unit for executing correction.

  The plurality of types of images are text images or natural images, and the image type determination unit counts the number of display data whose signal level is equal to or higher than a high level threshold (for example, HV) and outputs the first count value. A first counting circuit (for example, HV adder 331) that counts the number of display data whose signal level is equal to or lower than a low level threshold value (for example, LV), and outputs a second count value When the count value of the counting circuit (for example, the LV adder 333) and the first counting circuit is equal to or higher than the high gradation number threshold value (for example, Vth_H), or the count value of the second counting circuit is the low gradation number When the threshold value (for example, Vth_L) is greater than or equal to, or the count value of the first count circuit is greater than or equal to the high gradation number threshold value and the count value of the second count circuit is greater than or equal to the lower gradation number threshold value In some cases, it is determined that a text image is displayed on the display panel. And a determination circuit (for example, system determination circuit 340).

  The image type determination unit outputs a selection signal (for example, the first enable signal or the second enable signal) that enables only the gamma correction unit that performs gamma correction, and each gamma correction unit indicates the display data. Output from the table when the signal level and the gamma correction value are stored in association with each other (for example, the first LUT 410 and the second LUT 420) and the selection signal indicates that the gamma correction unit performs gamma correction. A selection circuit (for example, a first series data selection circuit 415 and a second series data selection circuit 425) that outputs the corrected gamma correction value may be included.

  According to the present invention, it is possible to visually recognize a plurality of types of images displayed on the display panel, and driving suitable for driving a display panel that displays a plurality of types of images according to the situation. A device can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a driving circuit (driving device) according to the present invention, an MPU (Micro Processing Unit) 40 (for example, an MPU of a mobile phone), which is an external device installed outside the driving circuit, and a liquid crystal display panel 10. It is a block diagram shown with it. In the example shown in FIG. 1, a TFT type liquid crystal display panel 10 in which TFTs are arranged in a matrix and liquid crystal is sandwiched between a pixel electrode and a common electrode is used.

  A drive circuit for driving the liquid crystal display panel 10 includes a source driver (data electrode driver) 12 to which each source electrode (source wiring) as a data electrode connected to the source of the TFT in the same column in the liquid crystal display panel 10 is connected, A gate driver (scanning electrode driver) 13 connected to each gate electrode (gate wiring) as a scanning electrode connected to the gate of the TFT in the same row in the liquid crystal display panel 10, and a voltage for generating a data voltage as a source driver 12 And a power supply circuit 14 for supplying a voltage for generating a selection voltage (ON voltage) and a non-selection voltage (OFF voltage) to the gate driver 13.

  The controller 11 as a control circuit has a RAM 111 that temporarily stores display data (pixel data) supplied from the MPU 40, and outputs a VSYNC signal corresponding to a signal indicating the start of a frame to the source driver 12 and the gate driver 13. In addition, a CP (control pulse) signal is output for each selection period (a period in which a selection voltage as an ON voltage is applied to one gate wiring). The interface input from the MPU 40 is a so-called MPU interface that outputs display data asynchronously, a so-called VSYNC interface that includes VSYNC (vertical synchronization signal) as a synchronization signal, and VSYNC and HSYNC (horizontal synchronization) as synchronization signals. A so-called RBG interface including a signal) or any other interface may be used.

  The gate driver 13 has a built-in counter, and resets the counter when the VSYNC signal is input, and increments the counter value by 1 when the CP signal is input. Then, a selection voltage for making the TFT gate conductive is applied to the gate wiring indicated by the counter value, and a non-selection voltage for making the TFT gate shut off is applied to the other gate wiring. A common voltage output unit 131 built in the gate driver 13 applies a common voltage to the common wiring.

  When the CP signal is input, the source driver 12 latches the data signal and applies a data voltage corresponding to the latched data signal to the source wiring. Since the gate driver 13 applies the selection voltage to the gate wiring in synchronization with the CP signal, the source driver 12 applies the data voltage to each source wiring in synchronization with the application of the selection voltage to the gate wiring.

  In the present embodiment, a gradation data control circuit 20 is provided between the controller 11 and the source driver 12. The gradation data control circuit 20 is a value indicating a data voltage corresponding to the gradation level of the data signal (display data) read from the RAM 111 and data indicating a value subjected to gamma correction as a data signal. It is a circuit to output. The installation position of the gradation data control circuit 20 is not limited to between the controller 11 and the source driver 12.

  The drive circuit of this embodiment is equipped with a plurality of gamma correction functions for performing gamma correction according to the type of image. In order to realize a plurality of gamma correction functions, a lookup table (LUT) for realizing each gamma correction function is stored in a RAM or a ROM built in the drive circuit.

  In this embodiment, two types of images, a natural image and a text image, are taken as an example. Note that the natural image may include text in a part (for example, an area of 30% or less of the entire display area).

  Hereinafter, the type of image is referred to as “series”. In this embodiment, two sequences are exemplified as a plurality of sequences. Therefore, two LUTs are provided. Note that the two sequences are examples, and there may be more sequences or fewer sequences. When there are k (k: a positive integer of 2 or more) series, k LUTs are provided.

  FIG. 2 is a block diagram illustrating a configuration example of the gradation data control circuit 20. In the example illustrated in FIG. 2, the gradation data control circuit 20 includes an image type determination circuit 300 and a gamma correction circuit 400. The gamma correction circuit 400 is provided with two LUTs. The image type determination circuit 300 outputs selection data indicating which LUT is used to the gamma correction circuit 400 based on the signal level of the display data.

  FIG. 3 is a block diagram illustrating a configuration example of the gamma correction circuit 400. In the example illustrated in FIG. 3, the gamma correction circuit 400 includes a first LUT 410 corresponding to the first series and a second LUT 420 corresponding to the second series. In this example, the first series corresponds to a natural image, and the second series corresponds to a text image. In each LUT, data indicating a data voltage (source voltage) value selection corresponding to the signal level indicated by the display data, and the data subjected to gamma correction are applied to each of the 64-level signal levels of 0 to 63. Correspondingly set. Note that, here, a case of performing 64-gradation display is taken as an example, but the number of gradations is arbitrary.

  The data output from the first LUT 410 is input to the first series selection circuit 415. The data output from the second LUT 420 is input to the second series selection circuit 425.

  The first sequence selection circuit 415 outputs a first sequence selection signal (first enable signal) indicating that the first sequence is used as selection data indicating which LUT is used from the image type determination circuit 300. Data output from the first LUT 410 is output to the source driver 12. The second series selection circuit 425 receives the data output from the second LUT 420 when the image type determination circuit 300 outputs the second series selection signal (second enable signal) indicating that the second series is used. Is output to the source driver 12.

  The image type determination circuit 300 outputs either the first enable signal or the second enable signal. Accordingly, either the data output from the first LUT 410 or the data output from the second LUT 420 is output to the source driver 12. Note that the output of the first series selection circuit 415 and the output of the second series selection circuit 425 are wired OR connected. The first series selection circuit 415 and the second series selection circuit 425 set the output to a high impedance state when the corresponding enable signal is not input.

  4A and 4B are explanatory diagrams illustrating configuration examples of the first LUT 410 and the second LUT 420. FIG. In each LUT, data indicating data voltage value selection corresponding to the signal level indicated by the display data is set. In the example shown in FIG. 4, data corresponding to positive polarity driving in the case of performing polarity inversion driving and Data corresponding to negative polarity driving is set. In FIG. 4, Vi_SELpj (i = 1 to 4, any of j = 0 to 63) indicates data corresponding to positive polarity driving, and Vi_SELnj indicates data corresponding to negative polarity driving.

  FIG. 5 is an explanatory diagram for explaining data set in the first LUT 410 and the second LUT 420. In FIG. 5, a curve a is a curve indicating applied voltage (specifically, signal level) -transmittance when γ = 2.2, and corresponds to a natural image. That is, when displaying a natural image corresponding to the first series, the transmittance indicated by the curve a is obtained according to each of the signal levels of 0 to 63. For example, assume that the transmittance desired to be obtained at level 30 is 30%. If the characteristic of the liquid crystal display panel 10 is the characteristic shown in FIG. 13, the applied voltage exhibiting a transmittance of 30% is 3.6V. Therefore, in the first LUT 410, data indicating 3.6V is set as data corresponding to the level 30. Other data in the first LUT 410 is determined based on the same concept as that for determining data corresponding to the level 30.

  In FIG. 5, a curve b corresponds to a text image. That is, when displaying a text image corresponding to the second series, the transmittance indicated by the curve b is obtained according to each of the signal levels of 0 to 63. Therefore, data indicating the applied voltage exhibiting the transmittance indicated by the curve b at each signal level is set in the second LUT 420.

  A curve a corresponding to a natural image shows a general characteristic of γ = 2.2, while a curve b corresponding to a text image shows a characteristic emphasizing contrast. That is, the level range corresponding to low transmittance and the level range corresponding to high transmittance are widened.

  FIG. 6 is an explanatory diagram illustrating an example of a pixel signal level histogram in a text-centered image (text image) and a pixel signal level histogram in a natural-image center image (natural image). The number of pixels having a signal level of 3 or less (low gradation pixels) in one screen, the number of pixels having a signal level of 60 or more (high gradation pixels), and the pixels having a signal level of more than 3 and less than 60 (halftone) An example of the number of pixels is shown on the vertical axis. In a text image, the number of low gradation pixels and the number of high gradation pixels are large. A natural image has a large number of halftone pixels. The signal level 60 is referred to as a high level threshold HV, and the signal level 3 is referred to as a low level threshold LV.

  Therefore, an image having a large number of low gradation pixels and a high gradation pixel on one screen can be determined as a text image, and an image having a large number of halftone pixels can be determined as a natural image. Specifically, when the number of low gradation pixels is equal to or greater than the low gradation number threshold Vth_L and the number of high gradation pixels is equal to or greater than the high gradation number threshold Vth_H, it can be determined as a text image. A text image can also be determined when the number of halftone pixels is equal to or less than the halftone threshold value Tth.

  FIG. 7 is an explanatory diagram for explaining a method for determining an image type in the present embodiment. A rectangle shown in FIG. 7 indicates display data (display data for one screen) of pixels for one frame stored in the RAM 111. “Address” shown in FIG. 7 indicates the address of the RAM 111. That is, in the RAM 111, display data is stored for each pixel in a region where addresses are continuous. In the RAM 111, the data in the (l + 1) th row is stored next to the data in the l (l: natural number) row in the liquid crystal display panel 10.

  In this embodiment, the image type determination circuit 300 extracts a predetermined number of display data discretely located on one screen from the display data for one screen as sampling points, and the extracted display data (pixels). It is determined whether the pixel is a low gradation pixel, a halftone pixel, or a high gradation pixel, and the determination results are totaled to determine whether the image is a text image.

  FIG. 8 is a block diagram illustrating a configuration example of the image type determination circuit 300. In the configuration example illustrated in FIG. 8, the image type determination circuit 300 includes a sample point determination circuit 310 that determines whether or not the pixel is a sampling point, and the sampling point pixel is a low gradation pixel, a halftone pixel, or a high gradation pixel. A level determination circuit 320 that performs level determination to determine whether there is an addition, an addition circuit 330 that performs addition processing on the determination result of the level determination circuit 320, and a first enable signal or a second enable signal based on the addition result of the addition circuit 330 And a system determination circuit 340 for outputting.

  FIG. 9 is a block diagram illustrating a configuration example of the level determination circuit 320. In the configuration example illustrated in FIG. 9, the level determination circuit 320 includes an HV (high value) determination unit 321 that determines whether the signal level is 60 or higher, and an LV (Low) that determines whether the signal level is 3 or lower. Value) determiner 322 and a logic circuit 323 that outputs a halftone signal based on the output of HV determiner 321 and the output of LV determiner 322. The logic circuit 323 outputs a halftone signal when the output of the HV determiner 321 and the output of the LV determiner 322 are “0”. The output of the HV determination device 321 becomes a high gradation signal as it is. The output of the LV determiner 322 becomes a low gradation signal as it is. Note that the output of the high gradation signal, the halftone signal, and the low gradation signal specifically means that the signal state becomes a high level (“1”).

  FIG. 10 is a block diagram illustrating a configuration example of the adder circuit 330. In the configuration example shown in FIG. 10, the adder circuit 330 includes an HV adder 331 that counts the number of times of output of a high gradation signal, a halftone adder 332 that counts the number of times of output of a halftone signal, and the number of times of output of a low gradation signal. LV adder 333 is included. Note that the count values (added values) of the HV adder 331, halftone adder 332, and LV adder 333 are cleared when, for example, a VSYNC signal is input.

  FIG. 11 is a block diagram illustrating a configuration example of the system determination circuit 340. In the example illustrated in FIG. 11, the system determination circuit 340 compares the addition value of the HV adder 331 with the high gradation number threshold value Vth_H and the addition value of the halftone adder 332 as the halftone threshold. A halftone comparator 342 for comparing with the value Tth and an LV comparator 343 for comparing the added value of the LV adder 333 with the low gradation number threshold Vth_L are included. Further, based on the output of the HV comparator 341, the output of the halftone comparator 342, and the output of the LV comparator 343, the logic circuit 344 that outputs the second enable signal and the output of the logic circuit 344 are inverted to the first. And an inverting circuit 345 for outputting as an enable signal.

  In the HV comparator 341, for example, the ratio of the added value of the HV adder 331 to the number of pixels at all sampling points in one screen is 0.3 (the number of pixels at all sampling points is 1.0) or more. Sometimes the output is set to high level (“1”). In the LV comparator 343, for example, the ratio of the addition value of the LV adder 333 to the number of pixels at all sampling points in one screen is 0.3 (the number of pixels at all sampling points is 1.0) or more. Sometimes the output is set to high level (“1”). In the halftone comparator 342, the ratio of the added value of the halftone adder 332 to the number of pixels at all sampling points in one screen exceeds 0.3 (the number of pixels at all sampling points is 1.0). The output is set to high level (“1”).

  In this example, the high gradation number threshold value Vth_H is 0.3, the low gradation number threshold value Vth_L is 0.3, and the halftone threshold value Tth is 0.3.

  The logic circuit 344 outputs when the output of the HV comparator 341 is at a high level, the output of the LV comparator 343 is at a high level, and the output of the halftone comparator 342 is at a low level (“0”). The second enable signal indicating the second system (text image) is output. The inverting circuit 345 inverts the output of the logic circuit 344 and outputs it as a first enable signal. That is, when one or both of the output of the HV comparator 341 and the output of the LV comparator 343 is low level, or the output of the halftone comparator 342 is at a high level, it is the first system (natural image). A first enable signal indicating that is output.

  That is, the system determination circuit 340 includes 30% or more high gradation pixels, 30% or more low gradation pixels, and the number of halftone pixels is 30% or less among all sampling points in one screen. In addition, it determines that the image displayed on the liquid crystal display panel 10 is a text image and outputs a first enable signal.

  The values of the high gradation number threshold value Vth_H, the low gradation number threshold value Vth_L, and the intermediate gradation threshold value Tth are examples, and the characteristics of the liquid crystal display panel 10 and the liquid crystal display panel 10 are incorporated. These values are determined as appropriate according to the specifications of a device such as a mobile phone. In this embodiment, the high level threshold is set to “60” and the low level threshold is set to “3”. These values are also examples. Again, depending on the characteristics of the liquid crystal display panel 10 and the specifications of the device, for example, the high level threshold value is set to an arbitrary value of 85% or more of the highest level value (63 in this example), or to a low level. The threshold value may be an arbitrary value that is 15% or less of the highest level value (63 in this example).

  Further, the determination method in the system determination circuit 340 is also an example. For example, it is determined based on only the output of the HV comparator 341 and the output of the LV comparator 343 (without using the output of the halftone comparator 342) or based on only the output of the HV comparator 341. Whether it is a text image, whether it is a text image based only on the output of the LV comparator 343, or whether it is a text image based only on the output of the halftone comparator 342. Also good. Furthermore, when the sum of the addition value of the HV adder 331 and the addition value of the LV adder 333 is a predetermined value or more, it may be determined that the image is a text image.

  Next, the operation of the drive circuit will be described. The RAM 111 shown in FIG. 1 stores R, G, and B display data output from the MPU 40 side. The gamma correction circuit 400 shown in FIG. 3 is a circuit that controls any one of the display data of R, G, and B. That is, actually, the gamma correction circuit 400 illustrated in FIG. 3 is provided for each of the R, G, and B display data.

  Further, a level determination circuit 320, an addition circuit 330, and a system determination circuit 340 in the image type determination circuit 300 shown in FIG. 8 are also provided for each of the R, G, and B display data. Note that the gradation data control circuit 20 may perform control on data obtained by collecting display data of R, G, and B. In that case, it is sufficient that one gamma correction circuit 400 shown in FIG. 3 is provided, and the level determination circuit 320, the addition circuit 330, and the system determination circuit 340 in the image type determination circuit 300 shown in FIG. It is only necessary to provide one each.

  Display data is read from the RAM 111 in synchronization with the CLK signal. The sample point determination circuit 310 is reset by the VSYNC signal and counts the CLK signal. When the count value reaches a predetermined value, a signal indicating that the display data of the sampling point has been read from the RAM 111 is output to the level determination circuit 320. There are a plurality of predetermined values, which are values indicating positions indicated by crosses in FIG. The positions corresponding to the predetermined value are preferably arranged in a distributed manner within one frame. Moreover, it is preferable that there are as many portions as possible indicated by x marks. Further, since the predetermined value and the CLK signal for counting the predetermined value are values corresponding to the read address of the RAM 111, FIG. 8 shows that the RAM address is input to the sample point determination circuit 310. Yes.

  The plurality of predetermined values are preferably stored in a register or RAM that can be referred to by the sample point determination circuit 310. If it is stored in a register or RAM, the contents can be easily changed, and the location indicated by a cross in FIG. 7 can be changed. Further, the locations indicated by the x marks may be set to a plurality of arbitrary locations in one row and set over a plurality of rows, instead of being set at random as a whole. When such a setting method is employed, the sampling point determination circuit 310 can find sampling points in units of rows.

  As illustrated in FIG. 9, the case where the display data (signal level) of R, G, B is (10111 11100 111111) will be described. Further, it is assumed that the level determination circuit 320 shown in FIG. 9 is the level determination circuit 320 corresponding to the B display data. Further, an example in which the HV determination unit 321 performs determination on the upper 4 bits of the display data and the LV determination unit 322 performs determination on the upper 4 bits of the display data is taken as an example.

  The HV determiner 321 compares (1111), which is the upper 4 bits of the B display data, with 60. When the upper 4 bits are (1111), (1111xx) of the original 6-bit data is 60 or more which is the high level threshold HV (x may be 0 or 1). In this case, HV determination The device 321 sets the output to “1”. When the upper 4 bits are (1111), the original 6-bit data (1111xx) is larger than 3 which is the low level threshold LV, so the LV decision unit 322 sets the output to “0”. . Therefore, a high gradation signal is output from the level determination circuit 320. Therefore, in this case, the HV adder 331 increases the addition value by 1 in the addition circuit 330 shown in FIG.

  The sample point determination circuit 310 outputs a signal indicating that the sampling point display data has been read from the RAM 111 every time the sampling point is found, that is, every time the sampling point display data is output from the RAM 111. When the signal is output, the level determination circuit 320 performs the above-described processing and outputs a high gradation signal, a halftone signal, or a low gradation signal. As a result, the HV adder 331, the halftone adder 332, or the LV adder 333 in the adder circuit 330 increases the added value by one.

  In the system determination circuit 340, the HV comparator 341, the halftone comparator 342, and the LV comparator 343, for example, when the VSYNC signal is input, are added values of the HV adder 331, the halftone adder 332, and the LV adder 333. And a comparison process for comparing the threshold value. Based on the outputs of the HV comparator 341, the halftone comparator 342, and the LV comparator 343, the logic circuit 344 and the inverting circuit 345 output the first enable signal or the second enable signal.

  Through the processing as described above, the system enable circuit 340 outputs the first enable signal or the second enable signal for each frame. That is, the image type determination circuit 300 outputs the first enable signal or the second enable signal to the gamma correction circuit 400 for each frame. Note that the gamma correction processing of the gamma correction circuit 400 based on the first enable signal or the second enable signal is performed on the image of the frame next to the frame subjected to the determination processing by the image type determination circuit 300.

  In the gamma correction circuit 400 shown in FIG. 3, the enable signal (first enable signal or second enable signal) output from the image type determination circuit 300 out of the first series data selection circuit 415 and the second series data selection circuit 425. Only the series data selection circuit corresponding to the signal) is ready for data output. Hereinafter, it is assumed that the second series data selection circuit 425 is in a data output enabled state.

  The controller 11 outputs display data stored in the RAM 111 to the gradation data control circuit 20. In the gradation data control circuit 20, display data is input to the first LUT 410 and the second LUT 420 in the gamma correction circuit 400. Each of the LUTs 410 and 420 outputs data indicating voltage value selection corresponding to the signal level of display data and subjected to gamma correction as a data signal. Since only the second series data selection circuit 425 is in a data output enabled state, the data from the second LUT 420 is output to the source driver 12.

FIG. 12 is a circuit diagram illustrating a configuration example of the voltage selection circuit in the source driver 12. In the configuration example shown in FIG. 12, the voltage of each voltage value obtained by dividing the reference voltage V _ref in the resistor circuit 121 including a large number of resistors R is output from the data output from the gamma correction circuit 400, that is, from the LUT. A switch circuit 122 for selecting according to data is provided. The switch circuit 122 selects a voltage having a voltage value indicated by the data output from the LUT and outputs it as a data voltage (source voltage). The output data voltage is applied to the source line.

  As described above, in the above embodiment, the drive circuit is provided with the LUT corresponding to the image type, and the selection data (the first enable signal or the first output) output from the image type determination circuit 300 based on the determination result. The LUT is selected in accordance with (2 enable signal), and the drive circuit is configured so that the selected LUT outputs data indicating a gamma-corrected voltage value corresponding to the display data. A plurality of types of images displayed on the screen can be visually recognized without a sense of incongruity.

  In addition, since the image type determination circuit 300 in the drive circuit determines which LUT should be used, even if the liquid crystal display device including the drive circuit is incorporated in any device, the device (externally viewed from the liquid crystal display device) Gamma correction suitable for the displayed image can be performed without changing the program executed by the MPU 40 in the apparatus.

  In the above embodiment, the description has been given by taking the display panel of normally black mode as an example. However, the present invention can also be applied to the case of using a display panel of normally white mode.

  Further, the drive circuit shown in FIG. 1 may be formed by a one-chip LSI. That is, a gamma correction function corresponding to each of the plurality of types of images may be incorporated in a one-chip LSI. When a gamma correction function corresponding to each of a plurality of types of images is incorporated in a one-chip LSI, an LSI having only one type of gamma correction function (for example, corresponding to γ = 2.2) is used. In comparison, since an LUT corresponding to the type of image displayed on the liquid crystal display panel 10 can be dynamically selected, appropriate gamma correction corresponding to the type of image displayed on the liquid crystal display panel 10 is performed. Can do. This is the same even when the LSI is not used.

  In addition, when an LUT is provided for each of the display data of R, G, and B, control that emphasizes a specific color can be realized according to the type of image. As an example, when the text image is set to be displayed in green, data for realizing the characteristics indicated by the curve b in FIG. 5 is stored in the green LUT in the second LUT corresponding to the text image. It is conceivable to set and set data for realizing the characteristic indicated by the curve a in FIG. 5 in the red and blue LUTs.

  In the above-described embodiment, two types of images, that is, a natural image and a text image are exemplified. However, three or more types of images may be used. For example, the image type determination circuit 300 further has a function of determining whether or not the displayed image is a moving image by detecting that the display data of the sampling point changes with time with a predetermined time period. May be. In such a configuration, an LUT corresponding to each of a natural image, a text image, and a moving image is provided. Then, appropriate gamma correction can be performed for each of the three types of images.

  In the above embodiment, the driving circuit for driving the TFT type liquid crystal display panel is taken as an example. However, when the gamma correction function is mounted on the driving circuit for driving the STN (Super Twisted Nematic) type liquid crystal display panel. The present invention can be applied. Further, the present invention may be applied to a case where a gamma correction function is mounted on a drive circuit that drives an organic EL (Electroluminescence) display panel. In the case of a drive circuit for driving an organic EL display panel, data indicating a current value is set in the LUT.

  The present invention is a drive device for driving a display panel, and is effectively applied to a drive device having a gamma correction function.

The block diagram which shows an example of a drive circuit with MPU and a liquid crystal display panel. FIG. 3 is a block diagram illustrating a configuration example of a gradation data control circuit. The block diagram which shows the structural example of a gamma correction circuit. Explanatory drawing which shows the structural example of a 1st LUT and a 2nd LUT. Explanatory drawing for demonstrating the data set to 1st LUT and 2nd LUT. Explanatory drawing which shows an example of the histogram of the signal level of the pixel in a text image, and the histogram of the signal level of the pixel in a natural image. Explanatory drawing for demonstrating the determination method of the kind of image. The block diagram which shows the structural example of an image kind determination circuit. The block diagram which shows the structural example of a level determination circuit. The block diagram which shows the structural example of an addition circuit. The block diagram which shows the structural example of a system | strain determination circuit. The circuit diagram which shows the structural example of a voltage selection circuit. Explanatory drawing which shows an example of the applied voltage-transmittance characteristic of a liquid crystal display panel. Explanatory drawing which shows an example of the relationship between a gradation level (signal level) and the transmittance | permeability.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display panel 11 Controller 12 Source driver 13 Gate driver 20 Gradation data control circuit 300 Image type determination circuit 310 Sample point determination circuit 320 Level determination circuit 330 Adder circuit 340 System determination circuit 400 Gamma correction circuit 410 1st LUT
415 First series selection circuit 420 Second LUT
425 Second series selection circuit

Claims (3)

In a driving device for driving a display panel and having a gamma correction function,
A plurality of gamma correction units for performing gamma correction for each of a plurality of types of images;
An image type determination unit that determines which type of image is displayed on the display panel based on the signal level of the display data and causes the gamma correction unit corresponding to the determination result to perform gamma correction. A drive device with a gamma correction function. The multiple types of images are text images or natural images,
The image type determination unit
A first counting circuit that counts the number of display data having a signal level equal to or higher than a high level threshold and outputs a first count value;
A second counting circuit that counts the number of display data having a signal level equal to or lower than a low level threshold and outputs a second count value;
When the count value of the first count circuit is greater than or equal to the high gradation number threshold value, or when the count value of the second count circuit is greater than or equal to the low gradation number threshold value, or the first count circuit And determining that the text image is displayed on the display panel when the count value of the second count circuit is equal to or greater than the threshold value of the low gradation number. A drive device having a gamma correction function according to claim 1. The image type determination unit outputs a selection signal that enables only the gamma correction unit that performs gamma correction,
Each gamma correction unit
A table for storing the signal level indicated by the display data and the data after gamma correction in association with each other;
The gamma correction function according to claim 1, further comprising: a selection circuit that outputs data output from the table when the selection signal indicates that the gamma correction unit is operable. Provided drive device.

Images