JP2013109145A - Display control circuit, liquid crystal display comprising the same, and display control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce or eliminate compression errors generated by quantization.SOLUTION: An image compression unit 11 in an overshoot compensation unit 23 provided in the display control circuit accumulates errors generated at quantization for each frame, and creates a rounding information table 16. In decoding data, an image decoding unit 15 decodes data from quantized values and corrects the decoded gradation data in accordance with contents in the rounding information table 16. Thereby, image quality degradation caused by compression errors can be reduced or eliminated.

Description

  The present invention relates to a display control circuit for displaying input image data given from the outside, a liquid crystal display device including the display control circuit, and a display control method, and more particularly, input given by using data one frame before. The present invention relates to a display control circuit for correcting image data, a liquid crystal display device including the display control circuit, and a display control method.

  The optical response time of liquid crystal molecules used in a liquid crystal display device varies, but there is nothing that can respond immediately, and generally a time of several tens of milliseconds is often required. Therefore, for example, when the display gradation in this liquid crystal display device is from 0 to 255, for example, when display is performed with 100 display gradations, one vertical display period (hereinafter referred to as “one frame”). Even when the previous display gradation is 0, it is preferable that the display gradation changes to 100 during one frame.

  However, as described above, since the liquid crystal molecules cannot respond so that the display gradation immediately changes to 100, the display gradation of 100 is actually reached after several tens of milliseconds. Therefore, until reaching the display gradation of 100, the liquid crystal display device continues to display a display gradation different from the gradation to be originally displayed (a gradation lower than 100 in the normally black display device). The display quality deteriorates.

  In order to solve the problem of the response speed with respect to the gradation change of the liquid crystal display device that deteriorates the display quality as described above, a drive method generally called overshoot drive is often used. In this method, it is necessary to hold one frame of image data for correction of the input image signal, and the display size is WXGA (1366 × 768), although there is a difference depending on the content of the image data one frame before being used. In a liquid crystal display device having a display panel with 8-bit RGB display gradations, the size of the image data to be stored in the image memory is about 25 million (= 1366 × 768 × 8 × 3) bits. It becomes. The size of the image memory is directly related to the manufacturing cost, and there is a problem that the manufacturing cost increases as a larger memory is required. Therefore, conventionally, in order to reduce the manufacturing cost, a method of compressing the image data and reducing the image memory size is used.

  For example, US Patent Application Publication No. 2005/0200631 describes a configuration in which this image data is appropriately compressed by a block truncation encoding method to reduce its data size and stored in an image memory. This encoding method is hereinafter referred to as a BTC (Block Truncation Coding) method. Although the compression method described in this specification is not described in detail, basically, (1) reduction of the number of bits, (2) color space conversion and downsampling, and (3) reduction of spatial redundancy. By using three methods, irreversible compression is performed. Among these, the compression by the BTC method is a compression method corresponding to the above (3). With such a configuration, the image memory can be reduced, and the manufacturing cost can be reduced.

  Japanese Patent Laid-Open No. 2010-2668 discloses a predicted value that is a difference between the gradation value of the input image data and the average gradation value in order to suppress the occurrence of the so-called afterimage noise that occurs in the conventional art. Compared with the threshold value, when one or more of the predicted values exceed the threshold value, control is performed so as to provide the input image data without providing the image compression unit with the reached gradation data predicted to increase the decoding error. This suppresses or eliminates afterimage noise.

US Patent Application Publication No. 2005/0200631 JP 2010-2668 A

  Here, it is generally well known that a compression error occurs when image data is compressed as described above. For example, as a method of compressing image data, if the difference value between adjacent pixel values is smaller than the threshold value, the difference value is used as a compression code. At the time of decoding, the image data is decoded from the adjacent pixel value and the difference value, and further adjacent. If the difference value from the pixel value is larger than the threshold value, it is possible to quantize the image data to obtain a compressed code with a smaller number of bits. Consider the errors that occur when using this method.

  First, when a difference value between adjacent image data is used as a compression code, an error due to compression does not occur. For example, when the adjacent image data is 100 and the image data of the target pixel is 105, the difference value 5 is a compression code, so that the original pixel value 105 can be decoded without error.

  However, when compression is performed by quantization, for example, when the image data of the target pixel is 100 and compressed to 4 bits, (100 + 8) ÷ 16 = 6.75, and the compression code is 6. When decoding based on this compression code, 6 × 16 = 96 is decoded as a pixel value, and a compression error of −4 occurs with respect to the original pixel value 100.

  Due to this compression error, the pixel value 96 is originally decoded as the previous frame image data where the pixel value 100 should be decoded. For this reason, for example, when overshoot driving is performed, display quality may be greatly deteriorated by calculating incorrect gradation data in the calculation of gradation data to be applied to the liquid crystal panel.

  For example, when the input image originally changes from the pixel value 100 to the pixel value 110, it is the transition amount of the pixel value 10. However, due to the occurrence of a compression error, in the above example, the transition from the pixel value 96 to the pixel value 110 becomes a transition amount of the pixel value 14. As a result, the gradation data applied to the panel is erroneously increased, and the display quality is greatly deteriorated.

  Accordingly, an object of the present invention is to provide a display control circuit that can suppress or eliminate a compression error that occurs during compression, a liquid crystal display device including the display control circuit, and a display control method.

A first invention is a display control circuit that receives input image data from outside and generates writing gradation data to be given to a display panel for displaying an image,
The input received according to the transition amount from the gradation indicated by the previous frame image data generated based on the input image data one frame period before the current time to the gradation indicated by the input image data received at the current time A writing gradation determination unit that generates writing gradation data by correcting the image data;
An arrival gradation determination unit that generates arrival gradation data estimated to be displayed after one frame period on the display panel to which the writing gradation data is given, according to the transition amount;
A compression unit that irreversibly compresses data by quantizing at least a part of pixel gradation data for each pixel constituting the image generated by the reaching gradation determination unit;
A storage unit for storing compression-coded data obtained by data compression by the compression unit;
The compressed gradation data stored in the storage unit is read and decoded as data corresponding to the previous frame image data after one frame period from the present time, and the writing gradation determination unit and the arrival gradation determination And a decoding unit to be provided to
The compression unit generates compressed statistical data in which information related to an error caused by the quantization is accumulated,
The decoding unit corrects the decoded data based on the compressed statistical data, and supplies the corrected data to the writing tone determination unit and the arrival tone determination unit.

According to a second invention, in the first invention,
The compression unit generates compressed statistical data including at least a part of an integrated amount of each round-up error and round-down error generated by the quantization or an integrated value of the number of occurrences,
The decoding unit calculates a correction value for correcting the decoded data in accordance with the respective integrated amount or the integrated value included in the compressed statistical data, and the decoding unit based on the calculated correction value It is characterized by correcting each of the data.

According to a third invention, in the second invention,
The compression unit calculates the number of round-up errors and round-down errors that occur due to the quantization and the number of times that the error does not occur due to the quantization during one frame period for each compression of the pixel gradation data. Generate compressed statistical data that includes the three integrated values,
The decoding unit calculates the correction value according to a result of comparing the three integrated values included in the compressed statistical data, and corrects the decoded data based on the calculated correction value, respectively. To do.

According to a fourth invention, in the second invention,
The compression unit calculates the number of round-up errors and round-down errors caused by the quantization and the number of times the error does not occur due to the quantization for each compression of the pixel gradation data and for the data compression. Generating compressed statistical data including a plurality of integrated values integrated for one frame period for each compression code of
The decoding unit calculates a correction value for each compressed code according to a result of comparing the number of occurrences and the number of non-occurrences for each compressed code among the plurality of integrated values included in the compressed statistical data. Then, each of the decoded data is corrected based on a correction value corresponding to the compressed code.

According to a fifth invention, in the first invention,
The compression unit compresses a difference value between a part of the pixel gradation data generated by the reaching gradation determination unit and pixel gradation data of a pixel adjacent to a pixel corresponding to the pixel gradation data. It is characterized by reversibly compressing data.

A sixth invention is a display control circuit according to any one of the first to fifth inventions;
A liquid crystal display panel that performs display using write gradation data supplied from the display control circuit, and that drives a plurality of video signal lines for transmitting a plurality of video signals corresponding to the write gradation data A signal line driving circuit, a scanning signal line driving circuit for driving a plurality of scanning signal lines intersecting with the plurality of video signal lines, and a matrix along the plurality of video signal lines and the plurality of scanning signal lines It is a liquid crystal display device comprising a liquid crystal display panel including a plurality of pixel forming portions to be arranged and a common electrode for applying a common potential to the plurality of pixel forming portions.

A seventh invention is a display control method for receiving input image data from the outside and generating writing gradation data to be given to a display panel for displaying an image,
The input received according to the transition amount from the gradation indicated by the previous frame image data generated based on the input image data one frame period before the current time to the gradation indicated by the input image data received at the current time A writing gradation determination step for generating writing gradation data by correcting the image data;
A reaching gradation determination step of generating arrival gradation data estimated to be displayed after one frame period on the display panel to which the writing gradation data is given, according to the transition amount;
A compression step of irreversibly compressing data by quantizing at least a part of the gradation data generated in the reached gradation determination step;
The previous frame image data one frame period after the current data decoded and read out from the compressed coded data stored in the storage unit for storing the compressed coded data obtained by compressing the data in the compression step And a decoding step given to the writing tone determination step and the reaching tone determination step as data corresponding to
In the compression step, compressed statistical data in which information related to an error caused by the quantization is accumulated is generated,
In the decoding step, the decoded data is corrected based on the compressed statistical data, and the corrected data is supplied to the writing gradation determination step and the reaching gradation determination step.

  According to the first aspect, the compression unit generates compressed statistical data in which information related to errors caused by quantization is generated, and the decoding unit corrects the decoded data based on the compressed statistical data. Since the written data is given to the writing gradation determination unit and the arrival gradation determination unit, if correction is made so as to reduce the compression error due to quantization, pixel gradation data for displaying an image can be calculated correctly. Therefore, display quality can be improved.

  According to the second aspect of the invention, the compressed statistical data including at least a part of the integrated value of the round-up error and the round-down error caused by quantization or the integrated value of the number of occurrences is generated, and depending on each integrated amount or integrated value Since the correction value for correcting the decoded data is calculated, the data is corrected with a correction value that reduces the compression error due to quantization, so that the pixel gradation data for displaying the image is correct. Since it can be calculated, display quality can be improved.

  According to the third aspect of the present invention, the number of occurrences of round-up error and round-down error caused by quantization and the number of non-occurrence of errors caused by quantization are accumulated for one frame period for each data compression. Since the compression statistical data including one integrated value is generated, the correction value further reduces the compression error, and the display quality can be further improved.

  According to the fourth aspect of the invention, the correction value for each compression code is calculated according to the result of comparing the number of occurrences and the number of occurrences for each compression code among the plurality of integrated values included in the compression statistical data. Therefore, the correction value is set finely for each compression code, the compression error is further reduced, and the display quality can be further improved.

  According to the fifth aspect of the invention, in some cases, the difference value with the pixel gradation data of adjacent pixels is reversibly compressed as a compression code, and in this case, no error occurs. Therefore, display quality can be further improved.

  According to the sixth aspect, the same effect as in the first aspect can be achieved in the liquid crystal display device.

  According to the seventh aspect, the same effect as that of the first aspect can be achieved in the display control method.

It is a block diagram which shows the whole structure of the liquid crystal television which concerns on one Embodiment of this invention. It is a block diagram which shows the whole structure of the liquid crystal display device in the said embodiment. It is a block diagram which shows the structure of the display control circuit in the said embodiment. It is a block diagram which shows the structure of the overshoot compensation part in the said embodiment. In the said embodiment, it is a figure which shows the arrival gradation data input into an image compression part, the produced | generated compression code, and its error. It is a figure which shows the 1st content example of the rounding information table in the said embodiment. It is a figure which shows the 2nd example of a content of the rounding information table in the said embodiment. In the said embodiment, it is a figure for demonstrating the error suppression of the data decoding in the 1st and 2nd content example. In the said embodiment, it is a figure which shows the error amount of data decoding in the 1st and 2nd content example.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
<1. Overall configuration of LCD TV>
FIG. 1 is a block diagram showing the overall configuration of a liquid crystal television according to an embodiment of the present invention. This liquid crystal television includes an antenna 2 for receiving television broadcasts, a tuner 3 for selecting desired transmission data from received radio waves, and video processing for decoding and extracting video data from the selected transmission data. A circuit 4 and a liquid crystal display device 5 that displays an image based on video data are provided. Since the present invention has a feature in the display control circuit provided in the liquid crystal display device 5, it will be described in detail below with reference to the drawings.

  FIG. 2 is a block diagram showing a detailed configuration of the liquid crystal display device 5. The liquid crystal display device 5 is an active matrix type liquid crystal display device, and includes a display control circuit 200, a video signal line drive circuit (source driver) 300, and a scanning signal line drive circuit (gate driver) 400. And a display unit 500 and a common electrode drive circuit 600. The display unit 500 includes a plurality (M) of video signal lines SL (1) to SL (M), a plurality (N) of scanning signal lines GL (1) to GL (N), and a plurality of these. A plurality of (M × N) pixels provided corresponding to the intersections of the video signal lines SL (1) to SL (M) and the plurality of scanning signal lines GL (1) to GL (N), respectively. Forming part. This pixel forming portion is a switching element having a gate terminal connected to the scanning signal line GL (n) passing through the corresponding intersection and a source terminal connected to the video signal line SL (m) passing through the intersection. A TFT (Thin Film Transistor), a pixel electrode connected to the drain terminal of the TFT, a common electrode (also referred to as a “counter electrode”) provided in common to each pixel formation portion, and common to each pixel electrode And a liquid crystal layer as an electro-optic element sandwiched between the electrodes. When the scanning signal G (n) applied to the scanning signal line GL (n) becomes active, this TFT is selected and becomes conductive. Then, the driving video signal S (m) is applied to the pixel electrode via the video signal line SL (m). As a result, the applied voltage of the driving video signal S (m) is written as a display value in the pixel formation portion including the pixel electrode.

  The display control circuit 200 receives input image data CD and a timing control signal TS sent from the outside, and controls writing gradation data WD that is a digital image signal and timing for displaying an image on the display unit 500. A source start pulse signal SSP, a source clock signal SCK, a latch strobe signal LS, a gate start pulse signal GSP, a gate clock signal GCK, and a polarity inversion signal φ are output.

  The video signal line driving circuit 300 receives the writing gradation data WD, the source start pulse signal SSP, the source clock signal SCK, and the latch strobe signal LS output from the display control circuit 200, and forms each pixel in the display unit 500. In order to charge the liquid crystal capacitor and the auxiliary capacitor of the unit, a driving video signal (here, writing gradation data WD described later) is applied to each video signal line SL (1) to SL (M). At this time, in the video signal line driving circuit 300, the write gradation data WD indicating the voltage to be applied to each of the video signal lines SL (1) to SL (M) is generated at the timing when the pulse of the source clock signal SCK is generated. Sequentially held. The held write gradation data WD is converted into an analog voltage at the timing when the pulse of the latch strobe signal LS is generated. The converted analog voltage is simultaneously applied to all the video signal lines SL (1) to SL (M) as a driving video signal. However, as described above, the desired gradation may not be reached depending on the optical response speed of the liquid crystal. Note that the video signals applied to the video signal lines SL (1) to SL (M) have their polarities according to the polarity inversion signal φ received from the display control circuit 200 for AC drive of the display unit 500. Is reversed.

  Based on the gate start pulse signal GSP and the gate clock signal GCK output from the display control circuit 200, the scanning signal line driving circuit 400 sends active scanning signals to the scanning signal lines GL (1) to GL (N). Apply rank.

  The common electrode drive circuit 600 generates a common voltage Vcom that is a voltage to be applied to the common electrode of the liquid crystal. In the present embodiment, in order to suppress the amplitude of the voltage of the video signal line, the potential of the common electrode is also changed according to the AC drive.

  As described above, the driving video signal is applied to the video signal lines SL (1) to SL (M) and the scanning signal is applied to the scanning signal lines GL (1) to GL (N). The image is displayed on the display unit 500.

<2. Configuration and operation of display control circuit>
FIG. 3 is a block diagram showing a configuration of the display control circuit 200 in the present embodiment. The display control circuit 200 includes a timing control circuit 21 that performs timing control, an image memory 22 that stores writing gradation data WD for one frame, and display values (displays) included in input image data CD provided from outside the apparatus. Gray scale data), and on the basis of a control signal from the timing control circuit 21, the received display value is referred to the write gradation data WD of the previous frame stored in the image memory 22 and overshoot driving is performed. And an overshoot compensator 23 for generating and outputting write gradation data WD (for performing optical response compensation of the liquid crystal).

  The timing control circuit 21 receives a timing control signal TS sent from the outside, a control signal CL for controlling the operation of the overshoot compensation unit 23, and a source start for controlling the timing for displaying an image on the display unit 500 A pulse signal SSP, a source clock signal SCK, a latch strobe signal LS, a gate start pulse signal GSP, a gate clock signal GCK, and a polarity inversion signal φ are output.

  The overshoot compensation unit 23 is read from the display value corresponding to one pixel included in the input image data CD sent from the outside, the control signal CL received from the timing control circuit 21, and the image memory 22. Write gradation in which overshoot driving is realized in display unit 500 based on data corresponding to past write gradation data WD of the corresponding pixel one frame before (hereinafter referred to as “previous frame image data PD”) Data WD is generated and output. A detailed configuration of the overshoot compensation unit 23 will be further described with reference to FIG.

<3. Configuration and operation of overshoot compensator>
FIG. 4 is a block diagram showing a configuration of the overshoot compensation unit in the present embodiment. As shown in FIG. 4, the overshoot compensation unit 23 is a liquid crystal display device including the present display control circuit based on input image data CD (in the current frame) and previous frame image data PD input from the outside. On the basis of the writing gradation determination unit 10 that outputs the writing gradation data WD for overshoot driving, the input image data CD, and the previous frame image data PD, the level reached after the lapse of one frame period in the liquid crystal display device. Reaching gradation determining unit 13 for outputting the reaching gradation data indicating the key, image compressing unit 11 for compressing the data output from the reaching gradation determining unit 13, and memory writing for writing the compressed data to the image memory 22 Unit 12, a memory reading unit 14 for reading compressed data from the image memory 22, and the read data for the previous frame image data It includes an image decoding unit 15 for decoding as data PD, and the information table 16 rounds storing rounding information RI from the image compression unit 11.

  The writing gradation determination unit 10 has a lookup table (LUT) (not shown) showing the relationship between the input image data CD and the writing gradation data WD corresponding to the previous frame image data PD. Write gradation data WD is output by referring to it. This LUT is created by calculating in advance optimum writing gradation data corresponding to the display characteristics of the liquid crystal display device, corresponding to the gradation transition amount from the image data of the previous frame.

  Based on the input image data CD and the previous frame image data PD input from the outside, the reached gradation determination unit 13 outputs the reached gradation data indicating the gradation reached after one frame period has elapsed in the liquid crystal display device. When the optical response speed of the liquid crystal is relatively slow, it may take one frame period or more to reach the gradation indicated by the write gradation data WD given to the liquid crystal display device. Therefore, more accurate driving can be performed by using the previous frame image data PD referred to when overshoot driving is performed as reaching gradation data that actually reaches after one frame period. The reached gradation determination unit 13 has a lookup table (LUT) (not shown) showing the relationship between the input image data CD and the reached gradation data corresponding to the previous frame image data PD, and refers to this LUT. Thus, the reached gradation data is output. This LUT is created by preliminarily calculating arrival gradation data that is predicted to actually arrive according to the display characteristics of the liquid crystal display device, corresponding to the gradation transition amount from the image data of the previous frame. .

  The image compression unit 11 receives the reached gradation data calculated by the reached gradation determination unit 13 and outputs a compression code using the compression method described above. In other words, if the difference value between adjacent pixel values is smaller than the threshold value, the difference value is output as a compressed code, and if the difference value is larger than the threshold value, the image data is quantized to be compressed into a smaller number of bits. Output data. Details will be described later with specific examples. Note that the data obtained by compressing the gradation value of each pixel as described above is also referred to as a compressed code here.

  The memory writing unit 12 manages the data writing position (address) to the image memory 22 and writes the compression code given from the image compression unit 11 to the writing position of the image memory 22.

  The memory reading unit 14 manages a data reading position (address) from the image memory 22 and reads a compression code corresponding to the previous frame image data PD from the reading position of the image memory 22.

  The image decoding unit 15 decodes the compressed data read from the memory reading unit 14 into the previous frame image data PD, and writes the decoded previous frame image data PD to the writing gradation determination unit 10 and the reached gradation determination unit 13. To give.

  The rounding information table 16 is a table that accumulates, for each frame, whether a round-down error has occurred, a round-up error has occurred, or has been quantized without any error when quantization is performed by the image compression unit 11. .

  In the present embodiment, by using the rounding information RI stored in the rounding information table 16, the occurrence of an error that should occur when the previous frame image data PD is decoded in the image decoding unit 15 is suppressed. The suppression of this error will be described in detail with reference to FIGS.

<4. Examples of errors and their suppression actions>
FIG. 5 is a diagram showing the reached gradation data input to the image compression unit, the generated compressed code, and its error. Consider an example in which each of the gradation data 51 (hereinafter referred to as “input data 51”) to be inputted is a 4-bit compression code.

  These 4 bits may represent a signed integer, and as will be described later, the most significant bit is an identification bit indicating whether or not it is a difference value, and the remaining 3 bits represent an unsigned integer. May be. Here, the latter is assumed. The identification bit is given when the data to be compressed is a value equal to or less than a predetermined threshold (here, 7) with respect to the immediately preceding adjacent data. Specific examples will be described below.

  The first data “96” in the input data 51 is quantized into 4 bits by the image compression unit 11 to obtain “6”, that is, a code 6 (96 ÷ 16 = 6) as a compression code. Here, at the time of decoding by the image decoding unit 15, 6 indicating 16 is multiplied by 16 to obtain 96 having the same value as the original value (6 × 16 = 96). Therefore, no error occurs in this case.

  Next, the second data “103” in the input data 51 is a difference value (by setting the identification bit), and the difference value from the first data “96” that is an adjacent value is 7 Therefore, the code 7 is obtained. Here, at the time of decoding, the difference value 7 is added to the data “96” corresponding to the code 6 corresponding to the first data, so that 96 having the same value as the original value is obtained. When the difference value is used in this way, naturally no error occurs.

  The third data “85” in the subsequent input data 51 obtains code 5 in the same manner (85 ÷ 16 = 5, remainder 5). Here, at the time of decoding, 5 indicating the compression code is multiplied by 16 to be 80, so that a round-down error occurs with respect to the original value of 85.

  Further, the fourth data “105” in the input data 51 similarly obtains the code 7 (105 ÷ 16 = 6, remainder 9). Here, at the time of decoding, 7 indicating the compression code is multiplied by 16 to become 112, so that a round-up error occurs with respect to the original value of 105.

  The image compression unit 11 stores the presence / absence and contents of the error in the rounding information table 16. The rounding information table 16 is described in a predetermined area on the memory, for example, written by the image compression unit 11, and appropriately read by the image decoding unit 15. In the following, two different content examples, and how to generate and use the rounding information table 16 will be described.

  FIG. 6 is a diagram illustrating a first content example of the rounding information table. The first content example 161 shown in FIG. 6 shows values obtained by accumulating the number of occurrences of a round-down error, the number of round-up errors, and the number of no errors over one frame. However, for convenience of explanation, the data of one frame period is actually only the input data 51 (although there are a large number of data) here, and integrated values for a total of five data are shown.

  FIG. 7 is a diagram illustrating a second content example of the rounding information table. The second content example 162 shown in FIG. 7 shows a value obtained by integrating the number of occurrences of round-down errors, the number of round-up errors, and the number of no errors over one frame for each compression code. . However, for convenience of explanation, the data of one frame period is actually only the input data 51 (although there are a large number of data) here, and integrated values for a total of five data are shown.

  The meaning of the data held in the rounding information table 16 shown as the first and second contents examples indicates the tendency of errors generated during quantization. By referring to this information, it is possible to suppress errors that occur during data decoding within one frame. Note that the rounding information table 16 only needs to include information that can determine such an error tendency, so it is not necessary to count errors for all pixel data in one frame. Alternatively, it may include contents other than the number of occurrences of error, for example, an integrated value of the error amount.

  FIG. 8 is a diagram for explaining error suppression of data decoding in the first and second content examples. FIG. 9 shows the error amount of data decoding in the first and second content examples. FIG.

  In FIG. 8, when the data compressed by the image compression unit 11 is decoded without being corrected by the image decoding unit 15 unlike the configuration of the present embodiment, the number indicating the compression code is simply multiplied by 16. Therefore, as described above, the code 6 is 96, the code 7 is 103 and indicates a difference value, the code 5 is 80, and the code 7 is 80. 112.

  FIG. 9 shows an error amount indicating how much the gradation value of the decoded data obtained in this way has changed from the gradation value of the input data 51 shown in FIG. 5 which is the gradation value before compression. It is as follows. That is, in FIG. 9, when the data compressed by the image compression unit 11 is decoded by the image decoding unit 15 and then corrected by the above correction value, the error amounts are 0 in the case of code 6 and code 7 When the difference value is indicated, the error amount is always 0 because it is decoded reversibly in the first place, is −5 in the case of code 5, and is +7 in the case of code 7.

  On the other hand, when the rounding information table 16 has the contents shown in FIG. 6 (shown in the first content example), the image decoding unit 15 refers to the rounding information table 16 and the round-off error occurrence count is rounded up. It is determined that the number is greater than the number of errors and the number without errors. In this case, since it tends to be rounded down, it can be seen that it is preferable to correct the data in the plus direction at the time of decoding in order to correct this. Therefore, the image decoding unit 15 performs correction to add 4 to the gradation values of all decoded data. That is, the correction value is set to +4.

  Here, this correction value will be described as being +4 for convenience, but this value can be determined as a certain value other than +4, or by accumulating errors generated during compression. It may be calculated by referring to a predetermined calculation formula or a correspondence table according to the obtained error integration amount or error integration count.

  In FIG. 8, when correcting in the first example, after the data compressed by the image compression unit 11 is decoded by the image decoding unit 15, 4 is added to all except when the value is a difference value. The code 6 is 100, the code 7 is 103 and indicates a difference value, the code 5 is 84, and the code 7 is 116.

  When the code 7 indicates a difference value, it is calculated by adding 7 to the gradation value 96 of the adjacent pixel, and is the gradation value of the adjacent pixel after correction. Adding 7 to 100 is not preferable because an error is generated instead of a difference value that does not cause an error.

  Next, when the rounding information table 16 has the contents shown in FIG. 7 (shown in the second content example), the image decoding unit 15 refers to the rounding information table 16 and determines the number of occurrences of the round-down error in the code 5. It is determined that the number of round-up errors is greater than the number of round-off errors and the number of round-off errors, and the number of occurrences of no error in code 6 is greater than the number of round-down errors and round-up errors. It is determined that the number of times is larger than the number of round-down errors and the number of times without errors. Since the number of data is small here, other codes have no difference in the number of occurrences.

  As described above, in the second content example, the error occurrence information is accumulated for each compressed code, and the error tendency is determined for each compressed code. Therefore, the error can be further reduced during decoding. That is, in the case of the code 5, since it tends to be rounded down, it can be seen that it is preferable to correct the data in the plus direction at the time of decoding in order to correct this. Therefore, the image decoding unit 15 performs correction to add 4 to the gradation value of the data obtained by decoding the code 5. That is, the correction value is set to +4. Note that this correction value is also convenient for the same reason as described above, and can be determined to be a certain other value, and the accumulated error amount obtained by accumulating errors generated during compression. Alternatively, it may be calculated by referring to a predetermined calculation formula or a correspondence table according to the number of error accumulations.

  Similarly, in the case of the code 6, since there is neither a tendency to round down nor a tendency to round up, the correction value for correcting this is set to zero. Furthermore, since the code 7 tends to be rounded up, it can be seen that it is preferable to correct the data in the minus direction at the time of decoding in order to correct this. Therefore, the image decoding unit 15 performs correction by subtracting 4 from the gradation value of the data obtained by decoding the code 7. That is, the correction value is set to -4. The calculation of other correction values is the same as described above, and a description thereof will be omitted.

  In FIG. 8, when the correction is performed in the second example, after the data compressed by the image compression unit 11 is decoded by the image decoding unit 15, the value is set for each compression code except when the value is a difference value. In order to add or subtract the correction value, the code 6 is 96, the code 7 is 103 when indicating a difference value, the code 5 is 84, and the code 7 Is 108.

  The amount of error indicating how much the gradation value of the decoded data obtained in this way has changed from the gradation value before compression is as shown in FIG. That is, in FIG. 9, when the data compressed by the image compression unit 11 is decoded by the image decoding unit 15 and then corrected with the above correction value for each compressed code, the error amount is 0 in the case of the code 6. Yes, in the case of code 7 indicating a differential value, the error amount is always 0 because it is decoded reversibly in the first place, in the case of code 5, it is -1, and in the case of code 7, it is +3. .

  Therefore, as can be seen by referring to FIG. 9, when the correction is performed in the first and second examples, the error is suppressed as compared with the case where the correction is not performed. It can also be seen that the error is suppressed more in the case of the correction in the second example than in the case of the correction in the first example.

<5. Effect>
As described above, the image decoding unit 15 of the display control circuit according to the present embodiment refers to the rounding information table 16 indicating the statistical data related to the compression error at the time of compression in the image compression unit 11, and determines the (quantization) compression error. The decoded data is corrected with the correction value as described above so as to reduce it. As a result, the gradation data given to the display panel for displaying the image can be calculated correctly, and the display quality can be improved.

DESCRIPTION OF SYMBOLS 5 ... Liquid crystal display device 10 ... Writing gradation determination part 11 ... Image compression part 12 ... Memory writing part 13 ... Arrival gradation determination part 14 ... Memory reading part 15 ... Image decoding part 16 ... Rounding information table 21 ... Timing control circuit 22 ... Image memory 23 ... Overshoot compensation unit 200 ... Display control circuit 300 ... Video signal line drive circuit (source driver)
400 ... Scanning signal line drive circuit (gate driver)
500 ... Display unit 600 ... Common electrode drive circuit CD ... Input image data WD ... Write gradation data PD ... Previous frame image data RI ... Rounding information

Claims (7)

A display control circuit that receives input image data from outside and generates writing gradation data to be given to a display panel that displays an image,
The input received according to the transition amount from the gradation indicated by the previous frame image data generated based on the input image data one frame period before the current time to the gradation indicated by the input image data received at the current time A writing gradation determination unit that generates writing gradation data by correcting the image data;
An arrival gradation determination unit that generates arrival gradation data estimated to be displayed after one frame period on the display panel to which the writing gradation data is given, according to the transition amount;
A compression unit that irreversibly compresses data by quantizing at least a part of pixel gradation data for each pixel constituting the image generated by the reaching gradation determination unit;
A storage unit for storing compression-coded data obtained by data compression by the compression unit;
The compressed gradation data stored in the storage unit is read and decoded as data corresponding to the previous frame image data after one frame period from the present time, and the writing gradation determination unit and the arrival gradation determination And a decoding unit to be provided to
The compression unit generates compressed statistical data in which information related to an error caused by the quantization is accumulated,
The decoding unit corrects the decoded data based on the compressed statistical data, and supplies the corrected data to the writing tone determination unit and the reached tone determination unit. circuit. The compression unit generates compressed statistical data including at least a part of an integrated amount of each round-up error and round-down error generated by the quantization or an integrated value of the number of occurrences,
The decoding unit calculates a correction value for correcting the decoded data in accordance with the respective integrated amount or the integrated value included in the compressed statistical data, and the decoding unit based on the calculated correction value The display control circuit according to claim 1, wherein each of the corrected data is corrected. The compression unit calculates the number of round-up errors and round-down errors that occur due to the quantization and the number of times that the error does not occur due to the quantization during one frame period for each compression of the pixel gradation data. Generate compressed statistical data that includes the three integrated values,
The decoding unit calculates the correction value according to a result of comparing the three integrated values included in the compressed statistical data, and corrects the decoded data based on the calculated correction value, respectively. The display control circuit according to claim 2. The compression unit calculates the number of round-up errors and round-down errors caused by the quantization and the number of times the error does not occur due to the quantization for each compression of the pixel gradation data and for the data compression. Generating compressed statistical data including a plurality of integrated values integrated for one frame period for each compression code of
The decoding unit calculates a correction value for each compressed code according to a result of comparing the number of occurrences and the number of non-occurrences for each compressed code among the plurality of integrated values included in the compressed statistical data. The display control circuit according to claim 2, wherein each of the decoded data is corrected based on a correction value corresponding to the compression code.   The compression unit compresses a difference value between a part of the pixel gradation data generated by the reaching gradation determination unit and pixel gradation data of a pixel adjacent to a pixel corresponding to the pixel gradation data. The display control circuit according to claim 1, wherein the data is reversibly compressed. A display control circuit according to any one of claims 1 to 5,
A liquid crystal display panel that performs display using write gradation data supplied from the display control circuit, and that drives a plurality of video signal lines for transmitting a plurality of video signals corresponding to the write gradation data A signal line driving circuit, a scanning signal line driving circuit for driving a plurality of scanning signal lines intersecting with the plurality of video signal lines, and a matrix along the plurality of video signal lines and the plurality of scanning signal lines A liquid crystal display device comprising: a plurality of pixel formation portions to be arranged; and a liquid crystal display panel including a common electrode that applies a common potential to the plurality of pixel formation portions. A display control method for receiving input image data from outside and generating writing gradation data to be given to a display panel for displaying an image,
The input received according to the transition amount from the gradation indicated by the previous frame image data generated based on the input image data one frame period before the current time to the gradation indicated by the input image data received at the current time A writing gradation determination step for generating writing gradation data by correcting the image data;
A reaching gradation determination step of generating arrival gradation data estimated to be displayed after one frame period on the display panel to which the writing gradation data is given, according to the transition amount;
A compression step of irreversibly compressing data by quantizing at least a part of the gradation data generated in the reached gradation determination step;
The previous frame image data one frame period after the current data decoded and read out from the compressed coded data stored in the storage unit for storing the compressed coded data obtained by compressing the data in the compression step And a decoding step given to the writing tone determination step and the reaching tone determination step as data corresponding to
In the compression step, compressed statistical data in which information related to an error caused by the quantization is accumulated is generated,
The decoding step corrects the decoded data based on the compression statistical data, and provides the corrected data to the writing gradation determination step and the reached gradation determination step. Method.

Images