JP2013088483A - Image display device and driving method for image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform optimum stereoscopic display in which cross-talk is suppressed, according to a liquid crystal response time, which changes according to a factor such as a panel temperature, in a spectacle system image display device used for stereoscopic display.SOLUTION: Image data transmitted to a liquid crystal panel 37 is compressed and encoded by an image encoding circuit 16, and it is decoded by an image decoding circuit 35. Thereby the transfer rate of image data is increased and the scanning period of a display panel is shortened. A compression rate for the encoding of the image data is determined based on a panel temperature detected by a temperature sensor 31.

Description

  The present invention relates to a glasses-type image display device used for stereoscopic display and a driving method thereof.

  2. Description of the Related Art Conventionally, glasses-type stereoscopic display devices that realize stereoscopic viewing by wearing special glasses for stereoscopic viewing using a liquid crystal panel and displaying separate images with parallax in both eyes of an observer are known. . In order to realize stereoscopic vision, it is necessary to show different parallax images for the left eye and the right eye, and thus two parallax images of the left eye image and the right eye image are necessary.

  In the glasses-type stereoscopic display device, the left-eye image and the right-eye image are alternately displayed on a two-dimensional panel in a time-sharing manner, and the shutter of the shutter glasses is alternately turned on / off in synchronization with the display timing. Stereoscopic vision is realized by controlling. However, in the case of a liquid crystal display panel, there is a problem with the response time of the liquid crystal. When the liquid crystal is driven from the upper part of the panel to the lower part of the panel, before the response of the liquid crystal at the lower part of the panel is completed, the panel of the next frame Since the upper liquid crystal drive is started, crosstalk (a mixture of the left eye image and the right eye image) occurs.

  In order to eliminate the crosstalk, for example, when the left-eye image is L and the right-eye image is R, there is a method of displaying images in the order of L, L, R, and R within a frame period of 60 Hz. In this case, since the same image is written twice, the crosstalk can be reduced as compared with the case where the left and right image displays are displayed one by one. Furthermore, in an image display device using a liquid crystal panel, there is a method in which the backlight is not always lit but only when the liquid crystal response is stable, in order to reduce crosstalk during stereoscopic viewing.

JP 2011-75668 A (published April 14, 2011) JP 2010-286555 A (published on December 24, 2010)

  In order to suppress crosstalk during stereoscopic display, Patent Document 1 includes a first drive mode and a second drive mode with a shorter scanning period, and the temperature is higher than a predetermined temperature. In addition, by selecting the second drive mode, it is possible to achieve optimal stereoscopic display under an environment other than low temperature.

  However, the image display device of Patent Document 1 cannot suppress crosstalk in a low temperature environment. In a normal liquid crystal display panel, a scanning period is set so that proper writing can be performed in a low temperature environment in order to guarantee writing in a low temperature environment. For this reason, there is a margin in the scanning period other than in the low temperature environment, and in Patent Document 1, the scanning period for the margin is shortened only in an environment other than the low temperature to realize the second drive mode.

  Further, since the response time of the liquid crystal depends not only on the temperature but also on the characteristics of the liquid crystal and the transistor characteristics, it is necessary to select two or more types of optimum scanning periods in view of these.

  In Patent Document 1, in order to shorten the scanning period in the second drive mode, the transfer rate between the timing controller and the source driver becomes a bottleneck, so it is necessary to reduce the transfer amount using image compression. There is. The YUV conversion (converting the RGB image signal into the luminance signal Y and the color difference signal UV) employed in Patent Document 1 has a problem that the compression rate cannot be made variable.

  Further, in Patent Document 2, as a method for suppressing the crosstalk, a means for optimizing the backlight lighting period using the parallax amount and contrast between the left eye image and the right eye image is presented. In particular, the crosstalk cannot be eliminated without eliminating the period in which the left eye image and the right eye image are mixed.

  The present invention has been made in view of the above problems, and an image display device capable of optimal three-dimensional display with reduced crosstalk according to a liquid crystal response time that varies depending on factors such as panel temperature, and a driving method thereof. The purpose is to provide.

  In order to solve the above problems, an image display device according to the present invention encodes image data transmitted to the display panel in an image display device having a display panel and a backlight. An image encoding means having a variable compression rate when performing the encoding, an image decoding means for decoding the image data encoded by the image encoding means into original image data, and a panel of the display panel A temperature detecting means for detecting temperature; a compression ratio determining means for determining a compression ratio when data encoding is performed by the image encoding means based on the panel temperature detected by the temperature detecting means; and the compression ratio Based on the compression ratio determined by the determining means, a scanning period calculating means for calculating a scanning period in the display panel, and a backlight for controlling the lighting period of the backlight. And the compression rate determining means determines the compression rate so that the sum of the liquid crystal response time corresponding to the panel temperature and the scanning period does not exceed one frame period. The backlight control means controls the lighting of the backlight so that the backlight is lit in a state where the liquid crystal response is completed in all the pixels in the display panel.

  According to the above configuration, the image data transmitted to the display panel is compressed and encoded, and the image data encoded on the display panel side is decoded into the original image data, thereby transferring the image data transfer rate. The scanning period in the display panel can be shortened. The compression rate at the time of encoding is variable, and the compression rate is determined based on the panel temperature detected by the temperature detection means. Thereby, the scanning period in the display panel is appropriately shortened according to the panel temperature of the display panel, and the liquid crystal response is completed within one frame (avoids mixing of L image and R image within the same frame). The occurrence of talk can be prevented.

  At this time, the scanning period in the display panel is calculated based on the compression rate, and the backlight control means turns on the backlight in a state where the liquid crystal response is completed in all the pixels in the display panel. In addition, the lighting control of the backlight is performed.

  In the image display device, the compression rate determining means selects the lowest compression rate from a plurality of settable compression rates, and the scanning period calculation circuit is based on the compression rate. The scanning period is calculated, and the backlight control means can be configured such that a period obtained by subtracting the liquid crystal response time and the scanning period from one frame period is set as the backlight lighting period.

  Further, in the image display device, the backlight control means sets a predetermined period as a backlight lighting period, and the scanning period calculation circuit starts from one frame period to the liquid crystal response time and the liquid crystal response time. A period obtained by subtracting the backlight lighting period is calculated as the scanning period, and the compression rate determining means may determine the compression rate so that the scanning period can be achieved.

  In order to solve the above-described problem, a driving method for an image display device according to the present invention is a temperature detection step for detecting a panel temperature of the display panel in the driving method for an image display device having a display panel and a backlight. And a compression rate determination step for determining a compression rate when encoding image data transmitted to the display panel based on the panel temperature detected by the temperature detection step, and the compression rate determination step. Based on the compression ratio, an image encoding process for encoding image data transmitted to the display panel, and a scanning period in the display panel is calculated based on the compression ratio determined by the compression ratio determination process. A scanning period calculating step, an image decoding step for decoding the image data encoded by the image encoding step into original image data, and the buffer A backlight control process for controlling the lighting period of the light, and in the compression ratio determination process, the total of the liquid crystal response time corresponding to the panel temperature and the scanning period does not exceed one frame period. In addition, the compression rate is determined, and in the backlight control step, backlight lighting control is performed so that the backlight is turned on in a state where the liquid crystal response is completed in all the pixels in the display panel. It is a feature.

  According to the above configuration, similarly to the image display device described above, the scanning period in the display panel is appropriately shortened according to the panel temperature of the display panel, and the liquid crystal response is completed within one frame (within the same frame). The occurrence of crosstalk can be prevented by avoiding mixing of the L image and the R image.

  The present invention encodes image data transmitted to the display panel in an image display device having a display panel and a backlight, and an image code having a variable compression rate when performing the data encoding. Means, image decoding means for decoding the image data encoded by the image encoding means into original image data, temperature detection means for detecting the panel temperature of the display panel, and temperature detection means Based on the panel temperature detected by the image encoding means, a compression ratio determining means for determining a compression ratio when data encoding is performed, and a compression ratio determined by the compression ratio determining means based on the compression ratio A scanning period calculating means for calculating a scanning period in the display panel; and a backlight control means for controlling the lighting period of the backlight. The stage determines the compression rate so that the sum of the liquid crystal response time corresponding to the panel temperature and the scanning period does not exceed one frame period, and the backlight control means includes the display panel. The backlight lighting control is performed so that the backlight is turned on in a state where the liquid crystal response is completed in all the pixels.

  Therefore, the scanning period in the display panel is appropriately shortened according to the panel temperature of the display panel, and the liquid crystal response is completed within one frame (avoids mixing of L image and R image within the same frame). There is an effect that the occurrence of talk can be prevented.

1 is a block diagram illustrating a configuration of an image display device according to an embodiment of the present invention. It is a figure which shows the scanning period and liquid crystal response time of a liquid crystal panel when it is a case where an image is output at the frame rate of 120 Hz, and image data is not compressed. It is a figure which shows one example of liquid crystal response time information. 6 is a diagram illustrating a scanning period of a liquid crystal panel, a liquid crystal response time, and a backlight lighting timing in Example 1. FIG. It is a figure which shows the scanning period and liquid crystal response time of a liquid crystal panel when the same image is output twice at a frame rate of 240 Hz and image data is not compressed. It is a figure which shows the scanning period and liquid crystal response time of a liquid crystal panel in Example 2, and a backlight lighting timing. FIG. 7 is a block diagram illustrating a configuration of an image display device according to Example 3 in accordance with an embodiment of the present invention. It is a figure which shows the scanning period and liquid crystal response time of a liquid crystal panel in Example 3, and a backlight lighting timing.

[Configuration of image display device]
FIG. 1 is a diagram showing an overall configuration of an image display apparatus according to the present embodiment. The image display device includes a timing controller (TCON) 10, an external ROM (Read Only Memory) 30, a temperature sensor 31, shutter glasses 32, a gate driver 33, a source driver 34, a backlight 36, and a liquid crystal panel 37. Has been.

  The timing controller 10 includes a reception unit 11, a gamma correction circuit 12, an overdrive circuit 13, an image encoding circuit 16, a liquid crystal response time information storage unit 17, a compression rate determination circuit 18, a scanning period calculation circuit 27, and a temperature data measurement circuit 19. , Frame memories 14 and 15, a format unit 20, a transmission unit 21, and a timing generator 22.

  The timing generator 22 includes a backlight control circuit 23, a glasses control circuit 24, a gate control circuit 25, and a source control circuit 26. Further, the source driver 34 has an image decoding circuit 35.

  The receiving unit 11 receives an input image signal transferred from the outside. The gamma correction circuit 12 corrects the gamma characteristic by converting the input image by a LUT (Look Up Table). The overdrive circuit 13 inputs the image data of the previous frame and the image data of the current frame stored in the frame memory 15 to the LUT, and converts the image data of the current frame. The image encoding circuit 16 converts the image data into encoded data at the compression rate determined by the compression rate determination circuit 18.

  The format unit 20 converts an array of encoded data according to the transmission format of the source driver 34. The transmission unit 21 performs signal transfer according to the transmission method of the source driver 34.

  The source control circuit 26 generates a control signal for the source driver 34. The gate control circuit 25 generates a control signal for the gate driver 33. The eyeglass control circuit 24 controls On / Off of the shutter of the shutter eyeglasses 32.

  The external ROM 30 stores information for determining the operation of the timing controller 10. The stored information includes the LUT of the gamma correction circuit 12, the LUT of the overdrive circuit 13, the liquid crystal response time information 17 for each temperature, and the like. The liquid crystal response time information 17 is provided as an LUT.

  The temperature data measurement circuit 19 periodically measures the panel temperature data of the liquid crystal panel 37 using the temperature sensor 31 and stores the measured temperature data. The measured panel temperature data is input to the liquid crystal response time information 17, and the liquid crystal response time of the corresponding temperature in the liquid crystal response time information 17 is selected.

  The compression rate determination circuit 18 sets the compression rate so that the sum of the liquid crystal response time selected by the selected temperature data and the scanning time is equal to or less than the frame period (8.3 ms when the frame rate is 120 Hz). To decide. This compression rate is a compression rate when the image encoding circuit 16 converts image data into encoded data. The compression rate determined by the compression rate determination circuit 18 is transferred to the image encoding circuit 16, the scanning period calculation circuit 27, and the image decoding circuit 35. The scanning period calculation circuit 27 calculates a scanning period from the compression rate. The scanning period is calculated by multiplying the scanning period when the image data is not compressed (determined from the number of output horizontal clocks, the internal clock period, and the number of vertical lines) by the compression rate.

  The backlight control circuit 23 controls the lighting start timing and lighting period of the backlight 36. The backlight control circuit 23 determines the lighting start timing and lighting period of the backlight 36 from the liquid crystal response time and the scanning period obtained as described above.

[Example 1]
FIG. 2 shows an example of the scanning period and the liquid crystal response time when the frame rate is 120 Hz (the frame period is 8.3 ms) and the image data is not compressed. The time from the start of scanning at the top of the panel to the start of scanning at the bottom of the panel takes a scanning period, and the time from the start of scanning until the response of the liquid crystal is completed is the liquid crystal response time. In the case of FIG. 2, the response time of the liquid crystal at the lower part of the L image panel overlaps with the start of the scanning period at the upper part of the R image panel.

  FIG. 3 shows an example of the liquid crystal response time information 17. The liquid crystal response time information 17 stores the liquid crystal response time for each temperature, and the corresponding liquid crystal response time is selected from the temperature read from the temperature sensor.

  FIG. 4 shows the scanning period and the liquid crystal response time in the first embodiment. The panel temperature at this time shall be 20 degreeC. The scanning period when compression is not performed is assumed to be 8.0 ms. If the current panel temperature of 20 ° C. is input to the liquid crystal response time information 17 shown in FIG. 3, it is output that the liquid crystal response time is 4.0 ms. Since the frame period is 8.3 ms, at this time, in order to complete the liquid crystal response within one frame, the scanning period needs to be 4.3 ms or less. Since the scanning period without compression is 8.0 ms, if the compression rate is set to 50%, the scanning period becomes 4.0 ms, and the liquid crystal response is completed within one frame as shown in FIG. The occurrence of crosstalk can be prevented by avoiding mixing of the L image and the R image in the frame.

  Further, the remainder obtained by subtracting the scanning period of 4.0 ms and the liquid crystal response time of 4.0 ms from one frame period of 8.3 ms is 0.3 ms, and this is the backlight lighting period. Therefore, the backlight control circuit 23 starts lighting after 8.0 ms from the search start time at the top of the panel, and controls the backlight 36 so that the lighting time becomes 0.3 ms.

  The compression rate in the first embodiment is set so that the crosstalk can be reduced and the lowest compression rate is selected from a plurality of settable compression rates. This is because the image quality is generally deteriorated when the compression rate is high, and therefore it is desirable that the compression rate is as low as possible. For example, in the above example, in order to set the scanning period to 4.3 ms or less, the compression rate may be 40% instead of 50%, but in order to make the compression rate as low as possible, a compression rate of 50% is selected. .

As a method used for image encoding and image decoding, any method can be used as long as the compression rate can be varied. For example, it is possible to use a fixed-length encoding method that switches between DPCM (Differential Pulse Code Modulation) and PCM (Pulse Code Modulation) according to the difference value between adjacent pixels. If this compression method is used, the following variations exist as types of compression rates, and the compression rate is selected from the variations. In the following example, it is assumed that the original image data is 30 bits (RGB each 10 bits).
28/30: Quantized data 27 bits (9 bits for each RGB) + Coding mode 1 bit
25/30: Quantized data 24 bits (RGB each 8 bits) + coding mode 1 bit
22/30: Quantized data 21 bits (RGB each 7 bits) + coding mode 1 bit
19/30: Quantized data 18 bits (RGB each 6 bits) + coding mode 1 bit
16/30: Quantization data 15 bits (RGB each 5 bits) + coding mode 1 bit
13/30: Quantized data 12 bits (RGB each 4 bits) + coding mode 1 bit
In the first embodiment, since the backlight lighting time is set according to the compression rate of the image data, there is a possibility that the backlight lighting time varies depending on the compression rate. For this reason, if the brightness of the backlight is constant, there is a possibility that a difference in image brightness may occur even when the same image display is displayed. In order to avoid this, the backlight may be an active backlight and the backlight brightness may be adjusted according to the backlight lighting time. If an LED is used as the light source of the backlight, it is possible to adjust the brightness with the current value. Even if the backlight lighting time changes, the change in the brightness of the displayed image can be adjusted by adjusting the backlight brightness. Can be compensated by.

[Example 2]
FIG. 5 shows an example of a scanning period and a liquid crystal response time when image data is not compressed when the frame rate is 240 Hz (when the same image is output twice). In the case of FIG. 5, since the liquid crystal response time at the bottom of the L image panel overlaps with the start of the scanning period at the top of the R image panel, crosstalk occurs in which the L image and the R image appear to be mixed.

  FIG. 6 shows the scanning period and the liquid crystal response time in the second embodiment. The panel temperature at this time shall be 10 degreeC. Further, it is assumed that the scanning period when compression is not performed is 4.0 ms. If the current panel temperature of 10 ° C. is input to the liquid crystal response time information 17 shown in FIG. 3, it is output that the liquid crystal response time is 4.4 ms. Since the frame period is 8.3 ms, at this time, in order to complete the liquid crystal response within one frame, the scanning period needs to be 3.9 ms or less. Since the scanning period without compression is 8.0 ms, if the compression rate is set to 80%, the scanning period becomes 3.2 ms, and the liquid crystal response is completed within one frame as shown in FIG. The occurrence of crosstalk can be prevented by avoiding mixing of the L image and the R image in the frame.

  Further, the remainder obtained by subtracting the scanning period 3.2 ms and the liquid crystal response time 4.4 ms from the one frame period 8.3 ms is 0.7 ms, and this is the backlight lighting period. Therefore, the backlight control circuit 23 starts lighting after 7.6 ms from the search start time at the top of the panel, and controls the backlight 36 so that the lighting time becomes 0.7 ms.

Example 3
FIG. 7 is a diagram illustrating the overall configuration of the image display apparatus according to the third embodiment. The configuration of the image display apparatus shown in FIG. 7 is almost the same as the configuration of FIG. 1, so only the differences will be described, and the description of the same configuration as FIG. 1 will be omitted.

  In the image display apparatus according to the third embodiment, information about the lighting period of the backlight is given to the backlight control circuit 22 in advance. The scanning period is calculated from the backlight lighting time and the liquid crystal response time corresponding to the measured temperature data. The compression rate determination circuit 18 determines the compression rate so as to satisfy the calculated scanning period.

  FIG. 5 shows an example of a scanning period and a liquid crystal response time when image data is not compressed when the frame rate is 240 Hz (when the same image is output twice). In the case of FIG. 5, since the liquid crystal response time at the bottom of the L image panel overlaps with the start of the scanning period at the top of the R image panel, crosstalk occurs in which the L image and the R image appear to be mixed.

  FIG. 8 shows an example of the scanning period and the liquid crystal response time when the frame rate is 240 Hz (when the same image is output twice) and the backlight lighting time is determined to be 1.6 ms in advance. Yes. The liquid crystal response time at this time is 4.4 ms (panel temperature 10 ° C.), which is the same as in the second embodiment. At this time, since the lighting time of the backlight is determined to be 1.6 ms, it is necessary to set the scanning period to 2.4 ms. As a result, the compression rate is set to 60%.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be used for an image display device used for glasses-type stereoscopic display.

10 Timing controller 14, 15 Frame memory 16 Image coding circuit (image coding means)
17 Liquid crystal response time information 18 Compression rate determination circuit (compression rate determination means)
19 Temperature data measurement circuit (temperature detection means)
22 Timing generator 23 Backlight control circuit (backlight control means)
27 Scanning period calculation circuit (scanning period calculation means)
31 Temperature sensor (temperature detection means)
33 Gate driver 34 Source driver 35 Image decoding circuit (image decoding means)
36 Backlight 37 LCD panel (display panel)

Claims (4)

In an image display device having a display panel and a backlight,
Image encoding means for encoding image data transmitted to the display panel, and an image encoding means having a variable compression rate when performing the data encoding;
Image decoding means for decoding the image data encoded by the image encoding means into original image data;
Temperature detecting means for detecting the panel temperature of the display panel;
Based on the panel temperature detected by the temperature detection unit, a compression rate determination unit that determines a compression rate when data encoding is performed by the image encoding unit;
Scanning period calculation means for calculating a scanning period in the display panel based on the compression ratio determined by the compression ratio determination means;
A backlight control means for controlling the lighting period of the backlight,
The compression rate determining means determines the compression rate so that the total of the liquid crystal response time corresponding to the panel temperature and the scanning period does not exceed one frame period.
The image display apparatus, wherein the backlight control unit controls the lighting of the backlight so that the backlight is lit in a state where the liquid crystal response is completed in all the pixels in the display panel. The compression rate determination means selects the lowest compression rate from a plurality of settable compression rates,
The scanning period calculation circuit calculates a scanning period based on the compression rate,
The image display device according to claim 1, wherein the backlight control unit sets a period obtained by subtracting a liquid crystal response time and a scanning period from one frame period as a lighting period of the backlight. The backlight control means uses a predetermined period as a backlight lighting period,
The scanning period calculation circuit calculates a period obtained by subtracting the liquid crystal response time and the backlight lighting period from one frame period as the scanning period.
The image display device according to claim 1, wherein the compression rate determination unit determines the compression rate so that the scanning period can be achieved. In a driving method of an image display device having a display panel and a backlight,
A temperature detecting step for detecting the panel temperature of the display panel;
Based on the panel temperature detected by the temperature detection step, a compression rate determination step for determining a compression rate when encoding the image data transmitted to the display panel;
An image encoding step for encoding image data to be transmitted to the display panel based on the compression rate determined by the compression rate determination step;
A scanning period calculation step of calculating a scanning period in the display panel based on the compression rate determined by the compression rate determination step;
An image decoding step of decoding the image data encoded by the image encoding step into the original image data;
A backlight control process for controlling the lighting period of the backlight,
In the compression rate determination step, the compression rate is determined so that the total of the liquid crystal response time corresponding to the panel temperature and the scanning period does not exceed one frame period,
The method for driving an image display device, wherein in the backlight control step, the backlight is controlled so that the backlight is lit in a state where the liquid crystal response is completed in all the pixels in the display panel.

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