Patent Application
20080252583
1. Field of the Invention
The present invention relates to a liquid-crystal display apparatus, control method thereof, and computer program.
2. Description of the Related Art
Recently, liquid-crystal display apparatuses have been used as a TV receiver and the display device of a PC. Liquid-crystal display apparatuses can have flat panels, achieve space saving and power reduction, and thus are widely used. However, liquid-crystal display apparatuses suffer a long response time until image data is actually displayed. As a liquid-crystal display apparatus driving method for increasing the response speed, there is proposed a method of comparing image data to be displayed next with previous image data, and performing overdrive in accordance with the comparison result (see Japanese Patent Laid-Open No. 11-126050).
When overdrive is performed on only one side (positive or negative side) of AC driving, a DC component remains, as shown in
This liquid-crystal display apparatus adopts the structure in which at least either the pixel electrode or opposite electrode is formed from an ITO film. This structure can suppress degradation of the reliability caused by a DC component left after overdrive. However, this structure cannot be widely applied to a variety of liquid-crystal display apparatuses because the panel structure of the liquid-crystal display apparatus must be changed.
As described above, a conventional display apparatus cannot increase the response speed and reliability by removing an unbalanced DC component generated by overdrive without changing the panel structure.
It is an object of the present invention to provide an invention capable of removing an unbalanced DC component generated by overdrive and increasing the response speed and reliability without changing the panel structure.
An invention corresponding to one aspect of the present invention relates to a liquid-crystal display apparatus comprising a liquid-crystal display device driven by an AC voltage, an image divider configured to temporally divide input image data into N (N≧2) for each frame, a correction unit configured to correct a driving voltage for driving the liquid-crystal display device based on a difference between adjacent divided image data obtained by the N division, a polarity inverter configured to invert a polarity to make drive polarities of adjacent divided image data different, out of the divided image data obtained by the N division including the divided image data for which driving voltage is corrected by correction unit, a driver configured to drive the liquid-crystal display device using the polarity-inverted divided image data, and an inversion order alteration unit which alters an inversion order for the drive polarities.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments do not limit the claims of the present invention, and not all combinations of features set forth in the embodiments are essential in solving means of the present invention.
In
The structure of the projection display engine D1 according to the first embodiment of the present invention will be explained with reference to
In
A parabolic reflector 10 surrounds a lamp (light source) 1, and converts light L1 emitted from the lamp 1 into a parallel beam L2. The reflector 10 may be not parabolic but elliptic, and may convert the light L1 into a convergent beam. As the lamp 1, a metal halide lamp, xenon lamp, or the like is available. Fly-eye integrators 40 and 41 are arranged on the optical path of light emitted from the lamp 1 so as to be conjugate to the liquid-crystal panels 2R, 2G, and 2B. The fly-eye integrators 40 and 41 improve the non-uniformity of the light source. A relay lens 11 and mirror 12 are arranged in the order named on the light exit side of the fly-eye integrators 40 and 41. At the subsequent stage, two dichroic mirrors 13 and 14 are arranged to split light emitted from the lamp 1 into three beams. Relay lenses 15 and mirrors 16, 17, and 18 are arranged to guide these beams to the liquid-crystal panels 2R, 2G, and 2B. Reference numeral 19 denotes a field lens.
The liquid-crystal panels 2R, 2G, and 2B are connected to a video signal input unit 3 and the like as shown in
Processing of an electrical signal by the projection display engine D1 according to the first embodiment will be described.
In the video signal processing unit 3, a switch 30 switches between a video signal input from a PC via a terminal 50 and an NTSC signal input from a terminal 51. NTSC signals include the video signals of general TV broadcast programs. NTSC signals also include video signals obtained from recording apparatuses (e.g., videotape recorder, DVD recorder, and HDD recorder) which record video signals on a medium, and playback apparatuses (e.g., DVD player and LD player) which play back video signals recorded on a medium. A signal processing circuit 52 performs signal processes such as decoding of an NTSC signal, noise reduction, bandpass filtering, and signal level adjustment for an NTSC signal input from the terminal 51. An A/D converter 31 converts an input analog video signal into a digital signal.
A DSP (Digital Signal Processor) 32 receives A/D-converted digital image data, executes predetermined signal processing, and outputs the execution result to a frame rate converter 101. The predetermined signal processing includes image processes such as contrast/brightness adjustment, color conversion, and resolution conversion. The frame rate converter 101 converts the frame rate of input image data. A memory 33 holds the current image data, image data to be displayed by the next frame, and the like.
A timing generator (TG) 34 outputs a timing signal which defines the operation timing of each unit. A memory 102 stores previous image data in order to correct the response speed. A response speed correction unit 103 compares image data output from the frame rate converter 101 with image data via the memory 102, and corrects the response speed by correcting the driving voltage. A polarity inverter 106 inverts the polarity of an image signal on the basis of input image data.
A polarity inversion controller 131 instructs the polarity inverter 106 to alter the polarity inversion order. A timing detector 132 detects the timing to alter the polarity inversion order. A D/A converter 35 converts digital image data into an analog image signal, and outputs the analog image signal to a panel driver 36. By the analog image signal, video signals and power are supplied to the R, G, and B liquid-crystal panels 2R, 2G, and 2B via the panel driver 36.
A ballast 57 is a lamp power supply connected to the lamp 1. A power supply 58 functions as a power supply means for supplying the operating power of the display apparatus 200. Reference numeral 60 denotes an AC inlet. A remote controller 61 designates various operations of the display apparatus 200. A control panel 62 receives a signal from the remote controller 61.
Reference numeral 204 denotes a brightness adjustment switch. A brightness adjusting switch detector 109 detects the operation of the brightness adjusting switch 204. A digitizer detector 118 detects coordinates indicated by the digitizer 202. Reference numeral 107 denotes a USB interface (I/F); 63, a CPU; 64, a ROM; and 65, a RAM. The CPU 63 is connected to the video signal input unit 3, control panel 62, ballast 57, brightness adjusting switch detector 109, digitizer detector 118, USB I/F 107, and the like. The CPU 63 performs driving control of the liquid-crystal panels 2R, 2G and 2B, the lamp 1, and the like, and enlarges/reduces/moves a display image.
The brightness adjusting switch detector 109, digitizer detector 118, USB I/F 107, and the like are connected to the CPU 63 in the first embodiment, but may also be incorporated in the CPU or executed in accordance with programs.
The arrangement of a PC (Personal Computer) 300 connected to the display apparatus 200 will be explained. The PC 300 comprises a CPU 301, HD (Hard disk) 302, RAM 303, ROM 304, video memory 305, graphic controller 306, mouse I/F 307, and USB I/F 308. The PC 300 further comprises a video output terminal 309, USB input terminal 310, and mouse input terminal 311. A mouse 312 functions as a pointing device, and is connected to the mouse input terminal 311.
The operation of the display apparatus 200 according to the first embodiment will be explained in detail with reference to
In the display apparatus 200, the switch 30 selects either a video signal input from the PC input terminal 50 or a video signal input from the NTSC input terminal 51. The A/D converter 31 converts the selected video signal from an analog signal into a digital signal. The DSP 32 performs image processes such as contrast/brightness adjustment and color conversion for the digital image data. The frame rate converter 101 converts the image data output from the DSP 32 into data with a desired resolution and frame rate.
The frame rate converter 101 temporally divides one frame into N by image division. N is an arbitrary integer of 2 or more, and the frame rate is multiplied by N in accordance with the division count. In the first embodiment, as an example of N division, N=2, i.e., a video input signal at a vertical frequency of 60 Hz is converted into a signal with a frame rate at a double vertical frequency of 120 Hz. At this time, image data of at least one input frame is stored in the memory 33. An input image signal can be converted into a divided image signal having a different frame rate by changing the readout speed of image data from the memory 33.
In the first embodiment, the frame rate converter 101 converts the frame rate of an image from 60 Hz into 120 Hz. The frame rate converter 101 doubles the frame rate by reading out image data successively twice from the memory 33. To increase the response speed of the display apparatus 200, the response speed correction unit 103 corrects the driving voltage and executes so-called overdrive.
The response speed correction unit 103 compares image data of an immediately preceding frame stored in the memory 102 with the current image data. If the image data has changed, the response speed correction unit 103 performs overdrive in accordance with the comparison result. In the example of
Further, frame 4 is different from immediately preceding frame 3′. Thus, the voltage V2 is corrected to execute overdrive at a voltage V2′ in frame 4. The difference value between the voltages V2′ and V2 is a correction value corresponding to the voltage V2 before transition and the voltage V1 after transition. In frames 4′ and subsequent frames in
In
As a response speed correction method, the correction amount may be changed in accordance with the input level of image data of an immediately preceding frame and that of currently displayed image data on the basis of the LUT. Alternatively, the correction amount may be determined in accordance with the difference between image data of an immediately preceding frame and currently displayed image data. According to the method using the LUT, overdrive optimum for the change level is possible by increasing the correction amount at halftone at which the response speed is low.
The polarity inverter 106 inverts the polarity of the signal and outputs the signal every frame after the speed is doubled.
In
An example of altering the polarity inversion order will be explained with reference to
In the first embodiment, the user operates the remote controller 61 to switch an input signal to the display apparatus 200. The polarity inversion order is altered at the timing when the input signal is switched. Polarity inversion order alteration processing will be explained with reference to
When the user operates the remote controller 61 to input an input switching instruction, the control panel 62 receives a signal transmitted from the remote controller 61 in accordance with the operation in step S901. The control panel 62 notifies the CPU 63 of the reception of the signal from the remote controller. In response to this notification, the CPU 63 controls the DSP 32 to change the display screen to a black display in step S902. By changing the display screen to a black display, switching noise by the switch 30 when inputting the input switching instruction can be hidden.
While the black display is output, the CPU 63 controls the polarity inversion controller 131 to output a polarity inversion order alteration instruction to the polarity inverter 106 and alter the polarity inversion order in step S903. In step S904, the CPU 63 designates switching of the switch 30 to switch the input to the PC input 50 or NTSC input 51. In step S905, the CPU 63 cancels the black display setting by the DSP 32.
In this manner, the polarity inversion order is altered when the black display is output in input switching. This can suppress degradation of the image quality caused by the flicker of the display screen that occurs when the same polarity continues in altering the polarity inversion order.
In
Response speed correction processing according to the first embodiment will be described with reference to
In step S1001, the frame rate converter 101 receives current image data processed by the DSP 32. In step S1002, the frame rate converter 101 doubles the frame rate of the input current image data. In step S1003, the current image data whose frame rate has been doubled is compared with image data of an immediately preceding frame stored in the memory 33.
If the two image data coincide with each other (“YES” in step S1004), the process shifts to step S1006. If the two image data are different from each other (“NO” in step S1004), the process shifts to step S1005. In step S1005, the response speed correction unit 103 increases or decreases the driving voltage of the current image data in accordance with the transition direction from the image of an immediately preceding frame to that of the current image in order to perform overdrive. More specifically, if the transition direction from the image of an immediately preceding frame to that of the current image is an up direction, the response speed correction unit 103 further increases the driving voltage. To the contrary, if the transition direction from the image of an immediately preceding frame to that of the current image is a down direction, the response speed correction unit 103 further decreases the driving voltage. In step S1006, it is determined whether to alter the polarity inversion order. This determination is based on whether the timing detector 132 has detected the timing to alter the polarity inversion order and the polarity inversion controller 131 designates alteration of the polarity inversion order. If it is determined to alter the polarity inversion order (“YES” in step S1006), the process shifts to step S1007. If it is determined that the polarity inversion order need not be altered (“NO” in step S1006), the process shifts to step S1008.
In step S1007, the polarity inversion controller 131 sets alteration of the polarity inversion order, and the process shifts to step S1008. In step S1008, the polarity inverter 106 inverts the polarity of the signal every frame, and outputs the resultant signal to the D/A converter 35. In step S1009, the R, G, and B liquid-crystal panels 2R, 2G, and 2B are driven for display on the basis of a signal output from the D/A converter 35. In step S1010, it is determined whether to end the image display processing. If it is determined not to end the image display processing (“NO” in step S1010), the process returns to step S1001 to continue the process. If it is determined to end the display processing (“YES” in step S1010), the process ends.
As a result, overdrive is executed uniformly in forward driving and backward driving.
As described above, the first embodiment can balance overdrive voltages in forward driving and backward driving, and improve the reliability of a display image.
The second embodiment of the present invention will be explained. The second embodiment will describe a method of altering the polarity inversion order more frequently than in the first embodiment.
The scene change detector 1101 determines whether a scene change has occurred, by comparing the average luminance value of the image of an (immediately) preceding frame output from a memory 102 with that of the image of the current frame output from the frame rate converter 101. In the second embodiment, whether a scene change has occurred is determined on the basis of the degree of change of the average luminance value, e.g., whether the average luminance value has changed by 50%.
If the scene change detector 1101 detects that a scene change has occurred, it notifies a timing detector 132 of the generation of the scene change. In response to this notification, the timing detector 132 notifies a polarity inversion controller 131 that the timing to invert the polarity has come. In response to this notification, the polarity inversion controller 131 sets the polarity inversion order. A polarity inverter 106 alters the polarity inversion order in accordance with the setting, and drives the liquid-crystal panel.
When the polarity inversion order is altered, the flicker may degrade the image quality. However, the degradation of the image quality can be prevented by altering the order when the luminance of the screen greatly changes, e.g., when a scene changes.
In the second embodiment, whether a scene change has occurred is determined from the average luminance. However, the present invention is not limited to this, and the maximum or minimum value of the luminance, color information, or scene information embedded in advance in an image is also available.
In this fashion, the second embodiment can more frequently alter the polarity inversion order using generation of a scene change as a trigger. The second embodiment can balance overdrive voltages in forward driving and backward driving, and further improve the reliability.
The third embodiment of the present invention will be explained. The third embodiment will describe an application of the above-described polarity inversion order alteration to a projection display apparatus having a stop mechanism of controlling the light amount to be projected.
The third embodiment will be explained in detail with reference to the accompanying drawings.
The light modulation device P displays a halftone image by controlling the light transmission or reflection state. The projection optical system PL1 projects transmitted or reflected light of light entering the light modulation device P. The illumination unit BL1 emits light to the light modulation device P, and includes a reflector 1203 and arc tube 1202. A color filter 1204, telecentric lenses 1205a and 1205b, and fly-eye integrators 1206a and 1206b are interposed between the illumination unit BL1 and the light modulation device P. Light integrated by the fly-eye integrators 1206a and 1206b is condensed to the light modulation device P via a collecting/reflecting mirror 1207.
The projection image display apparatus 1201 further comprises a write signal processor 1210, projection light amount controller 1220, and control signal generator 1230. The write signal processor 1210 modulates a write signal to the light modulation device P. The projection light amount controller 1220 controls the amount of light having passed through or reflected by the light modulation device P. The control signal generator 1230 controls the write signal processor 1210 and projection light amount controller 1220.
When the luminance level is high (i.e., as the luminance level is higher), the control signal generator 1230 generates a control signal on the basis of the luminance level of an input image signal so as to increase the projection light amount and less modulate the write signal. When the luminance level is low (i.e., as the luminance level is lower), the control signal generator 1230 generates a control signal so as to decrease the projection light amount and greatly modulate the write signal.
In the third embodiment, the projection optical system PL1 is preferably formed from so-called schlieren optics. The projection light amount controller 1220 includes a movable stop 1220a and stop driving unit 1220b, and is arranged not to be conjugate to the light modulation device P. The projection light amount controller 1220 controls the stop value by opening or closing the movable stop 1220a by the stop driving unit 1220b in accordance with the luminance level of an input image signal.
The control signal generator 1230 comprises a luminance level calculation unit 1230a which calculates the luminance level of an input image signal, and a projection light amount calculation unit 1230b which calculates the amount of light projected from the projection optical system in accordance with the calculated luminance level. The control signal generator 1230 generates a control signal for the projection light amount controller 1220 on the basis of the projection light amount calculated by the projection light amount calculation unit 1230b. Also, the control signal generator 1230 generates a control signal for the write signal processor 1210 on the basis of the luminance level calculated by the luminance level calculation unit 1230a and the calculated projection light amount.
The luminance level calculation unit 1230a calculates, as a maximum luminance, the maximum value of the luminance signal of each pixel in each field or frame of an input image signal. In this case, the maximum luminance can be calculated by sequentially comparing input image signals within one field or frame. It is desirable to calculate the cumulative histogram of luminance signals of each pixel, and calculate, as a maximum luminance, a luminance level at which the cumulative histogram reaches a predetermined level or more.
When the luminance level calculation unit 1230a sets the maximum or average luminance to be equal to or lower than a predetermined level, the movable stop 1220a is narrowed down to reduce the projection light amount, providing a sharp black display with less backlight bleeding. At this time, the polarity inversion order of the signal can be altered without degrading the display quality by the flicker.
Even when the control amount of the movable stop 1220a is large and the light amount greatly changes, degradation of the image quality by the flicker upon alteration of the polarity inversion order can be prevented. Hence, this timing is preferable for inverting the polarity. In this case, the threshold of the control amount is set. When the control amount exceeds the threshold as a result of comparison with the threshold, the timing to alter the polarity inversion order can be determined.
The third embodiment has described the method of controlling, by the movable stop serving as a light amount modulator, the amount of light reflected by the light modulation device P. However, the present invention is not limited to this, and the light amount modulator may also control the amount of light incident on the light modulation device P. As the light amount modulator, a unit which controls the light amount by using, e.g., deflection of light is also available instead of the stop. However, the present invention is not limited to this.
The light amount modulator is applicable not only to a reflection type element such as an LCOS or DMD, but also to a transmission type liquid-crystal panel.
As described above, the third embodiment can more frequently alter the polarity inversion order using the light amount control status as a trigger. The third embodiment can balance overdrive voltages in forward driving and backward driving, and further improve the reliability.
The fourth embodiment of the present invention will be explained. In the fourth embodiment, a method of altering the polarity inversion order by a simpler method than the above-described embodiments will be described with reference to
When supply of operating power starts by turning on a power supply 58 with a power supply SW (not shown), a CPU 63 detects the power ON state, and reads out polarity inversion order information in a previous power OFF state from a nonvolatile RAM 65. A polarity inversion order different from the polarity inversion information read out from the nonvolatile RAM 65 is set in a polarity inversion controller 131. A polarity inverter 106 drives the display panel in a polarity inversion order different from the previous one.
When supply of the operating power stops by turning off the power supply 58 with the power supply SW (not shown), the CPU 63 detects the power OFF state, and writes polarity inversion order information in the power OFF state in the nonvolatile RAM 65.
In this way, the fourth embodiment can more frequently alter the polarity inversion order using the ON/OFF operation of the power switch as a trigger. The fourth embodiment can balance overdrive voltages in forward driving and backward driving, and further improve the reliability.
In the fourth embodiment, the polarity inversion order is altered when the power supply is turned on. However, the present invention is not limited to this, and the polarity inversion order may also be altered when the power supply is turned off.
The fifth embodiment of the present invention will be explained. In the fifth embodiment, a method of altering the polarity inversion order by a simpler method than the above-described embodiments will be described with reference to
By using the timer function of a CPU 63, a polarity inversion controller 131 alters the polarity inversion order every time a predetermined time has elapsed. The alteration time preferably falls within the range of about 10 min to 60 min in terms of liquid-crystal characteristics.
By a combination of the timer function and the above-described embodiments, various conditions may also be detected when the arrival of a predetermined time is detected. That is, when the input or channel is switched or a scene change occurs after a predetermined time comes, the polarity inversion order can be altered. In this case, the polarity inversion order can be altered periodically, and degradation of the image quality upon alteration can be prevented.
As has been described above, according to the first to fifth embodiments, the order of forward driving and backward driving is altered at predetermined timings in a liquid-crystal display apparatus which performs AC voltage driving. This can suppress degradation of a signal caused by a DC component upon overdrive. Especially, the arrangement of the embodiments is applicable to a general display apparatus without employing a special structure. The embodiments can provide a high-quality display apparatus without decreasing the reliability.
Note that the present invention can be applied to an apparatus comprising a single device or to system constituted by a plurality of devices.
Furthermore, the invention can be implemented by supplying a software program, which implements the functions of the foregoing embodiments, directly or indirectly to a system or apparatus, reading the supplied program code with a computer of the system or apparatus, and then executing the program code. In this case, so long as the system or apparatus has the functions of the program, the mode of implementation need not rely upon a program.
Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the claims of the present invention also cover a computer program for the purpose of implementing the functions of the present invention.
In this case, so long as the system or apparatus has the functions of the program, the program may be executed in any form, such as an object code, a program executed by an interpreter, or script data supplied to an operating system.
Examples of storage media that can be used for supplying the program are a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a magnetic tape, a non-volatile type memory card, a ROM, and a DVD (DVD-ROM, DVD-R or DVD-RW).
As for the method of supplying the program, a client computer can be connected to a website on the Internet using a browser of the client computer, and the computer program of the present invention or an automatically-installable compressed file of the program can be downloaded to a recording medium such as a hard disk. Further, the program of the present invention can be supplied by dividing the program code constituting the program into a plurality of files and downloading the files from different websites. In other words, a WWW (World Wide Web) server that downloads, to multiple users, the program files that implement the functions of the present invention by computer is also covered by the claims of the present invention.
It is also possible to encrypt and store the program of the present invention on a storage medium such as a CD-ROM, distribute the storage medium to users, allow users who meet certain requirements to download decryption key information from a website via the Internet, and allow these users to decrypt the encrypted program by using the key information, whereby the program is installed in the user computer.
Besides the cases where the aforementioned functions according to the embodiments are implemented by executing the read program by computer, an operating system or the like running on the computer may perform all or a part of the actual processing so that the functions of the foregoing embodiments can be implemented by this processing.
Furthermore, after the program read from the storage medium is written to a function expansion board inserted into the computer or to a memory provided in a function expansion unit connected to the computer, a CPU or the like mounted on the function expansion board or function expansion unit performs all or a part of the actual processing so that the functions of the foregoing embodiments can be implemented by this processing.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2006-325925, filed Dec. 1, 2006, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-325925 | Dec 2006 | JP | national |
