JP2014021143A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve moving image visibility (liquid crystal response) to display a bright image when displaying an image by using a liquid crystal element without performing impulse type display.SOLUTION: An image display device 1000 includes: a light source 527 that has a variable light emission rate; a liquid crystal element 100 that receives light from the light source, and has a variable transmission/reflection rate that is a transmission rate or a reflection rate when transmitting or reflecting the light; and control means 501 and 601 for controlling the light emission rate of the light source and the transmission/reflection rate of the liquid crystal element so that target gradation can be obtained in a display image formed by light from the liquid crystal element. The control means switches between a first state where the transmission/reflection rate of the liquid crystal element is higher than the light emission rate of the light source, and a second state where the transmission/reflection rate of the liquid crystal element is lower than the light emission rate of the light source, for each frame of the image.

Description

  The present invention relates to an image display device such as a projector or a direct-view display, and more particularly to an image display device using a liquid crystal panel as a display element.

  In the image display device as described above, the transmittance and reflectance of each pixel of the transmissive liquid crystal panel and the reflective liquid crystal panel in which light is incident from the light source (hereinafter collectively referred to as transmission / reflectance) are controlled. Thus, a target gradation is obtained for each pixel of the display image.

  In Patent Document 1, two liquid crystal panels for adjusting the amount of light and two liquid crystal panels for image formation are used in an overlapping manner, and the transmittance / reflectance is set so that a target gradation can be obtained for each corresponding pixel of these two liquid crystal panels. An image display device that can be controlled is disclosed. In this image display device, the light quantity adjustment liquid crystal panel is driven so that its liquid crystal response waveform is sawtooth-shaped, and the amount of light incident on the image forming liquid crystal panel is controlled, whereby the impulse of the pixels of the display image blinks. A mold display is used to improve the visibility of the video.

JP 2008-015289 A

  However, the image display device disclosed in Patent Document 1 has a problem in that the brightness of the display image is substantially reduced by performing the impulse-type display.

  The present invention provides an image display device capable of displaying a bright image while improving moving image visibility (liquid crystal responsiveness) without performing impulse-type display.

  An image display device according to one aspect of the present invention includes a light source having a variable light emission rate, and a transmittance / reflectance as a transmittance or a reflectance when light from the light source enters and transmits or reflects the light. And a control means for controlling the light emission rate of the light source and the transmission / reflection rate of the liquid crystal device so that a target gradation can be obtained in a display image formed by light from the liquid crystal device. Then, for each frame of the image, the control means includes a first state in which the transmittance / reflectance of the liquid crystal element is higher than the light emission rate of the light source, and It is characterized by switching between two states.

  In the present invention, the relationship between the light emission rate of the light source set to obtain the target gradation in the display image and the transmission / reflection rate of the liquid crystal element is switched for each frame of the display image. Thereby, according to this invention, the liquid crystal response of a liquid crystal element can be improved, and moving image visibility can be improved. In addition, since an impulse type display is not performed, a bright image can be displayed.

1 is a block diagram showing a configuration of a liquid crystal projector that is an embodiment of the present invention. The figure which shows the image DA conversion part in the liquid crystal projector of an Example. The timing chart which shows the operation timing of the said image DA conversion part. FIG. 2 is a block diagram illustrating a configuration of a liquid crystal panel in the liquid crystal projector of the embodiment. 4 is a timing chart showing the operation timing of the liquid crystal panel. The figure which shows the circuit of the said liquid crystal panel. 1 is a diagram showing a configuration of an optical system of a liquid crystal projector of an embodiment. The figure which shows the structure of the light source (LED array) of the liquid crystal projector of an Example. 6 is a flowchart showing the operation of the liquid crystal projector of the embodiment. FIG. 3 is a block diagram illustrating a configuration of a liquid crystal driving unit in the liquid crystal projector of the embodiment. The graph which shows the liquid-crystal responsiveness in an Example. The graph which shows the liquid-crystal drive conditions in an Example. FIG. 6 is a diagram illustrating a setting example of drive voltages for the image forming panel and the contrast adjustment panel in the liquid crystal projector of the embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration of a liquid crystal projector as an image display apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1000 denotes a projector. Reference numeral 501 denotes a control unit that performs various calculations and control of each unit to be described later based on data such as various setting values read from the storage unit 510, and communicates with other devices via the communication unit 552. .

  A distance measuring unit 201 detects a distance from the projector 1000 to a projection surface such as a screen or a wall (not shown) using a distance measuring sensor (not shown). A signal indicating the detected distance (distance signal) is input to the control unit 501. The control unit 501 controls the lens driving unit 541 based on the distance signal, and the projection image (display image) in which the AF lens 542 included in the projection optical unit 529 is focused on the projection surface through the projection optical unit 529. ) Is projected. Further, the lens driving unit 541 moves the zoom lens 543 included in the projection optical unit 529 to change the projection magnification of the projection image.

  Reference numeral 202 denotes an image detection unit that captures a projected image on the projection surface by an image sensor such as a CCD sensor or a CMOS sensor, and inputs an image pickup signal to the control unit 501 via the image input processing unit 203. Reference numeral 204 denotes a flicker detection unit that detects flicker in the projected image and inputs the result to the control unit 501.

  A lens shift unit 544 shifts the projection optical unit 529 up, down, left, and right, and shifts the projection image up, down, left, and right on the projection surface.

  Reference numeral 100 denotes an image forming liquid crystal panel (liquid crystal element: hereinafter referred to as an image forming panel). The image forming panel 100 changes the transmittance / reflectance for each pixel in accordance with a liquid crystal driving signal (liquid crystal driving voltage) from the liquid crystal driving unit 601, and applies an image (image light) to light incident from a light source 527 described later. Let it form.

  Here, “transmission / reflectance” indicates a variable transmittance or reflectance of the liquid crystal element (image forming panel 100) that transmits or reflects incident light. As will be described later, in this embodiment, since a reflective liquid crystal panel is used as the image forming panel 100, “transmission / reflectance” is referred to as reflectance in the following description.

  The gradation (brightness) for each pixel of the projected image is determined by a value obtained by multiplying the reflectance of each pixel of the image forming panel 100 and the light emission rate (variable value) of an LED in a light source 527 described later corresponding to that pixel. ) Is decided.

  Reference numeral 551 denotes a video input terminal to which a video signal (analog signal or digital signal) from an external video source source is input. The control unit 501 transmits a control signal to the image input unit 522 in accordance with setting information such as a display mode and zoom setting set by the user at the input unit 530. The image input unit 522 performs input processing such as A / D conversion processing and decoding processing on the video signal input from the video input terminal 551 in accordance with the control signal. The image processing unit 523 performs image processing such as noise removal, contour enhancement, scaling, and keystone correction on the video signal after input processing output from the image input unit 522, and generates image data generated by the image processing. Is output to the liquid crystal driver 601.

  The liquid crystal driving unit 601 uses a memory 524 having an image data holding function to add a synchronization signal of double speed driving timing to the image data or perform processing such as gamma conversion. Then, liquid crystal driving data (liquid crystal driving signal) for driving each pixel of the image forming panel 100 is generated and output from the processed image data. Further, the liquid crystal driving unit 601 generates and outputs LED driving data for driving each LED of the light source 527 described later. The control unit 501 and the liquid crystal drive unit 601 constitute a control unit.

  The liquid crystal drive signal is input to the image forming panel 100 after being converted into an analog signal by the image DA converter 531.

  In this embodiment, three image forming panels 100 for red (R), green (G), and blue (B) are provided. Each image forming panel 100 receives the synchronization signal of the double speed driving timing and the liquid crystal driving signal converted into the analog signal by the image DA converter 531 so that the reflectance of each pixel becomes a value corresponding to the liquid crystal driving signal. Driven.

  The light source drive unit 526 that has received the drive signal from the control unit 501 turns on the LED as the light source 527. The configuration of the light source 527 will be described in detail later.

  The optical system 800 converts white light and non-polarized light from the light source 527 into polarized light having a specific polarization direction, and separates the light into R light, G light, and B light, which are used for R, G, and B light. Guide to the image forming panel 100. The image forming panel 100 for R, G, and B reflects and modulates R light, G light, and B light with a reflectance controlled for each pixel, thereby modulating R image light, G image light, and B image. Produce light.

  Further, the optical system 800 combines the R image light, the G image light, and the B image light from the R, G, and B image forming panels 100 and guides them to the projection optical unit 529. The projection optical unit 529 enlarges and projects the projection image on the projection surface.

  The reference DA conversion unit 520 receives a communication signal from the control unit 501, a Vcom voltage that is a voltage of a common electrode facing the pixel electrode of the image forming panel 100, an image DA conversion unit 531, and a contrast DA conversion. The drive voltage of the unit 532 is generated.

  FIG. 2 shows an image DA converter 531. The image DA converter 531 receives a CLK (clock) signal, a DATA (image data), a Latch signal, and an INV signal that are input signals from the liquid crystal driver 601 shown in FIG. 1, and receives a liquid crystal drive signal (Video signal). Video0 to Video7 are generated. 3A to 3C show the input timing of the CLK signal, DATA, and Latch signal to the image DA conversion unit 531 and the output timing of Video0 to Video7. The image DA converter 531 transfers DATA corresponding to the video output to a register (not shown) in the image DA converter 531 at the rising edge of the CLK signal. Further, the image DA conversion unit 531 outputs the INV signal by inverting +/− of the video output, which is an analog voltage corresponding to DATA, with respect to the predetermined center voltage. In this embodiment, since there are 8 video outputs, the image DA converter 531 latches DATA at the rising edge of the Latch signal after transferring DATA for 8 clocks.

  The image DA converter 531 updates the Video signal to the Video signal corresponding to the DATA before the Latch signal rises at the rise of the CLK signal after the Latch signal falls. The image DA converter 531 generates a liquid crystal drive signal by repeating this process.

  FIG. 4 shows the configuration of the image forming panel 100. The image forming panel 100 includes an H (horizontal) shift register 110, a V (vertical) shift register 120, and a pixel unit 130 in which a plurality of pixels are arranged. The H shift register 110 performs scanning in the H direction (H scanning) illustrated in FIG. 5 in accordance with the HS signal and the HCLK signal input from the liquid crystal driving unit 601.

  Specifically, the H shift register 110 uses the HS signal as a horizontal reset signal and a horizontal start signal, and updates Video 0 to Video 7 for each clock of the HCLK signal, while maintaining eight H lines (horizontal pixel columns) in the vertical direction. Turn on the signal line. The HCLK signal and the Latch signal shown in FIG. 3A are signals having the same frequency. When the resolution of the image forming panel 100 is XGA (H: 1024 × V: 768), the H scan of the pixel unit 130 is performed with 128 clocks of the HCLK signal. Then, the H shift register 110 performs H scanning of the next eight vertical lines using the next HS signal as a horizontal reset signal and a horizontal start signal. Actually, the H scan is performed at the number of clocks obtained by adding blanking by an arbitrary number of clocks to 128 clocks of the HCLK signal necessary for the H scan.

  Further, the V shift register 120 performs scanning in the V direction (V scanning) illustrated in FIG. 5 in accordance with the VS signal and the VCLK signal input from the liquid crystal driving unit 601. Specifically, the V shift register 120 shifts the H line by one line for each clock of the VCLK signal using the VS signal as a vertical reset signal and a vertical start signal. As described above, when the resolution of the image forming panel 100 is XGA (H: 1024 × V: 768), V scanning of the pixel unit 130 is performed at 768 clocks of the VCLK signal. Actually, similarly to the H scan, the V scan is performed at a clock number obtained by adding blanking by an arbitrary number of clocks to the 768 clocks of the VCLK signal necessary for the V scan.

  The H shift register 110 and the V shift register 120 apply a liquid crystal drive signal to each pixel of the pixel unit 130 in accordance with the H scanning signal (HLON) and the V scanning signal (VLON). Thereby, the reflectance of each pixel of the pixel unit 130 is controlled to a value according to Video0 to Video7.

  It should be noted that eight black region pixels to which the same voltage as the Vcom voltage is applied to the pixel electrode are provided on the pixel electrode 130 at the top, bottom, left, and right of the display pixel of H: 1024 × V: 768. A liquid crystal drive signal is applied to the area pixels in accordance with a blanking clock. These black area pixels are used as display pixels when mounting positions of the image forming panels 100r, 100g, and 100b and the contrast adjustment panels 700r, 700g, and 700b, which will be described later, are generated, and the projected image cannot be shifted. Like that.

  The pixel unit 130 is configured as shown in FIG. A pixel transistor 141 as a pixel switching element, a pixel capacitor 142, and a liquid crystal (LC) 143 are provided at a location where the H scanning line 146 and the video line (data line) 147 intersect. These pixel transistor 141, pixel capacitor 142, and liquid crystal (LC) 143 constitute one pixel.

  As described above, the H shift register 110 turns on the transfer SW 145 by the H shift register output 148 in accordance with the HCLK signal, and the voltage of the Video signal 149 (Video signal voltage) from the image DA converter 531 is applied to the signal line 147. Apply. The shift register output 146 of the V shift register 120 drives the gate of the pixel transistor 141 and accumulates the Video signal voltage in the pixel capacitor 142. The liquid crystal 143 changes the reflectance according to the video signal voltage accumulated in the pixel capacitor 142.

  FIG. 7 shows a specific configuration example of the entire optical system including the light source 527, the optical system 800, the image forming panel 100, and the projection optical unit 529 in the projector 1000 shown in FIG. As shown in FIG. 8, the light source 527 is configured by an LED array configured by using three colors of RGB LEDs. Specifically, one LED set is formed by one R LED, two G LEDs, and one B LED, and a plurality of the LED sets are arranged in the horizontal and vertical directions. Have Each LED corresponds to one pixel of the image forming panel 100. That is, light from one LED enters one pixel of the image forming panel 100.

  The polarization conversion element 803 converts the non-polarized light from the light source (LED) 527 into linearly polarized light having a specific polarization direction (in this embodiment, with respect to first to third polarization beam splitters 813a, 813b, and 813c described later). Converted into S-polarized light). A plurality of light beams as polarized light are condensed by a condenser lens 804 on three image forming panels 100r, 100g, and 100b, which will be described later, and are made telecentric by a field lens 806.

  The white light emitted from the field lens 806 is separated by the dichroic mirror 808 into G light passing therethrough and R light and B light reflected thereby. Each of the first to third polarization beam splitters 813a, 813b, and 813c includes polarization separation films 814a, 814b, and 814c having characteristics of reflecting S-polarized light and transmitting P-polarized light. The G light incident on the first polarization beam splitter 813a from the dichroic mirror 808 and reflected by the polarization separation film 814a as S-polarized light is transmitted through the quarter phase plate 810g and the birefringence filter 811g, and is used for the G image. Incident on the forming panel 100g.

  Further, the R light and B light from the dichroic mirror 808 enter the color selective phase difference plate 809a. The color selective phase difference plate 809a rotates only the polarization direction of the B light by 90 ° to change the B light into P-polarized light. The S-polarized R light emitted from the color selective phase difference plate 809a is reflected by the polarization separation film 814b of the second polarization beam splitter 813b, and is transmitted through the quarter phase difference plate 810r and the birefringence filter 811r. Then, the light enters the R image forming panel 100r. On the other hand, the B light as P-polarized light emitted from the color selective phase difference plate 809a is transmitted through the polarization separation film 814b of the second polarization beam splitter 813b, and passes through the quarter phase difference plate 810b and the birefringence filter 811b. The light passes through and enters the B image forming panel 100b.

The quarter retardation plates 810r, 810g, and 810b convert linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. The birefringent filters 811r, 811g, and 811b are uniaxial filters as birefringent phase difference compensation elements that correct a phase difference that occurs when each image forming pixel liquid crystal panel is in a black display state.
The image forming panels 100r, 100g, and 100b are reflective liquid crystal panels as described above, and reflect and modulate incident light with reflectivity according to the input video signals (Video 0 to Video 7) described above. Thereby, R, G, and B image light is generated. The G image light from the G image forming panel 100g is transmitted again through the birefringence filter 811g and the quarter retardation plate 810g, and is transmitted through the polarization separation film 814a of the first polarization beam splitter 813a. Then, the light enters the third polarizing beam splitter 813 c, is reflected by the polarization separation film 814 c, and proceeds to the projection optical unit 529.

  Further, the R image light from the R image forming panel 100r is transmitted again through the birefringence filter 811r and the quarter retardation plate 810r, and is transmitted through the polarization separation film 814b of the second polarization beam splitter 813b. Then, the light enters the third polarization beam splitter 813 c, passes through the polarization separation film 814 c, and proceeds to the projection optical unit 529. Further, the B image light from the B image forming panel 100b is transmitted again through the birefringence filter 811b and the quarter retardation plate 810b and reflected by the polarization separation film 814b of the second polarization beam splitter 813b. Then, the light enters the third polarizing beam splitter 813c, passes through the polarization separation film 814c, and proceeds to the projection optical unit 529. Thus, the G image light, the R image light, and the B image light are combined and enlarged and projected onto the projection surface by the projection optical unit 529.

  The operation of projector 1000 configured as described above will be described using the flowchart of FIG. This operation is performed by the control unit 501 in accordance with a computer program. First, in step S101, the control unit 501 determines whether or not the power SW provided in the input unit 530 is turned on. When the power SW is turned on, the control unit 501 proceeds to step S103 and performs initial setting. Specifically, the control unit 501 reads an initial setting value from the storage unit 510 and communicates with each unit. Further, the control unit 501 performs initial setting of the image input unit 522 in step S105, initial setting of the image processing unit 523 in step S107, and initial setting of the liquid crystal driving unit 601 in step S109. The initial setting of the liquid crystal driving unit 601 will be described in detail later.

  Next, in step S <b> 110, the control unit 501 performs initial setting of the reference DA conversion unit 520 that outputs a voltage to the image forming panel 100 and the image DA conversion unit 531.

  If the power SW is turned on in step S101, the control unit 501 performs an initial setting process for the projection optical unit 529 in parallel with the initial setting process for the liquid crystal driving described above. That is, first, in step S111, the lens reset in the projection optical unit 529 is performed. In this lens reset, the control unit 501 moves the AF lens 542 and the zoom lens 543 to a predetermined initial lens position via the lens driving unit 541 based on the initial position data stored in the storage unit 510. Further, the shift position of the projection optical unit 529 is moved to a predetermined initial shift position via the lens shift unit 544.

  When the lens reset is completed, the control unit 501 performs driving for displaying a predetermined initial image on the image forming panel 100 in step S113. Then, the light source 527 is turned on to project the initial image on the projection surface.

  Next, in step S115, the control unit 501 causes the distance measuring unit 201 to detect the distance from the projector 1000 to the projection surface using the phase difference method, and in step S116, moves the AF lens 542 through the lens driving unit 541. Focus on the subject.

  When the above power-on setting process (steps S103 to S116) is completed, the control unit 501 confirms that the power-on setting process has been completed in step S117, and then proceeds to step S119. In step S119, the control unit 501 inputs a video signal (image data) input from the video input terminal 551 and passed through the image input unit 522 and the image processing unit 523 to the liquid crystal driving unit 601. The liquid crystal driving unit 601 applies a liquid crystal driving signal to the image forming panel 100 via the image DA conversion unit 531 and starts driving the liquid crystal driving signal. Thereby, a projection image corresponding to the image formed on the image forming panel 100 is displayed on the projection surface.

  Next, a detailed configuration of the liquid crystal driving unit 601 will be described with reference to FIG. In FIG. 10, the liquid crystal driving unit 601 receives video input (image data) from the image processing unit 523, and writes image data for one frame of the video input to the memory 524 by the double speed conversion circuit 611. Then, the liquid crystal driving unit 601 reads out the image data for one frame twice, thereby generating a data signal for performing double speed driving (driving at 120 Hz) that performs 60 Hz liquid crystal driving twice. The data signal output from the double speed conversion circuit 611 is distributed by the hue / luminance distribution circuit 614 as a data signal (liquid crystal drive data) for the image forming panel 100 and a data signal (LED drive data) for the light source 527.

  The gamma circuit 615 corrects the data signal (liquid crystal drive data) from the hue / brightness distribution circuit 614 in accordance with the gamma characteristic of the image forming panel 100. The image output processing circuit 616 rearranges the data in the horizontal and vertical directions that are the scanning direction of the image forming panel 100 in the liquid crystal data signal output from the gamma circuit 615, and outputs the data via the selector circuit 617. The image is output to the image DA converter 531. The image DA converter 531 drives the image forming panel 100 by outputting a voltage as a liquid crystal drive signal based on the data from the selector circuit 617. The image TG circuit 618 outputs a timing signal indicating the driving timing of the image forming panel 100 (the operation timing of the H and V shift registers) by the liquid crystal driving signal output from the image DA converter 531. The PLL circuit 612 optimizes the clock / data phase of each circuit at a multiplication rate.

  On the other hand, the luminance correction circuit 620 performs luminance correction on the data signal (LED drive data) from the hue / luminance distribution circuit 614. The LED output processing circuit 621 rearranges the data in the horizontal direction and the vertical direction that are the scanning direction of the LED array as the light source 527 in the LED data signal output from the luminance correction circuit 620. Then, the data is output to the light source driver 526. The light source driver 526 outputs an LED drive signal corresponding to the data signal to drive the LED array. The LED drive signal is a constant current signal for controlling a current value flowing through the LED or a PWM modulation signal for controlling the lighting time of the LED. The LEDTG circuit 623 outputs a timing signal indicating the driving timing of the LED array by the LED driving signal. The register circuit 613 performs setting of each circuit and writing of an adjustment value.

  Next, driving of the image forming panel 100 and the light source (LED) 527 by the liquid crystal driving unit 601 will be described with reference to FIGS. 11 and 12. First, FIGS. 11A and 11B show the relationship between general liquid crystal response, that is, the change in transmission / reflectance and the response time indicating the speed at which the change is obtained. The horizontal axis represents transmission / reflectance, and the vertical axis represents response time (response speed).

  As shown in FIG. 11A, the response time when the transmittance / reflectance changes from low to high and changes from 0 to 10% is about 23 ms. On the other hand, the response time when changing from 0 to 100% is about 4.5 ms, and is about 1/5 of the time when changing from 0 to 10%. As described above, the responsiveness of the liquid crystal is good in an image with high luminance, but the responsiveness is conspicuous in an image with low luminance. On the other hand, as shown in FIG. 11B, the response time when the transmittance / reflectance changes from high to low and changes from 10 to 0% is about 3 ms. In contrast, the response time when changing from 100 to 0% is about 2 ms, which is almost the same as when changing from 10 to 0%. From this, it can be said that in order to improve the liquid crystal responsiveness, it is sufficient to drive in a state where the transmittance / reflectance is as high as possible. However, this cannot express tone.

  Therefore, in this embodiment, the light source 527 and the image forming panel 100 are driven so as to satisfy the two conditions shown in FIG. As a first condition, light emission / reflectance (light emission / transmission / reflectance), which is a combined value (product) of the light emission rate of the light source 527 and the reflectance of the image forming panel 100, corresponds to the target gradation in the projection image. To a value (target emission / transmission / reflectance: hereinafter referred to as target emission / reflection). The light emission rate (also called output rate) of the light source 527 is a ratio of the actual light emission amount to the maximum light emission amount of each LED constituting the light source 527. Further, as a second condition, for each frame of the projection image, a first state in which the reflectance of the image forming panel 100 is higher than the light emission rate of the light source 527, and a reflection of the image forming panel 100 than the light emission rate of the light source 527. Switch to the second state where the rate is low. Hereinafter, the frame of the projected image is referred to as an image frame.

  Furthermore, in the first and second states, it is desirable that the reflectance of the image forming panel 100 be higher than the target light emission / reflectance. However, this is not the case when the target light emission / reflectance is high to some extent.

  In FIG. 12, (A) in a region where the light emission / reflectance is lower than a predetermined value (for example, 55%) indicates the lower of the reflectance of the image forming panel 100 and the light emission of the light source 527, and (B) is high. Shows the direction.

  To explain a specific example, when the target light emission / reflectance corresponding to the target gradation is 10%, the reflectance of the image forming panel 100 and the light emission rate of the light source 527 are set to 13% (A ) And 75% (B) alternately for each image frame. The light emission / reflectance of about 10% is obtained by 13% × 75%. When the target light emission / reflectance is 30%, the reflectance of the image forming panel 100 and the light emission rate of the light source 527 are set for each image frame between 40% (A) and 75% (B). Switch alternately. Light emission / reflectance of 30% can be obtained by 40% × 75%.

  The second condition described above is performed when the target light emission / reflectance (that is, the target gradation) is lower than a predetermined value, and when the target light emission / reflectance is higher than the predetermined value, the reflection of the image forming panel 100 is performed. And the light emission rate of the light source 527 are set to be the same (however, they may be different from each other).

  FIG. 12 shows a case where the higher one (B) of the reflectance and the light emission rate is fixed to 75% when the target light emission / reflectance is lower than the predetermined value. The rate may be other than 75%, or the higher one may be changed according to the target light emission / reflectance.

  FIG. 13 shows an example of driving a pixel of the image forming panel 100 (hereinafter referred to as a panel pixel) and an LED of a light source 527 corresponding to the panel pixel for each image frame. As shown in FIG. 13A, the target light emission / reflectance, which is the light emission / reflectance corresponding to the target gradation of the pixel on the projection image corresponding to the panel pixel and LED, is the image frame (circled 1-4). Each). In order to obtain the target light emission / reflectance for each image frame, the reflectance of the panel pixel is changed as shown in FIG. 13B, and the light emission rate of the LED is changed as shown in FIG. 13C. In this embodiment, inversion driving is performed in which the polarity (positive / negative) of the voltage as a liquid crystal driving signal applied to the image forming panel 100 is inverted once in one image frame.

  In the following description, a state where the reflectance of the panel pixel is higher than the light emission rate of the LED is referred to as a first state. A state in which the reflectance of the panel pixel is lower than the light emission rate of the LED is referred to as a second state.

  For example, when the target light emission / reflectance in the first frame 1 is 12.5%, the reflectance of the panel pixel is set to 75%, and the light emission rate of the LED is set to 16.7% (first state). Next, when the target light emission / reflectance in the frame 2 is 50%, the reflectance of the panel pixel is set to 66.7%, and the light emission rate of the LED is set to 75% (second state). Further, when the target light emission / reflectance in the next frame 3 is 25%, the reflectance of the panel pixel is set to 75%, and the light emission rate of the LED is set to 33.3% (first state). Further, when the target light emission / reflectance in the next frame 4 is 12.5%, the reflectance of the panel pixel is set to 16.7% and the light emission rate of the LED is set to 75% (second state).

  Thus, in this embodiment, even when the target gradation changes in successive image frames (that is, regardless of the change in the target gradation), the light emission / reflectance corresponding to the target gradation can be obtained. As described above, the first state and the second state described above are switched for each image frame. In other words, drive data for the image forming panel 100 and the light source 527 is generated so as to switch between the first state and the second state for each image frame.

  As a result, the image forming panel 100 can be driven such that the reflectance changes greatly for each image frame, that is, high responsiveness can be obtained. Specifically, for example, the liquid crystal drive data and the LED drive data are generated by the hue luminance distribution circuit 614 so that the image forming panel 100 can be driven at a response speed of about 10 mS.

  For example, the hue luminance distribution circuit 614 has table data corresponding to the graph shown in FIG. 12 stored in the ROM. Then, the hue luminance distribution circuit 614 uses the reflectance and the light emission rate shown in (A) and (B) of FIG. 12 as the reflectance of the image forming panel 100 and the light emission rate of the light source 527 for each image frame. Liquid crystal drive data and LED drive data are generated so as to be switched.

  As described above, in this embodiment, the relationship between the reflectance of the image forming panel 100 and the light emission rate of the light source 527 set so as to obtain the target gradation in the projected image is switched for each image frame. Thereby, the liquid crystal responsiveness of the image forming panel 100 can be improved, and the moving image visibility can be improved. In addition, since an impulse type display is not performed, a bright image can be projected.

  In this embodiment, the case where a reflective liquid crystal panel is used as the image forming panel has been described. However, a transmissive liquid crystal panel may be used.

  Further, in the present embodiment, the liquid crystal projector (image projection apparatus) has been described. However, as another embodiment of the present invention, an image display apparatus such as a so-called direct view display (liquid crystal monitor) is included.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  It is possible to provide an image display device such as a liquid crystal projector or a liquid crystal monitor that can display a bright image with good moving image visibility.

100 (100r, 100g, 100b) Image forming panel 501 Control unit 527 Light source 601 Liquid crystal driving unit

Claims (5)

A light source having a variable emission rate;
A liquid crystal element in which the light from the light source is incident and the transmittance / reflectance as a transmittance when the light is transmitted or reflected is variable;
Control means for controlling the light emission rate of the light source and the transmittance / reflectance of the liquid crystal device so as to obtain a target gradation in a display image formed by light from the liquid crystal device,
For each frame of the image, the control means includes a first state in which the transmittance / reflectance of the liquid crystal element is higher than the light emission ratio of the light source, and the transmittance / reflectance of the liquid crystal element is equal to that of the light source. An image display device that switches between a second state lower than the light emission rate.   In the first and second states, the control means sets the light emission rate and the transmission / reflectance corresponding to the target gradation to a target emission / transmission / reflectance value. The image display apparatus according to claim 1, wherein the transmission / reflectance is higher than the target light emission / transmission / reflectance.   The image display apparatus according to claim 1, wherein the control unit switches the first and second states for each frame regardless of a change in the target gradation for each frame.   The said control means switches the said 1st and 2nd state for every said frame, only when the said target gradation is lower than predetermined value, The any one of Claim 1 to 3 characterized by the above-mentioned. Image display device. The light source is constituted by an LED,
5. The image display device according to claim 1, wherein the control unit controls a current value flowing through the LED or controls a lighting time of the LED. 6.