JP2005274732A - Projection type image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection type image display apparatus capable of reducing flicker on a screen when a light amount is controlled to brightness of an image. <P>SOLUTION: An Average Picture Level (APL) data (8 bit data) is generated for every one frame period (every 1V) and an APL average value (8 bit data) is set as an average value of the APL data in a period of successive four frames. And a target level (four bit data: sixteen steps of 0 to 15) is set based on the successive four APL average values. The target level is updated every sixteen frames. A dimmer function data is generated so as to approach the target level. The light amount of a lamp is controlled based on the dimmer function data. One time changing (step) amount of the dimmer function is made to be two steps. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a projection display apparatus such as a liquid crystal projector.

Conventionally, a liquid crystal display device (see Patent Document 1) in which the display brightness and contrast are constant even when the average picture brightness (APL) changes, or the average brightness of the picture. There has been proposed a projection display apparatus that improves the contrast by reducing the lamp driving power when the brightness (APL) is bright and increasing the lamp driving power when the brightness (APL) is dark (see Patent Document 2).
JP-A-8-201812 Japanese Patent Laid-Open No. 3-179886

  However, further improvement in contrast and reduction in power consumption are desired, and in a liquid crystal projector, there is a problem of suppressing black float, which is a weak point. Here, when projecting bright images, the amount of emitted light is increased to brighten the projected image, and when projecting dark images, the amount of emitted light is decreased to darken the projected image, thereby improving contrast (reducing black float). The applicant of the present application previously proposed, but such control is simply performed, for example, when the image of the sea under the sun (bright scene) is switched to the image of the night scene (dark scene). Appears to blink. That is, there is a difference between the information generation time point (output light amount adjustment time point) about the image brightness and the actual image brightness at that time point. For example, when the light image changes to a dark image, the output light amount is still lowered. Is not executed, and a process in which the amount of emitted light is sharply lowered through a stage where the amount of emitted light remains high with respect to a dark image may cause the screen to appear to blink (see FIG. 4). Such control will be described again for comparison in the embodiment of the invention.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a projection display apparatus that can reduce screen blinks when light intensity control is performed on the brightness of an image.

  In order to solve the above-described problem, the projection display apparatus according to the present invention is a projection display apparatus that projects an image by modulating light emitted from a light source with a light valve. Means for generating information indicating the average brightness of the light source, and control for increasing the amount of light emitted from the light source when the information indicates a bright value, and reducing the amount of light emitted from the light source when the information indicates a dark value And the control means controls the increase / decrease in the amount of emitted light so as to be gentler than the change in the information.

  With the above configuration, for example, even when a low output light amount is not yet lowered at a time when a bright image is changed to a dark image, and a high output light amount is still applied to a dark image, the output light amount is subsequently changed. Is not sharply lowered, but the amount of emitted light is lowered gently, so that blinking of the screen can be reduced.

  The means for generating information indicating the average brightness of the video based on the video signal may be configured to generate a multi-frame average value that is an average value of the average brightness of a plurality of consecutive frames. . Further, the average value of the plurality of frames is sequentially acquired, a target level is set with the average value of the plurality of frames, and the increase / decrease of the amount of emitted light is executed step by step so as to approach the target level. It may be configured.

  According to the present invention, when the video signal shows a bright value, the amount of light emitted from the light source is increased. On the other hand, when the video signal shows a dark value, the amount of light emitted from the light source is reduced. There is an effect that it is possible to reduce the blinking of the screen when the image is changed to a bright image.

  A liquid crystal projector according to an embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a view showing a three-plate liquid crystal projector of this embodiment. The light emitting part in the light source 1 is composed of an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp or the like, and the irradiation light is emitted as parallel light by a parabolic reflector and guided to the integrator lens 4.

  The integrator lens 4 is composed of a pair of lens groups (fly eye lenses) 4a and 4b, and each lens portion guides light emitted from the light source 1 to the entire surface of a liquid crystal light valve to be described later. The partial luminance unevenness existing in the light source 1 is averaged, and the light amount difference between the center of the screen and the peripheral portion is reduced. The light passing through the integrator lens 4 is guided to the first dichroic mirror 7 after passing through the polarization conversion device 5 and the condenser lens 6.

  The polarization conversion device 5 is configured by a polarization beam splitter array (hereinafter referred to as a PBS array). The PBS array includes a polarization separation film and a phase difference plate (1 / 2λ plate). Each polarization separation film of the PBS array passes, for example, P-polarized light out of the light from the integrator lens 4 and changes the optical path of S-polarized light by 90 °. The optically polarized S-polarized light is reflected by the adjacent polarization separation film and emitted as it is. On the other hand, the P-polarized light transmitted through the polarization separation film is converted into S-polarized light by the retardation plate provided on the front side (light emitting side) and emitted. That is, in this case, almost all light is converted to S-polarized light.

  The first dichroic mirror 7 transmits light in the red wavelength band and reflects light in the cyan (green + blue) wavelength band. The light in the red wavelength band that has passed through the first dichroic mirror 7 is reflected by the reflection mirror 8 to change the optical path. The red light reflected by the reflection mirror 8 is light-modulated by passing through a lens 9 and a transmissive liquid crystal light valve 31 for red light. On the other hand, the light in the cyan wavelength band reflected by the first dichroic mirror 7 is guided to the second dichroic mirror 10.

  The second dichroic mirror 10 transmits light in the blue wavelength band and reflects light in the green wavelength band. The light in the green wavelength band reflected by the second dichroic mirror 10 is guided to the transmissive liquid crystal light valve 32 for green light through the lens 11 and is modulated by being transmitted therethrough. The light in the blue wavelength band that has passed through the second dichroic mirror 10 is guided to the blue-light transmissive liquid crystal light valve 33 through the total reflection mirror 12, total reflection mirror 13, and lens 14, and is transmitted therethrough. It is optically modulated.

  Each of the liquid crystal light valves 31, 32, 33 includes a panel portion 31b, in which liquid crystal is sealed between an incident-side polarizing plate 31a, 32a, 33a and a pair of glass substrates (with pixel electrodes and alignment films formed). 32b, 33b and output side polarizing plates 31c, 32c, 33c.

  The modulated light (each color video light) modulated by passing through the liquid crystal light valves 31, 32, 33 is synthesized by the cross dichroic prism 15 to become color video light. The color image light is enlarged and projected by the projection lens 16, and is projected and displayed on a screen (not shown).

  2A is a block diagram showing an image processing system and a light source control system of the projection display apparatus, and FIG. 2B is an explanatory diagram showing the light source control system by functional blocks. The video signal processing circuit 23 receives the video signal and performs processing such as frequency conversion (scanning line number conversion) and the like, and the average brightness (APL) of the frame video for each frame period based on the video signal (Y signal). : Generates data indicating Average Picture Lever). When an RGB signal is input as a video signal, Y data may be generated by matrix conversion of the RGB signal. The gamma correction circuit 24 performs correction processing in consideration of the applied voltage-light transmission characteristics of the liquid crystal light valve (LCD), and applies (drives) the corrected video signal (video data) to the liquid crystal light valve. The microcomputer 25 functions as a dimming calculation block shown in FIG. 5B, receives APL data and generates dimming data, and also functions as a lamp driver control block, and sends a dimming command to the lamp driver 26. Process to send. The lamp driver 26 receives the dimming command and controls the amount of light emitted from the light source (lamp).

  In the power supply section of the lamp driver 26, for example, a circuit is provided in which a plurality of resistors are connected in series so that a desired voltage can be taken out by a voltage drop generated at the connection point of each resistor. That is, a switch is connected to each connection point of each resistor, and the light source driving power can be switched depending on which switch is turned on. For example, when “1111” is received as the dimming command, the lamp driver 26 controls the switch so as to emit light at the maximum output watt (eg, 130 W), and “0000” as the dimming command. "Is received, the switch is controlled to emit light at a minimum output wattage (for example, 105 W). Of course, the power switching circuit is not limited to the above-described resistor and switch, and a circuit that switches power consumption by phase control, switching power supply control, or the like may be used.

  FIG. 3A is an explanatory diagram showing the relationship between APL data, APL average value generation, dimming data generation, and target level generation, and FIG. 3B is an explanatory diagram showing a change in the amount of emitted light. It is. In this example, APL data (here, 8-bit data) is generated for each frame period (every 1 V), and the APL average value (the same 8-bit data) is APL data for four consecutive frame periods. The average value of Then, a target level (4-bit data) is set based on four consecutive APL average values. This target level is updated every 16 frames. Further, for example, the target level may be output by inputting an APL average value as an address into a table (memory).

  Here, FIG. 4 used in the conventional section will be described again. APL data (8-bit data) is generated every frame period (every 1 V), and the APL average value (8-bit data) is the average value of APL data for four consecutive frame periods. Based on this APL average value, dimming data (4-bit data: 16 levels of 0 to 15) is generated, and the lamp light quantity is controlled by this dimming data. The dimming data has a delay of 4 frame periods with respect to the actual video brightness. Therefore, the lamp light amount is not yet reduced at the time of changing from a bright image to a dark image, and the lamp light amount is sharply lowered through a stage where the high output light amount remains unchanged for a dark image. You may see blinking. Further, such a problem can be solved by providing an image delay means such as a frame memory and matching the video brightness change time and the lamp light quantity adjustment time, but this increases the cost.

  On the other hand, in the present invention, a target level (16 bits of 4-bit data: 0 to 15) is set based on four consecutive APL average values, and dimming is performed so as to gradually approach the target level. Generate data. In the example of FIG. 3, the dimming data is updated every four frame periods, and the amount of change (stage) in one dimming data is two stages (two stages are examples, But not limited to this). That is, if the difference between the current dimming data and the target level is two or more steps, the change amount is two steps, if the difference is one step, the change amount is one step, and if there is no difference, the dimming data changes. do not do.

  Thereby, as can be seen from FIG. 4B, the change in the lamp light amount has a constant and relatively large time constant (the inclination of the change), and is slower than the change in the APL data. Therefore, for example, even when the light quantity is changed from a bright image to a dark image, the lamp light amount is not yet reduced and the dark light image undergoes a high output light amount step. Instead, the amount of light from the lamp is lowered slowly, so that blinking on the screen can be reduced.

  In the above example, the target level is set on the basis of four consecutive APL average values and the next four consecutive APL average values not including the four APL average values are set. However, the present invention is not limited to this. For example, the target value is set on the basis of four (a plurality of) continuous APL average values, and the next one APL average value is set. And the next target level is set based on a total of four (plural) APL average values (that is, the target level is determined by moving average). Good. In this case, the target level changes every 4 frame periods.

1 is a configuration diagram illustrating a liquid crystal projector according to an embodiment of the present invention. FIG. 4A is a block diagram showing a video processing system and a light source control system, and FIG. 4B is an explanatory diagram showing the light source control system by functional blocks. FIG. 6A is an explanatory diagram showing the relationship between APL data, APL average value generation, dimming data generation, and target level generation, and FIG. 6B is an explanatory diagram showing a change in the amount of emitted light. It is. FIG. 4A is an explanatory diagram showing the relationship between APL data, APL average value generation, and dimming data generation, and FIG. 4B is an explanatory diagram showing changes in the amount of emitted light.

Explanation of symbols

1 Light source 23 Video signal processing circuit 24 Gamma correction circuit 25 Microcomputer
26 Lamp driver 31, 32, 33 Liquid crystal light bulb

Claims (3)

In a projection display apparatus for projecting an image by modulating light emitted from a light source with a light valve, means for generating information indicating an average brightness of the image based on the image signal, and the information is a bright value Control means for increasing the amount of light emitted from the light source while indicating a dark value, and reducing the amount of light emitted from the light source when indicating a dark value. A projection-type image display apparatus, wherein the reduction is controlled to be gradual as compared with the change in information. 2. The projection type video display apparatus according to claim 1, wherein the means for generating information indicating the average brightness of the video based on the video signal is a plurality of frames which are average values of average brightness of a plurality of consecutive frames. A projection-type image display device configured to generate an average value. 3. The projection display apparatus according to claim 2, wherein the plurality of frame average values are sequentially obtained, a target level is set with the plurality of frame average values, and the amount of emitted light is increased / closed so as to approach the target level. A projection display apparatus characterized in that the reduction is executed step by step.

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