JP2005203942A - Projection type video display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection type video display device capable of relaxing a delay in a lamp output change with respect to a luminance change in an input video image. <P>SOLUTION: The projection type video display device, provided with a light source lamp and a light valve for displaying an image by modulating the intensity of the light of the light source lamp and capable of changing the illuminance of the light source lamp in accordance with a luminance change in the input video image, includes a delay means for delaying a video signal by a time equivalent to a delay time of the illuminance change in the light source lamp with respect to a luminance change in the input video image and transmitting the delayed video signal to the light valve. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projection-type video display device such as a liquid crystal projector, which includes a light source lamp and a light valve that displays an image by modulating light intensity of the light source lamp.

  Conventional projection-type image display devices (projectors) have been developed aiming at high-luminance output using not only liquid crystals but also light valves (light valves) such as DMDs in which minute reflectors are integrated. Nowadays, many products aim for high image quality as well as high brightness. One factor for realizing high image quality is a high contrast feeling.

  Contrast is the ratio of maximum brightness to minimum brightness. The higher this ratio, the higher the contrast. It is required to illuminate the screen brighter for the input image with the maximum luminance and illuminate the screen darker for the input image with the minimum luminance. However, the light transmittance at the maximum brightness in the light valve cannot physically exceed 100%, and on the other hand, it is also difficult to completely reduce the light transmittance at the minimum brightness to 0%. . The latter is particularly problematic. While light valves reduce pixel light transmission when projecting dark scenes, users are often frustrated with contrast because some light transmission does not provide a sufficiently dark screen output.

  Therefore, focusing on dark scenes, projectors have been developed that use a method of changing the illuminance of the light source according to the brightness of the input image as a method of increasing the contrast. However, many light sources are considered to operate at a constant illuminance, and the change in the illuminance of the light source may not follow the speed of the change in the luminance of the input image. Despite the delay in the illuminance change of the light source, the image written to the light valve changes from time to time, thus providing an unnatural screen output to the user.

  The signal processing related to the lamp output adjustment in this case will be described in detail below. Many projector light source lamps are always lit at a constant light output during use, but in recent years, some have changed the light intensity (illuminance). The average luminance is obtained from the signal intensity of the input video signal, and the light output (illuminance) of the light source lamp is changed according to the magnitude. The input / output relationship is arbitrary, but generally the optical output is monotonically increased with an increase in the input signal.

  For example, in the simplest example, as shown in FIG. 1, it can be considered that light is output at an intensity proportional to the average luminance. The lamp output is maximized when the input image becomes uniform white with the maximum luminance, and the lamp output becomes zero when the input image becomes uniform black with the minimum luminance. However, in light sources using discharge such as mercury lamps and xenon lamps used in general projectors, if the light output is lowered by lowering the applied voltage, the discharge stops when the light output falls below a certain level. That is, light emission is lost. Once light emission stops in this way, it takes several tens of seconds to discharge the light again and stabilize the light output. In a projector whose main purpose is to display moving images, Is not practical at all.

  Therefore, with respect to the average luminance of the input image, the light output increases monotonously only within a certain range as shown in FIG. Do not lower it too much. The monotonously increasing portion may be an arbitrary function.

  By controlling the lamp output in the manner described here, the lamp output is lowered when projecting a low-luminance video signal, so that the user can see a darker image when a dark scene is presented. It will be. Thereby, an improvement in contrast is obtained.

  However, on the other hand, there may be a problem that there is a delay amount in the control of the lamp power source and the light source lamp. Since the light source lamp and the lamp power source handle high power and high-speed power control is difficult, the change in the lamp output cannot follow the change in the luminance of the video signal, which is delayed. Since this delay amount is so large that it cannot be ignored, for example, when a video signal whose brightness changes rapidly changes is input to the projector, an unnatural screen output for the user is provided.

  Because of this problem, if the change width of the lamp output is increased, the contrast feeling increases, but the unnaturalness of the time delay also increases. Therefore, it is difficult to perform a design that allows a larger range of change.

Such lamp output delay includes a group delay that causes a delay as a whole in signal processing as shown in FIG. 3A, and a lamp drive control signal as shown in FIG. 3B. There is a gradual delay in which the lamp output changes gradually with respect to the change in the output.
Japanese Patent Laid-Open No. 03-179886 Japanese Patent Laid-Open No. 08-201812

  SUMMARY OF THE INVENTION An object of the present invention is to provide a projection type image display apparatus that can alleviate a delay in lamp output change with respect to a change in luminance of an input image.

  The invention described in claim 1 includes a light source lamp and a light valve that displays an image by modulating the light intensity of the light source lamp, and changes the illuminance of the light source lamp in accordance with the luminance change of the input video. A projection-type image display apparatus capable of delaying a video signal and sending it to a light valve by a time corresponding to a delay time of an illuminance change of a light source lamp with respect to a change in luminance of an input image. To do.

  According to a second aspect of the present invention, in the first aspect of the present invention, the light source lamp includes a time change emphasizing unit that emphasizes the time change of the luminance change of the input video, and based on the output of the time change emphasis unit. The illuminance is controlled.

  According to the present invention, the delay of the lamp output change with respect to the luminance change of the input video can be mitigated.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 4 shows the electrical configuration of the projection-type image display device.

  The analog video signal input to the projection video display device is converted into a digital video signal by the A / D converter 1. The digital video signal obtained by the A / D converter 1 is sent to the resolution conversion circuit 2 and also sent to the average luminance calculation circuit 11.

  The digital video signal whose resolution has been converted by the resolution conversion circuit 2 is temporarily stored in a buffer memory (delay means) 3 for delaying and outputting the digital video signal in order to alleviate the group delay of the lamp output described above. The The digital video signal read from the buffer memory 3 is written to the light valve 4. The image written in the light valve 4 is projected on a screen (not shown) by the light source lamp 14.

  On the other hand, the average luminance calculation circuit 11 calculates the average luminance of the input video signal for each frame. The average luminance calculated by the average luminance calculation circuit 11 is sent to a time change emphasis circuit (time change emphasis means) 12 composed of a differential filter, for example. The time change emphasis circuit 12 emphasizes the change in average luminance. The output of the time change emphasis circuit 12 is sent to the lamp power supply circuit 13. The lamp power supply circuit 13 controls the drive voltage of the light source lamp 14 according to the output of the time change emphasizing circuit 12.

  In this embodiment, the digital video signal output from the resolution conversion circuit 2 is output after passing through the buffer memory 3. Here, a delay time is added, and the delay amount is proportional to the buffer amount of the buffer memory 3. For example, if one frame image is held, the delay time is several tens of milliseconds. If the signal is 60 frames per second, the delay time is about 16.7 milliseconds. The delay time of the video signal by the buffer memory 3 is set to a time corresponding to the group delay time. Since the video signal by the buffer memory 3 is delayed, the unnaturalness with respect to the group delay of the lamp output is alleviated. Although the buffer memory 3 may be arranged in the previous stage of the resolution conversion circuit 2, if it is arranged in the subsequent stage of the resolution conversion circuit 2, the required amount of the buffer memory 3 becomes constant, so that the design becomes easier.

Buffer amount M required as a buffer memory 3, the group delay time and T _D seconds, the number of frames per second and F, the light valve total number of pixels is P, when the number of bits per pixel and B _pp, It is represented by the following formula (1).

M = T _D × F × P × B _pp (1)

  For example, in a projector with XGA resolution (1,024 × 768) pixels that displays video at a rate of 60 frames per second, if a general pixel holds 8 bits each for R, G, and B, a total of 24 bits 7 frames can be held by one 128 Mbit memory device, and the delay amount at this time is about 117 milliseconds.

  Note that the gradual delay of the lamp output described above can be made somewhat inconspicuous by using the overall delay processing as described above. In other words, as shown in FIG. 5, if the video signal is delayed as a whole by using the buffer method in addition to the amount of time corresponding to the group delay, the amount of time corresponding to the incremental delay can be considerably reduced. It can be carried out. The diagram on the left side of FIG. 5 shows changes in the input video signal (average luminance) a and changes in the lamp output light after the delay when the video signal is delayed by the buffer method by an amount corresponding to the group delay. 5 shows the input video signal after delay (average luminance) when the video signal is delayed by the buffer method by the amount of time corresponding to the group delay plus the amount of time corresponding to the incremental delay. ) Shows a change in a and a change in lamp output light b.

  However, from the user's point of view, the delay in the light output with respect to the change in the video signal is mitigated, and although the impression that the delay in the lamp output is accompanied as a whole becomes thin, strictly speaking, it is ahead of the change in the video signal. The lamp output appears to change.

  If such a progressive delay is processed with high accuracy, it is necessary to perform correction different from the overall delay. Therefore, in this embodiment, a time change enhancement method is used.

  As shown in FIG. 6, by using a time change emphasis circuit 12 such as a differential filter, the rise of the signal (average luminance) input to the lamp power supply circuit 13 is made steep, so that the lamp output light is gradually changed. Delay can be improved.

  The diagram on the left side of FIG. 6 shows changes in the input video signal (average luminance) a and changes in the lamp output light b after the delay when the video signal is delayed by the buffer method by an amount of time corresponding to the group delay. 6 indicates a change in the output signal c of the time change emphasis circuit 12 when the change in the average luminance of the input video signal is emphasized using the time change emphasis circuit 12.

  FIG. 7 shows a change in the output signal c of the time change emphasizing circuit 12 and a change in the lamp output light d.

  However, as the amount by which the rising edge of the average luminance signal is sharpened by the time change emphasizing circuit 12 is increased, the overall delay is increased as shown in the diagram on the right side of FIG. Accordingly, it is necessary to increase the delay amount of the input video signal by the buffer method.

  By combining a method of delaying the input video signal by the buffer memory 3 (buffer method) and a method of enhancing the average luminance change by the time change enhancement circuit 12 (average luminance change enhancement method), the overall group delay can be reduced. And gradual mitigation of delay. The average luminance change enhancement method involves an increase in the overall delay in order to improve the gradual delay, but the increase in the overall delay can be dealt with by increasing the buffer memory 3. is there.

  Further, instead of the method of delaying the input video signal by the buffer memory 3 (buffer method), the luminance change may be predicted using a prediction means such as a linear prediction method. For example, in a video signal that gradually becomes brighter, it is possible to predict that it will continue to become brighter in the middle of the video signal, so that the delay in the change in lamp output can be mitigated.

  Of course, both change emphasis means and prediction means may be used. Since the ramp control signal can be sent quickly by predicting the change, the buffer memory can be deleted.

  As the time change emphasis circuit 12, for example, as in “response speed improving means” disclosed in Japanese Patent Application Laid-Open No. 2003-44019 (name of invention: display control device and image display device), the time direction from the past is used. The difference in brightness change with respect to is calculated and added to the current brightness signal to improve the rise. Not only the analog voltage value change but also the digital value indicating the brightness level is similarly enhanced by the differential filter.

  For example, there may be a configuration in which there are only 16 levels of lamp power control even if there are 256 levels of luminance signals. After obtaining the average luminance value, it is replaced with a 16-step control signal and sent to the lamp power supply circuit, where it is decoded into an analog value of the power supply voltage inside the lamp power supply circuit and light is emitted at each lamp output. In this case, the range of values in 16 steps is arbitrary, and the steps are not necessarily equally spaced steps.

It is a graph which shows the example of the relationship between the average brightness | luminance and light output in the projector which controls the light output of a lamp | ramp based on average brightness | luminance. It is a graph which shows the other example of the relationship between the average brightness | luminance and light output in the projector which controls the light output of a lamp | ramp based on average brightness | luminance. 5 is a time chart for explaining a group delay that causes a delay overall as a result of signal processing, and a gradual delay in which a lamp output gradually changes with respect to a change in a lamp drive control signal. It is a block diagram which shows the electrical structure of a projection type video display apparatus. It is a time chart for explaining that the gradual delay of the lamp output can be made somewhat inconspicuous by using the overall delay processing. In order to explain that the gradual delay of the lamp output light can be improved by making the rising edge of the signal (average luminance) input to the lamp power supply circuit 13 steep using the time change emphasizing circuit 12. It is a time chart. 4 is a time chart showing a change in an output signal c of the time change emphasis circuit 12 and a change in lamp output light d.

Explanation of symbols

1 A / D converter 2 Resolution conversion circuit 3 Buffer memory (delay means)
4 Light valve 11 Average luminance calculation circuit 12 Time change enhancement circuit (time change enhancement means)
13 Lamp power circuit 14 Light source lamp

Claims (2)

In a projection-type video display device that includes a light source lamp and a light valve that displays an image by modulating the light intensity of the light source lamp, and can change the illuminance of the light source lamp in accordance with the luminance change of the input video,
A projection-type video display device comprising delay means for delaying a video signal by a time corresponding to a delay time of a change in illuminance of a light source lamp with respect to a change in luminance of an input video. 2. The projection according to claim 1, further comprising time change emphasizing means for emphasizing the time change of the luminance change of the input video, wherein the illuminance of the light source lamp is controlled based on the output of the time change emphasis means. Type image display device.

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