JP4862866B2 - Image display device and image display method - Google Patents

Description

  The present invention relates to an image display device and an image display method, and more particularly to an image display device that is excellent in video expression and that can obtain a video image with brightness suitable for the use environment and the user's preference.

  In recent years, the development of information equipment has been remarkable, and the demand for a high-resolution, low power consumption and thin image display device has increased, and research and development have been promoted. Among them, the liquid crystal display device is expected as a display device that can electrically control the alignment of liquid crystal molecules to change the optical characteristics and can meet the above-mentioned needs. As one form of such a liquid crystal display device, there is known a projection type liquid crystal display device (liquid crystal projector) that enlarges and projects an image emitted from an optical system using a liquid crystal light valve onto a screen through a projection lens. The projection type liquid crystal display device uses a liquid crystal light valve as an optical modulator, but the projection type display device includes a liquid crystal light valve and a digital mirror device (hereinafter abbreviated as DMD). An optical modulator is also in practical use. However, this type of conventional projection display device has the following problems.

(1) A sufficient contrast cannot be obtained due to light leakage and stray light generated by various optical elements constituting the optical system. Therefore, the gradation range (dynamic range) that can be displayed is narrow, and the quality and power of the video are inferior compared to existing television receivers using a cathode ray tube (CRT).
(2) Even if an attempt is made to improve the quality of video by various video signal processing, the dynamic range is fixed, so that a sufficient effect cannot be exhibited.

As a solution to the problem of such a projection display device, that is, a method of extending the dynamic range, it is conceivable to change the amount of light incident on the light modulator (light valve) according to the video signal. The simplest way to achieve this is to change the light output intensity of the lamp. In a projection type liquid crystal display device, a method for controlling output light of a metal halide lamp has been proposed (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 3-179886

High-pressure mercury lamps are currently mainstream as lamps used in projection-type liquid crystal display devices, but it is extremely difficult to control light output intensity with high-pressure mercury lamps. For this reason, there is a need for a method that can change the amount of light incident on the light modulation means in accordance with the video signal without changing the light output intensity itself of the lamp.
In addition to the above-mentioned problems, the brightness of the light source is fixed in the current projection display device. For example, the screen becomes too bright in a dark viewing environment, and the projection distance and zooming of the projection lens are also performed. When the projection screen size is changed by this, there is a problem that the brightness of the screen changes accordingly.

  The present invention has been made to solve the above-described problems, and can change the amount of light incident on the light modulation means without changing the light output intensity of the lamp. An object of the present invention is to provide an image display device and an image display method capable of exhibiting excellent effects in terms of adaptability.

  In order to achieve the above object, a first image display device of the present invention is an image display device in which a display image is adjusted by a dimming process of illumination light and an expansion process of an image signal. Image parameter extracting means for extracting an image parameter characterizing the length per unit time based on an image signal, and a control parameter for determining a system control parameter relating to a dimming process and an expansion process depending on a time change of the image parameter Determining means, and the control parameter determining means limits a change amount of the system control parameter per unit time to a predetermined amount or less.

  The present inventor has already applied for a projection display device including a dimming element that adjusts the amount of light based on information from the outside such as a video signal, a projection magnification ratio, and a brightness situation under a use environment. . According to this apparatus, the amount of light incident on the light modulator can be adjusted according to the image and the situation without changing the light output intensity of the light source itself by using the light control element, and the above object is achieved. can do. However, when the brightness of the image changes, there is a problem that unnecessary brightness flickering occurs due to the difference in the response characteristics of the light modulator and the light control element. In addition, brightness fluctuations are perceived at places where the brightness does not want to change, such as in a subtitle portion, and there is a sense of incongruity when viewing images.

  The image display device of the present invention aims to achieve the above object and at the same time solve the above problems. That is, in the image display device of the present invention, the image parameter extracting means extracts the image parameter per unit time based on the image signal, and the control parameter determining means depends on the time change of the image parameter. To decide. The “image parameter” referred to here is a parameter that characterizes the brightness of the image. For example, the average brightness of the image, the maximum brightness included in the image, or the top 10% of pixels from the maximum brightness is included. Brightness can be used as an image parameter. The “system control parameter” is a parameter used for performing dimming processing or expansion processing in the system, and specifically, a dimming coefficient or expansion coefficient described later corresponds to this. The “unit time” may be, for example, one frame or one field.

  In the first image display device of the present invention, the amount of change in the system control parameter per unit time is limited to a predetermined amount or less by the control parameter determination means, so that the brightness of the image by the dimming process or the expansion process is reduced. The variation in height is sufficiently small. As a result, even if the response characteristics of the dimming process and the extension process are different, the degree of flickering is reduced and it is difficult for the viewer to visually recognize, so that the quality of the video can be improved. In addition, even if the brightness changes slightly in the subtitle portion, which should originally have a constant brightness due to the light control, the viewer does not feel uncomfortable because the amount of change in brightness per unit time is small.

In the image display device having the above configuration, when the amount of change in the system control parameter per unit time is 100%, the brightness change is 5 in all the areas in the screen. It is desirable to limit it to be within%.
The reason is that if the change is within 5% per unit time, even if the response characteristics of the dimming process and the extension process are different, the flicker caused by the mismatch is not recognized.

  A second image display device of the present invention is an image display device in which a display image is adjusted by a dimming process of illumination light and an expansion process of an image signal, and an image parameter characterizing the brightness of the image is used as an image signal. An image parameter extracting means for extracting each unit time based on the image parameter, and a control parameter determining means for determining a system control parameter related to the dimming process and the expansion process depending on the time change of the image parameter. The means is characterized in that the change amount of the system control parameter per unit time is changed in accordance with the change amount of the image parameter per unit time.

  That is, in the second image display device of the present invention, the change amount of the system control parameter per unit time is not always constant, but changes according to the change amount of the image parameter per unit time. For example, the change amount of the system control parameter when the change amount of the image parameter is larger than the threshold value is made larger than the change amount of the system control parameter when the change amount of the image parameter is smaller than a predetermined threshold value. Can do. That is, when the change amount of the image parameter is relatively small, for example, when the brightness slightly changes in a certain video scene, the change amount per unit time of the system control parameter is reduced, Reduce the change rate of dimming and stretching. On the other hand, when the change amount of the image parameter is large, for example, when the video scene changes drastically, the change amount per unit time of the system control parameter is increased, and the change rate of dimming or expansion is increased. As a result, when the screen change is small in the same scene, it is possible to obtain an image in which the viewer does not feel flickering or strange. On the other hand, when the screen changes greatly due to a scene change, etc., adjustment is made with a short response time. It becomes possible to do.

In addition, in the second image display device of the present invention, when the change amount of the image parameter is smaller than a predetermined threshold value, the change amount of the system control parameter per unit time is made constant regardless of the change amount of the image parameter. It is also good.
According to this configuration, in the range below the threshold (when the screen change is small), it is possible to make the flickering less noticeable by making the fluctuation in brightness by the expansion process and the dimming process constant.

Alternatively, when the change amount of the image parameter is larger than a predetermined threshold value, a limit value may not be provided for the change amount of the system control parameter per unit time.
According to this configuration, it is possible to quickly adjust a large change in the display image, and it is possible to minimize a period in which the extension process, the light control process, and the display image do not match.

Alternatively, the system control parameter may be configured not to change when the change amount of the image parameter is smaller than a predetermined threshold.
According to this configuration, flickering can be eliminated because the expansion and dimming state does not change in a range equal to or less than the threshold (when the change in the screen is small).

  A third image display device of the present invention is an image display device in which a display image is adjusted by dimming processing of illumination light and image signal expansion processing, and an image parameter characterizing the brightness of the image is used as the image signal. An image parameter extracting means for extracting each unit time based on the image parameter, and a control parameter determining means for determining a system control parameter related to the dimming process and the expansion process depending on the time change of the image parameter. In the means, when the image parameter per unit time changes from the dark side to the bright side with respect to the change amount per unit time of the system control parameter when the image parameter per unit time changes from the bright side to the dark side. The amount of change per unit time of the system control parameter is increased.

  That is, the third image display device of the present invention changes the amount of change in the system control parameter when the image changes from the dark side to the bright side and when the image changes from the bright side to the dark side. The change amount of the system control parameter when the image parameter changes from the bright side to the dark side is small, and the change amount of the system control parameter when the image parameter changes from the dark side to the bright side is increased. The reason is that since the expansion ratio (expansion coefficient) is large on the dark side, the gradation on the bright side is crushed (compressed). In this state, if an image containing a lot of gradations on the bright side is displayed, the entire screen will be crushed on the bright side. Therefore, it is preferable for viewing that the dimming process and the expansion process are performed as quickly as possible for such a change in the display image. On the other hand, when the image changes from the bright side to the dark side, the above problem does not occur because the expansion rate (expansion coefficient) changes from the small side to the large side. As a result, it is possible to make it difficult for the viewer to feel flickering or discomfort with any display image change.

The first image display method of the present invention corresponds to the first image display device of the present invention.
In other words, the first image display method of the present invention is an image display method for adjusting a display image by dimming processing of illumination light and expansion processing of an image signal, and an image parameter characterizing the brightness of an image is set as an image signal. And a second step of determining a system control parameter related to the light control process and the expansion process depending on the time change of the image parameter. In this step, the change amount of the system control parameter per unit time is limited to a predetermined amount or less.

The second image display method of the present invention corresponds to the second image display device of the present invention.
In other words, the second image display method of the present invention is an image display method for adjusting a display image by dimming processing of illumination light and expansion processing of an image signal, and an image parameter characterizing the brightness of an image is set as an image signal. And a second step of determining a system control parameter related to the light control process and the expansion process depending on the time change of the image parameter. In this step, the change amount of the system control parameter per unit time is changed according to the change amount of the image parameter per unit time.

The third image display method of the present invention corresponds to the third image display device of the present invention.
That is, a third image display method of the present invention is an image display method for adjusting a display image by dimming processing of illumination light and expansion processing of an image signal, and an image parameter characterizing the brightness of an image is set as an image signal. And a second step of determining a system control parameter related to the light control process and the expansion process depending on the time change of the image parameter. In this step, the system control when the image parameter per unit time changes from the dark side to the bright side with respect to the change amount of the system control parameter when the image parameter per unit time changes from the bright side to the dark side. It is characterized by increasing the amount of parameter change.

[First Embodiment]
Hereinafter, a first embodiment of an image display device and an image display method of the present invention will be described in detail with reference to FIGS.
As an example of an image display device using the image display method of the present invention, a three-plate projection display device having a liquid crystal light valve for each color of R (red), G (green), and B (blue) is used. I will explain.

FIG. 1 is a schematic configuration diagram illustrating an example of a projection display device. As shown in FIG. 1, the projection display device according to the present embodiment includes a light source 510, a light control element 26, dichroic mirrors 513 and 514, reflection mirrors 515, 516 and 517, relay lenses 518, 519 and 520, red light. Liquid crystal light valve 522, green light liquid crystal light valve 523, blue light liquid crystal light valve 524, cross dichroic prism 525, and projection lens system 526.
As the light control element 26, for example, a liquid crystal panel whose transmittance is variable may be used, or a movable light shielding plate or the like may be used. A light control element using a liquid crystal panel has a relatively fast response speed, while a mechanical light control element using a movable light shielding plate has a relatively low response speed. In any case, the response speeds of the light control device and the liquid crystal light valve are different, and the technique of the present invention is effective in that it is difficult to visually recognize flicker and the like.

The light source 510 includes a lamp 511 such as an ultra-high pressure mercury lamp and a reflector 512 that reflects light from the lamp 511. Between the light source 510 and the dichroic mirror 513, a light control element 26 that adjusts the amount of light from the light source 510 is disposed.
The blue / green light reflecting dichroic mirror 513 transmits the red light LR of the white light from the light source 510 and reflects the blue light LB and the green light LG. The transmitted red light LR is reflected by the reflection mirror 517 and enters the liquid crystal light valve 522 for red light.
On the other hand, the green light LG reflected by the dichroic mirror 513 is reflected by the dichroic mirror 514 for reflecting green light and enters the liquid crystal light valve 523 for green light.
The blue light LB reflected by the dichroic mirror 513 is also transmitted through the dichroic mirror 514, and passes through a relay system 521 including a relay lens 518, a reflection mirror 515, a relay lens 519, a reflection mirror 516, and a relay lens 520, and then blue light. The liquid crystal light valve 524 is incident.

  The three color lights modulated by the liquid crystal light valves 522, 523, and 524 are incident on the cross dichroic prism 525. In this prism, four right-angle prisms are bonded together, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are formed in a cross shape on the inner surface thereof. These dielectric multilayer films combine the three color lights to form light representing a color image. The synthesized light is projected on the screen 527 by the projection lens system 526 which is a projection optical system, and the image is enlarged and displayed. Each of the liquid crystal light valves 522, 523, and 524 is connected to an image processing unit (not shown in FIG. 1) that performs predetermined image processing on each color light based on an image signal.

  FIG. 2 is a block diagram showing the configuration of the drive circuit of the projection display device. As shown in FIG. 2, an image analysis unit 24 is connected to the image processing unit 21, and based on image processing parameters (expansion coefficient, system control parameter) determined by the image analysis unit 24, an image signal is processed. Predetermined image processing, here brightness expansion processing, is performed. The image signal that has undergone predetermined image processing by the image processing unit 21 is supplied to the liquid crystal light valves 522, 523, and 524 via the light valve driver 22. On the other hand, dimming is performed on the light emitted from the light source 511 by the dimming element driver 25 and the dimming element 26 based on the dimming processing parameters (dimming coefficient, system control parameter) determined by the image analysis unit 24. Processing is to be performed.

FIG. 3 is a block diagram illustrating a configuration of the image analysis unit 24. As shown in FIG. 3, both the image signal and the horizontal / vertical synchronization signal are input to the histogram creation unit 31 (image parameter extraction means), and the histogram creation unit 31 creates a histogram. Based on the histogram, the parameter extraction unit 32 (image parameter extraction means) extracts and determines image parameters, and extracts and determines system control parameters such as dimming coefficients and expansion coefficients. However, the system control parameter determined here is a temporary value corresponding to each frame, and the true system control depending on the time change of the image parameter in the comparator 33 (control parameter determination means) in the next stage. Parameters (system control parameters that are actually used for dimming and expansion processing) are determined.
As for the dimming method, for example, the brightness control is adapted to the display image so that the amount of light increases in a bright video scene and the amount of light decreases in a dark scene. Control), control from the outside (control according to user's preference, etc.) may be performed, but here the extraction of image parameters and system control parameters is the same, taking the case of display video adaptive control as an example. A case where the method is used will be described.

  For example, a video signal including the number of gradations of 256 steps from 0 to 255 is assumed. When attention is paid to an arbitrary frame constituting a continuous video, it is assumed that the appearance number distribution (histogram) for each gradation number of pixel data included in the frame is as shown in FIG. In this example, since the brightest number of gradations included in the histogram is 190, the number of gradations 190 is set as the image parameter b (t). The method of using the maximum brightness gradation number as an image parameter is a method that can express the brightness most faithfully to the input video signal. Alternatively, the number of gradations having a certain ratio (for example, 10%) with respect to the number of appearances from the maximum brightness may be used as the image parameter. In the case of this method, it is possible to avoid the influence of brightness fluctuation in a small area.

  In this way, when the parameter extraction unit 32 determines, for example, the number of gradations 190 in an arbitrary frame as the image parameter b (t), the temporary dimming coefficient is based on the image parameter b (t). x ′ (t) is calculated. For example, if the relationship between gradation and brightness is linear, and the maximum brightness (number of gradations 255) is 100%, the provisional dimming coefficient x ′ (t) is x ′ (t) = 190/255. = 0.75 (75%). On the other hand, a temporary expansion coefficient is also calculated in the parameter extraction unit 32. For example, when the expansion is performed up to the maximum gradation range, in the above example, the temporary expansion coefficient y ′ (t) is y ′ (t) = 255. /190=1.34.

  Here, in the case of this embodiment, the change amount Δx of the dimming coefficient and the change amount Δy of the expansion coefficient for each frame are the change in the portion where the brightness changes most in the screen, and the maximum brightness of the screen is obtained. It is limited to 5% or less when 100% is assumed. Accordingly, when the temporary dimming coefficient x ′ (t) and the temporary expansion coefficient y ′ (t) in any one frame are calculated by the parameter extraction unit 32, these are sent to the comparator 33, and the comparator 33 , The dimming coefficient x ′ (t), the expansion coefficient y ′ (t), the dimming coefficient x ′ (t−1) and the expansion coefficient y ′ (t−) in the previous frame stored in the memory 34. 1) is compared. For example, if the video changes from the bright side to the dark side, the comparison results are x ′ (t) <x ′ (t−1), y ′ (t)> y ′ (t−1). In this case, the true dimming coefficient x (t) reflecting the direction of brightness change is x (t) = x ′ (t−1) −Δx, and the true expansion coefficient y (t) is y (t). ) = Y ′ (t−1) + Δy, and the dimming coefficient x (t) and the expansion coefficient y (t) are output.

Further, the dimming coefficient and the expansion coefficient are changed synchronously within one frame. That is, it is important to suppress the change amount Δx of the dimming coefficient and the change amount Δy of the expansion coefficient to a change amount that can be adjusted within one frame. This ensures that the response does not span frames. The “dimming coefficient” is the dimming rate of the illumination light, and changes with 1 or less when the standard display is performed (when the brightness is maximum). The “expansion coefficient” is an expansion rate of image data displayed on the liquid crystal light valve, and changes with 1 or more when standard display is performed. The dimming coefficient and the expansion coefficient have a substantially inverse relationship, and the dimming coefficient × the expansion coefficient≈1.
For example, when the relationship between gradation and brightness is linear, and the maximum brightness (number of gradations 255) is 100%, the temporary dimming coefficient x ′ is x ′ = 190/255 = 0.75 (75 Based on this, the true dimming coefficient x is calculated, and the dimming element 26 may be driven so that the amount of light corresponding to the dimming coefficient x is obtained. On the other hand, with regard to the expansion coefficient, for example, when expanding to the maximum gradation range, in the above example, the temporary expansion coefficient y ′ is y ′ = 255/190 = 1.34, and based on this, the true expansion coefficient y is calculated, and based on the expansion coefficient y, the image signal from the gradation number 0 to 190 shown in FIG. 4A is converted into the number of gradations as shown in FIG. Stretched from 0 to 255. By combining such dimming processing and expansion processing, smooth gradation expression can be realized while expanding the dynamic range of the video.

  By using the light control element 26 as in the present embodiment, the amount of light incident on the liquid crystal light valve can be adjusted according to the image without changing the light intensity of the light source itself, the dynamic range is wide, and the image A projection display device with excellent expressive power can be realized. However, since the response speed of the light control element and the liquid crystal light valve are usually different, as shown in FIGS. 8A and 8B, for example, when the response speed of the light control element is faster than that of the light valve, FIG. As shown in FIG. 8C, there is a problem that unnecessary brightness fluctuation (overshoot S) occurs in the brightness of the image on the screen, and it is visually recognized as flicker. Also, brightness fluctuations are perceived even in places where the brightness does not want to change, such as subtitles, and there is a sense of discomfort when viewing images.

  On the other hand, in the present embodiment, when the dimming process and the expansion process are performed, the dimming coefficient change amount Δx and the expansion coefficient change amount Δy for each frame are, for example, a brightness change of 5% or less. And so on. That is, since the change amounts of these coefficients are small, for example, as shown in FIGS. 5A and 5B, the brightness of the light control element and the brightness of the light valve change little by little for each frame. As a result, as shown in FIG. 5C, unnecessary brightness fluctuations (symbol S ′) are small even in the brightness of the image on the screen, and flickering can be made difficult to be visually recognized. In addition, it is difficult to visually perceive a change in brightness even in a portion where the brightness is not desired to change, such as a subtitle portion, and it is possible to provide an easy-to-view video without the viewer feeling uncomfortable.

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described with reference to FIG.
The basic configuration of the projection display device of this embodiment is exactly the same as that of the first embodiment, except that the dimming coefficient and the expansion coefficient for each frame are changed. Therefore, in this embodiment mode, description of the configuration of the projection display device and the configuration of the drive circuit is omitted.

In the first embodiment, regardless of the change amount of the image parameter b (t) for each frame, the change amount of the dimming coefficient and the expansion coefficient for each frame is uniformly limited to, for example, 5% or less. Was. In contrast, in the present embodiment, the dimming coefficient and the expansion coefficient according to the amount of change Δb (Δb = b (t) −b (t−1)) of the image parameter b (t) for each frame. The amount of change is changed. FIG. 6 shows an example of how to change the amount of change in the light control coefficient and the expansion coefficient. In the example of FIG. 6, the change amount Δb of the image parameter is a predetermined threshold value with respect to the change amount Δx (vertical axis) of the dimming coefficient when the change amount Δb (horizontal axis) of the image parameter is smaller than the predetermined threshold value. The change amount Δx of the dimming coefficient when the value is larger than that is larger. Here, the threshold is set to about 80 to 100, and Δb is positive (when the image changes from the dark side to the bright side) and negative (when the image changes from the bright side to the dark side). Therefore, the absolute value of the change amount Δx of the dimming coefficient is made equal. In FIG. 6, the dimming coefficient is taken as an example, but the expansion coefficient can be set similarly.
Also in the second embodiment, it is desirable to provide an upper limit value for the change amount Δx of the dimming coefficient per unit time in the region where the change amount Δb of the image parameter is small, as in the first embodiment. .

In the present embodiment, when the change amount Δb of the image parameter is relatively small (for example, less than 80), in other words, when the brightness slightly changes in a certain video scene, the dimming is performed. The coefficient change amount Δx is small, and the degree of adjustment is small. On the other hand, when the image parameter change amount Δb is large (for example, 100 or more), in other words, when the video scene changes from a bright scene to a dark scene, the dimming coefficient change amount Δx is large and the degree of adjustment is large. Also grows.
In the first embodiment, when the brightness of the screen suddenly changes due to a scene change or the like, it takes a long time to adjust the screen. However, in this embodiment, it is quick even in such a case. The screen can be adjusted. In addition, when the screen change is small in the same scene or the like, as in the first embodiment, it is possible to obtain an image in which the viewer does not feel flickering or uncomfortable.

In the example of FIG. 6, when the image parameter change amount Δb is smaller than a predetermined threshold value, the dimming coefficient change amount Δx is increased according to the value of Δb. When the parameter change amount Δb is smaller than a predetermined threshold, the dimming coefficient change amount Δx may be constant regardless of the image parameter change amount Δb.
According to this configuration, in the range below the threshold (when the screen change is small), it is possible to make the flickering less noticeable by making the fluctuation in brightness by the expansion process and the dimming process constant.
Alternatively, the dimming coefficient (expansion coefficient) may be prevented from changing when the image parameter change amount Δb is smaller than a predetermined threshold.
According to this configuration, since the dimming (extension) state does not change in a range that is equal to or smaller than the threshold (when the change in the screen is small), flicker can be eliminated.

Further, when the image parameter change amount Δb is larger than a predetermined threshold value, a limit value may not be provided for the dimming coefficient change amount Δx.
According to this configuration, it is possible to quickly adjust a large change in the display image, and it is possible to minimize a period in which the extension process, the light control process, and the display image do not match.

[Third Embodiment]
The third embodiment of the present invention will be described below with reference to FIG.
The basic configuration of the projection display device of this embodiment is exactly the same as that of the first embodiment, except that the dimming coefficient and the expansion coefficient for each frame are changed. Therefore, in this embodiment mode, description of the configuration of the projection display device and the configuration of the drive circuit is omitted.

  In the first embodiment, regardless of the change amount of the image parameter b (t) for each frame, the change amount of the dimming coefficient and the expansion coefficient for each frame is uniformly limited to 5% or less, for example. It was. In the second embodiment, the change amount Δx of the dimming coefficient is changed according to the change amount of the image parameter b (t). The change amount Δb of the image parameter is positive and negative. The absolute value of the change amount Δx of the dimming coefficient was set equal. On the other hand, in the present embodiment, the absolute value of the change amount Δx of the dimming coefficient is changed depending on whether the change amount Δb of the image parameter is positive or negative. Specifically, as shown in FIG. 7, when the image parameter change amount Δb (horizontal axis) is positive, that is, when the image changes from the dark side to the bright side, the dimming coefficient change amount Δx (vertical axis) ) Is large, and the change amount Δx of the dimming coefficient is small when the change amount Δb of the image parameter is negative, that is, when the image changes from the bright side to the dark side. In FIG. 7, the dimming coefficient is taken as an example, but the expansion coefficient can be set similarly.

In the present embodiment, considering expansion processing, since the expansion ratio (expansion coefficient) is large on the dark side of the image, the gradation on the bright side is crushed (compressed). In this state, if an image including a lot of gradations on the bright side is displayed, the entire screen is crushed on the bright side. Therefore, for such changes in the display image, it is preferable to perform the dimming process and the expansion process as quickly as possible for viewing. Therefore, when the image changes from the dark side to the bright side, it is desirable that the amount of change in the dimming coefficient or the expansion coefficient is large. On the other hand, when the image changes from the bright side to the dark side, since the expansion rate (expansion coefficient) changes from the small side to the large side, the above-described problem of gradation collapse on the bright side is Does not occur. As a result, also in the present embodiment, as in the first and second embodiments, it is possible to obtain an image in which the viewer is less likely to feel flicker or discomfort.
Also in the third embodiment, it is desirable to provide an upper limit value for the change amount Δx of the dimming coefficient per unit time in the region where the change amount Δb of the image parameter is small, as in the first embodiment. .

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the projection display device has been described as an image display device that can use the image display method of the present invention. However, the present invention is not limited to this, for example, a direct view display device or the like. It may be. Also, the specific configuration of the drive circuit of the projection display device can be changed as appropriate.
The image display method of the present invention can also be used for processing image signals of LCDs, electroluminescence, plasma displays, digital mirror devices, field emission devices, and the like.

It is a schematic block diagram of the projection type display apparatus of the 1st Embodiment of this invention. It is a block diagram which shows the structure of the drive circuit of a projection type display apparatus equally. FIG. 3 is a block diagram illustrating a configuration of an image analysis unit of the drive circuit. It is a figure which shows an example of the histogram produced in the histogram creation part of an image analysis part similarly. It is a figure which shows the tendency of the brightness change of the light control element of this embodiment, a light valve, and a screen image | video. It is a figure which shows the mode of the change of the light control coefficient in 2nd Embodiment of this invention. It is a figure which shows the mode of the change of the light control coefficient in 3rd Embodiment of this invention. It is a figure which shows the tendency of the brightness change of a common light control element, a light valve, and a screen image.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Image processing part, 24 ... Image analysis part, 26 ... Light control element, 31 ... Histogram preparation part (image parameter extraction means), 32 ... Parameter extraction part (image parameter extraction means), 33 ... Comparator (control parameter determination) Means), 522-524 ... Liquid crystal light valve (light modulator)

Claims (5)

An image display device in which a display image is adjusted by dimming processing of illumination light and expansion processing of an image signal,
Image parameter extracting means for extracting image parameters characterizing the brightness of the image every unit time based on an image signal, dimming coefficients related to the dimming processing depending on the time change of the image parameters, and the expansion processing Control parameter determining means for determining system control parameters including the expansion coefficient concerned,
In the control parameter determination means, the amount of change of the dimming coefficient and the expansion coefficient per unit time is changed according to the amount of change of the image parameter per unit time,
A change amount of the dimming coefficient and a change amount of the expansion coefficient are set to change amounts adjustable within one frame, and the dimming coefficient and the expansion coefficient are changed synchronously within one frame ;
The system control parameter when the amount of change of the image parameter is larger than a predetermined threshold with respect to the amount of change of the system control parameter per unit time when the amount of change of the image parameter is smaller than a predetermined threshold An image display device characterized by increasing the amount of change per unit time . Claim 1 of the change said image parameter, wherein the amount of change per unit time of the system control parameter is constant regardless of the amount of change in the image parameters that when less than a predetermined threshold value Image display device. 3. The image display according to claim 1, wherein when the change amount of the image parameter is larger than a predetermined threshold, no limit value is provided for the change amount of the system control parameter per unit time. 4. apparatus. The image display apparatus according to any one of claims 1 to 3 the amount of change the image parameters when less than a predetermined threshold value, characterized in that to the system control parameter is not changed. An image display method for adjusting a display image by dimming processing of illumination light and expansion processing of an image signal,
A first step of extracting an image parameter characterizing the brightness of the image every unit time based on an image signal; and a dimming coefficient related to the dimming process and an extension process depending on a time change of the image parameter. A second step of determining system control parameters including the expansion factor involved,
In the second step, the amount of change of the dimming coefficient and the expansion coefficient per unit time is changed according to the amount of change of the image parameter per unit time,
A change amount of the dimming coefficient and a change amount of the expansion coefficient are set to change amounts adjustable within one frame, and the dimming coefficient and the expansion coefficient are changed synchronously within one frame ;
The system control parameter when the amount of change of the image parameter is larger than a predetermined threshold with respect to the amount of change of the system control parameter per unit time when the amount of change of the image parameter is smaller than a predetermined threshold An image display method characterized by increasing the amount of change per unit time .

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