JP2006349924A - Image display device and image display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress overexposure without reducing the brightness of a display image.
An image parameter extracting unit that extracts an image parameter that characterizes brightness of the display image from the image signal at predetermined time intervals; and the image parameter extracted based on the image parameter extracted by the image parameter extracting unit. A dimming control parameter related to the dimming process is determined, a dimming control unit that controls the dimming process based on the dimming control parameter, and the image parameter extracted based on the image parameter extraction unit A decompression processing unit that determines a decompression control parameter related to the decompression processing and performs the decompression processing based on the decompression control parameter, and the image parameter extraction unit can output the gradation value of the image signal after the decompression processing The image parameter is determined so that the number of pixels exceeding the maximum gradation value is a predetermined number or less.
[Selection] Figure 2

Description

  The present invention relates to an image display device and an image display method.

 As one form of an image display device, a liquid crystal projector is known that enlarges and projects a display image emitted from an optical system using a liquid crystal light valve onto a screen through a projection lens. Such a liquid crystal projector 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. For this reason, the displayable gradation range (dynamic range) is narrow, and the quality and power of the displayed image are inferior compared with an existing television using a cathode ray tube (CRT).
(2) Even if an attempt is made to improve the quality of a display image by various image signal processing, the dynamic range is fixed, so that a sufficient effect cannot be exhibited.

As a solution to the problem of such a liquid crystal projector, that is, a method of extending the dynamic range, it is conceivable to change the light amount of the light source incident on the light modulator (light valve) according to the image signal. The simplest way to achieve this is to change the light output intensity of the light source lamp. For example, Patent Document 1 below discloses a technique for controlling output light from a light source lamp in accordance with an image signal in a liquid crystal projector.
JP-A-5-66501

   However, high-pressure mercury lamps are mainly used as light source lamps for liquid crystal projectors, but it is extremely difficult to control the light output intensity of the high-pressure mercury lamp. For this reason, there is a need for a method of changing 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 light source lamp. In addition to the above-mentioned problems, the light output intensity of the light source lamp is fixed. For example, in a dark viewing environment, the display image becomes too bright, or the projection screen size depends on the projection distance and zooming of the projection lens. There is also a problem in that the brightness of the display image changes in accordance with the change of.

   In order to solve such problems, in recent years, a structure in which a dimming louver (light shielding plate) is combined with a light source lamp of a liquid crystal projector has been proposed. Specifically, a light shielding plate is arranged on the optical axis of the light emitted from the light source lamp, and this is rotated around a rotation axis parallel to the main surface to partially shield the light source light. Dimming is performed.

   By adjusting the light source light according to the image signal by such a light control means, it is possible to obtain light with brightness according to the display image even when the light output intensity of the light source lamp remains constant. Can contribute to the expansion of the dynamic range. Similarly, it is possible to obtain light having a brightness according to the projection magnification ratio, the brightness condition in the usage environment, or the user's preference.

   However, on the principle that the black level is changed by such dimming processing and image signal expansion processing performed separately from the dimming processing, the dimming processing and expansion processing are performed in synchronization with the switching of the image signal. This causes an inadvertent brightness change in the image, which is recognized by the user as flickering on the display image. For this reason, in a conventional liquid crystal projector, flickering of a display image is prevented by performing dimming processing and expansion processing at a relatively low speed without being synchronized with switching of image signals. However, the delay of the dimming process and the expansion process for the image signal is caused by, for example, when the display image is switched from a dark scene to a bright scene, overexposure (gradation collapse on the high gradation side) occurs in the display image. Become.

 In order to avoid such overexposure, a method has been proposed in which the expansion process is performed so that the maximum gradation of the input image signal does not exceed the maximum gradation that can be displayed by the expansion process. Certainly, it is possible to avoid overexposure according to such decompression processing, but since the dimming processing is still a conventional processing method, the brightness of the display image is improved by performing the above-described decompression processing. There has been a problem of lowering.

   The present invention has been made in view of the above problems, and an object thereof is to suppress overexposure without reducing the brightness of a display image.

In order to solve the above-described problems, the present invention provides an image display apparatus that adjusts a display image by a dimming process of illumination light and a gradation value expansion process of an image signal, as a solution for the image display apparatus. , Image parameter extracting means for extracting image parameters characterizing the brightness of the display image from the image signal at predetermined time intervals, and the dimming processing based on the image parameters extracted by the image parameter extracting means. A dimming control parameter for determining the dimming control parameter and controlling the dimming process based on the dimming control parameter, and the expansion process based on the image parameter extracted by the image parameter extracting unit. A decompression processing unit that determines the decompression control parameter and performs the decompression process based on the decompression control parameter, and The parameter extracting means adopts means for determining the image parameter so that the number of pixels that the gradation value of the image signal exceeds the maximum gradation value that can be output after the decompression processing is equal to or less than a predetermined number. .
According to the present invention, the image parameter is determined so that the number of pixels in which the gradation value of the image signal exceeds the maximum gradation value that can be output after the decompression process is equal to or less than a predetermined number, and based on the image parameter. Since the expansion process and the light control process are performed, the light control process suitable for the expansion process can be performed. As a result, it is possible to suppress overexposure without reducing the brightness of the display image.

In the present invention, it is preferable that the predetermined number is 1% or less of the total number of pixels.
This numerical value is a value obtained from a result of the inventor of the present application assuming every image, displaying each image while adjusting the image parameter, and investigating the impression of the entire image. Therefore, according to the present invention, it is possible to suppress overexposure without reducing the brightness of the display image by the expansion process and the dimming process suitable particularly when the image is a still image.

According to the present invention, as a means for solving the image display device, an image display device that adjusts a display image by a dimming process of illumination light and a gradation value expansion process of an image signal, the brightness of the display image being adjusted. Image parameter extracting means for extracting image parameters that characterize the image signal from the image signal at predetermined time intervals, and dimming control parameters related to the dimming processing based on the image parameters extracted by the image parameter extracting means A dimming control means for controlling the dimming process based on the dimming control parameter, and a stretching control parameter for the stretching process based on the image parameter extracted by the image parameter extracting means. And an expansion processing means for performing the expansion processing based on the expansion control parameter, and the image parameter extraction means Wherein the predetermined tone value of the image signal to determine the image parameters so as not to exceed the maximum tone value that can be output after decompression processing, employing the means of.
According to the present invention, it is possible to suppress overexposure without reducing the brightness of the display image by the expansion process and the dimming process suitable particularly when the image is a moving image.

In the present invention, it is preferable that the image parameter extracting means determines, as an image parameter, a result obtained by multiplying a predetermined gradation value of the image signal by a first constant and adding a second constant.
According to the present invention, it is particularly suitable when the image is a moving image, and by arbitrarily setting the first constant and the second constant, it is desired to suppress overexposure without reducing the brightness of the display image. It is possible to perform image display.

In the present invention, it is preferable that the first constant and the second constant are set so as not to exceed a maximum gradation value that the image parameter can output.
According to the present invention, it is possible to suppress overexposure without reducing the brightness of the display image by the expansion process and the dimming process suitable particularly when the image is a moving image.

In the present invention, it is preferable that the predetermined gradation value of the image signal is a maximum gradation value of the image signal.
According to the present invention, it is possible to perform an extremely high-sensitivity expansion process with respect to the brightness fluctuation of the image signal, which is effective when it is desired to faithfully display a slight brightness fluctuation.

In the present invention, the predetermined gradation value of the image signal is a gradation value that is a constant ratio with respect to the appearance frequency from the maximum gradation value detected by the histogram relating to the gradation value included in the image signal. Is preferred.
According to the present invention, it is possible to perform expansion processing with reduced sensitivity to the brightness fluctuation of the image signal, and it is effective when the image is inconvenient to follow the slight brightness fluctuation.

Moreover, in this invention, it is preferable that the said fixed ratio is 1% or less.
This numerical value is a value obtained from a result of the inventor of the present application assuming every image, displaying each image while adjusting the image parameter, and investigating the impression of the entire image. According to the present invention, it is possible to suppress overexposure without reducing the brightness without impairing the impression of the display image.

On the other hand, the present invention provides an image display method for adjusting a display image by a dimming process of illumination light and a gradation value expansion process of an image signal, as a solving means related to the image display method, wherein the brightness of the display image is adjusted. A first step of extracting image parameters that characterize the image from the image signal at predetermined time intervals, and determining a dimming control parameter related to the dimming process based on the image parameter extracted in the first step A second step of controlling the dimming process based on the dimming control parameter; and determining a decompression control parameter related to the decompression process based on the image parameter extracted in the first step; A third step of performing the expansion process based on a control parameter. In the first step, the gradation value of the image signal is output after the expansion process. Possible number of pixels that exceeds the maximum tone value to determine the image parameters to a predetermined number or less, to adopt a means of.
According to the present invention, the image parameter is determined so that the number of pixels in which the gradation value of the image signal exceeds the maximum gradation value that can be output after the decompression process is equal to or less than a predetermined number, and based on the image parameter. Since the expansion process and the light control process are performed, the light control process suitable for the expansion process can be performed. As a result, it is possible to suppress overexposure without reducing the brightness of the display image.

Furthermore, in the present invention, as a means for solving the image display method, an image display method for adjusting a display image by dimming processing of illumination light and expansion processing of a gradation value of an image signal,
A first step of extracting image parameters characterizing the brightness of the display image from the image signal at predetermined time intervals, and a dimming process related to the dimming process based on the image parameters extracted in the first step. A second step of determining a light control parameter and controlling the dimming process based on the dimming control parameter; and an expansion control parameter related to the expansion process based on the image parameter extracted in the first step. Decide
A third step of performing the decompression process based on the decompression control parameter,
The step employs means for determining the image parameter so that a predetermined gradation value of the image signal does not exceed a maximum gradation value that can be output after the decompression process.
According to the present invention, it is possible to suppress overexposure without reducing the brightness of the display image by the expansion process and the dimming process suitable particularly when the image is a moving image.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As an example of an image display apparatus using the image display method of the present invention, a description will be given using a three-plate type liquid crystal projector provided with a liquid crystal light valve for each color of RGB.
FIG. 1 is a schematic configuration diagram illustrating an example of a liquid crystal projector. As shown in FIG. 1, the liquid crystal projector 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, a liquid crystal light valve for red light 522, a green color. The liquid crystal light valve 523 for light, the liquid crystal light valve 524 for blue light, the cross dichroic prism 525, and the projection lens system 526 are comprised.

   The light source 510 includes a lamp 511 such as an extra-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 light control element 26 is comprised by the liquid crystal panel which made the transmittance | permeability variable, for example.

 The dichroic mirror 513 transmits red light of white light incident from the light source 510 to the reflection mirror 517 and reflects blue light and green light to the dichroic mirror 514. The reflection mirror 517 reflects the red light incident from the dichroic mirror 513 to the liquid crystal light valve 522 for red light.

   On the other hand, the dichroic mirror 514 reflects green light to the liquid crystal light valve 523 for green light out of the blue light and green light incident from the dichroic mirror 513 and transmits the blue light to the relay lens 518. The blue light is incident on the blue light liquid crystal light valve 524 via 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.

   The liquid crystal light valve for red light 522, the liquid crystal light valve for green light 523, and the liquid crystal light valve for blue light 524 modulate the three color lights (red light, green light, blue light) incident on each, and cross dichroic prisms. The light is emitted to 525. The cross dichroic prism 525 has four right-angle prisms 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 onto the screen 527 by the projection lens system 526 which is a projection optical system, and the image is enlarged and displayed.

   FIG. 2 is a block diagram showing the configuration of the drive circuit of the present liquid crystal projector configured as described above. As shown in this figure, the driving circuit of the liquid crystal projector includes an A / D converter 1, an image parameter extraction unit 2, an expansion processing unit 3, a D / A converter 4, a light valve driver 5, a liquid crystal light valve 522 for red light, The liquid crystal light valve 523 for green light, the liquid crystal light valve 524 for blue light, the dimming control unit 6, the dimming element driver 7, and the dimming element 26 are configured.

 The A / D converter 1 performs A / D conversion on an image signal (analog signal) supplied from an external image supply device, and outputs it to the image parameter extraction unit 2 as a digital image signal. The image signal which is an analog signal has the magnitude of the voltage value as the brightness information of the image, but has the gradation value corresponding to the voltage value as the brightness information by being converted into the digital image signal. become. The image supply device is, for example, a DVD (Digital Versatile Disk) player or a PC (Personal Computer), and reproduces an image stored in a recording medium such as a DVD, and a synchronization signal together with an image signal indicating the image. (Not shown) is output to the liquid crystal projector.

  The image parameter extraction unit 2 extracts an image parameter (gradation value) characterizing the brightness of the display image from the digital image signal input from the A / D converter 1 by a predetermined extraction process, and the image parameter and digital The image signal is output to the expansion processing unit 3 and the image parameter is output to the dimming control unit 6. The image parameter extraction process of the image parameter extraction unit 2 will be described in detail later.

 The decompression processing unit 3 determines the decompression control parameter based on the image parameter, performs the decompression process of the gradation value constituting the digital image signal based on the decompression control parameter, and converts the digital image signal after the decompression process to D / A output to the converter 4. A method for determining such an extension control parameter will be described later.

 The D / A converter 4 D / A converts the digital image signal input from the decompression processing unit 3 and outputs it to the light valve driver 5 as an analog image signal. The light valve driver 5 drives to drive the red light liquid crystal light valve 522, the green light liquid crystal light valve 523, and the blue light liquid crystal light valve 524 based on the analog image signal input from the D / A converter 4. A signal is generated and output to each liquid crystal light valve. As described with reference to FIG. 1, the liquid crystal light valve for red light 522, the liquid crystal light valve for green light 523, and the liquid crystal light valve for blue light 524 are driven by the drive signal and are incident on the three color lights (red Light, green light, blue light).

 The dimming control unit 6 stores in advance a LUT (Look Up Table) indicating the correspondence between the image parameter input from the image parameter extraction unit 2 and the dimming control parameter, and the dimming control is performed based on the LUT. The parameter is determined, and the dimming control parameter is output to the dimming element driver 7. A method for determining the LUT and the dimming control parameter will be described later.

 The dimming element driver 7 generates a driving signal for driving the dimming element 26 shown in FIG. 1 based on the dimming control parameter input from the dimming control unit 6, and adjusts the driving signal. Output to the optical element 26. The light control element 26 is driven based on the drive signal, thereby changing the amount of light emitted from the light source 510.

Next, the expansion processing operation and the light control processing operation of the liquid crystal projector configured as described above will be described.
First, an image signal input from an external image supply device is converted into a digital image signal by the A / D converter 1 and input to the image parameter extraction unit 2. As described above, this digital image signal has gradation values corresponding to RGB of each pixel, which is a structural unit of the image, as brightness information of the image. In the present embodiment, a liquid crystal projector that performs 256 gradation display from 0 (black) to 255 (white) gradation is assumed.

 The image parameter extraction unit 2 creates brightness information included in an arbitrary frame, that is, the appearance number distribution (histogram) of gradation values from the digital image signal. For example, assume that the histogram of gradation values contained in one frame is as shown in FIG. In this case, as shown in FIG. 3A, the maximum gradation value in the one frame is 150 gradations. The image parameter extraction unit 2 determines an image parameter based on the histogram.

 Here, for example, a case is assumed in which 150 gradations that are maximum gradation values are determined as image parameters. When the image parameter extraction unit 2 extracts and determines the 150 gradations as image parameters, the image parameter extraction unit 2 outputs the image parameters to the expansion processing unit 3 and the dimming control unit 6, and outputs a digital image signal to the expansion processing unit 3. . The expansion processing unit 3 determines expansion control parameters based on the image parameters. In other words, in order to make maximum use of the dynamic range, the expansion control parameter is determined as expansion coefficient G = maximum tone value that can be output / image parameter = 255/150 = 1.7. By determining the expansion control parameter (expansion coefficient G) in this way, as shown in FIG. 3B, the input gradation value (the gradation value included in the digital image signal) is multiplied by the expansion control parameter. Can be expanded linearly up to the maximum gradation value that can be output, and the dynamic range can be maximized. In FIG. 3B, the output gradation value is a gradation value after the input gradation value is expanded.

 On the other hand, the light control unit 6 determines the light control parameter based on the image parameter. As described above, when the maximum gradation value (150 gradations) in the input gradation value is expanded, the output gradation value becomes 255 gradations, so that the display image becomes bright. Therefore, the dimming control unit 6 determines a dimming control parameter for driving the dimming element 26 so as to decrease the amount of light emitted from the light source 510 as the brightness is increased by the expansion process. Specifically, assuming that the light amount at the maximum gradation value (255 gradations) that can be output is 100%, the dimmer 26 is driven so that the light amount is reduced to 150/255 = 58.8%. Determine light control parameters. That is, since the light control element 26 is constituted by a liquid crystal panel, the light control parameter is a drive voltage value for driving the liquid crystal panel so as to reduce the amount of light emitted from the light source 510 to 58.8%. As determined.

 The dimming control unit 6 stores in advance an LUT indicating the correspondence between the image parameter and the dimming control parameter (the driving voltage value of the dimming element 26) as shown in FIG. When the image parameter is input, the dimming control parameter is determined based on the LUT, and the dimming control parameter is output to the dimming element driver 7. The dimming element driver 7 generates the drive voltage indicated by the dimming control parameter to drive the dimming element 26. As a result, the light amount emitted from the light source 510 is reduced to 58.8%. By such dimming processing, the amount of light emitted from the light source 510 is dimmed according to the image signal, thereby obtaining light with brightness according to the display image even when the light output intensity of the light source 510 remains constant. Can contribute to the expansion of the dynamic range of the liquid crystal projector.

 However, in the expansion processing as described above, when a digital image signal represented by a histogram as shown in FIG. 5A, for example, is input during image switching, a predetermined time is set to suppress flickering of the display image. Since the expansion processing unit 3 does not determine a new expansion control parameter at the moment when the image is switched for the purpose of performing the expansion process gradually with a constant, as shown in FIG. All the gradation values become 255 gradations after the expansion processing. Such a phenomenon is overexposure (gradation collapse on the high gradation side).

 In order to prevent such overexposure, for example, a predetermined constant C (C <1) is set in the expansion control parameter (expansion coefficient G) so that the gradation value after expansion processing does not exceed the maximum output gradation value. ). By determining the expansion control parameter in this way, it is possible to suppress overexposure as shown in FIG.

 However, in the expansion process as described above, it is possible to suppress overexposure. However, since the dimming control unit 6 still determines the dimming control parameter based on the image parameter of 150 gradations, the expansion process is performed. There is a problem in that a mismatch in the amount of light reduction with respect to processing occurs and the brightness of the display image decreases.

Therefore, in the present embodiment, in order to solve the above problem, the image parameter is determined by the following method.
(1) When the display image is a moving image First, the case where the display image is a moving image will be described. As described above, considering that it is necessary to perform expansion processing gradually with a predetermined time constant in order to suppress flickering of the display image, the gradation value after expansion processing does not exceed the maximum output gradation value. It is preferable. Therefore, assuming that the maximum gradation value among the gradation values included in any one frame in the digital image signal, that is, the input gradation value is max1, the image parameter max2 is determined based on the following conditional expression (1). In the following conditional expression (1), k is a first constant and j is a second constant.

 When the expansion control parameter, that is, the expansion coefficient G is calculated based on the image parameter max2 determined in this way, 1 ≦ G ≦ 255 / max2, and the maximum gradation value max1 among the input gradation values as shown in FIG. When = 150, the output gradation value does not exceed the maximum output gradation value, and overexposure can be suppressed. In addition, since the dimming control unit 6 determines the dimming control parameter based on the image parameter max2 as described above, a mismatch in the amount of light loss with respect to the expansion process does not occur, and a reduction in the brightness of the display image is prevented. Is possible.

As can be seen from the above conditional expression (1) and FIG. 6, when the first constant k or the second constant j is set large (that is, when the image parameter max2 is increased), the effect of the dimming process is reduced, but the high gradation The effect of suppressing overexposure on the side is enhanced, and overexposure can be suppressed even in an image having a sharp brightness fluctuation. Thus, when the image parameter max2 is determined to be a large value, it is suitable for a display mode in which image detail, that is, gradation display is emphasized.
On the other hand, if the first constant k or the second constant j is set small (that is, if the image parameter max2 is reduced), the risk of overexposure on the high gradation side increases, but the effect of the light control processing increases, Suitable for display modes where brightness and contrast are more important than detail.

 Note that, as a method of extracting the maximum gradation value max1 from the input gradation value of the digital image signal, the maximum gradation value max1 may be obtained from the histogram as described above, or simply by performing a maximum value search process of the input gradation value. You may ask.

 By the way, when the maximum gradation value max1 is extracted from the input gradation value of the digital image signal and the image parameter max2 is determined using the maximum gradation value max1 as described above, for example, a small number of bright pixels are obtained from a dark image. When the image is switched to an image that has been increased, the expansion and dimming processing is performed according to the gradation values of the few bright pixels, despite the fact that the overall image has a dark display. Therefore, there is a problem that the brightness of the entire image that is actually displayed increases, and a desired image cannot be displayed. That is, it reacts sensitively to slight brightness fluctuations in the image. This method is effective when it is desired to faithfully display slight brightness fluctuations.

In order to solve such a problem, the following method may be used. A histogram of input gradation values in an arbitrary frame of the digital image signal is created, and a gradation value that is a fixed ratio with respect to the number of appearances from the maximum gradation value max1 as shown in FIG.
The image parameter max2 is determined based on the following conditional expression (2). The certain ratio is preferably within 1% of the total number of appearances. In this way, by determining the image parameter max2, it is possible to perform appropriate expansion processing and light control processing with respect to image brightness fluctuations, and overexposure and brightness of the display image without impairing the overall image impression. It is possible to prevent a decrease in height.

(2) When Display Image is Still Image Next, the case where the display image is a still image will be described. When displaying a still image, if the number of pixels that the output gradation value after expansion processing exceeds the maximum output gradation value (exposes overexposure) is within the specified amount, the overall image will feel uncomfortable. It does not. This prescribed amount is preferably within 1% of the total number of pixels. This numerical value is a value obtained from a result of the inventor of the present application assuming every image, displaying each image while adjusting the image parameter, and investigating the impression of the entire image.

  Specifically, when the input gradation value is i, the expansion coefficient G may be determined so that the number of pixels satisfying G · i> 255 is within 1% of the total number of pixels. Therefore, a histogram of input gradation values in an arbitrary frame of the digital image signal is created, and gradation values that become a fixed ratio (within 1%) with respect to the number of appearances from the maximum gradation value max1 as shown in FIG. When determined as the image parameter his2, the expansion coefficient G ≦ 255 / his2, and the number of pixels exceeding the maximum gradation value that can be output after the expansion processing can be within 1% of the total number of pixels. As described above, in the case of a still image, by determining his2 as an image parameter, the dimming process suitable for the expansion process is performed while suppressing the discomfort of the entire image due to overexposure to the extent that the user does not care. It is possible to display an image using the maximum dynamic range.

  As described above, according to the present embodiment, by determining the image parameter itself according to the image signal, the image display can be performed in conjunction with the expansion process and the light control process, and as a result, the overexposure is performed. It is possible to prevent a decrease in brightness of the display image while suppressing the occurrence.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above embodiment, the first constant k and the second constant j for determining the image parameter max2 may be set in the image parameter extraction unit 2 in advance, or provided in the present liquid crystal projector. The operation panel or the like may be adjusted to a desired value by operating the user.

(2) In the above embodiment, the maximum gradation value m is used to determine the image parameter max2.
Although ax1 is multiplied by the first constant k and the second constant j is added, this is not restrictive, and the maximum gradation value m
The second constant j may be subtracted from the result of multiplying ax1 by the first constant k. Further, only the result of multiplying the maximum gradation value max1 by the first constant k without using the second constant j may be determined as the image parameter max2, or the maximum gradation value max1 without using the first constant k. Only the result of adding or subtracting the second constant j may be determined as the image parameter max2.

(3) In the above embodiment, a histogram of input gradation values in an arbitrary frame of a digital image signal is created, and gradation values that are a fixed ratio (within 1%) with respect to the number of appearances from the maximum gradation value max1 are set. Although it is set as his1 (in the case of a moving image) or his2 (in the case of a still image), the present invention is not limited thereto, and an average value of the number of appearances may be obtained and a gradation value corresponding to the average value may be set as his1 or his2. good.

(4) In the above embodiment, in the case of a still image, if the number of pixels within which the output gradation value after decompression processing exceeds the maximum outputable gradation value (which causes overexposure) is within a specified amount The image parameters are determined so that the number of pixels exceeding the maximum outputable gradation value is within the specified amount, assuming that the impression of the entire image does not cause a sense of incongruity. Similarly to the case, the image parameter may be determined so that the output gradation value after the decompression process does not exceed the maximum output gradation value. In the case of a moving image, as in the case of a still image, image parameters are determined so that the number of pixels within which the output gradation value after decompression processing exceeds the maximum output gradation value is within the specified amount. May be. The above embodiment is a good example for moving images and still images, and can be appropriately changed depending on the type of image.

(5) In the above embodiment, the liquid crystal panel is used as the light control element 26. However, the present invention is not limited to this. For example, a mechanical shutter or the like may be used. Further, the technical scope of the present invention is not limited to such a light control means. For example, for a projector using a light control means that directly changes the output intensity of a light source such as a high-pressure mercury lamp or LED (light emitting diode). The present invention can also be applied.

(6) In the above embodiment, a liquid crystal projector using a transmissive liquid crystal device as the light modulation means is exemplified. However, the technical scope of the present invention is not limited to such a transmission type. For example, the present invention is applied to a reflection type projector such as LCOS or a projector using a mirror type spatial light modulator based on the MEMS technology. The invention can also be applied.

1 is a schematic configuration diagram of a liquid crystal projector according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of a drive circuit of a liquid crystal projector in one embodiment of the present invention. It is the 1st explanatory view about the histogram of the gradation value contained in the digital image signal in one embodiment of the present invention. It is explanatory drawing of LUT memorize | stored in the light control part 6 in one Embodiment of this invention. It is the 2nd explanatory view about the histogram of the gradation value contained in the digital image signal in one embodiment of the present invention. It is the 1st explanatory view showing the decompression processing method in one embodiment of the present invention. It is the 2nd explanatory view showing the decompression processing method in one embodiment of the present invention.

Explanation of symbols

 DESCRIPTION OF SYMBOLS 1 ... A / D converter, 2 ... Image parameter extraction part, 3 ... Decompression processing part, 4 ... D / A converter, 5 ... Light valve driver, 6 ... Dimming control part, 7 ... Dimming element driver, 26 ... Dimming Optical element 510... Light source 511. Lamp 512 Reflector 513 514 Dichroic mirror 515 516 517 Reflecting mirror 518 519 520 Relay lens 522 Red light liquid crystal light valve 523 ... Liquid crystal light valve for green light, 524 ... Liquid crystal light valve for blue light, 525 ... Cross dichroic prism, 526 ... Projection lens system

Claims (10)

An image display device that adjusts a display image by dimming processing of illumination light and expansion processing of gradation values of an image signal,
Image parameter extracting means for extracting image parameters characterizing the brightness of the display image from the image signal at predetermined time intervals;
A dimming control unit for determining a dimming control parameter related to the dimming process based on the image parameter extracted by the image parameter extracting unit, and for controlling the dimming process based on the dimming control parameter;
Expansion processing means for determining expansion control parameters related to the expansion processing based on the image parameters extracted by the image parameter extraction means, and performing the expansion processing based on the expansion control parameters,
The image parameter extraction means determines the image parameter so that the number of pixels such that the gradation value of the image signal exceeds the maximum gradation value that can be output after the expansion processing is equal to or less than a predetermined number. An image display device. The image display apparatus according to claim 1, wherein the predetermined number is 1% or less of the total number of pixels. An image display device that adjusts a display image by dimming processing of illumination light and expansion processing of gradation values of an image signal,
Image parameter extracting means for extracting image parameters characterizing the brightness of the display image from the image signal at predetermined time intervals;
A dimming control unit for determining a dimming control parameter related to the dimming process based on the image parameter extracted by the image parameter extracting unit, and for controlling the dimming process based on the dimming control parameter;
Expansion processing means for determining expansion control parameters related to the expansion processing based on the image parameters extracted by the image parameter extraction means, and performing the expansion processing based on the expansion control parameters,
The image display device is characterized in that the image parameter extracting means determines the image parameter so that a predetermined gradation value of the image signal does not exceed a maximum gradation value that can be output after the decompression process. 4. The image display device according to claim 3, wherein the image parameter extracting means determines, as an image parameter, a result obtained by multiplying a predetermined gradation value of the image signal by a first constant and then adding a second constant. 5. The image display apparatus according to claim 4, wherein the first constant and the second constant are set so that the image parameter does not exceed a maximum gradation value that can be output. 6. The image display device according to claim 3, wherein the predetermined gradation value of the image signal is a maximum gradation value of the image signal.   The predetermined gradation value of the image signal is a gradation value that is a constant ratio with respect to appearance frequency from a maximum gradation value detected by a histogram relating to a gradation value included in the image signal. The image display apparatus in any one of 3-5.   The image display device according to claim 7, wherein the certain ratio is 1% or less. An image display method for adjusting a display image by dimming processing of illumination light and expansion processing of gradation values of an image signal,
A first step of extracting image parameters characterizing the brightness of the display image from the image signal at predetermined time intervals;
A second step of determining a dimming control parameter related to the dimming process based on the image parameter extracted in the first step, and controlling the dimming process based on the dimming control parameter;
A third step of determining a decompression control parameter related to the decompression process based on the image parameter extracted in the first step, and performing the decompression process based on the decompression control parameter;
In the first step, the image parameter is determined such that the number of pixels such that a gradation value of the image signal exceeds a maximum gradation value that can be output after the decompression process is equal to or less than a predetermined number. Image display method. An image display method for adjusting a display image by dimming processing of illumination light and expansion processing of gradation values of an image signal,
A first step of extracting image parameters characterizing the brightness of the display image from the image signal at predetermined time intervals;
A second step of determining a dimming control parameter related to the dimming process based on the image parameter extracted in the first step, and controlling the dimming process based on the dimming control parameter;
A third step of determining a decompression control parameter related to the decompression process based on the image parameter extracted in the first step, and performing the decompression process based on the decompression control parameter;
In the first step, the image parameter is determined so that a predetermined gradation value of the image signal does not exceed a maximum gradation value that can be output after the decompression process.

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