JPH11155116A - Projection image display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a still image display performance of characters, graphics, etc. in a projection type image display device using an optical writing type liquid crystal light valve, etc. by improving not only high brightness and high resolution but also sharpness. It is an object of the present invention to provide a projection type image display device capable of greatly improving the image quality. SOLUTION: A light emission characteristic near black is controlled in accordance with image information of image light written to a spatial light modulation element 101,
Performs image display suitable for the input video source. By controlling the light emission characteristics according to the various signal sources as described above, optimal display performance (luminance, gradation, sharpness) can be obtained when displaying an image such as a moving image and displaying a computer such as characters and figures. realizable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type image display device using a light modulation element such as a light-writing type liquid crystal light valve.

[0002]

2. Description of the Related Art Conventionally, since it is difficult to increase the size of a direct-view display, a projection type image display using a liquid crystal display such as a CRT or a liquid crystal panel driven by a thin film transistor has been proposed. It is difficult to achieve both high resolution and high resolution.

Therefore, a projection type image display apparatus using a light-writing type spatial light modulation element in which a photoconductive layer and a light modulation layer are combined is disclosed in JP-A-4-338924. .

FIG. 22 is a cross-sectional view of a conventional spatial light modulator. A spatial light modulator 101 has a glass substrate 10 having conductive transparent electrodes 103 and 103 'formed on the inner surface.
In this structure, a photoconductive layer 104, a light reflecting layer 105, and a light modulating layer 106, which are sequentially laminated, are sandwiched between the light emitting layers 2 and 102 '. The photoconductive layer 1 below the gap between the adjacent light reflecting layers 105
04 is etched, and the etched portion is filled with the light absorbing layer 107.

In the conventional spatial light modulator 101, when writing light is input to the photoconductive layer 104 from the glass substrate 102 side, the light modulating layer 10 according to the two-dimensional light intensity distribution.
6 changes, and the light modulation layer 106 switches. As a result, the read light input from the glass substrate 102 'side is modulated, reflected by the light reflection layer 105, and output from the glass substrate 102' side. The light absorbing layer 107 is for preventing the strong reading light from being input to the photoconductive layer 104 from the gap of the light reflecting layer 105 when input from the glass substrate 102 ′.

FIG. 23 is a system configuration diagram of a conventional projection type image display device using the spatial light modulator shown in FIG. 22. As the image source 108, a CRT, a TFT-LC
D or the like, and this output image light is used as a writing light 109 via a writing lens 110.
An image is formed on one photoconductive layer 104 to input an image. The reading light 112 from the light source 111 is
1 from the side of the glass substrate 102 ′
6, the light is reflected by the light reflection layer 105, passes through the light modulation layer 106 again, passes through the visualization unit 114 as output light 113, and is visualized, and the projection lens 1
15 enlarges and projects the image on a screen 116.

The photoconductive layer 1 of the spatial light modulator 101
Reference numeral 04 denotes amorphous silicon having a pin structure, a light modulation layer 106 includes a liquid crystal material such as a nematic liquid crystal and a ferroelectric liquid crystal, a visualization unit 114 includes a polarization beam splitter, and a light source 111 includes a metal halide lamp. , Xenon lamps and the like are used.

In such a projection type image display device, by increasing the brightness of the light source 111 and the resolution of the image source 108 which is an image input means to the spatial light modulator 101, high brightness and high resolution are achieved. Image display can be performed.

Next, a driving method of the conventional spatial light modulator 101 will be described. FIG. 24 is a general drive voltage waveform diagram of the spatial light modulator. The driving voltage includes an erasing period and a writing period, and is applied to the entire surface of the spatial light modulator 101 in synchronization with the vertical synchronization signal of the input video signal. The spatial light modulator 101 modulates the read light according to the light intensity input during the writing period and outputs the light. In the erasing period, initialization is forcibly performed regardless of the presence or absence of writing light, and the output becomes zero.

[0010]

However, in the configuration of the above-mentioned conventional projection type image display device, improvement in sharpness as well as brightness and resolution has been required.

In view of the above problems, the present invention provides a projection type image display device using a spatial light modulation element such as a light-writing type liquid crystal light valve, which has improved brightness and resolution, and improved sharpness. It is an object of the present invention to provide a projection type image display device using a spatial light modulation element such as a light-writing type liquid crystal light valve which can greatly improve the performance of displaying still images such as images and figures.

[0012]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention controls a light emission characteristic near black in accordance with image information of image light written to a spatial light modulator, and is suitable for an input video source. It is provided with performing image display.

According to the present invention, the resolution is controlled by controlling the spatial frequency of the image light according to the image information of the image light written in the spatial light modulator, and the sharpness is improved according to the input video source. It is provided with the following.

Further, the present invention is to control the drive waveform applied to the spatial light modulator to reduce various temporal changes of the spatial light modulator and to speed up the recovery time.

Further, the present invention is characterized in that the black level of the image light read from the spatial light modulator is detected and the black level of the written image light is controlled to stabilize the black level. It is.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a spatial light modulator, an image source for generating image light as writing light to the spatial light modulator, and an image of the image light. A projection type image display device comprising a light emission characteristic control unit for controlling light emission characteristics by controlling image light in the vicinity of black according to information, wherein the light emission characteristic control unit controls image light to emit light. By controlling the characteristics, there is an effect that an image suitable for an input video source is displayed.

According to a second aspect of the present invention, the light emission characteristic control unit sets the gamma characteristic determined by the image light and the spatial light modulator so as to have a linear characteristic for a moving image and a saturation characteristic for a still image. 2. The projection type image display device according to claim 1, wherein a gamma characteristic is set to a linear characteristic for a moving image and a saturation characteristic is set for a still image, thereby displaying an image suitable for an input video source. Having.

According to a third aspect of the present invention, the light emission characteristic control unit sets the black level to a high fidelity black level and a high temporal aperture ratio for a moving image, and a black compression black for a still image such as a character or a figure. 2. The projection type image display device according to claim 1, wherein the projection image display device is set to have a low time aperture ratio for a moving image and a low time aperture ratio for a still image. Has an effect of performing image display suitable for the input video source.

According to a fourth aspect of the present invention, the light emission characteristic control section controls the light emission characteristic of the image light near black so that the contrast on the screen is constant even when the time aperture ratio is changed. 2. The projection type image display device according to claim 1, wherein the contrast on the screen is kept constant even when the temporal aperture ratio is changed by controlling the light emission characteristics of the image light. Has an action.

According to a fifth aspect of the present invention, there is provided a spatial light modulator, an image source for generating image light which is writing light to the spatial light modulator, and a light source for image light according to image information of the image light. A projection type image display device comprising a spatial frequency characteristic control unit for controlling a spatial frequency to control a resolution characteristic, wherein the spatial frequency characteristic control unit controls a spatial frequency of image light according to image information. By controlling the resolution characteristics in this way, it has the effect of improving the sharpness suitable for the input video source.

According to a sixth aspect of the present invention, the spatial frequency characteristic control unit sets the spatial frequency characteristic to a wide band for a moving image,
6. The projection type image display device according to claim 5, wherein a spatial frequency characteristic is set to a narrow band for a still image, and the spatial frequency characteristic is set according to a moving image or a still image to be suitable for an input video source. And has the effect of improving sharpness.

According to a seventh aspect of the present invention, there is provided a spatial light modulator, an image source for generating image light which is writing light to the spatial light modulator, and a driving waveform applied to the spatial light modulator. What is claimed is: 1. A projection type image display device comprising: a driving waveform control section for controlling a driving waveform applied to a spatial light modulation element; and a driving waveform applied to the spatial light modulation element by the driving waveform control section. Has the effect of reducing the change over time of the spatial light modulator and hastening the recovery time.

According to an eighth aspect of the present invention, in the normal operation, the drive waveform control section generates a drive voltage having an erase period and a write period in synchronization with the vertical scanning frequency of the image light, and in a special operation. The projection type image display device according to claim 7, wherein a frequency and a drive voltage are controlled.
By controlling the frequency and the drive voltage by the drive waveform control unit, the spatial light modulator has the effect of reducing the change over time and hastening the recovery time.

According to a ninth aspect of the present invention, there is provided a spatial light modulator, an image source for generating image light which is writing light to the spatial light modulator, and a driving waveform applied to the spatial light modulator. A driving waveform generating unit that generates the image light; a reading unit that reads image light written to the spatial light modulator; and a black level that detects a black level of the read image light and controls a black level of the image source. A projection type image display device characterized by comprising a control means, wherein the black level of the image light read from the spatial light modulator is detected to control the black level of the written image light, and the black level By stabilizing, there is an effect that stable image display can be realized.

According to a tenth aspect of the present invention, the black level control means comprises a feedback control loop for detecting the reference light superimposed on the written image light and controlling the level of the image light. A projection-type image display device according to claim 9, wherein a stable image display can be realized by stabilizing a black level.

According to an eleventh aspect of the present invention, the black level control means detects the image signal written from the image source by superimposing the reference signal on the video signal and the reference signal of the read image light. 10. The projection-type image display device according to claim 9, comprising a feedback control loop for controlling a black level, wherein the stabilization of the black level achieves a stable image display. Have.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 is a system configuration diagram of a projection type image display device according to Embodiment 1 of the present invention. To explain with the same reference numerals, the image source 108
The image light from the camera is formed as a writing light 109 through a writing lens 110 onto the photoconductive layer of the spatial light modulator 101 to input an image. Read light 1 from light source 111
12 is a spatial light modulator 10 via the visualization means 114
1, after being modulated by the light modulating layer and reflected by the light reflecting layer, it passes through the light modulating layer again, and the output light 11
As 3, the light is visualized by passing through the visualization means 114, and is enlarged and projected on the screen by the projection lens 115. The configuration up to this point is the same as FIG. 23 showing a system configuration diagram of a conventional projection type image display device, but FIG. 1 showing a system configuration diagram of the projection type image display device in the first embodiment is different from FIG. However, between the input signal end and the image source 108, a light emission characteristic control unit 1 for controlling the light emission characteristics of the image source 108 composed of a cathode ray tube (hereinafter abbreviated as CRT) according to the input signal, that is, image information. And the point where the drive waveform generator 2 for driving the spatial light modulator 101 according to the input signal is inserted between the input signal end and the spatial light modulator 101.

The operation of the projection type image display apparatus according to the first embodiment configured as described above will be described below with reference to the light emission characteristic diagram of FIG. 2 showing the relationship between the input signal level and the illuminance on the screen. I do.

First, the display performance required when displaying a still image such as a character or graphic on a computer is different from the display performance required when displaying a video such as a moving image. Therefore, the light emission characteristic control unit 1 is controlled in accordance with the required performance. Then, an optimal light emission characteristic is selected to perform an optimal image display. At the time of displaying an image that requires gradation and color reproducibility, the light emission characteristic is a linear characteristic as shown by a broken line in the light emission characteristic diagram of FIG. At times,
The optimum image display is realized by setting the emission characteristics of the saturation characteristics shown by the solid line in FIG.

The display system of the projection type image display device shown in the system configuration diagram of FIG. 1 needs a concept of a time aperture ratio unlike a general direct-view type liquid crystal display or the like. This time aperture ratio will be described with reference to FIG.

When the light modulating layer in the spatial light modulating element 101 of the first embodiment is a ferroelectric liquid crystal, the liquid crystal is rotated at the same time as being written by light, and a white display is performed. Even if there is no more, it will be maintained until reset. This characteristic is generally called a memory effect of the ferroelectric liquid crystal. Due to this characteristic, the time aperture ratio is spatially different due to the difference between the reset and the write timing, and appears as uneven brightness. Further, the rotation angle and the rotation speed of the liquid crystal change depending on the intensity of the light intensity of the CRT, and the gradation can be expressed.

FIG. 3 is an explanatory diagram of the time aperture ratio, which describes the system of the gradation expression.
A reset pulse is applied once during the field period, the horizontal axis represents time, the vertical axis represents voltage, and 186 represents the image source 1
08 is the light emission characteristic of the CRT, the horizontal axis represents time, and the vertical axis represents the light emission intensity of the CRT, which decreases exponentially with time. Reference numerals 187 to 189 denote the light intensities of the output light 113 enlarged and projected on the screen by the projection lens 115. The light intensities of the CRT correspond to low, middle, and high, respectively, and the horizontal axis represents time, and the vertical axis represents time. The light intensity on the screen is shown.

FIG. 4A, FIG. 4B and FIG.
Of the time aperture ratio on the screen are shown at the top, that is, when written immediately after the reset pulse, at the middle, that is, when approximately half of one vertical period from when the reset pulse is written, and at the bottom, that is, FIG. 7 is a spatial distribution characteristic diagram of a gamma characteristic shown corresponding to a case where a reset is performed immediately after writing.

In FIG. 4A written in the upper part of the screen, 190 is a reset pulse, 191 is the light emission characteristic of the CRT, and the light emission intensity of the CRT decreases exponentially with time. Reference numeral 192 denotes the light intensity on the screen. Since the light is written by the light from the CRT immediately after the reset pulse, the light continues to be emitted for almost one field period. In this case, the time aperture ratio is approximately 10
0%. What is actually perceived by human eyes as brightness is not the peak value of light intensity, but the time average,
This is the area of the hatched portion in FIG. This area ratio can also be called a time aperture ratio.

In FIG. 4B written in the middle part of the screen, 193 is a reset pulse, 194 is the light emission characteristic of the CRT, 195 is the light intensity on the screen, 1
Written almost in the middle of the field. In this case, although the liquid crystal is written and white-displayed at the same time as in the case of FIG. 4A, the period until the reset pulse is about half as compared with the case of FIG. 4A. That is,
This means that the time aperture ratio decreases and darkens.

Next, in the state of FIG. 4C written at the lower part of the screen, a reset pulse is applied immediately after writing by the CRT. 196 is a reset pulse, 197 is the light emission characteristic of the CRT, and 198 is the light intensity on the screen. In such a case, even if the liquid crystal is reset, the state is written in the next field due to the persistence characteristics of the CRT, and the liquid crystal slightly rotates. Of course, since the intensity of the afterglow of the next field differs depending on the light intensity of the CRT, the light intensity on the screen changes.

As described above, gradation expression can be realized by changing the time aperture ratio. Next, the operation of the light emission characteristic control unit 1 in FIG. 1 will be described in detail. FIG. 5 is a circuit configuration diagram of the light emission characteristic control unit 1 for explaining the gamma correction operation, and FIGS. 6 and 7 are gamma characteristic diagrams.

In the circuit diagram of FIG. 5, 3 is a gamma input terminal, 4 is a gamma output terminal, 5 is a gamma input terminal 3, a base is a Vcc terminal via a resistor, and a collector is a ground via a resistor. 6 is a transistor having a base connected to the collector of the transistor 5, an emitter connected to the gamma output terminal 4, and a collector connected to the Vcc terminal. 7 is a series resistor connected between the control signal terminal 8 and the ground. A series circuit of a diode D1 and a resistor R1, a series circuit of a diode D2 and a resistor R2, a diode D3 and a resistor R are provided between the collector of the transistor 5, the base of the transistor 6, and the series resistor 7.
3 series circuits are inserted and connected in parallel.

In the circuit having the above configuration, when the signal level of the gamma input terminal 3 increases, the diodes D1 to D3 sequentially conduct, the load resistance of the transistor 5 is sequentially connected in parallel with the resistances R1 to R3, and the input level increases. The load resistance decreases accordingly. In this way, a polygonal line approximation of the gamma characteristic is performed. The control signal terminal 8 has 2
A control signal for performing dimensional gamma correction is input,
The light emission characteristics of each area are corrected. At this time, as shown in the gamma characteristic diagram of FIG. 7, the input / output characteristic of FIG. 5 for performing gamma correction is a characteristic before correction and a solid line after correction as shown in the gamma characteristic diagram of FIG. 7, thus dynamically controlling the gamma characteristic. As a result, the gamma characteristics on the screen are changed from the pre-correction light emission characteristics shown by the broken lines to the post-correction light emission characteristics shown by the solid line and one-dot dotted line as shown in the gamma characteristic diagram of FIG.

Therefore, the corrected light emission characteristics shown by the dashed line in FIG. 6 are the same as the light emission characteristics at the time of computer display of the solid characters and figures shown in FIG. 2, and the corrected light emission characteristics shown by the solid line in FIG. The light emission characteristics at the time of displaying the image indicated by the broken line in FIG. 2 are obtained, and the light emission characteristics can be easily controlled only by controlling the gamma correction.

Further, correction data corresponding to the two-dimensional spatial position is created by a digital method, and the gamma characteristic is dynamically changed by controlling the polygonal line set value of the polygonal line gamma correction circuit using the correction data. Needless to say, highly accurate gamma correction can be realized.

Next, the relationship between the gamma characteristic near black and the contrast will be described. FIG. 8 is a gamma characteristic diagram in which the light emission characteristics in the vicinity of black in FIG. 6 are enlarged. The solid line in FIG. 8 shows the light emission characteristics when displaying images, and the one-dotted dashed line in FIG. It is. As can be seen from FIG. 8, the gamma characteristic in the vicinity of black is such that the black signal is compressed when displayed on a computer. FIG. 9 is a contrast characteristic diagram when the two types of light emission characteristics shown in FIG. 8 are provided. The horizontal axis represents the time aperture ratio, and the vertical axis represents the contrast when a black window signal is projected on a white background. The contrast can be maintained up to a high temporal aperture ratio, and the sharpness of the character is improved. However, although the gradation near black is deteriorated, it is not so adversely affected during computer display.

As described above, at the time of displaying an image such as a moving image of a high-definition television or a current TV, faithful display performance such as contrast, resolution, gradation, and color reproducibility is required. Therefore, as shown by the solid line in FIG. 6, as a light emission characteristic capable of expressing faithful gradation and color reproducibility from white to black, the actual use state has a sharp contrast with sharpness when used at a high time aperture ratio. Expressing a video.

On the other hand, when displaying characters, figures, and the like on a computer, the sharpness of the characters over the entire screen is required. Therefore, as shown by the dashed line in FIG. 6, the light emission characteristics are set such that the image light on the CRT is set to the black level and the black is compressed to improve the average luminance. Is used to express images with greatly improved character sharpness.

Next, the principle of character sharpness deterioration when black characters are displayed on a white background when displayed on a computer will be described. FIG. 10 is a gamma characteristic diagram showing the input / output (gamma) characteristics of the spatial light modulator 101 for explaining the sharpness deterioration operation. The lower diagram shows the write system spot characteristics, and the left diagram shows the read system spot characteristics. Shown respectively. As shown by the dashed line, there is no deterioration in the read image when displaying a white character on a black background, but on the other hand, as the read image when displaying a black character on a white background shown by a solid line, the response is reduced, the character is thinned, and the sharpness is significantly deteriorated. Therefore, in the first embodiment, the driving is performed so that the image quality is optimal when displaying images and when displaying images on a computer.

As described above, according to the first embodiment,
By controlling the light emission characteristics in accordance with the image information of the image light written in the spatial light modulator, optimal display performance (brightness, gradation, sharpness) can be realized corresponding to various signal sources.

(Embodiment 2) FIG. 11 is a system configuration diagram of a projection type image display device according to Embodiment 2 of the present invention, and is a diagram showing a system configuration diagram of a projection type image display device according to Embodiment 1. The same reference numerals are given to the same portions as 1 and the description is omitted. 11 differs from FIG. 1 in that a spatial frequency characteristic for controlling a spatial frequency characteristic by controlling a video bandwidth applied to an image source 108 such as a CRT instead of the light emission characteristic control unit 1 in FIG. The point is that the control unit 9 is inserted.

The operation of the projection-type image display apparatus according to the second embodiment configured as described above will be described below with reference to the spatial frequency characteristic diagram of FIG.

In general, the required display performance differs between when displaying a character or a figure on a computer and when displaying an image such as a moving image. Therefore, the light emission characteristic control unit for an image source is controlled in accordance with the required performance to optimize the display. An optimal image display is performed by selecting light emission characteristics. At the time of displaying an image driven with a relatively low signal APL and a high time aperture ratio, high-resolution display is performed by setting a wide-band spatial frequency characteristic as shown by a solid line in FIG. Conversely, when the signal APL is relatively high (when displaying black characters on a white background), the narrow band spatial frequency characteristic is set as shown by the dashed line in FIG. Display is realized.

Next, in order to explain the control of the spatial frequency characteristic in detail, FIG. 13 which is a detailed block diagram of the spatial frequency characteristic control unit 9 in FIG. 11 and FIG. 14 (a) which is a spatial frequency characteristic diagram FIG. 14B, which is an operation waveform diagram,
(C) is used.

The video signal from the input terminal 10 is supplied to low-pass filters (hereinafter abbreviated as LPFs) 11 and 12, and two kinds of bandwidths are set as shown in FIG. The synchronization signal from the input terminal 13 is supplied to a signal discrimination circuit 14,
From the scanning frequency, it is determined whether the display is a video display (NTSC, HDTV) or a computer display. The discrimination signal from the signal discrimination circuit 14 is supplied to a switching circuit 15 for switching between signals from the LPF 11 and the LPF 12, and is switched based on the discrimination signal. The video signal from the switching circuit 15 is applied to the image source 108 through the video amplification circuit 16.
FIG. 14A shows the spatial frequency characteristics of each element of the projection type image display device. The solid line indicates the readout system, the one-dotted dashed line indicates the spatial light modulator, and the dashed line indicates the write system spatial frequency. As can be seen from FIG. 14A, when a CRT is used as the image source 108 as the optical writing means, the spatial frequency has a sharp drop characteristic due to the Gaussian distribution of the spot characteristic. Become. Therefore, one such as a computer
In the case of a signal in units of dots, as described in the gamma characteristic diagram of FIG. 10, when a black character signal is displayed on a white background, the sharpness of the character is remarkably deteriorated, so that the spatial frequency f1 shown in FIG. The corresponding character signal is apparently converted to the frequency axis corresponding to the spatial frequency f2 by limiting the band, and is converted to (c) in FIG. 14 to thereby reduce the amplitude reduction and character thinning of the character signal. ing.

Next, the gamma characteristic diagram of FIG. 15 will be used to describe in detail the effect of improving the sharpness at the time of displaying characters. FIG. 15 shows the input / output (gamma) characteristics of the spatial light modulator 101 in the same manner as FIG. 10, and the lower figure shows the write system spot characteristics and the left figure shows the read system spot characteristics. The dotted line in FIG. 15 shows the spot characteristics of the writing system and the reading system when the conventional band limitation is not performed. In this case, the response of the character signal is reduced, the character is thinned, and the sharpness is significantly deteriorated. Therefore, as shown by the solid line in FIG. 15, the band is limited and converted to a lower region on the spatial frequency axis, and the response is set to be higher and the character width is wider. Is driven so that the image quality can be improved and the optimum image quality at the time of computer display can be obtained.

As described above, according to the second embodiment, the spatial frequency of the image light is controlled according to the image information of the image light written to the spatial light modulator, and the resolution characteristic is controlled.
The sharpness can be improved according to the input video source.

(Embodiment 3) FIG. 16 is a system configuration diagram of a projection type image display device according to Embodiment 3 of the present invention, and is a diagram showing a system configuration diagram of a projection type image display device according to Embodiment 1. The same reference numerals are given to the same portions as 1 and the description is omitted. FIG. 16 differs from FIG. 1 in that a CRT driving unit 17 for driving an image source 108 such as a CRT is inserted instead of the emission characteristic control unit 1 in FIG. In addition, a driving waveform control unit 18 for driving the spatial light modulator 101 is inserted.

The operation of the projection-type image display apparatus according to the third embodiment having the above-described configuration will be described below with reference to the driving waveform diagram of FIG. 17 and the following Table 1 showing driving conditions.

[0056]

[Table 1]

In general, the spatial light modulation element 101 deteriorates image quality due to various temporal changes. Therefore, special driving conditions are provided in addition to the driving conditions during normal operation shown in Table 1.
The effect on image quality is reduced. By switching the driving conditions in this way, the temporal change of the spatial light modulation element 101 is reduced, and the recovery time is further shortened to stabilize the image quality. As shown in the drive waveform diagram of FIG. 17, the drive waveform has three parameters: pulse width, erase voltage, and write voltage. When the pulse width is wide, when the erasing voltage is high, and when the writing voltage is high, the brightness is dark.

In the special operation, the driving frequency is controlled in the higher direction (200 Hz), the writing voltage is controlled in the higher direction (0 V), the erasing voltage is controlled in the higher direction (15 V), and the pulse width is controlled in the wider direction. In particular, to suppress burn-in, black level, and fluctuations in efficiency.

Since the temporal change of the spatial light modulator 101 occurs due to the temperature characteristics of the liquid crystal, reset failure, light-shielding properties, etc., it is reduced by changing the parameters of each driving condition in accordance with the cause of the occurrence. . As a less noticeable control method, there is a method of sequentially changing the write voltage and the pulse width. The frequency has a problem in terms of brightness, and the erase voltage has a problem in terms of the reliability of the element. However, by sequentially controlling the four parameters, it is possible to efficiently reduce the change with time.

Further, in order to realize an efficient reduction of the change of the spatial light modulator 101 with time, the driving waveform controller 18
In addition to the above control, the CRT driving condition of the CRT driving unit 17 is also controlled by, for example, writing a white signal to the entire area, so that further improvement can be performed. Switching between the normal operation and the special operation is performed in a scene or a control method in which the change is not conspicuous.

As described above, according to the third embodiment, by controlling the driving waveform applied to the spatial light modulator 101,
Since various changes over time of the spatial light modulator 101 can be reduced and the recovery time can be shortened, stable image display can be realized.

(Embodiment 4) FIG. 18 is a system configuration diagram of a projection type image display device according to Embodiment 4 of the present invention, and is a system configuration diagram of a projection type image display device according to Embodiment 1. The same reference numerals are given to the same portions as 1 and the description is omitted. FIG. 18 differs from FIG. 1 in that the visualization unit 114 in FIG. 1 is provided with a detection unit 19 for detecting the black level light of the read image light, and instead of the light emission characteristic control unit 1 in FIG. The difference is that a cutoff control unit 20 for controlling a cutoff of a video signal applied to an image source 108 such as a CRT based on a detection signal from the detection unit 19 is provided.

The operation of the projection type image display apparatus of Embodiment 4 configured as described above will be described below with reference to the emission characteristic diagram of FIG.

In general, since the spatial light modulator is made of liquid crystal or the like, the light emission characteristics change depending on the temperature characteristics as shown in FIG. For this reason, the image light read from the spatial light modulator 101 and the black level light on the image forming surface are expanded and detected by the detection unit 19 composed of a photodiode or the like. The detection signal from the detection unit 19 is supplied to a cutoff control unit 20 that controls a DC potential of a drive voltage of an image source 108 such as a CRT to perform cutoff control. The cut-off control section 20 performs control based on the detection signals sequentially detected, and as shown in FIG.
01 is automatically compensated even when the light emission characteristic changes like a solid line or a wavy line, and stable image display can be performed.

Next, in order to explain this automatic cutoff control in detail, a block diagram of FIG. 20 showing the detection unit 19 and the cutoff control unit 20 in FIG. 18 in detail and FIG.
21 (a), (b) and (c), and FIG.
The characteristic diagram shown in FIG. The cutoff control may be performed by controlling the voltage applied to the image source 108 such as a CRT or the like and the driving voltage applied to the spatial light modulator 101.
The case where the signal applied to the image source 108 is controlled will be described.

In FIG. 20, the video signal is superimposed on the detection reference signal by the addition circuit 21 in the cut-off control section 20.
21 through the video amplification circuit 22 and the current detection circuit 23.
(A) is applied to the cathode electrode of an image source 108 such as a CRT. The cathode current detection signal of the detection reference signal of the current detection circuit 23 is supplied to the clamp circuit 25 through the switching circuit 24, and BLK is detected based on the control signal.
(Blanking of blanking) is clamped, and the cutoff control signal VG1 indicated by the broken line in FIG. 21B is applied to the grid electrode of the image source 108 such as a CRT. This feedback control loop is similar to a conventional auto cutoff system. Thereafter, when the emission characteristic of the spatial light modulator 101 shown in FIG. 19 changes from a solid line to a dashed line, the detection signal detected by the photodiode 26 changes from the dashed line shown in FIG. This detection signal is supplied to a peak detection circuit 27, the peak value of which is detected, and the normal VS1 to VS2
To increase. By supplying this information to the switching circuit 24 and performing feedback control, the cutoff control signal applied to the grid electrode becomes a solid line shown in FIG. 21B, and the light emission shown by a dashed line in FIG. The characteristics are compensated to become a solid line, and stable image display can be realized. As shown in the characteristic diagram of FIG. 21 (d), how the cutoff control voltage changes after the power is turned on.
8 is mainly caused by the spatial light modulation element 101 after that, and is operated by a conventional writing system (CRT cathode current detection) auto cut-off system for several minutes immediately after the power is turned on. , CRT
Readout system (image light detection) after image source 108 stabilizes
By switching to the auto cut-off system of
Efficient stabilization is attempted. With such a configuration, it is possible to compensate for the temporal change of both the image source 108 such as a CRT and the spatial light modulator 101.

As described above, according to the fourth embodiment, the black level of the image light read from the spatial light modulator 101 is detected, and the black level of the written image light is controlled. Thus, stable image display can be realized.

In the fourth embodiment, a projection type image display device using a light-writing type liquid crystal light valve or the like has been described for easy understanding. However, other projection type display devices are also effective. Needless to say, there is.

[0069]

As described above, according to the projection type image display apparatus of the present invention, the light emission characteristics near black are controlled in accordance with the image information of the image light written to the spatial light modulator, and various signals are obtained. Optimum display performance (luminance, gradation, sharpness) can be realized according to the source.

Further, by controlling the spatial frequency of the image light according to the image information of the image light written into the spatial light modulator to control the resolution characteristics, the optimum sharpness corresponding to various signal sources can be obtained. realizable.

Further, by controlling the drive waveform applied to the spatial light modulator, the various changes with time of the spatial light modulator can be reduced and the recovery time can be shortened, whereby a stable image display can be realized.

Further, by detecting the black level of the image light read from the spatial light modulator and controlling the black level of the written image light to stabilize the black level, a stable image display is realized. it can.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a projection-type image display device according to a first embodiment of the present invention.

FIG. 2 is a light emission characteristic diagram for describing a light emission characteristic control operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 3 is a time aperture ratio explanatory diagram for explaining the operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 4 is a spatial distribution characteristic diagram of a gamma characteristic for describing an operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of a light emission characteristic control unit for describing a gamma correction operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 6 is a gamma characteristic diagram for explaining the operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 7 is a gamma characteristic diagram for explaining the operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 8 is a gamma characteristic diagram showing an enlarged light emission characteristic in the vicinity of black for explaining the operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 9 is a contrast characteristic diagram for explaining an operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 10 is a gamma characteristic diagram showing input / output (gamma) characteristics of a spatial light modulator for describing the sharpness deterioration operation of the projection type image display device according to the first embodiment of the present invention.

FIG. 11 is a system configuration diagram of a projection-type image display device according to a second embodiment of the present invention.

FIG. 12 is a spatial frequency characteristic diagram for describing an operation of the projection type image display device according to the second embodiment of the present invention.

FIG. 13 is a detailed block diagram of a spatial frequency control unit for describing a control operation of a spatial frequency characteristic of the projection type image display device according to the second embodiment of the present invention.

14A is a spatial frequency characteristic diagram for explaining the operation of the projection-type image display device according to the second embodiment of the present invention. FIGS. 14B and 14C are the projection-type image display according to the second embodiment of the present invention. Operation waveform diagram for explaining the operation of the device

FIG. 15 is a gamma characteristic diagram showing input / output (gamma) characteristics of a spatial light modulator for describing an operation of the projection type image display device according to the second embodiment of the present invention.

FIG. 16 is a system configuration diagram of a projection-type image display device according to a third embodiment of the present invention.

FIG. 17 is a drive waveform diagram for describing a drive waveform control operation of the projection type image display device according to the third embodiment of the present invention.

FIG. 18 is a system configuration diagram of a projection-type image display device according to a fourth embodiment of the present invention.

FIG. 19 is a light emission characteristic diagram for explaining an operation of the projection type image display device according to the fourth embodiment of the present invention.

FIG. 20 is a block diagram specifically showing a detection unit and a cutoff control unit of the projection type image display device according to the fourth embodiment of the present invention.

FIGS. 21 (a), (b), and (c) are operation waveform diagrams for explaining the operation of the projection-type image display device according to the fourth embodiment of the present invention. (D) Projection according to the fourth embodiment of the present invention. Diagram for explaining the operation of the portable image display device

FIG. 22 is a cross-sectional configuration diagram of a spatial light modulator used in a conventional projection image display device.

FIG. 23 is a system configuration diagram of a conventional projection type image display device.

FIG. 24 is a drive voltage waveform diagram of a conventional spatial light modulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Emission characteristic control part 2 Drive waveform generation part 3 Gamma input terminal 4 Gamma output terminal 5, 6 Transistor 7 Series resistance 8 Control signal terminal 9 Spatial frequency characteristic control part 10, 13 Input terminal 11, 12 LPF 14 Signal discrimination circuit 15, Reference Signs List 24 Switching circuit 16 Video amplification circuit 17 CRT drive unit 18 Drive waveform control unit 19 Detection unit 20 Cutoff control unit 21 Addition circuit 22 Video amplification circuit 23 Current detection circuit 25 Clamp circuit 26 Photodiode 27 Peak detection circuit 101 Spatial light modulation element 102, 102 ′ Glass substrate 103, 103 ′ Conductive transparent electrode 104 Photoconductive layer 105 Light reflection layer 106 Light modulation layer 107 Light absorption layer 108 Image source 109 Writing light 110 Writing lens 111 Light source 112 Reading light 113 Output light 114 Visualization means 115 throw Lens 116 screen

Claims (11)

[Claims] 1. A spatial light modulator, an image source for generating image light as writing light to the spatial light modulator, and image light in the vicinity of black in accordance with image information of the image light to emit light. A projection type image display device comprising a light emission characteristic control unit for controlling characteristics. 2. A gamma characteristic determined by an image light and a spatial light modulation element, wherein a gamma characteristic determined by an image light and a spatial light modulator is set to a linear characteristic for a moving image and a saturation characteristic for a still image. 2. The projection type image display device according to 1. 3. A light emission characteristic control unit which sets a black level which is faithful to a moving picture and has a high temporal aperture ratio, and which sets a black level of black compression for a still image such as a character or a graphic and which has a low temporal aperture. 2. The projection type image display device according to claim 1, wherein the setting is made so as to be a ratio. 4. The light emission characteristic control section controls the light emission characteristic of the image light in the vicinity of black so that the contrast on the screen is constant even when the time aperture ratio is changed. Item 2. The projection type image display device according to Item 1. 5. A spatial light modulator, an image source for generating image light which is writing light to the spatial light modulator, and a resolution by controlling a spatial frequency of the image light according to image information of the image light. A projection-type image display device comprising a spatial frequency characteristic control unit for controlling characteristics. 6. The projection type image display device according to claim 5, wherein the spatial frequency characteristic control unit sets the spatial frequency characteristic to a wide band for a moving image and sets the spatial frequency characteristic to a narrow band for a still image. . 7. A spatial light modulator, an image source for generating image light which is writing light to the spatial light modulator, and a drive waveform controller for controlling a drive waveform applied to the spatial light modulator. A projection-type image display device, comprising: a control unit that controls a driving waveform applied to a spatial light modulation element. 8. A driving waveform control unit generates a driving voltage having an erasing period and a writing period in synchronization with a vertical scanning frequency of image light in a normal operation, and controls the frequency and the driving voltage in a special operation. The projection type image display device according to claim 7, wherein: 9. A spatial light modulator, an image source for generating image light that is writing light to the spatial light modulator, and a drive waveform generator for generating a drive waveform applied to the spatial light modulator. Reading means for reading image light written in the spatial light modulator, and black level control means for detecting a black level of the read image light and controlling a black level of the image source. A projection type image display device. 10. The apparatus according to claim 9, wherein said black level control means comprises a feedback control loop for detecting the reference light superimposed on the written image light and controlling the level of the image light. Projection image display device. 11. A feedback control for controlling a black level by detecting image light written from an image source by superimposing a reference signal on a video signal and a reference signal of the read image light. 10. The projection type image display device according to claim 9, wherein the projection type image display device is constituted by a loop.