JPH0389784A - Correction circuit for picture frame of projected picture from picture projection using liquid crystal light bulb - Google Patents

Abstract

PURPOSE:To remove the recognition of an unnatural picture due to a visual distortion feeling by changing simply the length of a horizontal blanking period in a video signal to be supplied to a liquid crystal light bulb correspondingly to a vertical scanning cycle, and fixing the potential of the blanking period to a black level. CONSTITUTION:A means 30 to change simply the length of the horizontal blanking period in the video signal to be supplied to the liquid crystal light bulb 8 corresponding to the vertical scanning cycle, and the means 31 to fix the potential of the blanking period to the black level are provided. Then, it is made possible to project the picture with a picture frame free from trapezoidal distortion on a screen. Accordingly, the trapezoid-shaped distortion caused in the picture frame projected on the screen is removed by the state of the black level in the horizontal blanking period whose length is made to change simply in the vertical scanning cycle. Thus, the projected picture is never recognized as the unnatural picture because of the visual distortion feeling.

Description

DETAILED DESCRIPTION OF THE INVENTION (Prior Art) The present invention relates to a circuit for correcting the image frame shape of a projected image from an image projector using a liquid crystal light valve.

(Prior art) The intensity of light from a light source is modulated by a liquid crystal light valve controlled by a video signal (image signal), and the light emitted from the liquid crystal light valve is imaged on a screen via a projection optical system. Image projectors that project images upward are known.

The image projector using the liquid crystal light valve described above solves the problems of the image projector using a cathode ray tube in 11'1, namely, the projection image is affected by the earth's magnetism, and the three primary colors of additive color mixture are used. Since the images of each primary color are optically superimposed by three optical systems provided for each primary color image, there is no problem such as the first problem that color shift tends to occur in the reproduced image and it is difficult to arbitrarily set the screen size. For example, if the image projector is placed 3.8 meters away from the screen, a large color image with a diagonal length of 2.5 meters can be projected onto the sedge green. Since it has the advantage of projecting a color image of any size onto a screen using a single projection optical system, an image projector using a liquid crystal light valve is used to project an image based on a video signal (image signal). (Problem to be solved by the invention) By the way, it is important to make sure that the optical axis of the projection optical system of the image projector and the normal to the center position of the screen match. If the image projector is installed in such a condition, there will be no distortion that would cause trapezoidal distortion in the image frame or image content of the image projected on the screen, but if the image projector is installed in front of the screen, When installing an image projector to project an image onto a screen, if the image projector is installed in such a way that the optical axis of its projection optical system coincides with the normal line to the center of the screen, the image projection Since the presence of the image projector may interfere with viewing the projected image on the screen, the image projector is installed on the floor or suspended from the ceiling.

However, as mentioned above, if you place the image projector on the floor,
Alternatively, if the device is mounted on a ceiling, trapezoidal distortion may occur in the image frame and image content projected onto the screen.

FIGS. 14 and 15 are diagrams for explaining the above-mentioned problems. In FIGS. 14 and 1-5, LA is an image projector using a liquid crystal light valve, and S is an image projector using a liquid crystal light valve. It's a screen.

Image projector LA using a liquid crystal light valve in Figure 14
The image projector T=A using the liquid crystal light valve shown by the solid line in FIG. In addition, the image projector LA using the liquid crystal light valve shown by the dashed-dotted line in FIG. 15(a) is shown as an example. The image projector LA using the liquid crystal display bulb shown in the solid line is moved in the direction of the thick arrow and is installed on the floor.

Image projector L using a liquid crystal light valve When the image projector L A using a liquid crystal light valve is installed at the position shown by the solid line in FIGS. 14 and 15 (a), the image projector L using a liquid crystal light valve
When the rectangular image frame image from A is projected onto the screen S, the images shown in FIGS. 14 and 15 (b) are displayed on the screen S.
a shown in a.

An image of a rectangular picture frame surrounded by points b, c, and d is projected.

However, if the image projector LA using a liquid crystal light valve is set at the position indicated by the - dot-dashed line in FIG. When projected upward, a', b,
A trapezoidally distorted picture frame surrounded by points e and d',
And a trapezoidally distorted image will be projected.

Now, assuming that the distance between the 0 point of the screen S and the 9 point on the image projector LA using a liquid crystal light valve is 3.8 meters as in the above example, the length of the diagonal line on the screen S is 2.5 meters. When an image of a rectangular picture frame is projected, an image projector LA using a liquid crystal light valve is installed at the position shown by the solid line in FIGS. 14 and 15 (a). When the image projectors I and A are moved from the state indicated by the -dotted chain line in FIG. % trapezoidal distortion occurred.

If a trapezoidal distortion occurs in the image frame projected onto the screen S as described above, the image will be perceived as unnatural due to the visual sense of distortion. Even if you install it in a
It was desired to at least prevent trapezoidal distortion from occurring in the image frame projected on the screen so that the image would be recognized as having a reduced visual sense of distortion.

Furthermore, it goes without saying that it is not desirable for the trapezoidal distortion to occur in the image content as described above.

Since it was required that the image being projected be projected onto the screen without trapezoidal distortion, the applicant's company developed In order to prevent trapezoidal distortion from occurring, the image to be displayed on the pixel array of the liquid crystal light valve is first distorted in the opposite direction. The period of the sampling pulse used for conversion is defined as the period of horizontally scanning one row of pixels of the liquid crystal light valve under the condition that the total number of sampling pulses in one horizontal scanning period is kept constant. Using the sampling pulse described above, the sampling period in each period is monotonically changed in the vertical scanning period, and the sampling period in each period is changed at least in a period set to include the period and a period other than the above-mentioned period. Column: A liquid crystal display system that stores extracted digital image data in a memory, reads out the digital image data using pulses having a constant repetition period, converts it into an analog video signal, and supplies the analog video signal to a liquid crystal light valve. The keystone distortion correction circuit of an image projector using a light valve, and the horizontal driving pulse supplied to the liquid crystal light valve for each horizontal scanning period in order to horizontally scan one row of pixels of the liquid crystal light valve. A liquid crystal light in which an image whose trapezoidal distortion is corrected is projected onto a screen via a liquid crystal light valve using a driving pulse generating means configured such that the repetition frequency of is monotonically changed in a vertical scanning period. Keystone distortion correction circuit for image projector using bulbs, and sequential 1
A first period is set to include at least a period of scanning one row of pixels of the liquid crystal light valve in the horizontal direction, as a pulse generation means for generating a predetermined number of pulses during the horizontal scanning period. and a second period corresponding to a period other than the first period described above, when one horizontal scanning period is divided into two periods, the above-mentioned first period set during one horizontal scanning period. The pulses generated corresponding to the period and the second period are such that the pulse generated during the first period is longer than the repetition period of the pulse generated twice during the second period, and Using a device configured such that the repetition period of the above-mentioned pulses is monotonically changed in the vertical scanning period, the pulses generated from the above-mentioned pulse generating means during the above-mentioned first period are used to generate sequential horizontal scanning periods. By performing horizontal scanning for one row of pixels of each liquid crystal light valve, an image with trapezoidal distortion corrected is projected onto the screen via the liquid crystal light valve. We proposed a keystone distortion correction circuit for an image projector using a light bulb, so that even when the image projector is installed on the floor or suspended from the ceiling as described above, there is no keystone distortion in the image content. image can be projected on the screen S.

However, by using the trapezoidal distortion correction circuit of the image projector using each of the previously proposed liquid crystal light valves, trapezoidal distortion can be caused in the image content even when the image projector is installed on the floor or suspended from the ceiling. Even if an image without any distortion is projected on the screen S, the image frame remains trapezoidally distorted, resulting in an unnatural image due to visual distortion. The problem of being perceived as such has become a problem, and measures to improve it have been sought.

(Means for Solving Problem R) The present invention modulates the intensity of light from a light source using a liquid crystal light pulse, in which a video signal and corresponding image information are formed, and uses the light emitted from the liquid crystal light valve to form a projection optical system. In an image projector that forms an image on a screen and projects it onto the screen, the length of the horizontal blanking period in the video signal supplied to the liquid crystal light valve is made monotonous in correspondence with the vertical scanning period. A liquid crystal light comprising means for changing the electric potential during the blanking period and means for fixing the electric potential during the blanking period to a black level, so that an image having an image frame without trapezoidal distortion can be projected on the screen. The intensity of the light from the light source is modulated by a correction circuit for the frame shape of the projected image from an image projector using a bulb, and a liquid crystal light valve where image information corresponding to the video signal is formed, and the light is emitted from the liquid crystal light valve. When light is imaged onto a screen via a projection optical system and projected onto the screen, an image with trapezoidal distortion corrected is displayed on the screen. In an image projector equipped with a circuit arrangement that corrects keystone distortion so that it is displayed on a liquid crystal light valve with a pixel arrangement, the length of the horizontal blanking period in the video signal supplied to the liquid crystal light valve The present invention uses a liquid crystal light valve that is equipped with means for changing the electric potential during the blanking period and means for fixing the electric potential during the blanking period described above at the black level, and is capable of projecting an image having an image frame without trapezoidal distortion on the screen. Provided is a circuit for correcting the image frame shape of a projected image from an image projector.

(Function) Monotonically changing the length of the horizontal blanking period in the video signal supplied to the liquid crystal light valve in correspondence with the vertical scanning period, fixing the potential of the blanking period described above at the black level, To project an image having an image frame without keystone distortion on a screen.

(Example) Hereinafter, a circuit for correcting the image frame shape of a projected image from an image projector using the liquid crystal light valve of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1, FIG. 5, FIG. 12, and FIG. 13 are block diagrams of different embodiments of the correction circuit for the frame shape of the projected image from the image projector using the liquid crystal light valve of the present invention. The figure is a block diagram of some of the constituent parts, and FIGS. 2 and 7 are explanatory diagrams of the image frame shape of the projected image,
FIGS. 3 and 4 and FIGS. 8 to 11 are waveform diagrams for explaining the operation.

Figure 1, Figure 5, Figure 6, Figure 12, and Figure 13.
In the figure, 1 is an input terminal for a video signal to be projected (Ryokai signal), 2 is an input terminal for a vertical synchronization signal SV, 7 is a liquid crystal light valve drive circuit, 8 is a liquid crystal light valve, 2
6 is a clamp circuit, 29 is an inverter, 30 is an OR circuit, SWe is a changeover switch, and in each of the above-mentioned times, 9 in each figure except FIG. 6 is a sawtooth wave generator.

First, a circuit for correcting the image frame shape of a projected image from an image projector using a liquid crystal light valve shown in FIG. 1 will be described.

(a) in FIG. 3 supplied to input terminal 1 in FIG.
The video signal (Ryōkai signal) Sp shown in FIG. Fixed contact C of SWc
given to.

The movable contact V of the changeover switch S W c is controlled by the changeover control signal Pv3 shown in FIG. 3(f) outputted from the OR circuit 30.
When v3 is at a low level, the movable contact V is switched to the fixed contact C side, and the switching control signal Pv3 is switched to the fixed contact C side.
When is at a high level, the movable contact V is connected to the fixed contact e
can be switched to the side.

The movable contact V of the changeover switch SWc described above is the fixed contact C.
In the state where the changeover switch SWe is switched to the side, the movable contact V of the changeover switch SWe outputs a video signal 5pb ((f in FIG. ) is supplied to the liquid crystal light valve 7, and when the movable contact V of the changeover switch SWc is switched to the fixed contact e side, the movable contact V of the changeover switch SWc is connected to the fixed contact e. The voltage of the current g31 is supplied to the liquid crystal light valve 7 as the voltage during the horizontal retrace period in the video signal. The voltage of the power supply 31 described above is set to a voltage value corresponding to the black level of the video signal.

The switching control signal Pv3 supplied from the OR circuit 30 to the changeover switch SWc monotonically increases or decreases the length of the blanking period in successive horizontal scanning periods within each vertical scanning period; That is, the length of the return Ra erasure period in successive horizontal scanning periods within each vertical scanning period can be changed monotonically.

Next, a description will be given of how the switching control signal PV3, which is supplied from the OR circuit 30 to the changeover switch SWc, is generated. In Fig. 1, the horizontal synchronizing signal Sh input to terminal 3 ((b) in Fig. 3)
) is supplied as a trigger signal to monostable multivibrators 33 and 34 whose output pulse widths are variable according to a control signal.

The monostable multivibrator 33, whose output pulse width is variable according to the control signal described above, generates a vertically periodic sawtooth wave output from the sawtooth wave generator 9, for example, as shown in FIG. 4(b). The wave signal Ss is supplied as a control voltage via the changeover switch SW, and an output pulse Pvl is generated every time it is triggered by the horizontal synchronization signal sh supplied from the terminal 3 (see (C) in Fig. 3). ) is the pulse width of the sawtooth signal (e.g. the vertical period sawtooth signal Ss shown in FIG. 4(b) or shown in FIG. 4(c)) at the time of triggering. The monostable multivibrator 34 is configured to be changed in accordance with the voltage value of the control voltage by the vertically periodic sawtooth wave signal (Ss bar), and the output pulse width is variable by the control signal described above. , a sawtooth wave signal with a vertical period output from the sawtooth wave generator II9 is applied to the inverter 32 via the changeover switch SW, and the inverter 32 generates a sawtooth wave signal (for example, CQ in FIG. 4) whose polarity is inverted. The vertical periodic sawtooth signal Ss bar or the fourth
Vertical periodic sawtooth wave signal Ss shown in (b) of the figure
) is supplied as a control voltage, and the pulse width of the output pulse Pv2 (see (d) in FIG. 3) generated each time it is triggered by the horizontal synchronizing signal sh supplied from the terminal 3 is The configuration is such that the control voltage is changed according to the voltage value of the control voltage based on the sawtooth wave signal at a certain point in time.

The monostable multivibrator 33, 34 whose output pulse width is variable according to the voltage of the control signal as described above can be easily obtained by having a configuration in which the time constant is changed according to the control voltage value. (This point applies to the monostable multivibrator 2:q whose output pulse width is variable according to the voltage of the control signal shown in each figure such as Fig. 5, Fig. 12, and Fig. 13. The same applies to

In addition, the monostable multivibrator 33°34 whose output pulse width is variable according to the control signal described above (depending on the voltage of the control signal shown in each figure such as Fig. 5, Fig. 12, and Fig. 13) (The same applies to the monostable multivibrator 23 whose output pulse width is variable). Instead, a voltage-controlled variable delay circuit is used to generate the horizontal synchronizing signal sh by applying the vertical period sawtooth wave signal to the control voltage. may be delayed.

A sawtooth wave generator 9 that generates a sawtooth wave signal Ss with a vertical period as shown in FIG. a) A sawtooth wave signal S having a repetition period of the vertical synchronization signal Sv in synchronization with
generate s.

The vertically periodic sawtooth wave signal Ss outputted from the sawtooth wave generator 9 described above is supplied to the fixed contact S of the changeover switch SW, and is also supplied to the fixed contactor via the inverter 24.

When the movable contact V of the changeover switch SW is switched to the fixed contact S side, the vertically periodic sawtooth wave signal Ss output from the sawtooth wave generator 9 is directly applied to the monostable multivibrator 33. and the inverter 32, and when the movable contact V of the changeover switch SW is switched to the fixed contact S side, the vertical period sawtooth wave signal output from the sawtooth wave generator 9 S
s is a monostable multivibrator 34 as a sawtooth wave signal S3 with a vertical period shown in FIG.
and the inverter 32.

Therefore, the monostable multivibrator 3 whose output pulse width is variable according to the voltage of the control signal by the switching operation of the movable contact V of the changeover switch SW described above.
The polarity of the vertically periodic sawtooth wave signal supplied as a control voltage to terminals 3 and 34 is switched.

And, as mentioned above, the monostable multivibrator 33.3 whose output pulse width is variable according to the voltage of the control signal
By switching the polarity of the vertically periodic sawtooth wave signal supplied to 4, the manner of correction of the image frame shape by the image frame shape correction circuit of the projected image from the image projector using the liquid crystal light valve is mutually reversed. The state is changed to .

The monostable multivibrator 33,34 whose output pulse width is variable according to the voltage of the control signal is connected to the terminal 3.
is triggered at the time position of the leading edge of the horizontal synchronizing signal sh supplied from the monostable multivibrator 33, as shown in FIG. An output pulse Pvl that is set to a high level is output from the time position of the edge, and the monostable multivibrator 34 outputs a signal before the horizontal synchronizing signal sh as illustrated in FIG. 3(d). Outputs an output pulse Pv2 that goes to a high level from the edge time position.

The pulse widths of the output pulses P vl and P v2 from the monostable multivibrators 33 and 34 whose output pulse widths are variable according to the voltage of the control signal as described above are the same as those of the monostable multivibrators 33 and 34 described above. The vertical period is varied in the range indicated by the arrows Xi and X2 in both directions in FIG.

The output pulse Pvl output from the monostable multivibrator 33 whose output pulse width is variable as illustrated in FIG. 3(c) according to the voltage of the control signal, that is, the pulse width is The changing Pvl is supplied to an OR circuit 30, and a monostable multivibrator 34 whose output pulse width is variable as illustrated in FIG. 3(d) according to the voltage of the 7 control signal. The output pulse Pv2 outputted from , that is, the pulse width Pv2 whose pulse width changes in a vertical period, is a pulse Pv2 bar whose signal polarity is inverted by the inverter 29 as illustrated in FIG. The signal is supplied to the OR circuit 30 as a signal.

Therefore, from the OR circuit 30 described above, the changeover switch SW
The switching control signal supplied to e is a pulse Pv3 whose horizontal blanking period monotonically changes with the vertical scanning period, as illustrated in FIG. 3(f).

As described above, by supplying the pulse Pv3 whose horizontal blanking period monotonically changes with the vertical scanning period as a switching control signal, a signal is output from the movable contact V of the changeover switch SWc. means that the length of the horizontal blanking period in successive horizontal scanning periods within each vertical scanning period in the video signal output from the clamp circuit 26 monotonically increases or decreases, that is, within each vertical scanning period M. The length of the horizontal blanking period in the sequential horizontal scanning periods is set to monotonically change, and each of the horizontal blanking periods is set to a predetermined black level potential. It is made to signal the state of being.

When the output signal from the changeover switch SWe is supplied to the liquid crystal light valve drive circuit 7 as a video signal targeted for projection, the projection image projected onto the screen S via the liquid crystal light valve 8 is In Figure 2, the hatched areas a, a', b, and d
, d' and c become black, the frame of the image projected onto the screen S becomes at b in Fig. 2.
, e, and d have a rectangular parallelepiped shape without trapezoidal distortion.

Parts a and a'b shown with diagonal lines in Figure 2,
and d, d' Since the c portion corresponds to the horizontal blanking period in the video signal, in order to make the image frame of the image projected on the screen S a rectangular parallelepiped, It is only necessary to appropriately set the state of change in the length of the horizontal blanking period in successive horizontal scanning periods in one vertical scanning period. This can be achieved by setting.

In the embodiment of the present invention that has been described with reference to the construction drawings, both frames of the image projected on the screen are projected onto the screen S with no trapezoidal distortion. The image content of the image projected onto the screen S included trapezoidal distortion. When the intensity of the light from the light source is modulated by the light source, and the light emitted from the liquid crystal light valve is imaged onto the screen via the projection optical system and projected onto the screen, the keystone distortion is corrected for the image on the screen. The present invention relates to an image projector equipped with a circuit arrangement in which keystone distortion is corrected so that an image exhibiting keystone distortion that can be displayed is displayed on a liquid crystal light valve having a two-dimensional pixel arrangement. An example in which this is implemented will be described with reference to FIGS. 5 to 13.

First, a correction circuit for the shape of the image projected from an image projector using a liquid crystal light valve shown in FIG. 5 sequentially generates a predetermined number of pulses during one horizontal scanning period. The means for generating pulses to be generated includes a first period set to include at least a period for horizontally scanning one row of pixels of the liquid crystal light valve, and the first period described above.
When one horizontal scanning period is divided into two periods with a second period corresponding to a period other than the period, the first period and the second period set during the upper horizontal scanning period. The repetition period of the pulses generated in the first period is longer than the repetition period of the pulses generated in the second period.

and a digital image in which a video signal is sampled by the pulses generated from the pulse generating means, using a device configured such that the repetition period of the pulses described above is monotonically changed in the vertical scanning period. means for obtaining data; a memory for storing said digital image data;
A constant-cycle pulse generating means for generating the predetermined constant number of pulses at a constant repetition period during one horizontal scanning period, and the above-described memory using the pulses generated by the constant-cycle pulse generating means. means for reading out digital image data from a computer and then converting it into an analog video signal; and supplying the analog video signal to a liquid crystal light valve so that an image with corrected keystone distortion is projected onto a screen via the liquid crystal light valve. If the image projector is equipped with a trapezoidal distortion correction circuit using a liquid crystal light valve, and a projection image with the image content whose trapezoidal distortion has been corrected is projected onto the screen S, the image FIG. 2 is a block diagram showing an embodiment of the present invention in which trapezoidal distortion of the image frame of the image frame can be corrected.

In FIG. 5, 1 is an input terminal for a video signal (image signal) to be projected, 2 is an input terminal for a vertical synchronizing signal Sv,
3 is an input terminal for the horizontal synchronization signal sh.

4 is an analog-to-digital converter, 5 is a memory (digital memory...for example, FIFO memory), 6 is a digital-to-analog converter, 7 is a driving circuit for a liquid crystal light valve, 8 is a liquid crystal light valve, and 9 is a sawtooth wave generator. , 10 is a monostable multivibrator, 11 is a multiplier, 12.18 is a sample and hold circuit, 13.19 is a low-pass filter, 14
is an adder, 15.20 is a voltage controlled oscillator, 1.6, 21
is a frequency divider, 17.22 is a trapezoidal wave generator, 23 is a monostable multivibrator whose output pulse width is variable according to a control signal, 24 is an inverter, and SWc is a changeover switch.

In FIG. 5, the loop consisting of the sample-and-hold circuit 8 → low-pass filter 19 → voltage-controlled oscillator 20 → frequency divider 21 → trapezoidal wave generator 22 → sample-and-hold circuit 18 is a well-known phase-locked loop ( P
The above-mentioned PLL outputs a pulse Pc having a predetermined constant repetition period in synchronization with the horizontal synchronizing signal sh supplied to the input terminal 3 from the voltage controlled oscillator 20. The pulse Pc output from the voltage controlled oscillator 20 described above is used as a read lock in the memory 5 and as a timing pulse in the digital-to-analog converter 6.

Also, sample hold circuit 12 → low pass filter 1
The loop consisting of the circuits 3 → adder 14 → voltage controlled oscillator 15 → frequency divider 16 → trapezoidal wave generator 17 → sample and hold circuit 12 is also a phase-locked loop (PLL).
), and the voltage controlled oscillator 15 generates a predetermined number of pulses during the period (IH period m) of the horizontal synchronizing signal sh supplied to the input terminal 3. The pulses output from the voltage controlled oscillator 15 described above have a repetition period depending on the control voltage supplied to the voltage controlled oscillator 15 from the adder 14 provided in the loop constituting the PLL described above. becomes something that is changing.

Then, the adder 14 receives the signal Ssm from the multiplier 11 outside the PLL loop, that is, (f
), within each horizontal scanning period, a period of a certain length in a high voltage state (first period) and a period of a certain length in a low voltage state (second period) ), and the voltage value within each horizontal scanning period described above monotonically increases or monotonically decreases in the vertical scanning period, that is, a state in which it changes monotonically in the vertical scanning period (
The signal Ssm (see (e) and (f) in FIG. 9) is added.

The signal Ssm supplied to the adder 4 mentioned above is generated as follows. That is, the horizontal synchronizing signal sh supplied to the input terminal 3 in FIG.
)) The monostable multivibrator 10 is triggered by the leading edge of the horizontal synchronizing signal sh, so that the monostable multivibrator 1o has a pulse width τ1 (time width τ1 of the first period) from the time position of the leading edge of the horizontal synchronization signal sh. The multiplier 1 generates the signal Sm illustrated in FIG.
Supply to 1.

The above-mentioned period of the pulse width τl of the signal Sm- forms the first period in one horizontal scanning period, and also forms the period excluding the above-mentioned first period in one horizontal scanning period IH, i.e. (
The period IH-τ1)=t'2 forms a second period.

Further, the above multiplier 1 is provided with a sawtooth wave generator 9 to which the vertical synchronizing signal Sv ((C) in FIG. 9) supplied to the input terminal 2 in FIG. 5 is supplied as a timing signal. The generated sawtooth signal Ss (
(d) in FIG. 9 is supplied through the circuit of the fixed contact S and the movable contact V of the changeover switch SW, or the circuit of the inverter 24 and the fixed contact and the movable contact V of the changeover switch SW described above. .

The polarity of the sawtooth wave signal Ss outputted from the movable contact V of the changeover switch SW is reversed by the changeover operation by the changeover switch SW described above.

(When the image projector LA using the liquid crystal light valve 8 is installed on the floor, for example, the changeover switch SW switches the movable contact V to the fixed contact S side. The output signal is supplied to a multiplier 1 and a monostable multivibrator 23 whose output pulse width is variable by a control # signal, and an image projector L using a liquid base light valve 8.
For example, when A is used in a ceiling-mounted state, its movable contact V is switched to the fixed contact S side, and the output signal from the changeover switch SW is set to the multiplier 1 and the output pulse width is variable by the control signal. The image projector LA using the liquid crystal light valve 8 can be installed on the floor or suspended from the ceiling, so that the image projector LA using the liquid crystal light valve 8 can be supplied to the monostable multivibrator 23, which is said to be
Even if the installation mode is changed, the screen S
The multiplier 11 (which is a switching means for properly correcting the trapezoidal distortion of the image projected onto the image)
Now, multiplying the voltages of the two signals Sm p S s,
The output signal Ssm as illustrated in FIG. 9(a)
is supplied to the adder 14.

(f) of FIG. 9 is an enlarged view of a part of the output signal Ssm illustrated in ce> of the 9th FM. The pulses generated in 5 are addition! The voltage of the signal Ssm supplied to 114 is
A pulse train and a repetition period of pulses Pa having a short repetition period within one horizontal scanning period 1H correspond to two periods: a first period in which the high state is set in H and a second period in which the low state is set. A pulse train of long pulses pb is arranged in series on the time axis ((c) in FIG. 10).

In addition, the above-mentioned 1. The repetition period of the pulses output during the second period changes in each successive horizontal scanning period so as to monotonically increase or monotonically decrease in the vertical scanning period.

Therefore, the number of pulses Pa generated in the first period of 5 successive l horizontal scanning periods is monotonically changing (monotonically increasing or monotonically decreasing) in the vertical scanning period, but the PLL is This is because the total number of pulses output from the voltage controlled oscillator 20 is a constant value for any one horizontal scanning period because it operates while being locked to the horizontal synchronizing signal sh.

The number of pulses pb generated in the second period of one horizontal scanning period after another also monotonically changes (monotonically decreases or monotonically increases) in the vertical scanning period.

Voltage controlled oscillator 1 in the PLL described above during one horizontal scanning period
The sum of the number of pulses Pa during the first period and the number of pulses Pb during the second period outputted from 5 is the same for each successive horizontal scanning period as described above.
The total number of pulses generated by the voltage controlled oscillator 15 in this PLL during one horizontal scanning period is the pulse Pc generated by the voltage controlled oscillator 20 in the PLL described above at a constant repetition period during one horizontal scanning period. equal to the total number of

FIG. 10 shows the video signal ((a) in FIG. 10) and the output signal Sm of the monostable multivibrator 10 ((b) in FIG. 10).
)), a short repetition period pulse Pa generated from the voltage controlled oscillator 15 of the PLL in the first period in one horizontal scanning period, and a long pulse Pa generated in the second period.
Pulse PC with a constant repetition period ((C) in FIG. 10) and pulse PC with a constant repetition period generated from the voltage controlled oscillator 20 of the PLL ((d) in FIG. 10)
)) and a write start pulse Ps ((e) in FIG. 10), which will be described later.

Now, the above-mentioned pulses Pa and Pb outputted from the voltage controlled oscillator 5 in the PLL are supplied to the analog-to-digital converter 4 and the memory 5, and are used as sampling pulses in the analog-to-digital converter 4. In the memory 5, it is used as a write pulse.

In FIG. 5, the video signal (image signal) supplied to the input terminal 1 is connected to the fixed contact C and the movable contact V of the changeover switch SWc after a specific part of the signal is fixed at a predetermined potential in the clamp circuit 26. The signal is supplied to the analog-to-digital converter 4 via the analog-to-digital converter 4.

Further, when the movable contact V of the changeover switch SWc is switched to the fixed contact e side, the voltage of the power supply 31 connected to the fixed contact e is supplied to the analog-to-digital converter 4.

The analog-to-digital converter 4 described above converts the signal output from the movable contact V of the changeover switch SWc and supplied thereto into digital image data. Since the pulses Pa and Pb output from the voltage controlled oscillator 15 are supplied as sampling pulses, the digital image data sampled and quantized in the analog-to-digital converter 4 and output is The same number of samples are extracted during the scanning period.

The position of the video signal at which the sampling is performed is determined by the pulses Pa and Pb supplied as sampling pulses from the voltage controlled oscillator 15 of the PLL for each successive horizontal scanning period. Therefore, it is shifted by one consecutive horizontal scanning period.

The digital image data output from the analog-to-digital converter 4 is sent to the voltage controlled oscillator 15 of the PLL described above.
Pulses Pa and P supplied as sampling pulses from
The data is written into the memory 5 (for example, a FIFO may be used) using b as a write pulse.

The digital image data written in the memory 5 described above is
A pulse Pc having a constant repetition period outputted from the voltage controlled oscillator 20 of the PLL described above is read out from the memory 5 as a read pulse and supplied to the digital-to-analog converter 6.

The digital-to-analog converter 6 performs digital-to-analog conversion on the digital image data supplied thereto, outputs it as an analog video signal, and supplies it to the liquid crystal light valve drive circuit 7 .

The output signal from the digital-to-analog converter 6 described above is
As described above, during the first period of one horizontal scanning period 1H in the image double amount supplied to the input terminal 1, the analog-to-digital converter 4 samples and quantizes the image using pulses Pa having a short repetition period. During the second period of one horizontal scanning period LH in the signal, the analog-to-digital converter 4
Since the sampled and quantized signals are sequentially stored in the memory 5 using pulses pb having a long repetition period, they are read out from the memory 5 using pulses Pc having a constant repetition period and converted into digital-to-analog. The analog signal (video signal) supplied from the digital-to-analog converter 6 to the drive circuit 7 of the liquid crystal light valve is a video signal corresponding to the first period in one horizontal scanning period of the video signal supplied to the input terminal 1. A state in which the time axis of the portion is expanded, and the time axis of the video portion corresponding to the second period in one horizontal scanning period of the video signal supplied to input terminal 1 is compressed. In addition, one horizontal scanning period consisting of the first period and the second period described above is made equal to one horizontal scanning period of the video signal supplied to the input terminal 1.

And in the drive circuit 7 of the liquid crystal light valve.

Operates to apply the video signals of each upper horizontal scanning period sequentially to the successive pixels in each horizontal row of pixel arrays in the two-dimensional pixel array in the liquid crystal light valve by driving pulses supplied thereto from the terminal 25. Therefore, if the original image is rectangular, the image displayed on the liquid crystal light valve 8 will be displayed as a distorted trapezoid, but as mentioned above, the image displayed on the liquid crystal light valve 8 as a trapezoidally distorted image displayed in .

By making it so that when it is projected onto the screen S, the correct rectangular image is projected on the screen S, the trapezoidal distortion of the image projector using the liquid crystal light valve can be well corrected. It will be possible.

That is, the image projector LA using the liquid crystal light valve 8
For example, when a rectangular image is projected onto the screen S from the image projector LA using the liquid crystal light valve 8, assuming that the position is indicated by the - dotted chain line in (,) in FIG. Since a trapezoidal image surrounded by each point a'btetd' shown in FIG. 15(b) is projected on the image projector LA, in this case, 8 displays an image of a trapezoid in which the length of the upper side is shorter than the length of the lower side, and displays a, b, a on the screen S shown in (b) of FIG.
, d is projected, and the image projector LA using the liquid crystal light valve 8 is mounted, for example, on the ceiling, and the liquid crystal light valve 8 is used. When a rectangular image is projected onto the screen S from the image projector LA, a trapezoidal image in which the length of the top side is shorter than the length of the bottom side is projected onto the screen S-, contrary to the above case. However, in this case, a trapezoidal image in which the length of the upper side is longer than the length of the lower side is displayed on the light valve 8 of the image projector LA, and the image shown in FIG. 15(b) is displayed on the screen S. a, b, a shown
, d so that a rectangular image surrounded by each point is projected.

By the way, in order to display an image with trapezoidal distortion corrected on the screen S as described above, it is necessary to display the trapezoidally distorted image on the liquid crystal light valve 8 as described above. It is necessary that the correct rectangular image is projected on the screen S when the image is projected onto the screen S. When applying a video signal to successive pixels in each successive horizontal pixel array in the two-dimensional pixel array in the liquid crystal light valve 8, writing of the video signal is started for each successive horizontal pixel array. Change the timing in vertical cycles.

Therefore, the drive circuit 7 for the liquid crystal light valve is supplied with a write start pulse P outputted from the monostable multivibrator 23 whose output pulse width is variable according to a control signal.
w ((e) in FIG. 10) is also supplied. The writing operation in the liquid crystal light valve driving circuit 7 is started at the falling edge of the writing start pulse Pw.

The drive circuit 7 of the liquid crystal light valve described above receives the reflection signal H from the digital-to-analog converter 6 as described above, and the write start pulse Pw from the monostable multivibrator 23 whose output pulse width is variable according to the control signal. Since the driving pulse from the terminal 25 is supplied, the liquid crystal light valve driving circuit 7 uses the driving pulse supplied from the terminal 25 every time the write start pulse Pw described above is applied. The video signals in the horizontal scanning period are applied to successive pixels in each horizontal row of pixel arrays in the two-dimensional pixel array in the liquid crystal light valve 8. If the original image is a rectangle, the image displayed will be distorted into a predetermined trapezoid shape.

Therefore, when the image displayed on the liquid crystal light valve 8 is projected onto the screen, an image with keystone distortion corrected will appear on the screen S as shown by the shaded area in FIG. It will be projected.

In addition, in the circuit for correcting the image frame shape of a projected image from an image projector using the liquid crystal light valve of the present invention, the switching operation of the movable contact V of the changeover switch SWe in the circuit arrangement shown in FIG. 5 is an OR circuit. By using the output signal Sm3 from 30 (see (f) in FIG. 8) as a switching control signal, the signal portion of the video signal during the period when the movable contact V of the changeover switch SWc is connected to the fixed contact e. is set to a black level voltage by the power supply 31, so that in the image projected on the screen, the shaded areas in FIG. 7 are displayed as black areas.

In other words, the trapezoidal distortion part in the 5-picture frame is expressed as black in the image.

In the circuit arrangement shown in FIG.
The output signal P+m3 of the OR circuit 30, which is to be supplied as a switching control signal to Wc, is connected to the 2@ monostable multivibrator 27, 28 triggered by the horizontal synchronizing signal sh supplied to the terminal 3 and the inverter. 29
It is generated by a circuit arrangement constituted by the above-mentioned OR circuit 30.

The monostable multivibrators 27 and 28 described above are triggered at the time position of the leading edge of the horizontal synchronizing signal sh shown in FIG. is a pulse P+m with a pulse width τ3
The monostable multivibrator Z8 outputs a pulse Pm2 having a pulse width τ4.

The output pulse P+ml of the monostable multivibrator 27 described above is generated by a write start pulse PW (depending on the control signal) that appears gradually delayed on the time axis with respect to the time position of the horizontal synchronizing signal sh that is sequentially cursed within one vertical scanning period. Monostable multivibrator 2 with variable output pulse width
1 among the write start pulses Pw) output from 3.
Write start pulse P w that appears latest on the time axis
e (Illustrated as P w e in (b) of FIG. 8. The write start pulses Pw, illustrated as Pwf in (b) of FIG. 8, appear sequentially within one vertical scanning period. In FIG. 8, there is a pulse that falls after the rising edge of the signal that appears earliest on the time axis with respect to the time position of the horizontal synchronizing signal sh.
d).

Furthermore, in a state where trapezoidal distortion has occurred in the image, the output pulse P@2 from the monostable multivibrator 28 is applied to the edge of one side of the image where the trapezoidal distortion is less (
In FIG. 7, the pulse width shown in FIG. 8(e) is such that the pulse width τ4 falls at the time when writing is performed on the pixel at point C on side b-40.

Among the output pulses P ml and P m2 from the two monostable multivibrators 27 and 28 mentioned above, the output pulse Pm1 from the monostable multivibrator 27 is as follows.

It is directly supplied to the OR circuit 30, and the output pulse Pm2 from the monostable multivibrator 28 is
Since the polarity is inverted by the inverter 29 and then supplied to the OR circuit 30, the output signal P3 from the OR circuit 30 is as shown in FIG. 8(f).

Therefore, a video signal as shown in FIG. 8(a) is supplied from the clamp circuit 26 to the fixed contact C of the changeover switch SWc, and a black level potential is supplied to the fixed contact e of the changeover switch SWC. If so, (f
) When the changeover switch SWc performs a switching operation in response to the output signal Pm3 from the OR circuit 30 shown in FIG. The result will be as shown in (g) of the figure. The range of X shown in FIG. 8(g) is an example of a range in which the length of the horizontal blanking period monotonically changes in one vertical scanning period.

Therefore, the projection image projected onto the screen S by the image projector equipped with a correction circuit for the image frame shape of the projection image from the image projector using the liquid crystal light valve shown in FIG. As illustrated in the figure, the trapezoidal distortion of the content of one image is well corrected, and the trapezoidal distortion part of the image frame is made black, so the trapezoidal distortion of the image frame is also well corrected. It will be corrected to .

Changeover switch SW in the circuit arrangement shown in FIG. 5 described above
The switching control signal c is generated by a circuit arrangement consisting of two monostable multivibrators 27 and 28 triggered by the horizontal synchronizing signal sh supplied to the terminal 3, an inverter 29, and the above-mentioned OR circuit 30. However, due to this circuit arrangement, the selector switch S
When a Wc switching control signal is generated.

This problem becomes more serious when the video signal has time axis fluctuations, such as a reproduced signal from a VTR.

Figure 6 shows a changeover switch S that does not cause the above problem.
6 is a block diagram showing an example configuration of a circuit for generating a switching control signal of Wc. In FIG. 6, 35 is a phase-locked loop (PLL) that operates by locking to the horizontal synchronizing signal sh supplied to the terminal 3; Further, 36 and 37 are counters, and in the circuit arrangement shown in FIG.
6 and 37 to generate a signal with a predetermined time width from the time position of each horizontal synchronization signal, and then supply it to the OR circuit 30 directly or via the inverter 29, and switch from the OR circuit 30. A switching control signal for the switch S W c is output.

Next, the correction circuit for the image frame shape of the projected image from the image projector using the liquid crystal light valve shown in FIG.
In order to scan one row of pixels of the liquid crystal light valve in the horizontal direction, the repetition frequency of the horizontal driving pulse supplied to the liquid crystal light valve is configured to be monotonically changed in the vertical scanning period for each successive horizontal scanning period. The image projector is equipped with a keystone distortion correction circuit for an image projector using a liquid crystal light valve, in which an image whose keystone distortion has been corrected using a driving pulse generating means is projected onto a screen via a liquid crystal light valve. , an embodiment of the present invention in which the keystone distortion of the image frame of the image can be corrected when a projection image of the image content with the keystone distortion corrected is projected onto the screen S. FIG.

FIG. 12 is a block diagram of an embodiment of a trapezoidal distortion correction circuit of an image projector using the liquid crystal light valve of the present invention,
In FIG. 12, 1 is an input terminal for a video signal (image signal) to be projected, 2 is an input terminal for a vertical synchronization signal Sv, 3 is an input terminal for a horizontal synchronization signal sh, 12 is a sample hold circuit, and 13 is an input terminal for a horizontal synchronization signal sh. 15 is a low-pass filter, and 15 is a voltage controlled oscillator.

38 is a programmable divider, 17 is a trapezoidal wave generator,
39 is an up/down counter; 40 is an input terminal for a switching signal for operating the up/down counter as an up counter or a down counter; 41 is a digital-to-analog converter; A variable monostable multivibrator, 7 a liquid crystal light valve drive circuit, and 8 a liquid crystal light valve.

In FIG. 12, a loop consisting of sample and hold circuit 12 → low-pass filter 13 → voltage controlled oscillator 15 → programmable divider 38 → trapezoidal wave generator 17 → sample and hold circuit 12 constitutes a phase-locked loop (PLL). The above-mentioned PLL operates by locking to the horizontal synchronizing signal sh supplied to the input terminal 3.

The pulses output from the voltage controlled oscillator 15 of the PLL described above are supplied to the liquid crystal light valve driving circuit 7, and the pulses output from the voltage controlled oscillator 15 of the PLL described above are supplied to the liquid crystal light valve driving circuit 7. It is used as a horizontal drive pulse to horizontally scan one row of pixels in a liquid crystal light valve having a dimensional pixel arrangement.

The programmable divider 38 provided in one loop of the PLL described above is configured so that its division ratio is changed according to the value given from the up/down counter 39.

The up/down counter 39 is connected to the terminal 40.
The switching signal supplied to the switch causes the switch to operate as an up-counter or as a down-counter; however, when it operates as an up-counter or as a down-counter In this case, the horizontal synchronizing signal sh supplied to the terminal 3 is used as the pulse to be counted after the state is set to the preset value by being reset by the vertical synchronizing signal SV supplied from the terminal 2. I do.

That is, when the up/down counter 39 is operating as an up counter, after the preset value is set at the time of the vertical synchronization signal, it outputs a numerical value that increases by l every horizontal scanning period. A value that is given to the programmable divider 38 and, if the up/down counter 39 is operating as a down counter, is a value that decreases by 1 every horizontal scanning period after being set to a predetermined preset value at the time of the vertical synchronization signal. is output and given to the programmable divider 38.

Thereby, when the up/down counter 39 is operating as an up counter, the programmable divider 3
8 operates in a state where the division ratio is monotonically increased every upper horizontal scanning period after being preset to a predetermined frequency division ratio at the time of the vertical synchronization signal, and the voltage control in the PLL described above The horizontal drive pulses supplied from the oscillator 15 to the liquid crystal light valve drive circuit 7 are of a state in which the repetition frequency decreases for each horizontal scanning period one after another.
Furthermore, the programmable divider 38 when the up/down counter 39 operates as a down counter is as follows:
After being preset to a predetermined division ratio at the time of the vertical synchronization signal, the division ratio is monotonically decreased every horizontal scanning period. The horizontal driving pulses supplied to the driving circuit 7 of the liquid crystal light valve have a repetition frequency increasing in each horizontal scanning period.

As mentioned above, the pulses whose repetition frequency decreases or increases in each successive upper horizontal scanning period in the vertical scanning period are arranged so that the pixels are spaced at regular intervals in the liquid crystal light valve 8 having a two-dimensional pixel arrangement. When used as a horizontal drive pulse to horizontally scan a sequential row of pixels arranged in a horizontal direction, trapezoidal distortion may occur in the image displayed on the liquid crystal light valve 8 due to the video signal. become.

In order to make the shape of the trapezoidal distortion that occurs in the image displayed on the liquid crystal light valve 8 bilaterally symmetrical as described above, it is necessary to monotonically shift the time point at which writing is to be started by the horizontal drive pulse in successive horizontal scanning periods. As shown in FIG. 12, as a means for generating a write pulse that shifts the start point of writing by a horizontal drive pulse by a predetermined amount in each successive horizontal scanning period, there is an up-down method as shown in FIG. A digital-to-analog converter 41 converts the numerical output from the counter 39 into a control signal of a magnitude corresponding to the numerical value, and supplies it to the monostable multivibrator 23 whose output pulse width is variable according to the control signal. The monostable multivibrator 23 whose output pulse width is variable according to the control signal described above is triggered by the horizontal synchronization signal sh supplied from the terminal 3 to generate a monostable multivibrator whose output pulse width is variable according to the control signal described above. The falling point of the write start pulse Pw output from the vibrator 23 may be set as the above-mentioned write start time.

Therefore, the liquid crystal light valve drive circuit 7 receives control signals 1. 'Therefore, a write start pulse Pw ((e) in FIG. 10) outputted from the monostable multivibrator 23 whose output pulse width is variable is also supplied. The writing operation in the liquid crystal light valve driving circuit 7 is started at the falling edge of the writing start pulse Pw.

For the drive circuit 7 of the liquid crystal light valve described above, after the video signal supplied to the terminal 1 and which is the object of projection is fixed to a specific potential by the clamp circuit 26, a predetermined signal portion of the video signal is fixed to a specific potential. , selector switch S
When applied via fixed contact 0 and movable contact V of Wc, the drive circuit 7 of the liquid crystal light valve sequentially generates images for each horizontal scanning period using the drive pulses supplied from the voltage controlled oscillator 15 described above. It operates so that a signal is applied to successive pixels in each horizontal row of pixel arrays in a two-dimensional pixel array in a liquid crystal light valve. Therefore, if the image displayed on the liquid crystal light valve 8 was originally a rectangle, it would be displayed as being distorted into a predetermined trapezoid shape.

Therefore, when the image displayed on the liquid crystal light valve 8 is projected onto the screen, an image with keystone distortion corrected will appear on the screen S as shown by the shaded area in FIG. Although the images will be projected, the frame of the five images will still be distorted into a trapezoidal shape.

Therefore, in the correction circuit for the image frame shape of the projected image from the image projector using the liquid crystal light valve of the present invention, the area indicated by diagonal lines in FIG. 7 is displayed as a black area. As described above, the length of the horizontal blanking period in the sequential horizontal scanning period within each vertical scanning period in the video signal supplied from the clamp circuit 26 to the liquid crystal light valve drive circuit 7 is monotonically changed. The keystone distortion part in the image frame is reduced to black in the image.
In the circuit arrangement shown in the first and second drawings, as in the case of the circuit arrangement shown in the fifth drawing described above, the fixed contact e of the changeover switch SWe to which the power supply 31 is connected is connected to the changeover switch SW C.
When the movable contact V of the changeover switch S W c is switched, a black level voltage is supplied from the power supply 31 to the drive circuit 7 of the liquid crystal light valve. The switching operation is performed using the output signal 5ia3 from the OR circuit 30 (see (f) in FIG. 8) as a switching control signal.

Changeover switch SWe in the circuit arrangement shown in FIG. 12
The above-mentioned off circuit 30 is supplied as a switching control signal to
The output signal Pm3 is generated by a circuit arrangement consisting of two monostable multivibrators 27 and 28 triggered by the horizontal synchronizing signal sh supplied to the terminal 3, an inverter 29, and the above-mentioned OR circuit 30, that is, the fifth It is generated by a circuit arrangement of the same construction as that already described with reference to the figure.

Therefore, by the switching control operation of the changeover switch SWC described above, even in the image projector equipped with a correction circuit for the image frame shape of the projected image from the image projector using the liquid crystal light valve shown in FIG. As in the case of the image projector shown in FIG. The operation is performed so that trapezoidal distortion can also be corrected well.

Next, a circuit for correcting the image frame shape of a projected image from an image projector using a liquid crystal light valve shown in FIG. 13 will be described.

A correction circuit for the image frame shape of a projected image from an image projector using a liquid crystal light valve shown in FIG. 13 generates pulses to generate a predetermined number of pulses during sequential upper horizontal scanning periods As a means, one of the liquid crystal light valves
There are two periods: a first period set to include a short period for horizontally scanning pixels in a column, and a second period corresponding to a period other than the first period described above. 1 per period
When the horizontal scanning period is divided, the pulses generated corresponding to the first period and the second period set during one horizontal scanning period are the pulses generated during the first period. is longer than the repetition period of the pulses generated during the second period, and the repetition period of the above-mentioned pulses is configured to change monotonically with the vertical scanning period. The pulses generated during the first period from the generating means cause horizontal scanning of one row of pixels of the liquid crystal light valve in each successive horizontal scanning period. A block diagram showing an embodiment in which the present invention is implemented in a trapezoidal distortion correction circuit of an image projector using a liquid crystal light valve, in which an image whose trapezoidal distortion has been corrected is projected onto a screen via a liquid crystal light valve. It is a diagram.

In FIG. 13, 1 is an input terminal for a video signal (image signal) to be projected, 2 is an input terminal for a vertical synchronization signal SV, and 3 is an input terminal for a horizontal synchronization signal sh.

12 is a sample hold circuit, 13 is a low pass filter, 15 is a voltage controlled oscillator, and 16 is a frequency divider.

17 is a trapezoidal wave generator, 9 is a sawtooth wave generator, 10 is a monostable multivibrator, 11 is a multiplier, 23 is a monostable multivibrator whose output pulse width is variable according to a control signal, and 7 is a liquid crystal light valve. A driving circuit, 8 a liquid crystal light valve, and 14 an adder.

In FIG. 13, sample hold circuit 12 → low pass filter 13 → adder 4 → voltage controlled oscillator 15 → frequency divider 16 → trapezoidal wave generator 17 → sample hold circuit 1
A loop consisting of two circuits constitutes a phase locked loop (PLL), and the PLL described above performs an operation locked to the horizontal synchronizing signal sh supplied to the input terminal 3. .

In Fig. 13, sample hold circuit] 2 → low pass filter] 3 → adder 14 → voltage controlled oscillator 15 → frequency divider 1, 6 → trapezoidal wave generator 17 → sample hold circuit 1
The phase mouth ν good loop (P
The voltage controlled oscillator 15 in LL) generates a predetermined number of pulses during the period (LH period) of the adjacent horizontal synchronizing signal sh supplied to the input terminal 3, and drives the liquid crystal light valve. The horizontal drive pulse is supplied to the circuit 7, and the water) F drive pulse is the same as the above-mentioned PL.
This is the output signal from the voltage controlled oscillator [5] whose repetition period changes according to the control voltage supplied from the adder 14 provided in the loop constituting L.

In the circuit arrangement shown in FIG.
The adder 14 provided in one loop of PL
The signal Ssm from the multiplier 11 outside the loop of L, that is, as shown in FIG. The voltage value within each of the above horizontal scanning periods is A state in which monotonically increases or decreases in the vertical scanning period, that is, a state in which it monotonically changes in the vertical scanning period ((eL (
The signal Ssm (see f) is added.

Since the signal 5STIN supplied to the adder 14 in FIG. 13 is the same as that already described with reference to FIG. 5, a detailed detailed explanation thereof will be omitted here. .

As described above, in the circuit arrangement shown in FIG. 13, the output signal of the adder 14 is generated by the voltage control oscillator 15, which is supplied as a voltage control signal, and is applied to the liquid crystal light valve drive circuit 7 as a horizontal drive pulse. The supplied pulses are output from the voltage controlled oscillator 5 whose repetition period changes according to the control voltage supplied from the adder 14 provided in the loop constituting the PLL described above. Therefore, in the circuit arrangement shown in FIG. 13, the pulse supplied as a horizontal drive pulse to the liquid crystal light valve drive circuit 7 is such that the voltage of the signal Ssm is high within one horizontal scanning period 1H. 1st done
Corresponding to the two periods, the period of 1 and the second period of the low state, a pulse train of pulses Pa with a short repetition period and a pulse train of pulses pb of a long repetition period are generated within one horizontal scanning period IH. They are arranged in series on the time axis ((c) in FIG. 10).

In addition, the above-mentioned 1. The repetition period of each pulse output in the second period changes in each successive horizontal scanning period so as to monotonically increase or monotonically decrease in the vertical scanning period. The number of pulses Pa generated during one period monotonically changes (monotonically increases or monotonically decreases) in the vertical scanning period.

Since the PLL operates while being locked to the horizontal synchronizing signal sh, the total number of pulses output from the voltage controlled oscillator 15 is a constant value for any horizontal scanning period.
The number of pulses Pb generated during the second period in successive l horizontal scanning periods also monotonically changes (monotonically decreases or monotonically increases) in the vertical scan period.

Figure 10 shows the video signal ((a) in Figure 10) and the output signal Sm of the monostable multivibrator 10 ((b) in Figure 1O).
)), a short repetition period pulse Pa generated from the voltage controlled oscillator 15 of the PLL in the first period in a certain horizontal scanning period, and a long repetition period pulse PC ( (C) in Fig. 10) and the pulse Pc (10th
10 is a diagram illustrating the timing relationship between (d) in the figure and a write start pulse Ps ((e) in FIG. 10), which will be described later.

Now, as described above, the pulses supplied as horizontal drive pulses to the liquid crystal light valve drive circuit 7 to which the video signal is supplied via the terminal 1 in the circuit arrangement shown in FIG. 13 have a vertical scanning period. The voltage of the signal Ssm whose voltage range is changed corresponds to two periods: a first period in which the voltage of the signal Ssm is in a high state within one horizontal scanning period IH, and a second period in which it is in a low state. , within one horizontal scanning period 1H, a pulse train of pulses Pa with a short repetition period and a pulse train of pulses Pb with a long repetition period are arranged in series on the time axis ((c) in Figure 10 and (c) in Figure 11). (C)) On the other hand, the spatial arrangement of the pixels of the liquid crystal light valve 8, which displays video signals on the two-dimensionally arranged pixels using the horizontal driving pulses described above, is as follows. , successive pixels are arranged spatially at regular intervals (an example of the pixel arrangement mode is shown in the 11th pixel arrangement).
As shown in (e) of the figure, sequential pixels spatially arranged at regular intervals in a liquid crystal light valve having a two-dimensional pixel arrangement as described above.
For pixels in a column, as described above, within one horizontal scanning period IH, a pulse train of pulses Pa with a short repetition period and a pulse train of pulses Pb with a long repetition period are arranged in series on the time axis. When an image corresponding to a video signal is displayed using the driving pulse, a trapezoidally distorted image is displayed on the liquid crystal light valve 8 having a two-dimensional pixel arrangement.

That is, as described above, the pulse of the first period in one horizontal scanning period LH is a pulse Pa with a short repetition period, and the pulse of the second period in the upper horizontal scanning period IH is a pulse with a long repetition period. Pb, and the above-mentioned first
The number of pulses Pa in the period is monotonically changed in each successive horizontal scanning period, and the number of pulses Pa in the first period and the number of pulses pb in the second period are different in any horizontal scanning period. A pulse train with a constant sum is used as a horizontal drive pulse to display an image based on a video signal on pixels in which successive pixels are arranged two-dimensionally at regular intervals. In this case, as a result, the video portion corresponding to the first period in one horizontal scanning period of the video signal supplied to the input terminal 1 has its time axis expanded, and the video signal supplied to the input terminal 1
This is because the video portion corresponding to the second period in one horizontal scanning period of the video signal supplied to is in a state where the time axis is compressed.

If the original image is rectangular, the image displayed on the liquid crystal light valve 8 will be displayed as being distorted into a trapezoidal shape.

So, using horizontal drive pulses as described above.

By applying trapezoidal distortion to the image displayed on the liquid crystal light valve 8 corresponding to the video signal, which is opposite to the trapezoidal distortion that occurs on the screen when the image of the liquid crystal light valve 8 is projected, the liquid crystal light valve Screen S via 8
It is possible to obtain an image without trapezoidal distortion as an image projected onto the image plane.

By the way, in order to display an image with trapezoidal distortion corrected on the screen S as described above, it is necessary to display the trapezoidally distorted image on the liquid crystal light valve 8 as described above. It is necessary that when the image is projected onto the screen S, the correct rectangular image is projected on the screen S. To do this, the image of each horizontal scanning period must be When applying a signal to successive pixels in each successive horizontal pixel array in the two-dimensional pixel array in the liquid crystal light valve 8, the timing of starting writing of a video signal for each successive horizontal pixel array. Vary with a vertical period.

Therefore, the drive circuit 7 for the liquid crystal light valve is supplied with a write start pulse P outputted from the monostable multivibrator 23 whose output pulse width is variable according to a control signal.
w ((e) in FIG. 10 and (d) in FIG. 11) is also supplied. The start of the write operation in the liquid crystal light valve drive circuit 7 is performed at the falling edge of the write start pulse Pw.

In the monostable multivibrator 23 whose output pulse width is variable according to the control signal described above, the sawtooth wave signal Ss shown in FIG. 9(d) output from the sawtooth wave generator 9 is a control voltage. The pulse width of the output pulse generated each time it is triggered by the horizontal synchronizing signal sh supplied from the terminal 3 is determined according to the voltage value of the control voltage by the sawtooth wave signal Ss at the time of triggering. The configuration is such that it can be changed depending on the situation.

In the drive circuit 7 of the liquid crystal light valve described above.

As mentioned above, the video signal from the input terminal 1, the write start pulse PW from the monostable multivibrator 23 whose output pulse width is variable according to the control signal, and the pulse Pa with a short repetition period within one horizontal scanning period IH. A horizontal drive pulse ((C) in FIG. 1O and (C) in FIG. 11) is supplied in which a pulse train caused by the pulse train and a pulse train caused by the pulse pb having a long repetition period are arranged in series on the time axis. Therefore, in the liquid crystal light valve drive circuit 7, each time the write start pulse Pw is applied, the video signal of each horizontal scanning period is sequentially converted into a two-dimensional image in the liquid crystal light valve by the horizontal drive pulse. It operates to apply to successive pixels in each row of pixels in the pixel array.

Therefore, if the original image is a rectangle, the image displayed on the liquid crystal light valve 8 will be displayed as being distorted into a predetermined trapezoid shape.

For the liquid crystal light valve driving circuit 7 described above, after the video signal supplied to the terminal l and which is the object of projection is fixed by the clamp circuit 26 to a predetermined signal portion of the video signal at a specific potential. , selector switch SW
When given through the fixed contact C and the movable contact V of c,
In the liquid crystal light valve driving circuit 7, the driving pulses supplied from the voltage controlled oscillator 15 are used to sequentially transmit video signals for each horizontal scanning period to each horizontal scanning period in the two-dimensional pixel array of the liquid crystal light valve. It operates to feed successive pixels in a column of pixel arrays. Therefore, if the original image is a rectangle, the image displayed on the liquid crystal light valve 8 will be displayed as being distorted into a predetermined trapezoid shape.

Therefore, when the image displayed on the liquid crystal light valve 8 is projected onto the screen, an image with keystone distortion corrected will appear on the screen S as shown by the shaded area in FIG. Although the image will be projected, the frame of the image will still be distorted into a trapezoidal shape.

Therefore, in the correction circuit for the image frame shape of the projected image from the image projector using the liquid crystal light valve of the present invention, the area indicated by diagonal lines in FIG. 7 is displayed as a black area. , monotonically changes the length of the horizontal blanking period in successive horizontal scanning periods within each vertical scanning period in the video signal supplied from the clamp circuit 26 to the liquid crystal light valve drive circuit 7 as described above. In order to reduce the trapezoidal distortion in the image frame to the black of the image.

In the circuit arrangement shown in FIG. 13, as in the case of the circuit arrangement shown in FIG. 5 and FIG. When switched, the drive circuit 7 of the liquid crystal light valve is supplied with a black level voltage from the power supply 31 described above, and the switching operation of the movable contact V of the changeover switch SWc is performed by the OR circuit 3.
This is done using the output signal Sm3 from 0 (see (f) in FIG. 8) as the switching control signal.

Changeover switch SWc in the circuit arrangement shown in FIG. 13
The aforementioned OR circuit 30 is supplied as a switching control signal to
The output signal Pm3 is generated by a circuit arrangement consisting of two monostable multivibrators 27 and 28 triggered by the horizontal synchronizing signal sh supplied to the terminal 3, an inverter 29, and the above-mentioned OR circuit 30, that is, the fifth It is generated by a circuit arrangement of the same construction as that already described with reference to the figure.

Therefore, by the switching control operation of the changeover switch SWe described above, even in the image projector equipped with a correction circuit for the image frame shape of the projected image from the image projector using the liquid crystal light valve shown in FIG. As in the case of the image projector shown in FIGS. 5 and 12, the trapezoidal distortion of the projected image projected onto the screen S is well corrected, and the trapezoidal distortion part of the image frame is set as black. The operation is performed so that trapezoidal distortion of the image frame can be well corrected.

(Effects of the Invention) As is clear from the above detailed explanation, the circuit for correcting the image frame shape of the projected image from the image projector using the liquid crystal light valve of the present invention is capable of correcting the image frame shape of the image projected from the image projector using the liquid crystal light valve of the present invention. In an image projector, the light from a light source is intensity-modulated by a liquid crystal light valve formed with a liquid crystal light valve, and the light emitted from the liquid crystal light valve is imaged on a screen via a projection optical system and projected onto the screen. means for monotonically changing the length of the horizontal blanking period in the video signal supplied to the liquid crystal light valve in correspondence with the vertical scanning period;
An image using a liquid crystal light valve, characterized in that the above-mentioned means for fixing the potential during the blanking period to the black level is provided, and an image having an image frame without trapezoidal distortion can be projected on the screen. The intensity of the light from the light source is modulated by a correction circuit for the image frame shape of the projected image from the projector, and a liquid crystal light valve where image information corresponding to the video signal is formed, and the light emitted from the liquid crystal light valve is used as projection optics. An image exhibiting trapezoidal distortion that can be displayed on the screen with the trapezoidal distortion corrected when the image is formed on a screen via a system and projected onto the screen is a two-dimensional pixel array. In an image projector having a circuit arrangement such that keystone distortion is corrected as displayed on the liquid crystal light valve, the length of the horizontal blanking period in the video signal supplied to the liquid crystal light valve is varied. and a means for fixing the potential during the blanking period to the black level, and is capable of projecting an image having an image frame free of trapezoidal distortion on a screen using a liquid crystal light valve. Since this is a correction circuit for the image frame shape of the projected image from , it is possible to project an image onto the screen that is not recognized as an unnatural image due to visual distortion, which has been a problem in the past, because it is removed by the state of the black level in the previous period. In addition, an image with trapezoidal distortion, which is the opposite of the trapezoidal distortion that occurs on the screen, is formed on the LCD light valve, so that the image can be displayed even when the image projector is installed on the floor or suspended from the ceiling. The light from the light source is projected onto the screen through the liquid crystal light valve so that an image without trapezoidal distortion can be projected on the screen S, and the keystone distortion is not caused on the screen. In addition to obtaining a corrected image, it is possible to project a natural-looking image onto a screen by further reducing the frame of the image to black. The above-mentioned conventional problems can be solved satisfactorily.

[Brief explanation of drawings]

FIG. 1, FIG. 5, FIG. I2, and FIG. 13 are block diagrams of different embodiments of correction circuits for the image frame shape and shape of a projected image from an image projector using the liquid crystal light valve of the present invention, FIG. 6 is a block diagram of some of the components,
Also, Figures 2 and 7 are illustrations of the image frame shape of the projected image, Figures 3 and 4, and Figures 8 to 11 are waveform diagrams for explaining the operation, and Figure 14 is a diagram of the liquid crystal light. Perspective view for explaining how to use an image projector using a bulb, No. 15
The figure is a diagram for explaining the problems of an image projector using a liquid crystal light valve. LA... Image projector using liquid crystal light valve, SW
, SWc...changeover switch, S...screen, 1
... input terminal for video signal (image signal), 2 ... input terminal for vertical synchronization signal Sv, 3 ... input terminal for horizontal synchronization signal sh, 4 ... analog-to-digital converter, 5 ...
Memory, 6...Digital-to-analog converter, 7: Liquid crystal drive circuit for light valve, 8: Liquid crystal light valve. 9... Sawtooth wave generator, 10,27,28... Monostable multivibrator, 11... Multiplier, 12.18
...Sample hold circuit, 13.19...Low pass filter, 14...Adder, 15.20...Voltage controlled oscillator, 16.21...Frequency divider, 17,22...
・Trapezoidal wave generator, 23, 33, 34... Monostable multi-noise generator whose output pulse width is variable according to the control signal, 24, 29, 32... Inverter, 25...
・Terminal, 26... Clamp circuit, 30... OR circuit, 31... Power supply, 35... PLL, 36, 37...
・Counter, 38...Frograma pull day paida, 3
9... Up/down counter, 40... Terminal, 41
...DA converter, he, no () list no \-no 1-1111 soup (+727 /''''S also figure 15 procedural amendment (voluntary) 1. Indication of case Heisei construction year patent Application No. 227235 2, Name of Invention Circuit 3 for correcting the shape of the image frame of an image projected from an image projector using a liquid crystal light valve, Relationship to the case of the person making the correction Patent Applicant Address Kana, Yokohama City, Kanagawa Prefecture 3-12 Moriya-cho, Yo-ku Name (432) Victor Company of Japan Co., Ltd. 4, Agent 6, Changed "prior art" to "industrial application field" on page 2, line 16 of the specification subject to amendment

Claims (1)

[Claims] 1. Intensity modulation of light from a light source by a liquid crystal light valve in which image information corresponding to a video signal is formed, and the light emitted from the liquid crystal light valve is imaged on a screen via a projection optical system. In the image projector, the image is projected onto a screen using means for monotonically changing the length of the horizontal blanking period in the video signal supplied to the liquid crystal light valve in correspondence with the vertical scanning period; An image projector using a liquid crystal light valve, characterized in that it is equipped with means for fixing the potential during the blanking period to a black level, and is capable of projecting an image having an image frame free of trapezoidal distortion on a screen. A correction circuit 2 for the shape of the image frame of the projected image, intensity modulates the light from the light source by a liquid crystal light valve in which image information corresponding to the video signal is formed, and transmits the light emitted from the liquid crystal light valve through the projection optical system. A liquid crystal light with a two-dimensional pixel arrangement produces an image that exhibits trapezoidal distortion so that when the image is formed on a screen and projected onto the screen, an image with the trapezoidal distortion corrected can be displayed on the screen. In an image projector having a circuit arrangement such that keystone distortion is corrected as displayed on the bulb, means for varying the length of a horizontal blanking period in a video signal supplied to a liquid crystal light valve; Projection from an image projector using a liquid crystal light valve, which is equipped with means for fixing the potential during the blanking period described above to a black level, and is capable of projecting an image having an image frame without trapezoidal distortion on a screen. Image frame shape correction circuit