JPH0276485A - Video signal processing circuit in projection tv - Google Patents

Abstract

PURPOSE:To facilitate the correction of the trapezoidal distortion by changing a reading timing by a constant time and changing the frequency of a reading clock by a constant frequency at the time of reading out of a line memory. CONSTITUTION:From a reading control circuit 17, a reading permitting signal, in which a generating timing is delayed by a constant time for a prescribed H based on the counted output of an H counter 16, is generated. In a PLL circuit 18, a frequency-dividing ratio N is incremented for a prescribed H by the control of a frequency-dividing ratio control circuit 19, and thus, a reading clock, in which the frequency rises constantly for the prescribed H, is generated. For example, at the time of N=288, first 1H data fetched into a line memory 13 by the writing clock of a constant frequency 4fsc are read from the memory 13 by the reading clock of the approximately same frequency 4fsc. At the time of N=289 in a next 1H, a reading clock frequency is higher, and therefore, the signal outputted from a D/A converter 20 is time-base-compressed.

Description

TECHNICAL FIELD The present invention relates to a video signal processing circuit for a projection TV, and more particularly to a video signal processing circuit suitable for use in a liquid crystal projection TV.

Background technology In a three-tube color projection TV, red (R
), green (G), and blue (B), the images reflected on three projection tubes coated with monochromatic phosphors are formed on a screen using a projection lens. By arranging them in the horizontal scanning direction of the screen, as shown in Figure 5, the R and B optical axes are incident at an angle of θ to the axis perpendicular to the screen surface (G optical axis), so the display screen This results in trapezoidal distortion having the top and bottom sides in the horizontal scanning direction.

To this end, conventionally, a convergence circuit as shown in Figure 6 is used to correct the color shift caused by keystone distortion by projecting a keystone distortion-corrected screen onto each of the R and B projection tubes. . That is, in addition to the main deflection yoke, correction sub-deflection yokes 61R and 61B are provided for each of the R and B projection tubes, and a predetermined waveform signal emitted from the convergence waveform generator 62 is sent to the level adjustment circuit 6.
After level adjustment with 3R and 63B, power amplifier 64R
, 64B to the sub-deflection yokes 61R and 161B to cause current to flow therethrough, a screen with trapezoidal distortion corrected is projected on each of the R and B projection tubes.

Incidentally, there is a projection TV using a liquid crystal light valve, but even in this liquid crystal projection TV, the above-mentioned trapezoidal distortion cannot be avoided. However, in the case of a liquid crystal projection TV in which the pixel cells are arranged in advance in a lattice pattern as shown in Fig. 7, if a screen with trapezoidal distortion corrected is projected onto the light valve. Since the shape of the display screen is a trapezoid with the top and bottom in the horizontal scanning direction, diagonal scanning is required, which makes it very difficult to scan the screen.

SUMMARY OF THE INVENTION Therefore, the present invention provides a video signal processing circuit for a projection TV that can easily correct keystone distortion even when using a light valve in which pixel cells are arranged in a grid pattern in advance. The purpose is to

A video signal processing circuit according to the present invention processes a digitized video signal in a projection TV in which the optical axis of a projection lens is inclined by a predetermined angle in the vertical scanning direction of a display screen with respect to an axis perpendicular to the screen surface. 1H (H:
a storage means capable of sequentially storing an amount equivalent to (horizontal scanning period);
Means for generating a clock synchronized with a synchronization signal included in a video signal and using it as a write clock for the storage means; and means for generating a clock whose frequency changes by a constant frequency every predetermined H and using it as a read clock for the storage means. and means for controlling the reading timing of stored information from the storage means while changing it by a fixed time every predetermined H, the fixed frequency and the fixed time being set according to the inclination angle of the optical axis of the projection lens. The structure is as follows.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

In FIG. 1 showing the configuration of a liquid crystal projection TV using, for example, three projection lenses according to the present invention, R, G,
Each projection lens IR, IG, IB of B is screen 2
are arranged in the vertical direction of the display screen, that is, in the vertical scanning direction of the display screen.
, 1B each optical axis is a projection lens IG perpendicular to the screen surface.
is inclined by an angle θ with respect to the optical axis of . These projection lenses IR, IG, and IB project an enlarged image onto the screen 2 using the optical system described below, but since the configuration of each optical system is the same, only the optical system of the projection lens IG is used. It is illustrated.

The projection light emitted as diffused light from the projection light source 3G is converted into parallel light by the condenser lens 4G and is irradiated onto the liquid crystal light valve 5G. The light passing through the liquid crystal light valve 5G is transmitted through a half mirror 6G and then enlarged and projected by the projection lens IG, so that the image written on the liquid crystal light valve 5G is enlarged and displayed on the screen 2. An image corresponding to the input video signal is written to the liquid crystal light valve 5G.

Here, the optical axes of the projection lenses IR and IB are incident on the axis perpendicular to the screen surface at an angle of θ, resulting in trapezoidal distortion whose apex and base are in the vertical scanning direction of the display screen. Therefore, the liquid crystal light valve 5R in these optical systems.

It is necessary to write a screen on which keystone distortion has been corrected on 5B. For this reason, the projection lens IR.

Liquid crystal light valve 5R in each IB optical system.

A video signal after keystone distortion correction processing is input to 5B.

FIG. 2 is a block diagram showing an embodiment of a video signal processing circuit according to the present invention that performs trapezoidal distortion correction processing. In the figure, a video signal is supplied to an A/D converter 11 and a sync separation circuit 12.

The video signal digitized by the A/D converter 11 is supplied to the line memory 13. In the synchronization separation circuit 12, the horizontal synchronization pulse (H5sync
) and vertical synchronization pulse (V 5sync) are separated and extracted. The PLL circuit 14 as a first clock generation means is
For example, a clock of 4 fsc (fsc is a color subcarrier frequency) is generated in synchronization with the horizontal synchronizing pulse, and is supplied as the sampling clock of the A/D converter 11 and the write clock of the line memory 13. The write control circuit 15 supplies the line memory 13 with a write permission signal synchronized with the horizontal synchronization pulse. In response to this write permission signal, the line memory 13 sequentially transfers the digitized video signal to 1H (
H: horizontal scanning period) is stored using the write clock.

On the other hand, an H counter 16 for counting horizontal synchronizing pulses is provided, and this H counter 16 is reset by vertical synchronizing pulses. The read control circuit 17 is for generating a read permission signal to the line memory 13, and is configured to generate, for example, the pulse width M (integer) of the write clock every predetermined H based on the count output of the H counter 15.
The read timing of stored information is controlled by changing the generation timing of the read permission signal by a fixed time given by multiplying the read permission signal. Further, a PLL circuit 18 that generates a read clock for the line memory 13 is provided as second clock generation means. The PLL circuit 18 has a frequency divider with a variable frequency division ratio N, and the frequency division ratio control circuit 19 controls the frequency division ratio N to a predetermined value.
By variably controlling the frequency division ratio N by a constant value each time,
Frequency (NX15.75 K
Generates a read clock whose frequency (Hz) changes. The constant time in the readout control circuit 17 and the constant frequency in the PLL circuit 18 are correlated with each other, and the projection lenses IR, I
Inclination angle θ of each optical axis of B with respect to the axis perpendicular to the screen surface
It is set accordingly. The digitized video signal read from the line memory 13 is converted into an analog signal by the D/A converter 20, and becomes the input video signal for the liquid crystal light valves 5R and 5B in the optical systems of the projection lenses IR and IB shown in FIG. .

Next, the operation of the circuit having such a configuration will be explained.

First, a 4fsc write clock is generated in synchronization with a horizontal synchronizing pulse in the PLL circuit 14, and in response to a write permission signal issued from the write control circuit 15, a digitized video signal corresponding to 1H is sequentially sent to the line memory 13. Stored by write clock.

On the other hand, the read control circuit 17 generates a read permission signal whose generation timing is delayed (or advanced) by a certain amount of time every predetermined H based on the count output of the H counter 16.
In addition, in the PLL circuit 18, the frequency division ratio N is incremented (or decremented) every predetermined H by the control of the frequency division ratio control circuit 19, so that a read clock whose frequency increases (or decreases) by a constant frequency every predetermined H is generated. generated.

Here, for example, if N-288, a constant frequency of 4 fs
The first 1H data taken into the line memory 13 with the write clock of c is read out from the line memory 13 with the read clock of approximately the same frequency of 4 fsc. In the next 1H, if N-289 is selected, the frequency of the read clock becomes high, so the video signal output via the D/A converter 20 is time-base compressed, and at the same time, the read permission signal generation timing Since the start position of the video signal is also delayed by a certain amount of time, the start position of the video signal is also delayed.

In this way, by delaying the readout timing by a fixed amount of time every predetermined H and increasing the readout clock frequency by a fixed frequency every predetermined H, the video signal corresponding to 1H is sequentially time-axis compressed, as shown in FIG. (a
) The screen shown in (b) can be obtained from the normal screen shown in (b). In addition, by performing the opposite operation, that is, by advancing the reading clock by a certain amount of time every predetermined H from the state where the readout clock is set slow, and by lowering the frequency of the readout clock by a certain frequency every predetermined H, the readout clock equivalent to 1H can be obtained. By gradually expanding the time axis of the video signal from the time axis compressed state, the normal screen as shown in Figure 3(a) can be changed to (
A screen like the one shown in C) can be obtained.

Therefore, the inclination of each optical axis of the projection lenses IR and IB in FIG. By setting according to the angle θ, trapezoidal distortion can be corrected, and a screen with trapezoidal distortion corrected can be written on the liquid crystal light valve. At this time, the scanning direction on the liquid crystal light valve matches the direction of the lattice of the liquid crystal cell as shown in Figure 3, so when using a liquid crystal light valve in which the liquid crystal cells are arranged in a lattice shape in advance, Even if there is, screen scanning can be easily performed.

In addition, in the above embodiment, a case was explained in which the case was applied to correction of keystone distortion in a liquid crystal projection TV using three projection lenses, but as shown in FIG.
In a liquid crystal projection TV that enlarges and projects G and B using a single projection lens 1, it can also be applied to correct keystone distortion that occurs when the screen 2 and the optical axis of the projection lens 1 are not perpendicular in the vertical scanning direction of the display screen. It is.

Furthermore, the present invention is applicable not only to liquid crystal projection TVs but also to any projection TV using a light valve in which pixel cells are arranged in a grid pattern.

Further, in the above embodiment, the fixed time and fixed frequency are fixed once they are set as constants, but it is also possible to set them manually. According to this, the projection side and the screen are separated. In the case of the above system, it is convenient because the above-mentioned fixed time and fixed frequency can be adjusted according to the inclination angle θ of the optical axis of the projection lens with respect to the axis perpendicular to the screen surface.

Effects of the Invention As explained above, according to the present invention, when reading stored information from a line memory, the read timing is changed by a certain time every predetermined H, and the frequency of the read clock is changed every predetermined H. By changing the frequency in constant increments and setting the constant time and -constant frequency according to the inclination angle of the optical axis of the projection lens with respect to the axis perpendicular to the screen surface, keystone distortion can be corrected and the scanning direction can be changed to horizontal scanning. Therefore, even when using a light valve in which pixel cells are arranged in a grid pattern in advance, trapezoidal distortion can be easily corrected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a liquid crystal projection TV using three projection lenses according to the present invention, FIG. 2 is a block diagram showing an embodiment of a video signal processing circuit according to the present invention, and FIG. 3 is a normal screen (a ), Figure 4 shows the configuration of a liquid crystal projection TV using one projection lens, and Figure 5 shows the principle of generation of trapezoidal distortion -13=. 6 is a block diagram of a convergence circuit for correcting color shift due to keystone distortion, and FIG. 7 is a diagram showing screen scanning according to the present invention for a liquid crystal light valve in which liquid crystal cells are arranged in a grid pattern. be. Explanation of symbols of main parts 1, IR, IG, IB...Projection lens 2...
...Screen 5.5R, 5G, 5B...LCD light bulb 1
3... Line memory 14. 18... PLL circuit 15... Write control circuit 17... Read control circuit 19... Frequency division ratio Control circuit applicant Pioneer Corporation

Claims (2)

[Claims] (1) A video signal processing circuit for a projection TV in which the optical axis of a projection lens is tilted at a predetermined angle in the vertical scanning direction of a display screen with respect to an axis perpendicular to the screen surface, and the circuit processes digitized video signals. a storage means capable of sequentially storing an amount equivalent to 1H (H: horizontal scanning period); and a first clock generation means that generates a clock synchronized with a synchronization signal included in the video signal and uses it as a write clock of the storage means. a second clock generation means that generates a clock whose frequency changes by a constant frequency every predetermined H and uses the clock as a read clock of the storage means; and a second clock generation means that makes the read timing of the stored information from the storage means constant every predetermined H. A video signal processing circuit comprising: a control means for controlling the constant frequency while changing it time by time, and wherein the constant frequency and the constant time are set according to the inclination angle of the optical axis. (2) The video signal processing circuit according to claim 1, wherein the projection TV is a liquid crystal projection TV having a liquid crystal light valve in which liquid crystal cells are arranged in a grid pattern.