JPH08186782A - LCD projector - Google Patents

Abstract

(57) [Abstract] [Purpose] A mask amount counter is used to generate a mask signal according to the amount of distortion of an image that protrudes from the screen due to trapezoidal distortion that occurs due to an irregular installation relationship between the liquid crystal projector and the screen. To prevent overflow and underflow in the mask signal and prevent discontinuity in the mask signal. A mask amount counter 13 counts the divided pulses from a divided pulse generation circuit 12 that divides a screen in the vertical direction, and a maximum value detection circuit 2 of the mask amount counter 13
1 and the minimum value detection circuit 23, and the means for controlling the supply of the divided pulse to the mask amount counter by the maximum value detection circuit 21 and the minimum value detection circuit 23 are provided, so that the counting operation is stopped and the counter overflows and underscores. Try not to flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal blanking circuit for masking an image protruding from a screen according to the trapezoidal distortion due to the trapezoidal distortion caused by the installation condition of a liquid crystal projector.

[0002]

2. Description of the Related Art In recent years, there has been an increase in the number of systems called home theaters that provide large-screen images using a video projector at home. Among them, the CRT type is being replaced by a liquid crystal type projector that is easy to use. However, in the liquid crystal type projector, there are restrictions in use due to the structure of the liquid crystal panel.

That is, as shown in FIG. 3A, when the installation relationship between the projector 1 and the screen 2 is not properly guaranteed, the image is projected on the screen in a trapezoidally distorted form as shown in FIG. The image will stick out.

In the case of a CRT type projector,
Change the deflection current as shown in (c) on the surface of the CRT,
The trapezoidal distortion can be corrected by correcting the inverse trapezoid.

However, a projector using a liquid crystal panel cannot do this because of the XY pixel structure. In order to realize this, a circuit for correcting trapezoidal distortion of a liquid crystal projector as disclosed in Japanese Patent Laid-Open No. 4-323979 has been proposed.

This is a system in which horizontal display pixels are thinned according to the amount of correction, and it is undeniable that unnaturalness remains in the image.

Therefore, there has been devised a means for simply masking and correcting the image portion protruding from the screen instead of thinning out the pixels. The conventional method will be described below.

In FIG. 4, 11 is a microcomputer interface circuit for setting data from the microcomputer in each circuit, and 12 is for dividing the screen according to the mask amount by counting the horizontal pulse H with the vertical pulse V as a reference. , A mask amount counter 13 for counting the number of divided pulses from the divided pulse generator 12 to generate a mask amount n, a horizontal counter 14 for counting a display clock for obtaining an absolute position in a horizontal cycle, Reference numeral 15 is reference start position data H from the microcomputer with reference to the horizontal counter 14.
An HBLK start position generation circuit that calculates t and n from the mask amount counter 13 to generate a horizontal blanking start position Hst, and 16 also calculates the display width D and the mask amount n from the microcomputer interface 11. , An HBLK end position generation circuit for generating a horizontal blanking end position Hed, and 17 for the HBLK start position generation circuit 15 and H
This is a flip-flop that outputs a horizontal blanking signal according to the mask amount by the BLK width determination circuit 16.

The operation of the liquid crystal display device configured as described above will be described with reference to FIGS. Figure 5
(A) is a conceptual diagram of horizontal blanking. The screen division number in the vertical direction is determined in advance by the mask amount of the trapezoidal distortion and is set in the division pulse generation circuit 12, so that the division pulse (b) corresponding to the division number is obtained. The mask amount n is obtained from the mask amount counter 13 by counting the divided pulses (b). The mask amount changes to 1, 2, 3, ... N and the number of screen divisions becomes 1 / n + 1.

Further, as shown in FIG. 6, the horizontal blanking start position is a comparison output Hst of a value obtained by adding the normal start position data Ht and the mask amount n from the microcomputer interface 11 and the output of the horizontal counter 14. From the HBLK start position generation circuit 15.

Next, at the end position, Hst obtained from the HBLK start position generating circuit 15 and D-2n obtained by subtracting left and right n from the display width D corresponding to the display pixel of the liquid crystal are calculated by the HBLK end position generating circuit 16. Perform and get Hed. The Hst and Hed can be input to the flip-flop 17 to obtain the trapezoidal distortion mask HBLK signal.

HBL obtained by the flip-flop 17
By supplying the K signal to a conventional blanking circuit, an inverted trapezoidal masked image for canceling the trapezoidal distortion projected on the screen as shown in FIG. 5 is displayed on the liquid crystal panel and the image is displayed on the screen. To be done.

As described above, the screen is divided vertically according to the amount of the trapezoidal distortion, the horizontal blanking amount is changed for each divided screen, and the trapezoidal display of the reverse correction is apparently displayed on the liquid crystal panel. Trapezoidal distortion correction can be performed.

[0014]

However, in the above-mentioned conventional structure in which the mask amount is limited and the number of bits of the mask amount counter is reduced, the divided pulse is further input when the counter value becomes maximum. Then, the maximum value changes to the minimum value, and the keystone correction becomes discontinuous.

An object of the present invention is to solve the above-mentioned conventional problems, and to prevent the maximum value from changing to the minimum value when further divided pulses are input when the counter value becomes maximum.

[0016]

In view of the above problems, the present invention detects the maximum value of the mask amount counter 13 and controls the counter input so that the mask amount counter does not operate from the maximum value to the minimum value. Have a configuration.

[0017]

With this configuration, it is possible to prevent the mask signal by the horizontal blanking pulse for correcting the trapezoidal distortion from becoming discontinuous.

[0018]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 13 has the same function as that of the conventional example. Reference numeral 21 is a maximum value detection circuit for detecting the maximum value of the mask amount counter 13, and 22 is the divided pulse generation circuit 1 of FIG.
This is a gate circuit for controlling the supply of the divided pulse from 2 to the mask amount counter 13.

The operation of the liquid crystal display device configured as described above will be described. The mask amount counter in the embodiment has 5 bits depending on the number of pixels of the liquid crystal panel and the mask amount. When the number of horizontal pixels is 480 dots, the maximum value is 63 in the case of 5 bits, which is n, and the trapezoidal distortion is 63 * 2/480, which is about 26%. It is considered that there is no problem with the mask amount.

The mask amount counter 13 counts the divided pulses and the count value n increases. Normally, it is a 5-bit counter, so it is incremented up to 63. At this time, the maximum value detection circuit 21 becomes active and the divided pulse control circuit 22
Is closed, the divided pulse is not supplied, the mask amount counter cannot count, and the count value 63 does not overflow and does not become 0. .

(Embodiment 2) With respect to the installation of the liquid crystal projector, not only the ceiling suspension but also the floor placement is required. In this case, the mask amount counter needs a down counter operation, and it is necessary to set the mask amount n in advance.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 13a is an up / down counter that counts up the divided pulses from the divided pulse generation circuit 12 and counts down from the masked amount n set by the microcomputer interface, and 13b indicates up / down counting. This is an up / down designating circuit.

Reference numerals 21 and 22 are the same as those in the first embodiment,
Reference numeral 23 is a minimum value detection circuit for detecting the minimum value, and 24 is an output O of the maximum value detection circuit 21 and the minimum value detection circuit 22.
It is an R circuit.

When the switching circuit 13b counts down, the switching signal becomes 0 and the minimum value detection circuit 2
When 3 becomes active and the mask amount counter 13a has the minimum value (0), the output becomes 0, 0 is added to the gate circuit 24 via the OR circuit 23, the gate circuit 24 is closed, and the mask amount counter 13a is closed. The clock is not supplied and the countdown cannot be done.

[0026]

As described above, according to the present invention, the mask value for the trapezoidal distortion correction is controlled by controlling the count value of the mask amount counter 13a so as not to go from the maximum value to the minimum value and from the minimum value to the maximum value. It is possible to prevent discontinuity of a certain horizontal blanking signal.

[Brief description of drawings]

FIG. 1 is a block diagram of a mask amount counter according to a first embodiment.

FIG. 2 is a block diagram of a mask amount counter according to a second embodiment.

FIG. 3 is an explanatory diagram of trapezoidal distortion in a liquid crystal projector.

FIG. 4 is a block diagram of a conventional HBLK generation circuit.

FIG. 5 is an explanatory diagram of a conventional HBLK generation circuit.

FIG. 6 is a timing waveform diagram of a conventional HBLK generation circuit.

[Explanation of symbols]

 11 Microcomputer Interface 12 Divided Pulse Generation Circuit 13 Mask Amount Counter 13a Mask Amount Counter 13b Up / Down Switching Circuit 14 Horizontal Counter 15 HBLK Start Position Generation Circuit 16 HBLK End Position Generation Circuit 17 Flip Flop 21 Maximum Value Detection Circuit 22 Gate Circuit 23 Minimum value detection circuit

Claims (2)

[Claims] 1. A microcomputer interface means for outputting data from a microcomputer to each control means, a division pulse generating means for dividing a vertical direction of a screen according to a mask amount from the microcomputer interface means, and the division pulse. A mask amount generating means for counting the divided pulses from the generating means and outputting a mask amount n according to the number of divisions, a horizontal position generating means for indicating a horizontal position of the image, and a blanking start by the microcomputer interface means. Mask start position generating means for calculating the position data and the mask amount n from the mask amount generating means and determining the mask start position from the output from the horizontal position generating means; and display width data from the microcomputer interface means. The mask amount n from the mask amount generating means is calculated and the mask is ended by the output from the horizontal position generating means. The mask signal is provided with mask end position generating means for determining a position, and mask signal generating means for receiving an output from the mask start position generating means and an output from the mask end position generating means to generate a mask signal. The mask signal from the generating means is used as a blanking signal to blank the video signal to form an inverted trapezoidal shape on the panel so that the image does not protrude from the screen, and the mask amount generating means counts the divided pulses. In this case, by providing a means for detecting the maximum value, and a control means for controlling the input of the divided pulse to the mask amount generating means by the output of the maximum value detecting means, the output of the mask amount generating means outputs the divided pulse. A liquid crystal projector characterized in that it does not overflow when counting. 2. A mask amount generating means having an up / down function capable of counting up the divided pulses from the divided pulse generating means, setting a mask amount n in advance from the microcomputer interface means, and counting down from the value. By providing up-down switching means for designating counting up or counting down, a vertical inversion function is provided so that the installation condition can be applied to either the ceiling or the floor, and at the time of counting the divided pulses in the mask amount generating means. By providing means for detecting the minimum value and control means for controlling the input of the divided pulse to the mask amount generation means by the output of the minimum value detection means, the output of the mask amount generation means counts the divided pulses. 2. The liquid crystal project according to claim 1, wherein underflow is prevented from occurring when the liquid crystal project is performed. Ta.