JPH06164966A - Vertical gate correcting device - Google Patents

Abstract

PURPOSE:To obtain the video of a high picture quality even in the LCD type projector of a large screen by correcting the distortion in a vertical direction of the video projected on a screen. CONSTITUTION:A digital video signal is weighted average-computed at respective two lines in a vertical direction, a writing control circuit 5 writes the digital video signal in a frame memory 4 at every other one line, and reduces the video in the vertical direction into 1/2. A first reading control circuit 6 enlarges the video reduced into 1/2 by a magnification corresponding to the height of the display video expanding by the inclination of a screen against an optical axis with the overlapped reading of the digital video signal in the frame memory 4. Then, a second reading control circuit 7 releases the overlapped reading of the first reading control circuit 6, and corrects the distortion in the vertical direction generated due to a projecting distance difference on the screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical tilt correction device for correcting vertical image distortion that occurs in an image on a screen.

[0002]

2. Description of the Related Art It is desirable to install a screen and a projector in a projection type projector in parallel with a wall and at the level of the eyes of a viewer, and also to install the projector on the central axis of the screen. When the central axis and the optical axis of the projector are aligned, the image on the screen does not flicker. However, in practice, even when the screen is installed parallel to the wall and at the eye level of the viewer, the projector is generally placed directly on the floor or hung on the ceiling. At this time, if the screen size becomes large, the height of the central axis will be several meters away from the floor or ceiling, so it will be difficult to place the projector on the central axis of the screen, and Occur. The larger the screen size, the more likely it is that the tilt will occur, and the higher the image quality becomes, the more noticeable it becomes.

The tilt can be divided into a horizontal distortion and a vertical distortion. Since horizontal distortion becomes trapezoidal distortion and is very noticeable visually, some distortion correction methods have already been implemented, but vertical distortion is visually notable when displaying characters and simple tables. Since there is no such correction, it has not been implemented until now.

[0004]

However, recently, in order to display precise drawings, high-quality CG, works of art, etc., there is an increasing demand for keeping the roundness accurate. Vertical tilt correction is indispensable to satisfy this requirement, but vertical tilt correction compatible with LCD projectors has not been implemented.

The present invention has been made to solve such a problem, and by correcting the vertical distortion of the image projected on the screen, a high image quality can be obtained even in a large-screen LCD projector. An object is to provide a vertical tilt correction device capable of obtaining an image.

[0006]

A vertical tilt correction apparatus according to the present invention is an apparatus for correcting vertical distortion of an image projected on a screen, and is an A / D conversion circuit for converting an analog image signal into a digital image signal. And a vertical filter circuit for performing a weighted average calculation of digital video signals for every two lines in the vertical direction, a frame memory for accumulating a digital video signal of one frame, and a control for writing the digital video signal of each line to the frame memory. And a write control circuit for reducing the image in the vertical direction by 1/2 and controlling the superimposition of a digital image signal of a predetermined line from the frame memory to reduce the image in the vertical direction by 1/2 to the screen for the optical axis. A first readout control circuit for enlarging a display image at a magnification corresponding to an extension rate in the height direction of a display image, and a first readout A second read-out control circuit that corrects vertical distortion caused by a difference in projection distance to the screen by eliminating over-reading of the control circuit, and D / that converts the digital video signal after vertical tilt correction into an analog video signal. And an A conversion circuit.

[0007]

The vertical tilt correction apparatus according to the present invention performs a weighted average calculation of digital video signals every two lines in the vertical direction, and writes the digital video signals into the frame memory every other line to halve the video in the vertical direction. A vertically reduced image that has been reduced by 1/2 is read by superimposing a digital image signal on a specified line from the frame memory at a magnification that corresponds to the expansion rate in the height direction of the displayed image due to the tilt of the screen with respect to the optical axis. Enlargement is performed to eliminate the overlapped reading of the first read control circuit and correct the vertical distortion caused by the difference in the projection distance to the screen.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments. FIG. 1 is a block diagram showing the configuration of a vertical tilt correction apparatus according to the present invention. In the figure, 1 is an analog / digital converter (A / D) for converting an analog video signal into an 8-bit digital video signal, and 2 is a horizontal synchronization signal (H
S) is a horizontal PLL circuit (HPLL) that generates a sampling clock that matches the horizontal resolution of the video signal, and the vertical filter 3 synchronizes with the sampling clock from HPLL2 to eliminate the missing line at 1/2 reduction. For this purpose, the digital video signal from the A / D 1 is weighted and averaged every two lines and output to the frame memory 4. The frame memory 4 is
It has the capacity to store one frame of digital video data so that the video data when the vertically half-reduced video data is expanded to the nearest neighborhood can be stored.

The write control circuit 5 controls the write line address to the frame memory 4 in order to perform 1/2 reduction. That is, the write line address is updated once every two lines to reduce the size by half. The first read control circuit 6 divides the lines from the frame memory 4 into two lines according to the enlargement ratio.
Read it once and enlarge the nearest 1 to 2 times the size of the reduced image. For example, when controlling reading twice with a maximum of 16 lines, 40 ways (16/15, 15/14, 14/13,
…, 13/7, 15/8, 16/8) can be set, but
6 bits are sufficient for setting the enlargement ratio from outside the device.

The second read control circuit 7 divides the vertical direction into a plurality of blocks to determine the thinning cycle for each block in order to correct the expansion of the image caused by the difference in the projection distances above and below the screen. A digital / analog converter (D / A) 8 converts the 8-bit digital video signal after tilt correction into an analog video signal, and an LCD type projector (LCD panel, LCD drive circuit, lamp, various lenses, etc.) LCD) 9 is output.

FIG. 2 is a schematic diagram for explaining vertical tilt distortion. The vertical tilting distortion is a distortion (1) that occurs because the height of the projection area of the screen (screen height) is relatively extended due to the central axis of the screen tilting with respect to the optical axis. Two types of distortion are included, which is distortion (2) caused by the difference in the projection distance to the top and bottom of the screen.

First, the distortion (1) will be described with reference to FIG. Assuming that the projection light from the light source is parallel light,
The screen height is defined by the following formula regardless of the projection distance. H2 = H1 / cosδ (1) However, H1: Screen height when the screen center axis and optical axis match H2: Screen height when the screen is tilted by δ degrees δ: Screen tilt angle

Next, the distortion (2) will be described with reference to FIG. The display image becomes small (low) when the projection distance is short, and becomes large (high) when the projection distance is long. The image size (height) is proportional to the projection distance, as shown in Eqs. (2) and (3). Ha ＝ L1 ・ h / f… (2) Hb ＝ L2 ・ h / f… (3) However, Ha: The height of the screen display image at the projection distance L1 when the center axis of the screen and the optical axis coincide. Hb: Height of the screen display image at the projection distance L2 when the center axis of the screen and the optical axis are aligned h: Panel size f: Lens focal length L1, L2: Projection distance

When the projection distance L2 is twice L1, Hb is Ha
It is twice as high as Therefore, the height of the display image of the final line of the image displayed on the tilted screen is twice the height of the display image of the first line. In the horizontal correction, the video signals of the other lines are reduced based on the first line having the shortest projection distance to perform the correction. Therefore, in the vertical correction, the video signals of the other lines are also reduced based on the shortest line. It will be corrected.

FIG. 3 is a block diagram showing a detailed configuration of the write control circuit 5, the first and second read control circuits 6 and 7 for the frame memory 4. The write control circuit 5 and the first read control circuit 6 correct the distortion (1), and the second read control circuit 7 corrects the distortion (2). The write control circuit 5 divides the period of the horizontal synchronizing signal (HS), which is the clock of the write control line counter 53, into 1/2,
The 1/2 divider circuit 51 that is reset by the vertical sync signal (VS) and the write control line counter 53 that is switched to the B side and updated once every two times, while switched to the A side by the correction stop signal The multiplexer (MPX) 53 that does not perform the reduction operation when the write operation is performed, and the write control line counter that updates the write line address in synchronization with the clock given through the MPX 52 and outputs the updated write line address to the frame memory 4.
It consists of 53 and.

The first read control circuit 6 has a 6-bit "distortion" given from the outside of the device in accordance with 40 kinds of enlargement ratios.
(1) Wait timing table 61 that generates a signal for overwriting timing corresponding to the "correction amount switching signal" and the same read by thinning out the horizontal synchronization signal (HS) that is a clock according to the signal generated by the wait timing table 61 It is composed of a read control line counter 62 which successively outputs line addresses and controls double reading of the same line.

The second read control circuit 7 determines the number of block divisions in the vertical direction of the video display line according to the "distortion (2) correction amount switching signal" from the outside of the device, and the first read control circuit 6 According to the vertical block number determination circuit 71 that determines the cancellation cycle of the double reading timing by the
The first read control circuit 6 comprises a read timing control line counter 62 and a wait timing cancel signal generation circuit 72 for generating a signal for canceling double reading.

First, the operation of correcting the distortion (1) will be described. It should be noted that, in the present embodiment, a case where a video source having 1000 display lines is processed will be described. Assuming that the projection light from the light source is parallel light, when the screen is tilted by 45 degrees, the screen height is expanded by 1.4142 times.
Therefore, the write control circuit 5 reduces it by 1/2 in the vertical direction.
If the digital video signal of 500 lines (0.7071 times) is expanded to 1.4000 times (7/5) by the first read control circuit 6 in the subsequent stage and becomes 700 lines (about 1.0 times), correction without line loss can do. When the screen is tilted by 30 degrees, the screen height expands 1.1547 times, so it is reduced by half to 500 (0.5774 times) digital video signals in the first read control circuit 6 in the subsequent stage. 1.7143 times (12 /
It should be expanded to 7) to make 857 (about 1.0 times).

Since the weight timing table 61 is 7/5 times when the tilt angle is 45 degrees, the weight is generated at a rate of 2 lines to 5 lines, and when the tilt angle is 30 degrees, it is 12/7 times, so it is 5 times to 7 lines. Weight is generated at the rate of lines. In addition, although the case where the screen inclination angle is 45 degrees and 30 degrees has been described in the present embodiment, the screen inclination angle may be considered to be 30 degrees or less in consideration of actual installation conditions.

Next, the operation of correcting the distortion (2) will be described. Figure 2
As shown in (b), the ratio of the projection distances L1 and L2 is
When the screen tilt angle is 45 degrees, L1: L2 = 1: 2,
When the inclination angle is 30 degrees, L1: L2 = 1: 1.5. It can be considered that the actual installation condition is that the screen inclination angle is 30 degrees or less. Therefore, in this embodiment, the case where the screen is inclined so that the relationship between the projection distances L1 and L2 is L1: L2 = 1: 1.5 will be described. The correction range is L2 / L1 is in the range of 1 to 1.5, but it is appropriate to adjust the control in increments of 0.05 in about 10 steps from the balance of circuit scale and control accuracy. That is, the vertical block number determination circuit 71 is provided from the outside of the device.
4 for the setting of the “distortion (2) correction amount switching signal” given to
A bit is enough.

The vertical block number determination circuit 71 determines the number of vertical block divisions according to the following equation. Where X is the number of divided blocks and N is the number of lines in each block. X = 1000 / N (4) X 0.75 / N = 1 (5) From formulas (4) and (5), N = 27.39 and X = 36.51. Here, in order to rationalize the wait timing cancel signal generation circuit 72, N and X are rounded to be integers. At that time, by rounding N to an integer less than 27.35, at least one line is thinned out in the first block. Rounding results in N = 25 and X = 40.

The wait timing cancel signal generation circuit 72 operates as follows according to the determination of N and X. The first block is thinned out from 25 lines. For the 40th block (final block), the projection distance of the final line is 1.5 times that of the first line, which is the shortest distance.
Lines will be thinned out. The thinning line number for each block is 40 divided by the line thinning number 8.3 in the final block, which is 4.8. Therefore, the thinning line number is increased by 1 for each 4.8 blocks. However, the line omission does not occur because the wait timing of the first read control circuit 6, that is, the double reading is eliminated to obtain the reduction effect, without actually thinning out the line.

In actual correction, in addition to the combination of switching the correction amount for distortion (1) and switching the correction amount for distortion (2), the viewpoint position is also an important factor, so circle patterns, crosshatch, etc. It is better to determine the correction amount while displaying the test pattern of 1) and observing the circularity of the entire image. The operation procedure is as follows: First, measure the screen tilt angle, calculate the distortion (1) on the desk, and then use that value to calculate the distortion.
(2) It is effective to temporarily set the correction amount and then perform visual adjustment using a test pattern.

[0024]

As described above, the vertical tilt correction apparatus according to the present invention corrects the tilt distortion in the vertical direction without losing the line information of the input video signal, and provides accurate drawings and high quality. It enables the faithful display of CG, works of art, etc., and has the excellent effect that high-quality images can be obtained even on large-screen LCD projectors.

[Brief description of drawings]

FIG. 1 is a block diagram of a vertical tilt correction apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating vertical tilt.

FIG. 3 is a detailed block diagram of a main part of a vertical tilt correction device according to the present invention.

[Explanation of symbols]

 3 Vertical Filter 4 Frame Memory 5 Write Control Circuit 6 First Read Control Circuit 7 Second Read Control Circuit

Claims (1)

[Claims] 1. An apparatus for correcting vertical distortion of an image projected on a screen, and an A / D conversion circuit for converting an analog video signal into a digital video signal, and a vertical direction 2
Vertical filter circuit that performs weighted average calculation of digital video signals line by line, frame memory that stores one frame of digital video signal, and control of writing digital video signal of each line to frame memory And a write control circuit for reducing by 1/2, and controlling overwriting of a digital video signal of a predetermined line from the frame memory, so that the 1/2 reduced vertical image is displayed as a display image by tilting the screen with respect to the optical axis. The first read control circuit that enlarges at a magnification according to the expansion rate in the height direction and the overwriting of the first read control circuit are canceled to correct vertical distortion caused by the difference in projection distance to the screen. A second read control circuit and a D / A converter for converting a digital video signal after vertical tilt correction into an analog video signal. Vertical perspective correction apparatus characterized by comprising a circuit.