JPH11331737A - Distortion correcting circuit for liquid crystal projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce discontinuous points, where a horizontal reduction rate is switched and to correct vertical distortion by allowing a trapezoid distortion correction part to insert virtual black-level data in both ends of input pixels of each line and weighted average data at a start point of an image and the virtual black-level data and a vertical distortion correction part to weight and average the data of each display line. SOLUTION: An example is shown in which video having a 4-dot upper side and an 8-dot lower side is obtained by converting video of 8 dots by 8 lines. Before trapezoid correcting conversion, one black-level dot each is added to both the ends of the video to obtain video consisting of 10 dots by 8 lines. With respect to the lines 0, 1, 2, and 3 interpolative reduction operation is performed from 10 dots to 6 dots and as for the lines 4, 5, and 6 interpolative reduction operation from 10 dots to 8 dots. Output video is obtained by adding differences from ideal trapezoid corrected components to the corrected components. The positions of the lines of the output video to the lines of the input video are obtained by adding the width between lines normally, each time a one-line display is finished and repeating it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distortion correction circuit for a liquid crystal projector, and more particularly, to a diagonal line that is smooth by reducing a discontinuity at a switching point of a horizontal reduction ratio in an image projected by the liquid crystal projector. In addition, the present invention relates to a distortion correction circuit for a liquid crystal projector that corrects vertical image distortion.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal projector using a lattice device such as a liquid crystal, when launch projection is performed beyond an optical shift angle, there is a problem that an image is distorted in a trapezoidal shape in the horizontal direction. In order to solve this problem, a method of correcting trapezoidal distortion by processing an image in an inverted trapezoid on a liquid crystal panel is known.

FIG. 4 is a diagram showing a conventional trapezoidal distortion correction method. The figure consists of an image of 8 dots x 8 lines. To convert this image to obtain an image with the upper side being 4 dots and the lower side being 8 dots, line0,1,2 are input dot
Discard 1,3,5,6 and output as 4 dots, line3,4,5,6
Will discard the input dots 3 and 6 and output it as 6 dots.
Performs a process of outputting the input 8 dots as they are.

In this processing, the information of the discarded dots is not reflected in the output video, and therefore, a smooth inverted trapezoidal image cannot be obtained from the generated trapezoidal output video.

For this reason, the present inventor has disclosed in Japanese Patent Application No. 9-128.
No. 319 proposes a method of leaving information of an input video in an output video by calculation. FIG. 5 is a diagram showing a method for correcting trapezoidal distortion using this method. This method uses li
ne0,1,2 outputs 8 dots by interpolating and reducing to 4 dots, line3,4,5,6 outputs 8 dots by interpolating and reducing 8 dots to 4 dots, and line7 denotes the input 8 dots Is output as it is.

Here, the interpolation reduction is described in Japanese Patent Application No. 9-128.
This is performed using the arithmetic method and linear interpolation proposed in No. 319. Here, dot1 of line0 of the output image is located between dot2 and dot3 of the input image according to the above-described calculation method, and is 1/3 from dot2.
It can be seen that the dots are apart. The luminance is represented by (dot2 + (dot3-dot2) × 1) / 3 (Equation 1) using linear interpolation.

Further, it can be seen that dot 1 of line 4 of the output image is located between dot 1 and dot 2 of the input image and is separated from dot 1 by 2/5 dot, and the luminance is obtained by using linear interpolation (dot1 + (dot2 −dot1) × 2) / 5 (Expression 2) In this method, a large amount of input video information remains in the output video due to the calculation. Therefore, a more natural image can be obtained as compared with the image obtained from FIG.

[0008]

However, according to the trapezoidal distortion correction method shown in FIG. 5, for example, line2 and li
Since the reduction ratio changes suddenly between ne3, there is a problem that it looks like there is a line, and the image edge becomes stepped. In addition, there is a problem that vertical distortion in which the upper side of the image extends in addition to the horizontal direction appears.

Accordingly, an object of the present invention is to provide a liquid crystal projector capable of reducing the discontinuity at the switching of the reduction ratio in the horizontal direction, smoothly expressing oblique lines, and correcting vertical image distortion. To provide a distortion correction circuit.

[0010]

According to the present invention, there is provided a liquid crystal projector distortion correction circuit for correcting horizontal and vertical distortion of a liquid crystal projector. An A / D converter for converting image data, a frame buffer for storing image information of the digital image data converted by the A / D converter, and a vertical resolution conversion of the digital image data, Vertical distortion corrector that corrects horizontal distortion, trapezoidal distortion corrector that performs horizontal resolution conversion of digital image data, and corrects horizontal trapezoidal distortion of the image, and vertical distortion corrector and trapezoidal distortion corrector. Converts digital image data with distortion corrected to analog image data and outputs it to a display unit such as a display A trapezoidal distortion correction unit that inserts virtual black level data at both ends of input pixels of each line, and weights the data of the image start point and the virtual black level data. The averaging is performed, and the vertical distortion corrector performs a weighted average for each display line, thereby providing a distortion correction circuit of the liquid crystal projector.

In the above configuration, the trapezoidal distortion correction section includes:
It is desirable to determine the number of dots of the input pixel and the output pixel of each line by calculation and calculate the distance from the dot position of the output pixel based on the dot position of the input pixel, and from the remainder obtained by the calculation. It is desirable to calculate the distance between the dot position of the input pixel and the dot position of the input pixel based on the reference when performing keystone correction. In this case, it is desirable that the remainder obtained by the calculation is proportional to the distance between the dot position of the input pixel and the reference dot position of the input pixel when the keystone correction is performed.

Further, the trapezoidal distortion correction section includes a distance between a reference dot position of the input pixel and a dot position of the output pixel, and a relation between a dot position of the input pixel and a reference dot of the input pixel when performing trapezoidal correction. It is desirable to add the position distance and perform linear interpolation.

Further, it is desirable that the virtual black level data be thinned out when displayed on the display unit.

Further, in the above configuration, the vertical distortion correction unit determines the width between lines before correction as a, the total number of lines as wy, the line after display as y, and the degree of deformation as t. It is desirable to obtain the width between the lines for each display line by aa × ((wy−2) −y × 2) / (wy−2) × t.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described in detail.

FIG. 1 is a diagram showing a configuration of a distortion correction circuit of a liquid crystal projector according to an embodiment of the present invention. This distortion correction circuit includes an A / D converter 1 for converting input analog image data into digital image data, and an A / D converter.
A frame buffer 2 for storing image information converted from analog image data into digital image data by the conversion unit 1, and a vertical resolution conversion of the digital image data stored in the frame buffer 2 is performed, thereby distorting the image in the vertical direction. And a trapezoidal distortion corrector 4 that performs horizontal resolution conversion of the digital image data and corrects horizontal trapezoidal distortion of the image.
And converting the digital image data, the distortion of which has been corrected by the vertical distortion correction unit 3 and the trapezoidal distortion correction unit 4, into analog image data, and a display unit such as a display (not shown).
And a D / A conversion unit 5 for outputting the data.

FIG. 2 is a diagram for explaining the operation of distortion correction by the distortion correction circuit shown in FIG. Here, an example is shown in which an image of 8 dots × 8 lines is converted to obtain an image of 4 dots on the upper side and 8 dots on the lower side.

First, the operation principle of the trapezoidal correction conversion will be described. Before the keystone correction conversion, one black level dot is added to each end of an 8 dot × 8 line image, and
It is assumed that the image is 0 dots × 8 lines. The dots of this black level are necessary to generate an output image from black to the beginning dot of the actual image or from the end dot of the actual image to black when performing ideal keystone correction. Things. Lines 0, 1, 2, and 3 perform an operation of interpolating and reducing 10 dots to 6 dots. Lines 4, 5, and 6 perform an operation of interpolating and reducing 10 dots to 8 dots. An output video is obtained by adding the difference from the ideal trapezoidal correction to the correction.

Here, for easy understanding, li in FIG.
The description will focus on ne6. In the figure, dashed lines indicate dot positions of the input video when performing interpolation reduction, and a0 to a7
Indicates the distance from the dot of the output image to the one-dot chain line at this time. Also, the two-dot chain line indicates the dot position of the input image when ideal trapezoidal correction is performed, and the distance from the one-dot chain line to the two-dot chain line is indicated by b0 to b7. Then, by adding the distance from the dot of the output video to the one-dot chain line and the distance from the one-dot chain line to the two-dot chain line, and setting it as a0 + b0-a7 + b7, the input video when ideal trapezoidal correction is performed from the dots of the output video The distance to the dot can be obtained, and an output image can be generated. The above is the operation principle of the trapezoidal correction conversion in the present invention.

Next, the operation of the horizontal keystone correction for the actual keystone correction will be described. In the actual calculation, a0-a7 and b0-
b7 needs to be understood as a numerical value. Therefore, first, the relationship between the line and the number of output dots will be considered.

Since line0 is a 6-dot output and line7 is a 10-dot output, the output dot number of lineL is (6/2 + int (2 × L / 7)) × 2 · int () Truncation function: (Equation 3) According to equation (3), the number of output dots of line0 is (3 + int (2 × 0/7)) × 2 = 6 The number of output dots of line1 is (3 + int (2 × 1/7)) × 2 = 6 The output dot number of line2 is (3 + int (2 × 2/7)) × 2 = 6 The output dot number of line3 is (3 + int (2 × 3/7)) × 2 = 6 The output dot number of line4 is (3 + int (2 × 4/7)) × 2 = 8 The output dot number of line5 is (3 + int (2 × 5/7)) × 2 = 8 The output dot number of line6 is (3 + int (2 × 6/7)) × 2 = 8 The number of output dots for line7 is (3 + int (2 × 7/7)) × 2 = 10, and the number of input dots and the number of output dots for each line are determined.

From the calculation method proposed in Japanese Patent Application No. 9-128319, it is possible to determine which input dot is used as a reference and how far away it is, that is, the distance from the output dot to the one-dot chain line. In line6, the output dot0 is the input
0/7 dots away from dot0, output dot1 is input dot1
The output dot2 is 4/7 dots away from the input dot2, the output dot3 is 6/7 dots away from the input dot3, and the output dot4 is 1/0 away from the input dot5.
The output dot5 is 3/7 dots away from the input dot6, the output dot6 is 5/7 dots away from the input dot7, and the output dot7 is 0/7 dots away from the input dot9. .

Further, the remainder obtained by the operation of (2 × L / 7) in the equation (3) for calculating the number of output dots is proportional to the distance from the one-dot chain line to the two-dot chain line at the input dot0. Is represented by ((2 × L) mod7) / 7 ··· mod is an operator for obtaining a remainder (Equation 4). B0 for each line is b0 = ((2 × 0) mod7) / 7 = 0/7 dots in line0, b0 = ((2 × 1) mod7) / 7 = 2/7 dots in line2, b0 = ((2 × 2) mod7) / 7 = 4/7 dots For line3, b0 = ((2 × 3) mod7) / 7 = 6/7 dots For line4, b0 = ((2 × 4) mod7) / 7 = 1/7 dot line5, b0 = ((2 × 5) mod7) / 7 = 3/7 dot line6, b0 = ((2 × 6) mod7) / 7 = 5/7 dot line7, b0 = ((2 × 7) mod7) / 7 = 0/7 dots.

B0 to b7 are maximum at the right end of the image, 0 at the center, and -b0 at the left end. Depending on the number of dots of the input image and the reference input dot position, b0.times. ((WD-1)- x '× 2) / (WD-1) (Equation 5) WD can be represented by the number of dots of the input image x' can be represented by the reference input dot position.

Considering b0 to b7 by paying attention to line6 in FIG. 2, since WD is 10 dots and b0 is based on input dot0, b0 = 5/7 × (9-0 × 2)
/ 9 = 45/63 dots b1 is based on input dot1, so b1 = 5/7 × (9-1 × 2)
/ 9 = 35/63 dots b2 is based on input dot2, so b2 = 5/7 × (9-2 × 2)
/ 9 = 25/63 dots b3 is based on the input dot3, so b3 = 5/7 × (9-3 × 2)
/ 9 = 15/63 dots b4 is based on input dot4, so b4 = 5/7 × (9-5 × 2)
/ 9 = -5/63 dot b5 is based on input dot5, so b5 = 5/7 × (9-6 × 2)
/ 9 = -15 / 63 dot b6 is based on input dot6, so b6 = 5/7 × (9-7 × 2)
/ 9 = -25 / 63 dot b7 is based on input dot7, so b7 = 5/7 × (9-9 × 2)
/ 9 = -45 / 63 dots.

These processes are performed for all lines. Now, since a0-a7 and b0-b7 are determined, a0 + b0-
a7 + b7 is also determined. By performing linear interpolation or the like using this numerical value, trapezoidal correction of 6 dots on the upper side and 10 dots on the lower side can be performed.

However, since the black level dots are added first, the number of dots at which an image is actually displayed on the uppermost line is 4 dots, and the number of dots at which the image is actually displayed on the lowermost line is 8 dots. Therefore, when displaying on the display, the rightmost dot and the leftmost dot are cut off to display eight horizontal dots. With the above method, the horizontal trapezoidal distortion can be corrected.

As described above, halftone can be obtained by inserting virtual black level data at both ends of an effective pixel and performing weighted averaging of the data at the starting point of the image and the virtual black level data.

As described above, when an image is launched and projected by a liquid crystal projector, a distortion appears in which the upper side of the image extends not only in the horizontal direction but also in the vertical direction. Correcting this is a difficult process because the launch angle of the optical system itself and the zoom ratio of the optical system are related. For this reason, processing is performed in which the upper part of the image is contracted in the vertical direction and the lower part is extended in the vertical direction.

The position of the line of the output image relative to the line of the input image is usually determined by adding the width between the lines and repeating the display each time one line is displayed. Here, the width between lines is defined as aa × ((wy−2) −y × 2)) / (wy−2) × t (Equation 6) for each display line. wy: Total number of lines y: Displayed line t: Degree of deformation Given that, the interval between the lines located on the upper side of the output video is narrowed, and the interval between the lines located on the lower side of the video is expanded by the narrower .

FIGS. 3A and 3B show an example of the distortion correction operation in the vertical direction. (A) shows an example of vertical line spacing when the total number of lines is 6 and no deformation is performed,
(B) shows an example of vertical line spacing when the total number of lines is 6 and the degree of deformation is 50%. As shown in the drawing, it can be seen that the portion narrowed between the 0-1 lines is spread between 4-5 lines, and the portion narrowed between the 1-2 lines is spread between 3-4 lines. By changing the degree of deformation, you can adjust how much the lines are narrowed or expanded, and according to the amount of distortion in the actual video, adjust the value to cancel the vertical distortion .

[0032]

As described above, according to the distortion correction circuit of the liquid crystal projector of the present invention, the A / D converter for converting the input analog image data into the digital image data and the A / D converter. A frame buffer for storing image information of the obtained digital image data, a vertical distortion correction unit for converting the vertical resolution of the digital image data to correct the vertical distortion of the image, and a horizontal resolution conversion of the digital image data A trapezoidal distortion corrector that corrects the horizontal trapezoidal distortion of the image, and converts the digital image data whose distortion has been corrected by the vertical distortion corrector and the trapezoidal distortion corrector into analog image data to a display unit such as a display. And a D / A converter for outputting, wherein the trapezoidal distortion corrector has virtual black levels at both ends of the input pixel of each line. Data, the weighted average of the data at the start point of the image and the virtual black level data, and the vertical distortion correction unit performs weighted averaging for each display line. It is possible to reduce the discontinuity of the eyes and smoothly express oblique lines, and correct vertical image distortion.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a distortion correction circuit of a liquid crystal projector according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a horizontal trapezoidal distortion correction operation.

FIG. 3 is a diagram illustrating a distortion correction operation in the vertical direction.

FIG. 4 is a diagram illustrating a conventional trapezoidal distortion correction operation.

FIG. 5 is a diagram illustrating a conventional trapezoidal distortion correction operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D conversion part 2 Frame buffer 3 Vertical distortion correction part 4 Trapezoid distortion correction part 5 D / A conversion part

Claims (7)

[Claims] 1. An A / D converter for converting input analog image data into digital image data in a distortion correction circuit of a liquid crystal projector for correcting horizontal and vertical distortions of the liquid crystal projector; A frame buffer that stores image information of the digital image data converted by the conversion unit, a trapezoidal distortion correction unit that performs horizontal resolution conversion of the digital image data, and corrects the horizontal keystone distortion of an image. A vertical distortion correction unit that performs vertical resolution conversion of the digital image data and corrects the vertical distortion of the image; and the digital whose distortion has been corrected by the vertical distortion correction unit and the trapezoidal distortion correction unit. D / A conversion for converting image data into analog image data and outputting it to a display unit such as a display The trapezoidal distortion correction unit, inserts virtual black level data at both ends of the effective pixel, performs a weighted average of the data of the start point of the image and the virtual black level data, the vertical A distortion correction circuit for a liquid crystal projector, wherein the distortion correction unit performs weighted averaging for each display line. 2. The method according to claim 1, wherein the trapezoidal distortion correction unit determines the number of dots of each input pixel and each output pixel of each line by calculation, and determines a distance from the dot position of the output pixel with respect to the dot position of the input pixel. The distortion correction circuit according to claim 1, wherein the distortion is calculated. 3. The trapezoidal distortion correction section calculates a distance between a dot position of an input pixel and a reference dot position of the input pixel when performing trapezoidal correction from a remainder obtained by the calculation. A distortion correction circuit for a liquid crystal projector according to claim 1. 4. The method according to claim 3, wherein a remainder obtained by the calculation is proportional to a distance between a dot position of the input pixel and a dot position of the input pixel based on the reference when performing trapezoidal correction. Correction circuit for liquid crystal projector. 5. The trapezoidal distortion correction unit includes: a distance between a dot position of an input pixel as a reference and a dot position of an output pixel; and a dot position of an input pixel and the reference when performing the trapezoidal correction. The linear interpolation is performed by adding the distances of the dot positions of the input pixels.
5. The distortion correction circuit for a liquid crystal projector according to any one of items 1 to 4. 6. The distortion correction circuit according to claim 1, wherein the virtual black level data is thinned out when the virtual black level data is displayed on the display unit. 7. The vertical distortion correction unit sets a width between lines before correction as a, a total number of lines as wy, a line after display as y, and a degree of deformation as t, between lines after correction. 2. The distortion correction of the liquid crystal projector according to claim 1, wherein the width of (a) is obtained by aa * ((wy-2) -y * 2) / (wy-2) * t for each of the display lines. circuit.