JP4186640B2 - Image processing apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing technique, and more particularly to a technique for adjusting an interpolated image.
[0002]
[Prior art]
In an image display device, it is often necessary to adjust an image in order to make an input original image suitable for an image display unit. For example, when the resolution of the original image is larger than the resolution that can be displayed by the image display unit, it is necessary to reduce the original image. Specifically, when an input SXGA original image is displayed on an image display unit capable of displaying an XGA image, the original image needs to be reduced.
[0003]
When the original image is reduced, the thinning process is usually performed on the original image. Further, when thinning processing is performed, interpolation processing is often performed. As such thinning-out processing, there is a method of selectively thinning out pixel groups (hereinafter also referred to as “line images”) arranged in the vertical or horizontal direction in an image. In addition, as an interpolation process, there is a method of interpolating a line image adjacent to a line image to be thinned. By such an interpolation process, it is possible to leave information on pixels to be thinned out in the image after the thinning process. For example, when a single white line image exists in a black image and the line image is a thinning target, a gray line image is generated in the black image by interpolation processing. It is possible to prevent the line information from being lost.
[0004]
Examples of conventional image processing techniques include Patent Documents 1 and 2.
[0005]
[Patent Document 1]
JP 09-107468 A
[Patent Document 2]
Japanese Patent Laid-Open No. 06-168326
[0006]
[Problems to be solved by the invention]
However, there is a problem that the image quality of the image subjected to the thinning / interpolation processing at the selective position as described above is deteriorated. That is, in the above example, the white line image in the black image is reproduced as a gray line image in the black image, and the information of the original image cannot be reproduced very accurately.
[0007]
The present invention has been made to solve the above-described problems in the prior art, and an object of the present invention is to provide a technique capable of reducing deterioration in image quality due to interpolation processing performed at the time of thinning processing.
[0008]
[Means for solving the problems and their functions and effects]
In order to solve at least a part of the problems described above, a first device of the present invention is an image processing device,
An image adjustment unit that adjusts the input original image
The image adjustment unit
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and An interpolation processing unit that generates an interpolated image by performing an interpolation process on pixels around the pixel that has become,
Of the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has changed by the interpolation processing and the pixel value of another pixel whose pixel value has not changed is small. And so that the distribution of pixel values of the interpolated image is substantially similar to the distribution of pixel values of the original image, A filter processing unit that performs a filtering process that substantially applies a spatial low-pass filter and a spatial high-pass filter to the interpolated image in this order, and a first image filter processing unit that performs a filtering process using the spatial low-pass filter And a second image filter processing unit that performs a filtering process using the spatial high-pass filter, and the filter processing unit
A contrast compensation unit for compensating for the contrast of the image processed by the filter processing unit;
With
The processing contents of the first and second image filter processing units are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation unit is determined by selecting from a plurality of types of contrast compensation values,
The selected first filter coefficient, the second filter coefficient, and the contrast compensation value are associated with each other in advance.
[0009]
The first device includes a filter processing unit. Therefore, the distribution of the pixel values of the interpolation image generated by the selective thinning / interpolation process can be adjusted to a similar distribution close to the distribution of the pixel values of the original image. As a result, it is possible to reduce deterioration of the image quality of the interpolated image.
[0010]
In the first device, since the first filter coefficient, the second filter coefficient, and the contrast compensation value are associated with each other, the processing contents by the first and second image filters of the filter processing unit, and Thus, the processing content of the contrast compensation unit can be easily determined.
[0011]
A second apparatus of the present invention is an image processing apparatus,
An image adjustment unit that adjusts the input original image
The image adjustment unit
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and An interpolation processing unit that generates an interpolated image by performing an interpolation process on pixels around the pixel that has become,
Of the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has changed by the interpolation processing and the pixel value of another pixel whose pixel value has not changed is small. And so that the distribution of pixel values of the interpolated image is substantially similar to the distribution of pixel values of the original image, A filter processing unit that performs a filtering process that substantially applies a spatial low-pass filter and a spatial high-pass filter to the interpolated image in this order, and a first image filter processing unit that performs a filtering process using the spatial low-pass filter And a second image filter processing unit that performs a filtering process using the spatial high-pass filter, and the filter processing unit
A contrast compensation unit for compensating for the contrast of the image processed by the filter processing unit;
With
The processing contents of the first and second image filter processing units are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation unit is determined by selecting from a plurality of types of contrast compensation values,
The selected second filter coefficient and the contrast compensation value are associated with each other in advance, and the first filter coefficient is selected independently of the second filter coefficient and the contrast compensation value. It is characterized by that.
[0012]
Similar to the first device, the second device includes a filter processing unit. Therefore, as in the first device, it is possible to reduce deterioration of the image quality of the interpolated image.
[0013]
Further, in the second apparatus, since the second filter coefficient and the contrast compensation value are associated with each other, it is possible to easily determine the processing content by the second image filter and the processing content of the contrast compensation unit. It becomes. In addition, since the first filter coefficient can be selected independently, a large number of processes in the filter processing unit and the contrast processing unit can be realized as compared with the first device.
[0014]
In the above apparatus,
You may make it provide the image display part which displays the image adjusted by the said image adjustment part.
[0015]
In the above apparatus,
The image processing device is a projection display device that projects and displays an image,
The interpolation processing unit may perform the thinning process on the original image to correct trapezoidal distortion.
[0016]
When the image processing apparatus is a projection display apparatus, trapezoidal distortion often occurs in an image displayed by projection because of the positional relationship between the projection display apparatus and the projection plane. When correcting trapezoidal distortion, a thinning process is usually required. The image processing apparatus of the present invention can reduce image quality deterioration due to thinning / interpolation processing even when correcting the trapezoidal distortion.
[0017]
A first method of the present invention is an image processing method,
A step of adjusting the input original image,
The original image adjustment step includes
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and A step of generating an interpolated image by performing an interpolation process on the pixels around the resulting pixel;
Of the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has changed by the interpolation processing and the pixel value of another pixel whose pixel value has not changed is small. And so that the distribution of pixel values of the interpolated image is substantially similar to the distribution of pixel values of the original image, A step of executing a filter process for applying a spatial low-pass filter and a spatial high-pass filter in this order to the interpolated image, wherein the filter process is a first image for performing a filter process by the spatial low-pass filter. A process comprising: a filtering process; and a second image filtering process for performing a filtering process using the spatial high-pass filter;
Compensating the contrast of the filtered image;
With
The processing contents of the first and second image filter processes are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation is determined by selecting from a plurality of types of contrast compensation values,
The selected first filter coefficient, the second filter coefficient, and the contrast compensation value are associated with each other in advance.
[0018]
Even when the first method is used, the same operations and effects as when the first device is used are provided.
[0019]
A second method of the present invention is an image processing method,
A step of adjusting the input original image,
The original image adjustment step includes
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and A step of generating an interpolated image by performing an interpolation process on the pixels around the resulting pixel;
Of the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has changed by the interpolation processing and the pixel value of another pixel whose pixel value has not changed is small. And so that the distribution of pixel values of the interpolated image is substantially similar to the distribution of pixel values of the original image, A step of executing a filter process for applying a spatial low-pass filter and a spatial high-pass filter in this order to the interpolated image, wherein the filter process is a first image for performing a filter process by the spatial low-pass filter. A process comprising: a filtering process; and a second image filtering process for performing a filtering process using the spatial high-pass filter;
Compensating the contrast of the filtered image;
With
The processing contents of the first and second image filter processes are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation is determined by selecting from a plurality of types of contrast compensation values,
The selected second filter coefficient and the contrast compensation value are associated with each other in advance, and the first filter coefficient is selected independently of the second filter coefficient and the contrast compensation value. It is characterized by that.
[0020]
Even when the second method is used, the same operations and effects as when the second device is used are provided.
[0021]
The present invention relates to an image display method and apparatus, an image processing method and apparatus, a computer program for realizing the functions of the method or apparatus, a recording medium recording the computer program, and a carrier including the computer program. It can be realized in various forms such as an embodied data signal.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
A. Overall configuration of the device:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is a block diagram showing the overall configuration of an image display apparatus as an embodiment of the present invention. This image display device is a projection display device that projects and displays an image on a screen SC. The image display apparatus includes a computer system including an A / D converter 20, a video decoder 22, a frame memory 24, a video processor 26, a liquid crystal panel drive circuit 30, a liquid crystal panel 32, and a remote control circuit 34. It is. The frame memory 24 and the video processor 26 are integrated as one image processing integrated circuit 60.
[0023]
The image display device also includes an illumination device 50 for illuminating the liquid crystal panel 32, and a projection optical system 52 that projects the image light emitted from the liquid crystal panel 32 onto the screen SC. The liquid crystal panel 32 is used as a light valve (light modulator) that modulates the illumination light emitted from the illumination device 50. The liquid crystal panel 32, the illumination device 50, and the projection optical system 52 of the present embodiment correspond to the image display unit in the present invention.
[0024]
Although not shown, this image display device has three liquid crystal panels 32 for three colors of R, G, and B. Each circuit described later has a function of processing image signals for three colors. The illumination device 50 has a color light separation optical system that separates white light into three colors of light, and the projection optical system 52 generates image light that represents a color image by combining the three colors of image light. A synthesizing optical system. Note that the configuration of the optical system of such a projection display device is described in detail in, for example, Japanese Patent Application Laid-Open No. 10-171045 disclosed by the applicant of the present application, and the description thereof is omitted here.
[0025]
An analog image signal AV1 output from a personal computer is input to the A-D converter 20, and an analog image signal AV2 output from a video recorder, a television, or the like is input to the video decoder 22. As the input image signal, either one of the two analog image signals AV1 and AV2 can be selectively used. The analog image signals AV1 and AV2 are converted into digital image signals including image signal components of three colors by the A / D converter 20 or the video decoder 22. In addition to the analog image signals AV1 and AV2, a digital image signal may be input.
[0026]
The image signal input to the video processor 26 is temporarily written in the frame memory 24, read out from the frame memory 24, and supplied to the liquid crystal panel drive circuit 30. The liquid crystal panel drive circuit 30 generates a drive signal for driving the liquid crystal panel 32 in accordance with the supplied image signal. The liquid crystal panel 32 modulates the illumination light according to this drive signal.
[0027]
The user can make various settings related to image display using the remote controller 40. Although not shown, the main body of the image display device is also provided with keys and buttons for inputting various setting values for image display.
[0028]
B. Internal configuration of the video processor 26:
FIG. 2 is a block diagram showing the internal configuration of the video processor 26. The video processor 26 includes a writing / reading control unit 62, a first image filter circuit 64, a second image filter circuit 66, a contrast compensation circuit 68, a contrast / brightness adjustment circuit 70, a CPU 72, and a RAM 74. And. The video processor 26 corresponds to the image adjustment unit in the present invention.
[0029]
The writing / reading control unit 62 writes the digital image signal DV0 supplied from the A / D converter 20 and the video decoder 22 shown in FIG. 1 into the frame memory 24 and reads the digital image signal DV1 from the frame memory 24. Control. The writing / reading control unit 62 can execute an image enlargement process and a reduction process. When the image reduction process is executed, the write / read control unit 62 performs a thinning process and an interpolation process.
[0030]
FIG. 3 is an explanatory diagram showing image reduction processing by the writing / reading control unit 62. FIG. 3A shows an original image before the reduction process, that is, an image represented by the digital image signal DV0. FIG. 3B shows an interpolation image after the reduction process, that is, an image represented by the digital image signal DV1.
[0031]
The original image shown in FIG. 3A is composed of 18 × 12 pixels and includes a grid-like figure. For convenience of illustration, a pixel with a cross hatch indicates a “white” pixel having a maximum pixel value, and a pixel without a hatch indicates a “black” pixel with a minimum pixel value. When reducing the vertical and horizontal sizes of the original image to 2/3 times (ie, 12 × 8 pixels), in other words, when the thinning rate in the vertical and horizontal directions is 1/3. Then, a thinning process for selectively erasing the vertical and horizontal line images of the original image at a rate of one in three is performed. At this time, interpolation processing is performed together with thinning processing.
[0032]
FIG. 3B shows an example of an interpolation image when the original image is reduced. In the present embodiment, the 3 × m (m is an integer) -th column and row line images are targets of thinning processing. Further, the line image ((3 · m−1) th line image) adjacent to the line image (3 · mth line image) to be subjected to the thinning process is the subject of the interpolation process. The interpolation processing in this embodiment is performed by averaging pixel values of the 3 · m-th line image and the (3 · m−1) -th line image. Note that the numbers on the upper and left sides of the images in FIGS. 3A and 3B indicate the column numbers and row numbers of the respective images. Also, the numbers given to the lower side and the right side of the original image in FIG. 3A correspond to the column number and row number of the interpolated image in FIG.
[0033]
For example, the “white” line image in the fourth column of the original image shown in FIG. 3A is not the target of the thinning process in the column direction, so the third column of the interpolated image shown in FIG. Construct an eye line image. On the other hand, since the “white” line image in the ninth column of the original image is the target of the thinning process in the column direction, the “black” line image in the eighth column is the target of the interpolation process. The “black” line image in the eighth column in the original image forms the “gray” line image in the sixth column of the interpolated image by interpolation processing.
[0034]
In this way, by performing the thinning process at a selective position according to the thinning rate set for the original image, and by performing the interpolation process on the pixels around the pixel that is the thinning target, An interpolated image is generated. As can be seen from this description, the writing / reading control unit 62 in FIG. 2 corresponds to the interpolation processing unit in the present invention.
[0035]
By the way, in the interpolated image shown in FIG. 3B, a part of the grid-like figure formed by the “white” line image in the original image is formed by the “gray” line image, and the image quality deteriorates. It has been done. In the present invention, this image quality degradation is reduced by filtering.
[0036]
The digital image signal DV1 representing the interpolated image output from the writing / reading control unit 62 in FIG. 2 is subjected to filter processing in the first image filter circuit 64 and the second image filter circuit 66. The first and second image filter circuits 64 and 66 of the present embodiment are digital filters for reducing image quality deterioration due to the thinning / interpolation process. The first image filter circuit 64 functions as a low-pass filter (LPF), adjusts the pixel value of a pixel group having a relatively high spatial frequency constituting the input digital image signal DV1, and outputs a digital image signal DV2. To do. On the other hand, the second image filter circuit 66 functions as a high-pass filter (HPF), adjusts the pixel value of a pixel group having a relatively low spatial frequency constituting the digital image signal DV2, and outputs the digital image signal DV3. .
[0037]
FIG. 4 is a block diagram showing a basic internal configuration of the first image filter circuit 64. The same applies to the second image filter circuit 66. The first image filter circuit 64 is a two-dimensional filter in which a horizontal filter 80 and a vertical filter 90 are connected in series. The horizontal filter 80 is a 3-tap FIR filter (finite impulse response filter) including two horizontal delay circuits 81 and 82, three multipliers 83 to 85, and an adder 86. The vertical filter 90 has the same configuration as the horizontal filter 80. However, the delay amount Du of the horizontal delay circuits 81 and 82 in the horizontal filter 80 is for one pixel, whereas the delay amount Dv of the vertical delay circuits 91 and 92 in the vertical filter 90 is for one scanning line. .
[0038]
The values ku1 to ku3 and kv1 to kv3 multiplied by the multipliers 83 to 85 and 93 to 95 constitute a set of filter coefficients. The RAM 74 shown in FIG. 2 stores a plurality of sets of first and second filter coefficients for realizing a plurality of types of first and second image filters having different frequency characteristics. By changing the values of the filter coefficients ku1 to ku3 and kv1 to kv3, various image filters having different frequency characteristics can be realized.
[0039]
For example, the low-pass filter can be realized with the following filter coefficients.
ku1 = ku3 = kv1 = kv3 = 1/4;
ku2 = kv2 = 1/2
[0040]
The high-pass filter can be realized with the following filter coefficients.
ku1 = ku3 = kv1 = kv3 = −1 / 4;
ku2 = kv2 = 1/2
[0041]
In the example of FIG. 4, the horizontal filter 80 and the vertical filter 90 are each configured by a 3-tap FIR filter. However, it is preferable to use an FIR filter having about 16 to 512 taps in practice. If a filter with a large number of taps is used, various filter characteristics can be realized. Note that the number of taps of the horizontal filter 80 and the vertical filter 90 may be different. As the image filter, a digital filter other than the FIR can be used.
[0042]
Note that the first and second image filter circuits 64 and 66 in FIG. 2 and the RAM 74 that stores the first and second filter coefficients used in the image filter circuits 64 and 66 are the filter processing unit in the present invention. It corresponds to.
[0043]
The contrast compensation circuit 68 in FIG. 2 compensates the contrast of the filtered digital image signal DV3 output from the two image filter circuits 64 and 66, and outputs the digital image signal DV4. Thereby, it is possible to improve the contrast of the image that is lowered by the filtering process. The contrast compensation circuit 68 can compensate the contrast of the input digital image signal based on various contrast compensation characteristics. The RAM 74 shown in FIG. 2 stores a plurality of types of contrast compensation values that determine contrast compensation characteristics. In the present specification, “contrast compensation” is synonymous with “contrast adjustment”.
[0044]
Note that the contrast compensation circuit 68 in FIG. 2 and the RAM 74 for storing the contrast compensation value used for this correspond to the contrast compensation unit in the present invention.
[0045]
FIG. 5 is an explanatory diagram showing various digital image signals DV0 to DV4. FIG. 5A shows a digital image signal DV0 representing the original image. The digital image signal DV0 includes a pixel area A1 having a relatively low spatial frequency illustrated on the left side and a pixel area A2 having a relatively high spatial frequency illustrated on the right side. The image area A2 includes a signal representing the horizontal line image of FIG. In the following description, attention is given to the six pixels DG1 to DG6 having relatively large pixel values.
[0046]
FIG. 5B shows a digital image signal DV1 representing an interpolation image. Similar to FIG. 5A, the right side of FIG. 5B includes a signal representing the horizontal line image of FIG. 3B. That is, the pixel area A2 having a relatively high spatial frequency includes “gray” pixels DG4 and DG6 generated by the interpolation process. As can be seen by comparing the two digital image signals DV0 and DV1, the interpolated image can leave the pixel information of the original image in the image, but the distribution of pixel values in the interpolated image is the pixel of the original image. The distribution of values is not reproduced well.
[0047]
FIG. 5C shows the digital image signal DV 2 output from the first image filter circuit 64. As described above, the first image filter circuit 64 functions as an LPF. Therefore, as can be seen by comparing the two digital image signals DV1 and DV2, the pixel values in the pixel area A1 having a relatively low spatial frequency are substantially the same, but in the pixel area A2 having a relatively high spatial frequency, the pixels The value is changing. Specifically, the pixel values of the pixels DG3 to DG6 included in the pixel region A2 are adjusted so as to have substantially the same pixel value. At this time, the pixel values between the pixels DG2 and DG3, between DG3 and DG4, and between DG4 and DG5 are slightly larger.
[0048]
FIG. 5D shows the digital image signal DV 3 output from the second image filter circuit 66. As described above, the second image filter circuit 66 functions as an HPF. Therefore, as can be seen by comparing the two digital image signals DV2 and DV3, the pixel values in the pixel region A2 having a relatively high spatial frequency are substantially the same, but in the pixel region A1 having a relatively low spatial frequency, The value is changing. Specifically, the pixel values of the pixels DG1 and DG2 included in the pixel region A1 are adjusted to be substantially the same as the pixel values of the pixels DG3 to DG6 included in the pixel region A2.
[0049]
In this way, by executing the filter processing, the distribution of pixel values of the interpolation image can be adjusted to a similar distribution close to the distribution of pixel values of the original image. Specifically, among the pixels DG1 to DG6 having substantially the same pixel value in the original image, the pixel values of the pixels DG4 and DG6 whose pixel values have changed by the interpolation processing and the other pixels DG0 to DG0 whose pixel values have not changed. The difference from the pixel values of DG3 and DG5 is reduced by the filtering process.
[0050]
FIG. 5E shows the digital image signal DV 4 output from the contrast compensation circuit 68. As shown in the figure, the contrast of the digital image signal DV3 (FIG. 5 (d)) lowered by the filter processing is increased by the contrast compensation circuit 68. At this time, as can be seen by comparing FIGS. 5A and 5E, the digital image signal DV0 (FIG. 5A) representing the original image is substantially reproduced in the digital image signal DV4.
[0051]
Note that the contrast adjustment in FIG. 5E is the maximum pixel value when each pixel included in the digital image signal DV3 (FIG. 5D) has a pixel value larger than the first pixel value L1. The contrast compensation characteristic is adjusted so that the pixel value is adjusted to be the minimum when the pixel value is smaller than the second pixel value L2.
[0052]
FIG. 6 is an explanatory diagram showing characteristics of input / output pixel values (contrast compensation characteristics) in the contrast compensation circuit 68. In the contrast compensation characteristics shown in FIG. 6, the input pixel value changes linearly between L1 and L2, and the output pixel value increases rapidly with respect to the input pixel value. If the contrast of the image is compensated based on such contrast compensation characteristics, the contrast of the image reduced by the filter process can be recovered (that is, compensated) well. Note that the contrast compensation characteristic is not limited to that shown in FIG.
[0053]
In the present embodiment, the first filter coefficient used in the first image filter circuit 64, the second filter coefficient used in the second image filter circuit 66, and the contrast compensation circuit 68 are used. The contrast compensation values indicating the contrast compensation characteristics are stored in the RAM 74 (FIG. 2) in association with each other in advance.
[0054]
FIG. 7 is an explanatory diagram showing the relationship between the first filter coefficient, the second filter coefficient, and the contrast compensation value stored in the RAM 74. In the figure, FT1a, FT1b,... Each indicate a set of filter coefficients used in the first image filter circuit 64, and FT2a, FT2b,. A set of filter coefficients is shown. Further, CPa, CPb... Indicate contrast compensation values that realize contrast compensation characteristics as shown in FIG.
[0055]
For example, when the user selects the first setting ADJ1, “FT1a” is selected as the first filter coefficient, “FT2a” is selected as the second filter coefficient, and “CPa” is selected as the contrast compensation value. The same applies to the case where other settings ADJ2, ADJ3, ADJ4. As described above, in the present embodiment, the first filter coefficient, the second filter coefficient, and the contrast compensation value are associated with each other. The processing contents of the second image filter circuits 64 and 66 and the contrast compensation circuit 68 can be easily determined. The setting can be selected by the user using the remote controller 40 (FIG. 1).
[0056]
As described above, in this embodiment, the first and second filter coefficients and the contrast compensation value are associated with each other, but the present invention is not limited to this. FIG. 8 is an explanatory diagram showing another relationship between the first filter coefficient, the second filter coefficient, and the contrast compensation value. In FIG. 8, sets of second filter coefficients and contrast compensation values are associated with each other, and the first filter coefficients are prepared independently. Therefore, in this case, the first filter coefficient and the set of the second filter coefficient and the contrast compensation value can be individually selected. In this case, for example, the first filter coefficient FT1a is selected, and a set of the second filter coefficient FT2b and the contrast compensation value CPb, a set of the second filter coefficient FT2c and the contrast compensation value CPc, and the like are selected. Can do. Therefore, a larger number of processing patterns can be realized than in the case of FIG.
[0057]
In addition, each of the first filter coefficient, the second filter coefficient, and the contrast compensation value may be independently selected. In this way, a larger number of processing patterns can be realized.
[0058]
However, as can be seen from FIGS. 5C to 5E, according to the digital image signal DV2, in other words, according to the first filter coefficient used in the first image filter circuit 64, the second The second filter coefficient used in the image filter circuit 66 is preferably determined. In addition, it is preferable to determine the contrast compensation value used in the contrast compensation circuit 68 according to the second filter coefficient used in the second image filter circuit 66. Therefore, it is convenient to associate the first filter coefficient, the second filter coefficient, and the contrast compensation value with each other as in this embodiment (FIG. 7).
[0059]
The digital image signal DV4 output from the contrast compensation circuit 68 (FIG. 2) is supplied to the contrast / luminance adjustment circuit. The contrast / luminance adjustment circuit 70 is a circuit for adjusting the contrast and luminance of an image, and the display characteristics of the liquid crystal panel 32 can be set by this adjustment. The contrast adjustment in the contrast / brightness adjustment circuit 70 is performed independently of the contrast adjustment in the contrast compensation circuit 68.
[0060]
The image display apparatus according to the present embodiment includes first and second image filter circuits 64 and 66 and a contrast compensation circuit 68 in order to adjust an interpolation image generated by selective thinning / interpolation processing. However, this image display device can also be used when the resolution of the input image is not changed. In this case, filter coefficients and contrast compensation values that allow signals to pass as they are may be given to the circuits 64, 66, and 68.
[0061]
As described above, the image display apparatus according to the present embodiment executes the filter process for performing the spatial low-pass filter and the spatial high-pass filter in this order on the interpolated image generated by the selective thinning / interpolation process. 1 and second image filter circuits 64 and 66 are provided. Therefore, the distribution of pixel values of the interpolated image can be adjusted so as to be similar to the distribution of pixel values of the original image, and as a result, deterioration in image quality can be reduced.
[0062]
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.
[0063]
(1) Although the two-dimensional image filter is used in the above-described embodiment as described with reference to FIG. 4, the present invention can also be applied when a one-dimensional image filter is used. Various configurations other than the FIR filter can be employed as the configuration of the filter. Furthermore, although the digital filter is used in the above embodiment, the present invention can also be applied to the case where an analog filter is used.
[0064]
(2) In the above embodiment, the two image filter circuits 64 and 66 are used as the filter processing unit. However, only one image filter circuit may be used. Specifically, filter coefficients obtained by combining the filter coefficients used in the first and second image filter circuits 64 and 66 may be prepared and supplied to one image filter circuit. In this way, it is possible to perform the filter processing more quickly than in the case where the two image filter circuits 64 and 66 are used. In general, the filter processing unit may perform a filter process that substantially applies a spatial low-pass filter and a spatial high-pass filter to the interpolated image in this order.
[0065]
(3) In the above embodiment, the present invention is applied when the input original image is reduced in the horizontal and vertical directions, but it is also applied when either the horizontal or vertical direction of the original image is reduced. Is possible.
[0066]
Further, when the image display device is a projection display device as in the above-described embodiment, trapezoidal distortion may occur in the projected and displayed image due to the positional relationship between the projection display device and the screen SC. Many. Even when such a trapezoidal distortion is corrected, the thinning / interpolation process is executed at a selective position, so that the deterioration of the image quality can be reduced by applying the present invention.
[0067]
In general, according to the present invention, when a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to an original image, the thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate. The present invention can be applied to a case where an interpolation image is generated by performing an interpolation process on the pixels around the pixel to be thinned.
[0068]
(4) In the above embodiment, the configuration of the projection display device using the transmissive liquid crystal panel has been described. However, the present invention can be applied to other types of projection display devices. Other types of projection display devices include those using a reflective liquid crystal panel, those using DMD (Digital Micromirror Device: trademark of Texas Instruments), and those using a CRT.
[0069]
The present invention is also applicable to image display devices other than projection display devices. For example, the present invention is also applied to an image display device having a direct-view image display unit such as a liquid crystal panel, a plasma display panel, and a CRT, and an image display device that allows a virtual image to be enlarged and observed like a head-mounted display. Is applicable.
[0070]
(5) In the above embodiment, a part of the configuration realized by hardware may be replaced with software, and conversely, a part of the configuration realized by software may be replaced with hardware. Also good. For example, the functions of the two image filter circuits 64 and 66 and the contrast compensation circuit 68 shown in FIG. 2 can be realized by a computer program.
[0071]
Such a computer program is provided in a form stored in a recording medium. The “recording medium” includes a flexible disk, CD-ROM, magneto-optical disk, IC card, ROM cartridge, punch card, printed matter on which a code such as a barcode is printed, an internal storage device of a computer (RAM, ROM, etc. A variety of computer-readable media, such as memory) and external storage devices, carrier waves for communication, and the like.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of an image display apparatus as an embodiment of the present invention.
2 is a block diagram showing an internal configuration of a video processor 26. FIG.
FIG. 3 is an explanatory diagram showing image reduction processing by a writing / reading control unit 62;
4 is a block diagram showing a basic internal configuration of a first image filter circuit 64. FIG.
FIG. 5 is an explanatory diagram showing various digital image signals DV0 to DV4.
FIG. 6 is an explanatory diagram showing input / output pixel value characteristics (contrast compensation characteristics) in a contrast compensation circuit 68;
FIG. 7 is an explanatory diagram showing a relationship between first filter coefficients, second filter coefficients, and contrast compensation values stored in a RAM 74;
FIG. 8 is an explanatory diagram showing another relationship between the first filter coefficient, the second filter coefficient, and the contrast compensation value.
[Explanation of symbols]
20 ... A-D converter
22. Video decoder
24 ... Frame memory
26 ... Video processor
30 ... Liquid crystal panel drive circuit
32 ... LCD panel
34. Remote control circuit
40 ... Remote control
50. Illumination device
52. Projection optical system
60. Integrated circuit for image processing
62: Write / read controller
64. First image filter circuit
66. Second image filter circuit
68. Contrast compensation circuit
70: Contrast / brightness adjustment circuit
72 ... CPU
74 ... RAM
80 ... Horizontal filter
81, 82 ... Horizontal delay circuit
83-85 ... multiplier
86 ... Adder
90 ... Vertical filter
91, 92 ... Vertical delay circuit
93-95 ... multiplier
96 ... adder
AV1, AV2 ... Analog image signal
DV0 to DV4 ... Digital image signal
SC ... Screen

Claims (8)

An image processing apparatus,
An image adjustment unit that adjusts the input original image
The image adjustment unit
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and An interpolation processing unit that generates an interpolated image by performing an interpolation process on pixels around the pixel that has become,
Among the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has been changed by the interpolation process and the pixel value of another pixel whose pixel value has not changed is reduced , A filter process is performed in which a spatial low-pass filter and a spatial high-pass filter are substantially applied in this order to the interpolated image so that the pixel value distribution of the interpolated image is substantially similar to the pixel value distribution of the original image. The filter processing unit includes: a first image filter processing unit that performs filter processing using the spatial low-pass filter; and a second image filter processing unit that performs filter processing using the spatial high-pass filter. When,
A contrast compensation unit for compensating for the contrast of the image processed by the filter processing unit;
With
The processing contents of the first and second image filter processing units are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation unit is determined by selecting from a plurality of types of contrast compensation values,
The image processing apparatus, wherein the selected first filter coefficient, the second filter coefficient, and the contrast compensation value are associated with each other in advance. An image processing apparatus,
An image adjustment unit that adjusts the input original image
The image adjustment unit
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and An interpolation processing unit that generates an interpolated image by performing an interpolation process on pixels around the pixel that has become,
Among the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has been changed by the interpolation process and the pixel value of another pixel whose pixel value has not changed is reduced , A filter process is performed in which a spatial low-pass filter and a spatial high-pass filter are substantially applied in this order to the interpolated image so that the pixel value distribution of the interpolated image is substantially similar to the pixel value distribution of the original image. The filter processing unit includes: a first image filter processing unit that performs filter processing using the spatial low-pass filter; and a second image filter processing unit that performs filter processing using the spatial high-pass filter. When,
A contrast compensation unit for compensating for the contrast of the image processed by the filter processing unit;
With
The processing contents of the first and second image filter processing units are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation unit is determined by selecting from a plurality of types of contrast compensation values,
The selected second filter coefficient and the contrast compensation value are associated with each other in advance, and the first filter coefficient is selected independently of the second filter coefficient and the contrast compensation value. An image processing apparatus. The image processing apparatus according to claim 1, further comprising:
An image processing apparatus comprising: an image display unit that displays an image adjusted by the image adjustment unit. The image processing apparatus according to claim 3,
The image processing device is a projection display device that projects and displays an image,
The interpolation processing unit performs the thinning process on the original image to correct a trapezoidal distortion. An image processing method comprising:
A step of adjusting the input original image,
The original image adjustment step includes
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and A step of generating an interpolated image by performing an interpolation process on the pixels around the resulting pixel;
Among the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has been changed by the interpolation process and the pixel value of another pixel whose pixel value has not changed is reduced , A filter process is performed in which a spatial low-pass filter and a spatial high-pass filter are substantially applied in this order to the interpolated image so that the pixel value distribution of the interpolated image is substantially similar to the pixel value distribution of the original image. The filtering process includes: a first image filtering process that performs a filtering process using the spatial low-pass filter; and a second image filtering process that performs a filtering process using the spatial high-pass filter; ,
Compensating the contrast of the filtered image;
With
The processing contents of the first and second image filter processes are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation is determined by selecting from a plurality of types of contrast compensation values,
The image processing method, wherein the selected first filter coefficient, the second filter coefficient, and the contrast compensation value are associated with each other in advance. An image processing method comprising:
A step of adjusting the input original image,
The original image adjustment step includes
When a thinning rate is set in at least one of the horizontal direction and the vertical direction with respect to the original image, a thinning process is performed at a selective position in the horizontal / vertical direction according to the thinning rate, and A step of generating an interpolated image by performing an interpolation process on the pixels around the resulting pixel;
Among the pixels having substantially the same pixel value in the original image, the difference between the pixel value of the pixel whose pixel value has been changed by the interpolation process and the pixel value of another pixel whose pixel value has not changed is reduced , A filter process is performed in which a spatial low-pass filter and a spatial high-pass filter are substantially applied in this order to the interpolated image so that the pixel value distribution of the interpolated image is substantially similar to the pixel value distribution of the original image. The filtering process includes: a first image filtering process that performs a filtering process using the spatial low-pass filter; and a second image filtering process that performs a filtering process using the spatial high-pass filter; ,
Compensating the contrast of the filtered image;
With
The processing contents of the first and second image filter processes are determined by selecting from a plurality of types of first and second filter coefficients, respectively.
The processing content of the contrast compensation is determined by selecting from a plurality of types of contrast compensation values,
The selected second filter coefficient and the contrast compensation value are associated with each other in advance, and the first filter coefficient is selected independently of the second filter coefficient and the contrast compensation value. An image processing method. The image processing method according to claim 5, further comprising:
An image processing method comprising a step of displaying the image adjusted in the original image adjustment step. The image processing method according to claim 7, comprising:
The image display step includes a step of projecting and displaying an image,
The interpolated image generation step includes an image processing method including a step of executing the thinning process on the original image to correct trapezoidal distortion.

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