JP2013092777A - Image display device, control method for image display device, and control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device which can prevent deterioration in image quality of a display image in accordance with various conversion rates of resolution.SOLUTION: An image display device 1 comprises: display means 2 for displaying an image; image processing means 34 for performing resolution conversion processing for converting resolution relative to an input image signal and also performing filter processing by a spatial low-pass filter; and control means 31 for controlling the image processing means 34. The control means 31 comprises: a filter factor calculation part 312 for calculating a filter factor of the spatial low-pass filter by multiplying a sampling function having a cutoff frequency as a parameter by a windowing function; and a cutoff frequency calibration part 313 for calibrating the cutoff frequency in accordance with a conversion rate of the resolution of the image signal by the resolution conversion processing.

Description

  The present invention relates to an image display device, a control method for an image display device, and a control program.

Conventionally, as an image display device using a fixed pixel display device such as a liquid crystal display, a PDP (Plasma Display Panel), an organic EL (Electro-Luminescence) display device, or a liquid crystal projector, an input image signal is fixed pixel. A configuration having a scaler that converts an image signal suitable for the resolution of a display device is known.
In the resolution conversion process by the scaler, when the resolution of the input image signal is higher than the resolution of the fixed pixel display device, a process of reducing pixels (reduction process) from the input image is performed. In the resolution conversion process, when the resolution of the input image signal is lower than the resolution of the fixed pixel display device, a process (enlargement process) for interpolating pixels in the input image is performed.
When the reduction process or the enlargement process is performed, the display image of the fixed pixel display device tends to be unnatural.
For this reason, the scaler further performs filtering using a spatial low-pass filter such as FIR (Finite Impulse Response) on the image signal that has been subjected to the resolution conversion processing, so that pixels in a region where the spatial frequency of the image signal is higher than the cutoff frequency. The value is adjusted (for example, refer to Patent Document 1).

JP 2005-57324 A

By the way, as a spatial low-pass filter, it is ideal that the transition region between the passband and the stopband is narrow and has a steep cutoff characteristic.
However, in reality, it is impossible to make the number of taps (the order of the filter) infinite and it must be set to a finite number, so that it is impossible to manufacture the ideal spatial low-pass filter described above. . In other words, the spatial low-pass filter that is actually obtained has a transition band of a predetermined width between the pass band and the stop band, and does not have a steep cutoff characteristic like an ideal spatial low-pass filter.

As described above, the actual spatial low-pass filter has different actual characteristics from the ideal spatial low-pass filter. Therefore, when filtering is performed using the spatial low-pass filter, frequency components such as transition regions are obtained. Therefore, information that originally exists in the process of signal processing cannot be sufficiently covered, and the remaining information is generated as aliasing noise.
Therefore, it is conceivable to reduce the frequency components in the transition region or the like in order to reduce the aliasing noise, that is, to set the cut-off frequency of the spatial low-pass filter lower.
However, the form of aliasing noise differs depending on the resolution conversion rate by the resolution conversion process. For this reason, for example, when the cut-off frequency of the spatial low-pass filter is uniquely determined as described above, the aliasing noise can be reduced in the case of a conversion rate of a predetermined resolution. In the case of the conversion rate, the aliasing noise cannot be reduced.
Therefore, there is a demand for a technique that can reduce aliasing noise and prevent image quality deterioration of a display image in accordance with conversion rates of various resolutions.

  An object of the present invention is to provide an image display device, a control method for the image display device, and a control program capable of preventing image quality deterioration of a display image corresponding to conversion rates of various resolutions.

  An image display apparatus according to the present invention includes a display unit that displays an image, an image processing unit that performs resolution conversion processing for converting resolution on input image information and performs filtering processing using a spatial low-pass filter, and the image processing unit. An image display device comprising: control means for controlling the filter, wherein the control means calculates a filter coefficient of the spatial low-pass filter by multiplying a sampling function having a cutoff frequency as a parameter by a window function And a cut-off frequency calibration unit that calibrates the cut-off frequency in accordance with a conversion rate of the resolution of the image information obtained by the resolution conversion process.

In the present invention, the control means for controlling the image processing means includes the filter coefficient calculation unit and the cut-off frequency calibration unit, so that the filter coefficient of the spatial low-pass filter can be calculated as described below.
That is, the cut-off frequency calibration unit obtains the resolution conversion rate when the image processing unit performs the resolution conversion process.
Examples of the resolution conversion rate include the ratio (%) of the number of pixels in the vertical direction of the display means to the number of pixels in the vertical direction of the input image information with reference to the vertical direction of the display means.
The cut-off frequency calibration unit calibrates the cut-off frequency of the spatial low-pass filter according to the resolution conversion rate (cut-off frequency calibration step).
Next, the filter coefficient calculation unit calculates a filter coefficient by multiplying a sampling function using the calibrated cutoff frequency as a parameter by a window function (filter coefficient calculation step). Then, the image processing means performs filter processing using a spatial low-pass filter with a calibrated cutoff frequency.
As described above, the cutoff frequency is calibrated in accordance with the conversion rate of resolution, so that aliasing noise can be reduced and image quality deterioration of the display image can be prevented according to the conversion rate of various resolutions.

In the image display device of the present invention, it is preferable that the cutoff frequency calibration unit calibrates the cutoff frequency when the conversion rate is 100% or more.
By the way, when the reduction processing is performed on the input image information, the spatial frequency band of the image information is narrowed on the high frequency side by thinning out pixels from the input image. That is, when the reduction process is performed, the display image is blurred as a result, so that aliasing noise hardly occurs.
In the present invention, the cut-off frequency calibration unit calibrates the cut-off frequency when the resolution conversion rate is 100% or more. In other words, the cut-off frequency is not calibrated in the reduction process in which aliasing noise hardly occurs. (The cut-off frequency is set as a preset reference cut-off frequency). Thus, since the cutoff frequency calibration process is performed only when necessary, the aliasing noise can be reduced efficiently, and the processing load on the control means can be reduced.

In the image display device of the present invention, the cut-off frequency calibration unit is configured to perform the conversion rate and the first calibration with respect to a preset reference cut-off frequency when the conversion rate is greater than 100% and equal to or less than 110%. It is preferable to calibrate the cutoff frequency by multiplying by a coefficient.
Here, the first calibration coefficient is preferably a value that makes the cutoff frequency lower than the reference cutoff frequency, that is, a value smaller than 1.

In the present invention, when enlarging processing is performed on input image information, it is noted that aliasing noise is particularly likely to occur in a minute conversion rate range (greater than 100% and 110% or less). In the case of a range, the cutoff frequency is calibrated. As described above, the cut-off frequency is calibrated only when necessary as described above, so that aliasing noise can be reduced efficiently and the processing load on the control means can be reduced.
Further, in the present invention, focusing on the fact that the aliasing noise increases as the conversion rate approaches 100%, the cutoff frequency is calibrated by multiplying the reference cutoff frequency by the conversion rate in addition to the first calibration coefficient. It is supposed to be. This makes it possible to calibrate so that the cut-off frequency becomes higher as the conversion rate becomes larger than 100% within the range of the above minute conversion rate, and the aliasing noise can be efficiently reduced within a range where the display image is not blurred. .

In the image display device of the present invention, the cut-off frequency calibration unit multiplies a preset reference cut-off frequency by a second calibration coefficient when the conversion rate is 100% to obtain the cut-off frequency. It is preferable to calibrate.
Here, as the second calibration coefficient, similarly to the first calibration coefficient, a cutoff frequency is set lower than the reference cutoff frequency, that is, a value smaller than 1 is preferable.
By the way, even when the resolution conversion rate is 100%, that is, when the reduction process or the enlargement process is not performed, the actual spatial low-pass filter is different from the ideal spatial low-pass filter. For this reason, noise different from aliasing noise is likely to occur.
In the present invention, when the resolution conversion rate is 100%, the cutoff frequency calibration unit multiplies the reference cutoff frequency by the second calibration coefficient so that the cutoff frequency becomes lower than the reference cutoff frequency. Calibrate the frequency. As a result, noise different from the aliasing noise can be reduced by blurring the display image.
As the second calibration coefficient, if a value smaller than 1 and a value in a range where the blur of the display image is not noticeable is selected, only noise different from the aliasing noise is reduced, and the display image is sufficiently clear. Can be secured.

The control method of the present invention comprises: display means for displaying an image; image processing means for performing resolution conversion processing for converting resolution on input image information and performing filtering processing using a spatial low-pass filter; and the image processing means. And a control means for controlling the image display device, wherein the control means calibrates a cutoff frequency of the spatial low-pass filter in accordance with a conversion rate of the resolution of the image information by the resolution conversion processing. A cut-off frequency calibration step, and a filter coefficient calculation step of calculating a filter coefficient of the spatial low-pass filter by multiplying a sampling function having the calibrated cut-off frequency as a parameter by a window function. .
Since the control method of the present invention is implemented by the above-described image display device, it can enjoy the same operations and effects as the above-described image display device.

The control program of the present invention comprises: display means for displaying an image; image processing means for performing resolution conversion processing for converting resolution on input image information and performing filtering processing by a spatial low-pass filter; and the image processing means. A control program for an image display device comprising a control means for controlling, wherein the control means executes the control method described above.
Since the control program of the present invention is used to implement the control method described above, it can enjoy the same operations and effects as the control method described above.

FIG. 2 is a schematic diagram showing a schematic configuration of a projector as an image display device in the present embodiment. The figure which shows typically the characteristic of the space low-pass filter in the said embodiment. 6 is a flowchart for explaining a projector control method according to the embodiment. The figure which shows an example in case the conversion rate of the resolution in the said embodiment is larger than 100% and 110% or less. The figure which shows the other example in case the conversion rate of the resolution in the said embodiment is larger than 100% and 110% or less.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[Schematic configuration of projector]
FIG. 1 is a schematic diagram showing a schematic configuration of a projector 1 as an image display device.
The projector 1 modulates a light beam emitted from a light source according to image information to form image light, and enlarges and projects the formed image light on a screen (not shown). As shown in FIG. 1, the projector 1 is roughly composed of an image projection device 2 as a display means, a control device 3 and the like.

The image projection device 2 forms image light and enlarges and projects it on the screen under the control of the control device 3. As shown in FIG. 1, the image projection apparatus 2 includes a light source device 21, a light modulation device 22, a projection optical device 23, and the like.
The light source device 21 emits a light beam toward the light modulation device 22 under the control of the control device 3. The light modulation device 22 is composed of a liquid crystal panel, modulates the light beam emitted from the light source device 21 into image light based on a drive signal from the control device 3, and emits it to the projection optical device 23.
The projection optical device 23 enlarges and projects the image light emitted from the light modulation device 22 toward the screen.

The control device 3 includes a CPU (Central Processing Unit) 31 as control means, and controls the entire projector 1 according to a control program stored in the memory 32. Hereinafter, in order to simplify the description, only the function of driving the light modulation device 22 as the control device 3 will be described, and description of other functions will be omitted.
As shown in FIG. 1, the control device 3 includes an AD conversion unit 33, a scaler 34 as an image processing unit, a panel drive unit 35, and a resolution detection unit 36 in addition to the CPU 31 and the memory 32.

The scaler 34 is an image signal in which an analog image signal (image information) from the outside is converted into a digital image signal by the AD conversion unit 33, or a digital signal input from the outside, for example, according to the HDMI (High-Definition-Multimedia Interface) standard or the like. An image signal (image information) is input.
Then, the scaler 34 performs resolution conversion processing for converting the input image signal into an image signal suitable for the display format of the light modulation device 22 to be driven.
In this resolution conversion process, when the resolution of the input image signal is higher than the resolution of the light modulation device 22, a process of thinning out pixels from the input image (reduction process) is performed, and conversely, the resolution of the input image signal is When the resolution is lower than that of the light modulation device 22, a process (enlargement process) for interpolating pixels in the input image is performed.

The scaler 34 uses a spatial low-pass filter such as an FIR filter for the image signal subjected to the resolution conversion process in order to prevent the display image from becoming unnatural due to the reduction process and the enlargement process. Apply the filtering process.
In this filter processing, the pixel value in the region where the spatial frequency of the image signal is higher than the cutoff frequency of the spatial low-pass filter is adjusted.
The scaler 34 temporarily stores the image signal subjected to the resolution conversion process and the filter process in the frame memory 34A.

  The panel drive unit 35 generates a drive signal for driving the light modulation device 22 based on the image signal stored in the frame memory 34A. The panel drive unit 35 outputs a drive signal to the light modulation device 22 to display an image corresponding to the image signal stored in the frame memory 34 </ b> A on the light modulation device 22.

  The resolution detection unit 36 detects the resolution of the input image from the input image signal. Examples of the resolution detection unit 36 include a frequency counter, and the resolution of the input image is detected from the frequency of a synchronization signal (horizontal synchronization signal) input together with the image signal. Then, the resolution detection unit 36 outputs the detection result to the CPU 31.

The CPU 31 reads the control program stored in the memory 32 and controls the operation of the scaler 34 according to the control program. As shown in FIG. 1, the CPU 31 includes a conversion rate setting unit 311, a filter coefficient calculation unit 312, and a cutoff frequency calibration unit 313.
Based on the resolution of the input image detected by the resolution detector 36 and the resolution of the light modulation device 22, the conversion rate setting unit 311 determines the conversion rate of the resolution used when the resolution conversion processing is performed in the scaler 34. Set.
For example, the conversion rate setting unit 311 sets, as the conversion rate, the ratio (%) of the number of pixels in the vertical direction of the light modulation device 22 to the number of pixels in the vertical direction of the input image with the vertical direction of the light modulation device 22 as a reference. .

The filter coefficient calculation unit 312 calculates a filter coefficient of a spatial low-pass filter used when the scaler 34 performs filter processing.
Specifically, the filter coefficient calculation unit 312 multiplies the sampling function (sinc function) with the cutoff frequency ω _c ′ as a parameter by the window function, and calculates the filter coefficient h (n) by the following equation (1). calculate.

Here, n is the number of taps of the filter. In the present embodiment, the number of taps is designed to be 8.
W (n) is a window function. As the window function, various window functions such as a square wave window, a Hanning window, a Hamming window, and a Blackman window may be adopted.

The cut-off frequency calibrating unit 313 uses the reference cut-off angular frequency ω _c that is a specified value stored in the memory 32 according to the conversion rate of the resolution set by the conversion rate setting unit 311, and uses the cut-off angle. Calibrate the frequency ω _c ′.
The reference cut-off angular frequency ω _c is expressed by the following expression (2) using the reference cut-off frequency f _c and the sampling frequency f _s .

In this embodiment, f _c / f _s is set to 0.5 so as to satisfy the sampling theorem.
That is, the reference cutoff angular frequency ω _c is set to π.

FIG. 2 is a diagram schematically illustrating the characteristics of the spatial low-pass filter.
In FIG. 2, the horizontal axis indicates the frequency, and the vertical axis indicates the amplitude ratio. In FIG. 2, the solid line indicates the characteristic of the spatial low-pass filter that is actually obtained, and the broken line indicates the characteristic of the ideal spatial low-pass filter.
In addition, as a characteristic of the spatial low-pass filter actually obtained, there are actually so-called ripples in the pass band and the stop band, but for convenience of explanation, the ripples are omitted in FIG.

By the way, as a spatial low-pass filter, as shown by the broken line in FIG. 2, it is ideal that the transition region between the passband and the stopband is narrow and has a steep cutoff characteristic.
However, since the spatial low-pass filter that is actually obtained cannot have an infinite number of taps and must be set to a finite number, as shown by the solid line in FIG. Have a transition region of a predetermined width and do not have a steep cutoff characteristic like an ideal spatial low-pass filter.
Therefore, the value of the cut-off frequency f _c is performed filtering with a spatial low-pass filter, the frequency components such as a transition zone, can not be sufficiently covered information originally present in the course of signal processing, left Information is generated as aliasing noise (or grid-like noise or vertical streak noise).

When the reduction process is performed on the input image signal, the spatial frequency band of the image signal is narrowed on the high frequency side by thinning out pixels from the input image. That is, when the reduction process is performed, the display image is blurred as a result, so that aliasing noise hardly occurs.
Therefore, in this embodiment, when the resolution conversion rate is larger than 100% (enlargement process), the cutoff frequency calibration unit 313 determines the cutoff angular frequency ω _c ′ (cutoff frequency) according to the resolution conversion rate. ) Is reduced so as to reduce frequency components in the transition region and the like, thereby reducing aliasing noise.
In the present embodiment, the cut-off frequency calibrating unit 313 does not calibrate the cut-off angular frequency ω _c ′ in the case of the reduction process, that is, the cut-off angular frequency ω _c ′ is used as the reference cut-off angular frequency. Let ω _c .

In addition, aliasing noise is particularly likely to occur in a conversion range of a minute resolution (greater than 100% and 110% or less), and becomes larger as the conversion rate is closer to 100%.
Therefore, in the present embodiment, the cutoff frequency calibration unit 313 calculates the cutoff angular frequency ω _c ′ by the following equation (3) when the resolution conversion rate is greater than 100% and equal to or less than 110%. It is configured.

In the present embodiment, the first calibration coefficient is set to 0.9.
That is, in the expression (3), since the conversion factor is multiplied by the first calibration coefficient, the coefficient by which the reference cut-off angular frequency ω _c is multiplied by 1% when the resolution conversion rate is between 101% and 110%. Is set to
The upper limit (110%) of the conversion rate is set as shown below.
That is, when a certain amount of attenuation characteristic is secured as a spatial low-pass filter that is actually obtained, a transition range of 5 to 10% with respect to the cutoff frequency is required.
In the present embodiment, assuming that there is a transition region of about 10%, it is considered that the aliasing noise can be reduced if the corresponding frequency component can be reduced, and the upper limit of the conversion rate is set to 110%. .

In addition, even when the resolution conversion rate is 100% (same size), that is, when the reduction process or the enlargement process is not performed, the spatial low-pass filter actually obtained is actually an ideal spatial low-pass filter. Therefore, noise different from the aliasing noise (hereinafter referred to as operational noise) is likely to occur.
Therefore, in this embodiment, the cutoff frequency calibration unit 313 is configured to calculate the cutoff angular frequency ω _c ′ by the following equation (4) when the resolution conversion rate is 100%.

In the present embodiment, the second calibration coefficient is set to 0.98. The second calibration coefficient is set to “0.98” which is close to “1” within a range where the blur of the display image by allowing the cut-off angular frequency ω _c ′ to be lowered.

The memory 32 stores a control program, a first calibration coefficient, a second calibration coefficient, and the like.
If the memory 32 is composed of a non-volatile memory capable of rewriting data, such as a flash memory, the first calibration coefficient and the second calibration coefficient are displayed on the menu screen by operating an operation means such as an operation panel (not shown). Can be changed to other values, or the first calibration coefficient and the second calibration coefficient can be changed to other values via the input terminal of the RS232C.

[Projector operation]
FIG. 3 is a flowchart illustrating a method for controlling projector 1.
Next, the processing operation of the control device 3 described above will be described.
First, the conversion rate setting unit 311 sets a resolution conversion rate based on the resolution of the input image detected by the resolution detection unit 36 and the resolution of the light modulation device 22 (step S1).
After step S1, the cutoff frequency calibration unit 313 recognizes the conversion rate of the resolution set in step S1, and determines whether the conversion rate is 100% or more (step S2).

  In step S2, if the CPU 31 determines “N”, that is, if it is determined that the resolution of the input image needs to be “reduced”, it outputs a control command including the resolution conversion rate to the scaler 34. . Then, the scaler 34 performs a reduction process on the input image signal in accordance with the resolution conversion rate included in the control command (step S3).

After step S3, the cutoff frequency calibrating unit 313 has a resolution conversion rate of less than 100%. Therefore, the cutoff frequency calibrating unit 313 uses the cutoff angular frequency ω _c ′ as a reference cut without performing calibration processing. and off-angle frequency ω _c (step S4).

After step S4, the filter coefficient calculation unit 312 calculates the filter coefficient h (n) by the equation (1) using the cutoff angular frequency ω _c ′ calculated by the cutoff frequency calibration unit 313 (step S4). S5: Filter coefficient calculation step). Then, the CPU 31 outputs a control command including the calculated filter coefficient h (n) to the scaler 34.
Then, the scaler 34 performs a filter process on the image signal subjected to the resolution conversion process using the filter coefficient h (n) included in the control command (step S6).
The image signal that has been subjected to resolution conversion processing and filter processing by the scaler 34 and accumulated in the frame memory 34A is output as a drive signal to the light modulation device 22 via the panel drive unit 35. A display image suitable for the display format of the modulation device 22 is formed.

On the other hand, if the cut-off frequency calibration unit 313 determines “Y” in step S2, that is, if it is determined that the resolution of the input image needs to be “enlarged”, it is further set in step S1. It is determined whether the conversion rate of the resolution is 110% or less (step S7).
In step S <b> 7, when the CPU 31 determines “N”, that is, when it is determined that the resolution conversion rate is greater than 110%, the CPU 31 outputs a control command including the resolution conversion rate to the scaler 34. Then, the scaler 34 enlarges the input image signal according to the resolution conversion rate included in the control command (step S8).

After step S8, the CPU 31 proceeds to the process of step S4.
In the process of step S4 performed after step S8, since the resolution conversion rate is larger than 110%, the cutoff angular frequency ω _c ′ is set to the reference cutoff angular frequency ω _c without performing the calibration process. Is done.

On the other hand, if the CPU 31 determines “Y” in step S7, that is, if it is determined that the resolution conversion rate is 100% or more and 110% or less, the CPU 31 further sets the resolution set in step S1. It is determined whether or not the conversion rate is 100% (step S9).
In step S9, when the cutoff frequency calibration unit 313 determines “Y”, that is, the resolution of the input image and the resolution of the light modulation device 22 are the same, and it is determined that the resolution conversion process need not be performed. In such a case, the cutoff angular frequency ω _c ′ is calculated from the equation (4) (step S10).
After step S10, the CPU 31 proceeds to the process of step S5.

On the other hand, if the CPU 31 determines “N” in step S 9, that is, if it is determined that the resolution of the input image is greater than 100% and 110% or less, a control command including a resolution conversion rate is assigned to the scaler. 34. Then, the scaler 34 enlarges the input image signal according to the resolution conversion rate included in the control command (step S11).
After step S11, the cut-off frequency calibration unit 313 calculates the cut-off angular frequency ω _c ′ using equation (3) (step S12).
After step S12, the CPU 31 proceeds to the process of step S5.
Steps S2, S4, S7, S9, S10, and S12 described above correspond to a cutoff frequency calibration step according to the present invention.

FIG. 4 is a diagram illustrating an example when the resolution conversion rate is greater than 100% and equal to or less than 110%.
Here, FIG. 4 shows a case where the signal format of the input image signal is XGA (resolution: 1024 × 768) and the display format of the light modulation device 22 is WXGA (resolution: 1280 × 800).
In the example illustrated in FIG. 4, the conversion rate setting unit 311 uses the vertical direction of the light modulation device 22 as a reference in step S <b> 1, and the vertical direction of the light modulation device 22 with respect to the vertical pixel count “768” of the input image. “104%”, which is the ratio of the number of pixels in the direction “800”, is set as the conversion rate.
In step S11, the scaler 34 performs an enlargement process according to the conversion rate “104%”, so that a display image with a resolution of 1066 × 800 (two-dot chain line shown in FIG. 4) is formed in the light modulation device 22. Will be.
Further, in step S12, the cutoff frequency calibration unit 313 calculates the cutoff angular frequency ω _c ′ as 0.94ω _{c according} to Equation (3).

FIG. 5 is a diagram illustrating another example when the resolution conversion rate is greater than 100% and equal to or less than 110%.
Here, in FIG. 5, the signal format of the input image signal is 1080p (resolution: 1766 × 994) with a display rate of 92%, and the display format of the light modulator 22 is 1080p (resolution: 1920 × 1080). Show.
Note that in video images, noise often appears outside the display frame, so the display rate is generally smaller than the image size (display rate: 92% in the case of FIG. 5). .
In the case of the example of FIG. 5, the conversion rate setting unit 311 uses the vertical direction of the light modulation device 22 as a reference in step S <b> 1, “108.6%”, which is the ratio of the number of pixels in the direction “1080”, is set as the conversion rate.
In step S11, the scaler 34 performs an enlargement process according to the conversion rate “108.6%”, so that a display image with a resolution of 1920 × 1080 (two-dot chain line shown in FIG. 5) is formed in the light modulation device 22. Will be.
Further, in step S12, the cutoff frequency calibration unit 313 calculates the cutoff angular frequency ω _c ′ as 0.98ω _{c according} to the equation (3).

The embodiment described above has the following effects.
In the present embodiment, the CPU 31 that controls the scaler 34 includes a filter coefficient calculation unit 312 and a cutoff frequency calibration unit 313. As a result, the cut-off angular frequency ω _c ′ (cut-off frequency) can be calibrated in accordance with the conversion rate of the resolution, so that aliasing noise is reduced and the image quality of the display image is degraded according to the conversion rate of various resolutions. Can be prevented.

Further, since the cutoff frequency calibration unit 313 calibrates the cutoff angular frequency ω _c ′ when the resolution conversion rate is 100% or more, in other words, in the reduction process in which aliasing noise is difficult to occur, the cutoff angle Do not calibrate the frequency ω _c ′. As a result, the correction processing of the cut-off angular frequency ω _c ′ is performed only when necessary, so that aliasing noise can be reduced efficiently and the processing load on the CPU 31 can be reduced.

Furthermore, when performing the enlargement process, paying attention to the fact that aliasing noise is particularly likely to occur in a minute conversion rate range (greater than 100% and 110% or less), and when the conversion rate is in the above range, the cutoff angular frequency ω _c ′ is calibrated. Thus, as described above, the correction processing of the cut-off angular frequency ω _c ′ is performed only when necessary, so that aliasing noise can be efficiently reduced and the processing load on the CPU 31 can be reduced.
Focusing on the fact that the aliasing noise increases as the resolution conversion rate approaches 100%, the cut-off angular frequency ω is multiplied by the conversion factor in addition to the first calibration coefficient to the reference cut-off angular frequency ω _c . _c 'is to be calibrated. As a result, the cut-off angular frequency ω _c ′ can be calibrated so that the conversion rate is higher than 100% within the above-mentioned range of the conversion rate, and the aliasing noise is efficiently used in the range where the display image is not blurred. Can be reduced.

Furthermore, the cutoff frequency calibration unit 313, when the resolution of the conversion rate is 100%, by multiplying the second calibration factor to the reference cutoff angular frequency omega _c, lower than the reference cutoff angular frequency omega _c The cutoff angular frequency ω _c ′ is calibrated so that As a result, the operational noise can be reduced by blurring the display image.
In addition, since the second calibration coefficient is set to a value smaller than 1 and “0.98” where the blur of the display image is not noticeable, only the noise in calculation is reduced and the display image is sufficiently clear. It can be secured.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
In the embodiment, when the conversion rate of resolution is in the range of more than 100% and not more than 110%, the cutoff angular frequency ω _c ′ is calibrated by the equation (3). Not limited to this.
That is, the upper limit of the conversion rate is preferably set according to the width of the transition region with respect to the cutoff frequency, and the width of the transition region varies depending on the number of filter taps, the type of the window function, etc. It can be set as appropriate.
In the above-described embodiment, a liquid crystal panel is used as the light modulation device 22. However, as the light modulation device 22, in addition to a transmissive liquid crystal panel and a reflective liquid crystal panel, DMD (Digital Micromirror Device) (Texas Instruments, USA) (Trademark of the company) or the like.
In the embodiment, the projector 1 is employed as the image display device. However, the present invention is not limited to this, and other image displays such as a liquid crystal display, a PDP, and an organic EL display device are possible as long as the projector 1 has a fixed pixel display device. An apparatus may be adopted.

  The image display apparatus according to the present invention can be used for image display apparatuses such as projectors used in presentations and home theaters, because image quality deterioration of display images can be prevented in accordance with conversion rates of various resolutions.

DESCRIPTION OF SYMBOLS 1 ... Projector (image display apparatus), 2 ... Image projection apparatus (display means), 31.
..CPU (control means), 34... Scaler (image processing means), 312... Filter coefficient calculation unit, 313... Cut-off frequency calibration unit, S2, S4, S7, S9, S10,
S12: Cut-off frequency calibration step, S5: Filter coefficient calculation step.

The image display device of the present invention is preset when the conversion rate of the resolution of the image information is 100% by display means for displaying an image and resolution conversion processing for converting the resolution of the input image information. The cutoff frequency calibration means for calibrating the cutoff frequency by multiplying the reference cutoff frequency by a coefficient that makes the cutoff frequency of the spatial low-pass filter lower than the reference cutoff frequency, and the calibrated cutoff frequency Filter coefficient calculation means for calculating a filter coefficient of the spatial low-pass filter by multiplying a sampling function having a parameter by a window function, and performing the resolution conversion process , and using the calculated filter coefficient, the spatial low-pass filter characterized in that it comprises an image processing means for performing a filtering process by the filter, the.

In the present invention, the control means for controlling the image processing means includes the filter coefficient calculation unit and the cut-off frequency calibration unit, so that the filter coefficient of the spatial low-pass filter can be calculated as described below.
That is, the cut-off frequency calibration unit obtains the resolution conversion rate when the image processing unit performs the resolution conversion process.
Examples of the resolution conversion rate include the ratio (%) of the number of pixels in the vertical direction of the display means to the number of pixels in the vertical direction of the input image information with reference to the vertical direction of the display means.
The cut-off frequency calibration unit calibrates the cut-off frequency of the spatial low-pass filter when the resolution conversion rate is 100% (cut-off frequency calibration step).
Next, the filter coefficient calculation unit calculates a filter coefficient by multiplying a sampling function using the calibrated cutoff frequency as a parameter by a window function (filter coefficient calculation step). Then, the image processing means performs filter processing using a spatial low-pass filter with a calibrated cutoff frequency.
As described above, since calibrating the cutoff frequency, reduced in fold return noise and prevent degradation in the image quality of the display image.

In the image display device of the present invention, the cut-off frequency calibrating unit sets the cut-off frequency of the spatial low-pass filter to the reference cut-off frequency with respect to a preset reference cut-off frequency when the conversion rate is 100%. multiplied by a coefficient lower than off frequency, it calibrates the cut-off frequency.
Here, as the coefficient, a value smaller than 1 is preferred.
100% conversion of resolution, i.e., for if not subjected to the reduction processing and enlargement processing, spatial low-pass filter obtained at the reality is that the actual characteristic is different from the ideal spatial low-pass filter, folded Noise different from noise is likely to occur.
In the present invention, the cutoff frequency calibration unit multiplies the reference cutoff frequency by the above coefficient when the resolution conversion rate is 100%, and sets the cutoff frequency to be lower than the reference cutoff frequency. Calibrate. As a result, noise different from the aliasing noise can be reduced by blurring the display image.
As the coefficient, if a value smaller than 1 and a range in which the blur of the display image is not conspicuous is selected, only noise different from the aliasing noise is reduced, and the display image is sufficiently clear. it can.

Incidentally, the cut-off frequency calibration unit, when the conversion rate is 100% or more, it is also possible to calibrate the cut-off frequency.
By the way, when the reduction processing is performed on the input image information, the spatial frequency band of the image information is narrowed on the high frequency side by thinning out pixels from the input image. That is, when the reduction process is performed, the display image is blurred as a result, so that aliasing noise hardly occurs.
In contrast, the cutoff frequency calibration unit, when the resolution of the conversion ratio of 100% or more, if calibrating the cut-off frequency, in other words, the cutoff frequency is reduced process aliasing noise hardly occurs Is not calibrated (the cut-off frequency is set to a preset reference cut-off frequency). Thus, since the cutoff frequency calibration process is performed only when necessary, the aliasing noise can be reduced efficiently, and the processing load on the control means can be reduced.

In the above case , the cutoff frequency calibration unit multiplies the preset reference cutoff frequency by the conversion rate and the first calibration coefficient when the conversion rate is greater than 100% and 110% or less. The cut-off frequency may be calibrated.
Here, the first calibration coefficient is preferably a value that makes the cutoff frequency lower than the reference cutoff frequency, that is, a value smaller than 1.

In the above-described configuration , when enlarging processing is performed on the input image information, it is noted that aliasing noise is particularly likely to occur in a minute conversion rate range (greater than 100% and 110% or less). In the case of a range, the cutoff frequency is calibrated. As described above, the cut-off frequency is calibrated only when necessary as described above, so that aliasing noise can be reduced efficiently and the processing load on the control means can be reduced.
In the above configuration , focusing on the fact that the aliasing noise increases as the conversion rate approaches 100%, the cutoff frequency is calibrated by multiplying the reference cutoff frequency by the conversion rate in addition to the first calibration coefficient. It is supposed to be. This makes it possible to calibrate so that the cut-off frequency becomes higher as the conversion rate becomes larger than 100% within the range of the above minute conversion rate, and the aliasing noise can be efficiently reduced within a range where the display image is not blurred. .

The control method of the present invention comprises: display means for displaying an image; image processing means for performing resolution conversion processing for converting resolution on input image information and performing filtering processing using a spatial low-pass filter; and the image processing means. A control method for an image display device comprising a control means for controlling, wherein the control means has a preset reference cut when the conversion rate of the resolution of the image information by the resolution conversion processing is 100%. A cutoff frequency calibration step of calibrating the cutoff frequency by multiplying the cutoff frequency by a coefficient that makes the cutoff frequency of the spatial low-pass filter lower than the reference cutoff frequency, and the calibrated cutoff frequency as a parameter The sampling function is multiplied by a window function to calculate the filter coefficient of the spatial low-pass filter. A motor coefficient calculation step, with performing the resolution conversion process, by using the calculated the filter coefficient, and executes a filter processing step of performing a filtering process by the spatial low-pass filter.
Since the control method of the present invention is implemented by the above-described image display device, it can enjoy the same operations and effects as the above-described image display device.

Claims (6)

Display means for displaying an image, image processing means for performing resolution conversion processing for converting the resolution of the input image information and filtering processing by a spatial low-pass filter, and control means for controlling the image processing means An image display device,
The control means includes
A filter coefficient calculation unit that calculates a filter coefficient of the spatial low-pass filter by multiplying a sampling function having a cutoff frequency as a parameter by a window function;
An image display device comprising: a cut-off frequency calibrating unit that calibrates the cut-off frequency in accordance with a conversion rate of resolution of the image information by the resolution conversion process. The image display device according to claim 1,
The cutoff frequency calibration unit is
The image display device, wherein the cut-off frequency is calibrated when the conversion rate is 100% or more. The image display device according to claim 2,
The cutoff frequency calibration unit is
When the conversion rate is greater than 100% and less than or equal to 110%, the cutoff frequency is calibrated by multiplying a preset reference cutoff frequency by the conversion rate and the first calibration coefficient. Image display device. In the image display device according to claim 2 or 3,
The cutoff frequency calibration unit is
When the conversion rate is 100%, the cutoff frequency is calibrated by multiplying a preset reference cutoff frequency by a second calibration coefficient. Display means for displaying an image, image processing means for performing resolution conversion processing for converting the resolution of the input image information and filtering processing by a spatial low-pass filter, and control means for controlling the image processing means A method for controlling an image display device,
The control means is
A cutoff frequency calibration step for calibrating the cutoff frequency of the spatial low-pass filter according to the conversion rate of the resolution of the image information by the resolution conversion process,
A filter coefficient calculation step of calculating a filter coefficient of the spatial low-pass filter by multiplying a sampling function having the calibrated cut-off frequency as a parameter by a window function. Display means for displaying an image, image processing means for performing resolution conversion processing for converting the resolution of the input image information and filtering processing by a spatial low-pass filter, and control means for controlling the image processing means An image display device control program,
A control program causing the control means to execute the control method according to claim 5.

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