JP2012129747A - Image projection apparatus, method for controlling the same, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make moire, which is easy to perceive through motion, inconspicuous even when a projection image is subjected to keystone correction processing.SOLUTION: An image projection apparatus: determines the occurrence of moire on the basis of information on spatial frequency components of input image data; calculates a motion amount in a region where the moire occurs; calculates a filter coefficient of filter processing to which the image data is to be subjected, on the basis of the calculated motion amount; filters the image data by using the calculated filter coefficient; and performs keystone correction on the filtered image data.

Description

  The present invention relates to an image projecting apparatus that projects an image so as to correct trapezoidal distortion of a projected image, a control method therefor, and a program.

  In a projection apparatus such as a projector, the position of the projection apparatus and the screen that is the projection target of the image are separated from each other. ) May cause trapezoidal distortion. For this reason, there has been proposed a technique for causing deformation of an image in the projection apparatus by interpolation processing of image data so as to correct the trapezoidal distortion (for example, Patent Document 1). When the trapezoidal correction as proposed in the above-mentioned patent document is performed, a projection image in which the trapezoidal distortion is corrected can be obtained.

  In general, when performing interpolation processing of image data, it is necessary to consider a signal band originally provided for the image data signal to be interpolated. In particular, when the resolution of the image display portion changes, the signal band that the image originally has may not be sufficiently expressed. In other words, if the band limitation of the interpolation filter is not set in consideration of the difference in input / output resolution, a signal aliasing component occurs. This causes jaggies and moire on the image and causes deterioration in image quality.

  On the other hand, it has been proposed that blurring processing is effective for suppressing moire (for example, see Patent Document 2). Although a method of applying a sufficiently strong low-pass filter so as not to cause moiré is conceivable, if the band is limited more than necessary, the sharpness is deteriorated. Therefore, when performing the blurring process, it is necessary to perform filtering that maintains sharpness while suppressing moire to some extent.

JP 2002-247614 A JP 2001-78039 A

  There is a problem that moire on a projected image caused by trapezoidal correction is noticeable in a moving image even when it is hardly noticeable in a still image. The moire pattern generated on the moving object on the projected image changes depending on the position of the moving object. Therefore, by perceiving the change in the pattern of moire, the existence of moire becomes stronger. However, with the conventional method, the moire reduction process was applied uniformly regardless of whether it was a moving image or a still image. was there.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to make moiré that is easily perceived by movement inconspicuous even when trapezoidal correction processing is performed on a projected image.

  In order to solve the above-described problems, the image projection apparatus of the present invention has the following configuration. That is, moire determination means for determining the occurrence of moire based on information on the spatial frequency component of the input image data, motion amount calculation means for calculating the amount of motion in the area where the moire is generated, and the motion amount calculation Filter coefficient calculation means for calculating a filter coefficient of filter processing to be applied to the image data based on the amount of motion calculated by the means, and filtering the image data using the filter coefficient calculated by the filter coefficient calculation means Filter means for applying, and keystone correction means for performing keystone correction on the image data filtered by the filter means.

  The present invention can make moiré that is easily perceived by movement inconspicuous even when trapezoidal correction processing is performed on a projected image.

Block diagram showing the configuration of the image projection apparatus 101 The flowchart which shows the procedure of the image projection process in 1st Embodiment. 1 is a block diagram showing the configuration of an image processing unit in the first embodiment. Graph showing filter characteristics for video and still images A block diagram showing composition of an image processing part in a 2nd embodiment. The figure which shows an example of the hardware constitutions of the image processing apparatus corresponding to this invention

  Hereinafter, the present invention will be described in detail based on the preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

<Embodiment 1>
FIG. 1 is a block diagram showing the configuration of the image projection apparatus of the present invention. The image projection apparatus 101 includes an optical system 102 for projecting an image on a screen and a control system 106 for controlling projection light. The optical system 102 includes a light source 103, a liquid crystal panel 104, and a projection optical system 105. The control system 106 includes a controller 107, an image processing unit 108, and a liquid crystal driver 109. The controller 107 includes a CPU 110 and a memory 111. The controller 107 controls the image processing unit 108 and the liquid crystal driver 109.

  FIG. 3 is a block diagram illustrating a configuration of the image processing unit 108. The image processing unit 108 includes a moire determination unit 301, a keystone correction preprocessing unit 302, a keystone correction unit 306, and an image quality adjustment unit 307. The keystone correction preprocessing unit 302 includes a motion amount calculation unit 303, a filter coefficient calculation unit 304, and a filtering unit 305. The image processing unit 108 processes an input image signal (image data) given from the outside by these processing units to generate an input signal to the liquid crystal driver 109. The moiré determination unit 301 determines whether moiré has occurred in the input image data. The trapezoid correction unit 306 performs a trapezoid correction process for correcting image distortion that occurs when the screen does not face the optical axis of the optical system 102 of the image projection apparatus 101, so-called trapezoid correction process. The keystone correction preprocessing unit 302 receives image data constituting an image from an external memory or the like, and transfers the image data to the keystone correction unit 306 or the image quality adjustment unit 307. Also, preprocessing of the image data prior to the keystone correction by the keystone correction unit 306 is performed. These processes will be described later. The image quality adjustment unit 307 executes image quality adjustment processing that is normally performed, such as brightness adjustment and color temperature correction.

  The liquid crystal driver 109 generates a drive signal for driving the liquid crystal panel 104 based on the image data input from the image processing unit 108. This drive signal is supplied to the liquid crystal panel 104 and used to control the amount of transmitted light of each pixel included in the liquid crystal panel 104. The light transmitted through the liquid crystal panel 104 is applied to the projection optical system 105.

  The projection optical system 105 projects the light emitted from the liquid crystal panel 104 onto the screen. The screen is irradiated with a predetermined illuminance ratio by the projection light. Note that the calculation of the correction amount for correcting the trapezoidal distortion can be performed by various methods, and the description thereof will be omitted.

  Next, image projection processing performed by the image projection apparatus 101 of the present embodiment will be described. FIG. 2 is a flowchart showing a process of image projection processing. This image projection processing is executed through an image projection start operation (not shown), for example.

  First, image data constituting an image to be projected is input to the image projection apparatus 101 (step S201). The input image data is temporarily stored in the memory 111 in preparation for processing to be described later.

  Next, the moire determination unit 301 determines whether or not moire reduction processing is necessary from the spatial frequency component of the input image data and the information on the reduction ratio at the time of trapezoid correction (step S202). If the image data has no component at a frequency higher than the reduced sampling frequency, moire does not occur, so it is determined that moire reduction processing is unnecessary. In the case of trapezoidal correction with a small inclination, moire reduction processing may not be performed because the generated moire is negligibly small. If it is determined in step S202 that moire reduction processing is unnecessary, the processing ends.

  Next, if it is determined in step S202 that moire reduction processing is necessary, the keystone correction preprocessing unit 302 executes keystone correction preprocessing prior to image processing (keystone correction) for correcting keystone distortion (step S203). ). This keystone correction pre-processing is intended to suppress a phenomenon in which moire is noticeable due to movement.

  In this step, the motion amount calculation unit 303 calculates the motion amount of the moire generation area. As the amount of motion, for example, the magnitude of the motion vector MV of the moire generation region in the reference frame and the target frame is calculated. As the magnitude of the motion vector, an absolute value error SAD (Sum of Absolute Differences) between frames is calculated as shown in the following equation.

  In each block (i, j), SAD is obtained for MV (dx, dy) of all blocks in the search range, and the minimum SAD is the amount of motion between the corresponding frames.

Subsequently, the filter coefficient calculation unit 304 calculates a low-pass filter coefficient based on the amount of motion. FIG. 4 is a graph showing the characteristics of the filter at the spatial frequency. The horizontal axis is the spatial frequency, and the vertical axis is the response characteristic of the filter. f _S represents the sampling frequency of the original signal, and f _c represents the sampling frequency after trapezoidal correction. the spatial frequency components above f _c, since the moire after keystone correction component since f _c is desirably as possible excluded. When the filter characteristic 401 in the case of a still picture, in the case of video, to perceive more strongly moire, to change the characteristics of the 402 in order to increase cutting f _c subsequent component. An example of the filter coefficient calculation method will be described below.

The sampling frequency f _S of the original _signal, the cutoff frequency f band limiting factor of the ideal LPF in _c A and the filter coefficient K (n) is given by the following equation.

Can be expressed as

Here, to determine the cut-off frequency f _c according to the motion amount SAD as follows.

  Subsequently, the formula (3) is multiplied by an arbitrary window function. Examples thereof include a cosine window and a raised cosine window. The filter coefficient is determined by rounding the tap coefficient multiplied by the window function to the expected bit precision. When the movement occurs according to the equation (4), the cut-off frequency is lowered. That is, it is equivalent to blurring more strongly in the case of moving images than in the case of still images. In other words, the filter coefficient is calculated so that the calculated amount of motion is proportional to the strength of the filter. In the present embodiment, an example is given in which the cutoff frequency is changed according to the amount of movement, but the present invention is not limited to this. For example, filter coefficients corresponding to the amount of motion may be stored in advance, and adaptation may be performed according to the amount of motion.

  Subsequently, the filtering unit 305 performs filtering on the image data. Filtering can be realized by using a multiplier (not shown) or by bit shift and addition processing. The filtering may be applied by two-stage processing in the horizontal direction and the vertical direction, or a two-dimensional filter may be applied in a two-dimensional manner by holding a two-dimensional tap in advance.

  Subsequent to the keystone correction pre-processing, the keystone correction unit 306 performs image processing (keystone correction) for correcting the keystone distortion (step S204). The trapezoidal correction, which is the image processing in step S204, corrects the image data and also performs thinning of the image data arranged in the scanning order.

  The outline of such trapezoidal correction is as follows. When trapezoidal distortion occurs in the image projected on the screen, if the LCD panel 104 generates an image distorted in a pattern opposite to this trapezoidal distortion, the image of the projection result on the screen is corrected for trapezoidal distortion. It becomes an image. When generating an image distorted in such a reverse pattern on the liquid crystal panel 104, the calculated trapezoidal correction amount is used, and the interval between pixels is narrowed due to the distortion of the image. Perform thinning.

  Following the trapezoidal correction described above, the image processing unit 108 scans and outputs the corrected image data to the liquid crystal driver 109 (step S205). If necessary, the image quality adjustment unit 307 executes image quality adjustment processing such as brightness adjustment and color temperature correction. The liquid crystal driver 109 drives and controls the liquid crystal panel 104 based on the image data that has received the scan output, and generates an image after the keystone correction on the liquid crystal panel 104. can get.

  According to the present invention, the filter characteristics are changed based on the magnitude of the motion vector in the moire area. The greater the movement of the image, the greater the blurring amount, so that the moire that is noticeable by the movement can be reduced. In this embodiment, the blurring amount of the filter is increased as the motion amount is increased. However, the motion amount and the blurring amount are not necessarily proportional to each other. For example, if the amount of motion is a certain amount or more, the human eye cannot follow, so a selection process may be provided so that the filtering process is not performed.

<Embodiment 2>
In the second embodiment, the moire reduction process is changed based on the moving direction of the moire part and the direction of the pattern of the moire itself. This is because when the moiré movement direction and the moire pattern are horizontal, it is difficult to perceive the change in the moire pattern, but as the relationship between the two directions approaches vertical, it becomes easier to perceive the change in the moire pattern. .

  The operation of the image projection apparatus 101 according to the present embodiment will be described with reference to the block diagram of FIG.

  In the image processing unit 108 in FIG. 5, reference numeral 501 denotes a motion direction detection unit for detecting a moving direction, and reference numeral 502 denotes a moire direction detection unit that detects the direction of moire appearing on the projection screen. The operation of the keystone correction preprocessing unit 302 will be described below.

  First, the motion amount calculation unit 303 calculates the motion amount of the moire generation region. As a method for calculating the amount of motion, SAD may be calculated using the same equation (1) as in the first embodiment.

Next, the motion direction detection unit calculates the motion direction of the moire generation region. The motion direction θ _MV is calculated using the motion vector MV (dx, dy) obtained by the equation (1).

Next, the moire direction detection unit 502 detects the moire pattern direction θ ₀ . For the direction θ _{0 of the} moire pattern, for example, the keystone correction may be performed without applying the moire reduction filter, and the edge direction of the moire pattern at the corresponding location may be detected.

Next, the filter coefficient calculation unit 304 calculates the filter coefficient. First, the angle difference Δθ between the movement direction θ _MV of the moire area and the moire direction θ ₀ is calculated using equation (6).
Δθ = | θ _MV −θ ₀ | (6)
Subsequently, using Δθ and SAD, it determines the cutoff frequency _{f c} (7) as expression.

According to the equation (7), when Δθ is 90 degrees, the moire change due to the movement is conspicuous, so that the correction amount for f ₀ is maximized. On the other hand, when Δθ is 0 degree, the moire change due to the movement is not conspicuous, so the correction for f ₀ is not performed. That is, the cutoff frequency is the same as that at rest. In this way, the cut-off frequency f _c and the first embodiment obtained (2), determines the filter coefficients using equation (3).

  Next, the filtering unit 305 performs filtering on the image data. Filtering can be realized by using a multiplier (not shown) or by bit shift and addition processing.

  Finally, the image data to the keystone correction unit 306 is output. Thereafter, the keystone correction unit 306 performs data processing so as to calibrate the keystone distortion, the image quality adjustment unit 307 performs luminance / chromaticity correction, and then the image after data processing is projected onto the screen.

  According to the present invention, the filter characteristics are changed based on the magnitude of the motion vector in the moire area, the direction of motion, and the direction of moire. The conspicuous change in moire can be suppressed by the relationship between the movement direction and the moire direction.

<Embodiment 3>
The processing performed by the image processing unit 108 can be executed by an image processing device other than the image projection device and input to the image projection device.

  FIG. 6 is a block diagram illustrating a configuration example of computer hardware applicable to the image processing apparatus according to the present embodiment.

  The CPU 601 controls the entire computer using computer programs and data stored in the RAM 602 and the ROM 603, and executes each process described above as performed by the image processing apparatus according to the present embodiment. That is, the CPU 601 functions as the image processing unit 108.

  The RAM 602 has an area for temporarily storing computer programs and data loaded from the external storage device 606, data acquired from the outside via an I / F (interface) 609, and the like. Further, the RAM 602 has a work area used when the CPU 601 executes various processes. That is, the RAM 602 can be allocated as a frame memory, for example, or can provide other various areas as appropriate.

  The ROM 603 stores setting data and a boot program for the computer. The operation unit 604 is configured by a keyboard, a mouse, and the like, and can input various instructions to the CPU 601 by operation of a user of the computer. A display unit 605 displays a processing result by the CPU 601. The display unit 605 is configured by a hold type display device such as a liquid crystal display or an impulse type display device such as a field emission type display device.

  The external storage device 606 is a mass information storage device represented by a hard disk drive device. The external storage device 606 stores an OS (Operating System) and computer programs for causing the CPU 601 to realize the functions of the image processing unit 108. Furthermore, each image data as a processing target may be stored in the external storage device 606.

  Computer programs and data stored in the external storage device 606 are appropriately loaded into the RAM 602 under the control of the CPU 601 and are processed by the CPU 601. A network such as a LAN or the Internet and other devices can be connected to the I / F 607, and the computer can acquire and send various information via the I / F 607. Reference numeral 608 denotes a bus connecting the above-described units.

  The operation having the above-described configuration is controlled by the CPU 601 centering on the operation described in the above flowchart.

<Other embodiments>
The image processing unit 108 illustrated in FIG. 1 has been described in the above embodiment as being configured by hardware. However, the processing performed by the image processing unit 108 may be configured by a computer program. In this case, the processing performed by the image processing unit 108 is performed by the CPU 110.

  The object of the present invention can also be achieved by supplying, to a system, a storage medium that records the code of a computer program that realizes the functions described above, and the system reads and executes the code of the computer program. In this case, the computer program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the computer program code constitutes the present invention. In addition, the operating system (OS) running on the computer performs part or all of the actual processing based on the code instruction of the program, and the above-described functions are realized by the processing. .

  Furthermore, you may implement | achieve with the following forms. That is, the computer program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. Then, based on the instruction of the code of the computer program, the above-described functions are realized by the CPU or the like provided in the function expansion card or function expansion unit performing part or all of the actual processing.

  When the present invention is applied to the above storage medium, the computer program code corresponding to the flowchart described above is stored in the storage medium.

Claims (6)

Moire determination means for determining the occurrence of moire based on information of the spatial frequency component of the input image data;
A motion amount calculating means for calculating the amount of motion in the area where moiré occurs;
Filter coefficient calculation means for calculating a filter coefficient based on the motion amount calculated by the motion amount calculation means;
Filter means for filtering the image data using the filter coefficient calculated by the filter coefficient calculation means;
An image projection apparatus comprising: a keystone correction unit that performs keystone correction on the image data filtered by the filter unit.   2. The image projection according to claim 1, wherein the filter coefficient calculation unit calculates a filter coefficient so that a motion amount calculated by the motion amount calculation unit is proportional to a filter strength of the filter unit. apparatus.   The image projection apparatus according to claim 1, wherein the moire determination unit determines the occurrence of moire based on spatial frequency components of input image data and information on a reduction ratio at the time of trapezoid correction.   Furthermore, it has a motion direction detecting means for detecting the moving direction of the moire area and a moire direction detecting means for detecting the direction of the moire pattern, and the filter coefficient calculating means is based on an angle between the motion direction and the moire direction. The image projecting device according to claim 1, wherein the filter coefficient is calculated by the calculation. A moire determination step of determining the occurrence of moire based on information on the spatial frequency component of the input image data;
A motion amount calculation step for calculating the amount of motion in the area where moiré occurs;
A filter coefficient calculation step for calculating a filter coefficient based on the amount of movement calculated by the movement amount calculation step;
A filtering step of filtering the image data using the filter coefficient calculated by the filter coefficient calculation step;
And a trapezoidal correction step of performing a keystone correction on the image data filtered by the filtering step.   A program that causes the computer to function as the image projection apparatus according to any one of claims 1 to 4 when the computer reads and executes the program.