JP2014235392A - Image display device and control method for image display device - Google Patents

Abstract

An image display apparatus capable of reducing deterioration in image quality when image signal compression processing and decompression processing are performed. An image display device (projector 1) is an image display device that performs display based on an image signal, and includes an image input unit (image signal input unit 30) to which the image signal is input, and smoothing of the image signal. A first filter unit 41 that performs a filter process for converting the image data, a compression unit 42 that compresses the smoothed image signal to generate compressed data, a storage unit (frame buffer 43) that stores the compressed data, The decompression unit 44 that reads and decompresses the compressed data stored in the storage unit, the second filter unit 45 that performs the inverse filter process of smoothing on the image signal decompressed by the decompression unit 44, and the inverse by the second filter unit A display unit (image projection unit 10) that performs display based on the image signal subjected to the filter processing. [Selection] Figure 2

Description

  The present invention relates to an image display device and a method for controlling the image display device.

  Conventionally, when performing image processing such as frame rate conversion in an image display device such as a projector, an image signal is temporarily stored in an external memory (frame buffer) such as a DRAM (Dynamic Random Access Memory). Read processing is being performed. In accessing the external memory at this time, there is a case where a compression process for compressing the image data is performed because there is a restriction (speed restriction) on the data transfer capability.

  Patent Document 1 discloses an image processing apparatus that can set the compression rate of an image signal in accordance with the operation status (load status) of the image processing apparatus. In such an image processing apparatus, image processing using a frame buffer can be performed efficiently.

JP 2013-17014 A

  However, when image data (image signal) compression processing and decompression processing are performed, image quality may be degraded. For example, as one of the compression processes, when a pixel value is compared with an adjacent pixel and the difference is small (when the number of bits is small), the difference value is used as data, whereas when the difference is large A compression process for compressing image data by performing an encoding process for rounding a difference value (or pixel value) (reducing the number of bits) is known. In such compression processing, information may be lost when decompressed, and image quality may deteriorate. That is, when the difference between the pixel values of adjacent pixels is large, there is a problem that information is deteriorated in the compression / decompression process and the image quality is deteriorated.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 An image display apparatus according to this application example is an image display apparatus that performs display based on an image signal, and performs an image input unit to which the image signal is input and smoothes the image signal. A first filter unit that performs a filtering process, a compression unit that compresses the smoothed image signal to generate compressed data, a storage unit that stores the compressed data, and the storage unit that stores the compressed data The decompression unit that reads and decompresses the compressed data, the second filter unit that performs the inverse filter processing of the smoothing on the image signal decompressed by the decompression unit, and the inverse filter processing by the second filter unit. And a display unit that performs display based on the received image signal.

  According to such an image display device, the first filter unit smoothes the image signal. The compression unit compresses the smoothed image signal. The storage unit stores the compressed data. The decompressing unit reads the decompressed data from the storage unit and decompresses it. The second filter unit performs inverse filter processing on the decompressed image signal. The display unit performs display based on the image signal that has been subjected to inverse filter processing. Thereby, since the image signal is smoothed by the first filter unit, it is possible to reduce the difference between the pixel values of adjacent pixels, and to suppress deterioration of the image signal in the compression and decompression processing. Become.

  Application Example 2 In the image display device according to the application example, a compression rate setting unit that sets a compression rate of the compression unit and a filter coefficient that is applied to the first filter unit are calculated based on the compression rate. And a filter inverse conversion unit that performs inverse conversion of the filter coefficient and calculates an inverse filter coefficient applied to the second filter unit.

  According to such an image display device, the compression rate setting unit sets the compression rate in the compression unit. The filter coefficient calculation unit calculates a filter coefficient applied to the first filter unit based on the compression rate. The filter inverse transform unit performs inverse transform of the filter coefficient and calculates an inverse filter coefficient applied to the second filter unit. Accordingly, it is possible to calculate the filter coefficient and the inverse filter coefficient based on the compression rate and apply them to the first filter unit and the second filter unit.

  Application Example 3 In the image display device according to the application example described above, the compression unit obtains a difference in pixel value between adjacent pixels for each pixel, and if the difference value is equal to or less than a predetermined value, the difference value Is stored in the storage unit, and when the difference value exceeds the predetermined value, the difference value or the pixel value is encoded and stored in the storage unit.

  According to such an image display device, the compression unit obtains a difference between pixel values of adjacent pixels, and if the difference value is equal to or less than a predetermined value, the difference value is stored in the storage unit and exceeds the predetermined value. In this case, the difference value or the pixel value is encoded and stored in the storage unit. As a result, when the difference between the pixel values of adjacent pixels is small, it is possible to avoid encoding. When the difference is small, it is possible to suppress data deterioration in the compression / decompression process.

  Application Example 4 An image display apparatus control method according to this application example is an image display apparatus control method including an image input unit to which an image signal is input and a display unit that performs display based on the image signal. A first filtering step for performing a filtering process for smoothing the input image signal; a compression step for compressing the smoothed image signal to generate compressed data; and A storage step for storing in the storage unit; a decompression step for reading and decompressing the compressed data stored in the storage unit; and a smoothing inverse filter process performed on the image signal decompressed by the decompression step. A table for causing the display unit to perform display based on the image signal that has been subjected to the inverse filter processing by the second filter step and the second filter step. A step, characterized in that it comprises a.

  According to such a control method of the image display device, since the image signal is smoothed in the first filter step, it is possible to reduce the difference between the pixel values of adjacent pixels, and the image in the compression / decompression process Signal deterioration can be suppressed.

  In addition, when the above-described image display device and the method for controlling the image display device are constructed using a computer provided in the image display device, the above-described embodiment and the application example are for realizing the function. Or a recording medium on which the program is recorded so as to be readable by the computer. Recording media include flexible disk, HDD (Hard Disk Drive), CD-ROM (Compact Disk Read Only Memory), DVD (Digital Versatile Disk), Blu-ray (registered trademark) Disc, magneto-optical disk, nonvolatile memory card In addition, the computer can read the internal storage device (RAM (Random Access Memory), ROM (Read Only Memory), etc.) and external storage device (USB (Universal Serial Bus) memory, etc.) of the image display device. Various media can be used.

1 is a block diagram showing a schematic configuration of a projector according to an embodiment. The block diagram which shows schematic structure of an image process part. It is explanatory drawing of the conversion process of the image signal in an image processing part, (a) is explanatory drawing of a pixel row | line | column, (b) is a graph showing the pixel value at the time of input, (c) is the smoothed pixel (D) is a graph representing pixel values after being compressed and decompressed, and (e) is a graph representing pixel values subjected to the second filter processing.

  Hereinafter, as an embodiment of an image display device, a projector that modulates light emitted from a light source based on an image signal to form an optical image and projects the optical image on an external screen or the like will be described with reference to the drawings. explain.

FIG. 1 is a block diagram illustrating a schematic configuration of a projector according to the present embodiment.
As shown in FIG. 1, the projector 1 includes an image projection unit 10 as a display unit, a control unit 20, an operation reception unit 21, an image signal input unit 30 as an image input unit, an image processing unit 40, and the like.

  The image projection unit 10 includes a light source device 11 as a light source, three liquid crystal light valves 12R, 12G, and 12B as light modulation devices, a projection lens 13 as a projection optical system, a liquid crystal drive unit 14, and the like. The image projection unit 10 modulates the light emitted from the light source device 11 into image light by the liquid crystal light valves 12R, 12G, and 12B, and projects the image light from the projection lens 13 to display an image on the projection surface S. .

  The light source device 11 includes a discharge-type light source lamp 11a made of an ultra-high pressure mercury lamp, a metal halide lamp, or the like, and a reflector 11b that reflects light emitted from the light source lamp 11a toward the liquid crystal light valves 12R, 12G, and 12B. Has been. The light emitted from the light source device 11 is converted into light having a substantially uniform luminance distribution by an integrator optical system (not shown), and red (R), green (G), which are the three primary colors of light by a color separation optical system (not shown), After being separated into blue (B) color light components, they are incident on the liquid crystal light valves 12R, 12G, and 12B, respectively.

  The liquid crystal light valves 12R, 12G, and 12B are configured by a liquid crystal panel in which liquid crystal is sealed between a pair of transparent substrates. The liquid crystal light valves 12R, 12G, and 12B include a rectangular pixel region in which a plurality of pixels (not shown) are arranged in a matrix, and a driving voltage can be applied to the liquid crystal for each pixel. Yes. When the liquid crystal driving unit 14 applies a driving voltage corresponding to the input image information to each pixel, each pixel is set to a light transmittance corresponding to the image information. For this reason, the light emitted from the light source device 11 is modulated by transmitting through the pixel regions of the liquid crystal light valves 12R, 12G, and 12B, and image light corresponding to image information is formed for each color light. The formed image light of each color is synthesized for each pixel by a color synthesis optical system (not shown) to become color image light, and then enlarged and projected by the projection lens 13.

  The control unit 20 includes a CPU (Central Processing Unit), a RAM used for temporary storage of various data, a non-volatile ROM, and the like, and the CPU operates according to a control program stored in the ROM so that the projector The operation of 1 is supervised. That is, the control unit 20 functions as a computer.

  The operation reception unit 21 includes a plurality of operation keys for the user to give various instructions to the projector 1. The operation keys included in the operation reception unit 21 of the present embodiment include a power key for switching on / off the power, an input switching key for switching an input video signal, and a menu for displaying menu images for various settings. There are a key, a direction key used for selecting an item in the menu image, and a decision key for confirming the selected item.

  When the user operates various operation keys of the operation reception unit 21, the operation reception unit 21 receives this operation and outputs a control signal corresponding to the operated operation key to the control unit 20. Then, when a control signal is input from the operation reception unit 21, the control unit 20 performs processing based on the input control signal and controls the operation of the projector 1. In addition, it is good also as a structure which used the remote control (not shown) which can be operated remotely instead of the operation reception part 21 or with the operation reception part 21 as an input operation part. In this case, the remote controller transmits an operation signal such as an infrared ray corresponding to the operation content of the user, and a remote control signal receiving unit (not shown) receives this and transmits it to the control unit 20.

  The image signal input unit 30 includes a plurality of input terminals, and various types of image signals are input to these input terminals from an external image supply device (not shown) such as a video reproduction device or a personal computer. The image signal input unit 30 converts the input image signal into digital image information and outputs the image information to the image processing unit 40.

  The image processing unit 40 processes and outputs the digital image signal input from the image signal input unit 30 for each image of one screen (one frame). Further, the image processing unit 40 performs various image processing such as frame rate conversion processing and resizing processing based on an instruction from the control unit 20. Further, the image processing unit 40 performs image quality adjustment processing for adjusting image quality such as brightness, contrast, sharpness, hue, and the like on the image signal, and outputs the processed image signal to the liquid crystal driving unit 14. .

Here, the image processing unit 40 when performing image processing such as frame rate conversion processing and resizing processing will be described.
FIG. 2 is a block diagram illustrating a schematic configuration of the image processing unit 40.

  As shown in FIG. 2, the image processing unit 40 includes a first filter unit 41, a compression unit 42, a frame buffer 43 as a storage unit, a decompression unit 44, a second filter unit 45, a compression rate setting unit 46, and a filter coefficient calculation. Unit 47, filter inverse conversion unit 48, and the like.

  The first filter unit 41 performs first filter processing on the input image signal based on the filter coefficient input from the filter coefficient calculation unit 47 and outputs the result to the compression unit 42. The first filter processing is filter processing using a filter (low-pass filter) for smoothing pixel values included in the image signal. That is, since the high-frequency component is removed, for example, when the difference in pixel value between adjacent pixels is large, the difference is small.

  The compression unit 42 compresses (encodes) the image signal input from the first filter unit 41 based on the compression rate set by the compression rate setting unit 46 and writes the compressed image signal in the frame buffer 43. The compressed image signal corresponds to compressed data.

  Here, the compression algorithm of this embodiment will be described. The compression unit 42 obtains a difference between pixel values from adjacent pixels. If the difference is small, specifically, if the difference value (difference value) can be expressed by a predetermined number of bits, the difference value is written in the frame buffer 43 as it is. When the difference is large, specifically, when the difference value exceeds a predetermined number of bits, the difference value (or pixel value) is encoded and written in the frame buffer 43. As a coding method, a method of reducing the number of bits by omitting lower bits of the difference value (or pixel value). At the time of decompression, the omitted bits are added and a predetermined value is set. This compression method is an irreversible compression, and when it is compressed by encoding, information deterioration may occur due to decompression. That is, the image quality may be deteriorated. In such a compression algorithm, as the number of pixel values having a large difference increases, that is, as the number of high-frequency components increases, the probability of information deterioration due to encoding increases.

  The frame buffer 43 includes a DRAM. The frame buffer 43 temporarily stores the compressed image signal being processed and is used for various image processing.

  The decompression unit 44 reads the compressed image signal from the frame buffer 43, decompresses (decodes) the image signal based on the compression rate, and outputs the decompressed image signal to the second filter unit 45. In the present embodiment, image processing such as frame rate conversion processing and resizing processing is performed when an image signal stored in the frame buffer 43 is read.

  The second filter unit 45 performs the second filter process based on the inverse filter coefficient input from the filter inverse transform unit 48. The second filter process is a filter process using a filter (high-pass filter) for enhancing (sharpening) high-frequency components, so that the image signal is in a state close to the image signal before the first filter process. Perform restoration. Here, the second filter process is a filter process using an inverse filter of the filter used in the first filter process. For this reason, the second filter process is also referred to as an inverse filter process.

  The compression rate setting unit 46 sets the compression rate that the compression unit 42 compresses. In the present embodiment, the compression rate set by the compression rate setting unit 46 is fixed when the projector 1 is designed. For example, the compression rate is changed according to the load of image processing. Also good. The compression rate set by the compression rate setting unit 46 is output to the compression unit 42, the decompression unit 44, and the filter coefficient calculation unit 47.

  The filter coefficient calculation unit 47 calculates a filter coefficient based on the set compression rate. Specifically, the filter coefficient calculation unit 47 derives from the compression rate information how many pixel value differences between the adjacent pixels occur and information deterioration due to compression and decompression. Then, the filter coefficient calculation unit 47 calculates a filter coefficient that reduces the difference based on the derived difference, that is, a smoothing filter coefficient. The filter coefficient is output to the first filter unit 41 and the filter inverse transform unit 48.

  The filter inverse conversion unit 48 receives the filter coefficient (smoothing filter coefficient) from the filter coefficient calculation unit 47 and performs inverse conversion, thereby calculating the inverse filter coefficient of the filter processing performed by the first filter unit 41. The filter inverse conversion unit 48 outputs the calculated inverse filter coefficient to the second filter unit 45.

  As described above, the second filter unit 45 performs the second filter process based on the inverse filter coefficient, and outputs the processed image signal.

Next, conversion processing such as first filter processing, compression processing, decompression processing, and second filter processing of the image signal in the image processing unit 40 will be described.
FIG. 3 is an explanatory diagram of image signal conversion processing in the image processing unit 40, (a) is an explanatory diagram of a pixel column, (b) is a graph showing a pixel value at the time of input, c) is a graph representing a smoothed pixel value, (d) is a graph representing a pixel value after being compressed and decompressed, and (e) is a pixel value subjected to the second filter processing. It is a graph showing.

  FIG. 3A shows a pixel row in which pixels P based on the input image signal are arranged. In the present embodiment, a pixel row in which nine pixels P are arranged is displayed. In FIG. 3B, a graph representing the pixel value corresponding to FIG. 3A, that is, the pixel value of the pixel P based on the input image signal is displayed.

  In FIG.3 (c), the pixel value smoothed by the 1st filter part 41 is represented as a graph. Here, when the pixel value is smoothed, the high-frequency component is cut and added to the adjacent pixel value. That is, when smoothing is performed, the difference between pixel values of adjacent pixels becomes small, and the probability of encoding at the time of compression becomes low.

  In FIG. 3D, pixel values that have been subjected to compression processing by the compression unit 42, written to the frame buffer 43, and subjected to decompression processing by the decompression unit 44 are shown as a graph. Here, since the pixel value is smoothed as described above, there is little information deterioration due to encoding.

  In FIG. 3E, the pixel values on which the second filter processing has been performed are represented as a graph. When the second filter process is performed, the high-frequency component is emphasized, the pixel value is restored, and the pixel value is close to that before the first filter process.

  Thus, the image signal input to the image processing unit 40 is output in a state where there is little information deterioration.

  Returning to FIG. 1, the image signal output from the image processing unit 40 is input to the liquid crystal driving unit 14.

  The liquid crystal drive unit 14 drives the liquid crystal light valves 12R, 12G, and 12B according to the image information input from the image processing unit 40. Thereby, the light emitted from the light source device 11 is modulated according to the image information by the liquid crystal light valves 12R, 12G, and 12B and projected from the projection lens 13.

According to the embodiment described above, the following effects can be obtained.
(1) The first filter unit 41 in the image processing unit 40 of the projector 1 smoothes the image signal. The compression unit 42 compresses the smoothed image signal and stores it in the frame buffer 43. As a compression algorithm at this time, a difference between pixel values of adjacent pixels is obtained. If the difference is small, the difference value is left as it is. If the difference is large, the difference value is encoded and stored in the frame buffer 43 It is a writing method. This compression method is irreversible compression, and when encoded and compressed, information degradation (degradation of image quality) may occur due to decompression. The decompressing unit 44 reads out and decompresses the compressed image signal data from the frame buffer 43. Then, the second filter unit 45 performs a smoothing inverse filter process on the decompressed image signal. With such a configuration of the image processing unit 40, since the first filter unit 41 smoothes the image signal, it is possible to reduce the difference between the pixel values of adjacent pixels. Therefore, since the difference value is encoded at the time of compression, deterioration of the image signal in the compression / decompression process can be suppressed. That is, image degradation can be suppressed.

  (2) The filter coefficient calculation unit 47 of the image processing unit 40 of the projector 1 calculates the filter coefficient applied to the first filter unit 41 based on the compression rate set by the compression rate setting unit 46. The filter inverse transform unit 48 performs inverse transform of the filter coefficient and calculates an inverse filter coefficient applied to the second filter unit 45. Thereby, if the compression rate is set, the filter coefficient and the inverse filter coefficient are calculated based on the compression rate and applied to the first filter unit 41 and the second filter unit 45, which is beneficial.

  In addition, it is not limited to embodiment mentioned above, It is possible to implement by adding various change, improvement, etc. A modification will be described below.

  (Modification 1) In the above embodiment, the projector 1 is described as an example. However, the image display device is not limited to the projector. For example, the present invention can be applied to a rear projector, a liquid crystal display, a plasma display, an organic EL (Electro Luminescence) display, and the like that are integrally provided with a transmissive screen.

  (Modification 2) In the above embodiment, the light source device 11 is configured to include the discharge-type light source lamp 11a, but a solid light source such as an LED light source or a laser, or other light sources can also be used.

  (Modification 3) In the above embodiment, the projector 1 uses the transmissive liquid crystal light valves 12R, 12G, and 12B as the light modulator, but the reflective light modulator such as a reflective liquid crystal light valve. It is also possible to use. In addition, it is possible to use a micromirror array device that modulates light emitted from a light source by controlling the emission direction of incident light for each micromirror as a pixel.

  DESCRIPTION OF SYMBOLS 1 ... Projector, 10 ... Image projection part, 11 ... Light source device, 11a ... Light source lamp, 11b ... Reflector, 12R, 12G, 12B ... Liquid crystal light valve, 13 ... Projection lens, 14 ... Liquid crystal drive part, 20 ... Control part, DESCRIPTION OF SYMBOLS 21 ... Operation reception part, 30 ... Image signal input part, 40 ... Image processing part, 41 ... 1st filter part, 42 ... Compression part, 43 ... Frame buffer, 44 ... Decompression part, 45 ... 2nd filter part, 46 ... Compression ratio setting unit, 47... Filter coefficient calculation unit, 48.

Claims (4)

An image display device that performs display based on an image signal,
An image input unit to which the image signal is input;
A first filter unit that performs filter processing for smoothing the image signal;
A compression unit that compresses the smoothed image signal to generate compressed data;
A storage unit for storing the compressed data;
A decompression unit that reads and decompresses the compressed data stored in the storage unit;
A second filter unit that performs the inverse filtering of the smoothing on the image signal decompressed by the decompression unit;
A display unit that performs display based on the image signal that has been subjected to the inverse filter processing by the second filter unit;
An image display device comprising: The image display device according to claim 1,
A compression rate setting unit for setting a compression rate of the compression unit;
A filter coefficient calculation unit that calculates a filter coefficient applied to the first filter unit based on the compression rate;
A filter inverse transform unit that performs inverse transform of the filter coefficient and calculates an inverse filter coefficient applied to the second filter unit;
An image display device further comprising: The image display device according to claim 1 or 2,
For each pixel, the compression unit obtains a difference in pixel value from an adjacent pixel. When the difference value is equal to or less than a predetermined value, the compression unit stores the difference value in the storage unit, and the difference value is the predetermined value. The image display device, wherein the difference value or the pixel value is encoded and stored in the storage unit. A control method for an image display device, comprising: an image input unit to which an image signal is input; and a display unit that performs display based on the image signal.
A first filter step for performing filter processing for smoothing the input image signal;
A compression step of compressing the smoothed image signal to generate compressed data;
A storage step of storing the compressed data in a storage unit;
A decompression step of reading and decompressing the compressed data stored in the storage unit;
A second filter step for performing the smoothing inverse filter process on the image signal decompressed by the decompression step;
A display step of causing the display unit to perform display based on the image signal that has been subjected to the inverse filter processing by the second filter step;
A control method for an image display device, comprising:

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