Image data compression device, image data decompression device, display device, image processing system, image data compression method, and image data decompression method

A compression and decompression module provided in a display device includes: a comparison unit that, when first image data and second image data in which a gradation value of each of a plurality of pixels is expressed in m bits are input, compares gradation values of corresponding pixels of the input first and second image data; a compression unit that compresses the second image data and that, when values of predetermined n bits (where n≦m) of the gradation values match each other in a comparison result of the comparison unit, generates compressed data including identification data indicating that the values of the n bits match each other; and a control unit that performs control to output data, which indicates the gradation value of the corresponding pixel of the first image data, and the compressed data generated by the compression unit so as to correspond to each other.

The entire disclosure of Japanese Patent Application No. 2012-221943, filed Oct. 4, 2012 is expressly incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a technique for compressing or decompressing image data.

2. Related Art

There is a technique for reducing the amount of data transmission by compressing image data showing a still image or a moving image. JP-A-2012-134847 discloses a technique of performing compression processing using the same compression algorithm for the entire image signal. JP-A-2002-354270 discloses a technique of comparing the data of a plurality of lines after compressing still image data in units of a line and transmitting only the header when the lines of the same data appear to overlap each other.

The invention disclosed in JP-A-2012-134847 is for compressing the entire image signal according to the same compression algorithm. Accordingly, it may be difficult to increase the compression rate efficiently. The invention disclosed in JP-A-2002-354270 is for comparing a plurality of lines after compressing still image data using a run-length compression method or the like and determines which of the still image data after line-unit compression and the header is to be transmitted. Therefore, in the invention disclosed in JP-A-2002-354270, compression processing of the still image data is not performed according to the matching of data of a plurality of lines.

SUMMARY

An advantage of some aspects of the invention is to provide a technique for compressing or decompressing image data using a method based on the matching of gradation values in a plurality of pieces of image data.

An image data compression device according to an aspect of the invention includes: a comparison unit that, when first image data and second image data in which a gradation value of each of a plurality of pixels is expressed in m bits are input, compares gradation values of corresponding pixels of the input first image data and second image data; a compression unit that compresses the second image data and that, when values of predetermined n bits (where n≦m) of the gradation values match each other in a comparison result of the comparison unit, generates compressed data including identification data indicating that the values of the n bits match each other; and a control unit that performs control to output data, which indicates the gradation value of the corresponding pixel of the first image data, and the compressed data generated by the compression unit so as to correspond to each other.

According to the aspect of the invention, the gradation values of corresponding pixels in the first image data and the second image data are compared, and when the values of predetermined n bits match each other, compressed data including the identification data indicating that the values match each other is generated. Therefore, it is possible to compress the image data using a method based on the matching of the gradation values in a plurality of pieces of image data.

The image data compression device according to the aspect of the invention may be configured such that, when pixels having the values of the n bits matching between the first image data and the second image data continue, the compression unit generates the compressed data including the identification data and the number of pixels by which the pixels continue.

With this configuration, it is possible to generate compressed data including the number of continuous pixels whose values of n bits match between the first image data and the second image data.

The image data compression device according to the aspect of the invention may be configured such that, when m>n, the compression unit generates the compressed data including the identification data and values other than the n bits of the gradation value of the corresponding pixel of the second image data.

With this configuration, even if the gradation values of corresponding pixels in the first image data and the second image data do not completely match each other, it is possible to compress the second image data.

The image data compression device according to the aspect of the invention may be configured such that the control unit detects movement of an image expressed by the first image data and the second image data and change the corresponding pixels of the first image data and the second image data according to the detected movement.

With this configuration, since the number of pixels whose values of n bits match each other can be increased, it is possible to increase the compression rate.

An image data decompression device according to another aspect of the invention includes: a first memory that stores first image data indicating a gradation value of each of a plurality of pixels; a second memory that stores second image data after compression that indicates a gradation value of each of a plurality of pixels and that, for a pixel whose values of predetermined n bits match a gradation value of a corresponding pixel of the first image data, includes identification data indicating that the values of the n bits match each other; and a decompression unit that reads the first image data from the first memory and reads the second image data from the second memory and decompresses the second image data and that outputs an m-bit (where m≧n) gradation value using the values of the n bits of the corresponding pixel of the read first image data when the identification data is read.

According to this aspect of the invention, when the identification data indicating that the values of predetermined n bits match each other is stored in a memory, the gradation value of the second image data is output using the values of n bits of the gradation value of the corresponding pixel in the first image data. Therefore, it is possible to decompress the image data using a method based on the matching of the gradation values in a plurality of pieces of image data.

The image data decompression device according to the aspect of the invention may be configured such that, when compressed data including the identification data and the number of pixels by which pixels having the values of the n bits matching between the first image data and the second image data continue is read, the decompression unit outputs gradation values of pixels of the number of pixels in m bits using the gradation value of the corresponding pixel of the first image data.

With this configuration, on the basis of the compressed data including the number of continuous pixels having the same gradation value in the first image data and the second image data, the second image data can be decompressed using the values of n bits in the gradation value of the first image data.

The image data decompression device according to the aspect of the invention may be configured such that, assuming that m>n, when compressed data including the identification data and values of (m−n) bits is read, the decompression unit outputs an m-bit gradation value using the values of the n bits of the corresponding pixel of the first image data and the values of the (m−n) bits included in the compressed data.

With this configuration, even if the gradation values of corresponding pixels in the first image data and the second image data do not completely match each other, the second image data can be decompressed using the values of n bits in the gradation value of the first image data.

A display device according to still another aspect of the invention includes: a first memory that stores first image data indicating a gradation value of each of a plurality of pixels; a second memory that stores second image data after compression that indicates a gradation value of each of a plurality of pixels and that, for a pixel whose values of predetermined n bits match a gradation value of a corresponding pixel of the first image data, includes identification data indicating that the values of the n bits match each other; a decompression unit that reads the first image data from the first memory and reads the second image data from the second memory and decompresses the second image data and that outputs an m-bit (where m≧n) gradation value using the values of the n bits of the corresponding pixel of the read first image data when the identification data is read; and a display unit that displays an image according to the gradation value of each of the pixels expressed by the first image data and the second image data and the gradation value of the second image data decompressed by the decompression unit.

According to this aspect of the invention, when the identification data indicating that the values of predetermined n bits match each other is stored in a memory, the gradation value of the second image data is output using the values of n bits of the gradation value of the corresponding pixel in the first image data. Therefore, it is possible to decompress the image data using a method based on the matching of the gradation values in a plurality of pieces of image data.

An image processing system according to yet another aspect of the invention includes: a comparison unit that, when first image data and second image data in which a gradation value of each of a plurality of pixels is expressed in m bits are input, compares gradation values of corresponding pixels of the input first image data and second image data; a compression unit that compresses the second image data and that, when values of predetermined n bits (where n≧m) of the gradation values match each other in a comparison result of the comparison unit, generates compressed data including identification data indicating that the values of the n bits match each other; a control unit that performs control to output data, which indicates the gradation value of the corresponding pixel of the first image data, and the compressed data generated by the compression unit so as to correspond to each other; a first memory that stores first image data including the data indicating the gradation value output from the control unit; a second memory that stores second image data that is second image data after compression by the compression unit and includes the compressed data output from the control unit; and a decompression unit that reads the first image data from the first memory and reads the second image data after compression from the second memory and decompresses the second image data after compression and that outputs an m-bit gradation value using the values of the n bits of the corresponding pixel of the read first image data when the identification data included in the compressed data is read.

According to this aspect of the invention, the gradation values of corresponding pixels in the first image data and the second image data are compared, and when the values of predetermined n bits match each other, compressed data including the identification data indicating that the values match each other is generated. Therefore, it is possible to compress the image data using a method based on the matching of the gradation values in a plurality of pieces of image data.

The image processing system according to the aspect of the invention may be configured such that the image processing system further includes a data amount storage unit that, when the comparison unit compares the values of the n bits in units of a partial region of an image expressed by the first image data and the second image data, stores the amount of the compressed data for each partial region, and the decompression unit decompresses the second image data after compression for each partial region on the basis of the amount of data stored in the data amount storage unit.

With this configuration, even if the amount of data changes with a partial region after compression, it is possible to read the image data corresponding to each partial region from the memory.

An image data compression method according to still yet another aspect of the invention includes: when first image data and second image data in which a gradation value of each of a plurality of pixels is expressed in m bits are input, comparing gradation values of corresponding pixels of the input first image data and second image data; compressing the second image data and, when values of predetermined n bits (where n≦m) of the gradation values match each other in a comparison result, generating compressed data including identification data indicating that the values of the n bits match each other; and performing control to output data, which indicates the gradation value of the corresponding pixel of the first image data, and the generated compressed data so as to correspond to each other.

According to this aspect of the invention, the gradation values of corresponding pixels in the first image data and the second image data are compared, and when the values of predetermined n bits match each other, compressed data including the identification data indicating that the values match each other is generated. Therefore, it is possible to compress the image data using a method based on the matching of the gradation values in a plurality of pieces of image data.

An image data decompression method according to further another aspect of the invention includes: reading, from a first memory that stores first image data indicating a gradation value of each of a plurality of pixels, the first image data; reading second image data from a second memory that stores the second image data after compression that indicates a gradation value of each of a plurality of pixels and that, for a pixel whose values of predetermined n bits match a gradation value of a corresponding pixel of the first image data, includes identification data indicating that the values of the n bits match each other; and decompressing the second image data and outputting an m-bit (where m≧n) gradation value using the values of the n bits of the corresponding pixel of the read first image data when the identification data is read.

According to this aspect of the invention, when the identification data indicating that the values of predetermined n bits match each other is stored in a memory, the gradation value of the second image data is output using the values of n bits of the gradation value of the corresponding pixel in the first image data. Therefore, it is possible to decompress the image data using a method based on the matching of the gradation values in a plurality of pieces of image data.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

First Embodiment

First, a first embodiment of the invention will be described.

FIG. 1is a block diagram showing the overall configuration of a display device according to the present embodiment. A display device1is an example of a display device for displaying a 3D image so that the user can perceive a 3D image with 3D glasses (not shown). As shown inFIG. 1, the display device1includes a control unit10, a signal input unit20, an image processing circuit30, a compression and decompression module40(an example of each of an image data compression device and an image data decompression device), and a display unit50.

The control unit10is a control circuit that controls each unit of the display device1in synchronization with a vertical scanning signal, a horizontal scanning signal, and a dot clock signal that are supplied from a high-level apparatus.

The signal input unit20receives an input of image data Vin from the high-level apparatus (for example, a video reproduction apparatus or a personal computer; not shown) and outputs data according to the input image data Vin. Here, the image data Vin input from the external apparatus is an analog signal. The signal input unit20converts the input image data Vin into image data Vd1, which is a digital signal, and outputs the image data Vd1to the image processing circuit30. The image data Vd1is data indicating the gradation values of three color components (R, G, and B) for each of a plurality of pixels. Here, the image data Vd1is data indicating the gradation values of a plurality of pixels for each frame. An image of each frame is formed by the arrangement of pixels in rows and columns. In the present embodiment, the gradation value of each color component is designated as 10 bits (=m bits) in the image data Vd1. Accordingly, in the image data Vd1, image data corresponding to one pixel expresses the gradation values of three color components as 30-bit data.

The image processing circuit30performs predetermined image processing (for example, 2D/3D conversion processing, frame interpolation processing, high resolution processing, Keystone correction processing, or color conversion processing) on the image data Vd1and outputs image data Vd21and image data Vd22to the compression and decompression module40as image data of two systems. When displaying a 3D image, image data of two systems corresponding to a left-eye image and a right-eye image with parallax is supplied, for example, in a time-division manner. Here, the image data Vd21is image data (an example of first image data) expressing the left-eye image, and the image data Vd22is image data (an example of the second image data) expressing the right-eye image. Since the image data Vd21and the image data Vd22are image data expressing the left-eye image and the right-eye image with parallax as described above, the image data Vd21and the image data Vd22express images having high similarity. Assuming that the format of the image data Vd21and Vd22is based on the Side by Side method, the relationship between the left-eye image and the right-eye image is that the left-eye image and the right-eye image are shifted from each other in a row direction by one or a plurality of pixels.

The compression and decompression module40compresses the image data Vd22using the image data Vd21and Vd22of two systems and then transmits these pieces of image data and outputs image data Vx to the display unit50. The configuration of the compression and decompression module40will be described later.

The display unit50is a display unit that has, for example, a transmissive liquid crystal panel and has a plurality of pixels arrayed in a matrix. In the liquid crystal panel, liquid crystal is sealed between a pair of transparent electrodes. One of the pair of transparent electrodes is divided into a plurality of pixels arrayed in a two-dimensional manner in a matrix. Liquid crystal of each pixel shows the optical characteristics (for example, a transmittance) according to the voltage applied between the transparent electrodes. In the display unit50, incident light can be modulated for each pixel by controlling the voltage applied to each pixel.

A control signal transmission unit60transmits a control signal R (/L) supplied from the control unit10to the 3D glasses, for example, by infrared communication. The control signal R (/L) is a control signal indicating the display period of the right-eye image or the display period of the left-eye image when displaying the 3D image. The 3D glasses control each of a liquid crystal shutter of a lens unit for a right eye and a liquid crystal shutter of a lens unit for a left eye so as to have a transmission state or a non-transmission state according to the received control signal R (/L). The specific configuration or the driving method of the 3D glasses is not particularly limited in the invention.

FIG. 2is a block diagram showing the configuration of the compression and decompression module40. The compression and decompression module40includes a first line buffer41a, a second line buffer41b, a comparison section42, a compression section43, a first frame memory44a, a second frame memory44b, a size information storage buffer45, a first line buffer46a, a second line buffer46b, and a decompression section47. The control unit10performs processing of reading data from each line buffer or each frame memory provided in the compression and decompression module40or processing of storing data in each line buffer or each frame memory.

Each buffer provided in the compression and decompression module40is a First In First Out (FIFO) memory in the present embodiment.

The first and second line buffers41aand41bare buffer memories for storing the image data of one row (that is, one line) in the image data Vd1. The first line buffer41astores the gradation value of each pixel expressed by the image data Vd21input from the image processing circuit30. The second line buffer41bstores the gradation value of each pixel expressed by the image data Vd22input from the image processing circuit30. Here, the image of one frame is assumed to be an image obtained by arraying x pixels in the row direction and y pixels in the column direction in a two-dimensional manner as shown inFIG. 3A. In this case, assuming that the format of the image data Vd21and Vd22for 3D display is based on the Side by Side method, it is preferable that each of the first and second line buffers41aand41bhave at least a capacity for storing the gradation values of pixels of the half of one line (that is, a half line) in the image data Vd1.

As shown inFIG. 3B, the Side by Side method is a method in which a total of two frames of one frame of image data for displaying the left-eye image100aand one frame of image data for displaying the right-eye image100aare compressed to ½ in the row direction and these are disposed side by side in the row direction to create one frame. Therefore, as shown inFIG. 3B, the position of the (x/2)-th pixel from the left in the diagram is a boundary of the left-eye image100aand the right-eye image100a.

When the image data Vd21is input from the first line buffer41aand the image data Vd22is input from the second line buffer41b, the comparison section42compares the gradation values of pixels corresponding to the input image data Vd21and Vd22. Here, for each color component, the comparison section42compares a total of 10 (=m) bits of the gradation values of pixels, which are present at the same position, in the image data Vd21and the image data Vd22. As indicated by the arrow inFIG. 3B, the control unit10reads the gradation values of pixels in each line sequentially from the first and second line buffers41aand41b, and makes the comparison section42compare the gradation values. Then, the comparison section42compares the gradation values of pixels, which are present on the same line and present at the same position in the row direction (that is, read timing is the same), in the left-eye image100aand the right-eye image100a. The comparison section42outputs the image data Vd21to the first frame memory44aand also outputs a comparison result, which indicates whether the gradation values of both pixels match each other, and the image data Vd22to the compression section43.

The compression section43compresses the image data Vd22to generate image data Vd22aand outputs the image data Vd22a. Specifically, when the compared gradation values (gradation values of all color components) of pixels match each other in the comparison result of the comparison section42, the compression section43sets the value of identification data Q, which indicates that the gradation values of compared pixels match each other, to “1” and outputs it to the second frame memory44b. When the value of the identification data Q is output as “1”, the compression section43does not output the gradation values of the compared pixels of the image data Vd22to the second frame memory44b. Thus, the compression section43generates and outputs compressed data including the identification data Q whose value is “1”.

On the other hand, when the gradation values of the compared pixels do not match each other, the compression section43outputs the value of the identification data Q as “0” and also outputs the gradation values of the compared pixels of the image data Vd22to the second frame memory44bas they are (that is, m=10 bits for each color component). For example, the compression section43sets “0”, which is the value of the identification data Q, as a header and outputs gradation values subsequent thereto.

In addition, the compression section43outputs size information SZ, which indicates the amount of data of each line in the image data Vd22a, to the size information storage buffer45. As described above, when the gradation values of the compared pixels do not match each other, the compression section43outputs 1-bit identification data Q (=0) and the gradation value of 30 bits. On the other hand, when the gradation values of the compared pixels match each other, the compression section43outputs 1-bit identification data Q (=1). Thus, the amount of data output from the compression section43corresponding to one pixel changes with matching/non-matching of the gradation values of the compared pixels. In addition, the compression section43outputs data similarly for each of a plurality of pixels that form one line. Accordingly, the compression section43outputs the size information SZ corresponding to each line so that it can be identified that the data stored in the second frame memory44bis data corresponding to which line (burst length for each line).

The first frame memory44a(an example of a first memory) and the second frame memory44b(an example of a second memory) are frame memories for storing the image data of one frame. The first frame memory44ais a frame memory for storing the image data Vd21output from the comparison section42. The second frame memory44bis a frame memory for storing the image data Vd22aincluding the gradation values and the compressed data output from the compression section43.

The size information storage buffer45(an example of a data amount storage section) is a buffer memory for storing the size information SZ output from the compression section43.

Each of the first and second line buffers46aand46bis a line buffer memory for storing the image data of one line. The first line buffer46ais a line buffer memory for storing the image data Vd21atransmitted from the first frame memory44afor each line. The second line buffer46bis a line buffer memory for storing the image data Vd22a, which is transmitted from the second frame memory44bfor each line, and the size information SZ, which is transmitted from the size information storage buffer45, so as to match each other.

The decompression section47decompresses image data Vd22bafter compression, which is read from the second line buffer46bfor each line, on the basis of the size information SZ. The decompression section47outputs the image data of one line alternately from the first and second line buffers46aand46b. Meanwhile, when “1” is input as the identification data Q from the second line buffer46b, the decompression section47outputs a gradation value of m (=10) bits for each color component using the gradation value of the corresponding pixel of image data Vd21b. When the identification data Q is “1”, the gradation values of pixels present at the same position in the image data Vd21band the image data Vd22bare the same. Accordingly, the decompression section47decompresses the image data Vd22busing the image data Vd21b.

FIGS. 4A and 4Bare diagrams for explaining the compression processing in the compression and decompression module40. Squares shown inFIG. 4Aindicate pixels at the same position in the same line for the image data Vd21and the image data Vd22, and pixel numbers of “1” to “12” will be given in order from the left for the sake of explanation. Here, the gradation values of pixels of the left-eye image100aare “1”, “2”, “3”, “4”, “5”, “5”, “5”, “5”, “5”, “5”, “6”, “6” in order from the left, and the gradation values of pixels of the right-eye image100bare “2”, “3”, “4”, “5”, “5”, “5”, “5”, “5”, “5”, “6”, “6”, “6” in order from the left. When these are compared, in the image data Vd21and the image data Vd22, the gradation values of the pixels of “5” to “9”, “11”, and “12” match each other and the gradation values of the other pixels do not match each other.

When the gradation values of the compared pixels do not match each other, the compression section43of the compression and decompression module40outputs “0” (1 bit) as the identification data Q and the gradation value (30 bits) of the pixel in the image data Vd22so as to correspond to each other. In this case, as shown inFIG. 4B, data output from the compression section43is expressed in a format of (identification data (Q=0), gradation value). For example, the compression section43outputs data (0, 2) for the pixel of the pixel number “1” and outputs data (0, 3) for the pixel of the pixel number “2”. On the other hand, when the gradation values of the compared pixels match each other, the compression section43outputs “1” (1 bit) as the identification data Q, which indicates that the gradation values match each other, and the number of continuous pixels, by which pixels of the same gradation values continue in the same line, so as to correspond to each other. In this case, the data output from the compression section43is expressed in a format of (identification data (Q=1), the number of continuous pixels). For example, the compression section43outputs data (1, 5) for the five pixels of the pixel numbers “1” to “5” and outputs the data (1, 2) for the pixels of the pixel numbers “11” and “12”. In the case of x=1920, since the number of continuous pixels can be expressed in 11 bits (211=2048>1920), the amount of data required before compression is a total of 12 bits per pixel. As a result, the amount of data of 18 bits (30 bits−12 bits) is reduced. In the example shown inFIG. 4A, the amount of image data Vd21, that is, the amount of image data when there is no compression is 30 bits×12=360 bits. On the other hand, the amount of image data Vd22aafter compression is 179 bits (31 bits×5+12 bits×2). Therefore, the amount of data is approximately halved by compression processing.

In addition, in the compression and decompression module40, when the gradation values of the compared pixels do not match each other, the value of the identification data Q is set to “0” and is made to correspond to the gradation value. In this case, the amount of data is increased rather. However, assuming that the gradation value of image data of one pixel is set to 10 bits for each color component and accordingly 30 bits are set for the three color components, even if the number of bits is increased to 31 bits due to the addition of the identification data Q, the amount of access to the memory is not changed given that 32-bit data is written into the memory under the conditions in which the bus width is 256 bits.

FIG. 5is a flow chart showing the operation of the display device1when compressing image data.

The control unit10stores the image data Vd21of one line output from the image processing circuit30in the first line buffer41a, and stores the image data Vd22of one line output from the image processing circuit30in the second line buffer41b(step SA1). Then, the comparison section42compares the gradation values of corresponding pixels in the image data Vd21read from the first line buffer41aand the image data Vd22read from the second line buffer41b(step SA2). Here, the control unit10reads the gradation values of the corresponding pixels in the image data Vd21and the image data Vd22at the same timing and supplies the read gradation values to the comparison section42. The comparison section42compares the gradation values of the respective color components of R, G, and B.

Then, the compression section43determines whether or not the gradation values of the pixels compared by the comparison section42match each other (step SA3). When the gradation values of the compared pixels do not match each other (step SA3; NO), the control unit10stores the gradation value of the pixel in the image data Vd21in the first frame memory44a(step SA4). Then, on the basis of the output data of the compression section43, the control unit10stores “0” as the identification data Q and the gradation value of the pixel in the image data Vd22in the second frame memory44bso as to correspond to each other (step SA5). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SA6). Here, the control unit10determines that the above processing has not been completed for the entire line (step SA6; NO), and returns to the process of step SA2.

When the gradation values of the compared pixels match each other (step SA3; YES), the control unit10stores the gradation value of the pixel in the image data Vd21in the first frame memory44a(step SA7). Then, on the basis of the output data of the compression section43, the control unit10stores “1” as the identification data Q and the number of continuous pixels, by which corresponding pixels of the image data Vd21and Vd22continue with the same gradation values (here, continue in the row direction), in the second frame memory44bso as to correspond to each other (step SA8). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SA6).

When it is determined that the processing has been completed for the entire line (step SA6; YES), the control unit10stores the amount of data that forms the line, as the size information SZ, in the size information storage buffer45(step SA9).

After the above processing steps are performed for one line, the display device1processes all pieces of the image data Vd21and Vd22by repeatedly performing the above processing steps while changing the line.

Up to now, the procedure of the compression processing has been described.

FIG. 6is a flow chart showing the operation of the display device1when decompressing image data.

The decompression section47reads the image data Vd21bof one line from the first frame memory44athrough the first line buffer46a(step SB1). On the basis of the image data Vd21bread by the decompression section47, the control unit10outputs the gradation value of each pixel to the display unit50so that the display unit50displays the image according to the gradation value (step SB2). Then, the decompression section47reads the size information SZ, which is stored in the size information storage buffer45, through the second line buffer46b, and reads the image data Vd22bof one line from the second frame memory44bthrough the second line buffer46bon the basis of the read size information SZ (step SB3). Then, the decompression section47determines whether or not the value of the identification data Q read from the second frame memory44bis “1” (step SB4). When it is determined that the value of the identification data Q is not “1”, that is, the value of the identification data Q is “0” (step SB4; NO), the decompression section47outputs a gradation value corresponding to the identification data Q (step SB5). Then, the control unit10outputs the gradation value, which is output from the decompression section47, to the display unit50to display the image (step SB6). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SB7). Here, the control unit10determines that the above processing has not been completed for the entire line (step SB7; NO), and returns to the process of step SB4.

When it is determined that the value of the identification data Q is “1” (step SB4; YES), the decompression section47repeatedly reads the gradation value of the image data Vd21bby the number of continuous pixels (step SB8). Then, the control unit10outputs the gradation value, which is read by the decompression section47, to the display unit50to display the image (step SB6). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SB7). When it is determined that the above processing has been completed for the entire line (step SB7; YES), the control unit10ends the decompression process.

After the above processing steps are performed for one line, the display device1repeatedly performs the above processing steps while changing the line. In the display device1, all pieces of the image data Vd21band Vd22bare processed, and the image data Vx is output to the display unit50.

Up to now, the procedure of the decompression processing has been described.

In the display device1according to the first embodiment described above, when the gradation values of corresponding pixels in image data of a left-eye image and a right-eye image at the time of 3D display match each other, the image data expressing the right-eye image is compressed using identification data. Therefore, according to the display device1, since it is possible to compress the image data using a method based on the matching of the gradation values in a plurality of pieces of image data, it is possible to increase the compression rate efficiently when compressing the image data of two systems having high similarity at the time of 3D display. In addition, since the display device1compresses image data by performing lossless compression, it is possible to prevent an image obtained by decompression processing from being degraded from the original image.

Second Embodiment

Next, a second embodiment of the invention will be described. In the first embodiment described above, the display device1determines whether or not the gradation values of image data of the left-eye image and image data of the right-eye image completely match each other. In contrast, in the present embodiment, predetermined n bits of m bits (where n<m) indicating the gradation value are compared. In addition, it can be said that the relationship of n=m is satisfied in the first embodiment described above.

Since the configuration of the display device1according to the present embodiment is the same as that in the first embodiment described above, explanation thereof will be omitted herein. In addition, in the present embodiment, values of high-order n bits (n=8 bits) of m bits (=10 bits) indicating the gradation value of each color component are compared. Although representative processing using the image data of one of the three color components will be described below, it is assumed that the same processing is performed by each color component.

FIGS. 7A and 7Bare diagrams for explaining the compression processing in the compression and decompression module40.FIG. 7Ashows the same pixel in the same line for the image data Vd21and the image data Vd22, and pixel numbers of “1” to “10” will be given in order from the highest order for the sake of explanation. Here, the values of m bits of the gradation value in the image data Vd21are “1”, “0”, “0”, “0”, “1”, “0”, “0”, “0”, “1”, “1” in order from the highest order, and the values of m bits of the gradation value in the image data Vd22are “1”, “0”, “0”, “0”, “1”, “0”, “0”, “0”, “0” in order from the highest order. When these are compared, in the image data Vd21and the image data Vd22, the values of high-order 8 bits (=n bits) match each other, and the values of low-order 2 bits (=m−n bits) do not match each other. Since the values of high-order 8 bits match each other, the gradation values of pixels on both sides do not completely match each other, but many of the pixels show relatively close gradations.

When the values of high-order n bits do not match between the gradation values of the compared pixels, the compression section43of the compression and decompression module40outputs “0” (1 bit) as the identification data Q, which indicates that the gradation values do not match each other, and the gradation value (30 bits) of the pixel in the image data Vd22so as to correspond to each other. On the other hand, as shown inFIG. 7B, when the values of high-order n bits match between the gradation values of the compared pixels, the compression section43generates and outputs the identification data Q (1 bit), which indicates that the gradation values match each other, and compressed data including the values of low-order (m−n) bits (=2 bits) of the gradation value of the pixel in the image data Vd22. In the example shown inFIGS. 7A and 7B, the value of the identification data Q is “1”, and the values of low-order (m−n) bits are “0” (ninth bit from the highest order) and “0” (tenth bit from the highest order). The amount of data of one pixel when there is no compression is 30 bits, while the amount of data of one pixel after compression is a total of 3 bits of 1 bit of the identification data Q and low-order 2 bits. Therefore, 27 bits are compressed for each pixel by the compression processing of the present embodiment.

FIG. 8is a flow chart showing the operation of the display device1when compressing image data.

The control unit10stores the image data Vd21of one line output from the image processing circuit30in the first line buffer41a, and stores the image data Vd22of one line output from the image processing circuit30in the second line buffer41b(step SC1). Then, the comparison section42compares high-order n bits between the gradation values of corresponding pixels in the image data Vd21read from the first line buffer41aand the image data Vd22read from the second line buffer41b(step SC2). Here, the control unit10reads the gradation values of the corresponding pixels in the image data Vd21and the image data Vd22at the same timing and supplies the read gradation values to the comparison section42.

Then, the compression section43determines whether or not the values of high-order n bits, among m bits indicating the gradation values of the pixels compared by the comparison section42, match each other (step SC3). When the values of the compared high-order n bits do not match each other (step SC3; NO), the control unit10stores the m-bit gradation value of the pixel, which is indicated by the image data Vd21, in the first frame memory44a(step SC4). Then, on the basis of the output data of the compression section43, the control unit10stores “0” as the identification data Q and the gradation value of the compared pixel in the image data Vd22in the second frame memory44bso as to correspond to each other (step SC5). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SC6). Here, the control unit10determines that the above processing has not been completed for the entire line (step SC6; NO), and returns to the process of step SC2.

When the values of the high-order n bits among the m bits indicating the gradation values of the compared pixels match each other (step SC3; YES), the control unit10stores the m-bit gradation value of the pixel, which is indicated by the image data Vd21, in the first frame memory44a(step SC7). Then, on the basis of the output data of the compression section43, the control unit10stores “1” as the identification data Q and the value of low-order (m−n) bits of the gradation value of the compared pixel in the image data Vd22in the second frame memory44bso as to correspond to each other (step SC8). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SC6). When it is determined that the processing has been completed for the entire line (step SC6; YES), the control unit10stores the amount of data that forms the line, as the size information SZ, in the size information storage buffer45(step SC9).

After the above processing steps are performed for one line, the display device1processes all pieces of the image data Vd21and Vd22by repeatedly performing the above processing steps while changing the line.

Up to now, the procedure of the compression processing has been described.

FIG. 9is a flow chart showing the operation of the display device1when decompressing image data.

The decompression section47reads the image data Vd21bof one line from the first frame memory44athrough the first line buffer46a(step SD1). On the basis of the image data Vd21bread by the decompression section47, the control unit10outputs the gradation value of each pixel to the display unit50so that the display unit50displays the image according to the gradation value (step SD2). Then, the decompression section47reads the size information SZ, which is stored in the size information storage buffer45, through the second line buffer46b, and reads the image data Vd22bof one line from the second frame memory44bthrough the second line buffer46bon the basis of the read size information SZ (step SD3). Then, the decompression section47determines whether or not the value of the identification data Q read from the second frame memory44bis “1” (step SD4). When it is determined that the value of the identification data Q is not “1”, that is, the value of the identification data Q is “0” (step SD4; NO), the decompression section47outputs a gradation value corresponding to the identification data Q (step SD5). The control unit10outputs the gradation value, which is output from the decompression section47, to the display unit50to display the image (step SD6). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SD7). Here, the control unit10determines that the above processing has not been completed for the entire line (step SD7; NO), and returns to the process of step SD4.

When it is determined that the value of the identification data Q is “1” (step SD4; YES), the decompression section47outputs an m-bit gradation value obtained by combining the values of high-order n bits of the gradation value of the corresponding pixel in the image data Vd21bwith the values of low-order (m−n) bits included in the same compressed data as the identification data Q (step SD8). The control unit10outputs the gradation value, which is output from the decompression section47, to the display unit50so that the display unit50displays the image according to the gradation value (step SD6). Then, the control unit10determines whether or not the above processing has been completed for the entire line (step SD7). When it is determined that the above processing has been completed for the entire line (step SD7; YES), the control unit10ends the decompression process.

After the above processing steps are performed for one line, the display device1repeatedly performs the above processing steps while changing the line. In the display device1, all pieces of the image data Vd21band Vd22bare processed, and the image data Vx is output to the display unit50.

Up to now, the procedure of the decompression processing has been described.

In the display device1according to the second embodiment described above, when the gradation values of corresponding pixels in image data of a left-eye image and a right-eye image at the time of 3D display match each other, the image data is compressed by outputting the identification data instead of the values of high-order n bits for the right-eye image. Therefore, according to the display device1, it is possible to compress the image data even if the gradation values do not completely match each other. According to the display device1of the present embodiment, it is also possible to increase the compression rate efficiently for image data having gradation values that change continuously, such as a gradation image. In addition, according to the display device1of the present embodiment, the same effects as in the display device1according to the first embodiment described above are obtained.

MODIFICATION EXAMPLES

The invention can be carried out indifferent forms from the embodiments described above. In addition, modification examples shown below may be appropriately combined.

First Modification Example

Although the display device1performs both image data compression processing and image data decompression processing in each of the embodiments described above, a device that compresses image data and a device that decompresses image data may be independent of each other.

FIG. 10is a block diagram showing the overall configuration of a display system1a(an example of an image processing system) of this modification example. The display system1aincludes a data compression device2and a data decompression device3. The data compression device2includes a control unit10a, a signal input unit20, an image processing circuit30, a compression module40a(an example of an image data compression device), and an image transmission unit70. The configuration and operation of the signal input unit20, the image processing circuit30, and the display unit50are the same as those described in each of the above embodiments. The data decompression device3includes a control unit10b, an image receiving unit80, a decompression module40b(an example of an image data decompression device), a display unit50, and a control signal transmission unit60. The configuration and operation of the display unit50and the control signal transmission unit60are the same as those described in each of the above embodiments.

First, the configuration of the data compression device2will be described.FIG. 11is a block diagram showing the configuration of the compression module40aprovided in the data compression device2.

The control unit10ais a control circuit that controls each unit of the data compression device2. The control unit10arealizes a function related to compression processing among the functions of the control unit10described in each of the embodiments described above. As shown inFIG. 11, the compression module40aincludes a first line buffer41a, a second line buffer41b, a comparison section42, a compression section43, a first frame memory44a, a second frame memory44b, and a size information storage buffer45. Since each component provided in the compression module40ais the same as the component having the same reference numeral in each of the embodiments described above, explanation thereof will be omitted herein. Here, the control unit10aoutputs the image data Vd21aand Vd22aread from the first and second frame memories44aand44bto the image transmission unit70, and outputs the size information SZ read from the size information storage buffer45to the image transmission unit70. The image transmission unit70transmits the data output from the compression module40a(specifically, the image data Vd21aand Vd22aand the size information SZ) to the data decompression device3.

Next, the configuration of the data decompression device3will be described.FIG. 12is a block diagram showing the configuration of the decompression module40bprovided in the data decompression device3.

The control unit10bis a control circuit that controls each unit of the data decompression device3. The control unit10brealizes a function related to decompression processing among the functions of the control unit10described in each of the embodiments described above. As shown inFIG. 12, the decompression module40bincludes a first line buffer46a, a second line buffer46b, and a decompression section47. Since each component provided in the decompression module40bis the same as the component having the same reference numeral in each of the embodiments described above, explanation thereof will be omitted herein. Here, the control unit10boutputs the data received by the image receiving unit80(specifically, the image data Vd21aand Vd22aand the size information SZ) to the first and second line buffers46aand46b.

Also in the display system1aof the first modification example, the same effects as in each of the embodiments described above are obtained.

Second Modification Example

In the display device1according to the second embodiment described above, when pixels for which the values of high-order n bits in the image data Vd21and Vd22match each other continue, it is possible to generate compressed data including the identification data Q (=“1”) and the number of continuous pixels, as in the display device1according to the first embodiment described above. In this manner, in the display device1, it is possible to compress image data with a higher compression rate. In contrast, in the display device1according to the first embodiment described above, compressed data may be made not to include the number of continuous pixels by outputting the identification data Q for all pixels, as in the display device1according to the second embodiment described above.

Third Modification Example

In each of the embodiments described above, the compression and decompression module40compresses image data for each line as a partial region. For example, the compression and decompression module40may compress image data for each pixel column that is a group of pixels in the column direction, or may divide partial regions for each block including a plurality of pixels in the row and column directions, or may divide partial regions every plural rows or plural columns. Also in this case, it is preferable that the compression and decompression module40store the size information of each partial region in the size information storage buffer45and perform decompression processing on the basis of the size information of each partial region stored in the size information storage buffer45.

Fourth Modification Example

The compression and decompression module40may compare the gradation values for some pixels (every other pixel) instead of comparing the gradation values for all pixels indicated by the input image data. In this case, even if the compression and decompression module40performs compression processing of replacing the gradation values of some pixels of the image data Vd22with the identification data Q, the effect of reducing the amount of data is obtained.

Fifth Modification Example

In each of the embodiments described above, the compression and decompression module40compresses the image data of the right-eye image without compressing the image data of the left-eye image. However, the compression and decompression module40may compress the image data of the left-eye image without compressing the image data of the right-eye image.

In the embodiment of the invention, the format of image data for 3D display may be based on methods other than the Side by Side method. For example, a method called Frame (Field) Sequential to display a left-eye image and a right-eye image alternately in units of a frame or a field may be used, and a method called Top-and-Bottom may be used.

In addition, the invention may also be applied to a device that performs 2D display without being limited to a device that performs 3D display. Also in this case, it is preferable that the compression and decompression module40compress one set of image data using two sets of image data.

Sixth Modification Example

In each of the embodiments described above, the display device1does not compress the image data Vd21. However, it is possible to compress the image data Vd21using a known compression algorithm. The display device1may compress the image data Vd21using either lossy compression or lossless compression and output the image data after compression indicating the gradation value of each pixel.

In this case, since the image data Vd22bis decompressed using the image data Vd21bin the display device1, it is preferable to perform lossless compression for the image data Vd21.

Seventh Modification Example

In the second embodiment described above, m is set to 10 and n is set to 8. However, the values of m and n may be values other than these as long as the relationship of m>n is satisfied. In this case, the values of m and n are values when the amount of image data has been reduced, compared with that before compression processing, by compression processing using the identification data Q. For example, when the value of the identification data Q is expressed in 1 bit, the amount of image data is reduced by compression processing if the value of n is 2 bits or more.

In addition, in the display device1, it is preferable to compare the values of predetermined n bits set in advance without being limited to the configuration of comparing the values of high-order n bits. In the display device1, the value of n may be manually set by the user or may be automatically set by the device with reference to image data.

Eighth Modification Example

In each of the embodiments described above, the display device1may detect the movement of an image expressed by the image data Vd21and Vd22and change a set of pixels to be compared between the image data Vd21and Vd22according to the detected movement. As described above, for example, in the case of the Side by Side method, the image data Vd21and Vd22is in a relationship in which both image data pieces have moved by one or a plurality of pixels from each other in the row direction. Accordingly, the similarity of both image data pieces is quite high. In this case, if the display device1stores the image data Vd21and Vd22by shifting one of the timing at which the image data Vd21is stored in the first line buffer41aand the timing at which the image data Vd22is stored in the second line buffer41bby the amount of movement, the number of pixels whose gradation values match each other in the image data Vd21and Vd22is further increased. Thus, according to the display device1of this modification example, it is possible to compress image data with a higher compression rate than that in each of the embodiments described above. Even if the format of image data is not based on the Side by Side method, the configuration of this modification can be applied.

Ninth Modification Example

In addition, the image data compression device and the image data decompression device of the embodiment of the invention can also be applied to a computer apparatus or the like, which stores image data that is not for display purposes, without being limited to being applied to the device that displays an image. Thus, the image data compression device and the image data decompression device of the embodiment of the invention can be applied to various apparatuses.

Tenth Modification Example

The display device1may correspond to color components other than R, G, and B, or may correspond to a single color component. In addition, the display device1is not limited to the display device using the transmissive liquid crystal panel. The display device1may be a display device using a reflective liquid crystal panel or may be a display device using an electro-optical element other than liquid crystal, such as an organic electro-luminescence (EL) panel.

Eleventh Modification Example

The detailed configuration of the display device1is not limited to that described inFIG. 1or2. Some of the components described inFIG. 1or2may be omitted in the display device1, or a processing unit that is not present inFIG. 1or2may be added to the display device1, or the order of the processing units may be changed.

Twelfth Modification Example

The display device1is not limited to a projector. The display device1may be a television set, a view-finder-type or monitor-direct-viewing-type video tape recorder, a car navigation system, a pager, an electronic organizer, a calculator, a word processor, a work station, a video phone, a POS terminal, a digital still camera, a mobile phone, a tablet terminal, or a personal computer.