Image compression apparatus and image compression method

1. Field of the Invention

The present invention relates to an image compression apparatus and method that measures the distance to a subject when capturing an image.

2. Description of the Related Art

Various techniques have been developed to impart presence to moving image data.

Presence can be imparted to moving image data by, for example, reproducing a three-dimensional image.

A three-dimensional image may be generated by, for example, acquiring two image data of the same subject from the viewpoints of the left and right eyes. When reproducing the three-dimensional image data, the image data for the left eye is to be viewed by the left eye while the image data for the right eye is to be viewed by the right eye. Hereinafter, image data acquired from the viewpoints of the left and right eyes are referred to as “parallax images”.

The simplest way to generate parallax images is to install two cameras at positions corresponding to the left and right eyes to capture two images. However, it takes significant effort and cost to capture images using this method. Therefore, a technique for generating three-dimensional image data on the basis of two-dimensional moving image data acquired with a single camera has been desired.

In order to generate three-dimensional image data on the basis of a single two-dimensional image, two parallax images are generated from the single two-dimensional image.

In order to generate two parallax images from a single two-dimensional image, distance information indicating the distance to each subject in the two-dimensional image data has been used to date.

To obtain the distance information, a human may view an image to estimate the distance from the viewpoint (camera position), at which the image was captured, to the subject. Disadvantageously, however, it may be difficult to automate this scheme, since a human estimates the distance.

Therefore, there has been desired a technique for automatically measuring the distance to a subject when generating a two-dimensional image.

Japanese Unexamined Patent Application Publication No. Hei 08-70473 (JP-A-Hei 08-70473) discloses a technique for automatically measuring the distance to a subject when generating a single two-dimensional image to provide image data with distance information.

However, the technique disclosed in JP-A-Hei 08-70473 generates an excessive amount of image data with distance information, which makes it difficult to store such image data in a storage medium. Because each pixel in the image data is provided with the distance information in the technique disclosed in JP-A-Hei 08-70473, the amount of information regarding distance may be about as large as the amount of information regarding the image data itself. Therefore, image data with distance information, even if compressed, may be of a much larger amount than image data without distance information.

In addition, since the distance is measured for each pixel in the technique disclosed in JP-A-Hei 08-70473, the distance measurement process may be burdensome, disadvantageously making it difficult to apply the technique to moving image data.

It is desirable to provide an image compression apparatus and an image compression method that makes the distance measurement process less burdensome and that generates image data with distance information of a smaller amount.

According to an embodiment of the present invention, there is provided an image compression apparatus including: a first imaging section for capturing an image of a subject to generate a first image signal; a second imaging section for capturing an image of the subject to generate a second image signal; a first encoding section for encoding the first image signal generated by the first imaging section to generate first image data; a second encoding section for encoding the second image signal generated by the second imaging section to generate second image data; a first distance measuring section for measuring a distance to the subject for each of image blocks, at the same time as the first imaging section performs image capturing, to generate first distance information; a second distance measuring section for measuring a distance to the subject for each of image blocks, at the same time as the second imaging section performs image capturing, to generate second distance information; a first multiplexing section for generating first multiplexed data on the basis of the first image data generated by the first encoding section and the distance measured by the first distance measuring section, the first multiplexed data being generated by multiplexing first distance data and the first image data, the first distance data being generated on the basis of the first distance information and indicating the distance to the subject for each of predefined pixel blocks in the first image data; a second multiplexing section for generating second multiplexed data on the basis of the second image data generated by the second encoding section and the distance measured by the second distance measuring section, the second multiplexed data being generated by multiplexing second distance data and the second image data, the second distance data being generated on the basis of the second distance information and indicating the distance to the subject for each of predefined pixel blocks in the second image data; and a compression processing section for reducing amounts of the first multiplexed data and the second multiplexed data to generate compressed data. The compression processing section generates the compressed data by extracting long-distance blocks, in which the distance to the subject is larger than a predetermined threshold, in the first image data on the basis of the first distance data contained in the first multiplexed data generated by the first multiplexing section, extracting long-distance blocks in the second image data on the basis of the second distance data contained in the second multiplexed data generated by the second multiplexing section, calculating a differential between the long-distance blocks in the first multiplexed data and the long-distance blocks in the second multiplexed data, and deleting the long-distance blocks in the first multiplexed data or the long-distance blocks in the second multiplexed data which are identical to their counterparts in the other multiplexed data.

According to another embodiment of the present invention, there is provided an image compression method including the steps of: capturing an image of a subject to generate first and second image signals, and at the same time, measuring a distance to the subject for each of image blocks to generate first and second distance information; encoding the first and second image signals generated in the image capturing and measuring step to generate first and second image data; generating first multiplexed data by multiplexing first distance data and the first image data, the first distance data being generated on the basis of the first distance information and indicating the distance to the subject for each of predefined pixel blocks in the first image data, and generating second multiplexed data by multiplexing second distance data and the second image data, the second distance data being generated on the basis of the second distance information and indicating the distance to the subject for each of predefined pixel blocks in the second image data; and generating compressed data by extracting long-distance blocks, in which the distance to the subject is larger than a predetermined threshold, in the first image data on the basis of the first distance data contained in the first multiplexed data, extracting long-distance blocks in the second image data on the basis of the second distance data contained in the second multiplexed data, calculating a differential between the long-distance blocks in the first multiplexed data and the long-distance blocks in the second multiplexed data, and deleting the long-distance blocks in the first multiplexed data or the long-distance blocks in the second multiplexed data which are identical to their counterparts in the other multiplexed data.

FIG. 1 is a block diagram showing an exemplary configuration of an image compression apparatus according to a first embodiment;

FIG. 2A illustrates how a compression processing section of the first embodiment compresses two multiplexed data on the basis of distance data, showing an image portion of one of the multiplexed data;

FIG. 2B illustrates how the compression processing section of the first embodiment compresses the two multiplexed data on the basis of the distance data, showing an image portion of the other of the multiplexed data;

FIG. 3A illustrates the temporal compression effect of a compression process performed by the compression processing section, showing an image portion of the one of the multiplexed data generated at a first time;

FIG. 3B illustrates the temporal compression effect of the compression process performed by the compression processing section, showing an image portion of the other of the multiplexed data generated at the same time as the image portion of FIG. 3A ;

FIG. 3C illustrates the temporal compression effect of the compression process performed by the compression processing section, showing an image portion of the one of the multiplexed data generated at a second time later than the first time;

FIG. 3D illustrates the temporal compression effect of the compression process performed by the compression processing section, showing an image portion of the other of the multiplexed data generated at the same time as the image portion of FIG. 3C ;

FIG. 4 is a flowchart illustrating an exemplary operation to generate a three-dimensional image of the image compression apparatus according to the first embodiment;

FIG. 5 shows an exemplary configuration of an image compression apparatus according to a second embodiment;

FIG. 6A illustrates how a compression processing section of the second embodiment compresses four multiplexed data on the basis of distance data embedded in the respective multiplexed data, showing an image portion of first multiplexed data;

FIG. 6B illustrates how the compression processing section of the second embodiment compresses the four multiplexed data on the basis of the distance data embedded in the respective multiplexed data, showing an image portion of second multiplexed data;

FIG. 6C illustrates how the compression processing section of the second embodiment compresses the four multiplexed data on the basis of the distance data embedded in the respective multiplexed data, showing an image portion of third multiplexed data; and

FIG. 6D illustrates how the compression processing section of the second embodiment compresses the four multiplexed data on the basis of the distance data embedded in the respective multiplexed data, showing an image portion of fourth multiplexed data.

Hereinafter, a description will be made regarding embodiments of the present invention.

<First Embodiment>

FIG. 1 is a block diagram showing an exemplary configuration of an image compression apparatus 100 according to a first embodiment.

As shown in FIG. 1 , the image compression apparatus 100 of the first embodiment includes an imaging section 1 A (corresponding to a first imaging section of the present invention), an imaging section 1 B (corresponding to a second imaging section of the present invention), an encoding section 2 A (corresponding to a first encoding section of the present invention), an encoding section 2 B (corresponding to a second encoding section of the present invention), a distance measuring sensor 3 A (corresponding to a first distance measuring section of the present invention), a distance measuring sensor 3 B (corresponding to a second distance measuring section of the present invention), a distance information processing section 4 A, a distance information processing section 4 B, a multiplexing section 5 A (corresponding to a first multiplexing section of the present invention), a multiplexing section 5 B (corresponding to a second multiplexing section of the present invention), a compression processing section 6 (corresponding to a compression processing section of the present invention), a storage section 7 , and an output section 8 .

As discussed above, the image compression apparatus 100 of the first embodiment includes two imaging sections, two encoding sections, two distance measuring sensors, two distance information processing sections, and two multiplexing sections. The configuration allows the acquisition of two image data, that is, image data to be viewed with the right eye and image data to be viewed with the left eye.

The following describes the details of the respective components.

The imaging section 1 A captures an image of a subject to generate an image signal 201 A, and may be an imaging device such as a digital still camera or a digital video camera.

The encoding section 2 A compresses the image signal 201 A generated by the imaging section 1 A for conversion into digital image data 202 A. The encoding section 2 A may use an image encoding technique such as MPEG1, MPEG2, MPEG4, DivX (a registered trademark of Divx, Inc.), Xvid and WMV9, for example. In this embodiment, the encoding section 2 A uses MPEG as the image encoding technique.

The distance measuring sensor 3 A is attached to the imaging section 1 A, and measures the distance to the subject when the imaging section 1 A captures an image of the subject and outputs the measured distance as distance information 203 A. The distance measuring sensor 3 A may be a sensor for measuring the distance by infrared rays or ultrasonic waves, for example. The distance measuring sensor 3 A measures the distance to the subject for pixels extracted from predefined pixel blocks composed of all the pixels of the imaging section 1 A.

The distance measuring sensor 3 A may use macro blocks (16×16 pixels) used in MPEG1 and MPEG 1 and blocks (8×8 pixels), for example, for the above-mentioned predefined pixel blocks. That is, in the case where distance measurement is performed for each macro block, for example, each distance measuring element of the distance measuring sensor 3 A may be provided for every 16×16 pixels of the imaging section 1 A.

That is, in the case where distance measurement is performed for each macro block, for example, the distance measuring sensor 3 may be prepared that has the same number of distance measuring elements as the number of the macro blocks in the digital image data 202 A generated by the encoding section 2 A. The plurality of distance measuring elements of the distance measuring sensor 3 A may be arranged in a matrix so as to correspond to the respective macro blocks, for example.

The distance information processing section 4 A generates distance data 204 A on the basis of the distance information 203 A generated by the distance measuring sensor 3 A. Since the distance data 204 A generated by the distance information processing section 4 A is based on the distance information 203 A generated by the distance measuring sensor 3 A, the distance data 204 A is generated for each predefined pixel block in the digital image data 202 A generated by the encoding section 2 A.

The multiplexing section 5 A multiplexes the digital image data 202 A generated by the encoding section 2 A and the distance data 204 A generated by the distance information processing section 4 A to generate multiplexed data 205 A. In the multiplexed data 205 A, each predefined pixel block in the digital image data 202 A has been embedded with the distance data 204 A corresponding to that block, for example.

The configurations of the imaging section 1 B through to the multiplexing section 5 B are substantially the same as the configurations of the above-mentioned imaging section 1 A through to the multiplexing section 5 A, respectively. It should be noted, however, that the imaging section 1 B generates an image signal 201 B, the encoding section 2 B generates digital image data 202 B, the distance measuring sensor 3 B generates distance information 203 B, the distance information processing section 4 B generates distance data 204 B, and the multiplexing section 5 B generates multiplexed data 205 B.

The imaging sections 1 A and 1 B are configured to perform image capturing simultaneously. This is because the imaging section 1 A captures an image of the subject to be viewed with the right eye and the imaging section 1 B captures an image of the subject to be viewed with the left eye, for example, in order to generate a three-dimensional image on the basis of two parallax images. In addition, the imaging sections 1 A and 1 B are located at equal distances from the subject.

The compression processing section 6 recompresses the multiplexed data 205 A and 205 B to generate compressed data 206 of a smaller amount. A compression scheme used by the compression processing section 6 will be described in detail later.

The storage section 7 is a memory for storing the compressed data 206 generated by the compression processing section 6 .

The output section 8 outputs the compressed data 206 generated by the compression processing section 6 to the outside via a predetermined transmission path. On the basis of the output compressed data 206 , a three-dimensional image generation apparatus (not shown) generates three-dimensional image data, for example. It should be noted, however, that the present invention does not limit how three-dimensional image data is generated on the basis of the compressed data 206 . For example, three-dimensional image data may be generated utilizing a technique used in the past.

Now, a description is made regarding how the compression processing section 6 recompresses the two multiplexed data 205 A and 205 B.

FIG. 2 illustrates how the two multiplexed data 205 A and 205 B are compressed on the basis of the distance data 204 A and 204 B.

FIG. 2A shows an image portion of the multiplexed data 205 A. In this embodiment, the multiplexed data 205 A shown in FIG. 2A is an image to be viewed with the left eye (hereinafter referred to as “left-eye image”), of two parallax images.

The image shown in FIG. 2A has been compression-encoded (in this embodiment, using MPEG) by the encoding section 2 A. Each block shown in FIG. 2A (in this embodiment, a macro block of 16×16 pixels) has been provided with the distance data 204 A for that block, which indicates the distance to the subject captured in that block.

In FIG. 2A , the blocks in which the distance to the subject is short are colored in gray while the blocks in which the distance to the subject is long are colored in white. The compression processing section 6 determines whether the distance to the subject is short or long by referencing the distance data 204 A for each block. Whether the distance to the subject indicated by the distance data 204 A is short or long may be determined according to whether the distance is shorter or longer than a fixed threshold of, for example, 20 meters. The threshold may be varied and may be, for example, a value obtained by doubling the average distance to the subject for all the blocks in an image. In the case where a block includes both the subject at a short distance and a background at a long distance, the distance for that block may be determined as short.

FIG. 2B shows an image portion of the multiplexed data 205 B. In this embodiment, the multiplexed data 205 B shown in FIG. 2B is an image to be viewed with the right eye (hereinafter referred to as “right-eye image”), of two parallax images. Also in FIG. 2B , the blocks in which the distance to the subject is short are colored in gray while the blocks in which the distance to the subject is long are colored in white.

The compression processing section 6 calculates the differential between the blocks in which the distance to the subject is long (hereinafter referred to as “long-distance blocks”) in the right-eye image shown in FIG. 2B and the long-distance blocks in the left-eye image shown in FIG. 2A . The X-marked blocks shown in FIG. 2B are long-distance blocks extracted as the differential, that is, long-distance blocks existing only in the right-eye image shown in FIG. 2B .

Then, the compression processing section 6 eliminates the long-distance blocks in the right-eye image shown in FIG. 2B which are identical to their counterparts in the left-eye image shown in FIG. 2A . That is, the long-distance blocks existing in both the right-eye image and the left-eye image are eliminated from one of the images. When the image with the eliminated long-distance blocks is to be decompressed, the long-distance blocks in the other image corresponding to the eliminated long-distance blocks are referenced and copied to substitute for the eliminated long-distance blocks. Information for allowing reference to the remaining long-distance blocks corresponding to the eliminated long-distance blocks is referred to as “reference information”. The present invention does not limit the format and style of the reference information.

Thus, the compressed data generated by the compression processing section 6 contains, as the image portion, data associated with short-distance blocks, data associated with long-distance blocks common to the left and right images, and data associated with long-distance blocks that are not common to the left and right images.

Since data (image data and distance data) for long-distance blocks in one of two parallax images can be eliminated in this way, the amount of information can be reduced significantly.

In the description above, common long-distance blocks in the right-eye image are eliminated while long-distance blocks in the left-eye image are reserved for reference. However, the present invention is not limited thereto, and conversely common long-distance blocks in the left-eye image may be eliminated while long-distance blocks in the right-eye image may be reserved for reference.

The compression process performed by the compression processing section 6 is also effective for temporal compression.

FIG. 3 illustrates the temporal compression effect of the compression process performed by the compression processing section 6 .

FIG. 3A shows an image portion of the multiplexed data 205 A generated at a first time, hereinafter referred to as “left-eye image T 1 ”. FIG. 3B shows an image portion of the multiplexed data 205 B generated at the same time as the left-eye image of FIG. 3A , hereinafter referred to as “right-eye image T 1 ”.

FIG. 3C shows an image portion of the multiplexed data 205 A generated at a second time later than the first time (for example, in the next frame), hereinafter referred to as “left-eye image T 2 ”. FIG. 3D shows an image portion of the multiplexed data 205 B generated at the same time as the left-eye image of FIG. 3C , hereinafter referred to as “right-eye image T 2 ”.

The compression processing section 6 calculates the differential between the left-eye image T 1 shown in FIG. 3A and the left-eye image T 2 shown in FIG. 3C to perform temporal compression by a motion compensation technique, for example. That is, the long-distance blocks in the left-eye image T 2 which are identical to their counterparts in the left-eye image T 1 are eliminated, and reference information for allowing reference to the blocks in the left-eye image T 1 in order to reproduce the corresponding eliminated long-distance blocks in the left-eye image T 2 is provided in place.

For the right-eye images T 1 and T 2 , meanwhile, the compression processing section 6 does not calculate the differential, but only performs compression by eliminating long-distance blocks referencing the respective left-eye images.

In the case where the differential between the right-eye images T 1 and T 2 is calculated to perform temporal compression, eliminated blocks in the right-eye image T 2 are decoded by referencing the corresponding blocks in the right-eye image T 1 , which in turn are obtained by referencing the left-eye image T 1 . In this case, errors that occur during the differential calculations accumulate, which might lower the accuracy of differential substitution and thus degrade the quality of an image to be reproduced. Therefore, the compression processing section 6 does not calculate the temporal differential for the right-eye images, but compresses the right-eye images by referencing the left-eye images, effectively reducing the amount of information.

Now, a description will be made regarding an exemplary operation to generate a three-dimensional image of the image compression apparatus 100 according to the first embodiment.

FIG. 4 is a flowchart illustrating an exemplary operation to generate a three-dimensional image of the image compression apparatus 100 according to the first embodiment.

The imaging section 1 A and the distance measuring sensor 3 A operate in sync with each other to capture an image of a subject and measure the distance to the subject, respectively, at the same time. The imaging section 1 A generates an image signal 201 A, and the distance measuring sensor 3 A generates distance information 203 A. Also at the same time, the imaging section 1 B and the distance measuring sensor 3 B operate in sync with each other to generate an image signal 201 B and distance information 203 B, respectively.

The encoding section 2 A ( 2 B) compression-encodes the image data 201 A ( 201 B) generated by the imaging section 1 A ( 1 B) using an image encoding technique such as MPEG to generate digital image data 202 A ( 202 B).

The distance information processing section 4 A ( 4 B) converts the distance information 203 A ( 203 B) indicating the distance measured by the distance measuring sensor 3 A ( 3 B) in step ST 1 into distance data 204 A ( 204 B).

The multiplexing section 5 A ( 5 B) multiplexes the digital image data 202 A ( 202 B) generated in step ST 2 and the distance data 204 A ( 204 B) generated in step ST 3 for each predefined pixel block and each frame to generate multiplexed data 205 A ( 205 B). Examples of a multiplexing scheme include embedding the distance data 204 A ( 204 B) into a header portion of the digital image data 202 A ( 202 B), for example.

The compression processing section 6 compresses (reduces the amount of information of) the multiplexed data 205 A and 205 B generated in step ST 4 to generate compressed data 206 .

The storage section 7 stores the compressed data 206 generated in step ST 5 .

The output section 8 outputs the compressed data 206 generated in step ST 5 through a predetermined transmission path.

It should be noted that steps ST 6 and ST 7 may be performed in a different order. That is, the output section 8 may output the compressed data 206 before, or at the same time as, the short-distance block 7 stores the compressed data 206 .

As has been described above, in the image compression apparatus 100 of the first embodiment, the encoding section 2 A ( 2 B) compresses the image signal 201 A ( 201 B) indicating the image captured by the imaging section 1 A ( 1 B) to generate digital image data 202 A ( 202 B). The distance measuring sensor 3 A ( 3 B) measures the distance to the subject at the same time as the imaging section 1 A ( 1 B) performs image capturing to generate distance information 203 A ( 203 B). The distance information processing section 4 A ( 4 B) generates distance data 204 A ( 204 B) on the basis of the distance information 203 A ( 203 B). The multiplexing section 5 A ( 5 B) multiplexes the digital image data 202 A ( 202 B) and the distance data 204 A ( 204 B) to generate multiplexed data 205 A ( 205 B). The compression processing section 6 eliminates long-distance blocks in one of the multiplexed data 205 A and 205 B on the basis of the multiplexed data 205 A and 205 B to generate compressed data 206 of a smaller amount.

According to the image compression apparatus 100 of the first embodiment, when multiplexing image data for two parallax images and distance data corresponding to the image data to generate multiplexed data, image data and corresponding distance data for long-distance portions in one of the parallax images are eliminated. Thus, it is possible to significantly reduce the amount of information of the multiplexed data, reducing the possibility that a large proportion of the capacity of the storage section 7 is taken up when it stores the compressed data 206 and a large proportion of the bandwidth of the output transmission path of the output section 8 is taken up when it outputs the compressed data 206 .

<Second Embodiment>

Hereinafter, a description will be made regarding an image compression apparatus 101 according to a second embodiment of the present invention.

An exemplary configuration of the image compression apparatus 101 according to the second embodiment is shown in FIG. 5 .

FIG. 5 shows an exemplary configuration of the image compression apparatus 101 according to the second embodiment.

As shown in FIG. 5 , the image compression apparatus 101 of the second embodiment includes imaging sections 1 C, 1 D, 1 E, 1 F, encoding sections 2 C, 2 D, 2 E, 2 F, distance measuring sensors 3 C, 3 D, 3 E, 3 F, distance information processing sections 4 C, 4 D, 4 E, 4 F, multiplexing sections 5 C, 5 D, 5 E, 5 F, a compression processing section 6 ′, a storage section 7 , and an output section 8 .

The image compression apparatus 101 of the second embodiment is different from the image compression apparatus 100 of the first embodiment in including four imaging sections, four encoding sections, four distance measuring sensors, four distance information processing sections, and four multiplexing sections as shown in FIG. 5 . Components other than those mentioned above (the compression processing section 6 ′, the storage section 7 and the output section 8 ) are substantially the same between the image compression apparatus 101 of the second embodiment and the image compression apparatus 100 of the first embodiment.

The following describes the details of the respective components of the image compression apparatus 101 of the second embodiment while focusing on the differences from the respective counterparts of the image compression apparatus 100 of the first embodiment.

The imaging sections 1 C, 1 D, 1 E, 1 F capture an image of a subject to generate image signals 201 C, 201 D, 201 E, 201 F, respectively, and each may be an imaging device such as a digital still camera and a digital video camera, for example.

The imaging sections 1 C and 1 D are located at equal distances from the subject. The imaging sections 1 E and 1 F are also located at equal distances from the subject. It should be noted, however, that the imaging section 1 C ( 1 D) and the imaging section 1 E ( 1 F) are located at different distances from the subject. Specifically, the imaging sections 1 E and 1 F may be located farther to the subject by a predetermined distance than the imaging sections 1 C and 1 D, for example. With the configuration, image signals for two distances can be generated when capturing an image of a single subject.

The encoding sections 2 C, 2 D, 2 E, 2 F compress the image signals 201 C, 201 D, 201 E, 201 F generated by the imaging sections 1 C, 1 D, 1 E, 1 F for conversion into digital image data 202 C, 202 D, 202 E, 202 F, respectively. The encoding sections 2 C, 2 D, 2 E, 2 F may use an image encoding technique such as MPEG1, MPEG2, MPEG4, DivX (a registered trademark of Divx, Inc.), Xvid and WMV9, for example.

The distance measuring sensors 3 C, 3 D, 3 E, 3 F are attached to the imaging sections 1 C, 1 D, 1 E, 1 F, and measure the distance to the subject when the imaging sections 1 C, 1 D, 1 E, 1 F capture an image of the subject and output the measured distance as distance information 203 C, 203 D, 203 E, 203 F, respectively. The distance measuring sensors 3 C, 3 D, 3 E, 3 F may each be a sensor for measuring the distance by infrared rays or ultrasonic waves, for example. The distance measuring sensors 3 C, 3 D, 3 E, 3 F measure the distance to the subject for pixels extracted from predefined pixel blocks composed of all the pixels of the imaging sections 1 C, 1 D, 1 E, 1 F, respectively.

The distance measuring sensors 3 C, 3 D, 3 E, 3 F may use macro blocks (16×16 pixels) used in MPEG1 and MPEG 1 and blocks (8×8 pixels), for example, for the above-mentioned predefined pixel blocks, as may be done by the distance measuring sensors 3 A and 3 B of the first embodiment. That is, in the case where distance measurement is performed for each macro block, for example, each distance measuring element of the distance measuring sensors 3 C, 3 D, 3 E, 3 F may be provided for every 16×16 pixels of the imaging sections 1 C, 1 D, 1 E, 1 F, respectively.

That is, in the case where distance measurement is performed for each macro block, for example, the distance measuring sensors 3 C, 3 D, 3 E, 3 F may be prepared that have the same number of distance measuring elements as the number of the macro blocks in the digital image data 202 C, 202 D, 202 E, 202 F generated by the encoding sections 2 C, 2 D, 2 E, 2 F, respectively. The plurality of distance measuring elements of the distance measuring sensors 3 C, 3 D, 3 E, 3 F may be arranged in a matrix so as to correspond to the respective macro blocks, for example.

The distance measuring sensors 3 C and 3 D are located at different distances from the subject than the distance measuring sensors 3 E and 3 F. Therefore, the number of distance measuring elements of the distance measuring sensors may be varied in accordance with the distance from the subject, for example. That is, the number of distance measuring elements may be increased for distance measuring sensors located closer to the subject while the number of distance measuring elements may be reduced for distance measuring sensors located farther to the subject.

The distance information processing sections 4 C, 4 D, 4 E, 4 F generate distance data 204 C, 204 D, 204 E, 204 F on the basis of the distance information 203 C, 203 D, 203 E, 203 F generated by the distance measuring sensors 3 C, 3 D, 3 E, 3 F, respectively. Since the distance data 204 C, 204 D, 204 E, 204 F generated by the distance information processing sections 4 C, 4 D, 4 E, 4 F are based on the distance information 203 C, 203 D, 203 E, 203 F generated by the distance measuring sensors 3 C, 3 D, 3 E, 3 F, respectively, the distance data 204 C, 204 D, 204 E, 204 F are generated for each predefined pixel block in the digital image data 202 C, 202 D, 202 E, 202 F generated by the encoding sections 2 C, 2 D, 2 E, 2 F, respectively.

The multiplexing sections 5 C, 5 D, 5 E, 5 F multiplex the digital image data 202 C, 202 D, 202 E, 202 F generated by the encoding sections 2 C, 2 D, 2 E, 2 F and the distance data 204 C, 204 D, 204 E, 204 F generated by the distance information processing sections 4 C, 4 D, 4 E, 4 F to generate multiplexed data 205 C, 205 D, 205 D, 205 F, respectively. In the multiplexed data 205 C, 205 D, 205 E, 205 F, each predefined pixel block in the digital image data 202 C, 202 D, 202 E, 202 F has been embedded with the distance data 204 C, 204 D, 204 E, 204 F corresponding to that block, respectively, for example.

The compression processing section 6 ′ recompresses the multiplexed data 205 C, 205 D, 205 E, 205 F to generate compressed data 206 ′ of a smaller amount. A compression scheme used by the compression processing section 6 ′ will be described in detail later.

The storage section 7 is a memory for storing the compressed data 206 ′ generated by the compression processing section 6 ′.

The output section 8 outputs the compressed data 206 ′ generated by the compression processing section 6 ′ to the outside via a predetermined transmission path.

With the image compression apparatus 101 of the second embodiment configured as discussed above, two parallax images can be obtained at two distances. This allows the generation of a more stereoscopic three-dimensional image based on the compressed data generated by the image compression apparatus 101 of the second embodiment.

The following describes the compression process performed by the compression processing section 6 ′ of the second embodiment.

FIG. 6 illustrates how the four multiplexed data 205 C, 205 D, 205 E, 205 F are compressed on the basis of the distance data 204 C, 204 B, 204 E, 204 F embedded in the respective multiplexed data.

FIG. 6A shows an image portion of the multiplexed data 205 C. In the second embodiment, the multiplexed data 205 C shown in FIG. 6A is an image to be viewed with the left eye (left-eye image), of four parallax images.

The image shown in FIG. 6A has been compression-encoded (in this embodiment, using MPEG) by the encoding section 2 C. Each block shown in FIG. 6A (in this embodiment, a macro block of 16×16 pixels) has been provided with the distance data 204 C for that block, which indicates the distance to the subject captured in that block.

In FIG. 6A , the blocks in which the distance to the subject is short are colored in gray while the blocks in which the distance to the subject is long are colored in white. The compression processing section 6 ′ determines whether the distance to the subject is short or long by referencing the distance data 204 C for each block. Whether the distance to the subject indicated by the distance data 204 A is short or long may be determined according to whether the distance is shorter or longer than a fixed threshold of, for example, 20 meters. The threshold may be varied and may be, for example, a value obtained by doubling the average distance to the subject for all the blocks in an image. In the case where a block includes both the subject at a short distance and a background at a long distance, the distance for that block may be determined as short.

FIG. 6B shows an image portion of the multiplexed data 205 D. In this embodiment, the multiplexed data 205 D shown in FIG. 6B is an image to be viewed with the right eye (right-eye image), of four parallax images. Also in FIG. 6B , the blocks in which the distance to the subject is short are colored in gray while the blocks in which the distance to the subject is long are colored in white.

FIG. 6C shows an image portion of the multiplexed data 205 E. In this embodiment, the multiplexed data 205 E shown in FIG. 6C is a left-eye image captured at a different distance than the multiplexed data 205 C. When the distance from the imaging sections 1 C and 1 D to the subject at the time when the image signals for the multiplexed data 205 C and 205 D were generated is defined as a first distance L 1 and the distance from the imaging section 1 E to the subject at the time when the image signal for the multiplexed data 205 E was generated is defined as a second distance L 2 , then the relation L 1 <L 2 is satisfied. Also in FIG. 6C , the blocks in which the distance to the subject is short are colored in gray while the blocks in which the distance to the subject is long are colored in white.

FIG. 6D shows an image portion of the multiplexed data 205 F. In this embodiment, the multiplexed data 205 F shown in FIG. 6D is a right-eye image captured at the second distance L 2 , as with the multiplexed data 205 E. Also in FIG. 6D , the blocks in which the distance to the subject is short are colored in gray while the blocks in which the distance to the subject is long are colored in white.

As shown in FIGS. 6A and 6B , the compression processing section 6 ′ extracts long-distance blocks from the image portions of the multiplexed data 205 C and 205 D, which contain image signals obtained at the first distance L 1 , by the same compression process as in the first embodiment. Then, the compression processing section 6 ′ calculates the differential between the image portions of the multiplexed data 205 C and 205 D to eliminate the long-distance blocks in the multiplexed data 205 D which are identical to their counterparts in the multiplexed data 205 C. At this time, reference information for allowing reference to the remaining long-distance blocks corresponding to the eliminated long-distance blocks is provided in place. As a matter of course, the blocks which are not identical are left as they are.

Likewise, as shown in FIGS. 6C and 6D , the compression processing section 6 ′ extracts long-distance blocks from the image portions of the multiplexed data 205 E and 205 F, which contain image signals obtained at the second distance L 2 . Then, the compression processing section 6 ′ calculates the differential between the image portions of the multiplexed data 205 E and 205 F to eliminate the long-distance blocks in one of the multiplexed data which are identical to their counterparts in the other, reducing the amount of information. Also, reference information for allowing reference to the remaining long-distance block corresponding to the eliminated long-distance blocks is provided in place.

Then, the compression processing section 6 ′ calculates the differential between the image portion of the multiplexed data 205 C shown in FIG. 6A and the image portion of the multiplexed data 205 E shown in FIG. 6C to eliminate the long-distance blocks which are identical between the multiplexed data from one of the multiplexed data. The elimination is performed on the assumption that the difference between the first distance L 1 and the second distance L 2 is not so large and, thus, there is not a great difference between the long-distance blocks in the multiplexed data 205 C obtained at the first distance L 1 and the long-distance blocks in the multiplexed data 205 E obtained at the second distance L 2 . Thus, in the image compression apparatus 101 of the second embodiment, the imaging section 1 C ( 1 D) and the imaging section 1 E ( 1 F) are located such that there is not a great difference between the distance L 1 from the imaging section 1 C ( 1 D) to the subject and the distance L 2 from the imaging section 1 E ( 1 F) to the subject.

In this embodiment, the long-distance blocks in the multiplexed data 205 E shown in FIG. 6C which are identical to their counterparts are eliminated, for example. At this time, the compression processing section 6 ′ generates reference information for allowing reference to the long-distance blocks in the multiplexed data 205 C corresponding to the eliminated long-distance blocks in the multiplexed data 205 E, and provides the reference information in place of the eliminated long-distance blocks.

As has been described above, according to the image compression apparatus 101 of the second embodiment, the compression processing section 6 ′ performs a compression process to eliminate long-distance blocks in the image portions of three multiplexed data, of the four multiplexed data 205 C, 205 D, 205 E, 205 F, and provide reference information for allowing reference to the remaining corresponding long-distance blocks. Therefore, the amount of information can be reduced significantly for the eliminated long-distance blocks.

The present invention is not limited to the above-described embodiments.

That is, the constituent elements of the above-described embodiments may be modified or altered in various ways without departing from the technical scope of the present invention or the scope of equivalents thereof in carrying out the present invention.

Although two imaging sections are located at the same distance from the subject and two additional imaging sections are located at a different distance from the subject in the image compression apparatus 101 of the second embodiment, the present invention is not limited thereto. That is, any number of pairs of imaging sections may be provided. In this case, the number of encoding sections, distance measuring sensors, distance information processing sections and multiplexing sections may be determined in accordance with the number of the imaging sections.

The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-167752 filed in the Japan Patent Office on Jun. 26, 2008, the entire content of which is hereby incorporated by reference.