JP2810585B2 - Image encoding method and image decoding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method in image data processing, and more particularly to an image encoding method capable of reducing the amount of image data while minimizing the deterioration of the image quality of a printed image, and an image decoding method. The present invention relates to a chemical treatment method.

[0002]

2. Description of the Related Art Generally, the amount of image data in the printing field is enormous as compared with a still image displayed on a television monitor. For example, the amount of image data in the latter is about 1 MB, whereas the amount of image data in the former is about 1 MB. A4 size manuscript 6
It reaches as much as 0 MB (400 lines / inch).

[0003] In order to store such a large amount of data as a database as it is, a huge memory is required, and the time required for data transmission becomes very long.

In order to cope with this, an encoding technique for reducing the amount of information of an image, that is, an image data compression technique has been studied, and a compression method such as an orthogonal transform encoding method or a vector quantization method has been conventionally developed. Have been. Among them, the orthogonal transform coding method is particularly employed in the international standard compression method for natural still images.

[0005] These compression methods are so-called irreversible encoding methods, and although a high compression rate can be expected, they have a drawback that even if they are restored, they do not completely return to the original image data.

Particularly in the case of a commercial print image, quality of the image quality (for example, smoothness of a woman's skin and sharpness of an outline) is often required rather than the content of the image itself. If an irreversible encoding method such as orthogonal transformation is applied to the image data and the image data is compressed at a high compression rate, the image quality deteriorates and the commercial value of the image is impaired.

[0007]

For this reason, there has been a study on an encoding method which saves as much information as necessary for a viewer while reducing the amount of image data and minimizes image quality deterioration due to compression of the relevant portion. Despite this, there was no effective image processing method.

An object of the present invention is to provide an image encoding method and an image decoding method for maintaining a clear image of a given object while keeping the amount of image data low irrespective of the type of image. The purpose is to provide.

[0009]

In order to achieve the above object, the image encoding method of the first configuration according to the present invention comprises the steps of: (a) setting an outline of an object in an image to be encoded; (B) dividing the image to be encoded into a plurality of pixel blocks; and (c) dividing the pixel block into at least one of the contours based on the contour data. A contour block group including a portion, an object block group including an object image within a closed area formed by the contour block, and the contour block group and the object block group removed from all the pixel blocks. (D) a first code that can obtain a relatively low compression ratio for each of the pixel blocks belonging to the contour block group and the object block group; Processing and a second encoding process, and by performing a third encoding process in which a relatively high compression ratio is obtained for the pixel blocks belonging to the non-target block group, each of the plurality of pixel blocks Obtaining image data coded for: and (e) expressing, for each of the plurality of pixel blocks, which of the outline block group, the object block group, and the non-object block group belongs to Generating attribute data to be attached to the encoded image data. Then, the compression of the first encoding process in the step (d) is performed.
The compression ratio is set lower than the compression ratio of the second encoding process.
ing.

[0010] However, "attached to image data" is a term including both a case where the image data is conceptually paired and a case where the image data is incorporated into the image data as a part of the image data. “Relatively low compression ratio” includes a case where the compression ratio is “1”, that is, a case where no encoding process is performed.

On the other hand, in the decoding processing method of the present invention,
(a) By referring to the attribute data attached to the encoded image data, each of the pixel blocks is one of the contour block group, the object block group, and the non-object block group. (B) decoding the encoded image data, and performing the first encoding for the pixel blocks determined to belong to the contour block group in step (a). In a first decoding process corresponding to the process, a pixel block determined to belong to the object block group in step (a) is subjected to a second decoding process corresponding to the second encoding process, For the pixel blocks determined to belong to the non-object block group in step (a), the third
A step of obtaining decoded image data by performing the respective steps in a third decoding process corresponding to the encoding process of (c), and (c) synthesizing each pixel block decoded in the step (b). Obtaining a restored image corresponding to the image.

[0012]

First, contour data is created by setting the contour of the object of the image, and the pixel blocks obtained by dividing the image data are classified based on the contour data into a contour block group including the contour and a target inside the contour block group. The object block group and the non-object block group other than these are distinguished, and the first and second encoding processes are performed on the outline block group and the object block group at a relatively low compression ratio. Further, a third encoding process corresponding to high-compression compression is performed on the non-target block group. For this reason, it is possible to minimize the deterioration of the image quality in the arbitrarily set contour while keeping the data amount of the entire image small. Also, the pressure of the first encoding process
The compression ratio is set lower than the compression ratio of the second encoding process.
ing. Therefore, in the decoded image,
Of the boundaries between the contour area and the area inside and outside,
At the boundary of the important inner part, the
Natural image displacement is reduced.

The encoded image data obtained by encoding the image data is stored. When the encoded image data is to be displayed on an output device such as a monitor, decoding must be performed. At the time of decoding, it is necessary to know at which compression rate each pixel block has been encoded. It is necessary.

For this reason, for each pixel block, attribute data representing which one of the outline block group, the object block group, and the non-object block group belongs is generated and attached to the image data.

The image decoding method according to the present invention is a method suitable for decoding an image encoded by the first encoding method, and is based on the attribute data. , The encoded pixel blocks are classified into a contour block group, an object block group, and a non-object block group, and a decoding process corresponding to each encoding is performed, and these decoded pixel blocks are combined. To obtain a restored image.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an image coding method and an image decoding method according to the present invention; Of course not.

This embodiment will be described in the following order.

(I) Method of Creating Contour Data (II) Classification Method of Pixel Blocks (III) Image Compression Method (IV) Image Restoration Method (V) Example of Apparatus for Performing Method According to the Present Embodiment (VI) Modification Examples To argue. (I) Method of Creating Contour Data In this embodiment, for the sake of convenience of explanation, image processing on a simple clock face image as shown in FIG. 7A will be considered.

When the operator wants to set the clock face 21 of the original image 20 as an object, the image data corresponding to the contour 21a displayed on the television monitor is all set to "1", and other data are set. The image data is set to “0”, whereby the contour data R shown in FIG. 7B is obtained.

Such contour data R can be easily obtained by, for example, a known contour cutting device. To create the contour data R by the contour clipping device, the original image 20 is displayed on a television monitor, and the cursor displayed on the screen is moved by the operator along the contour line 21a with the mouse at hand. The locus of this cursor movement is converted into an xy coordinate plane in the pixel matrix, and the outline data corresponding to the outline is changed to “1”.
And the other contour data are set to “0”.

The contour data created by assigning “0” and “1” in this way is compressed by vectorization and stored in the memory. (II) Pixel Block Classification Method (1) Blocking of Image Data First, image data obtained from the original image 20 is divided into a plurality of pixel blocks.

As schematically shown in FIG. 8A, the image data is composed of a large number of (H × V) pixels P, and each of the (M × N) pixels has a plurality of pixels. Are divided into pixel blocks Bxy.

FIG. 8B is a conceptual diagram showing the structure of one pixel block Bxy. The pixel block Bxy has (I
A pixel matrix composed of (.times.J) pixels is obtained, and image data fij is obtained for each pixel.

In the example shown in FIG. 8B, one pixel block Bxy is composed of (8 × 8) pixels.
It may be composed of (4 × 4) pixels or (16 × 16) pixels.

(2) Creation of Object Table Next, the contour data that has been vectorized and compressed and stored in the contour data creation method of (I) is restored by performing a decoding process corresponding to the vectorization. The contour data obtained by restoration is the same as the above image data (H × V)
And the pixel plane of this contour data is divided into (M × N) blocks in the same manner as in the above-described block (1) of pixel data. A corresponding contour data block Dxy is formed.

Further, a code table CT (x, y) of contour data having (M × N) areas corresponding to the (M × N) divided contour data blocks Dxy.
Prepare

The procedure for creating the code table CT (x, y) will be described with reference to the flowchart of FIG.

First, the process is started from the outline data block D00 with y = 0 and x = 0 (steps S31 and S3).
2).

If at least one of the plurality of contour data contained in the contour data block Dxy is "1", it can be determined that the contour data block Dxy contains contour data. , The code table CT (x, y) corresponding to the contour data block Dxy
Is set to "1" (steps S33, S34).

If all of the plurality of contour data included in the contour data block Dxy are "0", no contour data is included in the contour data block Dxy. The value of the code table CT (x, y) corresponding to the block Dxy is set to "0" (step S35).

Next, the variable x is incremented by "1", and if the value is less than M, which is the number of pixel blocks in the x coordinate direction, the processing of the y row has not been completed.
Returning to step S33, processing is performed on the next contour data block Dxy (steps S36 and S37).

If the variable x is M in step S37
If so, the operation on the y-th row has been completed. Therefore, “1” is incremented to the variable y, and if the value of the variable y at this time is smaller than N, which is the number of pixel blocks in the y-coordinate direction. For example, the process returns to step S32 to perform an operation on the contour data block Dxy of the next row (step S3).
8, S39). If the value of the variable y is equal to or greater than N, the process ends.

In this manner, the process of setting "0" or "1" to CT (x, y) of the code table by the contour data is performed from the upper leftmost contour data block D00 to the lower rightmost one. By performing the processing up to the outline data block D (M-1) (N-1), the code table 31 corresponding to the outline data R as shown in FIG. 9A is completed.

Next, the code table 3 of the contour data
1, the pixel block Bxy of the divided image data
Is defined as a pixel block group including an outline, a pixel block group including an object image in a closed area formed by the outline block group, and a pixel block group excluding the outline block group and the object block group (hereinafter, referred to as , In order, “contour block group”, “object block group”, “non-object block group”
That. ) Code table CT
Create (x, y).

The creation of the code table is basically achieved by performing a “painting” operation on an object area in a closed area formed by a contour block group including contour data.

For the "painting" operation, various methods have been devised in the field of image processing. For example, "Electronic Information and Communication Handbook, 2nd Volume, Electronic Information and Communication Society Edition" (Ohmsha, March 30, 1988) Date)
On page 1868.

A code table newly created by replacing the object area in the outline block group with “2” by the “painting” operation is the code table 32 shown in FIG. Is "attached data" attached to the image data, and is hereinafter referred to as an object table.

CT (x, y) of the code table 32
, It can be determined whether the corresponding pixel block Bxy is a contour block group, an object block group, or a non-object block group.

That is, if CT (x, y) = 1,
The corresponding pixel block Bxy is a contour block. Similarly, if CT (x, y) = 2, the corresponding pixel block Bxy is an object block and C
If T (x, y) = 0, it is understood that the corresponding pixel block Bxy is a non-object block group. (III) Image Compression Method Based on the object table 32, image compression is performed at a different compression ratio for each block group. The specific method is as follows.

First, the pixel blocks Bxy are sequentially called from the image data, and the CT of the corresponding object table 32 is read.
If the value of (x, y) is "1", it indicates that the corresponding pixel block Bxy is a contour block, and orthogonal transform coding, such as discrete cosine transform, is performed, and data of most frequency components is stored. The first encoding process is performed at a low compression ratio ra (compression A). In this case, the low compression includes a compression ratio of 1, that is, a case where no compression is performed at all.

When the value of CT (x, y) in the object table 32 corresponding to the pixel block Bxy is "2", it indicates that the corresponding pixel block Bxy is the object block. Low compression ratio rb that stores data of most frequency components using the same orthogonal transform coding method as
Performs the second encoding process (compression B).

The compression ratio ra in the first encoding process
And the compression ratio rb in the second encoding process may be the same, but if the compression ratio ra is set lower than the compression ratio rb, the outline becomes clearer when the image is restored. Thus, a sharper image can be given to a viewer.

If the value of CT (x, y) in the object table 32 corresponding to the pixel block Bxy is "0", it indicates that the corresponding pixel block Bxy is a non-object block, The data is encoded at a high compression ratio rc that preserves only low frequency components even in orthogonal transform encoding (compression C).

It is preferable that the object table 32 is also compressed. In this case, the object table 32
Since it is ternary data (2 bits) of “0”, “1”, and “2”, compression processing is performed using a lossless code. For example, the object table 32 may be compressed with an MR (Modified Read) code for each bit plane (compression D). Of course, if it is a lossless code, it may be compressed by another coding method, for example, a run-length compression method.

Then, the compressed image data and the object table are stored in different memory sections, respectively, are made into databases, or are transmitted via a communication line.

As described above, by performing a different encoding process for each region based on the object table 32, while maintaining the image quality of the important object image, a high value is applied to the non-important portions based on the initial contour setting. Since a compression ratio can be applied, image data can be largely reduced as a whole.

(IV) Image Restoration Method To restore image data compressed in this way,
The following procedure is used.

First, the compressed object table 32 is
A decompression process corresponding to the inverse conversion of the compression D is performed and restored.

Next, the compressed image data is stored in a block Bxy
CT of the restored object table 32
In comparison with the value of (x, y), the CT (x, y)
Is "1", decompression corresponding to the inverse conversion of the compression A is performed, and if the CT (x, y) is "2", the compression B
Is decompressed by a decompression process corresponding to the inverse transform of the above, and if the CT (x, y) is "0", it is decompressed and restored by a decompression process corresponding to the inverse transform of the compression C.

Finally, these decompressed image data are combined to finally restore the entire image.

At this time, if the image of the background area is subjected to smoothing processing, for example, using a 3 × 3 smoothing matrix, and the data deteriorated by the block distortion is corrected, the image of the non-object area becomes smooth. .

The original image is usually a color image in many cases, but in the case of such a color image, the color-separated yellow (Y), magenta (M), cyan (C), black (K) Alternatively, the above image processing is performed on components of red (R), green (G), blue (B) or color variables after color coordinate conversion, for example, luminance (Ys), color difference (Is, Qs), and the like. Finally, these are combined and restored. (V) Example of Apparatus for Implementing Method According to the Present Embodiment Next, an example of an image processing apparatus for implementing the above-described image encoding processing method and image decoding processing method will be described.

This image processing device comprises an image data compression device and an image data decompression device, both of which may be configured integrally or may be independently configured and arranged at different locations. Sometimes. (1) Image Data Compressor FIG. 1 is a block diagram showing the configuration of the image data compressor 100, and FIG. 3 is a flowchart showing the operation of the image data compressor 100.

First, the contour data of the image is obtained from an external contour creating device, and the object table creating unit 3 creates the object table 32 based on the contour data (steps S1, S2, where the object For details of table creation, refer to the above (II) (2)).

Next, the image data of the original image 20 stored in the image memory unit 1 is divided into a plurality of pixel blocks Bxy in the pixel block dividing unit 2 (step S3, details of the pixel block dividing method are described above. (See (1) of (II)).

Data CT of the object table 32
Based on (x, y), the pixel block determining unit 4
First, the processing is started from the upper left pixel block Boo (steps S4 and S5), and it is determined whether the value of CT (x, y) corresponding to the pixel block Bxy is "1" (step S6).

The image data compression apparatus 100 includes first to fourth compression units 5, 6, 7, and 8, and the value of CT (x, y) corresponding to the pixel block Bxy is "1". If so, the pixel block Bxy is a contour block, so the pixel block Bxy is sent to the first compression unit 5 to perform encoding processing (compression A) with a low compression ratio ra (step S7). Move to step S8.

In step S8, the pixel block Bxy
It is determined whether the value of CT (x, y) corresponding to “2” is “2”. If the value is “2”, the pixel block Bxy is an object block, and is sent to the second compression unit 6 to be low. Compression ratio r
b (compression B) (step S
9). If the value of CT (x, y) is not "2", the pixel block Bxy is a non-object block and is sent to the third compression unit 7 to perform the encoding process (compression C) using the high compression rate rc. Perform (Step S10).

When the processing of compression A, compression B or compression C is completed for the pixel block Bxy, the variable x is incremented by "1". If the value of the variable x at this time is smaller than M, the process proceeds to step S6. Then, the above process is repeated for the next pixel block Bxy (step S1).
1, S12) If M is equal to or more than M, the processing of that row has been completed, so the variable y is incremented by "1" and the process proceeds to the determination of the next row. Process is repeated. When the variable y becomes N, the processing is stopped (steps S13 and S14).

Finally, the data CT of the object table 32
(X, y) is compressed (compressed D) by MR encoding in the fourth compression unit 8 (step S15). The compressed image data and the compressed object table data thus obtained are
The object table and the color-separated image data are stored in different memory units 91 and 92 in the storage unit 9 formed of a magnetic disk or the like in a data state that can be distinguished from each other (step S16). End the compression work.

The compressed image data and the compression target table data are hereinafter collectively referred to as “compressed data”. (2) Image Data Decompression Device FIG. 2 is a block diagram of the configuration of the image data decompression device 200, and FIG. 4 is a flowchart showing the operation of decompressing compressed data in the image data decompression device 200.

The image data decompression device 200 has a storage unit 9a for compressed data. The image data decompression device 200 is integrated with the image data compression device 100 of FIG. If provided, the storage unit 9a may be shared with the storage unit 9 of the image data compression device 100.

The compressed data is read from the storage unit 9a. First, the compressed object table 32 is supplied from the memory unit 92a to the fourth decompression unit 10, and decompression corresponding to the inverse conversion of the compression D is performed. The processed data is decoded and stored in the memory unit 11 (step S17).

The compressed image data is stored in the memory 91a.
And is supplied to the compressed image data determination unit 12. Based on the CT (x, y) value of the object table 32 restored as described above, the compressed image data determination unit 12 determines whether each pixel block of the compressed image data is an outline block or an object block. Or whether the block is a non-object block.

That is, first, the judgment is started from the pixel block Bxy in which both the variable x and the variable y are “0” (steps S18 and S19), and the CT (x) of the object table corresponding to the pixel block Bxy is started. , Y) is referred to (step S20).

If the value of CT (x, y) in this object table is "1", the pixel block is an outline block, and is sent to the first decompression unit 13 to send the compressed A Decompression and expansion corresponding to inverse transformation (decompression A)
(Step S21).

If the value of CT (x, y) in the object table is not "1" in step S20, the flow shifts to step S22 to determine whether the value of CT (x, y) is "2". . If “2”, the process proceeds to step S23,
The second decompression unit 14 decompresses and decodes the data in a decompression process corresponding to the inverse conversion of the compression B (decompression B).

If the value of CT (x, y) in the object table is not "2" in step S22, the pixel block Bxy is a non-object block and is sent to the third decompression unit 15. This is then decompressed and decoded by decompression processing corresponding to the inverse conversion of compression C (decompression C) (step S24).

When the decoding process for each of the given pixel blocks is completed, the decompression unit 13, 14, 15 sends a signal to that effect to the compressed image data discrimination unit 1.
The compressed image data determination unit 12 receives the end signal and allocates the next pixel block to the corresponding decompression unit.

The decoding process here is the inverse transform of each encoding process. When the encoding process is, for example, the discrete cosine transform, the corresponding discrete cosine inverse transform may be used.

Thereafter, until the variable x is incremented by "1" and the variable x becomes M, the same process is sequentially repeated for the immediately right pixel block Bxy (step S2).
5, S26). When the variable x becomes M in step S26, it means that the processing of this row has been completed.
Is incremented (Step S27), and Step S27
19, the processing from step S19 to step S27 is repeated until the variable y becomes N, and
When the variable y becomes N, the processing is stopped.

When the image data is color image data, the above processing is performed for each color component.

The decompressed image data output from each of the first decompressing unit 13, the second decompressing unit 14, and the third decompressing unit 15 is output to the next stage at a timing corresponding to each position or address on the image plane. To the synthesizing unit 16. The synthesizing unit 18 synthesizes the restored image data of the respective pixel blocks of the object, the non-object, and the contour while referring to the position or address of each pixel block, thereby finally forming the original image. Obtain the corresponding image. When the image data is color image data, synthesis of image data for each color component is also performed.

The synthesizing section 16 can be provided with various image processing / editing functions. For example, a smoothing processing function is provided to perform smoothing processing on an image of a non-object area, for example, 3 × 3 smoothing. A non-target area close to the original image can be reproduced by performing a smoothing process using a conversion matrix and correcting data degraded by block distortion. In this case, the synthesis is performed after performing the smoothing process on the non-target object region. This is because if smoothing is to be performed after synthesis, a process of re-identifying the object block and the non-object block again and smoothing only the latter becomes necessary.

The image restored by the synthesizing unit 16 in this way is displayed on a display unit 17 such as a color display and stored in a restored image memory unit 18 for image recording or image editing processing. You. (VI) Modifications Various modifications are possible in the present embodiment.

(1) First, in the method of creating contour data described in (I), an operator creates an arbitrary contour by operating a known contour creating device as in the present embodiment, and a differential operator or the like. The contour data may be automatically obtained by image processing using. In particular, in an image in which the object is in focus and the background part is blurred, the contour part has a large difference in shading compared to other parts, and the differential value of the pixel block shows a characteristic value. Therefore, it is also possible to obtain the differential value of the pixel data value for each pixel block, extract the outline component based on this value, and create the outline data.

(2) In this embodiment, the compressed data is temporarily stored in the storage unit 9 in the image data compression device 100, and the data is transferred to the storage unit 9a, and the image is restored by the image data restoration device 200. However, each of the image data compression device 100 and the image data decompression device 200 may be provided with a data transmission unit and a data reception unit, and may transmit and receive compressed data directly via a communication line. A communication line function may be provided.

Further, the object table is created and compressed so that it can be distinguished from the compressed image data, and is stored separately in the storage unit 9, but this is not always necessary. Since the CT (x, y) value of the object table is ternary data of "0", "1", and "2", this data is input as information to two bits of the compressed data of the pixel block Bxy. In other words, when the compressed image data determination unit 15 reads out, it is possible to determine whether the block is a target block or a background block based on the identification data.

Thus, while having the same effect, the fourth compression section 8 in the image data compression apparatus 100 and the fourth decompression section 10 in the image data decompression apparatus 200 can be omitted, and the entire apparatus can be simplified. Can be achieved.

(3) Which side of the contour of the original image is regarded as the target area is determined according to the situation. For example, the image data compression apparatus 100 shown in FIG.
If a changeover switch is provided in the object table creation unit 3 to replace the values “0” and “2” of the data CT (x, y) in the object table 32, the object block can be easily replaced. The group and the non-object block group can be converted, and the operability is greatly improved.

(4) In the image data compression device 100 of FIG. 1, the compressed image data compressed by the first to third compression units 5, 6, 7 is stored in the same memory unit 9 of the storage unit 9.
1 is stored in the storage unit 9 as shown in FIG.
97 and a memory unit 98 for storing a compression target table, and storing the compressed data in the respective memory units, the structure of the image data restoration apparatus 200 as shown in FIG. Can be simplified.

That is, the compressed image data compressed at each compression ratio is taken out from each of the memory units 95a, 96a, 97a of the storage unit 9a corresponding to the storage unit 9 of FIG.
These compressed image data are converted into first, second, and third decompression units 1.
Since it can be directly decompressed at 3, 14, and 15,
Not only is the pixel block discriminating section 12 in FIG. 2 unnecessary, but also the feedback of the processing end signal from each of the decompressing sections 13, 14, 15 to the pixel block discriminating section 12 becomes unnecessary, and the circuit is greatly simplified. The first to third decompression units 13, 14, and 15 can simultaneously perform decompression processing, and the decompression processing time can be reduced. In addition,
In the image data restoring device of FIG. 6, the synthesizing unit 16 restores an image with reference to the object table decompressed by the fourth decompressing unit 10, but adds the address signal to each pixel block Bxy. If this is done, the direct synthesis unit 16
Only the original image can be directly synthesized.

(5) Further, a television monitor display section is provided in the image compression section 100, and a variable circuit is provided so that the compression ratio of each compression section can be freely set. It is also possible to achieve a delicate balance between the image and the background image.

In this case, when the image data compression device 100 and the image data decompression device 200 are integrated,
The display unit 19 of the image data restoration device 200 can be used as the television monitor display unit.

(6) In this embodiment, each pixel block of the non-target block group is subjected to high compression processing and stored. However, since the non-target area usually has many insignificant images, In some cases, only the average value of those block groups may be stored.

(7) In the image processing according to the present invention, the number of target colors is not limited, and not only monochrome but also four colors (Y,
M, C, and K), and image processing formed by a color system such as RGB and Lab.

The processing may be performed for each color space or for each dye block of an image. Further, after performing color conversion such as RGB-YIQ conversion used in the NTSC system on the image data, The image processing according to the present invention may be performed.

[0088]

The image coding method according to the first configuration of the present invention divides the data of the original image into pixel blocks as described above, and, based on the given contour data, creates a group of contour blocks. Since the object block group and the non-object block group are classified and different image processing is performed,
By compressing the image data of the former two pixel block groups at a low compression ratio and compressing the image data of the non-object block group at a high compression ratio, the important image necessary for the viewer Can be maintained sharply, but the amount of image data can be reduced as compared with the conventional method of lowering the image quality of the entire image. As a result, the memory capacity of the storage unit can be reduced, and
Transmission costs can be reduced.

Since the compression ratios of the outline block group and the object block group can be made different, for example, only the outline block group can be subjected to the lossless encoding process, and the edges of the image are stored as they are in the original image. And an image having a very high commercial value can be obtained. Furthermore, the first
Is smaller than the compression rate of the second encoding process.
Image is lower than
At the boundary between the contour area and the area inside and outside
The difference between the compression ratios at the boundary at the inner part
The resulting unnatural image shift is reduced.

Further, according to the image decoding processing method of the present invention, the image compressed as described above can be appropriately restored according to the compression mode.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of an image data compression device for implementing an image encoding processing method according to the present invention.

FIG. 2 is a block diagram showing an example of an image data restoring device for performing an image decoding processing method according to the present invention.

FIG. 3 is a flowchart illustrating an operation of the image data compression device of FIG. 1;

FIG. 4 is a flowchart illustrating an operation of a decompression process of compressed data in the image data restoration device of FIG. 2;

FIG. 5 is a block diagram showing another embodiment of the image data compression apparatus for performing the image encoding processing method according to the present invention.

FIG. 6 is a block diagram showing another embodiment of the image data restoring apparatus for performing the image decoding processing method according to the present invention.

FIG. 7 is a diagram illustrating an example of an original image and contour data created based on the image.

FIG. 8A is a diagram showing a pixel block of an image, and FIG. 8B is a diagram showing a state of a pixel array in the pixel block.

FIG. 9 is a diagram for explaining a procedure for creating an object table.

FIG. 10 is a flowchart showing a procedure for setting a position corresponding to contour data in a code table to “1”.

[Explanation of symbols]

 Reference Signs List 1 image memory unit 2 pixel block division unit 3 object table creation unit 4 pixel block discrimination unit 5 first compression unit 6 second compression unit 7 third compression unit 8 fourth compression unit 9, 9a storage unit 10 Fourth decompression unit 12 Compressed image data discrimination unit 13 First decompression unit 14 Second decompression unit 15 Third decompression unit 16 Combination unit 17 Display unit 18 Reconstructed image memory unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 1/41-1/419 H04N 7/24-7/68

Claims (2)

(57) [Claims] 1. A method of encoding image data for compressing image data of a given image, comprising: (a) setting a contour of an object in an image to be encoded; Forming data; (b) dividing the image to be subjected to the encoding process into a plurality of pixel blocks; and (c) converting the pixel blocks into at least a part of the contour based on the contour data. A contour block group that includes the contour block group; a target block group that includes a target image in a closed region formed by the contour block group; and a non-block obtained by removing the contour block group and the target block group from all the pixel blocks. (D) a first code that can obtain a relatively low compression ratio for each of the pixel blocks belonging to the contour block group and the object block group; And a second encoding process, and a third encoding process that can obtain a relatively high compression ratio for the pixel blocks belonging to the non-object block group, thereby performing the third encoding process on the plurality of pixel blocks. A step of obtaining coded image data for each, (e) for each of the plurality of pixel blocks, which of the contour block group, the object block group, and the non-object block group and a step of accompanying the encoded image data to create the attribute data representing the compression ratio of the first encoding processing in steps (d)
Is a compression rate lower than the compression rate of the second encoding process. 2. A method for decoding image data encoded by the method of claim 1, wherein: (a) referring to the attribute data attached to the encoded image data, Determining whether each of the pixel blocks belongs to the outline block group, the object block group, and the non-object block group; (b) decoding the encoded image data; Pixel blocks determined to belong to the contour block group in step (a) are subjected to a first decoding process corresponding to the first encoding process, and belong to the target block group in step (a). The determined pixel block is subjected to a second decoding process corresponding to the second encoding process, and the pixel block determined to belong to the non-object block group in step (a) is processed in the previous manner. A third decoding process corresponding to the third encoding process, a step of obtaining decoded image data by executing each of the third decoding processes; and (c) each pixel block decoded by the step (b). Synthesizing an image to obtain a restored image corresponding to the image.