JPH06350856A - Picture encoding device - Google Patents

Abstract

(57) [Summary] [Purpose] Change the EOB position according to the additional information,
It is an object of the present invention to provide an image coding apparatus that multiplexes coded information with coded data. [Structure] Image data is divided into blocks of 8 × 8 pixels, and DCT calculation and quantization processing is performed for each block (steps S1 and S2). This quantized data is zigzag-scanned for each block to add an EOB, and whether the position of the added EOB is an odd number or an even number is detected, and a table tab (i, j) format is created (steps S3, S).
4). The additional information is expanded into the code table code (i, j) (step S5), and this code table code is generated.
(I, j) is compared with the table tab (i, j), and the position of the EOB of the image data to be encoded is changed according to the code table code (i, j) (steps S6 to S6).
S8). After that, a normal encoding process is performed to add additional information to the encoded data of the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding apparatus, and more particularly to an image coding apparatus for adding other information such as character information when coding an image.

[0002]

2. Description of the Related Art As an international standard for image compression, JPEG (Jo
int Photographic Expert Group) and MPEG (Moving
There is a Picture Expert Group).

In particular, JPEG aims at compressing a still image, and the JPEG algorithm is roughly classified into two compression methods.

The first method is DCT (Discrete Cosine Tr
ansform: A method based on discrete cosine transform. The second method is DPCM (Differntial) in a two-dimensional space.
PCM) is a Spatial (spatial function) method.

The DCT method is a lossy encoding in which the original image is not completely reproduced because it includes quantization.
This is a basic method of the JPEG algorithm, which can obtain a sufficient decoded image quality even with a small number of bits.

On the other hand, the Spatial method is a reversible coding which has a small compression rate but completely reproduces the original image, and is a method added as a standard method to realize this characteristic.

[0007] The DCT method is further classified into two, that is, a baseline process (Baseline System) which is an essential function and an extended DCT process (Extended System) which is an optional function.

The baseline process is the minimum function that all encoders / decoders that implement the DCT method must have, and the ADCT method (Adaptive Descrete).
Cosine Transform Coding: Adaptive discrete cosine transform)
Is an algorithm based on.

In the image compression in the above baseline process, image data is processed in blocks of 8 × 8 pixels. The treatment process is as follows.

(1) Two-dimensional DCT transform process (2) DCT coefficient quantization process (3) Entropy coding process In the two-dimensional DCT transform process, first, an input image is divided into blocks of 8 × 8 pixels and each block is divided into blocks. For each block, a discrete cosine transform calculation is performed on each pixel in the block to convert it into frequency data. By this DCT conversion, image data of 8 × 8 pixels is converted into 8 × 8 (64 × 8) as shown in FIG.
Number) of two-dimensional DCT coefficients.

In the DCT coefficient shown in FIG. 13, the spatial frequency becomes higher toward the lower right, the DC component (DC component) is at the upper left end, and the AC component (AC component) is other than that.

In the DCT coefficient quantization process, the quantizer matrix is used to linearly quantize the DCT coefficient using a quantization matrix in which a different quantization step size is set for each coefficient. However, in order to control the code amount or the decoded image quality, a value obtained by multiplying a quantization matrix by a coefficient (scaling factor) specified from the outside is used as an actual matrix value for quantization. In this way, the 64 DCT coefficients are quantized into integer values with reference to the table. This quantization process results in lossy compression. The contents of the reference table used are not specified in JPEG. The quantization table is
Although it is created in consideration of human visual characteristics, since humans are not sensitive to visual information of high frequency components, this high frequency component is roughly quantized.

In the entropy coding process, first, the difference between the DC component and the quantized DC component in the left adjacent block is calculated and coded. This method is called DPCM. Further, the AC component is generally converted into a one-dimensional array in order from the coefficient at which energy is concentrated in the zigzag scan as shown in FIG. 13, that is, the coefficient at the upper left of FIG. 13, and encoded.

The Huffman coding method is used in the entropy coding of the baseline process. In the Huffman encoding process, it is determined by zigzag scanning whether or not each one-dimensionally arranged coefficient is zero, and the coefficient of consecutive zeros is counted as the run length. When a non-zero coefficient comes, two-dimensional Huffman coding is performed by combining the quantization result and the run length of the zero coefficient up to that point. The Huffman coding of the DC / AC coefficients is based on the given Huffman code table, but the quantization matrix and Huffman code table have no default values in order to be optimal in the situation in which they are used, if necessary. It is transferred from the encoder to the decoder for use.

In the coding of the AC coefficient, when the last AC coefficient in the block is 0, EOB (End Of Block) is added next to the code for the final effective coefficient.
The coding of the block is completed by EOB.

In an encoding device for performing such encoding, when transmitting additional information such as filter strength or character information for each block and character information, conventionally, a format having a dedicated area for transmitting additional information is set in advance. The additional information is transmitted by the encoding device having this format.

[0017]

By the way, in the conventional image encoding apparatus, when transmitting additional information such as character information, an image having a format having a dedicated area for transmitting additional information is provided. The only way to do this was to use an encoding device.

That is, in a format that does not have a dedicated area for transmitting additional information, a format that has been set once may have a dedicated area for transmitting additional information set later due to compatibility problems. Difficult and practically
The additional information could not be transmitted.

Therefore, an object of the present invention is to provide an image coding apparatus which can easily add additional information without having a dedicated area for transmitting additional information.

[0020]

An image coding apparatus according to the present invention divides image data for one screen into blocks each having a predetermined number of pixels, and for each block, image data for each pixel in the block is quantized. When the quantized data of each pixel is scanned by a predetermined scanning method and the scan data for each block is encoded into the encoded data by the predetermined encoding method, the code of the final effective coefficient in the block is Next, in an image encoding apparatus to which EOB is added, scan position detecting means for detecting a scan position by the scan method in the block of the EOB, and scan position data of each block detected by the scan position detecting means are provided. The scan position storage means for storing one screen and the information to be multiplexed with the encoded data are EO.
The multiplexed information storage means for storing as B scan position data, the stored content of the scan position storage means and the stored content of the multiplexed information storage means are compared, and the EOB position of the encoded data is multiplexed. The above object is achieved by including EOB position changing means for changing the stored contents of the information storing means.

In this case, for example, as described in claim 2, the scan position detecting means detects the scan position as an even-numbered position or an odd-numbered position of the scan by the scanning method, and stores the scan position. The means stores the scan position data indicating whether the position is an even-numbered position or an odd-numbered position in a scan in a 2-bit table format, and the multiplexing information storage means stores the multiplexing information as 2-bit code data. And the EO
The B position changing means may change the position of the EOB to an even position or an odd position of the scan based on the code data.

[0022]

According to the present invention, for each block obtained by dividing one screen of image data into a predetermined number of pixels, the image data of each pixel in the block is, for example, DCT-transformed and quantized, When the quantized data of each pixel is scanned by a predetermined scanning method, and the scan data for each block is encoded into encoded data by a predetermined encoding method,
E next to the sign for the last significant coefficient in the block
Although the OB is added, the scan position detecting means detects the scan position of this EOB in the block, for example, the odd position or the even position. The detected EOB scan position data of each block is stored in the scan position storage means for one screen, and the stored content and the information to be multiplexed with the encoded data are stored as the EOB scan position data, for example, 2 bits. Of the coded data in the code table format is compared with the stored content of the multiplexed information storage means, and the position of the EOB of the encoded data is determined according to the stored content of the multiplexed information storage means.
It is changed by the B position changing means.

Therefore, even in a format that does not have a dedicated area for transmitting additional information, additional information (multiplexed information) can be easily added simply by changing the position of the EOB, and compatibility is improved. The additional information can be transmitted while maintaining and without changing the format.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIGS. 1 to 12 are views showing an embodiment of an image coding apparatus according to the present invention, which is an example applied to an image coding apparatus based on the JPEG algorithm.

First, the structure will be described.

FIG. 1 is a block diagram of the image coding apparatus 1, in which the image coding apparatus 1 includes a frame memory 2, a DCT calculation unit 3, a quantization unit 4, and a quantization table ROM (Read Only). Memory) 5, entropy coding unit 6, entropy coding table ROM 7, data buffer 8, EOB RAM (Random Access Memory)
9, a code RAM 10, a control unit 11 and the like.

The frame memory 2 stores the original image data to be data-compressed, and the image data in the frame memory 2 is output to the DCT calculation section 3.

The DCT calculation unit 3 performs a two-dimensional DCT on the image data input from the frame memory 2 and D
The DCT calculation for obtaining the CT coefficient is performed, and the calculated DCT coefficient data is output to the quantizer 4.

The quantizer 4 quantizes the output data of the DCT calculator 3 according to the value of the quantization table ROM 5, and outputs the calculation result to the entropy encoder 6. The quantization table ROM 5 stores in advance a quantization table having quantization matrix values of different sizes for each DCT coefficient.

The entropy coding unit 6 performs entropy coding on the output of the quantizing unit 4 according to the value of the entropy coding table ROM 7, and writes the generated code amount of each block in the data buffer 8.

At the time of this coding, the entropy coding unit 6 zigzag-scans the DCT coefficients for each block in order from the energy-concentrated coefficient to convert the DCT coefficient into a one-dimensional array, and the last AC coefficient in the block is 0. In the case of, EOB is attached next to the code for the final effective coefficient.

The control unit 11 detects an even or odd scan position from the pixel position of the scan start of the EOB added by the entropy coding unit 6, and detects the scan position. The detection result is written in the EOB RAM 9 as scan position data for each block. The control unit 11 outputs the detection result, for example, “0” at the odd number and “1” at the even number.
R for EOB in a table format corresponding to each block of the image
Write to AM9.

The code RAM 10 stores, in a table format, coded information to be added (multiplexed) to the coded data, for example, character information and filter strength / strength information for each block. As the code data, for example, in the case of character information, a binary code (for example, a binary code in which ASCII code is expressed in binary) is assigned to the alphabet, and, for example, “KURAG
When the character "E" is used as the additional information, the binary code of the additional information as shown in FIG. 2 is stored in the table format.

The control section 11 controls each section of the image coding apparatus 1 to perform processing as the image adding apparatus 1, and detects the scan position of the EOB added by the entropy coding section 6 as described above. Then, the scan position data is written in the EOB RAM 9 in a table format, and the additional information table written in the code RAM 10 is compared with the scan position data table in the EOB RAM 9 to scan the additional information table. EOB position change processing is performed to change the EOB position so that the position data table matches.

Next, the operation of this embodiment will be described.

The image coding apparatus 1 performs coding processing according to the procedure shown in FIG.

That is, the original image data stored in the frame memory 2 is read out and output to the DCT operation unit 3, and the DCT operation unit 3 outputs the input image data of 8 × 8 pixels as shown in FIG. Divide into blocks (step S
1). In FIG. 4, the divided blocks have the upper left corner as (0, 0), the right j position, and the left i position block as Bij. Then, as shown in FIG. 5, each block Bij includes 8 × 8 pixels aij.

Next, the DCT calculation unit 3 performs DCT conversion on each block Bij in the DCT calculation process,
It is output to the quantizer 4 (step S2). Using the quantization table of the quantization table ROM 5 in the quantization unit 4, each pixel aij in each block Bij is quantized into quantized data bij as shown in FIG. 6, and output to the entropy encoding unit 6. Yes (step S2).

In FIG. 6, as bij, b00, b01,
.. are quantized data bij other than "0", and portions described by "0" are quantized data bij of "0". As can be seen from FIG. 6, the concentration of energy is small in the high frequency region (lower right side in FIG. 6) due to the property of DCT, and “0” appears in the lower right side in FIG.
Is increased, and finally, only “0” is obtained.

Then, in the entropy coding unit 6, FIG.
Zigzag scanning as shown in FIG. 3 is performed on the quantized data bij of each quantized block Bij shown in FIG. 6, and the quantized data bij is arranged one-dimensionally as shown in FIG. 7 (step S3). Further, normal encoding preprocessing for performing run length detection and the like of the one-dimensionally quantized data is performed to add EOB (step S).
3).

When the entropy coding unit 6 adds the EOB, the control unit 11 detects the position data of the EOB. That is, as shown in FIG. 7, the control unit 11 determines that the positions of the EOBs added to the one-dimensionally quantized data bij are odd-numbered (odd) in the scan order.
Or even-numbered (even), and the detection result is stored in the EOB RAM 9 as shown in FIG.
Each block Bij is sequentially stored in a table format corresponding to the block Bij position shown in FIG.
(I, j) is created (step S4). Note that in FIG. 8, the table tab (i, j) describes “o” for odd numbers and “e” for even numbers.
Actually, for example, “0” is written in the case of “e” and “1” is written in the table tab (i, j) when it is “o”.

EOB is detected for each block Bij,
When the table tab (i, j) is created, the control unit 1
1 encodes additional information (multiplexing information) to be added (multiplexed) to the encoded data in a predetermined code format, and as shown in FIG. 2, the code RAM 10 uses a code table code (i) of binary data. , J) are created (step S5).

In this way, the table tab (i,
j) and the code table code (i, j) are completed, the control unit 11 controls the code table code (i, j).
It is checked whether each code in j) matches the data at the corresponding table position in the table tab (i, j) (step S6).

Data comparison between the table tab (i, j) and the code table code (i, j) is performed assuming that "e" is "0" and "o" is "1" as described above. , Table tab (i, j) and code table cod
This is performed for the data at the position corresponding to e (i, j).

If YES in step S6, it is determined that the position of the EOB added in the encoding process matches the binary data of the additional information, and the code table cod
table tab for all data of e (i, j)
It is checked whether or not the data has been compared with the data of (i, j) (step S7), and when the above inspection processing has not been completed for all the data of the code table code (i, j), the process returns to step S6, and , Compare both tables. That is, this inspection process is performed in the table tab.
Code table code (i, j) of (i, j)
Perform only for the data corresponding to.

If NO in step S6, it is determined that the position of the EOB added in the encoding process does not match the binary data of the additional information, and the EOB changing process (see FIG. 9) described later is performed (step S8). ), It is checked whether all the data in the code table code (i, j) are compared with the data in the table tab (i, j) (step S7).

In step S7, all code tables c
Table tab for the data of ode (i, j)
When the comparison with the data of (i, j) is completed, the quantized data is encoded by a normal encoding process, and the process is terminated (step S9).

In the EOB changing process of step S8, as shown in FIG. 9, the code "1" is sent before the original EOB added by the entropy coding unit 6, and the EOB is added after the code. Thus, the position of EOB is changed (step T1). In this way, even if the code “1” is added, there is almost no effect on the redundancy or image quality as encoded data, and the position of the EOB can be easily changed to change the odd number and the even number. can do.

The EOB changing process is not limited to the method shown in FIG. 9. For example, as shown in FIG. 10, a code located before the original EOB, for example, FIGS. In this case, the position of the EOB is changed by performing a process (step T2) of omitting b41 and six consecutive "0" codes before this b41, for example, as shown in FIGS.
Then, the position may be changed to b22, and the odd number and the even number may be changed. However, according to this method, for example, b
Depending on the number of consecutive "0" codes before 41, it may not be possible to switch between the odd number and the even number.

Further, the EOB changing process may be performed by the following method.

That is, as shown in FIG. 11, the position of the EOB is changed to a position of a succession of "0" following the original position of the EOB in the quantized data and a sign after that (step T3). That is, the position of the EOB does not necessarily have to be added next to the code for the final effective coefficient, and when the “0” continues to some extent, the position of the EOB is appropriately placed before the final effective coefficient because of the relationship with the allowable error. It may be added next to the sign of the sign for the effective coefficient located, and in such a case, the position of the EOB is changed to the position of the subsequent "0" and the position of the sign thereafter. Also in this case, the odd number and the even number may not be changed depending on whether the changed EOB position is the odd number or the even number in the scan order. further,
It goes without saying that the EOB changing process is not limited to the above three methods.

Therefore, the changing process of the EOB may not be performed by only one method, but the changing method may be appropriately changed depending on the condition of the quantized data.

The coded data to which the additional (multiplexing) information has been added in this way is transferred to its own or another image decoding apparatus via a transmission path or the like, and the image data is decoded by this image decoding apparatus. At the same time, the additional information added to the encoded data is decoded and reproduced.

This reproduction process is performed as shown in FIG.

That is, first, the encoded data is decoded by a normal decoding method to form a code string as shown in FIG. 7 (step P1).

From this code string, it is detected whether the EOB position is an odd number (odd) or an even number (even), and the detection result is added to the odd and e as shown in FIG.
It is created as a table tab_d (i, j) of ven (step P2).

The contents of the table tab_d (i, j) are compared with a code table of additional information prepared in advance and converted into information (step P3). That is, the image decoding apparatus has a code table corresponding to various additional information such as character information in advance, and decodes the table tab_d (i, j) based on this code table,
Convert to additional information.

After that, the reverse zigzag scan is performed for each block as in the normal decoding process (step P).
4) Develop code data for each block. further,
Inverse quantization and inverse DCT calculation are performed for each block to reproduce an image for each block (step P5).

The image for each block reproduced in this way is formed into an image for one screen (step P6), and the reproduction process is terminated.

As described above, according to this embodiment,
For each block Bij obtained by dividing the image data for one screen into 8 × 8 pixels, the image data of each pixel aij in the block Bij is DCT-transformed and quantized, and then the quantized data bij of each pixel is zigzag. When scanning and converting the scan data for each block Bij into coded data by a predetermined coding method, E in the block Bij added is added.
The scan position of the OB is detected. The detected EOB scan position data of each block Bij is stored in the table tab (i, j) format for one screen as the odd-numbered (odd) and even-numbered (even) data of the scan. EOB information to be multiplexed with encrypted data
Code table co corresponding to the scan position data of
The contents of the code RAM 10 stored as de (i, j) are compared, and the position of the EOB of the encoded data is changed according to the code table code (i, j).

Therefore, even if the format does not have a dedicated area for transmitting additional information, additional information (multiplexed information) can be easily added by simply changing the position of the EOB, and compatibility is improved. The additional information can be transmitted while maintaining and without changing the format.

In this embodiment, the image coding apparatus is JP
This is an example applied to an image coding device based on the EG algorithm, but needless to say, the present invention is not limited to this and can be applied to any device as long as it performs a coding process for adding EOB. Further, anything that adds EOB may be used, and other encoding methods, scanning methods, and the like are not limited to those in the above-described embodiment.

[0064]

According to the present invention, even with an image coding apparatus having a format that does not have a dedicated area for transmitting additional information, additional information (multiplexed information) can be simply changed by changing the position of EOB. ) Can be easily added, and the additional information can be transmitted while maintaining compatibility and without changing the format. As a result, it is possible to improve the usability of the image encoding device.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an image encoding device.

FIG. 2 is a view showing an example of a code table code (i, j) stored in the code RAM of FIG.

FIG. 3 is a flowchart showing an image encoding process by the image encoding device.

FIG. 4 is a diagram showing a state in which image data for one screen is divided into blocks.

5 is a diagram showing pixel data in one block in FIG. 4. FIG.

FIG. 6 is a diagram showing a state in which pixel data in the block shown in FIG. 5 is quantized.

FIG. 7 is a diagram showing a state in which the quantized data of FIG. 6 is one-dimensionally arranged by zigzag scanning.

FIG. 8 is a diagram showing a table tab (i, j) of data of odd / even positions of EOB.

FIG. 9 is a flowchart showing an example of EOB change processing.

FIG. 10 is a flowchart showing another example of EOB change processing.

FIG. 11 is a flowchart showing still another example of EOB change processing.

FIG. 12 is a flowchart showing a decoding process.

FIG. 13 is an explanatory diagram of a zigzag scanning method.

[Explanation of symbols]

 1 Image Coding Device 2 Frame Memory 3 DCT Operation Unit 4 Quantization Unit 5 Quantization Table ROM 6 Entropy Encoding Unit 7 Entropy Encoding Table ROM 8 Data Buffer 9 EOB RAM 10 Code RAM 11 Control Unit

Claims (2)

[Claims] 1. Image data for one screen is divided into blocks each having a predetermined number of pixels, image data of each pixel in each block is quantized, and the quantized data of each pixel is scanned by a predetermined scanning method. In the image coding apparatus, the scan data is scanned for each block, and when the scan data for each block is coded into coded data by a predetermined coding method, EOB is added next to the code for the final effective coefficient in the block, Scan position detecting means for detecting a scan position by the scan method in the block of the EOB; scan position storing means for storing one screen of scan position data of each block detected by the scan position detecting means; Multiplexed information storage means for storing information to be multiplexed with the encoded data as EOB scan position data, The storage contents of the scan position storage means and the storage contents of the multiplexed information storage means are compared to each other to obtain E of the encoded data.
An image coding apparatus comprising: an EOB position changing unit that changes the position of the OB according to the storage content of the multiplexed information storage unit. 2. The scan position detecting means detects the scan position as an even-numbered position or an odd-numbered position of the scan according to the scanning method, and the scan-position storage means detects the scan position data as an even-numbered position of the scan. Position or odd-numbered position is stored in a 2-bit table format, the multiplexing information storage means stores the multiplexing information as 2-bit code data, and the EOB position changing means stores the EOB position. 2. The position is changed to an even-numbered position or an odd-numbered position of the scan based on the code data.
The image encoding device described.