JP3226637B2 - Coding device and decoding device for predictive coding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coding device and a decoding device for a predictive coding system.

[0002]

2. Description of the Related Art A predictive coding method is known as a coding method suitable for compressing image information data.

In the predictive coding method, attention is paid to each pixel of image information, a symbol of the pixel of interest is predicted with reference to each pixel in a certain range around the image information, and image information is encoded based on the prediction result. .

In general, when predicting the symbol of a pixel of interest, a data table showing the correspondence between the symbol pattern of each pixel to be referenced and the symbol appearance probability value is created as shown in FIG. Then, while sequentially performing the prediction operation of the pixel of interest, the past predictive accuracy is evaluated, and the symbol appearance probability value in the table is updated.

[0005] The larger the number of reference pixels, the higher the prediction accuracy and the higher the data compression effect. When the number of reference pixels is fixed, there is a correlation between the position of the reference pixel, the type of image, and the data compression effect. That is, in the image information of a specific image, the highest data compression effect can be obtained when the reference pixel is set at a specific position. For example, in general, in the case of a character image, the reference pixel position is preferably set to be concentrated in a certain range close to the target pixel. On the other hand, in the case of a pseudo halftone image, it is preferable to set a wide range from a position close to the target pixel to a position distant from the target pixel.

Conventionally, the number of reference pixels and their pixel positions have been fixedly set according to the type of image to be processed.

As is apparent from FIG. 8, the data amount of the data table increases in accordance with the number of reference pixels. An encoding device that encodes image information stores such a data table in a memory and executes the above-described processing.

Incidentally, depending on the device, one memory is often used not only for storing the data table but also for storing data for other processes.

In such an apparatus, most of the memory capacity is consumed in other processing, and the free space for storing the data table may be exhausted. In this case, the encoding process could not be executed.

In order to eliminate such a shortage of memory capacity, it is conceivable to reduce the number of reference pixels to reduce the data amount of the data table. However, when the number of reference pixels is reduced, the data compression effect always decreases.

[0011] In a decoding apparatus for decoding coded image information, the image information which is successively reconstructed is also decoded.
In order to execute the same processing as described above, a data table similar to that of the encoding device is created and stored in the memory. Therefore, a similar situation has occurred in the decoding device.

[0012]

As described above, conventionally,
There has been a problem that encoding and decoding processing cannot be performed due to insufficient memory capacity, and the data compression effect is constantly reduced.

[0013] The present invention solves the above-mentioned problems, and performs an encoding and decoding process without fail. The encoding apparatus and the decoding apparatus of the predictive encoding system can reduce the reduction of the data compression effect as much as possible. The purpose is to provide.

[0014]

For this purpose, the present invention increases or decreases the number of reference pixels at the start of encoding or decoding processing, thereby enabling the symbol pattern of the reference pixel and the symbol appearance probability to be compared. A data table showing the correspondence
The present invention is characterized in that a means for adjusting the data size to always fit in the free space of the memory is provided.

[0015]

As a result, it is possible to prevent the encoding and decoding processes from being unable to be executed due to insufficient memory capacity, and to prevent the data compression effect from being constantly reduced.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an encoding apparatus according to one embodiment of the present invention. In the figure,
The reference pixel extracting unit 1 focuses on each pixel of the input image information and extracts each pixel in a certain range around the pixel as a reference pixel. The template creating unit 2 creates a template indicating each pixel position to be extracted. The reference pixel number determination unit 3 determines the number of reference pixels to be extracted based on the free space of the memory 4. Memory 4 is
While storing a data table necessary for symbol prediction of the pixel of interest, other processing means (not shown) other than the encoding processing stores various data as necessary. The establishment evaluation prediction unit 5 predicts the symbol of the pixel of interest based on the symbol pattern of the reference pixel. In this case, it has a function of evaluating the past predictive accuracy while executing the prediction operation and correcting the predicted value. The encoding unit 6 generates a predetermined arithmetic code based on the prediction result of the target pixel symbol.

FIG. 2 is a block diagram showing a decoding apparatus for restoring the coded image information generated by the above-mentioned coding apparatus to the original image information. In the figure, the decoding unit 7
Is for sequentially restoring each pixel of the image information. Reference pixel extraction unit 8, template creation unit 9, establishment evaluation prediction unit 1
0 and the memory 11 execute the same processes as those of the units having the same names in FIG.

Next, the operation of the coding apparatus having the above configuration will be described.

When the encoding apparatus is started, as shown in FIG. 3, the reference pixel number determination unit 3 determines the free space of the memory 4 (process 101).

In this embodiment, since the memory 4 is shared between the encoding process and other processes, the free space of the memory 4 is
It fluctuates from time to time. The reference pixel number determination unit 3 increases the number of reference pixels when the free space of the memory 4 is large, and decreases the number of small reference pixels when the free space is small, according to a preset condition. The number of reference pixels is determined (process 102).

The template creating section 2 creates a template having the determined number of reference images. That is, as shown in FIG. 4A, 19 surrounding pixels are set for the target pixel position X in the template creating unit 2,
Each pixel has a priority. The template creation unit 2 creates a template indicating each pixel position for the number of reference pixels according to the priority order. For example,
When the number of reference pixels is eight, as shown in FIG. 7B, a template indicating each pixel position of priority order 1 to 8 is created. When the number of reference pixels is 13,
As shown in FIG. 9C, a template indicating each pixel position in the priority order 1 to 13 is created (process 103).

Thereafter, the encoding device sequentially inputs the image information one pixel at a time. Then, the reference pixel extraction unit 1, the establishment evaluation prediction unit 5, and the encoding unit 6 start a predetermined operation to execute an encoding process.

That is, the reference pixel extraction unit 1 focuses on each input pixel and extracts surrounding pixels indicated by the template. When starting the operation, the establishment evaluation prediction unit 5 stores the data table as shown in FIG.
To create. Now, for example, if the number of reference pixels is eight, there are two to eight power symbol patterns of reference pixels. In this data table, probability data corresponding to each symbol pattern is stored. This probability data indicates the probability that the pixel of interest appears as an inferior symbol or a superior symbol.

The establishment evaluation prediction unit 5 first sets an initial value of probability data in the data table. Then, prediction is sequentially made as to whether the target pixel is to be the inferior symbol or the superior symbol, and the corresponding probability data is sequentially read. Then, the information is output to the encoding unit 6 as prediction information. In addition, while executing the prediction operation, the past predictive accuracy is evaluated, and the probability data in the table is updated so that the prediction probability approaches the actual symbol appearance probability of the target pixel. The encoding unit 6 sequentially generates arithmetic codes based on the prediction information.

In this manner, the image information is encoded (the above is the processing 104).

Next, the operation of the decoding apparatus will be described.

In this embodiment, when a decoding process is executed by the decoding device, the number of reference pixels set by the coding device is set in the decoding device. This setting, for example,
Performed by operator operation.

When the decoding apparatus is started, as shown in FIG.
Is input (process 201). Then, similarly to the template creation unit 2, a template having the reference pixel number is created (process 202).

Thereafter, a predetermined decoding process is executed. That is, the decoding unit 7 sequentially inputs the coded image information, and restores the image information one pixel at a time based on the prediction information output from the establishment evaluation prediction unit 10. The reference pixel extracting unit 8 focuses on each pixel of the image information to be restored, and extracts reference pixels around the target pixel indicated by the template. Establishment evaluation prediction unit 1
0 creates a data table of symbol appearance probabilities in the memory 11 in the same way as the above-described probability evaluation prediction unit 5, predicts the symbol of the pixel of interest, and outputs the appearance probability to the decoding unit 7. Thus, the encoded image information is decoded (process 203).

As described above, in this embodiment, when the encoding process is started, the free space of the memory 4 is determined, and if the free space is small, the number of reference pixels is reduced. . If the number of reference pixels is reduced, the size of the data table for storing the symbol appearance probabilities may be small, so that the data can be stored even if the free space of the memory 4 is small. This prevents the encoding process from being unable to be executed due to insufficient memory capacity.

When the free space of the memory 4 is large, the number of reference pixels is increased. When the number of reference pixels is increased, the symbol prediction accuracy of the pixel of interest is improved, so that a high data compression effect can be obtained.

When a template is created, priorities are determined in advance at each pixel position around the target pixel, and
Each pixel for the number of reference pixels is set as a reference pixel according to the priority order.

There is a certain correlation between the pixel position of the reference pixel, the image type, and the data compression effect. Therefore,
By setting the pixel position of the reference pixel in advance as described above, a high data compression effect can be obtained for a specific image.

Next, another embodiment of the present invention will be described.

FIG. 6 is a block diagram of the image transmission apparatus according to the present embodiment. In the figure, an encoding device 301 and a transmitting device 302 are installed on the transmitting side, and a receiving device 303 and a decoding device 304 are installed on the receiving side, respectively, and both are connected by a communication line 305.

The coding apparatus 301 is the apparatus shown in FIG. 1 of the above embodiment. The transmission device 302 is a device that transmits encoded image information. The receiving device 303 includes the transmitting device 30
2 is a device that receives encoded image information by communicating with the second encoded image information. The decoding device 304 is the device shown in FIG. 2 of the above embodiment. In this case, the memory 11 in the decoding device 304
Is used in processing other than the decoding processing, and the free space is assumed to be indefinite.

In this embodiment, when the transmitting side and the receiving side communicate, as shown in FIG. 7, the receiving side first notifies the free side of the memory 11 in the decoding device 304 to the transmitting side. On the transmitting side, the notified free space of the memory 11
The free space of the memory 4 in the encoding device 301 is checked, and the number of reference pixels is determined according to the smaller free space. The transmitting side notifies the receiving side of the determined number of reference pixels. Thereafter, a template having the determined number of reference pixels is created, the image information is encoded, and transmitted to the receiving side.

On the receiving side, a template of the notified number of reference pixels is created. Then, the coded image information is received and decoded.

As described above, in the present embodiment, when transmitting the coded image information, the transmitting side checks not only the free space of the memory of the transmitting side but also the free space of the memory of the receiving side, and checks the reference pixel. I try to determine the number. This prevents the receiving side as well as the transmitting side from being unable to execute the decoding process due to insufficient memory capacity.

Although the above embodiment has been described with reference to an image transmission apparatus, the present invention can be similarly applied to a facsimile apparatus. For example, in the case of the G3 facsimile, in the transmission control procedure, the receiving side notifies the transmitting side of the free space of the memory with the NSF signal,
The transmitting side may notify the receiving side of the number of reference pixels by the NSS signal.

Also, as shown in FIG. 4, only one type of priority is set for the surrounding pixels. However, if a plurality of types are determined and used in accordance with the type of image, various types of images can be used. , A high data compression effect can be obtained.

[0043]

As described above, according to the present invention, when the encoding or decoding process is started, the number of reference pixels is increased or decreased, and the correspondence between the symbol pattern of the reference pixel and the symbol appearance probability is increased. The data table that indicates is always adjusted to the data size that fits in the free space of the memory,
It is possible to prevent the processing from being unable to be executed due to insufficient memory capacity and the data compression effect from being constantly reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an encoding device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a decoding device according to the embodiment.

FIG. 3 is an operation flowchart of an encoding process.

FIG. 4 is an explanatory diagram showing a method for creating a template.

FIG. 5 is an operation flowchart of a decoding process.

FIG. 6 is a block diagram of an image transmission apparatus according to another embodiment of the present invention.

FIG. 7 is an explanatory diagram of communication information between a transmitting side and a receiving side in the embodiment.

FIG. 8 is an explanatory diagram of a data table.

[Explanation of symbols]

 1, 8 reference pixel extraction unit 2, 9 template creation unit 3 reference pixel number determination unit 4, 11 memory 5, 10 establishment evaluation prediction unit 6 encoding unit 7 decoding unit 301 encoding device 302 transmitting device 303 receiving device 304, 304 decoding device

Claims (6)

(57) [Claims] 1. A memory having an undefined free space, a pixel extracting means for paying attention to each pixel of image information and extracting a fixed number of pixels around the pixel as a reference pixel, and according to a symbol pattern of the extracted reference pixel. Prediction means for predicting the appearance probability of the symbol of the pixel of interest, encoding means for generating an arithmetic code based on the prediction result, and a correspondence between the symbol pattern of the reference pixel and the appearance probability of the symbol as a data table Data table storage means for storing data in the memory; and table size adjusting means for adjusting the data table to a data size which always fits in the free space of the memory by increasing or decreasing the number of reference pixels when starting the encoding process. A coding device for a predictive coding method, comprising: 2. When transmitting the encoded image information and storing the data table in a memory having an undefined free space on the receiving side, the table size adjusting means stores the data table on the transmitting side and the receiving side. 2. A predictive coding method encoding apparatus according to claim 1, further comprising means for adjusting a data size to be stored in each of said memories. 3. The code according to claim 1, further comprising means for transmitting information on the number of pixels of the reference pixels to a receiving side when transmitting the encoded image information. Device. 4. A memory having an undefined free space, pixel extracting means for paying attention to each pixel of image information restored by decoding, and extracting each surrounding pixel as a reference pixel, and a symbol pattern of the extracted reference pixel. Prediction means for predicting the appearance probability of the symbol of the pixel of interest in accordance with, decoding means for restoring the original image information from the image information encoded based on the prediction result, and a symbol pattern of the reference pixel Data table storage means for storing the correspondence with the symbol appearance probability in the memory as a data table; means for receiving information on the number of reference pixels together with the coded image information from the coding apparatus; Means for adjusting the table size according to the number. 5. The predictive coding system according to claim 4, further comprising means for transmitting information on the free space of said memory to said coding device when receiving the coded image information. Decryption device. 6. The apparatus according to claim 1, further comprising a template creating means for fixedly setting each pixel position of said reference pixel according to the number of pixels set by said table size adjusting means. 5. A decoding device for a predictive coding system or a decoding device for a predictive coding system according to claim 4.