JP3215211B2 - Image information encoding device - 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 information encoding apparatus for compressing image information by predictive encoding.

[0002]

2. Description of the Related Art As a coding method suitable for compressing data of image information, an arithmetic code which is one of predictive coding methods is known.

FIG. 8 shows a conventional example of an encoding device that encodes image information using an arithmetic code. Binary image information is input to this encoding device line by line. The surrounding pixel extracting circuit 1 pays attention to each pixel of the input image information and extracts a certain number of pixels around the target pixel. The prediction circuit 2 predicts the symbol of the pixel of interest based on the symbol pattern of the extracted pixel, and outputs an appearance probability value of the inferior symbol.
The encoding circuit 3 generates a predetermined arithmetic code based on the occurrence probability value of the inferior symbol and the symbol of the actual pixel of interest. The probability evaluation unit 4 evaluates the past prediction accuracy of the prediction circuit 2 and changes prediction conditions as necessary.

[0004] In such an encoding device, when the prediction accuracy increases, the data amount of the generated code information decreases, so that the data compression effect increases.

At the start of the encoding process, since the appearance probability of the inferior symbol of the image information to be processed is unknown,
The prediction circuit 2 outputs “0.5” as an initial value of the appearance probability of the inferior symbol. That is, the process starts on the assumption that the superior symbol and the inferior symbol appear with the same probability. Then, the prediction condition of the prediction circuit 2 is changed by the probability evaluation unit 4 while executing the encoding process. As a result, the prediction accuracy of the prediction circuit 2 is gradually improved.

In general, in the case of a pseudo halftone image obtained by dithering a photograph or the like, since the correlation between the target pixel and surrounding pixels is low, the appearance probability of the inferior symbol is, for example, a value of "0.4". In the case of a character image, since the correlation is high, the appearance probability of the inferior symbol is a low value of, for example, “0.1”.

[0007]

Therefore, after the encoding process is started, it takes some time until the prediction circuit 2 outputs a highly accurate probability value corresponding to various images.

Conventionally, there has been a problem that the data compression effect is reduced because the prediction accuracy of the symbol of the pixel of interest is reduced during the period up to that time.

In recent years, JBIG (Joint Bi
-Level Image Coding Explorer
ts Group), a standard method for encoding binary image information is recommended. This standard method also employs the above arithmetic code, and has the same problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image information encoding device which can solve the above-mentioned problems and can improve the effect of compressing image information data.

[0011]

For this purpose, the present invention extracts the surrounding pixels for each pixel as a whole over the image information of one page to be processed, and determines whether the pixel of interest is inferior or inferior for each symbol pattern that appears. Calculate the probability value that appears as a dominant symbol, store the correspondence between each symbol pattern and the probability value, and then extract the surrounding pixels for each pixel again over the entire image information, It is characterized in that a probability value corresponding to a pattern is read out and code information is generated based on the probability value and the actual symbol of the pixel of interest.

[0012]

Since the probability of occurrence of the inferior or superior symbol of the entire image information is calculated in advance and the encoding process is executed based on the calculation result, the symbol of the pixel of interest is predicted from the start of the encoding process. Since the accuracy is higher, the data compression effect is improved.

[0013]

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 unit of an image processing apparatus according to one embodiment of the present invention.
In the figure, an image information memory 11 stores binary image information to be processed for one page. The switching circuit 12 selects input information to the surrounding pixel extraction circuit 13. The surrounding pixel extraction circuit 13 extracts a certain number of pixels around the target pixel of the image information. The appearance probability calculation circuit 14 calculates the appearance probability of the inferior symbol for each symbol pattern of the extracted pixel. The switching circuit 15
This is for selecting input information to the probability value memory 16.
The probability value memory 16 stores the calculated probability value data. The encoding circuit 17 generates arithmetic code information based on the appearance probability of the inferior symbol and the actual symbol of the target pixel.

FIG. 2 shows a block diagram of a decoding section of the image processing apparatus. In the figure, the decoding circuit 21
Restores the code information to the original image information. The probability value memory 22 stores the same probability value data as the probability value memory 16. Surrounding pixel extraction circuit 2
Reference numeral 3 is for extracting a certain number of pixels around the target pixel from the restored image information.

FIG. 3 shows the encoding process of the image processing apparatus according to the present embodiment. That is, when executing the encoding process, image information is sequentially input one pixel at a time from another device (not shown). The image information memory 11 sequentially stores the input image information. The input image information is input to the surrounding pixel extraction circuit 13 via the switching circuit 12. The surrounding pixel extraction circuit 13 pays attention to each pixel of the image information, and extracts a certain number of surrounding pixels at a certain position with respect to the pixel of interest.

If, for example, eight peripheral pixels are extracted, the symbol pattern of the extracted pixels is 2 to the eighth power, that is, 256 patterns. Therefore, every time one pixel of image information is input to this encoding unit, the surrounding pixel extraction circuit 13
Sequentially outputs 256 kinds of various symbol patterns.

As shown in FIG. 4 (a), the appearance probability calculation circuit 14 counts the appearance frequency of each output symbol pattern and the appearance frequency at which the pixel of interest becomes the inferior symbol at each time. I do.

The above operation is executed for one page of image information. Then, when the operation is completed, the appearance probability calculation circuit 14 calculates the appearance probability value of the inferior symbol from the appearance frequency of each symbol pattern and the appearance frequency of the inferior symbol, as shown in FIG. Yes
Process 101).

Next, the appearance probability calculation circuit 14 outputs probability value data for each calculated symbol pattern.
The output probability value data is output to the outside of the apparatus via the switching circuit 15 and is input to the probability value memory 16. The probability value memory 16 stores the probability value data (process 102). The reason why the probability value data is output to the outside is to use the probability value data in a decoding process described later.

Next, the image information stored in the image information memory 11 is sequentially read out pixel by pixel. The surrounding pixel extraction circuit 13
The image information is input via the switching circuit 12, and pixels surrounding each pixel are extracted in the same manner as described above. Probability value memory 16
Outputs the appearance probability value of the inferior symbol corresponding to the extracted symbol pattern of each pixel. Encoding circuit 17
Performs a predetermined operation using the appearance probability value of the inferior symbol and the symbol of the actual pixel of interest to generate code information of an arithmetic code.

Such an operation is performed in the image information memory 11 in the
This is executed for the image information of the page. As a result, the encoded image information is output from the encoding circuit 17 to the outside (process 103).

Next, when decoding the encoded image information, the decoding unit inputs the probability value data output from the encoding unit and stores it in the probability value memory 22, as shown in FIG. (Step 201). Thereafter, the code information is sequentially input to the decoding circuit 21.

The decoding circuit 21 converts the input code information into 1
The original image information is restored pixel by pixel. Surrounding pixel extraction circuit 23
Focuses on each pixel to be restored, and extracts a certain number of pixels around the target from the previously restored image information. The probability value memory 22 outputs an occurrence probability value of the inferior symbol corresponding to the extracted symbol pattern of each pixel. The decoding circuit 21 executes the above-mentioned image information restoring operation based on the occurrence probability value of the inferior symbol and the code information. Thus, the image information of one page is restored (process 202).

As described above, in the present embodiment, when the encoding process is executed, the surrounding pixels for each pixel are extracted over the entire image information of one page to be processed, and the inferior symbol of each extracted pixel is symbolized. The appearance probability is calculated and stored. After that, surrounding pixels are extracted again by paying attention to each pixel of the image information of one page, and a probability value corresponding to the symbol pattern of the extracted pixel is read out. Code information is generated based on the actual symbol of the target pixel.

Thus, from the start of the encoding process,
Since the symbol of the target pixel can be predicted with high precision, the data compression effect is improved.

Further, in the present embodiment, the encoding / decoding processing is executed by the arithmetic code. Even in the JBIG standard system, arithmetic codes are employed, so that a higher data compression effect than the standard system can be obtained while conforming to such a standard system to some extent.

By the way, in the above embodiment, the operation example of executing the operation of encoding the image information and restoring based on the encoded image information by the same device has been described.
The present invention can be similarly applied to a case where encoded image information is transmitted to another device as in a facsimile machine.

FIG. 6 shows an example of a communication procedure when transmitting encoded image information to another device. That is,
When the communication starts, the receiving side, as a function of its own device,
It notifies the transmitting side that it has the function of executing the above-described decoding processing.

After confirming the function of the device on the receiving side, the transmitting side stores the data in the probability value memory 16 and transmits data on the occurrence probability of the inferior symbol. Thereafter, code information obtained by encoding the image information is transmitted.

The receiving side stores the transmitted probability value data in the probability value memory 22, and thereafter receives the transmitted code information and sequentially restores it to image information.

As described above, the transmitting side transmits the occurrence probability value data of the inferior symbol together with the code information to the receiving side, so that the receiving side can smoothly decode various images.

When transmitting image information to another device as in the above embodiment, as shown in FIG. 7, the probability value data and the image information are coded together, and both are transmitted as code information. You may make it.

Further, in each of the above embodiments, the encoding process is executed based on the appearance probability of the inferior symbol, but may be executed based on the appearance probability of the superior symbol. In that case, it goes without saying that the appearance probability of the dominant symbol may be calculated in advance.

[0035]

As described above, according to the present invention, 1
Over the entire image information of the page, the appearance probability value of the inferior or superior symbol is calculated for each symbol pattern of the surrounding pixels to be extracted, and a predetermined encoding process is executed based on the calculated probability value. Therefore, since the prediction accuracy of the symbol of the pixel of interest is increased from the start of the encoding process, the data compression effect of the image information is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an encoding unit of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a decoding unit of the image processing apparatus.

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

FIG. 4 is an explanatory diagram showing an operation of an appearance probability calculation unit.

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

FIG. 6 is an explanatory diagram showing an example of a communication procedure when transmitting image information.

FIG. 7 is an explanatory diagram showing another example of a method for transmitting image information.

FIG. 8 is a block diagram showing a conventional example of an encoding device.

[Explanation of symbols]

 Reference Signs List 11 Image information memory 12, 15 Switching circuit 13, 23 Surrounding pixel extraction circuit 14 Appearance probability calculation circuit 16, 22 Probability value memory 17 Encoding circuit 21 Decoding circuit

Claims (4)

(57) [Claims] 1. A surrounding pixel extracting unit that focuses attention on each pixel of image information of one page to be processed and extracts a certain number of surrounding pixels for the pixel of interest, and the surrounding pixel extracting unit performs the surrounding operation over the entire image information. Appearance probability calculation means for calculating a probability value of a pixel of interest appearing as a inferior or superior symbol for each symbol pattern in which a pixel is extracted and appearing, and probability value storage means for storing a correspondence between the calculated probability value and each of the symbol patterns And a probability value reading means for reading out from the probability value storage means a probability value corresponding to each symbol pattern appearing by extracting the surrounding pixels again over the entire image information by the surrounding pixel extracting means, and the read probability value. Encoding means for generating code information based on an actual symbol of the pixel of interest. Encryption device. 2. The image information encoding apparatus according to claim 1, wherein said encoding means is means for generating code information by an arithmetic code encoding method. 3. When transmitting image information to another device,
2. The image information encoding apparatus according to claim 1, further comprising means for transmitting the code information generated together with the calculated information on the correspondence between the probability value and each of the symbol patterns. 4. The image information encoding apparatus according to claim 3, further comprising means for encoding and transmitting the correspondence information.