JP2002199228A - Image data coding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image data coding method that enhances efficiency much more. SOLUTION: An image coder adopting the image data coding method is provided with a difference data calculation section 2, a difference data storage section 3, a variable length coding table generating section 4, a variable length coding table storage section 1, a variable length coding section 5, and coding data storage section 6, calculates difference data from a pixel value of original image data, generates a variable length coding table on the basis of the obtained data, and converts the image data into variable length coded data. Through the configuration above, the image coder uses a coding table calculated in a preceding line and conducts coding of image data of a current line and generates the coding table of the current line in parallel by handling the input data as the image in the unit of lines. The image coder divides the image in the unit of lines and conducts a coding step where a target line is coded by using the coding table calculated in the preceding line and a step where the coding table is generated in parallel to attain high-speed processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data encoding method, for example, to an image data encoding method for performing variable length encoding of still image data.

[0002]

2. Description of the Related Art Conventionally, image data encoding methods generally include:
The present invention is applied to an image data encoding device that performs variable length encoding of still image data.

The frequency of occurrence of difference value data of pixel values is used to generate an encoding table in image data encoding. For this purpose, the difference values are calculated for the image pixels, and the difference value data of the pixel values is obtained.

[0004]

However, in the above-mentioned conventional method, the frequency of appearance of difference value data of pixel values is used for generating the encoding table, and the difference value has to be calculated for image pixels. Therefore, as compared with the method in which the encoding table is fixed, the processing speed is significantly reduced as the image data becomes larger. If no table is generated, encoding cannot be performed. For this reason, there is a possibility that efficient processing may not be performed in an apparatus capable of performing parallel processing of each processing unit.

An object of the present invention is to provide a more efficient image data encoding method.

[0006]

In order to achieve the above object, an image data encoding method according to the present invention calculates difference value data from pixel values of original image data and calculates the difference value data based on the obtained data. In a reversible image data encoding method that creates a variable-length encoding table and converts image data into variable-length encoded data, the input data uses the encoding table calculated in the previous row as a row unit of the image. The step of encoding the image data of the current row and the step of generating the encoding table of the current row are performed in parallel.

According to the first aspect of the present invention, an image is divided into rows, and coding of a row of interest is performed by performing coding using a coding table calculated in a previous row. By performing the steps of generating the encoding table in parallel, it is possible to increase the processing speed.

According to a second aspect of the present invention, in the image data encoding method of the first aspect, the method of generating the encoding table of the current row stores only a difference from the encoding table calculated in the previous row. It is characterized by a method of updating from a section.

According to the second aspect of the present invention, the rewriting process of the encoding table storage unit can be speeded up by rewriting only the difference from the encoding table calculated in the previous row.

According to a third aspect of the present invention, in the image data encoding method of the first aspect, if the encoding table of the previous row and the current row are similar, the table is not updated. It is characterized by.

According to the third aspect of the present invention, when the encoding table of the previous row and the current row are similar, the same table is used to speed up the processing.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an image data encoding method according to the present invention will be described in detail with reference to the accompanying drawings. Referring to FIG. 1, there is shown one embodiment of the image data encoding method of the present invention.

Hereinafter, the present invention will be described in detail. FIG.
FIG. 1 is a block diagram illustrating a configuration of an apparatus that performs an image data encoding method according to the present invention. This image data encoding device includes:
It comprises a difference value data calculation unit 2, a difference value data storage unit 3, a variable length coding table creation unit 4, a variable length coding table storage unit 1, a variable length coding unit 5, and a coded data storage unit 6.

The difference value data calculation unit 2 calculates difference value data by using one line data of an image as an input. The details of the calculation method are the same as in the related art, and thus will not be described. The calculated data is stored in the difference value data storage unit 3.

The variable-length coding table creating section 4 analyzes the frequency of occurrence of the above-mentioned difference value data, and generates a coding table in which short code data is assigned to data having a high frequency of occurrence. The generated table is stored in the variable length coding table storage 1.

By the way, in general, each row of an image has a high correlation with an adjacent row, so that the coding table generated in each row also has a high correlation. Therefore, it is expected that the compression ratio will not decrease so much even if the table in the previous row is used. Therefore, the variable length coding unit 5 codes the difference value data using the table already generated in the previous row. The encoded data is stored in the encoded data storage 6.

Here, assuming that each processing unit is a device capable of parallel processing, the above-described processing from calculation of difference value data to storage of an encoding table and processing from differential data encoding to storage of encoded data are performed in parallel. By performing the processing, the processing is performed sequentially on a line-by-line basis, and the processing speed is improved as compared with the conventional technique in which an encoding table is created based on all image data and then encoded. Further, since the processing is performed in units of rows, the capacity of the storage unit can be reduced.

Further, as described above, since the coding table generated in each row has a high correlation, it is expected that there are few changes from the previously calculated table. Therefore,
If the encoded data storage section 6 is rewritten only at the changed portion, the processing speed is improved.

Also, comparing the table of the previous row and the table of the current row, if the value indicating the degree of difference is within a certain threshold,
By performing the processing without rewriting the table, the processing speed can be improved without significantly reducing the compression ratio. In this case, it is necessary that the determination based on the threshold value can be performed at a higher speed than the rewriting process.

In this embodiment, the input data at one time is data of one line of the image, but may be input data of several lines.

In addition, there is a calculation of a threshold value in a process that does not rewrite the table. By performing this procedure at a frequency of every few rows, the processing speed may be improved without significantly reducing the compression ratio. There is.

[0022]

As is apparent from the above description, in the image data encoding method of the present invention, the input data is converted into the image row unit of the image using the coding table calculated in the previous row. The encoding of the data and the generation of the encoding table of the current row are performed in parallel. According to this image data encoding method, there is an effect that the compression speed of image data is improved.

According to the second aspect of the present invention, since the rewriting process of the encoding table storage is deleted as compared with the first aspect of the present invention, the processing speed can be improved.

According to the third aspect of the present invention, a further improvement in the compression speed can be expected without significantly lowering the compression ratio as compared with the first aspect of the invention.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image data encoding method according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 variable length coding table storage unit 2 difference value data calculation unit 3 difference value data storage unit 4 variable length coding table creation unit 5 variable length coding unit 6 coded data storage unit

Claims (3)

[Claims] 1. A reversible method for calculating difference value data from pixel values of original image data, creating a variable length encoding table based on the obtained data, and converting the image data into variable length encoded data. In a typical image data encoding method, input data is used as a line unit of an image, and encoding of image data of a current line is performed using an encoding table calculated in a previous line; and a code of the current line. Generating the conversion table in parallel. 2. The method according to claim 1, wherein the encoding table of the current row is generated by updating only the difference from the encoding table calculated in the previous row from the storage unit.
The image data encoding method described in the above. 3. The image data encoding method according to claim 1, wherein the table is not updated when the encoding table of the previous row and the current row are approximated.