JP3226358B2 - Run length encoding 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 run length encoding method for encoding black and white image data by a run length code.

[0002]

2. Description of the Related Art MH, MR, MMR and the like are known as encoding methods for compressing the amount of black and white image data, but these encoding methods are complicated. In order to achieve this, complicated and sophisticated processing is required.

[0003] On the other hand, the coding method of the run length format uses {MH, MR, MMR} described above in terms of coding efficiency.
Although it is inferior to the method, it is superior in its easiness of realization.

[0004] The conventional run length encoding method is shown in FIG.
As shown in FIG. 2, a continuous number of black pixels or white pixels, that is, a so-called run length, is described by a run length code 10 fixed to a 1-byte (8-bit) length, and as shown in FIG. By alternately arranging a run length code (white run length code) representing the length and a run length code (black run length code) representing the black run length, and further placing a line end code 1E at the end of the line, Black-and-white image data was encoded.

Since each run length code has a length of 1 byte, the run length (the number of continuations) of 0 to 255 pixels of the same color can be represented.

[0006]

However, according to such a configuration, there is a problem that the data compression efficiency by encoding is low.

The above problem occurs for the following reasons. That is, in the conventional run length coding method, the length of the run length code is fixed at 1 byte. Therefore, when a run length exceeding 255 is described, a plurality of run length codes are required and white code is required. A zero (0) run length code for alternately arranging the run length code and the black run length code must be inserted.

For example, in FIG.
When the number of black run lengths is described, a total of five run length codes 10 of three black run length codes and two white run length codes (run length = 0) are required as shown in FIG. , 5 bytes are required as data.

As described above, if there is a run length portion having a length (255 or more) that cannot be described by one run length code,
Not only a plurality of run length codes for sharing and describing the length but also a new zero run length code for alternately arranging a white run length code and a black run length code are required. This has reduced the data compression efficiency of various coding methods.

On the other hand, if the run length code is fixed to, for example, 2 bytes, 2 bytes are required to describe a short run length of 255 or less, and the data compression efficiency is still reduced. Actually, the run lengths of white and black have a high appearance frequency of 0 to 7, and in order to increase the compression ratio, it is more desirable to represent the run length using a code of 7 bytes or less.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and has as its object to provide a run length encoding method capable of improving data compression efficiency by encoding.

[0012]

SUMMARY OF THE INVENTION The present invention achieves the above objects.
The run length code that describes the number of consecutive black pixels and the white
The run length code that describes the number of consecutive pixels is alternately arranged.
In the run length encoding method, the run length codes are different from each other.
Prepare multiple types with predetermined sizes, and
The length code represents the type of run length code.
Rears are provided, and according to the number of continuous data,
This is provided with a configuration in which encoding is performed using different length codes .

[0013]

According to the present invention, the length of the run length code is optimized according to the run length and the range of the run length that can be described by one run length code is expanded by the above-described configuration. Since the number of zero run length codes for alternately arranging black run length codes can be reduced, it is possible to improve the data compression efficiency by encoding.

[0014]

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

In the drawings, the same reference numerals indicate the same or corresponding parts. FIG. 1 shows a run length encoding system according to the present invention together with a conventional system.
(A) shows the data configuration of the run length code used in the first embodiment of the present invention, and (B) shows the data configuration of the run length code used in the second embodiment of the present invention. .

First, a first embodiment of the present invention will be described with reference to FIGS. 1A and 2A.

In the first embodiment, as described below, an extended run length code for describing a run length having a certain length or more is used in addition to a normal length run length code.

As shown in FIG. 1A, the run length code according to the first embodiment has a 1-byte non-extended run length code 1.
There are two types of extended run length codes 12 having a length of 1 and 2 bytes, which can be used depending on the length of the run length. Each of the run length codes 12, 13 is a code length area (1 bit) 1A for indicating whether or not it is an extended run length code, and a run length portion (7 bits or 15 bits) for describing the run length. ) 1C.

The non-extended run length code 11 has a run length part 1C of 7 bits, and is used when describing 0 to 127 run lengths. The extended run length code 12 has a 15-bit run length part 1C, and is used when describing 128 or more run lengths.

FIG. 2A shows an example of image data encoding using the run length codes 11 and 12 shown in FIG. 1A. A non-extended run length code 12 of bytes is described, and a run length portion of 128 or more is described by an extended run length code 13 of 2 bytes.

In the example shown in FIG. 2A, there is a black run length portion in which 578 black pixels are continuous. This portion uses only one 2-byte extended run length encoding section 23. It has been described. 2E is a code indicating the end of the line.

In the above-described first embodiment, the run length portion having a length equal to or more than a certain length (> 127) is described at once by the extended run length coding portion 23 of 2 bytes, so that the run length code of the same color is obtained. Are significantly reduced in the frequency with which the zero run length code is placed. Thereby, the data compression efficiency by encoding can be improved.

Next, a second embodiment of the present invention will be described with reference to FIGS. 1 (B) and 2 (B).

In the second embodiment, as described below, run lengths are classified into a plurality of classes according to lengths, and encoding is performed using run length codes having different lengths for each class.

As shown in FIG. 1B, the run length code in the second embodiment includes a shortened run length code 13 having a length of 4 bits (half byte) and a non-extended run length having a length of 1 byte. Code 14
There are three types of extended run length codes 15 having a 2-byte length, which can be used depending on the length of the run length. Each of the run length codes 13, 14, 15 is a code length area (1 bit or 2 bits) 1A for indicating whether or not it is an extended run length code, and a run length portion (for describing the run length). (3 bits, 6 bits, or 14 bits) 1C.

The shortened run length code 13 has a 1-bit pointer area 1A and a 3-bit run length section 1C, and is used when describing 0 to 7 run lengths. The non-extended run length code 14 has a 2-bit pointer area 1A and a 6-bit run length section 1C, and is used when describing 8 to 63 run lengths. The extended run length encoding section 15 has a 2-bit pointer area 1A and a 14-bit run length section 1C.
Used when describing four or more run lengths.

FIG. 2B shows an example of image data encoding using the run length codes 13, 14, and 15 shown in FIG. 1B. Is described by a 4-bit shortened run length code 13, 8-63 run length portions are described by a 1-byte non-extended run length code 14, and 64 or more run length portions are a 2-byte extended run length code. 15.

In the example shown in FIG. 3B, there is a black run length portion where 578 black pixels are continuous, but this portion is expanded by 2 bytes as in the first embodiment. It is described using only one run length code unit 24. Also, 7
The short run length portion of less than or equal to the number is described by the shortened run length code 13 using only 4 bits. 1E is a code indicating the end of the line.

In the above-described second embodiment, the run length code of the same color is zero-run because the run length portion having a length equal to or more than a certain length (> 127) is described at once by the extended run length code of 2 bytes. The frequency of placing long codes is greatly reduced. Further, a short run length of 7 bits or less can be described by data of only 4 bits by the shortened run length code 11. Thereby, the data compression efficiency by encoding can be greatly improved.

FIG. 3 shows a first embodiment of a data processing apparatus for realizing the run length encoding method of the present invention.

The apparatus shown in FIG. 1 is configured as a facsimile communication apparatus, wherein 2 is a data terminal (DTE) for inputting / outputting run-length encoded data, and 3 is run-length encoding according to the present invention. , 4 is a run length decoding unit according to the present invention system, 5 is an image data encoding unit according to the {MH, MR, MMR} system, 6 is an image data decoding unit according to the {MH, MR, MMR} system, and 7 is The modem, L, is a line.

The run length encoding unit 3 selects a run length code length according to the run length of the input image data.
1 and performs coding optimized according to the run length.

The run length decoding unit 4 has a run length determining unit 41 for determining the length of the run length code from the input coded data, and the run length (the number of continuous pixels) described by the determined run length code is used. ) Is restored.

FIG. 4 shows a second embodiment of the data processing apparatus for realizing the run length encoding method of the present invention.

The apparatus shown in FIG. 1 is configured as an apparatus for performing a conversion of an encoding system off-line.
When performing the conversion from the {MH, MR, MMR} system to the run length coding, the data terminal (DTE) 2 transmits the {MH, MR, MMR}
After receiving the coded data according to the MR, MMR method and returning it to the original raw image data according to the {MH, MR, MMR} method at the image data decoding unit 6, the run length coding unit 3 The run length encoding according to the invention method is performed and the result is returned to the data terminal 2.

Also, from the run length encoding method, {MH, M
When the conversion to the R, MMR｝ system is performed, the run length encoded data according to the system of the present invention is received from the data terminal (DTE) 2, and this is returned to the original raw image data by the run length decoding unit 4. After that, the image data encoding unit 5 generates {MH, MR,
The data terminal 2 is coded according to the MMR｝
Return to

Although the embodiment has been described above, the present invention can be applied to other embodiments or modifications other than those described above. In addition, the encoding according to the method of the present invention can be performed by using non-images such as programs or character code strings. It can also be applied to data compression.

[0038]

As is apparent from the above description, according to the present invention, a code length area indicating the length of a run length code describing a run length is provided for each run length code, and the length of each run length code is set. By varying the run length for each run length, the length of the run length code is optimized in accordance with the run length, and the range of run lengths that can be described by one run length code is expanded. Since the number of zero run length codes for alternately arranging the run length codes can be reduced, there is an effect that the data compression efficiency by encoding can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a run length code used in a run length encoding method according to the present invention together with a conventional example.

FIG. 2 is a diagram showing an example of encoding by a run length encoding method according to the present invention together with a conventional example.

FIG. 3 is a diagram showing a first embodiment of a data processing device for realizing a run length encoding method according to the present invention;

FIG. 4 is a diagram showing a second embodiment of the data processing device for realizing the run length encoding method of the present invention.

[Explanation of symbols]

 13 Shortened run length code 14 Non-extended run length code 15 Extended run length code 1A Pointer area 1C Run length section 3 Run length encoding section 31 Run length calculation section 4 Run length decoding section 41 Run length determination section

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

Claims (1)

(57) [Claims] 1. A run length coding method and the run-length code that describes the number of successive run length code and white pixels describing the number of consecutive black pixels are alternately arranged, each said run-length code
A plurality of types having different predetermined sizes are prepared, each of the run length codes is provided with a code length area representing the type of the run length code, and the plurality of types of run length codes are selectively used according to the number of data continuations. Run length encoding method to be performed.