JPH01176165A - Picture signal coding system and its device - Google Patents

Abstract

PURPOSE:To realize the coding system immune to a transmission error by predetermining each individual variable length code to all combinations of picture elements in a block consisting of plural picture elements, reading the picture signal in the unit of blocks and outputting a variable length code corresponding to the picture signal in the unit of blocks. CONSTITUTION:The size of a block consisting of plural picture elements is decided prior to the coding of a binary picture signal. A rectangular block consisting of mXn picture elements is used as the block. As the combination of each picture element in the block, there are combinarions of 2(mXn) ways, and each variable length code is defined to each combination. In the actual coding, at first, the picture signal is read in the unit of blocks and the variable length code corresponding to the picture signal in the block unit is outputted for each block to realize the coding. Thus, as to the binary picture, since the coding in the unit of blocks is applied, the area affected by error is reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides an image signal encoding method and method for shortening the transmission time or storage capacity of a binary image signal consisting of white pixels and black pixels. Regarding the device.

(Prior art) Modified Huffman (hereinafter referred to as M
A coding method (abbreviated as H) and a modified read (abbreviated as MR hereinafter) are used as standard methods. Details of these methods are described in Document 1: Takahiko Fukinuki, "Digital signal processing of image f-elements J (Nikkan Kogyo Shimbun series), Chapter 12 (Problems to be solved by the invention)" Conventional binary images such as MH and MR (the elephant encoding method is
This is an encoding method that uses rows as units.

Therefore, when a transmission error occurs, there is a problem in that the error spreads from the position where the error occurs to all remaining pixels in that row. Furthermore, in the case of the MR method, there is a problem in that errors spread over several lines.

Furthermore, recently there has been a demand for a system that can perform both multilevel image encoding processing and binary image encoding processing in one system. However, there is a need for something that can realize both the encoding process of a multivalued surface f-image and the encoding process of a binary image. However, multilevel image encoding systems often encode square or rectangular blocks as units, such as discrete cosine transform encoding and block truncation encoding. However, conventional MH and MR
The binary image encoding method is a row-by-row encoding method. Therefore, there is very little hardware that can be commonly used for both. As a result, there is a problem in that the amount of hardware required for a system capable of encoding both multivalued images and binary images becomes enormous.

The present invention reduces the area where errors propagate by encoding binary images in units of blocks, and at the same time converts many parts of the hardware for encoding multilevel images into binary images. An object of the present invention is to provide an image signal encoding method and an apparatus therefor, which can be commonly used for encoding.

(Means for Solving the Problems) The image signal encoding method of the present invention, when encoding a binary image signal consisting of white pixels and black pixels, all pixels in a block consisting of a plurality of pixels. An individual variable length code is predetermined for each combination, the image fi signal is read out in units of blocks, and a variable length code which is multiplied by X'f6 to the image signal in each block is outputted. .

Furthermore, the image f-image signal encoding device of the present invention encodes each pixel by one
When encoding a binary image signal expressed by focus,
Individual variable length code information is stored for each combination of pixels in a block consisting of a plurality of pixels, and when the image signal in units of blocks is given as a read address, the corresponding variable length code information is stored. a code storage section for outputting; a block reading section for reading and storing the image signal in block units; and outputting the image signal as a read address of the code storage section; It consists of an encoding section that outputs a variable length code.

(effect) This will be explained as an image signal encoding method according to the present invention.

First, before encoding a binary image signal consisting of white pixels and black pixels, the size of a block consisting of a plurality of pixels is determined. Here, a description will be given assuming that a rectangular block consisting of mXn pixels is used as the block.

Each pixel within this block is either a white pixel or a black pixel. Therefore, there are 2 (mXn) combinations of the pixels in the block. Therefore, individual variable length codes are defined for each combination. In this case, considering the probability of occurrence of each combination, a short code is assigned to a combination with a high probability of occurrence, and a long code is assigned to a combination with a low probability of occurrence.

For example, since a binary image such as a normal document has many white parts, the probability of occurrence of a combination in which all pixels are white is extremely high. Therefore, a very short code with a code length of about 1 pinto is assigned to such a combination. The variable length code generated from the probability of occurrence is as follows:
Huffman codes are well known.

Then, when performing actual encoding, first the image signal is read out in block units. Encoding can be realized by outputting a variable length code corresponding to this image signal in units of blocks for each block.

Furthermore, if this block-based image signal is considered as the value of one pixel of a multi-valued image, this is done here.

Encoding is similar to the encoding process for multivalued images.

Therefore, many parts of the hardware for encoding one image on the multilevel side can be commonly used for encoding binary images.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an example of an encoding device that implements the image signal encoding method of the present invention. In the following description, a square block of 2×2 pixels is used as a block consisting of a plurality of pixels, but it is also possible to use blocks of different sizes or rectangular blocks.

As shown in FIG. 1, a block reading unit 1 reads out image signals consisting of white pixels and black pixels in units of blocks. In other words, the image signal is divided into 4 pixels (2 pixels vertically and 2 pixels horizontally) into 1
Read and store as a block. Here, since each pixel is expressed by 1 bit, the block readout unit 1
will store 4 bits.

FIG. 2 is an explanatory diagram showing combinations of pixels within a block. As shown in FIG. 2, each block is made up of four pixels, and each pixel is a white pixel or a black pixel, so there are 2 to the fourth power, that is, 16 combinations.

FIG. 3 is an explanatory diagram showing information on variable length codes stored in the code storage section 2. As shown in FIG. For combinations of pixels in a block as shown in Fig. 2, individual variable length codes and their code lengths as shown in Fig. 3 are defined, and corresponding to 4-bit addresses indicating each combination. , is stored in the code storage unit 2 as variable length code information.

However, since it is difficult to directly store variable length codes with different code lengths for each address, all variable length codes including unnecessary bits are stored as a fixed number of bits. For example, in the case shown in Figure 3, the maximum code length is 8
Therefore, codes shorter than this code length are stored with 0 inserted after them.

Even if such a storage method is used, since the code length of each variable length code is stored, the variable length code can be read out correctly.

Note that the unnecessary bits added after the code are
is removed and output to the transmission line. An example of the configuration of this encoding section 3 is described in FIG. 3 of Japanese Patent Application Laid-Open No. 57-199379.

Furthermore, as shown in FIG. 3, variable length codes are defined taking into consideration the probability of occurrence of each combination. For example, a short code is assigned to a combination with a high probability of occurrence, such as when all pixels in a block are white. Further, a long code is assigned to a combination with a low probability of occurrence, such as a combination in which white pixels and black pixels exist alternately. By defining such a variable length code, the amount of information can be compressed.

As the read address of the code storage section 2, the block-based image ft signal stored in the block reading section 1 is input. Therefore, the code storage unit 2 outputs a variable length code and its code length corresponding to the image signal of each block. The encoding unit 3 that receives these outputs a variable length code having a length indicated by the code length as an encoded output.

In such encoding processing, the block reading unit 1
The block unit image signal stored in the multi-value side 1 image
If we consider the value of one pixel, the encoding performed here is similar to the encoding process of a multivalued image. Therefore, the code storage section 2 and the encoding section 3 can be used in common for encoding multivalued images.

(Effects of the Invention) As described above, by using the image signal encoding method and apparatus of the present invention, it becomes possible to encode a binary image in units of blocks. This makes it possible to realize an encoding system that is more resistant to transmission errors than conventional row-by-row encoding systems. Further, in the binary image encoding method, a lot of hardware can be used in common with the multi-value image encoding method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an encoding device that implements the encoding method of the image signal of the present invention, FIG. 2 is an explanatory diagram showing combinations of pixels in a block, and FIG. 3 is a code storage. 3 is an explanatory diagram showing information on variable length codes stored in section 2. FIG. In the figure, 1...Block reading section, 2...Code recording/billion section,
3... Encoding section.

Claims (2)

[Claims] (1) When encoding a binary image signal consisting of white pixels and black pixels, individual variable length codes are determined in advance for all combinations of pixels in a block consisting of a plurality of pixels. An image signal encoding method characterized in that an image signal is read out in units and a variable length code corresponding to the image signal in blocks is output. (2) When encoding a binary image signal in which each pixel is expressed with 1 bit, information on individual variable length codes is stored for each combination of pixels in a block consisting of a plurality of pixels. a code storage unit that outputs information on a variable length code corresponding to a unit image signal given as a read address; and a block that reads and stores the image signal in units of blocks and outputs it as a read address of the code storage unit. An image signal encoding device comprising: a reading section; and an encoding section that receives information on a variable length code output from the code storage section and outputs the variable length code.