JP2936042B2 - Binary image transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binary image transmitting apparatus such as a facsimile, and more particularly, to a binary image transmitting apparatus.
The present invention relates to a binary image transmission device capable of transmitting a pseudo-halftone image.

[0002]

2. Description of the Related Art In recent years, there has been an increasing need to transmit halftone images such as photographs. However, transmitting a halftone image as it is requires the number of bits per pixel to be 8 bits or more, which greatly increases the amount of transmission code, and a device for printing a halftone image on paper or the like is very difficult. Due to the high cost, a method of transmitting a halftone image as it is has not been widely used.

Therefore, a pseudo halftone image representing a pseudo halftone is generated by using only a black and white binary image as a halftone image and using a change in density of black pixels as a gradation of the image. Attempts have been made to transmit images, such as photographs, by a popular facsimile machine as transmission.

[0004] As an encoding method used in a facsimile apparatus, an MH method, an MR method and the like are generally used. These systems are address coding based on run length, and appear continuously in black (white).
One codeword is assigned to each pixel. The MH method is based on Huffman coding of a scan length in a scanning line direction on a document image, and the MR method determines a difference between states of pixels based on a scanning line to be coded and a previous scanning line. This is a two-dimensional encoding method for encoding.

Further, as a recent binary image coding method,
There is one that considers information of a pixel to be encoded as a Markov information source based on a previously encoded pixel state and performs arithmetic encoding based on a state transition probability.

According to this method, if the distribution state of black (white) pixels has periodicity, it is possible to estimate the information of the pixel to be currently coded from the previously coded pixels with a high probability, and achieve high information compression. realizable.

[0007]

The above-mentioned MH system and M
Due to its characteristics, the R method works efficiently for a binary image containing only characters, and can obtain a high code compression rate. However, high code compression cannot be realized for a binary pseudo halftone image because the run length distribution of black (white) pixels is significantly different from the run length for an image of only characters.

In some cases, the binary pseudo-halftone image has little or no pixel periodicity due to its generation method, and high information compression may not be expected even with a method based on the state transition probability.

As a result, binary pseudo halftone images cannot achieve high information compression as described above, and therefore the amount of codes in transmission increases, so that transmission costs and transmission time are increased. There was a problem. For this reason, an encoding method for efficiently compressing and transmitting a binary pseudo halftone image is strongly desired.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a storage means for storing image data and a compression code for the image data stored in the storage means. A binary image transmission device comprising an encoding unit for encoding, and a decoding unit for decoding the compression-encoded image data, wherein the encoding unit converts the image data to be transmitted to a pseudo halftone image. Means for temporarily removing isolated points from the original image and enhancing edge portions of the image, and means for adaptively dividing the image into blocks of different sizes from 4 × 4 to 16 × 16. For a block of size 4 × 4, the pixel pattern information in the block in the original image is encoded, and for blocks of other sizes, the number of black pixels in the block is determined by counting. Block Means for encoding the tone information,
Means for encoding the size of each block.

When the decoding means receives the coded image data, if the block size is 4 × 4, the decoding means decodes the image of the block by using the following pattern information. If it is other than the above, based on the block gradation information, a means for restoring an image by randomly arranging black pixels in a block by random numbers based on the block gradation information and decoding a received code is provided. And

[0012]

In the above arrangement, when transmitting a binary image including a pseudo halftone image, the pseudo halftone region is obtained by temporarily removing isolated points from the original image and emphasizing the edges of the image. Means for adaptively dividing into blocks of different sizes from 4 × 4 to 16 × 16, and for blocks of 4 × 4 size, in order to preserve the edges of the image, By directly encoding the pixel pattern information of, and for blocks of other sizes, by encoding the grayscale information of the block obtained by counting the number of black pixels in the block,
Significantly reduce the amount of information to be transmitted.

On the receiving side, for a block other than the 4 × 4 block, based on the gradation information in the block,
Using random numbers, on the condition that the run length of the black pixel is set to 1 as much as possible, it is randomly arranged and restored in the block,
The edge portion of the image is restored by storing the pixel pattern of the original image to obtain a received image.

[0014]

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

FIG. 1 is a block diagram showing an embodiment of the present invention. An image transmitting apparatus includes a reading unit 1 for reading an image, an image storage memory 2 capable of storing read image data, and a read image. A preprocessing unit 9 for removing an isolated point from an original image and enhancing an edge portion of the image; a block determination unit for adaptively dividing the image data edge-emphasized by the preprocessing unit 9 into blocks having different sizes. 3. The size of the block determined by the block determination and the pixel pattern of the image data in the block, or the size and the pixel pattern of the block from the encoder and the received data, which determine and encode the block gradation, or An encoding / decoding unit 4 having a decoder for obtaining a block gradation, a network control unit 5 for controlling communication between devices through a line, and a block gradation of received data. Random number generator 6, which is referred to when restoring the pixel, recording unit 7 for outputting image data, comprising and a control unit 8 for controlling each device that is described above.

The reading section 1, the image storage memory 2, the preprocessing section 9, the encoding / decoding section 4, the random number generation section 6 and the recording section 7 are connected to a control section 8, respectively. The network control unit 5 is connected to the encoding / decoding unit 4.

Hereinafter, the operation of the image transmission apparatus having the above configuration will be described.

Image data read by the reading unit 1 is temporarily stored in an image storage memory 2. After the isolated points are removed from the accumulated image data by the pre-processing unit 9, the alock determination unit 3 performs ag to g shown in FIG.
It is divided into blocks of different sizes up to. Block a is a block composed of 4 × 4 pixels vertically and horizontally, block b is also 4 × 8, block c is 8 × 4, and block d.
Is 8 × 8, block e is 8 × 16, block f is 16 ×
8. Block g is a 16 × 16 pixel block. Blocks b and c have a block area twice that of block a, blocks e and f have a block area twice that of block d, and block g has a block area that is twice that of blocks e and f.

The block division is performed according to the conditions shown in FIG. The result of the isolated point removal by the preprocessing unit 9 is as follows:
It is referred only at the time of block judgment. By this processing, the edge portion of the image is emphasized, and the smallest block is more accurately assigned to the edge portion at the time of block determination. In the block division, the blocks are sequentially changed from the block a to the blocks b and c, and the number of black pixels in the preprocessed image of each block is set as the block gradation of the block, and the block gradation of the current block is set. And the block gradation of the block changed by one step is compared. If the difference of the block gradation per block area is equal to or smaller than the threshold value, the block is changed by one step. Divide into blocks. The threshold is set to 0 when the block is expanded from block a to block b and block c, and is set to 1 in other cases. This is because the block a having the minimum size is mainly assigned to the edge portion of the image, so that the conditions are made strict to increase the number of edge portions and to suppress the deterioration of the image quality. The position of the pixel once divided into blocks is stored, and when the block is changed, it is determined whether the pixel once divided into blocks is included again in the block, and if the pixel is once again included in the block, Changing the block is stopped and the block at that time is adopted. This prevents different blocks from including the same pixel.

Hereinafter, the flowchart of FIG. 3 will be described.
Assuming that A to G are the number of black pixels (gradations) included in each block when the blocks to be divided are blocks a to g, first in step S31, is the difference between 2A and B equal to or less than 0? Determine whether or not. Thus, it is determined whether or not the difference in block gradation per block area is 0 or less when the block to be divided is block a and block b. Here, if the difference is equal to or smaller than 0, the process proceeds to step S32, and if it is larger than 0, the process proceeds to step S39.

In step S39, the difference between 2A and C is zero.
It is determined whether or not: If the difference is greater than 0, the block to be divided is taken as block a, and if the difference is less than 0, the block to be divided is taken as block c.

In step S32, as in step S38, it is determined whether the difference between 2A and C is 1 or less. The difference is 1
If it is larger, the block to be divided is set to block b, and if the difference is 1 or less, the process proceeds to step S33.

In step S33, the difference between 2B and D is 1
It is determined whether or not: If the difference is greater than 1, the block to be divided is set to block c. If the difference is 1 or less, the process proceeds to step S34.

In step S34, the difference between 2C and D is 1
It is determined whether or not: If the difference is larger than 1, the block to be divided is set to block b. If the difference is 1 or smaller, the process proceeds to step S35.

In step S35, the difference between 2D and E is 1
It is determined whether or not: If the difference is greater than 1, the process proceeds to step S40. If the difference is 1 or less, the process proceeds to step S3.
Proceed to 6.

In step S40, the difference between 2D and F is 1
It is determined whether or not: If the difference is larger than 1, the divided block is set as a block d, and if the difference is 1 or smaller, the divided block is set as a block f.

In step S36, as in step S40, it is determined whether the difference between 2D and F is 1 or less. The difference is 1
If it is larger, the block to be divided is set to block e. If the difference is 1 or less, the process proceeds to step S37.

In step S37, the difference between 2E and G is 1
It is determined whether or not: If the difference is larger than 1, the block to be divided is set to block f. If the difference is 1 or smaller, the process proceeds to step S38.

In step S38, the difference between 2F and G is 1
It is determined whether or not: If the difference is larger than 1, the block to be divided is set to block e, and if the difference is 1 or less, the block to be divided is set to block g.

When a block is determined by the above processing, the encoding / decoding section 4 first encodes information on the size of the block. The block size coding calculates the difference between the block size information to be coded and the previous block size and, based on the appearance of the difference value, refers to the Huffman code table that minimizes the average code length and performs coding. Is done.

Subsequently, information on the state of the black pixel in the block is encoded.

The state of a black pixel in a block is represented by a block a
, One pixel is one bit, and the lower right corner is LSB as shown in FIG. 4, and goes from right to left, from bottom to top, and in a bit order such that it is the upper left corner or MSB, the black pixel is By assigning “1” to the white pixel and “0” to the white pixel, a 16-bit value is obtained as pattern data corresponding to the pixel pattern of the block. The pattern data is encoded by referring to a pattern code table defined in advance so that the average code length is minimized by establishing the appearance of each pattern.

For the other blocks, the block gradation, which is the number of black pixels in the block, is encoded. The block gradation is the number of black pixels in the block in the original image, and the difference between the block gradation to be coded and the block gradation of a block of the same block size that has been coded earlier is established by establishing the appearance of a difference value. The encoding is performed with reference to the gradation code table in which the average code length is minimum.

The encoded data is transmitted over the line by the network control unit 5 in the order of the block size code and the pattern data code or the block gradation code. The above-described procedure is sequentially repeated according to the scanning line direction to transmit image data.

At the time of reception, the data received by the network control unit 5 is passed to the encoding / decoding unit 4 and
Decodes the type of the block from the above data, and when the type of the received block is the block a, decodes the subsequent block pattern data by referring to the pattern code table. It is restored to the inner pixel pattern. The restored pixel pattern is stored in the image storage memory 2.

For other blocks, the block gradation is decoded with reference to the gradation code table. The block gradation is determined by determining the position where the black pixel is arranged in the block by the random number generator 6.
, Black pixels corresponding to the block gradation are randomly arranged in the block, and the pixel pattern of the block is restored.

At this time, the run length of the black pixel (or white pixel) of the pseudo halftone image is kept at 1 so as to avoid the vicinity of the already determined black pixel, in order to preserve the feature that it often becomes 1. Is determined.

This will be described in more detail with reference to FIG. 5. First, in step S51, the block gradation of the block to be restored is set to nb. Also, in step S52, the number nx of other black pixels that may be eight adjacent to a certain black pixel
Is set to nx = 0 as an initial setting.

In step S53, it is checked that nb> 0. Then, in step S54, each pixel in the block is replaced with a black pixel where the number of black pixels adjacent to its eight pixels is less than or equal to nx. It is a black pixel candidate that can be arranged.

In step S55, it is determined whether or not a black pixel candidate exists. If no black pixel candidate exists,
Proceeding to step S56, nx is incremented by 1, and then, in step S54, black pixel candidates are determined again.

If there is a black pixel candidate, step S57
Then, a position where a black pixel is to be set is determined by using a random number, and black pixels are randomly arranged.

After arranging the black pixels, in step S58, nb is decremented by one, and the process returns to step S54 to repeat the above processing while nb> 0. Thus, the block is restored.

As described above, the pixel pattern in the block is restored and stored in the image storage memory 2.

The image data stored in the image storage memory is output by the recording unit 7.

[0045]

According to the present invention, it is possible to transmit a pseudo halftone image with a smaller amount of information than the encoding by the conventional method, and it is possible to reduce the communication cost for transmission. Also,
The pseudo halftone image may generate a texture depending on the method of generating the pseudo halftone image. However, the texture can be eliminated by arranging pixels at random on the receiving side using random numbers.

[Brief description of the drawings]

FIG. 1 shows a circuit configuration of an embodiment of the present invention.

FIG. 2 shows the shape of a block used in the present invention.

FIG. 3 is a flowchart illustrating a procedure of block determination.

FIG. 4 is a diagram showing an order of converting a pixel pattern into a bit string in a block a.

FIG. 5 is a flowchart showing a procedure for restoring a block from a block gradation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reading part 2 Image storage memory 3 Block determination part 4 Encoding / coding part 5 Network control part 6 Random number generation part 7 Recording part 8 Control part 9 Preprocessing part

Claims (2)

(57) [Claims] A storage unit for storing image data; an encoding unit for compressing and encoding the image data stored in the storage unit; and a decoding unit for decoding the compressed and encoded image data. A binary image transmitting apparatus, wherein the encoding unit temporarily removes an isolated point from an original image and enhances an edge portion of the image when the transmitted image data is a pseudo halftone image. Means for adaptively transforming the image from 4 × 4 to 16
Means for dividing into blocks of different size of × 16, 4
For a block of size × 4, the pixel pattern information in the block in the original image is encoded, and for blocks of other sizes, the number of black pixels in the block is determined by counting the number of black pixels in the block. A binary image transmission device comprising: means for encoding gradation information; and means for encoding the size of each block. 2. When the decoding means receives the encoded image data, if the block size is 4 × 4, the decoding means decodes the image of the block by the following pattern information; If it is other than the above, based on the block gradation information, a means for restoring an image by randomly arranging black pixels in a block by random numbers based on the block gradation information and decoding a received code is provided. The binary image transmission device according to claim 1, wherein