JP2797851B2 - Binary image encoding / decoding 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 binary image encoding / decoding system capable of high-speed transmission and large-capacity storage.

[0002]

Conventionally, white and document that consists of a black, a picture signal obtained Mono 2 to scan the drawings and the like in a scanner as a method for encoding, modified international standard method of the facsimile coding・ Huffman (Modify
d Huffman: MH) and the method, Modified
A read (Modified READ : MR ) method is known. The MH method counts the run length of white pixels and the run length of black pixels of only the scanning line to be encoded, and encodes the run lengths of the white pixels and black pixels, and is a typical one-dimensional encoding method. It is a system. Also, M
The R method encodes a relative positional relationship between a white pixel to a black pixel or a changed pixel from a black pixel to a white pixel between a scan line to be encoded and a previous scan line that has already been encoded, This is a typical two-dimensional encoding method.

[0003] These schemes, document, and white and black, such as drawings
The have that image is constructed although excellent as a method of encoding from unsuitable for encoding pseudo-halftone image called Tei Ru halftone photographs or dither method may be used in the newspaper or the like. This is a halftone photographs or dither to have artificially expressing halftone images by the white and black pixels, the run length of white pixels and black pixels becomes larger number of run shorter. Further, because already also reduced correlation between changes in pixel positions from a white pixel of the scanning lines to be coded scanning line and coded into a black pixel, or from black pixels to white pixels. However, as a method of encoding the halftone image or the pseudo halftone image subjected to the dither processing, the periodicity of the binarized image is used, and the binarized image is converted to convert the white pixel and the black pixel. There is known a method in which the run length is lengthened and the converted binary image is encoded by the MH method. This conversion method is disclosed , for example, in Japanese Patent Publication No. 63-025748 (Patent
No. 1503644), which is described in detail in the publication "Encoding Device for Image Signal". Hereinafter, this conversion method is referred to as convolution conversion.

Further, in general binary images, there are many binary images in which black-and-white binary images such as documents and drawings and pseudo halftone images typified by halftone photographs and dither are mixed. Conventionally, an encoding method for encoding a binary image in which a black-and-white binary image and a pseudo halftone image are mixed has been as follows. First, 2 of the scan lines to be encoded scanned by the scanner
Divide the value image into multiple small blocks. Then, the above-described convolution conversion is performed on each of the divided small blocks.
Here, a case where the image scanned by the scanner is not converted is also referred to as a through conversion because it is a kind of conversion means.
That is, each of the small blocks scanned by the scanner and divided into small blocks is subjected to two types of conversion processing of convolution conversion and through conversion. Then, for each small block, the number of changed pixels of the binary image after conversion by each conversion means is counted, and the number of changed pixels is compared.
A binary image subjected to the process with the smaller number of changed pixels counted as the value image is selected. Thereafter, the selected plurality of converted small blocks are collectively subjected to one-dimensional encoding as an image of one scanning line, and a selection result for each small block is added as a mode signal on a code string.

[0005]

As described above, in the conventional encoding method, a binary image in which a black-and-white binary image such as a document or a drawing and a pseudo halftone image represented by a halftone dot photograph or dither are mixed. In the case of encoding, a plurality of selected converted small blocks are collectively subjected to one-dimensional encoding as an image of one scanning line.

In general, an image obtained by performing a convolution conversion process on a pseudo halftone image has almost no correlation between scanning lines. Therefore, when an image is encoded by a two-dimensional encoding method, it is compared with a one-dimensional encoding method. On the contrary, the coding efficiency decreases. However, for an image obtained by through-transforming an image such as a document or a drawing, the encoding efficiency is higher when the image is encoded by the two-dimensional encoding system than by the one-dimensional encoding system. Therefore, when encoding a plurality of selected small blocks after conversion, the through-transformed blocks are two-dimensionally encoded by an MR encoding method rather than one-dimensionally encoded by a run-length encoding method. A higher compression rate can be obtained by encoding a small block by using the correlation with a block that has already been encoded by using. However, in the above-described conventional encoding method, one scan line is configured by a plurality of small blocks after conversion, and one-dimensional encoding is performed in units of one scan line. All one
There is a problem that the compression efficiency cannot be increased due to the dimensional encoding.

[0007]

According to the present invention , a binary image is divided into a plurality of small blocks, and a through conversion and a convolution conversion are performed for each of the small blocks. Are selected, and a conversion processing unit that minimizes the number of changed pixels in each of the obtained conversion processing results is selected for each small block, and the conversion processing result obtained by the selected conversion processing unit is two-dimensionally encoded. Convolution conversion is selected
How conversion processing means coding added to result binary image coding apparatus or is selected as the mode signal for each of said small blocks of said two conversion means together when the one-dimensional coding when-option And a signal encoded by the binary image encoding apparatus, and a mode signal indicating the conversion processing means selected in each of the small blocks is restored from the received signal. coding scheme selected at block determines the one-dimensional coding or 2D coding, restores the encoded results using the decoding method corresponding to the coding method determined for each small block, this An inverse transform processing means for inversely transforming the restored conversion processing result according to the restored mode signal, and a plurality of small blocks inversely transformed by the inverse transform processing means are combined to obtain a binary image. Value image Binary image encoding and decoding method, characterized in Rukoto is composed of a Goka device is obtained.

The binary image encoding apparatus includes a dividing unit for dividing an input binary image of one scanning line into a plurality of small blocks, and first and second units for performing a conversion process on the divided small block images. A conversion processing unit, a first and second conversion change pixel counter for counting the number of change pixels in a small block of the image after the conversion processing, and a change read from the first and second conversion change pixel counters. A small block determination unit for comparing the number of pixels, first and second one-block delay memories for storing converted images of one block of the first and second conversion processing units, A two-dimensional encoder for two-dimensionally encoding the image in the block delay memory, a one-dimensional encoder for one-dimensionally encoding the image in the second one-block delay memory, and a comparison result of the small block determination unit. The first and second one block A small block selection selector for selecting one of the block delay memory outputs, a reference line memory for storing the image of the converted one block selected by the small block selection selector, and a comparison result of the small block determination unit. An encoder selection selector for selecting one of the two-dimensional encoder output and the one-dimensional encoder output; and a mode signal adding unit for adding a mode signal to the encoder selection selector output according to the comparison result of the small block determination unit. binary image encoding and decoding, wherein Rukoto with bets
And the first conversion processing unit is a through conversion unit that performs through conversion of the input small block image, and the second conversion processing unit is a convolution conversion of the input small block image. Even the convolution converter
Good .

The binary image decoding apparatus further includes a mode signal separating unit for separating the mode signal from the received code string, and restores the designation of the conversion processing for the small block selected at the time of coding from the mode signal. A two-dimensional decoder, a one-dimensional decoder, and a two-dimensional decoder that respectively perform two-dimensional decoding and one-dimensional decoding of a code string from which the mode signal has been separated according to the specification of the mode restoring unit. first inversely transforming respective decoded results by one-dimensional decoder and the second inverse transform unit, the first synthesized in one scan line a plurality of small blocks from the second inverse transformation unit 2
2, wherein Rukoto a synthesizing unit for outputting a value image
A value image encoding / decoding scheme is obtained, and
Is a through inverse transform unit that performs inverse inverse transform of the two-dimensional decoder output, and the second inverse transform unit is a convolution inverse transform unit that performs convolution inverse transform of the one-dimensional decoder output. Good .

[0010]

Next, the present invention will be described with reference to the drawings. 1 and 2 are block diagrams showing a binary image encoding apparatus and a binary image decoding apparatus according to an embodiment of the present invention.

In the binary image encoding apparatus according to this embodiment, a through conversion unit 2 for performing a through conversion process and a convolution conversion unit 3 for performing a convolution conversion process are used as conversion processing means.

In FIG. 1, first, a through conversion change pixel counter 5 and a convolution conversion change pixel counter 7 are reset. This reset is performed at the start of encoding of one block.

Next, the separating section 1 divides the input binary image of one scanning line into a plurality of small blocks. The divided small blocks are sent to the through converter 2 and the convolution converter 3.

In the through conversion unit 2, the input small block image is through converted and sent to the one block delay memory 4 and the through conversion change pixel counter 5. The through conversion change pixel counter 5 counts the number of changed pixels in a small block of the image after the through conversion.

At the same time, the convolution converter 3 performs convolution conversion on the input small block image and sends it to the one-block delay memory 6 and convolution conversion change pixel counter 7. The convolution conversion change pixel counter 7 counts the number of change pixels in a small block of the image after the convolution conversion.

When the conversion of the small blocks and the counting of the number of changed pixels are completed, the small block determination unit 8 reads the number of changed pixels from the through conversion changed pixel counter 5 and the convolution conversion changed pixel counter 7. Then, the read number of changed pixels is compared.

As a result of the comparison, if the value of the through conversion change pixel counter 5 is larger than the value of the convolution conversion change pixel counter 7, a mode signal for instructing the mode signal adding section 14 to select and output the convolution conversion is added. Let it. next,
The output of the encoder selection selector 13 selects the output of the one-dimensional encoder 10. Then, the small block selection selector 9 selects the output of the one-block delay memory 6, which is the output of the convolution converter 3.

If the result of the comparison indicates that the value of the convolution conversion changing pixel counter 7 is larger than the value of the through conversion changing pixel counter 5, the mode signal is instructed to the mode code adding section 14 to select and output the through conversion. Is added. Next, the output of the encoder selection selector 13 is the two-dimensional encoder 12
Select the output of Then, the small block selection selector 9
Then, the output of the one-block delay memory 4, which is the output of the through conversion unit 2, is selected.

[0019] 1-dimensional encoder 10 performs a one-dimensional coding, such as run-length encoding with respect to the converted image for one block stored in 1 block delay memory 6. At the same time, the two-dimensional encoder 12 applies the reference line memory 11 to the converted image of one block stored in the one-block delay memory 4.
, Two-dimensional encoding such as MR encoding is performed.

The image of one block after the conversion is encoded in block units, and stored in the reference line memory 11 for reference in encoding the next scanning line, and the contents are updated in block units. However, the capacity of the reference line memory 11 is such that a converted image for one scanning line can be stored. Then, in the two-dimensional encoding, the converted image of the small block corresponding to the position immediately above is referred to.

The above operation is continued until one image is completed.

The binary image decoding apparatus according to this embodiment is provided on the receiving side, receives a signal encoded by the binary image encoding apparatus on the transmitting side shown in FIG. 1, decodes the signal, and converts it. This is to obtain the previous binary image.

In FIG. 2, first, the mode signal separating section 20
Separates the mode signal indicating the conversion process for the small block from the received code string, and sends the separated mode signal to the mode restoration unit 21. The code string from which the mode signal has been separated is sent to the one-dimensional decoder 23 or the two-dimensional decoder 25 via the code demultiplexer 22. Mode signal transfer separation and mode signal since the mode signal is attached to the head of each small block is done near the respective small blocks.

Next, the mode restoring section 21 is provided with the mode separating section 2
Receiving the mode signal separated from 0, the designation of the conversion process for the small block selected at the time of encoding is restored, and the output destination of the code demultiplexer 22 is determined from the designation of the restored conversion process. Here, if the conversion processing designation of the received small block is the through conversion, the received code string is input to the two-dimensional decoder 25 to obtain the decoded converted processing result. If the conversion processing designation of the received small block is a convolution conversion, the received code string is converted to a one-dimensional decoder 23.
To obtain the processing result after conversion decoded by the one-dimensional decoder 23.

In the one-dimensional decoder 23, the mode separating section 20
Is restored to the processing result after the conversion. The decoding method of the one-dimensional decoder 23 is a method of restoring the encoding used by the one-dimensional encoder 12 on the opposite transmitting side. Also, the one-dimensional decoder 23 performs the processing until the restored converted processing result reaches the number of pixels of the small block. The restored processing result is sent to the inverse convolution unit 27, and the reference line memory 24 is used for decoding the next scanning line.
And the content is updated in units of one block. However, the capacity of the reference line memory 24 is set so that the processed result after conversion restored for one scanning line can be stored.

In the two-dimensional decoder 25, the mode separation unit 20
With reference to the stored contents of the code string received from the reference line memory 24, the processing result after conversion is restored. The image to be referred to is the converted image of the small block corresponding to the position immediately above. The decoding method of the two-dimensional decoder 25 is a method of restoring the encoding used in the two-dimensional encoder 10 of the opposing transmitter. Also, the two-dimensional decoder 25 performs the processing until the restored converted processing result reaches the number of pixels of the small block. The restored processing result after conversion is sent to the through inverse conversion unit 26, and is stored in the reference line memory 24 for decoding reference of the next scanning line, and the contents are updated in units of one block.

The picture signal before conversion by inputting to the inverse transform the one-dimensional decoder 23 processes the result of the converted decoded in the inverse transform unit 27 convolution is Ru obtained. Further, the image signal before the conversion by the inverse transform processing result after converting decoded by the 2-dimensional decoder 25 by through inverse transform unit 26
Is obtained . Here, the inverse conversion process of the through inverse transformation unit 26, so that it can restore a binary image before conversion from the processing result after restored transform, inverse of the through conversion section 2 provided on the transmission side Processing. In addition, the convolution inverse conversion unit 27
Inverse conversion process that, as can be restored binary image before conversion from the processing result after restored transform is the inverse of the processing to the convolution transform unit 3 provided on the transmission side.

Next, when the inverse conversion processing is completed for all the small blocks of one scanning line, the synthesizing section 28 synthesizes the plurality of inversely converted small blocks into one scanning line and outputs the synthesized one scanning line. Output a binary image.

The above operation is continued until one image is completed.

It should be noted that the conversion process for the pseudo halftone image is not limited to the convolution conversion process shown in the present embodiment, but may be constituted by a filter for removing the periodicity of the pseudo halftone image. Further, as the conversion processing for documents and drawings, not only the through conversion processing but also filters for improving the image quality of document drawings, such as notch and isolated point removal filters, may be used.

[0031]

As described above, according to the present invention, the compression efficiency of a binary image in which a black-and-white binary image such as a document or a drawing and a pseudo halftone image represented by a halftone picture or dither are mixed. The effect that it can raise is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a binary image encoding device in an embodiment of a binary image encoding / decoding method according to the present invention.

FIG. 2 is a block diagram illustrating a binary image decoding device according to an embodiment of the binary image encoding / decoding method of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 separation unit 2 through conversion unit 3 convolution conversion unit 4, 6 1 block delay memory 5 through conversion change pixel counter 7 convolution conversion change pixel counter 8 small block determination unit 9 small block selection selector 10 one-dimensional encoder 11, 24 reference line Memory 12 Two-dimensional encoder 13 Encoder selection selector 14 Mode signal addition unit 20 Mode signal separation unit 21 Mode restoration unit 22 Code demultiplexer 23 One-dimensional decoder 25 Two-dimensional decoder 26 Through inverse conversion unit 27 Convolution inverse conversion unit 28 Synthesis unit

Claims (5)

(57) [Claims] 1. A binary image is divided into a plurality of small blocks,
Through conversion and convolution conversion are performed for each small block.
Then, the number of changed pixels of each conversion processing result is obtained,
The conversion processing unit that minimizes the number of changed pixels of each of the obtained conversion processing results is selected for each small block, and the conversion processing result obtained by the selected conversion processing unit is subjected to two-dimensional encoding.
And, encoded as any conversion processing unit mode signal for each of the small blocks or is selected among the two conversion processing means <br/> together with the one-dimensional coding when convolution transform is selected A binary image encoding device to be added to the result, a signal encoded by the binary image encoding device being received, and a mode signal indicating the conversion processing means selected for each of the small blocks being restored from the received signal In accordance with the restored mode signal, it is determined whether the encoding system selected for each small block is one-dimensional encoding or two-dimensional encoding, and a decoding system corresponding to the encoding system determined for each small block is determined. in restoring the encoded result, the inverse conversion processing means for inverse transformation according to the restored transform processing result mode signal the restoration, the inverse transformed plurality of small blocks in the inverse transform processing means synthesizes and 2 And a binary image decoding apparatus for obtaining an image
Constructed binary image encoding and decoding method according to claim Rukoto. 2. The binary image encoding apparatus according to claim 1, wherein the binary image encoding device divides the input binary image of one scan line into a plurality of small blocks, and performs first and second conversion processes on the divided small block images. A conversion processing unit, a first and second conversion change pixel counter for counting the number of change pixels in a small block of the image after the conversion processing, and a change read from the first and second conversion change pixel counters. A small block determination unit for comparing the number of pixels, first and second one-block delay memories for storing converted images of one block of the first and second conversion processing units, A two-dimensional encoder for two-dimensionally encoding the image in the block delay memory, a one-dimensional encoder for one-dimensionally encoding the image in the second one-block delay memory, and a comparison result of the small block determination unit. The first and second one block delays A small block selection selector for selecting one of the extended memory outputs; a reference line memory for storing the image of the converted one block selected by the small block selection selector; and a reference line memory according to the comparison result of the small block determination unit. An encoder selection selector for selecting one of a two-dimensional encoder output and the one-dimensional encoder output; and a mode signal adding unit for adding a mode signal to the encoder selection selector output according to the comparison result of the small block determination unit. 2. The binary image encoding / decoding method according to claim 1, further comprising: 3. The first conversion processing unit is a through conversion unit that performs through conversion on the input image of the small block,
3. The binary image encoding / decoding method according to claim 2, wherein the second conversion processing unit is a convolution conversion unit that performs convolution conversion on the input image of the small block. 4. The binary image decoding apparatus according to claim 1, wherein
A mode signal separation unit that separates the mode signal from a column;
From the mode signal to the small block selected during encoding
A mode restoring unit for restoring the designation of the conversion process for the
The mode signal is separated according to the specification of the mode restoration unit.
Two-dimensional decoding and one-dimensional decoding
Two-dimensional decoder, one-dimensional decoder, and the two-dimensional decoder, 1
Inverse transform each result decoded by dimensional decoder
First and second inverse transform sections, and the first and second inverse transform sections
Combining multiple small blocks from a single scan line into a binary image
Characterized in that it comprises a combining unit for outputting claim 1
The binary image encoding / decoding method described in the above. 5. The two-dimensional decoder according to claim 1, wherein the first inverse transform unit is a two-dimensional decoder.
A through inverse conversion unit for performing an inverse through conversion of the output,
The inverse transform unit 2 is a convolution inverse transform of the one-dimensional decoder output.
5. The convolution inverse transform unit according to claim 4, wherein
The binary image encoding / decoding method described in the above.