JP3349873B2 - Multi-level image data transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to encoding multi-valued image data read by raster scanning in units of bit planes extracted and formed for each same bit position.
The present invention relates to a multilevel image data transmission method for transmitting the encoded data.

[0002]

2. Description of the Related Art In recent years, it is desired to communicate a monochrome multi-tone image composed of a plurality of bits per pixel or a color multi-tone image composed of a plurality of color components and one color component composed of a plurality of bits per pixel. The demand has come out. In such a case, there is also a demand for setting the number of bits per pixel to about 8 bits to communicate a high-quality image.

Here, as is well known, since the data amount of image data is very large, if data communication is performed as it is, for example, a long communication time is required or necessary for storing. Since the capacity of a storage device becomes enormous or the time required for data processing becomes excessive, data communication is usually performed in a state where image data is encoded and compressed to reduce the data amount. In particular,
The black-and-white multi-tone image and the color multi-tone image described above are
Since the number of bits per pixel is as large as 8 bits, there is a demand for a coding method capable of coding and compressing with higher efficiency.

Therefore, for example, when encoding and compressing a black-and-white multi-tone image, bit data having the same bit order in the black-and-white multi-tone image is extracted for each pixel to form a plurality of bit planes. A coding method of a so-called bit plane method (hereinafter, referred to as a bit plane coding method) that performs binary coding processing and codes and compresses an original image has been put to practical use. In this case, the binary encoding process includes, for example, MH method, MR method, MMR method,
An appropriate binary image encoding method such as the JBIG method is adopted.

[0005]

Here, from the trade-off between the image quality of the image to be transmitted and the amount of data to be transmitted, it is necessary to minimize the image quality and to reduce the number of bit planes to be transmitted. A so-called multi-value dither method has been devised as an image processing method that enables the image processing.

However, when an image to which this multi-valued dither method is applied is decomposed into bit planes, the correlation between pixels is significantly reduced in each bit plane because the statistical properties of the image change significantly. As a result, a situation has arisen in which the coding compression rate of each bit plane is deteriorated.

The present invention has been made in view of the above circumstances, and has as its object to provide a multi-valued image data transmission method that can reduce image quality degradation and increase the encoding compression rate.

[0008]

According to the present invention, multi-valued image data obtained by raster scanning is encoded in units of bit planes formed by extracting the same for each same bit position, and the encoded data is transmitted. In the multi-valued image data transmission method, the multi-valued image data is divided into two bit groups, an upper bit group and a lower bit group, and the upper bit group is encoded in units of bit planes. , A binary plane is formed to form one bit plane, the new bit plane is encoded as a lower bit plane, and code data of each bit plane of the upper bit group and code of the lower bit plane are encoded. Along with transmitting the data collectively as one multi-valued image data, The binarization process uses a process of converting multi-valued image data into binary image data by an error diffusion method when the reading resolution of the multi-valued image data is low, while reading the multi-valued image data. When the resolution is other than the low resolution, a process of converting multi-valued image data into binary image data by the systematic dither method is used.

A multi-valued image data transmission method for encoding multi-valued image data read by raster scanning in units of bit planes extracted and formed for each same bit position and transmitting the encoded data. The multi-valued image data is divided into two bit groups, an upper bit group and a lower bit group. The upper bit group is coded in units of bit planes, and the lower bit group is binarized. A new bit plane is coded as a lower bit plane, and the code data of each bit plane of the upper bit group and the code data of the lower bit plane are combined into one multi-level While transmitting as image data, the receiving side Of the value image data, for the bit planes of the upper bit group, the code data of the corresponding bit plane is decoded to form image data, and for the bit planes of the lower bit group, the code data of the lower bit plane are set. On the other hand, based on the image data formed by decoding the image data, the image data of all lower bit planes is formed, while the binarization processing is performed when the reading resolution of the multi-valued image data is low. While the process of converting multi-valued image data into binary image data by an error diffusion method is used, when the reading resolution of the multi-valued image data is other than low resolution, the multi-valued image data is converted into a binary image by an organized dither method. In this case, a process of converting into data is used.

[0010]

[0011]

[0012]

[0013]

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
Embodiments of the present invention will be described in detail.

FIG. 1 shows a multi-level image transmission apparatus according to one embodiment of the present invention. This multi-level image transmission device has a group 3 facsimile device function as a communication function.

In FIG. 1, a control unit 1 performs a control process of each unit of the multi-level image transmission apparatus and a facsimile transmission control procedure process.
The control unit 1 stores a control processing program to be executed, various data necessary for executing the processing program, and the like, and constitutes a work area of the control unit 1. The parameter memory 3 stores the multi-valued data. This is for storing various information unique to the image transmission device.

The multi-value scanner 4 reads a document image at a predetermined resolution and outputs the read image data as multi-value data (for example, 8 bits / pixel). The operation display section 6 is for operating the facsimile apparatus, and is provided with various operation keys and various display devices. Become.

The encoding / decoding section 7 encodes and compresses the multi-valued image data and decodes the encoded and compressed multi-valued image information into the original multi-valued image data. The storage device 8 is for storing a large number of multi-valued image information in an encoded and compressed state.

The group 3 facsimile modem 9 is for realizing a group 3 facsimile modem function. The group 3 facsimile modem 9 is a low-speed modem function (V.21 modem) for exchanging transmission procedure signals, and mainly exchanges image information. High-speed modem function (V.17 modem, V.17
33 modem; 29 modem, V.29. 27ter modem etc.).

The network control device 10 is for connecting the facsimile machine to a public telephone line network, and has an automatic transmission / reception function.

These control unit 1, system memory 2,
The parameter memory 3, the multi-value scanner 4, the multi-value plotter 5, the operation display unit 6, the encoding / decoding unit 7, the image storage device 8, the group 3 facsimile modem 9, and the network control device 10 are connected to the internal bus 11. The exchange of data between these elements is mainly performed via the internal bus 11.

Data exchange between the network controller 10 and the group 3 facsimile modem 9 is directly performed.

FIG. 2 shows an encoding unit of the encoding / decoding section 7 according to one embodiment of the present invention.

In FIG. 1, image data P having a width of 8 bits
X is added to the bit plane development unit 21 and its eighth
The eighth bit (most significant bit) plane data PD8, the seventh bit plane data PD7, the sixth bit plane data PD6, the fifth bit plane data PD5, and the fourth bit are formed by sequentially extracting data of bit to second bit. The bit plane data PD4, the third bit plane data PD3, and the second bit plane data PD8 are respectively added to the bit plane memory 22, and are stored for each bit plane. Also, the first bit (least significant bit) plane data PD1 is discarded.

Of the bit plane data stored in the bit plane memory 22, the eighth bit plane data BP8, the seventh bit plane data BP7, and the sixth bit plane data BP6 are added to the encoding unit 23, 5-bit plane data BP5, fourth bit plane data BP4, third bit plane data BP
3 and the second bit plane data BP2 are added to the dither binarization unit 24.

The dither binarizing unit 24 converts 4-bit image data into 1-bit binarized image data using a 4 × 4 dither matrix (threshold matrix). The result is added to the encoding unit 23 as lower bit plane data BPL. Here, a well-known dither matrix (for example, Bayer type) based on an organized dither method is used as the dither matrix used in the dither method binarization unit 24.

The coding unit 23 applies a binary coding process to each of the eighth bit plane data BP8, the seventh bit plane data BP7, the sixth bit plane data BP6, and the lower bit plane data BPL. Are formed to form multi-level code data CX. The multi-level code data CX is transmitted to the next-stage device (for example,
The data is output to the group 3 facsimile modem 9) and transmitted to the partner terminal via the transmission line.

In this case, the binary coding process applied by the coding unit 23 includes JBI with a good coding compression rate.
It is preferable to use the G method.

Here, the multi-level code data CX is, for example,
As shown in FIG. 3, at the beginning, the number of bit planes corresponding to the number of bits of the original image data PX (in this case, “8”)
And header information indicating the number of encoding planes from the most significant bit plane included in the multi-level code data CX (in this case, “4”), followed by eighth bit plane code data, seventh bit plane code data, 6-bit plane code data and lower-order bit plane code data are sequentially arranged.

FIG. 4 shows a decoding unit of the coding and decoding unit 7 according to one embodiment of the present invention. This decoding unit forms the original image data based on the multi-level code data CX formed by the coding unit of FIG.

In FIG. 3, the decoding unit 25 converts the code data of each bit plane in bit plane units from the most significant bit plane to the lower bit plane based on the multi-level code data CX received from the partner terminal. The bit plane image data CDx obtained by the decoding process is added to the bit plane storage unit 26. Further, the decoding unit 25 extracts the header information added to the head of the multi-level code data CX, and outputs it to the bit plane storage unit 26 as plane number data PNd.

The bit plane storage unit 26 stores the bit plane image data CDx sequentially added from the most significant bit plane in units of bit planes from the decoding unit 25 based on the plane number data PNd. 7-bit plane data PP
7, sixth bit plane data PP6, fifth bit plane data PP5, fourth bit plane data PP4,
Third bit plane data PP3, second bit plane data PP2, and first bit plane data PP
1 is stored in the corresponding bit plane of the bit plane memory 27.

In this case, since the value of the number of bit planes obtained as the plane number data PNd is “8” and the value of the number of encoding planes is “4”, the bit plane image data CDx input first is converted to the eighth. Bit plane data P
P8, the second input bit plane image data CDx is output as seventh bit plane data PP7, the third input bit plane image data CDx is output as sixth bit plane data PP6, and the fourth Input bit plane image data CDx
For the fifth bit plane data PP5, the fourth bit plane data PP4, and the third bit plane data P
P3, the second bit plane data PP2, and the first
The bit plane data PP1 is sequentially output to the bit plane memory 27.

The data output unit 28 sequentially extracts data PPn of each pixel from the eighth bit plane data to the first bit plane data stored in the bit plane memory 27, and outputs 8-bit data at the same pixel position. The multi-valued image data CD is collectively formed, and the multi-valued image data CD is output to, for example, the multi-valued plotter 5, whereby the received image is recorded and output from the multi-valued plotter 5.

As described above, in the present embodiment, the upper 3 bits of the 8-bit original image data are directly bit-plane coded, the lower 5 bits are discarded, and the least significant bit data is discarded. Since dither binarization processing is performed on the 4-bit data, and the lower bit plane data obtained as a result is bit-plane coded as one bit plane, the multi-level code data CX is substantially the data in the case of a 4-bit plane. Therefore, the data amount of the multi-level code data CX can be significantly reduced.

Further, assuming that the original image is a halftone image such as a photographic image, the image data of the higher-order bit plane out of the bit planes of the original 8-bit image data is better preserved in image characteristics. However, the lower bit image data gradually loses the characteristics of the image, and the least significant bit becomes a noise-like image.

In this embodiment, the upper bit group (consisting of the eighth bit plane, the seventh bit plane, and the sixth bit plane) that well preserves the features of the image is
Since encoding is performed for each bit plane, most of the features of the image can be represented in the multi-level code data CX without being lost.

The lower bit group (consisting of the fifth bit plane, the fourth bit plane, the third bit plane, and the second bit plane) is binarized as 4-bit data (pseudo halftone binarization processing). ) To form one lower-order bit plane and encode the lower-order bit plane, so that the image feature of this lower-order bit group can also be represented in the multi-level code data CX. Note that, as described above, since the least significant bit plane becomes an almost noise-like image,
Discarding does not affect image quality.

As a result, in the present embodiment, it is possible to transmit an image with high image quality despite a large encoding compression ratio and a small amount of transmission data.

FIG. 5 shows an encoding unit of the encoding / decoding section 7 according to another embodiment of the present invention. Note that, in the figure, the same parts as those in FIG. 2 and corresponding parts are denoted by the same reference numerals.

In the figure, image data P having a width of 8 bits
X is added to the bit plane development unit 21 and its eighth
The eighth bit (most significant bit) plane data PD8, the seventh bit plane data PD7, the sixth bit plane data PD6, the fifth bit plane data PD5, and the fourth bit are formed by sequentially extracting data of bit to second bit. The bit plane data PD4, the third bit plane data PD3, and the second bit plane data PD8 are respectively added to the bit plane memory 22, and are stored for each bit plane. Also, the first bit (least significant bit) plane data PD1 is discarded.

Of the bit plane data stored in the bit plane memory 22, the eighth bit plane data BP8, the seventh bit plane data BP7, and the sixth bit plane data BP6 are added to the encoding unit 30, The 5-bit plane data BP5 is applied to the common input / connection end of the switch 31, and the fourth bit plane data BP4, the third bit plane data BP3, and the second bit plane data BP2 are sent to the dither binarization circuit 32. Have been added.

The switch 31 sets the mode data MD supplied from the control unit 1 to data "0" representing the low image quality mode.
, The fifth bit plane data BP
5 is added to the dithering binarization unit 32 and the fifth bit plane data BP5 is added to the encoding unit 30 when the mode data MD is data “1” representing the high image quality mode.

When the mode data MD applied from the control unit 1 is data "0" representing the low image quality mode, the dither method binarization circuit 32 adds the fifth bit plane data BP5 and the fourth bit plane For the data BP4, the third bit plane data BP3, and the second bit plane data BP2, 4-bit image data is converted into 1-bit binary image data using a 4 × 4 dither matrix (threshold matrix). When the mode data MD is converted to data "1" indicating the high image quality mode, the added fourth bit plane data BP4, third bit plane data BP3, and second bit plane data BP2 are added.
Using a 3 × 3 dither matrix,
The 4-bit image data is converted into 1-bit binary image data, and the processing result is added to the encoding unit 30 as lower bit plane data BPL. Here, as the dither matrix used in the dither binarization circuit 32, a well-known dither matrix (for example, Bayer type) based on an organized dither method is used.

When the mode data MD added from the control unit 1 is data "0" representing the low image quality mode, the encoding unit 30 sets the eighth bit plane data BP8, the seventh bit plane data BP7 and the sixth bit plane data BP7. The binary encoding process is applied to the bit plane data BP6 and the lower bit plane data BPL, and the code data formed for each bit plane is combined to form multi-level code data CXa and the mode data MD Is the data "1" representing the high image quality mode, the eighth bit plane data BP8, the seventh bit plane data BP7, the sixth bit plane data BP6, the fifth bit plane data BP5, and the lower bit plane data For BPL, each binary mark Treated apply, collectively encoded data formed for each bit plane,
The multi-level code data CXa is formed, and the multi-level code data CXa is output to a next-stage device (for example, a group 3 facsimile modem 9) and is transmitted through a transmission line.
It is transmitted to the partner terminal.

Therefore, in this case, the multi-level code data C
When the mode data MD is data "0" representing the low image quality mode, Xa becomes data of the same signal format as shown in FIG. 3, and the mode data MD becomes data "1" representing the high image quality mode. , The data is in the signal format as shown in FIG.

That is, the number of bit planes (in this case, “8”) corresponding to the number of bits of the original image data PX at the beginning and the number of encoding planes from the most significant bit plane included in the multi-level code data CX ( In this case, following the header information indicating “5”), the eighth bit plane code data, the seventh bit plane code data,
Bit plane code data, fifth bit plane code data, and lower bit plane code data are sequentially arranged.

Therefore, when the user does not select the high image quality mode, the mode data MD output from the control unit 1 becomes data "0" representing the low image quality mode. The fifth bit plane data BP5 read from the memory 22 is added to the dither binarization unit 32. The dither binarization circuit 32 adds the fifth bit plane data BP5, the fourth bit plane data BP4, and the third bit. Plain data BP
3 and the second bit plane data BP2, the 4-bit image data is converted to 1-bit binary image data using a 4 × 4 dither matrix, and the processing result is converted to the lower bit plane data BPL. And outputs the result to the encoding unit 30.

At this time, the encoding unit 30 performs a binary encoding process on the eighth bit plane data BP8, the seventh bit plane data BP7, the sixth bit plane data BP6, and the lower bit plane data BPL. Is applied, and the code data formed for each bit plane is put together to form and output multi-level code data CXa.

When the user selects the high image quality mode, the mode data MD output from the control unit 1 becomes data "1" representing the high image quality mode. Is added to the encoding unit 30 and the fifth bit plane data BP5 read from
The dither method binarization circuit 32 outputs the added fourth bit plane data BP4, third bit plane data BP3,
And for the second bit plane data BP2, 3
Using a × 3 size dither matrix, 3-bit image data is converted into 1-bit binary image data, and the processing result is output to the encoding unit 30 as lower bit plane data BPL.

Also, at this time, the encoding unit 30 determines the eighth bit plane data BP8, the seventh bit plane data BP7, the sixth bit plane data BP6, the fifth bit plane data BP5, and the lower bit plane data BPL. , Each of which is subjected to a binary encoding process, and collectively forms the code data formed for each bit plane to form and output multi-level code data CXa.

As described above, in this embodiment, when the user selects the high image quality mode, the upper bit groups to be encoded for each bit plane are the eighth bit plane, the seventh bit plane, and the sixth bit plane. And the fifth bit plane, one bit plane is added as compared with the case where the user selects the low image quality mode.
Higher quality images can be transmitted.

When the high image quality mode is selected, the amount of transmission data per page increases as compared with the case where the low image quality mode is selected. Therefore, the user can reduce the transmission time (by selecting the low image quality mode). ), Or whether to prioritize the image quality of the transmission image (when the high image quality mode is selected), and thus the usability of the image transmission apparatus is improved.

In the above-described embodiment, two types of image quality modes, that is, a high image quality mode and a low image quality mode, can be set. However, more image quality modes can be set. For example, when three types of image quality modes, that is, a high image quality mode, a normal mode, and a low image quality mode, are provided, the number of bit planes of the upper bit group may be set to 4, 3, and 2, respectively.

The decoding unit in this embodiment can use the same decoding unit as in FIG.

FIG. 7 shows an encoding unit of the encoding / decoding section 7 according to still another embodiment of the present invention. Note that, in the figure, the same parts as those in FIG. 2 and corresponding parts are denoted by the same reference numerals.

In the figure, image data P having a width of 8 bits
X is added to the bit plane development unit 21 and its eighth
The eighth bit (most significant bit) plane data PD8, the seventh bit plane data PD7, the sixth bit plane data PD6, the fifth bit plane data PD5, and the fourth bit are formed by sequentially extracting data of bit to second bit. The bit plane data PD4, the third bit plane data PD3, and the second bit plane data PD8 are respectively added to the bit plane memory 22, and are stored for each bit plane. Also, the first bit (least significant bit) plane data PD1 is discarded.

Of the bit plane data stored in the bit plane memory 22, the eighth bit plane data BP8, the seventh bit plane data BP7, and the sixth bit plane data BP6 are added to the encoding unit 23, 5-bit plane data BP5, fourth bit plane data BP4, third bit plane data BP
3 and the second bit plane data BP2 are applied to the switch 35.

When the resolution data DI applied from the control unit 1 is data "0" indicating high resolution, the switch 35 sets the fifth bit plane data BP5,
Fourth bit plane data BP4, third bit plane data BP3, and second bit plane data BP
2 is added to the dither method binarization unit 36, and when the resolution data DI is data “1” representing low resolution, the fifth bit plane data BP5, the fourth bit plane data BP4, and the third bit plane data BP3 and second bit plane data BP2 are added to the error diffusion method binarization unit 37.

The dither binarization circuit 36 is enabled when the resolution data DI applied from the control unit 1 is data "0" representing high resolution, and the added fifth bit plane data BP5 and fourth data For the bit plane data BP4, the third bit plane data BP3, and the second bit plane data BP2, 4 ×
The 4-bit image data is converted into 1-bit binary image data using a 4-size dither matrix (threshold matrix), and the processing result is converted to lower-order bit plane data BPLa by the switch 38. It is applied to one switching input. The dither binarization circuit 36 is disabled and does not operate when the resolution data DI is data "1" indicating low resolution. Here, as the dither matrix used in the dither binarization circuit 32, a well-known dither matrix (for example, Bayer type) based on an organized dither method is used.

The error diffusion method binarization circuit 37 is enabled when the resolution data DI supplied from the control unit 1 is data "1" representing low resolution, and the fifth bit plane data BP5, 4 bit plane data BP4, 3rd bit plane data BP3,
Further, with respect to the second bit plane data BP2, binarization processing by a known error diffusion method is applied to convert 4-bit image data into 1-bit binarized image data. , Lower bit plane data BPLb at the other switch input terminal of the switch 38. The error diffusion method binarization circuit 37 is disabled and does not operate when the resolution data DI is data "0" representing high resolution.

When the resolution data DI is data "0" indicating high resolution, the switch 38 outputs the lower bit plane data BPLa output from the dither binarization unit 36 and applied to one of the switching input terminals. Is selected as the lower bit plane data BPL by the encoding unit 2
3 and when the resolution data DI is data "1" representing low resolution, the lower bit plane data BPLb output from the error diffusion method binarization unit 37 and applied to the other switching input terminal is output. Select
It is output to the encoding unit 23 as lower bit plane data BPL.

The coding unit 23 applies a binary coding process to each of the eighth bit plane data BP8, the seventh bit plane data BP7, the sixth bit plane data BP6, and the lower bit plane data BPL. Is formed to form multi-level code data CX. The multi-level code data CXa is output to a next-stage device (for example, a group 3 facsimile modem 9) and transmitted to a transmission line. Is transmitted to the partner terminal via

Therefore, when transmitting an image, if the resolution of the image data that can be processed by the partner terminal notified by the partner terminal in the pre-image transmission procedure is high and the input image data PX is high resolution, the control is performed. The resolution data DI output from the unit 1 becomes data “0” representing high resolution.

As a result, the switch 35 switches the fifth bit plane data BP5 and the fourth bit plane data BP5.
Fourth, the third bit plane data BP3 and the second bit plane data BP2 are added to the dither binarization unit 36, and the dither binarization unit 36 is enabled and output from the dither binarization unit 36. The lower bit plane data BPLa is selected by the switch 38 and is added to the encoder 23 as lower bit plane data BPL.

When the resolution of the image data that can be processed by the other terminal notified by the other terminal is low and the input image data PX is low, the resolution data DI output from the control unit 1 is used. Becomes data “1” representing low resolution.

As a result, the switching unit 35 sets the fifth bit plane data BP5 and the fourth bit plane data BP5.
4, while adding the third bit plane data BP3 and the second bit plane data BP2 to the error diffusion method binarization section 37, the error diffusion method binarization section 37 is enabled, and the error diffusion method binarization section 37 The lower bit plane data BPLb output from the encoder 38 is selected by the switch 38, and is encoded by the encoder 2 as lower bit plane data BPL.
Added to 3.

Therefore, when the image data PX has a low resolution, the lower bit plane data BPLb by the error diffusion method, which is visually evaluated as having higher image quality at the lower resolution, is used as the lower bit plane data BPL. It is possible to improve the quality of a transmitted image when the transmission resolution is low.

Further, in this embodiment, the contents of the pseudo halftone binarization processing are changed in the case of the low resolution and the case of the high resolution, respectively. It is also possible to use the error diffusion method binarization unit and to use the dither method binarization unit when the high-speed mode is selected, so that the operation mode desired by the user can be selected.

The decoding unit in this embodiment can use the same decoding unit as in FIG.

In the above-described embodiment, the case where black-and-white multi-valued image data is transmitted has been described.
The same applies to the case where color multi-valued image data is transmitted. Further, the present invention can be similarly applied to the case where multi-valued image data is stored as well as transmitted.

Further, in the above-described embodiment, the case where the present invention is applied to a device having a group 3 facsimile transmission function as a transmission function has been described. The same can be applied to those having the data transmission function.

In the above-described embodiment, the JBIG system is described as being suitable as the coding system of the coding unit. However, in view of the complexity of the apparatus configuration, the MH system and the MMR system are more preferable than the JBIG system. Therefore, these encoding methods can be applied depending on the case (for example, cost priority).

[0074]

As described above, according to the present invention,
When the image data has a low resolution, the lower bit plane data based on the error diffusion method, which is evaluated as having higher image quality at the lower resolution, is used. Therefore, the image quality of the transmission image when the transmission resolution is low is improved. The effect that can be obtained.

[0075]

[0076]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a multi-level image transmission device according to one embodiment of the present invention.

FIG. 2 is a block diagram showing an encoding unit of an encoding and decoding unit according to one embodiment of the present invention.

FIG. 3 is a schematic diagram showing an example of a signal format of multi-level code data.

FIG. 4 is a block diagram showing a decoding unit of the coding and decoding unit according to one embodiment of the present invention;

FIG. 5 is a block diagram showing an encoding unit of an encoding and decoding unit according to another embodiment of the present invention.

FIG. 6 is a schematic diagram showing another example of a signal format of multi-level code data.

FIG. 7 is a block diagram illustrating an encoding unit of an encoding and decoding unit according to still another embodiment of the present invention.

[Explanation of symbols]

 21 Bit plane expansion unit 22, 27 Bit plane memory 23, 30 Encoding unit 24, 32, 36 Dither method binarization unit 25 Decoding unit 26 Bit plane storage unit 31, 35, 38 Switch 37 Error diffusion method binary Transformation part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/41-1/419 H04N 1/40-1/409

Claims (2)

(57) [Claims] 1. A multi-valued image data transmission method for encoding multi-valued image data read by raster scanning in units of bit planes extracted and formed for each same bit position and transmitting the encoded data. The multi-valued image data is divided into two bit groups, an upper bit group and a lower bit group. The upper bit group is coded in units of bit planes, and the lower bit group is binarized. A new bit plane is coded as a lower bit plane, and the code data of each bit plane of the upper bit group and the code data of the lower bit plane are combined into one multi-level In addition to transmitting as image data, the binarization process When the reading resolution of the image data is low, the process of converting the multi-valued image data into binary image data by the error diffusion method is used. A multivalued image data transmission method, which is a process of converting multivalued image data into binary image data by a dynamic dither method. 2. A multi-valued image data transmission method for encoding multi-valued image data obtained by reading by raster scan in units of bit planes extracted and formed for each same bit position and transmitting the encoded data. The multi-valued image data is divided into two bit groups, an upper bit group and a lower bit group. The upper bit group is coded in units of bit planes, and the lower bit group is binarized. A new bit plane is coded as a lower bit plane, and the code data of each bit plane of the upper bit group and the code data of the lower bit plane are combined into one multi-level While transmitting as image data, the receiving side Of the image data, for the bit plane of the upper bit group, the code data of the corresponding bit plane is decoded to form image data, and for the bit plane of the lower bit group, the code data of the lower bit plane is On the other hand, based on the image data formed by decoding, image data of all lower bit planes is formed. On the other hand, the above-mentioned binarization processing has an error when the reading resolution of the multi-valued image data is low. While the process of converting the multi-valued image data into the binary image data by the diffusion method is used, when the reading resolution of the multi-valued image data is other than the low resolution, the multi-valued image data is converted into the binary image data by the systematic dither method. A multivalued image data transmission method characterized by using a process of converting to multivalued image data.