JPH09252408A - Multi-tone image decoding device - Google Patents

Abstract

(57) Abstract: The present invention is a multi-gradation method for decoding a code string of a multi-gradation image with a simple configuration, performing image processing according to the type and characteristics of the image, and outputting a high-quality image. An image decoding device is provided. A bit plane decoding unit 20 decodes and reproduces an input code string by an arithmetic coding method, and outputs the code string to an image creating unit and a number-of-states statistics unit. When the decoding for one bit plane is completed, the number-of-states statistics unit 23 counts the number of appearances for each state after decoding, and the image determination unit 24 determines the type and characteristics of the decoded image based on the statistical information. To do. The image creating unit 21 creates an entire image by synthesizing the images decoded by the bit plane decoding unit 20 for each bit plane unit, and the output processing unit 22 determines the image created by the image creating unit 21 as an image determining unit. Based on the determination result input from 24, image processing that is optimal for the image and optimal for the image output characteristic is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-tone image decoding device, and more particularly to a multi-tone image decoding device for decoding a black-and-white multi-valued image or a color image at high speed with high image quality.

[0002]

2. Description of the Related Art Conventionally, in an encoding / decoding apparatus, for example, a facsimile apparatus, at the time of transmission, image data of an original read by a scanner is encoded by an encoding / decoding unit.
MH (Modified Huffman) coding system, MR (Modufied)
Relative element address designate) encoding method,
Alternatively, 2 such as MMR (Modified MR) coding method
After compression encoding with the standard encoding method for value facsimile,
The image is temporarily stored in the image memory and output to the line to be transmitted to the facsimile machine of the other party. When receiving, the facsimile device receives the encoded image data sent via the line, temporarily stores it in the image memory, and then decodes it into the original image data by the encoding / decoding unit. Then, the plotter prints it on the printing paper.

In such a facsimile machine,
Conventionally, only binary image data, that is, black-and-white binary image data, has been handled. Recently, however, with the development of a recording method, one pixel can be recorded with a plurality of gradations. Also in the data transmission method, it is necessary to transmit multi-tone image data.

That is, in recent years, an encoding / decoding apparatus typified by a facsimile apparatus has been improved in speed and image quality, and an encoding / decoding capable of handling a multi-tone image represented by a color image. Although an apparatus (for example, a color facsimile apparatus) has been introduced, since the information that can be handled by the encoding / decoding apparatus represented by the conventional facsimile apparatus is binary information, the original image is scanned by a scanner or the like. Then, it is converted into binary information and then coded and transmitted. Therefore, even if the original image is an image with gradation, 2
There is a problem that information is lost due to the binarization and the image quality is deteriorated (especially in an image including a photograph).

As a method for reducing the image quality deterioration due to this information loss, there are image signal coding / decoding methods as described in JP-A-2-122767 and JP-A-61-212167. In these documents, a method has been proposed in which the original image is not binarized but is converted into information having a certain gradation and then coded and transmitted. This is one of the multi-valued encoding methods typified by the encoding methods used in color facsimile machines that have recently appeared, and handles multi-gradation images, so that deterioration in image quality can be considerably reduced. Is.

However, the multi-tone image has an extremely large amount of data as compared with the case where a binary image is handled, and if the data is encoded and transmitted by the conventional encoding method,
Communication time is reduced, and communication costs are increased. For example, when comparing the data amount of a black-and-white binary image and the data amount of a black-and-white 256-tone image, the number of bits required for one pixel is 1 bit for a binary image, and 8 bits for a 256-tone image. Therefore, as a whole, the 256 gradation image has a data amount eight times as large as the binary image. The fact that the amount of data is large means that the amount of data to be processed is correspondingly large and the processing time is increased, and communication devices such as facsimile apparatuses have a serious problem that the communication time is increased.

One method for reducing the transmission time is to efficiently encode a multi-tone image to reduce the amount of data to be transmitted, and a multi-tone image (including a color image). There are roughly two types of encoding methods.

[0008] That is, as a multi-gradation image encoding method, an encoding method (Lossy method) in which the information amount of the original image is partially reduced to the extent that the image quality is not deteriorated by utilizing human visual characteristics is used. Coding system) and a coding system that performs coding without impairing the information amount of the original image (called a lossless coding system).

As a representative of the former, ITU-T (former CC
J using the Discrete Cosine Transform (hereinafter DCT), which has been standardized by the ITT) and ISO (International Organization for Standardization)
There is a PEG method, and the JPEG method is a method of converting image information into frequency information and then encoding the image information. The visual quality of human beings (limit of gradation recognition ability) is used to deteriorate the image quality too much. The encoding is performed by reducing the information amount of the original image to the extent that it does not exist.

Similarly, as a representative of the latter, ITU-T
And the JBIG method, which has been standardized by ISO,
The JBIG method basically decomposes an image into binary bit planes and encodes it using a binary arithmetic encoding method called QM-Coder.

[0011]

However, these coding methods also have advantages and disadvantages. That is, JPE
The G method enables efficient encoding without deteriorating the image quality, but has a drawback that the image quality becomes extremely poor if the character image portion is blurred or the encoding efficiency is too high. In the case of a facsimile machine, JP
Since the EG method cannot handle a binary image, it is necessary to mount both an encoding unit for the binary image encoding method and an encoding section for the multi-valued image JPEG method, which causes a problem of high cost. . On the other hand, since the JBIG system is basically a binary encoding system, even when it is applied to a facsimile machine, it is not necessary to mount two types of encoding units, and there is a problem in terms of cost. However, in a multi-tone image, there is a problem that the coding efficiency is generally lower than that of the JPEG method.

On the other hand, on the receiving side of a communication device such as a facsimile device, in order to output a transmitted image with high image quality, it is possible to perform image processing adapted to the output characteristics of the device itself in consideration of the type of image. Many. In particular, processing the image by performing pictogram separation is extremely effective in improving the quality of the image. For example, in the character image portion, the relationship between the original image density and the output image density (γ curve) as shown in FIG. Is performed and high-quality images are output. Further, in a halftone image such as a photograph, a high-quality image can be obtained by applying a smooth gradation to the image by a γ curve as shown in FIG. Is being output.

The relationship between these character images and halftone images such as photographs is contradictory, and when the processing performed on the halftone images such as photographs is performed on the character images, the adverse effect is obtained, and the image quality deteriorates. On the contrary, if the processing for the character image is performed on the halftone image such as a photograph, the image quality is similarly deteriorated.

Therefore, the invention according to claim 1 is the JBIG
In the arithmetic coding by the method, when there are many delicate gradation expressions such as a halftone image such as a photographic image at the time of decoding, the number of appearances in each state is average, and the variation between states is small. On the contrary, in the character image, the number of appearances in a specific state is large, and the variation between states is large. Therefore, when decoding and reproducing a black-and-white multi-tone image from a code string encoded in bit plane units, at the end of the code for each bit plane, statistical processing of the number of appearances for each state is performed, and the appearance for each state is performed. A binary value is obtained by determining the type and characteristics of the decoded image based on the number-of-times information and performing optimal image processing at the time of image output based on the determination result, for example, edge enhancement, smoothing processing or smoothing processing. An object of the present invention is to provide a multi-tone image decoding device capable of decoding an image and outputting a black-and-white multi-tone image with high image quality.

According to a second aspect of the present invention, when a color image is decoded and reproduced from a code string encoded in bit plane units, the number of appearances in each state at the end of decoding for each bit plane in the first color component By performing the statistical processing of 1., the type and characteristics of the code image are determined based on the appearance count information for each state, and the optimal image processing at the time of image output is performed based on the determination result. It is an object of the present invention to provide a multi-tone image decoding apparatus capable of decoding a multi-tone image and outputting a color multi-tone image with high image quality.

According to a third aspect of the invention, the structure is simple by performing the statistical processing of only the statistical processing of the number of appearances in only a specific state and determining the type and characteristics of the image based on the statistical information. It is an object of the present invention to provide a multi-tone image decoding device that can output high-quality images at low cost.

The invention according to claim 4 is simpler in configuration by determining whether or not it is a character image based on only statistical processing of the number of appearances only in a characteristic state as a character image. Moreover, it is an object of the present invention to provide a multi-tone image decoding device that can output a high quality image at a lower cost.

According to the fifth aspect of the present invention, only the most significant bit plane to be decoded first is subjected to statistical processing of the number of appearances of only a predetermined characteristic state in the character image, and the appearance of the characteristic state in the character image is performed. (EN) It is possible to provide a multi-gradation image decoding device that can output a high quality image with a simpler configuration and at a lower cost by determining whether or not it is a character image based on the number of times. Has an aim.

According to the sixth aspect of the present invention, when it is determined that the upper bit plane is a character image, the subsequent lower bit plane is not subjected to the decoding process, and the bit plane which is not subjected to the decoding process is the highest bit. It is an object of the present invention to provide a multi-gradation image decoding device that can output a high quality image with a simpler configuration and at a lower cost by reproducing an image by copying the bit plane of There is.

[0020]

According to a first aspect of the present invention, there is provided a multi-tone image decoding apparatus, wherein a black-and-white multi-tone image represented by n bits per pixel is decomposed into n bit planes for each bit order. Then, a bit plane decoding means for sequentially decoding in bit plane units from a code string encoded for each bit plane unit to reproduce image information, and the number of appearances for each state after decoding by the bit plane decoding means State number statistical means for performing statistical processing, image determination means for determining the type and characteristics of the decoded image based on the statistical information of the state number statistical means, and for each bit plane reproduced by the bit plane decoding means Image creating means for creating an entire image based on the image information of the above, and for outputting a high quality image to the image created by the image creating means based on the judgment result of the image judging means. And output processing means for performing predetermined image processing, by providing, have achieved the above objects.

Here, in the arithmetic coding by the JBIG method, when there are many delicate gradation expressions such as a halftone image such as a photographic image at the time of decoding, the number of appearances in each state is average and There is little variation between spaces. On the contrary, in the character image, the number of appearances in a specific state is large, and the variation between states is large. Therefore, it is possible to determine whether the image is a gradation image such as a photographic image or a line image such as a character image based on the statistical quantity (statistical information) of the number of appearances in each state, and the type and characteristics of the image, etc. Accordingly, image processing for high-quality output, such as edge enhancement, smoothing processing or smoothing processing, can be performed.

According to the above configuration, when decoding a black-and-white multi-tone image from a code string encoded in bit plane units, statistical processing of the number of appearances in each state is performed at the end of the code for each bit plane. Then, the type and characteristics of the decoded image can be determined based on the appearance count information for each state, and the optimum image processing at the time of image output can be performed based on the determination result, and the binary image can be decoded. In addition, it is possible to output a black-and-white multi-tone image with high image quality.

In the multi-gradation image decoding device according to the second aspect of the present invention, a color image in which a color component of one pixel is represented by m bits and a color accuracy is represented by n bits is decomposed into m × n bit planes. Then, a bit plane decoding means for sequentially decoding the bit plane unit from the code string encoded for each bit plane unit to reproduce the image information, and the bit plane decoding means for decoding the first color component State number statistical means for performing statistical processing of the number of appearances for each state after decoding, image determination means for determining the type and characteristics of the decoded image based on the statistical information of the state number statistical means, and the bit plane decoding An image creating means for creating an image for each of m color components based on the image information for each bit plane reproduced by the means, and an entire image based on the image for each color component created by the image creating means A color component synthesizing unit that creates a color image, and an output process that performs predetermined image processing for outputting a high-quality image to the color image created by the color component synthesizing unit based on the determination result of the image determining unit. Means and means are provided to achieve the above object.

According to the above configuration, when a color image is decoded and reproduced from a code string encoded in bit plane units, at the end of decoding for each bit plane in the first color component, statistics of the number of appearances for each state By performing the processing, the type and characteristics of the decoded image are determined based on the appearance count information for each state, and the optimum image processing at the time of image output can be performed based on the determination result. It is possible to decode and output a color multi-gradation image with high image quality.

In each of the above cases, for example, as described in claim 3, the number-of-states statistical means performs statistical processing on the number of appearances of only a certain specific state, and the image determination means causes the image determination means to perform the specific state. The type and characteristics of the image may be determined based on the appearance frequency information.

According to the above configuration, it is possible to perform the statistical processing of only the statistical processing of the number of appearances of only a specific state, and determine the type and characteristics of the decoded image based on the statistical information, and the state number statistics. The means and the image determination means can have a simple structure. As a result, a multi-gradation image decoding device capable of outputting a high-quality image can be made simple and inexpensive.

Further, for example, as described in claim 4, the number-of-states statistical means performs statistical processing of the number of appearances of only a state having a predetermined characteristic in a character image, and the image determination means, the number-of-states is calculated. Whether or not it is a character image may be determined based on the statistical information of the statistical means.

According to the above configuration, the character image having a high density and the background image having a low density are appropriately determined based on only the statistical processing of the number of appearances only in the characteristic state as the character image, and the character image is obtained. It is possible to make a multi-tone image decoding device capable of determining whether or not it is possible to output a high quality image with a simpler structure and at a lower cost.

Further, for example, as described in claim 5, the state number statistical means statistically counts the number of appearances of only a characteristic state in the character image only in the most significant bit plane decoded first. The image determination means may determine whether or not the image is a character image based on the statistical information of the state number statistical means.

According to the above configuration, only the most significant bit plane to be decoded first is subjected to statistical processing of the number of appearances of only a predetermined characteristic state in the character image, and the appearance number of the characteristic state in the character image is calculated. A multi-gradation image decoding device capable of determining whether or not a character image is based on a high-quality image, and having a simpler structure and further lower cost be able to.

Further, for example, as described in claim 6, when the bit plane decoding means determines that the image determining means is a character image, the bit plane decoding means subsequently performs decoding processing on the lower bit plane. Alternatively, the image creating means may reproduce the image by copying the highest bit plane of the bit plane that has not been subjected to the decoding process.

According to the above configuration, when it is determined that the character image is in the upper bit plane, the decoding process for the lower bit plane that is subsequently performed is not performed, and the highest bit of the bit plane that has not been subjected to the decoding process is performed. Since the decoded image of the plane is duplicated to reproduce the image, the decoding device for the multi-tone image can have a simpler structure and can be made more inexpensive.

[0033]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, although the embodiment described below is a preferred embodiment of the present invention, various technically preferable limitations are added.
The scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

1 to 5 are views showing a first embodiment of a multi-gradation image decoding apparatus of the present invention. This embodiment is based on a code string coded in bit plane units. When decoding and reproducing a black-and-white multi-gradation image, at the end of the code for each bit plane, statistical processing of the number of appearances for each state is performed, and the type and characteristics of the code image are determined based on the appearance number information for each state. The determination is made and the optimum image processing is performed at the time of image output based on the information, which corresponds to claim 1.

The present embodiment is applied to a facsimile machine, and FIG. 1 shows a facsimile machine 1 on the transmission side and a receiving machine to which the first embodiment of the multi-gradation image decoding apparatus of the present invention is applied. It is a principal part block diagram of the facsimile apparatus 2 of the side.

In FIG. 1, the facsimile apparatus 1 on the transmitting side is shown.
Includes an image reading unit 3, an image processing unit 4, an encoding unit 5, and the like, and the receiving-side facsimile device 2 includes an image output unit 6, an image processing unit 7, a decoding unit 8, and the like. Although not shown in FIG. 1, in addition to the above, the transmission side facsimile apparatus 1 includes an image memory, an image output section, a communication control section, a decoding section, etc., and the reception side facsimile apparatus 2 includes An image memory, an image reading unit, an encoding unit, a communication control unit and the like are provided. Then, the transmission side facsimile apparatus 1 and the reception side facsimile apparatus 2 are connected to a line (transmission path) 9 to the communication control section thereof, and the communication control section transmits and receives image data through the transmission path 9.

First, the transmission side facsimile apparatus 1 will be described. The image reading section 3 uses, for example, a CCD (Charge).
An image scanner using a Coupled Device) is used, and not only a binary image of a binary image, but also an original image of a monochrome multi-tone image or a color multi-tone image is scanned to determine an original image. Read at the resolution of. The image reading unit 3
The image data of the read document is output to the image processing unit 4.

The image processing unit 4 performs, for example, resolution conversion and size conversion on a binary image, and color (color component) conversion, resolution conversion and size conversion on a multi-gradation image including a color image. And so on.

The encoding unit 5 compression-encodes the image data input from the image processing unit 4 by the arithmetic encoding system used in the JBIG system, and the communication control unit receives the data via the transmission line 9 on the receiving side. It is transmitted to the facsimile device 2.

Next, the receiving side facsimile apparatus 2 will be described. The image output section 6 uses, for example, an electrophotographic recording apparatus, which records and outputs a binary image on a recording sheet, and a black and white multi-tone image and A color multi-tone image is recorded and output on a recording paper at a predetermined resolution.

Similar to the image processing unit 4, the image processing unit 7 performs resolution conversion and size conversion on a binary image, for example, and in a multi-gradation image including a color image, color (color Component conversion, resolution conversion, size conversion, etc. are performed.

The decoding section 8 decodes the code string coded by the transmission side coding section 5 by the same coding method as that of the coding section 5. That is, the decoding unit 8
By the arithmetic coding method used in the IG method, the coded image data received via the communication control unit (not shown) is decoded by the JBIG method and output to the image processing unit 7. The image processing unit 7 performs necessary image processing on the decoded image and outputs it to the image output unit 6, and the image output unit 6
Prints and outputs an image on a recording sheet based on the image data image-processed by the image processing unit 7.

Next, the JBIG arithmetic coding method, which is the coding method in the coding unit 5 and the decoding unit 8, will be described below with reference to FIG.

In the arithmetic coding system, as shown in FIG. 2, the coding unit 5 generally includes a prediction information creating circuit 10 and an arithmetic coding circuit 11, and the decoding unit 8 includes a prediction information creating circuit 12. And an arithmetic decoding circuit 13.

The prediction information generating circuit (also referred to as a template) 10 of the encoding unit 5 generates prediction data (prediction information) obtained by performing Markov separation of the information source according to the situation of the pixel to be encoded and surrounding pixels. It is created and output to the arithmetic coding circuit 11.

The arithmetic coding circuit 11 codes the coded pixels while dynamically evaluating the prediction data based on the prediction data input from the prediction information creating circuit 10.

On the other hand, the decoding section 8 performs an operation which is completely opposite to that of the encoding section 5. That is, the prediction information creation circuit 12
Input encoded data (encoded image data)
By performing Markov separation of the information source according to the situation with the pixels around the pixel to be decoded with the already decoded pixel,
Prediction data (prediction information) of encoded data to be decoded is created and output to the arithmetic decoding circuit 13.

The arithmetic decoding circuit 13 decodes the coded data while dynamically evaluating the prediction data based on the prediction data input from the prediction information creating circuit 12.

This arithmetic coding system will be described in more detail with reference to FIG. 3. In the arithmetic coding system, as shown in FIG. 3, the corresponding section (2
In decimal, [0.0 ... 0, 0.1 ... 1]) is divided into unequal lengths according to the occurrence probabilities of each symbol, and the target symbol sequence is assigned to the corresponding partial section. , Recursively repeat division. The coordinates of the points included in the section thus obtained can be distinguished from at least other sections.
It is expressed as a decimal number and used as it is as a code.

The concept of arithmetic coding will be described with reference to FIG. 3 by taking the symbol sequence '0100' as an example. First, at the time of coding the first symbol, the entire section is composed of symbols of '0' and '1'. It is divided into A (0) and A (1) according to the ratio of the occurrence probabilities, and the section A (0) is selected by the occurrence of '0'. Next, at the time of encoding the second symbol, A (0) is further divided by the occurrence probability ratio of both symbols in that state, and A (0) is set as an interval corresponding to the generated symbol sequence.
(01) is selected. Encoding is performed by repeating such division and selection processing.

On the other hand, in the decoding, the processing which is completely opposite to that in the coding is performed, and the symbol is reproduced based on the binary decimal represented by the code. At this time, the width of the number line at the time of encoding the symbol is important, and if the width of the number line does not match at the start of encoding and at the start of decoding, the symbol cannot be accurately reproduced. Normally, the width of this number line is set to "1" on the encoding side and the decoding side.

The above-mentioned arithmetic coding system generally has higher coding efficiency than the conventional run-length coding system (MH method, MR method).

The decoding unit 8 of the receiving side facsimile apparatus 2 is constructed as shown in FIG. That is, the decoding unit 8 includes a bit plane decoding unit 20, an image creation unit 21, an output processing unit 22, a state number statistic unit 23, an image determination unit 24, and the like.

The bit plane decoding unit 20 decomposes the input image information (input image data) having a bit precision of n into n pieces of binary image information (bit planes) sequentially from the most significant bit and uses the arithmetic coding method. Bit planes are sequentially decoded from the encoded code string and output to the image creating unit 21 and the number-of-states statistics unit 23. The bit plane decoding method in the bit plane decoding unit 20 is the same encoding method as the encoding method in the encoding unit 5 of the transmitting side facsimile apparatus 1 and is an arithmetic encoding method. This code string is
As shown in FIG. 5, n information indicating the bit information of the input image is added to the beginning of the code string, and subsequently n codes for each bit plane are arranged.

The image creating section (image creating means) 21 creates an entire image based on the image for each bit plane unit reproduced by the bit plane decoding section 20, and outputs it to the output processing section 22.

The state number statistic section (state number statistic means) 23 is
The bit plane decoding unit 20 performs statistical processing on the number of appearances in each state after decoding each bit plane, and outputs statistical information that is the statistical result to the image determination unit 24.

The image determination unit (image determination means) 24 determines the type and characteristics of the image decoded by the bit plane decoding unit 20 based on the statistical information input from the state number statistics unit 23, and the determination result. Is output to the output processing unit 22.

The output processing unit 22 is optimal for the image created by the image creating unit 21 based on the determination result input from the image determining unit 24 and for the output characteristics of the image output unit 6. Image processing, for example, for character images, the edge portion is emphasized by a γ curve as shown in FIG. 9, or the contour is smoothed by smoothing processing, and for photographic images, it is shown in FIG. Using such a γ curve, a smooth gradation is provided, or smoothing processing using surrounding pixels is performed and output to the image processing unit 7 shown in FIG. 1. The image processing unit 7 performs the above-described resolution conversion, size conversion, etc., and outputs it to the image output unit 6, and the image output unit 6 displays the image on the recording paper based on the image information sent from the image processing unit 7. Record and output.

Next, the operation will be described. When the receiving side facsimile apparatus 2 receives the code string transmitted from the transmitting side facsimile apparatus 1, the decoding section 8 decodes the code string and the kind of the decoded image. After performing image processing suitable for high-quality image output based on the characteristics, characteristics, etc., the image processing unit 7 performs necessary image processing such as resolution conversion and size conversion, and then the image output unit 6 prints the recording paper. Record and output.

Then, the decoding section 8 decodes / reproduces the input code string by the bit plane decoding section 20 by the coding method by the coding section 5 of the transmitting side facsimile apparatus 1, that is, the arithmetic coding method. And outputs it to the image creation unit 21 and the number-of-states statistics unit 23. That is, the bit plane decoding unit 20 sequentially performs decoding in bit plane units from the bit plane of the most significant bit, and when the decoding of one bit plane is completed, the bit plane decoding unit 20 performs the same decoding process on the bit plane one level below. Finally, the entire decoding is performed by sequentially performing the same decoding up to the lowest bit plane.

When the bit plane coding unit 20 completes the decoding for one bit plane, the state number statistics unit 23 counts the number of appearances for each state after decoding and outputs the count information to the image determination unit 24. . The state here generally refers to a state in which information sources are separated by a template used in the arithmetic coding method.

When the statistical processing in the number-of-states statistic section 23 is completed and the statistical information is input, the image determination section 24, based on the statistical information, specifically, the deviation of the number of appearances and the specific state. The type, characteristics, etc. of the image decoded by the bit plane decoding unit 20 are determined based on the number of appearances in the. According to an experiment by the applicant, generally, in a photographic image, the number of appearances in each state is average,
There is little variation between states. On the contrary, in the character image, the number of appearances in a specific state is large, and the variation between states is large. Further, in the character image, the character portion and the background portion are largely divided, so that the number of appearances of the specific state representing them becomes very large. Therefore,
By utilizing these properties, it is possible to determine whether the image is a gradation image like a photographic image or a line image like a character image. For example, if there is a large variation in the number of appearances for each state based on the statistical value of the number of appearances for each state, or if the number of types in which a state appears is relatively small, or if both of them are satisfied, then it is determined as a character image. can do. When the image determination unit 24 determines the type and characteristics of the image by the method described above, the image determination unit 24 outputs the determination result to the output processing unit 22.

The image for each bit plane unit decoded by the bit plane decoding unit 20 is output to the image creating unit 21, and the image creating unit 21 synthesizes the image for each bit plane unit to generate the entire image. An image is created and output to the output processing unit 22. The output processing unit 22 performs image processing on the image created by the image creating unit 21 based on the determination result input from the image determining unit 24, which is optimal for the image and optimal for the output characteristics of the image output unit 6. And output to the image processing unit 7. The image processing unit 7 performs necessary image processing and outputs it to the image output unit 6, and the image output unit 6 records and outputs an image on a recording paper based on the image information sent from the image processing unit 7. .

As described above, according to the facsimile apparatus 2 of the present embodiment, when a code string encoded by the JBIG system arithmetic encoding is decoded, there are many delicate gradation expressions like a halftone image. In this case, the number of appearances in each state is average, there is little variation between the states, and conversely, there are few pixels in the middle gradation and many pixels in the high level or low level gradation, such as in a character image. In particular, the number of appearances in a particular state is large, and paying attention to the large variation between states, when decoding and reproducing a monochrome multi-tone image from a code string encoded in bit plane units, At the end of decoding for each bit plane, statistical processing of the number of appearances for each state is performed, the type and characteristics of the decoded image are determined based on the number-of-appearance information for each state, and the image is output based on the determination result. Optimal It is doing the image processing.

Therefore, it is possible to decode a binary image, decode a monochrome multi-tone image, and output a high-quality multi-tone image.

6 and 7 are diagrams showing a second embodiment of the multi-gradation image decoding apparatus of the present invention. In this embodiment, the color component of one pixel is m bits, and the color accuracy is When a color image represented by n bits is decoded and reproduced from a code string encoded in bit plane units, the number of appearances in each state at the end of decoding for each bit plane in the first color component The statistical processing is performed to determine the type and characteristics of the decoded image based on the appearance count information for each state, and the optimal image processing for image output is performed based on the determination result. Corresponding.

The present embodiment is applied to the same facsimile machine as the first embodiment.

In FIG. 6, the decoding unit 30 includes a bit plane decoding unit 31, an image creating unit 32, a color component synthesizing unit 33,
Output processing unit 34, number-of-states statistics unit 35, and image determination unit 36
Etc. are provided.

The received coded color image information is input to the bit plane decoding unit 31, and this color code string has a color component number of m and a bit precision of n is a color image of JBIG system. It is a code string that is decomposed and encoded into m × n binary bit planes in bit order by an encoding method. As shown in FIG. 7, this code string is added with m, which indicates the number of color components of the input image, and n, which indicates the bit precision of the input image, at the beginning of the code string. Codes are arranged for each bit plane. The bit plane decoding unit 31 sequentially decodes the code sequence in bit plane units for each color component, and outputs the code string to the image creating unit 32 and the state number statistic unit 35. The bit plane decoding method in the bit plane decoding unit 31 is the same encoding method as the encoding method in the encoding unit 5 of the transmitting side facsimile apparatus 1, and the decoding is performed by the arithmetic encoding method.

The image creating section 32 creates an image for each color component based on the image for each bit plane reproduced by the bit plane decoding section 31, and outputs the image to the color component synthesizing section 33.

The color component synthesizing section 33 creates an entire color image from the image created by the image creating section 32 for each color component, and outputs the color image to the output processing section 34.

The state number statistic section (state number statistic means) 35 is
The bit plane decoding unit 31 performs statistical processing on the number of appearances for each state after decoding each bit plane, and outputs statistical information that is the statistical result to the image determination unit 36.

The image determination unit (image determination means) 36 determines the type and characteristics of the image decoded by the bit plane decoding unit 31 based on the statistical information input from the state number statistical unit 35, and the determination result Is output to the output processing unit 34.

The output processing section (output processing means) 34 determines the color image created by the color component synthesizing section 33 from the image determining section 36.
Image processing that is optimal for the image and optimal for the output characteristics of the image output unit 6 based on the determination result input from
For example, for a character image, the edge portion is emphasized by a γ curve as shown in FIG. 9, or the contour is smoothed by a smoothing process, and for a photographic image, a γ curve as shown in FIG. Is used to provide a smooth gradation, and smoothing processing using surrounding pixels is performed and output.

Next, the operation will be described. When the receiving side facsimile device 2 receives the code string transmitted from the transmitting side facsimile device 1, the receiving side facsimile device 2 decodes the code string and at the same time, the kind of the decoded image. The image processing unit 7 performs necessary image processing such as resolution conversion and size conversion after performing image processing suitable for the characteristics, characteristics, and the like, and then the image output unit 6 records and outputs the recording paper.

Then, the decoding section 30 decodes the input code string for each color component by the bit plane decoding section 31 by the coding method of the coding section 5 of the transmitting side facsimile apparatus 1, that is, the arithmetic coding method. -Reproduce and output to the image creation unit 32 and the number-of-states statistics unit 35. That is, the bit plane decoding unit 31 sequentially decodes the bit planes of the upper bits for each color component in bit plane units,
When the decoding of one bit plane of the first color component is completed, the same decoding process is performed on the bit plane one lower, and finally, the same decoding is sequentially performed up to the lowest bit plane, By performing the same process for the next color component, the entire decoding is performed.

When the bit plane encoding unit 31 completes the decoding of one bit plane of the first color component, the number-of-states statistics unit 31 counts the number of appearances for each state after decoding, and the count information is displayed as an image. It outputs to the determination unit 36.

When the statistical processing in the number-of-states statistics section 35 is completed and the statistical information is input, the image determination section 36 receives the statistical information and the type of the image decoded by the bit plane decoding section 31 and the like. The characteristics and the like are determined, and the determination result is output to the output processing unit 34.

The image for each bit plane unit decoded by the bit plane decoding unit 31 is output to the image forming unit 32, and the image forming unit 32 synthesizes the image for each color component on a bit plane unit basis. Then, an image for each color component is created and output to the color component combining unit 33. Color component synthesizer 3
3 synthesizes the images for each color component input from the image creating unit 32 to create a color image, and outputs the color image to the output processing unit 34.

The output processing unit 34 is optimal for the color image created by the color component synthesizing unit 33 based on the determination result input from the image determining unit 36, and outputs the image from the image output unit 6. Image processing suitable for the characteristics is performed and output to the image processing unit 7. The image processing unit 7 performs the above-mentioned resolution conversion, size conversion, etc., and outputs the result to the image output unit 6, and the image output unit 6 colors the recording paper based on the color image information sent from the image processing unit 7. Record and output the image.

As described above, according to the facsimile apparatus 2 of the present embodiment, when the code string of the color image coded by the arithmetic coding by the JBIG system is decoded, the gradation is delicate like a halftone image. When there are many expressions, the number of appearances in each state is average, there is little variation between the states, and conversely, there are few pixels with intermediate gradations such as character images and pixels with high or low level gradations. If there are many
Paying attention to the large number of appearances in a particular state and the large variation between states, when decoding and reproducing a color multi-gradation image from a code string encoded in bit plane units, At the end of decoding, the number of appearances for each state is statistically processed, the type and characteristics of the color image are determined based on the number of appearances information for each state, and the optimum for color image output based on the statistical information. Image processing.

Therefore, it is possible to decode a binary image, decode a color multi-gradation image, perform image processing suitable for high quality output, and output a high quality color image.

FIG. 8 is a diagram showing a third embodiment of a multi-gradation image decoding apparatus of the present invention. In this embodiment, a bit plane decoding unit and an image creating unit are provided for each color. It is intended to increase the processing speed.

This embodiment is applied to the same facsimile machine as that of the second embodiment, and in the description of this embodiment, the same reference numerals are given to the same components as those in FIG. Will be attached and detailed description thereof will be omitted.

In FIG. 8, the decoding unit 40 includes a code decomposing unit 41 and bit plane decoding units 31a, 31b and 31.
c, image creation units 32a, 32b, 32c, a color component synthesis unit 33, an output processing unit 34, a state number statistic unit 35, an image determination unit 36, and the like.

The code decomposition unit 41 decomposes the input code string into code strings for each color component, and the decomposed code strings for each color component are respectively bit-plane code units 31a, 31b, 31.
output to c.

Bit plane decoding units 31a, 31b, 3
1c is the same as the bit plane decoding unit 31 of the second embodiment, and in this embodiment, 1c is provided as many as the number of input color components. That is, the bit plane decoding unit 31a sequentially decodes the bit line unit code sequence of the first color component decomposed by the code decomposition unit 41,
It is output to the image creating unit 32a and the number-of-states statistics unit 35. Then, the state number statistic unit 35 is not connected to the bit plane decoding unit 31b and the bit plane decoding unit 31c, but only the image creating units 32b and 32c are connected.
Therefore, the bit plane decoding creation unit 31b sequentially decodes the bit line unit code string of the next color component,
The image is output to the image creation unit 32b, and the bit plane decoding unit 31 is output.
The c further decodes the code string of the next color component in bit plane units and outputs the code string to the image creating unit 32c.

The image creating sections 32a, 32b, 32c are the same as the image creating section 32 of the second embodiment, and in this embodiment, the number of input color components is provided. That is, the image creating unit 32a creates an entire image of the color component based on the image for each bit plane unit reproduced by the bit plane decoding unit 31a, and outputs the image to the color component synthesizing unit 33. The image creating unit 32b creates an entire image of the color component based on the image for each bit plane unit reproduced by the bit plane decoding unit 31b, and outputs the image to the color component synthesizing unit 33. An entire image of the color component is created based on the image for each bit plane unit reproduced by the bit plane decoding unit 31c and output to the color component synthesizing unit 33.

The color component synthesizing section 33 includes an image creating section 32a,
An entire color image is created from the images created for each color component in 32b and 32c and output to the output processing unit 34.

The number-of-states statistics unit 35 performs statistical processing of the number of appearances for each state after decoding each bit plane in the bit plane decoding unit 31a, and outputs statistical information as the statistical result to the image determination unit 36. To do. The image determination unit 36 determines the type and characteristics of the image subsequently decoded by the bit plane decoding unit 31 based on the statistical information input from the state number statistical unit 35, as in the second embodiment. Then, the determination result is output to the output processing unit 34. Output processing unit 34
Is similar to the above, the color image created by the color component synthesizing unit 33 is optimal for the image based on the determination result input from the image determining unit 36 and the output characteristic of the image output unit 6. Performs image processing and outputs.

Therefore, according to the present embodiment, when the color multi-gradation image is decoded and reproduced for each color component from the code string coded in bit plane units, the first color component At the end of decoding for each bit plane, statistical processing of the number of appearances for each state is performed, the type and characteristics of the code image are determined based on the number of appearances information for each state, and the image is output based on the determination result. Optimal image processing can be performed. As a result, the binary image can be decoded and the color multi-gradation image can be output with high image quality.

In each of the above embodiments, as described above, generally, in photographic images, there is not much difference in the number of appearances in each state, and the number of types of states that appear is large. On the other hand, in a character image, the number of appearances of a particular state is large, and the types of states that appear are small. Therefore, in each of the above-described embodiments, when the variation in the number of appearances for each state is large based on the statistical value of the number of appearances for each state, or when the number of types in which a state appears is relatively small, or both are satisfied. In this case, it is determined to be a character image.

However, utilizing the fact that the number of appearances of a particular state increases remarkably depending on the type of image, only the number of appearances of the particular state is statistically processed by the state number statistic units 23 and 35, and the image determination unit If the types and characteristics of images are determined by 24 and 36, the configurations of the number-of-states statistics units 23 and 35 and the image determination units 24 and 36 can be simplified, and the decoding units 8 and 30 can be performed. , 40, and thus the facsimile device 2 can be made inexpensive.

Further, since the character image is largely divided into the character portion and the background portion, the number of appearances of the states representing them increases, and only the appearance number of these specific states is statistically calculated by the state number statistic units 23 and 35. Image processing unit 24, 3
If the type and characteristics of the image are determined in 6, the state number statistical units 23 and 35 and the encoding determination units 24 and 36 can be made simpler, and the decoding units 8 and 3 can be configured.
It is possible to make the 0, 40, and thus the facsimile device 2 more inexpensive.

Further, in the case of a character image, the statistical processing of the number of appearances of only the characteristic states of the character image is performed only in the bit plane formed by the most significant bit to be encoded first. 35, and the image determination units 24 and 36 determine the type and characteristics of the image based on the appearance probability of the number of appearances, the state number statistical units 23 and 35 and the image determination units 24 and 36. Can be made even simpler, and the decoding units 8, 30,
40, and thus the facsimile apparatus 2 can be made even cheaper.

If it is determined that the image is a character image, the decoded image of the highest bit plane is duplicated as the image of the lower bit plane without decoding the lower bit plane. The processing speed of can be greatly improved.

Although the invention made by the present inventor has been specifically described based on the preferred embodiments, the present invention is not limited to the above, and various modifications can be made without departing from the gist thereof. It goes without saying that it is possible.

[0098]

According to the multi-gradation image decoding device of the first aspect of the present invention, when decoding a monochrome multi-gradation image from a code string coded in bit plane units and reproducing the same, At the end of the code, statistical processing of the number of appearances for each state is performed, and the type and characteristics of the decoded image are determined based on the number of appearances information for each state, and the optimal image at the time of image output based on the determination result. Processing can be performed, a binary image can be decoded, and a monochrome multi-tone image can be output with high image quality.

According to the multi-gradation image decoding device of the second aspect of the invention, when decoding and reproducing a color image from a code string coded in bit plane units, each bit plane in the first color component is reproduced. At the end of decoding, statistical processing of the number of appearances for each state is performed, and the type and characteristics of the decoded image are determined based on the number of appearances information for each state. Image processing can be performed, a binary image can be decoded, and a color multi-tone image can be output with high image quality.

According to the multi-gradation image decoding apparatus of the third aspect of the present invention, the statistical processing of only the statistical processing of the number of appearances of only a specific state is performed, and the type of the decoded image and the decoded image are calculated based on the statistical information. The characteristics and the like can be determined, and the number-of-states statistical means and the image determination means can have a simple structure. As a result, a multi-gradation image decoding device capable of outputting a high-quality image can be made simple and inexpensive.

According to the multi-gradation image decoding device of the fourth aspect of the present invention, the character image having a high density and the background having a low density are based on only the statistical processing of the number of appearances only in the characteristic state of the character image. A multi-gradation image decoding device capable of appropriately determining an image to determine whether or not it is a character image and capable of outputting a high-quality image has a simpler structure and is less expensive. It can be anything.

According to the multi-gradation image decoding apparatus of the fifth aspect of the present invention, only the most significant bit plane to be decoded first is subjected to the statistical processing of the number of appearances only in a predetermined characteristic state in the character image. , It is possible to determine whether or not the character image is a character image based on the number of appearances of a characteristic state in the character image, and a simpler multi-gradation image decoding device capable of performing high-quality image output. The structure can be made more inexpensive.

According to the multi-gradation image decoding apparatus of the sixth aspect of the present invention, when it is determined that the upper bit plane is a character image, the decoding process for the lower bit plane that is subsequently performed is not performed, and the decoding process is performed. For the bit planes that have not been subjected to the above, the decoded image of the highest bit plane is duplicated to reproduce the image, so that the decoding device for the multi-gradation image has a simpler structure and is more inexpensive. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of a transmission side and reception side facsimile apparatus to which a first embodiment of a multi-tone image decoding apparatus of the present invention is applied.

FIG. 2 is a general block configuration diagram of an arithmetic coding system of an encoding unit and a decoding unit in FIG.

FIG. 3 is an explanatory diagram of encoding processing by an arithmetic encoding method.

FIG. 4 is a detailed block configuration diagram of a decoding unit in FIG.

5 is a diagram showing an example of a code string input to the decoding unit in FIG.

FIG. 6 is a block configuration diagram of a decoding unit of a facsimile apparatus to which a second embodiment of a multi-tone image decoding apparatus of the present invention is applied.

7 is a diagram showing an example of a code string input to the decoding unit in FIG.

FIG. 8 is a block configuration diagram of a decoding unit of a facsimile device to which a third embodiment of a multi-tone image decoding device of the present invention has been applied.

FIG. 9 is a diagram showing an example of a γ curve when performing image processing on a character image.

FIG. 10 is a diagram showing an example of a γ curve when performing image processing on a photographic image.

[Explanation of symbols]

 1 Facsimile device on the sending side 2 Facsimile device on the receiving side 3 Image reading unit 4, 7 Image processing unit 5 Encoding unit 6 Image output unit 8 Decoding unit 9 Transmission unit 10, 12 Prediction information creating circuit 11 Arithmetic encoding circuit 13 Arithmetic decoding Decoding circuit 20, 31, 31a to 31c Bit plane decoding unit 21, 32, 32a to 32c Image creation unit 22, 34 Output processing unit 23, 35 State number statistic unit 24, 36 Image determination unit 33 Color component synthesis unit 41 Code decomposition Department

Claims (6)

[Claims] 1. A black-and-white multi-tone image represented by n bits per pixel is decomposed into n bit planes for each bit order, and a code string encoded for each bit plane unit is sequentially arranged for each bit plane unit. Bit plane decoding means for decoding and reproducing image information, state number statistical means for performing statistical processing of the number of appearances for each state after decoding in the bit plane decoding means, and statistical information for the state number statistical means Image determination means for determining the type and characteristics of the decoded image based on
An image creating unit that creates an entire image based on the image information for each bit plane reproduced by the bit plane decoding unit, and an image created by the image creating unit based on the determination result of the image determining unit. A multi-gradation image decoding device, comprising: an output processing unit that performs a predetermined image process for outputting a high-quality image. 2. A code string obtained by decomposing a color image in which the color component of one pixel is m bits and the color accuracy is n bits into m × n bit planes and encoding for each bit plane unit. From the bit plane decoding means for sequentially decoding the image information in units of the bit planes, and at the time of decoding the first color component, statistical processing of the number of appearances for each state after decoding by the bit plane decoding means is performed. Based on the number-of-states statistics means, an image determination means for determining the type and characteristics of the decoded image based on the statistical information of the number-of-states statistics means, and the image information for each bit plane reproduced by the bit plane decoding means. An image creating means for creating an image for each of m color components; a color component combining means for creating an entire color image based on the image for each color component created by the image creating means; Output processing means for performing a predetermined image processing for outputting a high quality image to the color image created by the color component synthesizing means based on the determination result of the image determining means. A gradation image decoding device. 3. The number-of-states statistical means performs statistical processing on the number of appearances of only a certain specific state, and the image determination means determines the type and characteristics of the image from information of the number of appearances of the certain specific state. Claim 1 characterized by the above.
Alternatively, the multi-tone image decoding device according to claim 2. 4. The number-of-states statistical means performs a statistical process of the number of appearances of only a state having a predetermined characteristic in a character image, and the image determination means is a character image based on the statistical information of the number-of-states statistical means. 4. The multi-gradation image decoding device according to claim 3, wherein it is determined whether or not there is. 5. The number-of-states statistic means statistically processes the number of appearances of only characteristic states in the character image only in the most significant bit plane to be decoded first, and the image determination means determines the state. 5. The multi-gradation image decoding device according to claim 4, wherein it is determined whether or not the image is a character image based on the statistical information of the number statistical means. 6. The bit plane decoding means, when the image determining means determines that the image is a character image, does not perform subsequent decoding processing on the lower bit plane, and the image creating means does the decoding processing. 6. A multi-gradation image decoding device according to claim 4, wherein the image is reproduced by copying the highest bit plane of the bit planes that have not been processed.