JP2000307879A - Method and device for color image communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of a binary image such as a character image by reducing mosquito noise, that occurs when JPEG type coding and decoding are performed in communication equipment which handles color images. SOLUTION: This color image communication equipment decides the image area of a mixed image to a luminance signal in a color component signal in a decision circuit 1070, quantizes a halftone image by using a quantization reference value (a), quantizes binary image data by using a qunatization reference value (b) (a<b) and transmits them. A receiving side performs asymmetrical inverse quantization of the binary image data by using a reference value, whose value is the same as the value (a) and clamps a part which protrudes outside the dynamic range of luminance by a clamping circuit 1132.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image communication method and a color image communication apparatus, and more particularly to a color image communication method for communicating an image in which a halftone image such as a photograph and a binary image such as a character and a line drawing are mixed. And a color image communication device.

[0002]

2. Description of the Related Art As a coding method of a halftone image such as a photograph, a discrete cosine transform (DCT:
Transform coding using Discrete Cosine Transform is widely used. Transform coding converts a two-dimensional array of images into a two-dimensional array of spatial frequency components using an orthogonal function such as DCT.

[0003] Natural images, such as portraits and landscape photographs, have a high adjacent correlation between pixels, and therefore have many low spatial frequency components and relatively few high spatial frequency components. On the other hand, it is known that even if the high spatial frequency component is roughly approximated, the deterioration of the image quality is not noticeable, and the data amount can be reduced by finely quantizing the low spatial frequency component and coarsely quantizing the high frequency component.

Since each quantized frequency component follows a probability distribution corresponding to image information, it is necessary to use a Huffman code or an arithmetic code to compress the number of bits asymptotically to the entpy determined by the probability distribution and the code symbol without impairing the information. Can be.

[0005]

However, when JPEG encoding is performed on a mixed image, mist noise (mosquito noise) appears around the edges of the restored image. This occurs because a binary image such as a character image has many high spatial frequency components due to an edge portion, and the high frequency components are lost by quantization.

[0006] Such noise is not bothersome on the display, but when error diffusion processing (for example, halftone processing) is performed to print out with a binary output printer, the area gradation is preserved and the edge is saved. Black pixels appear as isolated points in the periphery and become apparent, deteriorating the image quality.

The present invention has been made in view of such a problem, and greatly reduces the deterioration of the image quality of a binary image (such as a character image) that occurs when JPEG encoding and decoding are performed. An object of the present invention is to remarkably improve the image quality of a restored image (especially, an image in which photographs and characters are mixed).

[0008]

According to a first aspect of the present invention, there is provided a color image communication method for separating a color image into a luminance signal and a color difference signal, and determining whether the luminance signal is a halftone image or a binary image. Judgment, the data judged to be data for the binary image is quantized using the first quantization reference value to obtain a quantization value, and the quantization value is encoded and transmitted.
After decoding the transmitted code, inverse quantization is performed using a reference value larger than the first quantization reference value.

[0009] In this method, quantization is asymmetrical between the transmitting side and the receiving side. The image quality degradation of the binary image is caused by the fact that there is a light gray pixel near a white pixel or a dark gray pixel near a black pixel, and the boundary between white and black becomes unclear. In the case of the method of the present invention, on the receiving side, the dynamic range of the luminance is widened as compared with the case of symmetric quantization, so that an appropriate white level or black level is set, and anything exceeding the level is converted to white or black. Can be determined. As a result, there is no pixel having a slightly different luminance near the black pixel or the white pixel, a sharp edge is obtained, and the image quality is improved.

According to a second aspect of the present invention, there is provided a color image communication apparatus comprising:
The color image is separated into a luminance signal and a color difference signal, and it is determined whether the data for the luminance signal is a halftone image or a binary image. To obtain a first quantized value, and in the case of data of a binary image, quantize using a second quantized reference value to obtain a second quantized value. The identification information and the first and second quantized values are encoded by an encoding unit and transmitted. On the receiving side, the transmitted code is decoded by a decoding unit, and then the identification The attribute of the decoded data is identified by referring to the information, and the decoded data corresponding to the first quantized value is dequantized using the same reference value as the first quantized reference value. , The decoded data corresponding to the second quantized value is the second quantity Was such that the inverse quantization using a reference value of a value greater than the referential value.

In the case of performing encoding (decoding) including a quantization process on a mixed image, for example, a halftone image and a binary image are distinguished from each other, and the processing of a binary image whose image quality tends to deteriorate is asymmetrically quantized. By introducing such a new process, both the halftone image and the binary image can be clearly restored.

According to a third aspect of the present invention, there is provided a color image communication apparatus, comprising: separating means for separating a color image into a color component signal of a luminance signal and a color difference signal; and whether the luminance signal data is data on a halftone image. Determining means for determining whether the data is a binary image, orthogonal transform means for orthogonally transforming the luminance signal data, and selecting a quantization reference value according to a result of the determination by the determining means; A quantizing means for quantizing a transform coefficient output from the orthogonal transform means using a quantized reference value; and an encoding means for encoding a quantized value output from the quantizing means and determination information by the determining means. Means for transmitting data, decoding means for decoding the transmitted code, and determining the attribute of the data based on the determination information. Inverse quantization is performed using a reference value having the same value as the quantization reference value used at the time of quantization, and data about a binary image is larger than the quantization reference value used at the time of quantization. Inverse quantization means for performing inverse quantization using a reference value of the value, inverse transformation means for performing inverse transformation of the orthogonal transformation, and composition means for composing each color component signal inversely transformed by the inverse transformation means And a reception processing means having the following.

[0013] A new image communication apparatus is realized in which both the transmission system and the reception system have a function of identifying the attribute of image data, and can perform asymmetric quantization on data of a binary image. .

According to a fourth aspect of the present invention, in the color image communication apparatus according to the third aspect, the color image communication apparatus includes an image reading unit, a color image forming unit, and a modem functioning as a communication interface. This is realized as a facsimile machine having the following.

As a result, a high-performance facsimile apparatus capable of reproducing a clearer image than before can be obtained while satisfying the requirements of compactness and low price.

[0016]

Next, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram for explaining a configuration of a color image communication apparatus according to an embodiment of the present invention and a color image communication method using the apparatus.

In FIG. 1, 10
Is a color image separation circuit for separating a color image into component signals of a luminance signal and a color difference signal. The color space is used for, for example, commonly used La * b * and YCbCr. The separated color component signals are stored in a luminance signal (L) memory 11, a color difference signal (a *) memory 12, and a color difference signal (b *) memory 13, respectively. 14
Is a selector, which switches the outputs of the memories 11 to 13 and supplies them to the encoding processing device 1000a. Details of the encoding processing device 1000a will be described with reference to FIG.

Next, as a configuration on the receiving side, a decoding processing device 1000b decodes the color component signals and stores the color component signals via the selector 17 in the opposite direction to the transmitting side. As a result, the luminance signal L is stored in the memory 1
8, the color difference signal a * is restored to the memory 19, and the color difference signal b * is restored to the memory 20. Reference numeral 21 denotes a color synthesizing circuit, which synthesizes a color image from the restored luminance signal and color difference signal.

FIG. 2 is a block diagram of the encoding processing apparatus 10 shown in FIG.
00a and a configuration diagram of a decryption processing device 1000b.

A feature of the present embodiment is that, for read image data, it is determined whether an area from which the data is cut out is a binary image area or a halftone area, and the determination result is also encoded. To transmit the binary image data, quantization and inverse quantization are asymmetrically performed using different reference values to realize sharp edge restoration of the binary image.

In the figure, reference numeral 1000a indicates an encoding processing device on the transmitting side, and reference numeral 1000b indicates a decoding processing device on the receiving side. The encoding processing device 1000a includes a wired transmission path L
1 to the decoding device 1000b.

The coding processing apparatus 1000a includes a blocking circuit 1010, a two-dimensional DCT circuit 1020, a quantization circuit 1030, an arithmetic encoder 1040, a multiplier 1050 for multiplying a reciprocal of a scaling factor, and a scaling factor selection circuit. Means 1060 and image area determining means 107
0 and a quantization table 1080.

Blocking means 1010 reads image data from an image memory (not shown) and blocks the image data into a two-dimensional array Pj, k (j, k = 0 to 7) of 8 × 8 pixels. In the following description, each pixel has 256 gradations.

The image area determination circuit 1070 determines whether the target block is a binary image such as a character or not (that is,
Is determined as to whether the block is a halftone block such as a photograph or the like, and identification information (block identification information) 1090 indicating the determination result is output to the scaling factor selection unit 1060 and the arithmetic encoder 10.
Send to 40. Here, as shown in FIG. 1, when a color component signal is input, the image area determination is performed on the luminance component. Then, this determination result is applied to the corresponding color difference signal.

Basically, the image area is determined by looking at the luminance distribution of the pixels in the block. However, even after determining that the image is a binary image, the image may be further classified into a plurality of types by judging whether there are many edges in the horizontal direction or many edges in the vertical direction. In this case, a quantization table and a scaling factor corresponding to the classification number are prepared. In addition, when a block of interest is determined in consideration of not only pixels in one block but also attributes of surrounding blocks (whether it is a block of a halftone image or a block of a binary image), Accurate judgment can be made.

The two-dimensional DCT circuit 1020 has a pixel array P
With respect to j and k, using the intermediate value 128 as an offset, (Pj, k-1
28) is subjected to a two-dimensional discrete cosine transform. The resulting transform coefficients represent spatial frequency components, and will be represented as Sj, k (j, k = 0 to 7).

The transform coefficients are quantized by a quantization circuit 1030 with reference to a quantization reference value (Qj, k / aj or Qj, k / bj) for each transform coefficient. That is, quantization is a process of dividing a transform coefficient by a quantization reference value and rounding down a fraction (rounding data).

The quantization reference value is a unit used as a reference when quantization is performed by the quantization circuit 1030. Although the table value of the quantization table 1080 can be used as it is as the quantization reference value, in the present embodiment, a scaling factor is prepared in order to perform adaptive processing efficiently, and the stored value of the quantization table 1080 is stored. (Quantization table value) is multiplied by the reciprocal of the scaling factor to obtain a quantization reference value.

In this embodiment, two types of scaling factors aj and bj (aj <bj) are prepared and used for processing a halftone image and for processing a binary image. The scaling factor selection circuit 1060 performs such use of the scaling factor.

That is, the scaling factor selection circuit 1060 selects whether to use a plurality of predetermined scaling factors [aj] or {bj} according to the determination result of the image area determination circuit 1070. I do. For example, when the scaling factor is aj, quantization is performed using an integer value obtained by dividing all values Qj, k set in the quantization table by aj. It should be noted that when aj and bj are increased, the image quality is improved and the code amount is also increased.

FIG. 3 shows an example of the values (quantization table values) stored in the quantization table 1080. As shown in the drawing, fine quantization is performed around a DC (direct current) component, and coarse quantization is performed for a high frequency component.

Arithmetic encoder 1040 arithmetically encodes the quantized data (quantized value) and the identification information indicating the image area determination result, and transmits the encoded data.

On the other hand, the decryption processing device 1000b on the receiving side
Is an arithmetic decoder 1110, an inverse quantization circuit 1120,
It comprises a two-dimensional IDCT (inverse DCT) transform circuit 1130, a clamp circuit 1132, a block restoration circuit 1140, a scaling factor selection circuit 1150, a quantization table 1160, and a multiplier 1170 for multiplying the reciprocal of the scaling factor. , Decoding is performed to restore image data.

Here, it should be noted that the inverse quantization circuit 1
The reference value in the inverse quantization at 120 is Qj, k / aj, and the clamp processing of the luminance level using the clamp circuit 1132 is performed after the two-dimensional inverse DCT processing.

That is, the halftone image data is quantized using the quantized reference value Qj, k / aj, and inversely quantized using the same reference value Qj, k / aj. Processing is performed. Therefore, a good halftone image is reproduced by encoding and decoding by the JPEG method.

On the other hand, for the binary image data, quantization is performed using the quantization reference value Qj, k / bj, and inverse quantization is performed using the reference value Qj, k / aj having a larger value. And therefore an asymmetric process.

This asymmetric processing is described with reference to FIGS.
This will be specifically described with reference to FIG. FIG.
(C) is a diagram (luminance histogram) showing the luminance distribution of the restored image.

Normally, quantization and inverse quantization are designed symmetrically for encoding and decoding. That is, the same reference value as used when quantization is used in inverse quantization. Assuming that b is used as a scaling factor, at the time of encoding, the DCT coefficient Sj, k is divided by Qj, k / b and converted into an integer as follows.

QSj, k = round (Sj, k / round (Qj, k / b)) (1) In equation (1), round represents a rounding process of a fraction. On the other hand, on the receiving side, QSj, k is decoded, and round (Qj, k / b)
And inverse quantization. As a result, Sj, k is changed to round (Qj, k /
The value quantized in b) can be reproduced. At this time, the quantization error is equal to or less than round (Qj, k / b). Sj, k <round (Qj, k / b)
Is zero. Then, the luminance value (DPx, y) of the pixel restored after the inverse DCT transform is obtained by calculating Gx, y by the inverse D
Assuming that the orthogonal function represents CT, it is expressed as follows except for a constant multiple.

DPx, y = ΣΣQSj, k · Gx, y (2) Conventionally, symmetric quantization and inverse quantization have been performed in this manner. However, as far as binary images are concerned, DPx, y is −1
It should have valid values around 28 (gradation 0) and +127 (gradation 255), which appear as mosquito noise. This state is shown in FIG.

Next, a case where a value a smaller than the quantization is selected as the scaling factor for the inverse quantization as in the present embodiment will be considered. By the inverse quantization, the above (1)
In the formula, round (Qj, k / a) is multiplied by r
ound (Qj, k / b), the signal component QSj,
k is larger than the encoding side. Here, since the orthogonal function Gx, y for inversely converting to an image signal is the same, the spatial frequency of the image is the same, and the dynamic range of luminance is expanded. This state is shown in FIG. When a binary image is processed in this way, the binary nature becomes more pronounced.

Then, when 128 is added to DPx, j and cut off (clamped) at the normal gradations "255" and "0", the signal component serving as noise is regarded as "white" or "black".
Forcibly converge to the level of the gradation "255" or "0". This state is shown in FIG.

As a result, mosquito noise is eliminated. The gain of this dynamic range is substantially b / a (b> a). In this way, JPEG
Even when encoding and decoding are performed in a system, a significantly better binary image can be reproduced than in the past.

As a result of the experiment, it was found that when a = 1.0 and b = 2.0, no mosquito noise appeared and an ideal binary image with clear edges was reproduced.

When a = 1.0 and b = 1.2 to 1.5, a slight halftone component appears in the character outline. However, the mosquito noise could be eliminated in this case as well. If there is a misjudgment in the photographic area, the image quality will deteriorate, so in reality, a = 1.0, b = 1.2 ~
Around 1.5 is considered appropriate.

FIG. 5 summarizes the procedure of the transmission process (block encoding process) described above.

That is, after inputting the block image and calculating the statistic (step 2010), the image area of the block is determined (step 2020), and the intermediate value 128 is subtracted from the pixel value. Step 2030). Subsequently, if it is determined that the area is a binary area (step 2040), “1” is selected as a flag indicating that (step 2050), and quantization is performed using the scaling factor b (step 2040). 206
0). On the other hand, if it is determined in step 2040 that the area is not a binary area, “0” is selected as a flag indicating that (step 2070), and quantization is performed using the scaling factor a (step 2080). Subsequently, coding of DC coefficients (DC components) and coding of AC coefficients are performed (steps 2090 and 2100).

FIG. 6 summarizes the procedure of the decoding process on the receiving side.

That is, the arithmetic decoder 1110 of FIG.
First, a symbol indicating the attribute of the block (that is, “1”)
Or "0") is decoded, and it is determined which block it is based on the value.

Steps 2130 and 2140 are DC components,
Decoding of the AC component. Then, it is determined whether the area is a binary area (step 2150), and in either case, inverse quantization is performed using the scaling factor “a” (step 2150).
160, 2170). In other words, Qj, k
Performs processing to multiply / aj. Subsequently, a cosine inverse transform operation is performed, and 128 is added to the value to obtain a restored pixel DPj, k (step 2180). Next, the clamp circuit 113
2 performs a luminance level clamping process (step 21)
90). That is, the restored pixel DPj, k is cut off at the luminance level 255 and the luminance level 0, and if DPj, k is larger than 255,
If it is smaller than 5, 0, it is set to 0. Otherwise, leave DPj, k. Thus, the restoration of one block is completed. By such a process, an adaptive process of finely quantizing a binary image block and coarsely quantizing a halftone block can be easily realized.

In FIG. 2, an arithmetic coder is used as the coder. The coder uses identification information indicating an image area determination result and DCT transform coefficients (information of different types).
This is because arithmetic codes can be unified and transmitted, the code amount can be reduced, and the decoding process is simplified.

However, the present invention is not necessarily limited to this, and entropy coding methods other than arithmetic codes, for example, Huffman coding as shown in FIG. 6 can be adopted.

In the communication apparatus shown in FIG. 7, as in the case of FIG. 2, the image area determination and the asymmetric quantization and the inverse quantization of the binary image data are performed in the same manner. The transmitting device includes a blocking circuit 5010 and a two-dimensional DCT.
It has a circuit 5020, a quantization circuit 5030, a scaling factor selection circuit 5060, an image area determination circuit 5070, and a quantization table 5080, which are the same as those in FIG.

In the receiving apparatus, the scaling factor selection circuit 5150, the inverse quantization circuit 5120,
Two-dimensional IDCT circuit 5130, block image restoration circuit 5
The point having 140 is also the same as FIG.

However, when encoding is performed using the Huffman encoder 5040, a process of multiplexing the identification flag data and the transform coefficient data by the multiplexing circuit 5050 is required. In response to this, it is necessary to provide an information separating circuit 5100 on the receiving side and perform a process of separating information.

(Embodiment 2) FIG. 8 is a diagram for explaining the contents of an image communication method and an image communication apparatus according to Embodiment 2.

The device on the transmitting side in FIG.
010, a two-dimensional DCT circuit 6020, and a quantization circuit 6
030, an encoder 6040 using an arithmetic code, a Huffman code or the like, and a scaling factor selection circuit 6060
, Image area determination circuit 6070 and quantization table 6080
And a multiplier 6050. On the receiving side, a decoder 6110, an inverse quantization circuit 6120, and a two-dimensional ID
It includes a CT circuit 6130, a clamp circuit 6132, a block restoration processing circuit 6140, an automatic scaling factor selection circuit 6150, a quantization table 6160, and a multiplier 6170.

As shown, the basic configuration of the communication device is the same as that of FIG. 2, and an image area is determined on the transmitting side.
Quantization is performed using a different scaling factor according to the determination result.
The point that the inverse quantization is performed is common to the above-described embodiment.

However, in this embodiment, the image area determination result is not transmitted, and the receiving side uses a predetermined reference value (a reference value determined independently of the image area determination) without performing the image area determination. This is different from the above-described embodiment in that inverse quantization is performed.

That is, in the above-described embodiment, the scaling factor “a” or “b (>”
a) ”, and the receiving side performs inverse quantization using the scaling factor“ a (<b) ”. Therefore, at the time of inverse quantization on the receiving side, identification information of the image attribute is basically unnecessary.

That is, there are two types of scaling factors (that is, quantization reference values) used, and the scaling factor (reference value) used for decoding is the scaling factor (quantization reference value) used for quantization. In the case where it matches one of the reference values, decoding can be performed on the receiving side without identification information.

From such a viewpoint, in the present embodiment,
It was decided not to send identification information. On the decoding side, inverse quantization is performed using “a reference value determined independently of identification information”. Here, the "reference value determined independently of the identification information" is a reference value uniquely determined regardless of the image area determination result on the transmission side. As a method of the determination, a scaling factor used for inverse quantization is determined in advance, or a method of selecting a scaling factor used for inverse quantization is determined in advance.

In the present embodiment, “2 used for quantization
The inverse quantization is performed using the smaller one of the two scaling factors aj and bj. " Since aj <bj, aj is eventually selected,
Inverse quantization is performed using this aj.

In this embodiment, since there is no need to transmit identification information, even if an entropy coding method other than an arithmetic code such as a Huffman coding method is adopted, the multiplexing as shown in FIG. There is no need for a conversion process, and there is no concern about an increase in the code amount. Therefore, various coding methods can be adopted without any problem.

Further, since a special configuration is not required as the decoding processing circuit, the same IC as that of the conventional device can be used, which is also convenient.

FIG. 9 summarizes the decoding procedure in this embodiment. That is, DC component, AC
The components are restored (steps 6200 and 6210), and a predetermined rule selected by an agreement between the encoder and the decoder (in this embodiment, an agreement to use the smaller one of the scaling factors used for quantization). Inverse quantization is performed using the scaling factor (step 622).
0). Subsequently, inverse cosine transform is performed (step 623).
0), a predetermined clamping process is performed (6240).

(Embodiment 3) FIG. 10 shows Embodiment 3 of the present invention.
1 shows a configuration of an image communication apparatus according to the first embodiment. In the case of FIG. 10, since the configuration is almost the same as that of the apparatus of FIG. 2, the same parts as those of FIG. 2 are denoted by the same reference numerals.

The feature of this embodiment is that the decoding side
Selector 1160 and binary block image processing circuit 1170
And a halftone block image processing circuit 1180, which sends information indicating the attribute of the block restored by the arithmetic decoder 1110 to the selector 1160, and converts the data restored by the selector 1160 into binary data for each block. The purpose is to separate image data and halftone data, perform special processing on each of them, and further improve the image quality of the restored image.

In the binary block image processing circuit 1170,
The restored binary data is subjected to, for example, edge emphasis processing to make edges of characters and the like visible. Or,
Regarding the removal of mosquito noise on the restoration side, the threshold level for clamping the restoration pixel to white and black is set to 2 using constants α and β instead of 255 and 0 used in the above-described embodiment.
The noise removal effect can also be improved by transforming to 55-α, β.

The halftone block image processing circuit 118
A value of 0 performs, for example, filtering on the restored halftone image to reduce fine noise.

As described above, the decoding side utilizes the fact that the attributes of each transmitted block can be known, and adaptive processing such as filtering of a restored image according to a binary image or a halftone image is performed. And the image quality of the restored image is further improved in combination with the effects of the above-described nonlinear quantization and inverse quantization.

(Embodiment 4) FIG. 11 shows Embodiment 4 of the present invention.
1 is a diagram showing a configuration of a facsimile apparatus according to the first embodiment.

The facsimile apparatus 101 shown in FIG. 11 includes a host processor 102, an MH / MR / MMR encoding / decoding circuit 103, a resolution conversion circuit 104, a color CO
A DEC 105, an image line memory 106, a code memory 107, a communication interface such as a modem (functioning as an interface for wired transmission using a telephone line 113 or the like), and an image input device 111 such as a scanner.
And an image recording / display device 112 such as a printer. Each of the blocks can exchange information with each other via the internal buses 109 and 110.

The circuit for performing the encoding and decoding described in the above embodiment is mounted on the color CODEC 105.

Since the encoding / decoding circuit according to the present invention has a simplified configuration, it can be sufficiently mounted even in a facsimile apparatus which requires miniaturization and cost reduction, and is widely used. This contributes to improving the image quality of the device.

Although the present invention has been described with reference to the four embodiments, the present invention is not limited to this, and the present invention can be variously modified. For example, when it is known that the image to be transmitted is an image of only characters, encoding / decoding (non-linear quantization, inverse quantization) may be performed without performing image area determination.

[0078]

As described above, according to the present invention, 2
Mosquito noise generated when encoding and decoding the value image using the JPEG method is greatly reduced, and the image quality of the restored image can be remarkably improved. Further, even when a halftone image such as a photograph and a binary image such as a character are mixed, each image area is determined and an appropriate process is performed on each image area.
Good images can be reproduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a color image communication device according to the present invention.

FIG. 2 is a block diagram showing a main configuration of the color image communication apparatus according to the first embodiment of the present invention;

FIG. 3 is a diagram illustrating an example of a quantization table value;

FIG. 4A is a diagram showing luminance distribution of pixels when symmetrical quantization and inverse quantization are performed on binary image data; FIG. 4B is asymmetrical quantization on binary image data; The figure which shows the luminance distribution of the pixel when performing inverse quantization (c) The figure which shows the luminance distribution of the pixel after clamping

FIG. 5 is a diagram illustrating a procedure of an encoding process of the color image communication apparatus according to the first embodiment;

FIG. 6 is a diagram showing a procedure of a decoding process of the color image communication device according to the first embodiment;

FIG. 7 is a diagram illustrating a configuration of a modification of the color image communication apparatus according to the first embodiment;

FIG. 8 is a diagram showing a main configuration of a color image communication apparatus according to a second embodiment of the present invention;

FIG. 9 is a diagram showing a procedure of a decoding process according to the second embodiment;

FIG. 10 is a diagram showing a main configuration of a color image communication apparatus according to a third embodiment of the present invention;

FIG. 11 is a diagram showing a configuration of a facsimile apparatus according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1010 Image block processing unit 1020 Two-dimensional DCT converter 1030 Quantizer 1040 Arithmetic encoder 1050 Multiplier 1060 Scaling factor selection circuit (encoding side) 1070 Image area determination circuit 1080 Quantization table 1090 Quantization table identification information ( Block identification information) 1110 arithmetic decoder 1120 inverse quantizer 1130 two-dimensional inverse DCT converter 1140 block restored image 1150 scaling factor selection unit (decoding side) 1160 quantization table 1170 multiplier

Continued on front page F term (reference) 5C075 CA90 FF02 FF04 5C077 LL02 LL18 LL19 MP06 MP07 MP08 PP23 PP27 PP28 PP36 PP47 PP49 PP66 PQ08 PQ23 RR01 RR16 RR21 5C078 AA09 BA21 CA22 5C079 HA02 HB08 LA06 LA27 LA27

Claims (4)

[Claims] 1. A color image is separated into a luminance signal and a color difference signal, an image area is determined for the luminance signal as a halftone image or a binary image, and data determined as data for the binary image is determined as first data. Quantized using the quantized reference value to obtain a quantized value,
The quantized value is encoded and transmitted, and on the receiving side, after decoding the transmitted code, inverse quantization is performed using a reference value larger than the first quantized reference value. Color image communication method. 2. A color image is separated into a luminance signal and a color difference signal, and it is determined whether the data for the luminance signal is a halftone image or a binary image. A first quantized value is obtained by performing quantization using a quantized reference value, and in the case of binary image data, a second quantized value is obtained by performing quantization using a second quantized reference value. The identification information indicating the determination result and the first and second quantized values are encoded by an encoding unit and transmitted. On the receiving side, the transmitted code is decoded by a decoding unit. The attribute of the decoded data is identified by referring to the identification information indicating the determination result, and a reference value having the same value as the first quantization reference value is assigned to the decoded data corresponding to the first quantization value. And the decoded data corresponding to the second quantized value A color image communication method, characterized in that inverse quantization is performed using a reference value larger than the second quantization reference value. 3. A separating means for separating a color image into color component signals of a luminance signal and a color difference signal, and determining whether the luminance signal data is data of a halftone image or data of a binary image. Determining means, an orthogonal transform means for orthogonally transforming the luminance signal data, and selecting a quantization reference value according to a determination result by the determination means, and using the selected quantized reference value, the orthogonal transform means A transmitting means comprising: a quantizing means for quantizing a transform coefficient outputted from the encoding means; and a coding means for coding a quantized value outputted from the quantizing means and decision information by the decision means. Decoding means for decoding the encoded code, and the attribute of the data is determined based on the determination information, and the data for the halftone image is the same as the quantization reference value used in the quantization. Inverse quantization is performed using the reference value of the value, and the data about the binary image is inversely quantized using the reference value having a value larger than the quantization reference value used in the quantization. Color image communication comprising: a conversion unit; an inverse conversion unit that performs an inverse conversion of the orthogonal conversion; and a synthesis unit that synthesizes each color component signal that has been inversely converted by the inverse conversion unit. apparatus. 4. The color image forming apparatus according to claim 3, wherein the color image communication device is a facsimile device including an image reading unit, a color image forming unit, and a modem functioning as a communication interface. Image communication device.