JPH10108027A - Still image transmission method and still image transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of transmission data and to shorten transmission time, even in the case of fixing the method of encoding by executing error spreading dither after reducing respective lines for constituting images, enlarging them to original sizes and performing MH encodings. SOLUTION: When an image input means 1 reads the images of a graycale and stores them in a frame memory 2, a CPU 3 reduces and converts the stored images to 1/2 for each line and stores them in a RAM 4. Then, the CPU 3 executes the error spreading dither to 1/2 reduced data, stores them in the RAM 4, enlarges and converts dither data to be doubled for each line, stores them in the RAM 4, MH encodes enlarged data and stores them in the RAM as facsimile data. Then, a modem 5 transmits the stored facsimile data through a telephone line. Thus, the images for which at least two pixels continuously become black or white are MH encoded, encoding efficiency is improved, a transmission data amount is reduced and the transmission time is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a still image transmission method and a still image transmission apparatus for transmitting transmission data encoded by a fixed encoding method such as a facsimile (hereinafter, "FAX"). In particular, reducing the amount of transmitted data,
The present invention relates to a still image transmission method and a still image transmission device that can reduce transmission time.

[0002]

2. Description of the Related Art In a fixed coding method, coding efficiency may be significantly reduced. Here, a facsimile will be described as an example of still image transmission employing such a fixed encoding method. The FAX standard is ITU-
In the so-called G3 FAX, which has been determined based on the recommendation of T and has been widely used in recent years, an encoding method for encoding an image is fixed. That is, the code is not adaptively changed according to the content of the image.

A conventional still picture transmission apparatus will be described with reference to FIG. FIG. 2 is a configuration block diagram of a conventional still image transmission device. As shown in FIG. 2, a conventional still image transmission apparatus includes an image input unit 1, a frame memory 2, a CPU,
3, a RAM 4, and a modem 5. In addition, as a facsimile, the image input means 1
Although there is a configuration that outputs a synchronization signal according to the reading speed, the overall configuration is described here.
They have been omitted.

Next, the function of each part will be described in detail. The image input means 1 is usually an optical scanner,
The still image is read and stored as digital data (hereinafter, “still image data”) in the frame memory 2. Here, the still image data stored in the frame memory 2 is often so-called gray scale data having only lightness (luminance value), but even if it is color, there is no significant change in the following description. .

[0005] The CPU 3 binarizes the still image data stored in the frame memory 2 and stores it as bit image data in the RAM 4. The CPU 3 further encodes the bit image data into MH (Modified Huffman) to generate facsimile data. The data is converted and output to the modem 5.

Although there are various binarization processes, it is common in FAX to employ error diffusion dither. The error diffusion dither method will be described later. The MH encoding will be described later. The modem 5 transmits facsimile data via a telephone line.

Here, a method of binarization processing using error diffusion dither in the CPU 3 will be described with reference to FIG. FIG. 3 shows an example of the error diffusion dither 2 in the CPU 3.
It is a flowchart figure of the method of a value process. In the following description, the CPU 3 includes a register indicating an error (referred to as an “error register”), a register indicating a calculated luminance (referred to as a “calculated luminance register”), and a register indicating an original luminance (“an original luminance register”). ). Here, the original luminance indicates the read luminance value itself for each pixel.

The CPU 3 first substitutes "0" into a register indicating an error (S1), and the luminance of the first pixel (original luminance).
Is substituted into the original luminance register (S2). And CPU3
Adds the contents of the original luminance register and the contents of the error register and substitutes them into the calculated luminance register (S3).

Then, the CPU 3 determines whether the content of the calculated brightness register is "128" or more (S4).
If it is "128" or more (if Yes), the pixel is set to "white" (S5), and the value obtained by subtracting "255" from the content of the calculated luminance register is substituted for the error register (S6).

This is because the gray scale is set to “256” levels, and the reference value “12” in the process S4 is used.
"8" represents a half value of "256". Therefore, in the “16” stage, the reference value in the processing S4 should be “8” instead of “128”, and
The value to be subtracted in the process S5 should be “15”.

In step S4, if the content of the calculated luminance register is smaller than "128" (if No), the pixel is set to "black" (S7), and the content of the calculated luminance register is directly substituted into the error register. (S8).

Then, the CPU 3 determines whether or not the processing for one line of pixels has been completed (S9). If the processing has not been completed ("unfinished"), the process returns to the processing S2.
If the processing has been completed in step S9 (if “finished”), the processing for the line is completed.

If there is a next line, the CPU
No. 3 repeats the process from the process S1 again.

Here, the case of gray scale is shown, but when the read image is a color image, the still image data is R (RED), G (Green), B (Bul
Since this can be expressed as the gray value of the three primary colors of e), it is converted to a gray scale (luminance signal Y).
It is well known that the following formula can be used for this purpose.

[0015]

(Equation 1)

The MH coding will be described. Although the MH code here is similar to a well-known code, it is known that the compression efficiency is originally increased by adaptive coding that changes the coding method for each image. As already explained, T.U. In the so-called G3 FAX based on the four recommendations, the encoding method is fixed.

The run lengths from 0 to 63 are encoded by a terminating code, and run lengths that are multiples of 64 are encoded by a code called a makeup code. That is, the run length up to 63 is represented by one terminating code, and the run length of 70 or more, for example, 70 or more is one makeup code representing 64 and 7
0-64 = 6 and one terminating code representing a run length.

Specifically, when an image such as "white-white-white-black-white ... black-white-white-white-white" is subjected to MH coding in G3 FAX, if, for example, intermediate black continues for 70 pixels, first, The first four white pixels are “1011”
The makeup code “11011” representing 64 pixels in the middle black and the terminating code “1110” representing 6 pixels are combined to obtain “1101111”.
10 ”, and the last four white pixels are again encoded as“ 101 ”.
1 ", so that it is coded as" 10111101111101011 "as a whole in 17 bits.

By the way, in an image subjected to error diffusion dither, generally, only one of a white pixel and a black pixel is not continuous for a long time.
Often lined up like. Therefore, when this is subjected to MH coding, two black pixels are “11” and three white pixels are “1000”.
0 ”, one black pixel is“ 010 ”, and one white pixel is“ 00011 ”.
"1", so that "1110000010"
000111010000111 "and 25 bits.

While the 78 pixels illustrated above are encoded to 17 bits, the latter 9 pixels are encoded to as long as 25 bits.
This is because, in the coding of the code, the code length for one white pixel is 6 bits, which is set longer than 4 bits for two white pixels.

Next, the operation of the conventional image transmission apparatus will be described. The image input means 1 reads an image and stores it in the frame memory 2 as still image data. The CPU 3 binarizes the still image data by error diffusion dither, further MH-encodes it into facsimile data, and the modem 5 Transmit.

Here, the color or gray scale image is subjected to error diffusion dither, and only one of the white pixel and the black pixel is not continuous for a long time.
The data amount of the encoded facsimile data increases.

[0023]

As described above, in the above-described conventional still image transmission method and still image transmission apparatus, when the encoding method is fixed, if the encoding method is not appropriate, the amount of data to be transmitted is small. However, there is a problem that the transmission time becomes longer.

The present invention has been made in view of the above circumstances, and even when the encoding method is fixed,
It is an object of the present invention to provide a still image transmission method and a still image transmission device that can reduce the amount of transmission data and shorten the transmission time.

[0025]

According to the first aspect of the present invention, a still image is input as digital data, the digital data is converted to gray scale data, and the gray scale data is converted to gray scale data. The scale data is reduced and converted to 1/2 for each line to obtain 1/2 reduced data, the 1/2 reduced data is binarized to obtain binary data, and the binary data is converted to binary data for each line. It is characterized in that the data is enlarged and converted by a factor of two, and the enlarged data is encoded and transmitted as facsimile data.
The amount of data to be transmitted can be reduced, and the transmission time can be shortened.

According to a second aspect of the present invention, there is provided a still picture transmission method according to the first aspect, wherein error diffusion dither is used for binarization, and MH code is used for encoding. In FAX, the amount of data to be transmitted can be reduced and the transmission time can be shortened.

According to a third aspect of the present invention, there is provided a frame memory for storing digital data, a RAM for storing data obtained by processing the digital data, and a still image. Image input means for reading digital data from the frame memory and storing the digital data in the frame memory;
Is stored as gray-scale data, and the width of one line of the gray-scale data is reduced to 1/2 and converted to 1 /
The half reduced data is stored in the RAM, the 1/2 reduced data is subjected to error diffusion dither to be binarized, and stored as dither data in the RAM.
A CPU for enlarging and converting the line width by a factor of 2 and storing the enlarged data in the RAM as enlarged data;
And a modem for transmitting the facsimile data stored in the RAM. In FAX, the amount of data to be transmitted can be reduced, and the transmission time can be shortened.

[0028]

Embodiments of the present invention will be described with reference to the drawings. A still image transmission apparatus (this apparatus) according to the present invention processes an image before encoding so that the image is efficiently encoded by the encoding.
AX is subjected to error diffusion dither after reducing each line constituting the image, and is then enlarged to its original size.
By performing MH coding after at least two pixels are continuous, the amount of facsimile data is reduced, and the transmission time can be shortened.

Hereinafter, a case where the present apparatus is applied to a facsimile will be described as an example. This device has the same configuration as the conventional still image transmission device shown in FIG. 2, but differs in the processing in the CPU 3. Thus, the processing in the CPU 3 will be described with reference to FIG. FIG. 1 is an explanatory diagram showing processing in the CPU 3 of the present apparatus.

The RAM 4 stores C as described below.
A memory used as a work memory of the PU3,
Gray scale data and 1
/ 2 reduced data, dither data, enlarged data, and facsimile data are stored separately.

The CPU 3 converts a grayscale image into a grayscale image as it is, and converts a color image into a grayscale image in the same manner as before, and stores it in the RAM 4 as grayscale data. Then, the CPU 3 reduces and converts the width of one line of the gray scale data to half (S11), and
The data is stored in the RAM 4 as reduced data.

Then, the CPU 3 applies error diffusion dither to the 1/2 reduced data in the same manner as in the prior art to binarize the data (S1).
2) and store this as dither data in RAM 4
The width of one line is enlarged and converted twice (S13), and stored in the RAM 4 as enlarged data.

Then, the CPU 3 subjects the enlarged data to MH encoding (S14), and converts it into facsimile data in the RAM 4
To be stored.

Next, the operation of the present apparatus will be described. When the image input means 1 of the present apparatus reads a grayscale image and stores it in the frame memory 2, the CPU 3 reduces and converts the image stored in the frame memory 2 to に for each line to 縮小. The data is stored in the RAM 4 as data.

Then, the CPU 3 applies error diffusion dither to the 1/2 reduced data and stores it in the RAM 4 as dither data, further enlarges and converts the dither data twice for each line, and stores it in the RAM 4 as enlarged data. Then, the expanded data is MH-encoded and converted to facsimile data by RA.
Store it in M4.

Then, the modem 5 transmits the facsimile data stored in the RAM 4 via a telephone line.

According to the present apparatus, the data is reduced to に in the line direction and then subjected to error diffusion dither, and is doubled and subjected to MH coding. The image to be black or white is subjected to MH encoding, and the image is converted so that the MH encoding conforms to the MH encoding in G3 FAX. Therefore, the encoding efficiency is increased and the amount of transmission data is reduced. Transmission time can be shortened.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the still picture transmitting apparatus according to the present invention will be described. In the following description, it is assumed that an image to be transmitted is a gray scale of 256 × 256 pixels. First, as in the prior art, the image was subjected to error diffusion dither as it was and MH-encoded, requiring 188,976 bits. That is, the data amount per pixel was about 2.88 bits.

Next, each bit is thinned out to obtain 1/2 reduced data, error diffusion dither is performed, and each bit is repeated twice to obtain double enlarged data.
As a result of encoding, the total number of bits is 77,080 bits, and the data amount per pixel is approximately 1.1.
It became 6 bits.

According to the still picture transmission apparatus of the present embodiment, there is an effect that the amount of data to be transmitted is reduced to 2/5 and the transmission time can be shortened.

[0041]

According to the first aspect of the present invention, a still image represented by digital data is converted into gray scale data, which is reduced to 1/2 for each line, and then converted to gray scale data.
Since the method is a still image transmission method in which the image is binarized, the binarized image is doubled for each line, encoded and transmitted as facsimile data, two white pixels or two black pixels are consecutively encoded. In the case where the encoding is a short code, the encoding efficiency can be increased, the amount of transmission data can be reduced, and the transmission time can be shortened.

According to the second aspect of the present invention, error diffusion dither is used as a binarization method, and M is used as a coding method.
Since the still image transmission method according to claim 1 uses H coding, the method can be adapted to FAX, and has an effect of reducing the amount of transmission data in FAX and shortening the transmission time.

According to the third aspect of the present invention, the digital data of the still image read by the CPU is converted into a gray scale, the width is converted into half, and then error diffusion dither is applied to binarize the digital data. Is converted into a facsimile data by performing MH encoding and facsimile data which is transmitted by a modem, so that it is converted into an image having at least two continuous white or black pixels. , The amount of data encoded by MH encoding specific to G3 FAX is reduced, the amount of data to be transmitted can be reduced, and the transmission time can be shortened.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing processing in a CPU 3 of the present apparatus.

FIG. 2 is a configuration block diagram of a conventional still image transmission device.

FIG. 3 is a flowchart of a binarization processing method using error diffusion dither in a CPU 3;

[Explanation of symbols]

1. Image input means 2. Frame memory 3. CP
U, 4 ... RAM, 5 ... Modem

Claims (3)

[Claims] 1. A still image is input as digital data, the digital data is converted to gray scale data, and the gray scale data is halved every line.
The reduced data is converted to 1/2 reduced data, the 1/2 reduced data is binarized to be binarized data, and the binarized data is expanded and converted into double data for each line to obtain expanded data.
A still image transmission method, characterized in that the enlarged data is encoded and transmitted as facsimile data. 2. An error diffusion dither is used for a binarization method.
2. An MH encoding method is used for encoding.
The still image transmission method described in the above. 3. A frame memory for storing digital data, a RAM for storing data obtained by processing the digital data, an image input means for reading a still image and storing it as digital data in the frame memory; The digital data is taken out from the frame memory, converted to gray scale and stored as gray scale data in the RAM, and the width of one line of the gray scale data is reduced to 1/2 and converted to 1/2 reduced data. The data is stored in the RAM, and the 1/2 reduced data is subjected to error diffusion dither to be binarized, stored as dither data in the RAM, and the width of one line of the dither data is double-converted to be enlarged data. Stored in the RAM as the above, and MH-encodes the enlarged data to generate facsimile data A still image transmission apparatus comprising: a CPU that stores the facsimile data stored in the RAM; and a modem that transmits the facsimile data stored in the RAM.