JPH036173A - Half tone encoding system - Google Patents

Abstract

PURPOSE:To improve the encoding efficiency at the time of facsimile transmission, etc., by transmitting a dither image to converting it to the run length corresponding to a run length code whose generation probability is high. CONSTITUTION:With respect to a dither image, a conversion table 10a obtained by allowing the run whose generation probability is high to correspond to the run whose generation probability of run length encoding is high and its reverse conversion table 11a are generated in advance. First of all, a half tone image to be transmitted is converted to the dither image in a dither image output part 1. Subsequently, in a dither image/run data converter 10, the input dither image is converted to run length data, based on the table 10a. Next, the converted run length data is transmitted to a receiving part 4 from a transmitting part 4. In a run data/dither image converter 11, the received run length code is demodulated to the dither image by using the table 11a. An output part 5 outputs the image data demodulated to the dither image onto recording paper as an image.

Description

[Detailed Description of the Invention] [Summary] The purpose is to improve the coding efficiency during facsimile transmission using a halftone coding method used in facsimile machines, etc., and the probability of occurrence of white runs and black runs in dithered images. is calculated using a statistical method, and has a built-in conversion table that corresponds runs with a high probability of occurrence to runs with a high probability of occurrence in run-length encoding.The input dither image is converted to run-length encoding based on the conversion table. a dithered image/run data converter that converts the output of the dithered image/run data converter into run data; a transmitter that receives the output of the dithered image/run data converter, encodes it into a run length, and outputs it to the line; and a run length code sent from the line. It has a built-in receiving section that receives and converts the run data into corresponding run data, and an inverse conversion table that receives the output of the receiving section and inversely converts the run data into the original dither image. The run data dither image converter demodulates the run data dither image into the original dither image based on an inverse conversion table, and an output section outputs the output of the run data dither image converter onto recording paper.

[Industrial Field of Application] The present invention relates to a halftone encoding method for facsimile machines and the like.

In facsimile machines, dithered images are used as a means of expressing halftone images. However, this dithered image is not compatible with the run-length encoding method used in facsimile apparatuses, resulting in poor efficiency during facsimile transmission. Therefore, a halftone encoding method with high encoding efficiency is required.

[Prior Art] When transmitting image information (including character information) using a facsimile machine, the run-length encoding method described above is used. As this type of run-length encoding method, for example, an MH (Modified Huffman) encoding method is used. FIG. 5 is a diagram showing part of a run-length code. As shown in the figure, the run-length code is such that data with a short bit length is assigned to the white run and the black run that have the highest degree of appearance. For example, consider the case where the run length is 2.

In this case, run-length encoding is performed on bit data in which two pieces of white (data "1") continue as 0 and 0, and two pieces of black (data "0") follow as .

In the former case, "0111" is assigned, and in the latter case, "11°" is assigned.Even if the run length is 2, the number of bits of the black run is short, which means that the data that follows . . . appears more frequently. It is shown that.

The same applies to encoding of other run lengths. In other words, the run-length encoding method is a variable length encoding method.

By the way, when transmitting a halftone image using a facsimile machine, it cannot be transmitted as is, so it is necessary to convert it into a binary image. As a means for binarizing this halftone image, a method is used in which the halftone image is binarized using a dither matrix.

An image that is binarized using a dither matrix is called a dither image. Dithered images are often used because they have good reproducibility when output as images by a printer.

FIG. 6 is an explanatory diagram of dither image generation.

(A) is a halftone image, which is an image signal obtained by reading an original image using a photoelectric conversion means such as a CCD and converting it into digital data using an A/D converter. The diagram shows 4X4
It shows what is expressed as a matrix. "8" shown in the figure
”, “9” etc. represent the brightness. The larger the number, the brighter the pixel is. This halftone image (
Binarize using the 4×4 dither matrix shown in b). This dither matrix defines a threshold value for each pixel at a corresponding position. The halftone image is then compared to the corresponding threshold. If the halftone image data is larger than the threshold value, O (indicates “1”), and if it is smaller than the threshold value,
0”).

If we compare each pixel with the corresponding threshold value, we get (
An image (dithered image) as shown in (c) is obtained. This dithered image is a binary image in which 0 is "1" and . is "0". For example, the second row and second column in (a) The value of is "a9". The corresponding (mouth) threshold is "4". "9" and "
4", the comparison result is O(1") because "9° is larger." When other pixels are found in the same way, the dithered image shown in (C) is obtained.

Note that there are various types of dither matrices, such as Bayer type and spiral type, and which dither matrix is optimal depends on the type of document image.

FIG. 7 is a block diagram showing a configuration example of a conventional halftone encoding method. The input halftone image as shown in FIG. 6(A) is input to the dithered image output unit 1 and compared using a dither matrix as shown in FIG. 6(B) as a threshold. A dithered image as shown in FIG. 6(c) is output. The output dithered image enters the subsequent transmitter 2. The transmitter 2 receives the input dithered image, counts the number of white runs and black runs, encodes the run length, and outputs the encoded image to a line 3 (for example, a telephone line). Here, the above-mentioned MH encoding method is used as the run-length encoding method. The above is the operation on the sending side.

The dithered image sent from the line 3 is received by the receiver 4, and the run-length code is converted into the original dithered image. The converted dithered image is outputted to recording paper as image information by the output unit 5. The above is the operation on the receiving side.

It is incompatible with the method. This will be explained using FIG.

The data in the first line of (a) are 8.8 and 10.11 in that order. For example, if these data are binarized with one threshold value of 7, the result will be 1, 1, 1.1, and the same run will continue (4 white runs), so if run-length encoding is performed, the encoding efficiency will improve. do. However, in the dither method, each pixel is binarized using its own threshold value, so a series of 1s or a series of 0s becomes (
As shown in c), it does not last long. This indicates that run-length encoding deteriorates encoding efficiency.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a halftone encoding method that can improve encoding efficiency during facsimile transmission.

[Problems to be Solved by the Invention] In the conventional method described above, the obtained dithered image is directly run-length encoded and transmitted.

However, the dithered image is run-length encoded [Means for Solving the Problem] FIG. 1 is a block diagram of the principle of the method of the present invention.

Components that are the same as those in FIG. 7 are designated by the same reference numerals.

In the figure, 10 is a white run for the dithered image.

It has a built-in conversion table 10a that calculates the probability of a black run occurring using a statistical method and matches a run with a high probability of occurrence to a run with a high probability of occurrence in run-length encoding, and converts a manually dithered image into a conversion table 10a. A dither image/run data converter 2 converts the data into run data for run length encoding based on the dither image/run data converter 10.
This is a transmitter that receives the output of , encodes it in run length, and outputs it to line 3. The above is the sending side.

Reference numeral 4 denotes a receiving unit that receives the run length code sent from line 3 and converts it into corresponding run data, and 11 receives the output of the receiving unit 4 and converts the run data back into the original dither image. A conversion table 11a is built-in, and the run data output from the facsimile receiving section 4 is converted into an inverse conversion table 1.
1a to demodulate the original dithered image.
The dither image converter 5 is an output unit that outputs the output of the run data/dither image converter 11 as an image onto recording paper.

The above is the receiving side.

[Operation] The dithered image/run data converter 10 converts the dithered image with a higher probability of occurrence into a run-length code with a higher probability of occurrence and transmits the code, and the receiving side converts the received run-length code into a run data/dithered image. The converter 11 performs the opposite conversion to that on the transmitting side to restore the dithered image. The present invention can take advantage of the advantages of both the dithering method and the run-length encoding method, so even dithered images can improve the encoding efficiency during facsimile transmission, and improve image reproducibility. Good too.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. Components that are the same as those in FIGS. 1 and 7 are designated by the same reference numerals. In the figure, reference numeral 1 denotes a dithered image output unit that inputs a human halftone image, compares it with a threshold value pixel by pixel, and converts it into a dithered image. As the threshold value, for example, a dither matrix as described with reference to FIG. 6 is used. The configuration after the dithered image/run data converter 10 which receives the output of the dithered image output section 1 is the same as that shown in FIG.

The operation of the circuit configured in this manner will be explained with reference to the operation flowchart shown in FIG.

First, the probability of occurrence of white runs and black runs in the dithered image is calculated using a statistical method, and a conversion table is created in which runs with a high probability of occurrence correspond to runs with a high probability of occurrence in run-length encoding. 10a and its inverse conversion table 12a
is created in advance (Sl).

FIG. 4 is a diagram showing an example of a conversion table and an inverse conversion table. In the figure, white run 2 means 0°0 and two white characters, and black run 2 means .

・This means two consecutive black characters. First, we will explain the conversion table shown in (a). For example, in a dithered image, as a result of calculation using a statistical method, it is 0 for each of white and black. .o, .

・Assuming that the pattern shown in FIG. 5 has the highest probability of occurrence, this pattern is made to correspond to the run length with the highest probability of occurrence of the run-length code shown in FIG.

For example, in FIG. 5, the run lengths with a high probability of white occurrence are from 2 to 7. Here, it is made to correspond to run length data 3 of these. As shown in FIG. 5, the run length with the next highest probability of black occurrence is run length 2.3. Here, it is made to correspond to run length data 2.

Next, assuming that the probability of occurrence of a pattern O8.1.. is high for each of white and black, run length data 2 is associated with white, and run length data 3 is associated with black. Thereafter, a table as shown in FIG. 4(a) is created in the same manner.

Once a table like the one shown in Figure 4 (a) is created, an inverse conversion table showing the correspondence between white runs and black runs from run length data can be easily created using (a). )
It will look like the one shown below. Among these tables, the conversion table 10a is stored in the dither image/run data converter 10 on the transmitting side. The inverse conversion table 11a is stored in the run data/dither image converter 11 on the receiving side.

Once created, these tables can be stored in ROM. Therefore, a ROM can be used as the conversion table 10a and the inverse conversion table 11a.

Next, the halftone image to be transmitted is converted into a dither image using a dither matrix (S2). Specifically, halftone images inputted by the dithered image output unit 1 are compared using a dither matrix as a threshold value to obtain a dithered image. The generation of the dithered image is the same as the method shown in FIG. 6, for example. Once the dithered image is obtained in this way, the obtained dithered image is converted into run length data using a conversion table (S3). The conversion algorithm is as explained in FIG. In other words, for example, in the case of a dithered image that continues 0, 0, the rerun length data 3 is calculated from the conversion table 10a.
Convert to Run length data is obtained by repeating the above sequence for all dithered images.

Next, send the converted run length data to the receiving device (
S4). Specifically, it is output from the transmitter 2 to the line 3.

The transmitter 2 encodes the input run length data and transmits it to the line 3.

The receiving device demodulates the received run-length code into a dithered image using the inverse conversion table 11a (S5).
. Specifically, first, the run length code received by the receiver 4 is converted into run length data. This run length data enters the subsequent run data/dither image converter 11, as shown in FIG.
Using the inverse conversion table shown in b), the original white run,
Demodulated to black run data (dithered image). For example, when the run length is white 3 in the receiver 4, the binary image of white run 2 (
dithered image), if the run length is black 3, then 2 of black run 3
The value image (dithered image is demodulated for each 1 g). The image data demodulated to the dithered image for all the run length data is outputted as an image on the recording paper by the output unit 5 (S6). According to the invention, since a dithered image is converted to a run length corresponding to a run length code with a high probability of occurrence and transmitted, it is possible to take advantage of the features of the run length encoding method and improve encoding efficiency. can.

In the above explanation, the MH method was used as an example of the run-length encoding method, but the present invention is not limited to this, and can be similarly applied to other methods such as modified read encoding methods. .

It goes without saying that the present invention is not limited to facsimile machines, but can be applied to any device that transmits and receives halftone data.

[Effects of the Invention] As described above in detail, according to the present invention, a dithered image is converted to a run length corresponding to a run length code with a high probability of occurrence and transmitted, so that the run length encoding method is It is possible to provide a halftone encoding method that can take advantage of the features and improve encoding efficiency, and has extremely large practical effects.

[Brief explanation of drawings]

Fig. 1 is a principle block diagram of the method of the present invention, Fig. 2 is a configuration block diagram showing an embodiment of the method of the present invention, Fig. 3 is a flowchart showing the operation of the method of the present invention, and Fig. 4 is a reverse conversion table. Figure 5 is a diagram showing an example of a conversion table, Figure 5 is a diagram showing part of a run-length code, Figure 6 is an explanatory diagram of dither image generation, and Figure 7 is a block diagram showing a configuration example of a conventional halftone encoding method. It is a diagram. In FIG. 1, 2 is a transmitting section, 3 is a line, 4 is a receiving section, 5 is an output section, 10 is a dithered image Φ run data converter, 10a is a conversion table, 11 is a run data/dithered image converter, 11a is the inverse translation table.

Claims (1)

[Claims] The probability of white runs and black runs occurring in a dithered image is calculated using a statistical method, and the runs with a high probability of occurrence are made to correspond to the runs with a high probability of occurrence in run-length encoding. A dither image/run data converter (1) has a built-in conversion table (10a) and converts an input dither image into run data for run length encoding based on the conversion table (10a).
0), a transmitter (2) that receives the output of the dither image/run data converter (10), encodes the run length, and outputs it to the line (3), and a run length sent from the line (3). Built-in receiving section (4) that receives the code and converts it into corresponding run data; and an inverse conversion table (11a) that receives the output of the receiving section (4) and inversely converts the run data into the original dithered image. and a run data/dither image converter (11) that demodulates the run data output from the receiving unit (4) into the original dither image based on the inverse conversion table (11a); and the run data/dither image converter (11) An output unit (5) outputs the output as an image onto recording paper.