JPH0436625B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for separating an image containing a mixture of halftone photographs and line drawings such as characters into a halftone photograph area and a line drawing area.

(Prior art and its problems) With the spread of facsimile in recent years, there are increasing opportunities to transmit not only line drawings such as characters but also images such as printed photographs. When printing, halftone photographs are generally used. If this halftone photo is input from a facsimile, moiré may occur. A binarization method that can suppress the occurrence of moire is also known, but if a special binarization method is used to suppress the occurrence of moire, it will cause unnecessary cuts in thin lines and around the lines in line drawings. Notsuchi sometimes appeared. Therefore, several devices have been proposed for separating the halftone photographic area and the line drawing area in order to separate the two and apply binarization methods suitable for each. These methods detect patterns unique to halftone photographs and distinguish between the two. However, these methods are not effective unless the unique patterns of halftone photographs are known in advance. Therefore, sufficient image area separation could not be achieved for images in which various numbers of lines and angles were generated, and the initial goal could not be achieved.

(Object of the Invention) The object of the present invention is to eliminate the above-mentioned disadvantages, and to perform image area separation that effectively separates the halftone dot area and the line drawing area even when halftone photographs and line drawings with unpredictable line counts and angles coexist. The goal is to provide equipment.

(Structure of the Invention) According to the present invention, there is provided a means for converting an input image increase signal into a binary image signal, and a means for converting an input image increase signal into a binary image signal, and It is characterized by comprising means for determining whether an area is a halftone photographic area or a line drawing area, and a storage means for storing the determination result with priority given to the result that the area is a halftone photographic area. An image area separation device is obtained.

(Principle of the Invention) Halftone photography expresses gradation information using the areas of minute white or black dots. Therefore, in the halftone photographic area, a characteristic repetition of white or black dots occurs. In the present invention, this dot, that is, a black area surrounded by white or a white area surrounded by black, is called a closed area, and the presence or absence of this closed area is used to determine whether or not it is a halftone photographic area. . First, the input image is once binarized, and then if there is a closed area surrounded by white or black pixels within the set area, it is determined that it is a halftone dot area, otherwise it is determined that it is a line drawing area. to decide. Finally, the judgment result is stored in memory. Since the binary image signal used here is only used to separate image areas, there is no problem even if moire occurs, so binarization using a fixed threshold may be used. Detection of a closed area is determined based on whether or not the area of interest is surrounded by the same color, white or black, and there are pixels in the area of interest that have a different color from the surrounding pixels. This judgment result is written in all reference areas, and is stored in the memory that stores the judgment result so that the result that it is a halftone photograph has priority over the previous result that it is a line drawing.

(Example) Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of an apparatus for realizing the present invention. An image signal inputted from a terminal 101 is converted into a fixed threshold binary image signal by a binarization circuit 11. Next, the closed area detection circuit 12 determines whether or not there is a black pixel surrounded by white or a white pixel surrounded by black in the area of interest, and if there is, it is determined that a closed area exists. , outputs 1, otherwise outputs 0. In the write circuit 13, the closed area detection circuit 12
After receiving the output, the closed area detection result is written to the corresponding position in the built-in image memory. During this writing, writing is performed so that 1 has priority. The written result is output from the terminal 102.

FIG. 2 shows a block diagram of the closed area detection circuit 12. Here, for simplicity, the size of the region of interest used for closed region detection is set to 5 x 5 pixels, but 7
It is also possible to increase the size to ×7 or 9×9 pixels using almost the same circuit configuration. FIG. 4 shows the positional relationship between peripheral pixels in the region of interest and pixels inside the region. In the figure, A1, A2, A3, and A4 correspond to the peripheral portion, and B corresponds to the inside thereof. The pixel values indicated by x in the figure are ignored. A binary image signal is supplied from a terminal 201. 1 pixel delay element 22A, 22B, 22
C outputs the pixel value corresponding to A3 in Fig. 4,
Supply to ROM23A (READ ONLY MEMORY). ROM23A is A
It is determined whether all pixels of No. 3 are white, black, or a mixture of both. In the same way, the contents of the one-pixel delay elements 22H, 22L, and 22P, that is, FIG.
Part 4 is ROM23F, 22Q, 22R, 2
The contents of 2S, that is, the A1 part is in ROM23E.
Then, the delay element 21A, which has 4 pixels less than one line,
The output of 21B and 21C, that is, the A2 part is
Determined by ROM23H. The output of each ROM is A1, A2, A3, A in ROM24A again.
It is determined whether all 4 are white, black, or a mixture of both. Next, A1, A2, A3 in Fig. 4,
It is determined whether the part B surrounded by A4 is entirely white, black, or a mixture of both in the following manner.
The outputs of the 1-pixel delay elements 22E, 22F, and 22G are
The ROM 23B determines whether everything is white, black, or a mixture of both. Similarly, ROM2
In 3C, 1 pixel delay element 22I, 22J, 22K
The ROM 23D determines the contents of the 1-pixel delay elements 22M, 22N, and 22O.
These determination results are again determined in the ROM 24B as to whether all are white, black, or a mixture of both. ROM2
The outputs of 4A and ROM 24B are input to ROM 25A, and it is determined whether or not a closed area has been detected. If a closed area has been detected, a value of 1 is output. A closed area is determined to exist if the output of ROM24A is all white and the output of ROM24B is all black or a mixture of white and black, and
This is a case where the output of the ROM 24B is all black and the output of the ROM 24B is all white or a mixture of white and black.
After all, if there is a pixel of a color different from the surrounding area within an area surrounded by the same color, it is determined that there is a closed area. The ROM 23G and ROM 25B determine the existence of a closed area in the case of 3×3 pixels as shown in FIG. The outputs of ROM25A and ROM25B are logically ORed by OR gate 26 and output to terminal 202.

FIG. 3 is a block diagram of the write circuit 13. 0 is always supplied from terminal 301, and terminal 3
The output of the closed area detection circuit 12 is supplied from 02. Image area separation results are stored in an image memory consisting of delay elements 31A to 31D, which are 4 pixels less than one line, and 1 pixel delay elements 32A to 32T. Information that exists is given priority and written. This result is output from terminal 303.

In the above explanation, an example has been described in which the closed area detection circuit determines the closed area and the write circuit determines the priority in units of 5 x 5 pixels, but the unit of processing is not limited to this size. . Further, the unit of processing may be changed between the closed area detection circuit and the writing circuit.

(Effects of the Invention) As described above, according to the image area separation device according to the present invention, even if halftone photographs and line drawings with unpredictable line counts and angles coexist, halftone areas and line drawing areas can be effectively separated. can be separated.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a block diagram of the closed area detection circuit, FIG. 3 is a block diagram of the writing circuit, and FIG. 4 is a diagram showing the positional relationship between surrounding pixels and pixels of the content when the area of interest is 5 x 5 pixels. FIG. 5 is a block diagram showing the positional relationship between peripheral pixels and internal pixels in the case of 3×3 pixels. In the figure, 11...binarization circuit with fixed threshold, 12...closed area detection circuit, 13...
...Writing circuit, 21A, 21B, 21C, 21
D...Delay element with 4 pixels less than 1 line, 22
A, 22B, 22C, 22D, 22E, 22F,
22G, 22H, 22I, 22J, 22K, 22
L, 22M, 22N, 22O, 22P, 22Q,
22R, 22S, 22T...1 pixel delay element, 2
3A, 23B, 23C, 23D, 23E, 23
F, 23G, 23H...ROM (read-only memory), 24A, 24B...ROM (read-only memory), 26...Logic OR gate, 31A,
31B, 31C, 31D...delay element with 4 pixels less than 1 line, 32A, 32B, 32C, 32
D, 32E, 32F, 32G, 32H, 32I,
32J, 32K, 32L, 32M, 32N, 32
O, 32P, 32Q, 32R, 32S, 32T...
...1 pixel delay element, 33A, 33B, 33C, 3
3D, 33E, 33F, 33G, 33H, 33
I, 33J, 33K, 33L, 33M, 33N,
33O, 33P, 33Q, 33R, 33S, 33
T, 33U, 33V, 33W, 33X, 33Y...
…It is a logical OR gate.

Claims (1)

[Claims] 1. A device for separating an image containing a mixture of halftone photographs and line drawings such as characters into a halftone photograph area and a line drawing area,
means for converting the input image signal into a binary image signal; and a means for converting the input image signal into a binary image signal; Image area separation characterized by comprising means for determining whether the area is a halftone photograph area, and a storage means for storing the determination result by giving priority to the result that the area is a halftone photograph area over the result that the area is a line drawing area. Device. 2. The means for determining whether the predetermined area is a halftone photographic area or a line drawing area is provided by setting a rectangle as the predetermined area and surrounding it by peripheral pixels excluding pixels at the four corners of the rectangle. The image area separation device according to claim 1, characterized in that the image area separation device is a means for determining whether the area is a halftone photograph area or a line drawing area depending on the presence or absence of a closed area included in the image area. .