JPH0533870B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an image area separation device, and more specifically, to a device for separating an image containing a mixture of halftone photographs and line drawings such as characters into a halftone photograph region and a line drawing region. Regarding.

2. Description of the Related Art 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 photographs, generally halftone photographs are often used. If this halftone photo is input from a facsimile, moiré may occur. When a special binarization method was used to suppress the occurrence of moiré, breaks in thin lines and unnecessary notches sometimes appeared around the lines in line drawings. Therefore, in order to separate the two and apply binarization methods suitable for each, several devices for separating the halftone photographic area and the line drawing area have been proposed. Among these methods, there is a method that can handle various halftone dots, and uses two types of threshold values to separate the halftone photograph area from the line drawing area due to the existence of closed areas peculiar to halftone photographs. We have proposed a device that can separate halftone photographic areas with a certain degree of accuracy even in halftone photographic areas with various line numbers and angles, by applying a method that applies this to halftone dots, and a method that uses the periodicity of halftone dots to separate halftone photographic areas from line drawing areas. has been done.

Problems to be Solved by the Invention However, among the conventional methods described above, due to the existence of closed regions peculiar to halftone photographs, a method for separating halftone photograph regions from line drawing regions is applied using two types of threshold values. Although this method is effective for halftone photographs with a density of about 50% in area ratio, there are still some areas where the halftone dots cannot be separated, especially when the halftone dot angle is around 90 degrees. There were parts that weren't there. In addition, although the method that uses the periodicity of halftone dots can solve the problems of the method that uses closed areas described above, depending on the conditions when the original is scanned with an image input device, the halftone If there is an error in the period, the problem is that the period cannot be captured.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore, an object of the present invention is to provide a novel image area separation device that makes it possible to eliminate the above-mentioned drawbacks inherent in the conventional technology. It is in.

Means for Solving the Problems In order to achieve the above object, an image area separation device according to the present invention includes a binarization unit that compares an input image signal with a threshold value and converts it into a binary image signal, and halftone dot center detection means for detecting the center of a series of black pixels or white pixel rows on the main scanning line from the binary image signal converted by the conversion means; and halftone dot period information according to the detection result of the halftone center detection means. is written to the center of the series of black pixels or white pixels for two or more pixels; a first storage means for storing the writing results; and a predetermined area on the main scanning line from the detection results stored in the first storage means determining means for determining whether the predetermined area is a halftone photograph area or a line drawing area according to whether or not a certain period exists in the area; and a second storage means for storing a result indicating that the area is an area with priority over a result indicating that the area is a line drawing area.

Embodiment Hereinafter, a preferred embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an image area separation device according to the present invention.

An image signal input from a terminal 101 is converted into a binary image signal by a binarization circuit 11. Next, the binary image signal output from the binarization circuit 11 is determined by the halftone dot center detection circuit 12 if both ends of one line are white pixels and all the pixels between are black pixels, or For each of the opposite cases,
It is determined whether any of the patterns shown in FIG. , in the opposite case, white pixel column center information (hereinafter both will be collectively referred to as period information) is output. Periodic information storage circuit 13
Now, the output (period information) of the halftone dot center detection circuit 12 is written to a position on the built-in image memory corresponding to the center of each halftone dot center detection pattern (FIG. 2). At this time, considering the case where an error occurs in the period of halftone dots, this period information is outputted to two locations shown in FIG. 2 for all patterns. However, for pattern A, there is only one pixel between them, so only one pixel is included. By doing this, when detecting the period, 4, 5,
Even if there is an error of about one pixel such as 4, 5, etc., it becomes possible to detect the period of halftone dots. Of course, even if the error in the halftone dot period becomes large, it can be dealt with by writing in two or more locations.

The periodic information written in the periodic information storage circuit 13 has a certain periodicity if it is a halftone area and has a certain periodicity if it is a line drawing area when viewed from the main scanning line of one line. There is a characteristic that there is no Utilizing this feature, in order to separate an image containing a mixture of halftone photographs and line drawings such as characters into halftone dot areas and line drawing areas, it is possible to The detection circuit 14 detects whether there is periodicity. Here, for convenience of explanation, we will take as an example a case where it is determined that the area is a halftone dot area when the black pixel row center information and the white pixel row center information mutually exist for two periods. Of each pattern in FIG. 3, only the pixels marked ◎ and ☆ are referenced, and the other unmarked portions are not referenced.
Further, the reference pixels marked with ◎ and ☆ are arranged alternately in two locations at the same interval in each reference pattern. This makes it possible to detect whether two black halftone dots and two white halftone dots are alternately present in the image. In reality, the black pixel row center information indicating the position of the black halftone dot in the image is located at all the positions marked with ◎, and the white pixel row center information indicating the position of the white halftone dot is located at all the positions marked with a star. Alternatively, it is detected whether black pixel row center information exists in all the positions marked with ☆ and white pixel row center information exists in all the positions marked with ◎, and if they exist, the 1 is output because a halftone dot exists in the area. Also,
Otherwise, it outputs 0 (hereinafter, the output here will be referred to as separation information). The separation information storage circuit 15 receives the output of the period detection circuit 14 and writes separation information, which is a period detection result, into a corresponding position of the built-in image memory. At this time, writing is performed so that 1 has priority, and is finally output from the terminal 102.

FIG. 4 shows the halftone dot center detection circuit 1 shown in FIG.
2 shows a specific block configuration.

Here, for convenience of explanation, seven types of halftone dot center detection patterns A to G as shown in FIG. 2 are assumed to be used to find the center position of a halftone dot. of course,
It is also possible to increase the number of patterns beyond this.
The binary image signal is supplied from the terminal 401 to 1-pixel delay elements 41A, 41B, 41C, 41D, 41
E, 41F, 41G, 41H, 41I output the corresponding pixel values of patterns A to G in FIG.
Supply to ROM42 (READ ONLY MEMORY). Here, the outputs of the one-pixel delay elements 41A to 41I are sequentially output from the leftmost pixel of each pattern in FIG.
They correspond as 1A, 41B...41I. In the ROM 42, it is determined whether the pattern shown in FIG. 2 exists or not for each case where both ends of one line are white pixels and all the pixels in between are black pixels, or vice versa. In this case, if both ends are white pixels and all the pixels in between are black pixels, black pixel column center information is sent, and vice versa, white pixel column center information is sent to terminals 1A to 10A.
Output from each. Here, among the terminals 1A to 10A, 1A to 5A output black pixel column center information, and terminals 6A to 10A output white pixel column center information. 5 and 6 show specific block configurations of the periodic information storage circuit 13 shown in FIG. 1.

FIG. 5 shows a circuit for storing black pixel column center information, and FIG. 6 shows a circuit for storing white pixel column center information. Both have exactly the same circuit configuration. Terminals 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8
A, 9A, and 10A supply the output of the halftone dot center detection circuit 12. At this time, the output terminal names of the halftone dot center detection circuit 12 and the input terminal names of the period information storage circuit 13 are the same and are connected to each other. Further, 0 is always supplied from the terminals 501 and 601. 1 pixel delay elements 51A to 51O
and 61A to 61O, logical OR gates 52A, 52B, 52C, 52D,
52E, 62A, 62B, 62C, 62D, 62
E writes black pixel column center information or white pixel column center information. This result is the terminal 1B
~10B, and output from 1C~10C.

FIG. 7 shows a specific block configuration of the period detection circuit 14 shown in FIG. 1.

Here, for convenience of explanation, there are three types of cycle detection reference patterns used to know the cycle of halftone dots, shown in FIG. Of course, it is also possible to increase the number of patterns beyond this. Terminal 1B
~10B and 1C~10C supply the output of the periodic information storage circuit 13. At this time, the same output terminal name of the period information storage circuit 13 and the same input terminal name of the period detection circuit 14 are connected. Further, the positional relationship between each terminal and the pixels of the period detection reference pattern is shown in FIG. ROM
At 71A, it is determined whether or not there are two periods of black pixel column center information in the period detection reference pattern shown in FIG. 3, and if there is, 1 is output as it is a halftone dot area candidate. At this time, ROM71A
outputs the detection results for each cycle detection reference pattern separately. Similarly, the ROM 71B determines whether two periods of white pixel row center information exist, and if so, outputs 1 as a halftone dot area candidate. Next, each output of ROM71A and each output of ROM71B are logical AND
The gates 72A, 72B, and 72C control the respective terminals 703, 704 only when two cycles of black pixel column center information and two cycles of white pixel column center information exist simultaneously, that is, when a halftone dot area exists. ,7
Outputs 1 from 05. On the other hand, logical AND
The outputs of gates 72A, 72B, 72C are logic
The OR gate 73 outputs 1 from the terminal 702 when at least one of the three types of cycle detection reference patterns exists.

FIG. 8 shows a specific block configuration of the separation information storage circuit 15 shown in FIG. 1.

Terminals 702, 703, 70 in this block diagram
4,705 supplies the output of the period detection circuit 14. At this time, the output terminal name of the period detection circuit 14 and the input terminal name of the separation information storage circuit 15 are the same and are connected to each other. Here, for the sake of simplicity, when a period is detected by the period detection circuit 14, the length of the pattern in which the period was detected x
Let's make five lines the halftone dot area. Of course, it can be done in the same way with other lengths and other numbers of lines. From the input terminal of the ROM 81, the detection results of the cycle detection reference patterns are input separately. Then, among the period detection reference patterns, the length of the area of the pattern whose period has been detected is outputted from the output terminal of the ROM 81 in pixel units.
At this time, if the period is detected simultaneously by two or three types of period detection reference patterns, the one with the longer pattern area is output. Down counter 82 has a 1 on terminal 702.
When input, from that point on, 1 is output for the number of pixels corresponding to the length of the cycle detection reference pattern given by the ROM 81. Always 0 from terminal 801
are supplied, and one scanning line delay elements 83A, 83B,
The image memory consisting of 83C and 83D stores period detection results, that is, separation information. 1 scanning line delay elements 83A, 83 of this image memory
The outputs of each of B, 83C and 83D and the output of the down counter 82 are connected to a logic OR gate
4A, 84B, 84C, 84D, and 84E, 1 is written in an area corresponding to the length of the cycle detection reference pattern x 5 lines. That is, the information that the area is a halftone dot area is written with priority over the information that the area is a line drawing area. This result is output from terminal 802.

Effects of the Invention As explained above, according to the present invention, it is possible to effectively separate the halftone dot area and the line drawing area even when halftone photographs and line drawings with unpredictable line counts and angles coexist. In image area separation using the periodicity of dots, even if an error occurs in the period of halftone dots, it is possible to effectively separate the halftone dot area and line drawing area.
This has the effect of greatly increasing separation accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a reference pattern used in halftone dot center detection, and FIG. 3 is an example of a reference pattern used in period detection. FIG. 4 is a block configuration diagram showing details of the halftone dot center detection circuit, FIG. 5 is a block configuration diagram showing details of a circuit for storing black pixel center information in the periodic information storage circuit, and FIG. 7 is a block diagram showing details of the periodic information storage circuit that stores white pixel column center information, FIG. 7 is a block diagram showing details of the periodic detection circuit, and FIG. 8 is a detailed diagram of the separation information storage circuit. FIG. 11...Binarization circuit with fixed threshold value, 12...
Halftone dot center detection circuit, 13... Periodic information storage circuit,
14... Period detection circuit, 15... Separation information storage circuit, 41A, 41B, 41C, 41D, 41E,
41F, 41G, 41H, 41I, 51A, 51
B, 51C, 51D, 51E, 51F, 51G,
51H, 51I, 51J, 51K, 51L, 51
M, 51N, 51O, 61A, 61B, 61C,
61D, 61E, 61F, 61G, 61H, 61
I, 61J, 61K, 61L, 61M, 61N,
61O...1 pixel delay element, 42, 71A, 71
B, 81...ROM (read-only memory), 52
A, 52B, 52C, 52D, 52E, 62A,
62B, 62C, 62D, 62E, 73, 84
A, 84B, 84C, 84D, 84E...Logic
OR gate, 72A, 72B, 72C...logic
AND gate, 82...down counter, 83
A, 83B, 83C, 83D...1 scanning line delay element.

Claims (1)

[Claims] 1. In a device that separates an image containing a mixture of halftone photographs and line drawings such as characters into a halftone photograph area and a line drawing area,
A binarization means for comparing an input image signal with a threshold value and converting it into a binary image signal, and a center of a series of black pixels or a row of white pixels on the main scanning line from the binary image signal converted by the binarization means. a halftone dot center detecting means for detecting the halftone dot center detecting means; and a first halftone dot center detecting means for writing halftone dot period information for two or more pixels at the center of the series of black pixels or a row of white pixels according to the detection result by the halftone dot center detecting means and storing the writing result. and whether or not the predetermined region on the main scanning line is a halftone photographic region, based on the detection results stored in the first storage means. a determining means for determining whether the area is a line drawing area, and a determination result by the determining means that stores a result indicating that the area is a halftone photograph area in preference to a result indicating that the area is a line drawing area, and making a single determination by the determining unit; An image area separation device comprising: second storage means for adding arbitrary lines in the sub-scanning direction to the reference area, expanding the halftone dot area, and storing the expanded halftone area.