JPH0955847A - Pixel density conversion method and pixel density conversion device - Google Patents

Abstract

(57) Abstract: When a low density image subjected to pseudo halftone processing is enlarged both vertically and horizontally by using a projection method, the converted image exists in a state in which black pixels are biased. In such a case, if the black pixels are not the pixels existing in the edge portion of the image, it is possible to obtain a more preferable image in which the black pixels are scattered over the entire image. SOLUTION: A converted image obtained by converting the number of pixels of an original image in the vertical direction and the horizontal direction at an arbitrary magnification is generated, and the converted image and the original image are associated with each other based on a predetermined relationship. Then, the pixels of the converted image corresponding to the respective black pixels existing in the original image are specified, and the pixels of the converted image specified by the black pixels are defined as black pixels a to i. In the converted image in which is a black pixel, for each pixel other than the pixels a to i that are black pixels, the distance between that pixel and the black pixel closest to that pixel is calculated, and the calculated distance is Based on this, a new black pixel is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pixel density conversion method and a pixel density conversion device suitable for variable-magnification processing of binary images, especially pseudo-halftone images.

[0002]

2. Description of the Related Art For example, as shown in FIG.
There is an original image of a value, and the original image is scaled by converting the number of pixels forming this original image in both the vertical and horizontal directions by a predetermined magnification. FIG. 2B shows an example in which the number of pixels of the original image is doubled in both vertical and horizontal directions. That is, taking the pixel G1 of the original image as an example, this pixel G1 is composed of four pixels G11, G12, G13, and G14 after conversion. In addition, in FIG. 16, the shaded portion is a black pixel, and in this figure, the character “0” is represented.

A projection method is one of the methods for performing the scaling processing of such a binary image. In the projection method, for example, when performing enlargement processing, the original image is projected on an enlarged image plane having different resolutions, and the ratio of black of the original image to the area of one pixel after enlargement is determined. 1 of the pixel after obtaining and enlarging
White and black are determined for each one.

In this projection method, in the case of an image representing a character or a line, there is no problem because the image before enlargement is enlarged as it is stored.

[0005]

However, in the case of a pseudo-halftone processed image such as a photograph, the following problems occur.

That is, the pseudo-halftone processed image is
The density is represented by the number of dots in a certain area. For example, FIG.
The image shown in 7 (a) is an image composed of 8 pixels × 8 pixels of 8 pixels in the horizontal direction (i direction) and the vertical direction (j direction) as a whole. That is, when divided into four blocks composed of 4 pixels × 4 pixels, only one pixel in each block is an image having black pixels (hatched). Therefore, this image is an image in which four black pixels are evenly distributed in the entire image, and such an image is a very low-density image such as light gray as a whole.

When such a low-density image is enlarged in the number of pixels in the vertical and horizontal directions by the projection method, the result is as shown in FIG. The image of FIG. 17 (b) is 16 in total.
In an image of pixels × 16 pixels, the number of black pixels is four times as many as 16 pixels as compared with the original image, but the positions of black pixels are the same as in FIG. At this time, the number of pixels is quadrupled to 16, so the density is preserved. However, the image of FIG. 17B has four images in the same way as in FIG. 17A. When divided into blocks and considered within one block composed of 8 pixels × 8 pixels, four black pixels existing in each block exist in one state in a biased manner. Therefore, there is a problem that black pixels exist in a biased state even when viewed in the entire image.

In this case, the number of pixels of the original image is doubled vertically and horizontally, and the number of black pixels is also four times. Therefore, as shown in FIG. It is considered that a more preferable image can be obtained by making it scattered all over.

The present invention has been made in order to solve such a problem. When the number of pixels of the original image is converted at any magnification in both vertical and horizontal directions, black pixels existing in the original image are biased in the converted image. A good image can be obtained by scattering the black pixels over the entire image without existing in the state. Also, it is determined whether the black pixels are pixels existing in the edge portion, and If it is determined that the pixel is a pixel that exists in the area, the black pixel newly generated corresponding to the black pixel is generated adjacent to the black pixel, so that the sharpness of the edge part is generated even in the converted image. It is an object of the present invention to provide a pixel density conversion method and a pixel density conversion device capable of maintaining the above.

[0010]

The pixel density conversion method of the present invention is a pixel density conversion method for converting the pixel density by converting the number of pixels of an original image in the vertical direction and the horizontal direction at an arbitrary magnification. Existing in the original image by generating a converted image obtained by converting the number of pixels in the vertical direction and the horizontal direction at an arbitrary magnification and associating the converted image with the original image based on a predetermined relationship. The converted image in which the pixels of the converted image corresponding to the respective black pixels are specified, the pixels of the converted image specified thereby are made black pixels, and the predetermined pixels are made black pixels by being associated with the original image. At
The distance between each black pixel and a pixel other than the black pixel is calculated, and for each pixel, the distance between that pixel and the black pixel closest to that pixel is calculated, and the calculated distance is Based on this, a new black pixel is generated.

As the distance between the certain pixel and the black pixel closest to the pixel, any one of the Euclidean distance, the 4-neighbor distance, and the 8-neighbor distance is used.

Further, in the process of obtaining the distance between the certain pixel and the black pixel closest to the pixel, a maximum value is set in advance for the obtained distance, and a black pixel is not found within the distance of the maximum value. Does not calculate the distance to that pixel.

Then, in the process of generating a new black pixel based on the distance, when a certain black pixel is set as a target black pixel, the group of pixels which is the closest to the target black pixel is set as A search is performed from the calculated distance, and a pixel existing at the farthest position from the target black pixel in the group of pixels is set as a new black pixel.

As another example of the process of generating a new black pixel based on this distance, when a certain black pixel is set as a target black pixel, a group of pixels that are considered to be closest to the target black pixel. From the obtained distance, paying attention to a part of the group of pixels, and in the focused part, the pixel farthest from the focused black pixel is set as a new black pixel. , Or, a group of pixels that are said to be closest to the black pixel of interest is searched from the obtained distance,
A method of randomly selecting a certain pixel from among the connections of the pixels forming the outline of the group of pixels and setting the selected pixel as a new black pixel, and further, the method closest to the black pixel of interest. Is searched for from the determined distance, and a certain part of the connection of pixels forming the outline of the pixel group is focused, and a certain pixel is selected from the focused part. There is a method of randomly selecting the selected pixel as a new black pixel.

By adopting the above method,
When converting the number of pixels of the original image vertically and horizontally at any magnification, black pixels existing in the original image do not exist in a biased state in the converted image, and black pixels can be scattered over the entire image, which is good. It is possible to obtain a clear image.

In the pixel density conversion method of the present invention, the number of pixels of the original image is converted in the pixel density conversion method of converting the number of pixels of the original image in the vertical direction and the horizontal direction at an arbitrary magnification to convert the pixel density. By generating a converted image obtained by converting in the vertical direction and the horizontal direction at an arbitrary magnification and associating the converted image with the original image on the basis of a predetermined relationship, each black existing in the original image is generated. In the converted image in which the pixels of the converted image corresponding to the pixels are specified, the pixels of the converted image specified thereby are made black pixels, and the predetermined pixels are made black pixels by being associated with the original image, The distance between a pixel other than the pixel set as the pixel and a black pixel is calculated, and for each pixel, the distance between the pixel and the black pixel closest to the pixel is calculated, and a certain black in this converted image is calculated. Black pixels that focus on pixels When the determines whether black pixels that interest exists in an edge portion of the image, if the black pixel of interest is determined to not exist in the edge portion,
Based on the obtained distance value, a pixel existing at a position away from the black pixel of interest is selected, the selected pixel is set as a new black pixel, and the black pixel of interest exists in the edge portion. If it is determined that the black pixel of interest exists, one of the pixels adjacent to the black pixel of interest is set as a new black pixel.

To determine whether or not the black pixel of interest exists at the edge portion of the image, a group of pixels that are considered to be closest to the black pixel of interest is searched from the obtained distance, and the group of pixels is searched. In the connection of pixels forming the contour of the, the distance from the target black pixel to the target black pixel at the farthest position, and the target black pixel at the closest position from the target black pixel The ratio to the distance to the pixel is obtained, and based on the size of the ratio, it is determined whether or not the black pixel of interest belongs to the edge portion.

Then, in the process of generating a new black pixel when it is determined that the black pixel of interest does not exist in the edge portion, the group of pixels which is the closest to the black pixel of interest is obtained. A search is performed from the distance, and the pixel existing farthest from the target black pixel in the group of pixels is set as a new black pixel.

The process of generating a new black pixel when it is determined that the black pixel of interest does not exist in the edge portion is
As another method, a group of pixels that are said to be closest to the target black pixel is searched from the obtained distance, and a certain part of the group of pixels is focused, and in the focused part,
A method in which a pixel existing at the farthest position from the target black pixel is set as a new black pixel, or a group of pixels that are considered to be closest to the target black pixel is searched from the obtained distance, and the group of pixels is searched. A method of randomly selecting a certain pixel from among the pixels forming the outline of the pixel and setting the selected pixel as a new black pixel, and further, a pixel that is the closest to the black pixel of interest. A group of pixels is searched from the obtained distance, a certain part of the connection of pixels forming the outline of the pixel group is focused, and a certain pixel is randomly selected in the focused part. There is a method of setting the selected pixel as a new black pixel.

By adopting the above method,
It is determined whether the black pixel of interest is a pixel existing in the edge portion, and when it is determined that the black pixel is an edge portion, a black pixel newly generated corresponding to the black pixel. Should be generated adjacent to the black pixel instead of being generated at positions scattered far away. Thereby, the sharpness of the edge portion can be maintained even in the converted image. Further, when it is determined that the pixel is not the pixel existing in the edge portion, the black pixel newly generated corresponding to the black pixel can be generated at positions scattered far, and exists in the original image. It is possible to disperse black pixels in the entire image without the black pixels existing in a biased state in the converted image, and it is possible to obtain a good image.

The pixel density conversion device of the present invention is a pixel density conversion device for converting the pixel number of an original image in the vertical direction and the horizontal direction at an arbitrary magnification to convert the pixel density. Based on the correspondence relationship between the converted image and the original image obtained by converting in the vertical direction and the horizontal direction at an arbitrary magnification, the black pixels of the original image and the pixels of the converted image are associated with each other, and the associated conversion is performed. In the conversion image in which a pixel of an image is a black pixel and a predetermined pixel is a black pixel by being associated with an original image, each pixel other than the pixel that is the black pixel and each black pixel A distance calculation means for calculating the distance between the pixels and a distance between the pixel and the black pixel closest to the pixel, and a new black pixel based on the distance calculated by the distance calculation means. Black pixel generation means for generating It has a configuration.

As the distance between a pixel and the black pixel closest to the pixel calculated by the distance calculating means, any one of the Euclidean distance, the 4-neighbor distance and the 8-neighbor distance is used.

Then, in the process of obtaining the distance between a pixel and the black pixel closest to the pixel by the distance calculating means, a maximum value is set in advance to the obtained distance, and the black pixel is within the distance of the maximum value. If is not found, the distance to that pixel is not calculated.

Further, when a certain black pixel is set as the black pixel of interest, the black pixel generation means searches for a group of pixels that are said to be closest to the black pixel of interest from the obtained distance, Among the group of pixels, the pixel existing farthest from the target black pixel is set as a new black pixel.

In addition to this, the black pixel generating means searches for a group of pixels that are considered to be closest to the black pixel of interest from the obtained distance, focuses on a part of the group of pixels, and Among the above-mentioned portions, the pixel existing at the farthest position from the target black pixel may be set as a new black pixel, or a group of pixels which are considered to be closest to the target black pixel may be obtained as the distance It is also possible to randomly select one pixel from among the connections of pixels forming the outline of the group of pixels and select that pixel as a new black pixel. A group of pixels determined to be the closest is searched from the obtained distance, attention is paid to a part of connection of pixels forming the contour of the group of pixels, and a random one of Select one pixel and select that pixel Or it may be a Tana black pixels.

With the above configuration, when the number of pixels of the original image is converted at an arbitrary magnification both vertically and horizontally, black pixels existing in the original image do not exist in a biased state in the converted image and black Pixels can be scattered throughout the image, and a good image can be obtained.

Further, the pixel density conversion device of the present invention is a pixel density conversion device for converting the pixel density of an original image in the vertical direction and the horizontal direction at an arbitrary magnification to convert the pixel density. Based on the correspondence between the converted image obtained by converting at any magnification in the vertical and horizontal directions and the original image, the black pixels of the original image and the pixels of the converted image are associated with each other, and the associated converted image Between the black pixel and each black pixel in the converted image in which a predetermined pixel is made a black pixel by being associated with the original image. Distance calculation means for calculating the distance between the pixel and the black pixel closest to the pixel for each pixel, and when a certain black pixel in the converted image is set as the black pixel of interest , The black pixel of interest exists at the edge of the image. And an edge determining unit that determines whether the black pixel of interest does not exist in the edge portion, the edge determining unit based on the obtained distance value. A pixel existing at a position distant from the black pixel is selected, and the first black pixel generation unit that makes the selected pixel a new black pixel and the edge determination unit cause the target black pixel to be an edge portion. When it is determined that the black pixel of interest exists, one of the pixels adjacent to the black pixel of interest is set as a new black pixel.
And a black pixel generating means.

The edge determining means searches for a group of pixels that are said to be closest to the black pixel of interest from the obtained distance, and pays attention in the connection of pixels forming the contour of the group of pixels. Find the ratio of the distance from the black pixel to the black pixel of interest at the farthest pixel and the distance to the black pixel of interest from the black pixel at the closest position, and calculate the ratio Based on this, it is determined whether or not the black pixel of interest is a pixel belonging to the edge portion.

In addition, the first black pixel generation means may be arranged such that, in the group of pixels that are closest to the target black pixel,
The pixel existing farthest from the target black pixel is set as a new black pixel.

In addition, the first black pixel generating means may be a new black pixel which is the pixel farthest from the black pixel of interest in the part of interest. It is also possible to randomly select a certain pixel from among the connections of the pixels forming the outline of the group of pixels that are considered to be closest to the black pixel of interest, and select that selected pixel as the new black pixel. , And further, paying attention to a part of the connection of the pixels forming the contour of the group of pixels that are said to be closest to the black pixel of interest, and randomly selecting one pixel in the focused part. The pixel may be selected and the selected pixel may be a new black pixel.

With the above configuration, it is determined whether the black pixel of interest is the pixel existing in the edge portion, and if it is determined that the black pixel is the pixel existing in the edge portion, the determination is made. The black pixels newly generated corresponding to the black pixels are generated adjacent to each other instead of being generated at positions scattered far away. Thereby, the sharpness of the edge portion can be maintained even in the converted image. If it is determined that the pixel does not exist in the edge portion, the black pixel newly generated corresponding to the black pixel is
It is possible to generate at a position scattered far away, the black pixels existing in the original image do not exist in a biased state in the converted image, and the black pixels can be scattered throughout the image, and a good image can be obtained. Obtainable.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION In the scaling processing of a binary image,
For example, considering the case where the number of pixels is doubled both vertically and horizontally, the number of black pixels appearing in the converted image should be four times. The usual way to use it is 2 in both length and width.
In the case of double conversion, the number of black pixels appearing in the converted image may be four times that of the original image. However, the resolution of the converted image is an arbitrary magnification, and it is also necessary that the number of black pixels appearing in the image after the conversion can be an arbitrary number. For example, depending on the characteristics of an output device such as a printer, the resolution may be doubled both vertically and horizontally, but in some cases it may be desired to double the number of black pixels instead of four. For example, if the ratio of the area of the dot diameter of the black pixel of the device that outputs the original image to the area of the dot diameter of the output device that outputs the converted image is 2: 1, the ratio of the number of black pixels is 1: 2. By doing so, the concentration is maintained.

As an example of dealing with such a case, in the embodiment of the invention described below, the number of pixels is doubled both vertically and horizontally, and the number of black pixels appearing in the converted image is doubled. explain.

(First Embodiment) In the first embodiment, the number of pixels of a pseudo halftone original image as shown in FIG. Accordingly, an example in which the number of black pixels is doubled will be described. For the sake of convenience of explanation, the original image shown in FIG. 1 is composed of 10 pixels × 10 pixels, and the number of pixels of this original image is 2 vertically and horizontally.
Doubled to generate a converted image of 20 pixels × 20 pixels. In the following description, when a specific pixel is represented, it is represented by coordinate values in the i direction and the j direction. For example, the black pixel A in FIG. 1 is represented as (i1, j1). Hereinafter, the processing procedure will be divided into several steps and will be described in order. [1] First processing step First, the number of pixels of the original image shown in FIG. 1 is doubled vertically and horizontally, and as shown in FIG. A converted image of 20 pixels × 20 pixels is generated (see FIG. 2). Therefore, one pixel of the original image corresponds to four pixels of the converted image. For example, the pixel of (i1, j1) of the original image is (i1, j1) of the converted image.
1), (i2, j1), (i1, j2), (i2, j
This corresponds to the four pixels of 2). At this point, there are no black pixels in the converted image. And
For each black pixel (shaded) of the original image, specify the pixel of the converted image that has the closest center distance between the pixels of the converted image and each pixel of the converted image, and designate the specified pixel as the black pixel. To do. By this processing, in the converted image, the pixel at the position corresponding to the black pixel portion of the original image (FIG. 1) becomes the black pixel. This state is shown in FIG. In FIG. 3, the pixels in the shaded areas are black pixels.

The process of converting the pixels of the converted image corresponding to the original image into black pixels is specifically performed as follows. As described above, the pixel of the converted image having the center point closest to each center point of each black pixel in the original image is defined as a black pixel, and this is the black pixel A existing in (i1, j1) of the original image.
Will be described as an example.

The central point of the black pixel A in this original image is p
If the pixel of the converted image closest to the center point p1 is 1, the image of FIG. 1 and the image of FIG.
In this case, the center point p1 is (i1, j1), (i2, j
1), (i1, j2), and (i2, j2) are located at the boundary points of the four pixels, and one pixel cannot be specified. Therefore, in such a case, the original image of FIG. 1 is superimposed on the converted image of FIG. 2 with a slight shift in the diagonally upper left direction in the drawing. This allows
Since the center point p1 of the black pixel A of the original image is located on the pixel (i1, j1) of the converted image of FIG. 2, the center point of the black pixel A is (i1, j1) of the converted image. Since the center point p2 of the pixel exists at the closest position, the pixel in the converted image having the center point closest to the center point of the black pixel A in the original image is (i1, j1) in the converted image.
That means the pixel. In such a state, the pixel in the conversion pixel closest to the center point of each of the other black pixels B, C, D, ..., I of the original image is specified.

FIG. 3 shows a case in which the pixel specified in this way is a black pixel. The black pixel is shaded and black pixel A is black pixel a and pixel B is black. Is black pixel b, black pixel C is black pixel c, black pixel D is black pixel d, black pixel E is black pixel e, and so on. Black pixels a to i corresponding to ~ I are generated.

In the processing described above, in order to make it easier to determine the distance between the center points, the closest distance between the center points is obtained while the original image is slightly displaced from the converted image. This is a measure for coping with the fact that a certain center point of the original image is located at the boundary point of each pixel in the converted image and one certain pixel cannot be specified, as described above. . In this way, in the example in which a certain center point of the original image is located at the boundary point of the converted pixels, the same thing occurs when the number of pixels is converted to an even multiple in both the vertical and horizontal directions. By performing the processing as described above, the black pixel corresponding to the original image is specified in the converted image.

[2] Second Processing Step Next, for each of the black pixels a to i in the converted image obtained as described above, which pixel of the converted image (each pixel not converted to black) is The distance that is closest to the black pixel and is the distance is calculated for each pixel. As this distance, three types of distances such as Euclidean distance, 4-neighbor distance, and 8-neighbor distance can be used. Here, an example using the Euclidean distance will be described. This Euclidean distance is defined as the distance between two points p1 and p2, and p
The coordinate of 1 is (pi1, pj1), and the coordinate of p2 is (pi
2, pj2)

[0040]

[Equation 1]

Is the distance obtained by

In FIG. 3, for example, (i4, j1)
The pixel of is calculated to be apart from the black pixel a by the square root (= 3) of 9 according to the equation (1). In this way, for each pixel other than the black pixels a to i, the distance to the black pixel closest to that pixel is calculated, and the calculation result is described in each pixel is shown in FIG. It should be noted that the numerical values shown in FIG. 4 are the values before the square root is calculated by the equation (1) for the convenience of the drawing. For example, (i4, j1)
When the pixel of is calculated to be apart from the black pixel a by the square root of 9 by the formula (1), the numerical value of “9” is shown. Therefore, the actual value is the square root of the value shown. For example, the pixel (i4, j1) is actually at a distance of "3" from the black pixel a.
Further, the pixel of (i7, j6) is described as “13” in FIG. 4 with respect to the black pixel c, but in reality, it is “1”.
It shows that they are separated by the square root of 3 ”(≈3.6). The pixel of (i7, j6) is separated from the black pixel e by the square root of "13" (≈3.6). Further, in FIG. 4, the pixel indicated by the horizontal line is a pixel forming an outline portion of a group of pixels which is the closest to the black pixel e, which will be described later.

In this way, for the black pixels a to i, each pixel of the converted image (each pixel not converted to black)
Is calculated for each pixel to determine which black pixel is closest to the pixel and how far the pixel is. The value of the obtained distance is shown in each pixel of FIG. As described above, this value is the value before calculating the square root in the equation (1).

By the way, in the process for obtaining the distance in this way, if the maximum value is set for the distance to be obtained and none of the black pixels a to i is found within the maximum value, the distance is not obtained for that pixel. To do so.

For example, if "8" is set as the maximum value, as shown in FIG. 5, all the pixels existing in the blank portion where the distance value is not described are all black pixels (here, shaded areas are shaded). Since the distance to the four black pixels that have been applied is greater than “8” (in the drawing, the value before the square root is calculated, it is “64”). Does not perform the process of obtaining the distance. As a result, the total calculation amount can be reduced.

[3] Third Processing Step When the distance between each pixel in the converted image and the closest black pixel is calculated as described above, it is obtained as the next processing step. Based on the distance, which of the black pixels a to i is to be a new black pixel is determined.
This process will be described with reference to FIG. In FIG. 4, an example of determining a new black pixel for the black pixel e will be described here. First, consider a group of pixels in which the black pixel e is the closest black pixel among the black pixels a to i. Considering the obtained distance, this group of pixels is found to be the pixels within the range surrounded by the pixels with the horizontal lines in FIG.
Then, in the group of pixels, the pixel existing at the farthest distance from the black pixel e is found. This processing will be described below.

As can be seen from FIG. 4, the farthest distance in the group of pixels determined to be the closest to the black pixel e is “26” (≈5.1), which exists at that position. The pixel is a pixel of (i10, j8). Therefore, it is determined that this pixel is a pixel that is newly made a black pixel. However, the pixel of (i10, j8) was processed as being closest to the black pixel e in this case, but in reality, it is a group of pixels that are closest to the black pixel c (shown in FIG. 4). Of the black pixel e and the black pixel c are the same distance “2”.
6 ”). In this way, when there are pixels that are present at the same distance with respect to two or more black pixels, it is considered as a group on the black pixel side that is currently focused. Therefore, in this case, the pixel (i10, j8) is the black pixel e
Judged to belong to the group closest to.

In this way, the pixel is closest to the black pixel e and is present at the farthest position (i1).
The pixel of 0, j8) is determined as a pixel to be a new black pixel.

In the above processing, if there are a plurality of pixels at the furthest position in the group of pixels that are considered to be closest to the black pixel of interest, some rule is determined in advance and Any one pixel is determined based on the rule. This example will be described below.

In the case of FIG. 4, for the target black pixel e,
The distance "26" is the farthest distance, and there is only one distance for the black pixel e, but if "26" is not present, "25" becomes the farthest distance. , The pixels located at the distance of “25” are (i1, j6), (i10, j) as can be seen from FIG.
9), there are three pixels of (i8, j13). As described above, the processing when a plurality of pixels farthest from the target black pixel are present will be described with reference to FIG.

FIG. 6 shows a group of pixels that are closest to the black pixel e (pixels within a range surrounded by horizontal lines) when the black pixel e is the target pixel. Here, as described above, the pixel located at the farthest position in the group of pixels that is the closest to the black pixel e is the pixel shown in FIG.
As can be seen from (i1, j6), (i10, j
9) and three pixels of (i8, j13) exist.

In such a case, there may be some predetermined rules, but first, for example,
In FIG. 6, (i1, j6), (i10, j9),
A pixel is randomly selected from the three pixels (i8, j13), and the selected pixel is determined as a pixel to be a new black pixel. Further, as a second rule, for example, a group of pixels that are considered to be closest to the black pixel e is divided into three areas Z1, Z2, and Z3 as shown in FIG. Starting from the row L1 extending from the pixel e to the right, the rows L2, L3, and C3 are clockwise.
..., the pixel having the largest distance value among the pixels belonging to the row is searched for in each row. And
In this case, when the search is performed up to the row L5, the area is moved to the area Z2, and this time, the row L6 located at the bottom is used as a base point and the rows L6, L7, L8, ... The pixel having the largest distance value among the pixels belonging to is searched. And in this case, when searching up to the line L13,
Next, moving to the area Z3, this time, with the row Ll4 located at the uppermost position as a base point, the rows L15, L16, ..., L17.
In this way, the pixel having the largest distance value among the pixels belonging to the row is searched for in each row. Such a search order is determined in advance, and the pixel having the largest distance value searched is first determined as a pixel to be a new black pixel. In this case, the pixel of (i10, j9) is determined as a pixel to be a new black pixel. In this way, when a pixel to be a new black pixel for a certain black pixel of interest is determined, the pixel is processed as a black pixel.

[4] Fourth Processing Step After the processing of generating a new black pixel for a certain black pixel of interest is performed as described above, the distance that also considers the new black pixel is taken as the next processing step. Calculate. That is, in the example of FIG. 4, since the pixel of (i10, j8) has become a new black pixel, the distance calculation is performed by also considering this new black pixel. FIG. 7 shows the result. In FIG. 7, a portion surrounded by a horizontal line pixel is a group of pixels that are the closest to a new black pixel (which is represented by e1), and this portion is shown by the appearance of the new black pixel e1. This is a modified part of 5. The fourth processing step can be omitted.

[5] Fifth Processing Step Then, in the state of FIG. 7, the second to fourth processing steps as described above are applied to the next black pixel, for example, the black pixel f. When the new black pixel generation processing for this black pixel f is completed, the black pixel g is then subjected to the above-described second to fourth processing steps until the last black pixel i. The second to fourth processing steps are repeated.

At this time, each newly generated black pixel is distinguished from the original black pixels a to i, and a new black pixel for this newly generated black pixel is not generated. Not performed.

By performing the above-described processing, one new black pixel is generated corresponding to each of the black pixels a to i, and each new black pixel is a black pixel existing from the beginning. It will exist in a position away from any of a to i. That is, the black pixels a to i are present at positions approximately in the middle between neighboring black pixels. Therefore, when the original image as shown in FIG. 1 is converted at an arbitrary magnification, the black pixels existing in the original image do not exist in a biased state in the converted image, and the black pixels can be scattered over the entire image. , A good image can be obtained.

In the first embodiment, the number of pixels is doubled vertically and horizontally, and the number of black pixels is doubled instead of four. However, the number of pixels is doubled vertically and horizontally.
In the case of doubling the number of black pixels and accordingly quadrupling the number of black pixels, firstly, after performing the second to fourth processing steps, the newly generated black pixels are also taken into consideration, and the second to second processing steps are performed again. 4 may be performed.

The process of determining a new black pixel in the third processing step has been described above.
In the group of pixels closest to the target black pixel, the method of setting the pixel farthest from the target black pixel was used.
In addition to this method, the following first to third methods may be used.

The first method is a method of paying attention to a part of a group of pixels closest to the target black pixel and selecting the pixel at the farthest position as the black pixel.
In this method, for example, in FIG. 4, the group closest to the black pixel of interest (for example, black pixel e) is divided into several areas, and one area out of several areas is focused, This is a method in which a pixel existing at a position farthest from the black pixel e in the noted area is set as a new black pixel.

In the second method, the pixels existing on the boundary between the group of pixels closest to the black pixel of interest and the group of pixels closest to the black pixels existing around the black pixel of interest. Randomly select any one pixel from the
This is a method of making the selected pixel a black pixel. The boundary here is, for example, in FIG. 4, a connection of pixels forming an outline of a group of pixels closest to the black pixel e (a pixel group with horizontal lines in FIG. 4). Then, in the connection of pixels forming these contours, a certain one pixel is randomly selected and made to be a black pixel.

In the third method, the pixels existing on the boundary between the group of pixels closest to the black pixel of interest and the group of pixels closest to the black pixels existing around the black pixel of interest. Connection (pixel group with horizontal lines in Fig. 4)
, The connection of pixels existing on the boundary is divided into several blocks, attention is paid to a certain block, and one of the pixels in the focused block is randomly selected. The selected pixel is a black pixel.

A new black pixel may be determined using these methods.

By the way, the means for realizing the above-described first embodiment will be briefly described below.

FIG. 8 is an overall schematic configuration diagram of the first embodiment, which comprises a shortest distance pixel search unit 1, a distance calculation unit 2, a black pixel generation unit 3, a conversion pixel buffer 4 and the like. . The shortest distance pixel search unit 1 inputs the original image data and performs the processing described in the first processing step based on the content of the converted image buffer 4. It is detected to which pixel in the converted image a certain black pixel of is closest, and the pixel of the corresponding converted image is set as the black pixel (see FIG. 3). Further, the distance calculation unit 2 performs the processing described in the second processing step, and for each black pixel a to i in the converted image, each pixel of the converted image (each pixel that has not been converted to black) is The distance is calculated for each pixel, which black pixel is closest to the black pixel and how much the distance is. Further, the black pixel generation unit 3 performs the processing described in the third to fifth processing steps, and based on the content obtained by the distance calculation unit 2, each of the black pixels a to i. A group of pixels closest to the black pixel is obtained, and a new black pixel is generated based on this.

Further, FIG. 9 shows a schematic configuration of the black pixel generation unit 3. FIG. 9A shows a method of setting a pixel farthest from a black pixel of interest as a black pixel in a group of pixels closest to the black pixel of interest, or a group of pixels closest to the black pixel of interest. 3 shows a schematic configuration for realizing a method in which a pixel at the farthest position among them is set as a black pixel by paying attention to a part of the black pixel detecting unit 3.
1, a neighboring pixel detection unit 32, a longest distance pixel detection unit 33, and the like. The converted image buffer 4 and the distance calculator 2 are the same as those shown in FIG. In such a configuration, the black pixel detection unit 31 detects black pixels (black pixels a to i in the above example) based on the contents of the converted image buffer 4, and the neighboring pixel detection unit 32 detects each black pixel. Each time, a group of pixels that is considered to be closest to the black pixel is detected. Then, from the group of these pixels, the longest distance pixel detection unit 33 detects the longest distance pixel as a pixel for making a new black pixel.

FIG. 9B shows pixels among the pixels existing on the boundary between the group of pixels closest to the target black pixel and the group of pixels closest to the black pixel existing around the target black pixel. From the above, a method of randomly selecting any one pixel from the above and setting the selected pixel as a black pixel, or dividing the pixels existing on the boundary into several blocks, and paying attention to one certain block, 1 shows a schematic configuration for realizing a method of randomly selecting any one pixel from the pixels in the block of interest and setting the selected pixel as a black pixel. It is composed of a neighboring pixel detection unit 32, a boundary pixel detection unit 34, a random pixel selection unit 35, and the like. The converted image buffer 4 is the same as that shown in FIG. In such a configuration, the black pixel detection unit 31 detects black pixels (black pixels a to i in the above example) based on the contents of the converted image buffer 4, and the neighboring pixel detection unit 32 detects each black pixel. Each time, a group of pixels that is considered to be closest to the black pixel is detected. Then, from the group of these pixels, the pixel that becomes the boundary with the group of pixels that is the closest to the other black pixels is
The boundary pixel detection part 34 detects the pixel, and randomly detects one of the boundary pixels detected as a pixel to be a new black pixel.

The programs for performing the various processes in the first embodiment described above are stored in a storage medium such as a floppy disk, and the present invention also includes the storage medium.

(Second Embodiment) The first embodiment described above is the processing in the case where the black pixels are scattered in the original image, but the second embodiment is
A process will be described in which it is determined whether or not the edge portion of the image exists in the original image, and it is determined that the edge exists. That is, in the case of an image as shown in FIG. 1 in which the edge portion does not exist in the image, the process of scattering the black pixels described in the first embodiment is good, but when the edge portion exists, the edge portion does not exist. This is because if the black pixels of are scattered in the converted image, the sharpness of the edge is reduced, and a desirable result cannot be obtained.

The schematic processing of the second embodiment will be described with reference to the flowchart of FIG. In FIG. 10, first, it is determined whether or not there are black pixels in the original image (step s1). If there are black pixels, it is determined to which pixel in the converted image a certain black pixel is closest. The pixel of the corresponding converted image is detected and set as a black pixel (step s2). The processes of steps s1 and s2 are performed for all black pixels of the original image, which is a process corresponding to the first processing step described in the first embodiment. Then, after determining whether or not there is a black pixel corresponding to the black pixel of the original image in the converted image (step s3), if there is a black pixel, it is determined whether or not the black pixel is an edge portion. Is determined (step s4). In this determination, if it is determined that it is not an edge portion, the first black pixel generation processing is performed (step s5), and if it is determined that it is an edge, the second black pixel generation processing is performed (step s6). . The processing when there is no edge, that is, the processing of steps s1 to s5 corresponds to the processing described in the first embodiment.

The edge determination processing and the second black pixel generation processing will be described below.

First, the edge determination process will be described.
For example, assume that there is a converted image as shown in FIG. In this converted image, the shaded pixels are black pixel portions that have been made black pixels corresponding to the original image by the first processing step described in the first embodiment, and these black pixel portions Numerical values given to pixels other than represent the distance value to the nearest black pixel. Here, (i9, j
An example will be described in which the black pixel (9) (represented by m) is set as the target black pixel, and it is determined whether or not the black pixel m is a pixel existing in the edge portion.

First, a group of pixels closest to the black pixel m of interest is found, and in this group, the group of pixels existing near the black pixel m and closest to the black pixel exists. Find the pixel to be used. That is, the connection of the pixels forming the contour of the group of pixels closest to the black pixel m is obtained (FIG. 1).
1, the pixel with the horizontal line). Next, the distances between the pixel farthest from the black pixel m and the pixel closest to the black pixel m are obtained from the connections of the pixels forming the contour of the group of pixels closest to the black pixel m. Then, the ratio of the respective distances is compared with a predetermined threshold value to determine whether or not the black pixel m is a pixel belonging to an edge. Hereinafter, this determination will be described.

Now, in the connection of the pixels forming the contour of the group of pixels closest to the target black pixel, the distance to the pixel farthest from the target black pixel is d1, and the distance to the closest pixel is d2. If the threshold value is th1, it is determined that the black pixel belongs to an edge when (d1 / d2)> th1 and the black pixel is not an edge when (d1 / d2) ≦ th1.

For example, considering the black pixel m as an example,
Among the connections of pixels forming the outline of the group of pixels closest to the black pixel m, the pixel farthest from the black pixel m (i1
The distance d1 to (3, j11) is the square root of "20" (= 4.
47), the distance to the nearest pixel, for example, the pixel of (i9, j8) is the square root (= 1) of "1". Further, it has been found that a good result is obtained when the threshold value th1 is th1 = 2 to 3. Therefore, in this case, (d1 / d2)
Since> th1, the black pixel m is determined to be an edge.

By the way, based on the ratio of the distance d1 to the pixel farthest from the black pixel of interest and the distance d2 to the closest pixel, it can be determined whether or not the black pixel of interest is an edge. Is due to the following reasons. That is, when the pixel of interest is an edge, the black pixel of interest is not located near the center of the closed loop drawn by the connections of the pixels forming the outline of the pixel group, and the black pixel of interest can be seen from FIG. As described above, since it always exists in a biased position in the closed loop, the ratio of the distance d1 to the pixel farthest from the target black pixel and the distance d2 to the closest pixel inevitably becomes large. Therefore, the distances d1 and d
By taking the ratio of 2, it is possible to determine whether or not the black pixel is an edge.

In this way, when it is determined that the black pixel of interest is an edge, the black pixel is generated by performing the second black pixel generation processing. In the second black pixel generation processing, one of the eight pixels adjacent to the black pixel of interest at that time is set as a new black pixel according to the state at that time. A rule is set in advance to determine which of the eight adjacent black pixels is to be a new black pixel,
For example, when the position of the black pixel of interest is (i, j), the pixel of (i + 1, j + 1) may be determined as a new black pixel, or any of the eight adjacent black pixels may be selected. May be determined at random. For example,
If the pixel of (i + 1, j + 1) is decided to be a new black pixel, the black pixel m of interest in this case is (i9, j9) in the case of FIG.
The pixel of 0, j10) becomes a new black pixel.

After the process of generating a new black pixel for a certain target black pixel m is performed as described above, the distance calculation considering the new black pixel is performed as the next process step. Then, the next black pixel, for example, the black pixel n, is subjected to the above-described edge determination processing, and then a new black pixel generation processing is performed for this black pixel n. Then, the above-described processing steps are repeated until the last black pixel, such as performing the same processing steps as described above.

At this time, each newly generated black pixel is distinguished from the existing black pixel, and a new black pixel is not generated for this newly generated black pixel. .

By performing the above processing, new black pixels are generated one by one corresponding to the black pixels m, n, .... Moreover, if each new black pixel is a black pixel m, n, ...
It is generated adjacent to the black pixel.

In the second embodiment, an example in which the number of pixels is doubled vertically and horizontally and the number of black pixels is doubled instead of four times, the number of pixels is doubled vertically and horizontally.
If you want to double the number of black pixels,
Similar to the above embodiment, the above-mentioned processing may be repeated twice.

As described above, in the second embodiment, if it is determined that the black pixel of interest is the pixel existing in the edge portion, the black newly generated corresponding to the black pixel. Pixels are generated adjacent to each other instead of being generated at positions scattered far away. Thereby, the sharpness of the edge portion can be maintained even in the converted image.

Means for realizing the above-described second embodiment will be briefly described below.

FIG. 12 is an overall schematic configuration diagram of the second embodiment. In FIG. 12, the shortest distance pixel search unit 1, the distance calculation unit 2, and the conversion pixel buffer 4 are the same as those shown in FIG. 8 used in the description of the first embodiment. In the case of the embodiment, in addition to these, the edge determination unit 5, the first black pixel generation unit 6, the second black pixel generation unit 7, and the like are provided. The first
The black pixel generation unit 6 corresponds to the black pixel generation unit 3 in FIG. In addition, the second black pixel generation unit 7 performs the above-described second black pixel generation processing, and when the edge determination unit 5 determines that the black pixel of interest is the black pixel existing in the edge portion. Then, the black pixel generation processing as described above is performed.

FIG. 13 shows a schematic structure of the edge determination section 5, which includes a neighboring pixel detection section 51, a boundary pixel detection section 52, a boundary longest distance pixel detection section 53, and a boundary shortest distance pixel detection section. 54, a distance ratio comparison unit 55, and the like. The converted image buffer 4 is the same as that shown in FIG. In such a configuration, the closest pixel detection unit 51 detects a group of pixels closest to the target black pixel, and the boundary pixel detection unit 52 detects pixels forming the contour of the group. Then, the longest boundary distance pixel detection unit 53 detects the pixel at the farthest position from the black pixel of interest, and the shortest boundary distance pixel detection unit 54 detects the pixel at the closest position to the black pixel of interest. , The respective distances d in the distance ratio comparison unit 55.
1 and d2 are obtained, the ratio between them is calculated, and the result is compared with the threshold value th1 to output the determination result as to whether or not the pixel exists at the edge.

The programs for performing the various processes in the above-described second embodiment are stored in a storage medium such as a floppy disk, and the present invention also includes the storage medium.

As described above, in the second embodiment, it is determined whether the black pixel of interest is the pixel existing in the edge portion, and if it is determined that the black pixel is not present in the edge portion. Are generated by the first black pixel generation processing by dispersing new black pixels as described in the first embodiment, and are determined to be pixels existing in the edge portion. In this case, the newly generated black pixel is generated adjacent to the target black pixel. Thereby, the sharpness can be maintained even after the edge portion of the image is converted.

In the first and second embodiments described above, the distance to the black pixel of interest in the converted image is explained by using the Euclidean distance, but the distance is not limited to the Euclidean distance. For example, the same operation can be performed using a 4-neighbor distance or 8-neighbor distance.

The four-neighborhood distance is the distance between two points 1 and p2.
And the coordinates of p1 are (pi1, pj1) and the coordinates of p2 are (pi2, pj2), d = | pi1-pi2 | + | pj1-pj2 | ... (2). Also, the 8 neighborhood distance is
Similarly, the distance between two points p1 and p2 is d, the coordinates of p1 are (pi1, pj1), and the coordinates of p2 are (pi2, pj).
2), d = max (| pi1-pi2 |, | pj1-pj2 |) ... (3). The expression (3) is
pi1-pi2 | and | pj1-pj2 | are calculated and the maximum value is set as the distance between two points.

FIG. 14 shows FIG. 4 using the four-neighbor distance, and FIG. 15 shows FIG. 4 using the eight-neighbor distance. The numerical values representing the distances shown in FIGS. 14 and 15 are different from the numerical expressions shown in FIG. 4, and the numerical values themselves represent the distances. Even when such a 4-neighborhood distance or 8-neighborhood distance is used, the numerical value representing the distance is different from the case where the Euclidean distance described in the first and second embodiments is used, but the processing is the same as in the first embodiment. It can be implemented in the same manner as described in the first and second embodiments.

[0090]

As described above, according to the present invention, when converting an original image at an arbitrary magnification, in the converted image,
The black pixel newly generated by the magnification conversion is generated at a position away from any of the black pixels existing from the beginning, so when the original image is scale-converted, it is converted into the original image. The existing black pixels do not exist in a biased state in the converted image after the magnification conversion, the black pixels can be scattered over the entire image, and a good image can be obtained.

Further, according to the present invention, it is judged in the converted image whether the black pixel in the converted image corresponding to the black pixel in the original image exists in the edge portion of the image, and it is judged that the pixel is not the pixel existing in the edge portion. If, as described above,
If black pixels do not exist in a biased state in the converted image after magnification conversion, the black pixels are scattered over the entire image, and if it is determined that black pixels exist in the edge part, the black pixels The black pixel newly generated corresponding to is generated at a position adjacent to the black pixel existing from the beginning. Thereby, the sharpness of the edge portion can be maintained even in the converted image.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an original image for explaining a first embodiment of the present invention.

FIG. 2 is a diagram showing a converted image in which the number of pixels is doubled vertically and horizontally with respect to the original image.

FIG. 3 is a diagram showing an example in which a pixel of a converted image closest to a center point of a black pixel of an original image is a black pixel.

FIG. 4 shows for each black pixel defined in FIG. 3, each pixel of the converted image (each pixel that has not been converted to black) is closest to which black pixel and how much distance there is. The figure which shows the result of distance calculation for every one pixel, and the example of the group of pixels which are the closest to a certain black pixel of interest.

FIG. 5 is a diagram illustrating an example of limiting a range for obtaining a distance to a black pixel of interest when a group of pixels closest to a certain black pixel of interest is obtained.

FIG. 6 is a diagram illustrating an example of a rule for determining a new black pixel for a certain target black pixel.

FIG. 7 is a diagram showing a result of distance calculation in consideration of a new black pixel.

FIG. 8 is a block diagram showing the overall configuration of the first embodiment.

FIG. 9 is a block diagram showing a configuration of a black pixel generation unit according to the first embodiment.

FIG. 10 is a flowchart illustrating the outline of the overall processing according to the second embodiment.

FIG. 11 is a diagram showing an example of an image for explaining edge determination in the second embodiment.

FIG. 12 is a block diagram showing an overall configuration of a second embodiment.

FIG. 13 is a block diagram showing a configuration of an edge determination unit according to the second embodiment.

FIG. 14 is a diagram showing an example of a converted image when four neighboring distances are used as a distance.

FIG. 15 is a diagram showing an example of a converted image when 8 neighboring distances are used as a distance.

FIG. 16 is a diagram illustrating an example of enlarging an image such as a character or a line drawing by using a projection method.

FIG. 17 is a diagram illustrating an example of a conventional method of enlarging an image that has been pseudo-halftone processed using the projection method.

[Explanation of symbols]

A, B, ..., I ... Black pixels existing in the original image a, b, ..., i ... Black pixels corresponding to the original image in the converted image e1 ... Black pixels in the converted image New black pixel for a 1 ... Shortest distance pixel search unit 2 ... Distance calculation unit 3 ... Black pixel generation unit 4 ... Converted image buffer 5 ... Edge determination unit 6 ... First Black pixel generation unit 7 ... second black pixel generation unit 31 ... black pixel detection unit 32 ... neighboring pixel detection unit 33 ... longest distance pixel detection unit 34 ... boundary pixel detection unit 35 ... Random pixel selection section 53 ... Longest boundary distance pixel detection section 54 ... Shortest boundary distance pixel detection section 55 ... Distance ratio comparison section Z1, Z2, Z3 ... Area L1, 12, ...・ 、 L17 ・ ・ ・ Line

Claims (26)

[Claims] 1. A pixel density conversion method for converting a pixel density by converting the number of pixels of an original image in a vertical direction and a horizontal direction at an arbitrary scale factor. By generating a converted image obtained by converting in, by associating the converted image and the original image based on a predetermined relationship,
The pixels of the converted image corresponding to each black pixel existing in the original image are specified, and the pixels of the converted image specified by this are made black pixels, and the predetermined pixels are made black pixels by being associated with the original image. In the converted image, the distance between each black pixel and each pixel other than the black pixel is calculated, and the distance between that pixel and the black pixel closest to that pixel is calculated for each pixel. A pixel density conversion method characterized in that a new black pixel is generated based on the obtained distance. 2. A distance between the certain pixel and a black pixel closest to the certain pixel is a Euclidean distance, a neighborhood distance, 8
2. Any one of the near distances is used.
The described pixel density conversion method. 3. In a process of obtaining a distance between the certain pixel and a black pixel closest to the pixel, a maximum value is set in advance for the obtained distance, and a black pixel is not found within the distance of the maximum value. The pixel density conversion method according to claim 1, wherein the distance to the pixel is not calculated. 4. The process of generating a new black pixel based on the distance is such that, when a certain black pixel is set as a target black pixel, a group of pixels that are the closest to the target black pixel is set as the target pixel. Search from the obtained distance, in the group of pixels,
The pixel density conversion method according to claim 1, wherein a pixel existing at a position farthest from the black pixel of interest is set as a new black pixel. 5. The process of generating a new black pixel based on the distance, when a certain black pixel is set as a target black pixel, sets a group of pixels that are the closest to the target black pixel as the target black pixel. Searching from the obtained distance, paying attention to a certain part of the group of pixels, and in the focused part, a pixel farthest from the focused black pixel is set as a new black pixel. The pixel density conversion method according to claim 1. 6. The process of generating a new black pixel based on the distance is such that, when a certain black pixel is set as a target black pixel, a group of pixels that is the closest to the target black pixel is set as the target pixel. The present invention is characterized in that a certain one pixel is randomly selected in the connection of pixels forming the contour of the group of pixels by searching from the obtained distance, and the selected pixel is set as a new black pixel. The pixel density conversion method according to claim 1. 7. The process of generating a new black pixel based on the distance is such that, when a certain black pixel is set as a target black pixel, a group of pixels which is closest to the target black pixel is set as the Searching from the obtained distance, paying attention to a certain part of the connection of pixels forming the outline of the pixel group, randomly selecting a certain pixel in the focused part, and selecting it. The pixel density conversion method according to claim 1, wherein the pixel is a new black pixel. 8. A pixel density conversion method for converting the number of pixels of an original image in the vertical direction and the horizontal direction at an arbitrary magnification to convert the pixel density, wherein the number of pixels of the original image is arbitrarily adjusted in the vertical direction and the horizontal direction. By generating a converted image obtained by converting in, by associating the converted image and the original image based on a predetermined relationship,
The pixels of the converted image corresponding to each black pixel existing in the original image are specified, and the pixels of the converted image specified by this are made black pixels, and the predetermined pixels are made black pixels by being associated with the original image. In the converted image, the distance between a pixel other than the black pixel and the black pixel is calculated, and for each pixel, the distance between the pixel and the black pixel closest to the pixel is calculated. When a certain black pixel in this converted image is set as the black pixel of interest, it is determined whether the black pixel of interest exists in the edge portion of the image, and the black pixel of interest exists in the edge portion. If it is determined that there is not, a pixel existing at a position away from the black pixel of interest is selected based on the obtained distance value, the selected pixel is set as a new black pixel, and the black of interest is selected. It is determined that the pixel exists at the edge. If determined, one of the pixels adjacent to the target black pixel is set as a new black pixel, and the pixel density conversion method is characterized. 9. The determination of whether or not the black pixel of interest is present at an edge portion of an image is performed by searching a group of pixels that are said to be closest to the black pixel of interest from the obtained distance and In the connection of pixels forming the outline of the group of
Find the ratio of the distance from the target black pixel to the target black pixel at the farthest pixel and the distance from the target black pixel to the closest black pixel to the target black pixel, and calculate the ratio. 9. The pixel density conversion method according to claim 8, wherein it is determined whether or not the black pixel of interest is a pixel belonging to an edge portion based on the size of. 10. The process of generating a new black pixel when it is determined that the black pixel of interest does not exist in the edge portion, the group of pixels determined to be closest to the black pixel of interest is obtained. Search from the distance, within the group of pixels,
The pixel density conversion method according to claim 8, wherein a pixel existing at a position farthest from the black pixel of interest is set as a new black pixel. 11. A process of generating a new black pixel when it is determined that the black pixel of interest does not exist in an edge portion, the group of pixels determined to be closest to the black pixel of interest is obtained. It is characterized in that a search is performed from a distance, attention is paid to a certain part of the group of pixels, and a pixel existing at a position farthest from the noted black pixel in the noted part is set as a new black pixel. The pixel density conversion method according to claim 8. 12. The process of generating a new black pixel when it is determined that the black pixel of interest does not exist in the edge portion, the group of pixels determined to be closest to the black pixel of interest is obtained. 7. A method of searching from a distance, randomly selecting a certain pixel from among the connections of pixels forming the contour of the group of pixels, and selecting the selected pixel as a new black pixel. 8. The pixel density conversion method as described in 8. 13. The process of generating a new black pixel when it is determined that the black pixel of interest does not exist in the edge portion, the group of pixels that is the closest to the black pixel of interest is obtained. Searching from the distance, paying attention to a part of the connection of pixels forming the outline of the pixel group, randomly selecting one pixel in the focused part, and selecting the selected pixel. The pixel density conversion method according to claim 8, wherein a new black pixel is used. 14. A pixel density conversion device for converting the number of pixels of an original image in the vertical direction and the horizontal direction at an arbitrary scale factor to convert the pixel density. Based on the correspondence between the converted image and the original image obtained by
Means for associating the black pixels of the original image with the pixels of the converted image and setting the associated pixels of the converted image as black pixels; In the converted image, the distance between each black pixel and each pixel other than the black pixel is calculated, and the distance between each pixel and the black pixel closest to that pixel is calculated. A pixel density conversion device comprising: a calculation means; and a black pixel generation means for generating a new black pixel based on the distance obtained by the distance calculation means. 15. The distance between a pixel and a black pixel closest to the pixel calculated by the distance calculation means is
15. The pixel density conversion device according to claim 14, wherein any one of Euclidean distance, 4 neighborhood distance, and 8 neighborhood distance is used. 16. The process of obtaining the distance between a pixel and a black pixel closest to the pixel by the distance calculating means sets a maximum value in advance to the obtained distance, and sets the black pixel within the distance of the maximum value. 2. If the distance is not found, the distance to the pixel is not calculated.
4. The pixel density conversion device described in 4. 17. The black pixel generation means, when a certain black pixel is set as a black pixel of interest, searches for a group of pixels that are said to be closest to the black pixel of interest from the obtained distance, 15. The pixel density conversion device according to claim 14, wherein a pixel existing farthest from the black pixel of interest in the group of pixels is set as a new black pixel. 18. The black pixel generation means, when a certain black pixel is set as a black pixel of interest, searches for a group of pixels that are said to be closest to the black pixel of interest from the obtained distance, 15. The pixel according to claim 14, wherein a certain part of a group of pixels is focused on, and a pixel existing at a position farthest from the focused black pixel is set as a new black pixel in the focused part. Density converter. 19. The black pixel generation means, when a certain black pixel is set as a black pixel of interest, searches for a group of pixels that are said to be closest to the black pixel of interest from the obtained distance, 15. The pixel density conversion device according to claim 14, wherein one of the pixels forming a contour of the group of pixels is randomly selected and a new black pixel is selected as the pixel. 20. When the black pixel of interest is a black pixel of interest, the black pixel generation means searches for a group of pixels that are said to be closest to the black pixel of interest from the obtained distance, and A feature is that attention is paid to a certain part of the connection of pixels forming the outline of a group of pixels, and one pixel is randomly selected in the attention part and the pixel is set as a new black pixel. The pixel density conversion device according to claim 14. 21. A pixel density conversion device for converting the number of pixels of an original image in the vertical direction and the horizontal direction at an arbitrary ratio to convert the pixel density. A means for associating the black pixels of the original image with the pixels of the converted image based on the correspondence relationship between the converted image and the original image obtained by converting the pixels of the associated converted image to black pixels; , In the converted image in which predetermined pixels are black pixels by being associated with the original image, the distance between each black pixel and each pixel other than the black pixel is calculated, and for each pixel , A distance calculating means for obtaining a distance between the pixel and a black pixel closest to the pixel, and, when a certain black pixel in the converted image is set as the target black pixel, the target black pixel is Edge judgment to determine whether or not the edge exists The determining unit and the edge determining unit determine that the black pixel of interest does not exist in the edge portion, and the position is separated from the black pixel of interest based on the obtained distance value. It is determined by the first black pixel generation unit that selects an existing pixel and uses the selected pixel as a new black pixel and the edge determination unit that the target black pixel is present in the edge portion. In this case, the pixel density conversion device further includes a second black pixel generation unit that makes any of the pixels adjacent to the target black pixel a new black pixel. 22. The edge determining means searches for a group of pixels that is said to be closest to the black pixel of interest from the obtained distance, and in a connection of pixels forming an outline of the group of pixels, Find the ratio of the distance from the target black pixel to the target black pixel at the farthest pixel and the distance from the target black pixel to the closest black pixel to the target black pixel, and calculate the ratio. 22. The pixel density conversion device according to claim 21, wherein it is determined whether or not the black pixel of interest is a pixel belonging to an edge portion based on the size of the. 23. The first black pixel generation means selects a pixel existing farthest from the black pixel of interest from among a group of pixels closest to the black pixel of interest as a new black pixel. The pixel density conversion device according to claim 21, wherein the pixel density conversion device is a pixel. 24. The first black pixel generation means focuses on a portion of a group of pixels that is said to be closest to the focused black pixel, and the focused black pixel is included in the focused portion. 22. The pixel density conversion device according to claim 21, wherein a pixel existing at a position farthest from is a new black pixel. 25. The first black pixel generation means randomly selects a certain pixel from among the connections of pixels forming an outline of a group of pixels that are the closest to the target black pixel. 22. The pixel density conversion device according to claim 21, wherein the selected pixel is a new black pixel. 26. The first black pixel generation means pays attention to a part of a connection of pixels forming an outline of a group of pixels that are the closest to the black pixel of interest, and the focused part 22. The pixel density conversion device according to claim 21, wherein one of the pixels is randomly selected, and the selected pixel is set as a new black pixel.