JP3024975B2 - Reduction conversion method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduction conversion method for an image expressed in black and white binary with little image quality deterioration. In particular,
This is a reduction conversion method that prevents the disappearance of a fine line so as not to generate a cut even for an irregular fine line generated when an image is read from an image reading device such as a facsimile.

(Prior Art) As a conventional binary image reduction conversion method, an SPC method (Selecti
ve Processing Conversion: Proceedings of the 7th Annual Conference of the Institute of Image Electronics Engineers of Japan, Proceedings No. 10, May 19, 1975, and area determination methods (IEICE Technical Report PRL81-92, February 19, 1982) Has been announced.

In the SPC method, when the converted image is mapped to the original image, the value of the pixel (original pixel) of the original image (original pixel) closest to the pixel (or converted pixel) of the converted image to be obtained is, for example, This is a method of substituting a value representing white or black in the case of being represented by two values of white and black --- similarly referred to as "value" in the present specification. In the area determination method, the four original pixels closest to the converted pixel are selected, the average density of the four original pixels projected onto the converted pixel position is calculated, threshold processing is performed, and the value of the converted pixel is calculated. It is a method.

However, in these conversion methods, if there is a black or white thin line on the original image, the thin line is not the original pixel closest to the converted pixel position, or the average density projected by the four original pixels is thresholded. As a result, when the value of the conversion pixel closest to the position of the thin line does not match the value of the thin line, the corresponding thin line may disappear on the conversion screen.

FIG. 14 shows an example in which the thin line disappears. FIG. 14 shows a correspondence relationship between original pixels and converted pixels in the black-and-white binary image reduction conversion when the conversion ratio α in the horizontal direction is α = 1/4. Here, P _{i−4 to} P _{i + 3} represent the original pixels, and Q _{j−1 to} Q _{j + 1}
Indicates a converted pixel. ○ is the original pixel of white value,
● is the original pixel of the black value. The distance between the original pixels is set to 1
And the distance between the conversion pixels is represented by 1 / α.

The SPC method or area determination method, in the example of Figure 14, Q _j-1
Is assigned the value of P _i-4 , Q _j is assigned the value of P _i , and Q _{j + 1} is assigned the value of P _{i + 3} , so that Q _j−1 , Q _j and Q _{j + 1} are all white. Value, and there is no converted pixel to save the value of the black thin line.
In both cases (a) and (b) of FIG. 14, the disappearance of the thin line occurs. That is, in FIG. 14A, a thin line having a line width of 3 pixels located on the left side of Q _j disappears, and in FIG. 14B, a thin line having a line width of 2 pixels located on the right side of Q _j disappears. As described above, these conversion methods have a disadvantage that the image quality is not good because the black fine line disappears and the blur is generated, and the white fine line disappears.

In addition, in order to prevent the black thin line from disappearing, a method of calculating a logical sum of a plurality of original pixels and assigning the calculation result to a converted pixel (logical sum method) has been considered (facsimile line density). Examination of conversion, IEEJ Journal, Vo17, 197
8). However, in the logical sum method, when a white thin line is present on the original image, the white thin line may disappear on the converted image, and there is a disadvantage that the image quality is deteriorated due to collapse.

Also, when there is a black thin line having a line width of 1 pixel on the original image, the values of the two converted pixels positioned so as to sandwich the thin line may both be black, and as a result, the value of the thin line on the converted image It is thicker even though it is performing reduction conversion,
There is a drawback that image quality deteriorates.

In addition, in order to solve the drawbacks of the above-described conversion method, a thin line is determined, and if there is a thin line, the value of the thin line is substituted into a conversion pixel to prevent the line width of the thin line from disappearing (Thin Line Preserva- tion).
tion Method: Fine line loss prevention reduction conversion method, IEICE ED84-
26, June 22, 1984). But TP
Since the method targets only one pixel as the line width of the thin line, the thin line disappears when the conversion ratio decreases. 14th
In the cases of FIGS. 9A and 9B, even in the TP method, the thin line disappears because there is no converted pixel for storing the value of the thin line (in the figure, ●). As described above, in the TP method, a thin line having a line width of 2 pixels or more disappears, and there is a disadvantage that image quality is deteriorated.

Furthermore, in order to solve the drawbacks of the above-mentioned conversion method, a thin line having a line width of 1 pixel or more is determined, and if there is a thin line, the value of the thin line is substituted for the converted pixel to prevent the line width of the thin line from disappearing. A conversion method (Japanese Patent Application No. 62-236087, hereinafter referred to as the X method on September 22, 1987) has been proposed.

In the X method, the thin line is determined using the reference pixels shown in FIG. That is, as the thin line determination condition, two (n + 1) = 8 original pixels in one column are referred to in the horizontal and vertical directions centering on the original pixel at the shortest distance to the conversion pixel of interest. However, when a fine line has irregularities when using a reference pixel of the X method, the fine line may disappear. An example is shown in FIG.

FIG. 16 shows a case where a thin line having a line width of 1 pixel exists in the horizontal direction from P _−4,1 to P _1,1 and there are two protrusions at P _−3,0 , P _0,0 . Is shown. In FIG. 16, in the X method, P _−3,0 ,
P _-2,0, P _{-1, 0,} the value of P _0.0, determines that the vertical white thin line having a line width of 2 pixels P _-2,0 and P _{-1, 0} present, to the target converted pixel A white value is substituted, and a thin line with a horizontal line width of one pixel from P _−4,1 to P _1,1 disappears. As described above, when the fine lines have irregularities, the fine lines may not be preserved, and there is a disadvantage that the image quality is deteriorated.

(Object of the Invention) The present invention solves the above-mentioned drawbacks of the reduction conversion method.
When the conversion ratio α is 1 / n> α ≧ 1 / (n + 1), a reference pixel is selected according to the conversion ratio so that all thin lines having a line width of n pixels or less that can be lost can be determined. Judge thin lines using pixels, save them on the conversion screen so that they do not disappear, prevent image quality degradation, and create uneven lines that occur when images are read from image reading devices such as facsimile. Another object of the present invention is to provide a reduction conversion method capable of preventing the disappearance of a thin line so as not to cause disconnection.

(Constitution of the Invention) The present invention provides a conversion ratio α _x in the horizontal direction and the vertical direction,
If α _y is 1 / n _x > α _x ≧ 1 / (n _x +1), 1 / _ny > α _y ≧ 1 / (n _y +1), where _nx and _ny are natural numbers, mainly refers horizontal 2 (n _x +1) pieces × vertical 2 (n _y +1) total 4 (n _x +1) consisting of pieces × (n _y +1) all pieces of original pixels or part, the original The line width in the image is the horizontal line width
n _x pixels is less and vertical line width n _y pixels below a thin line, and detects the fine line of the horizontal, vertical and diagonal directions to a predetermined value or more in length, at the time of thin line detection and conversion of the shortest distance to the fine line It is characterized in that a value of a thin line is substituted into a pixel in a form representing the thin line so that the thin line does not disappear.

The difference between the TP method and the conventional reduced conversion method except the X method is that a thin line is determined and a unit for storing the determined thin line is provided.

Further, the TP method has means for judging a thin line and storing the thin line. However, the condition for judging the thin line is limited to only a thin line having a line width of 1 pixel.
Not only the thin line of the pixel but also the area of reference of the original pixel is changed according to the reduction conversion ratio, and all of the horizontal line width _nx pixels or less and the vertical line width _ny pixels or less that may be lost The difference is that the thin line is used as a determination target.

Further, since the X method has no means for determining the length of the fine line, the fine line disappears when the fine line has irregularities. On the other hand, in the present invention, a thin line having a length equal to or more than a predetermined value in the horizontal / vertical / diagonal direction is used as a thin line, and a means for determining a thin line even when there is unevenness in the thin line is provided. The difference is that the uneven fine line is prevented from disappearing.

From the above, as compared with the conventional conversion method, the horizontal line width n _x pixels or less and vertical line widths n _y of the horizontal, vertical and diagonal directions at pixels or less fine line even if there is unevenness in the fine line The difference is that the loss can be prevented.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention.
Is an original image reading means for reading the original image, 2 is a converted pixel position detecting means for obtaining a positional relationship between the converted pixels and the original pixels when each converted pixel is mapped to the original image, and 3 is a horizontal direction centering on the converted pixel of interest. 2 (n _x +1) × vertical 2 (n _y
+1) reference pixel reading means for reading the value of the original pixels, 4 is less fine lines and line width n _y pixels in the vertical direction is less than the value from the line width n _x pixels of the reference pixels read out by said means 3 horizontal A thin line detecting means for detecting a thin line in the direction,
5 is a means for obtaining a conversion pixel having the shortest distance from the thin line detected by the means 4, and 6 is a means for converting the value of the thin line by the means 5 when the conversion pixel of interest is the conversion pixel having the shortest distance to the thin line. Means 7 for substituting into the pixel, when the fine line is not detected by the means 4 and when the converted pixel of the shortest distance to the fine line is not the converted pixel of interest even if the thin line is detected, the conversion of interest is performed by a predetermined logical operation method. The conversion pixel value calculation means 8 for calculating the pixel value is a conversion pixel value determination means for determining the conversion pixel value from the means 6 and 7.

FIG. 2 shows an example of the flow of the reduction conversion method according to the present invention. In the reduction conversion process, a value of a conversion pixel is determined in order according to a fixed rule, and the conversion image is created by repeatedly performing the determination. Hereinafter, the reduction conversion method of the present invention will be described with reference to the embodiment of FIG. 1 and FIG.

When the conversion ratio in the horizontal direction is different from the conversion ratio in the vertical direction, it can be realized by performing the conversion separately in the horizontal direction and the vertical direction. In the following description, it is assumed that the conversion ratio in the horizontal direction and the vertical direction is the same, and the conversion ratio α is 1 / n> α ≧ 1 / (n + 1), where n is a natural number.

The original image is read by the original image reading means 1, the converted image is first mapped onto the original image by the converted pixel position detecting means 2, and the position of the focused converted pixel on the original image is obtained.

Next, the reference pixel reading means 3 sets 2 (n + 1) pixels in the horizontal direction × 2 (n) in the vertical direction around the conversion pixel of interest.
Read out +1) original images as reference pixels. FIG. 3 shows an example of an original image to be read when the conversion ratio α is 1/3> α ≧ 1/4.

As shown in FIG. 3, 2 (n + 1) horizontal directions × 2 (n + 1) vertical directions = 8 × 8 =
Refers to 64 original images. As a specific example of the reference method, the position of the conversion pixel of interest in the original image is detected, and the contents of the line memory for 2 (n + 1) lines of the original image are stored in the horizontal direction 2 ( n +
This can be realized by sequentially reading 1) × 2 (n + 1) original images in the vertical direction.

Next, a thin line existing in the reference pixel is detected by the thin line detecting means 4 according to a predetermined thin line determination condition of a line width of n pixels or less.

FIG. 4 shows that when the conversion ratio α is 1/2> α ≧ 1/3,
A specific example 1 (referred to as a method A) of a thin line determination condition according to the present invention is shown.

In FIG. 4, Q ₀ indicates the position of the conversion pixel of interest. The position of the conversion pixel Q ₀ of interest is determined based on the positional relationship with the four nearest original images surrounding Q ₀ , and the four original pixels P _0,0 , P _−1,0 , P _0,1 , P
Classification can be made in a total of four _types when the shortest distance is _-1 , ₁ .

There is a case where the position of the conversion pixel Q ₀ of interest is equidistant from two adjacent pixels among the four nearest neighbor original pixels, or a case where the position is equidistant from all the four nearest neighbors. By determining the shortest distance original pixel, the position of the conversion pixel Q ₀ of interest can be classified into the four types described above.

From FIG. 4 onward, a thin line determination condition formula will be shown according to these four classifications. In the A method, m original images having the same value are continuous (where m is a natural number equal to or less than n), and the m original images on both sides thereof are different from the values of the m original pixels. In this method, when a thin line having a width of m pixels has a length of 2 pixels or more, the thin line is determined.

FIG. 4 shows the reference pixel and thin line determination conditions when the conversion ratio α is 1/2> α ≧ 1/3. In method A, 2 (n + 1) horizontal directions × 2 vertical directions
Of the (n + 1) reference pixels, 4 (2n + 1) reference pixels are used for the thin line determination condition.

That is, when the conversion ratio α is 1/2> α ≧ 1/3, 20 reference pixels are used. A specific example of a thin line determination condition is shown in the figure.

Equations A- (1) to A- in FIGS. 4 (1) to (4)
(4), Formulas A- (7) to A- (10), Formulas A- (13) to
Equations A- (16), A- (19) to A- (22) are conditions for determining a thin line having a line width of one pixel. Fig. 4 (1)-
Formulas A- (5), A- (6), A- (11) of (4),
Formula A- (12), Formula A- (17), Formula A- (18), Formula A-
(23), Expression A- (24) are conditions for determining a thin line having a line width of 2 pixels. The position of the conversion pixel Q ₀ of interest is located near the four original pixels P _0,0 ,
P _-1,0, P _0,1, determines whether the shortest distance to any of the P _-1,1, Fig. 4 according to the determination (1) for selecting one of the - (4) . It is checked whether the conditions of the expressions A- (1) to A- (24) are satisfied in any of the selected FIGS. 4 (1) to (4). And
If there is no formula that holds, it is possible to detect a thin line having a length of 2 pixels or more by determining that there is no thin line.

FIG. 5 shows the reference pixel and thin line determination conditions according to the method A of the present invention when the conversion ratio α is 1/3> α ≧ 1/4.
In this case, of the 2 (n + 1) × 2 (n + 1) reference pixels extracted in the horizontal direction, 4 (2n + 1) reference pixels, that is, 28 reference pixels are used.

A specific example of a thin line determination condition is shown in the figure. Formulas A- (25) to A- (30), A-
Expressions (37) to A- (42), Expressions A- (49) to A- (54), and Expressions A- (61) to-(66) are conditions for determining a thin line having a line width of one pixel.

In addition, the equations A- (31) to A- of FIGS. 5 (1) to (12) are used.
(34), Formulas A- (43) to A- (46), Formulas A- (55) to
A- (58) and Expressions A- (67) to A- (70) are conditions for determining a thin line having a line width of 2 pixels.

In addition, equations A- (35) to A- in FIGS. 5 (1) to (12) are used.
(36), Formulas A- (47) to A- (48), Formulas A- (59) to
A- (60) and Expressions A- (71) to-(72) are conditions for determining a thin line having a line width of 3 pixels.

The position of the conversion pixel Q ₀ of interest is located near the four original pixels P _0,0 , P
_{-1, 0,} P _{0, 1,} determines whether the shortest distance to any of the P _-1,1, Figure 5 in accordance with the determination (1) for selecting one of the - (12). It is checked whether or not the conditions of Expressions A- (25) to A- (72) are satisfied in any of the selected FIGS. 5 (1) to (12). And
When there is no formula that holds, it is possible to detect a thin line having a length of 2 pixels or more when 1/3> α ≧ 1/4 by determining that there is no thin line.

Compared with the method A of the present invention, the conversion ratio α is 1/2> α ≧ 1/3.
Although the case where 1/3> α ≧ 1/4 has been described, generally 1 / n
In the case of> α ≧ 1 / (n + 1), a thin line can be detected in the same manner as in the above method.

In FIG. 6, when the conversion ratio α is 1/1> α ≧ 1/2,
7 shows a specific example 2 (referred to as a method B) of a thin line determination condition according to the present invention.

In the method B, a thin line having a line width of m pixels exists and the line width is m.
This is a method of determining a thin line when a thin line of pixels exists with a length of 3 pixels or more.

FIG. 6 shows the reference pixel and thin line determination conditions when the conversion ratio α is 1/1> α ≧ 1/2. In the B method, 2 (n + 1) horizontal directions × 2 vertical directions
2 (n + 2) (n + 1) of (n + 1) reference pixels
The reference pixels are used as the thin line determination condition.

That is, when the conversion ratio α is 1/1> α ≧ 1/2, 12 reference pixels are used. A specific example of a thin line determination condition is shown in the figure. Equations B- (1) to B- (8) are conditions for determining a thin line having a line width of one pixel.

The position of the conversion pixel Q ₀ of interest is located near the four original pixels P _0,0 , P
_{-1, 0,} P _{0, 1,} determines whether the shortest distance to any of the P _-1,1, selects a determination condition expression in accordance with the determination. Judgment condition formula B
It is checked whether or not the condition of the determination condition selected from-(1) to Expression B- (8) is satisfied. If there is an expression that is satisfied, it is determined that a thin line exists. By making it absent, a thin line having a length of 3 pixels or more can be detected.

FIG. 7 shows the reference pixel and thin line determination conditions according to the method B of the present invention when the conversion ratio α is 1/2> α ≧ 1/3.

In the method B, 2 (n + 2) (n) of 2 (n + 1) × 2 (n + 1) reference pixels extracted in the horizontal direction
+1) reference pixels, that is, the conversion ratio α is 1/2> α
If ≧ 1 /, 24 reference pixels are used. A specific example of a thin line determination condition is shown in the figure. Fig. 7 (1)-
Formulas B- (9) to B- (12) and B- (15) to B- (4)
-(18), Formulas B- (21) to B- (24), Formulas B- (27) to
B- (30) is a conditional expression for determining a thin line having a line width of one pixel. Equations B- (13) to B- (14), B- (19) to B- (20), and B- (25) to B- (26) in FIGS. 7 (1) to (4) ,
Expressions B- (31) to B- (32) are conditions for determining a thin line having a line width of 2 pixels.

The position of the conversion pixel Q ₀ of interest is located near the four original pixels P _0,0 , P
_{-1, 0,} P _{0, 1,} determines whether the shortest distance to any of the P _-1,1, Figure 7 according to the determination (1) selects - one from (4). It is checked whether or not the conditions of equations B- (9) to B- (32) are satisfied in any of the selected FIGS. 7 (1) to (4). If there is no formula that holds, it is possible to detect a thin line having a length of 3 pixels or more by assuming that there is no thin line.

FIG. 8 shows the reference pixel and thin line determination conditions according to the method B of the present invention when the conversion ratio α is 1/3> α ≧ 1/4. In the method B, 2 (n + 1) of 2 (n + 1) × 2 (n + 1) reference pixels extracted in the horizontal direction are extracted.
2) (n + 1) reference pixels, that is, the conversion ratio α is
When 1/3> α ≧ 1/4, 40 reference pixels are used. A specific example of a thin line determination condition is shown in the figure.

Equations B- (33) to B- (3) in FIGS. 8 (1) to (12)
8), Formula B- (45) to Formula B- (50), Formula B- (57) to Formula B- (62), Formula B- (69) to Formula B- (74) are thin lines having a line width of 1 pixel. Is the determination condition.

Also, equations B- (33) to B- in FIGS. 8 (1) to (12) are used.
(38), Formula B- (45) to Formula B- (50), Formula B- (57)
Equations B- (62), B- (69) to B- (74) are conditions for determining a thin line having a line width of one pixel.

In addition, equations B- (39) to B- in FIGS. 8 (1) to (12) are used.
(42), Formula B- (51) to Formula B- (54), Formula B- (63)
Formula B- (66) Formula B- (75) to Formula B- (78) are conditions for determining a thin line having a line width of 2 pixels.

In addition, equations B- (43) to B- in FIGS. 8 (1) to (12) are used.
(44), Formula B- (55) to Formula B- (56), Formula B- (67)
Formula B- (68) Formula B- (79) to Formula B- (80) are conditions for determining a thin line having a line width of 3 pixels. It is determined to which of the four neighboring original pixels P _0,0 , P _−1,0 , P _0,1 , P _−1,1 the position of the conversion pixel Q ₀ of _interest is closest, and according to the determination, Fig. 8 (1)-
Select one from (12). Selected Fig. 8 (1)-
In any one of (12), the formulas B- (33) to B- (80)
It is checked whether or not an expression that satisfies the condition is satisfied. If there is an expression that is satisfied, it is assumed that a thin line exists. If there is no expression that is satisfied, it is determined that there is no thin line. Detection is possible.

For the method B of the present invention, the conversion ratio α is 1/1> α ≧ 1/2, 1 /
2> α ≧ 1/3, 1/3> α ≧ 1/4
In general, also in the case of 1 / n> α ≧ 1 (n + 1), a thin line can be similarly detected by the method described above.

In FIG. 9, when the conversion ratio α is 1/1> α ≧ 1/2,
A specific example 3 (referred to as a C method) of a thin line determination condition according to the present invention is shown.

In the C method, a thin line having a line width of m pixels exists and the thin line m
When a thin line of pixels exists in the vertical, horizontal, and oblique directions with a length of 3 pixels or more, or when a thin line with a line width of 1 pixel exists in the diagonal direction with a length of 2 pixels or more, it is determined to be a thin line. How to

FIG. 9 shows reference pixel and thin line determination conditions when the conversion ratio α is 1/1> α ≧ 1/2. In the C method, 16 reference pixels are used when the conversion ratio α is 1/1> α ≧ 1/2. A specific example of a thin line determination condition is shown in the figure.

Equations C- (1) to C- (12) in FIG. 9 are conditions for determining a thin line having a line width of one pixel. In addition, Formula C- (3), Formula C-
(6), Expression C- (9), and Expression C- (12) are conditions for determining a thin line in which a thin line having a line width of 1 pixel exists in a diagonal direction with a length of 2 pixels or more.

In addition, the position of the conversion pixel Q ₀ of interest is located near four original pixels P _0,0 ,
P _-1,0, P _0,1, to determine whether it is the shortest distance to any of the P _-1,1, to select the judgment conditions in accordance with the determination. Judgment condition formula C-
It is checked whether or not the condition of the judgment condition formula selected from (1) to C- (12) is satisfied. If there is a formula that is satisfied, a thin line exists. If there is no formula, no thin line exists. By doing so, it is possible to detect a thin line having a length of 3 pixels or more in the vertical, horizontal and oblique directions, and to detect a thin line having a line width of 1 pixel and a length of 2 pixels or more in the oblique direction.

FIG. 10 shows the case where the conversion ratio α is 1 / 2α ≧ 1/3,
9 illustrates a reference pixel and a thin line determination condition according to the method C of the present invention. In the C method, when the conversion ratio α is ＞> α ≧ 1 /, the extracted horizontal direction is 2 (n + 1) × vertical direction 2 (n + 1)
Of the 4 reference pixels, 4 (n + 1) ² -4 reference pixels,
That is, 32 reference pixels are used. A specific example of a thin line determination condition is shown in the figure.

Equations C- (13) to C- (1) in FIGS. 10 (1) to (14)
6), Formula C- (20) to Formula C- (23), Formula C- (27) to Formula C- (30), Formula C- (34) to Formula C- (37) have a line width of one pixel. This is a determination condition formula for a thin line having a length of 3 pixels or more in the vertical, horizontal, and oblique directions.

Further, the equations C- (17) to C- in FIGS. 10 (1) to (4) are used.
(18), Formula C- (24) to Formula C- (25), Formula C- (31)
Expressions C- (32) and C- (38) to C- (39) are conditions for determining a thin line having a line width of 2 pixels and a length of 3 pixels or more in vertical, horizontal, and oblique directions.

Further, the equations C- (19) and C- in FIGS. 10 (1) to (4) are used.
(26), Equations C- (33) and C- (40) are conditions for determining a thin line having a line width of 1 pixel and a diagonal length of 2 pixels or more.

The position of the conversion pixel Q ₀ of interest is the nearest four original pixels P _0,0 , P
_{-1, 0,} P _{0, 1,} determines whether the shortest distance to any of the P _-1,1, Figure 10 according to the determination (1) selecting one from - (4). It is checked whether or not the conditions of the expressions C- (13) to C- (40) are satisfied in any of the selected FIGS. 10 (1) to (4). If there is no formula that holds, it is determined that there is no thin line, so that a thin line having a length of 3 pixels or more in the vertical, horizontal, and oblique directions is detected, and a line width of 1 pixel and a length of 2 pixels or more in the oblique direction are detected. Detection of fine lines is possible.

FIG. 11 shows an example in which thin lines are stored by the present conversion method C in the case of FIG. 10 (1). FIG. 11 (a) Example 1
This is an example of a thin line that satisfies the expression C- (13), and shows a case of a connected pixel having a line width of 1 pixel and a length of 3 in the vertical direction and the diagonally up left direction.

FIG. 11 (b) Example 2 is an example of a thin line satisfying the expression C- (15), where the line width is 1 pixel and the length of the connected pixels is 3 in the obliquely rightward upward direction. Is shown.

FIG. 11 (c) Example No. 3 is an example of a thin line satisfying the expression C- (17), which has a line width of 2 pixels, two connected pixels in the vertical direction, a line width of 1 pixel, and a diagonally right line. This figure shows a case of three connected pixels having a total length of one ascending direction.

Example 4 of FIG. 11 (d) is an example of a thin line satisfying the expression C- (19). In the case of a connected pixel having a line width of 1 pixel and a length of 2 pixels which is obliquely ascending to the left. Is shown.

FIG. 11 shows an example in which thin lines are preserved by the present conversion method C in the case of FIG. 10 (1), but the same applies to all other FIGS. 10 (2) to (4). The thin line is preserved.

As described above, the conversion ratio α is 1/1> α ≧ 1 with respect to the method C of the present invention.
Although the detection of a thin line has been described in the case of / 2, 1/2> α ≧ 1/3, the case of 1 / n> α ≧ 1 / (n + 1) is generally similar to the detection of a thin line in the same manner as described above. Can be detected.

In the example of FIG. 16 in which thin lines disappear by the X method,
Method, method B and method C have a vertical length of 2 pixels or 3 pixels.
Since pixels or more are thin lines, P− _2,0 and P− _1,0 are not determined as white thin lines, and a black value is substituted for the conversion pixel of interest, so that a horizontal thin line can be preserved. Similarly, a fixed value is determined, and only a thin line having a length equal to or longer than that value is set as a thin line. Thus, an original thin line can be detected without detecting an uneven portion as a thin line. Therefore, according to the present invention, fine lines can be detected well even in an original image having uneven lines.

When there is a black or white thin line on the original image, when the thin line is the original pixel closest to the conversion pixel position, or when the average density projected by the four original pixels is thresholded, the thin line When the value of the conversion pixel closest to the position matches the value of the thin line, the thin line does not disappear on the conversion screen in the SPC method or the area determination method.
That is, as shown in the example of the FIG. 14, thin lines of line width m that may be missing, instead of in the form including the original pixels P _i of the shortest distance to Q _j, the P _i It is located on the right or left side (or above or below the conversion pixel). For this reason, a thin line determination condition is determined by determining a thin line having a line width m with respect to 2 (n + 1) original pixels in the horizontal direction and 2 (n + 1) original pixels in the vertical direction centering on the converted pixel in each of the horizontal and vertical directions. It becomes possible to detect a thin line having a line width of n pixels or less near _{i which} disappears.

When a thin line is detected, the conversion pixel calculating means 5 for the shortest distance to the thin line checks whether or not the conversion pixel of interest is the shortest distance conversion pixel for the detected thin line. To substitute the value of the thin line into the converted pixel.

The determination that the conversion pixel of interest is closer to the thin line than the other conversion pixels can be made by the following method. The center line of the detected thin line is calculated. This is possible by comparing the distance from the center line of the thin line to each of the neighboring converted pixels, detecting the nearest converted pixel, and determining whether the nearest converted pixel is the target converted pixel. . If the distance between the original pixels is 1, the distance between the converted pixels is 1 / α, and the center between the converted pixels is 1 / (2α) from both converted pixels. Or up / down distance 1 / (2
By determining whether or not the center line of the thin line is included in the region of α), it can be checked whether or not the thin line is the shortest distance conversion pixel.

On the other hand, when the thin line is not detected, when the converted pixel of interest is not the shortest distance converted pixel to the detected thin line even if the thin line is detected, the value of the converted pixel is calculated from the calculating means 7 by a predetermined logical operation method. I do. As a specific example of the logical operation method, the above-described PSC method, area determination method, or the like can be used.

By the above method, the value of the converted pixel can be determined by the means 8, and the converted image in which the thin line is preserved can be created by repeatedly performing the process on all the converted pixels.

In this embodiment, 2 (n + 1) horizontal directions × 2 vertical directions
Although the method of reading all (n + 1) original pixels and detecting a thin line by using a part thereof has been described, a converted image can be created by a method of reading only the original pixels necessary for detecting the thin line.

The detection of the presence / absence of a thin line has been described above. To summarize the above, for example, in the example shown in FIG.
Paying attention to _{-1, 0,} right pixels of the pixel _{P -1,0 P 0,0} and the left pixel P
_-2,0 are both, if present as different has a value, and the pixels having the same value as the pixel P _{-1, 0,} for example, in the vertical direction of the pixel P _-1,1 the pixel P _{-1, 0} , Pixel P− _1,0 and pixel P
Considers that there is a vertical thin line consisting _-1,1 Metropolitan example 4 (1) lower left diagram of an example, the same value as the pixel P _-2,0 pixel P _{-1, 0} existing in the horizontal direction different values and pixels P _-3,0 pixel P _0,0 of both ends and is connected pixels connected pixels are connected with rice (i.e. there are horizontal connected pixels), pixel P _-2 to the _{coupling, 0,} the number of P _{-1, 0} is less than 2 or more n _x, the pixels in the vertical direction or an oblique direction having the same value as the horizontal connected pixels, for example, P
_-2,1 or P- _1,1 , if there is more than a predetermined number,
It is assumed that there is a horizontally connected pixel including the pixel P− _2,0 and the pixel P− _1,0 .

This detection method is described in claim (2) of the present application as detecting a thin line in the horizontal direction. The detection of a vertical thin line is described in claim (3) of the present application. Claim (4) of the present application defines “a predetermined number”.

FIG. 12 is an example of a reduced converted image (2) of the original image (1) according to the present invention. For comparison, examples of conversion images of the SPC method and the X method, which are the conventional conversion methods shown in (3), and the A method and the B method of the present invention are also shown. It can be seen that the conversion images of the methods A and B of the present invention are the best conversion images by preventing the disappearance of uneven fine lines.

FIG. 13 is an example of a reduced converted image (2) of the original image (1) for the horizontal, vertical and oblique thin lines by the method C of the present invention. For comparison, the conventional method shown in (3), SPC
And the conversion image examples of the method B of the present invention. It can be seen that the converted image example of the method C of the present invention is the best converted image by preventing the disappearance of thin lines in the horizontal, vertical, and oblique directions.

(Effects of the Invention) As described above, according to the present invention, it is possible to determine the thin lines existing in the original image when the image is reduced, and to save these thin lines on the conversion screen without disappearing.
It is possible to prevent the disappearance of the fine line even when the image is read from an image reading device such as a facsimile, and to obtain a converted image with little image quality deterioration. In addition, it is possible to prevent the disappearance of fine lines in horizontal, vertical, and oblique directions, thereby obtaining a good converted image.

Although only the case where the conversion ratio between the horizontal direction and the vertical direction is the same has been described, according to the present invention, any reduction conversion with a different conversion ratio between the horizontal direction and the vertical direction is of course possible. The present invention can be applied to a case where the one direction is not converted or a case where the enlargement conversion is performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a reduced conversion function for realizing the present invention, FIG. 2 is a diagram for explaining the flow of a conversion process of the present invention, FIG. 3 is a specific example diagram of an original pixel referred to by the present invention, 4th
FIG. 5 and FIG. 5 are diagrams showing a method for judging a thin line according to the method A of the present invention, and FIGS. 6, 7, and 8 are diagrams showing a method for judging a thin line according to the method B according to the present invention. FIG. 10 is a diagram showing a method of discriminating fine lines by the method C of the present invention, FIG. 11 is a diagram showing an example in which fine lines are stored by the method C of the present invention, and FIGS. 12 and 13 are conversion images according to the present invention. FIGS. 14 (a) and 14 (b) are diagrams showing an arrangement of original pixels and converted pixels for explaining an example in which a thin line disappears, and FIG. 15 is a diagram showing an example of reference pixels in the X method. FIG. 16 is a diagram showing an example in which thin lines disappear by the X method. 1 ... Original image reading means, 2 ... Converted pixel position detecting means, 3 ... Reference pixel reading means, 4 ... Fine line detecting means, 5 ... Converted pixel calculating means with the shortest distance to the thin line, 6 ...
... Means for substituting the value of the thin line into the converted pixel, 7... Means for calculating the value of the converted pixel, 8... Means for determining the value of the converted pixel.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-196976 (JP, A) JP-A-61-1199376 (JP, A) JP-A-61-147668 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04N 1/387-1/393 G06T 3/40

Claims (4)

(57) [Claims] The conversion ratio α _{x of} a binary original image smaller than 1 in the horizontal direction and the conversion ratio α _y α _x smaller than 1 in the vertical direction are 1 / n _x > α _x ≧ 1 / (n _x +1). α _y is 1 / _ny > α _y ≧ 1 / ( _ny + 1), where _nx and _ny are conversion methods to obtain a converted image by reducing by a natural number. When the converted image is mapped to the original image obtains the positional relationship between the target conversion pixels and the original image having original pixels on the conversion image, respectively one side in the horizontal direction and the vertical direction about the position of the target converted pixel is 2 (n _x +1) and 2 (n _y +1 ) sets a rectangular region consisting of pieces of original pixels, using _{4 (n x +1) × (} n y +1) pieces all original pixels or part of the original pixels in the rectangular area, with a specific value neighboring at both ends of said one coordinate direction relative to the number of pixel groups (positive integer where 1 ≦ n ≦ n _x the n _y) arranged in one coordinate direction n Two pixels are present with different values and pixels having the same value as the pixel group having the specific value is the that 1
When connecting a predetermined value or more in a coordinate direction or a diagonal direction orthogonal to the two coordinate directions, it is determined that a line segment having a predetermined width and a predetermined length exists in the rectangular area. When a line segment exists in the rectangular area and the conversion pixel of interest is the conversion pixel closest to the detected line segment, the value of the conversion pixel of interest is set to the pixel value of the line segment. Conversion method. 2. The method according to claim 1, wherein one pixel having a specific value exists in the original image with adjacent pixels having different values on the left and right, and one pixel having a specific value exists in the original image. When a pixel having the same value is connected to the pixel in the vertical or oblique direction by a predetermined value or more, or a pixel having the same value is connected in the horizontal direction, and the value of the connected pixel is different at both ends of the connection. There is a horizontally connected pixel having an adjacent pixel, and the number of connected pixels is 2 or more and _nx or less, and a pixel having the same value as the horizontally connected pixel is predetermined in the vertical direction or the oblique direction with the horizontally connected pixel. The reduction conversion method according to claim 1, wherein it is determined that a line segment exists in the original image when the number of connected lines is equal to or larger than the number of lines. 3. The method according to claim 1, wherein one pixel having a specific value exists in the original image with adjacent pixels having different values above and below, and one pixel having a specific value exists in the original image. When a pixel having the same value is connected to the pixel by a predetermined value in the horizontal or diagonal direction, or a pixel having the same value is connected in the vertical direction, and the value of the connected pixel is different at both ends of the connection. There is a vertically connected pixel having an adjacent pixel, and the number of connected pixels is 2 or more and _ny or less, and a pixel having the same value as the vertical connected pixel is predetermined in the horizontal or oblique direction with the vertical connected pixel. The reduction conversion method according to claim 1, wherein it is determined that a line segment exists in the original image when the number of connected lines is equal to or larger than the number of lines. 4. The reduction conversion method according to claim 2, wherein the predetermined number is at least two pixels in the original image.