JPH0991412A - Picture element density conversion method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the conversion processing and to attain high speed processing in the case of converting picture element density attended with magnification or reduction in an equipment conducting image processing with digital signal processing for a wordprocessor or a copying machine or the like. SOLUTION: When a magnification of a converted image with respect to an original image is expressed by natural numbers being prime to each other, a picture element conversion section 5 obtains a density calculation equation used for a relative position relation of a picture element of a converted image with respect to a picture element of an original image repeated periodically and for a density of plural adjacent picture elements of the original image surrounding each picture element when the converted image is projected onto the original image to obtain a table and it is stored in a table memory 15. In the case of actual conversion processing, after a relative coordinate for each picture element is obtained, the density calculation equation is not obtained and a table is referred to read the density calculation equipment from a residue of dividing the coordinate of each picture element of the converted image by a magnification, the density of an adjacent picture element is substituted to the density calculation equation to calculate the density of each picture element of the converted image.

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 for enlarging or reducing an image, which is preferably implemented in an apparatus such as a word processor or a digital copying machine which performs image processing by digital signal processing.

[0002]

2. Description of the Related Art In a word processor, a digital copying machine or the like, an image whose pixel density is converted such as a converted image obtained by enlarging a part of an original image or a converted image obtained by reducing an entire original image is created. Processing may be required. Even when creating a converted image of the same size as the original image, the pixel density of the original image determined by the resolution of the image sensor and the pixel density of the converted image determined by the resolution of the printer, etc. When a difference occurs in, the image processing for converting the pixel density is required.

FIG. 5 is a diagram for explaining the concept of the pixel density conversion method as described above. For example, a digital copying machine creates a converted image F by multiplying an original image f formed on a document by p times and q times in the x-axis direction and the y-axis direction, respectively.
Is formed on recording paper and output. The original image f has pixels dhi (h
= 1, 2, ..., H, i = 1, 2, ..., I), and the converted image F has pixels Djk (j = 1, 2 ,.
J, k = 1, 2, ..., K). Therefore, it can be expressed as H = J / p (1) I = K / q (2) from the above-mentioned magnifications p and q.

In obtaining the density of each pixel Djk of the converted image F, in a typical conventional technique, as shown in FIG. 6, first, in step t1, the magnifications p and q are calculated as follows.
The absolute coordinate value (xj, yk) of the pixel djk obtained by projecting the pixel Djk of the converted image F to be obtained on the original image f is obtained.

Next, at step t2, the pixel dj
The four closest adjacent pixels da, db, d surrounding k
c and dd are required. Here, if the coordinates of the pixel da are da: (| xj |, | yk |) (3), the pixels db, dc, dd are respectively: db: (| xj |, | yk | +1) ... (4) dc: (| xj | +1, | yk | +1) ... (5) dd: (| xj | +1, | yk |) ... (6). However, | xj | and | yk |
It represents the maximum natural number that does not exceed j, yk.

At step t3, each of the adjacent pixels da,
The pixel d within the relative coordinate system defined by db, dc, dd
The relative coordinate value of jk is obtained. In step t4, the distance between the adjacent pixel da, db, dc, dd and the pixel djk among the divided areas in the relative coordinate system divided into a plurality of areas corresponding to each pixel density conversion method as described later. Which divided area the pixel djk belongs to is calculated from the difference or the like. In step t5, the density of the pixel Djk of the converted image F is determined from the densities of the adjacent pixels da, db, dc, and dd in the original image f based on the density calculation formula defined in the divided area to which the pixel djk belongs. To be done.

At step t6, all the pixels D11 to D
It is determined whether or not the density has been obtained for JK, and if not, the process returns to step t1, and the above-described density calculation is performed for all the pixels D11 to DJK, and the pixel density conversion is completed. To do.

However, in such a conversion method,
The amount of calculation is enormous. For example, the converted image F is 400 dp.
If the image is an A4 image of i, the values J and K are about 3000 and 4000, respectively, and if the processes of steps t1 to t5 are performed on all 12 million pixels, the total number of processes is 60 million. Also extends. Therefore, there is a problem that the conversion process takes a long time.

On the other hand, another conventional technique devised to reduce the time required for the conversion process is disclosed in Japanese Patent Laid-Open No. 6-103.
No. 372 publication. In this conventional technique, the x-axis direction coordinate value and the y-axis direction coordinate value of the original image corresponding to the x-axis direction coordinate value and the y-axis direction coordinate value of the converted image are calculated in advance and stored in a table. And
When the original image to be converted is input, the coordinate value of the pixel of the original image corresponding to each pixel of the converted image is read from the table, and the density of the pixel at the coordinate value is set as the density of the pixel of the converted image. To be done. In this way, the coordinate value calculation on the original image for each pixel of the converted image is simplified and the speed is increased.

According to this conventional technique, the pixel density conversion method rounds off the first digit after the decimal point of the x-axis coordinate value and the y-axis coordinate value when each pixel of the converted image is projected on the original image, This is a technique applied when it is the nearest neighbor method in which the x-axis coordinate value and the y-axis coordinate value of the pixel of the original image with respect to the pixel of the converted image are applied, but the steps in the pixel density conversion method as described above. Of the five steps of t1 to t5, it can be applied to the calculation of the absolute coordinate value in step t1 and the simplification of the calculation of the relative coordinate value in step t3.

For example, when applied to the simplification of the step t3, the pixel Djk (j = 1, 2,
, J, k = 1, 2, ..., K), J and K in advance
Prepare a table with the elements of x and y, calculate the relative coordinate values in the x-axis direction and the relative coordinate values in the y-axis direction in each table, and substitute them, and simplify the process of referencing them when executing the conversion process. It is possible to realize speeding up.

[0012]

However, in the above-mentioned conventional technique, the calculation of the belonging area of the relative coordinate value at step t4, which is relatively complicated compared to other processing steps, still remains. In the calculation, for example, when the pixel density conversion method is a high-speed projection method, it is determined whether or not xr> 0 with respect to the relative coordinate value (xr, yr), and yr.
Three processing steps are required, whether> 0 and whether their relative coordinate values xr, yr are on one side or the other side of the hyperbola.

An object of the present invention is to provide a pixel density conversion method capable of further simplifying the conversion process and thus increasing the speed.

[0014]

According to a pixel density conversion method of the present invention, an absolute coordinate value of each pixel of a converted image to be output in an original image is obtained, and an adjacent pixel surrounding the obtained absolute coordinate value. In the pixel density conversion method for converting the pixel density by obtaining the density of each pixel of the converted image based on the density of, a natural number in which the ratio of the converted image and the original image is relatively prime from the set conversion magnification. When calculating the density, the relative positional relationship of each pixel of the converted image with respect to the pixel of the original image, which is to be periodically repeated in a state where each pixel of the converted image is projected in advance on the original image, is used as a unit. Find only the period and store it in the table,
For the input original image, the absolute coordinate value of each pixel of the converted image on the original image is obtained, and the adjacent pixels of the plurality of closest original images surrounding the obtained absolute coordinate value are obtained,
From the table, obtain the relative positional relationship of the absolute coordinate value to the adjacent pixel, from the density of each adjacent pixel,
The density of each pixel of the converted image is calculated based on a density calculation formula preset according to the obtained relative positional relationship.

According to the above arrangement, when the magnification is, for example, 1.2 times, six pixels of the converted image correspond to five pixels of the original image from the natural numbers that are relatively prime. Therefore, in the converted image, the relative positional relationship of the pixels of the converted image with respect to the pixels of the original image is repeated with six pixels as a unit cycle. Therefore, in the present invention, the absolute coordinate value when each pixel of the converted image is projected on the original image is obtained only in the pixel region of the unit cycle, and each adjacent pixel of the closest original image that surrounds the absolute coordinate value. A table is created by obtaining the relative positional relationship between the original image and the absolute coordinate value, and the table is repeatedly used in the actual conversion process for the input original image, and the pixels of the converted image and the original image are used. Of the relative position between each adjacent pixel of,
According to the obtained relative positional relationship, the density of each pixel of the converted image is calculated from the density obtained from each adjacent pixel based on the density calculation formula defined for each pixel density conversion method.

Therefore, the relative positional relationship between each pixel of the converted image and the pixel of the original image need only be calculated for the pixel region of the unit cycle, and the conversion process can be simplified and the speed can be increased.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding one embodiment of the present invention,
The following is a description based on FIGS. 1 to 5.

FIG. 1 is a functional block diagram of a word processor 1 in which a pixel density conversion method according to an embodiment of the present invention is used. User interface such as keyboard 2
In response to the input operation from, the processing unit 3 realized by a microcomputer or the like reads the image data of the original image by the digital image input unit 4 realized by an image scanner or the like. The read image data corresponds to image editing such as enlargement and reduction in the image conversion unit 5,
After the pixel density is converted as described later, the image is output by the image output unit 6 realized by a printer, a display device, or the like.

The image conversion section 5 comprises an area table creation section 11, a coordinate calculation section 12, a density calculation section 13, an image memory 14 and a table memory 15. The image data from the digital image input unit 4 is stored in the image memory 14 realized by a random access memory or the like, and the area table creating unit 11 is also provided.
Is input to

The area table creating unit 11 defines a relative coordinate system α required for density calculation in the density calculating unit 13 described later with reference to FIG. 5, and each pixel djk in the relative coordinate system α. The relative coordinate value (xr, yr) of (xj, yk) is calculated for a unit period, and a region table in which a divided region for density determination to which the relative coordinate value belongs is calculated is created and realized by a random access memory or the like. The table memory 15 is stored.

That is, first, referring to FIG.
When the axial magnification is p and the y-axis magnification is q, these magnifications p and q are expressed as p = p1 / p2 (7) q = q1 / q2 (8), and Period lengths p1 and p2, which are prime natural numbers
And the cycle lengths q1 and q2 are obtained. For example, p =
1.2 and q = 1.6, p1 = 6 and p, respectively
2 = 5, q1 = 8, and q2 = 5. Therefore, the unit cycle is 6 pixels in the x-axis direction in the converted image F,
There are 8 pixels in the y-axis direction.

Next, the relative coordinate value (xr, yr) is obtained as follows. A certain pixel D of the converted image F
Considering jk (Xj, Yk), as shown in FIG. 5, the pixel djk (xj,
yk) adjacent pixels da, db, dc, dd of the original image f that are enclosed so as to include yk) are obtained, and the area defined by these adjacent pixels da, db, dc, dd is set in the relative coordinate system α. Is set.

FIG. 2 is a diagram showing an example of the relative coordinate system α, which represents the relative coordinate system used when the pixel density conversion method is the high-speed projection method. Each of the adjacent pixels da, db, d
With the center between c and dd as the origin, each adjacent pixel da, db,
The coordinates of dc and dd are (-0.5, 0.5),
(-0.5, -0.5), (0.5, -0.5),
It is set to (0.5, 0.5). Therefore, the relative coordinate value (xr, yr) in the relative coordinate system α is obtained by xr = xj- | xj | -0.5 (9) yr = 0.5-yk + | yk | (10) . However, | xj | and | yk | are maximum natural numbers that do not exceed xj and yk, respectively.

From the above equations 1, 2, 9 and 10, xr = Xj / p- | Xj / p | -0.5 (11) yr = 0.5-Yk / q + | Yk / q | (12) However, | Xj / p | and | Yk / q | are natural numbers that do not exceed Xj / p and Yk / q, respectively.

Therefore, the relative coordinate value (xr, yr)
Represents the absolute coordinate value (Xj, Yk) of the pixel Djk by the magnification p,
It can be determined depending on the remainder after the decimal point when divided by q. For example, when p = 1.2, the relative coordinate value xr of the x-axis is as shown in Table 1, and the relative coordinate value is It is understood that (xr, yr) need only be calculated for a unit period.

[0026]

[Table 1]

Subsequently, in the relative coordinate system α defined as described above, the divided area to which the pixel djk belongs is obtained. For example, in the case of the high-speed projection method, as shown in FIG. 2, the relative coordinate system α is divided into eight divided areas G1 to G8 (hereinafter collectively referred to as reference numeral G) for density determination. ing.

Further, in the divided areas G1 and G5 with xr <0 and yr> 0, a curve that divides these divided areas G1 and G5 is β1, and in the divided areas G2 and G6 with xr <0 and yr <0, Let β2 be a curve that divides the divided regions G2 and G6, and the divided regions G3 and G7 in the divided regions G3 and G7 where xr> 0 and yr <0.
Is set to β3, and in the divided regions G4 and G8 of xr> 0 and yr> 0, these divided regions G4 and G8
Let β4 be a curve for partitioning β: (0.5-p · xr) (0.5 + q · yr) = 0.5 (13) β2: (0.5-p · xr) (0. 5-q · yr) = 0.5 (14) β3: (0.5 + p · xr) (0.5−q · yr) = 0.5 (15) β4: (0.5 + p · xr) ( 0.5 + q · yr) = 0.5 (16)

Therefore, the magnification p in the x-axis direction is set to 1.
2 and the magnification q in the y-axis direction is 1.6, the divided area G to which the pixel djk in the relative coordinate system α belongs corresponds to the remainder in the x-axis direction and the remainder in the y-axis direction. 2, the calculation of the relative coordinate value and the calculation of the belonging divided area may be performed only p1 × q1 times.

[0030]

[Table 2]

However, ∨ indicates that the plurality of divided areas are straddled. For example, G1∨G2 indicates that the area is at the boundary between the divided areas G1 and G2.

In this way, the area table creating unit 11
Corresponds to the magnification p in the x-axis direction and the magnification q in the y-axis direction set by the processing unit 3, and creates an area table for the pixel area of the unit cycle as shown in Table 2 necessary for the density calculation. It is created and stored in the table memory 15.

Further, in the table memory 15, density calculation formulas corresponding to the pixel density conversion method, that is, the density calculation formulas for each of the divided areas G1 to G8 as shown in Table 3 in Table 2 for the high speed projection method are stored. Correspondingly stored.

[0034]

[Table 3]

However, Ia, Ib, Ic and Id are the densities of the adjacent pixels da, db, dc and dd, respectively, and ∧
Represents the logical product and ∨ represents the logical sum. That is, for example, when the relative coordinate value (xr, yr) belongs to the divided area G1, it means that only the adjacent pixel da is affected, and when the density Ia of the adjacent pixel da is “1”. , The density of the pixel Djk of the converted image F is “1”, and when the density Ia is “0”, the pixel Djk is
Indicates that the concentration of is "0". When the relative coordinate value (xr, yr) belongs to the divided area G5, the density Ia is "1" and the adjacent pixels db, dc, dd
When any one of the densities Ib, Ic, Id of the above is “1” or when all the densities Ib, Ic, Id are “1”, the density of the pixel Djk of the converted image F becomes “1”, In other cases, it represents "0".

On the other hand, each pixel Djk of the actual converted image F
The density of (Xj, Yk) is first stored in the table memory 15 in the density calculation unit 13 according to the pixel density conversion method set by the processing unit 3 in response to the input operation to the user interface 2. From the area table shown in Table 2, the absolute coordinate value (Xj, Y
The divided area to which the absolute coordinate value (Xj, Yk) belongs is determined from the remainder obtained by dividing k) by the scaling factors p and q. A density calculation formula corresponding to the divided area is further read from the table shown in Table 3 stored in the table memory 15, and the pixel djk (xj, yk) is excluded based on the read density calculation formula. Pixel densities Ia, Ib, I of four surrounding adjacent pixels da, db, dc, dd
From c and Id, the density of the converted pixel Djk is determined. The determined pixel density is displayed and output from the image output unit 6.

FIG. 3 is a flow chart for explaining the pixel density conversion processing operation as described above. When the magnifications p and q are set from the user interface 2, the processing unit 3 activates the image conversion unit 5, and first, in step s1, the area table creating unit 11 first calculates the pixels of the unit cycle from the set magnifications p and q. The period length p1 in the x-axis direction and the period length q1 in the y-axis direction that define the region are calculated. Next, in step s2, the area table creating unit 11 sets the magnification p,
Relative coordinate values (xr, yr) as shown in Table 1 are calculated from q based on the equations 11 and 12, respectively. Then, in step s3, the area table creating unit 11 corresponds to the pixel density conversion method set by the user interface 2 and calculates the relative coordinate value (x
The divided area G to which r, yr) belongs is obtained, an area table as shown in Table 2 above is created, and the table memory 15
To memorize. After creating the region table in this way,
The operation proceeds to the density calculation operation after step s4.

In step s4, the variable k of the y-axis coordinate value is set to 1, and in step s5 the variable k is set to the maximum value K.
It is determined whether or not it has become larger, and if so, the operation is ended, and if not, the process moves to step s6, and the variable j of the x-axis coordinate value is set to 1. In step s7, it is determined whether or not the variable j has become larger than the maximum value J, and if not, the process proceeds to step s8.

In step s8, the coordinate calculation unit 12 causes the pixel Djk of the converted image F represented by the variables j and k.
Absolute coordinate value (xj, of the pixel djk of the original image f corresponding to
yk) is calculated. In step s9, the pixel dj
Four adjacent pixels da, db, d of the original image f surrounding k
c and dd are obtained from the above equations 3 to 6, and their pixels d
The densities Ia, Ib, Ic and Id of a, db, dc and dd are read from the image memory 14.

In step s10, the remainders restx and resty are obtained by dividing the coordinate value (Xj, Yk) of the pixel Djk by the magnifications p and q, respectively. Step s11
Then, the remainder rest obtained in step s10
The divided area G to which x, resty belongs is obtained from the above table 2, and the density calculation formula corresponding to the obtained area is read out from the above table 3.

In step s12, the density I of the adjacent pixels da, db, dc, dd read in step s9 is read.
The density calculation formula obtained in step s11 is applied to a, Ib, Ic, and Id to calculate the density of the pixel Djk of the converted image F. In step s13, 1 is added to the variable j to be updated, and then the process returns to step s7. When the conversion process is completed over one line in the x-axis direction in this way, the process proceeds from step s7 to s14.

In step s14, the variable k in the y-axis direction is incremented by 1 and updated, and then the process returns to step s5. In this way, when the conversion process is completed until the final row in the y-axis direction, that is, k = K, the operation ends from step s5.

When the pixel density conversion method set by the user interface 2 is the nine-division method, the relative coordinate system α is 9 of G1 to G9 as shown in FIG.
The density calculation formula, which is divided into two areas and is read from the area table and used for density calculation, is set as shown in Table 4. In addition, another method such as a projection method that obtains the density of each pixel of the converted image F from a plurality of pixels of the original image f may be used.

[0044]

[Table 4]

As described above, in the pixel density conversion method according to the present invention, when the relative positional relationship between the pixels of the converted image F and the pixels of the original image f is periodically repeated from the set magnifications p and q, the absolute coordinate values are The relative coordinate value (xr, yr) that (xj, yk) can take is calculated, and the relative coordinate value (xr, yr) is calculated in advance.
yr) is found in which divided area in the relative coordinate system α, an area table is created, and a density calculation formula table corresponding to each divided area is created in advance. The density I of the adjacent pixels da, db, dc, dd that will surround each pixel djk when projected onto f
The density of each pixel of the converted image F is calculated from a, Ib, Ic, and Id according to the density calculation formula.

Therefore, for example, 1000 pixels × 10
When the original image f of 00 pixels is converted into the converted image F of 2000 pixels × 2000 pixels, the magnifications p and q are 2 respectively, and the relative coordinate values (xr, yr) have only two kinds of values, In the calculation method according to the present invention, the number of relative coordinate values to be actually calculated is only four. On the other hand, according to Japanese Unexamined Patent Publication No. 6-103372 described in the prior art, a total of 4000 pieces in the x-axis direction and 2000 pieces in the y-axis direction are required. As described above, according to the present invention, the calculation of the relative coordinate value can be remarkably simplified, the conversion processing can be speeded up, and the capacity of the memory for storing the relative coordinate value can be reduced.

[0047]

As described above, in the pixel density conversion method according to the present invention, when the magnification of the converted image with respect to the original image is obtained from natural numbers that are relatively prime, the pixel of the converted image is relative to the pixel of the original image. Utilizing the fact that the positional relationship is cyclically repeated, only the pixel area of the unit cycle is surrounded by the projected pixel when projecting each pixel of the converted image onto the original image. The relative positional relationship with each adjacent pixel of the original image is obtained in advance and stored in a table,
During the actual conversion process, the table is repeatedly used to use the density calculation formula corresponding to the density of each adjacent pixel surrounding the absolute coordinate value of each pixel of the converted image on the original image and the relative positional relationship. Then, the density of each pixel of the converted image is calculated.

Therefore, the relative positional relationship between each pixel of the converted image and the pixel of the original image need only be calculated for the pixel region of the unit cycle, and the conversion process can be simplified and the speed can be increased. .

[Brief description of drawings]

FIG. 1 is a functional block diagram of a word processor in which a pixel density conversion method according to an embodiment of the present invention is used.

FIG. 2 is a diagram for explaining a method of dividing a relative coordinate system α when the pixel density conversion is performed by a high speed projection method.

FIG. 3 is a flowchart for explaining a conversion processing operation of the pixel density conversion method according to the present invention.

FIG. 4 is a diagram for explaining a division method of a relative coordinate system α when the pixel density conversion is performed by a nine division method.

FIG. 5 is a diagram for explaining the concept of a pixel density conversion method.

FIG. 6 is a flowchart for explaining a typical pixel density conversion processing operation of a conventional technique.

[Explanation of symbols]

 1 word processor 2 user interface 3 processing unit 4 digital image input unit 5 image conversion unit 6 image output unit 11 area table creation unit 12 coordinate calculation unit 13 density calculation unit 14 image memory 15 table memory

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Michihiro Ohno 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (1)

[Claims] 1. The absolute coordinate value of each pixel of the converted image to be output in the original image is calculated, and the density of each pixel of the converted image is calculated based on the density of the adjacent pixels surrounding the calculated absolute coordinate value. In the pixel density conversion method of converting the pixel density by obtaining, when the ratio of the converted image and the original image is expressed by a natural number that is a prime to each other from the set conversion magnification, the conversion is performed in advance in obtaining the density. The relative positional relationship of each pixel of the converted image with respect to the pixel of the original image, which will be repeated cyclically with each pixel of the image projected on the original image, is calculated for a unit period, stored in a table, and input. For each original image, the absolute coordinate value of each pixel of the converted image on the original image is obtained, and the adjacent pixels of the plurality of closest original images surrounding the obtained absolute coordinate value are obtained. From the determined relative positional relationship of the absolute coordinate values for the neighboring pixels, on the basis of the from the density of each adjacent pixels, the density equation which is set in advance in accordance with the relative positional relationship in which the determined,
A pixel density conversion method comprising calculating the density of each pixel of a converted image.