JP3504078B2 - Method of creating threshold matrix pattern and method of recording halftone image - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of creating a threshold matrix pattern used in halftoning multi-tone image data by using an image recording apparatus, and a halftone using this threshold matrix. The present invention relates to an image recording method.

[0002]

2. Description of the Related Art In the field of printing, a halftone image is produced by halftoning a continuous-tone original image. At the time of halftoning, the image recording signal representing the halftone image is generated by comparing the image data of the original image with the threshold values read from the threshold matrix. As a halftoning method, there are a method using halftone dots and a method called frequency modulation screening (FM screening).

The halftone dots are arranged in a grid pattern at regular intervals, and the density of the halftone dot image is expressed by the area of halftone dots per unit area. That is, the halftone dots have a fixed arrangement and the size of each halftone dot changes according to the density of the original image. In other words, the reproduction of the image by the halftone dot is amplitude modulation (A
This is a method of expressing the light and shade of an image by M).

On the other hand, FM screening is a method of expressing the contrast of an image by frequency modulation. That is, in FM screening, the size of dots on which ink is placed is constant, and the appearance frequency of dots changes according to the density of the image. In the FM screening, a large number of small dots are dispersed in the halftone region as compared with the conventional halftone dot, and therefore, it is possible to reproduce a continuous tone original image with high resolution.

In FM screening, the size of each dot depends on the spot pitch of the image recording apparatus. In this specification, the "spot" means one unit of recording on / off in the image recording apparatus. On the other hand, “dot” means the smallest recording unit observed in a halftone image. One dot may be composed of a plurality of spots. The image recording device (also referred to as an image output device) is an optical image recording device that optically records an image on a photosensitive medium, or a digital printing machine that creates printed matter by directly applying (or spraying) ink on printing paper. Etc. are included.

Generally, the smaller the spot pitch of the image recording apparatus, the smaller the dot size can be made. It is desirable that each dot be small in order to obtain a smoother image. However, if the spot pitch of the image recording device is made smaller to make the dots smaller, the sum of the perimeters of the dots becomes longer, and as a result, a large dot gain (dot thickening) or dot loss (dot thinning) tends to occur. Known to be. The reason why a predetermined number of spots (for example, 3 × 3 spots) is set as the minimum dot unit is to reduce such dot gain and dot loss. It is generally said that the minimum printable dot size is around 20 microns.

FIG. 1 is an explanatory diagram showing an example of the relationship between the spot SP and the dot DT. In this example, one dot DT is formed by nine spots SP arranged in 3 × 3.
Is configured. In addition, the sub-scanning direction x and the main scanning direction y
Spot pitches Psx and Psy along the spot width Ws
Equivalent to x and Wsy respectively. Also, the dot pitch Pdx,
Pdy is also equal to the dot widths Wdx and Wdy, respectively.

[0008]

When the spot pitches Psx and Psy are equal to the spot widths Wsx and Wsy, as in the example of FIG. 1, a halftone image that reproduces the image density of the document with high precision is recorded. be able to. But,
Actually, the spot pitch and the spot width may not be equal depending on the image recording apparatus. FIG. 2 is an explanatory diagram showing a case where the spot pitch and the spot width are not equal. FIG. 2A is the same as FIG. 1 and has the same spot pitch and spot width.

FIG. 2B shows an example of an image recording apparatus in which the spot width Wsy in the main scanning direction y is larger than the spot pitch Psy. In this case, one spot has a vertically long shape. FIG. 3 is an explanatory diagram showing the power distribution of such a vertically long spot. In FIG. 3, two single optical spots form one composite optical spot. In this image output device, since one optical spot does not provide sufficient output, two optical spots are used together to secure the output. One such composite optical spot corresponds to one spot SP (also referred to as a recording spot) in FIG. 2B. Figure 2
(C) is an example of an image recording apparatus in which the spot width Wsx in the sub-scanning direction x is larger than the spot pitch Psx. Figure 2
The spot SP in (C) is also the composite optical spot described in FIG. In FIG. 2D, the spot widths Wsy and Wsx in the main scanning direction y and the sub scanning direction x are both the spot pitch P.
This is an example of an image recording apparatus larger than sy and Psx. Such spots are formed when the diameter of one optical spot cannot be sufficiently narrowed.

In the example of FIG. 2B, since the spot width Wsy in the main scanning direction is larger than the spot pitch Psy, 3 ×
The width Wdy in the main scanning direction of one dot DT composed of nine spots in three arrays becomes larger than the dot pitch Pdy. Similarly, in FIG. 2C, the dot width Wdx in the sub-scanning direction is larger than the dot pitch Pdx. Further, in FIG. 2D, the dot width Wd in the main scanning direction and the sub scanning direction
y and Wdx are larger than the respective dot pitches Pdy and Pdx.

As described above, when the spot pitch and the spot width of the image recording apparatus are not equal to each other, the dot width and the dot pitch do not coincide with each other. Therefore, the density of the recorded halftone image is considerably higher than the desired image density. There was the problem of becoming expensive.

The present invention has been made to solve the above-mentioned problems in the prior art, and obtains a halftone image having a desired density even when the spot pitch and the spot width of the image recording apparatus are not equal. The purpose is to provide a technology capable of doing so.

[0013]

Means for Solving the Problem and Its Action / Effect To solve at least a part of the above-mentioned problem, a first invention is to halftone multi-tone image data by using an image recording apparatus. A method of creating a threshold matrix pattern to be used, wherein the threshold matrix area is divided into a plurality of unit areas each associated with one dot which is a minimum unit of recording in a halftone image, and each unit area is A recording area including N (N is an integer of 1 or more) spot positions for recording spots, each of which is a minimum unit that can be recorded by the image recording apparatus, and a non-recording area including at least one spot position. And assigning a threshold for recording the spot according to an image data level of less than 100% to each spot position in the recording area. To, wherein the respective spot positions of the non-recording area, in the image data level of at least less than 100% and allocates a threshold recording is not performed in the spot.

Here, "recording" is a term including various cases in which the spot position is recorded by some method. For example, in an optical image recording apparatus using a light beam, this means exposing each spot position with the light beam. Further, in an image recording apparatus in which a printed matter is directly printed by applying ink, it means applying ink to each spot position.

According to the first aspect, at an image data level of less than 100%, no spot is recorded at the spot position in the non-recording area, and a spot is recorded only at the spot position in the recording area. Therefore, even if the spot width is larger than the spot pitch, it is possible to form dots of a desired size by the spots recorded at the spot positions in the recording area. As a result, a halftone image having a desired density can be obtained.

In the first aspect of the invention, the non-recording area is parallel to at least one of the main scanning direction and the sub scanning direction in the area of the threshold matrix, and has a constant pitch equal to the pitch of the unit area. Is preferably set so as to form strip-shaped regions regularly arranged.

When the spot width is larger than the spot pitch, the area where the spot protrudes from the spot position is fixed for each image recording apparatus, and this protruding area is present in at least one of the main scanning direction and the sub scanning direction due to the recording operation. Since it continues regularly, the dots of the desired size can be effectively formed by forming the non-recording area as described above.

In the first aspect of the invention, it is preferable that the same threshold value is assigned to the N spot positions in each recording area.

In this way, N spots are simultaneously recorded to form one dot according to one image data level.

A second invention is a method for recording a halftone image on a recording medium using an image recording device,
(A) a step of comparing the threshold value read from the threshold value matrix pattern created by the method of the first invention with multi-tone image data, and generating an image recording signal according to the comparison result; b) recording a halftone image on the recording medium by controlling on / off of a spot, which is a minimum unit that can be recorded in the image recording apparatus, according to the image recording signal. Characterize.

In this way, a halftone image having a desired density can be recorded.

In the second invention, the step (a)
(1) The width Wsy of the spots in the main scanning direction in the image recording apparatus is the pitch Psy of the spots in the main scanning direction.
And at least one of the main scanning direction width Wsy and the main scanning direction pitch Psy is adjusted so that the sub scanning direction width Wsx of the spot becomes an integer multiple of the sub scanning direction pitch Psx. To adjust at least one of the width Wsx in the sub-scanning direction and the pitch Psx in the sub-scanning direction, and (2) the area of the unit area is recorded at each of the N spot positions in the recording area. And (3) setting the area of the non-recording area from the area of the unit area to the pitch Psy in the main scanning direction of the spot.
Area N, which is N times the area obtained by multiplying by Psx and the sub-scanning direction pitch Psx
Setting a value obtained by subtracting Psy and Psx.

In this way, when N spots are recorded in the recording area, one dot having an area equal to the area of the unit area can be formed.

Alternatively, in the second aspect of the invention, the step (a) is formed by (1) recording the area of the unit region and the spots at the N spot positions in the recording region, respectively. Setting one dot to be equal to the area of the deformed dot after being deformed by the dot gain, and (2) the area of the non-recording area from the area of the unit area in the main scanning direction of the spot. A step of setting a value obtained by subtracting an area N · Psy · Psx, which is N times the area obtained by multiplying the pitch Psy by the sub-scanning direction pitch Psx, may be provided.

In this way, the area of the deformed dots after the dot gain becomes equal to the area of the unit area, so that it is possible to obtain a halftone image having a desired density in consideration of the dot gain.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described based on examples. FIG. 4 is an explanatory diagram showing three examples of the area division of the threshold matrix in the embodiment of the present invention. Each of FIGS. 4 (A), (B), and (C) is 3 ×
9 unit areas UA arranged in 3 are included. Each unit area UA includes a recording area RA and a non-recording area N.
It is divided into RA. The recording area RA is an area where spots are recorded at an image data level of less than 100%. The non-recorded area NRA is at least 100
In the image data level of less than%, it is an area where no spot is recorded. As will be described later, the non-recording area N
In RA, spots may be recorded at the image data level of 100%, or no spots may be recorded even at the image data level of 100%.

In the example of FIG. 4A, the non-recording area NRA forms a strip-shaped area parallel to the sub-scanning direction x. These strip-shaped non-recording areas NRA are regularly arranged at a pitch equal to the pitch of the unit areas UA along the main scanning direction y. As will be described later, the recording area RA in each unit area UA has N (N is an integer of 1 or more) spot positions. The non-recording area NRA also has one or more spot positions.

In the example of FIG. 4B, the non-recording area NRA forms a strip-shaped area parallel to the main scanning direction y, and these strip-shaped non-recording areas NRA extend along the sub-scanning direction x. They are regularly arranged at a pitch equal to the pitch of the unit areas UA. In the example of FIG. 4C, the non-recording areas NRA form strip-shaped areas that are parallel to the main scanning direction y and the sub-scanning direction x, respectively.
The unit areas UA are regularly arranged at a pitch equal to the pitch in the main scanning direction y and the sub scanning direction x.

FIG. 5 is an explanatory diagram showing a specific example of the threshold value matrix of FIG. 4A, showing an example of the threshold value matrix having a strip-shaped non-recording area NRA parallel to the sub-scanning direction. The threshold matrix is a matrix in which a threshold is assigned to each spot position arranged in a grid. As shown in the upper left of FIG. 5, one unit area UA is 3 × 3.
It contains 9 spot positions arrayed in. Also,
One recording area RA has 6 spot positions arranged in 3 × 2, and one non-recording area NRA has 3 × 1.
It has three spot positions arranged in a line.

The threshold matrix of FIG. 5 is a set of threshold matrices for reproducing image densities of 0% to 100% according to image data levels of 0 to 255. By repeatedly applying this threshold matrix to the entire image area in a tiled manner, a halftone image in a density range of 0% to 100% can be recorded. However, in reality,
It is preferable to halftone the entire image area by using a large-sized threshold matrix in which a plurality of types of threshold matrices having slightly different threshold arrangements are arranged.

FIG. 6 is an explanatory diagram showing how dots are printed using the threshold matrix shown in FIG. Figure 6
(A) shows one unit area UA. 67 is assigned as a threshold value to each spot position in the recording area RA. Further, 255 is assigned as a threshold value to each spot position in the non-recording area NRA. In this embodiment, the recording (on) and non-recording (off) of the spot are determined by the following inequality.

[0032] Image data ID> threshold value TD: ON (1a) Image data ID ≦ threshold value TD: OFF (1b)

The image data ID is 8-bit digital data and has a value in the range of 0 to 255. Recording area RA
At each spot position inside, a spot is recorded when the image data ID is at a level of 68 or higher. On the other hand, since 255 is assigned as the threshold to the spot position in the non-recording area NRA, the image data has 255 (that is, 100
No spots are recorded even when the (% image data level) is reached.

FIG. 6B shows a state in which a spot is recorded at one spot position in the recording area RA. In FIG. 6B, the spot position (the center position of the spot) in the recording area RA is indicated by a black circle “•”. The spot pitches Psx and Psy are the pitches of the spot positions and are shown in FIG.
In the above example, the spot pitches Psx and Psy are 6 μm.

FIG. 6C shows the structure of one spot. The one spot SP is formed by partially overlapping two substantially circular optical spots. The spot width Wsx in the sub-scanning direction is equal to the spot pitch Psx in the sub-scanning direction. The spot width Wsy in the main scanning direction is equal to twice the spot pitch Psy in the main scanning direction. In general, the spot width Wsx in the sub-scanning direction is set to Nx times the spot pitch Psx in the sub-scanning direction (Nx is an integer of 1 or more), and the spot width Wsy in the main scanning direction is the spot pitch Psy in the main scanning direction. May be set to Ny times (Ny is an integer of 1 or more). However, one of Nx and Ny is 2 or more.

FIG. 6D shows a state in which spots are recorded at six spot positions in the recording area RA. At this time, one square dot DT is formed by the six spots. The width of one side of the dot DT is 18 μm, which is equal to the width of one side of the unit area UA. Here, the dot DT is the minimum unit of recording observed in a halftone image. The shape of the dot DT does not have to be square, but it is preferable to make it close to a rectangle.

As can be seen from FIG. 6D, the dot DT formed by the six spots is one unit area U.
A part is protruding from A to the outside. This unit area UA
In the inner non-recording area NRA, a portion where dots are not formed is left. The deviation between the dot DT and the unit area UA is 3 μm. Further, the area where the dot DT extends outside the unit area UA and the area where no dot is formed in the non-recording area NRA have the same shape. Thus, although each unit area UA is associated with one dot DT, one dot DT is included in each unit area UA.
Need not be formed.

FIG. 6E shows a state in which two vertically adjacent dots are formed. As can be understood from this, when spots are recorded at six spot positions in each recording area RA in a plurality of adjacent unit areas UA, dots DT are formed without any gap. To do this, in this embodiment, the unit area UA,
The sizes of the recording area RA and the non-recording area NRA are determined as follows.

FIG. 7 is an explanatory diagram showing the relationship among the area Sdt of the dot DT, the area Sua of the unit area UA, the area Sra of the recording area RA, and the area Snra of the non-recording area NRA in the example of FIG. is there. FIG. 7 (A) is the same as FIG. 6 (D) and shows the positional relationship between one unit area UA and one dot DT. 7B and 7C show the unit area U
A and dot DT are drawn separately.
The area Sua of the unit area UA is equal to the area Sdt of one dot DT formed by recording a spot at each spot position in the recording area RA. As described above, the spot widths Wsx and Wsy are the spot pitches Psx and Ps.
It is set to an integer multiple of sy. Therefore, the area Sdt of one dot DT (that is, the area Sua of the unit area UA)
Is equal to M times the area Psx · Psy multiplied by the spot pitch in the main scanning direction and the spot pitch in the sub scanning direction. Here, the integer M is the number of spot positions included in the unit area UA, and M = 9 in the example of FIG. 7. Area Snra of non-recording area NRA
Is set to a value obtained by subtracting the value N · Psy · Psx N times the area Psx · Psy obtained by multiplying the spot pitch in the main scanning direction and the sub-scanning direction from the area Sua of the unit area UA. Where N
Is the number of spot positions included in the recording area RA,
In the example of FIG. 7, N = 6. Therefore, the non-recording area NRA
Area Snra is (MN) Psy ・ Psx = 3Psy ・ Psx
Is. The area Sra of the recording region RA is set to a value N times the area Psx / Psy obtained by multiplying the spot pitch in the main scanning direction and the spot pitch in the sub scanning direction.

As described above, in the embodiment shown in FIGS. 5 to 7, since the non-recording area NRA having a predetermined size is set in one unit area UA, the spot width is larger than the spot pitch. Even if it is large, by recording the spot at the spot position in the recording area RA, 1
It is possible to form dots DT having an area equal to one unit area UA.

FIG. 8 is an explanatory diagram showing an example in which a flat screen (halftone image with uniform density) is recorded using the threshold matrix shown in FIG. FIG. 8A shows a flat screen having a density (dot area ratio) of 25%. Thick lines indicate boundaries of the threshold matrix arrangement, and thin lines indicate boundaries of the dot arrangement. One dot is a square having a side width of 18 μm. Further, the threshold matrix arrangement and the dot arrangement are displaced by 3 μm. As can be seen by carefully observing FIG. 8A, in this 25% flat screen, one dot is recorded in each dot group arranged in 2 × 2. The positions of the dots recorded in each dot group are randomly selected. FIG. 8B shows a flat screen having a density of 50%. In this 50% flat mesh, 2
Two dots are recorded in each dot group arranged in × 2. The positions of the dots recorded in each dot group are randomly selected. As described above, in the threshold value matrix of FIG. 5, the distribution of threshold values is determined so that the dots are dispersed without being solidified at the density (dot area ratio) of 50% or less. By using such a threshold matrix, it is possible to reproduce a good-quality flat screen with less roughness.

The level of the image data ID is 100%.
When (= 255), all dots in the threshold matrix are recorded, and a so-called solid image is formed. As shown in FIG. 5, a threshold value equal to the 100% image data level is assigned to the three spot positions in the non-recording area NRA, so no spot is recorded even at the 100% image data level. Nevertheless, a solid image can be obtained at the 100% image data level. As described above, in the embodiment shown in FIGS. 5 to 8, no spot is recorded at the spot position in the non-recording area NRA, but since the size of one spot is larger than the spot pitch, 100% image data is obtained. A solid image can be recorded at the time of level.

As can be understood from the above description, the thresholds of the three spot positions in the non-recording area NRA are
A threshold value that is recorded for the first time at the 100% image data level may be assigned. Specifically, a threshold value of 254 may be assigned to each spot position in the non-recording area NRA. In general, it is sufficient to assign a threshold value to each spot position in the non-recording area NRA so that the spot is not recorded below at least 100% image data level. On the other hand, each spot position in the recording area RA is assigned a threshold value such that a spot is recorded for an image data level of less than 100%.

As can be understood from FIG. 8, the threshold matrix of FIG. 5 is a threshold matrix for FM screening. That is, in the halftone image recorded using the threshold matrix of FIG. 5, the size of the dot on which the ink is deposited is constant at 18 μm × 18 μm, and the appearance frequency of the dot changes according to the density of the image.

FIG. 9 is an explanatory view showing a specific example of the threshold matrix shown in FIG. 4B, and shows an example of the threshold matrix having a strip-shaped non-recording area NRA parallel to the main scanning direction. As shown in the upper left of FIG. 9, one unit area UA includes 9 spot positions arranged in 3 × 3. Further, one recording area RA has 6 spot positions arranged in 2 × 3, and one non-recording area NRA has 3 spot positions arranged in 1 × 3. . The threshold matrix shown in FIG. 9 is the non-recording area NRA parallel to the sub-scanning direction in the threshold matrix shown in FIG.
Is changed to a region parallel to the main scanning direction. Therefore, the contents described with reference to FIGS. 6 to 8 can be similarly applied to the threshold matrix of FIG. 9 only by exchanging the sub scanning direction and the main scanning direction.

FIG. 10 is an explanatory diagram showing a specific example of the threshold value matrix of FIG. 4C, showing an example of the threshold value matrix having strip-shaped non-recording areas NRA parallel to the main scanning direction and the sub scanning direction. There is. As shown in the upper left of FIG. 10, one unit area UA includes nine spot positions arranged in 3 × 3. Moreover, one recording area RA is 2 × 2.
Has four spot positions, and one non-recording area NRA has five spot positions arranged in an inverted L shape. The entire non-recording area NRA has a lattice shape in which strip-shaped areas parallel to the main scanning direction and strip-shaped areas parallel to the sub-scanning direction intersect in a cross shape.

FIG. 11 is an explanatory diagram showing how dots are printed using the threshold matrix shown in FIG. Figure 1
1 (A) shows one unit area UA. 67 is assigned as a threshold value to each spot position in the recording area RA. Further, 255 is assigned as a threshold value to each spot position in the non-recording area NRA.

FIG. 11B shows a state in which one spot in the recording area RA is recorded. Spot pitch Ps
x and Psy are 6 μm. One spot SP is composed of one substantially circular optical spot. Spot width Ws
x and Wsy are double the spot pitches Psx and Psy, respectively.

FIG. 11C shows a state in which spots are recorded at four spot positions (indicated by black circles) in the recording area RA. At this time, one dot DT is formed by the four spots. Dot DT
The width of one side is 18 μm, which is equal to the width of one side of the unit area UA. As can be seen from FIG. 11C, 1 dot DT
Partially protrudes from one unit area UA to the outside, and a non-recorded area NRA in this unit area UA has a portion where dots are not formed. The deviation between the area of the dot DT and the unit area UA is 3 μm in each of the main scanning direction and the sub scanning direction. An area in which the dot DT extends outside the unit area UA and a non-recording area NR
It has the same shape as the area where dots are not formed in A.

FIG. 11D shows a state in which four adjacent dots are formed. As can be understood from this, when spots are recorded at four spot positions in each recording area RA in a plurality of adjacent unit areas UA, dots DT are formed without gaps.

FIG. 12 shows the dot DT in the example of FIG.
Area Sdt, unit area UA area Sua, and recording area R
FIG. 6 is an explanatory diagram showing a relationship between an area Sra of A and an area Snra of a non-recording area NRA. FIG. 12 (A) is the same as FIG. 11 (C) and shows one unit area UA and one dot DT.
Shows the positional relationship with. 12 (B) and (C),
The unit area UA and the dot DT are drawn separately. As in the case of FIG. 7, the area S of the unit area UA is
ua is equal to the area Sdt of one dot DT. The area Sdt of one dot DT (that is, the area Sua of the unit area UA)
Is M · Psx · Psy = 9Psx · Psy (M is the unit area UA
Number of spot positions in). The area Snra of the non-recording area NRA is (M−N) Psy · Psx = 5Psy · Psx
(N is the number of spot positions in the recording area RA).
The area Sra of the recording area RA is N · Psx · Psy = 4Psx ·
Equal to Psy.

As described above, also in the embodiment shown in FIGS. 10 to 12, since the non-recording area NRA having a predetermined size is set in one unit area UA, the spot width is equal to the spot pitch. Even if it is larger than the above, by recording the spot at the spot position in the recording area RA, it is possible to form the dot DT having the same area as one unit area UA.

FIG. 13 is an explanatory diagram showing an example in which a flat screen is recorded by using the threshold matrix shown in FIG. FIG.
(A) shows a flat screen having a density (dot area ratio) of 25%. Thick lines indicate the arrangement of the threshold matrix, and thin lines indicate the arrangement of the dots. One dot is a square having a side width of 18 μm. Further, the threshold matrix arrangement and the dot arrangement are displaced by 3 μm in the main scanning direction and the sub-scanning direction, respectively. As can be seen by carefully observing FIG. 13A, in this 25% flat screen, one dot is recorded in each dot group arranged in 2 × 2. The positions of the dots recorded in each dot group are randomly selected. FIG. 13B shows a flat screen having a density of 50%. In this 50% flat screen, two dots are recorded in each dot group arranged in 2 × 2, and the positions of the dots recorded in each dot group are randomly selected. As described above, in the threshold matrix of FIG. 10, the threshold distribution is determined so that the dots are dispersed without being solidified at the density (dot area ratio) of 50% or less. By using such a threshold matrix, it is possible to reproduce a good-quality flat screen with less roughness.

In each of the above-described embodiments, the unit area UA is obtained by recording N spots in the recording area RA.
The same size dot DT was formed. However,
Dot D by dot gain depending on the printing plate making process
It may be necessary to determine the size of the dot DT in consideration of the fatness of T. Here, the "dot gain" is an increase rate of the image density between two images in the printing plate making process, and simply means "dot thickening".
The printing plate making process includes a halftone film output process for forming a halftone image recorded on a halftone film based on the image data of the original image, and a transfer for transferring the halftone image of the halftone film to another halftone film or printing plate. Process, or a printing process of printing a halftone image using a printing plate. For example, the dot gain DG in the film output process is calculated by the following equation (2).

[0055] DG (Ior) = (Ihf-Ior) / Ior (2)

Here, Ior is the density (%) in the original image, Ihf is the density (dot%) of the halftone image recorded on the halftone film, and DG (Ior) is the dot gain in the density Ior of the original image.

When it is necessary to consider such a dot gain DG, the size of the dot DT formed by the recording of the spot is determined in consideration of the dot gain, as described below.

FIG. 14 is an explanatory diagram showing the sizes of the dots DT in comparison with and without consideration of the dot gain. FIG. 14A shows a case where the dot gain is not taken into consideration, which is the same as that shown in FIG. 11C. In this case, the widths Wdx and Wdy of the dot DT are equal to the widths Wux and Wuy of the unit area UA, respectively. 14
(B) shows the case where the dot gain is taken into consideration.
In this case, the widths Wdx, Wdy of the dots DT formed by recording four spots are the widths Wux, W of the unit area UA.
Each is smaller than uy. In other words, in the case of FIG. 14B, the spot width is not an integral multiple of the spot pitch. In FIG. 14B, the shaded dot gain area DGA is an area thickened from the first dot DT by the dot gain. The width of the modified dot DT ′ (= DT + DGA) after the dot gain is the unit area U
It is equal to the widths Wux and Wuy of A, respectively. 14
In order to obtain the deformed dot DT ′ as in (B), the dot gain DG in the printing plate making process is measured in advance, and the deformed dot D after the dot gain DG is taken into consideration.
At least one of the spot pitch and the spot size may be adjusted so that T ′ has the same size as the unit area UA.

FIG. 15 is an explanatory diagram showing an adjusting method when the spot pitch and the spot width do not match. Figure 15
In (A), the spot widths Wsx 'and Wsy' of the spot SP 'considering the dot gain are the spot pitches Psx and Psx.
It is not an integral multiple of sy. FIG. 15B shows a method of adjusting the spot width to be an integral multiple of the spot pitch by reducing the spot pitch. That is, in the example of FIG. 15B, the spot pitches Psx ′ and Psy ′ are smaller than the spot pitches Psx and Psy of FIG. 15A. As a result,
Spot widths Wsx 'and Wsy' considering dot gain are
It is an integral multiple of the reduced spot pitch Psx ', Psy'. The adjustment of the spot pitch can be realized by adjusting the on / off timing in the image recording device.

FIG. 15C shows a method of reducing the spot width. That is, in the example of FIG. 15C, the spot widths Wsx "and Wsy" considering the dot gain are larger than the spot widths Wsx 'and Wsy' of FIG. 15A. As a result, the spot widths Wsx "and Wsy" in consideration of the dot gain become the spot pitch Ps.
It is an integer multiple of x and Psy. To adjust the spot width,
In an optical image recording device, it can be realized by adjusting the size of the optical spot. In an image recording apparatus of the type that applies ink to spots, it can be realized by adjusting the ink ejection amount. Note that both the spot pitch and the spot width may be adjusted.

The adjustment of the spot pitch and the spot width described with reference to FIG. 15 can be similarly applied even when the dot gain is not considered. In this case, at least one of the spot width and the spot pitch may be adjusted so that the spot widths Wsx and Wsy without considering the dot gain are integral multiples of the spot pitches Psx and Psy.

FIG. 16 is an explanatory diagram showing how dots are recorded in consideration of dot gain using the threshold matrix shown in FIG. 10, and is a diagram corresponding to FIG. 11. Figure 1
As can be understood by comparing 1 (A) to (D) with FIGS. 16 (A) to (D), when the dot gain is considered, the size of the dot DT to be recorded is the unit area UA. Slightly smaller than the size of. FIG. 17 shows FIG. 16 (D).
From this state, the dot gain area DGA is added by the dot gain in the printing plate making process (for example, the net film output process, the transfer process, the printing process, or a plurality of these processes). in this way,
At the time of recording a halftone image, a dot DT smaller than the size of the unit area UA by an area (dot gain area DGA) thickened by the dot gain is recorded, so that the deformed dot after the dot gain is recorded. It is possible to make the size of DT ′ equal to the unit area UA.

FIG. 18 is a block diagram showing the arrangement of an image recording apparatus to which the embodiment of the present invention is applied. This image recording apparatus includes an image memory 20 for storing multi-gradation image data IDs, address generators 24, 26 for generating sub-scanning addresses (X addresses) and main scanning addresses (Y addresses) of an image plane, respectively. Threshold matrix memory 30 for storing a threshold matrix, sub-scanning address (x address) and main scanning address (y address) in the threshold matrix
Address generators 32 and 34 for respectively generating, a comparator 40, and an output device 50 are provided. The image memory 20 stores a different threshold matrix for each color component. The image memory 20 and the threshold matrix memory 30 are provided with a color component designation signal Sc indicating any one of a plurality of color components from a controller (for example, CPU) not shown.

From the image memory 20, the color component designation signal S
The multi-tone image data ID of the color component corresponding to c is read according to the X address and the Y address. In addition, the threshold value TD of the color component corresponding to the color component designation signal Sc is read from the threshold value matrix memory 30 according to the x address and the y address.

The comparator 40 compares the multi-gradation image data ID with the threshold value TD, generates a recording signal RS indicating ON / OFF of each spot according to the comparison result, and supplies the recording signal RS to the output device 50. As the output device 50, for example, a recording scanner that records a halftone image on a photosensitive medium such as a photosensitive film, a digital printer that creates a printed matter by directly applying ink on a printing paper, or the like can be used. . Since the image recording apparatus shown in FIG. 18 uses the threshold matrix described above, it is possible to record a halftone image having a desired density even when the spot pitch and the spot width of the output device 50 are not equal.

The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the scope of the invention.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a relationship between spots SP and dots DT.

FIG. 2 is an explanatory diagram showing a case where a spot pitch and a spot width are not equal.

FIG. 3 is an explanatory diagram showing a power distribution of a vertically long spot.

FIG. 4 is an explanatory diagram showing three examples of area divisions of a threshold matrix in the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an example of a threshold matrix having a strip-shaped non-recording area NRA parallel to the sub-scanning direction.

FIG. 6 is an explanatory diagram showing how dots are recorded using the threshold matrix shown in FIG.

FIG. 7 is an area Sdt of a dot DT in the embodiment of FIG.
And the area Sua of the unit area UA and the area S of the recording area RA
Explanatory drawing which shows the relationship between ra and the area Snra of the non-recording area | region NRA.

8 is an explanatory diagram showing an example in which a flat screen is recorded by using the threshold matrix shown in FIG.

FIG. 9 is an explanatory diagram showing an example of a threshold matrix having a strip-shaped non-recording area NRA parallel to the main scanning direction.

FIG. 10 is an explanatory diagram showing an example of a threshold matrix having strip-shaped non-recording areas NRA parallel to the main scanning direction and the sub scanning direction.

11 is an explanatory diagram showing how dots are printed using the threshold matrix shown in FIG.

12 is an area S of dots DT in the embodiment of FIG.
FIG. 6 is an explanatory diagram showing the relationship among dt, the area Sua of the unit area UA, the area Sra of the recording area RA, and the area Snra of the non-recording area NRA.

13 is an explanatory diagram showing an example in which a flat screen is recorded using the threshold matrix shown in FIG.

FIG. 14 is an explanatory diagram showing the sizes of dots DT in comparison with and without consideration of dot gain.

FIG. 15 is an explanatory diagram showing an adjustment method when the spot pitch and the spot width do not match.

16 is an explanatory diagram showing how dots are recorded in consideration of dot gain using the threshold matrix shown in FIG.

FIG. 17 is an explanatory diagram showing a state where a dot gain area DGA is added by dot gain from the state of FIG. 16 (D).

FIG. 18 is a block diagram showing the configuration of an image recording apparatus to which an embodiment of the present invention is applied.

[Explanation of symbols]

20 ... Image memory 24, 26 ... Address generator 30 ... Matrix memory 32, 34 ... Address generator 40 ... Comparator 50 ... Output device NRA ... Non-recording area Psx. Psy ... Spot pitch Pdx, Pdy ... Dot pitch RA ... Recording area RS ... Recording signal Sdt ... Area of dot DT Snra ... Area of non-recording area NRA Sra ... Area of recording area RA Sua: Area of unit area UA SP ... spot Sc ... Color component designation signal UA ... Unit area x ... Sub-scanning direction y ... Main scanning direction

Front page continued (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/405 G03F 3/00

Claims (6)

(57) [Claims] 1. A method for creating a threshold matrix pattern used when halftoning multi-tone image data using an image recording device, wherein the threshold matrix region is recorded in a halftone image. The unit area is divided into a plurality of unit areas respectively associated with one dot, and each unit area is recorded with N spots, which are the smallest unit that can be recorded by the image recording apparatus (N is 1).
The recording area is divided into a recording area including a spot position of (the above integer) and a non-recording area including at least one spot position, and each spot position in the recording area corresponds to an image data level of less than 100%. A threshold for recording the spot is assigned, and at least 1 is assigned to each spot position in the non-recording area.
A method of creating a threshold matrix pattern, characterized in that a threshold that does not record the spot is assigned at an image data level of less than 00%. 2. The method of creating a threshold matrix pattern according to claim 1, wherein the non-recording area is parallel to at least one of a main scanning direction and a sub scanning direction in the area of the threshold matrix, A method for producing a threshold matrix pattern, which is set so as to form strip-shaped regions regularly arranged at a constant pitch equal to the pitch of the unit region. 3. The method for creating a threshold matrix pattern according to claim 1, wherein the same threshold value is assigned to the N spot positions in each recording area. Method. 4. A method of recording a halftone image on a recording medium using an image recording device, comprising: (a)
(3) comparing the threshold value read from the threshold value matrix pattern created by the method described in any one of (1) to (3) with multi-tone image data, and generating an image recording signal according to the comparison result; ) Recording a halftone image on the recording medium by controlling on / off of a spot, which is a minimum unit that can be recorded in the image recording apparatus, according to the image recording signal. How to record halftone images. 5. The halftone image recording method according to claim 4, wherein in the step (a), (1) the main scanning direction width Wsy of the spot in the image recording apparatus is the main scanning direction of the spot. At least one of the main scanning direction width Wsy and the main scanning direction pitch Psy is adjusted so as to be an integer multiple of the pitch Psy, and the sub-scanning direction width Wsx of the spot is an integral multiple of the sub-scanning direction pitch Psx. Adjusting at least one of the width Wsx in the sub-scanning direction and the pitch Psx in the sub-scanning direction so that (2) the area of the unit area, the spots at the N spot positions in the recording area, respectively. And (3) setting the area of the non-recording area from the area of the unit area to a pitch in the main scanning direction of the spot. Method of recording halftone image comprising the steps of: setting a value obtained by subtracting the N times of the area N · Psy · Psx area obtained by multiplying the Psy and the sub-scanning direction pitch Psx, the. 6. The method of recording a halftone image according to claim 4, wherein in the step (a), (1) the area of the unit area is set at the N spot positions in the recording area. A step of setting one dot formed by recording each spot to be equal to the area of the deformed dot after being deformed by the dot gain; and (2) setting the area of the non-recording area to the area of the unit area. To a value obtained by subtracting the area N · Psy · Psx, which is N times the area obtained by multiplying the spot pitch Psy in the main scanning direction by the pitch Psx in the sub-scanning direction, to a halftone image recording method.