JPH07212605A - Half tone generator - Google Patents

Abstract

PURPOSE:To provide the inexpensive half tone generator in which an approximated half tone picture of equi-dot pitch is obtained and a half tone of a color separate version different from a screen angle is outputted by a same scanning line density. CONSTITUTION:A converter 100 converts data so as to provide modification to a picture in response to a screen angle (theta) corresponding to input multi-value picture data whose screen angle (theta) is set corresponding to the color separate version. A recording position counter 102 has a longitudinal and lateral size depending on the screen angle (theta) and a screen line number and specifies the recording position on a multi-level arrangement of unit areas having a threshold level matrix comprising mXn picture elements. A comparator 106 compares a value of the threshold level matrix at the specified position and picture data to binarize the picture data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a halftone creating apparatus for image processing, and more particularly to a technique for halftoning a continuous tone image to a line number which is not synchronized with a recording scan line density and an arbitrary screen angle.

[0002]

2. Description of the Related Art FIG. 11 is a diagram showing the execution of halftoning in a conventional halftone creating apparatus, and shows a general method for halftoning a continuous tone image. The density value distribution of the image is represented by the pixel value 311 for each subunit area 312. The threshold matrix for obtaining a halftone with a screen angle of 45 ° has a large value so that a halftone dot shape is formed from the center toward the periphery. The image density 32 for each subunit area is compared for each pixel with the value of the threshold matrix 33 at that position. If the value is larger than the matrix value, "1" is assigned, and if the value is smaller, "0" is assigned. The ratio expresses the average density of the opposite parts of the image, the halftone dot image 34 is obtained, and the density distribution can be converted into area modulation.

When printing a color image, Y is generally used.
(Yellow), M (magenta), C (cyan), K (black)
) 4 color distribution plate is made, each 90 °, 15
A halftone dot image having a screen angle of °, 75 °, 45 ° is printed to perform color expression. In this case, it is desirable that the screen rulings of each color separation plate have exactly the same value.

However, in the conventional halftone generating apparatus as described above, if the threshold matrix pixels and the recording pixels have the same size, they have rational tangents of 15 ° and 75 °.
Screen angle halftone, approx. 90 °, 4
In principle, it is impossible to make the number of lines of four kinds of halftone dot images of 5 ° the same.

In order to approximately realize the above processing,
It is possible to rotate the image data by ± 15 ° and 45 ° with 90 ° as a reference and then convert it into halftone dots to restore it to the original state, but the image processing is troublesome in computer processing and requires computer power. It has the drawback of being expensive.

In order to solve the above-mentioned drawbacks, the present inventors have already disclosed in Japanese Patent Laid-Open No. 4-130861 (hereinafter referred to as prior art 1) that input multivalued image data has a predetermined screen for each color. The threshold matrix is deformed in the main scanning direction according to the angle, and the halftone dot grows according to the density.The threshold matrix is deformed in the sub-scanning direction according to the predetermined screen angle, and both are acted to perform the halftone dot meshing. Then, by returning the deformation applied in the main scanning direction to the original, a "halftone creating device" can be created at low cost and with a simple operation, for an orthogonal halftone dot image of a predetermined screen angle and screen ruling of color image data. Was proposed.

Further, in Japanese Patent Laid-Open No. 63-125058 (hereinafter referred to as prior art 2), the scanning position coordinates are rotated by a specified angle θ with respect to the scanning origin (main / sub scanning starting point) of the original image. The rotation coordinates are calculated, and the threshold value is calculated according to the spatial distance between the rotation coordinates and the specific coordinates of the screen or the value on the calculation formula to binarize the original image. By configuring to output a halftone image by converting to a halftone pattern of a predetermined shape, it is possible to perform rotational coordinate calculation at any halftone dot angle and threshold calculation on a virtual screen of any size, As a result, an "image signal processing device" is disclosed in which each halftone dot having the same number of lines at a standard halftone dot angle can be realized.

[0008]

SUMMARY OF THE INVENTION In the above prior art 1,
The size of the threshold matrix is the same for each color, regardless of screen angle. Therefore, Prior Art 1
It is difficult to obtain a separated halftone image (halftone) of the same screen frequency.

Therefore, an object of the present invention is to obtain a halftone image having an approximately equal halftone dot pitch and to output halftones of color separation plates having different screen angles at the same scanning line density within one page. An object of the present invention is to provide an inexpensive halftone creating apparatus that can be used.

The prior art 2 is expensive because it requires a complicated process of rotating an image.

[0011]

In order to achieve the above object, a halftone producing apparatus according to the present invention uses a screen angle (θ) corresponding to one or a plurality of color separation plates (C, M, Y, K). ) Is set and the input multi-valued image data in which the gradation is digitized is converted so as to deform the image according to the corresponding screen angle (θ), and from the screen ruling and the screen angle (θ) A recording position specifying unit that specifies a recording position on a staggered array of unit areas that has a determined vertical / horizontal size and a threshold matrix consisting of m × n pixels, and a threshold matrix of the position specified by this recording position specifying unit. A unit for comparing the image value with the image data and binarizing the image data, and the unit area size is 90 ° according to the screen angle (θ). And, cos [theta] (sub-scanning direction) ×
1 / cos θ (main scanning direction), the step between adjacent unit area columns is sin θ, so that the unit area arrangement is set.

[0012]

In the halftone creating apparatus having the above structure, since the unit area array has regularity, it is easy to specify the recording position on the unit area array when the scanning line density of high-definition recording is given. It is also easy to perform binarization by comparing with the threshold at that position.

That is, the printing scan pitch and the pixel pitch of the threshold matrix are asynchronous, and the size and arrangement of the unit area are different depending on the color plate. However, by dividing the unit area into the same number of pixels, Each color plate can be converted into an orthogonal screen halftone image having the same number of screen lines with the same number of gradations. In this case, the monochrome image corresponds to one color plate.

Further, 90 ° halftone dot image and 45 ° halftone dot image, ± 1
By superimposing 5 ° halftone images in the sub-scanning direction, it is possible to output four types of color separation images on one page. In recording, in the former combination and the latter combination, only the recording density in the main scanning direction needs to be switched.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a halftone creating apparatus according to the present invention. In FIG. 1, when a screen angle (θ) is set corresponding to a plurality of color plates (Y, M, C, K), a converter 100 converts input multi-valued image data in which grayscale is digitized, The image is deformed so that the boundary of the unit area becomes 90 ° according to the corresponding screen angle θ. The image data transformed here is stored in the memory 101.

The threshold matrix pattern determined by the number of gradations and the screen angle (θ) is stored in the storage device 105 as a look-up table. The recording position counter 102, which receives the drive command from the control circuit 109 and specifies the recording position on the unit area pattern, detects the sub-scanning line counter signal from the sub-scanning line counter 107 and the main scanning direction from the read clock generating circuit 108. The following formula is calculated by the read clock, and the calculation result is notified to the selective read circuit 103 as the row number of the threshold matrix.

T = (Y n) α + (X m) β (mod N) t: integer value satisfying T-1 <t <T The selection read circuit 103 receives the threshold pattern selection signal from the control circuit 109 and outputs the storage device 105. A threshold matrix pattern is selected from, the threshold of the row number from the recording position counter 102 is read from this pattern, and it is sent to the comparator 106.

On the other hand, the image signal read-out circuit 104 uses the read-out clock from the control circuit 109 for the memory 1
The image signal is read from 01, and the amplitude of the recording pulse is modulated by the grayscale signal of the image. The recording pulse modulated here is sent to the comparator 106 and compared with the threshold value from the selective reading circuit 103. The comparison result is output as a binarized halftone signal.

In FIG. 1, 110 is a main scanning clock generator and 111 is a sub scanning clock generator. The output of the main scanning clock generator 110 is sent to the read clock generating circuit 108 and the control circuit 109, and the sub clock is generated. The output of the scan clock generator 111 is the sub-scan line counter 107.
And sent to the control circuit 109.

The control circuit 109 generates a threshold pattern selection signal and a drive command to the recording position counter 102 from the main scanning clock and the sub-scanning clock from the clock generators 110 and 111, and the reading clock generating circuit 108 reads the reading clock. In response to this, the image signal is read out and sent to the image signal reading circuit 104.

In the above structure, the control circuit 10
The binarization processing process of No. 9 will be described with reference to FIG.

First, the image signals of the scanning lines of Yn = 0 and Xm = 0 are read out, 1 is added to n (step S1), and Tm = (Yn) α + (Xm) β (mod N), and Xm = T _0,1 is obtained as ₀ (step S21),
Select t _0,1 row of the threshold pattern (step S22), Y
The Xm = 0 column of n = n is binarized (step S23). Similarly, binarization processing is performed for t _0,2 , t _0,3, ..., t _{0, n} .

Next, from T = (Yn) α + (Xm) β (mod N), t _{1, n} is obtained with Xm = 1 (step S31),
Select t _{1, n} rows of the threshold pattern (step S32), Y
The Xm = 1 column of n = n is binarized (step S33). Similarly, t _{2, n} , t _{3, n} , ... Are binarized,
Finally, from T = (Yn) α + (Xm) β (mod N), tm _{, n} is obtained with Xm = final column (step S4
1) Select the t _{m, n} rows of the threshold pattern (step S4
2), Yn = n, Xm = final column is binarized (step S43).

When the above processing is completed, it is judged whether or not Yn is final (step S5), and if it is final (Yes), the processing is terminated, and if it is not final (No), the process moves to the next scanning line (No). Return to step S6) and step S1.

The operation of the halftone creating apparatus having the above-described binarization process will be described with reference to numerical examples.

The number of screen lines is 175, the threshold matrix is M × N = 12 × 12, and the recording scan line density is 296.
9.85 lines / inch, main scanning recording density is 2969.85
dots / inch, scanning line density of image input is 395.98 lines /
Inch.

In the case of 45 ° halftone dots, the row pitch of the threshold matrix and the scanning line pitch are set equal in the sub-scanning direction. In this case, the head of the unit area comes periodically every 24 dots in the main scanning direction.

In the case of 15 ° halftone dot, α = 1.7320, β
= 0.27324, T = 0.732.Yn + 0.26794.Xm (m
od 12). A matrix row is selected by an integer value t satisfying T-1 <t <T. In this case, the main scanning direction is 2028.44 dots / inch synchronized with the threshold matrix.
Then, the image signal is amplitude-modulated in advance.

In the case of 0 ° halftone dot, α = 0.7071, β =
When it is set to 0, T = 0.7071 · Yn (mod 12) S is expressed. A matrix row is selected by an integer value t satisfying T-1 <t <T. In this case, the main scanning recording density is 2100.00 or 2969.85 dots / inch.
Then, the image signal is amplitude-modulated in advance.

Next, modification of image data will be described with reference to FIG. FIG. 3A shows an example before the deformation, and FIG. 3B shows an example after the deformation. The modification of this example is based on the following equation.

Cotφ = tanθ + cotθ Here, when θ = 0 °, cosφ = cot0 °, so φ = 0 °. When θ = 45 °, cotφ
= 2, tan φ = 0.5, so φ = 26.565 °
Is. When θ = ± 15 °, cotφ = ± 2 / s
Since in30 ° = ± 4, tan φ = ± 1/4, so φ =
It is 14.04 °.

Next, shaping of the unit area will be described with reference to FIG. 4 (a) is before and after shaping, FIG.
(B) has shown the relationship of each unit area after shaping. In this example, each column is shaped into a staggered array of constant values, where a is the size in the main scanning direction, b is the size in the sub scanning direction, and c is the size.
Indicates a step. Here, it is expressed as a = 1 / cos θ b = cos θ c = sin θ = a · tan φ.

For example, when θ = 45 °, a = √2 =
1.414213, b = √2 / 2 = 0.707106,
c = √2 / 2 → 0 (no step). Also, θ = ± 1
In case of 5 °, a = 1.0352759, b = 0.965
926, c = 0.258819 = a / 4.

Next, regarding the creation of the threshold matrix,
This will be described with reference to FIG. FIG. 5A shows a threshold matrix of 90 ° halftone dots, and FIG. 5B shows a matrix structure after division. Creating this threshold matrix is a ×
8x8, 12x12, 20x, regardless of the size of b
It is performed by dividing into 20. The threshold value is 50%, which is adjusted to make a good connection with the adjacent unit area.

Next, t number (threshold pattern line number)
Selection of will be described with reference to FIG. First, the threshold pattern of the unit area is M × N. With the recording scanning line pitch being p, α = p / (b / N) is obtained.

When recording a column of Xm = 0, T of T = αYn (mod N) is counted (Yn = 1, 2, ...). Also, T-
1 <t 0, _n <T is an integer which satisfies a _{t 0, n, t 0,} n row select threshold pattern string, as compared with the image data 2
Quantify.

When recording a column of Xm = 2, T is obtained from β = c / b T = α · Yn + β · 2 (mod N). _{Moreover, T-1 <t 2,} n <T: seeking t _{2, n} that satisfies (t ₂ integer), a portion of Xm = 2 rows t
Binarization is performed by comparing with the threshold pattern of the _{2nd and nth} rows.

Similarly, when recording Xm = m columns, T = αYn + mβ (mod N) (Yn = 1,
2, ...) is used to obtain T. _{Moreover, T-1 <t m,} n <T: t m that satisfies (t _m an _integer), obtains a _n, a portion of Xm = m columns t
Binarization is performed by comparing with the threshold pattern of the _{m, nth} row.

In the above case, the row number selection of the threshold pattern and the print scanning position are asynchronous, but when α and β are given, the threshold pattern at each print position is uniquely determined.

Next, binarization of the recording signal will be described with reference to FIG.

First, when recording a unit area column of Xm = 0 with a scanning line of Yn = 0, the row number l = t _0,0 of the threshold matrix is selected at the position (0,0), and the gray value of the image is selected. Is compared with the threshold value of the t _n row and binarized.

Next, in the scanning line of Yn = n, Ym =
When recording a unit area sequence of m, the position (m,
In n), the row number 1 = T _{m, n} of the threshold matrix is selected from T = α · Yn + β · Xm and binarized.

Let us consider a specific numerical example.

Here, a halftone dot: 175 lines, a threshold matrix: M × N = 12 × 12, and a recording scan line density is 296.
9.85 (about 3000) lines / inch, main scanning recording density:
2969.85 (about 400) lines / inch, image input scanning line density is 395.98 lines / inch (= 15.589 lines / inch)
mm).

In the case of 45 ° halftone dots, the image shown in FIG.
Is converted as shown in. At this time, s, a, and b are as follows.

S = (1/175) "= 0.145 mm a = (√2 / 175)" = 0.205263 mm b = (√2 / (2 × 175)) "= 0.102631 mm Main scanning recording density is 2969.85 / 2
= 1484.925 (about 1500) lines / inch.

In the case of 15 ° halftone dots, the image shown in FIG.
It is converted as shown in 0. S, a, b, c at this time
Are as follows.

S = (1/175) "= 0.145 mm a = (1/175)" × 1 / cos 15 ° = 0.1502
6 mm b = (1/175) ”× cos 15 ° = 0.1402 mm c = (1/175)” × sin 15 ° = 0.037565
7mm Also, α and β at this time are as follows.

Α = 0.7320 β = 0.267944 Furthermore, considering the rows of the threshold matrix, p = 0.1022631 / 12 = 0.008555258 mm b / 12 = 0.1402 / 12 = 0.0116833 mm c / 12 = 0.0375657 / 12 = 0.00313
It will be 047 mm.

As described above, in the halftone creating apparatus having the above structure, the unit area array has regularity. Therefore, when the scanning line density of high-definition recording is given, the recording position can be specified on the unit area array. Easy and
It is also easy to perform binarization by comparing with the threshold at that position.

That is, the printing scan pitch and the pixel pitch of the threshold matrix are asynchronous, and the size and arrangement of the unit area are different depending on the color plate, but by dividing the unit area to the same number of pixels, Each color plate can be converted into an orthogonal screen halftone image having the same number of screen lines with the same number of gradations. In this case, the monochrome image corresponds to one color plate.

Further, 90 ° halftone dot image and 45 ° halftone dot image, ± 1
By superimposing 5 ° halftone images in the sub-scanning direction, it is possible to output four types of color separation images on one page. In recording, in the former combination and the latter combination, only the recording density in the main scanning direction needs to be switched.

Therefore, according to the above configuration, a halftone image having an approximately halftone dot pitch can be obtained approximately, and halftones of color separation plates having different screen angles can be output in one page at the same scanning line density. can do.

Needless to say, the present invention is not limited to the above-described embodiments, and can be similarly implemented even if various modifications are made without departing from the gist of the present invention.

[0056]

As described above, according to the present invention, a halftone image having an approximately halftone dot pitch can be obtained approximately, and
It is possible to provide a halftone creating apparatus capable of outputting halftones of color separation plates having different screen angles at the same scanning line density in a page.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a halftone creating apparatus according to the present invention.

FIG. 2 is a flowchart showing a binarization processing process of the control circuit of the embodiment.

3A and 3B are diagrams for explaining deformation of image data according to the embodiment, FIG. 3A shows an example before deformation, and FIG. 3B shows an example after deformation.

4A and 4B are views for explaining shaping of unit areas in the embodiment, FIG. 4A shows a relationship between before and after shaping, and FIG. 4B shows a relationship between the unit areas after shaping.

5A and 5B are diagrams for explaining the creation of the threshold matrix of the embodiment, FIG. 5A shows a threshold matrix of 90 ° halftone dots, and FIG. 5B shows a matrix structure after division.

FIG. 6 is a diagram for explaining selection of threshold pattern line numbers in the embodiment.

FIG. 7 is a diagram for explaining binarization of a recording signal of the example.

FIG. 8 is a diagram showing an image example for explaining a specific conversion example in the embodiment.

FIG. 9 is a diagram showing an image when the image of FIG. 8 is converted into a 45 ° halftone dot image.

FIG. 10 is a diagram showing an image when the image of FIG. 8 is converted into a 15 ° halftone dot image.

FIG. 11 is a diagram showing execution of halftoning in a conventional halftone creating apparatus.

[Description of Reference Signs] 100 converter 101 memory 102 recording position counter 103 selective reading circuit 104 image signal reading circuit 105 storage device 106 comparator 107 sub-scanning line counter 108 read clock generating circuit 109 control circuit 110 main scanning clock generator 111 sub Scan clock generator

Claims (2)

[Claims] 1. One or more color separation versions (C, M,
The screen angle (θ) is set according to Y, K),
Transform means for transforming the input multi-valued image data whose tone is digitized so as to deform the image in accordance with the corresponding screen angle (θ), and the multi-valued image data converted by this transforming means corresponding to a threshold value. A conversion means for binarizing based on a matrix, wherein the conversion means gives a deviation vertically different in the main scanning direction of the image according to the screen angle (θ), and the screen angle. An arithmetic means for obtaining a unit area column having a step between adjacent columns determined by (θ) and a counting means for counting the row number of the threshold matrix corresponding to each printing scanning line and each unit area column are provided. A halftone creation device characterized by the above. 2. The threshold matrix has a size of M ×
In the case of N, the same one for each color separation plate is distorted into a parallelogram according to the screen angle (θ) and then shaped into a rectangular matrix having the same number of pixels. The converting means includes means for counting the position of the line in the sub-scanning direction as the Yn-th scanning line, and means for counting that the recording position next to the main-scanning direction is the Xm-th unit row. From the counting result of the counting means, T = (Yn) α + (Xm) β + γ (mod N) α: Pitch of scanning line / sub-direction of pixels of threshold matrix, β: Step of unit area row / sub of pixel of threshold matrix Scanning direction pitch γ: T is obtained by calculating a minute noise (added as necessary) having an average value of 0, and further T−1 <t <
An integer t satisfying T is obtained, and t in the threshold matrix is calculated.
2. The halftone creating apparatus according to claim 1, wherein a row of the threshold matrix is calculated according to a scanning position by selecting a row and comparing it with a pixel value to perform binarization.