JP2545965B2 - Halftone dot forming device - Google Patents

Description

The present invention relates to a halftone dot forming apparatus using a dot generator, and more particularly to a halftone dot forming apparatus capable of generating higher quality halftone dots. .

[Prior Art] Currently, in the field of plate making, a color scanner has been developed and put into practical use when making an original such as a color photograph. This color scanner color-separates and outputs image information of a document into four colors of Y (yellow), M (magenta), C (cyan), and BK (black). In this type of color scanner, a dot generator using laser light is often used as a means for generating halftone dots used in printing. A halftone dot forming device using this dot generator is a dot pattern signal (triangular wave) having a constant cycle corresponding to a conventionally used density distribution of a contact screen divided into strips, gradation conversion, sharpness, etc. By comparing with the image signal added with the condition (3), only the intersecting portion is exposed on the photosensitive material to generate a halftone dot.

By the way, as for the halftone dot forming device using this dot generator, various manufacturers have proposed various types, but by uniformly turning the laser light on and off, halftone dots are generated directly on the film. The method to do is most. The halftone dots generated by this type of method have stable output quality (a) because the halftone dots themselves have uniform density (the latitude is wide with respect to the shake of the developing device). (B) Image signal On the other hand, since a halftone dot signal directly corresponds to, a sharp image can be obtained.

(C) By changing the halftone dot generation program, it is possible to generate halftone dots suitable for various purposes.

It has excellent advantages such as

[Problems to be Solved by the Invention] However, on the other hand, compared with the halftone dots by the previous contact screen, the halftone dots themselves have uniform density,
The disadvantage is that halftone dots cannot be modified in the subsequent process. The reason for this is that when a dot generator generates a halftone dot, it simply turns the laser light on and off, so there are few fringes as shown in FIG. 5, and the halftone dot is corrected to a small size using a chemical ( This is because it is difficult to perform the process (hereinafter referred to as a reduction process). Therefore, in the reproduction of colors with high quality demands such as reproduction of women's skin and reproduction of works of art, it is difficult to reduce the disassembled plate, and it is necessary to disassemble it again, which in turn increases the work load. become.

The present invention has been made to solve the above problems, and takes advantage of the halftone dot formation by the dot generator, and has a higher quality halftone dot having a density gradient for facilitating the reduction process. An object of the present invention is to provide a highly reliable halftone dot forming device capable of generating dots.

[Means for Solving the Problems] In order to achieve the above object, first, a halftone dot forming apparatus according to the first aspect of the invention has a digital image signal obtained by digitizing an image signal output from a scanner, and a fixed value. Input the dot pattern signal of the cycle,
Halftone dot concentration control means for obtaining a multilevel signal for controlling the intensity of the laser light by comparing the two and creating a concentration gradient according to the difference, and the laser light output from the laser generator On / off and intensity are controlled by a multi-valued signal from the density control means, and a halftone dot generating means for exposing a photosensitive material to generate a halftone dot pattern is provided.

Further, the halftone dot forming apparatus of the invention according to claim 2 inputs the digital image signal obtained by digitizing the image signal output from the scanner and the halftone dot pattern signal of a constant period,
A comparison means for comparing the two and obtaining a binary signal representing a dot formation portion and a dot non-formation portion based on the magnitude relationship, and a binary signal from the comparison means is input, and the dot signal formation portion based on the binary signal. Halftone dot density control for obtaining the difference between the digital image signal and the halftone dot pattern signal based on the continuous amount of the, and creating a density gradient according to the difference to obtain a multivalued signal for controlling the intensity of the laser light Means for controlling the on / off and intensity of the laser light output from the laser generator by a multi-valued signal from the halftone dot density control means, and exposing the light-sensitive material to generate a halftone dot pattern. It is equipped with.

[Operation] Therefore, in the halftone dot forming apparatus of the present invention, since the halftone dots themselves have an appropriate density gradient when the halftone dots are generated by providing the above means, It is possible to generate a halftone dot having an appropriate fringe, which has the advantages of the halftone dot generated by the contact screen and is easy to correct the halftone dot in the subsequent process.

[Embodiment] In the present invention, as shown in FIG. 2, a halftone dot pattern signal (triangular wave) having a constant period corresponding to a density distribution of a conventionally used contact screen divided into strips.
In the dot generator that generates a halftone dot by exposing only the intersecting portion to the photosensitive material by comparing the image signal to which the conditions such as gradation conversion and sharpness are added,
By calculating not only the length of the halftone dot pattern signal and the image signal that intersect, but also the difference between the halftone dot pattern signal and the image signal, the intensity of the laser light is controlled to create a density gradient on the halftone dot itself. It is something to have.

An embodiment of the present invention based on the above concept will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example of a halftone dot forming apparatus using the dot generator of the present invention. In addition, in the present embodiment, the case of application to a color scanner will be described as an example. The halftone dot forming apparatus of this embodiment has an analog / digital converter (hereinafter referred to as an A / D converter) as shown in FIG.
1, a halftone dot pattern signal generator 2, a comparison circuit 3, a halftone dot density control circuit 4, a laser light control circuit 5, a laser generator 6, a beam splitter 7, a modulator 8, and a light amount adjustment. It is composed of a system 9 and a lens system 10.

Here, the A / D converter 1 converts the image information of the original color photograph into Y (yellow), M (magenta), C (cyan), and B.
The image signal A output from a color scanner (not shown), which is separated into four colors of K (black) and then output, is converted into a digital signal to obtain a digital image signal B. Further, the halftone dot pattern signal generator 2 generates a halftone dot pattern signal (for example, a plurality of triangular waves) C having a constant cycle corresponding to a conventionally used density distribution of a contact screen divided into strips. is there. Further, the comparison circuit 3 compares the image signal B from the A / D converter 1 with the halftone dot pattern signal C from the halftone dot pattern signal generator 2 to obtain a plurality of on / off binary signals D. Is what you get.

On the other hand, the halftone dot density control circuit 4 inputs the binary signal D from the comparison circuit 3, creates a density gradient from the binary signal, and controls the intensity of the laser light to control a multivalued signal (4 gradations). Or 8 gradations) E. The laser light control circuit 5 receives the multivalued signal E from the halftone dot density control circuit 4 and obtains a control signal for controlling the laser light by the multivalued signal E. Further, the laser generator 6 generates a laser beam, and the beam splitter 7 outputs several laser beams from the laser generator 6.
The beam is split into about 10 beams. Furthermore, the modulator 8 outputs the beam from the beam splitter to
ON / OFF and intensity are controlled by a control signal from the laser light control circuit 5, and a light sensitive material is exposed through a light amount adjusting system 9 and a lens system 10 to generate a halftone dot pattern. In this case, the halftone dot density control circuit 4 and the laser light control circuit 5 constitute halftone dot density control means, and the modulator 8, the light amount adjusting system 9 and the lens system 10 constitute halftone dot generating means.

Next, the operation of the halftone dot forming device configured as described above will be described.

In FIG. 1, an image signal A of a color photograph color-separated by a color scanner (not shown) is converted into a digital signal by an A / D converter 1 and converted into a digital image signal B. Further, in the halftone dot pattern signal generator 2, a halftone dot pattern signal (a plurality of triangular waves) C having a constant period, which corresponds to the density distribution of the contact screen divided into strips, is generated.
Is generated. Then, in the comparison circuit 3, the image signal B from the A / D converter 1 and the halftone dot pattern signal C from the halftone dot pattern signal generator 2 are compared as shown in FIG. A plurality of on / off binary signals D are output in accordance with the above. Further, the binary signal D is input to the halftone dot density control circuit 4, where a density gradient is created from the binary signal D and four or eight gradations for controlling the intensity of the laser light are generated. It is converted into a value signal E. In this case, 2
The value signal D is converted into the multivalued signal E as follows. That is, for example, as shown in FIG. 3A, the length a corresponding to the intersection of the halftone dot pattern signal C and the digital image signal B
From the above, a halftone dot pattern signal C is obtained by using a linear or quadratic function (in the figure, a functional expression of b = 1.5a is used and four gradations are used).
And a difference b between the image signal B and the image signal B is calculated to obtain a multilevel signal E. From this, a multi-valued signal E for changing the density according to the amount of deviation from the center is obtained. Then, the plurality of multi-valued signals E thus obtained are input to the laser light control circuit 5, based on which a control signal for controlling the laser light is obtained, and then input to the modulator 8. It Here, the density gradients of these multi-valued signals are different because they are determined by each intersection length a, and the formed dots eventually have various densities as shown in FIG. 3 (b). Reduction processing is easily performed.

On the other hand, the laser light generated from the laser generator 6 is split into several to ten beams by the beam splitter 7 and input to the modulator 8. The beam from the beam splitter 7 is turned on by the control signal from the laser light control circuit 5 in the modulator 8.
The off and strength are controlled, and the light is exposed through the light amount adjusting system 9 and the lens system 10 as a halftone dot pattern having an appropriate fringe on the film which is a light-sensitive material. FIG. 4 is a conceptual diagram showing a halftone dot pattern having an appropriate fringe generated as described above.

As described above, in this embodiment, a halftone dot pattern signal (triangular wave) C having a constant period, which corresponds to a conventionally used density distribution of a contact screen divided into strips, is formed.
And a digital image signal B to which conditions such as gradation conversion and sharpness are added are compared to each other to expose only the intersecting portion on a film as a light-sensitive material to generate a halftone dot. In the halftone dot forming device, a first-order or second-order function (functional expression of b = 1.5a, 4 gradations) is used from the length a where the halftone dot pattern signal C and the digital image signal B intersect. The difference b between the halftone dot pattern signal C and the image signal B is calculated and the intensity of the laser beam is controlled based on this difference. High halftone dots can be generated.

That is, it is possible to form a fringe (a low-density blurred portion) that is extremely close to the case where halftone dots are formed on the contact screen. This is because the halftone dot pattern signal C having a constant cycle generally has a peak in the central portion and the value thereof gradually decreases, so that the difference in the central portion becomes large when compared with the image data, and the peripheral portion becomes closer. The difference tends to be small, and thus a low density portion, that is, a fringe, is likely to be formed around the halftone dot.

 As a result, the following effects can be obtained.

(A) It is possible to easily carry out the reduction processing in the retouching process or the like, while the dots are stable by the dot generator.

(B) It is possible to appropriately select the fringe of halftone dots according to the type of the design of the color photograph which is the original.

(C) By adding an appropriate fringe to the dots,
This is extremely effective for patterns that have been reproduced with a rough feeling with halftone dots generated by a conventional dot generator.

In the above embodiment, the difference b between the halftone dot pattern signal C and the image signal B is calculated from the length a, which is the intersection of the halftone dot pattern signal C and the digital image signal B, to a primary or secondary order. Although the multilevel signal E is calculated by using a function, the signal levels of both signals may be actually measured without being limited to this.

Further, in the above embodiment, the case where the present invention is applied to a color scanner is described, but the present invention is not limited to this, and the same applies to various plotters for the purpose of generating halftone dots and monochrome scanners including newspapers. Is applicable to.

Further, in the above embodiment, the case where the original is a color photograph has been described, but it goes without saying that it may be other than this.

[Effects of the Invention] As described above, according to the present invention, when a halftone dot is generated, the halftone dot itself has an appropriate density gradient, so that a higher quality halftone dot is generated. It is possible to provide an extremely reliable halftone dot forming device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a halftone dot forming apparatus using a dot generator of the present invention, FIG. 2 is a diagram for explaining the concept of the present invention, and FIG. FIG. 4 is a diagram for explaining, FIG. 4 is a diagram showing halftone dots generated in the same embodiment, and FIG. 5 is a diagram for explaining a conventional technique. 1 ... A / D converter, 2 ... Halftone dot pattern signal generator, 3 ... Comparison circuit, 4 ... Halftone dot density control circuit, 5 ... Laser light control circuit, 6 ... Laser generator, 7 ... Beam splitter, 8 ...
Modulator, 9 ... Light intensity adjustment system, 10 ... Lens system.

Claims (2)

(57) [Claims] 1. A laser in which a digital image signal obtained by digitizing an image signal output from a scanner and a halftone dot pattern signal having a constant period are input, and the two are compared to create a density gradient corresponding to the difference between them. Halftone dot concentration control means for obtaining a multivalued signal for controlling the intensity of light, and on / off and intensity control of laser light output from a laser generator by a multivalued signal from the halftone dot concentration control means And a halftone dot generating means for exposing the photosensitive material to generate a halftone dot pattern. 2. A digital image signal obtained by digitizing an image signal output from a scanner and a halftone dot pattern signal having a constant period are input, and the two are compared to determine the halftone dot forming portion / non-dot based on the magnitude relationship. Comparing means for obtaining a binary signal representing the forming section, and inputting the binary signal from the comparing means, the digital image signal and the halftone dot pattern signal based on the continuous amount of the halftone dot forming section by the binary signal. The halftone dot concentration control means for obtaining a multi-valued signal for controlling the intensity of the laser light by obtaining the difference of the difference and creating a concentration gradient according to the difference, and the laser light output from the laser generator, A halftone dot forming device, comprising: a halftone dot generating means for controlling on / off and intensity according to a multi-valued signal from the halftone dot density control means, and exposing the photosensitive material to generate a halftone dot pattern. .