JP2584543B2 - Dot image recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dot image recording method,
In particular, the present invention relates to a technique for performing divided exposure.

[0002]

2. Description of the Related Art In a dot image recording apparatus such as an electronic control type plate making scanner, a given image signal is compared with a predetermined screen pattern signal, and an exposure light beam is turned on / off according to the comparison result. The halftone exposure recording is performed by scanning the photosensitive material while turning it off. This screen pattern signal is generated based on screen pattern data prepared in advance.

FIG. 4 shows an example of a screen pattern signal SPM. The screen pattern signal SPM is a halftone dot HD
Is divided into a matrix by using a small area A _P (hereinafter, “elementary area”) as a spatial quantization unit, and a threshold P
Is the data expressing the distribution of.

If the value of the image signal VD to be exposed is 30, the elementary area to be exposed among the halftone dots HD is an elementary area whose threshold value is 30 or less. Therefore, the dot HD
In the middle, exposure is performed in a shape as shown by hatching in FIG.

[0005]

However, the exposure shape shown in FIG. 5 is not smooth, and there is a problem that the image created by the halftone dots HD thus exposed gives a rough impression.

[0006] In order to solve the conventionally above problems, to increase the number of prime areas A _P having horns halftone HD1 with finer-containing region, the number of the gradation values of the image data VD (hereinafter "gradation degree") In addition, a method has been implemented in which the exposure shape is increased to make the exposure shape finer. However, in particular, in a plane scanning type plate making scanner, the light spot diameter of the light beam on the photosensitive material is reduced in order to make the element area finer, or the image data V
It is technically difficult to increase the operation clock of the image recording apparatus to follow the number of gradations of D, and there is a problem that the cost is increased due to an increase in the number of electronic circuits.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is intended to make the exposure shape of a halftone dot HD smooth without reducing the light spot diameter of a light beam or increasing an operation clock. This is done in order to obtain good image recording.

[0008]

According to the present invention, an image signal generated based on digital image data is sequentially compared with a screen pattern signal given to each elementary region within a halftone dot, and the comparison result is obtained. In a halftone image exposure method in which an exposure light beam scans and exposes a predetermined photosensitive material by an exposure output signal generated in accordance with A signal having a tone value signal to be compared and a select signal provided in advance for each element region is used. And (c) performing a plurality of types of delay processing on a comparison signal representing a magnitude relationship between the image signal and the gradation value signal to obtain a delay signal;
(D) selecting one signal from the comparison signal and the delay signal by the select signal; and (e) using the logical product of the one signal and a reference signal having an average delay time. Obtaining an exposure output signal.

[0009]

According to the present invention, an exposure pattern for dividing an elementary region is generated using a gradation value signal and an image signal. At this time, since an exposure pattern corresponding to the division mode is generated by the delay processing, an early operation clock is not required.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Overall Configuration FIG. 3 is a diagram showing the overall configuration of an embodiment in which the present invention is applied to a plane scanning type plate making scanner.

In FIG. 1, an image signal VD including image information to be recorded is input to a halftone output generation circuit 1 having a detailed configuration described later. This dot output generation circuit 1
Is an image signal VD input for each elementary region in a scanning line sequence.
, An exposure output signal S for giving a halftone image is generated. Further, a microcomputer 2 for control is connected to the halftone dot output generation circuit 1. The microcomputer 2 has a CPU 3 and a memory 4 and is connected to a keyboard 5 for control input.

On the other hand, a laser beam LB oscillated from a laser oscillator 7 as a light source for exposure recording is modulated in an acousto-optic modulator (AOM) 8 in accordance with the exposure output signal S, and then a beam expander. 14 is incident. The laser beam L emitted from the beam expander 14 is
The light reaches the galvanomirror (or polygon rotating mirror) 15 where it is deflected for scanning, and is irradiated via the fθ lens 16 onto the surface of the photosensitive material 17 with a light spot diameter of d.

The main scanning is achieved by periodically moving the laser beam L in the Y direction in the figure by the vibration of the galvanometer mirror 15 or the rotation of a polygon rotating mirror provided in place of the galvanometer mirror 15. . The sub-scanning is performed by moving the photosensitive material 17 in a direction penetrating the plane of the drawing. As a result, the photosensitive material 17
Is achieved, and a halftone image corresponding to the image signal VD is recorded on the photosensitive material 17.

B. Generation of Halftone Output Signal Next, a method of generating the halftone output signal will be described. FIG. 1 is a circuit diagram showing the internal configuration of the halftone dot output generation circuit 1. An image signal VD input to the comparator 1a is a gradation value signal GD in a similarly input screen pattern signal SPM.
And a signal C indicating a magnitude relationship along the main scanning direction.
Generate ₁ The gradation value signal GD plays the same role as the conventional screen pattern signal SPM. An example of the manner of generation of the signal C ₁ in FIG.

Consider the fourth elementary region sequence from the top of the halftone dot HD shown in FIG. Now, when the value of the image signal VD is 30, assuming that the gradation value signal GD is equal to the conventional screen pattern signal SPM, 60, 26, 14,
Since showing the threshold of exposure as 10,18,29,57, C ₁ is OFF when containing regions A ₆₀ and A _57, A _26,
It is ON in _{A 14, A 10, A 18} , A 29.

[0016] The signal C ₁ obtained as described above, the delay element group 1b, delays. The number of elements in the delay element group 1b is determined by the fineness of the divided exposure described later. In the case of performing the divisional exposure by the pattern for dividing the elementary region into n, (2n-2) delay elements are required. In this embodiment, n = 4, and six delay elements are provided.

For the sake of simplicity, the operation of the halftone output generation circuit 1 will be described by considering a simple signal before considering the signal of FIG. Now, consider a case where only is ON length T corresponding a signal C ₁ based on area one minute (Fig. 1). The delay time of each delay element group 1b is

[0018]

(Equation 1)

## EQU1 ## The signal thus delayed is represented by C k
And Note that these C The average of each delay time of k
C with close delay time_FourWhen the reference signal is
Quasi signal C_FourSignal C₁~ C_ThreeIs T / 4 increments
Signal and signal C_Five~ C₇Is a delay signal every T / 4
You.

The signal C thus generated k (k is 1
To an integer from 2n-1) to the selector 1c.
One of them is selected and the selector output signal C₀When
And input to the gate 1d. On the other hand, the reference signal C_FourAlso
Input to gate 1d. Gate 1d is an AND gate
The selector 1c outputs the signal C If you choose k,
Output signal S as exposure output signal S k is output. here
And the output signal S_FourIs the signal C with the same delay time_FourLogic between each other
Signal C_FourSignal C₁Is 3T
/ 4, and the output signal S₁~ S_Three, S_Five
~ S₇Is to AND the signals with different delay times.
So signal C₁As a partial signal divided at intervals of T / 4
Generated. Here, the selection of the selector 1c is based on the screen pattern.
The select signal SD described below in the turn signal SPM
Is controlled by

Screen pattern signal in the present invention
SPM is the floor corresponding to the conventional screen pattern signal.
It also has a select signal SD in addition to the tone signal GD.
For example, the gradation value signal GD is 8 bits, and the select signal SD is
In the case of 3 bits, the screen pattern signal SP
M is an 11-bit signal composed of both signals. Figure
6 shows the distribution of the select signal SD. This is in contrast to FIG.
For example, the uppermost element region A₄₂Gradation of
The value of the value signal GD is 42 and the select signal SD
Is 4. Similarly, the element region A₄₆Having
The value of the gradation value signal GD is 46, and the select signal S
D is 7. The value k of the select signal SD is
The signal C selected in the It defines k.
However, the select signal SD is a delay element for the reason described later.
Delay by 3T / 4 by group 1e. Select signal S
D is a screen pattern signal by the bit selection unit 1f.
No. SPM. At this time, the gradation value signal GD is also obtained.
Can be The bit selection section 1f can be easily implemented by a shift register or the like.
Be composed.

[0022] Now, then consider the case where entered indicated signal 7 as a signal C ₁ (pulse width 5T) to the delay element group 1b. FIG. 8 shows the select signal SD corresponding to FIG. By signal C ₁ is input to the delay element group 1b, the signal C ₂ -C ₆ has a waveform as shown. However, since 1 and 7 are not selected as the value of the select signal SD in the element region under consideration, C ₁ and C ₇ are omitted. In each elementary region, signals C _{2 to} C ₆ are selected according to the select signal SD.

First, in the elementary regions A ₆₀ and A ₂₆ , the signal C ₆ is selected as the selector output signal C ₀ . As described above, the signal C ₆ is delayed with respect to the output signal C ₁ of the comparator 1a, but the select signal SD is also delayed by 3T / 4 and the signal C ₆ and the reference signal C ₄ are delayed by the gate 1d. Since the logical product is obtained, the portion surrounded by the broken line eventually constitutes a part of the output signal S. Similarly, the elementary regions A ₁₄ , A ₁₀ , A ₁₈ , A ₂₉ ,
In A ₅₇ , the delayed signals C ₅ , C ₄ , C
_{Since 3} , C ₂ and C ₂ are selected and the logical product of the reference signal C ₄ is obtained by the gate 1d, the output signal S is constituted by the portion surrounded by the broken line after all.

The length of the signal S thus constituted is defined by the rising edge of the signal C _{6 and} the falling edge of the signal C ₂ as shown in the figure. Thus, exposure output signal S becomes the length of 4T, it is shorter by T than the length 5T of the output signal C ₁ of the comparator 1a.

Similarly, in other columns, the exposure output signal S
It is generally shorter than the output signal length of C ₁ comparator 1a length of. Thus, for the same image signal VD, the dot area according to the present invention is smaller than that of the conventional one.

In order to avoid this, a conventional halftone dot area can be obtained by applying a correction (for example, using a one-dimensional lookup table) to the image signal VD. However, if the numerical value of the gradation value signal GD written in the screen pattern signal SPM is corrected, almost the same halftone dot area as that of the image signal VD can be obtained without imposing a hardware burden.

Here, the select signal SD is supplied to the delay element group 1e.
Was subjected to delayed 3T / 4 by is for taking signals C ₄ having an average delay time in time reference. That is, in the case of smoothing a halftone dot, it is necessary to reduce the exposure area as the element region is farther from the center of the halftone dot in the main scanning direction. Therefore, the pattern of the select signal SD is selected as shown in FIG.

[0028]

(Equation 2)

In the case of the right side (the side where the main scanning coordinate Y is large)
The exposure area decreases from

[0030]

(Equation 3)

In the case of (1), the left side (the side where the main scanning coordinate Y is smaller)
It is desirable that the exposure area be reduced from the beginning. Therefore the signal C ₄ having an average delay time, by using a logical product of this and the selector output signal C ₀ is taken as a reference as a signal to expose the entire elementary area, as Yuku decreases the exposure area from the right or left It was. Since there are _seven signals to be selected, C _{1 to} C ₇ , the delay element 1 e
Bits are provided.

By performing the above-described processing over all the elementary regions, a halftone dot image can be smoothed. FIG. 9 is a halftone image to which the present invention is applied when the value of the image signal VD is 30, and corresponds to FIG. The frame shown by the thick line is the halftone image of FIG. 5, and the shaded portion is the halftone image when the present invention is applied. Although the entire area is shifted by ／ of the length of one side of the elementary region due to the delay time of 3T / 4, it can be seen that a halftone dot image smoother than the halftone dot image indicated by the thick line is obtained.

FIG. 2 is a flowchart in which the above procedures are arranged. First, in step S100, the gradation value signal GD and the select signal SD are separated from the screen pattern signal SPM. This is the bit selection unit 1f of FIG.
Corresponding to

Next, in step S200, the magnitude relationship between the gradation value signal GD and the image signal VD of the elementary region of interest is examined.
Obtaining a signal C ₁ corresponding thereto. This corresponds to the comparator 1a.

Next, at step S300, C₁Delay
Signal C Get k. This corresponds to the delay element group 1b.

[0036] The next step S400, obtaining a signal C ₀ in accordance with the select signal SD. This corresponds to the selector 1c.

Next, an exposure output signal S is obtained in step S500. This corresponds to the gate 1d.

[0038]

As described above, according to the present invention, the screen pattern signal given to each element includes the gradation value signal to be compared with the image signal, and the select signal which defines the exposure pattern of the elementary region. And delay processing is used when generating a plurality of exposure patterns that divide an elementary region based on the image signal and the gradation value signal. Therefore, the exposure state of the halftone dots can be made smooth without increasing the operation clock, and good image recording can be obtained.

[Brief description of the drawings]

FIG. 1 is a halftone dot output circuit 1 to which an embodiment of the present invention is applied;
FIG. 3 is a block diagram showing the configuration of FIG.

FIG. 2 is a flowchart showing a procedure of an embodiment of the present invention.

FIG. 3 is an overall configuration diagram of a plate making scanner to which the present invention is applied.

FIG. 4 is a distribution diagram of a tone value signal GD in a halftone dot HD.

FIG. 5 is an explanatory diagram showing a conventional technique.

FIG. 6 is a distribution diagram of a select signal SD in a halftone dot HD.

FIG. 7 is an explanatory diagram showing a conventional technique.

FIG. 8 is an explanatory diagram showing generation of an exposure output signal S.

FIG. 9 is an explanatory diagram of halftone dot exposure according to one embodiment of the present invention.

[Explanation of symbols]

VD image signal HD halftone A _P-containing region SPM screen pattern signal S exposure output signal L the laser beam 17 sensitive material GD gradation value signal SD select signal C ₀ -C ₇ signal

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshiyuki Nishigakiuchi 1 at 480 Takamiya-cho, Hikone-shi, Shiga Prefecture Dainippon Screen Mfg. Co., Ltd. Hikone district office (56) References JP-A-1-264076 (JP) , A)

Claims (1)

(57) [Claims] An image signal generated based on digital image data is sequentially compared with a screen pattern signal provided for each elementary region within a halftone dot, and an exposure output signal generated according to the comparison result. The exposure light beam scans and exposes a predetermined photosensitive material, thereby recording a halftone image on the photosensitive material, wherein the screen pattern signal is: A gradation value signal to be compared; and (b) a select signal provided in advance for each element region. In the comparison, (c) determining a magnitude relationship between the image signal and the gradation value signal. Performing a plurality of types of delay processing on the represented comparison signal to obtain a delay signal; and (d) selecting one signal from the comparison signal and the delay signal by the select signal. And (e) obtaining the exposure output signal using a logical product of the one signal and a reference signal having an average delay time.