JPS60196072A - Production of dot picture signal - Google Patents

Abstract

PURPOSE:To obtain a binary output for dot pictures through comparison between a threshold value signal and a picture signal, by obtaining the threshold value signal from the sum of the outputs of the 1st and 2nd dot signals having different phases which have the variance every scan and then the coincidence every prescribed scanning frequency with the same frequency. CONSTITUTION:Both outputs of dot signals (a) and (b) which have a phase variance every scan are added to each other by an adder 3 to obtain a superposition signal (c) having the amplitude changing every scan. The signal (c) is supplied to the comparator 5 as a threshold value signal and compared with a picture signal (e). Thus a binary output (f) for dot pictures can be easily obtained. When the signal (e) is binary coded with the signal (c), a signal which repeats both high and low levels in a prescribed cycle is obtained with the binary output of an area of the half-tone X2. Then a fixed signal of a high level is obtained when the binary coding is carried out with a signal (c') of a small amplitude. For a picture, both half-tone areas X2 and X3 are shown in black dots (Fig. E) with the signal repeating high and low levels. While only the area X3 is shown in black dots (Fig. F) with the fixed signal of a high level respectively.

Description

[Detailed description of the invention] Technical fields> The present invention relates to a method for forming a halftone image signal.

More specifically, the present invention relates to a method of forming a halftone image signal, which is a binary output for expressing halftones of shading of an original.

<Background and Prior Art> Conventionally, in recording devices, digital copying machines, facsimile machines, etc. that output only binary values of white and black, changing the density of black dots has been used as a method of expressing halftones. . A specific method for this is the dither method, which binarizes the input signal using a matrix in which multiple threshold values are arranged in a fixed order, but this method requires a large amount of memory to store each threshold value and its order. However, there is a problem in that the threshold value and matrix size cannot be arbitrarily changed in accordance with the characteristics of the original image. As a countermeasure to this problem, it may be possible to prepare a plurality of dither patterns, but this is not economical. There are also methods of changing the threshold by sequentially switching multiple reference voltages for each scanning line, and methods of periodically using two thresholds between scans, but in both cases, even if the device is simple, the expression The disadvantage is that the number of gradations that can be achieved is small. There is another method of generating halftone dot signals in the raw scanning direction and performing binarization by avoiding changes in the amplitude of the halftone dot signals in the sub-scanning direction. A flip-flop that selectively performs differentiation on the rising edge, an up-down counter that repeats the reference clock until it is cleared by the differentiator output, an adder that adds the count output of the up-down counter to the reference voltage, and an adder. The problem is that the structure becomes complicated because it requires an essential element such as an amplification switch that multiplies the output by a large number of digital setting values.

<Purpose> The present invention has been made in view of the above, and provides a method for forming a halftone image signal, which allows the gradation and resolution to be arbitrarily changed according to the original image without using memory, and which requires a short processing time. The purpose is to write.

<Configuration> The configuration of this invention to achieve the above object is as follows:
A signal for a threshold value is obtained by the sum of the signal outputs of a first halftone signal and a second halftone signal having the same frequency whose mutual phases shift every scan and match every predetermined number of scans, and the threshold value This is characterized in that a binary output for a halftone image is obtained by comparing the signal for the dot image with the image signal.

<Examples> Next, examples of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the principle of forming a halftone image signal.

The first halftone signal (
a), and a second halftone signal (b) output from a halftone signal generator (2) configured separately from the halftone signal generator (1).
) are signals having the same amplitude and the same frequency, and -C1 Furthermore, as is clear from (B) to ([) in FIG. 2, the first halftone dot signal (a) is It is a signal whose phase changes by a certain period in the second halftone dot signal (b
) is a signal whose phase advances by a period equal to that of the first halftone dot signal (a) for each scan.

More specifically, if the period of the first halftone dot signal (a) and the second halftone dot signal (b) is the king, then the phase of both signals shown in FIG. In the second scan shown in FIG. 2(B), a phase shift occurs by a fixed period T/N in the opposite direction to H, and in the third scan shown in FIG. 2(C), the odor point signal ( The phases of a>(b) match.

Note that FIG. 2(E) shows a state in which the phase shifts of the halftone dot signals (a) and (b) each occur by 1/4 period.

Then, if the outputs of the halftone dot signals (a) and (b), which have a phase shift for each scan as described above, are added by the adder (3), the amplitude changes for each scan as shown by the chain line in Figure 2. A superimposed signal (C) will be obtained.

The superimposed signal (C) thus obtained is input to the comparator (5) as a threshold signal, and compared with the image signal (e), the binary output (f) for both halftone images can be easily obtained. This means that it can be formed as follows. However, it is also possible to add a constant voltage (V) from the voltage source (4) to the superimposed signal (C). This point will be explained in further detail with reference to FIG. 3 and subsequent figures.

Figure 3 shows an original document (X
) is a block diagram illustrating the case of reading . Manuscript (X
), the (×1) portion is a white background, the (X4) portion is a black background, and the halftone (×2) has a lighter density than the halftone (×3). Also, (61) in the figure is a light source, and (62) is a lens (63) that directs the opposite light from the original (X).
(64) is a reflector that guides the COD driver (65).
) is a CCD line sensor driven by Furthermore (6
6) is contact glass, (67) is CPU, (68)
indicate ROMs, respectively.

As shown in Figure 4 (B), in the case of an original (X) containing halftones (x2) (X3), the voltage of the image signal (e) is output of V for the halftone (x2) part, output of ■3 for the halftone (x3) part, and output of V4 for the black background (x) part. are obtained respectively.

FIG. 4(C) shows an image signal (e) containing halftones (×) (×3) by the threshold value signal (C) in one scan, as shown by the solid line in FIG. 4(B). It shows the binary output (f) obtained as a result of binarizing the 4th
In Figure 4 (D), the image signal (e) is binarized using a threshold signal (C') in another scan, the amplitude of which is attenuated as shown by the dotted line in Figure 4 (B). The figure shows the binary output (f') obtained as a result. As is clear from these figures, image signal (e) is converted into signal (C) by 2
When converting into a binary value, a signal in which high level and low level repeat at a predetermined period is obtained as the binary output of the halftone (x2) part, and when converting into a binary signal with a small amplitude signal (C'), ,
A constant high level signal is obtained. In the former case, the image expressed by these signal outputs is
Both halftone (X2) and (X3) parts as shown in Figure (E) are expressed as black dots, and in the latter case, only the halftone (X3) part as shown in Figure 4 (F) is expressed as black dots. That will happen.

Therefore, if a binary output (f) is obtained for each scan using a threshold signal whose amplitude changes stepwise for each scan, a halftone corresponding to the density can be expressed.

Note that it is also possible to fix the phase of either the first halftone signal (a) or the second halftone signal (b), and in this case, the threshold signal (C) has only the amplitude. In addition, since the phase also changes, the direction in which the halftone dots are arranged can be made different from that of the above embodiment.

Further, if a constant voltage is applied to the superimposed signal (C), the level of the threshold signal changes as a whole, so by changing this constant voltage value, the brightness and darkness of the entire image can be adjusted.

Effect> As described above, according to the method for forming a halftone image signal according to the present invention, the first halftone dot signal and the first halftone dot signal each having the same frequency whose mutual phases shift every scan and match every predetermined number of scans. 2
Since the threshold signal is obtained by the sum of the outputs of both the halftone dot signals, the threshold signal can be easily changed for each scan without using complicated equipment, making it very economical to use the halftone dot signal. It has the unique effect of being able to form a point image signal and shortening the processing time since there is no extra circuit.

In addition, the contrast can be easily changed by simply changing the amplitude of the side halftone signal, and the pitch of halftone dots can also be changed by adjusting the period of the halftone dot signal and the degree of phase shift for each scan. It also has the unique effect of being able to arbitrarily adjust the floor adjustment and resolution.

Furthermore, by adding a constant voltage to the superimposed signal and changing this constant voltage, the brightness of the entire image can be easily changed.
? That will happen.

[Brief explanation of drawings]

The figures show an embodiment of the invention, with Fig. 1 being a block diagram showing the basic principle, Fig. 2 being a graph showing the state of phase shift of halftone dot signals, and Fig. 3 showing an example of applied use. The block diagram, Figure 4 (A) shows the original image for reading, Figure 4 (
B) is a miniature representation of the image signal and the signal for the threshold; FIG. 4(C)
4(D) is a diagram of the binary output, and FIGS. 4(E) and 4(F) are enlarged views showing a part of the expressed image. (11(2)...halftone signal generator, (3)...adder, (4)...voltage source, (5)...comparator, (a)
...first halftone dot signal, (b)...second halftone dot signal,
(C)...Threshold signal, (e)...Image signal, (
f)...Binary output which is a halftone image signal, (Vl...
Constant voltage. Patent Applicant: Sanda Kogyo Co., Ltd. (Figure 1, Figure 2, Figure 4 Procedures, Amendments, Writing Method) July 26, 1980 1. Display of the case 1982 Patent Application No. 52783 2. Name of the invention Halftone image signal Formation method 3, relationship with the case of the person making the amendment Patent applicant address 1-2-28 Tamatsukuri, Higashi-ku, Osaka Name (6
15) Sanda Kogyo Co., Ltd. Representative 3 1) Kei 4, Agent 5, Date of amendment order: June 6, 1980 (Shipping date: June 26, 1980) 6
, Brief explanation of drawings 7, Contents of amendment (1) "Figure 4 (A)" in lines 2 to 6 of page 10 of the specification in the specification to be amended.
This is an enlarged view. "Figure 4 is an explanatory diagram showing the halftone image forming operation, the back (Δ) is a diagram showing the original image for reading, and (B) is a diagram of the image signal and the signal for threshold value. , (C) and (D) are diagrams of binary output,
(E) and (F) are enlarged views showing a portion of the rendered image. ” he corrected.

Claims (1)

[Claims] 1. The threshold value is determined by the sum of the outputs of the first halftone signal ζ and the second halftone signal, each of which has the same frequency whose mutual phase shifts every scan and matches every predetermined number of scans. A method for forming a halftone image signal, the method comprising: obtaining a signal for a threshold, and comparing the signal for a threshold with an image signal to obtain a binary output for a halftone image. 2. Forming a halftone image signal according to claim 1, in which the phases of the first halftone signal and the second halftone signal are shifted by the same period in mutually opposite directions for each scan. Method.