JPS5938790B2 - Halftone reproduction method in facsimile, etc. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a facsimile machine that digitizes an analog image signal including halftones and records it as a difference in pulse density corresponding to the original halftones in a facsimile machine that records only with binary signals. Regarding halftone reproduction methods in et al.

In conventional inkjet, thermal, electrostatic, and other recording methods used in facsimile machines that record only with binary signals, analog image signals containing halftones are converted into digital signals of several bits, and differences in the original halftones are detected. Various methods have been proposed for recording the difference in pulse density.

However, although the recording signal created by a recording device can have sufficient gradation, when actually viewed as a recorded image, there is often almost no difference between the gradations that are close to each other. Despite the fact that a signal with 9 gradations is created, there is a problem in that only about 4 to 5 gradations can be expressed as a recorded image. The present invention solves these problems and aims to provide a halftone reproduction method for facsimiles and the like using pulse density conversion that can clearly express tone differences. Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a block diagram showing an embodiment of the halftone reproduction method according to the present invention, and FIG. 2 is an operation waveform diagram for explaining its operation. 1 with n+l bits (n is a positive integer)
This is an A/D conversion circuit that converts an analog image signal including halftones input from the terminal 12 into an n+1 bit digital signal.

Reference numeral 2 denotes an n-bit storage circuit, which synchronizes the output signal of the A/D conversion circuit 1 with the reference clock signal a input from the input terminal 13.

Here, the memory circuit 2 divides the output signal of n+1 bits from the A/D conversion circuit 1, and divides the output signal c of the lower n bits, the output signal P of the upper position bit, and the A total of three types of output signals are created, including the output signal c which is the complement of ''. 3 is a first selection circuit which selects one of the two types of output signals containing black information from the storage circuit 2 as an output signal, and depending on the value of the l-bit signal p of the white information, Either n bits c or c is selected as the output signal e.

4 is a designation circuit that designates and outputs two types of numerical values set in advance.

5 is a second selection circuit which selects one of the two numerical values of the designation circuit 4 according to the output signal p of the processing bit of the storage circuit 2, and outputs it as an n+l bit digital signal g.

Reference numeral 6 denotes an adder circuit which adds the output signal e of the first selection circuit 3 and the output signal g of the second selection circuit 5 and outputs the result as an n+1 bit signal f.

Here, since the output signal e has n bits, the (n+1)th bit is always processed as O. Reference numeral 7 denotes a gate circuit, which sets the output signal 1 to 1 only when the signals indicating each bit of the output signal e of the first selection circuit 3 are all 1.

8 is an n+l bit counting circuit, which counts the reference clock signal a.

Reference numeral 9 denotes an n+1 bit comparison circuit, which compares the contents of the output signal f of the adder circuit 6 and the output signal k of the counting circuit 8, and only when the strength of the contents of the output signal k of the counting circuit 8 is not small. The pulse output signal 1 is output as a pulse output signal 1 having a period twice that of the reference clock signal a.

Reference numeral 11 denotes a switching circuit, which is switched depending on the value of the output signal p of the memory circuit 2.

10 is an inverter circuit, and 14 is an output terminal.

Next, the operation of the device configured as described above will be explained using the case where n=3 as an example.

An analog image signal b including halftones input from an input terminal 12 is divided into 16 gradations by a 4-bit A/D conversion circuit 1. The A/D converted 4-bit digital signal is temporarily stored in a 4-bit storage circuit 2 in order to be synchronized with the reference clock pulse signal a input from the input terminal 13. Here, as described above, the 16 gradations are divided into 8 gradations containing a lot of black information and 8 gradations containing a lot of white information. The 8 gradations on the white information side are based on white as before, and one pulse of black enters the white at a different period to obtain an intermediate tone close to white, and the 8 gradations on the black information side are On the contrary, by using black as a base and inserting l pulses of a white signal into the black at different periods, a half tone close to black is obtained. Therefore, the storage circuit 2 stores three types of signals: a signal p indicating the high-order 1 bit of the stored content, a signal C representing the remaining low-order 3 bits, and a signal c representing the 2's complement of the signal c. The first selection circuit 3 receives the signal from the storage circuit 2, and outputs the same signal c as before for the 8 gradations on the white information side, and reversely outputs the signal c for the 8 gradations on the black information side. Select and output. In other words, when the signal p is ``0'', it is a halftone close to black, the first selection circuit 3 selects and outputs the signal c, and when the signal p is 6F'', it is a halftone close to white. Yes, selection) The circuit 3 selects and outputs the signal c.

Figure 3 shows the relationship between the gradation number and signal P, signal C, signal C and signal e in each of these gradations, and the relationship between signal e and signal G,
It is a figure which shows the relationship with the signal f. Now, if we focus on the signal e, the gradation filters 7 and 8 are both "0, 0, 0", and the pulses of 1 pulse of the white signal and 1 pulse of the black signal, which are the contact points of the black information side halftone and the white information side halftone. Since this is a pulse signal with a ratio of 1 to 1, the gradation waterfall 8 is the contact point between the black information side halftone and the white information side halftone.Therefore, in the adding circuit 6, the white information side 8th floor It is necessary to add ``1'' to the tone, and conversely add ``2'' to the 8 gradations on the black information side in order to make them inversely symmetrical with the gradation 7f68 as the center. The number is designated by the designation circuit 4.
The output signal p of the memory circuit 2 is input to the second selection circuit 5,
Output signal ゛0 indicating that the signal p is a halftone on the black information side
”, the second selection circuit 5 selects “2” of the two output signals of the designation circuit 4 and outputs it as the signal g, and conversely outputs the signal p indicating that it is the white information side halftone. Signal 8F”
In this case, the selection circuit 5 selects one of the two outputs of the designation circuit 4.
F' is selected and output as the output signal g. In this way, the output signal f of the adder circuit 6 becomes an output as shown in FIG. When there is no reference clock signal a, a pulse signal 1 having a period twice that of the reference clock signal a is output. At the same time, the counting circuit 8 is cleared or preset. Here, pulse signal 1
indicates the eight gray levels on the white side, and the signal indicating the eight gray levels on the black side is the signal m obtained by passing the pulse signal 1 through the inverter circuit 10. signal 1 and signal m
The switching between the two is performed in the switching circuit 11 using the output signal p of the memory circuit 2. When the signal p is 10゛, the signal m is output as the pulse density signal n, and when the signal p is ゛1゛, the signal m is output as the pulse density signal n. Signal 1 is output as pulse density signal n. Next, a case where the input image signal b is a pure black or pure white signal will be described.

In the above-mentioned pulse density conversion force formula, true black or pure white signals are excluded, and all these signals are treated as halftones and processed. Therefore, the corrective force method will be explained below. In the signal C of FIG. 3, if we pay attention to the gradation level 0, which should be a pure black signal, and the gradation level 15, which should be a pure white signal, both are represented by a "1, 1, 1" signal. Therefore, the output signal of the memory circuit 2 is applied to the gate circuit 7 which outputs an output signal "1" only when each bit of the input signal is "1", and the output signal of the gate circuit 7 is applied to the clear terminal of the counting circuit 8. By applying the output signal 1, the counting circuit 8
The output signal Dk becomes 0' when the input image signal is at a pure white or pure black level. Furthermore, since the output signal Df of the adder circuit 6 is always greater than ``1'', the comparator circuit 9 does not output in this case. Since the signal m is always 61° in this case, the pulse signal is sent out continuously.Also, since the switching circuit 11 is switched by the signal p as described above,
A distinction is made between a pure black signal and a pure white signal. In this way, the tone characteristics of the output signal n obtained by pulse density conversion of the input image signal b are as shown in FIG. In addition,
The memory circuit 2, selection circuit 3, designation circuit 4, selection circuit 5, addition circuit 6, and gate circuit 7 can be replaced with one ROM.

Also, the total number of gradations is N, and the number of gradations on the black information side is M (M<N
) and the number of gradations on the white information side is (NM), then the number M can be arbitrarily set by adjusting the addition circuit 6 or the subtraction circuit replaced by the addition circuit 6. As mentioned,
The present invention divides an analog image signal including halftones into N gradations, and further divides these n gradations into M (N>M) gradations on the black information side and (N-M) gradations on the white information side. Divide into two, M on the black information side
The gradation is based on a black signal, and a pulse signal indicating one piece of white information is generated at a different cycle for each gradation, and the (N-M) gradation on the white information side is based on a white signal and generates one piece of black information. A pulse signal indicating
Since a pulse density signal corresponding to the analog image signal is obtained, an apparently natural gray scale difference between intermediate tones can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of a halftone reproduction circuit for realizing the halftone reproduction power formula in facsimile machines, etc. according to the present invention, Fig. 2 is a waveform diagram showing its operation, and Fig. 3 is its outline. FIG. 4 is a waveform diagram of pulse density signals of each tonality obtained by the present invention. 1... A/D conversion circuit, 2... Memory circuit, 3... Selection circuit, 4... Designation circuit, 5...... Selection circuit, 6... Addition circuit, 7... Gate circuit, 8... Counting circuit, 9... Comparison circuit, 10...・Inverter circuit, 11...Switching circuit, 12...
. . . Image signal input terminal, 13 . . . Basic clock signal input terminal, 14 . . . Pulse density conversion signal output terminal.

Claims (1)

[Claims] 1 Divide the analog image signal including halftones into n gradations, and divide these n gradations into m (n>m) gradations on the black information side and (n>m) on the white information side.
The M gradation on the black information side generates a pulse signal indicating one piece of white information at a different period for each gradation based on the black signal, and nm) A halftone reproduction method for facsimiles, etc., characterized in that the gradation is based on a white signal and a pulse signal representing one piece of black information is generated at a different cycle for each gradation.