JPS6019709B2 - Signal binarization device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a facsimile and a copying machine that use a photoelectric conversion element or the like to scan information such as a written image on a document in a line shape, convert it into an analog image signal, and perform signal processing. The present invention relates to a signal binarization device such as the above.

Conventionally, as an example of this type of apparatus, a means as shown in the diagram of FIG. 1 has been used.

In the figure, A optically captures information such as a calligraphy image on the manuscript.
This is an analog image signal obtained by reading and scanning in a line using a photoelectric conversion element, where ``a'' is a fixed DC level threshold, and ``C'' is a binarized output waveform diagram at the edge of the analog image signal A. be. That is, as shown in FIG. 1, it has been common practice to binarize the optically converted analog image signal A at a threshold fixed at a predetermined level.
The originals used in this type of device often have varying background density and contrast within the same original, and high-density information exists within a low-density background.
There were some runner-up results, such as parts A and B in Figure A that could not be distinguished as shown in binarized output C.

This simulation was made to solve the runner-up problem of the conventional ones as described above, and by controlling the threshold by the low frequency component of the analog image signal A, information such as the calligraphy image on the manuscript can be detected. The aim is to reproduce it as faithfully as possible.

Hereinafter, one embodiment of the present invention will be explained with reference to the block diagram of FIG. 2. In the figure, 1 is a low-pass filter, 2 is a current limiting circuit, 8 is a signal delay circuit, and 4 is a binarization circuit. It is a circuit.

FIGS. 3, 4, and 5 are waveform diagrams of signals of each block. Now, when the low frequency component of the analog image signal A obtained by photoelectrically converting information such as a calligraphic image on a manuscript is extracted, the signal waveform becomes as shown by the broken line 2 in FIG. 3.

Therefore, if this signal 2 is taken as the dark value, it will become possible to distinguish between the A and B portions of analog card number A. This binarized output is the tree in Figure 3. However, because the low frequency component of analog image number A was set as a dark value, C, D, E, and F, which should originally be unified as white or black, were
In some parts, the discrimination becomes unstable due to slight differences in density or noise on the original, and even though the parts should originally be unified as white or black, the binary output becomes unstable as shown in (E). There is a manipulation of being judged by someone. Therefore, in the present invention, in order to eliminate the above-mentioned deficiencies, the current limiting circuit 2 limits the amplitude of the low frequency component 2 of the analog image signal A to prevent the dark value from shifting extremely toward the white or black level. FIG. 3 shows the level at which the amplitude is limited. E,
and Eo, and the output whose amplitude is limited by the current limiting circuit 2 becomes the signal waveform shown in FIG. Amplitude limit level E,
Normally, Eo is selected to be 75% of the white peak level, and Eo is selected to be 25% of the white peak level.If the analog signal A is binarized using the amplitude-limited signal as described above as the threshold value, as shown in Figure 4. As shown in Fig. 5, the binarized output has the effect that the A and B portions of the analog image signal A are faithfully determined, and the noise in the C, D, E, and F portions are determined and eliminated.
In order to obtain the above effects, the low-pass filter shown in Figure 2 has a passband gain of "1", a cutoff frequency lower than the highest image frequency of the analog image signal, and one cycle shorter than one scanning period. Usually, the highest image frequency is 1
/2 to 1/5. Furthermore, in reality, the phase of the signal that has passed through this low-pass filter is delayed by time t, so that the analog image signal A is also delayed by the delay time t caused by the low-pass filter by the delay circuit 3 in FIG. By delaying the signal, the signal shown in FIG. 5 is obtained. This signal chi is 2 at the break price
The converted output is obtained as shown in Figure 5. As described above, even if the background density and contrast within the same document, especially within one scan, are uneven, and even if there is high density information within a background of medium density, binarization can be performed faithfully. There are benefits to be gained.

In addition, in the area J where the white level continues for a long time as shown in FIG.
The threshold value shifts toward the black level, which has the effect of making it easier to distinguish white information within a black background. In the above embodiment, a facsimile machine and a copying machine that weave and scan information such as a written image on a document in a line are explained, but the same applies to other information equipment and video equipment that binarizes analog signals. It has the effect of

As described above, according to the present invention, when an analog signal is binarized, by controlling a predetermined frequency component of the analog signal, the background density or contrast within the same document, especially within one scan, is not uniform. In addition, it is possible to distinguish even when high density information exists within a medium density background, and even when the white or black level continues for a long time, black information within a white background or white information within a black background can be distinguished. This makes it easier to distinguish information such as a calligraphy image on a manuscript, thereby achieving the effect of faithfully reproducing information such as a calligraphy image on a manuscript.

[Brief explanation of the drawing]

FIG. 1 is an input/output signal waveform diagram of a conventional signal binarization device, FIG. 2 is a block diagram showing an embodiment of the signal binarization device of the present invention, and FIGS. 3 and 4 are diagrams of the signal binarization device of the present invention. Waveform diagrams for explanation, FIGS. 5 and 6, are waveform diagrams of various signals of the present invention. In the figure, 1: low-pass filter, 2: current limiting circuit, 3: signal delay circuit, 4: binarization circuit. In the drawings, the same reference numerals indicate the same or corresponding parts. Moat 1 map 2 blinds 3 blinds 5 fences 6

Claims (1)

[Claims] 1. A low-pass filter that extracts only low-frequency components below a predetermined frequency from an analog image signal obtained by photoelectrically converting information such as a document image, and limits the amplitude of the output signal of the low-pass filter to a predetermined level. A signal comprising a current limiting circuit, a delay circuit that delays the analog image signal by a predetermined time, and a binarization circuit that binarizes the analog signal output from the delay circuit using the output signal of the current limiting circuit as a threshold. Binarization device.