JPS5948589B2 - Image signal binarization conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that slices an analog image signal at an appropriate slice level in a photoelectric conversion section of a facsimile machine or the like and converts it into a black and white binary signal.

The photoelectric conversion unit of a facsimile machine scans the surface of the document to be read, converts the shading of the document surface into an electrical signal, and either modulates it linearly and transmits it directly, or converts it into binary black and white. One of two methods is used: converting the signal and transmitting it in the form of a binary signal.

The present invention relates to the latter circuit system for converting black and white binary signals. In the case of binarization, the image on the document surface may include shading, and the background may be pure white or may include halftones such as, for example, newspaper.

Therefore, if the image is simply sliced at a fixed slice level, thin characters will be converted to white, and halftones will become black, resulting in a loss of image fidelity. In order to eliminate the above-mentioned drawbacks, the present invention creates and synthesizes a reference voltage by an integrating circuit that operates in response to an image signal and a reference voltage that is proportional to the gray level of the background from the image signal, and slices the image signal to create a good image. It provides a means to obtain images.

FIG. 1 shows a block diagram of an embodiment of the present invention. In the figure, 1 is an analog image signal input terminal, 2 is an analog amplifier for the image signal, 3 is an integration circuit that operates in response to the level of the image signal, and 4 is an integration circuit that operates in response to the background level. diodes 5 and 6 are provided to add the outputs of the integration circuits 3 and 4 with low output impedance; 7 is a comparison circuit for comparing and slicing the image signal output from the analog amplifier 2 and the composite signal; The circuit 8 is a black and white binary output signal terminal. FIG. 2 is an explanatory diagram of the operation of this circuit, in which 10 in A is an image signal, 11
12 shows the output signal waveform of the integrating circuit 3, 12 shows the output signal waveform of the integrating circuit 4, and the numeral 12 shows the binarized output signal waveform of the output terminal 8. To explain in detail below, the image signal applied to the input terminal 1 is input to the analog amplifier 2, the integrating circuits 3 and 4.
added to.

The integration circuit 3 responds to this image signal and charges up as an integration time constant with a fast time constant in response to a change from the black level to the white level, and charges up with a fast time constant when changing from the white level to the black level. It has a characteristic of discharging with an appropriate time constant (approximately the highest image frequency) in response to a change in . As a result, the output of the integrating circuit 3 becomes a waveform 11 shown in FIG. 2A. The integrating circuit 4 responds to the image signal and charges up as an integration time constant with a fast time constant in response to the change from the black level to the white level, and charges up with a fast time constant when changing from the white level to the black level. has a characteristic of discharging with a sufficiently long time constant compared to the lowest frequency of the image signal. As a result, the output of the integrating circuit 4 becomes a waveform 12 in FIG. 2A. That is, the integrating circuit 3 obtains a slice reference voltage for the high frequency portion of the image signal, and the integrating circuit 4 obtains a voltage corresponding to the white level (background) of the image signal.

The output signals of the integrating circuits 3 and 4 explained above are added by the adding diodes 5 and 6, and then added to the comparator circuit 7, where they are combined with the image signal of the output of the analog amplifier 2 (waveform 10 in Figure 2 A). be compared.

As a result, the portion where waveform 10 is lower than waveform 11 or 12 in FIG. 2A is determined to be black, as represented by the binarized signal output waveform at the beginning of FIG. That is, for example, if the image is a thin character, the amplitude of the image signal will be small and its absolute output will be close to the pure white level, but the integration circuit 3
By this function, the slice reference voltage of the waveform 11 automatically moves toward the true white level side, and the determination of white and black is performed.

In addition, when the background is a halftone like a newspaper, the white level of the image signal is lower than the pure black level, but in this case, the function of the integrating circuit 4 automatically moves the 12 slice reference voltages toward the pure black level. White. A black judgment is made. As explained above, according to the present invention, faithful whiteness can be achieved over a wide range of shading of the original image to be read and the shading of the background. Black binary values can be determined.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram according to the present invention, and the second
The figure is an explanatory diagram of the operation of the present invention. 1 is an image signal input terminal, 2 is an amplifier, 3 is an integration circuit, 4
is an integrating circuit, 5 and 6 are synthesis diodes, 7 is a comparator,
8 is an output terminal. 10 is an analog image signal, 11 is an output waveform of the integrating circuit 3, and 12 is an output waveform of the integrating circuit 4.

Claims (1)

[Claims] 1 The analog signal obtained by scanning the grayscale signal of the original image to be read by the photoelectric conversion unit of a facsimile machine, etc. is converted into two black and white signals.
When converting into a value signal, a first integrating circuit responds to the gray level signal of the image, charges with a fast time constant, and has a time constant corresponding to approximately the highest image frequency of the image signal when discharging; It has a second integrating circuit that charges at a constant rate and has a time constant long enough to correspond to the lowest image frequency of the image signal during discharging, and adds the outputs of both integrating circuits and uses this as a slice reference voltage to determine the image density. 1. A binarization conversion circuit for an image signal, characterized in that the circuit is added to a comparison circuit together with the signal and determines whether the image gradation signal has black or white binary values.