JPS6343945B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a circuit for binarizing image signals in facsimile, and when determining the black color of an image signal after reading an original written on a colored background, The present invention relates to a binarization circuit that can reliably discriminate even a thin black part following a .

[Conventional technology]

In FIG. 1, 1 is the slice level that is the standard for black and white discrimination according to the background color, and the slice level 1
By comparing the image signal 2 with the image signal 2, it is determined that the signal above slice level 1 is white and the signal below slice level 1 is black, and the image signal is transmitted as a binary signal 3 of white and black. There is a circuit.

In other words, if the ground color is dark, unless you lower the slice level, the dark colored ground itself will be judged as black, and even if characters or lines written on the dark colored ground are judged to be black, the received image will be black. The information may become cluttered and unreadable.

Therefore, the applicant previously filed an application for a slice level determination circuit that changes the slice level according to the ground color.

That is, in FIG. 2, a slice level determining circuit 7 is constituted by a clamp circuit 5 consisting of resistors r1 and r2, a capacitor C1, and a set value input diode 4, and an integrator 6. Binarization slice level 1 and image signal 2 determined in such a circuit
is input to the comparator 8 to determine whether it is white or black. That is, a binary signal 3 of the image signal as shown in FIG. 1 is obtained.

[Problem to be solved by the invention]

At this time, the slice level 1 decreases at the point where the image signal 2 changes from white to black, and returns at the point where the image signal 2 changes from black to white. That is, at the change point P1, the level decreases due to the discharge of the capacitor C1,
At the change point P2, recovery is performed by charging the capacitor C1. Now, the time constants due to the resistors r1 and r2 and the capacitor C1 in FIG. 2 are determined to be constant values. That is, when the time constant for charging the capacitor and the time constant for discharging the capacitor are the same, at slice level 1, the inclination angles θ1 and θ2 during discharging P1 and charging P2 are equal, as shown in the first diagram. Therefore,
Pale black parts B, B1, B2 in the middle of image signal 2
Even if there is heat, the slice level is 1 at the B1 position.
(At the B2 position, only a portion is determined as black, and the width of the black signal decreases.)

When such a phenomenon occurs, for example, even if a document 9 as shown in FIG. , there is a risk that not only the aesthetic appearance of the received image 16 will be spoiled, but also that the information will become unclear.

The present invention has been made to solve the above-mentioned drawbacks, and will be described below with reference to the drawings.

〔Example〕

FIG. 4 shows a binarization circuit T1 which is an embodiment of the present invention.
shows.

That is, the first resistor R1, the second resistor R2,
Clamp circuit 1 consisting of a third resistor R3, a fourth resistor R4, a charging diode D1, a discharging diode D2, and a set value input diode D3
7, and an integrating circuit 18 consisting of a capacitor C2 and a fifth resistor R5 constitute a slice level determining circuit 19, and the image signal L1 and slice level signal L2 are input to a comparator 8 to discriminate between white and black. be done.

The relationship of the resistance values between the above resistors R1 to R4 is R2/R1=R4/R3 |R1,R2≫R3,R4
| By making the resistors R3 and R4 smaller than the resistors R1 and R2, the current 11 flowing through the diode D1 becomes larger than the current 12 flowing through the diode D2, and the time constant also becomes larger. That is, capacitor C
The speed of charging to 2 is sufficiently faster than the speed of discharging, and the slice level signal returns quickly, resulting in a slice level characteristic curve L3 shown in FIG.

Therefore, the slice level signal L3 from the slice level determining circuit 19 is as shown in FIG.
At the point where the image signal L1 changes from black to white, the capacitor C2 is discharged via the resistors R1 and R2 and gradually drops, while at the point where the image signal L1 changes from black to white, the capacitor C2 is charged through the resistors R3 and R4. Since the battery is charged quickly, the rising angle θ3 becomes smaller and the return speed becomes faster.

Therefore, at the point of change from black to white, the slice level rises quickly and returns to a sufficiently high level, and the black signal can be extracted even in the next faint black image signals B1 and B2, and the slice level L2 and the image The binary signal L3 based on the signal L1 can reliably output the black portion of the image signal L1 as black.

Therefore, when transmitting a document as shown in FIG. 3, when the main scanning direction is the arrow (X), the short frame line 12 drawn on a white background following the black information 11 is also determined as black information using the above method. It has become possible to convert the thin line 15 or blank frame line 12 into black and transmit the binary signal.

〔Effect of the invention〕

As described above, in the present invention, the slice level, which is a reference for determining whether the image signal is black or white, is changed depending on the level of the image signal, and the recovery speed of the slice level is determined at the point where the image signal changes from black to white. Since the slice level is set to fall faster than the falling speed at the point where the signal changes from white to black, the slice level can be restored immediately in the white part after the black part of the image signal continues, and the thin black part in the white part can be quickly restored. Since the signal level is lower than the slice level, even faint black areas can be reliably converted into a binary signal as black, and a binary signal that is faithful to the original can be transmitted, and the receiving side can also receive the same as the original. images can be obtained and information can be transmitted accurately.

Further, in the present invention, resistors R1, R2, R3, R4
The rise and fall speed of the slice level can be switched by a simple circuit configuration in which the diodes D1 and D2 are set to a predetermined value and the diodes D1 and D2 are connected in opposite directions, and the level is set to a constant value (Vref).
Since the value (Vref) is set to an appropriate potential, the lowest limit of the slice level is always higher than the black solid part of the image signal, and the black solid part is erroneously judged as white. It has become a thing of the past.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a binary signal obtained from an image signal and slice level, Figure 2 is a diagram of a binary circuit that obtains the binary signal in Figure 1, and Figure 3 A is an example of a manuscript. 3B is a diagram showing an example of a received image received by a conventional device, FIG. 4 is a binarization circuit diagram showing an embodiment of the present invention, and FIG. 5 is a slice diagram using the same circuit. FIG. 3 is an explanatory diagram for obtaining a binarized signal from a level and an image signal. L1...Picture signal, L2...Slice level, L
3...Binarization signal, T1...Binarization circuit, 17...
...Clamp circuit, 18...Integrator circuit, 19, 20
...Slice level determination circuit.

Claims (1)

[Claims] 1. In a circuit that binarizes an analog signal obtained by scanning a document, the image signal is passed through a first resistor R1 and a second resistor R1.
2, a third resistor R3 and a fourth resistor R3;
Each voltage is divided by a series resistor consisting of a resistor R4, and the divided signal outputs are connected to a common capacitor via diodes connected in opposite directions, and the discharge output of the capacitor is set at a predetermined potential. Provide a clipping diode, and further set the values of each of the above resistances to R2/R1=R4/R3.
A binarization circuit for a facsimile, characterized in that the relationship is set to R1, R2>>R3, R4.