JPS627266A - Picture processor - Google Patents

Abstract

PURPOSE:To accomplish accurate binarization of a picture signal in accoreance with the existence/absence of noise and the characteristic of the picture signal by providing a means to decide a threshold for the binarization and altering the pursuit of the means in accordance with characteristic of the picture signal. CONSTITUTION:The threshold to convert the inputted picture signal into white- and-black binary information is determined by a half-wave rectification circuit and a peak holding circuit. An amplifier 15, together with diodes D1 and D2 and a resistor R4, constitutes the said rectification circuit, and the circuit's output is inputted to the peak holding circuit consisting of diodes D3-D5, resistors R5 and R6, and a capacitor C1. This circuit reserves a peak value as the accumulation potential of the capacitor C1. The C1 is charged in negative potential by the output from the amplifier 15, but is charged through the diode D5 at falling of a signal, but is discharged when the signal rises. By thus altering the pursuit of the threshold at the raising and the falling of the signal and setting it, the accurate binarization of the picture signal is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing device, and particularly to an image processing device that converts a given image signal into black and white binary information and outputs the converted information.

[Prior Art] Image processing as described above has conventionally been widely performed for computer processing (various types of processing such as magnetic recording, transmission, hard copying, etc.) on image information. Furthermore, this type of binarization processing is also performed in the field of automation of precision measurements such as gap measurement of magnetic heads.

[Problems to be Solved by the Invention] The z-value processing is performed by comparing the luminance level of the input image signal with a threshold value as a reference. A fixed value may be used as the threshold value, but Background brightness, presence of noise,
Alternatively, it is desirable to have a configuration in which the threshold value can be controlled depending on the shading of the image reading system.

Conventionally, the variable threshold control method is to integrate the input image signal to find the average level and determine the threshold based on this average value, or to find the peak value of the input image signal and set the threshold value to this peak value. Various methods are used, such as determining a threshold value based on the threshold value. These methods are effective when the level of the input signal changes relatively slowly, but cannot provide satisfactory results when the level changes rapidly.

FIG. 3 shows the configuration of a conventional image reading and binarizing circuit. Image information of originals and other objects to be scanned is provided by CCD.
It is read by the imaging device 10 using a sensor or the like.

The output of the imaging device 10 is amplified with a predetermined gain by the amplifier circuit 12, and then compared with a threshold value by the comparison circuit 14, and the comparison result is output as a binary signal.

The threshold value is determined by the dynamic slice level circuit 13 based on the input image signal by the above-mentioned average value method or peak value method. Figure 4 shows an example of a dynamic slice level circuit, with resistor R1
, and an integrating circuit including a capacitor C1. The integral value of the image signal stored in the capacitor C1 is connected to the resistor R2,
The signal is input as a threshold value to the comparator circuit 14 via the 7-tensioner R3.

For example, with the circuit as described above, FIG. 5(A), .
When reading a box 40 as shown in (B), (C) and (D), a card 41, a handwritten, printed or otherwise written manuscript 42, or a character, symbol 44 or gap length t of a magnetic core 43, , the image signal level output by the imaging device at the end of the card magnetic head, etc. may be affected by unevenness in the illumination system,
The output signal level may vary due to non-uniformity due to ground level dirt, etc.
Since it is not constant with respect to the time axis, the threshold value does not follow well, making accurate reading and binarization impossible. Furthermore, accurate reading and binarization become difficult even when the characters to be read, the symbol 0, have different thicknesses and shadings, or when there is a lot of background noise.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a configuration in which the followability of the means for determining the binarization threshold is changed according to the characteristics of the image signal. Adopted.

[Function] As shown in Fig. 1, the threshold value is determined by a half-wave rectifier circuit consisting of diodes Di and D2 connected to the amplifier 15, and a peak hold circuit consisting of diodes D3 to D5, resistors R5 and R6, and capacitor CI. Determined by. The time constant of the peak hold circuit is determined by diode D3. Due to the difference in direction of D4 and D5, the signal changes at the rise and fall of the signal. Thereby, the followability of the threshold value can be set to a desired characteristic according to the rising and falling characteristics of the image signal, and accurate binarization of the image signal can be performed.

[Example] The present invention will be described in detail below based on an example shown in one drawing.

FIG. 1 shows the configuration of an image processing device according to the present invention, in which image signals output from a CCD sensor or other imaging device are input to amplifiers 12 and 15 via resistors R1 and R2, respectively. The output of the amplifier 12 is led to a comparator circuit 14 composed of an operational amplifier and the like. On the other hand, at the input terminal of the amplifier 15, along with a resistor R2, a variable resistor R3 is used to adjust the input DC level, that is, to set an offset.
is connected. Amplifier 15 constitutes a half-wave rectifier circuit together with diodes D1-D2 and resistor R4, and its output is connected to diodes D3-D5 . It is input to a peak hold circuit consisting of resistors R5, R6 and capacitor C1.

This peak hold circuit stores the peak value as a band potential of the capacitor C1 like the known circuit, but its time constant is set to be different at the rise and fall of the signal. That is, the capacitor C1 is charged to the negative side by the output of the amplifier 15, but when the signal falls, it is charged via the diode D5, and when the signal rises, it is charged via the diode D3. D4. Capacitor CI by resistor R5
is discharged.

The solid line waveforms in the upper rows of FIGS. 2(A) to 2(C) are the outputs of the imaging device when scanning a certain image, respectively. The level of this signal fluctuates rapidly at both ends of the scanning area. Also,
The broken lines at the top of FIGS. 2(A) and 2(B) indicate the binarization threshold determined by conventional peak holding using a fixed time constant. In Figure 2 (A), the time constant is too large for changes in the image signal, so the threshold value does not follow the rapid level fluctuations at the edges of the image, and as a result, the binarized output is as shown in the lower part of the figure. Information at the edges of the image is lost. On the other hand, if the time constant is too small for the signal change as shown in Figure 2 (B), the letters,
When scanning symbols, etc., a phenomenon occurs where characters, signals, etc. become blurred.

On the other hand, if the time constant is set to be small at the falling edge and large at the rising edge as described above, it is possible to sufficiently follow the sudden falling edge at the start of image scanning as shown in FIG. 2 (C).
Also, information is no longer lost or blurred in text or other images.

In this way, by changing and setting the followability of the threshold according to the rising and falling edges of the signal, accurate images can be obtained.
Value conversion processing can be performed.

In the above example, the threshold is set to respond quickly at the falling edge and slow at the rising edge, but it is also possible to set the response to be the opposite of the above depending on the nature of the signal (for example, positive/negative direction, difference in rate of change), etc. However, it is also possible to change the followability as appropriate.

By the way, for the above peak hold circuit, amplifier 1
Inputting a signal through a half-wave rectifier circuit according to No. 5 has the following effects.

When reading a magnetic field gap as shown in Figure 5 (D), if the area near the gap to be read is black and there is noise, the reading output of the imaging device will be as shown in Figure 2 (D).
It will look like the solid line at the top.

If the threshold value is determined without rectification, the threshold value will also react to the noise portion at the front end of scanning, and noise will also appear in the binarized output.

Therefore, if the threshold value is generated from a signal whose noise has been eliminated by half-wave rectification as described above, it is possible to
), noise is not output in the binarized output, that is, when the level of the image signal is low, the threshold value is fixed at a constant level by adjusting the offset of the half-wave rectifier circuit. Noise cutting becomes possible.

The numbers and constants of the resistors, capacitors, and other elements shown above can be changed depending on the required circuit characteristics.

[Effects of the Invention] As is clear from the above description, according to the present invention, the followability of the binarization threshold is changed and set according to the image signal characteristics, so that the image signal characteristics, It is possible to provide an excellent image processing device that can accurately binarize an image signal depending on the presence or absence of noise.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an image processing device of the present invention;
2(A) to 2(E) are waveform diagrams for explaining the operation of the circuit in FIG. 1, FIG. 3 is a block diagram of a conventional image processing device, and FIG. 4 is a conventional threshold value determining circuit. The circuit diagram and FIGS. 5(A) to 5(D) are explanatory diagrams showing the state of the scanned image. 12.15...Amplifier 14...Comparison circuit R1-R6...Resistor C1.
・Capacitor D1 to D5 ・Diode

Claims (1)

[Claims] An image processing device that outputs an image signal as black and white binarized information, comprising means for determining a binarization threshold,
An image processing device characterized in that the followability of the threshold value determining means is set by changing it according to the characteristics of the image signal.