JPH0152952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image processing device that electrically processes a document image.

A facsimile device that transmits figures, characters, etc. via telephone lines first scans and reads the original, outputs a binary image signal, performs code conversion on the binary image signal, performs compression processing, and then The signal is modulated and transmitted over the telephone line. In order to obtain the binary image signal, the level difference of the analog signal obtained corresponding to the white or black image on the document is compared with a predetermined threshold value and converted into a binary image. Therefore, the setting level of the threshold value has a great influence on the quality of the information to be transmitted. FIGS. 1a to 1c show the process of obtaining a binary image signal from an original as described above. In FIG. 1a, consider the case where a document 2 illuminated by a light source 1 is scanned along a scanning line 3. In FIG. The white or black information on the scanning line 3 is provided by the lens system 5.
The image sensor 6 converts the white or black information into an analog electric signal (hereinafter referred to as an analog signal). FIG. 1b is a graph in which the horizontal axis shows time t and the vertical axis shows the output voltage of an analog signal. In Figure 1b,
The analog signal 7 is represented as a high level in the white part of the original 2 and a low level in the black part. In order to digitize (binarize) the analog signal shown in FIG. 1b, a threshold must be set. In conventional facsimile machines, the average value of analog signals determined by the density of information such as characters recorded on the original 2, the density of the paper itself of the original 2, the brightness of the light source 1, etc. is set as the threshold value. Was. However, in general, the above-mentioned characters, etc. are often not present near both ends of the original document 2, and in most cases, information such as characters is recorded several centimeters inside from both ends 2a, 2b of the original document. be. Furthermore, the density of the information such as the characters may be low. In such a case, if the threshold value is set using the average value of the analog signal for one scanning line, the threshold value 8 will be set at a high level (a portion close to the white level) shown in FIG. 1b. For this reason, the portion 4 where the document 2 is soiled
(often intermediate between the white level and the black level), the dirty portion will be confused with information such as text and will be binarized as a black signal. In other words, the analog signal 7 of the dirty area 4 on the original 2 in FIG. become). Then, the analog signal 7 shown in FIG. 1b is as shown in FIG. 1c.
It becomes a binary image signal 10 (digital signal) like
This results in a deterioration in the quality of the binary image signal to be transmitted.

The present invention has been made in view of the above points, and an object of the present invention is to highly accurately binarize an image signal obtained by scanning an original image and output a binary image signal. In an image processing device that binarizes an image signal output by scanning an original image and compares it with a threshold signal and outputs a binary image signal, a reference member provided in the device to obtain a white reference signal and a , a detection means for detecting an electric signal output from the imaging means as a white reference signal by scanning the reference member; and a control means for generating a control signal defining a predetermined section in a scanning line of the imaging means. , extraction means for extracting an image signal corresponding to a predetermined section in a scanning line of the imaging means from the electrical signal output from the imaging means by scanning a document image according to a control signal from the control means; forming means for forming a threshold signal whose level changes in accordance with a level change of the image signal extracted by the extracting means; and a white reference signal whose level of the threshold signal formed by the forming means is detected by the detecting means. The present invention provides an image processing apparatus having a suppressing means for suppressing a change in the level of a threshold signal when the level of the threshold signal becomes higher than or lower than a specific level determined according to the level of the threshold signal.

The present invention will be explained below with reference to the drawings.

FIGS. 2a to 2d show an embodiment showing the process of obtaining a binary image signal from an original in the information processing apparatus of the present invention. In FIG. 2a, consider the case where an original 12 illuminated by a light source 11 such as a light bulb or a fluorescent lamp is scanned along a scanning line 13. White or black information on the scanning line 13 passes through the lens system 15 to the image sensor 1.
6, the image sensor 16 converts the white or black information into an analog signal. At this time, the reference reflection section 18 provided to form white information is scanned immediately before scanning the original 12 (or immediately after scanning). FIG. 2b shows the time t on the horizontal axis and the output voltage of the analog signal on the vertical axis.

In FIG. 2b, the analog signal 17 is
The white part above 2 is represented as a high level, and the black part is represented as a low level. Therefore, a part of the analog signal 17 can form the reference signal 17a. As mentioned above, since the reference signal 17a is white information, the output voltage actually exhibits the maximum value Vamx. Then, by using Vmax as a reference level and comparing it with other levels in the analog signal 17, the density of the paper itself of the original 12 can be detected. Furthermore, the information processing apparatus of this embodiment extracts the information recorded in the center of the document and calculates the average value of the analog signal. The signal 20 shown _{in FIG} .
This shows that the average value of is output. In this way, the level of the average value becomes low, so that the dirty portion 14 of the original 12 is converted into a binary image signal as a "white" signal, and a high-quality binary image signal as shown in FIG.
A value image signal 21 is obtained. FIG. 3 is a block diagram of an electric circuit for processing information based on the configuration of FIG. 2a and the explanation of FIGS. 2b to 2d.

In FIG. 3, the image sensor 16 reads information from the reference reflection section 18 and original document 12 shown in FIG. The peak value detector 22, analog switch 26 and comparator 2
Send to 9. The detector 22 consists of an operational amplifier 22a, a diode 22b, and a capacitor 22c, and the analog signal 17 input to the (+) side input terminal of the operational amplifier 22a charges the capacitor 22c via the diode 22b and generates the reference signal 17a [second
See Figure b]. This signal is sent to the follower 23
(which can be composed of an operational amplifier, a transistor, etc.) is input to the voltage divider 24. The voltage divider 24 consists of resistors 24a to 24d and diodes 24e and 24f, and the resistors 24a and 24b are connected to the reference signal 17a.
% voltage or 0.7Vmax, resistors 24c and 24
d is a voltage of 30% of the reference signal 17a, that is,
Set to give 0.3Vmax to each.

The connecting portion between the resistors 24a and 24b is connected to a diode 24e, the connecting portion between the resistors 24c and 24d is connected to a diode 24f, and the other ends of the diodes 24e and 24f are connected to a comparator configured with an operational amplifier. Connect to the (+) side input terminal of 29. On the other hand, the analog switch 26 controls the conduction/cutoff of the analog signal 17 based on the control signal input from the control section 25, and connects the resistor 27a and capacitor ₂ only during times _t1 and t2 shown in FIG. 2c.
The analog signal 17 is sent to the average value circuit 27 consisting of 7b.
Enter. The average value circuit 27 receives the analog signal 17
The average value of
is led to the (+) side input terminal of the comparator 29 via the (+) input terminal of the comparator 29.
Comparator 29 receives analog signal 1 at the (-) side input terminal.
7 is input, and the output line 24g of the voltage divider 24 and the resistor 28b are connected to the (+) side input terminal as described above, so the analog signal 17 input from the (-) side input terminal is input from the (+) side input terminal. Input threshold value 19
Binary image signal 2 is obtained by comparing it with [Fig. 2 b].
1 (see FIG. 2d) can be output to the terminal 30. That is, in the above-described configuration, if the density of information such as characters recorded on the document is low, the level of the signal output from the average value circuit 27 will be high. This acts on the diode 24e of the voltage divider 24 via the follower 28 and the resistor 28b.
The conduction state of the diode 24e changes near the aforementioned 0.7Vmax, and when the diode 24e becomes conductive, the (+) side input terminal of the comparator 29 is held near 0.7Vmax to prevent the threshold value from becoming abnormally high. Therefore, the dirty portion 4 shown in FIG. 1a is not binarized as a black signal as shown in FIG. 1c. On the other hand, when the document is dark, the level of the signal output from the average value circuit 27 becomes low, and the low level signal that passes through the follower 28 and the resistor 28b acts on the diode 24f. The conduction state of the diode 24f changes near the aforementioned 0.3Vmax, and when the diode 24f conducts, the comparator 2
The (+) side input terminal of 9 is maintained near 0.3Vmax to prevent the threshold value from becoming abnormally low. Therefore,
If a document with white characters written on black paper has a dirty part, the dirty part is not binarized as a white signal.

FIG. 4 is a graph showing the characteristics of the threshold value setting means (comprised of voltage divider 24 and resistor 28b in FIG. 3a) used in the information processing apparatus of this embodiment. Fourth
The horizontal axis of the figure is the output 2 of the follower 28 shown in Figure 3.
8a, the vertical axis shows the threshold set by the output line 24g, and the line 31 shows the average value (horizontal axis)
When the level of becomes below 0.3Vmax and 0.7Vmax
This indicates that the change in the threshold value (vertical axis) is suppressed when the value exceeds the threshold value. Here, Vmax is the reference reflection section 1
8 (see FIG. 2a), so it is always constant without being affected by the density of the original paper itself.

Therefore, the signal output from the comparator 29 becomes a high-quality binary image signal 21 as shown in FIG. 2d.

In this way, the information processing apparatus of this embodiment sets the threshold level to an optimal value for various originals with different densities such as the density of the original paper itself and the density of characters, etc. It is possible to transmit a high quality signal by returning the signal to the same as the original signal.

As explained above, according to the present invention, in an image processing apparatus that binarizes an image signal outputted by scanning a document image by an imaging means with a threshold signal and outputs a binary image signal,
A threshold value that extracts an image signal corresponding to a predetermined section in the scanning line of the imaging means from the electrical signal output from the imaging means by scanning the original image, and changes the level to follow the level change of the extracted image signal. Since a signal is formed, the image signal is binarized using a threshold value suitable for the original image density, and furthermore,
In order to obtain a white reference signal, the electrical signal output from the imaging means is detected as a white reference signal by scanning a reference member provided in the device, and the level of the formed threshold signal is determined by the level of the detected white reference signal. Since the change in the level of the threshold signal is suppressed when the level exceeds or falls below a specific level determined depending on the level, it is possible to suppress changes in the level of the threshold signal. This makes it possible to satisfactorily binarize image signals even for documents with dark spots.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the waveform of an analog signal and the waveform of a binary image signal output by an image sensor that converts image information into an electrical signal, and Fig. 2a shows the configuration for converting image information into an electrical signal in the present invention. Perspective view, Figure 2b
is a waveform diagram of the analog signal output by the image sensor shown in Figure 2a, Figure 2c is a waveform diagram showing conduction of the analog switch, and Figure 2d is a binary diagram based on the waveform in Figure 2b. FIG. 3 is a waveform diagram of an image signal, FIG. 3 is a configuration diagram of an electric circuit in the information processing apparatus of the present invention, and FIG. 4 is a graph diagram showing characteristics of threshold value setting means. In the figure, 11...light source, 12...document, 15...lens system, 16...imaging device, 18
...Reference reflecting section, 22...Detector, 23, 28...
... Follower, 24 ... Voltage divider, 25 ... Control section,
26... Analog switch, 27... Average value circuit, 29... Comparator.

Claims (1)

[Claims] 1. In an image processing device that binarizes and outputs a binary image signal by comparing an image signal outputted by scanning an original image with an imaging means with a threshold signal, the white reference signal is obtained. a reference member provided in the apparatus for the purpose of the present invention; a detection means for detecting an electric signal outputted from the imaging means as a white reference signal by scanning the reference member; control means for generating a predetermined control signal; and control means for generating an image signal corresponding to a predetermined section in a scanning line of the image pickup means from an electric signal output from the image pickup means by scanning a document image. an extraction means for extracting according to a signal; a forming means for forming a threshold signal whose level changes in accordance with a level change of the image signal extracted by the extraction means; a level of the threshold signal formed by the forming means; Image processing characterized by comprising a suppressing means for suppressing a change in the level of the threshold signal when the level of the white reference signal detected by the detecting means exceeds or falls below a specific level determined according to the level of the white reference signal. Device.