JPH0191571A - Picture processor - Google Patents

Abstract

PURPOSE:To attain accurate binarization of a picture signal by using a single threshold voltage even with a delicate picture to be read by applying 2nd-order differentiation to an analog picture signal read by a picture reader by a 2nd order differentiation circuit and comparing the result with a threshold voltage of a prescribed level. CONSTITUTION:A 2nd order differentiation circuit 2 applying 2nd order differentiation to an analog form picture signal VS read by a picture reader 1 and a comparision circuit 3 comparing the signal VIN subjected to 2nd order differentiation by the circuit 2 with a prescribed level of threshold voltage VTH to output a binarized signal VOUT are provided. That is, the circuit 2 makes the upward convex and downward convex parts in the picture signal VS clear and the signal VIN subjected to 2nd order differentiation is compared with a prescribed level of threshold voltage VTH at the comparator circuit 3 and binarized and then a binarized signal VOUT is outputted. Thus, the accurate binarized signal VOUT is obtained with the picture signal VS of the delicate read picture is obtained by using a single threshold voltage VTH.

Description

[Detailed Description of the Invention] [Summary] Regarding an image processing device that binarizes and outputs an analog image signal read by an image reader, a single threshold voltage is used to process a delicate image to be read. The purpose is to accurately binarize the image signal even when the image is read by an image reader. and a comparison circuit that compares the voltage with a threshold voltage of a predetermined level and outputs a binary signal.

[Industrial application field]

The present invention relates to an image processing device, and particularly to an image processing device that binarizes and outputs an analog image signal read by an image reader.

[Conventional technology]

2. Description of the Related Art Conventionally, images in facsimile machines, image scanners, and the like are usually read using image sensors. The image signal read by this image sensor is an analog format signal, and an image processing device is used to binarize (digitize) the image signal.

FIG. 5 is a diagram for explaining a conventional general image processing device. As shown in FIG. 2A, a conventional general image processing apparatus for binarizing an image signal includes a comparison circuit 103. An image signal vi, which is the output of an image sensor or the like, is applied to one input terminal 131 of the comparison circuit 103, and a threshold voltage V of a predetermined level is applied to the other input terminal 132 of the comparison circuit 103. has been done. Then, the comparison circuit 103 converts the image signal V'
In and threshold voltage Vth are compared, and a binarized signal v out is output.

That is, as shown in the figure (b), the image signal Vin, which is an analog signal, is compared with the threshold voltage ■ by the comparison circuit 103, and as shown in the figure (c), the image signal Vin corresponding to white is And the emotion equivalent to black! A binary signal (digital signal) V out of 1' OJ is output.

[Problem that the invention seeks to solve]

As mentioned above, the conventional image processing device uses the comparator circuit 10
3, the image signal Vin and the threshold voltage ■tk are compared to generate a binarized signal ■. It is designed to output □.

By the way, as shown in FIG. 6, when an image sensor reads a document (image to be read) in which a thin black line B exists on a white background or a thin white line W exists on a black background, In the read image signal V in , a thin black line B in a white background or a thin white line W in a black background is detected as a signal at a level different from the normal black level B or white level W. In other words, due to the resolution of the reading lens used to form an image on the image sensor and the leakage current between the elements constituting the image sensor,
As shown in a), the thin black line B4 on the white background is detected as a value larger than the normal black level B, and the thin white line W on the black background is detected as a value smaller than the normal white level W. will be detected as.

In this way, the image signal V i+q is set to a single threshold voltage v
th+ or Vt&! When compared and binarized, the result is a thin black line L% Bt on a white background and a thin white line W on a black background.

It is difficult to detect both accurately. That is, when the image signal V i R is compared using a threshold voltage Vtk that allows a thin black line BL on a white background to be distinguished from the black level B, as shown in FIG. 6(b), a thin white line W on a black background is compared. , cannot be detected as the white level W. On the other hand, a thin white line W on a black background.

If the image signal Via is compared using a threshold voltage v thz that can be determined to be the white level W, the thin black line Bt in the white background cannot be detected as the black level W, as shown in FIG. 6(c). .

In view of the problems of the conventional image processing apparatus described above, the present invention aims to accurately binarize image signals even for delicate images to be read using a single threshold voltage. do.

[Means for solving problems]

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to the present invention.

According to the present invention, there is provided a second-order differentiating circuit 2 for second-order differentiating the analog-format image signal V3 read by the image reader 1, and a second-order differentiating circuit 2 that sets the second-order differentiated signal VIN to a predetermined level threshold. Binarized signal ■ compared with voltage VtH. An image processing device is provided that includes a comparison circuit 3 that outputs u7.

[For production]

According to the image processing device of the present invention having the above-described configuration,
An analog format image signal V read by an image reader l,
is second-order differentiated by the second-order differentiation circuit 2. This second-order differentiating circuit 2 clarifies the upwardly convex portion and the downwardly convex portion in the image signal (3). Then, the second-order differentiated signal VIN is compared with a threshold voltage VTM of a predetermined level in a comparator circuit 3, and is binarized to obtain a binarized signal V. ut will be output.

As a result, an accurate binarized signal (2) can be obtained even for the image signal V of a delicate image to be read using a single threshold voltage VTH. t+'r can be obtained.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image processing apparatus according to the present invention will be described below with reference to the drawings.

FIG. 2 is a block circuit diagram showing an embodiment of the image processing apparatus of the present invention, and FIG. 3 is a diagram showing waveforms of various parts in the image processing apparatus of FIG.

As shown in FIG. 2, the image processing device of this embodiment is
A document (an image to be read) 7 is irradiated with light from a light source 5, and an image of the document 7 is formed on the image sensor 1 by a reading lens 6. The image sensor 1 photoelectrically converts the reflected light from the original 7 and generates an image signal 3 corresponding to the original 7.
Output.

The image signal V is then supplied to the second-order differentiator circuit 2 as an input signal. Figure 3(a) shows the image signal ■
3, and corresponds to FIG. 6(a) described above.

As shown in FIG. 3(b), in the second-order differential circuit 2,
The image signal V is second-order differentiated and compared with the threshold voltage TH. In other words, the normal black part bone B in the image signal V3
and the white portion W are converted into positive and negative values, respectively, by second-order differentiation.

Furthermore, since the thin black line Bt in the white background in the image signal V is convex downward, it is converted into a positive value, whereas the thin white line WL in the black background is convex upward, so it is converted into a negative value.

The signal VIN second-order differentiated by the second-order differentiator 2 is applied to one input terminal 31 of the hysteresis comparison circuit 3.

A threshold voltage vtn of a predetermined level (for example, OV) is applied to the other input terminal 32 of the hysteresis comparison circuit 3, and as shown in FIG. It is designed to be compared with the voltage Va. That is, as shown in FIG. 3(c), the part where the level of the input signal VIN of the hysteresis comparator circuit 3 is higher than the threshold voltage VTQ becomes the information "1", and the part where the level is lower than the threshold voltage A9. is binarized so that it becomes information "0". Here, the potential of the threshold voltage VT□ may be configured to be variable near Ov.

A signal V output from the output terminal 33 of the hysteresis comparison circuit 3. LIT is supplied to the inverter circuit 4 and inverted. That is, the output signal ■ of the hysteresis comparator circuit 3. U? is the inverted version of the image signal ■, so it is restored by inverting it with the inverter circuit 4,
A signal ■ as shown in FIG. 3(d). (Black is information 'OJ'
, a binary signal in which white corresponds to information "1" is output.

FIG. 4 is a diagram for explaining the comparison circuit in the image processing apparatus of FIG. 2, and is for explaining the hysteresis comparison circuit (comparison circuit having hysteresis characteristics) 3. In FIG. As shown in FIG. 3(a), one input terminal 31 of the hysteresis comparison circuit 3 is supplied with a second-order differentiated signal V.
IN is applied, and a threshold voltage ■I is applied to the other input terminal 32, whereby the input signal VIN is compared with the threshold voltage VT)l and binarized, and the binarized output signal is output from the output 33. y. It is designed to output IIT.

This hysteresis comparator circuit 3 has a hysteresis characteristic as shown in FIG. 4(b), and the input signal V0
It is designed to remove noise, etc. included in the image. That is, noise components and minute irregularities of the input signal VtN existing between the low threshold voltage VIL and the high threshold voltage VIN are removed, and the signal is compared with the threshold voltage vTN and binarized. Due to the hysteresis characteristic of the hysteresis comparison circuit 3, as shown in FIG. 4(d), noise contained in the input signal VIN and unnecessary minute irregularities in the image signal V are removed.

With the apparatus of the embodiment described above, it is possible to accurately binarize the image signal V and obtain a faithfully reproduced image of the original. Furthermore, it is possible to accurately detect both the thin black line Bt in a white background and the thin white line W in a black background, and it is also possible to accurately detect the image to be read even in an alternating black and white pattern with a pitch close to the pixel density of the sensor. Can be read accurately.

〔Effect of the invention〕

As detailed above, the image processing device according to the present invention includes:
The analog format image signal read by the image reader is
By performing second-order differentiation in a step-differentiation circuit and comparing it with a threshold voltage of a predetermined level, it is possible to perform accurate binarization of image signals even for delicate read images using a single threshold voltage. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an image processing device according to the present invention, FIG. 2 is a block circuit diagram showing an embodiment of the image processing device of the present invention, and FIG. 3 is a block diagram showing the configuration of an image processing device according to the present invention. A diagram showing the waveforms of each part; FIG. 4 is a diagram for explaining the comparison circuit in the image processing device of FIG. 2; FIG. 5 is a diagram for explaining a conventional general image processing device; 5 is a diagram for explaining the problem of the image processing apparatus shown in FIG. 5. FIG. (Explanation of symbols) 1... Image reader (image sensor), 2... Second order differential circuit, 3... Comparison circuit (hysteresis comparison circuit), 4...
Inverter circuit, 5... Light source, 6... Reading lens, 7... Original (image to be read), ■,... Image signal (image sensor output signal), V
IN...Second differentiated signal (input signal of hysteresis comparison circuit), VtM...Threshold voltage, (2). 8. ...Binarized signal (output signal of the hysteresis comparison circuit), Vo...output signal of the image processing device.

Claims (1)

[Claims] 1. A second-order differentiating circuit (2) for second-order differentiating an analog format image signal (V_3) read by an image reader (1); Differentiated signal (V_I_
A comparison circuit (3
). 2. The device according to claim 1, wherein the image reader (1) includes an image sensor. 3. The device according to claim 1, wherein the comparison circuit (3) has a hysteresis characteristic.