JPH0778830B2 - Image signal processor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing device, and more particularly to an image signal processing device including means for converting an image signal into a digital signal.

For example, a copying machine or a facsimile device can read an original document and reproduce or transmit the image in a desired state. As a device therefor, an image signal processing device for processing the read image signal is provided. There is. The present invention is directed to improvement of such an image signal processing device.

<Prior Art> By the way, one of the signal processes performed by the image signal processing device is a contour extraction process. Japanese Unexamined Patent Publication No. 60-59484 discloses a prior art image information contour extraction method which is of interest to the present invention. The method described in the patent publication, as shown in FIG. 9, binarizes the image information. At that time, two binary values based on two threshold values L1 and L2 are used.
Quantize and take out only the signal component L in the intermediate region,
The contour line is extracted.

<Problems to be Solved by the Invention> In the above-mentioned image information contour extraction method, when binarizing,
Since it was necessary to set two low threshold values L1 and L2, it was difficult to set the threshold values. For example, when the image signal to be binarized is a signal of a character having a very low density described on a white background or a signal of a character having a high density described on a black background, the background and the character are The signal level difference of is small. Therefore, if the level difference between the high and low threshold values L1 and L2 is too large, the image signal cannot be binarized at two levels as shown in FIG. 10, and the contour line cannot be extracted. In such a case, the level difference between the two threshold values may be reduced,
If this level difference is made too small, the image signal may fluctuate somewhat due to noise or the like, so that it becomes difficult to accurately extract the component in the intermediate region between the two threshold values.

Further, for an image including a halftone such as a photograph, the binarization causes the halftone image itself to collapse or malfunction as shown in FIG.

The present invention has been made against the background of such prior art. From a certain aspect, an image signal capable of digitally processing an image signal and extracting the contour of image information in the signal easily and at high speed. An object is to provide a processing device.

Further, according to another aspect of the present invention, when the input image signal includes a halftone signal having a very white or extremely black background component, the background can be arbitrarily inverted to either white or black. An object is to provide an image signal processing device.

<Means for Solving the Problems> From a certain aspect of the present invention, the density level greatly changes from the white level side or the black level side to the opposite black level side or the white level side through the intermediate level. Conversion means for converting an analog image signal containing a halftone component in which the change in the character component and the density level is relatively small, into a digital image signal in which the density level is relatively expressed in multiple gradations, and the conversion means. A cyclic shift means for shifting a relatively multi-tone digital image signal so that its signal components cyclically move between respective density levels of a white level, an intermediate level and a black level. The amount is set so that the signal component on the black level side or the white level side in the character component can be transferred to the white level side or the black level side on the opposite side. The cyclic shift means can shift the white level component and the black level component to the white level side or the black level side, and the intermediate level component to the opposite black level side or the white level side by cyclic shift. An output for converting the relatively multi-tone digital image signal shifted by the cyclic shift means into a multi-value signal of an arbitrary tone number having a tone number smaller than the tone number. An image signal processing device, comprising: multi-value processing means.

According to another aspect of the present invention, an analog image signal including a background component whose density level is close to a white level or a black level is made to correspond to the density level of the analog image signal,
A converting means for converting into a digital image signal having a relatively multi-tone density level and the digital image signal having a relatively multi-tone density level converted by the converting means are cyclically set to a set amount. In the cyclic shift means for shifting, the set amount of cyclic shift is set based on the level amount from the white level or black level to the background component, and the background component can be set to either the white level side or the black level side. A cyclic shift means having a set amount that can be moved, and a digital image signal cyclically shifted by the cyclic shift means,
An image signal processing device, comprising: an output processing unit that performs an output process of a component that is moved to the black level side as a black background and an output process of the component that is moved to the white level side as a white background.

In the image signal processing apparatus according to any one of the above, in order to determine the shift amount by the cyclic shift means, means for prescanning the content of the document, detecting the density distribution thereof, and calculating the shift amount based on it It is preferable to include.

<Operation> The digital image signal converted by the conversion means and having a relatively multi-gradation level is cyclically shifted by a predetermined amount by the cyclic shift means. Here, the cyclic shift means cyclically shifting the density level in the order of white level → intermediate level → black level → white level. Then, by adjusting the cyclic shift amount, it is possible to bring a certain signal component to the white level side and another signal component different from the signal component to the opposite black level side. Therefore, when the signal component is a character component that greatly changes from the white level side to the black level side through the intermediate level, the signal forming the character is shifted to the white level side, and the outline part of the character is shifted to the black level side. By doing so, it becomes possible to extract the outline of the character. Also, the white level side background component and the black level side background component can be inverted to black or white.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a digital copying machine to which an embodiment of the present invention is adopted.

The digital copying machine is provided with a scanner unit 12 for reading the original image 11. The scanner unit 12 has a CCD
An image sensor such as
The 11th image is output as a digital image signal of 8 bits = 256 steps, for example. The output of the scanner section 12 is given to a cyclic shift device 13, in which the digital image signal is cyclically shifted by a predetermined level amount. Cyclic shift is 256 steps from 0 (white level) to 255 (black level).
By shifting the signal divided into stages by a certain amount (for example, 20 stages) from the white level side to the black level side, returning the data overflowing from 255 stages from the 0 stage side, and cyclically shifting the data. is there.

The 8-bit digital data cyclically shifted by a predetermined level by the cyclic shift device 13 is multivalued, for example, five-valued, in the multivalue processing device 14.

The output of the multi-value quantization processing device 14 is given to the printer unit 17.
The printer unit 17 includes a known image forming mechanism such as a semiconductor laser, a polygon mirror for scanning light, a photoconductor, and a developing device. The printer unit 17 is a multi-value processing device.
Image formation is performed based on the output of 14 and the result is a copy.
18 is obtained.

FIG. 2 is a block diagram showing a detailed configuration of the scanner unit 12. The scanner unit 12 is provided with an objective lens 121,
The data of the original image 11 is given to the CCD 122 through the objective lens 121. The CCD 122 converts the optical signal into an electric signal and supplies the even signal and the odd signal to the amplifiers 123 and 124, respectively. The signals amplified by the amplifiers 123 and 124 are respectively A
The signals are converted into digital signals by the / D converters 125 and 126, and both signals are combined by the combiner 127. Then, the output of the synthesizer 127 is given to the correction circuit 128, where shading correction, density correction, and the like are performed, and then output as an 8-bit digital signal.

The detailed configuration of the scanner unit 12 is not limited to the configuration shown in FIG. 2, and another configuration may be adopted.

FIG. 3 is a circuit block diagram showing an example of the cyclic shift device 13. The cyclic shift device 13 includes, for example, eight full adders 21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h.
The 8-bit digital image signal supplied from the scanner unit 12 has the most significant digit applied to one input terminal A of the full adder 21a, and the corresponding digits are sequentially applied from the next digit onward. Input to the input terminal A of 21b to 21g, and the input terminal A of the full adder 21h is supplied with the least significant digit of 8-bit data.

On the other hand, the corresponding input digit of the subtraction data is given to the other input terminal B of each full adder 21a to 21h via the inverter 22.
Therefore, the 8-bit data is shifted by a predetermined level based on the subtraction data and output by the eight full adders 21a to 21h.

FIG. 4A is a block diagram showing a configuration example of the multi-value processing circuit 14. FIG. 4 (A) shows an example of a five-valued circuit as the multi-value processing circuit 14. The five-valued circuit 14 includes four comparators 141, 142, 143 and 1 connected in parallel.
44, and threshold setting circuits 145, 146, 147, and 148 connected to the comparators 141 to 144, respectively. Each threshold value setting circuit 145 connected to the four comparators 141 to 144
Different thresholds are set in each of ~ 148.
Therefore, one pixel component input to this circuit is compared with a predetermined threshold value by each of the four comparators 141 to 144,
The comparators 141 to 144 output "1" or "0" depending on the density of the pixel component.

A pulse generator is provided on the output side of each comparator 141-144.
151-154 are connected and four pulse generators 141-1
The output of 54 is ORed with an OR gate 149. Of the pulse generators 151 to 154, the 1/4 pulse generator 151 generates 1/4 pulse according to the “1” input from the comparator 141. The 2/4 pulse generator 152 also generates 2/4 pulses in response to the “1” input from the comparator 142. Similarly, the 3/4 pulse generator 153 outputs 3/4 pulses in response to the “1” input from the comparator 143, and the 4/4 pulse generator 154 outputs 4 pulses in response to the “1” input from the comparator 144. / 4 pulse is generated. Any of the comparators 141
If the output of ~ 144 is also "0", any pulse generator 151
No output pulse is derived for both ~ 154.

Therefore, based on the input of one pixel component, the aogate 149
Output of 0.1 / 4, 2/4, 3/4, as shown in FIG. 4 (B).
It will be one of the 5 stages of output of 4/4.

The multi-value processing circuit 14 may be a processing circuit using a dither matrix instead of the circuit shown in FIG.

FIG. 5 is a signal waveform diagram for explaining one of the features of the apparatus of FIG.

The scanner unit will be described with reference to FIGS. 1 to 5.
It is assumed that the 8-bit digital image signal output from 12 includes character and photo signal components as shown in FIG. 5 (A1). In this waveform diagram, the bottom is 0
The white level of the columns and the black level of the uppermost 255 stages are shown. This signal component is cyclically shifted by the cyclic shift device 13 and is shown in FIG. 5 (A2). That is, the signal component is cyclically shifted to the black level by a predetermined amount. As a result, only the blackest component among the character components has moved to the white level side.

Therefore, if this is multivalued by the multivalued processing device 14,
The signal of FIG. 5 (A3) is obtained. As shown in FIG. 5 (A3), the character component is white in the middle and the contour is extracted, and the photographic component is multi-valued with almost the original image.

FIG. 6 is a signal waveform diagram for explaining another feature of the apparatus of FIG. 1, and shows a case where the signal component output from the scanner unit 12 is a photograph with a very white background.

When the signal component of FIG. 6 (A1) is cyclically shifted to the white level side, the background component is shifted to the black level side (FIG. 6 (A1)).
2)). That is, the amount shifted by the cyclic shift device 13 is selected to be a little larger than the level difference from the white level to the background component, and the signal component is shifted to the white level side.

As a result, the white background is inverted to black (Fig. 6 (A3)). When the background of the original image 11 is extremely black, the background can be inverted to white by shifting the signal component in the opposite direction.

FIG. 7 shows a sample actually processed by the digital copying machine according to this embodiment. FIG. 7 (A) is the original picture 11, and FIG. 7 (B) is the copy 18 with the background inverted to black. By comparing the original image 11 and the copy 18 in FIG. 7, the outline of the dark character in the original image 11 is extracted in the copy 18, and even the thin character of the original image 11 is clearly reflected in the copy 18. I know that It can also be seen that the picture of the original picture 11 is copied almost as it is in black and white.

FIG. 8 is a block diagram showing an example of a shift direction and shift amount determination circuit for cyclic shift. The original image 11 is pre-scanned by the scanner unit 12, and the 8-bit signal output from the scanner unit 12 is given to the pre-scan RAM 31 shown in FIG.
Once stored in AM31. The density distribution measuring circuit 32 connected to the pre-scan RAM 31 measures the density distribution of the 8-bit signal of the RAM 31 and gives its output to the arithmetic circuit 33 and the comparator 34. A threshold value setting circuit 35 is connected to the comparator 34, and a predetermined threshold value is given from the threshold value setting circuit. The comparator 34 compares this threshold value with the output given from the concentration distribution measuring circuit 32, and outputs the result to the arithmetic circuit 33. In the arithmetic circuit 33, the concentration distribution measuring circuit
The calculation is performed based on the signal given from 32 and the signal given from the comparator 34 to calculate the direction and the shift amount of cyclic shift. The output of the arithmetic circuit 33 is given to the cyclic shift device 13.

In the above embodiments, the input signal is first converted into the digital image signal and then the cyclic shift is performed. The reason is that the cyclic shift can be easily performed in the digital signal, and the cyclic shift device to be realized has a simple structure. Because it is good. However, the analog signal may be cyclically shifted as it is, and the cyclically shifted analog signal may be multi-valued based on one predetermined threshold value.

<Effects of the Invention> The present invention is configured as described above, and after the input signal is converted into a digital image signal, the digital image signal is cyclically shifted to obtain a white level side or a black level side. Since it is possible to transfer the signal component of, the contour line of the image signal can be extracted and the background can be inverted in black and white.

[Brief description of drawings]

FIG. 1 is a block diagram of a digital copying machine to which an embodiment of the present invention is applied. FIG. 2 is a block diagram showing a detailed configuration of the scanner unit 12. FIG. 3 is a diagram showing a specific circuit example of the cyclic shift device. FIG. 4 is a block diagram and an output waveform diagram showing an example of a multilevel processing circuit. 5 and 6 are waveform charts for explaining the operation of the apparatus shown in FIG. The seventh is a sample showing an example of an original image and a copy actually performed by the digital copying machine according to this embodiment. FIG. 8 is a block diagram showing an example of the configuration of a circuit that determines the direction and amount of cyclic shift by prescan. FIG. 9 is a waveform diagram for explaining a conventional image information contour extraction method. FIG. 10 and FIG. 11 are diagrams for explaining problems in the conventional image information contour extraction method. In the figure, 11 ... Original image, 12 ... Scanner section, 13 ... Cyclic shift device, 14 ... Multi-valued processing device, 15 ... Threshold setting circuit, 16 ... Comparator, 21 ... Full adder, 122 ... CCD, 125,12
6 ... Indicates an A / D converter.

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Claims (3)

[Claims] 1. A character component whose density level largely changes from a white level side or a black level side to a black level side or a white level side on the opposite side through an intermediate level, and a change in the density level is relatively small. Conversion means for converting an analog image signal containing a tonal component into a digital image signal whose density level is represented by relatively multiple gradations; and a relatively multi-tone digital image signal converted by the conversion means, Cyclic shift means for shifting the signal component so as to cyclically move between the density levels of the white level, the intermediate level and the black level, the shift amount being the black level side or the white level in the character component. It is set to the amount that can shift the signal component on the side to the white level side or the black level side on the opposite side. And a black level component can be shifted to the white level side or the black level side, and an intermediate level component can be shifted to the opposite black level side or the white level side, and the shift can be performed by the cyclic shift means. And a multi-value output processing unit for converting the digital image signal of the relatively multi-gradation that has been converted into a multi-value signal of an arbitrary gradation number having a smaller number of gradations than the relevant gradation number. An image signal processing device characterized by: 2. A digital image signal having relatively multi-gradation density levels corresponding to an analog image signal including a background component whose density level is close to a white level or a black level, corresponding to the density level of the analog image signal. Conversion means for converting into a cyclic shift means for cyclically shifting a digital image signal of a relatively multi-tone density level converted by the conversion means by a set amount, wherein the cyclic shift is set. The amount is set based on the level amount from the white level or the black level to the background component, and the cyclic shift means having a set amount that can bring the background component to either the white level side or the black level side, The digital image signal cyclically shifted by the cyclic shift means is converted into a black background with the component shifted to the black level side. And output processing, the image signal processing apparatus which comprises a component that is closer to the white level side and the output processing means for outputting processed as white background, the. 3. The image signal processing apparatus according to claim 1, wherein in order to determine the shift amount by the cyclic shift means, the contents of the document are pre-scanned and the density distribution thereof is detected, An image signal processing device comprising means for calculating a shift amount.