JPS6342904B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention performs appropriate binarization processing on an analog image signal obtained by photoelectrically converting an original image to produce a binarized signal as close to the original image as possible. The present invention relates to an image signal binarization device for obtaining an image signal.

(Prior art and problems to be solved by the invention) Photoelectric conversion of original images (hereinafter referred to as original binary images, although not strictly binary) printed in black and white, such as documents, charts, etc. When converted into an electrical signal, it should ideally be a binary signal, but it becomes an analog signal that has been distorted by a photoelectric conversion system that generally has low-pass characteristics. We would like to binarize this analog signal and obtain a binarized signal that faithfully represents the original binary image.

For this reason, various binarization devices have been devised in the past.In these devices, a threshold value is set in the middle of the highest and lowest values of the analog signal, and when the analog signal is larger than the threshold value, white is displayed, and when it is smaller than the threshold value, it is black (electrical signal The high level corresponds to the white of the original image, and the low level corresponds to the black.) For example, when the analog signal is a in FIG. 1, this device compares its magnitude with the threshold value indicated by the dotted line, and binarizes it into b in the same figure. According to this method, P, Q of signal a
Although depressions and protrusions in the parts are ignored, in fact, as will be seen later, it is more appropriate to perform binarization on these parts in the opposite way to b.

In this way, conventional methods obtain a binarized signal that roughly matches the original binary image, but there is no guarantee to what extent this actually matches the original binary image, and it is often the case that erroneous binarization occurs. There are drawbacks to doing so.

An object of the present invention is to provide an image signal binarization device that eliminates the drawbacks of the conventional methods and obtains a binarized signal that matches the original binary image with high accuracy.

(Means for Solving the Problems) The present invention is an image signal binarization device comprising the following (a) to (e).

(a) a photoelectric conversion means for photoelectrically converting the original binary image to obtain a photoelectric conversion signal; (b) a means for binarizing the photoelectric conversion signal to obtain a first binary signal; (c) a means for obtaining a first binary signal; means for obtaining an approximation signal of the photoelectric conversion signal from the first binary signal, which is a filter simulating frequency characteristics; (d) means for obtaining a difference signal between the photoelectric conversion signal and the approximation signal; ) means for correcting the first binarized signal using the difference signal to obtain a second binarized signal close to the original binary image;

According to the present invention, it is possible to obtain a binary image signal that always matches the original binary image with high precision.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings.

FIG. 2 is an example of a block diagram when the present invention is applied to an image input device such as a facsimile.

The original binary image 1 is scanned horizontally from left to right, and when it reaches the right end, it returns to the left end and continues scanning along the scanning line one step below. The original binary image 1 is converted into an analog electrical signal 14 (photoelectric conversion signal A) by the photoelectric conversion circuit 2 in scanning order, and is input to the binarization circuit 3. The binarization circuit 3 provides a threshold value in the center between the highest value and the lowest value of the input analog signal 14, and binarizes the input analog signal 14 based on the magnitude of the threshold value.
A binary signal 15 is obtained. In the conventional method, this binary signal 15 is output as is, but in the present invention, the binary signal 15 is input to a correction circuit 4 and is also applied to a filter 5 that simulates the characteristics of the photoelectric conversion circuit 2. As the filter 5, for example, a low-pass filter as shown in FIG. 3 is used. The analog signal 14 is delayed by the delay circuit 13 by an amount corresponding to the delay of the filter 5, and then compared with the output of the filter 5, and the difference signal 6 is applied to the correction circuit 4.

If the difference signal 6 is so small as to be almost negligible, it is considered that the first binary signal almost matches the original binary image, but generally the difference signal 6 becomes large in some parts. Since the first binary signal is considered to be different from the original binary image in that part, the correction circuit 4 performs correction.

Next, the internal operation of the correction circuit 4 will be explained.

When the difference signal 6 exceeds a certain value (l _B ), the threshold circuit 8 having a positive threshold outputs a high level. Further, when the difference signal 6 becomes less than a certain value (-l _B ), the threshold circuit 9 having a negative threshold outputs a high level.
In response to this, the OR gate 10 operates the threshold circuits 8 and 9.
When any one of them outputs a high level, a high level signal is applied to the first input terminal of the exclusive OR gate 11 to instruct that the first binarized signal should be corrected.

The first binary signal is delayed by the delay circuit 17 by an amount corresponding to the delay of the filter 5, the subtraction circuit 12, and the threshold circuits 8 and 9, and then the second
is applied to the input terminal of The binary signal at the second terminal is inverted and becomes a second binary signal 7 when the correction instruction signal at the first terminal is at a high level. This device outputs this as a binary image signal.

FIG. 1 shows an example of the above signal processing process.
a is an analog image signal obtained by photoelectrically converting an original binary image, b is a first binary signal of analog signal a, c is a first approximate signal of analog signal a, and c is a second approximation signal of analog signal a.
It is produced from the binary signal b by the filter 5 shown in the figure. d is the first difference signal obtained by subtracting the analog signal a from the approximate signal c, and e is the second binary signal obtained by subtracting the analog signal a from the approximate signal c.
The value signal b is converted into a large part of the difference signal d (P, Q of a
(corresponding to the part above the positive and negative thresholds shown by dotted lines).

In the embodiment described above, the binarization circuit 3
Although a one-dimensional filter that performs only horizontal processing is used as the filter 5, various modifications can be made based on this embodiment, such as using a two-dimensional filter that also performs vertical processing.

(Effects of the Invention) As described above, the image signal binarization device according to the present invention has the feature of providing a binarized signal that is highly accurate and matches the original binary image.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the operation of the present invention, FIG. 2 is a block diagram when the present invention is applied to an image input device, and FIG. 3 is a diagram showing an example of a filter forming a part of the present invention. . In the figure, 1...original binary image, 2...
Photoelectric conversion circuit, 3...Binarization circuit, 4...Modification circuit, 5...Filter, 6...Difference signal, 7...Modified binary signal, 8...Positive threshold circuit, 9...Negative threshold Circuit, 10... OR gate, 11... Exclusive OR gate, 12... Subtraction circuit, 13, 17...
Delay circuit, 15...binarized signal, 14...photoelectric conversion signal.

Claims (1)

[Claims] 1. An image signal binarization device comprising the following (a) to (e). (a) a photoelectric conversion means for photoelectrically converting the original binary image to obtain a photoelectric conversion signal; (b) a means for binarizing the photoelectric conversion signal to obtain a first binary signal; (c) a means for obtaining a first binary signal; means for obtaining an approximation signal of the photoelectric conversion signal from the first binary signal, which is a filter simulating frequency characteristics; (d) means for obtaining a difference signal between the photoelectric conversion signal and the approximation signal; ) Means for correcting the first binarized signal using the difference signal to obtain a second binarized signal close to the original binary image.