JPS61274581A - Compression and conversion system for document picture - Google Patents

Abstract

PURPOSE:To enable the conversion of a document picture in which crushing is suppressed and to make a binary coding and a thinning process possible with a simple circuit by setting a threshold in compression at an object picture value side nearer than the threshold in non-compression. CONSTITUTION:An electrical signal 1 that a read out picture is photoelectrically converted is converted to a binary-coded signal 4 with a fixed threshold system that consists of a comparator 2 and a switching part 8 which selects a threshold Va in compression or a threshold Vb in non-compression from a threshold generator 9. The signal 4 is inputted to a compression conversion part 6 with an OR system through a thinning part 5. In compression and conversion, a control signal 10 is outputted from the conversion part 6 to set a threshold at the value Va to perform thinning.

Description

[Detailed Description of the Invention] [Summary] By utilizing the fact that the low spatial frequency components of a document image converted into an electrical signal are emphasized by the spatial frequency characteristics of the reading optical system or the frequency characteristics of the electrical signal system, By approaching the threshold value for conversion from the background density value (white level) to the target image value (black level), the thinned binary image signal is
It is designed to be obtained at the same time as value conversion.

[Industrial application field]

The present invention relates to image reading devices such as facsimile machines, copiers, scanners, etc., and particularly to a method for reducing a read image or converting a read image from a high-density image to a low-density image.

[Conventional technology]

Methods for reducing and converting document images can be roughly divided into those that directly optically convert the image, and those that replace the image with electrical signals.

In the former case, it is necessary to adjust the optical system according to the reduction ratio.

The latter can obtain similar results in a compact and low-cost manner by applying periodic data processing to images converted into electrical signals. This data processing method includes the affine method, sp
The c-method, the logical sum method, the majority voting method, the 9-division method, the projection method, etc. are known.

2. A known facsimile machine converts a read image into an electrical signal and then performs reduction conversion. Since an image generally has a large amount of data, the image is reduced and converted into a binary digital signal. Fixed threshold method and envelope method are methods for obtaining binary digital signals.

There are various methods such as similar waveform method, comparison method, multiple slice level method, and histogram method.

FIG. 3 shows a block diagram of a conventional document image reduction method.

In the figure, the electrical signal 1 obtained by photoelectrically converting the read image is
It is converted into a binarized symbol 4 using a fixed threshold method using a threshold value V generated by a comparator 2 and a threshold value generator 3.

The binarized symbol 4 is thinned by a thinning section 5 such as that known in Japanese Patent Application Laid-Open No. 58-182952, and is further inputted to a reduction conversion section 6 of various types as described above to form a reduced image 7.

FIGS. 4(al), (bl, and (c)) are explanatory diagrams of the operation of the conventional document image reduction process. In this explanation, the reduction method will be described using the logical sum method as an example.

Here, it is assumed that the read image is reduced to 1/2. In FIG. 4 (al), a read image 11 is read with the arrow 12 direction as the main scanning direction. This read image 11 is converted into an electric signal 1 by a photoelectric conversion system, and is binarized at a threshold value ■.Threshold value ■ or more Electrical signal level 14 side electrical signal l
When the signal is on the electric signal level 15 side, it is set as "1", and when it is on the electric signal level 15 side, it is set as 0. This binarization is performed when the timing signal 13 supplied from the photoelectric conversion system is at the "H" level.

Next, as shown in FIG. 4(b), the thinning unit 5
The thinned image 16 (displayed by solid lines) that has undergone complicated thinning processing is divided into nxm pixels in both the main and sub-scanning directions. Here, n and m indicate the number of pixels corresponding to each scanning direction, and when line thinning is not performed, the image becomes like a binarized image 17 displayed with a broken line.

Next, reduction conversion is performed using the logical sum method. The logical sum method takes the logical sum of the number of converted pixels X (X>1) corresponding to one pixel of the converted image, and uses the result as one pixel of the converted image. Therefore, the reduced image 18 is 1B(is, J b) =
16(Iza-t, Jza-+) + 16(hm,
Jzm-t) + 16 (Izm-+, Jza) + 1
6 (Iza, Jzm) However, 1B (ia, jb) is the ia, jb pixel of the reduced image 18, and the 16 (1, J, S) is the I,, J, pixel of the binarized image 16.

In other words, as shown in FIG. 4(C), when reducing the size to 1/2, one pixel of the converted image is the logical sum of four pixels of the converted image, so even one of the four pixels is "black". ”, one pixel of the converted image becomes “black”, and when the overall line is thinned, it becomes a reduced image 18 shown by a solid line, and when it is not thinned, it becomes a reduced image 19 shown by a broken line “ The result is an image that is likely to cause "flecks".

[Problem that the invention seeks to solve]

When converting a document image optically, the mechanism for doing so is thick (and expensive), and when converting it into an electrical signal, complicated hardware is required to thin the line. There are drawbacks that require it.

The present invention has been created in view of the above-mentioned drawbacks of the conventional art, and is a method of converting pixel density with a reduced pixel density to suppress the occurrence of "blurring" by simultaneously thinning the converted image using a simple circuit. It is intended for the purpose of providing.

[Means to solve the problem]

As shown in FIG. 1, the document image reduction conversion method of the present invention includes a comparator 2 for binarizing an analog document image signal 1, a threshold generator 9 connected to the input of the comparator 2, and a 2
A reduction converting section 6 converts the output of the signal into a reduced or non-reduced signal 7, and a switching section 8 that switches and sets the threshold of the threshold generator 9 to two types: reduction/non-reduction. The method is characterized in that thinning is performed simultaneously with the binarization based on the threshold value.

[Effect]

By setting the threshold value Va at the time of reduction to the target image value (black level) side than the threshold value Vb at the time of non-reduction, the same effect as line thinning can be obtained at the same time as the binarization. It is possible to perform document image conversion with less "blurring".

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

In order to make the explanation of the configuration and operation easier to understand, the same parts are denoted by the same reference numerals throughout the drawings, and repeated explanation thereof will be omitted.

FIG. 1 shows a block diagram of an embodiment of the invention. In the figure, 8 indicates a switching section, and 9 indicates a threshold value generation section.

The electric signal 1 obtained by photoelectrically converting the read image is sent to a comparator 2,
The signal is converted into a binary signal 4 using a fixed threshold method including a switching section 8 that selects and switches between a threshold value Va for reduction generated by a threshold generator 9 and a threshold value Vb for non-reduction.

The binarized signal 4 is inputted via the line thinning section 5 to a reduction conversion section 6 using an OR method, and becomes a reduced image signal 7. At the time of reduction conversion, a control signal 10 is outputted from the reduction conversion unit 6 in order to set the threshold value to the value Va for thinning the lines.

FIGS. 2(a), 2(b), and 2(C) are explanatory views of the operation of the embodiment of the present invention. In FIG. 2(a), the threshold value for binarization is set closer to the electric signal level 14 side, such as the threshold value Va during reduction, than the threshold value Vb during non-reduction. As a result, the binarized image 20 shown in FIG. 2 (ill) becomes a thinned image with fewer "1"s than the binarized image 17 according to the conventional method shown in FIG. 4 (tl). Even if the binarized image 2o is reduced using the logical sum method, as shown in FIG. 2(C), “
It is possible to obtain a good reduced image 21 without "bleeding".

In the present invention, the thinning process is simultaneously performed during binarization, and the subsequent reduction conversion is intended to be performed, so the combination of the binarization method and the reduction conversion method is not concerned.

〔Effect of the invention〕

As described in detail above, according to the document image reduction conversion method of the present invention, hardware for binarization processing can be used in combination with line thinning processing, so that it is possible to construct a reduction conversion apparatus at a low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2(a),
(bl, (C) is an explanatory diagram of the operation of the embodiment of the present invention, No. 3
The figure is a block diagram of the conventional example, and Figures 4 (al, 4b) and 4 (c) are diagrams explaining the reduction effect of the conventional example. In the figure, 1 is an analog document image signal, 2 is a comparator,
Reference numeral 6 indicates a reduction conversion section, 8 indicates a switching section, and 9 indicates a threshold value generator. (b) (C) O-kaimei zume sashisetsumon 112 Figure

Claims (1)

[Claims] Comparator (2) that binarizes the analog document image signal (1)
and a threshold generator (
9), a reduction converter (6) that converts the output of the comparator (2) into a reduced or non-reduced signal, and a threshold value of the threshold generator (9) to be set to two types: reduced/non-reduced. A document image reduction conversion method, characterized in that a switching unit (8) is provided to perform switching settings, and at the time of reduction, binarization and thinning are performed at the same time based on the threshold value.