JPS63232573A - Threshold deciding circuit - Google Patents

Abstract

PURPOSE:To remarkably simplify a threshold deciding circuit, by reading out the threshold level corresponding to a notable picture element position from a memory after the level is once stored in the memory and correcting the level by moving it upward or downward by means of a level changing means in corresponding to the designation of the density at the time of reading an original. CONSTITUTION:A ROM 11 for outputting threshold level which inputs levels of picture elements P, Q, R, and S in the vicinity of a notable picture element A and decides at which threshold level the notable picture element is binary coded, is provided. The ROM 11 reads out the threshold level of the notable picture element A from the correlation among the picture elements P, Q, R, and S. With respect to the output of the ROM 11, the process of the density mode designated at the time of reading an original is performed by means of a density switching device 12 in such a way that, when the density mode is designated to 'dark', the threshold level is lowered and, when designated to 'light', the threshold level is raised. In other words, the threshold level is decided by means of the combination of the ROM 11 and switching device 12 and binary signals are produced after the threshold level is com pared with the notable picture element A at a comparator 13. Therefore, this circuit is made smaller in size and simpler in constitution. In addition, this circuit can be changed easily.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a method for inputting the levels of neighboring pixels to a pixel of interest on a document to provide a threshold value to a binarization circuit. The level is inputted and stored in a memory that is a threshold level for the pixel position of interest, and then read out and set to lower or raise the level using a level switching means in accordance with the specification of shading when reading an original. This makes it possible to output a threshold value with a simple and easily changeable configuration.

[Industrial application field]

The present invention relates to a threshold value determination circuit that scans a line of a document using an image reading device, determines a threshold value for a pixel of interest, and supplies the threshold value to a binarization circuit.

[Conventional technology]

Conventionally, in an image reading device used in a document reading section of a facsimile machine, when a document is scanned and binarized by a binarization circuit, a threshold value is determined to give a sharp value.

In other words, 3×3 shown in (5) in the same figure in line scanning
For example, the center person, upper and lower PRs, and left and right QBs are represented at a 4-bit level using a window of pixel columns.

In the configuration diagram in (6) of the same figure, each of these P, Q, R, S and A is shown in the diagram (1) 1, (
If) 2 , (1103, QV) 4 Vc large input, calculate the difference, put it in the adder 5 and add it, and multiply it by a predetermined coefficient in the coefficient multiplier 6.

As a result, a value indicating the influence of surrounding pixels on the pixel of interest is obtained.

Next, an adder 7 adds this value to the pixel of interest, and this combined value is entered into a comparator 8 and compared with a separately set threshold level to output a binary signal.

Figure (6) shows another configuration diagram, in which a coefficient multiplier (1) is installed between the subtracters (1) 1, (II) 2, etc. in figure (6) and the adder 5. ? , (n) with 10 etc. inserted. That is, the influence of surrounding pixels is P,
This method is suitable for cases where Q, R, and S are different.

[Problem that the invention seeks to solve]

In the above conventional configuration, as shown in FIG. 3 (6), the threshold level is constant from beginning to end, and the influence of the four surrounding pixels is added to the pixel of interest, and an appropriate level is determined based on this. is set to create a binary signal. Even if the pixel arrangement around the pixel of interest changes in this way, an optimal binary signal will not be created that takes this into account, and there is no problem in that respect, but as shown in Figure (6). In addition, the configuration has to have four subtracters 1 to 4, two adders 5.7, and a coefficient multiplier 6 before the comparator 8 that generates a binary signal, making the circuit large and complicated. There is a drawback.

The present inventor discovered that while the conventional method keeps the threshold level constant and makes the level difference between the pixel of interest and surrounding pixels variable, in the present invention, the threshold level of the pixel of interest is We focused on the fact that the configuration can be greatly simplified by making the settings variable and storing these data in memory and using it.

An object of the present invention is to provide a threshold determining circuit provided with a memory for variably setting and outputting a threshold level based on surrounding pixels of a pixel of interest position.

[Means for solving problems]

In order to achieve the above object, in the present invention, when inputting the level of a pixel in the vicinity of a pixel of interest on a document and supplying a threshold value to a binarization circuit, the threshold level for the pixel of interest position is stored in a memory. This is then read out and modified to lower or raise the level using a level switching means in accordance with the specification of shading when reading the original.

[For production]

According to the above configuration, as shown in the principle explanatory diagram of FIG. A revised threshold value is obtained by switching between shades of time.

〔Example〕

FIG. 2 is an explanatory diagram of the configuration of an embodiment of the present invention.

In the figure, a ROM 11 is provided for inputting the P, Q, R, and S levels of neighboring pixels of the pixel of interest and outputting a threshold level at which threshold level the pixel of interest should be binarized. This ROM 11 stores neighboring pixels P and Q.

The threshold level of the pixel of interest can be read out based on the correlation between R and S. For the output of this ROM 11, the density switcher 12 performs processing in the density mode specified when reading the document. When specified, raise the threshold level. That is, R
A threshold level is determined by the combination of the OM 11 and the gray scale switch 12, and this threshold level and the target pixel A are compared by the comparator 13 to create a binary signal.

〔Effect of the invention〕

As explained above, conventional methods use multiple subtracters and adders to determine the pixel level, resulting in a large and complex circuit, whereas the present invention uses a memory that can set the threshold level as variable. By making it possible to reduce the number of circuits, the scale of the multiple circuits can be reduced and simplified, and changes can be made easily.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of the configuration of an embodiment of the present invention, and Figs. 3 (α) to (c) are explanatory diagrams of a conventional example. In the figure, 11 is a memory (ROM), 12 is a carburizing switch, and 13 is a comparator.

Claims (1)

[Claims] In a threshold determination circuit that lines scans a document using an image reading device, determines a threshold value for a pixel of interest, and supplies it to a binarization circuit, the levels of a plurality of pixels in the vicinity of the pixel of interest are input. and a means for storing and outputting a threshold value for the pixel position of interest; and a grayscale switching means for changing the level of the output of the storage means according to a grayscale specification when reading a document. threshold determination circuit.