JPS631252A - Binarization system for picture - Google Patents

Abstract

PURPOSE:To perform the binarization processing with the picture information having satisfactory reproducibility of thin lines, by changing the threshold level for binarizing the present picture elements in response to the density level of the preceding picture element. CONSTITUTION:A circuit consisting of an arithmetic amplifier A2, a transistor T, a capacitor C and an arithmetic amplifier A3 forms a sample holding circuit which protects the potential at a point (b) in response to a sample pulse signal SP and delays it by an amount equal to a single picture element. An arithmetic amplifier A4 serves as a differential amplifier which secures the difference between the potential of a point (c) and the threshold level set at a point (a). The signal of a point (d) at the output side is obtained by adding the signal of the point (c) to the fixed threshold level of the point (a). Then the signal of the point (d) varies in accordance with the density level of the preceding picture element. Thus it is possible to obtain the binarized output apporoximate to the conventional one undergone the MTF correction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image binarization method for binarizing image information.

Tome Genkasa Conventionally, original image information obtained by optically scanning the image surface of a document is photoelectrically converted using an image sensor, and the image information is sampled pixel by pixel and read, and then the image information is binarized and recorded as pixels. If the original image is to be converted into a ! MTF to improve I4 processability of II line
Let's make corrections - is set.

That is, as shown in FIG. 3, the image signal output from the image sensor 1 is passed through the AD converter 2 to be multi-level quantized, and the digital image information having the density levels of the multi-gradation is stored in the memory 3. Store lines.

Since the image information of the third line is read, predetermined arithmetic processing is performed in the ITF correction circuit 4, and the MTF corrected image information ff< is given to the binarization circuit 5 for binarization processing. There is.

The calculation contents in the MTF correction circuit 4 are as follows:
As shown in Fig. 4, the density levels of the pixel of interest E and each of the pixels B, D, F, and H before, after, to the left, and to the right of the pixel of interest E in a 3x3 pixel area centered on the pixel of interest E to be processed. Focusing on each density level Db of pixels B, D, E, and F from the memory 3.

Dd, De, and Df are read out, and together with the density level Dh of the image iH currently being read, the MTF-corrected density level De' of the pixel of interest E is calculated according to the following equation. In the figure, X indicates the main scanning direction, and Y indicates the sub-scanning direction.

Da'=3De-(Db+Dd+Df+Dh)/2 However, if an image binarization means that performs MTF correction as such preprocessing is used, the entire circuit configuration becomes complicated.

The present invention has been made in consideration of the above points, and is an image binarization method that allows image information to be binarized with good reproducibility of A-line by simple means. It provides a method.

In order to achieve this objective, the present invention binarizes the image information obtained by sampling the image pixel by pixel at the threshold level, and binarizes the current pixel according to the density level of the previous pixel. I am trying to take measures to change the threshold level.

Specifically, the threshold level is determined by adding a predetermined value corresponding to the difference between the density level of the previous pixel and the fixed threshold level at the time of processing the previous pixel to the fixed threshold level when binarizing the current pixel. I am trying to get them to do this.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an example of a circuit configuration for concretely implementing the image binarization method according to the present invention, in which a variable threshold level method is particularly used for shading correction. Reference white level information is stored in the shading correction memory 6 in advance, and the memory 6
The reference white level information read from is converted into an analog value by the DA converter 7 and output as a threshold level signal SH, which is divided into resistors so that the potential at the 0 point becomes a fixed threshold level. There is.

The operational amplifier A1 is a differential amplifier that multiplies the difference between the potential at the 0 point and the image signal BS output from the image sensor 1 by 1/A (A: gain), and its output, that is, the signal at the 0 point, is the image signal BS. This indicates how large or small the threshold is relative to the fixed threshold level.

Also, operational amplifier A2. A circuit consisting of a transistor T, a capacitor C, and an operational amplifier A3 constitutes a sample hold circuit that protects the potential at the 0 point and delays it by one pixel in response to the sample pulse signal S.sub.2). In other words, the signal at point 0 is the signal (S) at point 0 delayed by one pixel.

Furthermore, the operational amplifier A-i is a differential amplifier that takes the difference between the potential at the 0 point and the fixed threshold level at the 0 point, and its amplification factor is set to 1, and the output side is 0.
The signal of the point (a) is the fixed threshold level of the 0 point plus the signal of the 0 point.In this case, the signal of the 0 point is one pixel before (number 4, so the signal of the 0 point is It will change depending on the density level of the pixel.

This 0 point signal, which changes according to the density level of the previous pixel, is set as a threshold level to the combo barre 90M, and the image signal BS is then binarized.

As described above, according to the present invention, the threshold level at which the single-picture signal BS is binarized changes depending on the density level of the previous pixel (specifically, when the output level of the previous pixel is close to white, the threshold level increases). (and decreases when it is close to black),
A binarized output that approximates the conventional MTI" corrected output can be obtained.

FIG. 2 shows a time chart of various signals. Here, the fixed threshold level of 0 point is set to 50%. In the binary output, fine lines are well reproduced by sampling the 0 portion, but in the case of the binary output without correction, the fine lines are lost.

Above all, in the image binarization method according to the present invention, by taking a simple means of changing the threshold level for binarizing the current pixel according to the density level of the previous pixel, it is possible to This has the excellent advantage that it is possible to perform binarization processing of image information with good reproducibility of thin lines, which is equivalent to performing M1'F correction as preprocessing for image processing.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing a configuration example for concretely implementing the image binarization method according to the present invention, and FIG. 2 is a time chart of signals of various parts in the same embodiment. FIG. 3 is a block diagram showing the circuit configuration for conventional image binarization, and the fourth part is a diagram showing the configuration of a 3×3 pixel area.

Claims (1)

[Claims] 1. When image information obtained by sampling an image pixel by pixel is binarized at a threshold level, a threshold level is used to binarize the current pixel according to the density level of the previous pixel. An image binarization method that takes measures to change the 2. The threshold level is formed by adding a predetermined value corresponding to the difference between the density level of the previous pixel and the fixed threshold level at the time of processing the previous pixel to the fixed threshold level when the current pixel is binarized. An image binarization method using storage according to item 1 above. 3. The image binarization method according to item 2, wherein the fixed threshold level is determined by a shading correction output stored in a memory in advance.