JPS6378670A - Image reader - Google Patents

Abstract

PURPOSE:To attain a stable binarization without fail by changing a threshold only when the black and white peak values of a picture signal lie within a prescribed range. CONSTITUTION:A data W-PK about the white peak values of eight lines including a current line is stored in a memory. Data lying eight line before is updated for the unit of the line. Next, data obtained from a black peak detection circuit 111 is stored as a black peak value B-PK in the memory. Density data obtained from a white peak detection circuit 110 is read in a CPU. Only if the read-in data is lower a prescribed value, a slice level is updated. Thus, the threshold does not follow an image at an abnormal density, thereby executing a precise binarization.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an image reading device that binarizes an image information signal obtained by scanning a document image and photoelectrically converting it into each pixel. .

(Prior Art) Conventionally, in this type of image reading device, an electrical image (information) signal obtained from a CCD (charge-coupled device) image sensor or the like as a photoelectric conversion element is generally
Applied to one side of the comparator, the voltage obtained by dividing the image signal into h1 by an integrating circuit including a capacitor is set as a threshold.
Binarization was performed by applying it to the other input of the comparator.

[Problem that the invention seeks to solve]

However, in the conventional binarization method as described above, when the image information signal of the image does not change for a long time, the value of the previous period approaches the level of the human image signal, so the binary value is The drawback was that the conversion operation became unstable.

Furthermore, due to the time constant of the integrating circuit for integration, the ability to follow changes in the density of the background or character parts of a document, for example, is not good, and if the background density changes dynamically, the correct 2
There was a problem that the value conversion process was not performed.

The present invention has been made in view of the above-mentioned problems, and eliminates the above-mentioned drawbacks, as well as providing a stable dual
The object of the present invention is to provide an image reading device that can perform value conversion processing.

(Means for Solving the Problem) Therefore, in the present invention, the white peak value and the black peak value of the photoelectrically converted image signal are used as threshold value determining means for binarization in this type of image reading device. This is intended to achieve the above object by configuring the threshold value to be changeable only when the value is within a predetermined range.

[Effect]

With the above-described configuration, in the present invention, the threshold always properly follows dynamic fluctuations in the image/character and background density of the original document. Since the threshold value does not follow, accurate binarization processing becomes possible.

〔Example〕

The present invention will be explained below based on examples.

FIG. 1 is a block diagram of an embodiment of a binarization processing circuit configuration according to the present invention.

(Structure) (Fig. 1) 101 is an optical lens, 102 is a photoelectric conversion element C
OD line image sensor 106 is a CCD drive circuit. The image (information) signal imaged on the CCD line image sensor 102 is amplified by the amplifier 103,
5-bit analog/digital (A/D) converter 10
4 is input. The image signal converted into a 5-bit digital signal is latched into a D flip-flop 105 by a clock generated for each pixel obtained from a timing signal generation circuit 107, and then output to a digital comparator 108 and a peak value for each main scanning line. The signal is input to a white peak detection circuit 110 and a black peak detection circuit 111, which detect the signal.

The data obtained from each peak detection circuit 110, 111 is input to a CPU (Central Processing Unit), and the CPU determines a slice level for each main scanning line using the n' data, and 109. In the digital comparator 108,
The image signal obtained from the D flip-flop block 105 is compared with the slice level obtained from the D flip-flop 109 and latched for each main scanning line, and a binary signal THOUT is output.

(Operation) (Fig. 2) Next, the slice level determination method will be explained based on Fig. 2. FIG. 2 is a sequence flowchart of the slice level determination operation. The range of the input density data is θ to 31, where 0 represents pure white and 31 represents pure black.

Further, the program shown in FIG. 2 is activated for each main scanning line to determine the slice level for the next line.

Each step will be explained in order below. In step S21, the density data obtained from the white peak detection circuit 110 (FIG. 1) is read into the CPU, and in step SP2, the process proceeds to step SP3 only if the read data is smaller than 10; If so, terminate the program without updating the slice level. this is,
This is to prevent the slice level from following when the original image is abnormal.

In step SP3, the white peak value data W-PK for eight previous lines including the current line is stored in the memory, and the data for eight lines before is updated for each line. Next, in step SP4, Oir
The data obtained from the black rake detection circuit 111 is stored in the memory as a black peak value B-PK. In step SP5, the process proceeds to step SP6 only when this black peak value B-PK is greater than 10, and in other cases, the program is terminated without updating the slice level.

This is because the slice level is not made to follow an abnormal original image, as in step SP2 described in +W.

Step SP6 is the white peak value W-AV of the current line.
D is being calculated and determined by the following formula.

(W-AVD) n-1) == (1) In the above equation, (W-AVD)n is the white peak sum of the n-th line, and from the n-7th line to the n-th line. The average value, that is, the average white peak value in the vicinity of the current line, so to speak, in a short section, and the W-AVD one line before, that is, the average white peak value in a long section from the start of scanning, are averaged. It is required as something that has been done.

1. For example, when the background density is not constant and tends to fluctuate over a short period of time, such as a blue-printed original, the white peak value, that is, the density level of the background, is set so that the slice level is not affected. For that, using the average value of 8 lines,
This is also to stabilize the slice level by taking into consideration the background average density over a long period.

In step SP7, the slice level S is determined by finding the intermediate value between the white peak value W-AVD found by the above method and the black peak value B-PK on the current line. Further, in step SP8, the set slice level S is written into the D flip-flop 10109 (FIG. 7), and the program is ended.

Here, the comparison value 10 set in each step SP2.3P5 is obtained experimentally in this example, and it goes without saying that it differs depending on each application example.

(Effects of the Invention) As described in detail above, according to the present invention, even if there are dynamic changes in the image 431 (including characters) and the background density of the original document, the threshold value for the binarization process can be maintained. Since it is possible to properly follow the image and not to follow the higher density of the image, it is possible to provide an image reading device that can accurately perform the binarization process.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a configuration of an embodiment of a binarization processing circuit according to the present invention, and FIG. 2 is a flowchart of a slice level determination operation sequence according to FIG.

Claims (1)

[Claims] An image reading device that scans an original image and binarizes a photoelectrically converted image signal, comprising: a holding means for holding a white peak value and a black peak value of the image signal for each main scanning line; threshold determining means for determining a threshold for binarization for each main scanning line using a white peak value and a black peak value; An image reading device characterized in that a threshold value can be changed only when a peak value and a black peak value are within a predetermined range.