JPH11215375A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stable binarization and to simplify a user operation by generating the density histogram distribution of an input data holding part and generating a binarization threshold from density histogram distribution. SOLUTION: An image read part optically reads an image on a medium, where the picture to be read is recorded and converts it into an electrical signal. An image signal processing part binarizes an image signal outputted from the image read part. An input data holding part temporarily holds input data from the image read part at the time of reading a line. A density histogram distribution generation part generates density histogram distribution from input data. A threshold generation part generates a binarized threshold to the image signal processing part from the white peak value of a base value and the black peak value of a character in density histogram distribution. Namely, the input value of the line of a sensor is held, white/black peak values showing the white which is a base and the black of the character are obtained from density histogram distribution, and the threshold is decided with the reference values when the fluctuations of a read value are large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input device such as a scanner or a facsimile, and more specifically, to optically read an image on a reading medium and convert it into an analog electric signal. The present invention relates to an image input device that further converts a signal into a signal and outputs the signal.

[0002]

2. Description of the Related Art Conventionally, there is an image input device shown in FIG. 12 as an image reading circuit (patent application number: 63-296557). According to this image reading apparatus, a peak holding circuit for holding a peak value of a read value based on one-line reading of an input document is provided, and this peak value is used as a reference value for generating a binarization threshold.

[0003]

However, in the prior art, when the fluctuation of the read value caused by the fluctuation of the sensitivity of the sensor or the fluctuation of the light source is large, the white peak value of one line is held and this value is set as the reference value. However, since the input level greatly fluctuates, a threshold value cannot be generated stably, and there has been a problem that image binarization processing is not performed correctly.

Accordingly, an object of the present invention is to provide an image input device capable of performing stable binarization and simplifying a user operation.

[0005]

In an image reading apparatus for optically reading an image on a reading medium and converting the image into an electric signal, an input data holding section for temporarily holding one line of input data, and an input data holding section The object of the present invention is attained by an image reading apparatus having a density histogram distribution generating section for generating a density histogram distribution of a section, and a threshold generating section for generating a binarization threshold from the density histogram distribution.

In particular, there is provided a correction unit for performing shading correction of input data, wherein the corrected input data is stored in the input data storage unit. Further, the threshold value generation unit calculates a white peak value (W) of the paper white portion from the density histogram distribution generated by the density histogram distribution generation unit.
P), the black peak value (BP) of the character black part is determined, and the threshold is α
It is characterized in that a threshold value is generated under the condition of × (WP−BP) + BP (0 <α <1).

Further, the input data holding section is characterized in that it holds only input data at a limited place on one line designated in advance. Still further, the input data holding unit reads one line of the target paper before reading and holds the read data in the input data holding unit.
More specifically, the input data holding unit holds the read data in the input data holding unit at the beginning of the read target,
The read data of the last one line to be read is held in the input data holding unit, or the input data at the time of line reading is held at a ratio of one line to N lines (N: an integer of 1 or more) for reading. The density of the input data is distributed between the density of the background of the paper and the density of the character portion (ink). In general, since the character area includes a space between characters, the density of the background of the paper is distributed at a constant rate. Also, if the optical resolution of the scanner is high, the distribution of the character lines also includes the ink density level at a fixed rate. Therefore, the background level and the black level of the character portion can be detected from the density histogram distribution.

[0008] Even for input data of a sensor in which sensitivity variation occurs due to the influence of a sensor, illumination, or the like, the white peak value (white peak: WP) of the input level of the base (white) of the paper is obtained from the density histogram distribution of the input data. , And a black peak value (black peak value: BP) of the input level of the character portion are held as reference values. By generating a threshold value from this reference value, the determined threshold value does not exceed the white and black levels, and correct binarization can always be performed.

As a method of correcting static sensitivity variation of a sensor, illumination, or the like, there is a shading correction process of correcting at a monochrome input level read in advance. Performing the shading correction processing has the effect of expanding the input dynamic range over the entire sensor area. First,
The input data after the shading correction processing is held. From this input data, a reference value for threshold generation is obtained, and a threshold is generated. According to this method, a pseudo-halftone input using a dither (defined by combining a plurality of binarized data in a certain area) with an expanded dynamic range can always be processed with a correct threshold value.

The threshold value generated by the threshold value generation unit is: threshold value = α × (white peak value−black peak value) + black peak value
By generating according to (0 <α <1), it is possible to generate an optimum threshold value that does not exceed the white and black levels. In particular, the case where α = 0.5 corresponds to the case where the maximum margin is set for the white and black levels.

When the paper to be read is shorter than the sensor length of the image reading unit (for example, when reading a business card with an A6 size scanner), the density histogram distribution includes white peak values and black peaks including those other than the target paper. Find the value. By generating a threshold value using a white peak value and a black peak value from a density histogram distribution of input data at a limited place (for example, a business card size) on one line designated in advance, a density range other than a density range to be read is obtained. Can be generated even when the background is input at the same time.

When a process of generating a density histogram from input data and obtaining a black and white peak value is performed by software, it takes a lot of processing time. Therefore, a series of these processes is performed separately from the actual reading process. In addition to the original reading operation, one line of the paper is read only once, and the generation of the optimal binarization threshold is determined. Subsequent paper of the same type uses the same binarization threshold,
The binarization processing can be performed without causing a delay in the reading processing.

When reading a process of generating a density histogram from input data and obtaining a black and white peak value (of an area)
At the beginning of Optimal binarization processing can be performed on the area to be read. In many cases, the same type of paper is continuously read. In particular, when the reading area is smaller than the document size, it can be expected that both the background and the characters are included at the end of the reading. Therefore, input data is read at the end of reading. For the next reading, an optimal binarization process can be performed by generating a density histogram from the held input data and performing a process of obtaining a monochrome peak value.

The base of the paper may have a locally different white color. By generating the density histogram distribution from the input data and sequentially performing the processing for obtaining the black and white peak value simultaneously with the reading of the data, the optimum binarization processing can be always performed.

[0015]

FIG. 1 is a drawing showing a configuration of an image reading apparatus according to an embodiment of the present invention. The image reading apparatus according to the present embodiment optically reads an image on a medium on which an image to be read is recorded, converts the image into an electric signal, and binarizes the image signal output from the image reading section. Image signal processing unit (binarizing unit), an input data holding unit for temporarily holding input data from the image reading unit at the time of line reading, and a density histogram distribution generating unit for generating a density histogram distribution from the input data And a threshold generation unit that generates a binary threshold for the image signal processing unit from the white peak value of the background value of the density histogram distribution and the black peak value of the character.

The image reading section includes a sensor section and an A / D conversion section. As the sensor unit, a line sensor configured by a CCD or the like is used in the present embodiment. Since the sensor type is not directly related to the present invention, any other type of sensor can be used.
The sensor unit outputs an analog electric signal having a value corresponding to the density of the image read from the medium.

The A / D converter converts an analog electric signal output from the sensor into a digital signal. Here, if an 8-bit digital signal is handled,
If the read result is white, 255 is set to A /
Output from the D conversion unit. FIG. 2 is a diagram showing a flow of the binarization processing according to the present embodiment. As shown in FIG. 2, in the image reading apparatus according to the present embodiment, a process of generating a threshold value and a process of binarizing a read image are executed.

First, in order to generate a threshold value, one line of an image of a background (white portion) including characters of a medium is read, data is input, and the data is stored in a line data holding unit. Also, the input data is passed to the density histogram distribution generation unit. The density histogram distribution generation unit generates a density histogram distribution from the density values of the input data for each pixel. In the threshold generation unit, based on the density histogram generated by the density histogram distribution generation unit, a white peak value indicating white of the background and a black peak indicating black of characters are obtained, and a threshold is generated from the black and white peak value, It is sent to the image processing unit (binarization unit). 1
When the read area of the line is all black or all white, the white peak value and the black peak value cannot be obtained only by reading one line. In this case, a threshold is generated using a white maximum value (255) and a black minimum value (0) prepared in advance.
The following processing is performed.

Next, in the image reading process, the image processing unit performs a process of binarizing the digital image signal from the image reading unit using the threshold value of the threshold value generation unit. The threshold value generated by the threshold value generation unit is generated from input data obtained by reading the base (white part) and the character part (black part) of the medium.
The threshold value is optimal for the document, and the binarization is performed correctly. FIG. 3 shows an overview of a pen-type scanner device, which is an example in which the image reading device shown in FIG. 1 is incorporated, and an internal configuration diagram thereof. The pen-type scanner device according to the present embodiment employs a form in which an image reading unit is brought into close contact with a document to read the document. By moving the pen-shaped scanner on the read document and scanning the document in this way, and binarizing the obtained input data based on the determined threshold, the binarized image data is output. I have. FIG. 4 illustrates the control of reading an image and the flow of data in the pen-type scanner illustrated in FIG. 3. In this example, an example of reading data for four lines is shown. In FIG. 4, the encoder pulse corresponds to a movement signal output from the movement detector. Further, the line sensor activation signal is a signal generated every one driving cycle of the line sensor, and the signal transfer from the line sensor is started based on the signal. FIG.
Corresponds to a drive signal. The line sensor image signal is an image signal output from the line sensor based on the line sensor activation signal. The signal that has been subjected to the image processing is an image signal that has been subjected to the binarization processing.

The data transfer interrupt to the apparatus is performed from the image reading apparatus to the information processing apparatus when transferring the image data from the image reading apparatus to the external information processing apparatus, which will be described in detail later. Hereinafter, the control of the reading operation and the flow of data will be described with reference to FIGS. The image reading unit includes a line sensor, a light source (LED or cold-cathode tube), and a lens, and reads an image in a contact type with a reading medium. During reading, the light source is turned on, and the line sensor is started to read by a start signal, so that the amount of light reflected at each position on the sensor is converted into an electric signal and output as an analog signal. The movement amount detection unit converts the movement amount on the reading medium into a pulse signal by an encoder and outputs the pulse signal. Thus, the amount of movement of the image reading device relative to the medium is detected. The image signal processing unit digitizes the image signal from the image reading unit by an A / D conversion circuit, and performs a binarized image process using a threshold determined from the density histogram distribution.
The control unit performs overall reading control and data transfer to the information processing device. The activation signal to the line sensor is always generated during the medium reading period, and the line data (image data) after the image processing is stored in a buffer inside the image reading apparatus.

When the control section detects a movement pulse (encoder pulse) from the movement amount detection section, it raises an interrupt to the information processing apparatus and transfers data of image-processed line data stored in the buffer. The travel pulse is
During normal operation, only one line sensor is output in one driving cycle (line sensor image signal 1 in FIG. 4). When the binarization process is performed, a data transfer interruption is performed from the image reading device to the information processing device, and the image data is transferred to the information processing device.

However, if the movement pulse is detected twice or more within one driving cycle of the line sensor, the control unit determines that the movement of the scanner has occurred more than the reading performance of the scanner, and the movement pulse for one movement pulse is detected. Transfer only data.
In the example of FIG. 4, it corresponds to the line sensor image signal 2. Here, two encoder pulses appear between the line sensor activation signals. On the other hand, if the movement pulse is not detected within one drive cycle of the line sensor, it means that the scanner has not moved. In FIG. 4, it corresponds to the line sensor image signal 3 portion. Here, no encoder pulse appears between the line sensor activation signals. In this case, the image-processed line data stored in the buffer is discarded, and the read data (line sensor image signal 4) of the next line is held.

The I / F unit is an electrical interface to an information processing device connected to the image reading device, and performs interruption and data access to the information processing device. The binarized data transferred to the information processing device is displayed on a display unit of the information processing device. Therefore, the operator can confirm the image data being read from the display unit. FIG. 5 is a block diagram showing an image reading apparatus according to the second embodiment. The image reading apparatus illustrated in FIG. 5 includes an image reading unit that optically reads an image on a reading medium and converts the image into an electric signal, and an image signal that binarizes an image signal output from the image reading unit after shading correction. A processing section (binarization section); an input data holding section for holding input data after shading correction at the time of line reading; a density histogram generating section for generating a density histogram distribution from data in the input data holding section; A threshold generation unit for generating a binarization threshold for the image signal processing unit from the white peak value of the base value and the black peak value of the character;

The image reading section is composed of a sensor section and an A / D conversion section, and digitizes and outputs an image signal to be read (for example, in the case of 8 bits, white is 255 and black is 0). The output of the image reading unit is converted by the shading correction unit into an output from which influences such as surface unevenness have been removed.
The background value read in advance is stored as a white shading correction value, and the input image signal is always converted and output according to the following equation (1).

Input image signal: x (i), signal after correction: y (i) White shading correction value: ww (i) y (i) = 255x (i) / ww (i). . . (1) The image signal converted by the above equation is binarized in the same manner as in the first embodiment. Therefore, the input data for one line, which has been subjected to shading correction, is held in the input data holding unit. On the other hand, a threshold is generated from the input data in the same manner as in the first embodiment. Here, the processing of the white shading correction has been described, but the black shading correction may be similarly performed. FIG. 6 is a view for explaining an image reading operation according to the third embodiment of the present invention, and is a graph showing a relationship between an input waveform of a background, a density histogram distribution, and a determined threshold. The graph on the left side of the figure shows the input values of the read signal for one line, including the background of the read document and black portions corresponding to characters. The horizontal axis is the pixel in the lateral direction of the medium (pixel)
And the vertical axis indicates the density value. The graph on the right side of the figure shows the density histogram distribution of the pixels. The horizontal axis in the figure shows the density value, and the vertical axis shows the frequency of occurrence of the density value.

Here, even if the sensitivity of the sensor varies, a white peak value (WP) indicating the background and a black peak value (BP) indicating the character appear in the density histogram distribution. Therefore, if a threshold value is generated inside the white peak value and the black peak value, the read image can be binarized. That is, if a threshold value is generated at a position as shown in the figure, a signal near the black peak value is correctly output as black, and a signal near the white peak value is correctly output as white. The threshold is calculated by the following equation.

Threshold = α × (WP-BP) + BP (1 <α <1) Here, α is a coefficient for determining the threshold, and an arbitrary value can be applied. The value of α depends on the density of the original to be read,
What is necessary is just to select suitably according to the image quality of a desired output image, etc. Thus, the white peak value (W
P), black peak value (BP),
Value conversion can be performed. FIG. 7 shows an image reading apparatus according to the fourth embodiment. If the width of the sheet to be read is shorter than the reading area of the image reading unit, even if a line input data value is obtained, a portion outside the target (outside the document) is also read. Therefore, data irrelevant to the medium is input, and the density histogram distribution of the paper cannot be correctly obtained. Therefore, in the present embodiment, the effective area specifying unit uses as input data values of only data of a limited place on a previously specified line,
Generate a density histogram distribution. The specification of the effective area is
For example, the width of the medium to be read may be specified. The image reading device recognizes a portion to be treated as a valid signal among the signals read based on the designation of the valid region, generates a density histogram only for the portion, and generates a threshold (FIG. 7 valid region). This makes it possible to generate an optimal binarization threshold even for a sheet shorter than the line length of the image reading unit. FIG. 8 is a view illustrating an image reading apparatus according to a fifth embodiment of the present invention. FIGS. 9 to 11 are flowcharts showing a procedure of a reading process in the image reading apparatus shown in FIG.

The above drawing shows the relationship between holding of line input data for determining a threshold value and actual reading processing. The line input for determining the threshold is configured in four ways. 1) Separate processing type In addition to actual image reading, one line input of paper is performed, and a threshold value is determined in advance from the density histogram distribution.
In the subsequent reading, the binarization process is performed at the determined threshold. 2) Pre-read type One leading line at the start of reading is input, a threshold is determined from the density histogram distribution obtained as a result of reading, and at the time of reading, binarization processing is performed using the threshold determined at the top. 3) Post-reading type One line at which reading is completed is input, and a threshold is determined from the density histogram distribution. Subsequent reading of the document performs binarization processing using the threshold determined at the end of the previous reading. 4) Sequential type Simultaneously with the input of an image of one line, a threshold is determined from the density histogram distribution for each line, and the binarization process is always performed with the latest threshold using the determined threshold.

By adopting such a configuration,
A configuration according to the hardware configuration and the priority of the processing time can be selected.

[0030]

As described above, according to the present invention, in the image input device, when the fluctuation of the read value caused by the fluctuation of the sensitivity of the sensor or the fluctuation of the light source is large, the input value of the line of the sensor is changed. , And a black and white peak value representing white of the background and black of the character is obtained from the density histogram distribution. By determining the threshold value with this reference value, binarization can always be performed correctly, but an image input device can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration of an image reading apparatus according to an embodiment of the present invention;

FIG. 2 is a diagram showing an image reading processing procedure according to an embodiment;

FIG. 3 is a specific configuration example of an image reading device;

FIG. 4 is a timing chart of image reading,

FIG. 5 is a configuration of an image reading apparatus according to a second embodiment,

FIG. 6 is a diagram showing a relationship between a read image signal and a density histogram,

FIG. 7 is a view for explaining an example in which the effective area is smaller than the reading range of the image reading apparatus;

FIG. 8 is a diagram illustrating image reading according to another embodiment;

FIG. 9 is a diagram showing a binarization processing procedure according to another embodiment;

FIG. 10 is a drawing showing still another binarization processing procedure;

FIG. 11 is a drawing showing still another binarization processing procedure;

FIGS. 12A and 12B are drawings showing a conventional binarization process.

Claims (6)

[Claims] An image reading apparatus for optically reading an image on a reading medium and converting the image into an electric signal, wherein an input data holding unit for temporarily holding input data and a density histogram distribution of the input data holding unit are generated. An image reading apparatus, comprising: a density histogram distribution generating unit that performs binarization; and a threshold generation unit that generates a binarization threshold from the density histogram distribution. 2. The image reading apparatus according to claim 1, further comprising a correction unit configured to perform shading correction of the input data, and storing the corrected input data in the input data storage unit. Image reading device. 3. The image reading apparatus according to claim 1, wherein the threshold value generation unit determines a white peak value (WP) of a paper white portion and a black peak value (BP) of a character black portion from the density histogram distribution generated by the density histogram distribution generation unit. 2. The image reading apparatus according to claim 1, wherein a threshold is generated under a condition of α × (WP−BP) + BP (0 <α <1). 4. The image reading apparatus according to claim 1, wherein the image reading apparatus generates a density histogram based on only input data within a limited range on one predetermined line. . 5. The image reading apparatus according to claim 1, wherein the input data holding unit reads a specific one line of a medium to be read, holds the read data in the input data holding unit, and generates a threshold value. apparatus 6. The input data holding unit according to claim 1, wherein the input data at the time of line reading is held at a ratio of one line to N lines (N: an integer of 1 or more) for reading. Image reading device.