JPH1175073A - Image processing unit, image processing method, and record medium recording image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a processing efficiency of a black/white image by accurately discriminating a color image from the black/white image, and accurately discriminating the black/white image including a medium tone component and the black/white image not including it and using only the image not including the medium tone component as the black/white image. SOLUTION: The processing unit is provided with a read section 10 that obtains plural color signal data (RGB) from each pixel of an image and a color.black/white image discrimination section 25 of the read section 10 discriminates the image to be a black/white image not including a medium tone image when a gradation level difference of each of color signal data (RGB) is <= a prescribed value and a mean value of gradation levels of each of the color signal data (RGB) is <= a 1st threshold level or >= a 2nd threshold level that is higher than the 1st threshold level in the all pixels of the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus applied to a color facsimile apparatus, an image processing method used in the apparatus, and a recording medium storing an image processing program for executing the method.

[0002]

2. Description of the Related Art In recent years, facsimile machines and copying machines (copiers) have been developed that can read color images. Is increasing. In this type of image processing apparatus, generally, an image corresponding to each of the three primary colors of light (RGB) is read by an optical color sensor, and these are mixed to form a color image.

[0003] The data of the formed color image is encoded in the case of a facsimile apparatus and transmitted to another facsimile apparatus, and in the case of a copying machine, color printing is performed from a printer on recording paper. .

[0004]

However, in the above-described conventional image processing apparatus, even if a black-and-white image is read, the same image processing as that for a color image is performed. And the communication time for facsimile transmission has also been long. For example, when an A4-size original is read at a resolution of 200 dpi, if a color image is expressed by full-color 8-bit color, even if it can be compressed (encoded) to about 1/20 by JPEG or the like, the data is On the other hand, for a black-and-white image, the MH or MR
When compressed by codes, the data amount becomes several tens KB.

[0005] In addition, when an image including a photograph or the like is expressed as a halftone image by an error diffusion method or the like, even if the image is a black and white image, compression may not be expected depending on the image. The present invention has been made in view of such circumstances, and accurately distinguishes a color image from a black-and-white image, and even a black-and-white image including a halftone portion and a black-and-white image not including the halftone portion. Image processing apparatus, image processing method and recording medium in which an image processing program is recorded, in which only an image that does not include a halftone portion is converted to a black-and-white image, and the processing efficiency when the image is a black-and-white image is increased. It is intended to provide.

[0006]

In order to achieve the above object, an image processing apparatus according to a first aspect of the present invention includes a reading unit for obtaining a plurality of color signal data from each pixel of an image. In all pixels of the image, the gradation level difference of each color signal data is equal to or less than a predetermined value, and the average value of the gradation levels of each color signal data is equal to or less than a first threshold. Is larger than or equal to the second threshold, the image is determined to be a black-and-white image that does not include a halftone image.

Here, as a first condition, that the gradation level difference of each color signal data is equal to or smaller than a predetermined value means that the gradation levels of each color signal data are substantially equal.
For example, if the color signal data is three types of RGB, and if the three gradation levels are equal, the pixel is an achromatic pixel that has no color and can be expressed stepwise only with lightness from white to black. Indicates that there is.

As a second condition, a condition that the average value of the gradation levels of each color signal data is equal to or less than the first threshold value is that the pixel is a black pixel by satisfying the first condition.
The fact that the average value of each gradation level is equal to or greater than a second threshold value that is larger than the first threshold value indicates that the pixel is a white pixel.
Therefore, if both conditions are satisfied, the image can be determined to be a monochrome image that does not include a halftone image (gray level).

The color signal obtained by the reading unit is generally RGB (red, green, blue) which is an additive color expression.
Data signals such as subtractive CMYK (cyan, magenta, yellow, and black) and color-sensitive CIE XYZ may be used. Claim 2 proposes an image processing method used by the image processing device according to claim 1. That is, in this image processing method, a plurality of color signal data is read from each pixel of the image, and the gradation level difference of each color signal data is equal to or less than a predetermined value in all the pixels of the image, and When the average of the gradation levels is equal to or less than the first threshold or equal to or greater than the second threshold that is larger than the first threshold, the image is processed as a black-and-white image not including a halftone image.

[0010] Claim 3 proposes a recording medium in which an image processing program for executing the image processing method according to claim 2 is recorded. That is, the recording medium is read by the image processing apparatus according to the first aspect, and thereafter, the image processing is performed according to the program. Note that the recording medium includes a ROM and a hard disk in addition to a floppy disk and an optical disk.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of the image processing apparatus. Here, the configuration of the color facsimile apparatus F is shown as one of the image processing apparatuses, but the present invention is not limited to this, and is also applicable to a color copier, an image scanner, and the like.

The CPU 1 not only controls each unit of the facsimile apparatus F but also executes a facsimile communication procedure. The image memory 2 temporarily stores data such as facsimile communication. The ROM 3 stores a program for controlling the operation of the facsimile machine F in advance.
The RAM 4 stores not only temporary data generated during execution of the processing but also a facsimile number (telephone number) of the other party in advance.

The medium reading section 5 reads an image processing program from a recording medium fd such as a floppy disk. The read program is executed by the CPU 1 together with the program stored in the ROM 3 in advance. The modem 6 modulates and demodulates a signal for facsimile communication. NCU 7 closes communication line L (analog line),
Open. When connecting a digital line such as an ISDN line, a DS 6 is used instead of the modem 6 and the NCU 7.
It has an ISDN interface to connect to U.

The image codec 8 converts a monochrome binary image to MH
In addition to encoding / decoding using an encoding method such as RM or MR, a color image is encoded / decoding using an encoding method such as JPEG or JBIG. When a color image is encoded, RGB color signal data is converted into XYZ color system data, and further converted into Lab color system data, and then the above encoding is performed.

The operation panel 9 is a facsimile machine F
Operating means such as various keys for performing various input settings for
The facsimile apparatus F is configured by a display means such as a liquid crystal display device or an LED for displaying an operation state and an operation procedure of the facsimile apparatus F. The reading unit 10 reads a color image from a set document. That is, a plurality of color signal data such as RGB is obtained from each pixel of the image. The recording unit 11 is configured by a color printer, and records (prints out) data received from another facsimile machine or the like or data read from the reading unit 10 on recording paper.

The facsimile machine F is operated by an operation panel 9
The image data read from the reading unit 10 by the operation described above is encoded by the image codec 8, temporarily stored in the image memory 2, and sequentially transmitted through the communication line L, while the image data received through the communication line L is temporarily The basic operation of storing the data in the image memory 2 and sequentially printing out the data from the recording unit 11 while decoding the image codec 8 is performed.

The present invention has a feature in the processing in the reading unit 10. If it is determined that the read image is composed of only a black and white image, a black and white binarization process is performed, so that the image is compared with a color image. The amount of encoded data can be greatly reduced. FIG. 2 is a block diagram illustrating the configuration of the reading unit 10. In the figure, reference numeral 20 denotes the three primary colors of light (R
GB) An optical color sensor that reads the same image three times separately, an analog processing unit 21 that processes the read color signal as an analog signal, and an A / D converter 22 that converts an input analog signal into a digital signal and outputs the digital signal. A shading correction unit for correcting shading distortion and high-frequency distortion to obtain image data free from unevenness in illumination of the light source and unevenness in sensitivity of the sensor 20; and 24, color signal data ( An input masking section for correcting RGB) is a black-and-white / color discriminating section for discriminating between a black-and-white image and a color image, which is a feature of the present invention, and 26 and 27 are based on a discrimination result of the black-and-white / color discriminating section 25, respectively. hand,
A color processing unit and a black-and-white processing unit that perform processing on each image.

The color signal data read by the color sensor 20 is subjected to shading correction and input masking as a digital signal.
It is determined whether the image is a black-and-white image or a color image. When the image is determined to be a color image, the color expression is changed from the RGB method to the CMYK method by the color processing unit 26 as usual, and then the error diffusion method is used. The signal is converted into a multi-valued color signal, printed out from the recording unit 11 as a color image, or transmitted by facsimile after being encoded by the image codec 8.

On the other hand, when it is determined that the image is a monochrome image, the image is converted into binary data by the monochrome processing unit 27 and
Facsimile after being encoded by
The recording unit 11 prints and outputs a monochrome image. In addition,
In the figure, the black-and-white processing unit 27 processes only the G signal, but is not limited to this, and other signals and
The logical product of a plurality (2 or 3) of signals may be the target.

The monochrome / color discriminating section 25 discriminates whether or not the image is a monochrome image based on the color signal data of all the pixels of the predetermined image. Specifically, the gradation level difference of each color signal data of each pixel is equal to or less than a predetermined value, and
When the average value of the gradation levels of each color signal data is equal to or less than the first threshold value or equal to or greater than the second threshold value which is larger than the first threshold value, the image is determined to be a monochrome image not including a halftone image.

The predetermined image includes a document unit (multiple pages) image, a page unit image, and the like. However, in consideration of the processing capability and the actual use form, the image type (black and white) is set for each page. / Color) is appropriate.
Here, that the gradation level difference of each color signal data is equal to or smaller than a predetermined value means that the gradation levels of each color signal data are substantially equal, that is, the pixel is expressed stepwise from uncolored white to black. Indicates that the pixel is an achromatic pixel.

In addition, that the average value of the gradation levels of each color signal data is equal to or less than the first threshold value means that the pixel is a black pixel because the condition of the achromatic color is satisfied, and the average value is the first pixel value.
Being greater than or equal to the second threshold greater than the threshold indicates that the pixel is a white pixel. Therefore, if both conditions are satisfied, the image can be determined to be a black and white image that does not include a halftone image (gray level).

These conditions are expressed by the following equations.

[0024]

(Equation 1)

[0025]

(Equation 2)

In equation (1), since the absolute value of the difference between the gradation level value of each color signal data and its average value is equal to or less than a predetermined value (k), there is almost no difference in the gradation level of each color signal data. Is determined. Therefore, the predetermined value (k)
Is ideally a positive numerical value close to “0”. On the other hand, in Expression 2, the average of the gradation level values of the respective color signal data is smaller than the first threshold value (α) which is a criterion for determining a black pixel, or the second threshold value (β ), It is determined whether the average of the gradation level values of each color signal data is larger.

That is, both formulas determine that the tone level values of the respective color signal data are almost the same, and that the values are either black and white values. Next, Equation 2 will be described with reference to FIG. For example, when the AA 'line of a black-and-white image as shown in (a) is read, the RGB gradation distribution at that time is as shown in (b). Here, the gradation level is divided into 256 levels from 0 to 255. When a white background portion is read, the gradation level value becomes 230, and when a black background portion is read, the gradation level value becomes 20. Become. Therefore,
In this case, the first threshold (α) in Expression 2 may be set to a value slightly larger than 20, and the second threshold (β) may be set to a value slightly smaller than 230.

FIG. 4 shows the operation of the above two equations as black / white /
4 shows an example of a circuit configuration in a case where the color determination circuit 25 performs the processing in hardware. Therefore, a division circuit 25a for calculating the average of the RGB gradation level values, a subtraction circuit 25b for calculating the gradation level difference, and a comparator 25c for comparing each of the threshold values (k, α, β). , 25d, 25e, etc. With such a configuration, a determination signal (for example, “1” for a monochrome image and “0” for a color image) is output from the input color signal. The subtraction circuit 25b
Indicates that the three calculations in Equation 1 are performed.

FIG. 5 is a flowchart (100 to 105) showing a case where the calculation of the black / white / color discriminating circuit 25 is performed by software. Here, only when all the pixels of all the scanning lines of one page satisfy the conditions of Expressions 1 and 2, the image of the page is determined to be a black and white image, The processing shifts to processing (104). Step 1 is also used here.
00 indicates that the three calculations in Equation 1 are being performed.

An image processing program for executing such an image processing method is executed by the medium reading unit 5.
It can be read from the recording medium fd. Thus, the image processing apparatus can provide the reading unit 10 with the functions of the black-and-white / color discriminating unit 25 and the black-and-white processing unit 27 in addition to the conventional color image processing function simply by reading this program.

[0031]

As can be understood from the above description, in the image processing apparatus according to the first aspect of the present invention, each pixel is determined based on the color signal data of all the pixels of the read image as follows. If the two conditions are satisfied, the image is determined to be a monochrome image that does not include a halftone image. The first condition is that the gradation level difference of each color signal data is equal to or less than a predetermined value, and the second condition is whether the average value of the gradation levels of each color signal data is equal to or less than a first threshold value. , Which is greater than or equal to a second threshold larger than the first threshold. That is, if the gradation levels of the respective color signal data are almost the same and the level is one of the white pixels and the black pixels, it is determined that the image is a monochrome image.

If a monochrome image can be determined in this way, the amount of data can be greatly reduced as compared with the case where the image is processed as a normal color image. At the time of transmission, communication time can be reduced, and communication costs can be saved. According to the image processing method of the present invention, a monochrome image can be easily extracted from a color image, and the subsequent processing efficiency can be improved.

Further, since the image processing program for executing the image processing method according to the second aspect is recorded on the recording medium according to the third aspect, the image processing apparatus can be read only by reading this recording medium. A function of discriminating between a color image and a black-and-white image is provided. When the image is discriminated as a black-and-white image, the processing efficiency can be greatly improved as compared with a color image.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of the overall configuration of an image processing apparatus according to the present invention.

FIG. 2 is a block diagram illustrating an example of a configuration of a reading unit.

FIG. 3 is a diagram for explaining processing of a reading unit.

FIG. 4 is a diagram illustrating an example of a circuit configuration that implements processing of a reading unit.

FIG. 5 is a flowchart illustrating an example of an operation of a reading unit.

[Explanation of symbols]

 F: color facsimile apparatus 1: CPU 5: medium reading unit 8: image codec 10: reading unit fd: recording medium 20: color sensor 25: monochrome / color Discrimination unit 26: color processing unit 27: black-and-white processing unit α: first threshold β: second threshold

Claims (3)

[Claims] 1. A reading unit for obtaining a plurality of color signal data from each pixel of an image, wherein the reading unit has a gradation level difference of each color signal data of not more than a predetermined value in all pixels of the image, When the average value of the gradation levels of the respective color signal data is equal to or less than the first threshold value or equal to or greater than the second threshold value which is larger than the first threshold value, the image is determined to be a monochrome image not including a halftone image. An image processing apparatus characterized by the above-mentioned. 2. A method for reading a plurality of color signal data from each pixel of an image, wherein a gradation level difference of each color signal data is equal to or less than a predetermined value and a gradation level of each color signal data in all pixels of the image. An image processing method that processes the image as a black-and-white image that does not include a halftone image when the average value is equal to or less than a first threshold value or equal to or greater than a second threshold value that is larger than the first threshold value. 3. A recording medium on which an image processing program for executing the image processing method according to claim 2 is recorded.