JP2005059444A - Color image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently restrain toner consumption to the extent of making outputs useful. <P>SOLUTION: Color picture elements are converted to monochrome picture elements (Step T3) when the kind of a copy is judged as a monochrome copy (YES at Step T2). The density of color picture elements that are not color edge picture elements is converted to 1/n (n is a positive number) (Step T6) when the kind of a copy is judged as a business color copy (YES at Step T4). When the kind of a copy is judged as a color copy (NO at Step T4), the density of color picture elements is converted to 1/m (m is a positive number and <n) (Step T7). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus such as a digital color copying machine.

  Conventionally, based on color image data (red (R), green (G), and blue (B) density value data) of a document read by an image reading unit (such as a scanner), cyan (C), magenta ( There is known a color image forming apparatus capable of forming a full-color image by a so-called electrophotographic method by superimposing monochromatic toners of M), yellow (Y), and black (Bk) on a recording sheet.

Some color image forming apparatuses of this type can execute a mode (toner save mode) in which toner consumption during image formation is suppressed (see, for example, Patent Document 1). In the toner save mode, for example, the drive voltage of the developing device is reduced, the irradiation time when irradiating light based on image data to the surface of the photoconductor is shortened, or the number of pixels to which toner is attached is reduced. Thus, the image forming process is performed with a smaller amount of toner.
JP-A-6-14167

  Business color manuscripts that contain color images such as color letters and color line drawings (for example, graphs) but do not contain photographic images, unlike color manuscripts that contain photographic images, constitute the image outline. As long as the density of the edge pixel is maintained, the output can be used even if the density of the pixel that is not the edge pixel is low.

  On the other hand, a color document including a photographic image may not be used as an output unless the color and gradation changes of the entire image are smooth.

  Therefore, if the process suitable for the type of document is performed, the toner consumption can be more effectively suppressed. On the other hand, if the process suitable for the type of document is not performed, the output product cannot be used. End up.

  The present invention has been made under such background, and an object thereof is to provide a color image forming apparatus capable of efficiently suppressing toner consumption within a range of use as an output product.

  The invention described in claim 1 for achieving the above object includes an original reading unit (1, 2) for reading an image of an original, and an image based on the color image data of the original read by the original reading unit, A color image forming apparatus capable of transferring onto a recording sheet using a plurality of colors of toner, a document discriminating means (1, 12) for discriminating a document type, and a color pixel from each pixel of the document image Color pixel detecting means (1, 11, T1) for detecting the image, edge pixel detecting means (1, 13) for detecting edge pixels from each pixel of the document image, and the document type is determined to be a business color document In this case, the color image forming apparatus includes a non-edge color pixel density adjusting unit (1, 11, T6) that performs processing for reducing the density of color pixels other than the edge pixels.

  The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.

  The edge pixel is, for example, a pixel that forms the contour of an image.

  The business color manuscript is a manuscript that includes color images such as color characters and color line drawings (for example, graphs) but does not include photographic images.

  Business color manuscripts that include color images such as color letters and color line drawings, but do not contain photographic images, are different from color manuscripts that contain photographic images (color manuscripts other than business color manuscripts). As long as the density of the color pixel is maintained, it can be used as an output product even if the density of the color pixel other than the edge pixel is low.

  According to the configuration of the present invention, when the document type is determined to be a business color document, a process for reducing the density of the color pixels other than the edge pixels is performed. It is possible to efficiently suppress toner consumption.

  The invention according to claim 2 includes monochrome conversion processing means (1, 11, T3) for performing processing for converting color pixels into monochrome pixels when the document type is determined to be a monochrome document. The color image forming apparatus according to claim 1.

  Usually, the amount of toner used for full-color output using a combination of toners of a plurality of colors is larger than the amount of toner used for monochrome output using only black toner.

  According to the configuration of the present invention, when the document type is determined to be a monochrome document, it is possible to convert color pixels to monochrome pixels and output image data by monochrome output. Therefore, it is possible to efficiently suppress the toner consumption within a range where it is used as an output product.

  The invention according to claim 3 includes color pixel density adjusting means (1, 11, T7) for performing processing for lowering the density of color pixels when the document type is determined to be a color document that is not a business color document. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is a color image forming apparatus.

  A color document including a photographic image may not be used as an output unless the color and gradation changes of the entire image are smooth.

  According to the configuration of the present invention, when the document type is determined to be a color document that is not a business color document, the process is performed to reduce the density of all color pixels instead of some color pixels. The toner consumption can be efficiently suppressed within the range of use as a product.

  The rate at which the color pixel density adjusting unit lowers the density of the color pixel is preferably smaller than the rate at which the non-edge color pixel density adjusting unit reduces the density of the color pixels other than the edge pixels.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus including an image processing apparatus 1 according to an embodiment of the present invention.

  This image forming apparatus uses cyan (C), magenta (based on color image data (red (R), green (G), and blue (B) density value data) of a document read by the image reading unit 2). This is a digital color copying machine capable of forming a full-color image by a so-called electrophotographic system by superimposing monochromatic toners of M), yellow (Y) and black (Bk) on a recording sheet.

  The image reading unit 2 is provided with, for example, a scanner (not shown) for irradiating light toward the original, and the image data of the original is based on reflected light of light emitted from the scanner toward the original. Obtained as an electrical signal. More specifically, the scanner includes a light source for irradiating light toward the original and a CCD image sensor that receives reflected light from the original and outputs an electrical signal. The main scanning of the document is achieved by the electrical scanning in, and the sub scanning of the document is achieved by moving the light source in the sub scanning direction while irradiating light toward the document.

  The image processing apparatus 1 performs predetermined image processing on image data of a document read by the image reading unit 2. The image processing apparatus 1 includes a microcomputer and functionally includes an image processing unit 11, a document discrimination unit 12, an edge detection unit 13, and the like. The image data of the document read by the image reading unit 2 is input to the image processing unit 11, the document determination unit 12, and the edge detection unit 13.

  Based on the document image data input from the image reading unit 2, the document determination unit 12 determines whether the document type is a monochrome document, a business color document, or a color document (a color document other than a business color document). Can be determined. Here, the business color manuscript is a manuscript including a color image such as a color character or a color line drawing (for example, a graph) but not including a photographic image. Specific processing contents in the document discrimination unit 12 will be described later. Data of the discrimination result in the document discrimination unit 12 is input to the image processing unit 11.

  The edge detection unit 13 detects pixels (edge pixels) constituting the contour of the image based on the document image data input from the image reading unit 2. More specifically, each pixel constituting the document image is sequentially set as a target pixel, and a filter process using an edge detection filter (for example, a Laplacian filter) is performed on the density value of each RGB color of the target pixel and surrounding pixels. Then, the edge pixel is detected by comparing the filtered value with a predetermined threshold value. The detection result data in the edge detection unit 13 is input to the image processing unit 11.

  The image processing unit 11 performs image processing on the image data of the document input from the image reading unit 2 based on data input from the document determination unit 12 and the edge detection unit 13, and then performs the image processing. Is supplied to the image output unit 3. Then, in the image output unit 3, an image based on the image data after the image processing is transferred (output) to the recording paper, thereby achieving an image forming process.

  The configuration of the image output unit 3 is a known configuration including, for example, a photoconductor, a main charger, a developing device, a transfer device, and the like. That is, at the time of image formation, the surface of the substantially cylindrical photoconductor is uniformly charged by the main charger, and the surface of the photoconductor is irradiated with light based on image data, so that the surface of the photoconductor is so-called static. An electrostatic latent image is formed. A monochromatic toner is selectively attached to the surface of the photoconductor on which the electrostatic latent image is formed by a developing device to form a toner image. The toner image formed on the surface of the photoconductor is transferred to a recording sheet by the action of a transfer device.

  FIG. 2 is a block diagram showing the configuration of the document discrimination unit 12.

  Referring to FIG. 2, the document determination unit 12 includes a first color pixel detection unit 121, a color block detection unit 122, a first color line detection unit 123, a second color pixel detection unit 124, and a second color line detection unit 125. And the determination part 126 is functionally provided. The document image data from the image reading unit 2 is input to the first color pixel detection unit 121 and the second color pixel detection unit 124.

  In the first color pixel detection unit 121, based on the image data of the document from the image reading unit 2, for example, a color pixel (first pixel) that expresses a relatively dark color in a narrow range, such as a pixel constituting a color character. 1 color pixel) is detected. More specifically, each pixel constituting the document image is sequentially set as a target pixel, and difference values (| BG |, | GR |, and | RB |) of the RGB color values of the target pixel are set. And the difference values thereof are respectively compared with predetermined threshold values (THBG1, THGR1, and THRB1). When at least one of the following three conditions is satisfied, the target pixel is detected as the first color pixel.

・ | B-G | ≧ THBG1
・ | G-R | ≧ THGR1
・ | R-B | ≧ THRB1
In the second color pixel detection unit 124, based on the image data of the document from the image reading unit 2, for example, a color pixel that expresses a relatively light color in a wide range, such as a pixel constituting the background of color paper. (Second color pixel) is detected. More specifically, each pixel constituting the document image is sequentially set as a target pixel, and difference values (| BG |, | GR |, and | RB |) of the RGB color values of the target pixel are set. And the difference values thereof are respectively compared with predetermined threshold values (THBG2, THGR2, and THRB2). However, THBG1> THBG2, THGR1> THGR2, and THRB1> THRB2. When at least one of the following three conditions is satisfied, the target pixel is detected as the second color pixel.

・ | B-G | ≧ THBG2
・ | G-R | ≧ THGR2
・ | R-B | ≧ THRB2
The detection result data in the first color pixel detection unit 121 is input to the color block detection unit 122.

  FIG. 3 is a conceptual diagram for explaining a mode of processing in the color block detection unit 122. In FIG. 3, “1” shown for each pixel indicates that the pixel is the first color pixel, and “x” shown for each pixel indicates that the pixel is not the first color pixel. Represents.

  As shown in FIG. 3, in the color block detection unit 122, based on the detection result data from the first color pixel detection unit 121, the first color pixel is predetermined in each line (each row in the main scanning direction) of the document image. It is determined whether or not the threshold value THPIX1 (for example, “5”) is continuous.

  When the first color pixels are continuous for the threshold value THPIX1 or more in each line of the document image, the first color pixels are detected as one color block.

  Referring again to FIG. 2, the detection result data in the color block detection unit 122 is input to the first color line detection unit 123. The first color line detection unit 123 determines whether each line of the document image is the first color line based on the detection result data from the color block detection unit 122. More specifically, it is determined whether or not the number of color blocks included in each line of the document image is equal to or greater than a predetermined threshold value THBLK. If the number of color blocks is equal to or greater than the threshold value THBLK, the line is detected as the first color line.

  On the other hand, the detection result data in the second color pixel detection unit 124 is input to the second color line detection unit 125. Based on the detection result data from the second color pixel detector 124, the second color line detector 125 determines whether each line of the document image is a second color line. More specifically, it is determined whether or not the second color pixel continues for a predetermined threshold value THPIX2 or more in each line of the document image. If the second color pixel is continuous for the threshold value THPIX2 or more, the line is detected as the second color line. However, THPIX2> THPIX1.

  The determination unit 126 receives the detection result data from the first color line detection unit 123 and the detection result data from the second color line detection unit 125. In the determination unit 126, based on the detection result data in the first color line detection unit 123 and the detection result data in the second color line detection unit 125, the document type is a monochrome document, a business color document, or a color document. Which one is determined.

  The determination result data in the determination unit 126, the detection result data in the first color pixel detection unit 121, and the detection result data in the second color pixel detection unit 124 are input to the image processing unit 11.

  FIG. 4 is a flowchart showing the contents of processing in the determination unit 126.

  Referring to FIG. 4, determination unit 126 first includes a document image based on detection result data in first color line detection unit 123 and detection result data in second color line detection unit 125. The number of first color lines and the number of second color lines are calculated, and the number of lines (color lines) that are at least one of the first color line and the second color line is calculated (step S1).

  If the number of color lines is less than the predetermined threshold value THLINE (YES in step S2), that is, if the number of color lines included in the document image is relatively small, the document type is determined to be a monochrome document ( Step S3).

  If the number of color lines is equal to or greater than the threshold THLINE (NO in step S2) and the first color line number is larger than the second color line number (YES in step S4), that is, the number of color lines included in the document image If there are a large number of color pixels that express a relatively dark color in a narrow range, the type of the original is determined to be a business color original (step S5).

  When the number of color lines is equal to or greater than the threshold THLINE (NO in step S2) and the first number of color lines is equal to or less than the second number of color lines (NO in step S4), that is, the number of color lines included in the original image. If there are a large number of color pixels that express a relatively light color in a wide range, the type of the document is determined to be a color document (step S6).

  This image forming apparatus can execute a mode (toner save mode) in which toner consumption during image formation is suppressed. When the toner save mode is selected, the image processing unit 11 uses the data input from the document discrimination unit 12 (the discrimination result data in the discrimination unit 126, the detection result data in the first color pixel detection unit 121, and the first Image data of a document input from the image reading unit 2 based on data (detection result data in the two-color pixel detection unit 124) and data input from the edge detection unit 13 (data of detection result in the edge detection unit 13). Then, processing corresponding to the type of document (processing for suppressing toner consumption) is performed.

  FIG. 5 is a flowchart showing the contents of processing in the image processing unit 11.

  Referring to FIG. 5, in the image processing unit 11, first, based on the detection result data in the first color pixel detection unit 121 and the detection result data in the second color pixel detection unit 124, the first color pixel and A pixel (color pixel) that is at least one of the second color pixels is detected (step T1).

  If the document type is determined to be a monochrome document (YES in step T2), the density value of the color pixel is binarized and converted to a monochrome pixel (step T3), cyan (C), Image data from the image processing unit 11 to the image output unit 3 is not a full color output using a combination of magenta (M) and yellow (Y) single color toners, but a monochrome output using only black (Bk) toner. Is output.

  Normally, the amount of toner used for full-color output is larger than the amount of toner used for monochrome output. Therefore, by outputting image data in monochrome output, the toner can be efficiently used within the range that can be used as output. Consumption can be reduced.

  When it is determined that the document type is a business color document (NO in step T2 and YES in step T4), an edge pixel (color edge pixel) that is a color pixel is based on the detection result data in the edge detection unit 13. ) Is detected (step T5). Then, by converting the density value of the color pixel that is not the color edge pixel into a value of 1 / n (n is a positive number) (step T6), processing for reducing the density of the color pixel that is not the color edge pixel is performed. At this time, the density value of the color edge pixel is not converted.

  Business color manuscripts that include color images such as color letters and color line drawings, but do not contain photographic images, differ from color manuscripts that contain photographic images, as long as the color edge pixel density is maintained. Even if the density of the color pixels other than the color edge pixels is low, it can be used as an output product. Accordingly, when the type of document is determined to be a business color document, the processing for lowering the density of color pixels that are not color edge pixels is performed, so that it can be used as an output product. It is possible to efficiently suppress toner consumption.

  If it is determined that the document type is a color document (NO in step T4), the color pixel density value is converted to a value of 1 / m (m is a positive number and m <n). (Step T7) A process for reducing the density of the color pixel is performed.

  A color document including a photographic image may not be used as an output unless the color and gradation changes of the entire image are smooth. Therefore, when the type of document is determined to be a color document, a process for lowering the density of all color pixels, not some of the color pixels, is used as an output product. As a result, the toner consumption can be efficiently suppressed within the range of the above.

  However, when the type of document is determined to be a business color document or a color document, the process for suppressing the toner consumption is not limited to the process of converting the density value of each pixel to a lower value. For example, the driving voltage of the developing device is reduced, the irradiation time when irradiating the surface of the photoconductor with light based on image data is shortened, or the number of pixels to which toner is attached is reduced. May be.

  The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims.

  For example, the document discrimination method, the color pixel detection method, and the edge pixel detection method are not limited to those described above, and may be based on other methods.

  In the above-described embodiment, the digital color copying machine is described as an example of the image forming apparatus. However, the present invention is not limited to the digital color copying machine but can be applied to other image forming apparatuses such as a facsimile.

1 is a block diagram illustrating a schematic configuration of an image forming apparatus including an image processing apparatus according to an embodiment of the present invention. 3 is a block diagram illustrating a configuration of a document discrimination unit. FIG. It is a conceptual diagram for demonstrating the aspect of the process in a color block detection part. It is a flowchart which shows the content of the process in a determination part. It is a flowchart which shows the content of the process in an image process part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image processing apparatus 2 Image reading part 11 Image processing part 12 Document discrimination | determination part 13 Edge detection part

Claims (3)

A color image forming apparatus that includes an original reading unit for reading an image of an original and can transfer an image based on color image data of the original read by the original reading unit onto a recording sheet using a plurality of colors of toner. There,
A document discriminating means for discriminating a document type;
Color pixel detection means for detecting a color pixel from each pixel of the document image;
Edge pixel detection means for detecting edge pixels from each pixel of the document image;
A color image forming apparatus comprising: a non-edge color pixel density adjusting unit that performs processing for reducing the density of color pixels other than edge pixels when the document type is determined to be a business color document.   2. The color image forming apparatus according to claim 1, further comprising a monochrome conversion processing unit that performs processing for converting color pixels into monochrome pixels when the document type is determined to be a monochrome document.   3. A color image forming apparatus according to claim 1, further comprising color pixel density adjusting means for performing processing for reducing the density of color pixels when the document type is determined to be a color original that is not a business color original. .

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