JP5501425B2 - Image processing method, image processing apparatus, and program - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program for performing monochrome conversion of image data.

  In recent years, a shift from monochrome printers to color printers has progressed in the printer market. However, color printing and color copying are still expensive, and in many cases, color originals are often copied in black and white or printed in black and white.

  Among them, when copying or printing a color document in black and white or mono color, it is common for a document read by a reader composed of a plurality of channels of red, green, and blue to be image-processed into one black channel. is there. The process of converting the read color image into the black channel is hereinafter referred to as color / monochrome conversion.

  Regarding color / monochrome conversion, Patent Document 1 describes a method of separating a character, an image, and a background from a color document and converting the character into monochrome so that only the character can be easily read. Specifically, the luminance difference is obtained by comparing the luminance of the monochrome character data with the luminance of one of the monochrome image data and the monochrome background data. A method is described in which when the luminance difference is equal to or smaller than a predetermined value, the luminance of the monochrome character data is changed in a direction in which the luminance difference is increased.

  In normal color / monochrome conversion, there is a problem that characters drawn in yellow in a color original are difficult to see when printed in black and white or printed in black and white. Therefore, the reproducibility of the yellow pixels when the yellow pixels are converted to black and white is improved by setting the mixture ratio of the read red, green, and blue signals to a mixture ratio with high reproducibility of the yellow pixels. It was.

JP2003-283848

However, in the color / monochrome conversion with improved reproducibility of yellow pixels, there is a problem that invisible yellow security information embedded in a copied material becomes apparent by monochrome copying. It is not desirable to reveal the yellow security information by copying.
Patent Document 1 does not disclose a measure for reproducing yellow security information included in a document by monochrome copying.
Accordingly, an object of the present invention is to provide an image processing apparatus capable of performing monochrome output so that security information does not become apparent when a document including security information is read by a reading unit and converted into monochrome when the document includes security information. And providing a method.

  In order to achieve the above object, an image processing apparatus of the present invention has the following configuration.

An image processing apparatus having a reading unit that reads an original, and when outputting an image obtained by converting a color image generated by reading an original into a monochrome image on a recording medium, security information included in the color image The color image is converted into a monochrome image using a color / monochrome conversion method that converts the image so that it is difficult for human eyes to identify, and an image obtained by converting the color image generated from the job input from the external device into monochrome is recorded. When outputting on a medium, the color image is converted into a monochrome image by using a color / monochrome conversion method selected from the plurality of color / monochrome conversion methods via the operation unit of the external device or the image processing device. Conversion means.

Alternatively, when a monochrome image of a color image generated from a job generated by reading a document by a reading unit is output on a recording medium, security information included in the color image is difficult to identify with human eyes. An image obtained by converting the color image into a monochrome image using the color / monochrome conversion method for converting the image into a monochrome image and converting the color image generated from a job other than the job generated by reading by the reading unit into a monochrome image is recorded Conversion means for converting the color image into a monochrome image using a color / monochrome conversion method selected via an operation unit of an external device or an image processing device from among a plurality of color / monochrome conversion methods. Have

  According to the present invention, when a document including security information is read by a reading unit to generate a monochrome-converted image, and the generated image is output on a recording medium, it is difficult to identify the security information with human eyes. In this way, monochrome output is possible.

Block diagram of this embodiment Block diagram of the image processing unit 105 of the present embodiment Flow chart of the first embodiment Operation unit 109 of this embodiment The figure showing the change of the data which carried out the color monochrome conversion of a present Example Example of color input image and monochrome output image of this embodiment Example of color input image and monochrome output image of this embodiment Block diagram of the image processing unit 105 according to the second embodiment. Flow chart of embodiment 2 Example 2 Example of color input image and monochrome output image Flow chart of embodiment 3 Document Mode Setting Operation Unit 109 of Embodiment 3

Example 1
Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  A first embodiment of the present invention will be described with reference to the flowcharts of FIGS. FIG. 1 shows a configuration of an MFP 101 (Multi Function Peripheral) and a PC 102 (Personal Computer) that can perform image processing according to this embodiment. FIG. 3 is a flowchart showing the flow of processing of this embodiment. A program for realizing the flowchart of FIG. 3 is stored in the HDD 108. The stored program is read into the RAM 110, and the CPU executes the program, whereby the flowchart of FIG. 3 is executed.

  With reference to FIG. In FIG. 1, an MFP 101 and a PC 102 are connected via a network 103. The MFP 101 includes a scanner 104, an image processing unit 105, a printing unit 106, a CPU 107, an HDD 108, an operation unit 109, and a RAM 110.

  Next, FIG. 3 will be described. First, a case will be described in which data in a page description language (Page Description Language = PDL) is transmitted from a PC to a printer, and printing is performed by the printer.

  First, in S301 in FIG. 3, a print start is instructed by instructing printing from a UI (User Interface) of a driver (not shown) of the PC 102 in FIG. When printing is instructed in step S <b> 301, the PDL data stored in the PC 102 is sent to the image processing unit 105 via the network 103. In step S302, PDL data is received as a print job. In step S303, the PDL data is interpreted to determine whether to print the data in monochrome. If it is determined in S303 that the data is not to be printed in monochrome, the color printing is performed in S304. If it is determined in step S303 that the data is to be printed in monochrome, the process proceeds to step S305, and it is determined whether the data is a scan job (a job in which an original is read and generated by the scanner 104).

  In this case, it is not a scan job because of PDL, so the flow proceeds to color / monochrome conversion switching reference in S306, and the setting of the color / monochrome conversion method shown in FIG. 4 is referred to. Normally, sRGB is set, and in S307, equation (1) is set so that color monochrome conversion processing for sRGB is performed using equation (1).

ND1 = 0.21 x R2 + 0.72 x G2 + 0.07 x B2 (1)
In S306, the conversion method of color / monochrome conversion can be selected from sRGB 402, NTSC 403, and color equality 404 using the UI 401 of FIG. Conversion of color / monochrome conversion is performed. When NTSC 403 is selected, color / monochrome conversion of the NTSC conversion method is performed using equation (2). When the color equality 404 is selected, the color / monochrome conversion of the RGB color equalization method is performed using the equation (3).
ND1 = 0.3125 x R2 + 0.5625 x G2 + 0.1250 x B2 (2)
ND1 = (R2 + G2 + B2) / 3 (3)
Next, color / monochrome conversion is performed in S308, and monochrome printing is performed using a monochrome signal in S309.

  Here, the color / monochrome conversion performed in S308 of FIG. 3 will be described with reference to FIG. First, the input color space adjustment unit 202 performs input color space adjustment according to the color space of the input color data. When the color space of the input color data is sRGB, it is only necessary to pass sRGB as it is to the next processing, so the input color space adjustment unit 202 does not perform processing and passes the data to the color / monochrome conversion unit 203. The color / monochrome conversion unit 203 converts the RGB signal (R2, G2, B2) output from the input color space adjustment unit 202 into a monochrome ND1 signal using Expression (1). In this example, monochrome processing is described with a single channel signal of ND1, but there is also a method in which R = G = B and processing is performed with a plurality of signals, and finally one channel is obtained. FIG. 5 shows values obtained by signal conversion of ND1 (luminance) from the RGB signals (R2, G2, B2) output from the input color space adjustment unit 202.

In FIG. 5, for example, yellow (R, G, B) = (255, 255, 0) is converted into 237 by Expression (1). Next, in order to print, the luminance density conversion unit 204 converts the luminance signal into a density signal. For example, the luminance signal output from the color / monochrome conversion unit 203 is converted into a density signal using the following equation (4).
ND2 = −255 / 1.60 × LOG10 (ND1 / 255) (4)
Specifically, signal conversion from the input signal ND1 to the output signal ND2 is performed. In this example, a single channel signal of ND2 is described as monochrome, but there is also a method of processing with a plurality of C = M = Y signals to finally make one channel.

Further, it can be seen that the value of ND1 and the value of ND2 converted from (R2, G2, B2) are different depending on the sRGB method, NTSC method, or color equalization method set from the UI 401 in FIG.
For example, a yellow dot has a dot output density value of 5 when color monochrome conversion is performed using the sRGB method, and a dot output density value of 9 when color monochrome conversion is performed using the NTSC method. In addition, when yellow dots are subjected to color monochrome conversion by the RGB equalization method, the yellow dot signal that is difficult to see becomes the output density value 28, and it can be seen that the density is nearly three times larger.

  In actual printing, the yellow characters of the input color signals (R1, G1, B1) = (255, 255, 0) in FIG. 6A are converted into ND1 by the RGB monochrome color monochrome conversion in FIG. 6C. = 170 (luminance signal). Further, ND1 = 237 (luminance signal) is obtained by the sRGB color / monochrome conversion of FIG. It can be seen that yellow dots are darker and darker when the monochrome conversion is performed using the equal setting in FIG. 6C than when the monochrome conversion is performed using the sRGB setting in FIG. 6B. .

  Next, a case in which an original is read by a scanner (reading unit), copy processing, send processing, and fax transmission will be described. First, in S301 of FIG. 3, an instruction to scan and print a document from a UI (User Interface) of the operation unit 109 of FIG. 1 is issued. When instructed, the scanner 104 reads the document, and the document data is sent to the image processing unit 105 in FIG. In S302, the original data is received as a print job. In S303, it is determined whether the received job is a job for monochrome printing. If the received job is color printing designation instead of monochrome designation, color printing is performed in S304. Printing is executed. If it is determined in step S303 that the received job is a monochrome print job, it is determined in step S305 whether the job is a scan job. Since this job is a job read by the scanner, the process proceeds to step S307. In step S307, a predetermined color / monochrome conversion formula is set. The predetermined color / monochrome conversion formula is, for example, the color / monochrome conversion formula for sRGB described in formula (1). In S307, when an image obtained by monochrome conversion of security information (for example, yellow dots) is output on a recording medium, a color image including the security information is displayed as a monochrome image so that the security information is difficult to identify with human eyes. The conversion method to convert to is set.

  In step S308, color / monochrome conversion is performed using the color / monochrome conversion formula set in step S307. In step S309, monochrome printing is performed using the monochrome signal. Here, the color / monochrome conversion performed in S308 of FIG. 3 will be described with reference to FIG. First, the input color space adjustment unit 202 performs input color space adjustment according to the color space of the input color data. When the color space of the input color data is sRGB, it is only necessary to pass sRGB as it is to the next processing, so the input color space adjustment unit 202 does not perform processing and passes the data to the color / monochrome conversion unit 203. The color / monochrome conversion unit 203 converts the RGB signal (R2, G2, B2) output from the input color space adjustment unit 202 into a monochrome ND1 signal using Expression (1). For example, yellow (R, G, B) = (255, 255, 0) is converted into 237 by the expression (1). Next, in order to perform printing, the luminance density conversion unit 204 converts the luminance signal into a density signal. For example, the luminance signal output from the color / monochrome conversion unit 203 is converted into a density signal using Equation (4). Specifically, signal conversion from the input signal ND1 to the output signal ND2 is performed.

  When the input job is a scan job, the yellow dots in the document are converted by sRGB color monochrome conversion. As a result, the output density value becomes 5, and the density is very small (the larger the value, the darker). You can see that it is a signal.

  In actual printing, invisible yellow dots of the input color signals (R1, G1, B1) = (255, 255, 0) in FIG. 7A are converted into color monochrome conversion with sRGB setting, and FIG. Are converted into dots of ND1 = 237 (luminance signal) as shown in FIG. The converted dots are thin and difficult to see. Therefore, it can be seen that even if a color image to which yellow dots are added is converted into monochrome, the invisible yellow dots can be maintained. In the case of a PDL job, RGB equality can be selected as a color / monochrome conversion formula. When color / monochrome conversion is performed on yellow dots using the RGB equivalent color / monochrome conversion formula, invisible yellow dots are converted to ND1 = 170 (luminance signal) dots as shown in FIG. 7C. It can be seen that the converted dots are darker than the sRGB setting and are noticeable, and the dots are visible due to monochrome conversion, and the image quality deteriorates.

  In this embodiment, when the input job is PDL data, the color / monochrome conversion method can be selected from the sRGB method, the NTSC method, and the RGB color equalization method. However, when the input job is a scan job, color / monochrome conversion is performed by the sRGB method, and other color / monochrome conversion methods cannot be selected.

  This is because in the case of PDL data, yellow security dots that do not want to be revealed by monochrome conversion are not included in the PDL data. It will not become. However, in the case of a scan job, there is a possibility that yellow security dots may be included in the read document. Therefore, it is preferable that the color / monochrome conversion is performed by the sRGB method in which yellow dots do not appear by the color / monochrome conversion. In the case of a scan job, if color / monochrome conversion is performed using the RGB equalization method, the yellow security dots included in the original document become apparent as described above.

  It should be noted that a color / monochrome conversion method other than the sRGB method may be used as long as the yellow security dots contained in the document do not become apparent due to the color / monochrome conversion.

  In this embodiment, a plurality of monochrome conversion methods having different mixing ratios of RGB components of a color image, which are used when a color image is converted into a monochrome image, are provided. The plurality of monochrome conversion methods are, for example, the monochrome conversion method for sRGB of Equation (1), the monochrome conversion method for NTSC of Equation (2), and the RGB color equalization method of Equation (3). Then, it is determined whether the color image is an image generated by reading a document with a reading unit or an image (for example, PDL, PDF, or PS data) input from an external device. Then, when it is determined that the color image is an image generated by reading the document with the reading unit, the monochrome conversion in which the ratio of the B component is smaller than the other monochrome conversion methods among the plurality of monochrome conversion methods. A system (for example, a monochrome conversion system for sRGB) is set. Also, when it is determined that the color image is an image input from an external device, a monochrome conversion method (for example, NTSC method or the like) having a larger B component ratio than the other monochrome conversion methods among the plurality of monochrome conversion methods. Color equality method) is set. Note that when a color image is input from an external device, an sRGB method can also be set.

  As described above, according to the method of the first embodiment, the image data obtained by scanning the original is subjected to the color / monochrome conversion using the monochrome conversion method in which the yellow dots do not appear, so that the yellow dots are converted into monochrome. It is possible to prevent visualization of converted dots. A plurality of monochrome conversion methods can be selected for a PDL job. For example, when the RGB equalization method is selected by the user, it is possible to make yellow characters and yellow objects that are difficult to see in a color document appear in a monochrome image for easy viewing.

(Example 2)
In the first embodiment, when a document is scanned, the color / monochrome conversion method in the color / monochrome conversion unit 203 is fixed to the sRGB method for all images. In the second embodiment, the color / monochrome conversion method is fixed to the sRGB method for only yellow isolated pixels, and the color / monochrome conversion method can be selected for pixels other than the yellow isolated pixels. Thereby, for example, by performing monochrome conversion on pixels other than yellow isolated pixels by the RGB equalization method, dark dots can be generated in a monochrome image, and image quality degradation can be reduced.

  FIG. 8 shows the configuration of the image processing unit 105 in the second embodiment. In FIG. 8, an isolated point determination unit 801 is added to the configuration of the image processing unit 105 in FIG. The isolated point determination unit 801 detects yellow isolated dots from the input image signal. The pixel position of the isolated point detected by the isolated point determination unit 801 is input to the color / monochrome conversion unit 203, and the color / monochrome conversion unit 203 performs color / monochrome conversion on the yellow isolated pixel using the sRGB method. Thereby, yellow dots can be made difficult to see.

  The isolated point determination unit 801 determines yellow isolated dots using an isolated point detection method that has been conventionally used. For example, it is possible to determine a yellow isolated dot by determining whether the target pixel is yellow and then determining that there is no yellow pixel near the target pixel. Isolated points 1001 and 1002 in the color input image of FIG. 10A can be detected by the isolated point determination unit 801. The isolated point determination unit 801 generates the isolated point determination image shown in FIG. 10B, and reproduces the isolated point portion in black and the other portions in white.

  FIG. 9 is a flowchart obtained by adding isolated point determination to the flowchart of FIG. 3 of the first embodiment. The difference from the flowchart of FIG. 3 is that the isolated point determination of S901 is added. FIG. 9 is a flowchart illustrating a flow of processing according to the second embodiment. A program for realizing the flowchart of FIG. 9 is stored in the HDD 108. The stored program is read into the RAM 110, and the CPU executes the program, whereby the flowchart of FIG. 9 is executed.

  The processing of S301 to S309 in FIG. 9 is the same as the processing of S301 to S309 in FIG. In S901 of FIG. 9, the isolated point determination unit 801 determines an isolated point. If an isolated point exists, the position information of the isolated point is stored in the RAM 110 and the process proceeds to S307. If no isolated point exists, the process proceeds to S306.

  In the isolated point determination in S901, an isolated point determination image shown in FIG. 10B is generated, and the black pixel of the isolated point determination image is determined as an isolated point. When it is determined in S901 that there is an isolated point, the sRGB method is set for the pixel of the isolated point in S307, and color monochrome conversion of the sRGB method is performed in S308. By the SRGB monochrome conversion, the density of isolated point pixels becomes thin and difficult to be realized. In S901, for a pixel determined to be not an isolated point (a pixel other than an isolated point) (for example, an ellipse 1003 in FIG. 10A), the color monochrome selected by the user from a plurality of color monochrome conversion methods. Conversion method is applied. For example, if the RGB uniform method is selected in S306 with reference to the color / monochrome conversion method, the elliptical portion 1008 is reproduced with a high density as shown in FIG.

  As described above, according to the second embodiment, as a result of the monochrome conversion, the pixel of the yellow isolated dot is difficult to see (the density is small), and the pixel of the other yellow object is easily visible (the density is high). .

  In addition, since security dots are used by various companies, it is possible to reliably make it difficult to see invisible dots by registering the pattern.

(Example 3)
FIG. 11 is a flowchart obtained by adding the grandchild copy determination of S1101 to the flowchart of FIG. 3 of the first embodiment. The difference from the flowchart of FIG. 3 is that the grandchild copy determination of S1101 is added instead of S305 of FIG. FIG. 11 is a flowchart illustrating the processing flow of the third embodiment. A program for realizing the flowchart of FIG. 11 is stored in the HDD 108. The stored program is read into the RAM 110, and the CPU executes the program, whereby the flowchart of FIG. 11 is executed.

  The processes of S301 to S304 and S306 to S309 in FIG. 11 are the same as the processes of S301 to S304 and S306 to S309 in FIG. S1101 in FIG. 11 refers to the mode set in the original mode setting 1201 on the operation unit 109, and determines whether it is the grandchild copy mode. If it is determined in S1101 that the grandchild copy mode is set, the process proceeds to S307. If it is determined in S1101 that it is not the grandchild copy mode, the process proceeds to S306.

  Here, the grandchild copy mode is a mode for copying a copy of a document. Currently, in office machines, invisible dots are generally placed in a copy from the viewpoint of security. Therefore, in the grandchild copy mode, since there is a high possibility of copying a copy containing invisible dots, the color / monochrome conversion method is set to the sRGB method in order to prevent the invisible dots from being revealed as a result of the monochrome conversion.

  If the original mode is determined in S1101 and it is determined that the original mode is the grandchild copy mode, the sRGB method is set in S307, and the sRGB color / monochrome conversion is performed in S308. By the monochrome conversion of the sRGB method, the density of yellow dots is reduced and the yellow dots are not easily revealed. If it is determined in S1101 that the copy mode is not the grandchild copy mode, a color / monochrome conversion method selected by the user from a plurality of color / monochrome conversion methods is applied. For example, in S306, when the RGB uniform method is selected with reference to the color / monochrome conversion method, the density of yellow pixels that are not invisible dots is reproduced deeply.

  In the original mode setting 1201 of FIG. 12, the character mode 1203 is used when copying an original containing only pencil characters. The character printing mode 1202 is used when copying a halftone dot original that further includes characters.

(Example 4)
In the first, second, and third embodiments, PDL data received from the outside or data scanned by a scanner has been described. It goes without saying that the same effect can be obtained by storing these data in the HDD 108 and printing and printing from the HDD 108 by performing the same processing and determination as in the first, second, and third embodiments.

(Other examples)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (7)

An image processing apparatus having a reading unit for reading a document,
In the case where an image obtained by monochrome conversion of a color image generated by reading a document by the reading unit is output on a recording medium, color monochrome that converts security information included in the color image so that it is difficult for human eyes to identify When converting a color image into a monochrome image using a conversion method, and outputting an image obtained by converting a color image generated from a job input from an external device into a monochrome image on a recording medium, a plurality of color monochrome conversion methods are used. An image processing apparatus comprising: conversion means for converting the color image into a monochrome image using a color / monochrome conversion method selected from among the external devices or the operation unit of the image processing apparatus. When outputting on a recording medium an image obtained by converting a color image generated from a job generated by reading a document by a reading unit onto a recording medium, security information included in the color image is difficult to identify with human eyes. An image obtained by converting a color image generated from a job other than the job generated by converting the color image into a monochrome image using a color / monochrome conversion method for conversion and reading by the reading unit is recorded on a recording medium. When outputting, the image processing apparatus includes a conversion unit that converts the color image into a monochrome image using a color / monochrome conversion method selected from an external device or an operation unit of the image processing apparatus among a plurality of color / monochrome conversion methods. An image processing apparatus. Wherein the security information, the image processing apparatus according to claim 1 or 2, characterized in that the yellow dot. The external device or the color monochrome conversion method operating unit selected via the image processing apparatus, at least the NTSC system, sRGB mode, claims 1 to 3, characterized in that it is one of the methods of the RGB equivalent scheme The image processing apparatus according to any one of the above. An image processing method in an image processing apparatus having a reading unit for reading a document, wherein when a color image generated by reading a document by the reading unit is monochrome-converted and output on a recording medium, the color image Using a color / monochrome conversion method that converts the included security information so that it is difficult for the human eye to identify, the color image is converted to a monochrome image, and the color image generated from the job input from the external device is converted to monochrome. When outputting the image to a recording medium, the color image is converted using a color / monochrome conversion method selected from among a plurality of color / monochrome conversion methods via the external device or the operation unit of the image processing device. An image processing method comprising a conversion step of converting into a monochrome image. When outputting on a recording medium an image obtained by converting a color image generated from a job generated by reading a document by a reading unit onto a recording medium, security information included in the color image is difficult to identify with human eyes. An image obtained by converting a color image generated from a job other than the job generated by converting the color image into a monochrome image using a color / monochrome conversion method for conversion and reading by the reading unit is recorded on a recording medium. When outputting, a conversion step of converting the color image into a monochrome image using a color / monochrome conversion method selected from among a plurality of color / monochrome conversion methods via an operation unit of an external apparatus or an image processing apparatus. An image processing method. A program for causing a computer to function as the image processing apparatus according to any one of claims 1 to 4 .