JP2008172677A - Image processor and ground color detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of accurately detecting a ground color on the basis of the image data of a color system for which components relating to brightness and components relating to hues are separated, and a color judgement method. <P>SOLUTION: The YCC image data (image data expressed in YCbCr color space) of an original are acquired on the basis of RGB image data acquired by reading the prescribed region of an original, and a luminance histogram h indicating the luminance distribution of the image data is prepared. Then, a section wherein a degree exceeds a prescribed threshold W in the luminance histogram h is extracted as a recording object section R, and the image data belonging to the recording object section R are detected as ground color image data due to the ground color of the original. The luminance component and color difference component of the ground color image data are recorded as the maximum/minimum values of the color region of the base color, and the base color included in the original is specified. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus having a function for detecting the background color of a document and a method for detecting the background color of a document.

  In the present specification, “brightness” includes “brightness” (for example, Y component in the YCbCr color system) as brightness as a side light amount and “brightness” (for example, brightness as perceptual color). L * a * b * L component in the color system). “Color” is a component separated from “brightness” in a three-dimensional color space. For example, Cb component and Cr component (color difference component) in the YCbCr color system, L * a * b * The a component and b component in the color system correspond to this.

  Among image processing devices that perform various types of processing on image data obtained by reading a document, such as facsimile machines, copiers, and printers, select a processing mode according to the color of the image data to be processed. There is something that can be done. For example, when the image is color, the image processing is executed in a processing mode suitable for a color image, and when the original is monochrome, the image processing is executed in a processing mode suitable for a monochrome image. By switching the processing mode in this way, it is possible to execute appropriate processing according to the color of the document.

  In order to select such a processing mode, it is necessary to determine the color of image data to be processed. Therefore, a color determination function (so-called ACS (Auto Color Selection) function) that automatically determines whether image data to be processed is color or monochrome has been devised.

  In the color determination function, there may be employed a method of first detecting the background color of the document (background color existing in the document) and determining the color of the document based on the detection result of the background color. First, by identifying the background color of the document and determining the color of the document from the color distribution of the image data excluding the background color, for example, a document with black characters written on a yellow background is not a color image but a monochrome image It can be judged.

  A technique for detecting the ground color is disclosed in Patent Document 1, for example. Here, a histogram is created for each of the R value, G value, and B value (that is, tristimulus values of the RGB color system) of the image data, and the vicinity of the section with the highest frequency is determined as the ground color range. Yes.

  Further, in Patent Document 2, when creating a histogram for each of the R value, G value, and B value of image data, the memory capacity necessary for creating the histogram is increased by creating a histogram with the upper 5 bits of the data. Techniques for reducing are disclosed.

JP 2001-313832 A JP 2000-22971 A

  Incidentally, RGB color system image data acquired by a reading device such as a CCD line sensor is difficult to handle in color adjustment processing and the like, and therefore, a color system (for example, a component related to brightness and a component related to color are separated) , YCbCr color system, L * a * b * color system, etc.).

  For example, in a copying machine, RGB color system image data obtained by reading a document is converted into a YCbCr color system or L * a * b * color system, and various image processing (for example, image correction processing) is performed. In many cases, the image data is converted into CMYK image data and printed out.

  Therefore, instead of the RGB color system, it is based on image data of a color system in which a component related to brightness and a component related to color are separated, such as the YCbCr color system and the L * a * b * color system. There is a need for technology to detect ground color.

  The present invention has been made in view of such circumstances, and accurately detects a ground color based on colorimetric image data in which a component related to brightness and a component related to color are separated. An object of the present invention is to provide an image processing apparatus and a color determination method capable of performing the above.

  The invention according to claim 1 is an image processing apparatus having a function of detecting a ground color of a document based on color system image data in which a brightness component and a color component are separated, and the image data A brightness histogram creating means for creating a brightness histogram showing a distribution of brightness components; a recording target section detecting means for detecting a section whose frequency exceeds a predetermined value in the brightness histogram as a recording target section; Image data belonging to the recording target category is detected as ground color image data resulting from the ground color of the document, and the ground color included in the document is determined based on the brightness component and the color component of the ground color image data. Ground color detection means for specifying.

  According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, first image data acquisition means for acquiring image data of a first area of the original as first image data, and first of the original A second image data acquisition means for acquiring the image data of the area 2 as the second image data, and a histogram showing the distribution of the brightness component of the first image data with a first section width, A refined histogram creation means to acquire, and a ground color latent area extracting means for identifying a section with the highest frequency in the refined histogram and extracting a section area including the section as a ground color latent area, and the brightness A histogram creating means generates a brightness histogram indicating a distribution of the brightness component of the second previous image data in the ground color latent area according to the first section width. Also created in fine second section width.

  A third aspect of the present invention is the image processing apparatus according to the second aspect, wherein the maximum degree value in the brightness histogram is smaller than a value obtained by converting the maximum degree value in the narrowed histogram into the second section width. An error detecting means for determining that the detection of the ground color image data has failed.

  The invention of claim 4 is the image processing apparatus according to any one of claims 1 to 3, wherein the ground color detection means detects the recording target section when the recording target section detection means detects the recording target section. Image data counted thereafter as image data belonging to the recording target section is detected as the ground color image data.

  A fifth aspect of the present invention is the image processing apparatus according to any one of the first to fourth aspects, wherein the color system is a YCbCr color system, and the brightness component is a luminance component.

  The invention according to claim 6 is a method for detecting the ground color of the document based on the color system image data in which the brightness component and the color component are separated, wherein the brightness component of the image data A brightness histogram creating step for creating a brightness histogram showing a distribution, a recording target category detecting step for detecting a category whose frequency exceeds a predetermined value in the brightness histogram as a recording target category, and the recording target category A ground color for detecting ground image data belonging to the background color of the document and identifying a ground color included in the document based on the brightness component and the color component of the ground color image data A detection step.

  According to the first and sixth aspects of the present invention, it is possible to detect the ground color based on the color component image data in which the component related to brightness and the component related to color are separated, particularly based on the brightness component. . In addition, image data belonging to a section whose frequency exceeds a predetermined value in the brightness histogram is determined as ground color image data resulting from the ground color of the document. That is, it is determined that the image data belonging to the section whose frequency is less than the predetermined value is not the ground color image data. According to this configuration, since the image data caused by other than the ground color is not erroneously detected as the ground color image data, the ground color can be accurately detected.

  According to the second aspect of the present invention, the ground color latent area is first identified using the histogram having the first section width, and the brightness histogram of the ground color latent area is finer than the first section width. Therefore, the ground color can be detected with high accuracy while saving hardware resources, as compared with the case of creating a brightness histogram over the entire brightness component.

  According to the third aspect of the present invention, when the maximum value of the frequency of the brightness histogram is smaller than the value obtained by converting the maximum value of the frequency of the narrowed histogram into a fine section width (second section width), that is, narrowing down If the ground color latent area specified in the histogram is not appropriate as the ground color area, it is determined that the ground color detection has failed, so that a situation in which the ground color is erroneously detected can be prevented.

[First Embodiment]
<1. Constitution>
<1-1. Digital MFP>
A configuration of a digital multi-function peripheral 1 incorporating a function of an image processing apparatus corresponding to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a digital multi-function peripheral 1 according to an embodiment of the present invention.

  The digital multi-function peripheral 1 is configured as a multi-function peripheral (MFP apparatus) having a plurality of functions such as a FAX function, a copy function, a scan function, and a print function. The digital multi-functional peripheral 1 includes a control unit 11, a ROM 12, a RAM 13, a flash memory 14, an operation unit 15, a display unit 16, an image processing unit 17, an image reading unit 18, an image recording unit 19, The image memory 20, the large-capacity storage unit 21, and the communication-related functional units 22 to 25 are electrically connected via a bus line 26.

  The control unit 11 is composed of a CPU. The control unit 11 controls each of the above hardware units based on a program stored in the ROM 12 to realize the functions of the digital multi-function peripheral 1.

  The ROM 12 is a read-only storage device that stores programs and data necessary for controlling the digital multifunction machine 1 in advance.

  The RAM 13 is a storage device that can be read and written, and temporarily stores various data that are temporarily stored, such as image data, FAX numbers, and mail addresses, and data that is generated during arithmetic processing by the control unit 11. Remember. The RAM 13 is composed of SRAM or the like.

  The flash memory 14 is a non-volatile memory in which stored contents can be rewritten, and stores various types of information that should be retained continuously.

  The operation unit 15 includes various keys such as character keys, numeric keys, and function keys, and accepts user operations such as input of commands and text data. The user operation received by the operation unit 15 is input to the control unit 11 as a signal. The control unit 11 controls the operation of each unit based on a user operation.

  The display unit 16 is a display device that displays the operation state of the digital multi-function peripheral 1, image data, and the like, and includes a display device such as a liquid crystal display. Various keys provided on the operation unit 15 may be realized by a touch panel provided on the display screen of the display unit 16.

  The image processing unit 17 is a processing unit that performs various image processes on the received image data and the image data acquired from the image reading unit 18. For example, A / D conversion, various correction processes (for example, shading correction and gamma correction), and color system conversion process (for example, matrix conversion converts RGB color system image data to YCbCr color system image data. Conversion processing), color adjustment, image synthesis, and the like. The image processing unit 17 may be realized by software by a program stored in the ROM 12.

  The image reading unit 18 is a scanner that reads an image on a document with a reading element (CCD line sensor 181). The image data acquired by the image reading unit 18 is compressed by, for example, the JPEG method by the CODEC 22 and stored in the image memory 20. The image reading unit 18 may be a scanner of a type (FBS (Flat Bed Scanner)) type in which a reading element scans the surface of a document placed on a glass table and reads the image. This is a type (ADF type) scanner that transports a document placed on a table (not shown) by an ADF (Auto Document Feeder), scans the surface of the transported document with a stationary reading element, and reads an image. May be. The ADF method includes a method of reading a moving document with a stationary reading optical system (sheet-through method) and a method of reading a stationary document with a moving reading optical system. Good. When the latter method is adopted, the image reading unit 18 repeatedly executes a reading procedure in which the original is stopped on the contact glass, the stationary original is read by the moving reading optical system, and the original that has been read is discharged. .

  The CCD line sensor 181 receives light guided from the reading optical system that scans the document at a predetermined scanning speed (relative movement speed between the document and the reading optical system), and repeats reading at a constant cycle. Image data expressed in the RGB color space, that is, image data (RGB image data) having R (red), G (green), and B (blue) color component data is generated. Note that the scanning speed of the reading optical system is set based on the resolution of the image data generated by the CCD line sensor 181 (more specifically, the resolution in the sub-scanning direction). That is, the higher the resolution in the sub-scanning direction, the slower the scanning speed of the reading optical system is set, and the lower the resolution in the sub-scanning direction, the higher the scanning speed of the reading optical system.

  The image recording unit 19 is a printer that records image data and the like stored in the image memory 20 on a recording sheet. For the image recording unit 19, for example, an electrophotographic printer can be employed.

  The image memory 20 temporarily stores image data received from the external devices 29, 32, and 34 through the LAN I / F 24 and the NCU 25, image data acquired by the image reading unit 18, image data processed by the image processing unit 17, and the like. Is a storage device. The image memory 20 is configured by a memory such as a DRAM capable of reading and writing.

  The large capacity storage unit 21 is configured by a hard disk or the like. The large capacity storage unit 21 can store the image data processed by the image reading unit 18.

  Further, the digital multi-function peripheral 1 includes a codec (CODEC) 22 that encodes / decodes image data and the like corresponding to a plurality of protocols, and a modem 23 that modulates and demodulates transmission / reception data as communication-related functional units. In addition, a LAN I / F 24 corresponding to an interface with a LAN (local area network) 27 and an NCU 25 that controls opening / closing of a telephone line are electrically connected via a bus line 26.

  As encoding by CODEC 22, when binary data is encoded, MH (Modified Huffman), MR (Modified Read), MMR (Modified MR), and JBIG (Joint Bi-level Image experts Group). Either method is adopted. The CODEC 22 also encodes multi-value data. Multi-level data is encoded by, for example, the JPEG method.

  Next, the communication environment of the digital multifunction device 1 will be described. The digital multifunction device 1 is connected to the LAN 27. A mail server 28 and an external terminal 29 are connected to the LAN 27. The LAN 27 is connected to the Internet 31 through a router 30 and the like. With this configuration, the digital multifunction peripheral 1 can perform e-mail communication with the external terminal 29 connected via the LAN 27 and the external terminal 32 connected via the Internet 31. Further, the digital multi-function peripheral 1 is connected to a PSTN (Public Switched Telephone Network) 33 which is a data communication network for analog lines. Thus, the digital multi-function peripheral 1 can communicate with the external terminal 34 connected via the PSTN 33. The external terminals 29, 32, and 34 are personal computers connected by modems, devices similar to the digital multi-function peripheral 1, fixed telephones, mobile phones, FAX dedicated machines, and the like.

<1-2. Color judgment function>
The digital multi-function peripheral 1 has a function (so-called ACS function) for determining the color of multi-tone image data (for example, image data of a document read by the image reading unit 18).

  In this color determination function, first, the background color of the document is detected. More specifically, as shown in FIG. 2, the background color of the document is detected based on the image data obtained by reading the front area P of the document divided into a plurality of areas.

  Then, in response to the ground color detection result, the color of the document is determined based on the image data obtained by reading the subsequent block area Bi (i = 1, 2,...). That is, it is determined whether the document is a color image, a gray image, a binary image, or a blank sheet (colored sheet). More specifically, a color distribution of the image data is created by masking the previously detected ground color area, and the color of the document is determined based on the color distribution. For example, in the case of a document in which black characters are written on a yellow background, the color distribution of only the black existing on the document can be obtained by creating a color distribution of the document by masking the color area of the detected ground color. Therefore, it can be determined that the document is monochrome instead of color.

  In response to the color determination result, the digital multi-function peripheral 1 selects a processing mode for processing the image data. For example, if the document is determined to be a color image, the process is executed in “color mode”, and if it is determined to be a gray image or a binary image, the process is executed in “monochrome mode”. By changing the operation mode according to the color determination of the document, it is possible to increase the operation efficiency of the apparatus and to execute appropriate processing according to the color type of the image.

  When the image data acquisition process is executed in the color mode, the image processing unit 17 uses the multi-gradation YCC image data of the document (that is, the multi-gradation RGB image data acquired by the image reading unit 18 reading the document). The CODEC 22 compresses the multi-gradation YCC image data (image data expressed in the YCbCr color space) into the image memory 20 using the JPEG method or the like.

  When the image data acquisition process is executed in the monochrome mode, first, the image processing unit 17 binarizes the luminance component of the multi-tone YCC image data of the document. However, in this binarization processing, the systematic dither method or the like is used when the document is a gray document, and the simple binarization method or the like is used when the document is a monochrome document. Then, the CODEC 22 compresses the obtained two-tone data of the YCC image data by the MMR method or the like and stores it in the image memory 20.

  When executing the image data recording process in the color mode, first, the multi-tone L * a * b * image data of the original (that is, the multi-tone RGB image data acquired by the image reading unit 18 reading the original). Is converted into multi-gradation Lab image data (image data expressed in Lab color space) by the image processing unit 17, and the multi-tone CMYK image data is converted by the image processing unit 17. The image data is converted into (image data expressed in a CMYK color space), and the obtained multi-tone CMYK image data is binarized into two-tone CMYK image data. Subsequently, the image recording unit 19 forms an image of the obtained two-tone CMYK image data on a recording sheet. More specifically, a necessary image forming engine (an image forming engine necessary for expressing a color included in an image) among “Y”, “M”, “C”, and “K” image forming engines is used. To form an image. For example, if the color classification of the color included in the image is only “Y”, only the image forming engine “Y” is operated. If the color classification of the color included in the image is “R”, only the “Y” and “M” image forming engines are operated.

  When executing the image data recording process in the monochrome mode, first, the image processing unit 17 binarizes the luminance component of the multi-tone YCC image data of the document. Subsequently, the image recording unit 19 forms an image of the obtained two-tone luminance component on the recording paper using the “K” image forming engine.

<1-3. Configuration related to ground color determination>
The background color determination function in the digital multi-function peripheral 1 will be described with reference to FIG. FIG. 3 is a block diagram showing a configuration relating to ground color determination. The digital multifunction peripheral 1 detects the brightness component of the ground color as a configuration related to ground color determination (more specifically, detects the maximum value and the minimum value of the brightness component (Y component) of the ground color in the YCbCr color space. The ground color luminance determination unit 101 detects the color component of the ground color (more specifically, the maximum and minimum values of the color difference components (Cb component and Cr component) of the ground color in the YCbCr color space are detected. A ground color difference determination unit 102. The ground color area in the YCbCr color space is detected by the ground color brightness area detected by the ground color brightness determination unit 101 and the ground color difference area detected by the ground color difference determination unit 102. Each of these functional units is a component realized by the control unit 11 executing a program.

<Ground color luminance judgment part>
The ground color luminance determination unit 101 includes a first front region data acquisition unit 111, a second front region data acquisition unit 112, a narrowed histogram generation unit 113, a ground color latent region specification unit 114, and a luminance histogram generation unit 115. , A recording target category detection unit 116, a luminance maximum / minimum value recording unit 117, and a histogram evaluation unit 118.

  The first previous data acquisition unit 111 acquires the image data of the first half area (first front area P1) (see FIG. 2) of the previous area P as “first front area data dP1”. More specifically, the image processing unit 17 performs predetermined processing (converts RGB image data into YCC image data) for the RGB color system image data acquired by the image reading unit 18 reading the first front area P1. Image data (YCC image data) obtained by performing a matrix transformation process and various correction processes is acquired as first pre-region data dP1. Note that data in units of “unit images” may be created from data in units of “pixels” by causing the image processing unit 17 to execute a predetermined averaging process. The “unit image” is an image composed of n pixels (n is a natural number) adjacent to each other, and the data of the unit image is an average value of n pixel data included in the unit image. When the image processing unit 17 performs the averaging process, the first previous area data acquisition unit 111 acquires the unit image data of the first previous area as the first previous area data dP1.

  The second front area data acquisition unit 112 acquires the image data of the rear half area (second front area P2) (see FIG. 2) of the front area P as “second front area data dP2”. More specifically, the image processing unit 17 performs predetermined processing (converts RGB image data into YCC image data) for the RGB color system image data acquired by the image reading unit 18 reading the second front area P2. Image data (YCC image data) obtained by performing a matrix conversion process, various correction processes, an averaging process, etc.) is acquired as second pre-region data dP2.

  The narrowed-down histogram creating unit 113 creates a histogram indicating the luminance distribution of the first previous area data dP1 and obtains it as “a narrowed-down histogram ho”. More specifically, the entire area that can be taken by the luminance component of the YCC image data (for example, the area of luminance value 0 to luminance value 255 in the case of 256 gradations) is defined as a predetermined division number T1 (for example, T1 = 16 (16 A histogram is created by counting the number of elements of the first previous area data dP1 belonging to each section (see FIG. 4).

  The ground color latent area specifying unit 114 specifies the section having the highest frequency (the luminance maximum section M1 of the first previous area) in the narrowed-down histogram ho. Then, the section area including the specified maximum brightness section M1 is extracted as the “ground color latent area S”. The ground color latent area S is an area that the ground color latent segmented area specifying unit 114 roughly determines that a ground color luminance area is included. More specifically, the ground color latent segment area specifying unit 114 notifies the luminance histogram creating unit 115 of the maximum luminance segment M1 and a segment area obtained by adding segments adjacent to both sides of the segment as the ground color latent area S. (See FIG. 4). When the region of the luminance value 0 to the luminance value 255 is divided into 16, the region including the maximum luminance division M1 and three divisions including the front and rear divisions adjacent to the division M1 is set as the ground color latent region S. If the ground color latent area S is set in this way, it has been confirmed by the inventors of the present application that the ground color luminance area is surely included in the ground color latent area S.

  The luminance histogram creation unit 115 creates a histogram indicating the luminance distribution of the second previous region data dP2 in the ground color latent region S, and acquires it as “luminance histogram h”. More specifically, each of the divisions included in the ground color latent area S is divided by a predetermined division division number T2 (for example, T2 = 4 (four divisions)), and the second previous area data dP2 belonging to each division A histogram is created by counting the number of elements (see FIG. 4).

  Therefore, the narrowed-down histogram has a relatively rough first section width, and the luminance histogram has a relatively fine second section width. In other words, the second section width is smaller than the first section width, and the second section width in the illustrated example is “one integer” (specifically, ¼) of the first section width. Each section in these examples corresponds to a unit section called “class” in histogram terms.

  The recording target section detection unit 116 detects a section whose frequency exceeds a predetermined threshold W as the recording target section R in the luminance histogram h (see FIG. 4). The threshold W is an arbitrary value set in advance, and may be defined based on, for example, the number of data elements included in the second previous area data dP2. In addition, the determination criterion corresponding to the threshold value may be determined not as the frequency itself but as a frequency ratio (a ratio occupied in the total number of pixels for which a histogram is created). “Frequency” in this specification includes a case where it is expressed by an occupation ratio or a ratio value.

  The luminance maximum / minimum value recording unit 117 detects data belonging to the recording target section R as data (ground color image data) caused by the background color of the document, and uses the luminance component of the data as the background color luminance (ground color luminance). ) Is recorded as the maximum value (or minimum value). More specifically, when a notification indicating that a specific luminance category is set as the recording target category R is received from the recording target category extracting unit 116, the luminance as data belonging to the recording target category R is received after the notification is received. The data counted by the histogram creation unit 115 is detected as ground color image data. If the detected brightness value of the ground color image data is larger than the currently recorded maximum ground color brightness value, the brightness value of the data is recorded as a new maximum value. Further, in the case of a value smaller than the currently recorded minimum value of the ground color luminance, the luminance value of the data is recorded as a new minimum value.

  The histogram evaluation unit 118 evaluates whether or not the luminance histogram h is a ground color region histogram. More specifically, in the brightness histogram h, the section having the maximum data count (the brightness maximum section M2 of the second previous region) is specified. Then, the frequency value of the specified luminance maximum section M2 of the second previous area is a value obtained by converting the power value of the luminance maximum section M1 of the first previous area into the same classification width as the luminance histogram h (that is, the first previous area). The luminance histogram h is determined not to be a histogram of the ground color area when it is smaller than the value obtained by dividing the frequency value of the maximum luminance division M1 by the value of the division division number T2. That is, it is determined that the ground color detection has failed. In this case, the histogram evaluation unit 118 performs predetermined error processing.

<Background color difference judgment part>
The ground color difference determination unit 102 includes a color difference maximum / minimum value recording unit 121.

  The color difference maximum / minimum value recording unit 121 converts the color difference component (that is, each of the Cb component and Cr component) of the data detected by the luminance maximum / minimum value recording unit 117 as the ground color image data to the color difference of the ground color (ground color difference). ) Is recorded as the maximum value (or minimum value). More specifically, when the color difference value of the data detected as the ground color image data by the brightness maximum / minimum value recording unit 117 is larger than the maximum value of the ground color difference currently recorded, the color difference of the data Record the value as the new maximum. If the value is smaller than the minimum value of the ground color difference currently recorded, the color difference value of the data is recorded as a new minimum value.

<2. Processing action>
Next, background color determination processing performed as one process of color determination processing in the digital multi-function peripheral 1 will be described with reference to FIGS. The ground color determination process is executed in three stages of a first process, a second process, and a third process.

<2-1. First treatment>
The first process is a process for roughly specifying the luminance area of the ground color. The first process will be described with reference to FIGS. 4 and 5. FIG. 4 is a diagram for explaining the narrowing-down histogram ho and the luminance histogram h. FIG. 5 is a diagram showing the flow of the first process in the ground color determination process.

  First, the first previous area data acquisition unit 111 acquires the first previous area data dP1 (step S11).

  Subsequently, the narrowed-down histogram creating unit 113 creates a histogram indicating the brightness distribution of the first previous area data dP1 acquired in step S11 (the brightness distribution in all areas that can be taken by the brightness component of the YCC image data), and the narrowed-down histogram. Acquired as ho (see FIG. 4) (step S12).

  When the processing in step S12 is completed, the ground color latent area specifying unit 114 subsequently selects the section with the highest frequency (the maximum brightness section M1 in the first previous area) in the narrowed-down histogram ho created in step S12. Specify (step S13).

  Subsequently, the ground color latent area specifying unit 114 specifies, as the ground color latent area S, a divided area obtained by adding the sections before and after the section M1 to the luminance maximum section M1 of the first previous area specified in step S13. The specified ground color latent area S is notified to the luminance histogram creating unit 115 (step S14). Thus, the first process is completed, and then the second process is performed.

  In step S14 of the first process, it is determined whether or not the frequency value of the luminance maximum section M1 of the first previous region is larger than a predetermined threshold value. The background color determination process may be terminated without performing the second process by determining that it has failed.

<2-2. Second treatment>
The second process is a process of further narrowing down the ground color luminance region (ground color latent region S) roughly specified in the first process and specifying the maximum and minimum values of the ground color luminance and the ground color difference. . The second process will be described with reference to FIGS. 4 and 6. FIG. 6 is a diagram showing the flow of the second process in the ground color determination process.

  First, the second previous area data acquisition unit 112 acquires the second previous area data dP2 (step S21).

  Subsequently, the luminance histogram creating unit 115 displays a histogram (luminance) indicating the luminance distribution of the second previous area data dP2 acquired in step S21 (the luminance distribution in the ground color latent area S notified in step S14 of the first process). Creation of the histogram h) is started (step S22).

  Subsequently, the recording target category detection unit 116 determines whether or not a category whose frequency exceeds a predetermined threshold W is detected in the luminance histogram h (step S23).

  When it is determined in step S23 that the division whose frequency exceeds the predetermined threshold W is detected, the recording target category extracting unit 116 notifies the luminance maximum / minimum value recording unit 117 as the recording target category R ( Step S24).

  The luminance maximum / minimum value recording unit 117 determines whether there is data newly counted by the luminance histogram creating unit 115 as data belonging to the recording target section R (step S25).

  If it is determined in step S25 that there is newly counted data as data belonging to the recording target section R, the luminance maximum / minimum value recording unit 117 detects the data as ground color image data. Then, the detected luminance component of the ground color image data is recorded as the maximum value (or minimum value) of the ground color luminance (step S26). Further, the color difference maximum / minimum value recording unit 121 records the detected color difference component of the ground color image data as the maximum value (or minimum value) of the ground color difference (step S27).

  When the count of all data included in the second previous area data dP2 is completed (YES in step S28), the luminance maximum / minimum value recording unit 117 uses the maximum / minimum values recorded at that time as the ground color luminance. The maximum and minimum values are determined (step S29). Similarly, the color difference maximum / minimum value recording unit 121 determines the maximum / minimum value recorded at that time as the maximum / minimum value of the ground color difference (step S30). Thus, the second process is completed, and then the third process is performed.

<2-3. Third treatment>
The third process is a process of determining whether or not the maximum / minimum values of the ground color brightness and the ground color difference specified in the second process can be adopted as the ground color brightness and the ground color difference. The third process will be described with reference to FIGS. 4 and 7. FIG. 7 is a diagram showing the flow of the third process in the ground color determination process. The following processing is executed by the histogram evaluation unit 118.

  First, in the narrowed-down histogram ho created in step S12 of the first process, the frequency value N1 of the section having the maximum data count (the maximum brightness section M1 of the first previous region) is acquired (step S31).

  Subsequently, in the brightness histogram h created in step S22 of the second process, the section having the maximum data count (the brightness maximum section M2 of the second previous area) is specified, and the frequency value N2 of the section is determined. Obtain (step S32).

  Subsequently, a value (converted value) obtained by converting the power value N1 acquired in step S31 into the same segment width as the luminance histogram h is acquired (step S33). However, the conversion value is obtained by dividing the frequency value N1 by the value of the division division number T2 (T2 = 4 in the case of FIG. 4).

  Subsequently, it is determined whether or not the frequency value N2 acquired in step S32 is smaller than the converted value acquired in step S33 (step S34). If the frequency value N2 is smaller than the converted value, a negative evaluation is given to the luminance histogram h. That is, in this case, the ground color latent area S in the first process has failed to be identified (that is, the ground color does not exist in the ground color latent area S identified in the first process), and the ground color image data is detected. Therefore, it is determined that the ground color luminance and the ground color difference maximum / minimum values specified in the second process should not be adopted as the ground color area. Conversely, if the frequency value N2 is not smaller than the converted value, a positive evaluation is given to the luminance histogram h. That is, in this case, it is determined that the ground color latent area S has been successfully identified in the first process, and the ground color image data has been properly detected. It is determined that the minimum value can be adopted as the ground color area.

  When a negative evaluation is obtained in step S34, the histogram evaluation unit 118 performs a predetermined error process (for example, a process for notifying the control unit 11 of the background color detection failure) (step S35). In this case, the ground color determination process is terminated because the detection of the ground color has failed.

  If a positive evaluation is obtained in step S34, the ground color luminance determining unit 101 stores the maximum and minimum values of the ground color luminance determined in step S28 of the second process as the ground color luminance range (step S36) The maximum / minimum value of the ground color difference determined in step S29 is stored as a ground color difference range (step S37). Thus, the ground color determination process ends.

<3. effect>
According to the above embodiment, the background color can be easily detected using the value of the brightness component based on the image data expressed in the color system in which the brightness component is separated, such as YCC image data. can do.

  In addition, image data belonging to a section whose frequency exceeds a predetermined threshold W in the luminance histogram h is detected as ground color image data. In other words, it is determined that image data belonging to a category whose frequency is less than a predetermined value is not ground color image data, and luminance component values and color difference component values of such image data are recorded as maximum and minimum values of the ground color region. do not do. According to this configuration, image data caused by a color other than the ground color (for example, dust attached to the ground color) is not erroneously detected as ground color image data. Therefore, it is possible to correctly detect the ground color and accurately identify the color region of the ground color.

  Further, according to the above embodiment, the narrowed-down histogram ho is generated in the first process to roughly specify the luminance area of the ground color, and the luminance area (ground color latent potential) specified in the first process is specified in the second process. A luminance histogram h is created for the region S) to further narrow down the luminance region of the ground color, and specify the maximum and minimum values of the ground color luminance and the color difference. Here, the brightness histogram h is not a histogram covering the entire brightness area, but a histogram for the ground color latent area S is created and the ground color is detected, so that the ground with high accuracy can be obtained without complicating the circuit and processing. Color detection can be performed.

  If the luminance area of the background color of the document is properly detected as the background color latent area S in the first process, a sufficient luminance deviation exists in the luminance histogram h that is the brightness distribution of the second previous area data dP2. . That is, the frequency value N2 of the luminance maximum section M2 in the second previous region is never smaller than the converted value. On the other hand, when the luminance area of the background color of the document is not properly detected as the background color latent area S (for example, only the leading end portion (first front area) of the document is discolored, and the luminance area of the discolored color) Is mistakenly detected as the ground color latent area S), there is no sufficient luminance bias in the luminance histogram h. That is, the power value of the maximum luminance division M2 in the second front area is smaller than the converted value. In the above-described embodiment, the histogram evaluation unit 118 determines that the frequency value N2 of the luminance maximum segment M2 of the second previous region in the luminance histogram h is the frequency value N1 of the luminance maximum segment M1 of the first previous region in the narrowed-down histogram ho. Is smaller than the converted value converted to the same segment width as the luminance histogram h, and if it is smaller, it is determined that the ground color detection has failed and a predetermined error processing is performed, so the ground color is incorrect. Can be prevented in advance.

[Second Embodiment]
A digital multifunction peripheral 2 incorporating the function of an image processing apparatus corresponding to the second embodiment of the present invention will be described. In the following, points that differ from the first embodiment will be described, and descriptions of points that are not different will be omitted. Moreover, when showing the same component, the reference numerals used in the description of the first embodiment are used.

  The digital multifunction device 2 has the same hardware configuration as that of the digital multifunction device 1 according to the first embodiment (see FIG. 1), and has a function of determining the color of multi-gradation image data.

<1. Configuration related to ground color detection>
The background color determination function in the digital multi-function peripheral 2 will be described with reference to FIG. FIG. 8 is a block diagram showing a configuration related to ground color determination. The digital multifunction peripheral 2 includes a ground color luminance determination unit 201 that detects a brightness component of a ground color and a ground color difference determination unit 202 that detects a tint component of the ground color as a configuration related to ground color determination. . A ground color region in the YCbCr color space is detected by the ground color luminance region specified by the ground color luminance determination unit 201 and the ground color difference region detected by the ground color difference determination unit 202. Each of these functional units is a component realized by the control unit 11 executing a program.

<Ground color luminance judgment part>
The ground color luminance determination unit 201 includes a previous area data acquisition unit 211, a luminance histogram creation unit 212, a recording target category detection unit 213, and a luminance maximum / minimum value recording unit 214.

  The previous area data acquisition unit 211 acquires the image data of the previous area P (see FIG. 2) as the previous area data dP. More specifically, for the RGB color system image data acquired by the image reading unit 18 reading the previous area P, the image processing unit 17 performs predetermined processing (a matrix for converting RGB image data into YCC image data). Image data (YCC image data) obtained by performing conversion processing, various correction processing, averaging processing, and the like) is acquired as the previous region data dP.

  The luminance histogram creation unit 212 creates a histogram indicating the luminance distribution of the previous area data dP and acquires it as the luminance histogram h. More specifically, the entire area that can be taken by the luminance component of the YCC image data (for example, the area of luminance value 0 to luminance value 255 in the case of 256 gradations) is divided by a predetermined number of divisions before A histogram is created by counting the number of elements of the area data dP (see FIG. 9).

  The recording target section detection unit 213 detects a section whose frequency exceeds a predetermined threshold W as the recording target section R in the luminance histogram h (see FIG. 9).

  The luminance maximum / minimum value recording unit 214 detects data belonging to the recording target section R as ground color image data, and records the luminance component of the data as the maximum value (or minimum value) of the ground color luminance. Specific processing executed by the luminance maximum / minimum value recording unit 214 is the same as that of the luminance maximum / minimum value recording unit 117.

<Background color difference judgment part>
The ground color difference determination unit 202 includes a color difference maximum / minimum value recording unit 221.

  The color difference maximum / minimum value recording unit 221 records the color difference component of the data detected by the luminance maximum / minimum value recording unit 214 as the ground color image data as the maximum value (or minimum value) of the ground color difference. The specific processing executed by the color difference maximum / minimum value recording unit 221 is the same as that of the color difference maximum / minimum value recording unit 121.

<2. Processing action>
Next, ground color determination processing performed as one process of color determination processing in the digital multi-function peripheral 2 will be described with reference to FIGS. 9 and 10. FIG. 9 is a diagram for explaining the luminance histogram h. FIG. 10 is a diagram illustrating the flow of the ground color determination process.

  First, the previous area data acquisition unit 211 acquires the previous area data dP (step S101).

  Subsequently, the histogram creation unit 212 starts creating a histogram (luminance histogram h) indicating the brightness distribution of the previous region data dP acquired in step S101 (step S102).

  Subsequently, the recording target category detection unit 213 determines whether or not a category whose frequency exceeds a predetermined threshold W is detected in the luminance histogram h (step S103).

  When it is determined in step S103 that the division whose frequency exceeds the predetermined threshold W has been detected, the recording target category detection unit 213 notifies the luminance maximum / minimum value recording unit 214 of the category as the recording target category R ( Step S104).

  The luminance maximum / minimum value recording unit 214 determines whether or not there is data newly counted by the luminance histogram creation unit 212 as data belonging to the recording target section R (step S105).

  If it is determined in step S105 that there is newly counted data as data belonging to the recording target section R, the luminance maximum / minimum value recording unit 214 detects the data as ground color image data. Then, the detected luminance component of the ground color image data is recorded as the maximum value (or minimum value) of the ground color ground color luminance (step S106). Further, the color difference maximum / minimum value recording unit 221 records the detected color difference component of the ground color image data as the maximum value (or minimum value) of the ground color difference (step S107).

  When the counting of all data included in the second previous area data dP2 is completed (YES in step S108), the luminance maximum / minimum value recording unit 214 sets the maximum / minimum values recorded at that time as the ground color luminance. The maximum / minimum value is stored (step S109). Similarly, the color difference maximum / minimum value recording unit 221 stores the maximum / minimum value recorded at that time as the maximum / minimum value of the ground color difference (step S110). Thus, the ground color determination process ends.

<3. effect>
According to the above embodiment, as in the first embodiment, the value of the brightness component is based on the image data expressed in the color system in which the brightness component is separated, such as YCC image data. The ground color can be easily detected by using. Further, it is determined that the image data belonging to the category whose frequency does not satisfy the predetermined threshold W is not ground color image data, and the luminance component value and color difference component value of such image data are set as the maximum and minimum values of the ground color region. Since it is not recorded, it is possible to correctly detect the ground color and accurately specify the color region of the ground color.

[Modification]
In the first embodiment described above, first, the ground color luminance area is roughly narrowed down in the first process, and the ground color brightness area narrowed down in the first process is further narrowed down in the second process. The maximum and minimum luminance values are specified. That is, the luminance of the ground color is detected by two stages of processing. This may be configured to detect the luminance of the ground color through three or more stages of processing.

  For example, when the ground color luminance is detected in three stages, the following process may be performed. That is, first, in the first process, a first narrowed histogram in which the luminance area is divided by a predetermined number of divisions is created. And the maximum frequency division in the said 1st narrowing-down histogram is detected, and the ground color latent area containing the said division is specified. That is, the ground color luminance region is roughly narrowed down. In the subsequent second process, a second narrowed histogram is created by further dividing the ground color latent area specified in the first process by a predetermined number of divisions. And the maximum frequency division in the said 2nd narrowing-down histogram is detected, and the ground color latent area containing the said division is specified. That is, the luminance area of the ground color is further narrowed down. In the subsequent third process, a luminance histogram is created by further dividing the ground color latent area specified in the second process by a predetermined number of divisions, and the maximum value and minimum value of the ground color luminance are specified based on the luminance histogram. To do.

  In each of the above embodiments, the ground color determination is performed based on the YCC image data, but various color systems (for example, L * a *) in which the brightness component and the color component are separated. (b * color system, YIQ color system, Luv color system, etc.) image data can be determined in the same manner.

  In each of the above embodiments, the ground color is determined based on the data obtained by reading the front area of the document. However, the present invention is not limited to this. The ground color determination may be performed using, for example, image data of a part of the rear end of the target image or the front end of the right end.

  In each of the above-described embodiments, the ground color luminance determination units 101 and 201 and the ground color difference determination units 102 and 202 are components realized by the control unit 11 executing a program. Alternatively, it may be realized in a circuit (hardware) manner.

1 is a block diagram showing a configuration of a digital multifunction peripheral according to an embodiment of the present invention. It is a figure which shows typically the front area | region which divided | segmented the original into several area | regions. It is a block diagram which shows the structure regarding a ground color determination. It is a figure explaining a narrowing-down histogram and a brightness | luminance histogram. It is a figure which shows the flow of the 1st process in a ground color determination process. It is a figure which shows the flow of the 2nd process in a ground color determination process. It is a figure which shows the flow of the 3rd process in a ground color determination process. It is a block diagram which shows the structure regarding a ground color determination. It is a figure explaining a brightness | luminance histogram. It is a figure which shows the flow of a ground color determination process.

Explanation of symbols

1, 2 Digital MFP 101, 201 Ground color luminance determination unit 102, 202 Ground color difference determination unit 111 First previous area data acquisition unit 112 Second previous area data acquisition unit 113 Narrowed histogram creation unit 114 Background color latent division area specification 115, 212 Luminance histogram creation unit 116, 213 Recording target category extraction unit 117, 214 Luminance maximum / minimum value recording unit 118 Histogram evaluation unit 121, 221 Color difference maximum / minimum value recording unit 211 Pre-region data acquisition unit

Claims (6)

An image processing apparatus having a function of detecting a ground color of a document based on color system image data in which a brightness component and a color component are separated,
A brightness histogram creating means for creating a brightness histogram indicating the distribution of the brightness component of the image data;
In the brightness histogram, a recording target section detection means for detecting a section whose frequency exceeds a predetermined value as a recording target section;
Image data belonging to the recording target category is detected as ground color image data resulting from the ground color of the document, and a ground color included in the document based on the brightness component and the color component of the ground color image data Ground color detection means for identifying
An image processing apparatus comprising: The image processing apparatus according to claim 1,
First image data acquisition means for acquiring image data of the first region of the document as first image data;
Second image data acquisition means for acquiring image data of the second region of the document as second image data;
A narrowed histogram creating means for creating a histogram indicating the distribution of the brightness component of the first image data with a first section width and acquiring the histogram as a narrowed histogram;
In the narrowed-down histogram, a ground color latent area extracting unit that identifies a section having the highest frequency and extracts a section area including the section as a ground color latent area;
With
The brightness histogram creating means creates a brightness histogram showing a distribution of the brightness component of the second previous image data in the ground color latent area with a second section width smaller than the first section width. An image processing apparatus. The image processing apparatus according to claim 2,
An error detection means for determining that the detection of the ground color image data has failed when a maximum power value in the brightness histogram is smaller than a value obtained by converting the maximum power value in the narrowing histogram into the second section width;
An image processing apparatus comprising: The image processing apparatus according to any one of claims 1 to 3,
The ground color detecting means is
When the recording target section detection unit detects the recording target section, image data that is subsequently counted as image data belonging to the recording target section is detected as the ground color image data. apparatus. The image processing apparatus according to any one of claims 1 to 4,
An image processing apparatus, wherein the color system is a YCbCr color system, and the brightness component is a luminance component. A method for detecting the background color of a document based on color system image data in which a brightness component and a color component are separated,
A brightness histogram creating step of creating a brightness histogram showing a distribution of the brightness component of the image data;
In the brightness histogram, a recording target section detection step of detecting a section whose frequency exceeds a predetermined value as a recording target section;
Image data belonging to the recording target category is detected as ground color image data resulting from the ground color of the document, and a ground color included in the document based on the brightness component and the color component of the ground color image data A ground color detection process for identifying
A ground color detection method comprising:

Images