JP2008271364A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for determining with high accuracy as to whether a colorless original is monochromatic. <P>SOLUTION: It is determined whether the original read by a read section is colorless, and when it is, a luminance counter 306 extracts the luminance components of the original to generate a histogram. When the number of distribution is larger than the counted number obtained by multiplying a maximum value of an appearing peak by 0.5, in a region darker than a ground color region of the generated histogram, it is decided that the original is gray. Alternatively, it is decided that the original is gray, when the gray count of a block exceeds the gray count threshold, in a region that is darker than the ground color region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing apparatus capable of automatically determining whether a read original is monochrome or gray.

  In recent years, there has been proposed an image processing apparatus having an automatic color determination (ACS) function for automatically determining whether or not a read document is color (Patent Document 1). In this case, if the RGB (Red Green Blue) signals for one line match, it is determined that the color is achromatic, that is, black and white. Furthermore, if these signals are either 0V or 1V, it is determined as monochrome, and if they are intermediate values between 0 and 1V, they are determined as gray.

Japanese Patent Laid-Open No. 2001-285587

  However, as described above, whether or not the RGB signal is an intermediate value is a very ambiguous standard, and whether the image represented by the signal is the background color of the document is significant. It seems not to be able to make an accurate judgment as to whether it is an image. Therefore, an object of the present invention is to provide a technique for determining with high accuracy whether monochrome or gray when an achromatic color is determined.

In order to solve the above-described problem, the first invention provides a reading unit that reads a document, an extraction unit that extracts a brightness component of the document, and a predetermined number of brightness components extracted by the extraction unit. A generating unit that divides into regions and creates a histogram of count numbers, and a peak that detects a maximum value of the distribution number in a second region excluding a predetermined first region based on the histogram created by the creating unit An image processing unit including: a detection unit; and a determination unit that determines that the original is monochrome when the distribution is greater than the number of distributions obtained by multiplying the maximum value by a predetermined coefficient over the second region of the histogram. Device.
Here, the “brightness component” refers to a parameter that represents only the brightness of an achromatic color regardless of the color (color tone, hue, etc.). For example, the luminance Y in the YCbCr color system, and the lightness L ^* in the L ^* a ^* b ^* color system. Of course, it is not limited to luminance Y and lightness L ^* .

  2nd invention is 1st invention, Comprising: The said judgment part judges that the said original is gray when the sum total of the count number of the said 2nd area exceeds the predetermined | prescribed 1st threshold value in the said histogram. To do.

  3rd invention is 1st invention, Comprising: In the said 2nd area | region of the said histogram, the said judgment part, when the difference of the count number of each said adjacent area | region exceeds predetermined 2nd threshold value, Judge the document as gray.

  According to a fourth aspect of the present invention, there is provided a reading step of reading a document, an extraction step of extracting a brightness component of the document read in the reading step, and a predetermined number of the brightness components extracted in the extraction step. A peak for detecting the maximum value of the distribution number in the second region excluding the predetermined first region based on the creation step of creating a histogram of count numbers by dividing into regions and the histogram created in the creation step In the detection step and the second region of the histogram created in the creation step, when the distribution is larger than the number of distributions obtained by multiplying the maximum value by a predetermined coefficient, the determination that the document is determined to be monochrome And an image processing method.

  According to the first invention, for the brightness component histogram, the maximum value of the distribution number in the second region is detected, and the distribution number is larger than the distribution number obtained by multiplying the maximum value by the predetermined distribution number over the second region. If the document is distributed, the document is determined to be monochrome, so that monochrome / gray determination can be performed with high accuracy.

  According to the second aspect of the invention, when the total number of counts in the second region of the histogram exceeds the first threshold value, the document is determined to be gray, so monochrome / gray determination can be performed with higher accuracy. It becomes.

  According to the third invention, in the second area of the histogram, when the difference in the number of counts of adjacent areas exceeds the second threshold value, the original is determined to be gray, so monochrome / gray determination can be performed with higher accuracy. Can be done.

  According to the fourth invention, with respect to the histogram of the brightness component, the maximum value of the distribution number in the second region is detected, and the distribution is more than the distribution number obtained by multiplying the maximum value by the predetermined coefficient over the second region. The document is determined to be monochrome, so monochrome / gray determination can be performed with high accuracy.

<First Embodiment>
Hereinafter, a copying machine will be described as an example of the image processing apparatus according to the first embodiment of the present invention with reference to the drawings.

<Configuration>
FIG. 1 is a perspective view showing a configuration example of a copier 10 according to the first embodiment of the present invention. The copying machine 10 reads an original, generates image data, and draws it on a recording sheet based on the image data. In the following drawings including FIG. 1, only elements and / or functions related to the present invention are shown. The copier 10 uses the luminance Y of the YCbCr color system as the brightness component.

  The operation unit 11 includes mechanical switches such as numeric keys and various function keys necessary for operating the copier 10. The operation unit 11 receives instructions for executing various commands such as scanning and copying of a document by operating these keys by the user.

  The display unit 12 is a general display configured by a display device such as an LCD, and displays various types of information on the screen as images. Note that a touch panel display may be applied to the display unit 12 so as to have a part or all of the functions of the operation unit 11.

  The reading unit 13 sequentially reads a document placed on a document placing unit 14 having an ADF (Automatic Document Feeder) with an image pickup device such as a CCD line sensor (not shown) and puts it on the document. Image data is generated based on the recorded image. The read original is discharged to the original discharge tray 15. Here, the original does not necessarily need to be read by the ADF, but may be read by an FBS (Flat Bed Scanner) method. Note that the FBS method is a method of executing a reading procedure in which a document placed on a contact glass (not shown) is read by an image sensor and a document that has been read is discharged.

  The drawing unit 16 is an electrophotographic printer device, and prints out and records the image data generated by the reading unit 13 as a hard copy. Although not shown, specifically, first, toner supplied from the toner cassette is attached to the photosensitive drum based on the image data. The recording sheet is transferred onto the recording sheet conveyed from the recording sheet cassette 17 by the recording sheet conveying section, and the transferred recording sheet is discharged to the recording sheet discharge tray 18. Note that the image data recorded by the drawing unit 16 is not necessarily image data generated by the reading unit 13, and when the copier 10 is connected to a communication network, an image received by the communication network is used. It may be data.

  FIG. 2 is a block diagram illustrating a configuration example of the copy machine 10. In addition to being electrically connected through the bus 20, each of the above-described components is also electrically connected to the following components.

  The image processing unit 21 is an image processing LSI having an ACS (Auto Color Selector) function for determining whether the image data generated by the reading unit 13 is color, gray, monochrome, or blank paper. is there. The detailed processing contents of the image processing unit 21 will be described in detail later.

  The MPU 22 receives input signals such as command execution instructions from the operation unit 11, data calculation based on the input signals, generation of output signals, control of display contents on the display unit 12, control of the reading unit 13, and control of the drawing unit 16. Control and control of the image processing unit 21 are performed. The ROM 23 stores programs executed by the MPU 22 and data necessary for control, and the RAM 24 temporarily stores data necessary for overall control by the MPU 22. Thereby, various functions of the copy machine 10 are realized. That is, the MPU 22 controls each component of the copier 10 in cooperation with the ROM 23 and the RAM 24.

<Processing content of image processing unit>
FIG. 3 is a block diagram showing the image processing unit 21, and FIG. 4 is an example showing a range of a document processed by the image processing unit 21. Here, the short side direction of the document 40 is the main scanning direction of the reading unit 13 (CCD line sensor arrangement direction), and the long side direction is the sub-scanning direction (direction perpendicular to the CCD line sensor arrangement direction). The image processing unit 21 divides the document 40 represented by the image data generated by the reading unit 13 into a plurality of predetermined regions, and executes processing corresponding to each region.

In the ACS function of the image processing unit 21, first, the averaging reduction unit 301 obtains, for example, the average of the gradation values of the target pixel and its right, lower right, and lower pixels, and substitutes it for the converted pixel. Thereafter, the γ correction unit 302 adjusts the ratio of the change in the voltage conversion value to the change in the brightness of the image. When the original is expressed by the RGB color system, such as when the original is read by a color CCD, the matrix conversion unit 303 converts this to the YCbCr color system. After executing these, the image processing unit 21 has the following processing state, and the ground color mask unit 304 to the block recording unit 311 cooperate to perform the following processing. Ie;
(1) Pretreatment 1:
In the preprocessing 1 area 41, the presence / absence of the background color of the document, the background color area and the brightness area are determined.
(2) Pretreatment 2:
When it is determined in the preprocessing 1 that the document is a background color document, a threshold value used in the block processing is determined in the preprocessing 2 area 42.
(3) Block processing:
Based on the results obtained in the preprocessing 1 and the preprocessing 2, it is determined whether the image is color, gray, monochrome, or blank paper. Note that the color here does not include the case where only the ground color is a chromatic color.
(4) Recording of image determination data:
In order to determine the type of image data by software, the following data is recorded.
(A) Judgment of the ground color and recording the area of the ground color in the CbCr color difference plane;
(B) Record the maximum and minimum values of YCbCr in the ground color area;
(C) record the total luminance counter value in each luminance area;
(D) Record the total color counter value in each color area;
(E) Record the color block number and color judgment area in the block processing;
(F) Record gray block number and gray determination area in block processing.

In the preprocessing 1 and the preprocessing 2 described above, the color ground color determination is performed. The color ground color determination is independent of the luminance ground color determination. When the following conditions are satisfied, the area is determined as a ground color area. Ie;
(1) In the preprocessing 1, the count number of one area exceeds the first ground color determination threshold value.
(2) The sum of the counts of adjacent areas exceeds the second ground color determination threshold.

  Here, the first ground color determination threshold value is a threshold value when the count number of one area is determined as the ground color, and the second ground color determination threshold value is the sum of the count numbers of adjacent areas. It is a threshold when determining. However, adjacent regions may be adjacent in any direction.

  In the determination of the color ground color, a pre-processed chromatic color mask is used in the pre-processing 1 and pre-processing 2, and the selected mask is applied by enabling the ground color determination in the block processing. There are two types of block processing masks, a hue mask and a ground color mask, both of which extend the mask range to the ground color range detected in the preprocessing 1 and the preprocessing 2. Regardless of whether or not the background color is determined, the block processing uses a value obtained by adding the margin value of each hue to any mask. Here, the “mask” refers to an area in a color space that is determined to be achromatic even if it is chromatic.

  Specifically, in the preprocessing 1 area 41 and the preprocessing 2 area 42, the hue determination counter 305, the luminance counter 306, and the extreme value recording unit 307 cooperate with each other so that the document 40 is chromatic or achromatic. Determine if there is. When the document 40 is achromatic, the brightness counter 306 extracts and counts the brightness of the document to create a histogram. On the other hand, when the document 40 is a chromatic color, normal color image processing is performed. Here, the brightness counter 306 corresponds to the extraction unit and the creation unit of the present invention. The extreme value recording unit 307 corresponds to the peak detection unit of the present invention.

  5 and 6 are diagrams showing histograms created by the brightness counter 306. FIG. Here, FIG. 5 is a histogram when the majority of the image on the document is characters, and FIG. 6 is a histogram when the majority of the image on the document is a photograph. As shown in FIG. 5, the luminance counter 306 divides a region from a black region (B side on the horizontal axis in FIG. 5) to a white region (W side on the horizontal axis in FIG. 5) into a predetermined number ( For example, the pixels having luminance values for each area are counted and divided into 16 to create histograms 50a and 50b.

  For the histograms 50a and 50b to be created, the ground color detection unit 308 detects the white region side as the ground color region (first region 53) from the threshold value 51 determined by the peak P detected on the white region side. Note that the ground color detected by the ground color detection unit 308 does not necessarily have to be on the white area side of the threshold 51. For example, when the color of the document used in the copier 10 is set in advance, a threshold value corresponding to the color may be set.

  Hereinafter, the processing content of the image processing unit 21 will be described in more detail.

<Color judgment>
In the determination of color, in order not to determine the ground color as a color, a process of masking the color is performed. Here, masks defined as a hue mask, a ground color mask, and a zero area mask will be described.

<Hue mask>
FIG. 7 shows a hue mask. The hue mask 71 applies a mask to an achromatic region at the center of the CbCr plane 70. Further, when the mask 71a is selected as a mask to be used in the block processing, a region in which the ground color is detected (hereinafter referred to as a hue mask 71). The expanded mask 71b is applied to 72) (referred to as "ground color region").

  That is, the coordinates of the ground color area 72 detected in the preprocessing 1 and the preprocessing 2 are moved so that the center of the ground color area 72 comes to the center of the CbCr plane in the block processing. At this time, since the achromatic center before the coordinate movement is moved to an area outside the mask 71a, the mask 71b is applied to the area. Here, the division of the area in the CbCr plane is based on the area division table shown in FIG.

<Background mask>
FIG. 9 is a diagram illustrating a ground color mask. The ground color mask 91 is used in the block processing by selecting the ground color mask 91 when the ground color is detected in the same manner as the hue mask 71. The ground color mask 91 is used together with the hue mask 71, and is determined as follows for the ground color region detected in the preprocessing 1 and the preprocessing 2. That is,
(1) The larger absolute value of the center coordinates 92 of the ground color is set as the x axis, and the smaller absolute value is set as the y axis.
(2) It is detected in which region of the straight lines 93a to 93h the inclination of the center coordinate 92 is 1/8 from y = x / 8 to y = x.
(3) A straight line (straight line 93d in FIG. 9) that is one level higher than the center coordinate 92 of the ground color from the center coordinate of x and the minimum coordinate of y of the ground color region toward the hue mask 71. A parallel straight line 94d is drawn. A mask region is defined above the straight line 94d (+ y direction) and on the upper side including the hue mask 71.
(4) Similarly to (3) above, a straight line that is one level lower than the center coordinates 92 of the ground color from the center coordinates of the ground color area and the coordinates of the maximum value of y toward the hue mask 71 A straight line 94e parallel to (the straight line 93e in FIG. 9) is drawn. An area below (−y direction) the straight line 94e and having an x coordinate of zero or more is set as a mask area.
(5) An area including an area where the two mask areas set in (3) and (4) above overlap and a rectangular area 95 surrounded by the maximum and minimum values of the x and y coordinates of the ground color area Is the ground color mask 91.

  Points that are beyond the mask enhancement are determined to be in the mask, and a margin can be added to the range of each mask. Here, unlike the hue mask 71, the ground color mask 91 does not move the origin, so that the color of each region does not shift to another region.

<Zero area mask>
FIG. 10 shows a zero area mask. As the mask, in addition to the hue mask 71 and the ground color mask 91 described above, the zero area mask 101 can be set. The zero area mask 101 is a mask in which a region covered with the zero area mask 101 is achromatic in a region where Cb is positive. When the ground color region 102 can be specified, the ground color region 102 is determined to be achromatic by rotating the region 102 using the rotation matrix on the CbCr plane and moving it within the zero area mask 101.

<Determination of brightness>
Each luminance threshold value in the block processing is determined from the luminance range of the ground color in the preprocessing. Note that when the ground color detection is OFF, a predetermined default value is applied.

<Pretreatment 1>
In pre-processing 1, the luminance area is divided into 16 areas, and the area with the largest number of counts is detected, and the area is determined as the ground color area. Since the current luminance distribution of the ground color may extend over a wide range depending on the type of the document or the like, or it may span two areas, the area with the largest number of counts is roughly detected here. Determine the color area. However, if the count number is less than the first ground color determination threshold, it is determined that the count number sufficient for determining the ground color is not obtained, and a flag GBGF (Gray Back Ground Fail) is set.

<Pretreatment 2>
In the preprocessing 2, when the count number exceeds a value preset in the register for the area including the areas before and after the area with the largest count number in the preprocessing 1, the luminance in that area is thereafter set to the extreme value recording unit 307. The target of the maximum and minimum values recorded by. However, what is recorded is not to record the extreme value of the area until then after the count number is exceeded. Further, only when the luminance enters the ground color luminance region, extreme value recording of CbCr in the ground color of the color is performed. If the maximum count value here is less than one-fourth of the maximum count value in the preprocessing 1, it is considered that the count number is insufficient, and a ground color determination error GBGF is set. The presence or absence of an achromatic background color is determined from the brightness of the background color.

<Block processing>
In each block (the first block processing area 43, the second block processing area 44,...), With respect to a block having a high possibility of gray from the luminance distribution, data serving as a material for determining whether or not the block is gray Record. First, as a tendency of the luminance distribution of a monochrome character document (see FIG. 5), the gray portion is stable regardless of the luminance, and a peak appears in the count number of the all black region corresponding to the character density (histogram). 50a). Or, even if there is no peak, there is a tendency that the count number is not so small with respect to the maximum value of gray (histogram 50b). In addition, there is a tendency that the proportion of all black in the whole is relatively low (for example, less than about 20%).

Therefore, a gray block is recorded when either of the following two conditions is satisfied. Ie;
(1) Based on the histograms 50a and 50b, the maximum count number in the area (second area 54) excluding the ground color area (first area 53) and the all black area (area 0 in FIG. 5) is the minimum count number. Is over. In addition, when a flag is set in an area exceeding the count number obtained by multiplying the maximum count number by a predetermined coefficient (for example, 0.5 in the present embodiment), the area set in advance in the register No flag is set in the dark region (region 1) (in the case of the histogram 50b).
(2) The gray count of the block exceeds a predetermined gray count threshold (first threshold). That is, the ratio of all black in the whole is relatively high (for example, about 20% or more).

  For example, when the histogram 61 as shown in FIG. 6 is created, the above condition (2) is not satisfied because the gray count of the block does not exceed the gray count threshold. However, since the ground color area is the area D, the areas C to F are excluded from the luminance determination, and the area 7 exceeding the count number obtained by multiplying the area 7 having the largest count number in the areas 0 to B by 1/2 ( When the flag is set in the areas 2, 3, and 7), since the flag is not set in the area 1, the above condition (1) is satisfied.

  Accordingly, the ground color mask unit 304 to the block recording unit 311 cooperate to perform processing corresponding to the determination unit of the present invention.

  In block processing, in addition to this gray block determination, bright point block detection and non-blank block detection are performed. In the case of a bright point, the number of blocks is counted in a bright point block counter, and in the case of a non-blank block, these are recorded in a terminal block blank check.

<Operation of Copy Machine 10>
The copier 10 performs the following operation by providing the above configuration. FIG. 11 is a flowchart showing the monochrome / gray determination procedure. In this flowchart, only processing operations for the copying machine 10 to perform monochrome / gray determination are shown, and illustration and description of other processing operations are omitted. Further, unless otherwise specified, a series of processing operations in the copier 10 is automatically performed under the control of the MPU 22.

  First, in a state where the power of the copier 10 is ON, the apparatus waits until a user inputs a document reading command for reading the document 40 placed on the document placement unit 14 (step S1101). When a document reading command is input, Yes is selected in step S1101, and the document 40 placed on the document placing portion 14 is read (reading step: step S1102). When the original 40 is read in step S1102, the hue determination counter 305 determines whether the read original 40 is achromatic with respect to the preprocess 1 area 41 and the preprocess 2 area 42 (step S1103). ).

  If the document 40 has a chromatic color, No is selected in step S1103, and normal color image processing is performed (step S1104). On the other hand, if the original is an achromatic color, Yes is selected in step S1103, the luminance counter 306 extracts the luminance component (step S1105), and creates a histogram of the luminance component (creation process: step S1106).

  The extreme value recording unit 307 detects a peak for the created histogram (step S1107), and the ground color mask unit 304 to the block recording unit 311 cooperate to perform ground color determination (step S1108). Then, it is determined whether the document 40 is monochrome or gray (determination step: step S1109). Thereafter, based on the determination result, the drawing unit 16 transfers the image data of the document 40 onto the recording paper conveyed from the recording paper cassette 17 or stores it in a storage unit (not shown).

<Effect>
As described above, the maximum value of the number of distributions in the second region 54 is detected in the luminance component histogram, and the distribution is more than the number of distributions obtained by multiplying the maximum value by a predetermined coefficient over the second region 54. In this case, since the document is determined to be monochrome, monochrome / gray determination can be performed with high accuracy.

  Alternatively, when the sum of the counts of the second region 54 in the histogram exceeds the first threshold value (gray count threshold value), the document is determined to be gray, so monochrome / gray determination can be performed with higher accuracy. It becomes.

<Modification>
As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment. For example, in the second area 54 of the histogram, the document may be determined to be gray when the difference between the count numbers of adjacent areas exceeds a predetermined threshold (second threshold). This also makes it possible to perform monochrome / gray determination with high accuracy.

  In this embodiment, the case where the document is read by the reading unit 13 has been described as an example. However, based on the RGB color system RAW data read from a digital camera or the like, the matrix conversion unit 303 uses the YCbCr table. The image processing unit 21 may perform image processing after conversion to the color system. Alternatively, the image processing unit 21 may perform image processing after reading a JPEG image file from a PC (Personal Computer) or the like, decoding the image file, and extracting YCbCr.

  In addition to the above-described method, there is a method for performing monochrome / gray determination using software. For example, in each area, obtain the expected value where the count bit of the area stands, check whether there is a big difference from the recorded result, and if the difference is small, it is monochrome, if the difference is large, for each block There is a method of determining gray because the distribution is different.

  Further, since the total count when the luminance is divided into 16 is recorded, the average value of the number of counts in one block is obtained from this value. In the case of only character information, if it is assumed that the distribution does not change so much between blocks, it can be determined that the block is a gray block if a block with a greatly different distribution is recorded.

  Further, the present invention is not limited to the copier 10, and may be a scanner or a facsimile, or may be an MFP (Multi Function Peripherals) combining these. Furthermore, it may be a circuit configuration capable of performing the above-described processing, and is not limited to the above-described steps.

1 is a perspective view illustrating a configuration example of a copier according to a first embodiment of the present invention. 1 is a block diagram illustrating a configuration example of a copier. It is a block diagram which shows an image process part. It is a figure which shows the range of the original document which an image process part processes. It is a figure which shows the histogram which an image process part produces. It is a figure which shows the histogram which an image process part produces. It is a figure which shows a hue mask. It is a figure which shows the division | segmentation table of an area | region. It is a figure which shows a ground color mask. It is a figure which shows a zero area mask. It is a flowchart which shows a monochrome / gray determination procedure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Copy machine 13 Reading part 21 Image processing part 304 Ground color mask part 305 Hue determination counter 306 Luminance counter 307 Extreme value recording part 308 Ground color detection part 309 Color mask setting part 310 Luminance threshold value setting part 311 Block recording part 53 1st area | region 54 Second area

Claims (4)

A reading section for reading a document;
An extraction unit for extracting a brightness component of the document;
A creation unit that divides the brightness component extracted by the extraction unit into a predetermined number of regions and creates a histogram of count numbers;
Based on the histogram created by the creation unit, a peak detection unit that detects a maximum value of the distribution number in the second region excluding the predetermined first region;
An image processing apparatus comprising: a determination unit configured to determine that the document is monochrome when the distribution is greater than the distribution number obtained by multiplying the maximum value by a predetermined coefficient over the second region of the histogram. The image processing apparatus according to claim 1,
The determination unit is an image processing apparatus that determines that the original is gray when the total number of counts of the second area exceeds a predetermined first threshold in the histogram. The image processing apparatus according to claim 1,
The determination unit determines that the document is gray when the difference in the number of counts of adjacent regions in the second region of the histogram exceeds a predetermined second threshold value. A reading process for reading a document;
An extraction step of extracting a brightness component of the document read in the reading step;
A step of creating the count number histogram by dividing the brightness component extracted in the extraction step into a predetermined number of regions;
Based on the histogram created in the creation step, a peak detection step of detecting a maximum value of the distribution number in the second region excluding the predetermined first region;
A determination step of determining that the original is monochrome when the distribution is greater than the number of distributions obtained by multiplying the maximum value by a predetermined coefficient over the second region of the histogram created in the creation step. , Image processing method.

Images