JP2013051652A - Image processing device, image reading device, and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently determine whether each block is a black-and-white block, a gray block and a chromatic block using a histogram.SOLUTION: In an image processing device, an image represented in a YCbCr color space is divided into plural blocks to create a histogram of a value of Y-component of pixels constituting the block for each block. A most frequent value of the Y-component and a ratio of the most frequent value are found for each block, and whether the block is a monochrome block or a multicolor block is determined based on the ratio of the most frequent value. Whether the monochrome block is an achromatic block or a chromatic block is determined, and the achromatic block is determined as a black-and-white block when the most frequent value of the Y-component is not more than a first threshold or not less than a second threshold larger than the first threshold, and otherwise is determined as a gray block.

Description

  The present invention relates to a technique for dividing an image into a plurality of blocks and determining whether each block is a monochrome block, a gray block, or a chromatic block.

Conventionally, an image processing apparatus that converts R, G, and B signals of three primary colors into a brightness signal to create a histogram of the brightness signal (corresponding to the Y component in the YCbCr color space) and determines the document type from the created histogram is known. (For example, refer to Patent Document 1).
In the image processing apparatus described above, for example, the ratio of the number of chromatic pixels and the total number of chromatic and achromatic pixels (= number of chromatic pixels / (number of chromatic pixels + The number of achromatic pixels)) is obtained, and if the ratio is greater than the reference value, it is determined that the document is a color original.

JP-A-8-251402

By the way, the above-described conventional technique determines whether or not the type of the document (hereinafter referred to as “image”) is a color image, but the determination of the type of image is not limited to this, and a plain image In some cases, it is determined whether the image is a monochrome image, a gray image, or a color image.
When making such a determination, the histogram of the brightness signal is used to determine whether each block is a black and white block, a gray block, or a chromatic block, and the determination result is used to determine whether the document is a plain image, In some cases, it is determined whether the image is a monochrome image, a gray image, or a color image.
Conventionally, when such a determination is made, it has not been sufficiently studied to efficiently determine whether each block is a monochrome block, a gray block, or a chromatic block.

  In the present specification, a technique is disclosed in which when a block is used to determine whether a block is a black and white block, a gray block, or a chromatic block using a histogram, the determination can be performed efficiently.

  The image processing apparatus disclosed in the present specification divides an image represented in the YCbCr color space into a plurality of blocks, creates a histogram of the Y component values of the pixels constituting the block for each block, The block unit mode value calculation unit for determining the mode value and the mode value ratio in the histogram, and the block is monochromatic based on the mode value ratio obtained by the block unit mode value calculation unit A single color / multicolor block determination unit that determines whether the block is a multicolor block or a block that is determined to be a single color block by the single color / multicolor block determination unit is an achromatic block The first achromatic / chromatic color block determination unit that determines whether the block is a chromatic block or the first achromatic / chromatic block determination unit For the block determined to be a block, the mode value obtained by the block unit mode value calculation unit is not more than a first threshold value or not less than a second threshold value that is greater than the first threshold value. A first black-and-white / gray block determining unit that determines a black-and-white block, and determines that the mode is a gray block when the mode value is larger than the first threshold value and smaller than the second threshold value.

  Furthermore, the image processing apparatus determines a second block for determining whether the block is an achromatic block or a chromatic block for the block determined to be a multicolor block by the single color / multicolor block determination unit. For the block determined to be an achromatic color block by the achromatic / chromatic color block determining unit and the achromatic / chromatic color determining unit, the value of the Y component in the histogram created by the block unit mode value calculating unit is A total ratio of pixels that are equal to or smaller than the third threshold and pixels whose Y component value is equal to or greater than the fourth threshold that is greater than the third threshold is obtained, and the block is a black and white block based on the total ratio. Or a second black and white / gray block determination unit that determines whether the block is a gray block.

  Further, the image processing apparatus is a single color image in which the ratio of the single color block is equal to or higher than a predetermined ratio based on the ratio of the single color block in the image, or a multicolor image in which the ratio of the single color block is less than the predetermined ratio. A single-color / multi-color image determination unit that determines whether the image is a single-color image by the single-color / multi-color image determination unit; Further, based on the mode value calculation unit that creates a histogram of the mode value and obtains the mode value ratio in the histogram, and the mode value ratio obtained by the image unit mode value calculation unit A plain image determination unit that determines whether or not the image is a plain image, and when the plain image determination unit determines that the image is not a plain image, the image is a monochrome image or a gray image Alternatively, the black and white blocks which of a color image, the gray block, and a determining monochrome / gray / color image determining unit on the basis of the ratio of the chromatic color blocks, may be provided.

  The present invention can be realized in various modes such as an image reading apparatus, an image processing program, an image processing method, and a recording medium on which the image processing program is recorded.

According to the above image processing device, the first monochrome / multicolor block determination unit determines that the block is a single color block and the achromatic / chromatic block determination unit determines that the block is an achromatic block. When the gray block determination unit determines whether the block is a black and white block or a gray block, the determination is made based on the mode value obtained by the block unit mode value calculation unit.
That is, according to the above image processing apparatus, the mode value obtained by the block unit mode value calculation unit is used for determining whether the block is a black and white block or a gray block. When it is used to determine whether the block is a black and white block, a gray block, or a chromatic color block, the determination can be performed efficiently.

FIG. 3 is a block diagram illustrating an electrical configuration of the multifunction peripheral according to the first embodiment. The schematic diagram which shows the division | segmentation of an image. The schematic diagram for demonstrating the classification | category of a block. The flowchart which shows the whole flow of an image classification determination process. The flowchart which shows the flow of a block classification process. The schematic diagram which shows an example of the histogram of the value of the Y component of a monochrome block. The schematic diagram which shows an example of the histogram of the value of the Y component of a multicolor block. The schematic diagram which shows an example of the histogram of the value of the Y component of a multicolor block. The flowchart which shows the flow of an image determination process. The flowchart which shows the flow of the block classification process as a comparative example. The flowchart which shows the flow of the image determination process as a comparative example.

<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS.
(1) Configuration of Multifunction Device FIG. 1 is a block diagram showing a simplified electrical configuration of a multifunction device 1 as an image processing apparatus according to the first embodiment. The multi-function device 1 includes a control unit 10, a reading unit 11, a printing unit 12, an operation unit 13, a storage unit 14, and a communication interface (communication I / F) unit 15.

  The control unit 10 includes a CPU 10a, a ROM 10b, and a RAM 10c. The CPU 10a controls each unit of the multifunction device 1 by executing a program stored in the ROM 10b or the storage unit 14. The ROM 10b stores a control program for controlling the operation of the multifunction machine 1 and various data. The RAM 10c is used as a main storage device for the CPU 10a to execute various processes.

  The reading unit 11 includes a platen glass on which an original is placed, a light source that irradiates the original placed on the platen glass, an image sensor that outputs an image signal corresponding to the received light, and an image of light reflected on the original. An optical system that forms an image on the sensor, a conveyance unit that conveys the image sensor along the platen glass surface, an A / D conversion circuit that performs A / D conversion on an image signal output from the image sensor, and an output from the A / D conversion circuit An image is generated based on the generated image signal, and an image processing circuit 11a for performing various image processes on the generated image is provided.

  When the image processing circuit 11a generates an image based on the image signal output from the A / D conversion circuit, the image processing circuit 11a determines the type of the generated image and performs image processing according to the type of image. Since switching of image processing according to the type of image has been performed conventionally, description of image processing according to the type of image is omitted.

  The image processing circuit 11a includes a block unit mode value calculation unit, a single color / multicolor block determination unit, a first achromatic / chromatic block determination unit, a first black / white / gray block determination unit, a second achromatic / Chromatic color block determination unit, second monochrome / gray block determination unit, single color / multicolor image determination unit, image unit mode value calculation unit, plain image determination unit, monochrome / gray / color image determination unit, and color space It is an example of a conversion part.

  The printing unit 12 prints the image generated by the reading unit 11 or the image received from the external device by the communication interface unit 15 on a sheet such as printing paper by an electrophotographic method or an inkjet method.

  The operation unit 13 includes a liquid crystal display and various buttons, and the user can perform various operations such as selection of a reading mode and a document reading instruction by operating the operation unit 13. In this embodiment, “color / gray / monochrome / auto” can be selected as the reading mode.

  The storage unit 14 is a device that stores various programs and data using a non-volatile memory such as a hard disk or a flash memory. The storage unit 14 stores an image generated by the reading unit 11 and an image received from an external device by the communication interface unit 15.

  The communication interface unit 15 is communicably connected to an external device such as a personal computer (PC) or a portable information terminal via a communication network such as a LAN (Local Area Network) or the Internet, and an image to be printed from the external device. And transmission of an image generated by the reading unit 11 to an external device. The communication interface unit 15 may be configured to be connected to an external device via a USB (Universal Serial Bus), a parallel line, or the like.

(2) Image Types In this embodiment, four types of images, namely, plain images, black and white images, gray images, and color images will be described as examples.

The plain image includes not only a blank image on which nothing is printed when printed on a sheet but also an image that is entirely filled with one color. Examples of the plain image include a white image as a whole, a black image as a whole, a specific gray image as a whole, and a specific chromatic color image as a whole.
Here, for example, if white to black is expressed with 256 gradations, there are 254 gradations of gray except for white and black. That means.

A black and white image is an image composed of white and black. An example of a black-and-white image is a document image with a white background and black characters.
A gray image is an image composed of two or more grays. An example of a gray image is an image composed of two or more grays having different gradations, such as a monochrome photographic image. Note that, as described above, in the present embodiment, an image with a specific gray color as a whole is classified as a plain image, and therefore an image with a specific gray color as a whole is excluded from the gray image.

  A color image is an image composed of two or more colors, and at least one of the two or more colors is a chromatic color. As an example of a color image, a color photographic image generated by imaging a subject with a digital camera can be given.

(3) Outline of determination of image type In this embodiment, for example, even if a part of a plain image has a part that cannot be said to be plain, if it is recognized as plain as a whole when viewed by a person, it is plain. It is determined to be an image. For example, even if a non-white portion is included in the image, if the image is recognized as white as a whole when viewed by a person, it is determined that the entire image is a solid white image, that is, a plain image. The same applies to black and white images, gray images, and color images.

  In order to make such a determination, that is, in order to determine a type that matches a type recognized when viewed by a person, in this embodiment, an image 20 is divided into a plurality of blocks as shown in FIG. The divided blocks are classified by color, and the type of the image is determined based on the ratio of the classified blocks. In FIG. 2, only one block is given a reference numeral.

  Here, when determining the type of image, it is also possible to determine the type of image by determining the color of each pixel instead of dividing into blocks. For example, if 90% or more of all pixels are white, it can be determined that the image is a single white image. However, since such a determination has the following problem, in this embodiment, the determination is made by dividing into blocks.

  For example, in a document image generated by reading a document original, a pixel forming a character outline among pixels constituting a character (in other words, an area other than a character and a character among pixels constituting a character). The color of the pixel in contact with the boundary may become a color due to a color shift at the time of reading. In this case, if it is determined that the color image is a color image if the number of color pixels is equal to or greater than a predetermined ratio, the color image is determined in spite of being a black and white document image due to the large number of pixels determined to be color due to color shift. May be misjudged.

  On the other hand, when divided into blocks, color misregistration occurs only in the pixels that form the outline of the character. Therefore, the entire block generally does not become color, and the block is partially colored by color misregistration. Even if this pixel is included, it is classified as a black and white block which will be described later as a whole. In other words, color pixels caused by color misregistration at the time of reading are not concentrated locally but scattered throughout the image, so dividing into blocks eliminates the influence of color pixels when classifying blocks by color, and misjudgment Can be reduced.

(4) Overview of Block Classification by Color FIG. 3 is a schematic diagram for explaining block classification by color. As shown in the figure, the blocks are roughly classified into single color blocks and multicolor blocks.
A single color block is a block composed of one color. As an example of the single color block, there are a block of white as a whole, a block of black as a whole, a block of specific gray as a whole, a block of specific chromatic color as a whole.

  A multicolor block is a block composed of two or more colors. Examples of multicolor blocks include blocks that consist of two monochrome colors, such as blocks that make up a document image with white background and black characters, and blocks that make up a monochrome photo image. A block composed of two or more grays having different tones, a block composed of two or more colors such as a block constituting a color photographic image, and a block in which at least one of the two or more colors is a chromatic color Is mentioned.

The single color block and the multicolor block are further classified into an achromatic color block and a chromatic color block, respectively.
An achromatic block is a block composed of achromatic pixels, and a chromatic block is a block composed of chromatic pixels. Here, the achromatic color means white, black, and gray, and the chromatic color means a color other than white, black, and gray.

In the case of the above-described single color block, the whole block of white color, the whole block of black color, and the whole block of specific gray color are achromatic blocks, and the whole block of specific chromatic color is It is a chromatic color block (also referred to as “color block” in this embodiment).
In the case of the above-described multicolor block, a block composed of two colors of black and white and a block composed of two or more grays having different gradations are achromatic blocks, and a block composed of two or more colors. A block in which at least one of the above colors is a chromatic color is a chromatic color block (also referred to as a “color block” in the present embodiment).

The achromatic color block is further classified into a black and white block and a gray block.
In the case of the above-described single color block, the entire white block, the entire black block is a black and white block, and the almost specific gray block is a gray block.
In the case of the above-described multicolor block, a block composed of two monochrome colors is a monochrome block, and a block composed of two or more grays having different gradations is a gray block.

  As in the case of the image type, in the block classification, for example, even if a part of the black and white block is not black and white, if it is recognized as black and white as a whole when viewed by a person, it is black and white. Judged to be a block. The same applies to a single color block, a multicolor block, an achromatic color block, a chromatic color block, and a gray block.

(5) Image Type Determination Process FIG. 4 is a flowchart showing the flow of the image type determination process. This process is started when “Auto” is selected as the reading mode, and in this case, the original is read in color and an image is generated.
In S101, the image processing circuit 11a converts the color space of the generated image into a YCbCr color space.

In S102, the image processing circuit 11a divides the image into a plurality of blocks in a grid pattern as shown in FIG. The block size can be selected as appropriate, but in this embodiment, the block is divided into blocks of 32 pixels in length and width.
In S103, the image processing circuit 11a selects one block. When the process of S103 is the second time or later, a block that has not been selected is selected.

In S104, the image processing circuit 11a executes block classification processing for classifying the selected block by color. Details of the block classification processing will be described later.
In S105, the image processing circuit 11a determines whether or not all blocks have been selected. If all the blocks have been selected, the process proceeds to S106, and if there is a block that has not been selected, the process returns to S103 and repeats the process. .

  In S106, the image processing circuit 11a executes an image determination process for determining the type of the image based on the ratio of the blocks classified by the block classification process. Details of the image determination process will be described later.

(5-1) Block Classification Processing FIG. 5 is a flowchart showing the flow of block classification processing.
In S201, the image processing circuit 11a creates a Y component value histogram, a Cb component value histogram, and a Cr component value histogram of the pixels constituting the block selected in S103, and a Y component histogram. Thus, the mode value of the Y component and the ratio of pixels in which the value of the Y component matches the mode value in the block (hereinafter referred to as “the ratio of the mode value of the Y component”) are obtained.

For example, if the number of pixels making up the block is 10, and the Y component value of each pixel is 5, 2, 6, 7, 2, 4, 2, 9, 5, 1, respectively, Since 2 is the most, the mode value of the Y component is 2. Since the number of pixels whose Y component value matches the mode value “2” is 3, the ratio of the Y component mode value is 3/10 (= 30%).
The mode value of the Y component obtained here is also used in S205 and S302 described later. Therefore, the image processing circuit 11a stores the obtained mode value of the Y component in the RAM 10c.

  In S202, the image processing circuit 11a determines whether the block is a single color block or a multicolor block based on the ratio of the mode value of the Y component of the block. This will be specifically described below.

  FIG. 6 is a schematic diagram showing an example of the histogram of the Y component value of a single-color block, and is a schematic diagram showing an example of a histogram of an almost white block as a whole. Since the white component value of white is close to 255, a block that is almost white as a whole has a peak in the vicinity of 255 in the histogram of the Y component value as shown in FIG. 6, and this peak occupies the number of pixels of the entire block. The ratio of the number of pixels, that is, the ratio of the mode value of the Y component is 90% or more. The same applies to a block that is substantially black as a whole, a block that is substantially specific to gray, and a block that is substantially specific to chromatic color, except that the peak positions are different.

  FIG. 7 is a schematic diagram illustrating an example of a histogram of Y component values of a multi-color block, and is a schematic diagram illustrating an example of a histogram of Y component values of a color block. Since color blocks vary in color, they generally cannot have an extreme peak, and the ratio of the mode value of the Y component does not exceed 90%. The same applies to blocks composed of two or more grays having different gradations, such as blocks constituting a monochrome photographic image.

  FIG. 8 is a schematic diagram showing an example of a histogram of the Y component values of a multicolor block, and an example of a histogram of a black and white block constituting a document image in which the ground color is white and the characters are black. It is a schematic diagram shown. A block constituting such a document image has peaks in the vicinity of 0 and 255 in the histogram of the value of the Y component, but since the peaks are dispersed in white and black, the mode value of the Y component The percentage does not exceed 90%.

Therefore, the image processing circuit 11a determines that the mode is a single color block if the ratio of the mode value of the Y component is 90% or more, and determines that it is a multicolor block if it is less than 90%.
Here, even if the ratio of the mode value of the Y component is 90% or more, if the Cb and Cr components are different, there are two or more colors, but generally the mode value of the Y component is 90 in block units. %, The Cb and Cr components are unlikely to be different, and such determination is empirically sufficient. Therefore, in this embodiment, whether the block is a single color block or a multicolor block is determined only by the Y component value. judge.
Note that whether the block is a single color block or a multicolor block may be determined in consideration of the Cb and Cr components. The above 90% is an example, and what percentage can be selected as appropriate. The same applies to other threshold values in the present embodiment.
If the image processing circuit 11a determines that the block is a single color block, the process proceeds to S203. If the image processing circuit 11a determines that the block is a multicolor block, the process proceeds to S208.

The processing of S203 to S207 described below is processing when it is determined as a single color block in S202.
In S203, the image processing circuit 11a determines whether the block is an achromatic block or a chromatic block. This will be specifically described below.
In the YCbCr color space, assuming that the range of Cb and Cr component values is 0 to 255, when Cb and Cr are close to intermediate values (= 127), the pixel color is close to an achromatic color. Therefore, the image processing circuit 11a determines that the block is an achromatic color block if both of the following formulas 1 and 2 are satisfied, and determines that the block is a chromatic color block if at least one of them is not satisfied. To do.

“Pixel ratio satisfying 120 ≦ Cb ≦ 135” ≧ 90% Equation 1
“Pixel ratio satisfying 120 ≦ Cr ≦ 135” ≧ 90% Expression 2
If the image processing circuit 11a determines that the block is a chromatic block, the process proceeds to S204. If the image processing circuit 11a determines that the block is an achromatic block, the process proceeds to S205.

In S204, the image processing circuit 11a determines that the block is a chromatic color block in a single color block, that is, a color block.
In S205, the image processing circuit 11a determines whether the block is a monochrome block or a gray block. This will be specifically described below.

In the YCbCr color space, assuming that the range of the Y component value is 0 to 255, when Cb and Cr are close to an intermediate value (= 127), if the Y component value is close to 0, the pixel color is black. If the values are close and the value of the Y component is close to 255, the pixel color is close to white. Therefore, the image processing circuit 11a determines that the mode is a black and white block if the mode value of the Y component obtained in S201 has one of the following expressions 3 and 4, and both are satisfied. If not, it is determined as a gray block.
“Mode of Y component” ≦ 50 Equation 3
220 ≦ “mode of the Y component” Expression 4

The reason for this determination is that S205 is executed when the ratio of the mode value of the Y component is 90% or more, and that the mode value of the Y component is 50 or less is 90% or more of the whole. Is white and the mode of the Y component is 220 or more, 90% or more of the whole is black, so if either of the above formulas is satisfied, the block This is because it can be determined that the color is white or black. Here, 50 is an example of a first threshold value, and 220 is an example of a second threshold value.
If the image processing circuit 11a determines that the block is a black and white block, the process proceeds to S206. If the image processing circuit 11a determines that the block is a gray block, the process proceeds to S207.

In S206, the image processing circuit 11a determines that the block is a monochrome block in a single color block.
In S207, the image processing circuit 11a determines that the block is a gray block in a single color block.

The processing of S208 to S213 described below is processing when it is determined as a multicolor block in S202.
Since the process of S208 is the same as S203, description is abbreviate | omitted.
In S209, the image processing circuit 11a determines that the block is a chromatic block in the multicolor block, that is, a color block.

In S210, the image processing circuit 11a obtains the number of pixels satisfying the following Expression 5 and the number of pixels satisfying the following Expression 6 from the histogram of the Y component values of the block. Here, 50 is an example of a third threshold value, and 220 is an example of a fourth threshold value. In the following description, a pixel that satisfies Expression 5 is referred to as a white pixel, and a pixel that satisfies Expression 6 is referred to as a black pixel.
Y ≦ 50 Equation 5
220 ≦ Y Expression 6

In S211, the image processing circuit 11a adds up the number of white pixels and the number of black pixels obtained in S210, and the ratio of the total number to the number of pixels in the entire block, that is, the value of the Y component is 50 or less. The total ratio of pixels that are equal to and 220 or more is determined. If the calculated total ratio is 90% or more, it is determined as a black and white block, and if it is less than 90%, it is determined as a gray block.
If the image processing circuit 11a determines that the block is a black and white block, the process proceeds to S212. If the image processing circuit 11a determines that the block is a gray block, the process proceeds to S213.

In S212, the image processing circuit 11a determines that the block is a monochrome block in the multicolor block.
In S213, the image processing circuit 11a determines that the block is a gray block in the multicolor block.

(5-2) Image Determination Processing FIG. 9 is a flowchart showing the flow of image determination processing.
In S301, the image processing circuit 11a obtains the ratio of the single color block in all the blocks constituting the image. If the ratio is less than 90%, the process proceeds to S305 on the assumption that the single-color block ratio is a multicolor image with a ratio less than a certain ratio.

Here, as an example of an image in which the ratio of the single color block is determined to be 90% or more in S301, in addition to a plain image, each region is divided into two or more regions and each region is filled with a different color. For example, an image including two or more colors such as an image in which almost all blocks are determined as a single color block when viewed in block units. That is, the monochromatic image is not limited to a solid image that is entirely filled with one color, and even an image composed of two or more colors may be determined as a monochromatic image.
On the other hand, a color image, a gray image, and a black and white image generally occupy a large number of multicolor blocks, and thus are determined to be multicolor images in many cases.

S302 to S303 described below are processes executed when it is determined that the ratio of the single color block is 90% or more.
In S302, the image processing circuit 11a creates a histogram for the mode value obtained for each block in S201 for a single color block among the blocks constituting the image, and in other words, the ratio of the mode value in the histogram, in other words, The ratio of the number of blocks whose mode value matches the mode value in the histogram to the number of all monochrome blocks is obtained.

In S303, the image processing circuit 11a determines whether or not the image is a plain image based on the mode value ratio obtained in S302. This will be specifically described below.
When the histogram for the mode value obtained for each block is created, in the case of a plain image, since the mode value of each block is almost the same value, an extreme peak can be generated as in the histogram shown in FIG. The ratio of the block of the peak in the whole, in other words, the ratio of the block whose mode value coincides with “the mode value in the histogram for the mode value obtained for each block” is 90% or more.

On the other hand, in the case of an image consisting of two or more colors but almost all blocks are determined to be single color blocks when viewed in block units, the mode varies depending on the block, so the extreme peak in the histogram is Can not.
Therefore, the image processing circuit 11a determines that the mode is a plain image if the ratio of the blocks whose mode value matches the “mode value in the histogram for the mode value determined for each block” is 90% or more. If it is less than 90%, it is determined that the image is not a plain image.
If the image processing circuit 11a determines that the image is a plain image, the process proceeds to S304. If the image processing circuit 11a determines that the image is not a plain image, the process proceeds to S305.

In S304, the image processing circuit 11a determines that the image is a plain image.
In S305, the image processing circuit 11a determines whether the image is a color image. Specifically, the image processing circuit 11a first calculates the proportion of color blocks in all blocks constituting the image. The color block here includes a color block in a single color block and a color block in a multicolor block. The image processing circuit 11a determines that the image is a color image if the calculated ratio is 90% or more, and determines that the image is not a color image if it is less than 90%.
If the image processing circuit 11a determines that the image is a color image, the process proceeds to S306. If the image processing circuit 11a determines that the image is not a color image, the process proceeds to S307.

In S306, the image processing circuit 11a determines that the image is a color image.
In S307, the image processing circuit 11a determines whether the image is a gray image or a monochrome image. Specifically, the image processing circuit 11a first calculates the ratio of gray blocks in all blocks constituting the image. The gray block here includes a gray block in a single color block and a gray block in a multicolor block. The image processing circuit 11a determines that the image is a gray image if the calculated ratio is 90% or more, and determines that the image is a monochrome image if the calculated ratio is less than 90%.
If the image processing circuit 11a determines that the image is a black and white image, the process proceeds to S308. If the image processing circuit 11a determines that the image is a gray image, the process proceeds to S309.

In S308, the image processing circuit 11a determines that the image is a monochrome image.
In S309, the image processing circuit 11a determines that the image is a gray image.

(6) Effect of Embodiment Hereinafter, the effect of Embodiment 1 will be described in comparison with a comparative example.
FIG. 10 is a flowchart showing the flow of block classification processing as a comparative example. Here, the same processes as those in the flowchart shown in FIG. In the flowchart shown in FIG. 10, when it is determined that the block is a single color block in S202 and the block is an achromatic block in S203, it is determined whether the block is a black and white block or a gray block. The determination is made by executing S210 and S211 instead of S205.

  Of course, it is possible to determine whether the block is a black and white block or a gray block by executing S210 and S211. In this case, the number of pixels satisfying Expression 5 described above from the histogram of the Y component value The number of pixels satisfying Equation 6 must be totaled.

On the other hand, according to the flowchart shown in FIG. 5, since the determination is made using the mode value of the Y component obtained in S201, the process of S210 need not be executed. Since the process of S210 requires a certain amount of time, the processing efficiency improves if the process of S210 is not executed.
As described above, according to the MFP 1, when determining whether the block is a black and white block or a gray block in S205 of the flowchart shown in FIG. 5, the determination is performed using the mode value of the Y component obtained in S201. Therefore, when determining whether each block is a black-and-white block, a gray block, or a chromatic block using a histogram, the determination can be performed efficiently.

  Furthermore, according to the multifunction device 1, in the image determination process shown in FIG. 9, it is determined whether the image is a plain image (S302, S303). Whether the image is a monochrome image, a gray image, or a color image. Since this determination is performed before the determination (S305 to S309), the number of determination steps can be greatly reduced. Hereinafter, a specific example will be described using a comparative example.

  FIG. 11 is a flowchart illustrating a flow of image determination processing as a comparative example. Although detailed description is omitted, in the flowchart shown in FIG. 11, it is determined whether the image is a plain image / color image or a plain image / gray image before determining whether the image is a plain image. Is going. Although the order of determination as shown in FIG. 11 is possible, the number of steps is significantly increased as compared with the flowchart shown in FIG.

  On the other hand, according to the multifunction device 1, as shown in FIG. 9, it is determined whether or not the image is a plain image in the image determination process before determining whether the image is a monochrome image, a gray image, or a color image. Therefore, the number of determination steps can be greatly reduced.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) In the above-described embodiment, the multifunction apparatus is described as an example of the image processing apparatus. However, the image processing apparatus may be a single-function image reading apparatus, or an image corresponding to the type of image to be printed. It may be a printer that performs processing and prints.

The image processing apparatus may be a personal computer (PC), a portable information terminal, or the like.
For example, in a PC that is communicably connected to the image reading apparatus, the scanner driver is executed to instruct the image reading apparatus to read a document, and an image generated by the image reading apparatus is acquired. Image processing according to the type of the image may be performed. In this case, the scanner driver is an example of an image processing program.

  Alternatively, in a PC that is communicably connected to the printer, an image to be printed may be subjected to image processing corresponding to the type of the image by executing a printer driver and transmitted to the printer. In this case, the printer driver is an example of an image processing program.

  (2) In the above embodiment, the case where the flowchart shown in FIG. 9 is used as the image determination processing has been described as an example, but the flowchart shown in FIG. 11 may be used.

  (3) Although the case where the image type determination is executed by the image processing circuit 11a has been described as an example in the above embodiment, it may be realized by the CPU 10a, or may be realized by the CPU and the ASIC.

DESCRIPTION OF SYMBOLS 1 ... Multifunction machine, 10 ... Control part, 10a ... CPU, 10b ... ROM, 10c ... RAM, 11 ... Reading part, 11a ... Image processing circuit, 12 ... Print unit, 13 ... operation unit, 14 ... storage unit, 15 ... communication interface unit, 20 ... image, 21 ... block

Claims (5)

The image represented in the YCbCr color space is divided into a plurality of blocks, a histogram of the Y component values of the pixels constituting the block is created for each block, and the mode value in the histogram and the mode value A block unit mode value calculation unit for obtaining a ratio;
A single color / multicolor block determination unit that determines whether the block is a single color block or a multicolor block based on the mode value ratio obtained by the block unit mode value calculation unit;
A first achromatic / chromatic block determining unit that determines whether the block is an achromatic block or a chromatic block for the block determined by the single color / multicolor block determining unit; ,
Whether the mode value obtained by the block unit mode value calculation unit is less than or equal to a first threshold for a block that is determined to be an achromatic color block by the first achromatic / chromatic color block determination unit Alternatively, it is determined as a black-and-white block if it is greater than or equal to a second threshold value that is greater than the first threshold value, and is determined to be a gray block if the mode value is greater than the first threshold value and less than the second threshold value. A first black-and-white / gray block determination unit,
An image processing apparatus comprising: The image processing apparatus according to claim 1,
A second achromatic / chromatic color block determination unit that determines whether the block is a multicolor block or not by a single color / multicolor block determination unit. When,
For a block that is determined to be an achromatic color block by the achromatic / chromatic color determination unit, a pixel whose Y component value is equal to or less than a third threshold in the histogram created by the block unit mode value calculation unit, and , Determining a total ratio of pixels having a Y component value equal to or greater than a fourth threshold value greater than the third threshold value, and determining whether the block is a black and white block or a gray block based on the total ratio. 2 black and white / gray block determination units;
An image processing apparatus comprising: The image processing apparatus according to claim 2,
Based on the ratio of the monochromatic block in the image, it is determined whether the monochromatic image is a monochromatic image in which the ratio of the monochromatic block is equal to or greater than a certain ratio or a multicolor image in which the ratio of the monochromatic block is less than the certain ratio. A multicolor image determination unit;
When the single color / multicolor image determination unit determines that the image is a single color image, the mode unit calculating unit calculates a mode histogram of the mode value obtained for each block. An image unit mode value calculation unit for obtaining a ratio of mode values;
A plain image determination unit that determines whether or not the image is a plain image based on a ratio of the mode value obtained by the image unit mode value calculation unit;
When the plain image determination unit determines that the image is not a plain image, whether the image is a monochrome image, a gray image, or a color image is determined based on the monochrome block, the gray block, and the chromatic color block. A black and white / gray / color image determination unit for determination based on the ratio;
An image processing apparatus comprising: A reading unit that reads an original and generates an image;
A color space conversion unit that converts the color space of the image generated by the reading unit into a YCbCr color space;
The image converted into the YCbCr color space by the color space conversion unit is divided into a plurality of blocks, and a histogram of the Y component values of the pixels constituting the block is created for each block. A block unit mode value calculation unit for obtaining a value and a ratio of the mode value;
A single color / multicolor block determination unit that determines whether the block is a single color block or a multicolor block based on the mode value ratio obtained by the block unit mode value calculation unit;
A first achromatic / chromatic block determining unit that determines whether the block is an achromatic block or a chromatic block for the block determined by the single color / multicolor block determining unit; ,
Whether the mode value obtained by the block unit mode value calculation unit is less than or equal to a first threshold for a block that is determined to be an achromatic color block by the first achromatic / chromatic color block determination unit Alternatively, it is determined as a black-and-white block if it is greater than or equal to a second threshold value that is greater than the first threshold value, and is determined to be a gray block if the mode value is greater than the first threshold value and less than the second threshold value. A first black-and-white / gray block determination unit,
An image reading apparatus comprising: The image represented in the YCbCr color space is divided into a plurality of blocks, a histogram of the Y component values of the pixels constituting the block is created for each block, and the mode value in the histogram and the mode value A block unit mode value calculation process for obtaining a ratio;
A monochrome / multicolor block determination process for determining whether the block is a single color block or a multicolor block based on the mode value ratio obtained by the block unit mode value calculation process;
A first achromatic / chromatic block determination process for determining whether the block is a monochrome block or a chromatic block for the block determined to be a monochrome block by the monochrome / multicolor block determination process; ,
Whether the mode value obtained by the block mode mode value calculation process is less than or equal to a first threshold value for a block that is determined to be an achromatic color block by the first achromatic / chromatic color block determination process Alternatively, it is determined as a black-and-white block if it is greater than or equal to a second threshold value that is greater than the first threshold value, and is determined to be a gray block if the mode value is greater than the first threshold value and less than the second threshold value. First black and white / gray block determination processing,
An image processing program for causing a computer to execute.

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