JP2009246838A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology that accurately detects regions drawn in regular patterns and reduces the interference between the regions drawn in regular patterns and dither images, thereby offering the color images desired by a user. <P>SOLUTION: A two-color ratio calculation section 404 performs the counting-up when four pixels close to the reference pixel consist of two colors. A continuous pixel ratio calculation section 405 detects pixel streams consisting of pixels having the same pixel values to determine a total value of the lengths of each detected pixel streams. A difference calculation section 406 determines a difference value denoting a difference between a pixel block already subject to the resolution conversion processing and a pixel block of interest. A pattern detection section 407 determines whether the pixel block of interest is a pixel block including the regular patterns according to the magnitude comparison result with the total value, difference value, count value, and a preset threshold value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing technique.

  Conventionally, in an application software used in a personal computer, when trying to realize a pseudo color and transparency by drawing a regular pattern image, the dither pattern and the regular pattern image interfere with each other. I was waking up. As a result, there is a problem that a desired color does not appear or the picture disappears due to interference depending on the situation.

On the other hand, there has been proposed a method for solving these obstacles by shifting the phase of the cycle between the dither pattern and the pattern image. In addition, a method has been proposed in which foreground and background extraction processing is performed on a semi-transparent object, and an average value of both pixels is calculated so as not to generate moire or roughness. Furthermore, a technique for solving these problems by selecting an optimal dither pattern according to the regularity of a specified image and reproducing an ideal color has been proposed.
Japanese Patent Laid-Open No. 2002-225381 JP 2002-152526 A JP 2003-281557 A

  However, in the conventional method, it is necessary to prepare a special processing system when extracting an image having such a regular pattern, and the processing is complicated. Further, in the case of being dependent on the page description language, there may be a case where the detection process cannot be performed on an image input as a raster image. In the future, the types of regular patterns that will be expected with the multi-functionality of applications will vary widely, and it is difficult to deal with all of them.

  The present invention has been made in view of the above problems, accurately detects a region drawn in a regular pattern, and prevents interference between the region drawn in a regular pattern and a dither image. It is an object to provide a technique for suppressing and providing an image having a user-desired color.

  In order to achieve the object of the present invention, for example, an image processing apparatus of the present invention comprises the following arrangement.

That is, a dividing unit that divides an image into a plurality of pixel blocks;
For each pixel block divided by the dividing means, reference is made to each pixel in the pixel block of interest, and counting means for counting up when the four neighboring pixels of the referenced pixel are composed of two colors,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Means,
Calculation means for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
It is determined whether or not the pixel block of interest is a pixel block including a regular pattern based on a comparison result of the total value, the difference value, the count value by the counting means, and a preset threshold value. Determination means to perform,
When the pixel block of interest is a pixel block including a regular pattern, the pixel block of interest includes processing means for performing processing for reducing image quality on the pixel block of interest.

  In order to achieve the object of the present invention, for example, an image processing apparatus of the present invention comprises the following arrangement.

That is, a dividing unit that divides an image into a plurality of pixel blocks;
For each pixel block divided by the dividing means, reference is made to each pixel in the pixel block of interest, and counting means for counting up when the four neighboring pixels of the referenced pixel are composed of two colors,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Means,
Calculation means for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
Determining means for determining the attribute of the pixel block of interest;
A determination process for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a comparison result between the total value, the count value by the counting unit, and a preset threshold value; Alternatively, among the determination processes for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a magnitude comparison result between the difference value and a preset threshold value. Determination means for executing one determination process determined according to the attribute determined by the means;
When the pixel block of interest is a pixel block including a regular pattern, the pixel block of interest includes processing means for performing processing for reducing image quality on the pixel block of interest.

  In order to achieve the object of the present invention, for example, an image processing method of the present invention comprises the following arrangement.

That is, a dividing step of dividing an image into a plurality of pixel blocks;
With respect to each pixel block divided in the division step, each pixel block in the target pixel block is referred to, and when the four pixels in the vicinity of the referenced pixel are composed of two colors, a counting step for counting up,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Process,
A calculation step for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
It is determined whether or not the pixel block of interest is a pixel block including a regular pattern based on a magnitude comparison result between the total value, the difference value, the count value obtained by the counting step, and a preset threshold value. A determination step to
When the pixel block of interest is a pixel block including a regular pattern, the pixel block includes a processing step of performing a process for reducing image quality on the pixel block of interest.

  In order to achieve the object of the present invention, for example, an image processing method of the present invention comprises the following arrangement.

That is, a dividing step of dividing an image into a plurality of pixel blocks;
With respect to each pixel block divided in the division step, each pixel block in the target pixel block is referred to, and when the four pixels in the vicinity of the referenced pixel are composed of two colors, a counting step for counting up,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Process,
A calculation step for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
A determination step of determining an attribute of the pixel block of interest;
A determination process for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a comparison result between the total value, the count value obtained by the counting step, and a preset threshold value; Alternatively, among the determination processes for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a magnitude comparison result between the difference value and a preset threshold value. A determination process for executing one determination process determined according to the attribute determined in the process;
When the pixel block of interest is a pixel block including a regular pattern, the pixel block includes a processing step of performing a process for reducing image quality on the pixel block of interest.

  According to the configuration of the present invention, the region drawn with the regular pattern is accurately detected, the interference between the region drawn with the regular pattern and the dither image is suppressed, and the user-desired color tone is obtained. Images can be provided.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. The embodiment described below shows an example when the present invention is specifically implemented, and is one of the specific examples of the configurations described in the claims.

[First Embodiment]
FIG. 1 is a block diagram illustrating a configuration example of a system to which the image processing apparatus according to the present embodiment is applied. As shown in FIG. 1, the system includes a printer device 10 that functions as an image processing device according to the present embodiment, and a host computer 50.

  First, the printer apparatus 10 will be described. The printer device 10 is a device that receives a print job transmitted from the host computer 50 and forms a visible image on a recording medium such as recording paper based on the received print job. The printer apparatus 10 includes a control unit 11, a printer engine 14, and an HDD (Hard Disk Drive) 105.

  The control unit 11 controls the entire printer device 10 and executes processes described later as what the printer device 10 performs. The control unit 11 analyzes the print job transmitted from the host computer 50 and generates image data in a form that can be provided to the printer engine 14. Such processing is actually performed by the CPU 12 of the control unit 11. The CPU 12 performs such processing by executing a program stored in the memory 13. Of course, the memory 13 stores programs and data for causing the CPU 12 to execute other processes.

  The printer engine 14 operates according to control by the control unit 11 and forms a visible image on a recording sheet according to image data sent from the control unit 11. Note that various printer engines such as an electrophotographic system, an inkjet system, and a thermal system can be applied to the printer engine 14.

  The HDD 105 stores a print job sent from the host computer 50.

  Next, the host computer 50 will be described.

  In order to cause the printer apparatus 10 to perform a printing operation and to acquire information related to the printer apparatus 10 from the printer apparatus 10, driver software (so-called printer driver) of the printer apparatus 10 is preinstalled in the host computer 50. . For example, it is assumed that an instruction for printing a document is issued using an application running on the host computer 50. In this case, the installed printer driver generates a “print job configured in a page description language (PDL) that can be analyzed by the printer device 10” of the document, and the host computer 50 executes this print job. Transmit to the printer device 10.

  The print job data transmitted to the printer apparatus 10 is temporarily stored in the HDD 105 of the printer apparatus 10. Next, the CPU 12 performs PDL analysis on the print job and renders a bitmap image on the memory 13 based on the PDL. Further, the control unit 11 obtains attribute information for each pixel during PDL analysis and generates attribute flag data. That is, by referring to the information indicating the command type in the PDL command, attribute information for identifying the pixels constituting the black character pixel is generated for each pixel and used as attribute data. Note that the attribute data is not limited to those indicating black characters. For example, multi-bit information indicating various attributes such as a color character region, a halftone dot region, and a vector graphics region is used as the attribute flag data. it can.

  Then, the control unit 11 outputs the bitmap image obtained thereby to the printer engine 14.

  Here, in the present embodiment, the CPU 12 divides the rendered bitmap image into a plurality of pixel blocks, and detects an image area including a regular pattern for each pixel block. And about the pixel block which detected the image area containing a regular pattern, the process for reducing an image quality, such as a smoothing filtering process, is performed. The data of each pixel block is sequentially sent to the printer engine 14.

  Next, a process performed by the printer device 10 on a bitmap image will be described in detail.

  Here, the bitmap image (image) may be a monochrome multi-valued image, but in the present embodiment, it is assumed that each pixel is a color image expressed in RGB. Since each of R, G, and B is expressed by 8 bits, each luminance value of R, G, and B can take a value of 0-255. The image size is assumed to be W pixels in the horizontal direction and H pixels in the vertical direction. Also, component numbers 0, 1, and 2 are assigned to R, G, and B, respectively, and the upper left corner of the bitmap image is set to the coordinates (0, 0), and is at the horizontal pixel position x and the vertical pixel position y. The pixel value of the pixel with component number C is represented as P (x, y, C). For example, if the pixel at position (x, y) = (3, 4) has a pixel value of (R, G, B) = (255, 128, 0), P (3, 4, 0) = 255 , P (3, 4, 1) = 128 and P (3, 4, 2) = 0.

  FIG. 4 is a block diagram illustrating a functional configuration example of the control unit 11. Hereinafter, a process performed on the image by the control unit 11 will be described with reference to FIG.

  The CPU 12 renders an image on the buffer 401 based on the print job transmitted from the host computer 50. The buffer 401 is a partial area in the memory 13.

  The block dividing unit 402 as one function of the CPU 12 divides the image for one stripe into a plurality of pixel blocks when the image for one stripe (image for Th line) is stored in the buffer 401. Here, the size of the pixel block is assumed to be a horizontal direction Tw pixel and a vertical direction Th pixel. For convenience of explanation, it is assumed that the number of pixels W in the horizontal direction of the image is an integral multiple of Tw. In the following description, the pixel block composed of the horizontal direction Tw pixels and the vertical direction Th pixels may be referred to as a tile.

  The buffer 403 has an area for storing pixel block data for one tile, and sequentially stores the pixel block data output from the block dividing unit 402. Accordingly, the minimum capacity required for the buffer 403 is Tw × Th × 3 (RGB) bytes. In the pixel block for one tile stored in the buffer 403, the luminance value of the component c of the pixel at the horizontal pixel position x and the vertical pixel position y is defined as P (x, y, c). X = 0 to (Tw-1), y = 0 to (Th-1), and c is any one of 0 to 2 (that is, the component number corresponding to any of R, G, and B). ).

  Next, when the two-color rate calculation unit 404 as one function of the CPU 12 reads data of one pixel block (target pixel block) from the buffer 403, the two color rate calculation unit 404 refers to each pixel constituting the target pixel block in raster scan order. . Then, it is checked whether or not the four pixels in the vicinity of the currently referred pixel are composed of two colors. FIG. 6 is a diagram illustrating a pixel that is currently referred to and four neighboring pixels. In FIG. 6, x is a pixel currently referred to. a, b, c, and d are four pixels in the vicinity of the pixel x. Therefore, in the case of FIG. 6, the pixel values of the respective pixels a, b, c, and d are referred to, and the relationship between the pixel values is a = b and c = d, or a = c and b = d, or a = If either d or b = c, it can be determined that “the four neighboring pixels are composed of two colors”. When it is determined that “the four neighboring pixels are composed of two colors”, the count value is incremented by one. Of course, the count value is initialized for each pixel block. That is, it is already initialized to 0 before the two-color rate calculation unit 404 starts processing for the pixel block of interest.

  Such processing is performed for each pixel constituting the target pixel block. Thereby, in the pixel block of interest, the number of pixels x such that “the four neighboring pixels a to d are composed of two colors” can be counted.

  Here, since the number of pixels constituting the pixel block of interest is ThxTw, if the result of counting the pixel block of interest is T, the pixel x in which the surrounding four pixels a to d are composed of two colors is focused. The appearance probability in the pixel block is represented by T / (ThxTw). The appearance probability is a result of dividing the count value counted for the target pixel block by the number of pixels constituting the target pixel block. This appearance probability is referred to as “two-color ratio” in the following description, and the two-color ratio calculation unit 404 outputs this appearance probability as “two-color ratio”. That is, the two color rate calculation unit 404 outputs the two color rate for each pixel block.

  Next, when the data of one pixel block (target pixel block) is read from the buffer 403, the continuous pixel rate calculation unit 405 as one function of the CPU 12 refers to each pixel constituting the target pixel block in the raster scan order. . Then, a pixel column composed of pixels having the same pixel value is detected in the target pixel block. Then, the length of each detected pixel column is obtained, and the total value of the obtained lengths of each pixel row is obtained. Since the number of pixels constituting the target pixel block is Th × Tw as described above, when the total value is R, the appearance probability of the pixel column in the target pixel block is represented by R / (ThxTw). The appearance probability is a result of dividing the total value obtained for the target pixel block by the number of pixels constituting the target pixel block. This appearance probability is referred to as “run rate” in the following description, and the continuous pixel rate calculation unit 405 outputs this appearance probability as “run rate”. That is, the continuous pixel rate calculation unit 405 outputs the run rate for each pixel block.

  Next, the difference calculation unit 406 as one function of the CPU 12 reads data of one pixel block (target pixel block) from the buffer 403. Then, a difference value indicating a difference between the resolution-converted pixel block obtained by performing the resolution conversion process on the read target pixel block and the read target pixel block is obtained.

  Here, the process performed by the difference calculation unit 406 will be described in more detail. FIG. 5A is a diagram showing each pixel constituting the target pixel block read from the buffer 403. FIG. 5B is a diagram showing each pixel constituting a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel block of interest read from the buffer 403.

The upper left corner of the pixel block of interest is (0, 0), and the horizontal x coordinate and the vertical y coordinate are defined. In this case, the pixel value of the pixel at the coordinate position (p, q) in the pixel block of interest is represented as V ′ _{(p, q)} . Similarly, the upper left corner of the pixel block having undergone resolution conversion is (0, 0), and the horizontal direction x coordinate and the vertical direction y coordinate are defined. In this case, the pixel value of the pixel at the coordinate position (p, q) in the resolution-converted pixel block is represented as V _{(p, q)} .

First, the difference calculation unit 406 performs resolution conversion on the pixel block of interest, and generates a reduced tile pixel block (resolution conversion-processed pixel block) that has been reduced to 1/2 the size in both the horizontal and vertical directions. Specifically, the pixel value of the pixel located at (x, y) in the pixel block of interest is V ′ _{(x, y)} , and the pixel value of the pixel located at _{(x, y) in} the resolution-converted pixel block Is V _{(x, y)} , the following equation is calculated for all x and y. Here, calculating for all x and y means calculating for each of x = 0 to (Tw−2) / 2 and y = 0 to (Th−2) / 2. Thereby, a pixel block having undergone resolution conversion processing can be generated.

V _{(x, y)} = (V ' _{(2x, 2y)} + V' _{(2x + 1, y)} + V ' _{(2x, 2y + 1)} + V' _{(2x + 1,2y + 1)} ) / 4
This process is performed for each of R, G, and B color components. In FIG. 5, the average value of V ′ ₍₀ , ₀₎ , V ′ ₍₁ , ₀₎ , V ′ ₍₀ , ₁₎ , V ′ _{(1, 1)} is V _{(0, 0)} .

  Thereby, a resolution-converted pixel block having a size of (Tw / 2) pixels × (Th / 2) pixels can be generated.

  Next, the difference calculation unit 406 calculates a difference value between the pixel block of interest and the resolution-converted pixel block based on the following formula.

  Thereby, the difference value D can be obtained.

  Next, the pattern detection unit 407 as one function of the CPU 12 acquires three pieces of information output from each of the two-color rate calculation unit 404, the continuous pixel rate calculation unit 405, and the difference calculation unit 406. Then, the pattern detection unit 407 uses these three pieces of information to determine whether or not the pixel block of interest is a pixel block including a pattern (regular pattern) that is a region having a large change in image quality due to resolution conversion or the like. To do. As an example of a pixel block including a regular pattern, there is an image formed by one dot and one space as shown in FIG. Hereinafter, the operation of the pattern detection unit 407 will be described using the pixel block illustrated in FIG. Of course, the following description is not limited to the pixel block.

  In the case of the pixel block illustrated in FIG. 7, the two-color rate Tr is close to 100%, the run rate Rr is close to 0%, and the difference value D is large. On the other hand, in the natural image, the two-color rate Tr and the difference value D are small, and the run rate Rr is slightly high. Therefore, the preset threshold value St for the two color ratios is set to 20, the threshold value Sr for the run ratio is set to 30, and the threshold value Sd for the difference value is set to 100, so that the pixel block of interest is Tr> St and Rr <Sr and D When> Sd is satisfied, it is determined that the pixel block of interest includes a regular pattern.

  In this way, by setting a threshold for each of the two color ratios, the run ratio, and the difference value, and simply performing a magnitude comparison with the threshold for each of the two color ratios, the run ratio, and the difference value (only the magnitude comparison result) Pixel blocks containing a regular pattern can be detected.

  Thereafter, the pattern detection unit 407 directly determines a pixel block that does not include a regular pattern as a PDL creation processing target. On the other hand, for the pixel block including a regular pattern, the pattern detection unit 407 performs processing for reducing image quality, such as filtering processing using a smoothing filter, before making it a PDL creation processing target. As a result, the periodic pattern is smoothed and the images become blurred. Then, this smoothing process can reduce interference with dither, which is a subsequent process, and can realize a color close to what the user has seen on other image display devices such as a display.

  Note that various processes other than the process using the smoothing filter can be applied to the process for reducing the image quality. For example, instead of a pixel block including a regular pattern, the pixel block obtained by doubling the vertical and horizontal resolution-converted pixel blocks obtained by the above-described processing may be output.

  Next, processing that the printer apparatus 10 performs on the bitmap image will be described below with reference to FIG. 2 showing a flowchart of the processing. Since each process in each step is as described above, it will be briefly described here.

  First, in step S201, when an image for one stripe (an image for Th line) is stored in the buffer 401, the block dividing unit 402 as a function of the CPU 12 converts the image for one stripe into a plurality of pixel blocks. Divide into

  Next, in step S <b> 202, when the two-color rate calculation unit 404 as a function of the CPU 12 reads data of one pixel block (target pixel block) from the buffer 403, each pixel constituting the target pixel block is rasterized. Browse in scan order. Then, it is checked whether or not the four pixels in the vicinity of the currently referred pixel are composed of two colors. When it is determined that “the four neighboring pixels are composed of two colors”, the count value is incremented by one. Then, the appearance probability of the pixel in which the surrounding four pixels are composed of two colors in the target pixel block is obtained as the two-color rate Tr.

  On the other hand, in step S203, when the continuous pixel rate calculation unit 405 as a function of the CPU 12 reads data of one pixel block (target pixel block) from the buffer 403, each pixel constituting the target pixel block is raster-scanned. Refer to them in order. Then, a pixel column composed of pixels having the same pixel value is detected in the target pixel block. Then, the length of each detected pixel column is obtained, and the total value of the obtained lengths of each pixel row is obtained. Since the number of pixels constituting the pixel block of interest is Th × Tw as described above, when the total value is R, the appearance probability of the pixel column in the pixel block of interest is represented by R / (ThxTw). The rate calculation unit 405 outputs this appearance probability as a run rate Rr.

  On the other hand, in step S <b> 204, the difference calculation unit 406 as a function of the CPU 12 reads data of one pixel block (target pixel block) from the buffer 403. Then, a difference value D indicating the difference between the resolution-converted pixel block obtained by performing the resolution conversion process on the read target pixel block and the read target pixel block is obtained.

  Next, in step S205, the pattern detection unit 407 as a function of the CPU 12 determines whether or not the target pixel block satisfies Tr> St and Rr <Sr and D> Sd. If the pixel block of interest satisfies Tr> St and Rr <Sr and D> Sd as a result of the determination, the process proceeds to step S206. If not, the process proceeds to step S207.

  In step S206, the pattern detection unit 407 performs processing for reducing the image quality, such as filter processing using a smoothing filter, on the pixel block of interest.

  In step S207, in order to make the pixel block of interest a PDL creation process target, the data of the pixel block of interest is output to the PDL creation process.

  Next, in step S208, the CPU 12 determines whether or not the processing in steps S202 to S207 has been performed for all the pixel blocks divided in step S201, and if so, ends the present processing. On the other hand, if the processes of steps S202 to S207 are still performed and the inner pixel block remains, the process is returned to immediately after step S201, and the process after step S202 is performed on the remaining pixel block.

[Second Embodiment]
In the first embodiment, as shown in FIG. 7, an example of an image having a pattern of one dot and one space has been described. However, there are various types of patterns, and two color ratios according to the types. There is a possibility that the trend of run rate and difference value will change. Therefore, the pattern detection conditions may be changed according to the pattern type.

  For example, there is a function capable of selecting a shaded transmittance in a semi-transparent process, and the pattern image has a completely different parameter distribution from an image of one dot and one space depending on the transmittance. For example, in the shaded portion where the transmittance is less than 20%, the two-color rate is low and the run rate is high, and the difference value is also low. Therefore, the threshold of the pattern detection condition is relaxed such that the threshold St for the two color ratios is 10%, the threshold Sr for the run ratio is 50%, and the threshold Sd for the difference value is 60. A threshold is set so that it can respond. However, although the accuracy of pattern detection increases only by relaxing the parameter threshold value, it is problematic because misjudgments other than the pattern region are frequently made. Therefore, a parameter may be added to the pattern detection condition in order to suppress erroneous determination.

  FIG. 8 is a block diagram illustrating a functional configuration example of the control unit 11. Hereinafter, processing performed by the control unit 11 on an image will be described with reference to FIG. In FIG. 8, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  When the neighborhood matching pixel calculation unit 501 as one function of the CPU 12 reads data of one pixel block (target pixel block) from the buffer 403, the neighboring pixel calculation unit 501 refers to each pixel constituting the target pixel block in the raster scan order. If there is a pixel having the same pixel value as that of the currently referenced pixel x among the four neighboring pixels of the currently referenced pixel x, the pixel x is regarded as a neighborhood matching pixel, and one count value K is set. Count up. The count value K is initialized for each pixel block. That is, the neighborhood matching pixel calculation unit 501 has already been initialized to 0 before starting the process for the pixel block of interest. Further, the neighborhood matching pixel calculation unit 501 increments the count value K ′ by one when the four neighboring pixels of the pixel regarded as the neighborhood matching pixel are configured in two colors. The count value K ′ is initialized for each pixel block. That is, the neighborhood matching pixel calculation unit 501 has already been initialized to 0 before starting the process for the pixel block of interest.

  Such processing is performed for each pixel constituting the target pixel block. Accordingly, in the pixel block of interest, the number K of pixels x regarded as neighboring matching pixels and the number K ′ of pixels regarded as neighboring matching pixels and having four neighboring pixels composed of two colors are counted. can do. Then, the neighborhood matching pixel calculation unit 501 calculates K ′ / K using the count values K and K ′ thus determined, and sends the calculated K ′ / K to the pattern detection unit 502. Here, K ′ / K represents the ratio of pixels in which the four neighboring pixels among the neighboring matching pixels are configured in two colors. That is, the neighborhood matching pixel calculation unit 501 outputs, for each pixel block, “a ratio of pixels in which the neighborhood 4 pixels are configured by two colors among the neighborhood matching pixels”. The relationship between the pixel x and the four neighboring pixels is, for example, the relationship between the pixel x and the four neighboring pixels a to d as shown in FIG.

  The pattern detection unit 502 also acquires information from the neighborhood matching pixel calculation unit 501 in addition to information from each of the two-color rate calculation unit 404, the continuous pixel rate calculation unit 405, and the difference calculation unit 406. Then, it is determined whether or not the pixel block of interest is a pixel block including a pattern (regular pattern) that is a region having a large image quality change due to resolution conversion or the like.

  The “ratio of pixels in which four neighboring pixels are composed of two colors among neighboring matching pixels” (= Q) is distributed in the vicinity of approximately 100% in the pattern area, but 60% to 80% in the natural image area. It is distributed around. Therefore, the pattern detection unit 502 uses Q in addition to the two-color rate, the run rate, and the difference value, and adds “Is Q close to 100%?” In the determination processing in step S205. If the condition described in the first embodiment for step S205 is satisfied and Q is close to 100%, it is determined that the pixel block of interest is a pixel block including a regular pattern. As a result, the erroneous determination of the natural image region that has occurred by relaxing the two-color rate, the run rate, and the difference value is suppressed, and it is possible to perform a good detection process regardless of the type of pattern.

[Third Embodiment]
In the second embodiment, an example in which the parameter is different due to the difference in the shaded transmittance has been described. However, the distribution tendency of the parameter differs depending not only on the pattern type but also on the background image. In the present embodiment, the pattern detection method is switched according to the background of the pattern to be detected.

  FIG. 3 is a block diagram illustrating a functional configuration example of the control unit 11. Hereinafter, a process performed on the image by the control unit 11 will be described with reference to FIG. In FIG. 3, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 3, the functional configuration of the control unit 11 according to the present embodiment includes a switch 702, an attribute buffer 703, and an image determination unit 701 in addition to the configuration of the control unit 11 according to the first embodiment (FIG. 4). At the same time, the attribute information is input to the buffer 401 in addition to the image.

  As described above, attribute information is input to the buffer 401 in addition to the image. This attribute information is a set of flags indicating the attributes of each pixel constituting the image. For example, if the target pixel is a pixel constituting a character, the flag value corresponding to the target pixel has a value of 1, and if the target pixel is a pixel other than a character, the flag value corresponding to the target pixel has a value of 0. . As described above, the flag value is associated with each pixel, and attribute information is obtained by arranging corresponding flags in the same arrangement as the arrangement of pixels.

  The block dividing unit 402 divides an image into a plurality of image blocks as in the first embodiment. In the present embodiment, the attribute information is further divided into a plurality of image blocks. Thereby, attribute information (division attribute information) corresponding to each pixel block can be obtained. Each divided attribute information obtained by the division is stored in the attribute buffer 703.

  The image discriminating unit 701 refers to each piece of division attribute information and determines the attribute of the corresponding pixel block. For example, if the number of flags having the value “1” among the flags constituting the target split attribute information is equal to or greater than a predetermined ratio with respect to the number of flags constituting the target split attribute information, the target split attribute information The pixel block corresponding to is determined to be a pixel block including characters. On the other hand, if the number of flags having a value of “0” among the flags constituting the target split attribute information is equal to or greater than a predetermined ratio with respect to the number of flags constituting the target split attribute information, the target split attribute information It is determined that the pixel block corresponding to is a pixel block including a natural image.

  If the image determination unit 701 determines that the pixel block corresponding to the target division attribute information is a pixel block including characters, the image determination unit 701 outputs determination information “0” to the switch 702 and the pattern detection unit 407. To do. On the other hand, when the image determination unit 701 determines that the pixel block corresponding to the target division attribute information is a pixel block including a natural image, the image determination unit 701 sends the determination information “1” to the switch 702 and the pattern detection unit 407. Output.

  The switch 702 reads pixel block data for one tile from the buffer 403 and obtains determination information corresponding to the pixel block from the image determination unit 701. Therefore, the switch 702 can determine whether the pixel block read from the buffer 401 is a pixel block including characters or an image block including a natural image. The switch 702 connects to the terminal a when receiving the discrimination information “0” from the image discrimination unit 701. As a result, pixel block data including characters is sent from the buffer 403 to the two-color rate calculation unit 404 and the continuous pixel rate calculation unit 405 via the switch 702. On the other hand, the switch 702 is connected to the terminal b when receiving the discrimination information “1” from the image discrimination unit 701. Thereby, the pixel block data including the natural image is sent from the buffer 403 to the difference calculation unit 406 via the switch 702.

  When receiving the discrimination information “0” from the image discrimination unit 701, the pattern detection unit 407 acquires information transmitted from the two-color rate calculation unit 404 and the continuous pixel rate calculation unit 405. Then, the pattern detection unit 407 uses the acquired two pieces of information to determine whether or not the pixel block of interest is a pixel block including a pattern (regular pattern) that is a region having a large image quality change due to resolution conversion or the like. Determine whether. Handling of each of the two pieces of information in the pattern detection unit 407 is the same as in the first embodiment.

  On the other hand, when receiving the discrimination information “1” from the image discrimination unit 701, the pattern detection unit 407 acquires information sent from the difference calculation unit 406. Then, the pattern detection unit 407 uses this acquired information to determine whether or not the pixel block of interest is a pixel block including a pattern (regular pattern) that is a region having a large change in image quality due to resolution conversion or the like. judge. Handling of information sent from the difference calculation unit 406 in the pattern detection unit 407 is the same as that in the first embodiment.

  This is because the distribution of the two color rates and the run rate does not change in the area where the pattern and the character overlap, but the parameter distribution of the difference values is scattered and the pattern detection is difficult, so only the two color rate and the run rate are detected. This is because it is possible to detect a pattern even by using. Further, in the case of a pattern region in which the shaded color and the background color are similar, the parameter distribution of the two-color rate and the run rate does not change, but the difference value becomes small. Pattern detection is performed using only the rate and run rate.

  On the other hand, the area where the pattern and the natural image overlap has a parameter distribution similar to that of the natural image area where the two-color rate is low and the run rate is high. For this reason, it is difficult to improve the detection accuracy of the pattern area by using the two color rate or the run rate, but the difference value is as high as 1 dot 1 space and the distribution tendency does not change. Pattern detection is possible by using the difference value. Therefore, pattern detection is performed using only the difference value. In other words, the pattern can be detected by a simpler method simply by changing the parameter setting depending on the type of image.

  In this embodiment, in order to simplify the description, an image having attribute information is input, and the attribute of each pixel block is determined using the attribute information. However, using other methods, The attribute of each pixel block may be determined. For example, the pixel block data output from the buffer 403 is used to count the number of colors existing in the pixel block, and based on the counting result, whether the pixel block includes a natural image or a character. May be determined.

  Note that the pixel block output from the pattern detection unit 407 may be processed according to the attribute of the pixel block. For example, the filter coefficient used for the filtering process for the target pixel block may be switched using the target division attribute information corresponding to the target pixel block. In addition, processing (for example, dither coefficient) or the like for reducing interference between the pixel block of interest and dither may be switched in accordance with the target division attribute information.

  The various technical matters described above may be used in appropriate combination.

  Each process described in the above embodiment has been described as being performed by the printer apparatus 10, but may be performed by a general PC (personal computer). That is, the PC divides the processing target image into a plurality of pixel blocks, and pixel blocks including a regular pattern among the pixel blocks are used to reduce image quality such as filtering using a smoothing filter. You may make it perform the process of.

[Other Embodiments]
Needless to say, the object of the present invention can be achieved as follows. That is, a recording medium (or storage medium) that records a program code (computer program) of software that implements the functions of the above-described embodiments is supplied to the system or apparatus. Needless to say, such a storage medium is a computer-readable storage medium. Then, the computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the recording medium. In this case, the program code itself read from the recording medium realizes the functions of the above-described embodiment, and the recording medium on which the program code is recorded constitutes the present invention.

  Further, by executing the program code read by the computer, an operating system (OS) or the like running on the computer performs part or all of the actual processing based on the instruction of the program code. Needless to say, the process includes the case where the functions of the above-described embodiments are realized.

  Furthermore, it is assumed that the program code read from the recording medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer. After that, based on the instruction of the program code, the CPU included in the function expansion card or function expansion unit performs part or all of the actual processing, and the function of the above-described embodiment is realized by the processing. Needless to say.

  When the present invention is applied to the recording medium, program code corresponding to the flowchart described above is stored in the recording medium.

1 is a block diagram illustrating a configuration example of a system to which an image processing apparatus according to a first embodiment of the present invention is applied. 4 is a flowchart of processing performed by the printer device 10 on a bitmap image. 3 is a block diagram illustrating a functional configuration example of a control unit 11. FIG. 3 is a block diagram illustrating a functional configuration example of a control unit 11. FIG. (A) is a diagram showing each pixel constituting the target pixel block read from the buffer 403, and (b) is a resolution converted pixel obtained by performing resolution conversion processing on the target pixel block read from the buffer 403. It is a figure which shows each pixel which comprises a block. It is a figure which shows the pixel currently referred and its four neighboring pixels. It is a figure which shows an example of a pixel block. 3 is a block diagram illustrating a functional configuration example of a control unit 11. FIG.

Claims (9)

A dividing means for dividing the image into a plurality of pixel blocks;
For each pixel block divided by the dividing means, reference is made to each pixel in the pixel block of interest, and counting means for counting up when the four neighboring pixels of the referenced pixel are composed of two colors,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Means,
Calculation means for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
It is determined whether or not the pixel block of interest is a pixel block including a regular pattern based on a comparison result of the total value, the difference value, the count value by the counting means, and a preset threshold value. Determination means to perform,
When the pixel block of interest is a pixel block including a regular pattern, an image processing apparatus comprising: processing means for performing processing for reducing image quality on the pixel block of interest. V ′ _{(x, y)} is the pixel value of the pixel located at the coordinate position (x, y) in the pixel block of interest, and the pixel value of the pixel located at (x, y) in the resolution-converted pixel block. If V _{(x, y)} ,
The calculation means uses the following formula: V _{(x, y)} = (V ′ _{(2x, 2y)} + V ′ _{(2x + 1, y)} + V ′ _{(2x, 2y + 1)} + V ′ _{(2x + 1, 2y + 1)} ) / 4
Is calculated for all x and y to generate a resolution-converted pixel block, and the difference value D is expressed by the following equation:

The image processing apparatus according to claim 1, wherein the image processing apparatus calculates the value by calculating.   The determination means has a result obtained by dividing the count value by the number of pixels constituting the target pixel block larger than a preset threshold value, and the total value is divided by the number of pixels constituting the target pixel block. When the result is smaller than a preset threshold value and the difference value is larger than a preset threshold value, it is determined that the pixel block of interest is a pixel block including a regular pattern. Item 8. The image processing apparatus according to Item 1.   2. The processing unit according to claim 1, wherein when the pixel block of interest is a pixel block including a regular pattern, a filtering process using a smoothing filter is performed on the pixel block of interest. The image processing apparatus described. A dividing means for dividing the image into a plurality of pixel blocks;
For each pixel block divided by the dividing means, reference is made to each pixel in the pixel block of interest, and counting means for counting up when the four neighboring pixels of the referenced pixel are composed of two colors,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Means,
Calculation means for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
Determining means for determining the attribute of the pixel block of interest;
A determination process for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a comparison result between the total value, the count value by the counting unit, and a preset threshold value; Alternatively, among the determination processes for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a magnitude comparison result between the difference value and a preset threshold value. Determination means for executing one determination process determined according to the attribute determined by the means;
When the pixel block of interest is a pixel block including a regular pattern, an image processing apparatus comprising: processing means for performing processing for reducing image quality on the pixel block of interest. A dividing step of dividing the image into a plurality of pixel blocks;
With respect to each pixel block divided in the division step, each pixel block in the target pixel block is referred to, and when the four pixels in the vicinity of the referenced pixel are composed of two colors, a counting step for counting up,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Process,
A calculation step for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
It is determined whether or not the pixel block of interest is a pixel block including a regular pattern based on a magnitude comparison result between the total value, the difference value, the count value obtained by the counting step, and a preset threshold value. A determination step to
When the pixel block of interest is a pixel block including a regular pattern, the image processing method includes a processing step of performing a process for reducing image quality on the pixel block of interest. A dividing step of dividing the image into a plurality of pixel blocks;
With respect to each pixel block divided in the division step, each pixel block in the target pixel block is referred to, and when the four pixels in the vicinity of the referenced pixel are composed of two colors, a counting step for counting up,
In the pixel block of interest, a pixel column composed of pixels having the same pixel value is detected, the length of each detected pixel column is obtained, and the total value of the obtained lengths of the respective pixel columns is obtained. Process,
A calculation step for obtaining a difference value indicating a difference between a resolution-converted pixel block obtained by performing resolution conversion processing on the pixel-of-interest block and the pixel-of-interest block;
A determination step of determining an attribute of the pixel block of interest;
A determination process for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a comparison result between the total value, the count value obtained by the counting step, and a preset threshold value; Alternatively, among the determination processes for determining whether or not the pixel block of interest is a pixel block including a regular pattern based on a magnitude comparison result between the difference value and a preset threshold value. A determination process for executing one determination process determined according to the attribute determined in the process;
When the pixel block of interest is a pixel block including a regular pattern, the image processing method includes a processing step of performing a process for reducing image quality on the pixel block of interest.   A computer program for causing a computer to function as each unit included in the image processing apparatus according to any one of claims 1 to 5.   A computer-readable storage medium storing the computer program according to claim 8.

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