JP2010074627A - Image processor and method of processing image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To not only use a screen adapted to a feature of an image but also reduce the image deterioration caused by using a plurality of screens. <P>SOLUTION: An image processor includes: screen processing portions 2a and 2b that each carries out screen processing by using a plurality of different screens for an image so as to generate images processed by each screen; a feature analyzing portion 1 for carrying out feature analysis of the image; and a combining portion 3 that determines the combination proportion of each image processed by the plurality of the screens based on the results of the feature analysis and outputs the image generated by combining each processed image according to the combining proportion. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method.

As the number of screen lines decreases, the gradation becomes more stable as the number of lines decreases, and the resolution increases as the number of lines increases. Therefore, a screen with a high number of screen lines is used for an area where the resolution is important, such as characters, and the gradation is emphasized like a solid image (area filled with the same density). It is preferable to use a region with a low screen line number.
However, it is difficult to satisfy both the resolution and the gradation when an image including characters and solid images is uniformly screen-processed using the same screen.

  Therefore, the screen used for each area is switched. For example, tag information indicating whether a text (Text), a line drawing (Graphics), or a photograph (Image) is added to each object as a drawing unit. An appropriate screen is switched to the character, line drawing, or photographic image for each area of the character, line drawing, or photographic image identified by the tag information.

There is also a method in which the image is separated into a highlight part (bright part of the image) and other parts, a screen with a low line number is used for the highlight part, and a screen with a high line number is used for the other parts. It is disclosed (for example, see Patent Document 1).
Furthermore, a method is also disclosed in which an edge is detected from an image, a screen that differs depending on the presence or absence of an edge is used, and when there is an edge, a screen corresponding to the edge strength is used (see, for example, Patent Document 2).
JP 2006-270655 A JP-A-9-294208

  However, when a photographic image includes hair or characters (for example, a bottle label or a T-shirt character), the region separation method using tag information as described above, or Patent Documents 1 and 2 In the area separation method described in 1), accurate separation is difficult, and an appropriate screen may not be used.

  For a character having a halftone density, when a screen with a low number of lines is used, image quality deterioration called jaggy with jagged edges of the character occurs. In order to avoid such image quality degradation, the tag information indicates that the character is a character, and a screen with a high line number for the character may be used. However, under various printing conditions, the tag information is displayed in this way. It may not be accurately reflected.

  Also, if the image contains vertical and horizontal lines with halftone density, screen processing using a screen with a screen angle other than 45 ° will change the line width of the vertical and horizontal lines depending on the orientation of the screen. Therefore, there is a problem that the reproducibility of the line image is lowered.

  Furthermore, when a plurality of types of screens are switched and used in the same image, the switching portion is noticeable enough to be visually recognized, and unnecessary noise may be generated.

  An object of the present invention is to use a screen suitable for image characteristics with high accuracy.

According to the invention of claim 1,
A screen processing unit that performs screen processing on each image using a plurality of different screens, and generates a processed image by each screen;
A feature analysis unit for performing feature analysis of the image;
Determining a synthesis ratio of each processed image by the plurality of screens based on a result of the feature analysis, and a synthesis unit that outputs a synthesized image obtained by synthesizing each processed image according to the synthesis ratio;
An image processing apparatus is provided.

According to invention of Claim 2,
The image processing apparatus according to claim 1, wherein the feature analysis is wavelet analysis.

According to invention of Claim 3,
The image processing apparatus according to claim 2, wherein an area unit for performing the screen processing and an area unit for performing the wavelet analysis have an integer multiple relationship.

According to invention of Claim 4,
4. The image processing apparatus according to claim 2, wherein the plurality of different screens have a screen line number of each screen in an integral multiple relationship.

According to the invention of claim 5,
4. The image processing apparatus according to claim 2, wherein the plurality of different screens are in a relationship in which growth centers of dots formed by the respective screens periodically overlap each other in the screen processing.

According to the invention of claim 6,
The feature analysis unit determines whether or not there is a feature of at least a thin line structure, an edge or an isolated point by wavelet analysis, and determines whether or not there is a feature of a solid image or a gradation,
When the characteristic analysis unit determines that the feature analysis unit has a fine line structure, an edge, or an isolated point, the synthesis unit increases a synthesis ratio of processed images using a screen with a high line number among the plurality of different screens. When the feature analysis unit determines that there is a solid image or gradation feature, the processing image synthesis ratio using a screen with a low number of lines among the plurality of different screens is increased. An image processing apparatus according to claim 1 is provided.

According to the invention of claim 7,
The different screens include screens for line images having a halftone density and extending in the main scanning direction or sub-scanning direction of the image,
The feature analysis unit determines whether or not there is a feature of a line image having a halftone density and extending in a main scanning direction or a sub-scanning direction of the image by wavelet analysis,
When the characteristic analysis unit determines that the characteristic analysis unit has the density of the halftone and has the characteristics of the line image extending in the main scanning direction or the sub-scanning direction of the image, the combining unit displays the screen for the line image. The image processing apparatus according to any one of claims 2 to 6, wherein the composition ratio of the used processed image is determined to be 100%.

According to the invention described in claim 8,
The image processing apparatus according to claim 7, wherein the screen for line images having the halftone density and extending in the main scanning direction or the sub-scanning direction of the image is a screen having a screen angle of 45 °.

According to the invention of claim 9,
The image processing apparatus according to claim 1, further comprising a post-processing unit that performs error diffusion processing or noise addition processing on the composite image.

According to the invention of claim 10,
The image is subjected to screen processing using a plurality of different screens, and a processed image is generated by each screen; and
Performing a feature analysis of the image;
Determining a composite ratio of each processed image based on the plurality of screens based on the result of the feature analysis, and outputting a composite image obtained by combining the processed images according to the composite ratio;
An image processing method is provided.

  According to the present invention, it is possible to obtain a composite image in which a screen suitable for each characteristic image portion is accurately used.

  In the present embodiment, an example in which the present invention is applied to an MFP (Multi Function Peripheral) will be described. The MFP is a composite image forming apparatus having a plurality of functions such as a copying function and a printing function.

FIG. 1 shows a functional configuration of the MFP according to the present embodiment.
The MFP 100 is connected to an external PC (personal computer) 200, and can generate image data from PDL (Page Description Language) format data transmitted from the external PC 200 and print the image.

  As illustrated in FIG. 1, the MFP 100 includes a controller 20, an image processing unit 10, a control unit 11, a reading unit 12, an operation unit 13, a display unit 14, a storage unit 15, an image memory 16, and a printing device 17. ing.

The controller 20 generates image data for each pixel by rasterization processing.
For example, document data created in the external PC 200 is converted into PDL format by the printer driver software and transmitted to the controller 20. The controller 20 analyzes the PDL command included in the transmitted PDL data by rasterization processing, assigns a pixel to each image unit to be rendered (this is called an object), and sets the pixel value for each assigned pixel. Generate data for An image is generated for each color of C (cyan), M (magenta), Y (yellow), and K (black).
In the present embodiment, the configuration in which the controller 20 is built in the MFP 100 has been described. However, the controller 20 may be provided outside the MFP 100.

  The control unit 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The control unit 11 performs various processes by performing calculations and centrally controlling each unit of the MFP 100 in cooperation with various processing programs stored in the storage unit 15.

  The reading unit 12 includes a scanner having an optical system and a CCD (Charge Coupled Device), and generates an image signal (analog signal) by optically scanning the document. The generated image signal is subjected to various correction processes in a processing unit (not shown), then digitally converted and output to the image processing unit 10.

The operation unit 13 is used to input an operation instruction from an operator, and includes various keys, a touch panel configured integrally with the display unit 14, and the like. The operation unit 13 generates an operation signal corresponding to an operation of a key or the like and outputs the operation signal to the control unit 11.
The display unit 14 displays an operation screen or the like on the display according to the control of the control unit 11.
The storage unit 15 stores parameters and setting data necessary for processing in addition to various processing programs. A hard disk or the like can be used as the storage unit 15.
The image memory 16 is a memory for storing image data. As the image memory 16, DRAM (Dynamic RAM) or the like can be used.

The printing device 17 performs printing based on the printing image input from the image processing unit 10. The image for printing is an image generated by the image processing unit 10 performing image processing on the image generated by the controller 20.
The printing device 17 performs electrophotographic printing, and includes, for example, a paper feeding unit, an exposure unit, a developing unit, a fixing unit, and the like. At the time of printing, the exposure unit irradiates the photosensitive drum with laser light based on the image data to form an electrostatic latent image. The electrostatic latent image is developed by the developing unit, and a toner image is formed on the sightseeing drum. The toner image is formed on each color image of C, M, Y, and K, and each color toner image is transferred onto the intermediate transfer belt to be a color image. The color image is transferred onto a sheet fed from a sheet feeding unit by a transfer roller or the like, and subjected to a fixing process by a fixing unit.

Next, the image processing unit 10 will be further described.
The image processing unit 10 performs image processing on the image input from the controller 20 and the image input from the reading unit 12. For example, the image processing unit 10 performs color conversion processing for converting RGB into CMYK colors for the image input from the reading unit 12. The image processing unit 10 also performs gradation correction processing and screen processing on the image to generate a print image.

The screen processing will be further described.
FIG. 2 is a diagram illustrating main components that function during screen processing in the image processing unit 10. As shown in FIG. 2, the image processing unit 10 includes a feature analysis unit 1, a first screen processing unit 2 a, a second screen processing unit 2 b, a synthesis unit 3, and a post-processing unit 4.

  The feature analysis unit 1 performs feature analysis of an image for each region unit. The feature analysis is wavelet analysis, and the feature analysis unit 1 determines the presence or absence of at least a fine line structure, an edge, an isolated point, a solid image, or a gradation feature by wavelet analysis. The fine line structure means a line image having a width of several pixels. A solid image is an image filled with a specific density.

A specific wavelet analysis method will be described.
Hereinafter, although an example of analysis using a Haar wavelet is shown, any wavelet may be used for wavelet analysis.
It is preferable that the area unit for performing the wavelet analysis and the area unit for performing the screen processing have an integer multiple relationship. As will be described later, the first screen used in the first screen processing unit 2a is a 4 × 4 pixel square screen, and the second screen used in the second screen processing unit 2b is a 2 × 2 pixel square screen. is there. The first screen processing unit 2a uses an 8 × 8 pixel supercell combining four first screens, and the second screen processing unit 2b uses an 8 × 8 pixel supercell combining sixteen second screens. Screen processing. In the present embodiment, an example will be described in which wavelet analysis is performed with 8 × 8 pixels that are the same as the 8 × 8 pixels that are the region unit of the screen processing, that is, with a unit relationship of 1 ×.

FIG. 3 shows an outline of primary to tertiary wavelet analysis performed on an 8 × 8 pixel region.
As shown in FIG. 3, in the primary analysis, the feature analysis unit 1 adds pixel values between adjacent pixels in the main scanning direction for each pixel of 8 × 8 pixels, and obtains 4 × 8 pixels composed of the added values. obtain. Similarly, pixel values are added between pixels adjacent in the sub-scanning direction of 8 × 8 pixels, and 8 × 4 pixels including the added value are obtained.

Next, the feature analysis unit 1 adds the pixel values between the adjacent pixels in the sub-scanning direction to the 4 × 8 pixels made up of the added values to obtain 4 × 4 pixels made up of the added values, and between the adjacent pixels The pixel value is subtracted to obtain 4 × 4 pixels composed of the difference value. 4 × 4 pixels consisting of the added value is a first interpretation result P ₁ of the total value in the main scanning direction and the sub-scanning direction, first-order difference total value 4 × 4 pixels consisting of the difference values in the sub-scanning direction The analysis result P _y1 . On the other hand, the feature analysis unit 1 targets 8 × 4 pixels composed of the added values, and obtains 4 × 4 pixels composed of the difference values by subtracting pixel values between pixels adjacent in the main scanning direction. The 4 × 4 pixels made up of this difference value is the primary analysis result P _x1 of the difference total value in the main scanning direction.

In the secondary analysis, the feature analysis unit 1 performs addition between pixels adjacent to each other in the main scanning direction for the 4 × 8 pixels made up of the added values used in the primary analysis to obtain 2 × 8 pixels made up of the added values. As shown in FIG. 3, 2 × 8 pixels composed of the added values and 4 × 4 pixels composed of the added values obtained in the primary analysis (total values in the main scanning direction and the sub-scanning direction) The same processing as in the next analysis is repeated twice to obtain secondary analysis results P ₂ , P _x2 and P _y2 . The secondary analysis results P ₂ , P _x2 , and P _y2 are values of 2 × 2 pixels.

In the tertiary analysis, the feature analysis unit 1 performs addition between pixels adjacent to each other in the main scanning direction for 2 × 8 pixels made up of the added values used in the secondary analysis to obtain 1 × 8 pixels made up of the added values. As shown in FIG. 3, the above-mentioned 1 × 8 pixels made up of the added values and 2 × 2 pixels made up of the added values obtained by the secondary analysis (total values in the main scanning direction and the sub-scanning direction) are used. The same processing as the next analysis is repeated three times to obtain the _third analysis results P ₃ , P _x3 and P _y3 . The tertiary analysis results P ₃ , P _x3 , and P _y3 are values of 1 × 1 pixel.

Of the analysis results obtained by the wavelet analysis as described above, the feature analysis unit 1 determines whether or not there is a feature based on P ₃ , P _x3 , and P _y3 that are tertiary analysis results. The determination is performed in the order of the fine line structure, the edge, the isolated point, the solid image, and the gradation, and the determination ends when it is determined that any of the features is present. For example, the feature analysis unit 1 is configured as shown in FIG. As shown in FIG. 4, the feature analysis unit 1 determines whether or not there is a feature using the wavelet analysis unit S <b> 1 that performs the above-described wavelet analysis on an input image in units of 8 × 8 pixels. It includes a fine line structure determination unit S2, an edge determination unit S3, an isolated point determination unit S4, a solid image determination unit S5, and a gradation determination unit S6.

  The wavelet analysis result obtained by the wavelet analysis unit S1 is output to the thin line structure determination unit S2. If the fine line structure determination unit S2 determines that the thin line structure determination unit S2 has the characteristics of the thin line structure based on the result of the wavelet analysis, the thin line structure determination unit S2 outputs a signal indicating the determination result to the synthesis unit 3. On the other hand, when it cannot be determined that the thin line structure determining unit S2 has the characteristics of the thin line structure, the thin line structure determining unit S2 outputs the wavelet analysis result to the subsequent edge determining unit S3. The subsequent edge determination unit S3, isolated point determination unit S4, solid image determination unit S5, and gradation determination unit S6 determine whether or not each has a characteristic to be determined using the wavelet analysis result in the same manner as the thin line structure determination unit S2. To do. When it is determined that the characteristic to be determined is present, the edge determination unit S3, the isolated point determination unit S4, the solid image determination unit S5, or the gradation determination unit S6 outputs a signal indicating the determination result and has the characteristic to be determined. If it cannot be determined, the wavelet analysis result is output to the determination unit at the subsequent stage. Finally, if the gradation determination unit S6 cannot determine the gradation, that is, if the gradation determination unit S6 cannot determine any feature of the fine line structure, the edge, the isolated point, the solid image, or the gradation, the gradation determination unit S6 has the corresponding feature. A signal indicating that there is no output is output.

  This order of determination is the order of features for which a high-line-number screen is suitable. Features such as thin line structures, edges, and isolated points that are suitable for high-line-number screens are judged before features that are suitable for low-line-number screens such as solid images and gradations. On the other hand, if a screen with a low number of lines is used by mistake, the degree of image quality deterioration increases.

  Also, features that are suitable for screens that achieve higher resolution than high gradation, such as thin line structures, edges, and isolated points, are judged together in the first half, and higher-order than high-resolution characteristics such as solid images and gradations. The features suitable for the screen that achieves tonality are determined together in the second half, so that a processing result to which the same type of screen is applied can be obtained even if the image features are not clear and the determination is incorrect. For example, in both the solid image and the gradation, the composition unit 3 described later has a high ratio of processing images screen-processed using a screen with a low number of lines used for composition. Therefore, even if the original feature is a solid image but it is erroneously determined to be a gradation, the ratio of processed images using the same type of screen in the composite image is the same, and there is no significant difference in processing results.

Next, a method for determining the presence or absence of features by each determination unit will be described.
(1) Judgment of fine line structure In the fine line structure, the result of wavelet analysis differs depending on the extending direction of the fine line. Therefore, the fine line structure determining unit S2 converts the line image into diagonal lines and vertical lines (extending in the sub-scanning direction of the image). Line image) or horizontal line (line image extending in the main scanning direction of the image).
(1.1) Judgment of oblique lines In the case of oblique lines, the total value P _{3 in the} main scanning direction and the sub-scanning direction is P ₃ > 0. Further, the difference total value P _{x3 in} the main scanning direction and the difference total value P _{y3 in the} sub scanning direction become P _x3 <0, P _y3 > 0, or P _x3 > 0, P _y3 depending on the direction in which the oblique lines extend. <0. Therefore, when the tertiary analysis results P ₃ , P _x3 , and P _y3 satisfy this condition, the fine line structure determination unit S2 determines that the region of 8 × 8 pixels subjected to the wavelet analysis has the characteristics of the oblique line structure. . On the other hand, if the condition is not satisfied, the fine line structure determination unit S2 determines that the diagonal line cannot be determined.

For example, in the 8 × 8 pixel region having the hatching structure of one pixel width as shown in FIG. 5, third-order analysis result of the wavelet analysis, the total value P ₃ of the main scanning direction and the sub-scanning direction is 870, the main scanning The total difference value P _x3 in the direction is −570, and the total difference value P _{y3 in the} sub-scanning direction is 570. Since the conditions of P ₃ > 0, P _x3 <0, and P _y3 > 0 are satisfied, it is determined that this 8 × 8 pixel region has the characteristics of the oblique thin line structure.

(1.2) Determination of Vertical Line and Horizontal Line In the case of a vertical line, the total value P _{3 in the} main scanning direction and the sub scanning direction is P ₃ > 0, and the total difference value P _{x3 in the} main scanning direction is P _x3 > 0, The total difference value P _{y3 in the} scanning direction is P _y3 = 0 or near zero. In the case of the horizontal line, the total value P ₃ is P ₃ > 0, the difference total value P _{x3 in} the main scanning direction is P _x3 = 0 or near 0, and the difference total value P _{y3 in the} sub-scanning direction is P _y3 > 0. Whether P _x3 or P _y3 is near 0 may be determined using a threshold value. When the tertiary analysis result satisfies the above conditions, the thin line structure determination unit S2 determines that the 8 × 8 pixel region subjected to the wavelet analysis has the characteristics of the vertical line or horizontal line thin line structure. When the condition is not satisfied, the fine line structure determination unit S2 determines that the vertical line or the horizontal line cannot be determined.

For example, in the region of 8 × 8 pixels having a vertical line structure with a width of 1 pixel as shown in FIG. 6, the tertiary analysis result of the wavelet analysis is 1600, the total value P _{3 in the} main scanning direction and the sub-scanning direction is 1600. The total difference value P _x3 in the scanning direction is 1600, and the total difference value P _{y3 in the} sub-scanning direction is 0. Since P ₃ > 0, P _x3 > 0, and P _y3 = 0 are satisfied, it is determined that this 8 × 8 pixel region has the characteristics of a vertical thin line structure.

When it is determined that the thin line structure has the characteristics of the vertical line or horizontal line, it is preferable that the thin line structure determination unit S2 further determines whether or not the thin line structure has a halftone density. Whether it is halftone or not is determined by preparing a threshold value for judging whether it is halftone density in advance and comparing this threshold value with the maximum pixel value in the region of 8 × 8 pixels. Good. Alternatively, the number of pixels having a pixel value greater than zero and counting wire structure determination unit S2, to obtain an average value by dividing the number of pixels obtained by counting the total value P ₃ is a wavelet analysis results. Then, the fine line structure determination unit S2 determines whether or not this average value is within a certain range that can be obtained if the fine line structure is a halftone density, and if it is within the certain range, it is a halftone density. You can judge. When it is determined that the vertical line or horizontal line thin line structure has a halftone density, the thin line structure determination unit S2 outputs a signal indicating the determination result.

(2) Determination of edge In the case of an edge, the total value P _{3 in the} main scanning direction and the sub-scanning direction is P ₃ > 0. Further, depending on the edge direction, the difference total value P _{x3 in} the main scanning direction and the difference total value P _{y3 in the} sub scanning direction are P _x3 = 0, P _y3 = P ₃ > 0, or P _x3 = P ₃ > 0, P _y3 = 0. Therefore, when the third-order analysis result of the wavelet analysis satisfies this condition, the edge determination unit S3 determines that the 8 × 8 pixel region subjected to the wavelet analysis has edge characteristics. If the condition is not satisfied, the edge determination unit S3 determines that the edge cannot be determined.

For example, in the region of 8 × 8 pixels including the edge as shown in FIG. 7, the tertiary analysis result of the wavelet analysis is that the total value P _{3 in the} main scanning direction and the sub scanning direction is 6120, and the difference total value in the main scanning direction P _x3 is 6120, and the total difference value P _{y3 in the} sub-scanning direction is 0. Since P ₃ > 0, P _x3 = P ₃ > 0, and P _y3 = 0, the region of 8 × 8 pixels is determined to have edge characteristics.

(3) Determination of isolated point In the case of an isolated point, the total value P ₃ in the main scanning direction and the sub scanning direction, the total difference value P _x3 in the main scanning direction, and the total difference value P _{y3 in the} sub scanning direction are P ₃ = P _x3 = _Py3 > 0. Therefore, when the result of the wavelet analysis satisfies this condition, the isolated point determination unit S4 determines that the region of 8 × 8 pixels subjected to the wavelet analysis has an isolated point feature. If the condition is not satisfied, the isolated point determination unit S4 determines that the isolated point cannot be determined.

For example, in an 8 × 8 pixel region including an isolated point as shown in FIG. 8, the tertiary analysis result of the wavelet analysis is that the total value P _{3 in the} main scanning direction and the sub scanning direction is 255, and the difference in the main scanning direction The value P _x3 is 255, and the total difference value P _{y3 in the} sub-scanning direction is 255. Since P ₃ = P _x3 = P _y3 > 0 is satisfied, it is determined that the 8 × 8 pixel region has the feature of an isolated point.

(4) Solid Image Determination In the case of a solid image, the total value P _{3 in the} main scanning direction and the sub scanning direction is P ₃ ≧ 0, and the difference total value P _{x3 in the} main scanning direction is P _x3 = 0, the difference in the sub scanning direction. The total value P _y3 is P _y3 = 0. Therefore, when the tertiary analysis result of the wavelet analysis satisfies this condition, the solid image determination unit S5 determines that the region of 8 × 8 pixels subjected to the wavelet analysis has the characteristics of the solid image. If the condition is not satisfied, the solid image determination unit S5 determines that the solid image cannot be determined.

For example, in the region of 8 × 8 pixels, such a solid image as shown in FIG. 9, the third-order analysis result of the wavelet analysis, the main scanning direction and the sub scanning direction of the total value P ₃ is 1920, the difference sum of the main scanning direction The value P _x3 is 0, and the total difference value P _{y3 in the} sub-scanning direction is 0. Since P ₃ ≧ 0, P _x3 = 0, and P _y3 = 0 are satisfied, it is determined that the 8 × 8 pixel region has the characteristics of a solid image.

(5) Determination of gradation In the case of gradation, the total value P _{3 in the} main scanning direction and the sub-scanning direction is P ₃ > 0. Also, the difference total value P _{x3 in} the main scanning direction and the difference total value P _{y3 in the} sub scanning direction are P ₃ > P _x3 > 0, P _y3 = 0, or P _x3 = 0, P ₃ > P _y3 > 0. Therefore, when the third-order analysis result of the wavelet analysis satisfies this condition, the gradation determination unit S6 determines that the 8 × 8 pixel area subjected to the wavelet analysis has gradation characteristics. If the condition is not satisfied, the gradation determination unit S6 cannot determine the gradation and determines that there is no corresponding feature.

For example, in the 8 × 8 pixel area having gradation as shown in FIG. 10, the third analysis result of the wavelet analysis is that the total value P _{3 in the} main scanning direction and the sub scanning direction is 8480, and the difference total value in the main scanning direction. P _x3 is 4480, and the total difference value P _{y3 in the} sub-scanning direction is 0. Since P ₃ > 0, P ₃ > P _x3 > 0, and P _y3 = 0, it is determined that the 8 × 8 pixel region has gradation characteristics.

Next, the first screen processing unit 2a and the second screen processing unit 2b will be described.
The first screen processing unit 2a and the second screen processing unit 2b perform screen processing on images using different screens.
Each screen preferably has an integer multiple of the screen line number. By setting an integral multiple, the positions of the screen lines periodically formed by the screen partially overlap. Thereby, when the processed image screen-processed by each screen is synthesize | combined later, the unnaturalness of the boundary part of the area | region where the screen used in the synthesized image differs can be reduced.

Similarly, in order to reduce unnaturalness due to the use of different screens, the screen angles of the respective screens are preferably the same.
However, for a vertical line or horizontal line image having a halftone density, it is preferable to use a screen dedicated to the line image in order to improve the reproducibility of the line image including the line width. An example of the dedicated screen is a screen having a screen angle of 45 °. In addition, as a dedicated screen, a screen having a screen angle orthogonal to the extending direction of the line, such as a screen having a screen angle of 0 ° for a vertical line and a screen having a screen angle of 90 ° for a horizontal line, can be used. .

  In the present embodiment, as a screen satisfying such a condition, the first screen processing unit 2a uses a first screen formed of a screen line number; 106 lines, a screen angle: 45 °, and a square of 4 × 4 pixels. An example in which the screen processing unit 2b uses a second screen composed of 212 lines, a screen angle of 45 °, and a square of 2 × 2 pixels will be described. The first screen and the second screen have the same screen angle of 45 °, and the number of lines of the second screen is twice that of the first screen.

  The screen processing is preferably performed by a supercell method in order to improve gradation. Since the screen size of the first screen is 4 × 4 pixels and the screen size of the second screen is 2 × 2 pixels, the first screen processing unit 2a and the second screen processing unit 2b have the common multiple of 8 × 8 pixels. Screen processing is performed in units of processing. That is, the first screen processing unit 2a uses a super cell that combines four first screens, and the second screen processing unit 2b uses a super cell that combines sixteen second screens.

FIG. 11 shows an example of an image using a supercell.
As shown in FIG. 11, the position where the supercell of the first screen is repeatedly applied to the image is the same as the position where the supercell of the second screen is repeatedly applied to the image. Note that one square shown in FIG. 11 represents 2 × 2 pixels. In FIG. 11, a line connecting the centers of the dots formed by the supercells on the first screen is a screen line formed by the first screen. A line connecting the centers of the dots formed by the supercell of the second screen is a screen line formed by the second screen. As shown in FIG. 11, all screen lines have a screen angle of 45 °. In addition, the screen lines of the second screen are formed at a half cycle of the screen lines formed by the first screen. That is, the screen lines of the first screen and the screen lines of the second screen partially overlap each other periodically.

  Due to the composition of the image by the composition unit 3, there are cases where dots formed by the first screen appear in a certain area and dots formed by the second screen appear in an adjacent area. However, as shown in FIG. 11, the dots appearing on different screens are arranged on the same screen line, or even if they are not on the same screen line, the interval between the dots becomes periodic. Therefore, the screen switching portion is less noticeable, and the deterioration of image quality due to the use of a plurality of screens can be reduced. In addition, it is possible to prevent the occurrence of moire due to the phase shift of dots.

  In this way, the processed image screen-processed by the first screen processing unit 2a and the processed image screen-processed by the second screen processing unit 2b are output to the combining unit 3, respectively.

  The combining unit 3 combines the processed image input from the first screen processing unit 2a and the processed image input from the second screen processing unit 2b based on the result of the feature analysis input from the feature analysis unit 1. Determine the ratio. At this time, if it is determined as a result of the feature analysis that the composition unit 3 has a fine line structure, an edge, or an isolated point, the composition unit 3 uses the second screen having the higher number of lines in the first screen or the second screen. Increase the composite ratio of processed images. On the other hand, when it is determined that the image has a solid image and gradation characteristics, the composition unit 3 increases the composition ratio of the processed image by the first screen having the lower number of lines in the first screen or the second screen. Then, the synthesizing unit 3 adds the pixel values of the pixels of the processed images at the determined combining ratio to generate a combined image obtained by combining the processed images.

  As a synthesis example, when it is determined by the feature analysis that the feature has the fine line structure, the synthesis unit 3 sets the synthesis ratio of the processed image of the second screen having a high number of lines between the first screen and the second screen to 100. %. That is, for the 8 × 8 pixel region determined to have the fine line structure feature, the processed image by the second screen is selected and output as it is. Similarly, when it is determined as an edge or an isolated point, the processed image of the second screen having a higher number of lines is output at a composition ratio of 100%.

  On the other hand, when it is determined that the image has the characteristics of a solid image or gradation, the composition unit 3 determines that the composition ratio of the processed image of the first screen that has the low number of lines of the first screen and the second screen is 100%. That is, for the 8 × 8 pixel area determined to have a solid image or gradation characteristics, a processed image by the first screen is selected and output as it is.

  When it is determined that none of the six types of features is applicable, the synthesis unit 3 determines the synthesis ratio of the processed image on the first screen and the processed image on the second screen to be 50%. The synthesizer 3 calculates and outputs an average value of each processed image for an 8 × 8 pixel area determined to be not applicable.

Note that even if it is determined that any of the features is present, the strength of the feature is present. Therefore, the strength of the feature may be determined step by step based on a threshold, and the composition ratio may be determined based on the strength. .
In the example of isolated points, as shown in FIG. 8, the image is not an image having a clear feature in which the periphery of an isolated point having a pixel value 255 is all pixel values 0, and noise is included in the periphery. There is a case. In such a case, the third-order analysis result of the wavelet analysis is not P ₃ = P _x3 = P _y3 = 255, and a difference of 5 or 10 or the like occurs between P ₃ , P _x3 , and P _y3 . Therefore, for example, 10 is set as the threshold value, and if the difference between P ₃ , P _x3 , and P _y3 is 0, the synthesis unit 3 determines that the feature of the isolated point is strong, and the second screen is set as described above. The composition ratio of the used processed image is set to 100%. On the other hand, if the difference is greater than 0 and less than or equal to the threshold value 10, the composition unit 3 determines that the feature of the isolated point is weak, and uses the second screen for the composition ratio of the processed image using the first screen of 10%. The synthesis ratio of the processed image is determined to be 90%. This makes it possible to use different screens depending on the strength of the features. Note that if the difference between each of P ₃ , P _x3 , and P _y3 is equal to or greater than the threshold 10, it may be determined that the feature analysis unit 1 cannot determine the isolated point.

When a determination result that a vertical line or horizontal line having a halftone density is input, the synthesis unit 3 sets the synthesis ratio of the processed image using a screen having a screen angle of 45 ° to 100%. Since both the first screen and the second screen have a screen angle of 45 °, they may be combined at any combination ratio. For example, in consideration of the thin line structure, the composition ratio of the processed image using the second screen having a high number of lines may be set to 100%, or the composition ratio of 50% is considered in consideration of the halftone density. It is good also as a ratio.
The composite image generated in this way is output to the post-processing unit 4.

  The post-processing unit 4 performs post-processing such as noise addition processing and error diffusion processing on the combined image output from the combining unit 3. In the noise addition process, the post-processing unit 4 adds, for example, pixel values corresponding to randomly generated noise to pixels at arbitrary positions in the composite image. In the error diffusion process, the post-processing unit 4 binarizes the pixel value of each pixel of the composite image by comparison with a threshold value, and adds an error from the threshold value at the time of binarization to surrounding pixels.

  As described above, according to the MFP 100 according to the present embodiment, the first screen processing unit 2a performs screen processing on an image using the first screen, and the second screen processing unit 2b is different from the first screen. Screen processing is performed using a screen, and each processed image is generated. Also, the feature analysis unit 1 performs feature analysis of the image, and based on the analysis result, the synthesis unit 3 determines a synthesis ratio of each processed image obtained by two different screens, and each processed image is determined by the synthesis ratio. A composite image obtained by combining is output.

  As a result, since the composition ratio can be changed for each image portion having a feature, even if image portions having various features are mixed in one image, a screen suitable for the feature for each image portion having a feature. Can be used to obtain a screen-processed composite image. Also, by combining processed images using different screens, the balance between resolution and gradation can be adjusted. Furthermore, the processing results from different screens can be output without a sense of incongruity by synthesis.

  Since the feature analysis of the feature analysis unit 1 is a wavelet analysis, it is possible to accurately determine a plurality of types of features from the analysis result.

  Further, the feature analysis unit 1 determines at least the presence or absence of features of the fine line structure, edge, isolated point, solid image, and gradation by wavelet analysis, and the synthesis unit 3 is determined to have the feature of the fine line structure, edge or isolated point. In this case, the composite ratio of the processed image using the second screen having the higher number of lines among the first screen and the second screen is made larger than that of the processed image using the first screen. As a result, high resolution can be realized for an image portion having features of a fine line structure, an edge, and an isolated point in the composite image. Further, when it is determined that the composition unit 3 has a solid image or gradation characteristic, the composition ratio of the processed image using the first screen having the lower number of lines of the first screen and the second screen is set to the second screen. To be larger than the processed image using. As a result, high gradation can be realized for a solid image or an image portion having gradation characteristics in the synthesized image.

  Also, the feature analysis unit 1 determines whether or not there is a vertical line or horizontal line feature having a halftone density, and if the synthesis unit 3 determines that the vertical line or horizontal line feature is present, the feature analysis unit 1 is dedicated to the vertical line or horizontal line. The synthetic ratio of the processed image using a screen having a screen angle of 45 ° is determined to be 100%. Thereby, it is possible to prevent a change in the line width of the vertical line or horizontal line having a halftone density in the composite image, and to improve the reproducibility of the vertical line or horizontal line.

  Further, since the post-processing unit 4 performs post-processing on the composite image, even when a composite image using different screens between adjacent image regions is obtained, the unnaturalness of the boundary portion can be reduced. .

The MFP 100 according to the above embodiment is a preferred example of the present invention, and the present invention is not limited to this.
For example, a plurality of different screens may have a relationship in which the growth centers of dots formed by the respective screens in the screen processing are periodically overlapped. The growth center is a position where a threshold is set so that dots are output most easily on the screen. In many cases, the growth of dots starts from this growth center. At this time, the position where the first screen processing unit 2a repeatedly uses the first screen for the image is adjusted so that the growth centers of the dots formed in the first screen and the second screen periodically overlap, or the first The two-screen processing unit 2b adjusts the position where the second screen is repeatedly used for the image.

FIG. 12 is a diagram illustrating an example of the adjustment result of the application position of the screen.
As shown in FIG. 12, the center of dot growth of the first screen is determined at the position of 2 pixels from the top and 2 pixels from the left (4 × 4 pixels) (dot growth start position of the first screen shown in FIG. 12). The dot growth center of the second screen is determined at the upper left position of 2 × 2 pixels (dot growth start position of the second screen shown in FIG. 12). In FIG. 12, one square represents one pixel. The first screen processing unit 2a adjusts the application position of the first screen to the image as shown in FIG. 12 in order to make the dot growth center of the first screen coincide with the dot growth center of the second screen. Since the first screen and the second screen have an integral multiple of screen lines, the same screen angle, and the same screen shape, as shown in FIG. 12, the period is half the period of dots formed by the first screen. Then, dots are formed by the second screen. As a result, the growth centers of dots formed by the first screen and the second screen partially overlap each other periodically.

  By combining images by the combining unit 3, there are cases where an area where each dot formed by the first screen appears is adjacent to an area where each dot formed by the second screen appears. However, as shown in FIG. 12, since the dots appearing on different screens partially overlap the growth center, even if different screens are used for each region, the unnaturalness of the boundary portion can be reduced, and a plurality of screens can be reduced. It is possible to reduce image quality deterioration due to use. In addition, it is possible to prevent the occurrence of moire due to the phase shift of dots.

  In the above screen processing, both the first screen and the second screen have a screen angle of 45 °. However, depending on the conditions, the screen angle of 45 ° suitable for a vertical line or horizontal line having a halftone density is used. The screen may not be used. For example, three screens with screen angles of 75 °, 75 °, and 15 ° are used. Under such circumstances, the synthesis unit 3 synthesizes the processed image with the screen angle of 75 ° and the processed image with the screen angle of 15 ° at a synthesis ratio of 50% so that a synthesized image with a screen angle of 45 ° is obtained as a result. do it.

  Moreover, although the example in which the first screen and the second screen are square screens has been described, screens of other shapes can be used. For example, in the case of a screen having a screen shape as shown in FIG. 13, the feature analysis can be performed in a processing unit of 4 × 4 pixels including the screen. At this time, in the 4 × 4 pixel region, pixels that do not correspond to the screen may be converted to a pixel value of 0 and subjected to feature analysis. Further, as shown in FIG. 13, the region to be subjected to feature analysis may be shifted in accordance with the shift position of the screen.

  In addition, the above-described feature analysis unit 1 determines the priority in the order of the fine line structure, the edge, the isolated point, the solid image, and the gradation, and outputs any one determination result to the synthesis unit 3. It is good also as giving a priority in the synthetic | combination part 3. FIG. For example, as shown in FIG. 14, the feature analysis unit 1 performs all determinations in parallel, and outputs the determination results to the synthesis unit 3. The synthesizer 3 receives the determination results and adopts the determination results in the order of fine line structure, edge, isolated point, solid image, and gradation. For example, when the determination result that the image has an edge feature and the determination result that the image has a solid image feature are input, the determination result that the image has an edge feature is preferentially adopted.

  In the case of the configuration shown in FIG. 14, the composition unit 3 preliminarily determines and adopts the composition ratio of the first screen and the second screen as a coefficient for multiplying the processed image with respect to the determination result of each feature. The processed image may be synthesized with a coefficient corresponding to the determination result. For example, a fine line structure, an edge, and an isolated point have a first screen coefficient of 0 (combination ratio 0%), a second screen coefficient of 1 (combination ratio 100%), and a solid image and gradation have a first screen coefficient of 1 (The composition ratio is 100%), and the coefficient of the second screen is set to 0 (the composition ratio is 0%). In FIG. 14, the ratio shown in the composition unit 3 indicates the type of screen and its coefficient. The screen type is indicated by a numerical value of 1 for the first screen and 2 for the second screen. For example, “1: 1” indicates that the coefficient of the first screen is 1.

  In addition, when the determination result that the combining unit 3 has two or more features is obtained, the coefficient may be corrected. For example, when the determination result that the edge and the solid image have the characteristics as described above is obtained, the edge determination result is prioritized. Therefore, the processed image of the second screen having a high number of lines originally suitable for the edge The coefficient for the first screen is 1 (combination ratio 100%), but the second screen coefficient is 0.9 (combination ratio 90%) and the first screen coefficient in consideration of the determination result that the image is a solid image. May be modified to 0.1 (combination ratio 10%).

If the feature of the image can be accurately determined, the result of the wavelet analysis may be determined using not only the tertiary analysis result but also the secondary analysis result.
For example, in the case of the oblique line shown in FIG. 5, the result shown in FIG. 15 is obtained as the secondary analysis result. As shown in FIG. 15, if the hatched wire structures, the main scanning direction and the sub scanning direction of the total value P ₂ is a set of two pixels which faces the 2 × 2 pixels is a value of 0, the other pair Becomes a value larger than 0. Further, the difference total value P _{x2 in} the main scanning direction and the difference total value P _{y2 in the} sub-scanning direction are such that one set of two opposed 2 × 2 pixels of P _x2 is 0, and the other set is 0. The value is a small value, and one set of two opposing pixels of _Py2 of 2 × 2 pixels has a value of 0, and the other set has a value greater than 0. Depending on the direction in which the diagonal line extends, the opposite of the 2 × 2 pixels of P _x2 is a value of 0, and the other set is a value greater than 0, so that 2 × 2 pixels of P _y2 One set of two opposing pixels has a value of 0, and the other set has a value smaller than 0. Therefore, it can be determined whether or not the structure is an oblique thin line structure depending on whether or not this condition is satisfied.

  In addition to the MFP, the present invention can be applied to any computer apparatus that performs image processing. In addition, the processing of the feature analysis unit 1, the first screen processing unit 2a, the second screen processing unit 2b, the synthesis unit 3, and the post-processing unit 4 described above is programmed, and image processing by software is performed using the program. Also good. In this case, as a computer-readable medium for the program, a non-volatile memory such as a ROM and a flash memory, and a portable recording medium such as a CD-ROM can be applied. A carrier wave is also used as a medium for providing program data via a communication line.

FIG. 2 is a diagram illustrating a functional configuration of an MFP according to the present embodiment. It is a figure which shows the component mainly functioned at the time of screen processing in the image processing part of FIG. It is a figure which shows the outline | summary of a wavelet analysis. FIG. 3 is a functional block diagram of a feature analysis unit in FIG. 2. It is a figure which shows the diagonal thin line structure and the example of a wavelet analysis result. It is a figure which shows the example of a thin line structure of a vertical line, and its wavelet analysis result. It is a figure which shows an edge and its wavelet analysis result example. It is a figure which shows an isolated point and the example of a wavelet analysis result. It is a figure which shows a solid image and the example of its wavelet analysis result. It is a figure which shows a gradation and its wavelet analysis result example. It is a figure which shows the supercell of two screens in which the screen line number has an integer multiple relationship. It is a figure which shows the two screens in which the growth center of a dot overlaps periodically. It is a figure explaining the area unit of the feature analysis in the case of using a non-square screen. It is a figure which shows the other structural example of a feature-analysis part and a synthetic | combination part. It is a figure which shows the secondary analysis result of the wavelet analysis about an oblique thin line structure.

Explanation of symbols

100 MFP
10 image processing unit 1 feature analysis unit 2a first screen processing unit 2b second screen processing unit 3 composition unit 4 post-processing unit

Claims (10)

A screen processing unit that performs screen processing on each image using a plurality of different screens, and generates a processed image by each screen;
A feature analysis unit for performing feature analysis of the image;
Determining a synthesis ratio of each processed image by the plurality of screens based on a result of the feature analysis, and a synthesis unit that outputs a synthesized image obtained by synthesizing each processed image according to the synthesis ratio;
An image processing apparatus comprising:   The image processing apparatus according to claim 1, wherein the feature analysis is wavelet analysis.   The image processing apparatus according to claim 2, wherein an area unit for performing the screen processing and an area unit for performing the wavelet analysis have an integer multiple relationship.   The image processing apparatus according to claim 2, wherein the plurality of different screens have an integer multiple of screen lines.   4. The image processing apparatus according to claim 2, wherein the plurality of different screens have a relationship in which growth centers of dots formed by the respective screens periodically overlap in the screen processing. The feature analysis unit determines whether or not there is a feature of at least a thin line structure, an edge or an isolated point by wavelet analysis, and determines whether or not there is a feature of a solid image or a gradation,
When the characteristic analysis unit determines that the feature analysis unit has a fine line structure, an edge, or an isolated point, the synthesis unit increases a synthesis ratio of processed images using a screen with a high line number among the plurality of different screens. When the feature analysis unit determines that there is a solid image or gradation feature, the processing image synthesis ratio using a screen with a low number of lines among the plurality of different screens is increased. An image processing apparatus according to claim 1. The different screens include screens for line images having a halftone density and extending in the main scanning direction or the sub-scanning direction of the image,
The feature analysis unit determines whether or not there is a feature of a line image having a halftone density and extending in the main scanning direction or the sub-scanning direction of the image by wavelet analysis,
When the characteristic analysis unit determines that the characteristic analysis unit has the density of the halftone and has the characteristics of the line image extending in the main scanning direction or the sub-scanning direction of the image, the combining unit displays the screen for the line image. The image processing apparatus according to claim 2, wherein a composite ratio of the used processed image is determined to be 100%.   The image processing apparatus according to claim 7, wherein the screen for line images having the halftone density and extending in the main scanning direction or the sub-scanning direction of the image is a screen having a screen angle of 45 °.   The image processing apparatus according to claim 1, further comprising a post-processing unit that performs error diffusion processing or noise addition processing on the composite image. The image is subjected to screen processing using a plurality of different screens, and a processed image is generated by each screen; and
Performing a feature analysis of the image;
Determining a composite ratio of each processed image based on the plurality of screens based on the result of the feature analysis, and outputting a composite image obtained by combining the processed images according to the composite ratio;
An image processing method including:

Images