JP2006287449A - Image processor and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of worm texture at error diffusion processing by means of a simpler process in comparison with prior arts. <P>SOLUTION: When a quantization section 1153 applies binary processing to a target pixel, a pattern matching section 1160 detects whether or not a plurality of pixels arranged consecutively to a target pixel and whose binary processing is finished are consecutively arranged by white pixels or black pixels only, and when the pattern matching section 1160 detects the consecutive arrangement, a threshold value change section 1161 changes a threshold value stored in a threshold value storage section 1154 so that the possibility of the consecutive arrangement of the target pixel and the pixels consecutively arranged thereto in a relation of white pixels or black pixels is lowered, and the quantization section 1153 applies binary processing to the target pixel by using the threshold value after being changed by the threshold value change section 161. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus such as a scanner or a multifunction peripheral, and more particularly to an image processing apparatus and an image processing program for performing error diffusion processing on an input image.

  Conventionally, when outputting a full-color image input signal with a printer or multifunction device having a limited number of gradation representations, such as only binary recording, in order to suppress a decrease in apparent resolution and gradation representation, A method of converting a full color image signal into a halftone image signal by performing processing by an error diffusion method is widely performed. In this error diffusion method, the difference (binarization error) between the density of the pixel of interest of the read image and the display density (binarization error) is distributed and added to the image signal of the pixel to be binarized thereafter. When viewed in a range, the average gradation of the binary image is to be brought closer to the gradation of the multi-valued image.

In the output image after the error diffusion processing, a regular striped pattern called a worm texture may appear and the image quality may deteriorate. For the purpose of preventing the occurrence of the worm texture, Patent Document 1 below describes An illustrated image processing method has been proposed. This image processing method uses a threshold matrix and a weighting coefficient matrix to make dot generation locally uniform in an input image signal with little change in density, thereby eliminating dot bias and generating a worm in a low density region. -It prevents the occurrence of texture.
JP 2003-274172 A

  However, in the case of the image processing method described in Patent Document 1, in order to prevent the occurrence of worm texture, as described above, the threshold value matrix and the weighting coefficient matrix for making the dot generation locally uniform are used. Since it is necessary, generation of a worm texture cannot be prevented unless complicated processing is performed.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to make it possible to suppress the occurrence of worm textures during error diffusion processing with simple processing compared to the prior art. is there.

The invention according to claim 1 of the present invention diffuses an error generated during binarization processing of a target pixel using a predetermined threshold value to peripheral pixels before binarization processing, and the error is diffused. In an image processing apparatus including an error diffusion processing unit that sequentially performs binarization processing using each pixel as a target pixel,
The error diffusion processing unit includes a threshold value storage unit that stores the threshold value, a binarization processing unit that performs the binarization process on the pixel of interest using the threshold value stored in the threshold value storage unit, and the binary value At the time of binarization processing of a target pixel by the binarization processing unit, it is detected whether a plurality of binarized pixels that are continuously arranged on the target pixel are arranged continuously between white pixels or black pixels And when the continuous detection is detected by the connection detection unit, the threshold value stored in the threshold value storage unit is determined based on whether the target pixel and the continuously arranged pixel are white pixels or black pixels. A threshold value changing unit that changes to a value that reduces the possibility that pixels are continuously arranged;
The binarization processing unit performs binarization processing of the target pixel using the threshold value changed by the threshold value changing unit.

The invention according to claim 6 diffuses an error generated during binarization processing of a target pixel using a predetermined threshold value to peripheral pixels before binarization processing, and the error is diffused. An image processing program that causes an information processing device to function as an image processing device including an error diffusion processing unit that sequentially performs binarization processing using each pixel as a target pixel,
The error diffusion processing unit includes a threshold value storage unit that stores the threshold value, a binarization processing unit that performs the binarization process on the pixel of interest using the threshold value stored in the threshold value storage unit, and the binary value At the time of binarization processing of a target pixel by the binarization processing unit, it is detected whether a plurality of binarized pixels that are continuously arranged on the target pixel are arranged continuously between white pixels or black pixels When the continuous arrangement is detected by the connection detection unit and the connection detection unit, the threshold value stored in the threshold value storage unit is determined based on whether the target pixel and the continuously arranged pixel are white pixels or black pixels. A threshold value changing unit that changes to a value that is difficult to be continuously arranged between pixels,
The image processing program causes the information processing apparatus to function so that the binarization processing unit performs binarization processing of a pixel of interest using a threshold value changed by the threshold value changing unit.

  In these configurations, when the binarization processing unit performs binarization processing on the target pixel, the connection detection unit causes the plurality of binarized pixels that are arranged consecutively to the target pixel to be white. It is detected whether the pixels are arranged continuously or between the black pixels. When the continuous arrangement is detected, the threshold value changing unit sets the threshold value stored in the threshold value storage unit to the pixel of interest and the continuous arrangement. The binarization processing unit is changed to a value that is unlikely to be continuously arranged between white pixels or black pixels, and the threshold value changing unit changes in this way. Reduces the occurrence of white pixels or black pixels continuously appearing in the image data after the binarization processing by the binarization processing unit by performing the binarization processing of the target pixel. Suppresses the occurrence of texture.

  The invention according to claim 2 is the image processing apparatus according to claim 1, wherein the threshold value changing unit is a plurality of binarized pixels that are arranged continuously to the target pixel. When the connection detection unit detects that the black pixels are continuously arranged between the black pixels, the threshold value stored in the threshold value storage unit is brought close to the value indicating the black pixel.

  According to this configuration, when a plurality of binarized pixels that are continuously arranged on the target pixel are arranged continuously with black pixels, the threshold value is brought close to a value indicating a black pixel. Thus, when the binarization processing unit performs the binarization process on the target pixel using the threshold value, the possibility that the target pixel is converted into a white pixel is increased.

  The invention according to claim 3 is the image processing apparatus according to claim 1 or 2, wherein the threshold value changing unit has been binarized and arranged continuously to the target pixel. When the connection detection unit detects that the plurality of pixels are continuously arranged with white pixels, the threshold value stored in the threshold value storage unit is brought close to a value indicating a white pixel.

  According to this configuration, when a plurality of binarized pixels that are continuously arranged with respect to the target pixel are continuously arranged with white pixels, the threshold value is brought close to a value indicating a white pixel. As a result, when the binarization processing unit performs the binarization process on the target pixel using the threshold value, the possibility that the target pixel is converted into a black pixel is increased.

According to a fourth aspect of the present invention, there is provided the image processing device according to any one of the first to third aspects, wherein an area for determining whether the target pixel belongs to a photographic image area or a character image area. Further comprising a discriminator;
The threshold value changing unit is stored in the threshold value storage unit when the continuous arrangement is detected by the connection detecting unit only when the pixel of interest is determined to belong to a photographic image region by the region determining unit. The above threshold value is changed.

  According to this configuration, only when the target pixel belongs to the photographic image area, the threshold value changing unit changes the threshold value when the continuous detection is detected by the connection detection unit. When it is assumed that it belongs to the image area, the state of the original image is maintained even after the binarization process, and it is difficult to cut off the continuous arrangement of white pixels or black pixels. It is possible to achieve both reproduction and gradation reproduction from which a worm texture for a photographic image is removed.

The invention according to claim 5 is the image processing apparatus according to any one of claims 1 to 4, further comprising an edge degree calculating means for obtaining an edge degree of the target pixel,
In the case where the edge degree obtained by the edge degree calculating means is higher than a preset edge degree, the threshold value changing unit may be the case where the continuous arrangement is detected by the connection detecting unit. The threshold value stored in the threshold value storage unit is not changed.

  According to this configuration, when the edge degree of the target pixel is high, the threshold value changing unit does not change the threshold value even if the continuous arrangement is detected by the connection detection unit, and is continuously arranged with the target pixel. It does not manipulate the possibility that pixels are continuously arranged between white pixels or black pixels. Thereby, when the edge degree of the target pixel is high, that is, when it is assumed that the target pixel indicates a character image, the state of the original image is maintained even after the binarization process, and the white pixels Or, since it is difficult to cut off the continuous arrangement of black pixels, good gradation reproduction for character images, and gradation reproduction that removes worms and textures for images that are assumed to be photographic areas where the edge of the target image is not high Can be made compatible.

  According to the first and sixth aspects of the present invention, when the binarization processing unit performs binarization processing on the target pixel, the binarization processing that has been continuously arranged on the target pixel has been performed. By changing the threshold value used for the binarization processing according to whether or not a plurality of pixels are continuously arranged between white pixels or between black pixels, the pixel of interest and the pixels arranged continuously are changed. Since the possibility that the white pixels or the black pixels are continuously arranged is reduced, the white pixel or the black pixel is added to the binarized image data by a simple process as compared with the conventional technique. It is possible to reduce the situation where they appear in a continuous arrangement, and to suppress the occurrence of worm texture.

  According to a second aspect of the present invention, when a plurality of binarized pixels that are arranged continuously with the target pixel are arranged continuously with black pixels, the threshold value is set to black pixels. To increase the possibility that the target pixel will be converted to a white pixel after the binarization process, so that a plurality of binarized and processed pixels arranged consecutively to the target pixel and the target pixel are displayed. The situation where pixels are continuously arranged with black pixels is suppressed, and the occurrence of worm texture can be suppressed.

  According to a third aspect of the present invention, when a plurality of binarized pixels that are continuously arranged on the target pixel are continuously arranged between white pixels, the threshold value is set to a white pixel. To increase the possibility that the target pixel will be converted to a black pixel after the binarization process, so that a plurality of binarized and processed pixels arranged consecutively to the target pixel and the target pixel are displayed. The situation where pixels are continuously arranged with white pixels is suppressed, and the occurrence of worm texture can be suppressed.

  According to the fourth aspect of the present invention, the threshold value changing unit performs the threshold value change only when the target pixel to be binarized belongs to the photo area. For example, the target pixel belongs to the character image area. Is assumed, the state of the original image is maintained even after the binarization process, the continuous arrangement of white pixels or black pixels is difficult to cut off, and good tone reproduction for character images and photographs It is possible to achieve both gradation reproduction from which the worm texture for the region is removed.

  According to the fifth aspect of the present invention, when the edge degree of the target pixel to be binarized is high, that is, when it is assumed that the target pixel indicates a character image, 2 The original image state is maintained even after the binarization process, and it is difficult to cut off the continuous arrangement of white pixels or black pixels. Therefore, it is possible to achieve both gradation reproduction from which the worm and texture are removed from the assumed image.

  Hereinafter, as an example of an image processing apparatus according to the present invention, a multifunction machine having a printer function will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an internal configuration of a multifunction machine 1 which is an example of an image processing apparatus according to an embodiment of the present invention. The multifunction device 1 has functions such as a copy function, a printer function, a scanner function, and a facsimile function. The multi-function device 1 includes a main body 2, a stack tray 3 disposed on the left side of the main body 2, a document reading unit 5 disposed on the top of the main body 2, and an upper side of the document reading unit 5. And a document feeding unit 6 disposed.

  An operation unit 47 is provided at the front part of the multifunction machine 1. The operation unit 47 displays a start key 471 for a user to input a print execution instruction, a ten key 472 for inputting the number of copies to be printed, operation guide information for various copying operations, and the like. A display unit 473 formed of a liquid crystal display or the like having a touch panel function, a reset key 474 for resetting setting contents set in the display unit 473, and a stop key for stopping a printing (image forming) operation being executed 475 and a function switching key 477 for switching between a copy function, a printer function, a scanner function, and a facsimile function.

  The document reading unit 5 includes a scanner unit 51 including a CCD (Charge Coupled Device) sensor and an exposure lamp, and a document table 52 and a document reading slit 53 made of a transparent member such as glass. The scanner unit 51 is configured to be movable by a drive unit (not shown). When reading a document placed on the document table 52, the scanner unit 51 is moved along the document surface at a position facing the document table 52, and the document image is scanned. The image data acquired while scanning is output to the control unit 10 (FIG. 2). Further, when reading a document fed by the document feeding unit 6, the document is moved to a position facing the document reading slit 53 and synchronized with the document feeding operation by the document feeding unit 6 via the document reading slit 53. The image of the original is acquired and the image data is output to the control unit 10.

  The document feeding unit 6 includes a document placing unit 61 for placing a document, a document discharge unit 62 for discharging a document whose image has been read, and a document placed on the document placing unit 61. A document transport mechanism 63 including a paper feed roller (not shown), a transport roller (not shown) and the like for feeding the paper one by one to a position facing the document reading slit 53 and discharging it to the document discharge section 62 is provided. The document conveyance mechanism 63 further includes a sheet reversing mechanism (not shown) that reverses the document and reversely conveys the document to a position facing the document reading slit 53, and scans both sides of the document through the document reading slit 53. 51 can be read.

  The document feeding unit 6 is provided so as to be rotatable with respect to the main body unit 2 so that the front side thereof can move upward. By moving the front side of the document feeder 6 upward to open the upper surface of the document table 52, the operator can place a read document, for example, a book in a spread state, on the upper surface of the document table 52. It has become.

  The main body 2 includes a plurality of paper feed cassettes 461, a paper feed roller 462 that feeds the recording paper from the paper feed cassette 461 one by one and transports it to the recording unit 40, and a recording paper transported from the paper feed cassette 461. And a recording unit 40 for forming an image.

  The recording unit 40 is based on a charge eliminating device 421 that removes residual charges from the surface of the photosensitive drum 43, a charging device 422 that charges the surface of the photosensitive drum 43 after charge removal, and image data acquired by the scanner unit 51. The laser beam is output to expose the surface of the photosensitive drum 43, and an exposure device 423 for forming an electrostatic latent image on the surface of the photosensitive drum 43, and on the photosensitive drum 43 based on the electrostatic latent image. , Cyan (C), magenta (M), yellow (Y), and black (K) toner images of respective colors formed on the photosensitive drum 43 and developing devices 44K, 44Y, 44M, and 44C that form toner images of the respective colors. The transfer drum 49 on which the image is transferred and superimposed, the transfer device 41 that transfers the toner image on the transfer drum 49 to the paper, and the paper on which the toner image has been transferred are heated to transfer the toner image to the paper And a fixing device 45 for fixing. Note that toner is supplied to each color of cyan, magenta, yellow, and black from a toner supply container (toner cartridge) (not shown). In addition, conveyance rollers 463 and 464 that convey the recording paper that has passed through the recording unit 40 to the stack tray 3 or the discharge tray 48 are provided.

  When forming images on both sides of the recording paper, the recording unit 40 forms an image on one side of the recording paper, and then the recording paper is nipped by the conveyance roller 463 on the discharge tray 48 side. In this state, the conveyance roller 463 is reversed to switch back the recording paper, and the recording paper is sent to the paper conveyance path L and conveyed again to the upstream area of the recording unit 40, and an image is formed on the other surface by the recording unit 40. Thereafter, the recording paper is discharged to the stack tray 3 or the discharge tray 48.

  FIG. 2 is a functional block diagram showing a schematic configuration of the multifunction machine 1 shown in FIG. The multifunction machine 1 includes a control unit 10 that controls the operation of the entire apparatus. The control unit 10 includes a document reading unit 5 including a scanner unit 51 and the like, a document feeding unit 6 including a document transport mechanism 63, and the like. Connected to the recording unit 40 including the developing device 44, the operation keys such as the start key 471 and the numeric keypad 472, the operation unit 47 including the display unit 473, the image memory 7, the HDD 8, the network I / F unit 9, and the image processing unit 11. Has been.

  The image memory 7 stores image data of a document (for example, a halftone document) read by the document reading unit 5 or image data transmitted from an external device (not shown) via a network I / F unit 9 described later. It is a memory that stores temporarily.

  An HDD (Hard Disk Drive) 8 is a storage device that stores image data of a document image read by the document reading unit 5, image data transmitted from an external device, an output format set in the image data, and the like. It is.

  The network I / F unit 9 uses a network interface (for example, 10 / 100Base-TX) or the like to transmit and receive various data to and from an external device connected via a network such as a LAN.

  The image processing unit 11 performs various image processes on a document image (image data) obtained by reading a document by the document reading unit 5. In the image processing unit 11, for example, A / D conversion of image data is performed on a document image read by the document reading unit 5, and various image processing is performed using the A / D converted image data. The image processing unit 11 includes a shading correction unit 111, an input γ correction unit 112, a filter processing unit 113, an enlargement / reduction processing unit 114, and an error diffusion processing unit 115.

  The shading correction unit 111 performs processing to add a shadow to the original image data read by the original reading unit 5 and the image data input to the network I / F unit 9 in order to provide a more stereoscopic effect. It is. The input γ correction unit 112 displays on a monitor or the like by using a density conversion curve indicating the relationship between the output density and the input density of the image data, that is, a method of correcting the shade of the image by changing the input / output relationship using the gamma curve. The process of adjusting the brightness of the image to be displayed and the color saturation is performed. The filter processing unit 113 performs image processing that gives a special effect to an image by performing calculation with respect to surrounding pixels for each pixel constituting the image data. For example, blurring, edge enhancement, noise processing, mosaic processing, or posterization image processing. The enlargement / reduction processing unit 114 performs processing for enlarging and reducing image data.

  The error diffusion processing unit 115 further proceeds the binarization process while diffusing the binarized pixel error to adjacent neighboring pixels so that the density error between the original grayscale image and the output image is minimized. This is what is called error diffusion processing. The error diffusion processing unit 115 performs binarization processing on the pixel of interest using a predetermined threshold value, diffuses an error generated during the binarization processing to surrounding pixels before the binarization processing, and the error The binarization process is sequentially performed for each pixel in which is diffused as the target pixel. The binarization process is a process of converting a grayscale image into a binary (1 bit) image that includes only white and black and does not have a gray level of an intermediate color. The present invention is characterized by this error diffusion processing (binarization processing) technique. Details of the configuration and processing of the error diffusion processing unit 115 will be described later. After the error diffusion processing by the error diffusion processing unit 115, necessary image processing such as background determination processing is performed as necessary, and then image data is output to the recording unit 40 or the like.

  The control unit 10 includes a ROM (Read Only Memory) that stores a control program of the multifunction device 1, a RAM (Random Access Memory) that temporarily stores data, and a micro information processing that reads and executes a control program from the ROM. The apparatus is composed of a device or the like, and executes processing for controlling the entire device in accordance with instruction information input in the operation unit 47 and detection signals from various sensors provided in various places of the device.

  Next, a specific configuration of the error diffusion processing unit 115 of the image processing unit 11 will be described. FIG. 3 is a block diagram showing a circuit configuration example in the case of performing error diffusion processing when processing a full color image (256 gradations) signal into a binarized (2 gradations) signal based on the present invention. The image input unit 1151 takes in the value held by the pixel of interest X from the image memory, and outputs the pixel value (density value) of the pixel of interest X to the adder 1152. The adder 1152 performs correction to add the accumulated error calculated by the accumulated error calculation unit 1158 to the pixel value of the input target pixel X.

  The quantization unit (binarization processing unit) 1153 performs a determination using a threshold necessary for binarizing the corrected pixel value input from the adder 1152. The quantization unit 1153 compares the corrected pixel value input from the adder 1152 with the threshold value stored in the threshold value storage unit 1154, and converts it to a value indicating either a white pixel or a black pixel. And output to the image output unit 1155.

  The subtractor 1156 calculates an error between the original pixel value before binarization and the pixel value after binarization, and the corrected pixel value (before binarization) input from the adder 1152. And a pixel value after binarization by the quantization unit 1153 is calculated. The generated error storage unit 1157 is a storage unit that stores the error value calculated by the subtracter 1156. The accumulated error calculation unit 1158 adds the accumulation of errors generated by the respective binarized pixels already binarized to the pixel to be binarized by the quantization unit 1153 as the next pixel of interest. In addition, the error generated by each binarized peripheral pixel is accumulated.

  The output image storage unit 1159 is a storage unit that stores the determination result of each pixel binarized by the quantization unit 1153. The pattern matching unit (connection detection unit) 1160 is continuously connected to the target pixel X based on each pixel value stored in the output image storage unit 1159 during the binarization process of the target pixel X by the quantization unit 1153. In other words, it is detected whether a plurality of already binarized pixels that are arranged in this manner are arranged continuously between white pixels or between black pixels.

  Here, the continuous arrangement detection process by the pattern matching unit 1160 will be described. FIG. 4 is a diagram showing a pixel arrangement of the image memory, in which A, B, C, and D are peripheral pixels, and X is a pixel of interest to be subjected to binarization processing. For example, as shown in FIG. 4, during the binarization process of the target pixel X, (1) the pattern matching unit 1160 is a peripheral pixel that has already been binarized before the target pixel X. Thus, it is detected whether the two peripheral pixels A and A arranged side by side with respect to the target pixel X are continuous as white pixels or black pixels. (2) Similarly, the pattern matching unit 1160 is a peripheral pixel that has already undergone binarization processing before the target pixel X, and is arranged in two diagonally with respect to the target pixel X. Whether the peripheral pixels B and B are continuous between white pixels or black pixels, or whether two peripheral pixels D and D that are arranged in the same diagonal direction are continuous between white pixels or black pixels (3) Furthermore, it is detected whether two peripheral pixels C, C arranged vertically with respect to the target pixel X are continuous between white pixels or black pixels. If the pattern matching unit 1160 detects that the two peripheral pixels are continuous as white pixels or black pixels, the pattern matching unit 1160 outputs a signal indicating that to the threshold value changing unit 1161.

  When the threshold value changing unit 1161 receives a signal from the pattern matching unit 1160 indicating that a continuous arrangement of two neighboring pixels between white pixels or black pixels is detected, the threshold value changing unit 1161 is stored in the threshold value storage unit 1154. The threshold value is changed to a value that reduces the possibility that the target pixel X and the pixels that are continuously arranged are continuously arranged between white pixels or black pixels.

  For example, when any one of the peripheral pixels A and A, the peripheral pixels B and B, the peripheral pixels C and C, and the peripheral pixels D and D is continuous between the black pixels, the threshold value changing unit 1161 includes the threshold value storage unit 1154. Is changed so as to approach a value indicating a black pixel. Specifically, when the black pixel has 256 gradation 255 and the white pixel has 256 gradation 0, and the threshold is 128, the threshold is brought close to 255. For example, the threshold value 128 is changed to any one of 160, 192, 224... So that the possibility that the target pixel X is converted to a black pixel is reduced (converted to a white pixel). Change the threshold). The threshold value to be changed can be arbitrarily set.

  When any one of the peripheral pixels A and A, the peripheral pixels B and B, the peripheral pixels C and C, and the peripheral pixels D and D are continuous with each other, the threshold value changing unit 1161 stores the threshold value storage unit 1154 in the threshold value storage unit 1154. The stored threshold value is changed so as to approach a value indicating a white pixel. Specifically, when the threshold value is an intermediate value of 128 in 256 gradations, the threshold value is brought close to 0. For example, the threshold value 128 is changed to one of 96, 64, 32,... So that the possibility that the target pixel X is converted into a white pixel is reduced (converted into a black pixel). Change the threshold).

  Note that the pattern matching unit 1160 did not detect the continuity of black pixels or white pixels in any of the peripheral pixels A and A, the peripheral pixels B and B, the peripheral pixels C and C, and the peripheral pixels D and D. In this case, the threshold value changing unit 1161 does not change the threshold value.

  The binarization process by the quantization unit 1153 performs the binarization process for the pixel of interest X based on the threshold value changed by the threshold value change unit 1161.

  The operation of the error diffusion processing unit 115 configured as described above will be described. The pixel value (density value) of the target pixel X input from the line memory via the image input unit 1151 is input to the adder 1152. Further, the accumulated error calculation unit 1158 also receives the accumulated error accumulated in the pixel during the error diffusion process of other pixels. The adder 1152 performs a process of adding the pixel value and the accumulated error, and outputs the result to the quantization unit 1153.

  At this time, based on each pixel value stored in the output image storage unit 1159, the pattern matching unit 1160 determines that a plurality of binarized pixels that are arranged continuously to the target pixel X are white. Whether the pixels are continuously arranged between the pixels or the black pixels is detected, and when the continuous arrangement is detected, the threshold value changing unit 1161 sets the threshold value stored in the threshold value storage unit 1154 as described above. The pixel of interest X and the continuously arranged pixels are changed to values that reduce the possibility that the white pixels or the black pixels are continuously arranged. The threshold value changing unit 1161 does not change the threshold value stored in the threshold value storage unit 1154 when the continuous arrangement is not detected.

  The quantization unit 1153 performs binarization in comparison with the threshold value stored in the threshold value storage unit 1154. For example, when the threshold value is set to 128 gradations, which is an intermediate value of 256 gradations, black (1) is determined if the correction pixel value is greater than 128, and white (0) is determined if the correction pixel value is smaller than 128. . The determination result is output toward the image output unit 1155.

  The determination result is also input to the subtracter 1156. On the other hand, the corrected pixel value output from the adder 1152 is also input to the subtractor 1156. A subtracter 1156 subtracts these values to calculate a binarization error. Specifically, when black (1) is handled as 256 gradation 255 and white (0) is treated as 256 gradation 0, and the quantization unit 1153 determines black (1), If the value obtained by subtracting 255 from the corrected pixel value output from the adder 1152 is determined to be white (0), the corrected pixel value is directly used as the subtraction value. A binarization error (generation error of the target pixel X) is assumed. Based on the binarization error of the pixel of interest X calculated in this way, the cumulative error calculation unit 1158 calculates the distribution amount to be distributed to each peripheral pixel viewed from the pixel of interest, and the binarization process is still performed. A cumulative error to be added to a target pixel that has not been performed is calculated and stored. The determination result of the quantization unit 1153 is also input to the output image storage unit 1159.

  As described above, when the error diffusion processing is performed by the error diffusion processing unit 115, as shown in FIG. 5A, the error diffusion processing unit 115 receives a worm texture caused by the continuous arrangement of black pixels or white pixels. An image with reduced is output. Incidentally, FIG. 5B is a diagram illustrating an image in which a worm / texture is generated without performing the threshold value change by the threshold value changing unit 1161. Note that the threshold value is changed by the threshold value changing unit 1161 so that the pixel of interest X and neighboring pixels continuously arranged therewith are completely separated from the same pixel. (In this case, for example, the threshold value is changed to either 255 indicating a black pixel or 0 indicating a white pixel so that the pixel of interest X is converted to a pixel different from the peripheral pixels. ), The image processing according to the present invention does not exclude such a threshold change, but does not completely cut off the continuity between the same pixels, and the value that reduces the possibility that the same pixels are continuously arranged. If the change is made to, error diffusion processing can be performed while maintaining the same degree of identity between the original image and the binarized image.

[Other preferred embodiments]
The present invention is not limited to the configuration of the above embodiment, and various modifications can be made.

  (A) In the above embodiment, when the pattern matching unit 1160 continuously arranges a plurality of binarized pixels that are continuously arranged on the target pixel X between white pixels or black pixels. When it is detected, the threshold value changing unit 1161 performs the threshold value change. However, the control unit 10 or the image processing unit 11 determines whether the target pixel X belongs to a photographic image region or a character image region. It is assumed that an area discriminating unit is further provided, and the threshold value changing unit 1161 is a case where the pattern matching unit 1160 detects the continuous arrangement when the pixel discriminating pixel X is discriminated to belong to the character image area. Even if it exists, you may make it not change the threshold value memorize | stored in the threshold value memory | storage part 1154. FIG.

  For example, (1) the region determination unit includes an edge degree calculation unit that obtains the edge degree of the pixel of interest X, and the threshold value changing unit 1161 uses the edge degree obtained by the edge degree calculation unit based on a preset edge degree. If it is higher, the threshold value stored in the threshold value storage unit 1154 may not be changed even when the pattern matching unit 1160 detects the continuous arrangement. This edge degree calculation method can include all forms calculated from the pixel value of the pixel of interest X and the pixel values of surrounding pixels.

  (2) Further, as the region determination unit, an intermediate density region determination unit that determines whether the target pixel X belongs to the intermediate density region (intermediate gradation region) based on the density value of the target pixel X, Thus, only when it is determined that the pixel of interest X belongs to the intermediate density region (when it is assumed that the pixel of interest X belongs to the photographic region, etc.), the threshold value changing unit 1161 may change the threshold value. Good. In this way, for character edges that require continuity of black pixels or white pixels, good image conversion is performed by preventing the continuity of black pixels or white pixels from being cut off by changing the threshold value. Can do.

  (B) It should be noted that the region discriminating unit (edge degree calculating unit, intermediate density region discriminating unit) of the control unit 10, the shading correction unit 111, the input γ correction unit 112 of the image processing unit 11, shown in the above embodiment, The filter processing unit 113, the enlargement / reduction processing unit 114, the error diffusion processing unit 115, etc. may be configured such that each of these units is individually configured with a circuit or the like, or the control circuit is stored in the HDD 8 or the like According to the above, it is possible to function as each of the above parts.

  (C) In the above-described embodiment, the multifunction peripheral is shown as an example of the image processing apparatus according to the present invention. However, the image processing apparatus according to the present invention is not limited to the multifunction peripheral, and other image formation is performed. Another device such as a device or an information processing device may be used.

1 is a schematic side view mainly showing a mechanical configuration of a multifunction peripheral according to an embodiment of an image processing apparatus of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of the multifunction machine illustrated in FIG. 1. FIG. 3 is a block diagram illustrating an embodiment of a specific configuration of an error diffusion processing unit illustrated in FIG. 2. It is a figure which shows the pixel arrangement | sequence of an image memory, A, B, C, D is a surrounding pixel, X is an attention pixel used as the object of a binarization process. (A) is a diagram showing an example of an image output from the error diffusion processing unit with a reduced worm texture, and (b) is a case where the threshold value is not changed by the threshold value changing unit and a worm texture is generated. FIG.

Explanation of symbols

1 MFP 11 Image Processing Unit 115 Error Diffusion Processing Unit 1151 Image Input Unit 1152 Adder 1153 Quantization Unit 1154 Threshold Storage Unit 1155 Image Output Unit 1156 Subtractor 1157 Generated Error Storage Unit 1158 Cumulative Error Calculation Unit 1159 Output Image Storage Unit 1160 Pattern matching unit 1161 Threshold value changing unit

Claims (6)

An error generated during binarization processing of a pixel of interest using a predetermined threshold value is diffused to surrounding pixels before the binarization processing, and binarization processing using each pixel in which the error is diffused as the pixel of interest In an image processing apparatus equipped with an error diffusion processing unit that sequentially performs
The error diffusion processing unit includes a threshold value storage unit that stores the threshold value, a binarization processing unit that performs the binarization process on the pixel of interest using the threshold value stored in the threshold value storage unit, and the binary value At the time of binarization processing of a target pixel by the binarization processing unit, it is detected whether a plurality of binarized pixels that are continuously arranged on the target pixel are arranged continuously between white pixels or black pixels And when the continuous detection is detected by the connection detection unit, the threshold value stored in the threshold value storage unit is determined based on whether the target pixel and the continuously arranged pixel are white pixels or black pixels. A threshold value changing unit that changes to a value that reduces the possibility that pixels are continuously arranged;
The binarization processing unit is an image processing apparatus that performs binarization processing of a pixel of interest using a threshold value changed by the threshold value changing unit.   The threshold value changing unit, when the connection detection unit detects that the plurality of binarized pixels that are continuously arranged in the target pixel are arranged in black pixels, The image processing apparatus according to claim 1, wherein the threshold value stored in the threshold value storage unit is brought close to a value indicating a black pixel.   The threshold value changing unit, when the connection detection unit detects that a plurality of binarized pixels that are continuously arranged in the target pixel are arranged in white pixels, The image processing apparatus according to claim 1, wherein the threshold value stored in the threshold value storage unit is close to a value indicating a white pixel. An area discriminating unit for discriminating whether the pixel of interest belongs to a photographic image area or a character image area;
The threshold value changing unit is stored in the threshold value storage unit when the continuous arrangement is detected by the connection detecting unit only when the pixel of interest is determined to belong to a photographic image region by the region determining unit. The image processing apparatus according to claim 1, wherein the threshold value is changed. An edge degree calculating means for obtaining an edge degree of the target pixel;
In the case where the edge degree obtained by the edge degree calculating means is higher than a preset edge degree, the threshold value changing unit may be the case where the continuous arrangement is detected by the connection detecting unit. The image processing apparatus according to claim 1, wherein the threshold value stored in the threshold value storage unit is not changed. An error generated during binarization processing of a pixel of interest using a predetermined threshold value is diffused to surrounding pixels before the binarization processing, and binarization processing using each pixel in which the error is diffused as the pixel of interest An image processing program for causing an information processing device to function as an image processing device including an error diffusion processing unit that sequentially performs processing,
The error diffusion processing unit includes a threshold value storage unit that stores the threshold value, a binarization processing unit that performs the binarization process on the pixel of interest using the threshold value stored in the threshold value storage unit, and the binary value At the time of binarization processing of a target pixel by the binarization processing unit, it is detected whether a plurality of binarized pixels that are continuously arranged on the target pixel are arranged continuously between white pixels or black pixels When the continuous arrangement is detected by the connection detection unit and the connection detection unit, the threshold value stored in the threshold value storage unit is determined based on whether the target pixel and the continuously arranged pixel are white pixels or black pixels. A threshold value changing unit that changes to a value that is difficult to be continuously arranged between pixels,
An image processing program for causing the information processing apparatus to function so that the binarization processing unit performs binarization processing on a pixel of interest using a threshold value changed by the threshold value changing unit.

Images