JP3826861B2 - Image processing apparatus, image forming apparatus, and image processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image processing apparatus, an image forming apparatus, and an image processing method, and more particularly to an image processing apparatus, an image forming apparatus, and an image processing method configured to perform a filtering process using a median filter.
[0002]
[Prior art]
  Due to the demand for high-definition printing, recent laser printers are capable of high-resolution printing at 600 dpi or higher. However, particularly when printing a multi-valued image, the amount of data becomes enormous at a resolution of 600 dpi, so that the printing speed decreases due to an increase in data processing time. On the other hand, for a photographic image or the like, even if data processing is performed with a resolution of 300 dpi, a print result that is comparable to the original image can be obtained. In other words, for a photographic image, even if a printer having a resolution of 600 dpi is used, it is sufficient to perform data processing at a resolution of 300 dpi, which makes it possible to realize high-speed printing. However, with respect to a diagram drawn with characters and solid lines, if data processing is performed at a resolution of 300 dpi, the contour jaggy (jagged shape) is conspicuous, giving the impression that the image is a low resolution image.
[0003]
[Problems to be solved by the invention]
  Therefore, once high-speed printing and high-definition printing are achieved by performing data processing once with the number of pixels equivalent to a resolution of 300 dpi, and then performing multi-pixel (600 dpi) processing (enlargement processing) and smoothing processing of the image data. A method can be considered. As the smoothing process, it is preferable to perform a filtering process using a median filter that can enhance the edge of a character by preventing blurring of the outline (unsharpness) and has little adverse effect on a photographic image.
[0004]
  Filtering processing techniques using a median filter applied when performing multi-pixel processing are described in JP 2000-99713A, JP 2001-338288A, JP 2002-44425A, and the like. . The technique disclosed in Japanese Patent Laid-Open No. 2000-99713 divides image data into an edge portion and a non-edge portion before the multi-pixel processing, and applies a median filter only to the edge portion after the multi-pixel processing. The technique disclosed in Japanese Patent Laid-Open No. 2001-338288 is an output image obtained by mixing an input image obtained by subjecting original image data to multi-pixel processing and image data obtained by performing filtering processing using a median filter at an arbitrary ratio. is there. The technique disclosed in Japanese Patent Application Laid-Open No. 2002-44425 reduces the filtering effect when the enlargement ratio is small in increasing the number of pixels of image data.
[0005]
  However, according to these techniques, although it is possible to emphasize the edge of a character while suppressing jaggies, an increase in data processing time accompanying an increase in data processing load causes printing to be performed based on image data, for example. Will reduce the printing speed.
[0006]
  Accordingly, an object of the present invention is to provide an image processing apparatus, an image processing apparatus, and an image processing apparatus capable of obtaining image data in which jaggies are suppressed and character edges are emphasized by a relatively small data processing load when performing image data multi-pixel processing A forming apparatus and an image processing method are provided.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, an image processing apparatus according to claim 1 of the present invention has a larger number of pixels than the original image data by replacing each pixel included in the original image data with a plurality of pixels. Multi-pixel image generation means for generating pixel image data, filtering means for filtering the multi-pixel image data generated by the multi-pixel image generation means using a median filter, and one pixel of the original image data And an exclusion point setting means for setting at least one exclusion point for filtering using the median filter by the filtering means in a plurality of pixels of the corresponding multi-pixel image data. AndThe multi-pixel image generation means replaces one pixel with 2 × 2 four pixels, and the exclusion point setting means performs vertical or horizontal in the 2 × 2 four pixels in which one pixel of the original image data is replaced. Two aligned pixels are set as the exclusion point.
[0008]
  Further, the claims of the present invention13In another aspect, the image processing method described in the above item replaces each pixel included in the original image data with a plurality of pixels, thereby generating multi-pixel image data having a larger number of pixels than the original image data. The multi-pixel image data generated in the multi-pixel image generation step so that at least one exclusion point is set in a plurality of pixels of the multi-pixel image data corresponding to one pixel of the original image data; And a filtering step of filtering using a median filter. AndIn the multi-pixel image generation step, 1 pixel is replaced with 2 × 2 4 pixels, and in the filtering step, the 2 × 2 4 pixels in which 1 pixel of the original image data is replaced are vertically or horizontally. Two aligned pixels are set as the exclusion point.
[0009]
  According to this, by performing a filtering process using a median filter on multi-pixel image data, it is possible to obtain multi-pixel image data in which jaggy is suppressed and character edges are emphasized. Further, by providing the filtering exclusion point, jaggies can be more suitably suppressed, the data processing load of the filtering process using the median filter is reduced, and the process can be performed in a short time.In addition, the dependence on the image shape becomes relatively small, and a more excellent smoothing effect can be obtained.
[0010]
[0011]
[0012]
[0013]
[0014]
  Claims of the invention2In the image processing apparatus described in (1), the median filter has a size of 3 × 3. According to this, the smoothing effect can be obtained while suppressing the calculation load.
According to a third aspect of the present invention, there is provided an image processing apparatus for generating multi-pixel image data having a larger number of pixels than the original image data by replacing each pixel included in the original image data with a plurality of pixels. Multi-pixel image generation means, filtering means for filtering the multi-pixel image data generated by the multi-pixel image generation means using a median filter, and a plurality of multi-pixel image data corresponding to one pixel of the original image data In this pixel, there are provided exclusion point setting means for setting at least one exclusion point for filtering using the median filter by the filtering means. The multi-pixel image generation unit replaces one pixel with 4 × 4 16 pixels, and the exclusion point setting unit replaces one pixel of the original image data with 4 × 4 16 pixels. The second pixel from the top in the right and leftmost columns and the first to third pixels from the top in the second and third columns from the right are set as the exclusion points.
The image processing method according to claim 14 of the present invention generates multi-pixel image data having a larger number of pixels than the original image data by replacing each pixel included in the original image data with a plurality of pixels. The multi-pixel image generation step and the multi-pixel image generated in the multi-pixel image generation step so that at least one exclusion point is set in a plurality of pixels of the multi-pixel image data corresponding to one pixel of the original image data A filtering step of filtering the image data using a median filter. Then, in the multi-pixel image generation step, one pixel is replaced with 4 × 4 16 pixels, and in the filtering step, the maximum of the 4 × 4 16 pixels in which one pixel of the original image data is replaced. The second pixel from the top in the right and leftmost columns and the first to third pixels from the top in the second and third columns from the right are set as the exclusion points.
According to this, by performing a filtering process using a median filter on multi-pixel image data, it is possible to obtain multi-pixel image data in which jaggy is suppressed and character edges are emphasized. Further, by providing the filtering exclusion point, jaggies can be more suitably suppressed, the data processing load of the filtering process using the median filter is reduced, and the process can be performed in a short time.
In an image processing apparatus according to a fourth aspect of the present invention, the median filter has a size of 5 × 5. According to this, the smoothing effect can be obtained while suppressing the calculation load.
[0015]
  Claims of the invention5In the image processing apparatus described in (1), the filtering unit is realized by a circuit as hardware. According to this, high-speed processing becomes possible, and the load on other arithmetic devices can be reduced.
[0016]
  Claims of the invention6In the image processing apparatus described in the item 1, the filtering unit performs filtering of pixels other than the exclusion point among the replaced pixels every time the multi-pixel image generation unit performs replacement from one pixel to a plurality of pixels. This is performed while referring to the image data.
[0017]
  Further, the claims of the present invention14In the image processing method described in the above, every time a replacement from one pixel to a plurality of pixels is performed in the multi-pixel image generation step, filtering of pixels other than the exclusion point is performed by the filtering step. This is performed while referring to the original image data.
[0018]
  This eliminates the need to store all the multi-pixel image data, thereby reducing the memory usage.
[0019]
  Claims of the invention7 or 9The image processing apparatus according to the item 1, wherein the multi-pixel image data filtered by the filtering unit is output to an image forming apparatus or a display apparatus.IsIs. According to this, it is possible to realize high-quality printing or display while reducing internal processing in the processing device. The multi-pixel image data may be formed or displayed with the same resolution as the original image data, or the multi-pixel image data may be formed or displayed with a resolution higher than that of the original image data.
[0020]
  Claims of the invention8The multi-pixel image data filtered by the filtering unit is output to the image forming apparatus without being buffered. According to this, it is not necessary to provide a memory for storing the image data after the filtering process in the image processing apparatus.
[0021]
  Further, the claims of the present invention10The image forming apparatus described in (1) includes the image processing apparatus as described above, and according to this, since the filtering process can be performed in a short time, an image forming apparatus capable of performing image formation at high speed is provided. it can.
[0022]
  Further, every time the multi-pixel image generating unit performs replacement from one pixel to a plurality of pixels, filtering of pixels other than the exclusion point among the pixels replaced by the filtering unit of the image processing device is performed as original image data. , The claims of the present invention.11The multi-pixel image data filtered by the filtering means is configured to be supplied to the image forming unit without being buffered. According to this, it is not necessary to provide a memory for storing the image data after the filtering process in the image forming apparatus.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0024]
  FIG. 1 is a block diagram of an image processing apparatus according to an embodiment of the present invention and a printer which is an image forming apparatus including the image processing apparatus. A printer 1 shown in FIG. 1 includes an image processing device 2 and a print engine 3. The image processing apparatus 2 performs various types of image processing on print data supplied from an external host computer and outputs the processed image data to the print engine 3. The print engine 3 includes an image forming unit such as a laser unit or an ink jet head.
[0025]
  In the image processing apparatus 2, hardware as shown in FIG. The CPU 41, the ASIC 42, and the ROMs 43 and 44 are connected to each other by an address bus and a data bus. The ROM 43 stores various programs and data used for controlling the operation of the laser printer. The CPU 41 performs various calculations based on a program stored in the ROM 43. The ASIC 42 performs image processing to be described later based on an instruction from the CPU 41, and the data processed here is sent to the scanner unit (print engine 3). The RAM 44 stores various calculation results in the CPU 41 and the ASIC 42 and image data such as print data. Then, by combining these hardware and software, each unit 11 to 23 described below is constructed in the image processing apparatus 2.
[0026]
  The image processing apparatus 2 includes an original image storage unit 11, a drawing data creation unit 13, a multi-pixel image generation unit 14, a filtering unit 15, and an exclusion point setting unit 16. The print data storage unit 11a and the original image storage unit 11b are configured by a RAM 44. Print data supplied from an external host computer or the like is temporarily stored in the print data storage unit 11a. The drawing data creation unit 13 creates drawing data by expanding the print data stored in the print data storage unit 11a into a bitmap, and the created drawing data is stored in the original image storage unit 11b. . The drawing data creation unit 13 is realized by the CPU 41.
[0027]
  The multi-pixel image generation unit 14 replaces each pixel in the original image data stored in the original image storage unit 11 with 2 × 2 four pixels, thereby multi-pixel image data having four times the number of pixels of the original image data. Is generated. Details thereof will be described with reference to FIGS. 3 (a) and 3 (b). FIG. 3A is a schematic diagram of one pixel included in the original image data, and this pixel has a gradation value of “00” in 8-bit hexadecimal notation. The multi-pixel image generation unit 14 converts one pixel depicted in FIG. 3A into four pixels of 2 vertical pixels × 2 horizontal pixels each having a gradation value “00” as shown in FIG. 3B. Replace. Since the multi-pixel image generation unit 14 performs the same processing for all the pixels included in the original image data, the multi-pixel image data has four times the number of pixels as the original image data.
[0028]
  The filtering unit 15 performs a filtering process using a 3 × 3 median filter on the multi-pixel image data generated by the multi-pixel image generation unit 14. Here, the median filter will be described with reference to FIG. The 3 × 3 median filter converts the gradation value of the pixel “E” at the center of the nine pixels shown in FIG. 4 to the median value of the gradation values of the nine pixels “A” to “I” ( This is a filter to be replaced with the fifth value). For example, the pixels “A”, “B”, “C”, “F”, “I” have a gradation value “FF”, and the remaining pixels “D”, “E”, “G”, “H” If the gradation value is “00”, the gradation value of the pixel “E” is changed to “FF” as a result of applying the median filter.
[0029]
  The exclusion point setting unit 16 sets at least one exclusion point for filtering using the median filter by the filtering unit 15 in four pixels of the multi-pixel image data corresponding to one pixel of the original image data. In the present embodiment, out of the four pixels shown in FIG. 3B, exclusion points are set at the upper left and upper right two pixels as shown in FIG. As will be described later, the exclusion point setting unit 16 may change the position of the exclusion point in the four pixels based on the shape of the multi-pixel image data or the original image data.
[0030]
  Further, in the present embodiment, every time one pixel in the original image data is replaced with 4 pixels in the multi-pixel image generation unit 14, 1 corresponding to the scan direction in the print engine 3 among the replaced 4 pixels. Filtering of pixels that are in the line and are not excluded points is performed by the filtering unit 15 while referring to the original image data stored in the original image storage unit 11. Therefore, as will be apparent from the description to be described later, if the replacement from one pixel to four pixels is performed twice for each pixel in the original image data, the pre-filtering process generated by the multi-pixel image generation unit 14 is performed. It is not necessary to store multi-pixel image data, and the required memory capacity can be reduced.
[0031]
  The multi-pixel image data filtered by the filtering unit 15 is output to the print engine 3 without being buffered in the image processing apparatus 2. As a result, a memory for storing the filtered multi-pixel image data need not be provided between the print engine 3 and the filtering unit 15. In the print engine 3, the multi-pixel image data may be printed with the same resolution as the original image data, or the multi-pixel image data may be printed with a larger resolution than the original image data.
[0032]
  As a modification, the image processing apparatus 2 illustrated in FIG. 1 may further include a multi-pixel image buffer 21, a filtered multi-pixel image buffer 22, and a halftoning processing unit 23 in addition to the above-described units.
[0033]
  The multi-pixel image buffer 21 includes a RAM 44, and temporarily stores the multi-pixel image generated by the multi-pixel image generation unit 14. When the multi-pixel image buffer 21 has a capacity for storing the entire multi-pixel image data in which all pixels of the original image data or a predetermined unit such as one page is replaced with four pixels, as described above Rather than performing a filtering process every time one pixel is replaced by four pixels in the image generation unit 14, the entire original image data or a predetermined unit can be converted into multi-pixel image data and then filtered. . In this case, the data output to the print engine 3 may be output for each line while performing the filtering process, or may be performed after the filtering process is performed collectively.
[0034]
  In addition, when the multi-pixel image buffer 21 has only a capacity for storing multi-pixel image data for one line corresponding to the scan direction, a filtering process is performed on four pixels in which one pixel of the original image data is replaced. The data for one line is output to the print engine 3, and the data for the remaining one line can be stored in the multi-pixel image buffer 21. In this way, as will be apparent from the description to be described later, the replacement of each pixel of the original image data with four pixels only needs to be performed once for each pixel, so the multi-pixel image buffer 21 is provided. The processing time can be shortened compared with the case where there is not.
[0035]
  The filtered multi-pixel image buffer 22 is composed of a RAM 44 and temporarily stores the multi-pixel image data filtered by the filtering unit 15. When the multi-pixel image data stored in the filtered multi-pixel image buffer 22 is a multi-valued image, the half-toning processing unit 23 performs a half-toning process on the multi-pixel image data and performs a half-toned multi-pixel image. Data is provided to the filtered multi-pixel image buffer 22. As a result, a multi-valued image can be expressed by the print engine 3 that can output only binary data. In the case of an apparatus configuration in which data preliminarily developed in a bitmap is stored from an external apparatus, it is not necessary to provide the print data storage unit 11b and the drawing data creation unit 13 in FIG.
[0036]
  Here, the multi-pixel image generation unit 14, the filtering unit 15, and the exclusion point setting unit 16 are realized by a circuit in the ASIC 42, and the ASIC 42 is stored in the original image storage unit 11b in the RAM 44 in response to an instruction from the CPU 41. The multi-pixel image generation unit 14, the filtering unit 15, and the exclusion point setting unit 16 perform processing while accessing the rendered data, and send the processed multi-pixel image data to the print engine 3. Among them, the filtering unit 15 may be a multi-stage connection of a plurality of filter elements, for example. In this case, each filter element is a two-input two-output element, and of the two input data, the larger value is output from the upper output terminal, and the smaller value is output from the lower output terminal. By connecting four such filter elements arranged in parallel per stage, the median value of the nine input gradation values is output from the output terminal corresponding to the center (fifth) of the final stage. Is done.
[0037]
  Next, the processing procedure by the image processing apparatus 2 according to the present embodiment will be described with reference to the flowchart of FIG. 6 and the examples of FIGS. When print data is received from a host computer or the like, the drawing data creation unit 13 (CPU 41) starts a process of expanding the print data into a bitmap, and expansion into a predetermined amount (for example, one page) of the bitmap is performed. The CPU 41 issues an instruction to the ASIC 42, and the ASIC 42 starts the process shown in FIG. In FIG. 7 to FIG. 12, the gradation value (“00” or “FF”) enclosed in parentheses () indicates that the gradation value after filtering processing is in an indeterminate state, and is underlined. The gradation value obtained by subtracting indicates that the pixel is an exclusion point of the filtering process.
[0038]
  FIG. 7 depicts original image data including a total of six pixels arranged in a matrix in three vertical columns X, Y, Z and two horizontal columns M, N. Among them, the gradation values of the three pixels (M, Z), (N, Y), and (N, Z) are “FF”, and the gradation values of the remaining three pixels are “00”. is there. When the original image data including the six pixels arranged in this way is replaced (multi-pixel) processing / filtering processing by the image processing apparatus 2, first, in step S1, as shown in FIG. (N, X) is a four-pixel image generation unit 14 that has four pixels (N1, X1), (N1, X2), (N2, X1), (N2, X2) each having a gradation value “00”. Is replaced by
[0039]
  In step S2, the filtering unit 15 uses the median filter shown in FIG. 4 to select the lower two pixels (N2, X1) and (N2, X2) among the four replaced pixels. Perform the filtering process. At this time, for example, in the case of the pixel (N2, X2), the gradation of a total of four pixels including the pixel (N, X) and the pixel (N, Y) and two pixels (not shown) below them in the original image data. If the values are known, the gradation values of the eight pixels that will be present around the pixel (N2, X2) after the replacement process can be known, so the level of the pixel (N2, X2) after the filtering process by the median filter The key value is determined. Therefore, the filtering process in step S2 is performed with reference to the original image data (having the same contents as shown in FIG. 7) stored in the original image storage unit 11. In this example, if two pixels (not shown) are set to “00”, as shown in FIG. 8, the gradation values of two pixels (N2, X1) and (N2, X2) are obtained even if filtering processing is performed. Remains “00”.
[0040]
  Subsequently, in Step S3, the filtering unit without buffering the gradation value data of the two pixels (N2, X1) and (N2, X2) in the N2 line, which is the filtering processing result in Step S2, in the middle. 15 to the print engine 3. In step S4, it is determined whether or not all the pixels in one line in the scanning direction in the original image data have been replaced with four pixels. As a result, when there are non-replaced pixels (S4: NO), the process returns to step S1 and the same processing is repeated. On the other hand, if there is no non-replaced pixel (S4: YES), the process proceeds to step S5 to determine whether or not the pixel replacement process for all lines has been completed. If there is an unreplaced line (S5: NO), the process returns to step S1 and the same process is repeated. On the other hand, when there is no unreplaced line (S5: YES), this process ends.
[0041]
  In the case of this example, after performing replacement / filtering processing on the lower line (N2 line) of the pixel (N, X), as shown in FIG. 9, the pixel (N, Y) and the pixel (N, Z) After the same replacement / filtering process is completed for the lower line (N2 line), the process proceeds to the process for the upper line (N1 line) of the next pixel (N, X). That is, the pixel (N, X) is replaced with 4 pixels again (S1), and the filtering process for pixels other than the excluded points is performed (S2). However, since the two pixels (N1, X1) and (N1, X2) in the N1 line are both excluded points, the filtering process is not substantially performed. Then, the gradation value data of the two pixels (N1, X1) and (N1, X2) in the N1 line are sent to the print engine 3 without being buffered in the middle (S3).
[0042]
  Further, the filtering process is similarly skipped after the next pixel (N, Y) is replaced with four pixels again (S1). That is, since the two pixels (N1, Y1) and (N1, Y2) in the N1 line are both excluded points, the filtering process is not substantially performed. Then, the tone value data of the two pixels (N1, Y1) and (N1, Y2) in the N1 line are sent to the print engine 3 without being buffered in the middle (S3). The same applies to the next pixel (N, Z). Then, a result as shown in FIG. 10 is obtained.
[0043]
  In the filtering process for the next line (M2 line), the filtering process is performed on (M2, X1), (M2, X1), and (M2, Y1). The process of “M2, Y2” is performed. As shown in FIG. 11, the gradation value of the pixel (M2, Y2) is “00” to “00” because five gradation values of the pixel and the surrounding eight pixels are “FF” in the original image data. FF ". Then, the replacement / filtering process for the M2 line and the M1 line is completed, and finally, the multi-pixel image data as shown in FIG. 12 is sent from the filtering unit 15 to the print engine 3.
[0044]
  As described above, according to the image processing apparatus 2 of the present embodiment, the filtering process using the median filter is performed on the four pixels in which each pixel of the original image data is replaced. As is clear from the comparison, jaggies can be suppressed by changing the gradation value of the pixel (M2, Y2) from “00” to “FF”. In addition, due to the characteristics of the median filter, the gradation value of the pixel (M2, Y2) is an intermediate gradation value other than the gradation values of the pixels around it (“00” and “FF” in this embodiment). Therefore, it is possible to obtain multi-pixel image data in which the edge of the character is emphasized as compared with the case where image processing is performed by the moving average method, for example. .
[0045]
  Furthermore, since the exclusion point setting unit 16 sets exclusion points for filtering processing by the median filter, it is possible to reduce the number of pixels to be subjected to filtering processing, eliminate the need for extra computation, and perform filtering processing at high speed. . Although not clear in the examples of FIGS. 7 to 12, as can be seen from the examples described later, there are cases where jaggies can be more suitably suppressed by setting exclusion points for filtering processing.
[0046]
  Therefore, for example, the drawing data creation unit 13 can generate 300 dpi original image data at a high speed, and the filtering unit 15 can also perform the processing at high speed, thereby enabling high-speed printing with the print engine 3. Become. In addition, since the multi-pixel image generation unit 14 converts the original image data of 300 dpi into a resolution of 600 dpi and further performs filtering processing with the median filter, as described above, the print result in which the edge of the character is enhanced while suppressing jaggies Can be obtained.
[0047]
  In addition, as described above, paying attention to the transmission of gradation value data for each line to the print engine 3, every time one pixel in the original image data is replaced with four pixels by the multi-pixel image generation unit 14. In addition, while referring to the surrounding original image data, filtering is performed on pixels in one line that are to be sent to the print engine 3 in four pixels and pixels other than the exclusion point. Since the data is sent to the print engine 3, the multi-pixel image generation unit 14 performs the replacement from 1 pixel to 4 pixels twice for each pixel in the original image data corresponding to the line. It is not necessary to store the generated multi-pixel image data before the filtering process, and the necessary memory capacity can be reduced.
[0048]
  In addition, since the exclusion point setting unit 16 sets two exclusion points in each of the four pixels in which one pixel of the original image data is replaced, the dependence on the image shape depends as will be apparent from the embodiments described later. The degree becomes relatively small, and a more excellent smoothing effect can be obtained.
[0049]
  Furthermore, in the present embodiment, the multi-pixel image generation unit 14 replaces each pixel included in the original image data with 2 × 2 4 pixels, whereas the filtering unit 15 has a 3 × 3 median size. Since the filter is used, the smoothing effect is easily exhibited. In addition, since the median filter is set to the minimum necessary size, the calculation load can be suppressed.
[0050]
  In addition, in the present embodiment, the exclusion point setting unit 16 sets two pixels arranged vertically or horizontally in the four pixels in which one pixel of the original image data is replaced as an exclusion point. The degree of dependence becomes relatively small, and a more excellent smoothing effect can be obtained.
[0051]
  Next, the image processing apparatus 2 is provided with a multi-pixel image buffer 21, and the multi-pixel image buffer 21 has a capacity sufficient to store multi-pixel image data for one line. The procedure of processing by the image processing apparatus 2 will be described with reference to FIGS. 13 to 15 based on the same example as described with reference to FIGS.
[0052]
  When the original image data as shown in FIG. 7 is replaced / filtered by the image processing apparatus 2, first, the lower left pixel (N, X) is converted into the gradation value “00” by the multi-pixel image generation unit 14. Are replaced with four pixels (N1, X1), (N1, X2), (N2, X1), and (N2, X2). Then, the filtering unit 15 performs a filtering process using a median filter for two pixels (N2, X1) and (N2, X2) other than the pixels (N1, X1) and (N1, X2) that are exclusion points. The The result is shown in FIG. After the filtering process, the tone value data of the two pixels (N2, X1) and (N2, X2) in the lower line (N2 line) is sent to the print engine 3 and is sent to the upper line (N1 line). The gradation value data of certain two pixels (N1, X1) and (N1, X2) are stored in the multi-pixel image buffer 21.
[0053]
  Subsequently, the pixel (N, Y) is converted into four pixels (N1, Y1), (N1, Y2), (N2, Y1), (N2, Y1) having the gradation value “FF” in the multi-pixel image generation unit 14. N2, Y2). Then, the filtering unit 15 performs filtering processing using a median filter on the two pixels (N2, Y1) and (N2, Y2) other than the pixels (N1, Y1) and (N1, Y2) which are exclusion points. The After the filtering process, the tone value data of the two pixels (N2, Y1) and (N2, Y2) in the N2 line are sent to the print engine 3, and the two pixels (N1, Y1) in the N1 line are sent. ), (N1, Y2) gradation value data is stored in the multi-pixel image buffer 21.
[0054]
  Similarly, when the replacement / filtering process for the next pixel (N, Z) is completed, the tone value data of the two pixels (N2, Z1) and (N2, Z2) on the N2 line are sent to the print engine 3. Then, the gradation value data of the two pixels (N1, Z1) and (N1, Z2) in the N1 line are stored in the multi-pixel image buffer 21. The result is shown in FIG. Thereafter, six pixels (N1, X1), (N1, X2), (N1, Y1), (N1, Y2), (N1, Z1), (N1, X1), (N1, X2) stored in the multi-pixel image buffer 21 After the gradation value data of (N1, Z2) is sent to the print engine 3, the process proceeds to the replacement / filtering process for the next pixel (M, X).
[0055]
  When the replacement / filtering processing of the pixel (M, X) is completed, the gradation value data of the two pixels (M2, X1) and (M2, X2) in the lower line (M2 line) are sent to the print engine 3. The gradation value data of the two pixels (M1, X1) and (M1, X2) in the upper line (M1 line) is stored in the multi-pixel image buffer 21. Then, the process proceeds to replacement / filtering processing for the next pixel (M, Y). By this filtering processing, as shown in FIG. 15, the gradation value of the pixel (M2, Y2) is converted from “00” to “FF”. When the pixel (M, Y) replacement / filtering process is completed, the tone value data of the two pixels (M2, Y1) and (M2, Y2) in the M2 line are sent to the print engine 3 and are sent to the M1 line. The gradation value data of two pixels (M1, Y1) and (M1, Y2) are stored in the multi-pixel image buffer 21. Similarly, when the pixel (M, Z) replacement / filtering process ends, the same result as shown in FIG. 12 is obtained. Then, the gradation value data of the two pixels (M2, Z1) and (M2, Z2) in the M2 line are sent to the print engine 3, and the two pixels (M1, Z1) and (M1 in the M1 line are sent. , Z2) is stored in the multi-pixel image buffer 21, the six pixels (M1, X1), (M1, X2), (M1, X2) in the M1 line stored in the multi-pixel image buffer 21 are stored. The gradation value data of (M1, Y1), (M1, Y2), (M1, Z1), (M1, Z2) is sent to the print engine 3.
[0056]
  As described above, according to the image processing device 2 of the present embodiment, the filtering process using the median filter is performed on the four pixels in which each pixel of the original image data is replaced, as is apparent from FIG. Thus, it is possible to obtain multi-pixel image data in which jaggies are suppressed and outline blurring does not occur and character edges are emphasized. Furthermore, since the exclusion point setting unit 16 sets exclusion points for filtering processing by the median filter, filtering processing can be performed at high speed. Therefore, high-speed printing with the print engine 3 can be realized.
[0057]
  In addition, since the multi-pixel image buffer 21 can store multi-pixel image data for one line, it is only necessary to replace each pixel of the original image data with four pixels once for each pixel. The processing time can be made shorter than when the buffer 21 is not provided.
[0058]
  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various design changes can be made as long as they are described in the claims. For example, the image processing device 2 may output the filtered multi-pixel image data to a display device such as a CRT or a liquid crystal display instead of the print engine 3. Further, the multi-pixel image generation unit 14 may replace one pixel of the original image data with an arbitrary plurality of pixels other than four pixels. In addition, a median filter having an arbitrary size other than 3 × 3 may be used. However, as in the above-described embodiment, each pixel included in the original image data is m × m.²When replaced with a pixel, the median filter preferably has a size of n × n (n = m + 1).
[0059]
AlsoIn the above-described embodiment, the exclusion points are arranged horizontally on the upper line in the four pixels. However, for example, they may be arranged horizontally on the lower line, or vertically on either the left or right line. May be. Further, the position and number of exclusion points may be changed as appropriate based on the shape of the original image data. In this case, different exclusion points may be set for a certain area of the original image data and another area. In this case, a more excellent smoothing effect may be obtained based on the characteristics of the image shape.
[0060]
  In the above-described embodiment, the case where there are two types of gradation values of pixels “00” and “FF” is described as an example. However, three or more types of gradation values are mixed in the original image data. However, the present invention is applicable. Furthermore, the image processing apparatus and the image processing method according to the present invention can be applied not only to image forming apparatuses such as printers and fax machines but also to various apparatuses that involve processing for increasing the number of pixels of image data.
[0061]
【Example】
  Next, examples and comparative examples of the present invention will be described.
[0062]
(Comparative Example 1)
  Consider a case in which original image data having a right-up slope and a left-up slope as shown in FIG. First, the result shown in FIG. 17 was obtained by the replacement processing of each pixel with four pixels by the multi-pixel image generation unit 14.This comparative exampleIn FIG. 18, it is assumed that the exclusion point setting unit 16 sets only the upper left pixel of the four pixels as the exclusion point as shown in FIG. At this time, as a result of the filtering process, multi-pixel image data as shown in FIG. 19 was obtained. FIG. 17 depicts an image stored in the case where the multi-pixel image buffer 21 is provided for convenience of explanation, and intermediate image data as shown in FIG. It may not actually be obtained. The same applies to FIG. 22 described later.
[0063]
  As is clear from FIG. 19, only one of the four pixels is an excluded point.Comparative Example 1According to this, although jaggedness can be suppressed in the upwardly inclined portion, jaggy cannot be suppressed in the upwardly inclined portion.
[0064]
(Example 1)
  After the pixel replacement processing by the multi-pixel image generation unit 14 is performed on the same original image data as shown in FIG. 16, two pixels of the upper left pixel and the upper right pixel among the four pixels as shown in FIG. 5. Was set as an exclusion point and filtered. Then, multi-pixel image data as shown in FIG. 20 was obtained.
[0065]
  As is apparent from FIG. 20, 2 out of 4 pixels are excluded points.Example 1According to this, jaggies can be suppressed in both the right-upward inclined portion and the left-upward inclined portion.Comparative Example 1 and Example 1From the above, when replacing one pixel of the original image data with four pixels, it can be seen that a more excellent jaggy suppression effect can be obtained by setting two exclusion points than by setting one exclusion point.
[0066]
(Example 2)
  Consider a case in which original image data having a right-up slope and a left-up slope as shown in FIG. In this embodiment, it is assumed that the multi-pixel image generation unit 14 replaces each pixel with 4 × 4 16 pixels. The result shown in FIG. 22 was obtained by this replacement process. In this embodiment, a median filter having a size of 5 × 5 as shown in FIG. 23 is used, and the exclusion point setting unit 16 excludes 8 pixels as shown in FIG. Shall be set as At this time, as a result of the filtering process, multi-pixel image data as shown in FIG. 25 was obtained.
[0067]
  As is clear from FIG. 25, 8 out of 16 pixels are excluded points.Example 2According to this, jaggies can be suitably suppressed in both the right-upward inclined portion and the left-upward inclined portion.
[0068]
(Comparative Example 2)
  After performing the replacement processing of each pixel to 16 pixels by the multi-pixel image generation unit 14 for the same original image data as shown in FIG. 21, a 5 × 5 median filter is used without setting an exclusion point. The filtering process was performed. Then, multi-pixel image data as shown in FIG. 26 was obtained. Thus, in this comparative example, since the exclusion point of the filtering process is not set, jaggies cannot be sufficiently suppressed.
[0069]
【The invention's effect】
  As described above, according to the present invention, by performing filtering processing using a median filter on multi-pixel image data, multi-pixel image data in which jaggy is suppressed and character edges are emphasized can be obtained. it can. Further, by providing the filtering exclusion point, jaggies can be more suitably suppressed, the data processing load of the filtering process using the median filter is reduced, and the process can be performed in a short time.
[Brief description of the drawings]
FIG. 1 is a block diagram of an image processing apparatus according to an embodiment of the present invention and a printer that is an image forming apparatus including the image processing apparatus.
FIG. 2 is a block diagram of a main board of a laser printer.
FIG. 3 is a schematic diagram illustrating a state in which each pixel in the original image data is replaced with 2 × 2 four pixels.
FIG. 4 is a schematic diagram of a 3 × 3 median filter.
FIG. 5 is a schematic diagram for explaining filtering exclusion points using a median filter;
FIG. 6 is a flowchart depicting an image processing procedure according to an embodiment of the present invention.
FIG. 7 is a schematic diagram for explaining an example of image processing according to an embodiment of the present invention.
FIG. 8 is a schematic diagram for explaining an example of image processing according to an embodiment of the present invention.
FIG. 9 is a schematic diagram for explaining an example of image processing according to an embodiment of the present invention.
FIG. 10 is a schematic diagram for explaining an example of image processing according to an embodiment of the present invention.
FIG. 11 is a schematic diagram for explaining an example of image processing according to an embodiment of the present invention.
FIG. 12 is a schematic diagram for explaining an example of image processing according to an embodiment of the present invention.
FIG. 13 is a schematic diagram for explaining an example of image processing according to a modification of the present invention.
FIG. 14 is a schematic diagram for explaining an example of image processing according to a modification of the present invention.
FIG. 15 is a schematic diagram for explaining an example of image processing according to a modification of the present invention.
FIG. 16 shows the present invention.Comparative Example 1 and Example 1It is a schematic diagram of the original image data concerning.
FIG. 17 shows the present invention.Comparative Example 1 and Example 1It is a schematic diagram of the multi-pixel image data before filtering according to.
FIG. 18 shows the present invention.Comparative Example 1It is a schematic diagram for demonstrating the position of the exclusion point in.
FIG. 19 shows the present invention.Comparative Example 1It is a schematic diagram for demonstrating the result by.
FIG. 20 shows the present invention.Example 1It is a schematic diagram for demonstrating the result by.
FIG. 21 shows the present invention.Example 2 and Comparative Example 2It is a schematic diagram of the original image data concerning.
FIG. 22 shows the present invention.Example 2 and Comparative Example 2It is a schematic diagram of the multi-pixel image data before filtering according to.
FIG. 23 shows the present invention.Example 2 and Comparative Example 2It is a schematic diagram of the median filter used in FIG.
FIG. 24 shows the present invention.Example 2It is a schematic diagram for demonstrating the position of the exclusion point in.
FIG. 25 shows the present invention.Example 2It is a schematic diagram for demonstrating the result by.
FIG. 26 of the present inventionComparative Example 2It is a schematic diagram for demonstrating the result by.
[Explanation of symbols]
  1 Printer
  2 Image processing unit
  3 Print engine
  11 Original image storage
  13 Drawing data generator
  14 Multi-pixel image generation unit (multi-pixel image generation means)
  15 Filtering unit (filtering means)
  16 Exclusion point setting section (exclusion point setting means)
  21 Multi-pixel image buffer
  22 Filtered multi-pixel image buffer
  23 Halftone processing section

Claims (14)

Multi-pixel image generation means for generating multi-pixel image data having a larger number of pixels than the original image data by replacing each pixel included in the original image data with a plurality of pixels;
Filtering means for filtering the multi-pixel image data generated by the multi-pixel image generating means using a median filter;
And exclusion point setting means for setting at least one exclusion point for filtering using the median filter by the filtering means in a plurality of pixels of multi-pixel image data corresponding to one pixel of original image data. and,
The multi-pixel image generating means replaces one pixel with 2 × 2 four pixels,
2. The image processing apparatus according to claim 1, wherein the exclusion point setting means sets, as the exclusion point, two pixels arranged in the vertical or horizontal direction in 2 × 2 four pixels in which one pixel of the original image data is replaced .   The image processing apparatus according to claim 1, wherein the median filter has a size of 3 × 3.   Multi-pixel image generation means for generating multi-pixel image data having a larger number of pixels than the original image data by replacing each pixel included in the original image data with a plurality of pixels;
  Filtering means for filtering the multi-pixel image data generated by the multi-pixel image generating means using a median filter;
  And exclusion point setting means for setting at least one exclusion point for filtering using the median filter by the filtering means in a plurality of pixels of multi-pixel image data corresponding to one pixel of original image data. And
  The multi-pixel image generating means replaces one pixel with 4 × 4 16 pixels,
  The exclusion point setting means includes the second pixel from the top in each of the rightmost and leftmost columns, and the second and third pixels from the right among the 16 pixels of 4 × 4 in which one pixel of the original image data is replaced. An image processing apparatus, wherein the first to third pixels from the top in each column are set as the exclusion points.   The image processing apparatus according to claim 3, wherein the median filter has a size of 5 × 5. The image processing apparatus according to any one of claims 1 to 4, characterized in that said filtering means is realized by a circuit as hardware. The filtering unit performs filtering of pixels other than the exclusion point among the replaced pixels with reference to the original image data every time the multi-pixel image generation unit performs replacement from one pixel to a plurality of pixels. the image processing apparatus according to any one of claims 1 to 5, wherein. The image processing apparatus according to any one of claims 1 to 6, the multi-pixel image data that has been filtered by the filtering means, characterized in that it is output to the image forming apparatus. The image processing apparatus according to claim 7 , wherein the multi-pixel image data filtered by the filtering unit is output to the image forming apparatus without being buffered. The image processing apparatus according to any one of claims 1 to 6, characterized in that the multi-pixel image data that has been filtered by the filtering means is output to the display device. Image forming apparatus including an image processing apparatus according to any one of claims 1-9. The image processing apparatus according to claim 6 or 8 , comprising:
An image forming apparatus configured to supply multi-pixel image data filtered by the filtering unit to an image forming unit without being buffered. A multi-pixel image generation step of generating multi-pixel image data having a larger number of pixels than the original image data by replacing each pixel included in the original image data with a plurality of pixels;
The median filter is used for the multi-pixel image data generated in the multi-pixel image generation step so that at least one exclusion point is set in a plurality of pixels of the multi-pixel image data corresponding to one pixel of the original image data. Filtering step for filtering,
In the multi-pixel image generation step, 1 pixel is replaced with 2 × 2 4 pixels,
2. The image processing method according to claim 1, wherein in the filtering step, two pixels arranged in the vertical or horizontal direction in 2 × 2 four pixels in which one pixel of the original image data is replaced are set as the exclusion points .   A multi-pixel image generation step of generating multi-pixel image data having a larger number of pixels than the original image data by replacing each pixel included in the original image data with a plurality of pixels;
  Using the median filter, the multi-pixel image data generated in the multi-pixel image generation step is set so that at least one exclusion point is set in a plurality of pixels of the multi-pixel image data corresponding to one pixel of the original image data. And a filtering step for filtering
  In the multi-pixel image generation step, one pixel is replaced with 4 × 4 16 pixels,
  In the filtering step, the second pixel from the top in each of the rightmost and leftmost columns and the second and third pixels from the right in the 4 × 4 16 pixels in which one pixel of the original image data is replaced. An image processing method, wherein the first to third pixels from the top in each column are set as the exclusion points. Each time replacement from one pixel to a plurality of pixels is performed in the multi-pixel image generation step, filtering of pixels other than the exclusion point among the replaced pixels is performed by referring to the original image data. The image processing method according to claim 12 or 13 , characterized in that:

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