JP2007005972A - Image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of preventing characters from being thickened and smashed or thin lines from being thinned and interrapted in the case of applying magnification processing to an input image and printing out the processed image. <P>SOLUTION: The image processing apparatus 1 includes: a magnification processing means for applying magnification processing to the input image; a detection means for detecting pixels of edge parts in a character line image region from the magnified image obtained by magnification processing; and a density revision means that applies processing of revising density of the pixels of the edge parts detected by the detection means so as to cause a density gradient in a way that the pixel density is lowered for pixels closer to white pixels adjacent to the edge parts. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus that performs image processing on a character or line drawing image included in an image.

  When the input image is enlarged (resolution conversion) in order to print out a low-resolution input image (input image data) with a high-resolution printer, the image is enlarged by pattern matching using a 3 × 3 matrix, for example. In general, a so-called smoothing process is performed in which a stepped portion (jaggy) of an image generated during processing is smoothed. As described above, as an apparatus for performing smoothing processing by pattern matching on an input image, there is one disclosed in Patent Document 1.

  The apparatus disclosed in Patent Literature 1 includes a 3 × 3 pixel pattern including a target pixel set for an input image and reference pixels adjacent to the target pixel, and a 3 × 3 pattern stored in advance. If the pixel of interest is a white pixel when these patterns match, a black pixel having an area of 1/4 is added to the pixel of interest as illustrated in FIG. After that, enlarge the image. If the pixel of interest is a black pixel, the enlargement process is performed after deleting a black pixel having an area of 1/4 with respect to the pixel of interest as illustrated in FIG.

By the way, when performing the smoothing process which is performed by the apparatus of Patent Document 1, if a step portion of an image is smoothed while deleting pixels (black pixels), a thin line included in the input image becomes thin and may be interrupted. For this reason, usually, a process of smoothing the step portion of the image while adding pixels (black pixels) is performed.
JP-A-6-38038

  However, when smoothing processing is performed to smooth the image of the stepped portion of the image while adding pixels as described above, so-called grandchild copying, such as copying the output image obtained by copying the input image However, there was a problem that the characters were fat and crushed. Such a phenomenon is particularly noticeable when a printer with a low resolution is used.

  The present invention has been made in view of the above problems, and prevents a character from becoming thick and crushed or a thin line from becoming thin when the input image is enlarged and printed. It is an object of the present invention to provide an image processing apparatus that can perform the above processing.

  In order to achieve the above object, an image processing apparatus according to claim 1, enlargement processing means for enlarging an input image, and detecting pixels at an edge portion in a character line drawing area from the enlarged image obtained by the enlargement processing. And a process of changing the pixel density with respect to the pixels of the edge portion detected by the detection means so as to give a density gradient so that the pixel density becomes lower as the white pixel adjacent to the edge part is closer to the white pixel. And a density changing means to perform.

  The image processing device according to claim 2 is the image processing device according to claim 1, wherein the pixels of the edge portion detected by the detection unit are adjacent to white pixels around the edge portion in the input image before the enlargement processing. It is characterized in that it is included in one obtained by enlarging one edge pixel.

  The image processing apparatus according to claim 3, wherein the image processing apparatus according to claim 1 or 2 determines whether an enlarged image obtained by the enlargement process is a character line drawing area or a halftone area. And the density changing means does not perform the process of changing the pixel density for the halftone area based on the determination result of the determining means, and changes the pixel density only for the character / line image area. It is characterized by performing processing.

  The image processing device according to claim 4 is defined in the image processing device according to any one of claims 1 to 3 for calculating a pixel density after the process of changing the pixel density is performed. Storage means for storing an arithmetic expression is provided, and the density changing means performs processing for changing the pixel density using an arithmetic expression stored in the storage means.

  According to the image processing apparatus of claim 1, with respect to the pixels of the edge portion detected by the detection means, in order to set the density gradient so that the pixel density is lower as the white pixel is adjacent to the edge portion. Since density changing means for changing the pixel density is provided, when the input image is enlarged and printed, the characters become thicker and crushed, or the thin lines become thinner and interrupted. And the reproducibility of images of characters and fine lines can be improved.

  According to the image processing apparatus of claim 2, the edge portion pixels detected by the detection unit are subjected to enlargement processing of one edge pixel adjacent to the white pixels around the edge portion in the input image before the enlargement processing. Therefore, the pixel density is not changed by using more pixels than the pixels obtained by enlarging one edge pixel in the input image as the edge portion pixels. Therefore, it is possible to prevent the character from becoming thick and crushed, or the thin line from being thinned and interrupted without missing the original pixel information that one edge pixel in the input image is a black pixel. .

  According to the image processing apparatus of claim 3, the halftone region that should not be subjected to the process of changing the pixel density is not performed, but only for the character line region including characters and fine lines. The image reproducibility can be improved by performing a process of changing the pixel density of the pixels in the edge portion.

  According to the image processing apparatus of the fourth aspect, since the process of changing the pixel density is performed using the arithmetic expression stored in the storage unit, the process of changing the pixel density by pattern matching is performed. It is not necessary to provide a memory for storing the matching pattern, and there is an advantage that the process of changing the pixel density can be easily performed.

  Hereinafter, a case where the image processing apparatus according to the embodiment of the present invention is applied to a multifunction machine having a copy function and a facsimile communication function will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of an image processing apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing the flow of data transfer when a process for changing the pixel density, which will be described later (hereinafter also referred to as “pixel density changing process”), is performed in the image processing apparatus 1.

  As illustrated, the image processing apparatus 1 includes a control unit (MPU: Microprocessing Unit) 2, a ROM (Read Only Memory) 3, a RAM (Random Access Memory) 4, a document reading unit 5, a codec (CODER: Coder and Decoder). ) 6, image memory 7, modem 8, NCU (Network Control Unit) 9, operation unit 10, display unit 11, enlargement processing circuit 12, image area determination circuit 13, selection circuit 14, print image data generation unit 15, and printer 16, and the units 2 to 16 are communicably connected via a bus 17.

  The control unit 2 controls the operation of each unit of the image processing apparatus 1. The ROM 3 stores various programs for the operation of each unit of the image processing apparatus 1 to be controlled by the control unit 2. The RAM 4 stores various data such as setting information and operation information used for the processing operation of the image processing apparatus 1 in a readable and writable state.

  The document reading unit 5 reads image data of a document. Although not shown, the document reading unit 5 includes an image sensor such as a CCD (Charge Coupled Device) and an optical system such as a light source (FBS: Flat Bed Scanner). And an automatic document feeder (ADF) and the like.

  The codec 6 encodes / decodes image data. Here, the image data of the document output from the document reading unit 5 is encoded by the JPEG, MH, MR, MMR, JBIG method, etc., and is encoded so that the printer 16 prints out the image data on paper. Decode the image data. The image memory 7 stores image data encoded by the codec 6, image data received by facsimile, and the like.

  The modem 8 is, for example, a recommendation V.16 of ITU-T (International Telecommunication Union Telecommunication Standardization Sector). Modulation and demodulation of transmission / reception data according to the 34 standard or the like. The NCU 9 is a line network control device that controls a telephone line to make or cut a call, and is connected to a PSTN (Public Switched Telephone Network) 18.

  Although not shown, the operation unit 10 includes a start key for instructing the document reading unit 5 to start a document reading operation, a numeric keypad for inputting a facsimile number and the number of copies, a cursor key for performing various settings, and the like. Various operation keys linked with the display unit 11 are provided. The display unit 11 includes a liquid crystal display device (LCD: Liquid Crystal Display) that displays various setting states and the operation state of the device 1 with characters and graphics, an LED lamp that is turned on or off, and the like. I have.

  The enlargement processing circuit 12 functions as enlargement processing means for enlarging input image data (hereinafter simply referred to as “input image”). Here, the enlargement processing circuit 12 is read from the image memory 7 and is read by the codec 6. The decoded monochrome binary input image is subjected to enlargement processing by converting the resolution in accordance with the resolution of the printer 16. For example, as illustrated in FIG. 3, when an input image of 100 dpi (main scanning direction) × 200 dpi (sub-scanning direction) is printed out by a printer 16 having a resolution of 600 dpi in the main scanning direction and 600 dpi in the sub-scanning direction, The enlargement processing circuit 12 enlarges the input image at a magnification of 6 times in the main scanning direction and 3 times in the sub scanning direction. The enlarged image (enlarged image data) obtained by the enlargement process of the enlargement processing circuit 12 is output to a predetermined output destination.

  The image area determination circuit 13 functions as a determination unit that determines whether the enlarged image obtained by the enlargement process is a character / line drawing area or a halftone area. The image area determination circuit 13 separates the enlarged image obtained by the enlargement process into an image area, thereby distinguishing the enlarged image into a character line drawing area such as a character or a line drawing and a halftone area such as a graphic or a photograph. Do. Specifically, the enlarged image obtained by the enlargement processing of the enlargement processing circuit 12 is divided into a plurality of regions, and image region determination for determining whether the region is a character line drawing region or a halftone region is performed for each region. And processing for outputting the determination result (determination result) to the selection circuit 14 is performed.

  As will be described in detail later, the selection circuit 14 selectively switches the output destination of each pixel (pixel data) constituting the enlarged image based on the determination result of the image area determination circuit 13. Specifically, based on the determination result of the image area determination circuit 13, the output destination is selectively selected between the character line pixels included in the character line drawing area and the halftone pixels included in the halftone area. To output each pixel. The character line pixel and the halftone pixel are output to different output destinations in the print image data generation unit 15.

  The print image data generation unit 15 performs a process of changing the pixel density (pixel density changing process) on the edge portion of the character line pixels input from the selection circuit 14 and the edge subjected to the pixel density changing process. Print image data used for the printing process of the printer 16 is generated based on the character line pixels including the partial pixels and the halftone pixels input from the selection circuit 14.

  The printer 16 performs a printing process on the print image data generated by the print image data generation unit 15. As this printer 16, for example, an LED array in which a plurality of LED (Light Emitting Diode) elements are arranged in a straight line is used as an optical writing light source for forming an electrostatic latent image on the surface of a photosensitive drum (not shown). An LED printer or a laser printer using a semiconductor laser (LD) as the optical writing light source can be used, but other printers may be used.

  The printer 16 is capable of multi-value printing. For example, when an LED printer is used, the output time of the LED element corresponding to one pixel is made constant to control (change) the output intensity. The intensity modulation (IM: Intensity Modulation) method that expresses gradation and the output of the LED element with binary values of ON or OFF, and the ON time of the output of the LED element corresponding to one pixel is controlled (changed). Thus, any one of a pulse width modulation (PWM) method that expresses a gray scale and a method using both of these methods may be used.

  Therefore, the print image data generated by the print image data generation unit 15 includes an intensity modulation signal generated by intensity modulation processing of an enlarged image obtained by changing the pixel density of pixels at the edge portion of the character line drawing area, and the character line drawing area. The pulse width modulation signal generated by pulse width modulation processing of the enlarged image obtained by changing the pixel density of the pixels of the edge portion of the image or the enlarged image obtained by changing the pixel density of the pixels of the edge portion of the character line drawing area Any one of the modulation signals generated by performing both modulation processes.

  The image processing apparatus 1 having the above configuration has a black and white 2 such as a copy function and a facsimile communication function as well as image data of a document read by the document reading unit 5 and image data of a document received by facsimile from an external device (not shown). A function that detects edge portions in a character / line drawing area from a value input image (input image data) and generates print image data by performing pixel density change processing in order to improve the reproducibility of the image of the detected edge portions. It has.

  Hereinafter, the print image data generation unit 15 that performs the pixel density change process and the print image data generation process will be described. As shown in FIG. 2, the print image data generation unit 15 includes an edge detection circuit 20, a print image data generation circuit 21, and a pixel density calculation memory 22.

  The edge detection circuit 20 functions as detection means for detecting pixels (black pixels) at the edge portion in the character / line drawing area from the enlarged image obtained by the enlargement processing of the enlargement processing circuit 12. Of the character line pixels and halftone pixels constituting the enlarged image, only the character line pixels are input to the edge detection circuit 20 by the selection circuit 14. Then, a process of detecting pixels at the edge portion in the character / line drawing area from the character / line pixels input from the selection circuit 14 is performed.

  The print image data generation circuit 21 changes the pixel density with respect to the pixels in the edge portion detected by the edge detection circuit 20 so as to give a density gradient so that the pixel density becomes lower as the white pixel adjacent to the edge portion becomes closer. It functions as a density changing means for performing the process (pixel density changing process). The print image data generation circuit 21 includes a DSP (Digital Signal Processor) that performs pixel density change processing in a software manner, and character line pixels input from the edge detection circuit 20 are set to 1 or 2 for each main scanning line. A line memory (not shown) capable of storing lines is provided, and the pixels for each main scanning line with respect to pixels (black pixels) at the edge of the character line pixels stored in the line memory Perform density change processing. Further, the print image data generation circuit 21 uses the printer 16 based on the character line pixels on which the pixel density change processing has been performed on the pixels in the edge portion and the halftone pixels on which the pixel density change processing has not been performed. Print image data (intensity modulation signal or pulse width modulation signal) used for the printing process is generated.

  The pixel density calculation memory 22 functions as a storage unit that stores an arithmetic expression defined for calculating the pixel density after the process of changing the pixel density. This pixel density calculation memory 22 is an arithmetic expression A used to change the pixel density of a pixel (black pixel) at an edge portion (edge rise) that changes from a white pixel to a black pixel, from black pixel to white pixel. Necessary for the expression B used to change the pixel density of the pixel (black pixel) of the edge portion (edge falling) that changes and the DSP of the print image data generation circuit 21 to perform the pixel density change processing. A pixel density change processing program is stored. The print image data generation circuit 21 performs a process of changing the pixel density using the arithmetic expressions A and B stored in the pixel density calculation memory 22 according to the pixel density change processing program.

  The configuration of each unit of the print image data generation unit 15 has been described above, but the processing performed on the input image that is actually read from the image memory 7 and decoded by the codec 6 is based on FIGS. 2 to 4. Will be described below. The processing operation of each unit of the image processing apparatus 1 described below is performed according to a control command issued by the control unit 2 based on a program in the ROM 3. In addition, the character line pixels shown in the figure and the halftone pixels not shown in the figure are represented by gradation values of “0” (white pixels) or “1” (black pixels). That is, the input image is binary data in the present embodiment.

  The input image read from the image memory 7 is decoded by the codec 6 and then input to the enlargement processing circuit 12. On the other hand, the enlargement processing circuit 12 performs the enlargement process as described above based on the resolution of the input image and the resolution of the printer 16 (see FIG. 3). The enlarged image obtained by the enlargement process of the enlargement processing circuit 12 is stored in the line memory 23 for each main scanning line. The line memory 23 can store an enlarged image for a predetermined line (for example, for 5 lines) for each main scanning line. When an enlarged image for a predetermined line is stored in the line memory 23, the image area determination circuit 13 divides the enlarged image into a plurality of areas, and each area is a character line drawing area or a halftone area. Image area determination processing is performed to determine (discriminate) whether or not there is.

  When image area determination processing is performed for each area in this way, the image area determination circuit 13 sets a target pixel and a plurality of adjacent pixels close to the pixel for the enlarged image stored in the line memory 23. When a determination process is performed to determine whether or not the number of adjacent pixels whose gradation value is different from the gradation value of the target pixel among a plurality of set adjacent pixels exceeds a predetermined value. The pixel of interest is a candidate for a character line pixel. Then, the above determination process is performed with each pixel as a pixel of interest, and if the ratio of character line pixel candidates occupying all the pixels included in one divided area exceeds a predetermined ratio, that area is treated as a character line drawing. It is determined that it is an area, and otherwise it is determined that it is a halftone area. The determination result of the image area determination circuit 13 is output to the selection circuit 14.

  The image area determination process performed in the image area determination circuit 13 is not limited to the above-described method, and the image area determination process may be performed using another known determination method. Further, in the method exemplified here, the process of determining whether the area is a character line drawing area or a halftone area is performed for each area obtained by dividing the enlarged image, but the image area determination process is limited to this. Instead, the image area determination process may be performed for each main scanning line on the enlarged image stored in the line memory 23, or the image area determination process may be performed for each pixel.

  Subsequently, each pixel of the enlarged image stored in the line memory 23 is used for the image area determination process by the image area determination circuit 13, and then sequentially read and output to the selection circuit 14. On the other hand, the selection circuit 14 outputs the character line pixels included in the character line drawing area to the edge detection circuit 20 based on the determination result of the image area determination circuit 13, and is included in the halftone area. The halftone pixel is output to the print image data generation circuit 21.

  The edge detection circuit 20 performs processing for detecting pixels of the edge portion from the character / line drawing region constituted by the input character / line pixels. The processing for detecting the pixels in the edge portion can be performed by, for example, comparing the gradation values of the input character line pixel (target pixel) and the surrounding character line pixels (peripheral pixels). When the edge detection circuit 20 performs processing for detecting pixels at the edge portion in this way, the detection result and each character line pixel subjected to the detection processing are output to the print image data generation circuit 21. The detection result here indicates that each character line pixel is an edge portion pixel (black pixel), an inter-edge portion pixel (black pixel) sandwiched between the edge portions, or around the edge portion. This is information indicating whether it is a pixel (white pixel).

  On the other hand, the print image data generation circuit 21 is input from the edge detection circuit 20 using the arithmetic expressions A and B stored in the pixel density calculation memory 22 based on the detection result of the edge detection circuit 20. Pixel density change processing is performed on the pixels in the edge portion in the coming character / line drawing area.

  4A and 4B are diagrams for explaining the pixel density changing process performed in the print image data generating circuit 21. FIG. 4A is a pixel distribution of character line pixels before the pixel density changing process, and FIG. (C) is the pixel line distribution of the character line pixels after the pixel density change process, (d) is the density distribution of the character line pixels shown in (c), and (e) is the figure (d). The density gradient in the case of approximating the rise of the edge portion and the fall of the edge portion of the density distribution shown is shown. FIG. 4 exemplifies the pixel density changing process performed on the character line pixels for 6 lines (main scanning lines) included in the enlarged image. The pixel density changing process is a character line. With respect to the enlarged image composed of only pixels, the other main scanning lines are similarly performed for each main scanning line.

  As illustrated in FIG. 4A, of the 24 black pixels continuous in the main scanning direction, six pixels (black) are detected by the edge detection circuit 20 at both the rising edge and falling edge. Pixel) is detected as a pixel in the edge portion. The edge portion pixels detected by the edge detection circuit 20 are included in an input image obtained by enlarging one edge pixel adjacent to a white pixel around the edge portion in the input image before the enlarging processing. It is. That is, the edge detection circuit 20 has more pixels than the plurality of pixels obtained by enlarging one edge pixel adjacent to the white pixels around the edge portion in the input image before the enlarging process as pixels in the edge portion. Is not detected by.

  Therefore, the enlarged image composed of the character line pixels shown in FIG. 4A is obtained by enlarging the input image before the enlargement process at an enlargement magnification of 6 times in the main scanning direction as shown in FIG. Therefore, each of the six pixels obtained by enlarging the one edge pixel 25 and 26 adjacent to the white pixel around the edge portion in the input image is detected as the edge portion pixel after the enlargement processing. (See FIG. 4A). Here, all six pixels that are continuous in the main scanning direction obtained by enlarging one edge pixel 25 and 26 adjacent to the white pixels around the edge portion in the input image before the enlarging process are included. The edge detection circuit 20 detects the edge portion pixels, but a smaller number of pixels may be detected as the edge portion pixels.

  As shown in FIG. 4B, the print image data generation circuit 21 is close to the white pixel adjacent to the edge portion (see FIG. 4A) with respect to the edge portion pixel having a constant pixel density. In order to provide a density gradient so that the pixel density becomes lower as the pixel density becomes lower, a process (pixel density change process) for changing the pixel density is performed on the pixels of the edge portion detected by the edge detection circuit 20. Specifically, for the rise of the edge portion that changes from the white pixel to the black pixel, an arithmetic expression A stored in the pixel density calculation memory 22 is used so that a density gradient of slope A1 is added. Then, the process of changing the pixel density is performed on the 6 pixels at the rising edge. Then, using the calculation formula B stored in the pixel density calculation memory 22 so that the gradient of the gradient B1 is given, the six pixels at the falling edge of the edge portion that changes from the black pixel to the white pixel are used. On the other hand, processing for changing the pixel density is performed (see FIGS. 4C to 4E).

  Incidentally, as described above, of the character line pixels and halftone pixels constituting the enlarged image, only the character line pixels are input to the edge detection circuit 20 by the selection circuit 14 based on the determination result of the image area determination circuit 13. Then, processing for detecting the pixels in the edge portion is performed. That is, the print image data generation circuit 21 does not perform the process of changing the pixel density for the halftone area based on the determination result of the image area determination circuit 13, and changes the pixel density only for the character line image area. Perform the process. In other words, the process of changing the pixel density is performed using only the character line pixels in the character / line drawing area without using the halftone pixels in the halftone area. Therefore, the reproducibility of the edge part can be improved only for the character line drawing area such as a character or a thin line, and the process of changing the pixel density of the edge part pixel for the halftone area which should not be subjected to this process. Never done.

  FIG. 5 exemplifies the output of the optical writing light source when the printer 16 is compatible with the pulse width modulation method and the output of the optical writing light source when the printer 16 is compatible with the intensity modulation method. FIG. The horizontal direction of each output indicates time, and the vertical direction indicates light intensity. In addition, two outputs are shown on the left side of the uppermost stage in the figure when the optical writing light source is turned on for the first 15% of the ON time in the case of 100% depending on the situation of the surrounding pixels. In the case of 100%, the first 85% of the ON time indicates that the optical writing light source is turned on for the remaining 15% time without turning on the optical writing light source.

  When the printer 16 that supports the pulse width modulation method is used, the print image data generation circuit 21 uses, for example, pixels and edge portions (edge portions and edge portions) of the edge portion of density a shown in FIG. A pulse width modulation signal is generated so that the optical writing light source of the printer 16 is lit for 90% ON time with a constant output. Then, a pulse width modulation signal is generated so that the optical writing light source is lit for 75% ON time with a constant output for the pixels at the edge portion of density b, and for the pixels at the edge portion of density c. A pulse width modulation signal is generated so that the optical writing light source is lit for 45% ON time with a constant output, and the optical writing light source has a constant output of 15% for pixels at the edge portion of density d. A pulse width modulation signal that is lit only for the ON time is generated. Note that, for the first two pixels at the rising edge, the pixel density is the same as that of the adjacent white pixel, so that a pulse width modulation signal is generated so as not to turn on the optical writing light source.

  On the other hand, when the printer 16 that supports the intensity modulation method is used, the print image data generation circuit 21 uses, for example, the optical writing light source of the printer 16 for the pixels at the edge portion and the edge portion of the density a. An intensity-modulated signal that is turned on at a light intensity (output) of 90% with a constant ON time is generated. Then, an intensity modulation signal is generated so that the optical writing light source of the printer 16 is turned on at a light intensity of 75% with respect to the pixels at the edge portion of density b with the ON time being constant, and the pixels at the edge portion of density c In contrast, the optical writing light source generates an intensity modulation signal that is lit at a light intensity of 45% with a constant ON time, and the optical writing light source has a constant ON time for pixels at the edge portion of density d. Thus, an intensity modulation signal that is lit at a light intensity of 15% is generated. For the first two pixels at the rising edge, an intensity modulation signal is generated in the same manner as in the pulse width modulation method.

  In the present embodiment, halftone pixels are directly input from the selection circuit 14 to the print image data generation circuit 21. However, the print image data generation circuit 21 only includes character line pixels as described above. Is used to perform pixel density change processing and print image data generation processing for the edge portion, and print image data is generated without performing pixel density change processing for pixels input as halftone pixels. That is, for halftone pixels, print image data is generated without performing pixel density change processing that gradually increases the density of the pixels from the end of the edge portion toward the edge portion.

  As is apparent from the above description, in the print image data generation circuit 21, the pixel density is closer to the white pixel adjacent to the edge portion than the edge portion pixel of the character / line drawing area included in the enlarged image. By generating the print image data after changing the pixel density so as to decrease, an image with improved reproducibility of the edge portion of the character / line image region can be recorded on the paper in the printer 16. The pixel density changing process performed in the print image data generation circuit 21 does not add a pixel (black pixel) or delete it on the contrary, and is adjacent to a white pixel around the edge portion in the input image. Since more pixels than the pixel obtained by enlarging the one pixel that has been obtained are not used as the edge portion pixels, the pixel information inherent in the input image is not lost, and the character line drawing area is not lost. The image reproducibility of the edge portion can be improved.

  Therefore, even if so-called grandchild copying is performed in which the recording paper that has been subjected to enlargement processing or smoothing processing on the input image and printed out (copied) is used as a document, Since the density gradient is set so that the pixel density becomes lower as it gets closer to the end of the part, the characters are not thickened and crushed, and the process of deleting the pixel (black pixel) is not performed. The thin line will not be cut off.

  In the present embodiment, different slopes A1 and B1 are given based on the arithmetic expressions A and B at the rise and fall of the edge portion, but at the rise and fall of the edge portion. The pixel density of the pixels in the edge portion may be changed so as to give a density gradient so as to have the same inclination.

  In addition, a plurality of arithmetic expressions are stored in the pixel density calculation memory 22 so that density gradients having different slopes can be given to the pixels in the edge portion according to the situation, and pixels from the rising edge to the falling edge portion are stored. The arithmetic expression used by the print image data generation circuit 21 for the pixel density changing process may be changed based on the number of continuous pixels (black pixels). For example, when the number of continuous pixels of black pixels in the main scanning direction is small, such as a vertical line (a line long in the sub-scanning direction), an arithmetic expression is selected so that the density gradient becomes steep, and pixels in the edge portion The pixel density is changed. Conversely, when the number of continuous pixels of black pixels in the main scanning direction is large, such as characters and horizontal lines, the calculation formula is selected so that the density gradient becomes gentle, and the pixel density for the edge part pixels To change. In addition, when a predetermined number or more of black pixels are continuous, the pixel density changing process may not be performed on the pixels in the edge portion.

  Further, the arithmetic expression used for the pixel density changing process may be changeable according to the situation of the surrounding pixels. In other words, a plurality of calculation formulas are stored in the pixel density calculation memory 22 so that density gradients with different slopes can be given to the pixels in the edge portion according to the situation, and continuous pixels of white pixels adjacent to the edge portion are stored. When the number of consecutive white pixel counts is large (for example, the number of consecutive pixels in the main scanning direction), the calculation formula is selected so that the density gradient is relatively gentle, and the counted white pixels When the number of continuous pixels is small, an arithmetic expression may be selected so that the density gradient is relatively steep, and the pixel density of the edge portion may be changed.

  In the present embodiment, the case where the input image is binary image data represented by black and white binary data has been described. However, the input image is multivalued image data represented by multiple values such as 8 bits. May be. In this case, the enlarged multi-value enlarged image may be binarized after the image area is separated by the image area determination circuit 13 and input to the print image data generation unit 15 from the selection circuit 14.

  The configuration of the image processing apparatus 1 shown in the present embodiment is only one aspect of the image processing apparatus according to the present invention, and it is needless to say that the design can be changed as appropriate without departing from the gist of the present invention. Any image processing apparatus having a function of enlarging an input image for printing or the like can be realized as, for example, a copier, a printer alone, or the like.

  The present invention is applicable to, for example, an image processing apparatus having a function of enlarging an input image for printing or the like.

It is the block diagram which showed the structural example of the image processing apparatus which concerns on embodiment of this invention. FIG. 5 is a block diagram showing a flow of data transfer when an input image is enlarged and printed out. It is a figure for demonstrating the expansion process performed with respect to an input image. It is a figure for demonstrating the pixel density change process performed in a print image data generation circuit. It is a figure for demonstrating the relationship between the density of the character line pixel in which the process which changes pixel density was performed, and the output of the optical writing light source of a printer. It is a figure for demonstrating the smoothing process performed with respect to an input image in the conventional apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image processing apparatus 2 Control part (MPU)
DESCRIPTION OF SYMBOLS 12 Enlargement processing circuit 13 Image area determination circuit 14 Selection circuit 15 Print image data generation part 20 Edge detection circuit 21 Print image data generation circuit 22 Pixel density calculation memory 25, 26 Edge pixel

Claims (4)

  Enlarging processing means for enlarging the input image, detecting means for detecting pixels at the edge portion in the character / line drawing region from the enlarged image obtained by the enlarging processing, and pixels closer to the white pixel adjacent to the edge portion An image processing apparatus comprising: a density changing unit that performs a process of changing a pixel density with respect to a pixel of an edge portion detected by the detecting unit so as to provide a density gradient so that the density is lowered.   The pixel of the edge portion detected by the detecting means is included in a pixel obtained by enlarging one edge pixel adjacent to a white pixel around the edge portion in the input image before the enlarging processing. The image processing apparatus according to claim 1, wherein:   A determination unit configured to determine whether the enlarged image obtained by the enlargement process is a character line drawing region or a halftone region; and the density changing unit is configured to determine a halftone region based on a determination result of the determination unit. 3. The image processing apparatus according to claim 1, wherein a process for changing the pixel density is performed only for a character / line drawing area without performing the process for changing the pixel density.   Storage means for storing an arithmetic expression defined for calculating the pixel density after the processing for changing the pixel density is performed, and the density changing means uses the arithmetic expression stored in the storage means. The image processing apparatus according to claim 1, wherein a process for changing the pixel density is performed.

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