JP2005045722A - Image processing method, image processing device, image forming device with image processing device and computer software - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing method and an image processing device for preventing moire caused by a definite dot pattern, and to provide an image forming device equipped with the image processing device and computer software. <P>SOLUTION: An image processing device 1 having a tone duplication processing unit for subjecting input image data to half-tone processing and generating output image data includes an additional information control unit 17 in which information for changing at least part of the dot position formed on a recording medium through a visible color material based on the output image data is applied to the output image data for feeding the image data. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing method, an image processing apparatus, an image forming apparatus including the image processing apparatus, and computer software for controlling the positions of dots formed on a recording medium with a visible color material based on output image data. .

Conventionally, as a method for outputting an image to a recording medium such as paper, various recording methods such as thermal transfer, electrophotography, or an ink jet method have been adopted. These recording methods are configured to form an image using halftone processing by a multi-value dither method (see, for example, Patent Document 1).
JP 58-24270 A Japanese Patent Laid-Open No. 9-193477 Toshiji Takahashi et al. “Adaptive Binarization Method for Mixed Text / Dot / Photo Images” Proceedings of IEICE Technical Committee 90-06-04, p. 19-24

  The conventional multi-value dither method has the following problems. In the dither process, the image data input according to the threshold value arranged in the dither matrix to be used is quantized to determine whether dots are turned on or off. However, since the pixel position where a dot is turned on is directly affected by the arrangement of threshold values in the dither matrix used, the dot that is turned on has regularity, and when this is printed on paper, a specific pattern (moire) occurs. It is a problem.

  For simplicity, an example of binary dither will be described with reference to FIG. FIG. 11B shows a dither matrix composed of 4 × 4 elements used, and the numbers in the matrix indicate threshold values. FIG. 11A shows a part of the input image, and the number in each pixel indicates the pixel value of each pixel. In FIG. 11A, the upper left pixel position is (x, y), and the lower right is (x + n, y + m). Similarly, each element position of the matrix in FIG. 11B is similarly set to (0, 0) in the upper left and (3, 3) in the lower right.

  First, the pixel (x, y) is compared with the threshold value 1 of (0, 0) in the dither matrix of FIG. 11B, and since it is larger than this, the pixel position (x, y) is turned on. Subsequently, the pixel position (x + 1, y) is compared with the threshold value 128 of the dither matrix (1, 0). Since the pixel position (x + 1, y) is smaller than this, the pixel position (x + 1, y) is turned off. By repeating this, an image as shown in FIG. 11C is obtained. FIG. 11C shows a pixel to be turned on by a mark ●. The pixels that are turned on in this way are determined by the arrangement of the threshold values of the dither matrix, and since the same dither matrix is repeatedly used, a certain dot pattern is generated and moire occurs.

  Although FIG. 11 illustrates binary dither as an example, it is clear that the same problem occurs even in the case of multi-value. In addition, even when other gradation reproduction methods, such as error diffusion, are used, the same problem, for example, a worm phenomenon occurs, and a radical solution has not been reached.

  The present invention solves the conventional problems, and provides an image processing method, an image processing apparatus, an image forming apparatus having the same, and computer software that do not generate a moire due to occurrence of a certain dot pattern. The purpose is to do.

  The present invention relates to dots formed on a recording medium with a visible color material based on output image data in an image processing apparatus including a gradation reproduction processing unit that performs halftone processing on input image data to generate output image data. Is an image processing apparatus including an additional information control unit that supplies information for changing at least a part of the position to the output image data.

  Thereby, even when a constant dot pattern such as moire is formed, it is possible to avoid image deterioration by adding information that eliminates the constant dot pattern regardless of more complicated processing.

  Further, the present invention is an image processing apparatus in which the additional information control unit variably controls the additional information.

  Thus, even when a constant density is continuous, information is appropriately variably controlled and added so that a constant dot pattern such as moire is eliminated, so that image deterioration can be avoided more effectively.

  In the image processing apparatus according to the present invention, the additional information includes information in consideration of human visual characteristics.

  Thereby, since the control based on the additional information considers human visual characteristics, higher image quality can be realized.

  Further, according to the present invention, the additional information control unit variably controls the additional information according to characteristics of an image such as input image data being a natural image or a graphic image, or characteristics of a color material to be used or a recording medium. An image processing apparatus.

  As a result, additional information is obtained in consideration of the characteristics of the image, the characteristics of the color material and the recording medium, and further processing according to the characteristics of the image, the color material used and the recording paper can be performed, and high image quality can be achieved. .

  The present invention also provides an image forming apparatus including the above-described image processing apparatus.

  As a result, it is possible to avoid deterioration of the image by adding information that eliminates a fixed dot pattern such as moire, so that an image forming apparatus (digital copier / multifunction machine) that can output a high-quality image. Or a printer).

  The present invention also provides an image forming apparatus that forms an image on a recording medium with a visible color material based on output image data that has been subjected to predetermined processing, and a visible image based on the output image data. The image forming system includes an additional information control unit that supplies the image forming apparatus with information for changing at least the positions of dots formed on the recording medium by the color material.

  As a result, since the additional information is externally provided, high image quality can be achieved without being limited by the storage capacity in the image forming apparatus.

  Furthermore, the present invention provides an image processing method comprising a gradation reproduction processing step that performs halftone processing on input image data to produce output image data, and is formed on a recording medium with a visible color material based on the output image data. This is an image processing method provided with an additional information control step of supplying information for changing at least the position of the dot to be output together with the output image data.

  Further, the present invention is computer software comprising a program for causing a computer to execute the above image processing method.

  As a result, it is possible to avoid deterioration of the image by adding information that eliminates a fixed dot pattern such as moire, so that an image processing method capable of outputting a high-quality image is read by a computer. Can be executed. Therefore, this image processing method can be general purpose.

  According to the present invention, it is possible to obtain an image processing method, an image processing apparatus, and an image forming apparatus provided with the image processing method, in which a constant dot pattern is not generated and moire is generated.

  An embodiment of the present invention will be described. Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  Example 1 will be described. The present embodiment is a color image processing apparatus, and FIG. 1 shows the configuration of a printer (image forming apparatus) 1 to which the present embodiment is applied. The color image processing apparatus 1 includes a decompression processing unit 11, a spatial filter processing unit 12, a color information processing unit 13, a black generation and under color removal unit 14, an output tone correction unit 15, a tone reproduction processing unit 16, and additional information control. The printing unit 22 is connected to the printing unit 22 and constitutes a color image forming apparatus (multifunction device or printer) as a whole.

  In the color image processing apparatus 1, an image captured by a digital camera or an image edited by using software on a computer includes USB (Universal Serial Bus) or IEEE 1394 (Institute of Electrical and Electronic Engineers: American Institute of Electrical and Electronics Engineers). ) Or the like.

  The operation panel 21 includes, for example, a display unit such as a liquid crystal display and a setting button. The operation of the color image processing / printing unit is controlled based on information input from the operation panel.

  Signals input to the color image processing apparatus 1 are processed in the color image processing apparatus by a decompression processing unit 11, a spatial filter processing unit 12, a color information processing unit 13, a black generation and under color removal unit 14, and an output tone correction unit 15. And the gradation reproduction processing unit 16 in this order, and output to the printing unit 22 as CMYK digital color signals.

  The decompression processing unit 11 decompresses the compressed image data transferred from the host computer according to each method. In the case of compressed image data in JPEG (Joint Photographic Experts Group) format, YCbCr (Y: luminance, Cb, Cr: color difference) signals are transferred. An orthogonal transformation is performed to convert the pixel data. The YCbCr signal is converted into an RGB signal.

  The spatial filter processing unit 12 performs spatial filter processing using a digital filter on the RGB signal image data input from the decompression processing unit 11, and corrects the spatial frequency characteristics to reduce blurring and graininess of the output image. It is a process to prevent.

  The color information processing unit 13 performs color correction according to the characteristics of the printing unit 22 and outputs the corrected data to the black generation and under color removal unit 14 at the subsequent stage.

  The black generation and under color removal unit 14 generates a black (K) signal from the CMY three-color signals after color correction, and subtracts the K signal obtained by black generation from the original CMY signal to generate a new CMY signal. The CMY three-color signal is converted into a CMYK four-color signal.

  As an example of the black generation process, there is a method (general method) for generating black by skeleton black. In this method, the input / output characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, the output data is C ′, M ′, Y ′, K ′, UCR (Under Color). Assuming that the (Removal) rate is α (0 <α <1), the black generation and under color removal processing is expressed by Equation 1 below.

出力階調補正部１５では、濃度信号などの信号を印字部の階調再現特性に応じた出力階調補正処理が行われる。

The output tone correction unit 15 performs an output tone correction process on the signal such as the density signal according to the tone reproduction characteristics of the printing unit.

  The gradation reproduction processing unit 16 performs gradation reproduction processing (halftone generation) so that the image can be finally separated into pixels and each gradation can be reproduced, and the image data of the CMYK signal is processed. Then, halftone processing is performed by multi-value dither processing.

  The additional information control unit 17 adds additional information for controlling the position of the dots output on the recording medium by the printing unit 22 to the output image data. Details will be described later.

  The image data subjected to the above-described processes is temporarily stored in a storage unit, read out at a predetermined timing, and input to the printing unit 22.

  The printing unit 22 outputs image data to a recording medium (for example, paper). For example, a color image output device using an electrophotographic method or an ink jet method can be used, but is not particularly limited. .

  In addition, this embodiment may be realized in a digital copying machine. Alternatively, the image processing apparatus and the printing unit (image output apparatus) may be realized by a network connection.

  As the gradation reproduction processing in this embodiment, a four-value dither method is used. The data after the gradation reproduction process is composed of simple density information, and is composed of only pixel values of 0 to 3, for example. 2A to 2D are enlarged views of one pixel, and thus, one pixel is expressed by being divided into four values. That is, when nothing is printed, a dot is not output without applying a drive pulse as a pixel value 0 as shown in FIG. When outputting dots, the number is controlled by the number of drive pulses. One is 1 dot (FIG. 2 (b)), two are 2 dots (FIG. 2 (c)), and 3 are 3 dots. (FIG. 2D) is output. In the case of the inkjet method, the drive pulse is given to a nozzle that ejects ink, and in the case of the electrophotographic method, the drive pulse is given to a laser drive unit that writes an electrostatic latent image on the photoreceptor.

  In the present embodiment, for example, a dither matrix as shown in FIG. 3 is used. FIG. 3A is a first matrix used to obtain a pixel value of 1 (1 dot). FIGS. 3B and 3C show pixel values of 2 (2 dots) and 3 (3 dots), respectively. A second and third matrix to obtain. The numbers in the matrix indicate the threshold used for quantization. Each pixel value of the input image data is compared with a threshold value in a corresponding element of the first matrix and subsequently compared with a corresponding threshold value in the second matrix and the third matrix. Here, the pixel value of the input image data is the pixel value 0 when the pixel value is less than or equal to the first matrix threshold value, the pixel value is 1 when the pixel value is greater than or equal to the threshold value of the first matrix and less than the threshold value of the second matrix, If the pixel value is equal to or greater than the threshold value of the third matrix, the pixel value 3 is output as the value of the pixel. For example, when the pixel value of the first pixel of the input image data is 50, it is compared with 1,97,177, which is the first threshold value of the first to third matrices, and a pixel value of 1 is output. Further, when the second pixel of the input image data is 200, it is compared with 49, 137, and 217 which are the first threshold values of the first to third matrices, and the pixel value 2 is output.

  As an example, consider a case where an input image is an image composed of 4 pixels × 4 pixels in which only a pixel having a pixel value of 50 is continuous. When the dither processing as described above is performed on the input image, a pixel value as shown in FIG. An image obtained by this output is shown in FIG. However, a normal input image is much larger than 4 pixels × 4 pixels, and in this case, the dot pattern shown in FIG. 3E is repeated, so that the user perceives it as a geometric pattern. It causes a problem. In this embodiment, a pulse information matrix as shown in FIG. 3F is further prepared as the additional information control unit 17, and numerical values corresponding to each pixel are supplied to the printing unit 22 as additional information. The numbers in the matrix define which pulse is used first as the pulse used for dot creation. For example, “1” in the pulse information matrix of FIG. 3 (f) represents the first pulse of FIG. 4 (a), “2” in FIG. 3 (f) represents the second pulse of FIG. “3” in 3 (f) indicates the third pulse in FIG. 4 (c). Further, the state of dots formed by each pulse is shown in the same figure. For example, the number of pulses used for the pixel value 1 is normally one and is not changed. In this embodiment, “which pulse is used” together with the output image data from the gradation reproduction processing unit 16. Is also transferred to the printing unit 22 (data in FIG. 3F). In this case, the printed image as shown in FIG. 3 (e) is as shown in FIG. 3 (g), the geometric pattern is improved, and the image is not perceived by the user (according to the pulse information matrix in FIG. 3 (f)). 3 (e), the positions of the dots are changed to become as shown in FIG. 3 (g)).

  FIG. 4 illustrates the use of the pulse information matrix for pixel value 1, but for pixel value 2, it is used as in FIG. A value 1 in the pulse information matrix with respect to the pixel value 2 means use of a pulse as shown in FIG. 5A, and FIGS. 5B and 5C show values 2 and 3 in the pulse information matrix, respectively. Correspond. FIGS. 5A, 5B, and 5C show the use of the first pulse and the second pulse, the second pulse and the third pulse, and the third pulse and the first pulse, respectively. In the example of FIG. 5, the pulse to be used is limited to the inside of the pixel to be printed. However, the present invention is not limited to this, and when there is no print data in the adjacent pixel, a method of using the pulse of the adjacent pixel is also effective. For example, FIG. For example, the value 4 can be prepared as information in the pulse information matrix, and the usage pattern of the pulse with respect to the value 4 can be defined as shown in FIG. FIG. 5D shows that the third pulse of the target pixel and the first pulse of the adjacent pixel are used. However, if there is print data in adjacent pixels, a separate process such as shifting the pulse to be used is necessary.

  In the above embodiment, the additional information to be used is a single pulse information matrix. However, a plurality of pulse information matrices shown in FIG. 3 (f) are prepared as the additional information control unit 17, or one pulse information matrix is read. It is possible to create not only the image of FIG. 3 (g) but also the image of FIG. 3 (h) for the output of FIG. 3 (d) by variable control such as changing the order. FIG. 3 (h) is created by the pulse information matrix of FIG. 3 (i) created by inverting the left and right of FIG. 3 (f). Such a single pulse information matrix may be variably controlled and used as a plurality of pulse information matrices, or a plurality of pulse information matrices may be prepared and used in advance, and a plurality of pulse information matrices may be variable. A plurality of pulse information matrices may be used under control, and may be determined according to the configuration of the image processing apparatus and the printing unit to be used.

  An example of creation / transfer of additional information will be described with reference to the flowchart of FIG. First, a pulse information matrix corresponding to the pixel value is selected (S101). Next, the contents of the pulse information matrix are variably controlled (S102). Then, the additional information is transferred to the printing unit (S103). In this way, additional information is created and transferred.

  The creation / transfer of additional information when the pulse information matrix is used when the object in the first embodiment is a photograph will be described with reference to FIG. First, it is determined whether the object is a photograph (S201). If it is a photograph, a pulse information matrix corresponding to the pixel value is selected (S211). Next, the contents of the pulse information matrix are variably controlled (S212). Then, the additional information is transferred to the printing unit (S213). In this way, additional information is created and transferred. Note that if it is not a photograph in step S201, the process ends.

  A method of printing from a plurality of pulse information does not generate a constant geometric pattern even when an image having a constant pixel value is input, such as a patch pattern, and a very good image is obtained. I can do it. It should be noted that a plurality of pulse information matrices prepared in advance, a pulse information matrix created in the image processing apparatus as represented by the relationship between FIG. 3 (h) and FIG. 3 (i), or a combination of these, the concept of a super matrix May be used. FIG. 3 (l) shows an example of this. FIG. 3 (l) is a diagram using the respective pulse information matrices shown in FIG. 3 (j) and FIG. 3 (k) obtained by inverting the pulse information matrix of FIG. 3 (f) and FIG. 3 (i). An 8 × 8 super matrix such as 3 (l) is created. The variable control of the pulse information matrix is not limited to a method of changing the reading order of the pulse information matrix stored in a memory (not shown) provided in the image processing apparatus as described above.

  The above describes the pulse information matrix for pixel value 1 using FIG. 3, but a pulse information matrix is similarly prepared for pixel value 2, and the pulse information matrix used for pixel value is switched. Configuration to be used. For example, FIG. 3 (m) is an example of a pulse information matrix for pixel value 2. “4” in the matrix of FIG. 3 (m) indicates the use of the pulse of FIG. 5 (a), “5” indicates the use of the pulse of FIG. 5 (b), and “6” indicates the use of the pulse of FIG. The use of the pulse information matrix for the pixel value 1 and the pixel value 2 is performed as follows, for example. For simplicity, it is assumed that FIG. 3F is used as the pulse information matrix for the pixel value 1 and only FIG. 3M is used as the pulse information matrix for the pixel value 2. Suppose pixel values (x, y), (x + 1, y), (x + 2, y), (x + 3, y), (x + 4, y), (x + 5, y),. , 1, 1, 2, 2,... It is assumed that the upper left of the pulse information matrix is (0, 0), the right neighbor is (1, 0), and is sequentially expressed as (2, 0). First, since the pixel value at the pixel position (x, y) is 1, the pulse information matrix uses “f” in FIG. 3 to transfer “1” of (0, 0) to the printing unit. Subsequently, since the pixel value at the pixel position (x + 1, y) is 2, the pulse information matrix uses (m) in FIG. 3 and (1, 0) 6 in the pulse information matrix is transferred to the printing unit. Similarly, 3 of (2, 0) in FIG. 3F is transferred as a pulse information matrix to the pixel position (x + 2, y). By repeating this, pulse information can be transferred to the printing unit even for an image in which pixel values are mixed.

  Furthermore, in the above embodiment, the image data after gradation reproduction processing and the pulse information as additional information are separately transferred to the printing unit, but it is also possible to transfer both to the printing unit as one data. Is more desirable. For example, consider a case where FIG. 3F and FIG. 3M are prepared as pulse information matrices for pixel values 1 and 2, respectively, and no pulse information is given to pixel value 3. In this case, using FIG. 3 (f) and FIG. 3 (m), the pulse information matrix for FIG. From information matrix FIG. 3 (m), 4 to 6 are supplied to the printing unit, and for pixel value 3, 7 is supplied to the printing unit. Such a configuration is more desirable because it is not necessary to separately transfer image data to the printing unit as described above.

  Since each pulse information matrix used as in the above embodiment directly affects the arrangement of dots, other problems such as roughening may occur contrary to expectation unless appropriate settings are made. It is possible. Therefore, it is more desirable that the pulse information matrix corresponding to the additional information has, for example, a blue noise characteristic or a 1 / f noise characteristic in consideration of human visual characteristics. For example, the pulse information matrix according to the blue noise characteristic is decomposed into frequency components by performing FFT (Fast Fourier Transform) on the pulse information matrix once created, and the amplitude value of the low frequency component is obtained. It can be easily obtained by performing inverse FFT after processing to reduce the size and increase the amplitude of the high-frequency component if necessary. Further, it is more preferable to prepare a pulse information matrix larger than the dither matrix without being limited to the same size as the dither matrix used in the gradation reproduction process as in the above embodiment. FIG. 6 shows a part of a matrix of 64 pixels × 64 pixels, and data 1 to 3 are arranged with blue noise characteristics. In FIG. 6, the size is 64 pixels × 64 pixels. However, for example, 128 × 128 pixels can be used, and further, the value 4 is not limited to the value 1 to the value 3, and the value 4 that can define the state of FIG. Good.

  In the above embodiment, additional information is given regardless of the image characteristics. Certain additional information is not always optimal for natural images and portraits, or the characteristics of the printing section (such as electrophotography and ink-jet systems) and the characteristics of color materials such as ink used (ink bleeding) It is not always optimal for all conditions, such as the condition of the toner, the condition of toner scattering, etc.), the external environment such as temperature and humidity, and the characteristics (color, surface condition, or electrical characteristics) of the paper as the recording medium. Absent. In this case, it is desirable to prepare a plurality of pulse information matrices that are additional information to be used, and switch them appropriately according to the characteristics of the image and the characteristics of the paper to be used. For example, in the case of an image forming apparatus having a character as an output device of the computer connected to an external computer (not shown) as in this embodiment, it is possible to select a recording sheet to be used at the same time when a printing operation is performed by the computer. Is possible. There is no problem when photo paper or OHP (Overhead Projector) film paper is selected as the recording paper, but when plain paper with large ink bleeding is selected and used, the above pulse information matrix is used. The case where it must be changed can be assumed. For example, when using plain paper with large bleeding, if the pulse as shown in FIG. 5C is used for the pixel value 2, dots due to pulses at both ends are connected by ink bleeding, and dots larger than necessary are formed. In this case, not the pulse information matrix as shown in FIG. 3 (m) but the pulse information matrix not using “6” corresponding to the use of the pulse shown in FIG. 5 (c). Need to use. In such a case, information that uses plain paper is usually included in the information that is transferred to the image forming apparatus at the same time as the execution of the print command of the computer. It is preferable to switch to FIG.

  The information used for the switching of the pulse information matrix as described above may be not only information relating to the recording paper transferred to the image forming apparatus but also image characteristics such as a photographic image or a text image. The determination of these image characteristics may use the result of the region separation processing that is normally performed, but for example, when used as a printer, it can be determined as follows. The print data transferred from the computer is converted into various page description languages (Page Description Language: PDL, for example, PostScript of Adobe System). At this time, the description format of the print data differs depending on the type of the object such as a character, a figure, and a photograph, and can be determined by reading the description format (for example, see Patent Document 2). This determination is performed by the CPU, for example. In this case, control such that the additional information as described above is not given is also possible. For example, in the case of an image such as monochrome text, if the additional information of the present invention is not given, the edge of the character is sharpened and can be output well (see the flowchart in FIG. 10. FIG. 10 shows a pulse when the object is a photograph. An example using an information matrix is also shown, but there are other examples in which a dedicated pulse matrix is used for computer graphic images, but it is not limited thereto.

  In this embodiment, it is recorded inside the additional information image forming apparatus to be used. However, for example, if it is not desirable to store it in the image forming apparatus due to a memory capacity problem, it is stored in an external device (not shown) and printed. It is also desirable to transfer the image data together with the image data to the image forming apparatus each time. For example, examples of the external device include a connected computer and a fax receiving unit. These are relatively less subject to storage capacity limitations and are effective for obtaining high image quality. In this configuration, for example, in order to compensate for image deterioration due to the life of the image forming apparatus, the additional information to be used is changed according to the number of prints and supplied to the printing unit, or additional information capable of printing higher image quality is updated. Work becomes more effective. Setting the additional information control unit outside the main body in this way is desirable for avoiding a decrease in the performance of the apparatus without imposing a load on the CPU of the image forming apparatus.

  Further, when the host computer driver does not have the function of the present invention, the function of the present invention, for example, an additional information control unit, or new additional information is provided via an electronic data recording medium such as a floppy (registered trademark) or CDROM. Or update it.

  A second embodiment will be described. In this embodiment, as shown in FIG. 7, a configuration in which a printer driver 3 is provided in a computer 4 is shown. Image data read by an image input device such as a scanner or image data downloaded via a network is subjected to image editing processing by application software as necessary, and the processed image data is output by a printer. You may do it. The image data subjected to the above processing is subjected to the above processing by the color information processing unit 13, the output tone correction unit 15, the tone reproduction processing unit 16, and the additional information control unit 17. The color information processing unit 13 includes a black generation and under color removal process. The image data output from the gradation reproduction processing unit 16 and the additional information from the additional information control unit 17 are converted into a printer language by the printer language translation unit 31, and a communication port driver 41, a communication port (RS232C, LAN, etc.) 42. To the printer (printing unit) 22.

  As the recording medium, a memory (not shown) such as a ROM itself may be a program medium because processing is performed by a microcomputer, or a program as an external storage device (not shown) may be used. It may be a program medium provided with a reading device and readable by inserting a recording medium therein.

  In any case, the stored program may be configured to be accessed and executed by the microprocessor, or in any case, the program is read and the read program is illustrated in the microcomputer. The program may be downloaded to a non-program storage area and executed. It is assumed that this download program is stored in the main device in advance.

  Here, the program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a floppy (registered trademark) disk or a hard disk, or a CD-ROM / MO /. Disk system of optical disks such as MD / DVD, card system such as IC card (including memory card) / optical card, or mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory) flash It may be a medium that carries a fixed program including a semiconductor memory such as a ROM.

  In the present embodiment, since the system configuration is such that a communication network including the Internet can be connected, a medium that fluidly carries the program so as to download the program from the communication network may be used. When the program is downloaded from the communication network in this way, the download program may be stored in the main device in advance or may be installed from another recording medium.

  The recording medium is read by a program reading device provided in a digital color image forming apparatus or a computer system, whereby the above-described image processing method is executed.

  A third embodiment will be described. The present invention can also be applied to a digital copying machine instead of a printer. FIG. 8 is a block diagram showing the configuration of a digital color copying machine including a color image processing apparatus 5 to which the configuration of the color image processing apparatus of the present invention is applied.

  As shown in FIG. 8, the color image processing apparatus 5 includes an A / D conversion unit 51, a shading correction unit 52, an input tone correction unit 53, a region separation processing unit 54, a color information processing unit 13, and a black generation under color removal. 14, a spatial filter processing unit 55, an output tone correction unit 15, a tone reproduction processing unit 16, and an additional information control unit 17, and a color image input device 61 and a color image output device ( A printing unit 62 is connected to form a digital color copying machine as a whole.

  The operation panel 21 includes a display unit such as a liquid crystal display and setting buttons, for example, and controls operations of a color image input device, color image processing, and color image output device based on information input from the operation panel. .

  The color image input device (image reading means) 61 is composed of a scanner unit equipped with, for example, a CCD (Charge Coupled Device), and converts the reflected light image from the original into RGB (R: red, G: green, B: blue). The analog signal is read by the CCD and input to the color image processing apparatus 5.

  An analog signal read by the color image input device 61 is converted into an A / D conversion unit 51, a shading correction unit 52, an input tone correction unit 53, a region separation processing unit 54, and a color information processing unit. 13, the black generation and under color removal unit 14, the spatial filter processing unit 55, the output tone correction unit 15, and the tone reproduction processing unit 16 are sent in this order and output to the color image output device 62 as CMYK digital color signals. Is done.

  The A / D (analog / digital) converter 51 converts RGB analog signals into digital signals, and the shading correction unit 52 applies the digital RGB signals sent from the A / D converter 51. A process for removing various distortions generated in the illumination system, the imaging system, and the imaging system of the color image input device 61 is performed.

  The input tone correction unit 53 adjusts the color balance of the RGB signal (RGB reflectance signal) from which various distortions have been removed by the shading correction unit 52, and simultaneously converts the RGB reflectance signal into a density signal. The conversion process is performed.

  The region separation processing unit 54 separates each pixel in the input image into one of a character region, a halftone dot region, and a photograph region from the RGB signal. Based on the separation result, the region separation processing unit 54 sends a region identification signal indicating to which region the pixel belongs to the black generation and under color removal unit 14, the spatial filter processing unit 55, and the gradation reproduction processing unit 16. In addition to the output, the input signal output from the input gradation correction unit 53 is output to the subsequent color information processing unit 13 as it is.

  Here, as the region separation processing, for example, a method described in Non-Patent Document 1 can be used. The outline will be described below. The following determination is performed in a block of M × N (M and N are natural numbers) pixels centered on the pixel of interest, and this is used as a region identification signal of the pixel of interest.

An average value (D _ave ) of signal levels is obtained for the central nine pixels in the block, and each pixel in the block is binarized using the average value. Further, the maximum pixel signal level (D _max ) and the minimum pixel signal level (D _min ) are also obtained at the same time.

In the halftone dot region, the halftone dot region is identified by utilizing the fact that the fluctuation of the image signal in the small region is large and the density is higher than the background. With respect to the binarized data, the number of changing points from 0 to 1 in the main scanning and sub-scanning directions is obtained, and the number of changing points from 1 to 0 is obtained as K _H and K _V , respectively, and the thresholds T _H and T _{V are obtained.} If both of them exceed the threshold, the halftone dot region is set. Further, in order to prevent erroneous determination with the background, D _max , D _min , and D _ave are compared with threshold _values B ₁ and B ₂ .

In the character area, since the difference between the maximum signal level and the minimum signal level is large and the density is considered high, the character area is identified as follows. Maximum was obtained previously in the non-halftone dot region, the minimum signal level and their difference (D _sub) the threshold P _A, P _B, compared to the P _C, any if one exceeds the character area, all threshold If it is below, it will be a photo area.

  The color information processing unit 13 performs color correction (C: Cyan (M: magenta / Y: yellow) color material including unnecessary absorption components) in accordance with the characteristics of the printing unit in order to achieve faithful color reproduction. Processing for removing color turbidity based on characteristics) is performed, and the corrected data is output to the black generation and under color removal unit 14 at the subsequent stage.

  The black generation and under color removal unit 14 generates a black (K) signal from the CMY three-color signals after color correction, and subtracts the K signal obtained by black generation from the original CMY signal to generate a new CMY signal. The CMY three-color signal is converted into a CMYK four-color signal.

  As an example of the black generation process, there is a method (general method) for generating black by skeleton black. In this method, the input / output characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, the output data is C ′, M ′, Y ′, K ′, UCR (Under Color). Assuming that the (Removal) rate is α (0 <α <1), the black generation and under color removal processing is expressed by Equation 1 below.

  The spatial filter processing unit 55 performs spatial filter processing using a digital filter on the image data of the CMYK signal input from the black generation and under color removal unit 14 based on the region identification signal, thereby correcting the spatial frequency characteristics. The gradation reproduction processing unit 16 performs processing so as to prevent blurring of the output image and deterioration of graininess. Similarly to the spatial filter processing unit 55, the gradation reproduction processing unit 16 also uses a region identification signal based on the image data of the CMYK signal. Is subjected to predetermined processing.

  For example, the region separated into characters by the region separation processing unit 54 has a high frequency enhancement amount in the sharp enhancement processing in the spatial filter processing by the spatial filter processing unit 55 in order to improve the reproducibility of black characters or color characters in particular. Increased. At the same time, the gradation reproduction processing unit selects binarization or multi-value processing on a high-resolution screen suitable for high-frequency reproduction.

  In addition, with respect to the region separated into halftone dots by the region separation processing unit 54, the spatial filter processing unit 55 performs low-pass filter processing for removing the input halftone component. The output tone correction unit 15 performs an output tone correction process for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the color image output device. Gradation reproduction processing (halftone generation) is performed so that the image is finally separated into pixels and each gradation is reproduced. For the region separated into photographs by the region separation processing unit 54, binarization or multi-value processing is performed on the screen with an emphasis on gradation reproducibility.

  The additional information control unit 17 adds additional information for controlling the position of the dots output on the recording medium by the printing unit to the output image data, and is controlled based on the region identification signal.

  The image data that has been subjected to the above-described processes is temporarily stored in the storage means, read out at a predetermined timing, and input to the color image output device 62. The image output device 62 outputs image data onto a recording medium (for example, paper). Examples of the image output device 62 include a color image output device using an electrophotographic method or an inkjet method, but are particularly limited. It is not a thing. The above process is controlled by a CPU (Central Processing Unit) (not shown).

  In the above embodiment, the dither method is used as the gradation reproduction processing method to be used, but this embodiment is not limited to the gradation reproduction processing method in adding information to the data after the gradation reproduction processing. Absent.

  The present embodiment can be applied not only to an inkjet or electrophotographic image forming apparatus but also to an image forming apparatus using, for example, a toner jet method or a thermal transfer method. Furthermore, it can be effectively used not only as a computer monitor or a television monitor that requires gradation reproduction processing, but also as an electronic paper using a liquid crystal device or a twist ball.

1 is an explanatory diagram of an image processing apparatus according to Embodiment 1. FIG. FIG. 2 is an enlarged view of a pixel in Embodiment 1. FIG. 3 is an explanatory diagram of a dither matrix in the first embodiment. FIG. 3 is an explanatory diagram of a pulse information matrix in the first embodiment. FIG. 3 is an explanatory diagram of a plurality of pulses in the first embodiment. FIG. 3 is an explanatory diagram of a large pulse information matrix in the first embodiment. FIG. 6 is an explanatory diagram of a computer according to the second embodiment. FIG. 6 is an explanatory diagram of an image processing apparatus according to a third embodiment. FIG. 3 is an explanatory diagram of a flowchart according to the first embodiment. Explanatory drawing of the flowchart at the time of using a pulse information matrix when the object in Example 1 is a photograph. Explanatory drawing of the example of the binary dither in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color image processing apparatus 11 Decompression | decompression processing part 12 Spatial filter process part 13 Color information processing part 14 Black production | generation under color removal part 15 Output gradation correction part 16 Gradation reproduction process part 17 Additional information control part 21 Operation panel 22 Printing part 3 Printer driver 31 Printer language translation unit 4 Computer 41 Communication port driver 42 Communication port 5 Color image processing device 51 A / D conversion unit 52 Shading correction unit 53 Input tone correction unit 54 Area separation processing unit 55 Spatial filter processing unit 61 Color Image input device 62 Color image output device

Claims (8)

In an image processing apparatus including a gradation reproduction processing unit that performs halftone processing on input image data to generate output image data,
An additional information control unit that supplies information for changing at least part of the positions of dots formed on a recording medium with a visible color material based on output image data, in addition to the output image data; An image processing apparatus. The image processing apparatus according to claim 1.
The image processing apparatus, wherein the additional information control unit variably controls the additional information. The image processing apparatus according to claim 1.
The image processing apparatus according to claim 1, wherein the additional information includes information considering human visual characteristics. The image processing apparatus according to any one of claims 1 to 3,
The additional information control unit variably controls the additional information according to characteristics of an image such as input image data being a natural image or a graphic image, or according to characteristics of a color material or a recording medium to be used. Processing equipment. An image forming apparatus comprising the image processing apparatus according to claim 1. An image forming apparatus that forms an image on a recording medium with a visible color material based on output image data subjected to a predetermined process;
An image forming system comprising: an additional information control unit that supplies information for changing at least a position of a dot formed on a recording medium with a visible color material to the image forming apparatus based on output image data . In an image processing method including a gradation reproduction processing step in which input image data is subjected to halftone processing to be output image data,
An image comprising an additional information control step of supplying, together with the output image data, information for changing at least the positions of dots formed on a recording medium with a visible color material based on the output image data Processing method. Computer software comprising a program for causing a computer to execute the image processing method according to claim 7.

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