JP4596964B2 - Image processing apparatus, image forming apparatus, image processing method, computer program, and recording medium - Google Patents

Description

  The present invention uses an error diffusion method that diffuses an error generated when quantizing each pixel of an input image to each non-quantized pixel around the pixel based on a corresponding diffusion coefficient. The present invention relates to an image processing apparatus, an image forming apparatus, an image processing method, a computer program for causing a computer to generate the halftone, and a recording medium on which the computer program is recorded.

  In recent years, digitalization of office automation equipment has been rapidly progressed, and demand for color image output has increased, so that output devices such as electrophotographic digital color copying machines and ink jet or thermal transfer color printers have become widely available. It is popular. For example, an image input from an input device such as a digital camera or an image scanner, or an image created by a computer is output using these output devices. These output devices often perform pseudo gradation reproduction processing on input images.

  One method of pseudo gradation reproduction processing is an error diffusion method. However, in the error diffusion method, since a fixed diffusion coefficient is applied to all the pixels, the accumulation error becomes periodic, resulting in a texture and a worm. In order to suppress the occurrence of texture, a technique has been proposed in which the arrangement of diffusion coefficients is switched randomly by switching the arrangement of weighting coefficients based on random numbers (see, for example, Patent Document 1).

Furthermore, as a technique for reproducing images with higher quality and detail, the edge area and the non-edge area are identified, the matrix size of the pixel that diffuses the quantization error in the edge area, and the quantization error in the non-edge area is diffused. A method for making the pixel size smaller than the pixel matrix size has been proposed (see, for example, Patent Document 1).
Japanese Patent Publication No. 6-44800 Toshiharu Kurosawa, “Output Image Characteristics by Improved Error Diffusion (MED) Method”, Journal of the Institute of Image Electronics Engineers, 1991, Vol. 20, No. 5, p. 443-449

  However, when the arrangement of the diffusion coefficients is switched at random, there is a problem that the reproducibility of the periodic pattern of halftone dots is deteriorated in a halftone photograph or a halftone area than when the diffusion coefficient is fixed. . On the other hand, in Patent Document 1, since the diffusion coefficient for each region is fixed, there is a problem that a texture is generated in a photographic paper photograph (continuous gradation photograph) or a photographic region (continuous gradation area such as a photographic paper photograph). is there.

  The present invention has been made in view of such circumstances, and identifies whether a pixel to be quantized is included in a continuous tone image or a continuous tone region or a halftone image or a halftone region, and an identification result Is a continuous tone image or continuous tone region, one of a plurality of sets of diffusion coefficients is selected at random, and if the identification result is a halftone image or halftone region, a predetermined diffusion coefficient is selected. By selecting a set of images and diffusing the error based on the diffusion coefficient of the selected set, halftone with an appropriate dot granularity according to the type of image to be processed (document type) or the region to which the pixel to be processed belongs. An object of the present invention is to provide an image processing apparatus, an image forming apparatus, an image processing method, a computer program, and a recording medium that can generate and improve image quality.

  Further, the present invention provides a spatial filter processing means for performing an enhancement process or a smoothing process on an image for generating a halftone, and a spatial filter when the identification result is a halftone image or when the identification result is a halftone area. It is another object of the present invention to provide an image processing apparatus and an image forming apparatus capable of improving the reproducibility of halftone dots by including control means for prohibiting processing by the processing means or causing the spatial filter processing means to perform enhancement processing. Objective.

  In addition, the present invention is configured to select any one set stored in the storage unit based on the random number generated by the random number generator, so that one set is randomly selected according to the random number. Another object is to provide an image processing apparatus and an image forming apparatus that can be selected.

  In the present invention, any one set stored in the storage unit is selected for each color component, so that dots of a plurality of colors overlap in a continuous tone image or continuous tone region. Another object of the present invention is to provide an image processing apparatus and an image forming apparatus that are difficult to improve and can improve the granularity of dots.

  Further, according to the present invention, a predetermined set stored in the storage unit is selected so that only one set common to all color components is selected. Another object of the present invention is to provide an image processing apparatus and an image forming apparatus capable of outputting a characteristic image and improving dot granularity.

The image processing apparatus according to the present invention provides an error generated when quantizing each pixel of a continuous tone image mainly having a continuous tone region and each pixel of a halftone image mainly having a dot region. In an image processing apparatus that generates halftones using an error diffusion method in which diffusion is performed based on a diffusion coefficient corresponding to each non-quantized pixel around the pixel, a range of error diffusion for a continuous tone image is The continuous tone image includes a storage unit for storing a plurality of sets of diffusion coefficients for continuous tone images and halftone dot images that are set to be wider than the error diffusion range for the halftone image, and pixels to be quantized. Identification means for identifying whether the image is included in a halftone dot image, spatial filter processing means for performing enhancement processing or smoothing processing on an image for generating halftones, and when the identification result by the identification means is a halftone image Spatial filter processing And control means for causing the enhancement process to prohibit or spatial filtering means by the processing means, the identification if the result is a continuous tone image, each time of performing error diffusion for each pixel, a continuous floor stored in the storage unit A selection unit that randomly selects one set from a set of diffusion coefficients for tonal images and selects the predetermined set stored in the storage unit when the identification result is a halftone image; An error is diffused based on a set of diffusion coefficients selected by the selection means.

The image processing apparatus according to the present invention provides a diffusion corresponding to each non-quantized pixel in the vicinity of the pixel for errors generated when quantizing each pixel of an image having a continuous tone region and a halftone dot region. In an image processing apparatus that generates halftones using an error diffusion method that diffuses based on coefficients, the range of error diffusion for continuous tone images is set to be wider than the range of error diffusion for halftone images. A storage unit that stores a plurality of sets of diffusion coefficients for continuous tone images and halftone images, and an identification unit that identifies whether a pixel to be quantized is included in a continuous tone region or a halftone dot region A spatial filter processing unit that performs enhancement processing or smoothing processing on an image that generates halftones; and when the identification result by the identification unit is a halftone dot region, the processing by the spatial filter processing unit is prohibited or spatial filtering processing. And control means for causing the emphasis processing means, when the identification result of the continuous tone region, each time for performing error diffusion for each pixel, from the set of the diffusion coefficient for the continuous-tone image stored in the storage unit When one set is selected at random, and the identification result is a halftone dot region, a selection means for selecting a predetermined set stored in the storage unit is provided, and the diffusion coefficient of the set selected by the selection means It is characterized by diffusing the error based on the above.

  An image processing apparatus according to the present invention includes a random number generator, and the selection unit is configured to select any one set stored in the storage unit based on a random number generated by the random number generator. It is characterized by being.

  In the image processing apparatus according to the present invention, each pixel includes a plurality of color components, and a halftone is generated by an error diffusion method for each color component, and the selection unit is any one of those stored in the storage unit. One set is configured to be selected for each color component.

  In the image processing apparatus according to the present invention, each pixel includes a plurality of color components, and a halftone is generated by an error diffusion method for each color component, and the selection unit is a predetermined unit stored in the storage unit. In this case, only one set common to all color components is selected.

  An image forming apparatus according to the present invention includes the above-described image processing apparatus according to the present invention and an image forming unit that forms an image on which a halftone has been generated by the image processing apparatus.

In the image processing method according to the present invention, errors generated when quantizing each pixel of a continuous tone image mainly having a continuous tone region and each pixel of a halftone image mainly having a halftone region are described above. In an image processing method that generates halftones using an error diffusion method that diffuses each non-quantized pixel around the pixel based on the corresponding diffusion coefficient, the pixel to be quantized is included in the continuous tone image And whether the halftone image is included in the halftone image, and if the identification result of the step is a halftone image, the enhancement processing or smoothing processing as the spatial filter processing is performed to generate halftones. process applied to the image to be, or a step of selectively performing either processing for shifting to the next step without spatial filtering, the range to the error diffusion for the continuous tone image, the halftone image Among the plurality of pairs of the diffusion coefficient for the continuous tone image and for halftone image is set to be wider than the range to be diffused, when the identification result is a continuous tone image, the error diffusion for each pixel Each time, one of the sets of diffusion coefficients for the continuous tone image is selected at random, and when the identification result is a halftone image, a predetermined set of diffusion coefficients is selected. The error is diffused based on a selected set of diffusion coefficients.

According to the image processing method of the present invention, an error generated when quantizing each pixel of an image having a continuous tone region and a halftone dot region is diffused corresponding to each unquantized pixel around the pixel. Identifying whether a pixel to be quantized is included in a continuous tone region or a halftone dot region in an image processing method for generating a halftone using an error diffusion method that diffuses based on a coefficient; In the case where the identification result in the step is a halftone dot region, among the enhancement processing or smoothing processing as the spatial filter processing, the processing for applying the enhancement processing to the image for generating the halftone, or without performing the spatial filtering processing and selectively perform either of a process of shifting to the next step, the range for error diffusion for continuous tone images, set to be wider than the range for error diffusion for halftone image Among the plurality of pairs of the diffusion coefficient for the continuous tone image and for halftone image were, when the identification result of the continuous tone region, each time for performing error diffusion for each pixel, the diffusion for continuous-tone image Randomly selecting one of the coefficient sets, and, when the identification result is a halftone dot region, selecting a predetermined set of diffusion coefficients, and based on the diffusion coefficient of the selected set And diffusing errors.

The computer program according to the present invention provides an error generated when quantizing each pixel of a continuous tone image mainly having a continuous tone region and each pixel of a halftone image mainly having a dot region. In a computer program that causes a computer to generate a halftone using an error diffusion method that diffuses to each neighboring non-quantized pixel based on a corresponding diffusion coefficient, the computer to quantize a continuous tone image And when the identification result of the procedure is a halftone dot image, the computer performs the enhancement process among the enhancement process or the smoothing process as a spatial filter process. A procedure for selectively executing one of a process to be performed on an image for generating a halftone or a process for shifting to the next procedure without performing the spatial filter process; The computer, a range for error diffusion for a continuous tone image, among a plurality of sets of the diffusion coefficient for the continuous tone image and for halftone image is set to be wider than the range for error diffusion for halftone images, When the identification result is a continuous tone image, each time error diffusion is performed for each pixel, any one set is randomly selected from the set of diffusion coefficients for the continuous tone image, and the identification result is a halftone dot. In the case of an image, the method includes a procedure of selecting a predetermined set of diffusion coefficients, and causing the computer to diffuse an error based on the selected set of diffusion coefficients.

The computer program according to the present invention provides a diffusion coefficient corresponding to each non-quantized pixel in the vicinity of the pixel with an error generated when each pixel of an image having a continuous tone region and a halftone dot region is quantized. In a computer program that causes a computer to generate a halftone using an error diffusion method that diffuses based on the image, allows the computer to identify whether the pixel to be quantized is included in a continuous tone region or a halftone dot region A procedure and a computer that performs an enhancement process on an image that generates halftones among an enhancement process or a smoothing process as a spatial filter process when the identification result of the procedure is a halftone dot region, or the spatial filter and procedures for either the process of shifting the process to the next step without selectively executed, the computer, the error expansion for a continuous tone image Range is found among the plurality of sets of the diffusion coefficient for the continuous tone image and for halftone image is set to be wider than the range for error diffusion for halftone images, when the identification result of the continuous tone area Each time error diffusion is performed for each pixel, any one set is selected from a set of diffusion coefficients for continuous tone images, and when the identification result is a halftone dot region, a predetermined diffusion coefficient is set. And causing the computer to diffuse the error based on the selected set of diffusion coefficients.

  A recording medium according to the present invention stores the above-described computer program of the present invention.

  In the present invention, when a pixel to be quantized is included in a continuous tone image or a continuous tone region, any one of a plurality of sets of diffusion coefficients is randomly selected, and the pixel to be quantized is When included in a halftone image or halftone dot region, a predetermined set of diffusion coefficients is selected, and an error is diffused based on the selected set of diffusion coefficients, whereby the type of image to be processed (document type) or Halftone generation can be performed with appropriate dot granularity according to the region to which the pixel to be processed belongs. For example, when the diffusion coefficient is selected randomly, the error rate accumulated from each quantized pixel varies compared to the case where the diffusion coefficient is fixed. , Excessive dot overlap can be suppressed. In addition, when the diffusion coefficient is fixed, since the ratio of errors accumulated from each quantized pixel is constant as compared with the case where the diffusion coefficient is switched at random, each network in the input image is fixed. It can be suppressed that dots are output to a portion having a low pixel value such as between dots, and that dots are not output to a portion having a high pixel value forming a halftone dot. Here, the halftone generation process using the error diffusion method described above can be executed not only by the image processing apparatus or the image forming apparatus that forms an image on a sheet but also by a computer. When the computer executes the process, a computer program for executing the process is provided to the computer by recording it on a recording medium.

  In the present invention, when the identification result is a halftone image or when the identification result is a halftone area, the processing by the spatial filter processing means for performing the enhancement process or the smoothing process is prohibited or the enhancement process is performed. Since it is controlled by means, the reproducibility of halftone dots can be improved. Conventionally, smoothing processing is performed on a halftone dot region in order to prevent moire. However, when smoothing processing is performed, the halftone dot shape is lost, and the reproducibility of halftone dots is reduced. However, in the present invention, it is possible to prevent the halftone dot form from being broken by passing through the spatial filter process (prohibiting the process) or performing a weak emphasis process on the halftone dot region.

  In the present invention, since the selection means selects any one set stored in the storage unit based on the random number generated by the random number generator, one set is randomly selected according to the random number. can do. For example, among the sets A to E, the set A can be a predetermined set, and any one of the sets B to E can be selected at random. Alternatively, for example, among the sets A to D, the set A may be a predetermined set, and any one of the sets A to D may be selected at random. In the latter case, since the group A is used in common, the circuit capacity can be reduced by reducing the memory capacity and the like.

  In the present invention, any one set stored in the storage unit is selected for each color component by the selection unit, and halftone generation is performed for each color component by an error diffusion method. In the area, compared with the case where the same diffusion coefficient is used for all color components, the ratio of errors accumulated for each pixel of each color component varies, and there are color components with a large ratio of accumulated errors and few color components. Arise. For this reason, it is difficult for dots of a plurality of colors to overlap at a relatively light density of gray, red, green, yellow, or a color close to these, and the graininess of the dots can be improved.

  In the present invention, the selection means selects only one set common to all color components from the predetermined set stored in the storage unit, and generates a halftone by an error diffusion method for each color component. Black, red, green, blue, and other halftone dots are processed with the same set of fixed diffusion coefficients, and cyan, magenta, and yellow three- or two-color quantized values and error diffusion are applied to each pixel. Therefore, compared to the case of using different sets of diffusion coefficients for each color component, the ratio of pixels output in the halftone color of the original image is larger, and the image has a graininess close to that of the original image. Can be output.

  According to the present invention, halftone generation can be performed with appropriate dot granularity according to the type of image to be processed (document type) or the region to which the pixel to be processed belongs, and the image quality can be improved.

  According to the present invention, the reproducibility of halftone dots can be improved. An image close to the original image can be output in the halftone dot region.

  According to the present invention, one set can be randomly selected from a plurality of sets according to a random number.

  According to the present invention, it is difficult for dots of a plurality of colors to overlap in a continuous tone region, and the graininess of the dots can be improved.

  According to the present invention, in a halftone dot region, an image having a graininess close to that of a document image can be output, and the dot graininess can be improved.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
(Embodiment 1)
FIG. 1 is a block diagram showing a schematic configuration of a digital color copying machine (image forming apparatus) 20 provided with an image processing apparatus 10 according to the present invention. The digital color copying machine 20 includes an image input device 22, an image output device (image forming means) 24, and an operation panel 26. The image processing apparatus 10 includes an A / D (analog / digital) conversion unit 11, a shading correction unit 12, an input tone correction unit 13, a region separation processing unit 14, a color correction unit 15, and a black generation and under color removal unit 16. A spatial filter processing unit 17, an output tone correction unit 18, and a tone reproduction processing unit 19.

  The image input device 22 includes, for example, an image scanner using a CCD (Charge Coupled Device). For example, a reflected light image from a sheet on which a document image is recorded is converted into analog RGB (R: Red, G: Green, B: Blue) signals are read and output to the image processing apparatus 10. The analog RGB signals read by the image input device 22 are converted into an A / D conversion unit 11, a shading correction unit 12, an input tone correction unit 13, a region separation processing unit 14, a color correction unit 15, Black generation / under color removal unit 16, spatial filter processing unit 17, output gradation correction unit 18, and gradation reproduction processing unit 19 are sent in this order, and finally digital CMYK (C: cyan, M: magenta, Y: yellow). , K: black) signal is output to the image output device 24.

  The A / D converter 11 converts the input analog RGB signal into a digital RGB signal. The shading correction unit 12 responds to various digital RGB signals (hereinafter abbreviated as RGB signals) sent from the A / D conversion unit 11 in the illumination system, imaging system, and imaging system of the image input device 22. A process for removing distortion is performed. The input tone correction unit 13 adjusts the color balance of the RGB signal (RGB reflectance signal) from which various distortions have been removed by the shading correction unit 12 and is employed in the image processing apparatus 10 for density signals and the like. The signal is converted into a signal that can be handled easily by the image processing system.

  The region separation processing unit 14 separates each pixel in the input image into a plurality of regions such as a character region, a halftone region, and a photograph (continuous gradation) region based on the input RGB signal. Further, the region separation processing unit 14 outputs a region identification signal indicating which region the pixel belongs to based on the separation result, the color correction unit 15, the black generation and under color removal unit 16, the spatial filter processing unit 17, and the floor. In addition to the output to the tone reproduction processing unit 19, the RGB signal output from the input tone correction unit 13 is output as it is to the subsequent color correction unit 15.

  As the region separation processing, for example, a maximum density difference that is a difference between a minimum density value (minimum pixel value) and a maximum density value (maximum pixel value) in an n × m block (for example, 15 × 15) including the target pixel is used. By calculating the total density busyness, which is the sum of absolute values of density differences between adjacent pixels, and comparing it with a plurality of predetermined threshold values, a background area, a photo area (continuous tone area), and a character area Or can be separated into halftone dot regions (see, for example, Japanese Patent Application Laid-Open No. 2002-232708).

  Since the density distribution of the base region usually has little density change, both the maximum density difference and the total density busyness are very small. The density distribution in the photographic area has a smooth density change, and the maximum density difference and the total density busyness are both small, but somewhat larger than the background area. In the density distribution of the halftone dot area, the maximum density difference varies depending on the halftone dot, but the total density busyness changes by the number of halftone dots, so the ratio of the total density busyness to the maximum density difference is large. Become. Therefore, when the total density busyness is larger than the product of the maximum density difference and the character / halftone dot determination threshold (one of the plurality of thresholds), it is determined that the area is a halftone area. In the density distribution of the character area, the maximum density difference is large and the total density busyness increases accordingly. However, since the density change is smaller than that of the halftone dot area, the total density busyness is smaller than that of the halftone dot area. Therefore, when the total density busyness is smaller than the product of the maximum density difference and the character / halftone dot determination threshold, the character area is determined.

  Therefore, a comparison between the calculated maximum density difference and the maximum density difference threshold, and a comparison between the calculated total density busyness and the total density busyness threshold, the maximum density difference is smaller than the maximum density difference threshold, If the total density busyness is smaller than the total density busyness threshold, it is determined that the pixel of interest is a background / photo area, and otherwise, it is determined to be a character / halftone area. If it is determined to be the background / photo area, the calculated maximum density difference is compared with the background / photo determination threshold. If the maximum density difference is smaller, it is determined to be the background area, and the maximum density difference is determined. If is larger, it is determined to be a photo area. When it is determined that the area is a character / halftone area, the calculated total density busyness is compared with the value obtained by multiplying the maximum density difference by the character / halftone threshold, and the total density busyness is smaller. Is determined to be a character region, and if the total density busyness is larger, it is determined to be a halftone dot region.

  The color correction unit 15 performs processing for removing color turbidity based on spectral characteristics of CMY color materials including unnecessary absorption components in order to faithfully reproduce colors. As a processing method, a method of having a correspondence relationship between an input RGB signal and an output CMY signal as an LUT (Look Up Table),

There is a color masking method using a transformation matrix such as For example, when the color masking method is used, an L ^* a ^* b ^* value (CIE 1976 L ^* a ^* b ^* signal (CIE: Commission International de l ^{) of} a color output when certain CMY data is given to the image output device 24. RGB data when the image input device 22 is read with a color patch having the same L ^* a ^* b ^* as'Eclairage; International Lighting Commission, L ^* : brightness, a ^* , b ^* : chromaticity)) If, it provides a number of sets of CMY data given to the image output device 24 calculates the coefficient of the transformation matrix than a combination thereof from a ₁₁ of formula 1 to a _33, a color correction processing by using the calculated coefficients Do. In order to increase the accuracy, it is only necessary to add a second or higher order term.

  The black generation and under color removal unit 16 performs black generation for generating a black (K) signal from the color-corrected CMY signal, and a process for generating a new CMY signal by subtracting a portion where the original CMY signal overlaps. Are converted into four-color CMYK signals. The spatial filter processing unit (spatial filter processing means) 17 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 16 based on the region identification signal, and performs spatial frequency processing. By correcting the characteristics, blurring of output images and deterioration of graininess are prevented.

  For example, a region separated as a character region by the region separation processing unit 14 emphasizes high-frequency components by sharp enhancement processing in the spatial filter processing of the spatial filter processing unit 17 in order to improve the reproducibility of black characters or color characters. . In addition, the region separated as the halftone dot region by the region separation processing unit 14 is reproduced by the spatial filter processing unit 17 as much as possible without performing the low-pass filter processing for removing the halftone dot component. As possible, high-frequency components are emphasized by passing through (prohibiting) spatial filtering or sharpening enhancement.

  Conventionally, the halftone dot region has been subjected to a smoothing process to prevent moire. However, when the smoothing process is performed, the halftone dot shape is lost, which is not preferable in reproducing the halftone dot. Therefore, in the present invention, the halftone dot form is preserved by performing no processing on the halftone dot region (through the spatial filter processing) or by performing weak enhancement processing. FIG. 2 is a diagram illustrating an example of filter coefficients used for weak enhancement processing. The spatial filter processing in the spatial filter processing unit 14 is a through process or a sharp enhancement process in the case of a halftone dot area, but a common filter process can be performed regardless of the area.

  The output tone correction unit 18 performs output tone correction processing for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the image output device 24. The gradation reproduction processing unit 19 performs gradation reproduction processing (halftone generation) on the image data of the CMYK signal based on the region identification signal so that the image can finally reproduce the gradation in a pseudo manner. Is. For example, halftones are generated using an error diffusion method.

  The image data subjected to the above-described processes is temporarily stored in a storage unit (not shown), read at a predetermined timing, and output to the image output device 24. The image output device 24 outputs an image on a recording medium (for example, paper), and can include, for example, an electrophotographic or inkjet color image output device, but is not particularly limited. .

  The operation panel 26 includes, for example, a touch panel in which a display unit such as a liquid crystal display and an operation unit such as a setting button are integrated. Based on information input from the operation panel 26, the image input device 22, image processing, and the like. The operations of the apparatus 10 and the image output apparatus 24 are controlled. Each of the above processes is controlled by a CPU (Central Processing Unit: control means) not shown.

  FIG. 3 is a block diagram showing a schematic main configuration of the gradation reproduction processing unit 19 of the image processing apparatus 10. The gradation reproduction processing unit 19 includes an adder 30, a quantization processing unit 32 including a comparator, a quantization threshold storage unit 34 such as a ROM (Read Only Memory), a quantization error calculation unit 36 such as a subtractor, and multiplication. A diffusion error calculation unit 38 including a storage unit, a diffusion coefficient storage unit 42 such as a ROM, a storage error storage unit 40 such as a RAM (Random Access Memory), and a random number generator 44. However, each pixel of the image data is composed of four color components CMYK, and halftone generation using the error diffusion method is performed for each color component. For this reason, error diffusion processing for each color component of CMYK is sequentially performed by a common circuit, or error diffusion processing for each color component of CMYK is performed in parallel by separate circuits. However, since error diffusion for each color component is performed in substantially the same manner, in the following description, processing for one color component will be described, and processing for other color components will be described only for different points.

  The adder 30 adds the accumulation error corresponding to the pixel position stored in the accumulation error storage unit 40 to the pixel value (density value) of each pixel to be processed of the input image data. The added pixel value is output to the quantization processing unit 32. The quantization processing unit 32 performs quantization by comparing the pixel value to which the accumulation error has been added with the quantization threshold value stored in the quantization threshold value storage unit 34, and outputs a pixel value (hereinafter referred to as pixel value) of the output image data. Output). The quantization error calculation unit 36 obtains an error (quantization error) between the quantization value output from the quantization processing unit 32 and the pixel value input to the quantization processing unit 32, and diffuses the obtained quantization error. The data is output to the error calculation unit 38.

  Based on the quantization error and the set of diffusion coefficients stored in the diffusion coefficient storage unit 42, the diffusion error calculation unit 38 obtains a diffusion error that diffuses to each unprocessed pixel around the pixel. The obtained diffusion error is stored in the accumulation error storage unit 40. However, a plurality of sets of diffusion coefficients are stored in the diffusion coefficient storage unit (storage unit, selection means) 42, and the combination of diffusion coefficients used by the diffusion error calculation unit 38 is an area identification signal and random number generator 44. Is selected according to a random number generated for each pixel. In the present embodiment, the diffusion coefficient storage unit (identification means) 42 identifies whether it is a halftone dot region or a photo (continuous tone) region based on the region identification signal.

  4 and 5A to 5D are diagrams showing examples of sets of diffusion coefficients. In the figure, the pixel to be quantized is indicated by “*”, FIG. 4 is an example of a set selected in the case of a halftone dot region, and FIGS. 5A to 5D are selection candidates in the case of a photographic region. 4 sets of examples are shown. When an area identification signal indicating a halftone dot area is input from the area separation processing unit 14, the diffusion coefficient storage unit 42 selects a set of diffusion coefficients illustrated in FIG. 4. The selected set is common to each color component of CMYK.

  On the other hand, when the region identification signal indicating the photograph region is input from the region separation processing unit 14, the diffusion coefficient storage unit 42 corresponds to the random number value generated by the random number generator 44, as shown in FIGS. One of the four sets of diffusion coefficients shown in FIG. For example, a random number generator generates a 2-bit (0 to 3) random number. FIG. 5A shows the case of “0”, FIG. 5B shows the case of “1”, and FIG. In the case of 5 (c) and “3”, the diffusion coefficient shown in FIG. 5 (d) is selected. Here, the random number generator 44 is provided separately for each color component, and can generate a random number for each random number generator, or can generate a random number for each color component from one random number generator. Thereby, different sets of diffusion coefficients are selected for each color component.

  Note that a diffusion coefficient may be separately prepared for the region separated as the character region by the region separation processing unit 14, but the same one as the halftone dot region may be selected. In the latter case, error diffusion of pixels belonging to the character area is processed in the same manner as the halftone dot area. Also, regarding the base region, a diffusion coefficient may be prepared separately, but the same one as the photographic region may be selected. In the latter case, error diffusion of pixels belonging to the base area is processed in the same manner as in the photographic area.

  When the diffusion coefficient is switched randomly for each pixel, the ratio of errors accumulated from each quantized pixel varies as compared with the case where the diffusion coefficient is fixed. In addition, when the diffusion coefficient is selected with a random number for each color component, the ratio of errors accumulated from each quantized pixel varies for each color component. Therefore, it is possible to suppress excessive overlapping of dots in the photographic area.

  On the other hand, when the diffusion coefficient is fixed, the ratio of errors accumulated from each quantized pixel is constant as compared with the case where the diffusion coefficient is switched randomly for each pixel. It is possible to suppress a dot from being output to a portion having a low pixel value such as between two halftone dots and a dot from being output to a portion having a high pixel value forming a halftone dot. Therefore, it is possible to suppress the image quality deterioration in the halftone area. Further, in the present invention, since error diffusion without periodicity is used as halftone processing, moire that occurs due to halftone dot and dither processing does not occur.

(Embodiment 2)
FIG. 6 is a block diagram showing a configuration example of an image forming system including the image processing apparatus according to the present invention. This image forming system includes a computer (image processing apparatus) 50 and a printer (image output apparatus, image forming means) 55. The printer 55 may be a digital multifunction machine having a copy function and a facsimile function in addition to the printer function. The printer 55 performs electrophotographic or ink jet image formation.

  For example, image data is input to the computer 50 from an image scanner such as a flatbed scanner or a film scanner or a digital camera, and stored in a storage device such as a hard disk (not shown). The image data input to the computer 50 can be processed and edited by executing various application programs. The computer 50 includes an area separation processing unit 51 that determines an area of each pixel of output image data output to the printer 55, a gradation reproduction processing unit 52 that performs halftone generation processing, and conversion of output image data into a printer language. It operates as a printer language translation unit 53 or the like that performs the above. The region separation processing unit 51 performs the same region separation processing as the region separation processing unit 14 of the image processing apparatus 10 of the first embodiment described above, and the gradation reproduction processing unit 52 of the image processing apparatus 10 of the first embodiment. A halftone generation process using an error diffusion method similar to that of the gradation reproduction processing unit 19 is performed. Although not shown, the computer 50 includes the color correction unit 15, the black generation and under color removal unit 16, and the spatial filter processing unit (spatial filter processing unit) 17 of the image processing apparatus 10 according to the first embodiment described above. The same processing is also performed. The data converted into the printer language by the printer language translation unit 53 is output to the printer 55 via the communication port 54 (Centronics port, LAN (Local Area Network) port, etc.).

  FIG. 7 is a block diagram illustrating a configuration example of a computer. The computer 50 controls communication with the CPU 61, RAM 62, hard disk drive (hereinafter abbreviated as hard disk) 63, external storage unit 64 such as a flexible disk drive or CD (Compact Disk) -ROM drive, and the printer 55. And a communication port 54 to perform. The computer 50 includes an input unit 65 such as a keyboard or a mouse, and a display unit 66 such as a CRT (Cathode Ray Tube) display or a liquid crystal display. The communication port 54 includes a network card or a modem, and can be connected to a communication network such as a LAN, the Internet, or a telephone line.

  CPU61 controls each part 62-66 and 54 mentioned above. Further, the CPU 61 stores the program or data received from the input unit 65 or the communication port 54 or the program or data read from the hard disk 63 or the external storage unit 64 in the RAM 62, and executes the program stored in the RAM 62 or the data Various processes such as computation are performed, and various process results or temporary data used for various processes are stored in the RAM 62. Data such as calculation results stored in the RAM 62 is stored in the hard disk 63 or output from the display unit 66 or the communication port 54 by the CPU 61.

  The CPU 61 operates as the above-described region separation processing unit 51, gradation reproduction processing unit 52, printer language translation unit 53, and the like. Further, the image data is input to the computer 50 from, for example, a scanner or a digital camera and stored in the hard disk 63. The CPU 61 operates as the adder 30, the quantization processing unit 32, the quantization error calculation unit 36, the diffusion error calculation unit 38, and the random number generator 44 of the first embodiment (FIG. 3). The RAM 62 or the hard disk 63 operates as the quantization threshold storage unit 34, the accumulation error storage unit 40, and the diffusion coefficient storage unit 42. For example, the set of diffusion coefficients shown in FIGS. 4 and 5A to 5D is stored in the hard disk (storage unit) 63.

  A computer program recorded on a recording medium 69 such as a CD-ROM is read by the external storage unit 64, stored in the hard disk 63 or RAM 62, and executed by the CPU 61, thereby causing the computer 50 to operate as the above-described units or units. Is possible. It is also possible to accept a computer program from another device through the communication port 54 connected to a LAN or the like and store it in the hard disk 63 or the RAM 62. Note that the computer program for realizing the error diffusion processing according to the present invention may be included in the printer driver or may be included in the application software for image processing.

  FIG. 8 is a flowchart illustrating an example of a halftone generation processing procedure using the error diffusion method. The CPU 61 adds the accumulation error stored in the RAM 62 or the hard disk 63 to the pixel value to be processed of the image data read from the hard disk 63 to the RAM 62 (S10). The CPU 61 compares the pixel value obtained by adding the accumulation error with the quantization threshold stored in the hard disk 63 to perform quantization processing (S12), and stores the obtained quantization value in the RAM 62. The CPU 61 calculates a quantization error by performing subtraction between the pixel value to which the accumulation error is added and the obtained quantization value (S14), and stores the calculated quantization error in the RAM 62. The CPU (identification means, selection means) 61 identifies the area to which the pixel to be processed belongs, and when the area is a halftone dot area (S16: YES), a plurality of sets of diffusion coefficients stored in the hard disk 63 are stored. A predetermined set of diffusion coefficients is selected from (S18). If the area is not a halftone dot area (photograph area) (S16: NO), a random number is generated, and a set of diffusion coefficients is randomly selected according to the random number. Is selected (S20). The CPU 61 calculates the diffusion error by multiplying the selected set of diffusion coefficients by the calculated quantization error, and stores it in the RAM 62 or the hard disk 63 (S22). The above-described processing is performed on each pixel of the image data (S24: NO). Error diffusion and identification of a region to which a pixel belongs are performed in the same manner as in the first embodiment. The CPU (control means) 61 also performs through (prohibition) of spatial filter processing.

(Embodiment 3)
In the above-described embodiment, switching between a fixed diffusion coefficient group and a randomly selected diffusion coefficient group is performed based on the region to which each pixel of the input image belongs. It is also possible to switch between a fixed diffusion coefficient set and a randomly selected diffusion coefficient set based on the type (original type) of the input image (original) such as (continuous tone photograph).

  FIG. 9 is a block diagram showing a schematic configuration of a digital color copying machine (image forming apparatus) 20a provided with the image processing apparatus 10a according to the present invention for switching the diffusion coefficient based on the document type. The digital color copying machine 20a includes an image input device 22, an image output device (image forming means) 24, and an operation panel 26 similar to those in the first embodiment (FIG. 1). In addition, the image processing apparatus 10a includes an A / D conversion unit 11, a shading correction unit 12, an input tone correction unit 13, a region separation processing unit 14, a color correction unit 15, and black as in the first embodiment (FIG. 1). A generation under color removal unit 16, a spatial filter processing unit 17, an output gradation correction unit 18, and a gradation reproduction processing unit 19 are provided.

  In the present embodiment, a document type determination unit 21 that determines the type (document type) of the input image is provided between the shading correction unit 12 and the input tone correction unit 13. The original type discriminating unit 21 employs an RGB signal (RGB reflectance signal) from which various distortions have been removed by the shading correction unit 12 and color balance adjustment has been performed in an image processing apparatus 10a such as a density signal. It is converted into a signal that can be easily handled by the existing image processing system, and the document type is determined. The document type discrimination result (document type discrimination signal) is output to the input tone correction unit 13, color correction unit 15, black generation and under color removal unit 16, spatial filter processing unit 17, and tone reproduction processing unit 19. The In the present embodiment, the input tone correction unit 13 performs image quality adjustment processing such as background density removal and contrast.

  As a method for determining the type (document type) of the input image, it can be performed in the same manner as the above-described region determination (region separation process). For example, using the input image data that has been pre-scanned, the region to which each pixel belongs is determined in the same manner as the region separation process described above, the number of pixels is counted for each region, and a preset ground region, The document type (document type) is determined by comparing with threshold values corresponding to the photo (continuous gradation) region, the halftone dot region, and the character region. For example, if the ratio of the character area and the ratio of the halftone dot area are equal to or greater than the threshold value, respectively, it is determined that the character / halftone photograph (character / printed photograph). Assuming that the detection accuracy is high in the order of characters, halftone dots, and photographs (photographic paper photographs), if the ratio of the character area is 30% of the total number of pixels, the ratio of the character original and the halftone area is all pixels. In the case of 20% of the number, it is determined that the image is a photographic paper photo when the ratio of the halftone dot photo and the photo (photographic paper photo) area is 10% of the total number of pixels. The document type can be determined using not only the pre-scanned input image but also image data stored in a storage device such as a hard disk.

  When a plurality of areas are not mixed in the input image (original), the same processing as that according to the above-described area according to the first embodiment is performed in the processing after the input tone correction unit 13. For example, when it is determined that the input image (original) is a text original, the input gradation correction processing is performed using a correction curve that removes excessive highlights or increases contrast. In addition, color correction processing that emphasizes saturation is performed for color characters, and a large black generation amount is set for black generation and under color removal processing for black characters. In addition, for characters, the edge is emphasized by spatial filter processing, and parameter switching such as setting the filter coefficient so as to weaken the smoothing processing is performed.

  On the other hand, when a plurality of regions are mixed in the input image, processing is performed using intermediate parameters of parameters corresponding to the respective regions included in the input image in the processing after the input tone correction unit 13. . For example, when it is determined that the input image is a character / photographic paper photograph, a process using an intermediate parameter between a parameter corresponding to a character document and a parameter corresponding to a photographic paper photograph is performed. Depending on whether text documents or photographic paper photos are important, the input tone correction processing uses highlight parameters and contrast between parameters corresponding to photographic paper photos and parameters corresponding to text documents. In addition, color correction processing is performed so that the intensity of saturation and the balance of gradation are not excessive. In the black generation and under color removal processing, the black generation amount is adjusted to such an extent that the photographic paper photograph is not affected.

  FIG. 10 is a block diagram showing a schematic main configuration of the gradation reproduction processing unit 19 of the image processing apparatus 10a, and the basic configuration is the same as that of the first embodiment (FIG. 3). However, a document type determination signal is input to the diffusion coefficient storage unit 42a, and a fixed diffusion coefficient or a set of diffusion coefficients corresponding to a random number is selected according to the document type. For example, when it is determined that the input image is a halftone photo (printed photo) or a character / halftone photo including characters, the diffusion coefficient shown in FIG. 4 is selected for the entire input image, and the input image is selected. Is determined to be a photographic paper photograph (continuous gradation photograph) or a character / photographic paper photograph including characters, any of the input images shown in FIGS. Can be selected based on random values.

(Embodiment 4)
FIG. 11 is a block diagram showing another configuration example of the image forming system including the image processing apparatus according to the present invention. This image forming system includes a computer (image processing apparatus) 50 and a printer (image output apparatus, image forming means) 55. For example, image data is input to the computer 50 from an image scanner such as a flatbed scanner or a film scanner or a digital camera, and stored in a storage device such as a hard disk (not shown). The image data input to the computer 50 can be processed and edited by executing various application programs.

  The computer 50 performs a document type determination unit 56 that determines the document type of output image data to be output to the printer 55, a gradation reproduction processing unit 52 that performs halftone generation processing, and conversion of output image data into a printer language. It operates as the printer language translation unit 53 or the like. The document type determination unit 56 performs the same document determination process as the document type determination unit 21 of the image processing apparatus 10a of the third embodiment (FIG. 9) described above, and the gradation reproduction processing unit 52 performs the image reproduction of the third embodiment. A halftone generation process using an error diffusion method similar to that of the gradation reproduction processing unit 19 of the processing apparatus 10a is performed. Although not shown, the computer 50 includes the area separation processing unit 14, the color correction unit 15, the black generation and under color removal unit 16, and the spatial filter processing unit (space) of the image processing apparatus 10 a according to Embodiment 3 described above. The same processing as that of the filter processing means) 17 is also performed. The data converted into the printer language by the printer language translation unit 53 is output to the printer 55 via the communication port 54.

  FIG. 12 is a block diagram showing an example of the configuration of a computer. The basic configuration is the same as that of the second embodiment (FIG. 7), but in this embodiment, the CPU 61 performs the above-described document type determination unit 56. , The tone reproduction processing unit 52, the printer language translation unit 53, and the like. Further, the CPU 61 operates as the adder 30, the quantization processing unit 32, the quantization error calculation unit 36, the diffusion error calculation unit 38, and the random number generator 44 according to the third embodiment (FIG. 10). The RAM 62 or the hard disk (storage unit) 63 operates as the quantization threshold storage unit 34, the accumulation error storage unit 40, and the diffusion coefficient storage unit 42a.

  A computer program recorded on a recording medium 69 such as a CD-ROM is read by the external storage unit 64, stored in the hard disk 63 or RAM 62, and executed by the CPU 61, thereby causing the computer 50 to operate as the above-described units or units. Is possible. It is also possible to accept a computer program from another device through the communication port 54 connected to a LAN or the like and store it in the hard disk 63 or the RAM 62. Note that the computer program for realizing the error diffusion processing according to the present invention may be included in the printer driver or may be included in the application software for image processing.

  FIG. 13 is a flowchart showing another example of a halftone generation processing procedure using the error diffusion method. As in the second embodiment (FIG. 8), the accumulation error is added to the pixel value to be processed (S10), the quantization process is performed (S12), and the quantization error is calculated (S14). In the present embodiment, the CPU (identification means, selection means) 61 discriminates the document type including the pixel to be processed, and if the document type is a halftone photo (halftone image) (S17: YES), the hard disk A predetermined set of diffusion coefficients is selected from a plurality of sets of diffusion coefficients stored in 63 (S18), and the document type is not a halftone photo (a photographic image (continuous tone image)) (S17: NO) generates a random number and randomly selects a set of diffusion coefficients according to the random number (S20). Thereafter, the same processing as in the second embodiment (FIG. 8) is performed. Error diffusion and document type discrimination are performed as in the third embodiment. The CPU (control means) 61 also performs through (prohibition) of spatial filter processing.

  As the document type, for example, selection of an image mode such as a text document, a halftone photo, a photographic paper (continuous tone) photo, or a text / halftone photo is received from the user via the operation panel 26 or the input unit 65. Is also possible. In this case, the CPU identifies the document type based on the selection received by the operation panel 26 or the input unit 65.

  As described in the second and fourth embodiments, a computer program that causes a computer to execute halftone generation using the error diffusion method according to the present invention is stored in a recording medium. A program medium such as a ROM (not shown) such as a ROM (not shown) may be provided so as to perform processing, and a program reading device such as an external storage unit 64 is provided and can be read by inserting a recording medium therein. It may be. In any case, the stored program may be configured to be accessed and executed by the microprocessor, and the program is read out, and the read program is stored in a program storage area (not shown) of the microcomputer. A method of downloading and executing the program may be used. In this case, it is assumed that the download program is stored in the main device in advance.

  The program medium is a recording medium configured to be separable from the main body, and includes a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a flexible disk and a hard disk, and a CD-ROM / MO (Magneto Optical) / MD (Mini disk) / DVD (Digital Versatile Disk) and other optical disk systems, IC (Integrated Circuit) cards (including memory cards) / optical card systems, mask ROM, EPROM (Erasable Programmable ROM), EEPROM (Electrically Erasable Programmable ROM), a medium carrying a fixed program including a semiconductor memory such as a flash ROM may be used.

  In the case of a system configuration that can be connected to a communication network including the Internet, it may be a medium that carries the program fluidly so as to download the program from the communication network. 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.

  In each of the embodiments described above, the diffusion coefficient shown in FIG. 4 is selected when it is determined as a halftone dot region or a halftone dot photograph. Instead, any one of FIGS. 5A to 5D is selected. It is also possible to select fixedly. In this case, since the number of sets of diffusion coefficients stored in the memory is reduced from 5 to 4, the circuit scale can be reduced by reducing the memory capacity.

1 is a block diagram illustrating a schematic configuration of a digital color copying machine (image forming apparatus) including an image processing apparatus according to the present invention. It is a figure which shows the example of the filter coefficient used for a weak emphasis process. It is a block diagram which shows the schematic principal part structure of the gradation reproduction process part of an image processing apparatus. It is a figure which shows the example of the group of a spreading | diffusion coefficient. It is a figure which shows the example of the group of a spreading | diffusion coefficient. 1 is a block diagram illustrating a configuration example of an image forming system including an image processing apparatus according to the present invention. It is a block diagram which shows the example of 1 structure of a computer. It is a flowchart which shows the example of the process sequence of a halftone production | generation using an error diffusion method. 1 is a block diagram showing a schematic configuration of a digital color copying machine (image forming apparatus) including an image processing apparatus according to the present invention that switches a diffusion coefficient based on a document type. It is a block diagram which shows the schematic principal part structure of the gradation reproduction process part of an image processing apparatus. It is a block diagram which shows the other structural example of the image forming system containing the image processing apparatus which concerns on this invention. It is a block diagram which shows the example of 1 structure of a computer. It is a flowchart which shows the other example of the process sequence of a halftone production | generation using an error diffusion method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image processing device 14, 51 Area separation processing unit 19, 52 Gradation reproduction processing unit 20 Digital color copying machine 21, 56 Document type discrimination unit 22 Image input device 24 Image output device 26 Operation panel 30 Adder 32 Quantization processing unit 34 Quantization threshold storage unit 36 Quantization error calculation unit 38 Diffusion error calculation unit 40 Accumulation error storage unit 42 Diffusion coefficient storage unit 44 Random number generator 50 Computer 55 Printer (image output device)
61 CPU
62 RAM
63 Hard disk 64 External storage 69 Recording medium

Claims (11)

Errors that occur when quantizing each pixel of a continuous tone image mainly having a continuous tone region and each pixel of a halftone image mainly having a halftone dot region are not quantized around the pixels. In an image processing apparatus that generates halftones using an error diffusion method in which diffusion is performed based on a diffusion coefficient corresponding to each pixel,
A storage unit for storing a plurality of sets of diffusion coefficients for continuous tone images and halftone images set so that a range where error diffusion is performed for continuous tone images is wider than a range where error diffusion is performed for halftone images ;
Identifying means for identifying whether a pixel to be quantized is included in a continuous tone image or a halftone image;
Spatial filter processing means for performing enhancement processing or smoothing processing on an image for generating a halftone;
When the identification result by the identification means is a halftone image, a control means for prohibiting the processing by the spatial filter processing means or causing the spatial filter processing means to perform an enhancement process;
When the identification result is a continuous tone image, each time error diffusion is performed for each pixel, one set is randomly selected from the set of diffusion coefficients for the continuous tone image stored in the storage unit, If the identification result is a halftone image, a selection unit that selects a predetermined set stored in the storage unit is provided, and the error is diffused based on the diffusion coefficient of the set selected by the selection unit. An image processing apparatus. An error diffusion method for diffusing an error generated when quantizing each pixel of an image having a continuous tone region and a halftone dot region to each non-quantized pixel around the pixel based on a corresponding diffusion coefficient In an image processing apparatus that generates a halftone using
A storage unit for storing a plurality of sets of diffusion coefficients for continuous tone images and halftone images set so that a range where error diffusion is performed for continuous tone images is wider than a range where error diffusion is performed for halftone images ;
Identifying means for identifying whether a pixel to be quantized is included in a continuous tone area or a halftone area;
Spatial filter processing means for performing enhancement processing or smoothing processing on an image for generating a halftone;
When the identification result by the identification means is a halftone dot region, the control means for prohibiting the processing by the spatial filter processing means or causing the spatial filter processing means to perform an enhancement process;
When the identification result is a continuous tone region, each time error diffusion is performed for each pixel, one set is randomly selected from a set of diffusion coefficients for continuous tone images stored in the storage unit, and When the identification result is a halftone dot region, the image processing apparatus includes selection means for selecting a predetermined set stored in the storage unit, and configured to diffuse an error based on the diffusion coefficient of the set selected by the selection means. An image processing apparatus. Equipped with a random number generator,
The said selection means is comprised so that any one group memorize | stored in the said memory | storage part may be selected based on the random number which the random number generator generate | occur | produced. Image processing apparatus. Each pixel includes a plurality of color components, and a halftone is generated by the error diffusion method for each color component.
The image according to any one of claims 1 to 3, wherein the selection unit is configured to select any one set stored in the storage unit for each color component. Processing equipment. Each pixel includes a plurality of color components, and a halftone is generated by the error diffusion method for each color component.
4. The apparatus according to claim 1, wherein the selection unit is configured to select only one set common to all color components from the predetermined set stored in the storage unit. 5. The image processing apparatus described. An image processing apparatus according to any one of claims 1 to 5,
An image forming apparatus comprising: an image forming unit that forms an image on which a halftone has been generated by the image processing apparatus; Errors that occur when quantizing each pixel of a continuous tone image mainly having a continuous tone region and each pixel of a halftone image mainly having a halftone dot region are not quantized around the pixels. In an image processing method for generating a halftone using an error diffusion method in which diffusion is performed based on a diffusion coefficient corresponding to each pixel,
Identifying whether the pixel to be quantized is contained in a continuous tone image or a halftone image;
When the identification result in this step is a halftone dot image, the emphasis process or the smoothing process as the spatial filter process, the process of applying the emphasis process to the image that generates halftones, or the following without performing the spatial filter process Selectively executing any one of the processes to be transferred to
Among the plurality of sets of diffusion coefficients for continuous tone images and halftone images set so that the error diffusion range for the continuous tone image is wider than the error diffusion range for the halftone image, the identification result Is a continuous tone image, each time error diffusion is performed for each pixel, one of the sets of diffusion coefficients for the continuous tone image is randomly selected and the identification result is a halftone image. Comprises a step of selecting a predetermined set of diffusion coefficients, and an error is diffused based on the selected set of diffusion coefficients. An error diffusion method for diffusing an error generated when quantizing each pixel of an image having a continuous tone region and a halftone dot region to each non-quantized pixel around the pixel based on a corresponding diffusion coefficient In an image processing method for generating a halftone using
Identifying whether a pixel to be quantized is included in a continuous tone region or a halftone dot region;
When the identification result in this step is a halftone dot region, the emphasis process or the smoothing process as the spatial filter process, the process of applying the emphasis process to the image that generates the halftone, or the following without performing the spatial filter process Selectively executing any one of the processes to be transferred to
Among the plurality of sets of diffusion coefficients for continuous tone images and halftone images set so that the error diffusion range for the continuous tone image is wider than the error diffusion range for the halftone image, the identification result Is a continuous tone area, each time error diffusion is performed for each pixel, one of the sets of diffusion coefficients for a continuous tone image is randomly selected, and the identification result is a halftone area. Comprises a step of selecting a predetermined set of diffusion coefficients, and an error is diffused based on the selected set of diffusion coefficients. Errors that occur when quantizing each pixel of a continuous tone image mainly having a continuous tone region and each pixel of a halftone image mainly having a halftone dot region are not quantized around the pixels. In a computer program that causes a computer to generate a halftone using an error diffusion method that diffuses to pixels based on a corresponding diffusion coefficient,
A procedure for causing a computer to identify whether a pixel to be quantized is included in a continuous tone image or a halftone image;
When the identification result according to the procedure is a halftone image, the computer performs a process of applying an enhancement process to an image that generates halftones, or a spatial filter process, out of an enhancement process or a smoothing process as a spatial filter process A procedure for selectively executing one of the processes to be transferred to the next procedure without
Among a plurality of sets of diffusion coefficients for continuous tone images and halftone images set so that the range in which error diffusion for continuous tone images is performed by the computer is wider than the range of error diffusion for halftone images, When the identification result is a continuous tone image, each time error diffusion is performed for each pixel, any one set is randomly selected from the set of diffusion coefficients for the continuous tone image, and the identification result is a halftone dot. In the case of an image, a computer program comprising: a step of selecting a predetermined set of diffusion coefficients; and causing the computer to diffuse an error based on the selected set of diffusion coefficients. An error diffusion method for diffusing an error generated when quantizing each pixel of an image having a continuous tone region and a halftone dot region to each non-quantized pixel around the pixel based on a corresponding diffusion coefficient In a computer program that causes a computer to generate a halftone,
A procedure for causing a computer to identify whether a pixel to be quantized is included in a continuous tone area or a halftone area;
When the identification result according to the procedure is a halftone dot area, the computer performs the processing for applying the enhancement processing to the image for generating the halftone in the enhancement processing or smoothing processing as the spatial filter processing, or the spatial filter processing. A procedure for selectively executing one of the processes to be transferred to the next procedure without
Among a plurality of sets of diffusion coefficients for continuous tone images and halftone images set so that the range in which error diffusion for continuous tone images is performed by the computer is wider than the range of error diffusion for halftone images, If the identification result is a continuous tone region, each time error diffusion is performed for each pixel, one set is randomly selected from a set of diffusion coefficients for continuous tone images, and the identification result is a halftone dot In the case of a region, a computer program comprising: a step of selecting a predetermined set of diffusion coefficients; and causing the computer to diffuse an error based on the selected set of diffusion coefficients.   A computer-readable recording medium on which the computer program according to claim 9 or 10 is recorded.

Images