JP4047097B2 - Image forming apparatus, image forming method, and image forming program causing computer to execute the method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus, an image processing method, and an image forming program provided with a quantization unit that converts image data into quantized data using a quantization threshold matrix.
[0002]
[Prior art]
As a halftone reproduction method in an image forming apparatus, a dither method, a density pattern method, and an error diffusion method are generally known.
[0003]
The dither method is a method of expressing a predetermined gradation using a plurality of pixels. When the dither method is used for a color image, a color is expressed by a combination thereof. The dither method used in general printing is excellent in graininess and can express a halftone image smoothly. In the so-called area gradation method typified by the dither method, resolution is deteriorated in order to obtain gradation. Further, in the dither method for generating a periodic image with respect to a printed image such as a halftone dot, moire is likely to occur.
[0004]
The error diffusion method is suitable for reproducing a character image because it can express gradation while maintaining the resolution faithfully to the original image. However, in a halftone image such as a photograph, isolated dots are dispersed or irregularly connected, so that the graininess of halftone dots is poor and a peculiar texture may occur. In particular, in an electrophotographic printer, an isolated dot is formed, so that an image is unstable, graininess is easily deteriorated due to density unevenness, and banding is likely to occur.
[0005]
[Problems to be solved by the invention]
In the error diffusion process, the product-sum operation is performed on the quantization error of the surrounding pixels, so the process is complicated and a long time is required for the process. In particular, as the image output density increases, the number of pixels per unit area increases and the amount of calculation increases. Specifically, if the pixel density is changed from 600 dpi to 1200 dpi, the number of pixels increases by 4 times, and by 2400 dpi, 16 times, which increases in proportion to the square of the resolution. Therefore, speeding up of processing is desired.
[0006]
For example, in Japanese Patent Application Laid-Open No. 7-295527, a technique aimed at speeding up error diffusion processing is to convert input image data to a high resolution by reducing the number of gradations by multi-value error diffusion. A method of binarizing the result to a higher resolution by a density pattern method or a dither method is disclosed. The purpose of this is to obtain a binary image signal having sufficient gradation at a high speed and to eliminate moire and rosette patterns. However, in this method, the dot reproducibility becomes worse as the dot arrangement becomes higher in density, and the image quality is not improved. Further, in the arrangement by the density pattern method or the dither method, the image has a periodicity, and moire may occur.
[0007]
Japanese Patent Application Laid-Open No. 11-1555064 discloses a method for converting binary data obtained by error diffusion at low resolution (600 dpi) into binary image data at high resolution (1200 dpi) by pattern matching. Yes. The purpose of this is to greatly improve the graininess of highlights with a small amount of buffer memory and a small amount of processing, but the improvement in image quality is not good compared to the error diffusion processing of 600 dpi.
[0008]
The present invention has been made in view of the above, and an object of the present invention is to provide an image forming apparatus capable of reducing the processing time while improving the image quality such as the granularity and resolution of halftone dots in an image. To do.
[0009]
[Means for Solving the Problems]
  In order to achieve the above object, an invention according to claim 1 is an image forming apparatus including a quantization unit that converts image data into quantized data using a quantization threshold matrix.A first step width block including a quantization threshold value which is determined according to at least one of a printing characteristic of the output device for outputting the quantized data and an image characteristic of the image data and is different for each first step width; Setting means for setting a quantization threshold matrix having a second step width block including different quantization thresholds for each second step width, and the quantization means includes the quantization set by the setting means The image data is converted into the quantized data using a threshold matrix.
[0010]
Here, the printing characteristics of the output device are output performances of the output device such as superiority or inferiority of graininess and superiority or inferiority of sharpness in an image output by the output device. The image characteristics of image data are image characteristics such as image type and image gradation. In addition, the image type includes, for example, an image representing characters and an image representing patterns.
[0011]
In addition, when a region representing characters and a region representing a pattern are included in one image, the setting unit sets a different quantization threshold matrix for each region, and the quantization unit sets each region. Different quantization threshold matrices may be used.
[0012]
According to the first aspect of the present invention, the quantization means uses the quantization threshold matrix corresponding to at least one of the print characteristics of the output device that outputs the quantized data and the image characteristics of the image data, Since data can be converted into quantized data, quantization processing suitable for the output device and image data can be performed. Therefore, the halftone dot graininess and stability in the formed image can be improved, and a better image can be obtained.
[0023]
Here, the step width is a difference between adjacent quantization thresholds when the quantization thresholds included in the quantization threshold matrix are arranged in ascending order.
[0024]
  Also,This claim1According to the invention, since the quantization means can use the quantization threshold matrix set to the step width according to the print characteristics and the image characteristics, for example, when the image shows characters, By using a quantization threshold matrix with a relatively small step width between quantization thresholds, sharpness can be improved. If the image shows a picture, the step width between the quantization thresholds is compared. By using a relatively large quantization threshold matrix, it is possible to improve the graininess of halftone dots forming an image. Further, for example, when the granularity in the image is inferior, the granularity can be improved by using a quantization threshold matrix having a relatively large step width, and when the image sharpness is inferior, the step width By using a quantization threshold matrix having a relatively small value, sharpness can be improved. In this way, a good image according to the image characteristics can be formed.
[0030]
  Also,This claim1According to the invention, since the quantization threshold matrix has two or more regions having different step widths between the quantization thresholds, the shape and generation of halftone dots can be controlled for each gradation of the image data. Thereby, since the granularity and stability of the halftone dot in a predetermined gradation can be improved, a better image can be obtained.
[0031]
  Claims2The invention according to claim1In the image forming apparatus, the setting unit may have the first step width larger than the second step width, and a quantization threshold in the first step width block may be the second step width block. A quantization threshold value matrix smaller than the quantization threshold value is set.
[0032]
  This claim2According to the invention, the step width in the first step width block having a relatively small quantization threshold included in the quantization threshold matrix used by the quantization means is the second step having a relatively large quantization threshold. Since it is larger than the step width in the width block, the stability and granularity of the halftone dot in the highlight can be improved. Therefore, a better image can be obtained.
[0039]
  Claims3The invention according toThe image forming apparatus according to claim 2, wherein the setting unit includes a first area in a central region of the quantization threshold matrix. 1 A step width block is set, and a quantization threshold matrix in which quantization thresholds adjacent to the central region in the main scanning direction are arranged in descending order along the order of using the quantization threshold is set. And
[0040]
  This claim3According to the invention, the quantization threshold in the quantization threshold matrix is in the order in which the quantization means uses the quantization threshold.descending orderIs arranged. That is, since the quantization threshold processed first is a large value, it is difficult for dots to be generated. Thereby, the stability and graininess of the halftone dots formed by the dots can be improved. Therefore, a better image can be formed.
[0041]
  Claims4The invention according toIn an image forming method executed by an image forming apparatus including a quantizing unit that converts image data into quantized data by using a quantization threshold matrix, the setting unit prints the output device that outputs the quantized data A first step width block including a quantization threshold value that is different for each first step width and a quantization threshold value that is different for each second step width, which is determined according to at least one of the characteristics and the image characteristics of the image data A setting step of setting a quantization threshold matrix having a second step width block including: the quantization means uses the quantization threshold matrix set in the setting step to convert the image data into the quantum And a quantization step for converting to quantized data.
[0042]
  This claim4According to the invention ofIn the quantization step, the pixel data may be converted into the quantized data using a quantization threshold matrix corresponding to at least one of the print characteristics of the output device that outputs the quantized data and the image characteristics of the image data. Therefore, quantization processing suitable for the output device and the image data can be performed. Therefore, the halftone dot graininess and stability in the formed image can be improved, and a better image can be obtained. According to the fourth aspect of the present invention, the quantization step can use a quantization threshold matrix set to a step width corresponding to the print characteristics and the image characteristics. For example, the image indicates characters. The sharpness can be improved by using a quantization threshold matrix with a relatively small step width between the quantization thresholds, and if the image shows a picture, the quantization threshold By using a quantization threshold matrix having a relatively large step width, it is possible to improve the graininess of halftone dots forming an image. Further, for example, when the granularity in the image is inferior, the granularity can be improved by using a quantization threshold matrix having a relatively large step width, and when the image sharpness is inferior, the step width By using a quantization threshold matrix having a relatively small value, sharpness can be improved. In this way, a good image according to the image characteristics can be formed. According to the fourth aspect of the present invention, since the quantization threshold matrix has two or more regions having different step widths between quantization thresholds, the shape and generation of halftone dots are controlled for each gradation of image data. can do. Thereby, since the granularity and stability of the halftone dot in a predetermined gradation can be improved, a better image can be obtained.
[0043]
  Claims5The invention according to5. The image forming method according to claim 4, wherein in the setting step, the first step width is larger than a second step width, and a quantization threshold in the first step width block is the second step width. A quantization threshold matrix smaller than the quantization threshold in the step width block is set.
[0044]
  This claim5According to the invention ofThe step width in the first step width block having a relatively small quantization threshold included in the quantization threshold matrix used by the quantization step is equal to the step width in the second step width block having a relatively large quantization threshold. Since it is larger than the above, it is possible to improve halftone dot stability and graininess in highlights. Therefore, a better image can be obtained.
[0045]
  Claims6The invention according to6. The image forming method according to claim 5, wherein the setting step includes the first step in a central region of the quantization threshold matrix. 1 A step width block is set, and a quantization threshold matrix in which quantization thresholds adjacent to the central region in the main scanning direction are arranged in descending order along the order of using the quantization threshold is set. And
[0046]
  This claim6According to the invention ofThe quantization thresholds in the quantization threshold matrix are arranged in descending order along the order in which the quantization means uses the quantization thresholds. That is, since the quantization threshold processed first is a large value, it is difficult for dots to be generated. Thereby, the stability and graininess of the halftone dots formed by the dots can be improved. Therefore, a better image can be formed.
[0047]
  Claims7The invention according toIn an image forming program executed by an image forming apparatus including a quantizing unit that converts image data into quantized data using a quantization threshold matrix, the setting unit prints the output device that outputs the quantized data A first step width block including a quantization threshold value that is different for each first step width and a quantization threshold value that is different for each second step width, which is determined according to at least one of the characteristics and the image characteristics of the image data A setting step of setting a quantization threshold matrix having a second step width block including: the quantization means uses the quantization threshold matrix set in the setting step to convert the image data into the quantum And a quantization step for converting into digitized data is executed by the image forming apparatus.
[0048]
  This claim7According to the invention ofIn the quantization step, the pixel data may be converted into the quantized data using a quantization threshold matrix corresponding to at least one of the print characteristics of the output device that outputs the quantized data and the image characteristics of the image data. Therefore, quantization processing suitable for the output device and the image data can be performed. Therefore, the halftone dot graininess and stability in the formed image can be improved, and a better image can be obtained. According to the seventh aspect of the present invention, since the quantization step can use a quantization threshold matrix set to a step width corresponding to the printing characteristics and image characteristics, for example, the image indicates characters. The sharpness can be improved by using a quantization threshold matrix with a relatively small step width between the quantization thresholds, and if the image shows a picture, the quantization threshold By using a quantization threshold matrix having a relatively large step width, it is possible to improve the graininess of halftone dots forming an image. Further, for example, when the granularity in the image is inferior, the granularity can be improved by using a quantization threshold matrix having a relatively large step width, and when the image sharpness is inferior, the step width By using a quantization threshold matrix having a relatively small value, sharpness can be improved. In this way, a good image according to the image characteristics can be formed. According to the invention of claim 7, since the quantization threshold matrix has two or more regions having different step widths between quantization thresholds, the shape and generation of halftone dots are controlled for each gradation of image data. can do. Thereby, since the granularity and stability of the halftone dot in a predetermined gradation can be improved, a better image can be obtained.
[0049]
  Claims8The invention according to8. The image forming program according to claim 7, wherein in the setting step, the first step width is larger than a second step width, and a quantization threshold in the first step width block is the second step width. The image forming apparatus causes the image forming apparatus to set a quantization threshold matrix smaller than the quantization threshold in the step width block.
[0050]
  This claim8According to the invention ofThe step width in the first step width block having a relatively small quantization threshold included in the quantization threshold matrix used by the quantization step is equal to the step width in the second step width block having a relatively large quantization threshold. Since it is larger than the above, it is possible to improve halftone dot stability and graininess in highlights. Therefore, a better image can be obtained.
[0051]
  Claims9The invention according toThe image forming program according to claim 8, wherein the setting step is performed in the central region of the quantization threshold matrix. 1 A step width block, and setting a quantization threshold matrix in which quantization thresholds adjacent to the central region in the main scanning direction are arranged in descending order along the order of using the quantization thresholds. It is executed by an image forming apparatus.
[0052]
  This claim9According to the invention ofThe quantization thresholds in the quantization threshold matrix are arranged in descending order along the order in which the quantization means uses the quantization thresholds. That is, since the quantization threshold processed first is a large value, it is difficult for dots to be generated. Thereby, the stability and graininess of the halftone dots formed by the dots can be improved. Therefore, a better image can be formed.
[0053]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of an image forming apparatus, an image processing method, and an image forming program for causing a computer to execute the method according to the present invention will be described below in detail with reference to the accompanying drawings.
[0054]
(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus may be a laser printer, a digital copying machine, a color laser printer, a digital color copying machine, or the like.
[0055]
The image forming apparatus 100 includes a scanner system processing unit 110 that corrects read data, a digital image processing unit 120 that processes and modifies a digital image, and a writing system processing unit 130 that modulates a writing LD (laser diode) 132. It has.
[0056]
The scanner system processing unit 110 includes a CCD 112, an AGC 114, an AD conversion unit 116, and a shading correction unit 118. The CCD 112 reads image data. The AGC 114 adjusts the data level of 600 dpi analog data read by the CCD 112. The AD converter 116 converts the analog data for each pixel into a digital value of 8 bits per pixel. The shading correction unit 118 corrects variations in pixels and illuminance in the reading CCD 112. Then, the image data is sent to the digital image processing unit 120.
[0057]
The digital image processing unit 120 includes a filter processing unit 122, a main scanning scaling unit 124, a γ correction unit 126, and a halftone processing unit 128. The filter processing unit 122 corrects the amplitude of the image by MTF correction, and corrects the halftone image smoothly by smoothing processing. The main scanning scaling unit 124 performs scaling processing in the main scanning direction according to the copying magnification. The γ correction unit 126 converts the writing density by γ correction. The halftone processing unit 128 performs halftone processing, converts the data into 1-bit or 2-bit data per dot, and sends the converted image data to the writing processing unit 130. In addition to this, background removal processing, flare removal processing, scanner γ, and image editing may be further performed.
[0058]
FIG. 2 is a functional block diagram showing detailed functions of the halftone processing unit 128. The halftone processing unit 128 includes a quantization unit 202, an error calculation unit 204, a subtracter 206, an adder 208, a conversion unit 230, a position control unit 232, a setting unit 210, and a quantization threshold matrix holding Unit 212, designation receiving unit 220, image recognition unit 224, and output device recognition unit 226.
[0059]
By the cooperation of the quantization unit 202, the error calculation unit 204, the subtractor 206, and the adder 208, a multi-level error is generated in units of pixels of low resolution input data (600 dpi) using a predetermined quantization threshold matrix. Using the diffusion method, pixel data corresponding to each pixel of the input data is converted into quantized data. Note that the quantization unit 202 quantizes the data of each color by using a separate quantization threshold matrix for each color of C (cyan), M (magenta), Y (yellow), and K (black) included in the image data. Convert to data. As another example, an average error minimum method may be used instead of the multilevel error diffusion method.
[0060]
The conversion unit 230 and the position control unit 232 cooperate to convert the quantized data converted by the quantization unit 202 into binary data at 1200 dpi as output data.
[0061]
On the other hand, the designation receiving unit 220 receives an instruction from the user and sends it to the setting unit 210. That is, the user can specify the quantization threshold matrix to be set via the instruction receiving unit 220.
[0062]
The image recognition unit 224 recognizes the image characteristics of image data input to the quantization unit 202 via the adder 208. Here, the image characteristics are image characteristics such as image type and image gradation. The image type is, for example, an image representing a character or an image representing a design. Note that the image recognition unit 224 sends the acquired image characteristics to the setting unit 210. Specifically, the image recognition unit 224 recognizes whether the image indicated by the image data is a character image representing a character or a design image representing a design by edge detection or the like.
[0063]
The output device recognition unit 226 recognizes the printing characteristics of a printer as an output device that should output image data. Specifically, the output device recognition unit 226 holds a correspondence table (not shown) that associates the model of the output device with the print characteristics corresponding to each model, and uses this correspondence table. The printing characteristics are determined from the model of the output device. The output device recognition unit 226 recognizes the printer model and the like from the printer driver installed in the image forming apparatus 100. Here, the print characteristics are information indicating the superiority or inferiority of the granularity of the halftone dots in the image output from the output device, information indicating the superiority or inferiority of the sharpness of the output image, and the like. The output device recognition unit 226 sends the recognized print characteristics to the setting unit 210.
[0064]
As another example, the output device recognition unit 226 may acquire the print characteristics from the printer driver when information about the print characteristics such as the maximum resolution of the printer can be acquired based on the printer driver.
[0065]
The quantization threshold value matrix holding unit 212 has a quantization threshold value matrix for each color of CMYK that should be used by the quantization unit 202.
[0066]
The setting unit 210 outputs the data after the conversion by the quantization unit 202, that is, the printing characteristics and processing of the output device that should output the 1200 dpi binary data further converted by the conversion unit 230 and the position control unit 232 A quantization threshold matrix determined according to at least one of the image characteristics of the target image data is set. That is, the setting unit 210 changes the quantization threshold in the quantization threshold matrix held in the quantization threshold matrix holding unit 212 according to at least one of the print characteristic and the image characteristic, and changes the changed quantization threshold. The matrix is set as a quantization threshold matrix to be used by the quantization unit 202.
[0067]
Note that the setting unit 210 acquires print characteristics of the output device from the output device recognition unit 226. The setting unit 210 acquires image characteristics from the image recognition unit 224. When the setting unit 210 receives a designation from the user via the designation receiving unit 220, the setting unit 210 sets a quantization threshold matrix based on the designation. That is, the quantization unit 202 converts the image data into quantized data using the quantization threshold matrix set by the setting unit 210.
[0068]
FIG. 3 shows a Y-version quantization threshold matrix used for data corresponding to the Y color held in the quantization threshold matrix holding unit 212. The quantization threshold matrix 150 is a matrix used when converting 600 dpi pixel data to 1200 dpi quantization data, and each cell 154 in the quantization threshold matrix 150 has one pixel at 1200 dpi. Equivalent to. That is, four cells correspond to one pixel at 600 dpi. The quantization threshold matrix 150 includes quantization thresholds ax (x = 1, 2,... 5), by (y = 1, 2,... 12), cw (w = 1, 2,... 9). ), Dz (z = 1, 2,... 11). Here, ax, by, cw, and dz indicate integer values. Each quantization threshold ax (x = 1, 2,... 5), by (y = 1, 2,... 12), cw (w = 1, 2,... 9), dz (z = 1, 2,... 11) are values that increase step by step in this order. Here, the step width is a difference between the nth quantization threshold and the (n + 1) th quantization threshold when the quantization thresholds are arranged in ascending order as described above. For example, when the step width is 4, the values of ax (x = 1, 2,... 5) are 40, 44, 48, 52, and 56 in order.
[0069]
As described above, the quantization threshold value in the quantization threshold matrix is set so that the quantization threshold value increases radially from the center of the minimum region 152 including the minimum value of the quantization threshold value. The arrangement of the quantization thresholds shown in FIG. 3 is merely an example, and it is not necessary that the quantization thresholds are strictly arranged in ascending order when the quantization thresholds increase radially as the distance from the minimum region 152 increases. In general, it only needs to be larger. Therefore, there may be a region where the sizes are reversed. Further, the minimum region 152 does not necessarily include the minimum value of the quantization threshold, and may be a region where a small quantization threshold is generally set.
[0070]
The setting unit 210 determines the step width in the quantization threshold matrix described in FIG. Hereinafter, a process in which the setting unit 210 changes the step width based on information received from the designation receiving unit 220, the image recognition unit 224, and the output device recognition unit 226 will be described.
[0071]
The setting unit 210 changes the step width in the quantization threshold matrix according to the type of image represented by the image data indicated by the image characteristics. Further, the setting unit 210 changes the step width in the quantization threshold matrix according to the printing characteristics recognized from the model of the output device. That is, the setting unit 210 changes the step width in the quantization threshold matrix according to the model of the output device.
[0072]
Hereinafter, specific processing steps of the setting unit 210 will be described with reference to FIG. FIG. 4 shows an algorithm by which the setting unit 210 determines the quantization threshold value in the quantization threshold matrix. In the present embodiment, the quantization threshold value matrix held in the quantization threshold value matrix holding unit 212 is set to be suitable for a character image and suitable for an output device with standard performance.
[0073]
The setting unit 210 acquires image characteristics from the image recognition unit 224. When the acquired image characteristics indicate that the image data is a pattern image (S200, Yes), the setting unit 210 sets the step width in the quantization threshold matrix held in the quantization threshold matrix holding unit 212. x is added (S202). If the print characteristic acquired from the output device recognition unit 226 indicates that the granularity of halftone dots in the output device is inferior (S204, Yes), the setting unit 210 adds y to the step width (S206). ).
[0074]
In the case of a picture image and when the granularity of halftone dots formed in the output device is inferior, it is necessary to improve the granularity of halftone dots. Thus, by increasing the step width in the quantization threshold matrix in this way, when forming halftone dots with each dot, the shape of the halftone dots can be adjusted. In addition, since the variation in the number of dots constituting a halftone dot is reduced at a portion where the density is uniform, the density fluctuation is also reduced, so that the graininess can be improved and stabilized.
[0075]
On the other hand, when the sharpness of the image formed in the output device to which the quantized data is to be output is poor (S208, Yes), the step width is reduced by w (S210). When the sharpness of the image formed in the output device is inferior, it is necessary to improve the sharpness. Therefore, sharpness can be improved by reducing the step width in the quantization threshold matrix in this way.
[0076]
Note that x, y, and w are all arbitrary integers. At least two of x, y, and w may be the same value. These values may be set in advance by the user.
[0077]
Thus, the setting unit 210 can set a step width that is more suitable for the image characteristics of the image data to be quantized and the print characteristics of the output device to which the quantized data is to be output. That is, a quantization threshold matrix suitable for image characteristics and print characteristics can be set.
[0078]
Next, a process of converting pixel data into quantized data using the quantization threshold matrix set by the setting unit 210 will be described in detail. Hereinafter, a process of converting Y data of image data into quantized data using the Y-version quantization threshold matrix shown in FIG. 3 will be described.
[0079]
Hereinafter, a process in the case where pixel data of 600 dpi is quantized by 5-value error diffusion processing and further output as 1-bit data of 1200 dpi will be described with reference to FIG.
[0080]
FIG. 5 shows one pixel at 600 dpi in the quantization threshold matrix 150 shown in FIG. In the Y version, four 3 × 3 pixel dither threshold matrices at 600 dpi are created from a 6 × 6 pixel dither threshold matrix at 1200 dpi. FIG. 5 shows a part of the quantization threshold matrix 150 shown in FIG. As a result, a halftone dot near line 200 is formed at 1200 dpi.
[0081]
As shown in FIG. 5, (110, 130, 150, 160) is set as a quantization threshold for four cells 162, 164, 166, 168 corresponding to one pixel at 600 dpi. In this case, the quantization unit 202 outputs 0 if the pixel data corresponding to this one pixel is less than 110, outputs 64 if the pixel data is 110 or more and less than 130, and the pixel data is 130 or more and less than 150. If the pixel data is 150 or more and less than 160, 192 is output. If the pixel data is 160 or more, 255 is output. As described above, the quantization unit 202 converts the input pixel data into quinary quantization data.
[0082]
Then, the difference between the pixel data and the quantization result in the pixel data is calculated by the error calculation unit 204, the subtracter 206, and the adder 208. This difference is indicated by the pixel data as an error in the pixel. It is added to the pixel arranged in the vicinity of the pixel.
[0083]
Next, the conversion unit 230 and the position control unit 232 cooperate to convert the quantized data quantized by the quantization unit 202 into an image with a higher resolution than the resolution of the image data before conversion of the quantized data. The data is converted into data, and the position of the pixel to be turned on in the image data is determined.
[0084]
Specifically, the conversion unit 230 and the position control unit 232 further convert the quantized quantized data into 1200 dpi output data. At this time, the number of output dots is first calculated. When the quantized data by quinarization is 0, the number of dots is 0. When 64, the number of dots is 1, 1. When 128, the number of dots is 2. When 192, the number of dots is 3. In the case of 255, the number of dots is determined to be 4.
[0085]
Next, the dot output position is determined. Of the four cells 212, 214, 216, and 218 at 1200 dpi shown in FIG. 5, the positions at which dots are to be output are determined based on the size of the quantization threshold value arranged in each cell. Specifically, dots are arranged in ascending order of quantization threshold. That is, in the four cells 162, 164, 166, and 168 at 1200 dpi shown in FIG. 5, dots are formed in the order of the lower right cell 166, the upper right cell 164, the upper left cell 162, and the lower left cell 168. In addition, since the quantization threshold array is different for each pixel, the dot formation order can be changed depending on the pixel position. By controlling the pixel position in this way, halftone dots can be easily formed.
[0086]
As described above, quinary error diffusion processing is performed on 600 dpi pixel data using four quantization threshold values set corresponding to the pixel, and the quantization result is converted to 2 × 2 pixels at 1200 dpi. Output as binary data for dots.
[0087]
FIG. 6 shows output data for a pattern image after processing with binary output. In the output data, a 200-line halftone dot is formed. In this way, the stability and graininess of the halftone dots could be improved. In addition, since error calculation is performed in units of 600 dpi pixels, the processing can be speeded up.
[0088]
As another example, the quantization threshold matrix may further use a dot concentration type quantization threshold. Furthermore, the output dot position may be controlled so that dots are concentrated in a dot pattern. Thereby, graininess and stability can be further improved.
[0089]
Next, the quantization threshold matrix held in the quantization threshold matrix holding unit 212 will be described. The quantization threshold matrix 212 holds different quantization threshold matrices for color data of CMYK colors. 7A shows a quantization threshold matrix 310 for the K version, FIG. 7B shows a quantization threshold matrix 320 for the C version, and FIG. 7C shows a quantization threshold matrix 330 for the M version. Yes.
[0090]
It should be noted that the C, M, Y, and K plate quantization threshold matrices respectively used for the CMYK color data have screen angles. Screen angles in the C, M, Y, and K quantization threshold matrices are 18.4 (108.4) degrees, 18.4 (71.6) degrees, 0 degrees, and 45 degrees, respectively. is there.
[0091]
By constructing with such an angle, it is possible to reduce misregistration and color blur. In addition, since the number of dither thresholds for each color is substantially the same, and the order of growth from the halftone dot nuclei is substantially the same, it is possible to form a well-balanced image that does not feel uncomfortable.
[0092]
Further, the number of lines of the quantization threshold matrix corresponding to each color is approximately the same 200 lines, and at 600 dpi, the repeated unit cell expanded two-dimensionally in the Y version quantization threshold matrix 150 shown in FIG. It is composed of 3 × 3 pixels. The quantization threshold matrix of other colors has a screen angle, and the repeating unit cell in the K plate is composed of 4 × 4 pixels, and the repeating unit cell in the C and M plates is composed of 10 × 10 pixels. ing.
[0093]
The Y version quantization threshold matrix 150 has 36 quantization thresholds. The K version quantization threshold matrix 310 has 32 quantization thresholds, and the C version and M version quantization threshold matrices 320 and 330 both have 40 quantization thresholds.
[0094]
In the K-version quantization threshold matrix 310 shown in FIG. 7A, the minimum threshold 312 is set as the center, and the quantization threshold is set to increase radially as the distance from the center increases.
[0095]
Similarly, in the C-version quantization threshold matrix 320 shown in FIG. 7B, the minimum threshold 322 is set as the center, and the quantization threshold is set to increase radially as the distance from the center increases. Further, in the M-version quantization threshold matrix 330 shown in FIG. 7C, the quantization threshold is set so as to increase radially with the minimum area 332 as the center and the distance from the stop.
[0096]
The method of setting the quantization threshold in the quantization threshold matrix of each CMK color and the pixel data quantization process using these quantization threshold matrices are the same as the process described in the case of using the Y version quantization threshold matrix. It is.
[0097]
Next, a configuration for outputting quantized output data in the image forming apparatus 100 will be described with reference to FIG. FIG. 8 is a schematic diagram illustrating a configuration related to printing in the image forming apparatus 100. The image forming apparatus 100 includes a scanner 1400 as an image reading apparatus, an image recording apparatus 1411 including a laser printer as an image forming unit, and a circuit to be described later. The scanner 1400 illuminates an original such as a bookbinding original placed on a flat original table 1403 with an illumination lamp 1502, and forms a reflected light image on a reading sensor 1507 via a mirror group 1503 to 1505 and a lens 1506. At the same time, the original is scanned by moving the illumination lamp 1502 and the mirror groups 1503 to 1505 to read the image information of the original and convert it into an electrical image signal. An image signal obtained by the reading sensor 1507 is sent to the printer 1411 through a circuit described later.
[0098]
The scanner 1400 transmits data read at 8 bits per pixel at 600 dpi, that is, 256 gradations. In the printer 1411, a writing device 1508 including a writing optical unit serving as an exposure unit converts the image signal into an optical signal and exposes it to an image carrier made of a photosensitive member, for example, a photosensitive drum 1509 to cope with a document image. An electrostatic latent image is formed by performing optical writing. The writing optical unit 1508 drives the semiconductor laser with the image signal by the light emission drive control unit, emits the laser beam whose intensity is modulated with the image signal, deflects and scans this laser beam with the rotary polygon mirror 1510, and f / θ. Irradiation to the photosensitive drum 1509 is performed via the lens and the reflection mirror 1511.
[0099]
As a standard, the printer 1411 writes binary data, that is, one dot on or off at 1200 dpi in both the main-scanning and sub-scanning directions, and forms a high-definition image. There is also a mode in which writing laser light is modulated at high speed and writing is performed with 2 bit data per dot, that is, with 4 values. Further, it has a function of changing the writing resolution according to the mode, and writing can be performed at a vertical and horizontal flat pitch of 2400 dpi, or 1200 dpi in the main scanning direction and 600 dpi in the sub scanning direction.
[0100]
The photosensitive drum 1509 is driven to rotate by a driving unit, rotates clockwise as indicated by an arrow, and is uniformly charged by a charger 1512 as a charging unit, and then an electrostatic latent image is formed by exposure by a writing optical unit 1508. It is formed. The electrostatic latent image on the photosensitive drum 1509 is developed by a developing device 1513 to become a toner image, and a transfer material made of transfer paper is one of a plurality of paper feeding units 1514 to 1518 and a manual paper feeding unit 1519. To the registration roller 1520.
[0101]
The registration roller 1520 sends the transfer paper to the toner image on the photosensitive drum 1509 in time, and the transfer belt 1521 conveys the transfer paper to which the transfer bias is applied from the transfer power source, and also the toner on the photosensitive drum 1509. Transfer the image to transfer paper. The transfer paper is conveyed by the conveyance belt 1521, the toner image is fixed by the fixing unit 1522, and is discharged as a copy to the paper discharge tray 1523. In addition, the photosensitive drum 1509 is cleaned by the cleaning device 1524 after the toner image is transferred and is gradually de-energized by the decelerator 1525 to prepare for the next image forming operation.
[0102]
The quantization processing program characteristic of the image forming apparatus 100 described above is an installable or executable file and can be read by a computer such as a CD-ROM, floppy (R) disk (FD), or DVD. Recorded on a simple recording medium.
[0103]
Further, the quantization processing program of the present embodiment may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network.
[0104]
The quantization processing program according to the present embodiment is loaded onto the main storage device by being read from the storage medium and executed by the image forming apparatus 100, and each unit described in the software configuration is generated on the main storage device. It has become so.
[0105]
(Embodiment 2)
The quantization threshold arrangement in the quantization threshold matrix held in the quantization threshold matrix holding unit 212 of the image forming apparatus 100 according to the second embodiment is the quantization held in the image forming apparatus 100 according to the first embodiment. This is different from the arrangement of quantization thresholds in the threshold matrix. In this respect, the image forming apparatus 100 according to the second embodiment is different from the image forming apparatus 100 according to the first embodiment.
[0106]
FIG. 9 shows a quantization threshold matrix held in the quantization threshold matrix holding unit 212 of the image forming apparatus 100 according to the second embodiment. FIG. 9A shows a Y-version quantization threshold matrix 340. FIG. 9B shows a K-version quantization threshold matrix 350. FIG. 9C shows a part of the C-version quantization threshold matrix 360. FIG. 9D shows a part of the M-version quantization threshold matrix 370.
[0107]
The Y-version quantization threshold matrix 340 shown in FIG. 9A includes an a1 quantization threshold block 342 having a plurality of pixels indicating the minimum quantization threshold value a1, and a plurality of quantization thresholds greater than a1. B1 quantization threshold block having pixels and each quantization threshold block having quantization threshold pixels indicating quantization thresholds c1, d1, e1, f1, g1, h1, i1 in ascending order. Then, the a1 quantization threshold block 300 having the minimum quantization threshold a1 among the quantization thresholds is centered, and each block is arranged so that the value of the quantization threshold increases radially as the distance from the center increases.
[0108]
For example, along the sub-scanning direction 348, an a1 quantization threshold block 342, a b1 quantization threshold block 344, an f1 quantization threshold block 345, and an i1 quantization threshold block 346 are arranged in this order. That is, the quantization threshold values are arranged in the order of a1, b1, f1, and i1, and the value of the quantization threshold value increases as the distance from the a1 quantization threshold block 342 increases.
[0109]
As described above, the quantization threshold value matrix according to the second embodiment has a plurality of blocks including the same quantization threshold value, and therefore can be easily set. As described above, even when the same quantization threshold is set for a plurality of pixels, the granularity in the output image is improved as in the case of the quantization process described in the first embodiment. And the sharpness of the image can be improved.
[0110]
In addition, each block is arranged so that the quantization threshold value indicated by each quantization threshold block increases in a radial pattern with the a1 quantization threshold block as the center, thereby improving the granularity of halftone dots. be able to.
[0111]
Other configurations and operations of the image forming apparatus 100 according to the second embodiment are the same as those of the image forming apparatus 100 according to the first embodiment.
[0112]
(Embodiment 3)
In the image forming apparatus 100 according to the third embodiment, the arrangement of the quantization thresholds in the quantization threshold matrix held in the quantization threshold matrix holding unit 212 is the image forming apparatus 100 according to the first and second embodiments. This is different from the arrangement of quantization thresholds in the quantization threshold matrix held in FIG. In this respect, the image forming apparatus 100 according to the third embodiment is different from the image forming apparatus 100 according to the first and second embodiments.
[0113]
FIG. 10 shows a Y-version quantization threshold matrix 380 held in the quantization threshold matrix holding unit 212 of the image forming apparatus 100 according to the third embodiment. In the quantization threshold matrix 380, with a relatively small quantization threshold as the center, a larger quantization threshold is arranged as the distance from the center increases. That is, it is set so that a halftone dot is formed. Further, the quantization threshold matrix 380 includes a first step width block 382 and a second step width block 382 arranged around the first step width block 382. The step width of the quantization threshold included in the first step width block 382 is larger than the step width of the quantization threshold included in the second step width block 384. For example, the step width in the central region 382 may be 6, and the step width in the peripheral region 384 may be 1. The first step width block 382 includes a relatively small quantization threshold ax (x = 1, 2,... 15), and the second step width block 384 includes a relatively large quantization threshold by (y = 1, 2, ... 21).
[0114]
As described above, by increasing the step width of the minimum area as compared with the step width of the other areas, it is possible to improve the graininess by stabilizing the highlight when the dot generation becomes a halftone dot shape. .
[0115]
Furthermore, in the image forming apparatus 100 according to the third embodiment, the setting unit 210 changes each of the plurality of step widths based on the algorithm described with reference to FIG. 4 in the first embodiment. Here, the plurality of step widths are a plurality of step widths set in the same quantization threshold matrix. At this time, each step width may be changed independently, and as another example, the same size may be changed.
[0116]
FIG. 11 is a conceptual graph showing the relationship between the position in the quantization threshold matrix and the magnitude of the quantization threshold set in the quantization threshold matrix.
[0117]
The horizontal axis of the graph shown in FIG. 11 indicates the distance from the position where the minimum value of the quantization threshold in the quantization threshold matrix is arranged. The vertical axis indicates the magnitude of the quantization threshold.
[0118]
The quantization threshold value in the quantization threshold value matrix 380 illustrated in FIG. As described above, by setting the step width in the region where the quantization threshold is relatively small, that is, in highlight, the halftone dot shape in highlight can be stabilized. That is, the graininess of halftone dots formed by dots can be improved. Note that the curve 412 has a large step width at the highlight similarly to the curve 440, and the granularity can be improved by stabilizing the halftone dot shape in the highlight portion. A curve 414 corresponds to the quantization threshold in the quantization threshold matrix in which the step width in the highlight portion and the shadow portion is larger than the step width in the middle. In this case, the shape of the halftone dots in the highlight part and the shadow part can be adjusted.
[0119]
As described above, by setting a large step width in the gradation for which halftone dot graininess is desired to be improved, the halftone dot graininess in a desired gradation can be improved.
[0120]
Other configurations and operations of the image forming apparatus 100 according to the third embodiment are the same as the configurations and operations of the image forming apparatus 100 according to the first and second embodiments.
[0121]
(Embodiment 4)
In the image forming apparatus 100 according to the fourth embodiment, the arrangement of the quantization thresholds in the quantization threshold matrix held in the quantization threshold matrix holding unit 212 is held in the image forming apparatus 100 according to another embodiment. This is different from the arrangement of quantization thresholds in the quantization threshold matrix. In this respect, the image forming apparatus 100 according to the fourth embodiment is different from the image forming apparatus 100 according to the other embodiments. The quantization threshold in the quantization threshold matrix held in the image forming apparatus 100 according to the fourth embodiment is set along the processing direction 512 in which pixel data is processed in the image forming apparatus 100, that is, the quantization unit 202. Are arranged so that the magnitudes of the quantization thresholds are generally in descending order along the order in which the quantization thresholds are used.
[0122]
The outline of the quantization threshold value matrix in Embodiment 4 is demonstrated referring FIG. 12, FIG. For convenience of explanation, a quantization threshold matrix in units of 4 × 4 cells when resolution is not converted will be described. FIG. 12B is a diagram for explaining the rules of quantization thresholds arranged in the quantization threshold matrix 620 in the fourth embodiment. FIG. 12A is a diagram for explaining an example of quantization threshold rules arranged in a conventional quantization threshold matrix.
[0123]
The quantization threshold value to be set in the quantization threshold value matrix 610 in the order of the values 1, 2,... Arranged in the cells 611, 612,... Included in the quantization threshold value matrix 610 shown in FIG. Are arranged in ascending order. The same applies to the cells 621, 622,... Included in the quantization threshold value matrix 620 shown in FIG. FIG. 13 shows a quantization threshold matrix 630 in which quantization thresholds are arranged according to the rules shown in FIG.
[0124]
For example, when pixel data at 256 gradations indicates 100 gradations,
100 / 255≈6.27 / 16 (Formula 1)
From the 4 × 4 cells shown in FIG. 12, the dots are placed on average from 6 cells to 7 cells, so dots are formed in the cells to which the numbers 1 to 6 or 7 are set.
[0125]
As shown in FIG. 12A, the quantization threshold 7 and the cells 611 and 614 in which the quantization thresholds that are processed relatively first among the quantization thresholds arranged in the main scanning direction, that is, the processing direction 512 are arranged. When 8 is set, dots are likely to be formed in the cells 611, 612, 613, 615, 616, 617 and the like in which the quantization thresholds 7, 1, 2, 3, 4, 5 are arranged. For this reason, with the setting shown in FIG. 12A, the graininess of the halftone dots tends to collapse.
[0126]
  On the other hand, in the quantization threshold matrix 620 shown in FIG.623Since relatively large quantization thresholds 12 and 11 are respectively set in FIG. 12, compared to the quantization threshold matrix 610 shown in FIG. That is, the graininess of halftone dots can be improved.
[0127]
More specifically, in the quantization threshold matrix 620 shown in FIG. 12B, the quantization unit 202 uses the quantization thresholds for the quantization thresholds arranged in 12 cells adjacent to the central region 628. Arranged in descending order along the order. In the upper row of the four cells in the center, the quantization thresholds are arranged in the order of 16, 15, 14, 13 in descending order along the order used by the quantization unit 202. In the second row from the top, the quantization thresholds are arranged in descending order of 12, 9 in the cells excluding the central region 628. Also in the third row from the top, in the cells excluding the central region 628, the quantization thresholds are arranged in substantially descending order as 11 and 8. In the bottom row, except for the rightmost cell 627, the quantization thresholds are arranged in descending order of 10, 6, and 5.
[0128]
In FIG. 12B, the quantization thresholds are not accurately arranged in descending order along the order in which the quantization unit 202 uses the quantization thresholds. For example, in the second and third rows, 12, 11, 10, and 9 should be placed in the cells 621, 622, 623, and 624, respectively, in order to be in descending order accurately in the order used by the quantization unit 202. . However, as shown in FIG. 12, in the present embodiment, in order to make it relatively easy to form halftone dots that are close to a rectangle, the arrangement of quantization thresholds is made different from that in descending order.
[0129]
In this way, the order in which dots are formed in a predetermined gradation is reversed with respect to the processing direction 512, that is, the quantization thresholds corresponding to the predetermined gradation are arranged in substantially descending order along the processing direction 512. By doing so, the granularity of halftone dots can be improved.
[0130]
A quantization threshold matrix 620 shown in FIG. 12B shows the rules for the arrangement of quantization thresholds in the quantization threshold matrix used in the fourth embodiment. In the quantization threshold matrix 620, the quantization thresholds are arranged in ascending order along the processing direction 512 for quantizing the pixel data. In this way, by arranging a larger quantization threshold at a position to be processed earlier, it is possible to prevent the occurrence of dots in that gradation from being too early. Therefore, by using the quantization threshold value matrix 630 shown in FIG. 13 in which the quantization threshold values are arranged according to the rules shown in FIG. 12B, the graininess of the halftone dots can be improved.
[0131]
FIG. 14 shows a quantization threshold matrix in the fourth embodiment. 14A shows a screen angle 0 degree, that is, a Y version quantization threshold matrix 510, and FIG. 14B shows a screen angle 45 degrees, ie, a K version quantization threshold matrix 520. Yes. Each quantization threshold value ax (x = 1, 2, 3, 4), by (y = 1, 2,... 11), cw (w = 1, 2) set in the quantization threshold value matrix 510, 520. ,... 10), dz (z = 1, 2,... 11) are values that increase in step widths in this order.
[0132]
Quantization threshold values a2 and a1 are arranged in this order along the processing direction, respectively, and quantization threshold values a4 and a3 and quantization threshold values b2 and b1 are arranged in this order. Further, the quantization threshold values b8, b7, and b6 are arranged in cells to be processed before the quantization threshold values b3, b4, and b5, respectively. Thereby, for example, the shape of the halftone dot in the gradation in which dots are formed can be stabilized by the quantization thresholds a2 and a1. The same applies to other quantization thresholds.
[0133]
As described above, by arranging the quantization thresholds in a specific gradation in the descending order along the processing direction, it is possible to concentrate dots in the gradation. Therefore, the formation of halftone dots can be further stabilized. In addition, by changing the arrangement of the quantization thresholds, it is possible to change the arrangement so that the dots are dispersed from the middle to the shadow so as to collect halftone dots in the highlight. That is, the shape of the halftone dot can be varied for each gradation.
[0134]
FIGS. 15B and 16B show output data quantized using the quantization threshold matrix 520 shown in FIG. 14B. FIG. 15A and FIG. 16A both show output data when a conventional quantization threshold matrix is used. As described above, the shape of the halftone dots formed in the output data is changed by using the quantization threshold matrix in which the quantization thresholds as shown in FIG. 14B are arranged in the descending order with respect to the processing direction. .
[0135]
FIG. 15B shows four output data 712, 714, 716, 718. The upper two output data 712 and 714 each have a halftone dot composed of about 8 dots. The lower two output data 716 and 718 each have a halftone dot of about 6 dots. Similar to the case of using the quantization threshold matrix that does not include the resolution conversion shown in FIG. 12, it is possible to improve the graininess of the halftone dot composed of 6 dots. Similarly, in the example shown in FIG. 16B, it is possible to improve the graininess of a halftone dot composed of 6 dots.
[0136]
Furthermore, for example, by switching and using a quantization threshold value that improves the granularity of halftone dots by designation from the user and other quantization threshold values, an area where the granularity of halftone dots is desired to be improved, and a halftone dot are selected. Appropriate quantization processing can be performed on each of the other regions such as to be dispersed.
[0137]
For example, a continuous portion having a relatively small density fluctuation is suitable for reproduction with a halftone dot having excellent graininess. For example, when it is desired to accurately reproduce details such as a character drawn on a picture, it is suitable for forming output data in which halftone dots are dispersed.
[0138]
Although the quantization processing considering the shape of halftone dots has been described above, the same processing can be performed even on a line, that is, appropriate quantization processing can be performed depending on the image by changing the threshold order. it can.
[0139]
Other configurations and operations of the image forming apparatus 100 according to the fourth embodiment are the same as the configurations and operations of the image forming apparatus 100 according to the other embodiments.
[0140]
Although the embodiment of the image forming apparatus has been described above, the technical scope of the present invention is not limited to the above embodiment. For example, the above embodiment may be changed or improved. Hereinafter, such modifications or improvements will be described.
[0141]
As a first modification, the quantization threshold value matrix holding unit 212 may hold a quantization threshold value matrix having a step width of 3, 2, 1, or 0 in advance. In this case, the setting unit 210 selects a quantization threshold matrix set to the step width determined by the algorithm described in FIG. 4 from the quantization threshold matrix holding unit 212, and uses this as a quantization threshold matrix to be used. Set. That is, the quantization threshold matrix is switched as appropriate according to the printer or according to the type of image. When the step width is set to 0, for example, in the case of quinarization, for example, the threshold value of each pixel used for quantization may always be four (32, 96, 160, 224) regardless of the pixel position. .
[0142]
As a second modification, the setting unit 210 may further determine the maximum value and the minimum value of the quantization threshold included in the quantization threshold matrix based on the gradation difference of the image data to be quantized. Specifically, the setting unit 210 sets the quantization threshold so that the difference between the maximum value and the minimum value of the quantization threshold to be included in the quantization threshold matrix is the same as the gradation difference of the image data. In this case, the gradation of the image shown in the image characteristics acquired from the image recognition unit 224 is used. As another example, a gradation difference of image data input to the image forming apparatus 100 may be set in advance as a specified value.
[0143]
In this way, by making the difference between the maximum and minimum values of the quantization threshold included in the quantization threshold matrix equal to the gradation difference of the image data to be processed, the graininess of the halftone dot of the image to be formed And stability can be improved.
[0144]
As a third modification, when the image data includes a character area indicating a character and a pattern area indicating a pattern or the like, a different quantization threshold matrix may be set for each area. In this case, the image recognition unit 224 recognizes a character area and a picture area in the image data by an image area separation method. Specifically, it is described in “Image Area Separation Method of Mixed Image of Character / Pattern (Dot, Photo)” (Electronic Information and Communication Society Transactions Vol. J75-DII No. 1 pp39-47 January 1992). Use the same method.
[0145]
  As a fourth modification, image characteristics may be received via the instruction receiving unit 220. For example, the user may select the type of target image data as the output mode in the output device via the user interface.Here, the output mode is a mode related to the type of image to be output, and is, for example, a picture mode in which an output condition suitable for a picture is set, a character mode in which an output condition suitable for a character is set, and the like. Specifically, the output condition suitable for the pattern is a setting condition that makes the graininess good, and the output condition that is suitable for the character is a setting condition that makes the sharpness good.As the output mode, a picture mode or a character mode may be selectable. In this case, when any one is selected by the user, the setting unit 210 may accept this selection via the designation receiving unit 220. The user interface may be a touch panel (not shown) provided on the housing of the image forming apparatus 100.
[0146]
【The invention's effect】
As described above, according to the first aspect of the present invention, the quantization means includes a quantization threshold matrix corresponding to at least one of the print characteristics of the output device that outputs the quantized data and the image characteristics of the image data. Since the pixel data can be converted into the quantized data by using, quantization processing suitable for the output device and the image data can be performed. Therefore, since the granularity and stability of the halftone dots in the formed image can be improved, there is an effect that a better image can be obtained.
[0151]
  Claims1According to the invention, the quantization means can use the quantization threshold matrix set to the step width corresponding to the printing characteristics and the image characteristics, so that the sharpness of the image to be output and the graininess of the halftone dots are output. Gender can be controlled. As described above, it is possible to form a good image according to the printing characteristics and the image characteristics.
[0154]
  Claims1According to the invention, since the quantization threshold matrix has two or more regions having different step widths between the quantization thresholds, the shape and generation of halftone dots can be controlled for each gradation of image data. Thereby, since the granularity and stability of the halftone dot in a predetermined gradation can be improved, there is an effect that a better image can be obtained.
[0155]
  Claims2According to the invention, the step width in the first step width block having the relatively small quantization threshold included in the quantization threshold matrix used by the quantization means is the second width having the relatively large quantization threshold. Since it is larger than the step width in the step width block, the stability and graininess of the halftone dot in the highlight can be improved. Therefore, there is an effect that a better image can be obtained.
[0159]
  Claims3According to the invention, the quantization threshold in the quantization threshold matrix is in the order in which the quantization means uses the quantization threshold.descending orderIs arranged. That is, since the quantization threshold processed first is a large value, it is difficult for dots to be generated. Thereby, the stability and graininess of the halftone dots formed by the dots can be improved. Therefore, there is an effect that a better image can be formed.
[0160]
  Claims4According to the invention concerningThe quantization step may convert the pixel data into the quantized data using a quantization threshold matrix corresponding to at least one of the print characteristics of the output device that outputs the quantized data and the image characteristics of the image data. Therefore, quantization processing suitable for the output device and the image data can be performed. Therefore, since the granularity and stability of the halftone dots in the formed image can be improved, there is an effect that a better image can be obtained. In addition, since the quantization step can use a quantization threshold matrix set to a step width corresponding to the print characteristics and image characteristics, the sharpness of the image to be output and the graininess of the halftone dots can be controlled. Can do. As described above, it is possible to form a good image according to the printing characteristics and the image characteristics. Further, since the quantization threshold matrix has two or more regions having different step widths between quantization thresholds, the shape and generation of halftone dots can be controlled for each gradation of image data. Thereby, since the granularity and stability of the halftone dot in a predetermined gradation can be improved, there is an effect that a better image can be obtained.
[0161]
  Claims5According to the invention concerningThe step width in the first step width block having a relatively small quantization threshold included in the quantization threshold matrix used by the quantization step is equal to the step width in the second step width block having a relatively large quantization threshold. Since it is larger than the above, it is possible to improve halftone dot stability and graininess in highlights. Therefore, there is an effect that a better image can be obtained.
[0162]
  Claims6According to the invention concerningThe quantization thresholds in the quantization threshold matrix are arranged in descending order along the order in which the quantization means uses the quantization thresholds. That is, since the quantization threshold processed first is a large value, it is difficult for dots to be generated. Thereby, the stability and graininess of the halftone dots formed by the dots can be improved. Therefore, there is an effect that a better image can be formed.
[0163]
  Claims7According to the invention concerningThe quantization step may convert the pixel data into the quantized data using a quantization threshold matrix corresponding to at least one of the print characteristics of the output device that outputs the quantized data and the image characteristics of the image data. Therefore, quantization processing suitable for the output device and the image data can be performed. Therefore, since the granularity and stability of the halftone dots in the formed image can be improved, there is an effect that a better image can be obtained. In addition, since the quantization step can use a quantization threshold matrix set to a step width corresponding to the print characteristics and image characteristics, the sharpness of the image to be output and the graininess of the halftone dots can be controlled. Can do. As described above, it is possible to form a good image according to the printing characteristics and the image characteristics. Further, since the quantization threshold matrix has two or more regions having different step widths between quantization thresholds, the shape and generation of halftone dots can be controlled for each gradation of image data. Thereby, since the granularity and stability of the halftone dot in a predetermined gradation can be improved, there is an effect that a better image can be obtained.
[0164]
  Claims8According to the invention concerningThe step width in the first step width block having a relatively small quantization threshold included in the quantization threshold matrix used by the quantization step is equal to the step width in the second step width block having a relatively large quantization threshold. Since it is larger than the above, it is possible to improve halftone dot stability and graininess in highlights. Therefore, there is an effect that a better image can be obtained.
[0165]
  Claims9According to the invention concerningThe quantization thresholds in the quantization threshold matrix are arranged in descending order along the order in which the quantization means uses the quantization thresholds. That is, since the quantization threshold processed first is a large value, it is difficult for dots to be generated. Thereby, the stability and graininess of the halftone dots formed by the dots can be improved. Therefore, there is an effect that a better image can be formed.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus according to a first embodiment.
FIG. 2 is a functional block diagram illustrating detailed functions of a halftone processing unit 128;
FIG. 3 is a diagram showing a Y-version quantization threshold matrix 150 held in a quantization threshold matrix holding unit 212;
FIG. 4 is a diagram illustrating an algorithm by which a setting unit 210 determines a quantization threshold value in a quantization threshold matrix.
FIG. 5 is a diagram illustrating one pixel at 600 dpi.
FIG. 6 is a diagram showing output data in binary output.
FIG. 7 is a diagram illustrating quantization threshold matrices for K, C, and M plates.
8 is a diagram illustrating a configuration relating to image formation in the image forming apparatus 100. FIG.
FIG. 9 is a diagram illustrating a quantization threshold matrix according to the second embodiment;
FIG. 10 is a diagram showing a Y-version quantization threshold matrix 380 according to the third embodiment;
FIG. 11 is a conceptual graph showing a relationship between a position in a quantization threshold matrix and a magnitude of a quantization threshold set in the quantization threshold matrix.
FIG. 12 is a diagram illustrating a quantization threshold matrix in units of 4 × 4 cells to be used when resolution is not converted.
13 is a diagram showing a quantization threshold matrix 630 in which quantization thresholds are arranged according to the rules shown in FIG. 12 (b).
14 is a diagram illustrating a quantization threshold matrix according to Embodiment 4. FIG.
FIG. 15 is a diagram illustrating output data quantized using a quantization threshold matrix;
FIG. 16 is a diagram illustrating output data quantized using a quantization threshold matrix.
[Explanation of symbols]
100 Image forming apparatus
110 Scanner system processing unit
116 AD converter
118 Shading correction unit
120 Digital image processing unit
122 Filter processing unit
124 Main scanning scaling unit
126 γ correction unit
128 Halftone processing unit
130 Write processing unit
202 Quantizer
204 Error calculator
206 Subtractor
208 adder
210 Setting section
212 Quantization threshold matrix holding unit
220 Designated reception
224 Image recognition unit
226 Output device recognition unit
230 Conversion unit
232 Position control unit
1400 scanner
1411 Printer
1509 Photosensitive drum

Claims (9)

In an image forming apparatus including a quantization unit that converts image data into quantized data using a quantization threshold matrix,
A first step width block including a quantization threshold value which is determined according to at least one of a printing characteristic of the output device for outputting the quantized data and an image characteristic of the image data and is different for each first step width; A setting means for setting a quantization threshold matrix having a second step width block including a quantization threshold different from each other by the second step width ;
The image forming apparatus , wherein the quantizing unit converts the image data into the quantized data by using the quantization threshold matrix set by the setting unit. The setting means has the first step width larger than the second step width, and the quantization threshold in the first step width block is smaller than the quantization threshold in the second step width block. The image forming apparatus according to claim 1 , wherein a quantization threshold matrix is set. The setting means is arranged in the central region of the quantization threshold matrix in the first region. 1 A step width block is set, and a quantization threshold matrix in which quantization thresholds adjacent to the central region in the main scanning direction are arranged in descending order along the order of using the quantization threshold is set. The image forming apparatus according to claim 2. In an image forming method executed by an image forming apparatus including a quantization unit that converts image data into quantized data using a quantization threshold matrix,
  The setting means includes a first quantization threshold that is determined according to at least one of a printing characteristic of the output device that outputs the quantized data and an image characteristic of the image data, and is different from each other by a first step width. A setting step for setting a quantization threshold matrix having a step width block and a second step width block including a quantization threshold that is different for each second step width;
  An image forming method comprising: a quantization step in which the quantization means converts the image data into the quantized data using the quantization threshold matrix set in the setting step. In the setting step, the first step width is larger than the second step width, and the quantization threshold in the first step width block is smaller than the quantization threshold in the second step width block. 5. The image forming method according to claim 4, wherein a quantization threshold matrix is set. In the setting step, the first region is placed in a central region of the quantization threshold matrix. 1 A step width block is set, and a quantization threshold matrix in which quantization thresholds adjacent to the central region in the main scanning direction are arranged in descending order along the order of using the quantization threshold is set. The image forming method according to claim 5. In an image forming program executed by an image forming apparatus including a quantization unit that converts image data into quantized data using a quantization threshold matrix,
  The setting means includes a first quantization threshold that is determined according to at least one of a printing characteristic of the output device that outputs the quantized data and an image characteristic of the image data, and is different from each other by a first step width. A setting step for setting a quantization threshold matrix having a step width block and a second step width block including a quantization threshold that is different for each second step width;
  The quantization unit causes the image forming apparatus to execute a quantization step of converting the image data into the quantized data using the quantization threshold matrix set in the setting step. An image forming program. In the setting step, the first step width is larger than the second step width, and the quantization threshold in the first step width block is smaller than the quantization threshold in the second step width block. The image forming program according to claim 7, wherein the image forming apparatus executes setting of a quantization threshold matrix. In the setting step, the first region is placed in a central region of the quantization threshold matrix. 1 And a quantization threshold matrix in which quantization thresholds adjacent to the central area in the main scanning direction are arranged in descending order along the order in which the quantization thresholds are used. The image forming program according to claim 8, wherein the image forming apparatus executes the process.

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