JP3711763B2 - Electrophotographic image processing apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image processing apparatus such as a printer or a copy and a method thereof, and the like, and more particularly to an image processing apparatus and a method thereof capable of suppressing the occurrence of uneven feeding and unevenness of a photosensitive drum and a transfer drum.
[0002]
[Prior art]
An electrophotographic apparatus such as a color printer or a color copy reproduces a color image using cyan, magenta, yellow, and black toners. In particular, page printers that use a laser beam to form a latent image on a photosensitive drum using a laser beam, develop it with charged toner, and transfer the developed toner image onto transfer paper are used in color printers. The region can be variously changed within the dots, and even when the number of dots per unit area is small, it is possible to reproduce a color image with higher resolution and higher gradation.
[0003]
In such color electrophotography, a dither method is widely used as a binarization method for gradation reproduction of grayscale images. According to this dither method, with respect to gradation data of each color as an input signal, a conversion table called a dither matrix or a threshold matrix having a correspondence between gradation data and image reproduction information is referred to, and The presence / absence (1,0) of the dot display is determined. A halftone dot is generated depending on whether or not a plurality of adjacent dots are displayed, and an intermediate gradation of a grayscale image is reproduced based on the size of the halftone dot.
[0004]
These halftone dots are arranged along the main scanning direction in which the laser beam is scanned and in the sub-scanning direction in which the transfer paper is sent, and as the gradation value of the dot gradation data becomes darker, growth nuclei are generated and the growth is increased. The size of halftone dots gradually increases from the nucleus.
[0005]
[Problems to be solved by the invention]
FIG. 12 is a diagram showing the transfer paper 1 on which a predetermined image is reproduced by a conventional electrophotographic apparatus. In an electrophotographic apparatus using a laser beam, due to mechanical reasons in the engine, rotation irregularities (jitter) of the photosensitive drum and the transfer drum occur in the sub-scanning direction, which is the transfer paper feeding direction. Such misregistration caused by rotation unevenness causes density of halftone dots in the sub-scanning direction, generates a linear pattern extending in the main scanning direction called banding or feed unevenness 2, and reduces the image quality of the reproduced image. Let
[0006]
Further, due to uneven charging in the engine, uneven development, and the like, a pattern called streak unevenness 3 due to the density of halftone dots is generated in the main scanning direction in the reproduced image, and the image quality is similarly reduced.
[0007]
It is known that these feed unevenness 2 and stripe unevenness 3 are conspicuous particularly in a halftone region having the same gradation (tone value) over a wide region. In particular, in the case of a single color halftone, the above-mentioned unevenness in feeding and unevenness appear remarkably, and the image quality is significantly lowered.
[0008]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrophotographic image processing apparatus capable of reproducing an image in which the occurrence of uneven feeding and unevenness is reproduced, a processing method thereof, and a recording medium recording the processing program. .
[0009]
[Means for Solving the Problems]
In order to achieve the above-described object, the present invention provides a method for processing halftone dots arranged in the main scanning direction in image processing of an electrophotographic image in which gradation is expressed by halftone dots formed from a plurality of dots and an image is reproduced. Image reproduction data is generated by shifting the position of the growth nucleus in the sub-scanning direction.
[0010]
In another invention, the position of the growth nucleus of the halftone dots arranged in the sub-scanning direction in the image processing of the electrophotography in which the gradation is expressed by the halftone dots formed from a plurality of dots and the image is reproduced. Image reproduction data is generated by shifting in the main scanning direction.
[0011]
Furthermore, in another invention, in the electrophotographic image processing in which gradation is expressed by halftone dots formed from a plurality of dots and an image is reproduced, growth nuclei of halftone dots arranged in the main scanning direction and the sub-scanning direction Is shifted in a random direction to generate image reproduction data.
[0012]
Further, in the above invention, it is desirable that the shift of the growth nuclei of the halftone dots is not performed in a region where the density of halftone dots is low, but is performed in a region where the density of halftone dots is high. Alternatively, it is desirable to generate the image reproduction data so that the sum of the shift vectors becomes substantially zero within a predetermined region.
[0013]
In order to achieve the above object, the present invention reproduces an image by expressing gradation by halftone dots formed from a plurality of dots, scans a beam in the main scanning direction, and converts the image onto a rotating drum. In an electrophotographic image processing apparatus that forms a corresponding latent image and transfers the latent image to a transfer sheet that is sent in a sub-scanning direction perpendicular to the main scanning direction.
A halftone processing unit that is supplied with gradation data and generates image reproduction data corresponding to the dots based on the gradation data according to a conversion table having a correspondence between the gradation data and the image reproduction information for each dot. Have
The halftone processing unit generates the image reproduction data by shifting a growth nucleus position of the halftone dots arranged in the main scanning direction (or sub-scanning direction) in the sub-scanning direction (or main scanning direction). It is characterized by that.
[0014]
According to the said invention, generation | occurrence | production of a feed unevenness or a stripe unevenness can be suppressed.
[0015]
In order to achieve the above object, according to another invention, the halftone processing unit randomly determines the positions of the growth nuclei of the halftone dots arranged in the main scanning direction and the sub scanning direction. The image reproduction data is generated by shifting.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. However, such an embodiment does not limit the technical scope of the present invention.
[0017]
[Image processing for gradation reproduction]
The present invention uses a dither method that reproduces the halftone of a grayscale image, and shifts the arrangement of growth nuclei of halftone dots generated in accordance with the dither method in a predetermined direction, thereby suppressing the occurrence of uneven feeding and unevenness. Therefore, the dither method and halftone dot growth nuclei will be briefly described.
[0018]
FIG. 1 is a diagram for explaining a binarization method for gradation reproduction of a grayscale image by the dither method. Image data is generated by an image creation program such as a host computer and supplied as input data to an image processing unit for electrophotography. This input image data is, for example, gradation data 10 indicating the gray value for each color dot. In FIG. 1, gradation data is entered in each dot. For the gradation data 10, the dither method uses a conversion table 20 called a threshold matrix in which the threshold value of each dot is changed according to a certain rule. More specifically, the gradation data of each dot is compared with the threshold value matrix threshold value. If the gradation data is larger than the corresponding dot threshold value, the image reproduction data 30 with drawing is generated. No image reproduction data 30 is generated. That is, the multi-tone data 10 for each dot is converted into binary image reproduction data 30 for each dot.
[0019]
The threshold value matrix shown in FIG. 1 is a conversion table having correspondence between gradation data and image reproduction information indicating whether or not drawing is performed. That is, the threshold value of each dot in the conversion table can be referred to as image reproduction information indicating whether or not drawing should be performed on the gradation data. The threshold value matrix 20 shown in FIG. 1 is a 4 × 4 matrix, and is a so-called dot concentration type that is low in the central portion and high in the peripheral portion.
[0020]
FIG. 2 is a diagram for explaining a threshold matrix of the dither method. FIG. 2 shows an image reproduced for each gradation when the dot concentration type threshold matrix 20 of FIG. 1 is used. An image to be reproduced is shown when the gradation becomes higher (intensity value is darker) in order from the upper left to the right and from the lower left to the right. That is, it is understood that a halftone dot grows around the center of a 4 × 4 halftone cell. It is known that such a dot concentration type threshold matrix is superior to the dot dispersion type when the dot density is increased to some extent.
[0021]
FIG. 3 is a diagram showing a change in the shape of a halftone dot formed using the dither method. By using the conversion table composed of the dot concentration type threshold matrix shown in FIGS. 1 and 2, the dots in the halftone cell composed of m × m gradually become thicker according to the gradation value (light / dark value). It is understood that it will grow. The gradation of the grayscale image is expressed by the two-dimensional halftone dot density. In the example of FIG. 3, the growth nuclei of halftone dots are arranged in a matrix along the main scanning direction in the row direction and the sub-scanning direction in the column direction.
[0022]
[Allocation of halftone dots in the embodiment]
In the embodiment of the present invention, the halftone dots are arranged in the main scanning direction where the growth nucleus (center of the halftone dots) is the scanning direction of the laser beam, and the growth nucleus is further shifted in the sub-scanning direction. . Alternatively, the growth nuclei of halftone dots are arranged in the sub-scanning direction, which is the transfer paper feeding direction, and the growth nuclei are further arranged shifted in the main scanning direction. In this case, the shift amount is set to be less than half of the screen pitch, which is the distance between the growth nuclei of the halftone dots. For example, when the engine of the electrophotographic apparatus has a capability of 600 dpi, the dot is about 40 μm square, and when the 4 × 4 conversion matrix is used as described above, the screen pitch is about 160 μm. Therefore, in this case, the shift amount of the growth nucleus in the main scanning direction or sub-scanning direction is set to about 80 μm or less, which is half the screen pitch.
[0023]
Alternatively, in the halftone dots in the embodiment of the present invention, the growth nuclei are arranged in the main scanning direction and the sub-scanning direction, and the growth nuclei are arranged shifted in a random direction.
[0024]
As a result, the cells for growing the halftone dots are arranged in the main scanning direction or the sub-scanning direction, but the position of the growing halftone dots is shifted in the sub-scanning direction or the main-scanning direction. Even when there is uneven rotation, uneven charging in the main scanning direction, or uneven development, the generation of conspicuous density stripes such as feed unevenness and unevenness in the reproduced image can be suppressed.
[0025]
The above-described processing for shifting the arrangement of the growth nuclei of the halftone dots is performed in a relatively high concentration region where unevenness in feeding and unevenness are conspicuous. And in the comparatively low density | concentration area | region where a feed unevenness and a stripe unevenness are not so conspicuous, the process which shifts the arrangement | positioning of the growth nucleus of a halftone dot is not performed. In the low density region, the halftone dots that have grown are not connected, and the feeding unevenness and the unevenness are not conspicuous. . Therefore, it is desirable to shift the position of the growth nucleus in a region where the density of halftone dots is relatively high.
[0026]
FIG. 4 is a diagram showing the arrangement of halftone dots when the gray value is light and the halftone density is low. FIG. 4 shows halftone dot cells CELL composed of a plurality of dots in four rows and four columns, and the arrangement of growth nuclei of halftone dots 5 in each cell CELL is shown. The example of FIG. 4 is an example in which a halftone dot grows from the center portion in the cell CELL by the conversion table as described in FIGS.
[0027]
As shown in FIG. 4, when the density of the halftone dots is low and the grown halftone dots in each cell are so far away that they do not come into contact with the halftone dots in the adjacent cells, the shading due to feeding unevenness or unevenness is not so noticeable. . Therefore, as shown in FIG. 4, the position of the growth nucleus of each halftone dot is aligned in the main scanning direction and the sub-scanning direction, and is not shifted in any direction.
[0028]
FIG. 5 is a diagram illustrating an arrangement example of halftone dots when the gray value is dark and the halftone density is high. The case of FIG. 5 is an example in which the size of the halftone dot 5 in each cell CELL is larger than that in FIG. 4, and eventually becomes large enough to come into contact with the halftone dot in the adjacent cell. When the density of the halftone dots increases in this way, the shading due to the occurrence of uneven feeding becomes conspicuous, and the streak 2 in the main scanning direction as shown in FIG. 12 becomes clearly visible.
[0029]
Therefore, in the example of FIG. 5, the positions of the growth nuclei of the halftone dots of the cells CELL00 to CELL03 arranged in the main scanning direction are shifted in the sub scanning direction. The cell growth nucleus of the cells CELL00 and CELL02 is located at the center of the cell, the cell growth nucleus of the cell CELL01 is located at the upper center of the cell, and the cell growth nucleus of the cell CELL03 is located at the lower center of the cell. To do. Similarly, the positions of the halftone dots in the four cells in the second row are arranged in order from the left, center lower, center, center upper, and center. In the third and fourth lines, as shown in the figure, the positions of the halftone dots are shifted in the sub-scanning direction.
[0030]
Furthermore, the halftone dot displacement vectors B ₀₁ , B ₀₃ , B ₁₀ , B ₁₂ , B ₂₁ , B ₂₃ , B ₃₀ , B ₃₂ in 4 rows and 4 columns are set to zero. Further, by repeating the region shown in FIG. 5, the amount and direction of halftone dot shifting are repeated regularly. In this way, the shift of the growth nuclei of the halftone dots is regularly repeated, and the total of the shift vectors within the predetermined area becomes zero, so that the graininess is deteriorated even if the growth nuclei of the halftone dots are shifted. Can be suppressed.
[0031]
In FIG. 5, the method of shifting the growth nuclei of the halftone dots may be changed for each of a plurality of cells. In consideration of consistency with engine resolution and the like, an optimal rule for shifting the growth nucleus of the halftone dot is set.
[0032]
According to the example of FIG. 5, by shifting the position of the growth nuclei of halftone dots arranged in the main scanning direction in the sub-scanning direction, banding (feeding unevenness) due to uneven rotation of the charging drum or the like occurs in the engine of the electrophotographic apparatus. Can be suppressed.
[0033]
FIG. 6 is a diagram showing an arrangement example of halftone dots when the gray value is dark and the halftone density is high. In this example, the position of the growth nuclei of the halftone dots of the cells arranged in the sub-scanning direction is shifted in the main scanning direction to suppress the occurrence of streaking. That is, the halftone dot of the cell CELL00 is arranged at the center of the cell, the halftone dot of the cell CELL10 is arranged at the left side of the cell, the halftone dot of the cell CELL20 is arranged at the center of the cell, and the halftone dot of the cell CELL30 is arranged at the right side of the cell. The Similarly, the second row is also regularly arranged in order from the top, left side, center, right side, and center. The same applies to the third and fourth rows.
[0034]
Also in the example of FIG. 6, the shift vectors B ₀₁ , B ₀₃ , B ₁₀ , B ₁₂ , B ₂₁ , B ₂₃ , B ₃₀ . total B ₃₂ is set to be zero. Further, by repeating the region shown in FIG. 6, the shift amount and the direction thereof are regularly repeated. As a result, it is possible to suppress the deterioration of the graininess even if the growth nuclei of the halftone dots are shifted.
[0035]
FIG. 7 is a diagram showing another arrangement example of halftone dots when the gray value is high and the halftone density is high. In this example, the position of the growth nucleus of the halftone dot of the cell arranged in the main scanning direction is shifted in the subscanning direction, and the position of the growth nucleus of the halftone dot of the cell arranged in the subscanning direction is shifted in the main scanning direction. Shift to That is, the cells CELL10 to CELL14 in the second row and the cells CELL30 to CELL34 in the fourth row are arranged such that the positions of the growth nuclei of the halftone dots in the cells are shifted in the sub-scanning direction. Further, the cells CELL01 to CELL41 in the second column and the cells CELL03 to CELL43 in the fourth column are arranged by shifting the positions of the growth nuclei of the halftone dots in the cells in the main scanning direction.
[0036]
FIG. 7 shows a cell with 5 rows and 5 columns to show a regular repetition of shifting the position of the growth nucleus of the halftone dots. However, when repeating regularly, the area | region which consists of a cell of 4 rows 4 columns on the upper left is repeated. Even in that case, although not shown in FIG. 7, the sum of the shift vectors is set to be zero. As a result, it is possible to suppress the deterioration of the graininess due to the shift.
[0037]
According to the example of FIG. 7, it is possible to suppress the occurrence of feed unevenness appearing in the main scanning direction and stripe unevenness appearing in the sub-scanning direction as shown in FIG.
[0038]
FIG. 8 is a diagram showing another arrangement example of halftone dots when the gray value is high and the halftone density is high. In this example, the position of the growth nucleus of the halftone dot in the cell is shifted at random. The shifting direction and the shifting amount are selected at random, and there is no regularity and repeatability. Even in such a way of shifting, it is possible to suppress the occurrence of uneven feeding and unevenness. However, also in the example of FIG. 8, the growth of the halftone dots in each cell grows around a nucleus at a certain position as the gray value increases. Further, when the gray value is relatively dark and the halftone dot density is high, random shifting is performed. When the gray value is relatively light and the halftone dot density is low, as shown in FIG. The position of is not shifted.
[0039]
[Electrophotographic system]
FIG. 9 is a configuration diagram of the electrophotographic system. In this example, the host computer 50 generates image data 56 composed of RGB gradation data (8 bits for each of 24 bits in total), and supplies the image data 56 to an electrophotographic apparatus 60 such as a page printer. The electrophotographic apparatus 60 such as a page printer reproduces a color image based on the supplied image data 56. The electrophotographic apparatus 60 includes a controller 62 that performs image processing and supplies laser drive data 69 to the engine, and an engine 70 that reproduces an image according to the drive data 69.
[0040]
In the host computer 50, character data, graphic data, bitmap data, and the like are generated by an application program 52 such as a word processor or a graphic tool. Each data generated by the application program 52 is rasterized by a driver 54 for an electrophotographic apparatus installed in the host computer 50, and is image data composed of gradation data of RGB colors for each pixel or dot. 56.
[0041]
The electrophotographic apparatus 60 also includes a microprocessor (not shown), and a controller 62 including a color conversion unit 64, a halftone processing unit 66, a pulse width modulation unit 68, and the like according to the microprocessor and a control program installed therein. Composed. In the engine 70, for example, the laser driver 72 drives the laser diode 74 for image drawing based on the drive data 69. The engine 70 includes a photosensitive drum, a transfer belt, and the like and a driving unit thereof, which are omitted in FIG.
[0042]
The color conversion unit 64 in the controller 62 converts the supplied RGB gradation data 56 for each dot into CMYK gradation data 10 having a complementary color relationship with RGB. The CMYK gradation data 10 is gradation data of 8 bits for each color, and has a maximum of 256 gradations. The color converter 64 converts the RGB gradation data 56 for each dot into gradation data 10 for each dot of the CMYK color plane. Therefore, the halftone processing unit 66 is supplied with the gradation data 10 corresponding to the dots (see the input data 10 in FIG. 1) for each color plane.
[0043]
The halftone processing unit 66 generates image reproduction data 30 for each dot by referring to a conversion table having correspondence between gradation data and image reproduction information created in advance for the gradation data 10 for each dot. To do. The halftone processing unit 66 uses the dither method described with reference to FIG. 1 to generate image reproduction data 30 that represents a halftone. For example, by using a conversion table composed of the threshold matrix 20 shown in FIG. 1, binary image reproduction data 30 can be generated for each dot. A plurality of types of conversion tables are generated by shifting the positions of the growth nuclei of each halftone dot, and the conversion nuclei positions of the halftone dots for each cell are created by repeatedly selecting and referencing these conversion tables. Can be shifted as shown in Fig. 5.6.7. When the binary image reproduction data 30 is generated, the pulse modulation unit 68 generates drive data 69 that includes the presence or absence of a laser drive pulse for each dot.
[0044]
In a preferred embodiment of the present invention, the halftone processing unit 66 uses the multi-value dither method to reproduce more gradations with high resolution at a dot density as low as about 600 dpi, such as a color printer. can do.
[0045]
FIG. 10 is a diagram showing an example of a multi-value dither conversion table in a preferred embodiment. In the binary dither method shown in FIG. 1, input data 10 composed of gradation data for each dot is compared with a threshold matrix 20 to generate image reproduction data 30 as to whether or not to draw for each dot. On the other hand, in the multi-value dither method shown in FIG. 10, for example, the dot P00 refers to the pattern number of the corresponding dot in the pattern matrix 21 with respect to the input data 10 composed of the gradation data for each dot, and the gradation The table corresponding to the pattern number is referred to from the gamma table 22 showing the correspondence between the pulse width of the laser and the pulse width of the laser drive, and converted to pulse width data corresponding to the gradation data of the dot P00. Therefore, the pattern matrix 21 and the gamma table 22 constitute a conversion table having correspondence between gradation data and image reproduction information.
[0046]
When irradiating each dot with a laser beam, not only binary image reproduction data that does not irradiate the laser beam inside the dot, but also multi-value image reproduction data that indicates which area within the dot is irradiated with the laser beam. By using this, it is possible to reproduce a grayscale image with more gradations. In the multi-value dither method, the halftone processing unit 66 generates the pulse width data of the laser beam as the image reproduction data 30 for each dot by using such a function.
[0047]
An electrophotographic apparatus such as a page printer does not irradiate a beam while scanning a laser beam in a direction perpendicular to the paper feed direction (main scanning direction), and irradiates a part of the area in the scanning direction within the dot. Can be controlled. Therefore, for example, by using 256 types of laser drive pulses, 256 types of latent images can be formed in the scanning direction within the dots.
[0048]
In the pattern matrix 21, eight types of patterns are arranged as shown. Furthermore, 256 types of pulse widths are associated with 256 gradations in the gamma table 22. Moreover, the correspondence between gradation and pulse width is different in each of the eight types of patterns. In the example of FIG. 10, for patterns 1 and 2 of the gamma table 22, pulse widths 0 to 255 are associated with gradations 0 to 63, and gradations 64 to 255 are all related. A pulse width of 255 (irradiating a beam to all the dots) is associated. Therefore, patterns 1 and 2 are dots that are grown even with relatively low gradation values. In the example of FIG. 10, for patterns 3 and 4 of the gamma table 22, a pulse width of 0 is associated with gradations 0 to 63 and a pulse width of gradations 64 to 127 is assigned. 0 to 255 are associated with each other, and a pulse width of 255 is associated with 128 to 255 having a higher gradation. Therefore, the patterns 3 and 4 correspond to dots in a halftone dot that grows for the next higher gradation value than the patterns 1 and 2.
[0049]
Similarly, with respect to the patterns 5 and 6 of the gamma table 22, the pulse width 0 is associated with the gradations 0 to 127, and the pulse width 0 to 255 is associated with the gradations 128 to 191. The pulse width 255 is associated with 192 to 255 having higher gradations. Further, with respect to the patterns 7 and 8 of the gamma table 22, the pulse width 0 corresponds to the gradation 0 to 191, and the pulse width 0 to 255 corresponds to the gradation 192 to 255. Attached. Therefore, the patterns 5 and 6 further correspond to dots that grow slower with respect to the increase in gradation, and the patterns 7 and 8 correspond to dots that grow slower than the latest.
[0050]
When the conversion table based on the multi-value dither method is used, the pattern matrix 21 includes a pattern matrix 21-1 in which the growth nucleus of the halftone dot is located in the center, The pattern matrix 21-2 in which the dot growth nucleus is located at the upper part and the pattern matrix 21-3 in which the dot growth nucleus is located at the lower part are sequentially selected and referred to with a certain regularity. In the arrangement example of the halftone dots shown in FIG. 5, the pattern matrices 21-1, 21-2, 21-1, 21-3 are selected in this order. As a result, the positions of the growth nuclei of the halftone dots as shown in FIG. 5 are regularly shifted.
[0051]
In the case of the example in FIG. 6 as well, three types of pattern matrices in which the positions of the growth nuclei of the halftone dots are center, left, and right are regularly and repeatedly selected. Furthermore, in the case of the example of FIG. 7, five types of pattern matrices are regularly and repeatedly selected. In the case of the example of randomly shifting in FIG. 8, for example, nine types of pattern matrix in which the positions of the growth nuclei of the halftone dots are arranged in the center, top, bottom, left, right, top left, top right, bottom right, bottom left Are randomly selected.
[0052]
The halftone processing unit 66 detects whether or not the gray value is a relatively dark region based on the supplied gradation data. This determination is performed by using an average value of gradation in a predetermined area. If the gray value is a relatively high region, the above-described pattern matrix is repeatedly selected while being regularly changed, and the gradation data is referred to by referring to the gamma table corresponding to the number in the selected pattern matrix. The pulse width data corresponding to is acquired. Then, the pulse width data 30 is supplied to the pulse width modulator 68.
[0053]
FIG. 11 is another configuration diagram of the electrophotographic system. This system configuration example is a modification of the system configuration example shown in FIG. In the system of FIG. 11, the driver 80 installed in the host computer 50 has a rasterization function 54, a color conversion function 64, and a halftone processing function 66. These functions 54, 64, and 66 are the same as the functions having the same reference numbers shown in FIG. Then, image reproduction data (pulse width data) 30 for each color generated by the halftone processing function is supplied to a pulse width modulation section 68 of a controller 62 in an electrophotographic apparatus 60 such as a page printer, and desired drive data. Is converted to 69 and given to the engine 70.
[0054]
In the system example of FIG. 11, color conversion processing and halftone processing are performed by a driver 80 installed on the host computer side. In the example of FIG. 9, it is performed by the controller in the electrophotographic apparatus, but in the example of FIG. 11, it is performed on the host computer 50 side. When the price of the electrophotographic apparatus 60 is required to be reduced, it is required to reduce the price by reducing the capacity of the controller 62. In that case, it is effective to implement some of the functions performed by the controller of FIG. 9 instead using a driver program installed in the host computer. When halftone processing is realized by the driver 80, a storage medium storing a program for causing the computer to execute the above-described halftone processing procedure is built in the host computer 50.
[0055]
【The invention's effect】
As described above, according to the present invention, since the arrangement of the growth nuclei of the halftone dots is shifted, generation of uneven feeding due to uneven rotation of the photosensitive drum or transfer drum in the engine in the electrophotographic apparatus, unevenness due to uneven charging, or uneven transfer occurs. Is suppressed. Accordingly, it is possible to prevent the image quality from being deteriorated due to the conventional unevenness in banding and unevenness.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a binarization method for gradation reproduction of a grayscale image by a dither method.
FIG. 2 is a diagram for explaining a threshold matrix of a dither method.
FIG. 3 is a diagram illustrating a change in the shape of a halftone dot formed using a dither method.
FIG. 4 is a diagram showing the arrangement of halftone dots when the gray value is light and the halftone density is low.
FIG. 5 is a diagram illustrating a halftone dot arrangement example (1) when the gray value is dark and the halftone density is high.
FIG. 6 is a diagram illustrating a halftone dot arrangement example (2) when the gray value is dark and the halftone density is high.
FIG. 7 is a diagram showing a halftone dot arrangement example (3) when the gray value is dark and the halftone density is high.
FIG. 8 is a diagram illustrating an arrangement example (4) of halftone dots when the gray value is dark and the halftone density is high.
FIG. 9 is a configuration diagram of an electrophotographic system.
FIG. 10 is a diagram illustrating an example of a multi-value dither conversion table.
FIG. 11 is another configuration diagram of the electrophotographic system.
FIG. 12 is a diagram showing a transfer paper 1 on which a predetermined image is reproduced by a conventional electrophotographic apparatus.
[Explanation of symbols]
10 input data, gradation data 20 conversion table, threshold matrix 30 image reproduction data, pulse width data 50 host computer 60 controller 66 halftone processing unit 70 engine

Claims (7)

An image is reproduced by expressing gradation by halftone dots formed from a plurality of dots, a beam is scanned in the main scanning direction to form a latent image corresponding to the image on a rotating drum, and the main scanning direction In an electrophotographic image processing apparatus for transferring the latent image to a transfer sheet sent in a vertical sub-scanning direction,
A halftone processing unit that is supplied with gradation data and generates image reproduction data corresponding to the dots based on the gradation data according to a conversion table having a correspondence between the gradation data and the image reproduction information for each dot. Have
The halftone processing unit generates the image reproduction data by randomly shifting the positions of the growth nuclei of the halftone dots arranged in the main scanning direction and the sub-scanning direction. apparatus. In claim 1,
The halftone processing unit sequentially lays out predetermined cells on the supplied gradation data, and has a correspondence between the gradation data specified for each dot in each cell and the image reproduction information. An image processing apparatus for electrophotography , wherein image reproduction data corresponding to the dots is generated with reference to a conversion table . In claim 1 or claim 2 ,
The halftone processing unit shifts the position of the growth nucleus of the halftone dot in the first halftone dot density region, and the halftone processing unit in the second halftone dot density region lower than the first halftone dot density. An electrophotographic image processing apparatus characterized by not shifting a position of a growth nucleus of a point. An image is reproduced by expressing gradation by halftone dots formed from a plurality of dots, a beam is scanned in the main scanning direction to form a latent image corresponding to the image on a rotating drum, and the main scanning direction In an electrophotographic image processing method for transferring the latent image to a transfer sheet sent in a vertical sub-scanning direction,
A halftone processing step of generating image reproduction data corresponding to the dots based on the gradation data in accordance with a conversion table that is supplied with gradation data and has a correspondence between the gradation data and the image reproduction information for each dot. Have
In the halftone processing step, the image reproduction data is generated by randomly shifting the positions of the growth nuclei of the halftone dots arranged in the main scanning direction and the sub-scanning direction. Method. In claim 4,
In the halftone processing step, predetermined cells are sequentially spread over the supplied gradation data, and the gradation data designated for each dot in each cell has a correspondence with the image reproduction information. An image processing method for electrophotography , wherein image reproduction data corresponding to the dots is generated with reference to a conversion table . Used in an electrophotographic apparatus that scans a beam in the main scanning direction to form a latent image corresponding to an image on a rotating drum and transfers the latent image to a transfer sheet that is sent in a sub-scanning direction perpendicular to the main scanning direction. In a recording medium on which an image processing program for causing a computer to execute an image processing procedure for reproducing an image by expressing gradation by halftone dots formed from a plurality of dots,
The image processing procedure includes:
A halftone processing procedure for generating image reproduction data corresponding to the dots based on the gradation data in accordance with a conversion table that is supplied with gradation data and has a correspondence between the gradation data and the image reproduction information for each dot. Have
Recording the image processing program, wherein the halftone processing procedure generates the image reproduction data by randomly shifting the growth nucleus positions of the halftone dots arranged in the main scanning direction and the sub-scanning direction. Recording medium. In claim 6,
In the halftone processing procedure, predetermined cells are sequentially spread over the supplied gradation data, and the gradation data designated for each dot in each cell has a correspondence with the image reproduction information. A recording medium recording an image processing program , wherein image reproduction data corresponding to the dots is generated with reference to a conversion table .

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