JPH11348353A - Color printer and color image printing method - Google Patents

Abstract

(57) [Summary] [Problem] To improve print quality, improve print speed, save memory, and simplify control during high-resolution printing. SOLUTION: One page of an image of each color of CMYK is divided into a plurality of portions, and each portion is individually exposed and developed. To improve the image quality, at least C and M
C, mask regions 49 randomly distributed in 47M
Is set, exposure and development of the mask area 49 are performed first,
Next, exposure and development of the non-mask area 51 are performed. In order to improve the printing speed, printing is started when a predetermined number of bands have been developed, even if not all of the one-page image has been developed,
The developed band is exposed and developed at one time, and the band not developed in time is exposed and developed at a subsequent time. In order to save memory, the image is divided into a plurality of bands, and development, exposure, and development are performed for each band. In order to simplify control during high-resolution printing, odd-numbered rasters and even-numbered rasters are separately exposed and developed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color printer using an electrophotographic system and a method for printing a color image.

[0002]

2. Description of the Related Art An electrophotographic color printer repeats a process of exposing an image and developing a toner and transferring a toner image formed on a photoreceptor to paper for four CMYK colors. This process is classified into a multiple transfer system and a multiple development system depending on how the CMYK toner images are superimposed. In the multiple transfer system, each color toner image is sequentially transferred to paper (or an intermediate transfer body) and superimposed at the time of transfer. In the multiple development method, a four-color toner image is superimposed directly on a photoconductor,
Transfer to paper at once.

[0003]

In this process, the overlapping position of the toner images may be shifted due to mechanical causes such as vibration of the developing device and fluctuations in the feed amount of the paper feeding device. Then, streak-like noises such as banding and jitter appear in the print image, and the print quality deteriorates.

In the image exposure, each color plane of an image for one page is drawn on a photosensitive member by a raster scan method. For this reason, printing cannot be started until the image of the entire page has been bit-mapped into the memory in advance.
This is a problem in printing speed. In addition, a large amount of memory is required especially for a printer corresponding to a large sheet such as an A3 sheet.

When the resolution of an image is different, the interval between rasters is different. Therefore, it is necessary to change the speed or distance of vertical scanning at the time of image exposure for each resolution.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to reduce streak-like noise on a printed image due to a shift in the overlapping position of a toner image, and to improve print quality.

Another object of the present invention is to improve printing speed by enabling printing to start only when an image of a part of one page is developed.

It is still another object of the present invention to save memory by enabling printing to be performed only by developing an image of a part of one page.

Yet another object of the present invention is to simplify the control of the apparatus by allowing the same vertical scan speed or spacing to be used when printing high resolution images as when printing low resolution images. Is to do.

[0010]

A color printer according to the present invention receives dot information of each of a plurality of color images forming a color image, draws the plurality of color images by electrophotography, and superimposes the plurality of color images on the color image. A print engine for generating an image, each of the plurality of color images constituting the color image is expanded into bitmap data on a memory, and the expanded plurality of color bitmap data is read from the memory and converted into dot information for printing. An image processing circuit for supplying the image processing circuit to the engine. The image processing circuit divides at least one color image of the plurality of color images into a plurality (N) of parts, and divides the N pieces of bitmap data into two or more drawing cycles of the print engine. And converts it into dot information and sends it to the print engine. This causes the print engine to operate at least one of the color images.
A color image is drawn in two or more drawing cycles.

According to this color printer, the above object can be achieved by arranging the way of dividing an image, the way of developing a bitmap, and the way of transferring a bitmap image to a print engine.

For example, if it is desired to improve the print quality by reducing noise due to the shift of the overlapping position of the toner images caused by mechanical vibration of the engine or the like, the image processing circuit is provided with (1) at least one color. Is divided into a mask area distributed in the image and a non-mask area other than the mask area. (2) The bitmap data of the mask area is converted into dot information in the first drawing cycle. (3) In the second drawing cycle, the bitmap data in the non-mask area is converted into dot information and sent to the print engine.

If it is desired to start printing only by developing an image of a part of one page and to increase the printing speed, an image processing circuit is provided to provide (1) a plurality of color images. (2) Develop bitmap data of one band selected from a plurality of bands using a memory area necessary for bitmap data development of one band of memory, and (3) at least one color Using one drawing cycle, the bit map data of the selected one band is read from the memory area, converted into dot information, and sent to the print engine. (4) The bit map data of the selected one band is At a location in the memory area that has already been read, expand the bitmap data of the selected other band, and (5) repeat the above (2) and (3) for all of the plurality of bands. It is possible to perform the work.

If it is desired to save the memory by making it possible to execute printing only by developing an image of a part of one page, an image processing circuit is provided to (1) convert a color image into a plurality of bands. (2) The plurality of bands are sequentially developed into bitmap data, and (3) After the development of the bitmap data of a predetermined number of bands is completed, all of the developed The bitmap data of the first color of the band is converted into dot information and sent to the print engine. (4) If there is a band that has not been developed yet while performing the above (3), The bitmap data of the first color of the band not yet finished is converted into dot information in another subsequent drawing cycle and sent to the print engine, and (5) the (3) and (4) are (6) After the above (5) For all of the plurality of bands, and sends the print engine f converts other color bit map data to the dot information, being able to perform the operation.

In order to simplify the control of the apparatus when printing at a resolution N times higher than the normal resolution, an image processing circuit is provided to (1) divide the color image by the raster number N. When the remainder is 0, 1,..., N−1, the data is divided into N fields. (2) The bitmap data of the N fields are mutually interpolated in different drawing cycles. It is possible to perform an operation of shifting the timing so as to perform a race, converting the dot information into dot information, and sending the dot information to the print engine.

By the way, the processing of the image processing circuit, particularly concerning division of an image, bitmap development, transfer control of bitmap data to an engine, and the like can be performed using a computer. The computer program for that can be loaded or installed on the computer through various means such as a semiconductor memory, a disk-type storage device, and a communication line.

[0017]

FIG. 1 is a sectional view showing a mechanical configuration of a print engine of an electrophotographic color printer according to an embodiment of the present invention.

The print engine 1 is a type of the multiple transfer system, and a laser scanner 5 and developing devices 7Y, 7M, 7C, 7 for four colors of YMCK are applied to a photosensitive drum 3.
K and an intermediate transfer belt 9 are provided. The intermediate transfer belt 9 contacts a sheet passing through the sheet path 11.

Each of the developing units 7Y, 7
M, 7C and 7K are selectively set in order. Conventionally, exposure and development of an image for one color of one page on the photosensitive drum 3 are performed by one rotation of the intermediate transfer belt 9 (hereinafter, exposing and developing to form a toner image is referred to as “drawing”). One rotation of the intermediate transfer belt 9 is referred to as “drawing cycle”). However, in this embodiment, the one-color image of one page is divided into a plurality of (N) parts, and each part is drawn in one drawing cycle, that is, the one-color image of one page is drawn a plurality of (N) times. Draw in a cycle. For example, when N = 2, in the first drawing cycle, only a predetermined portion of the one-color image of one page is drawn, the toner image is transferred to the intermediate transfer belt 9, and the remaining portion is transferred in the next drawing cycle. The image is drawn, and the toner image is transferred to the intermediate transfer belt 9. Therefore, N × 4 drawing cycles are performed until all the four color toner images of one page have been transferred to the intermediate transfer belt 9. The four color toner images are superimposed on the intermediate transfer belt 9, and the color image completed in this way is transferred onto the paper entering from the paper path 11 at one time.

FIG. 2 shows a functional configuration of the image processing circuit of the present embodiment using the print engine 1.

The controller 21 performs bitmap expansion of an image and controls the entire image processing circuit. The details of the processing operation will be described later. In the memory 23, an image to be printed is first bit-mapped (rasterized) by the controller 21.
The bitmap image data is transferred to the next mask circuit 25 in the raster scan order by DMA transfer.

The mask circuit 25 is used when a one-color image of one page is drawn in N = 2 drawing cycles, and converts each page of color image data transferred from the memory 23 in raster scan order. And has a function of selectively passing a region to be drawn in the first cycle (called a mask region) and a region to be drawn in the second cycle (called a non-mask region). To fulfill this function,
It has a mask matrix table 27 indicating the location of the mask area in one page. As detailed below,
The mask circuit 27 is used for eliminating jitter and banding caused by mechanical vibration of the printer engine 1 when printing a high-quality image.

The image data that has passed through the mask circuit 25 is
It is sent to the halftoning circuit 29. At this stage, the image data is pixel density data indicating the density of one pixel per color, for example, by an 8-bit word. The halftoning circuit 29 converts the transferred pixel density data into dot data representing dots of toner to be attached to paper. Various methods such as an error diffusion method and a dither method are known for the halftoning process, and any method can be used. However, in an electrophotographic color printer, a regular concentrated dot type dither method (halftone dot method, screen method) in which dots are regularly grown with an increase in pixel density is preferably used due to the nature of toner. So
Also in the present embodiment, a configuration using this screen method is representatively shown. That is, the screen processing circuit 31
Converts the pixel density data into dot pattern data using the dither threshold matrix stored in the dither matrix table 33.

The dot data output from the halftone processing circuit 29 is then sent to a PWM circuit 35. PW
The M circuit 35 generates a laser beam modulation pulse modulated to a pulse width corresponding to the dot size indicated by the dot data, and sends the pulse to the laser scanner 5 of the printer engine 1. The laser scanner 5 uses the pulses to modulate the exposure laser beam, thereby exposing a dot image on the surface of the photosensitive drum 3.

FIG. 3 shows a dither matrix table 33.
2 shows an example of a dither threshold matrix stored in the table.

In FIG. 3, reference numeral 43 is an example of a dither threshold matrix, which has a size of 5 pixels × 5 pixels in this example. This dither threshold matrix 4
3 is repeatedly applied on the image 41 of one page like a tile. This dither threshold matrix 43
Uses a cross-shaped screen cell as indicated by reference numeral 45. The number given to each pixel (each square area) in the screen cell 45 indicates the order in which the dots grow as the density increases (actually,
The dots grow in a plurality of stages in each pixel, but for the sake of simplicity, the detailed order of growth is not shown).

FIG. 4 shows an example of a suitable mask matrix when the dither threshold matrix as shown in FIG. 3 is used.

In FIG. 4, reference numeral 47C denotes a mask matrix applied to the C image, which corresponds to the size of the image 41 of one page shown in FIG. Correspond to the regions of the individual dither threshold matrices 43 shown in FIG. The square area 49 shown by hatching is a mask area, and the area 51 shown by white is a non-mask area. The mask area 49 is composed of an area of a dither threshold matrix selected at random from an image area of one page as shown in the figure. The same applies to the mask matrices 47M, 47Y, and 47K for MYK. Mask matrices 47C, 47M, 47Y, 47K for these four colors
As shown in the figure, the arrangement of the mask region 49 differs for each color.

FIG. 5 shows an example of another suitable mask matrix.

FIG. 5 shows a mask matrix 53 for C.
C is shown as a representative. This mask matrix 53
3 also corresponds to the area of the one-page image 41 shown in FIG. 3, and the individual cross-shaped areas therein correspond to the individual screen cells 45 applied to the one-page image 41 and are indicated by hatching. The mask region 55 is constituted by a region of the screen cell 45 selected at random. Although not shown, mask matrices for other colors have the same configuration. The arrangement of the mask area 55 in the mask matrix differs for each color.

As described above, the drawing and transfer of a one-page one-color image are divided into a mask area and a non-mask area.
This is performed in the drawing cycle. Therefore, when the mask matrices shown in FIGS. 4 and 5 are used, even if the color overlap position is shifted due to mechanical vibration or the like during drawing and transfer, the position shift does not appear on the entire page, and Appearing at randomly distributed locations in the image, image noise due to the displacement becomes inconspicuous to human eyes, and image quality is improved.

Note that a common mask area (that is, a common mask matrix) may be applied to all colors without changing the mask area for each color. Even in this case, if the mask areas are randomly distributed within the page, the noise due to the color misalignment is randomly distributed within the page, so that the image quality is improved. Further, the mask areas in the mask matrix may be regularly dispersed in the page, not randomly. Even in such a case, noise due to color misregistration is dispersed in the page, so that the image quality is also improved.

Also, the mask matrix is applied only for colors having a large influence of the color overlay position shift, such as C or M, and the drawing is performed in two drawing cycles. May be drawn in the drawing cycle. Even in such a case, compared to the case where all colors are drawn in two drawing cycles, image quality comparable to that obtained when printing is performed, and the printing time is shortened. The processing of FIG. 6 described below is based on a method using two drawing cycles only for C and M. When this method is used, a mask matrix for Y or K is naturally unnecessary.

FIG. 6 is a flowchart showing a processing flow of the controller 21 shown in FIG. 2 (and a flow of operations of each unit executed thereby).

To start printing an image, first, the image quality mode selected by the user is determined (step S).
1) If the high image quality mode is selected, step S
The process proceeds to step S2, and if the normal image quality mode is selected, the process proceeds to step S21.

In the high image quality mode, the mask mode is set in step S2, that is, the mask circuit 25 shown in FIG. 2 is enabled so that only the image data in the mask area is passed. Then, the developing device 7C for the first color, for example, C, is set on the photosensitive drum 3 (S3). The print engine 1 issues a vertical synchronizing signal (Vsync) every time the intermediate transfer belt 9 makes one rotation (that is, at the start of each drawing cycle). The operation of reading the image data of one page C and transferring it to the mask circuit 25 is started. The mask circuit 25 passes only the C image data corresponding to the mask area defined by the mask matrix for C, and discards the image data of the non-mask area (that is,
to null data). The C image data of the mask area that has passed through the mask circuit 25 is
Then, the image data is processed by the PWM circuit 35 and given to the laser scanner 5 of the print engine 1, which draws a latent image of the C image of the mask area on the photosensitive drum 3, and develops it by the developing unit 7C (S4). The C toner image in the mask area thus developed is transferred to the intermediate transfer belt 9 (S5).

When the intermediate transfer belt 9 makes exactly one revolution,
Since the next vertical synchronizing signal is issued, the image of C is transferred to the mask circuit 25 again in response to this. At this time, the mask circuit 25 passes only the image data of an area (non-mask area) other than the mask area defined by the mask matrix for C. Thus, the C image of the non-mask area is drawn on the photosensitive drum 3 (S6). The formed C toner image in the non-mask area is transferred to the intermediate transfer belt 9 (S7).

When the drawing of the C image of the non-mask area is completed,
The developing device 7M for the next color, for example, M, is set on the photosensitive drum 3 (S8). Subsequently, in response to a vertical synchronization signal indicating the start of the next drawing cycle, transfer of the M image data from the memory 23 to the mask circuit 25 is started. At this time, the mask circuit 25 passes only the M image data of the mask area defined by the M mask matrix. Therefore, the engine 1 performs drawing and transfer of the M image in the M mask area (S9, S10). Thereafter, drawing and transfer of an image of the M non-mask area are performed (S11, S12).

Thereafter, the Y developing unit 7Y is set to draw and transfer the Y image (S13 to S15), and then the K developing unit 7K is set to draw and transfer the K image (S13).
16-S18). With respect to the Y image and the K image, the mask circuit 25 is invalidated (complete through state), and one page image of each color is drawn and transferred in one drawing cycle. Processing may be performed in two drawing cycles separately for the region and the non-mask region.

In the above process, the four-color image of one page is superimposed on the intermediate transfer belt 9 to complete the color image. Subsequently, the paper is supplied, the color image is transferred to the paper (S19), and the transferred paper is passed through a fixing device (not shown) to fix the color image and then discharged (S20).

On the other hand, in the normal image quality mode, first, the mask mode is reset, that is, the mask circuit 25 is invalidated (S21), and then the C developing device 7C is set (S2).
2) The transfer of the C image from the memory 23 is started in accordance with the vertical synchronizing signal, and one page of C is written in one drawing cycle.
The image is drawn and transferred (S23, S24). continue,
The M image, the Y image, and the K image are sequentially drawn and transferred in one drawing cycle, respectively (S25 to S33). Thereafter, the process proceeds to step S19 to transfer the completed color image to a sheet, fix the image, and then discharge the sheet (S20).

According to the above operation, in the high image quality mode, noise called banding or jitter due to mechanical vibration of the print engine 1 becomes inconspicuous and print quality is improved.

Next, another print control process performed by the controller 21 for the main purpose of saving memory in this embodiment will be described.

In the control processing for the purpose of saving the memory, as shown in FIG. 7, the image 61 of one page is divided into two bands of the first half 63A and the second half 63B along the center raster line, The drawing and transfer of the part 63A and the latter part 63B are performed in different drawing cycles. FIG.
Shows the flow of the control process (and the operation of each unit by the control process). In this process, the mask circuit 25 in FIG. 2 is invalidated (complete through state) (mask circuit 2).
5 can be enabled and combined with the high-quality mode processing described above, but the processing becomes too complicated.
Not described here).

First, only the first half 63A of a one-page image is bitmap-developed in the memory 23 (S41). Next, the C developing device 7C is set on the photosensitive drum 3 (S4).
2) In response to the vertical synchronizing signal from the printer engine 1, the C image data of the first half 63A developed in the memory 23 is transferred to the halftone processing circuit 29, and the engine 1
Performs drawing and transfer of the C image of the first half 63A (S
43, S44). Next, the M developing device 7C is connected to the photosensitive drum 3
(S45), the transfer of the M image data of the first half 63A is started in response to the next vertical synchronization signal, and the drawing and transfer of the M image of the first half 63A are performed (S46, S4).
7). Next, similarly, the drawing and transfer of the Y image of the first half 63A (S48 to S50),
The K image of A is drawn and transferred (S51 to S53).

In the above process, the CMYK of the first half 63A
In parallel with the operation of reading and transferring the image data from the memory 23, the color image data of the latter half 63B is overwritten by bitmap development in the memory area of each color image data which has already been transferred and becomes unnecessary. I will do it. As a result, when all the image data of the first half 643A has been transferred, the image data of the second half 63B is completely expanded in the memory 23 (S54).

Subsequently, drawing and transfer are performed in the same manner in the order of the C image, the M image, the Y image, and the K image for the second half 63B (S55 to S66). In this process, the start timing of the operation of transferring and drawing each color image data of the second half 63B from the memory 23 is delayed by a time corresponding to the first half 63A from the time when the vertical synchronization signal is received. As a result, the second half portion 63B is transferred on the intermediate transfer belt 9 to a position subsequent to the first half portion 63A previously transferred, and a one-page image is completed.

When an image of one page is completed on the intermediate transfer belt 9 in this way, although not shown in FIG. 8, transfer to the sheet and fixing in steps S19 and S20 in FIG. 6 are performed.

According to the above-described control, the memory 23 uses only a half area of one page as an area for image development, so that memory is saved. In addition, printing can be started at the stage when half the image of one page has been developed, so that the printing time is shortened accordingly. One page image may be divided into three or more bands along a raster line, and image development and drawing may be performed for each band.

Next, another printing control process performed by the controller 21 for the main purpose of high-speed printing in the present embodiment will be described.

In the control processing for the purpose of high-speed printing,
As shown in FIG. 9, the image 61 of one page is divided into a number of bands 65 along a raster line, and a predetermined number of bands 65
The transfer of the Y image is started at the stage when the image data has been developed in the memory 23, and the already developed bands are combined and drawn and transferred in one drawing cycle. FIG. 9 shows a flow of the control process (and the operation of each unit thereby).
In this process, the mask circuit 25 shown in FIG. 2 is invalidated. (It is possible to enable the mask circuit 25 and combine it with the above-described high image quality mode process. However, the process becomes too complicated and the printing speed is reduced. It is not effective because it will fall).

First, when a predetermined number of one page, for example, the first three bands 65 are developed into a bit map (S71), the Y developing unit 7Y is set on the photosensitive drum 3 (S72), and the printer engine is operated. In response to the vertical synchronizing signal from the first band 1, the Y band image data of the first band 65 expanded in the memory 23 is transferred to the halftone processing circuit 29, and the Y image of the first three bands 65 is drawn by the engine 1. Perform (S73). In parallel with this drawing processing, the fourth and subsequent bands are also developed in the memory 23. At the stage immediately before the transfer of the Y image of the third band from the memory 23 is completed, it is checked whether or not the next fourth band has been developed in the memory 23 (S74). Simultaneously with the completion of the transfer of the third band, the transfer of the Y image of the fourth band is started, and the drawing process of the Y image of the fourth band is continuously performed (S75). In addition, the fourth band Y
Immediately before the image transfer is completed, it is checked whether or not the fifth band has already been developed (S74). If it has been completed, the drawing process of the fifth band is also performed (S75). In this way, the developed Y images of the band are continuously transferred and drawn in one drawing cycle.

Normally, since the image development to the memory 23 proceeds faster than the rendering processing by the engine 1, it is necessary to continuously render one page of the Y image from the first to the last band in one rendering cycle. Can be. However, the image development may be delayed from the drawing process and the next band may not be developed at the stage of step S74. In this case, in this drawing cycle, the transfer and drawing of the next band are abandoned, and the next band is waited until the next drawing cycle comes. After the development of the next band is completed, the transfer of the Y images of all the developed bands is restarted from the first band in response to the vertical synchronization signal indicating the start of the next drawing cycle.
Then, the transfer data of the band already drawn is invalid (n
(Ul), drawing is performed, and only the transfer data of the next band, which gave up drawing earlier, is regarded as valid (S7).
6).

The above operation is repeated until the last band (S
77) As a result, the photosensitive drum 3 of the Y image of one page
Is completed. Subsequently, the one-page Y image is transferred to the intermediate transfer belt 9 (S78).

At this stage, since the development of the image of one page has already been completed, the K image, C image,
The M images are sequentially drawn in a single drawing cycle as in the related art, and transferred to the intermediate transfer belt 9 (S79 to S8).
7). When an image of one page is completed on the intermediate transfer belt 9 in this way, the image is transferred to paper and fixed (S
88, S89).

With the above control, printing can be started when the first three bands have been developed, so that the printing time is reduced. Printing can be started when the first band has been developed, but this increases the probability that a situation will occur in which band development in the middle cannot be made in time, and the process proceeds to step S76 to delay printing. for that reason,
It is considered that it is better to start printing after the development of a plurality of appropriate bands (three bands are an example) in order to allow a certain margin at first as in the above control. In the above control, the Y image is first processed. The reason for this is that when the process proceeds to step S76, there is a possibility that misalignment noise may occur at the joint between bands, so that the noise is made most inconspicuous. For this reason, human eyes chose Y, which is the least sensitive.

Next, another print control process performed by the controller 21 for the purpose of high resolution in the present embodiment will be described.

As shown in FIG.
Comparing the dpi image 71 with an image 81 having twice the resolution of 1200 dpi, one raster 73 of the 600 dpi image corresponds to two rasters 83 and 85 of the 1200 dpi image 81, respectively. Therefore, the 600 dpi image 71
When printing a 1200 dpi image 81, one page is divided into two fields of an odd field consisting of an odd raster 83 and an even field consisting of an even raster 85. Each raster is sequentially drawn for each field.
FIG. 12 shows the flow of the control process (and the operation of each unit thereby). The mask circuit 25 of FIG. 2 is not used in this process.

To start printing an image, the resolution of the image to be printed is first determined (step S91).
If the resolution is high (for example, 1200 dpi), step S9
The process proceeds to step S114 if the resolution is normal (for example, 600 dpi).

In the high resolution mode, first, 1200 dp
The bitmap image of one page i is developed in the memory 23 (S92). Then, the C developing device 7C is connected to the photosensitive drum 3
(S93), and when a vertical synchronizing signal is received from the print engine 1, the C image data of the odd raster is sequentially read out from the memory 23 at the same time as the raster time in the normal resolution mode (600 dpi) and transferred. The engine 1 draws an odd-numbered field C image on the photosensitive drum 3 (S94) and transfers it to the intermediate transfer belt 9 (S95).

Subsequently, when the next vertical synchronizing signal arrives, the timing is delayed by a half raster time in the normal resolution mode of 600 dpi, and the C image data of the even raster is read from the memory 23 at the same speed as that of the odd raster. The image data is sequentially read and transferred, and the C image of the even field is drawn on the photosensitive drum 3 by the print engine 1 (S96), and is transferred to the intermediate transfer belt 9 (S97). As a result, on the intermediate transfer belt 9, the odd-numbered field C image is interlaced with the even-numbered field C image, and a one-page C image is completed.

Hereinafter, the M image, the Y image, and the K image are sequentially
The odd fields are drawn and transferred in the order of the previous drawing cycle, and the even fields are drawn and transferred in the order of the next drawing cycle (S98 to S111). When the image of one page is completed on the intermediate transfer belt 9 in this way, the image is transferred to a sheet (S112) and fixed (S113).

On the other hand, in the normal resolution mode,
The 0 dpi bitmap image is developed in the memory 23 (S
114) The C image, M image, Y image, and K image of one page are sequentially drawn and transferred in a single drawing cycle as before (S115 to S126), and when the image is completed on the intermediate transfer belt 9, This is transferred to paper (S11
2), fixation (S113).

By the above operation, the speed of the electrophotographic process becomes the same in both the high resolution mode and the normal resolution mode, so that the driving of the process is simplified and the accuracy is increased.
Although the case where the high resolution is twice the normal resolution has been described as an example, if this is generally described, when printing at a high resolution N times the normal resolution, the remainder obtained by dividing the raster number by N is used. Divides the image into N fields of 1, 2,..., N-1, 0, respectively, and performs drawing and transfer for each field. By using N raster times, those field images may be interlaced at the time of transfer.

Although the embodiment of the present invention using the multi-transfer type print engine has been described above, the present invention can be applied to the case where other types of printer engines are used. For example, one using a photoreceptor belt instead of a photoreceptor drum or L instead of a laser scanner
The present invention can be applied to an apparatus using an ED scanner. Further, the engine of the above embodiment is of a type called an intermediate transfer system among the multiple transfer systems, but the present invention can also be applied to other types of engines in the multiple transfer system as exemplified in FIG. FIG. 13A shows a type called a transfer drum method among multiple transfer methods.
(B) is a type called a tandem system.

In the transfer drum type engine shown in FIG. 13A, the paper entering from the paper passage 11 is once wound around the transfer drum 91, and the transfer drum 91 is sequentially rotated on the photosensitive drum 3 while being repeatedly rotated. The drawn four color toner images are sequentially transferred to paper. According to the present invention, this engine can also divide a one-page one-color image into a plurality of portions, individually draw and transfer them to paper.

In the tandem type engine shown in FIG. 13B, a drawing unit such as a photosensitive drum 3, a laser scanner 5, and a developing unit 7 is provided independently for each color. The drawing unit transfers the four color toner images onto the sheet passing through the sheet path 11. Also in this engine, by adding a loop-shaped paper path 93 so that the paper can be repeatedly passed through the drawing unit, a one-color image of one page is divided into a plurality of parts according to the present invention and drawn individually to form a paper. Can be transcribed.

Further, the present invention can be applied to an engine of a multiple development system as exemplified in FIG. 14 (A)
Is a type called a multi-rotation method among multiple development methods, and FIG. 14B is a type called a one-pass method.

The engine of the multiple developing system shown in FIG.
The color images are sequentially drawn on the photosensitive drum 3 and are superimposed on the photosensitive drum 3, and thereafter, are collectively transferred to paper. According to the present invention, this engine can also divide a one-page one-color image into a plurality of parts and draw each part individually.

The one-pass type engine shown in FIG. 14B has a drawing unit such as a laser scanner 5 and a developing unit 7 each of which is independent of the four colors around the photosensitive drum 3. During one rotation, drawing of four colors is performed simultaneously. According to the present invention, the one-color image of one page can be divided into a plurality of portions and each portion can be individually drawn each time the photosensitive drum 3 is used.

The embodiments of the present invention have been described above. However, the above embodiments are merely examples for describing the present invention, and are not intended to limit the present invention to only these embodiments. Therefore, the present invention can be implemented in various forms other than the above-described embodiment.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a mechanical configuration of a print engine of an electrophotographic color printer according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a functional configuration of the image processing circuit according to the embodiment.

FIG. 3 is an explanatory diagram showing an example of a dither threshold matrix stored in a dither matrix table 33.

FIG. 4 is an explanatory diagram showing an example of a suitable mask region when the dither threshold matrix shown in FIG. 3 is used.

FIG. 5 is an explanatory diagram showing an example of another suitable mask matrix.

FIG. 6 is a flowchart illustrating control of a controller 21 for high-quality printing and operation of each unit.

FIG. 7 is an explanatory diagram showing how to divide one page by a control process for saving memory.

FIG. 8 is a flowchart showing the control of the controller 21 for saving memory and the operation of each unit.

FIG. 9 is an explanatory diagram showing how to divide one page by a control process for high-speed printing.

FIG. 10 is a flowchart illustrating control of a controller 21 for high-speed printing and operation of each unit.

FIG. 11 is an explanatory diagram showing how to divide one page by a control process for printing at different resolutions.

FIG. 12: Controller 2 for printing at different resolutions
1 is a flowchart showing the control of FIG. 1 and the operation of each unit.

FIG. 13 is a cross-sectional view illustrating a configuration example of another print engine to which the present invention can be applied.

FIG. 14 is a cross-sectional view illustrating a configuration example of still another print engine to which the present invention can be applied.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 print engine 3 photosensitive drum 5 laser scanner 7 developing device 9 intermediate transfer belt 11 paper path 21 controller 23 memory 25 mask circuit 27 mask matrix table 29 halftone processing circuit 31 screen processing circuit 33 dither matrix table 35 PWM circuit 41, 6171 , 81 One-page image 43 Dither threshold matrix 45 Screen cell 47, 53 Mask matrix 49, 55 Mask area 51, 57 Non-mask area 63A Upper half of one-page image 63B Lower half of one-page image 65 Band 73 Raster 83 Odd raster 85 Even raster

Claims (16)

[Claims] 1. A print engine which receives dot information of each of a plurality of color images forming a color image, draws the plurality of color images by electrophotography and superimposes them to generate the color image, and has a memory. And developing each of the plurality of color images constituting the color image into bitmap data on the memory,
An image processing circuit that reads out the expanded plurality of color bitmap data from the memory, converts the bitmap data into the dot information, and supplies the dot information to the print engine. Is divided into a plurality of (N) portions, and the N
The bitmap data of each part is divided into two or more drawing cycles of the print engine, converted into dot information, and sent to the print engine. A color printer which draws a single color image in two or more drawing cycles. 2. The image processing circuit according to claim 1, wherein the image processing circuit comprises: (1) a mask region in which at least one color image is dispersedly arranged in the image; and a non-mask region other than the mask region. (2) The bitmap data of the mask area is converted to dot information in the first drawing cycle and sent to the print engine. (3) The bitmap of the non-mask area is converted in the second drawing cycle. A color printer that converts data into dot information and sends it to the print engine. 3. The image processing circuit according to claim 2, wherein the plurality of colors are CMYK, and the image processing circuit divides each color image into the mask area and the non-mask area at least for each of C and M. A color printer for sending dot information of the mask area and the non-mask area to the print engine in the first and second drawing cycles, respectively. 4. The color printer according to claim 2, wherein the mask areas are randomly distributed in the image. 5. The color printer according to claim 2, wherein an arrangement of the mask area is different for each color. 6. The image processing circuit according to claim 2, wherein the image processing circuit converts the bitmap data into the dot information using a dither threshold matrix, and the mask area is tiled on the image. A color printer comprising a large number of distributed dither threshold matrix corresponding areas selected from among the dither threshold matrix corresponding areas spread all over the area. 7. The image processing apparatus according to claim 2, wherein the image processing circuit converts the bitmap data into the dot information using a screen cell, and the mask area is tiled on the image. A color printer composed of a large number of screen cell corresponding areas distributed and selected from among the screen cell corresponding areas. 8. The memory according to claim 1, wherein the image processing circuit (1) divides the color image into a plurality of bands, and (2) a memory required for bitmap data development of one band in the memory. Using a region, develop bitmap data of one band selected from the plurality of bands, and (3) convert bitmap data of the selected one band using at least one drawing cycle for at least one color. Read from the memory area, convert it to dot information, and send it to the print engine. (4) At the location in the memory area where the bitmap data of the selected one band has already been read, another selected band is stored. (5) A color printer, wherein (5) the above (2) and (3) are repeated for all of the plurality of bands. 9. The image processing circuit according to claim 1, wherein the image processing circuit (1) divides the color image into a plurality of bands, and (2) sequentially converts the plurality of bands of the color image into bitmap data. (3) After the bitmap data of a predetermined number of bands have been expanded, the bitmap data of the first color of all the expanded bands is converted into dot information in one drawing cycle. (4) If there is a band that has not been developed yet while performing (3), the bitmap data of the first color of the band that has not been developed Is converted to dot information in another subsequent drawing cycle and sent to the print engine, (5) performing (3) and (4) for all of the plurality of bands, and (6) performing (5) Later, for all of the plurality of bands, A color printer which converts the bitmap data of the color of (1) into dot information and sends it to the print engine. 10. The image processing circuit according to claim 1, wherein the image processing circuit converts the color image into a normal resolution image.
When printing at twice the high resolution, (1) the color image is divided into N fields where the remainder when the raster number is divided by N is 0, 1, ..., N-1, respectively. 2) A color printer which converts the bitmap data of the N fields into dot information at different drawing cycles at different timings so as to interlace with each other and sends the dot information to the print engine. 11. A print engine that receives dot information of each of a plurality of color images constituting a color image, draws the plurality of color images by electrophotography, and superimposes the plurality of color images to generate the color image. A method of printing an image, comprising: (1) a dividing step of dividing at least one color image of a plurality of color images constituting the color image into a plurality (N) of parts; And (3) converting the bitmap data of the N parts of the at least one color image into two or more drawing cycles of the print engine. Separately converting the dot information into dot information and sending the dot information to the print engine.
A method of printing a color image, wherein the print engine causes at least one color image included in the color image to be drawn in two or more drawing cycles. 12. The method according to claim 11, wherein: (1) in the dividing step, an image of at least one color is divided into a mask region distributed in the image and a non-mask region other than the mask region. (2) In the transfer step, (2-1) the bitmap data of the mask area is converted into dot information in the first drawing cycle and sent to the print engine, and (2-2) the second The bitmap data of the non-mask area is converted into dot information and sent to the print engine in the drawing cycle. 13. The method according to claim 11, wherein (1) in the dividing step, the color image is divided into a plurality of bands; and (2) in the expanding step, bitmap data of one band in the memory is expanded. The bitmap data of one band selected from the plurality of bands is developed by using a memory area necessary for (3). (3) In the transfer step, the selection is performed using at least one drawing cycle for one color. The bitmap data of one band is read out from the memory area, converted into dot information, and sent to the print engine. (4) In the expansion process, the bitmap data of the selected one band has already been read out. The bitmap data of another selected band is developed at a location in the memory area, and (5) The steps (2) and (3) are repeated for all of the plurality of bands. Printing method of color image. 14. The method according to claim 11, wherein: (1) the dividing step divides the color image into a plurality of bands; and (2) the developing step sequentially divides the plurality of bands of the color image. (3) In the transfer process, (3-1) after the development of the bitmap data of a predetermined number of bands is completed, in one drawing cycle, all the developed bands are The bitmap data of the first color is converted to dot information and sent to the print engine. (3-2) When there is a band that has not been developed yet while performing the above (3-1) Converting the bitmap data of the first color of the band that has not been developed into dot information in another subsequent drawing cycle and sending it to the print engine; (3-3) the (3-1) Performing (3-2) for all of the plurality of bands, (3-4) After (3-3), for all of the plurality of bands, a color image printing method in which bitmap data of another color is converted into dot information and sent to the print engine. 15. The method according to claim 11, wherein the color image is printed at a high resolution N times the normal resolution. (1) In the dividing step, the color image is divided by a raster number N. The remainder of the time is 0, 1, ..., N-1
(2) In the transfer step, the bitmap data of the N fields is shifted in timing so as to interlace each other in different drawing cycles, A method for printing a color image, which is converted into dot information and sent to the print engine. 16. The color image forming apparatus according to claim 1, further comprising: receiving a dot information of each of the plurality of color images forming the color image; A method of printing an image, comprising: (1) a dividing step of dividing at least one color image of a plurality of color images constituting the color image into a plurality (N) of parts; And (3) rendering the bitmap data of the N portions of the at least one color image on the memory at least twice by the print engine. Controlling the transfer of the bitmap data from the memory to convert the bitmap data into dot information and send it to the print engine. A computer-readable program storing a program for causing a computer to execute a method of printing a color image, wherein the program causes the computer to draw at least one color image included in the color image in two or more drawing cycles. recoding media.