JP2011088385A - Image processor, control method and program thereof - Google Patents

Abstract

In electrophotographic image output, toner scattering is likely to occur depending on the amount of applied toner of the image, the image output environment, the conveyance speed of the printing paper, the physical properties of the printing paper, and the like. In order to reduce toner scattering, processing such as thinning out some dots of the image is performed. However, this processing is likely to cause image deterioration, and the image information is deteriorated conversely in an image in which scattering and tailing do not occur. There is a fear.
An image data is compared with a predetermined image pattern, an image area to be subjected to a thinning process that matches the predetermined image pattern is extracted from the image data, and upstream of a conveyance direction of a printing paper on which the image data is printed The thinning rate is set for each area of the image data so that the thinning rate on the side is larger than the thinning rate on the downstream side in the conveyance direction of the printing paper, and for the pixels in the extracted image area, The signal level is reduced at the set thinning rate.
[Selection] Figure 6

Description

  The present invention relates to an image processing apparatus for controlling a loading amount of a recording material, a control method therefor, and a program.

  In an image processing apparatus having a printing function, an opportunity to print data created by a personal computer or the like is increasing. In an image processing apparatus such as a laser beam printer, commands related to printing and encoded character and graphic information are received from a host computer such as a personal computer or a workstation. The received command information is converted into pixel information by the rendering means, and an image is formed based on an image signal generated based on the pixel information.

  Specifically, the photosensitive drum is first uniformly charged by a charging roller or the like, and an electrostatic latent image is formed on the photosensitive drum by exposing the photosensitive drum with laser light from an image signal based on the pixel information, for example. Form an image. The formed electrostatic latent image is developed by a developing device, and the developed toner image is transferred to a transfer material. The toner image is fixed on the transfer material by the fixing device, and the image can be printed.

  On the other hand, there is a problem that the amount of toner adhering at the time of development is large, that is, when the amount of applied toner is large, the toner is not properly fixed and the toner scatters, and the toner is lost at a portion where the dot density is high. It is known that the frequency of occurrence of such a problem varies depending on environmental conditions such as temperature and humidity where the image forming apparatus is placed. There are various types of media such as paper used for printing, and it is also known that the frequency of occurrence of such problems varies depending on the type of media.

  Conventionally, when a straight line is printed in the main scanning direction, there has been a problem in that the toner scatters behind the line 102 recorded on the transfer material 101 shown in FIG. As shown in FIG. 2, water vapor 202 is generated by moisture in the transfer material due to a rapid temperature rise when the transfer material 101 enters the fixing device 201. At this time, it is known that a phenomenon occurs in which the water vapor of the transfer material 101 having a large amount of toner 203 loses its escape and blows the toner backward in the transport direction. Hereinafter, for such a linear image in the main scanning direction, a phenomenon in which the toner scatters rearward in the sub scanning direction and disturbs the image is described as a “tailing phenomenon”.

  Conventionally, as a countermeasure against the tailing phenomenon, a method of reducing the adhesion amount of toner has been taken. Specifically, a general method is a method of reducing developability, that is, a developing bias is weakened, or a method of performing dot thinning processing on image data for image formation (for example, Patent Document 1 and Patent Document 2). reference). When developing property is lowered by changing the developing bias, the toner adhesion amount is reduced, which is effective for problems such as scattering and tailing of character images. However, the amount of toner applied to the edge portion of the image data is reduced, causing problems such as a reduction in image quality and a decrease in durability and density stability.

  Further, a problem of image deterioration has been pointed out in the past in the process of thinning out image data to reduce dot data. In particular, the degree of the tailing phenomenon varies depending on the environmental conditions, the type of media, and the area in the media, but it is known that if the thinning rate is increased until the phenomenon is almost eliminated depending on the degree of tailing, image degradation will occur. . For example, there are problems that the line width becomes narrow, the density becomes thin, and the image is lost. Further, by performing the thinning process even in an area where the tailing phenomenon does not occur, image deterioration occurs in which an image is lost even in a portion where the original image quality is desired to be maintained. Specifically, in the conventional technique, the same processing is performed on the entire surface of the image in order to prevent the occurrence of the tailing phenomenon. However, in the method of performing the same thinning process on the entire surface of the image, the thinning process is also performed on the part other than the part where the tailing phenomenon occurs, so that it is possible to cause image degradation in the part where the tailing phenomenon does not occur. There was sex. In view of this problem, there is a technique that performs thinning processing while preventing image deterioration for the purpose of improving the tailing phenomenon (for example, Patent Document 1 and Patent Document 3). The thinning process is performed only when is a predetermined thickness. In Patent Document 3, control is performed so that the amount of applied toner is optimized depending on the environment in which the output medium and the image processing apparatus are placed.

JP 2000-175029 A JP 2001-80112 A JP 2003-51902 A

  However, in Patent Document 1, since thinning processing is performed if the sub-scanning width of the image pattern is a predetermined thickness in all of the image area, it does not matter whether the image area is less likely to cause tailing. The thinning process is performed on the entire surface of the image. Also in Patent Document 3, control is performed so that the amount of toner applied to the entire surface of the image is optimized. Therefore, in the conventional technique, in order to reduce the tailing phenomenon, the amount of applied toner is reduced on the entire surface of the image, so that there is a possibility that the image quality of the area where the tailing phenomenon does not occur is deteriorated. .

  The present invention has been made in view of the above-described problems. Rather than performing the thinning process on the entire surface, the image degradation area due to the thinning process is minimized by specifying the thinning process area using the media transport direction as a parameter. The purpose of the present invention is to efficiently reduce the tailing phenomenon in an area in an image where the tailing phenomenon is likely to occur.

In order to solve the above problems, an image processing apparatus of the present invention has the following configuration.
Extracting means for comparing the image data with a predetermined image pattern and extracting an image area for performing a thinning process that matches the predetermined image pattern from the image data; and upstream side in the transport direction of the printing paper on which the image data is printed A decimation rate setting means for setting a decimation rate for each area of the image data so that a decimation rate is larger than a decimation rate downstream in the conveyance direction of the printing paper, and an image area extracted by the extraction means It has a thinning means for reducing the signal level at the thinning rate set by the thinning rate setting means for the pixels within.

  According to the present invention, it is possible to minimize the image degradation area by efficiently specifying the thinning processing area using the medium transport direction as a parameter, and to efficiently reduce the tailing phenomenon.

Diagram showing tailing phenomenon Diagram showing the mechanism of tailing phenomenon The figure which shows the structural example of the image processing apparatus of a present Example. The figure which shows the structural example of the image processing information acquisition part of a present Example. Flowchart of the area determination unit of the image processing information acquisition unit in the first embodiment. Flowchart of the thinning rate determination unit of the image processing information acquisition unit in the first embodiment The figure which shows the structural example of the image process part of a present Example. The figure which shows an example of the thinning pattern of a present Example The figure which shows the thinning process area in the medium of Example 1. The flowchart of the area determination part of Example 2. The figure which shows the thinning process area in the medium of Example 2. The figure which shows the flowchart of the thinning-out rate determination part of Example 2. Flowchart of area determination unit of embodiment 3 Flowchart of the thinning rate determination unit of the third embodiment The figure which shows the thinning-out process area in the medium of Example 3 FIG. 10 is a diagram illustrating a configuration of an image processing apparatus according to a fourth embodiment. The figure which shows the hardware constitutions of the image processing apparatus 304

[Example 1]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the following description, a case where the present invention is applied to a laser beam printer will be described. However, the present invention is not limited to this, and any printer, copier, or facsimile apparatus can be used without departing from the spirit of the present invention. The present invention can be applied to an electrophotographic image processing apparatus.

  FIG. 3 is a block diagram illustrating the configuration of the host computer 301 and the image processing apparatus 304 according to the present exemplary embodiment. The image processing apparatus 304 performs processing for converting drawing commands from the host computer 301 and printing the image data on paper. . A configuration example of a hardware configuration 1700 of the image processing apparatus 304 capable of performing the image processing of the present embodiment is shown in FIG. Reference numeral 1701 denotes a CPU, 1703 denotes a ROM storing programs and tables for executing various flowcharts described below, 1702 denotes a RAM, and 1704 denotes a secondary storage device such as a hard disk or flash memory. Reference numeral 1705 denotes a user interface (hereinafter referred to as UI) including a display device such as a button or liquid crystal. Reference numeral 1706 denotes an external interface such as a USB (trademark) or a memory card reader. Image data is read from the memory card 1709 or connected to the host computer 301 via the interface. Reference numeral 1707 denotes a document reading apparatus such as a scanner, and 311 denotes an image forming apparatus.

  In FIG. 3, an application 302 is an application that operates on the host computer 301. By using these applications, a page layout document, a word processor document, a graphic document, and the like can be created. Digital document data created by these applications 302 is transmitted to the printer driver 303, and a drawing command based on the digital document is generated. The drawing command generated here is generally a printer description language called PDL (Page Description Language) for creating page image data. The drawing command usually includes a drawing command for data such as characters, graphics, and images.

  The drawing command transmitted from the host computer is transmitted to an image processing apparatus 304 connected via a network or the like via an I / F unit (not shown), and the command analysis unit 305 first performs analysis processing. Next, the drawing object generation unit 306 generates a drawing object based on the analyzed data, and the image processing unit 307 performs image processing such as rendering processing, thinning processing, color conversion processing, and pseudo intermediate length processing. Further, in order to perform print output, image data converted into an image format that can be output by the image output unit 308 that outputs data to the image forming apparatus 311 is generated. Each process of the image processing apparatus 304 is controlled by the CPU 1701, the ROM 1703, and the RAM 1702 in FIG. 17, and the processes are executed using a necessary memory. Details of the image processing information acquisition unit 310 and the image processing unit 307 will be described later.

  Here, the occurrence condition of the tailing phenomenon varies depending on the image forming apparatus. In a 600 dpi image, when the straight image in the main scanning direction has a width of about 4 to 8 dots (150 μm to 300 μm) in the sub-scanning direction. It is known that it is likely to occur. Furthermore, the higher the humidity in which the image forming apparatus including the image processing apparatus is placed, the easier the tailing phenomenon occurs.

  Further, it has been found that the tailing phenomenon is likely to occur immediately after the medium enters the fixing device, that is, at the front end portion in the conveyance direction of the medium. This is presumably because the temperature difference between the fixing device and the medium immediately after the medium enters the fixing device is large, so that a rapid temperature rise occurs and water vapor is generated by moisture in the transfer material. On the other hand, the rear end part of the media in the transport direction may have passed a certain amount of time after the media has passed through the fixing device. Less water vapor is generated. Therefore, it is considered that the amount of tailing phenomenon is small. Furthermore, as a reason that the tailing phenomenon is likely to occur at the front end portion in the conveyance direction of the medium, there is an impact when the medium enters the fixing device. That is, since the physical impact at the time when the medium enters the fixing device is large at the front end portion of the medium in the conveyance direction, the toner on the recording material collapses and a tailing phenomenon occurs. On the other hand, since the impact at the rear end portion in the media transport direction is smaller than the impact when entering the fixing device, the tailing phenomenon tends not to occur.

  In addition, the frequency of the tailing phenomenon varies depending on the physical properties of the media. In particular, the air permeability of the media is known as a parameter for measuring the occurrence frequency of the tailing phenomenon. The air permeability is the time required for a certain amount of air to pass through a certain area of paper under a certain pressure, and the longer this time is, the more difficult it is for air to escape. Therefore, the high air permeability means that the amount of air contained in the paper when the paper passes through the fixing device is large. In other words, the amount of water vapor contained in the air is large. Therefore, the tailing phenomenon is likely to occur. In other words, the higher the air permeability of media such as recycled paper, the higher the occurrence frequency of the tailing phenomenon.

  Based on the above, the reason for the improvement of the tailing phenomenon in the thinning process executed in this embodiment is that the toner on the toner that suppresses the height of the toner on the recording material by thinning out the image data and generates the tailing phenomenon. Can be reduced.

FIG. 4 is a block diagram illustrating details of the image processing information acquisition unit 310.
The image processing information acquisition unit 310 searches the paper information database 309 for a medium to be used based on a user interface (not shown) or media instructed by the user from the host computer 301 or media sensor information acquired by the image forming apparatus 311. To do. The image processing information acquisition unit 310 acquires the physical property information of the medium (printing paper) retrieved from the paper information database 309, and the area determination unit 401 determines an area to be subjected to thinning processing in the sub-scanning direction. The thinning rate determination unit 402 determines a thinning rate for each area when performing the thinning process. The physical property information of the media to be used is specifically the air permeability of the media, and when using media with high air permeability, set a wide area for thinning processing and a high thinning rate. To do. The area information of the area in the medium subjected to the thinning process determined by the area determination unit 401 and the information of the thinning rate for each area determined by the thinning rate determination unit 402 are the thinning processing unit 703 to be described later. Sent to.

  The determination process of the thinning process area and the thinning rate determination process will be described with reference to the flowcharts of FIGS. A program for executing each process of the flowchart of FIG. 5 stored in the ROM 1703 is loaded into the RAM 1702, and the CPU 1701 executes the loaded program, whereby the flowchart of FIG. 5 is executed. The thinning processing area in this description is illustrated in FIG. In FIG. 9, the front end portion in the transport direction is area 1, and the remaining rear end portion is area 2.

First, the area determination process of the thinning process area will be described with reference to FIG.
In step S501, it is determined whether the medium retrieved from the paper database 309 is an OHP (Over-Head Projector) sheet or high-quality paper. If it is an OHP sheet or high-quality paper, no thinning process area is set (S502). This is because the thinning process is not performed because the OHP sheet and the high-quality paper tend to be less prone to tailing. On the other hand, in the case of a medium with high air permeability such as recycled paper, processing is performed in consideration of the moisture absorption state of the medium as described below.

If it is determined in S501 that the searched medium is not an OHP sheet or high-quality paper, the process proceeds to step S503. In step S503, it is determined whether the medium used is a medium with high air permeability such as recycled paper. If it is determined in S503 that the medium has high air permeability, the process proceeds to step S504. In step S504, the area in the medium is divided as indicated by reference numeral 901 in FIG. 9. Area 1 is set as a 60% area from the front end in the transport direction, and area 2 is set as a 40% area from the rear end in the transport direction in step S505.
If it is determined in step S503 that the medium used is not high-quality paper, OHP sheet, or recycled paper, the process proceeds to step S506. In step S506, the area in the medium is divided as shown at 902 in FIG. 9, and area 1 is made 30% from the front end in the transport direction, and area 2 is made 70% from the rear end in the transport direction in step S507. Set.

Next, the processing of the thinning rate determination unit 402 will be described with reference to FIG. The program for executing each process of the flowchart of FIG. 6 stored in the ROM 1703 is loaded into the RAM 1702, and the CPU 1701 executes the loaded program, whereby the flowchart of FIG. 6 is executed.
In step S601, the thinning rate determination unit 402 determines whether the medium is an OHP sheet or high-quality paper from the information in the paper database 309. If it is determined in step S601 that the medium is an OHP sheet or high-quality paper, the process proceeds to step S602. In step S602, since the thinning process is not performed, the thinning rate is not determined. If it is determined in step S601 that the medium is not an OHP sheet or high-quality paper, the process proceeds to step S603. In step S603, it is determined whether the medium has a high air permeability such as recycled paper. If it is determined in step S603 that the medium has high air permeability, the thinning rate of area 1 (upstream in the transport direction) of the area (901 in FIG. 9) determined by the area determination unit 401 is set to 60% ( S604), the thinning rate of area 2 (downstream in the transport direction) is set to 30% (S605). If it is not determined in step S603 that the medium has high air permeability, the thinning rate of area 1 (upstream in the transport direction) of the area determined by the area determination unit 401 (902 in FIG. 9) is set to 30%. It is set (S606), and the thinning rate is not set for area 2 (downstream in the transport direction) (S607).
In this embodiment, the thinning rate of area 1 is set to 60% and the thinning rate of area 2 is set to 30%. However, the thinning rate on the upstream side in the conveyance direction of the printing paper is the thinning rate on the downstream side in the conveyance direction of the printing paper. Other values may be used as long as they are larger.

  As described above, the image processing information acquisition unit 301 determines the area determination of the thinning processing area and the thinning rate for each area from the information in the paper database 309. In the thinning rate determination unit 402, thinning patterns of 0%, 10%, 30%, 60%, and 100% are registered.

Next, details of the image processing unit 307 will be described with reference to FIG. A program for executing each process of the flowchart of FIG. 7 stored in the ROM 1703 is loaded into the RAM 1702, and the CPU 1701 executes the loaded program, whereby the flowchart of FIG. 7 is executed.
The rendering processing unit 701 performs rendering processing on the drawing object generated by the drawing object generation unit 306. At this time, the image data subjected to the rendering process is input to the image pattern identification unit 702. The image pattern identification unit 702 compares the image data input to the image pattern identification unit 702 with a predetermined image pattern, and performs an image region for performing a thinning process that matches the predetermined image pattern from the input image data. Perform extraction.

  As described above, the tailing phenomenon is likely to occur in a linear image in the main scanning direction perpendicular to the transfer material conveyance direction having a specific line width in the sub-scanning direction parallel to the transfer material conveyance direction ( In the previous example, 4 to 8 dots wide at 600 dpi). Therefore, the image pattern identification unit 702 performs pattern matching processing in comparison with an image pattern that can extract a straight line in the main scanning direction having a specific width in the sub-scanning direction. There are many known techniques for pattern matching processing, and the recognition method is not limited in the present invention.

  The image data identified by the image pattern identifying unit 702 is sent to the thinning processing unit 703. The thinning processing unit 703 performs thinning processing by replacing the image data extracted by the image pattern identification unit 702 with a thinning pattern acquired from the thinning rate determination unit 402. That is, the thinning processing unit 703 performs a process of reducing the signal level at a predetermined ratio for each region on the pixels in the image region extracted by the image pattern identification unit 702. Specifically, the thinning process is performed according to the pattern shown in FIG. Although details of FIG. 8 will be described later, the original image data is stored in the black portion of the pattern, while the image data in the white portion is deleted.

  Further, in the thinning process, it is not necessary to delete all the pixels, and the signal level of one dot may be varied between 0% and 100%. As an example of changing the signal level per dot, there is a PWM (Pulse Width Modulation) method in which the laser irradiation time (exposure light amount) is changed within one dot. In the present invention, the signal level of thinning is set to 0%, 10%, 30%, 60%, and 100%.

  FIG. 8 shows an example of a thinning pattern applied to image data recognized as a 4-dot line. Reference numeral 801 denotes original image data before conversion, which is an image region having a width of 4 dots in the sub-scanning direction and continuous in the main scanning direction. The image area is, for example, a straight line or the like, which is the same as the matching pattern for extracting the image area to be subjected to the thinning process. The thinning patterns 802a, 802b, 802c to 805a, 805b, and 805c are image patterns used when the thinning processing unit 703 performs thinning processing. Reference numerals 802a, 802b, and 802c indicate that the laser light amount in the thinning process area is 0%, and reference numerals 803a, 803b, and 803c indicate that the laser light amount is 10%. Further, 804a, 804b, and 804c have a laser light amount of 30% in a thinning process region, and 805a, 805b, and 805c have a laser light amount of 60%.

  As described above, the image data subjected to the thinning processing by the thinning processing unit 703 becomes a bitmap image 704, and corresponds to four color materials of cyan (C), magenta (M), yellow (Y), and black (K). The image data to be transmitted is sent to the color space conversion processing unit 705. When the bitmap image 704 is RGB color space image data, the color space conversion processing unit 705 converts the bitmap image 704 that is RGB color space image data into CMYK color space image data using a lookup table or the like. . In general, the image output unit 308 can often output only low gradations such as 2, 4 and 16 gradations. Therefore, the color space conversion processing unit 705 performs pseudo halftone processing so that stable halftone expression is possible even in the image output unit 308 that can output only a small number of gradations. Finally, the image output unit 308 receives the image data converted into an outputable image format from the image processing unit 307 and outputs the image data to the image forming apparatus 311 (312).

  As described above, in the first embodiment, the thinning area in the medium is set using the sub-scanning direction as a parameter from the information on the medium to be used, and the thinning rate is changed for each area to perform the thinning process. As a result, by applying appropriate thinning processing to areas where tailing phenomenon is likely to occur and areas where tailing phenomenon is unlikely to occur, unnecessary tailing is effectively suppressed and tailing phenomenon is effectively improved. It becomes possible. Therefore, it is considered that the image quality is improved.

[Example 2]
In the first embodiment, the image thinning processing area and the thinning rate are determined without considering the environment such as humidity and temperature where the image forming apparatus is installed. However, it is known that the frequency of occurrence of the tailing phenomenon varies depending on environmental conditions such as temperature and humidity where the image forming apparatus is placed. Therefore, if the thinning processing area and the thinning rate are determined in consideration of the environmental conditions in the first embodiment, the occurrence of the tailing phenomenon can be prevented more efficiently according to the temperature and humidity where the image forming apparatus is placed. It is considered possible.

  Therefore, in the second embodiment, when determining the thinning processing area and the thinning rate, the thinning processing area and the thinning rate are determined based on environmental conditions such as temperature and humidity. Here, the processes other than the image processing information acquisition unit 310 are the same as those in the first embodiment, and thus the description thereof is omitted. The temperature / humidity may be acquired by arranging a sensor (not shown) in the image processing apparatus 304, the image forming apparatus 311 or the like and acquiring the temperature / humidity from the sensor, but it is preferable to arrange the sensor in the image forming apparatus 311.

  It is known that the tailing phenomenon is likely to occur in a high temperature and high humidity environment. Based on this, in the present embodiment, the thinning process areas are divided more finely in a high temperature / humidity environment, and a large thinning rate is set for each area. In this embodiment, the high temperature / humidity environment is an environment having a temperature of 30 ° C. and a humidity of 80%.

The process of the area determination unit 401 in this embodiment will be described with reference to FIG. A program for executing each process of the flowchart of FIG. 10 stored in the ROM 1703 is loaded into the RAM 1702, and the CPU 1701 executes the loaded program, whereby the flowchart of FIG. 10 is executed.
The area determination unit 401 determines whether the data from the paper database 309 is an OHP sheet or high-quality paper (S1001). In the case of an OHP sheet or high-quality paper, since no thinning process is performed, no thinning area is set (S1002). If it is determined in step S1001 that the sheet is not an OHP sheet or high-quality paper, it is determined from the information on the environmental conditions acquired from the image forming apparatus 311 whether or not the image forming apparatus 311 is placed in a high temperature / humidity environment (S1003). ). If it is determined in step S1003 that the image forming apparatus 311 is placed in a high temperature / humidity environment, the thinning processing area in the medium is divided into three (see 1101 in FIG. 11). Of these, area 1 is set to a 30% region from the front end in the transport direction (S1004), area 2 is set to a region 30% to 60% from the front end in the transport direction (S1005), and area 3 is set to a region 40% from the rear end in the transport direction. (S1006).

  If it is determined in step S1003 that the image forming apparatus 311 is not placed in a high temperature / humidity environment, the thinning processing area in the medium is divided into two (refer to 1102 in FIG. 11). Of these, area 1 is set to a 45% region from the front end in the transport direction (S1007), and area 2 is set to a region 55% from the rear end in the transport direction (S1008). As described above, the area determination unit 401 determines whether or not the environment in which the image forming apparatus 311 is placed is a high temperature / humidity environment, and changes the area division method.

Next, the control of the thinning rate determination unit 402 will be described.
A process when the area determination unit 401 divides the thinned area in the medium into three, that is, when the image forming apparatus 311 is placed in a high temperature / humidity environment will be described with reference to FIG. A program for executing each process of the flowchart of FIG. 12 stored in the ROM 1703 is loaded into the RAM 1702, and the CPU 1701 executes the loaded program, whereby the flowchart of FIG. 12 is executed.

In step S1201, it is determined whether the information from the paper database 309 is an OHP sheet or high-quality paper. If it is determined that the sheet is an OHP sheet or high-quality paper, the thinning rate is not set because the thinning process is not performed (S1202). If it is not an OHP sheet or high-quality paper, it is determined in step S1203 whether the paper is high in air permeability such as recycled paper. If it is determined in step S1203 that the paper has high air permeability, it is determined in step S1204 whether or not the image forming apparatus 311 is placed in a high temperature / humidity environment. When it is determined that the image forming apparatus 311 is placed in a high temperature / humidity environment, the thinning rate of the area 1 determined by the area determination unit 401 (see 1101 in FIG. 11) is set to 60% (S1205). The area 2 thinning rate is set to 30% (S1206), and the area 3 thinning rate is set to 10% (S1207). If it is determined in step S1204 that the image forming apparatus 311 is not placed in a high temperature / humidity environment, the area 1 thinning rate determined by the area determination unit 401 (see 1102 in FIG. 11) is 20%. It is set (S1208), and the thinning rate of area 2 is set to 10% (S1209).
In this embodiment, the thinning rate of area 1 is 60%, the thinning rate of area 2 is 30%, and the thinning rate of area 3 is 10%. Any other numerical value may be used as long as it is larger than the thinning rate on the downstream side in the sheet conveyance direction.

If it is determined in step S1203 that the paper is not high in air permeability, it is determined whether the image forming apparatus 311 is placed in a high temperature / humidity environment as in step S1204 (S1210). When it is determined that the image forming apparatus 311 is placed in a high-temperature and high-humidity environment, the area 1 thinning rate determined by the area determination unit 401 (see 1101 in FIG. 11) is set to 30% (S1211). The thinning rate for area 2 is set to 10% (S1212), and the thinning rate for area 3 is not set (S1213). If it is determined in step S1210 that the image forming apparatus 311 is not placed in a high-temperature and high-humidity environment, the area-decimation rate determined by the area determination unit 401 (see 1102 in FIG. 11) is 10%. It is set (S1214), and the thinning rate for area 2 is not set (S1215).
As described above, in the high temperature and high humidity environment, the thinning process area is divided more finely than in the high temperature and high humidity environment, and the thinning rate is made larger than that in the high temperature and high humidity environment.

  As described above, the thinning processing area is divided in detail according to the medium to be used and the environmental conditions in which the image forming apparatus 311 is placed, and the thinning rate in each area is further set step by step. An efficient thinning process can be performed. That is, no matter what environment the image forming apparatus 311 is placed in, it is possible to suppress the image deterioration and improve the tailing phenomenon, so that a higher quality image can be provided.

[Example 3]
In the first and second embodiments, when determining the image thinning processing area and the thinning rate, the medium to be used and the environment such as humidity and temperature where the image forming apparatus is placed are considered. However, it is known that the frequency of occurrence of the tailing phenomenon varies depending on the medium conveyance speed of the image forming apparatus. This is known to reduce the tailing phenomenon because the fixing property increases when the conveyance speed is low.

  Therefore, in the third embodiment, when determining the thinning processing area and the thinning rate, not only the medium to be used and the environmental conditions in which the image forming apparatus is placed, but also the conveyance speed of the medium is considered. Here, the processes other than the image processing information acquisition unit 310 are the same as those in the first embodiment, and thus the description thereof is omitted.

The process of the area determination unit 401 in this embodiment will be described with reference to FIG. The program for executing each process of the flowchart of FIG. 13 stored in the ROM 1703 is loaded into the RAM 1702, and the CPU 1701 executes the loaded program, whereby the flowchart of FIG. 13 is executed.
The area determination unit 401 determines whether the data from the paper database 309 is an OHP sheet or high-quality paper (S1301). In the case of an OHP sheet or high-quality paper, since no thinning process is performed, no thinning area is set (S1302). If it is determined in step S1301 that the sheet is not an OHP sheet or high-quality paper, information on the medium conveyance speed is acquired from the image forming apparatus 311, and it is determined whether or not the medium conveyance speed is half the default speed (S1303). ). When the media conveyance speed is half the default speed, the fixing property is better than that at the default time, so the thinning processing area is set narrower than usual. The thinning processing area is shown in FIG. In the case of the present embodiment, as indicated by 1501 in FIG. 15, area 1 is set as a 10% area from the front end in the transport direction (S1304), and area 2 is set as the remaining 90% area (S1305).

  If it is determined in step S1303 that the medium conveyance speed is not half of the default, it is determined whether or not the image forming apparatus 311 is placed in a high temperature / humidity environment (S1306). When the image forming apparatus 311 is placed in a high-temperature and high-humidity environment, the thinning processing area in the medium is divided into three (see 1101 in FIG. 11). Of these, area 1 is set as a 30% area from the front end in the transport direction (S1307), area 2 is set as a region between 30% and 60% from the front end in the transport direction (S1308), and area 3 is set as a 40% area from the rear end in the transport direction. (S1309).

  If it is determined in step S1306 that the image forming apparatus 311 is not placed in a high-temperature and high-humidity environment, the thinning processing area in the medium is divided into two (see 1102 in FIG. 11). Of these, area 1 is set to a 45% region from the front end in the transport direction (S1310), and area 2 is set to a region 55% from the rear end in the transport direction (S1311). As described above, the area determination unit 401 determines the thinning processing area in consideration of the medium conveyance speed of the image forming apparatus.

Next, the control of the thinning rate determination unit 402 will be described using the flowchart of FIG.
In step S1401, it is determined whether the medium to be used is an OHP sheet or high-quality paper. In the case of an OHP sheet or high-quality paper, since the thinning process is not performed, the thinning rate is not set (S1402). If the medium to be used is not an OHP sheet or high-quality paper, information on the medium conveyance speed is acquired from the image forming apparatus 311 to determine whether the medium conveyance speed is half the default speed (S1403). If the media transport speed is half the default speed, as described above, the fixability is better than the default speed, so set the thinning rate considering only the impact when the media enters the fixing device. . Specifically, the thinning rate of area 1 (see 1501 in FIG. 15) determined by the area determination unit is set to 30% (S1404), and the fixing performance of area 2 is excellent. Since there is no impact at the time of entry, thinning processing is not performed. Therefore, the thinning rate is not set (S1405).

  If it is determined in step S1403 that the medium conveyance speed is not half, it is determined in step S1406 whether the medium to be used is a sheet with high air permeability such as recycled paper. If it is determined in step S1406 that the paper has high air permeability, it is determined in step S1407 whether or not the image forming apparatus 311 is placed in a high temperature / humidity environment. When it is determined that the image forming apparatus 311 is placed in a high temperature / humidity environment, the area 1 thinning rate determined by the area determination unit 401 (see 1101 in FIG. 11) is set to 60% (S1408). The area 2 thinning rate is set to 30% (S1409), and the area 3 thinning rate is set to 10% (S1410). If it is determined in step S1407 that the image forming apparatus 311 is not placed in a high temperature / humidity environment, the area 1 thinning rate determined by the area determination unit (see 1102 in FIG. 11) is set to 20%. (S1411), the thinning rate of area 2 is set to 10% (S1412).

  If it is determined in step S1406 that the paper is not high in air permeability, it is determined whether the image forming apparatus 311 is placed in a high-temperature and high-humidity environment as in step S1407 (S1413). When it is determined that the image forming apparatus 311 is placed in a high temperature / humidity environment, the thinning rate of the area 1 determined by the area determination unit (see 1101 in FIG. 11) is set to 30% (S1414). The thinning rate for area 2 is set to 10% (S1415), and the thinning rate for area 3 is not set (S1416). If it is determined in step S1413 that the image forming apparatus 311 is not placed in a high-temperature and high-humidity environment, the area 1 thinning rate determined by the area determination unit 401 (see 1102 in FIG. 11) is 10%. It is set (S1417), and the thinning rate for area 2 is not set (S1418).

  As described above, the thinning processing area and the thinning rate in each area are set according to the conveyance speed of the medium of the image forming apparatus 311, the type of medium to be used, and the environmental conditions in which the image forming apparatus 311 is placed. . As a result, the tailing phenomenon can be improved while suppressing image deterioration.

[Example 4]
In the first to third embodiments, thinning processing is performed in a device including the image forming apparatus 311. However, if a hardware configuration for performing the thinning process cannot be obtained, the thinning process can be performed on the host computer. Therefore, as a fourth embodiment, a configuration of an image processing apparatus when thinning processing is performed by a host computer is shown. However, since the processing in the image processing apparatus is the same as the processing described in the first to third embodiments, description thereof is omitted.

FIG. 16 shows the configuration of the image processing apparatus when performing the thinning process on the host computer.
The difference between the first to third embodiments and the present embodiment is that the host computer 1600 includes an application 302, a printer driver 303, a command analysis unit 305, a drawing object generation unit 306, an image processing unit 307, and an image output unit 308. . In this case, image processing including thinning processing is different from the cases shown in the first to third embodiments in that software processing is performed on the host computer.

(Other examples)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (9)

Extracting means for comparing image data with a predetermined image pattern and extracting an image region for performing a thinning process that matches the predetermined image pattern from the image data;
Setting means for setting a thinning rate for each area of the image data so that a thinning rate on the upstream side in the conveyance direction of the printing paper for printing the image data is larger than a thinning rate on the downstream side in the conveyance direction of the printing paper. When,
An image processing apparatus comprising: a thinning unit that reduces a signal level at a thinning rate set by the setting unit with respect to pixels in the image region extracted by the extracting unit.   The image processing apparatus according to claim 1, wherein the setting unit changes a thinning rate set according to a type of printing paper on which the image data is printed.   The image processing apparatus according to claim 1, wherein when the printing paper is OHP or high-quality paper, the thinning unit does not perform thinning processing.   The image processing apparatus according to claim 1, wherein the setting unit changes a thinning rate that is set according to a conveyance speed of a printing paper on which the image data is printed.   5. The image processing apparatus according to claim 4, wherein the set thinning rate is set larger when the printing paper conveyance speed is faster than when the printing paper conveyance speed is slower.   The image processing apparatus according to claim 1, wherein the setting unit changes a thinning rate that is set according to an air permeability of a printing sheet on which the image data is printed.   The image processing apparatus according to claim 1, wherein the thinning unit reduces a signal level by performing a process of thinning dots of the image data. Comparing the image data with a predetermined image pattern, extracting from the image data an image region for performing a thinning process that matches the predetermined image pattern;
Setting the thinning rate for each area of the image data so that the thinning rate on the upstream side in the conveyance direction of the printing paper for printing the image data is larger than the thinning rate on the downstream side in the conveyance direction of the printing paper;
A control method for an image processing apparatus, wherein a signal level is reduced at the set thinning rate for pixels in the extracted image region.   A program for causing a computer to execute the control method according to claim 8.