JP2003060910A - Imaging device, imaging method, recording medium and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device that is stable among a plurality of dither processes from a medium to high density and implements optimum print for a highlight part. SOLUTION: Density correction sections A 705 to 708 and density correction sections B 173 to 716 convert received 8-bit data, with a medium density part to a high density part, depending on the density measured values into optimum 8-bit data and convert only a low density (highlight) part into 8-bit data having a predetermined density, independently of the measured density values. Dither processing sections A 709 to 712 and dither processing sections B717 to 720 respectively implement dither processes with the same number of lines and angle, but with different output information quantities. Dither changeover devices 701 to 704 select the dither processing sections A or B, according to a mode designated by a printing instruction in unit of pages and of drawn object (graphics, texts, images or the like).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print output device including an image forming unit such as a printer, a copying machine, and a facsimile.
Alternatively, the present invention relates to an image forming apparatus, an image forming method, a recording medium, and a program including a system configured by a print output apparatus that receives data and an image forming unit that transmits data, and particularly executes density correction for a plurality of dither processes. The present invention relates to an image forming apparatus having a function, an image forming method, a recording medium, and a program.

[0002]

2. Description of the Related Art Conventionally, density correction of a plurality of dither processes in an image forming apparatus has been performed for each dither process of each object. Also, the number of lines and the angle are the same,
The same density correction may be used even in the dither processing in which the amount of output information per pixel is different.

[0003]

However, since it is difficult to print with stable density in a laser beam printer or the like, dither processing in which the number of lines and angle are the same and the amount of output information per pixel is different, When each is output and the density correction parameter is obtained, the variation in the high density portion is large.

Further, when the same density correction parameter is used, there is a problem that a geometric pattern is conspicuous in a high density portion.

On the other hand, in the low-density portion (highlight) portion, an isolated dot of 1 pixel or less (for example, 1/2 pixel here) may not appear due to the performance of the printer engine.

The present invention has been made in view of the above-mentioned points, and an object thereof is an image which is stable between a plurality of dithers from a middle density portion to a high density portion and which can perform more optimal printing in a highlight portion. An object is to provide a forming apparatus, an image forming method, a recording medium, and a program.

[0007]

In order to achieve the above object, the invention of claim 1 is an image generating means for generating image information in accordance with print information inputted from an external device, and an image generating means for generating the image information. Image forming means for forming an image on a recording material according to image information, density measuring means for measuring density characteristics of the image information formed by the image forming means, and density measuring value measured by the density measuring means Then, the same density correction target is applied to the medium density part to the high density part of the image information, and the density correction target of only the low density part of the image information is changed to a predetermined predetermined density correction target value to perform the density correction of the image information. The dither processing is performed by inputting the density correction means and the image information whose density has been corrected by the density correction means. However, the number of lines and the angle are the same, and a plurality of output information amounts per pixel are different. And having a I The processing means, and a dither switching means for switching the plurality of the dither processing means in response to the control signal.

The predetermined density correction target value may be set to a density target value such that the low density portion of the image information is surely printed out.

Further, the plurality of dither processing means includes a first dither processing means having an output information amount per pixel of 1 bit and a second dither processing means having an output information amount per pixel of a plurality of bits. Can be included.

The plurality of bits may be 4 bits.

Further, the dither switching means may switch the plurality of dither processing means on a page-by-page basis or on an object-by-drawing basis according to the control signal.

The control signal may be generated from an operating means operable by a user.

Further, the image forming apparatus is a print output apparatus including an image forming section such as a printer, a copying machine, a facsimile, or a system constructed by a print output apparatus for receiving data and an image forming section for transmitting data. It can be characterized by including.

To achieve the above object, the invention of claim 8 is an image forming apparatus for generating image information according to print information input from an external device, and forming an image on a recording material according to the generated image information. In the image forming method, a density measuring step for measuring density characteristics of image information formed on the recording material, and a medium density portion to a high density portion of the image information according to the density measurement value obtained in the density measuring step. Is the same density correction target, and the density correction step is performed to correct the density of the image information by changing the density correction target only to a low density portion of the image information to a preset predetermined density correction target value,
Dither processing is performed by inputting the density-corrected image information in the density correction step, but according to a plurality of dither processing steps having the same number of lines and different angles and different output information amount per pixel, and a control signal. And a dither switching step for switching the plurality of dither processing steps.

To achieve the above object, the invention of claim 11 provides an image forming apparatus for generating image information according to print information input from an external device and forming an image on a recording material according to the generated image information. A recording medium recording a program for controlling by a computer, the program causing a computer to measure density characteristics of image information formed on the recording material, and an image according to the measured density measurement value. From the medium density portion to the high density portion of the information, the same density correction target is set, and only the low density portion of the image information is changed to the predetermined density correction target value set in advance to perform the density correction of the image information, Dither processing is performed by switching a plurality of dither processing units having the same number of lines and the same angle and different output information amount per pixel for the density-corrected image information. And characterized in that.

In order to achieve the above object, the invention of claim 14 is an image forming apparatus for generating image information according to print information input from an external device and forming an image on a recording material according to the generated image information. A program for controlling by a computer, a density measuring step of measuring a density characteristic of image information formed on the recording material,
According to the density measurement value obtained in the density measurement step, the same density correction target is set from the middle density portion to the high density portion of the image information, and the predetermined density correction target is set in advance only for the low density portion of the image information. The density correction step of changing the value to the density correction of the image information and the dither processing by inputting the image information density-corrected in the density correction step are performed. It is characterized by comprising a plurality of dither processing steps having different amounts of output information per hit, and a dither switching step of switching the plurality of dither processing steps according to a control signal.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an outline of a color laser beam printer according to an embodiment of the present invention. 2 in this figure
00 is a color laser beam printer, 100 is a host computer, 300 is a video controller, 400 is a printer engine, and 600 is a video interface that connects the video controller 300 and the printer engine 400. Reference numeral 500 denotes a host interface that connects the host computer 100 and the video controller 300.

Next, a typical printing operation of the color laser beam printer will be described with reference to FIG. First, the host computer 100 transmits a print command for starting printing to the color laser beam printer 200 according to a user's instruction. Specifically, the application software on the host computer 100 generates a print command having a command system based on the screen drawing command,
The print command is passed to the printer driver on the host computer 100. The printer driver generates a print command based on the printer language system that the printer 200 can interpret from the passed print command. The print command thus generated is transmitted from the printer driver of the host computer 100 via the host interface 500 to the video controller 3 of the color laser beam printer 200.
Sent to 00.

The host interface 500 is physically a Centronics interface or RS-232.
It is composed of an interface such as a C interface or an Ethernet (registered trademark) interface and a physical cable or a radio wave including infrared rays, and logically consists of a predetermined communication procedure called a protocol. There is.

The video controller 300 interprets the print command sent thereto and creates a raster image. The created raster image is transferred from the video controller 300 to the printer engine 4 using the video interface 600.
Sent to 00. Printer engine 400 is 600DP
Data of 8 bits for each pixel is received at a resolution of I (dots / inch), and the sent raster image is printed on paper using color toner.

Next, the video interface 6 for connecting the video controller 300 and the printer engine 400.
The 00 signal will be described with reference to FIG. Main video interface signals are described in FIG.

The / RDY signal is sent to the video controller 30.
0, which is a signal sent from the printer engine 400 to the printer engine 400.
The signal indicates that the print operation can be started at any time when the signal is received, or the print operation can be continued. The / PRNT signal is a signal sent from the video controller 300 to the printer engine 400, and is a signal for instructing to start the print operation or continue the print operation.

The / TOP signal is a synchronizing signal in the sub-scanning (vertical scanning) direction and is sent from the printer engine 400 to the video controller 300. / LSYNC
The signal is a synchronizing signal in the main scanning (horizontal scanning) direction, and is used for the video controller 300 to the printer engine
It is sent from 0.

The / VDO7 to / VDO0 signals are image signals sent from the video controller 300 to the printer engine 400 and indicate image density information to be printed by the printer engine 400. / VDO7 is the highest,
/ VDO0 is represented by the least significant 8 bits. The printer engine 400 prints at the maximum density of the color toner being developed when the signals / VDO7 to / VDO0 are 00H, and F
FH does not print.

The / VCLK signal is an image signal / VDO7- /
This is a transfer clock signal of VDO0 and is sent from the video controller 300 to the printer engine 400. The video controller 300 sends out the / VDO7 to / VDO0 signals in synchronization with the rising edge of the / VCLK signal.

FIG. 3 shows a hardware configuration example of the video controller 300 according to the embodiment of the present invention. In the figure, 301 is the printer controller 20.
A CPU (Central Processing Unit) that controls the functions of the printer through the host interface 304 and the video interface 305, and controls the entire 0.
Is. A ROM (Read Only Memory) 302 stores a control program of the CPU 301, font data and the like. Reference numeral 303 denotes a RAM (random access memory) used as a work area of the CPU 301. A host interface 304 is connected to the host computer 100 to connect to the host computer 10.
One-way communication or two-way communication is performed from 0 to the printer 200 to receive a print command described in a printer-specific language and to send the printer status.

Reference numeral 307 denotes an image memory, which has 6 bits each of 8 bits corresponding to toners of magenta (M), cyan (C), yellow (Y), and black (K) for printing.
The raster image data for one page of 00 DPI is stored. A video interface 305 is an interface circuit with the printer engine 400. Thirty
An operation panel 8 can be operated by the user to directly make various settings for the printer 200.

Reference numeral 309 denotes a bus, which is the CPU 301 and R
Storage devices such as OM302 and RAM303, and host interface 304 and video interface 305
Used for exchanging data with input / output devices such as.

In the above configuration, the print command input from the host interface 304 and described in the printer-specific language is interpreted in the video controller 300, and raster image data is created in the image memory 307 by a predetermined drawing algorithm. To be done. At this time, magenta (M), cyan (C), yellow (Y), and black (K) are expanded into raster image data of 600 DPI with one pixel of 8 bits. The expanded raster image data is sent to the printer engine 400 via the video interface 305.

FIG. 4 is a vertical cross-sectional view showing a structural example of the printer engine 400 of the color laser beam printer 200 according to the embodiment of the present invention. Here, by repeating the process of transferring the image (toner image) formed on the image carrier by charging, exposing, and developing onto the recording paper a plurality of times, an image in which a plurality of colors are superimposed is formed on the recording paper, A color laser beam printer for obtaining a color image will be described.

As shown in FIG. 4, a photosensitive drum 401, a corona charger 402, and a roller charger 403 are provided in the apparatus.
Further, on the right side of the photosensitive drum 401, a plurality of developing devices 404a, 404b, 404c, 404d are supported by a rotatable support body, and are arranged on the same cylinder centered on the support body rotation shaft 407. Each developing device 404a, 404b,
The development opening surfaces of 404c and 404d are set. Further, yellow toner, magenta toner, cyan toner, and black toner are stored in the developing units 404a, 404b, 404c, and 404d, respectively, and further, there are coating rollers 405a, 405b, 405c, and 405d, and the developing rollers 406a and 406b. , 406c, 406d, the toner applying rollers 405a, 405b,
405c and 405d, developing rollers 406a and 406
Toner is applied on b, 406c, and 406d. Also,
A developing unit 404a attached to the support rotating shaft 407,
The developing opening surfaces 404b, 404c, and 404d are always driven so as to face the photosensitive drum surface.

On the left side of the photosensitive drum 401, there is arranged a transfer roller 408 which holds the transfer paper and has a function of transferring the image on the photosensitive drum 401 onto the transfer paper. The photosensitive drum 401, the rotary shaft 407 of the support of the developing device, and the transfer roller 408 are driven in the direction of the arrow shown in FIG. 4 by driving means (not shown).

An optical unit 414 including a laser diode 409, which constitutes an exposure device, a rotary polygon mirror 411 that is driven to rotate by a high speed motor 410, a lens 412, and a folding mirror 413 is arranged above the main body of the apparatus.

When a signal according to, for example, a yellow print image is input to the laser diode 409, a laser beam corresponding to the signal is emitted from the laser diode 409, and the laser beam passes through the optical path 415 and the photosensitive drum. It is irradiated onto 401 to form a latent image. Further, when the photosensitive drum 401 advances in the direction of the arrow, the developing device 40
It is visualized by the yellow developing device of 4a, 404b, 404c, and 404d.

The transfer sheet is fed from the transfer cassette 416 to the transfer roller 408 by the pickup roller 417 in synchronization with the image on the photosensitive drum 401.

When the transfer paper is supplied to the transfer roller 408, the transfer paper is held by the gripper 418 of the transfer roller 408, and the toner image on the photosensitive drum 401 is transferred to the photosensitive drum 401 and the transfer roller 408 by a power source (not shown). It is transferred onto the transfer paper by the voltage between them. At the same time, the transfer paper is attracted to the transfer roller 408 by the charge injection (not shown) to the transfer paper. If necessary, a voltage may be applied between the transfer roller 408 and the suction roller 419 to suck the transfer paper in advance.

By carrying out the above steps in the same manner for magenta, cyan and black, toner images of a plurality of colors are formed on the transfer paper.

The transfer paper on which the toner images of a plurality of colors are formed is peeled off from the transfer roller 408 by the separation claw 420, and the color toner image on the transfer paper is melted and fixed by the fixing device 421 for heating and pressing. As a result, a color image is obtained, and finally the transfer paper is discharged onto a tray 424 outside the machine.

The transfer residual toner on the photosensitive drum 401 is cleaned by the cleaning device 422. Further, the toner on the transfer roller 408 is also cleaned by the transfer roller cleaning device 423 as needed.

FIG. 5 is a diagram for explaining a method of forming an electrostatic image on the photosensitive drum 401 based on an electric signal in the laser beam printer 200 according to the embodiment of the present invention. In the figure, 453 is a pulse width modulation unit for converting 8-bit image data signal / VDO7 to / VDO0 into a pulse width, 450 is a laser driver for driving a semiconductor laser, 409 is an optical pulse of an electric signal (laser beam). ) Is a semiconductor laser for converting. Further, 411 is a rotary polygon mirror (polygon mirror) for scanning the laser beam emitted from the semiconductor laser 409 onto the photosensitive drum 401, and 412 is f- for focusing the laser beam on the photosensitive drum 401. The θ lens 451 is a beam detector for detecting the scanning start of the main scanning line. Reference numeral 452 represents the main scanning line direction, and 401 is a photosensitive drum that forms an electrostatic image.

In the above configuration, the image data signals / VDO7 to / VDO0 sent to the printer engine 400 via the video interface 305 are processed by the pulse width modulation unit 453 into the image data signals / VDO7 to / VDO7.
It is converted into a pulse corresponding to the value of / VDO0. The semiconductor laser 409 is driven by the laser driver 450 according to this pulse signal.

The laser beam emitted from the semiconductor laser 409 is reflected by the rotary polygon mirror 411,
11 through the f-θ lens 412 arranged between the photosensitive drum 401 and the photosensitive drum 401, is guided onto the photosensitive drum 401, forms an image on the photosensitive drum 401, and is scanned in the main scanning direction by the rotary polygon mirror 411. A latent image is formed on the main scanning line 452.

Further, the beam detector 451 detects the scanning start of the main scanning line of the laser beam, and the printer engine 400 uses / LS as a synchronizing signal for determining the image writing timing in the main scanning direction from this detection signal.
YNC signal is generated, and the generated / LSYNC signal is used as the video interface 305 of the video controller 300.
Supply to. The video controller 300 can correctly print by sending the image data signals / VDO7 to / VDO0 to the printer engine 400 at a predetermined timing with respect to the / LSYNC signal on the video interface 305.

FIG. 6 shows an example of the configuration of the dither processing unit 700 which executes a plurality of dither processes to which the present invention is applied in the resolution conversion unit 306 of the video controller 300 of FIG. In FIG. 6, 701, 702, 703, 704
Is a dither switch for cyan, magenta, yellow, and black. 705, 706, 707, and 708 are cyan,
The density correction A is magenta, yellow, and black. 7
Reference numerals 09, 710, 711, and 712 are cyan, magenta, yellow, and black dither processing A. 713,71
4, 715 and 716 are cyan, magenta, yellow, and black density corrections B. 717, 718, 719,
Reference numeral 720 denotes cyan, magenta, yellow, and black dither processing B. The dither processing unit 700 includes
The coordinates of print image data (not shown) are also input.

The dither switchers 701 to 704 switch the dither processings A and B in page units or in units of drawn objects (graphics, texts, images, etc.) according to the mode designated by the print command. 705-7
08 density correction unit A, 713 to 716 density correction unit B
Converts the input 8-bit data into 8-bit data of optimum density from the medium density portion to the high density portion in accordance with the density measurement value measured by the density measuring means (not shown),
Only the low density part (highlight) part converts the input 8-bit data into 8-bit data having a predetermined density regardless of the density measurement value.

The dither processing unit A 709 to 712 inputs 8 bi in the case of, for example, 1 bit (bit) dither processing.
The output of t data is a binary value of 0 and 255, that is, 1b.
Outputs it information.

FIG. 7 shows an example of parameters for 1-bit dither processing. Each number represents a threshold of 0 to 254 in 10 steps. In this dithering process, the threshold value and the input pixel value at the coordinate where the two-dimensional coordinate of the image data and the two-dimensional coordinate where the dithering parameter is repeated are matched are compared, and if the input pixel value is larger than the threshold value, 255 is output, If the input pixel value is equal to or smaller than the threshold value, 0 is output.

On the other hand, FIG. 8 shows an example of parameters of the 4-bit dither processing executed by the dither processing unit B of 717 to 720, for example. An array of numbers of size 4 × 4 represents a threshold value, and if the input pixel value is larger than the threshold value, 0, 17, 34, 51, 68, 85, 102, 11 in order from the top.
9, 136, 153, 170, 187, 204, 22
16 types of values of 1,238,255 are output.

Here, comparing FIG. 7 and FIG. 8 below, the number of lines and the angle of the dither processing are almost the same for both the parameters of FIGS. 1 and 2, and in this example, the patterns at 17 locations are the same. In addition, the dither processing parameters are created so that the 17 density correction positions match. As a result, the density measurement image pattern used for density correction can be representatively output by, for example, 4-bit dither processing. Other than the 17 points, the patterns are different, but it is considered that they have almost the same density characteristics. Therefore, the density measurement image pattern used for all density correction can be represented by the 4-bit dither processing.

However, with respect to the low-density portion (highlight) portion, isolated dots of 1 pixel or less (for example, 1/2 pixel here) may not appear due to the performance of the printer engine.

Further, in the 1-bit dither, in order to increase the number of gradations, it is necessary to form the sub-matrix with an area larger than 4 bits for the same number of lines. For this reason,
The geometric pattern generated by using the sub-matrix may be conspicuous, and the image quality may look better if the pattern is intentionally changed.

In consideration of these matters, in the present embodiment, in the dither processing in which the number of lines and the angle are the same and the amount of output information per pixel is different, the preceding stages 705 to 7 are used.
The density correction unit A of 08 and the density correction unit B of 713 to 716 perform density correction aiming at the same density correction from the middle density portion to the high density portion of the input pixel, and the low density portion (highlight portion of the input pixel is highlighted. ) Only performs density correction for changing the density correction target value to a preset correction value.

As described above, according to the present invention, the density correction parameter in the 1-bit and 4-bit dither processing is changed according to the density value of the input pixel. Stable between dithers, and more optimal printing can be performed in the highlight area.

(Other Embodiments) Even if the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus composed of one device. (For example, a copying machine, a facsimile machine, etc.) may be applied.

Further, the object of the present invention is to supply a recording medium (storage medium) recording a program code of software for realizing the functions of the above-described embodiment to a system or apparatus, and to supply the computer of the system or apparatus. It is needless to say that (or CPU or MPU) can also be achieved by reading and executing the program code stored in the recording medium.

In this case, the program code itself read from the recording medium realizes the function of the above-described embodiment, and the recording medium recording the program code constitutes the present invention.

A recording medium for recording the program code and variable data such as a table is, for example, a floppy (registered trademark) disk (FD), hard disk, optical disk, magneto-optical disk, CD-ROM,
CD-R, magnetic tape, non-volatile memory card (IC
A memory card), a ROM, or the like can be used.

Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also the OS (the OS running on the computer based on the instruction of the program code). Needless to say, this also includes the case where the operating system) performs a part or all of the actual processing and the processing realizes the functions of the above-described embodiments.

[0060]

As described above, according to the present invention,
In the dither processing in which the number of lines and the angle are the same and the amount of output information per pixel is different, the same density correction target is set only for the middle density portion to the high density portion, and the density correction target is changed only for the low density portion. It is possible to stabilize between a plurality of dithers from the middle density portion to the high density portion, and it is possible to perform more optimal printing in the highlight portion.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a color laser beam printer according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing types of signals transmitted and received between the video controller and the printer engine of the color laser beam printer according to the embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a video controller of the color laser beam printer according to the embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view showing the internal configuration of the printer engine of the color laser beam printer according to the embodiment of the present invention.

FIG. 5 is a schematic diagram showing a configuration of an optical scanning system of a color laser beam printer according to an embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration example of a processing system for density correction and dither processing according to the first embodiment of the present invention.

FIG. 7 is a diagram illustrating an example of parameters of 1-bit dither processing.

FIG. 8 is a diagram showing an example of parameters of a 4-bit dither process used in the first embodiment of the present invention.

[Explanation of symbols]

100 host computer 200 color laser beam printer 300 video controller 301 CPU 302 ROM 303 RAM 304 host interface 305 video interface 306 Resolution converter 307 image memory 308 Operation panel 309 bus 400 printer engine 401 photosensitive drum 407 Developing device rotation holder 408 transfer roller 409 Semiconductor laser 411 rotating polygon mirror 412 f-θ lens 450 laser driver 451 beam detector 452 main scan line 453 Pulse width modulator 500 host interface 600 video interface 700 dither processor 701,702,703,704 Dither switch 705, 706, 707, 708 Density correction A 709, 710, 711, 712 dither processing A 713, 714, 715, 716 Density correction B 717, 718, 719, 720 Dither processing B

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G06T 5/00 200 H04N 1/40 101E H04N 1/407 B41J 3/00 AF term (reference) 2C262 AA24 AA26 AA27 AB13 AC07 BB01 BB06 BB22 BB25 BB27 BB36 BC07 EA04 EA06 EA16 GA02 2H027 DA09 DA32 DB01 DE02 DE07 EA02 EA20 EB04 EC04 EC06 EC07 EC20 ED06 EE01 EE07 EE10 EF09 FA30 FA35 ZA07 5B057 AA11 CA01 CA02 CA08 CA12 CA16 CB01 CB02 CB07 CB12 CB16 CC01 CE11 CE13 CH07 CH08 5C077 LL04 LL19 MP01 MP08 NN09 PP15 PP45 PQ08 PQ12 PQ20 PQ23 SS02 TT02

Claims (16)

[Claims] 1. An image generating unit that generates image information according to print information input from an external device; an image forming unit that forms an image on a recording material according to the image information generated by the image generating unit; Density measuring means for measuring the density characteristic of the image information formed by the forming means, and the medium density portion to the high density portion of the image information corresponding to the density measurement value measured by the density measuring means are the same density correction target, The density correction means for changing the density correction target to a preset predetermined density correction target value only for the low density portion of the image information, and the image information density-corrected by the density correction means are input. Dither processing is performed, but a plurality of dither processing means having the same number of lines and angles and different output information amount per pixel, and the plurality of dither processing according to control signals An image forming apparatus, comprising a dither switching means for switching the stage. 2. The image forming apparatus according to claim 1, wherein the predetermined density correction target value is set to a density target value such that a low density portion of the image information is surely printed out. . 3. The plurality of dither processing means includes a first dither processing means having an output information amount per pixel of 1 bit, and a second dither processing means having an output information amount per pixel of a plurality of bits. The image forming apparatus according to claim 1, further comprising: 4. The image forming apparatus according to claim 3, wherein the plurality of bits are 4 bits. 5. The dither switching means switches the plurality of dither processing means in page units or object units to be rendered according to the control signal. Image forming apparatus. 6. The image forming apparatus according to claim 1, wherein the control signal is generated from an operation unit that a user can operate. 7. The image forming apparatus is a print output apparatus including an image forming unit such as a printer, a copying machine, and a facsimile.
7. The image forming apparatus according to claim 1, further comprising a system constructed by a print output device for receiving data and an image forming unit for transmitting data. 8. An image forming method of an image forming apparatus, wherein image information is generated according to print information input from an external device, and an image is formed on a recording material according to the generated image information. The density measurement step of measuring the density characteristics of the image information, and the same density correction target is applied to the middle density area to the high density area of the image information according to the density measurement value obtained in the density measurement step. The density correction step for changing the density correction target of only a part to a preset predetermined density correction target value to perform density correction of image information, and the image information density-corrected in the density correction step are input to perform the dither processing. However, a plurality of dither processing steps having the same number of lines and different angles and different output information amount per pixel, and the plurality of dither processing steps according to the control signal are performed. Image forming method characterized by having a dither switching step of switching a. 9. The image forming method according to claim 8, wherein the predetermined density correction target value is set to a density target value such that a low density portion of the image information is surely printed out. . 10. The plurality of dither processing steps include a first dither processing step in which an output information amount per pixel is 1 bit and a second dither processing step in which an output information amount per pixel is 4 bits. The image forming method according to claim 8, further comprising: 11. A recording medium recording a program for controlling an image forming apparatus, which generates image information according to print information input from an external device and forms an image on a recording material according to the generated image information, by a computer. The program causes a computer to measure the density characteristic of the image information formed on the recording material, and the medium density portion to the high density portion of the image information have the same density according to the measured density measurement value. As the correction target, only the low density portion of the image information is changed to a predetermined density correction target value that is set in advance, and the density correction of the image information is performed. A program characterized by switching a plurality of dither processing units having the same angle and different output information amount per pixel to perform dither processing was recorded. recoding media. 12. The program according to claim 11, wherein the predetermined density correction target value is set to a density target value such that a low density portion of image information can be surely printed out. Recording medium. 13. The plurality of dither processing means includes a first dither processing means having an output information amount per pixel of 1 bit and a second dither processing means having an output information amount per pixel of 4 bits. A recording medium on which the program according to claim 11 or 12 is recorded. 14. A program for controlling, by a computer, an image forming apparatus that generates image information according to print information input from an external device and forms an image on a recording material according to the generated image information, The density measurement step of measuring the density characteristics of the image information formed on the recording material, and the same density correction target from the medium density portion to the high density portion of the image information according to the density measurement value obtained in the density measurement step. , A density correction step of changing the density correction target only in a low density portion of the image information to a preset predetermined density correction target value, and performing density correction of the image information; and image information density-corrected in the density correction step. Dither processing is performed by inputting, but the number of lines and angles are the same, and multiple dither processing steps with different output information amount per pixel Flip the program characterized by having a dither switching step for switching the plurality of dithering step. 15. The program according to claim 14, wherein the predetermined density correction target value is set to a density target value such that a low density portion of the image information is surely printed out. 16. The plurality of dither processing steps include a first dither processing step in which the output information amount per pixel is 1 bit and a second dither processing step in which the output information amount per pixel is 4 bits. 16. The program according to claim 14 or 15, comprising: