JP2001191588A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems that when various kinds of images are formed using images constituted of dots, it is difficult to enhance the quality of an image intended for putting emphasis on gradation and the quality of an image intended for putting emphasis on the highest density at the same time and it is difficult to obtain the highest density when the gradation is emphasized and insufficient to represent the gradation when the highest density is emphasized. SOLUTION: The size of dots in forming the image intended for emphasizing the gradation and the size of dots in forming the image intended for emphasizing the highest density are made different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image based on digital image data from a personal computer or an image reading apparatus, and more particularly to a density control for controlling the density of an image to be formed.

[0002]

2. Description of the Related Art In an image forming apparatus for forming an image based on digital image data from a document reading apparatus or a personal computer, a photosensitive member is subjected to dot exposure using a light beam from a light emitting element such as a laser diode. The gradation of an image is expressed by controlling the light emission of the light emitting element that generates the light emission based on the image data.

[0003] As a method of gradation expression, an area gradation method for changing an exposure area in accordance with image data is used. As the area gradation method, a method of changing the number of dots per unit area according to the density as shown in FIG. 1 is widely used, and for example, an error diffusion method is widely used.

[0004]

In a typical area gradation method, the gradation of an image to be formed is shown in FIGS. 1 (a) and 1 (b).
As shown in (1), it is expressed by changing the number of black pixels (or the number of white pixels) per unit area. The maximum density is expressed by setting all the pixels to black as shown in FIG. Theoretically, square pixels are assumed as shown in FIGS. 1A to 1C, and the entire surface is filled with black pixels as shown in FIG. . However, as shown in FIG. 1D, since the dots actually formed are circular, gaps are formed between the dots, and the density is reduced. For this reason, the maximum density that the image forming apparatus can output cannot be reflected in the image,
There is a problem that an image of sufficient quality cannot be formed.

As a countermeasure against such a problem, it is conceivable to increase the size of the dot. However, a new problem such as poor representation of a low-density portion or halftone occurs.

Accordingly, the present invention solves the above-mentioned problem that occurs when an image composed of dots is formed, and provides an image forming apparatus capable of forming both a halftone image and a high-density image. With the goal.

[0007]

The object of the present invention is achieved by the following invention.

(1) An image composed of dots is formed,
In an image forming apparatus having a tone emphasis mode emphasizing halftone expression and a high density mode emphasizing the highest density,
Control means for controlling the image density by controlling the image exposure device, the control means, the size of the dot of the highest density part in the high density mode, the size of the highest density part in the tone emphasis mode An image forming apparatus that performs control to make the size larger than a dot size.

(2) Normally, an image is formed in the tone emphasis mode, and when an operation for designating the high density mode is performed, the control means controls to switch to the high density mode. The image forming apparatus according to the above (1).

(3) The control means (1) or (2), wherein the control means controls the density in the tone emphasis mode based on a reference pattern formed on the image forming body. The image forming apparatus as described in the above.

(4) The image forming apparatus according to any one of (1) to (3), wherein the control unit switches the size of the dots by changing an output of a light emitting element. apparatus.

(5) The image according to any one of (1) to (4), wherein the control unit switches the size of the dots by changing a light emitting time of a light emitting element. Forming equipment.

(6) Image discriminating means for discriminating the type of image from the image data, wherein the control means switches between the tone emphasis mode and the high density mode based on the discrimination result of the image discriminating means. The image forming apparatus according to any one of (1) and (3) to (5), wherein

(7) The control means switches between the tone emphasis mode and the high-density mode in units of at least one page based on the judgment result of the image judgment means. Item).

(8) The image discriminating means performs image discrimination on a partial area of the image of one page, and the control means switches between the tone emphasis mode and the high density mode for each partial area of one page. The image forming apparatus according to the above mode (6), wherein the image forming is performed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A mechanical structure of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.

In FIG. 1, an image forming apparatus 1 includes an automatic document feeder A, a document image reading unit B for reading an image of a document fed by the automatic document feeder A, and image data obtained by reading. An image processing substrate C provided with an image processing circuit for processing, a writing device J on a drum-shaped photoreceptor 10 as an image carrier according to data after image processing, and a charging electrode 14, developing means 16 comprising a magnetic brush type developing device, transfer electrode 1
8, an image forming unit E including an image forming unit such as a separation electrode 20, a cleaning unit 21 and the like, and a storage unit F for paper feed trays 22 and 24 for storing the recording paper P.

The automatic document feeder A includes a document table 26
And a document transport processing unit 28 including a roller group including a roller R1 and switching means for appropriately switching a document movement path (no reference symbol).

The original image reading section B is located below the platen glass G and can move back and forth while maintaining the optical path length, a fixed imaging lens (hereinafter simply referred to as a lens) 33, and a line CCD. Image sensor 35 composed of
The writing device D includes a laser diode E5 as a light source, a rotary polygon mirror 106 as a deflecting unit, and the like.

When viewed from the direction of movement of the recording paper P as a transfer material, R10 is a registration roller in front of the transfer electrode 18, and H is a fixing unit downstream of the separation electrode 20.

In the embodiment, the fixing means H is composed of a roller having a built-in heating source and a pressure roller which rotates while being pressed against the roller.

Further, Z is a cleaning means for the fixing means H, and a cleaning web provided so as to be wound up is a main element.

One of the originals (not shown) placed on the original placing table 26 is transported by the original transport processing unit 28,
While passing under the roller R1, irradiation by the irradiation means L is performed.

The light reflected from the original passes through the mirror units 30 and 31 and the lens 33 at the fixed position and passes through the CCD 3.
5 and is read.

The image information read by the document image reading section B is subjected to image processing by the CPU, encoded, and stored in a memory provided on the image control board C.

Further, the image data is called in accordance with the image formation, and the laser diode E5 as a light emitting element in the writing device J is driven according to the image data, so that the photosensitive member 10 is exposed.

Prior to the exposure, the photoreceptor 10 rotating in the direction of the arrow (counterclockwise) is given a predetermined surface potential by the corona discharge action of the charging electrode 14. As a result, the electrostatic latent image is formed on the photoconductor 10 according to the image data.

The electrostatic latent image is reversely developed by the developing means 16 to be a visible image (toner image). On the other hand, the photoconductor 10
Before the leading end of the upper toner image reaches the transfer area, for example, one sheet of recording paper P in the sheet feed tray 22 is fed and reaches the registration roller R10, where the leading end is regulated.

The recording paper P is conveyed toward a transfer area by a registration roller R10 that starts rotating in synchronization with the toner image, that is, the image area on the photoconductor 10, so as to overlap.

In the transfer area, the toner image on the photoreceptor 10 is transferred onto the recording paper P by the urging of the transfer electrode 18,
Next, the recording paper P is separated from the photoconductor 10 by the bias of the separation electrode 20.

Thereafter, the pressure and heating of the fixing means H cause
The toner powder forming the toner image is melted and fixed on the recording paper P, and the recording paper P is discharged onto the discharge tray T via the discharge path 78 and the discharge roller 79.

In the embodiment, the paper feed trays 22 and 24 are arranged in two stages in the vertical direction. However, more paper feed trays may be provided.

The bottom (the same as the bottom wall) of the paper feed tray 24 arranged at the lower stage (in the embodiment, the lowermost stage because the paper feed tray is a two-stage stack, but the lower stage). A space 25 having a predetermined gap is formed between the apparatus and the bottom wall of the apparatus main body.

The space 25 is used in a mode (mode) in which images are formed on both sides of the recording paper P, and is cooperated with a second transport path 80 (described later) for reversing the recording paper. To achieve the reverse of the front and back.

Reference numerals 50 and 53 above the leading ends of the paper feed trays 22 and 24 (corresponding to the leading ends of the stored recording papers P when viewed from the paper feeding direction) denote paper feeding means (hereinafter referred to as feed-out means) comprising rollers. Rollers), 51 and 54
Is a feed roller, and 52 and 55 are double feed prevention rollers.

The feed rollers (50, 53) and the feed rollers (51, 54) are unitized, and a driving shaft connected to a driving source provided on the apparatus main body side or a locking means provided on a paper feeding section. It has a configuration that can be easily attached to and detached from.

The double feed prevention rollers (52, 55) are also unitized, and have a structure that can be easily attached to and detached from a fixing member provided on a fixing portion of the apparatus main body.

Reference numeral 60 denotes a manual paper feed tray of the manual paper feed unit, which can be opened and closed with the lower end serving as a fulcrum with respect to the main body side wall of the image forming apparatus 1.

Reference numeral 61 denotes a feed roller formed of a roller for feeding the recording paper placed on the manual feed tray 60 with the image formation, 63 denotes a feed roller provided downstream of the feed roller 61, and 65 denotes a feed roller. Roller 6
3, a double feed prevention roller for preventing a plurality of sheets of recording paper P from being fed, and has substantially the same configuration as that of the above-described paper feed trays 22 and 24.

Reference numeral 66 denotes a conveyance path for the recording paper P sent out from the manual paper feed tray 60, which communicates with a later-described junction via a pair of conveyance rollers immediately to the left of the feed roller 63.

Reference numeral 70 denotes a first conveyance path for forming an image on the recording paper P by transfer, and extends upward from below when viewed from the moving direction of the recording paper sent from an appropriate paper feed tray. .

Reference numeral 72 denotes a paper feed path for recording paper stored in the upper paper feed tray 22, reference numeral 74 denotes a paper feed path for recording paper stored in the lower paper feed tray 24, and reference numeral 76 denotes both trays 2.
It is a merging portion (a part of the first conveyance path 70) where the recording papers P sent from 2 and 24 merge.

Reference numeral 78 denotes a paper discharge path for discharging the recording paper on which a predetermined image has been formed onto the paper discharge tray T.

Numeral 80 denotes a second transport path for reversing the recording paper used for forming an image on both sides of the recording paper.
The upper part of the figure communicates with the first transport path.

The second transport path 80 extends downward from above when viewed from the direction of movement of the recording paper.

The lower end of the second conveying path 80 is a conveying path extending substantially vertically, and the lower end extends below the sheet feeding section of the lower sheet feeding tray 24.
0 (connected).

As understood from the above, the first transport path 7
0 and the second transport path 80 form a long loop in the longitudinal direction on one side wall side of the apparatus main body.

At the connecting portion between the first transport path 70 and the second transport path 80, there is provided a switchback roller R20 comprising a pair of reversible rollers.

Since the recording paper P is not continuously conveyed from the second conveyance path 80 to the first conveyance path 70, the connection part can be said to be a branch part for dividing the two conveyance paths.

Below the switchback roller R20, there is provided a passage leading to the space 25, and when the recording paper P is turned upside down, the recording paper P moving through the second transport path 80 is transferred to the space 25. Used to go to.

In the image forming process, the second transport path 8
When the recording paper P moving through the recording paper P is sent out toward the space 25, the rear end of the recording paper P is configured to be gripped by the switchback roller R20. 25 stores a part of the recording paper.

Reference numeral 90 denotes an (upper) branch guide which directs the recording paper P, on which an image has been formed on the first surface, to the paper discharge passage 78,
Alternatively, it is controlled so as to be directed to the second transport path 80. The branch guide 90 is controlled in accordance with the settings of the single-sided mode and the double-sided mode, and switches the recording paper transport path.

For example, when the mode for forming an image on both sides of the recording paper is set, the branch guide 90 transports the recording paper P on which the image is formed on the first side and which has the transfer toner image, to the second conveyance. After the recording paper is fed to the second conveyance path 80, the sheet is controlled via a control unit (not shown) so as to take the solid line position in the figure.

The first transport path 70 and the second transport path 8
A member that is located on 0 and indicated by a pair of circles (no reference symbol)
Is a transport roller.

The image forming process for the second side of the recording paper in the image forming apparatus having the above configuration is as follows.

As described above, when the recording paper P on which the image has been formed on the first surface moves up the first transport path 70 and its leading end reaches the branch guide 90, the branch guide 90 moves to the position indicated by the broken line in FIG. The recording paper P is kept in the second transport path 80
And continue to move.

The entrance of the second conveyance path 80 has a gentle arc, and ensures smooth movement of the recording paper P.

When the recording paper P descends on the second conveyance path 80 and reaches the lower end thereof, the recording paper P is nipped by the switchback roller R20 and conveyed downward from the second conveyance path to the lower sheet feeding tray 24. It is led to the space 25 formed below.

At this time, the first image formed on the recording paper P
The surface is facing down. Eventually, the rotation is stopped with the switchback roller R20 sandwiching the rear end of the recording paper P, and then the recording paper P is turned over, by reversing the rotation direction, that is, an image is formed. In the state where the second surface, which has not been processed, faces the photoconductor 10 side, the first transport path 7
0, and the leading end is regulated by the registration roller R10.

On the other hand, a second toner image is formed on the photoconductor 10 by the above-described process. When the registration roller R10 starts rotating in synchronization with the rotation of the photoconductor 10, the second toner image is formed. The recording paper P enters the transfer area while overlapping the image area.

Thereafter, when the leading end of the recording paper P on which the transfer processing, the separation processing, and the fixing processing have been performed reaches a certain portion of the branch guide 90, the branch guide 90 is kept at the position indicated by the solid line in FIG. Since the first transport path 70 and the paper discharge path 78 are in communication with each other and the communication with the second transport path 80 is cut off, the recording paper P enters the paper discharge path 78 and passes through the paper discharge rollers 79. The paper is discharged onto the paper discharge tray T. Thus, an image is formed on the recording paper.

FIG. 3 shows an electrical configuration of the image forming apparatus according to the embodiment of the present invention. The reading unit E1 has the image sensor 35 in FIG. 2, digitizes an analog image signal output from the image sensor 35, and outputs image data. The image data from the reading means E1 is subjected to image processing such as density conversion, filtering processing, gradation processing, and scaling processing in an image processing circuit E2, and then stored in an image memory E3. At the time of image formation, image data is read from the image memory E3, and the laser drive circuit E4
Is converted into a laser drive signal carrying image information, the laser drive signal causes the laser diode E5 to emit light, and the photosensitive member 10 is exposed. In the present embodiment, the image discriminating unit E6 processes the image data from the reading unit E1, and the image is an image to be reproduced with emphasis on halftone or an image to be reproduced with emphasis on the highest density. Is determined.

This determination is made according to the algorithm shown in FIG. FIG. 4 shows an algorithm for determining the type of image, and FIG. 5 shows a histogram used for the determination in FIG. The histogram in FIG. 5 shows the distribution of the number of pixels for each luminance, with the horizontal axis representing luminance and the vertical axis representing the number of pixels.

In FIG. 4, first, the reading means E1 reads an image. This reading may be for reading the entire surface of the document, or may be for reading a predetermined width of the leading end of the document, for example, a width of several mm. In reading using the automatic document feeder A, the leading end of the document is read. When the maximum number Hm of pixels forming an image in the document area read at 211 is smaller than the fixed value M1, that is, in FIG.
In the case of the image showing the histogram of (c), the image determining means E6 determines that the document image is a gradation image. If the maximum pixel number Hm is equal to or more than M1, the maximum pixel number Hm
Indicates information on the background (back) of the document. The document has a large proportion of the background in the image of the document. At 212, a peak Pk indicating the maximum number of pixels Hm
Is greater than the constant luminance value M2, that is,
In the case where the density distribution shown in FIG. 5A is shown, it is determined that a high-density character is formed on a low-density background, that is, a character image. When the luminance Im is not larger than M2, that is, in the case shown in FIG. 5B, it is determined that the image is an inverted (negative) image. In summary, FIG. 5A shows a character image, FIG. 5B shows an inverted image, and FIG. 5C shows a gradation image, whereby the image to be formed is roughly classified as a gradation image or a character image. It is possible. Then, the control means E 7
In the cases of (a) and (b), control for performing image formation with emphasis on the highest density, that is, control in the high-density mode is performed. In the case of FIG. Control in image formation to be performed, that is, control in the tone emphasis mode.

In the above-described example, the type of the original image is determined as a whole, and the control of the image formation by the control means E7 is performed by selecting the tone-weighted mode or the high-density mode for the entire image of at least one page. However, it is also possible that the type of image is determined for each pixel or for each image region including a plurality of pixels, and the control unit E7 selects the above-described image forming mode for each region. is there. Techniques for performing such image discrimination for each image region are known, and a known discrimination method can be used in the present embodiment.

Further, the user selects either the tone emphasis mode or the high density mode by operating the operation panel.
It is of course possible to perform the switching operation. In this case, the control means E7 selects at least one page between the tone emphasis mode and the high density mode. As an actual image forming apparatus, it is preferable that, in a normal operation, an image is formed in a tone-weighted mode and an image is formed in a high-density mode when an operation for designating the high-density mode is performed.

The control of image density in the tone emphasis mode and the control of image density in the high density mode are performed as follows.

The image density control in the tone emphasis mode is the area gradation method shown in FIG. 6A, that is, for example, the number of dots D1 per unit area of 4 × 4 pixels is controlled according to the input density data. It is performed by The diameter of the dot D1 is set substantially equal to the pixel pitch α.

The gradation control in the gradation emphasis mode is shown in FIG.
This is performed using the intermediate density Q shown in FIG. 7B and FIG. That is, a reference pattern q for gradation control corresponding to the intermediate density Q is formed on the photoconductor 10. The density of the pattern q is detected using a densitometer, and according to the detected density,
The amount of light emission of the laser diode E5, for example, the amount of light emission that provides the optimum density is set by PWM control for controlling the light emission time. This control is performed by the image processing circuit E2 by the control means E7 controlling the image processing circuit E2.
Is performed over the entire density curve shown in FIG. It is of course possible to obtain the density information of several points and adjust the gradation instead of the information on the intermediate density Q which is one point of the density curve in FIG. 6B.
That is, as shown in FIG. 7B, a plurality of gradation control reference patterns q1 to qi are formed on the photoreceptor 10, the density of these patterns is detected, and the gradation is adjusted. Is possible.

The image density in the high density mode is controlled by the area gradation method shown in FIG. 8A, that is, by controlling the number of dots D2 per unit area according to the input density data. Then, in the high density mode, a dot D2 larger than the diameter of the dot D1 is formed. Desirably, the diameter of the dot D2 is set to be larger than α√2 with respect to the pixel pitch α as shown in the figure. As a result, at the highest density, a toner layer is formed on the entire surface of the image, so that there is no gap between dots, and the highest density as the performance of the image forming apparatus is realized.

The control for changing the diameter of the dot is performed by increasing the drive voltage of the laser diode E5 to increase the emission intensity of the laser diode E5, or by extending the emission time by PWM control for increasing the width of the drive pulse. Or by using them in combination.

FIG. 8B shows the maximum density R in the tone emphasis mode and the maximum density Dmax in the high density mode, and there is a density difference Δ between the two.

[0073]

According to the first aspect of the present invention, it is possible to form a halftone image satisfactorily by emphasizing gradation expression and to form a high-density image clearly by emphasizing the density of the highest density portion. Thus, an image forming apparatus capable of performing the above is realized.

According to the second aspect of the present invention, since the image is formed in the tone emphasis mode in the normal operation, the operation is easy, and a generally good image is formed in the normal operation.

According to the fourth or fifth aspect of the present invention, the gradation is adjusted with high accuracy, and an image with a high degree of image characteristics such as density expression and contrast is formed.

According to the sixth aspect of the present invention, it is possible to form an optimum image according to the type of the original and the type of the image indicated by the input image data, so that the operation is simple and a high quality image is always obtained.

According to the seventh aspect of the present invention, since the image quality can be controlled for each page, it is possible to obtain a high quality image having no difference in image quality between pages of the formed image.

According to the eighth aspect of the present invention, even when images of different types are mixed in one page, an image in which the image of each portion is optimally adjusted is formed, and a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional gradation expression method.

FIG. 2 is a diagram showing a mechanical configuration of the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is a diagram showing an electrical configuration of the image forming apparatus according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating an algorithm of image discrimination.

FIG. 5 is a diagram illustrating a histogram used for image determination.

FIG. 6 is a diagram for explaining density control in a tone emphasis mode.

FIG. 7 is a diagram showing a reference pattern.

FIG. 8 is a diagram illustrating density control in a high-density mode.

[Explanation of symbols]

 Reference Signs List 10 photoconductor D1, D2 dot E1 reading means E2 image processing circuit E3 memory E4 laser drive circuit E5 laser diode E6 image discriminating means E7 control means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) H04N 1/40 F term (reference) 2C262 AA24 AA26 AA27 AB07 AC04 BB01 BB10 BB36 BB42 BB44 BC09 EA07 EA08 EA16 GA02 GA19 2H076 AB09 DA11 DA19 5B057 AA11 BA24 BA25 CA02 CA06 CA08 CA12 CA16 CB02 CB06 CB08 CB12 CB16 CC03 CE11 CH18 DA08 DB02 DB05 DB08 DB09 DC22 5C074 AA05 BB03 CC26 DD05 DD11 EE11 FF03 FF05 5C077 MM27 MP05 SS03

Claims (8)

[Claims] An image exposing apparatus is controlled in an image forming apparatus which forms an image composed of dots and has a tone emphasis mode emphasizing halftone expression and a high density mode emphasizing the highest density. Control means for controlling the image density according to the following formula: The control means makes the size of the dot of the highest density part in the high density mode larger than the size of the dot of the highest density part in the tone emphasis mode. An image forming apparatus that performs control. 2. An image forming apparatus according to claim 1, wherein an image is formed in the tone emphasis mode, and when an operation for designating the high density mode is performed, the control means performs control for switching to the high density mode. The image forming apparatus according to claim 1. 3. The image according to claim 1, wherein the control unit controls the density in the tone-weighted mode based on a reference pattern formed on the image forming body. Forming equipment. 4. The image forming apparatus according to claim 1, wherein the control unit switches the size of the dots by changing an output of a light emitting element. 5. The image forming apparatus according to claim 1, wherein the control unit switches the size of the dots by changing a light emitting time of a light emitting element. 6. An image discriminating means for discriminating a type of an image from image data, wherein said control means switches between the tone emphasis mode and the high density mode based on a discrimination result of the image discriminating means. 4. The method according to claim 1, wherein:
6. The image forming apparatus according to claim 5. 7. The method according to claim 6, wherein the control unit switches between the tone emphasizing mode and the high density mode in units of at least one page based on the determination result of the image determining unit. The image forming apparatus as described in the above. 8. The image discriminating means performs image discrimination on a partial area of an image of one page, and the control means switches between the tone emphasis mode and the high density mode for each partial area of one page. The image forming apparatus according to claim 6, wherein: