JP3377302B2 - Color image forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, and a printer.
Using an electrophotographic process such as facsimile, each color toner
Image forming apparatus that forms a color image by superimposing
About the installation. [0002] 2. Description of the Related Art A document image is read by a color scanner unit.
And processes the read image data, and the color printer
In digital color copiers that form images, black character images or
Are black line images (hereinafter, these images are referred to as “black line images”).
) And the intermediate color image forming the background etc.
The black linear image 1 is separated as shown in FIG.
Forming an image on transfer paper 3 using only toner 2 is disclosed in
This is a well-known technique according to Japanese Patent Application Laid-Open No. 61-13261.
FIG. 9 schematically shows the recording state after transfer and before fixing.
In (a) and the like, ○ indicates one dot (one pixel). During ~
The background image 4 of the intercolor image is Y (yellow), M (maze
Toner and C (cyan) color toner
The image is formed as a background color. Here, for color recording
The black image is originally three colors of Y, M and C
It can be formed by superimposing toner.
When the three colors of toner are superimposed on each other, the toner is placed on the transfer paper 3.
Is poor or has poor reproducibility as black
For example, a black linear image
1 with a black toner as a dedicated Bk (black) toner
To make it appear. In such a color record
As can be seen from FIG. 9B, the black linear image 1 (black
The base of the color toner 2) is the background (white) of the transfer paper 3. In this type of equipment, for example,
An image is formed sequentially for each toner, and the
Such as forming a color image on the transfer paper
Configuration, each color process on the color printer side
Between speed fluctuations (for example, speed fluctuation in the sub-scanning direction)
In some cases, the positional relationship between the black linear image 1 and the background image 4
May be shifted. For example, FIG.
In the case where the positional deviation as shown in FIG.
The background of the transfer paper 3 at a part of the boundary between 1 and the background image 4
A color missing portion (white missing portion) 5 in which white dots appear is generated. Practical
If it is a simple image example, the color is extracted to the state shown in FIG.
A shaded portion 5 occurs, and such a color missing portion 5 is quite noticeable.
Therefore, image quality is impaired, which is not preferable. However, the position
Cost is required for a configuration that performs high-precision driving to suppress displacement
Will be high. [0004] Therefore, without using high precision driving,
In order to eliminate the occurrence of the color missing portion 5 as described above,
According to Japanese Patent Application Laid-Open No. 61-13261, the circumference of the black linear image 1 is determined.
By superimposing Y, M, and C toner on the
Black images are also formed in an overlapping state.
According to this, it is assumed that the black linear image 1 and the back
Even if there is a displacement between the scenery image 4 and the
Displays a black image due to the superposition of Y, M, and C toners.
For the sake of clarity, the color between the black linear image 1 and the background image 4
No shading will occur. [0005] However, the displacement is
When it occurs, it appears at the boundary between the black linear image 1 and the background image 4
Black image due to superposition of Y, M, C toner
And as described in the same publication, Bk
Different from black image with toner, and black reproducibility
Bad (poor). As a result, if color misalignment occurs,
Although no shaded portion occurs, the outline of the black linear image 1 is blackened again.
It has a disadvantage of poor realism. [0006] A color image according to claim 1.
In the image forming apparatus, attention is paid to the input color image data.
A determination means for determining whether a pixel is a neutral color image or a black linear image is provided.
A black linear image according to the result of the determination by the determination means.
Is applied to each pixel of interest to form an image with black toner.
Image data processing and image output
-In the image forming apparatus, the black linear image
With background image to determine the presence or absence of a background image with a neutral color image
No discrimination means and when outputting a black linear image with a background image
Next, the background image with the background color is added to this black linear image.
Image processing means to form the pair, The black linear image and the front
Density determining means for determining the density with the background image;
The density of the background image is changed according to the judgment result of the degree judgment means.
Density changing means for changing the density of the black linear image.
In such a case, the density of the base image is reduced.. [0007] [0008] [0009] [0010] [0011] In the color image forming apparatus according to claim 1,
Is used for image processing when outputting a black linear image having a background image.
By means of a background image with a background color on a black linear image
Since the image is formed relatively, the background image and the black linear image
The background color only appears even if there is a misalignment between
No color dropouts, and the black linear image
Because everything is reproduced with black toner, including the hull part,
Black linear images with good reproducibilityIn particular, determine the image density
And change the density of the background image according to the density.
The color change of the black linear image due to the background color of the base image is small.
KunaYou. [0012] [0013] [0014] [0015] [0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.
Will be explained. The same parts as those shown in FIG. 9 and FIG.
It is shown using the same reference numerals. In this embodiment, the image carrier is
A ram-shaped photoreceptor and an intermediate transfer belt
Image in digital color copier using default
Image data to be recorded, applied to the recording device
Can be captured from its own color image reader,
-Can be imported from external devices such as a personal computer
It has a configuration. In other words, it is useful as a full-color copier.
Configuration that can be used as a full-color printer.
It is supposed to be done. FIG. 2 shows the entire digital color copier.
A schematic configuration diagram is shown in FIG. 3, and the photoconductor and the intermediate transfer belt are shown in FIG.
An enlarged view of the surrounding area is shown in FIG.
5 shows an example of an electrical system configuration including a data transfer relationship with the system. The color copier of this embodiment is roughly classified
Then, a color image reading device (hereinafter referred to as a color scanner)
) 11 and a color image recording device (hereinafter referred to as a color printer).
12). First, the color scanner 11 scans the original 13
The image is illuminated by illumination lamp 14, mirror group 15 and lens 16.
The image is formed on the color sensor 17 through the
Image data is stored for each color separation light of Blue, Green, Red, for example.
And converts it into an electrical image signal. And this
B, G, R color separation image signals obtained by the color scanner 11
The image processing unit performs color conversion processing based on the intensity level.
Black Bk, cyan C, magenta M, yellow Y
Is obtained. This is called Color Printer 1
2, visualization with Bk, C, M, and Y toners is performed.
No, overlapping these to form a four-color full-color image
You. Next, an outline of the color printer 12 will be described.
You. The writing optical unit 18 is provided with the color scanner 11.
Converts the color image data from the
Is performed, and an electrostatic latent image is formed on the photosensitive member 19.
Form. The photosensitive member 19 rotates counterclockwise as indicated by the arrow.
Around the cleaning unit 20
Lamp 21, charger 22, potential sensor 23, Bk developing device
24, C developing device 25, M developing device 26, Y developing device 27,
Image density pattern detector 28, intermediate transfer belt 29, etc.
Are located. Each of the developing units 24-27 displays an electrostatic latent image.
Rotate developer so that it faces photoconductor 19 to form an image
Developing sleeve (24a, 25a, 26a, 27a)
And a developing pad that rotates to pump and agitate the developer
And sensors for detecting toner concentration of developer
I have. Here, the order of the developing operation (color image forming order)
The operation will be described below with an example of Bk, C, M, Y
(However, the order of image formation is limited to this.
No). When the copy operation is started, the color scan is started.
Bk image data is read from a predetermined timing by the
Starts, and the laser light
Optical writing / latent image formation starts (hereinafter, Bk image data
Is referred to as a Bk latent image. About C, M, Y
The same applies). It can be developed from the tip of this Bk latent image.
To reach the developing position of Bk developing unit 24
Before the development, the rotation of the developing sleeve 24a is started to form the Bk latent image.
Develop with Bk toner. Then, the developing operation of the Bk latent image area
Continue the operation, but the trailing edge of the Bk latent image passes through the Bk development position.
At the time when the development is stopped. This is at least
Completed before the leading edge of the C latent image from the C image data arrives
Let it. Next, the Bk toner formed on the photosensitive member 19
An image is transferred to the intermediate transfer bell driven at the same speed as the photoconductor 19.
(Hereinafter, intermediate transfer from the photoconductor 19).
The transfer of the toner image to the copying belt 29 is referred to as “primary transfer”.
). The primary transfer is performed by the photosensitive member 19 and the intermediate transfer belt 29.
Is in contact with the transfer bias roller 30
By applying a predetermined bias voltage with the power supply described
Do. In addition, the intermediate transfer belt 29 is sequentially attached to the photoconductor 19.
The Bk, C, M, and Y toner images to be formed are sequentially arranged on the same surface.
To form a four-color superimposed primary transfer image.
Batch transfer (secondary transfer) is performed on paper 3. This intermediate transfer base
The unit configuration and operation of the router 29 will be described later. Here, on the photoconductor 19 side, after the Bk process,
Proceed to step C, but from a predetermined timing
11 starts reading the C image data,
A latent image is formed by writing laser light with a laser beam. The C developing device 25 is located
After the rear end of the Bk latent image has passed, and the front end of the C latent image
The rotation of the developing sleeve 25a is started before the
The image is developed with C toner. Then, the development of the C latent image area
Continue, but when the trailing edge of the latent image has passed,
As in the case of the container, the developing operation is disabled. This is also
It is completed before the leading end of the next M latent image arrives. The steps of M and Y are described below.
The operations of image data reading, latent image formation, and development
Since the steps are the same as steps k and C, the description is omitted. Next, the intermediate transfer belt unit will be described.
I will tell. The intermediate transfer belt 29 includes a driving roller 31,
Stretched around the transfer bias roller 30 and the driven roller group
And is driven and controlled by a drive motor. The belt cleaning unit 32 includes a
From the roller 32a, the rubber blade 32b and the belt.
It is constituted by a contact / separation mechanism 32c and the like. This cree
The contacting / separating operation timing of the
From the start Y (the fourth color of the final color) primary rotation of the rear end of the image
Until the printing is completed, keep it away from the surface of the intermediate transfer belt 29.
In advance, at a predetermined timing thereafter, the
Therefore, cleaning is performed by contacting the surface of the belt 29. The paper transfer unit 33 is provided with a paper transfer bias
Roller 33a, roller cleaning blade 33b and medium
And a mechanism 33c for contacting and separating from the intermediary transfer belt 29.
ing. This bias roller 33a is normally used for intermediate transfer.
Although it is separated from the belt 29 surface, the intermediate transfer belt 29
Transfer the four-color superimposed image formed on the surface to the transfer paper 3 at once
At the time when it is pressed by the contact / separation mechanism 33c,
A predetermined via is supplied to the roller 33a by a power supply described later.
The transfer to the transfer paper 3 is performed by applying a transfer voltage. The transfer paper 3 is fed by a paper feed roller 35 and a resist
The four color weight of the surface of the intermediate transfer belt 29 is
The timing when the leading edge of the image reaches the paper transfer position.
The paper is fed together. Thus, the four colors from the surface of the intermediate transfer belt 29
The transfer paper 3 on which the superimposed toner image is collectively transferred is placed in a paper transport unit.
Is transported to a fixing device 38 by a slot 37, and is controlled to a predetermined temperature.
The fixing roller 38a and the pressure roller 38b
-The image is melted and fixed, discharged to the copy tray 39, and
Get a copy. The surface of the photoreceptor 19 after the belt transfer is
After being cleaned by the cleaning unit 20,
Then, the charge is uniformly removed by the charge removing lamp 21. Cleaning of the intermediate transfer belt 29
Is, as described above, after the transfer of the final color Y image belt is completed.
The cleaning unit 32 at a predetermined timing
This is performed by pressing against the surface of the belt 29 by the mechanism 32c. The intermediate transfer belt 29 has one sheet.
Following the batch transfer process of the four-color superimposed image on the transfer paper,
The surface has been cleaned by the cleaning unit 32
The second Bk toner image is transferred to the area by belt transfer.
To After that, the operation becomes the same as that of the first sheet. The transfer paper cassettes 40 to 43 have various types.
Size transfer paper is stored and specified on the operation panel.
The timing from the paper cassette
The sheet is fed and conveyed in the direction of the dist roller 36. 44 is OH
It is a manual paper feed tray for P paper and thick paper. 45 is a roll
It is a paper feed table in which the paper cassettes 42 and 43 are built. The above is a copy mode for obtaining four full colors.
As described above, the three-color copy mode and the two-color copy mode
In the case of a password, the same applies to the specified color and required number of times.
The same operation is performed. Also, in the single color copy mode
In the case, the developer of the color is
Only the developing operation state, and exposes the intermediate transfer belt 29 to light.
Driving at a constant speed in the forward direction while contacting the surface of the body 19,
Further, the blade 32b was also brought into contact with the intermediate transfer belt 29.
The copy operation is performed as it is. FIG. 4 shows such a full-color copying operation.
As shown, under the control of the system controller 51,
The scanner controller 52 of the color scanner 11
R, G, B color image data obtained from
(Image processing device) Processed by 53 and at the color printer 12 side
To the write controller 54 of
You. Here, the IPU 53 has a system
CPU 55, ROM 56,
It has an area memory 57 and performs appropriate image processing.
It has a processing unit. Here, the scanner γ dot correction unit 5
8, filter / color converter 59, scaling unit 60, create
Unit 61, a filter γ correction / gradation unit 62, and a video controller.
Roll unit 63 writes with scanner controller 52
And the controller 54 in that order. Said
Image separation unit 64 branches to scanner γ dot correction unit 58
The image separation unit 64 is connected to the filter / color conversion unit 5
9 are connected to each part. Note that this image separation unit
64 is an interface for the system controller 51 side.
Are connected via a base 65. Further, in this embodiment, the personal computer
As a printout output device for the printer 66 etc.
Printer controller 67 feeds paper to make it available
It is added to the table 45 and the like. This printer controller
Reference numeral 67 denotes an interposed portion between the scaling unit 60 and the create unit 61.
Interface 68 to the IPU 53,
Function and printer function can be freely selected. That is,
-Change the printer mode with the operation unit of the personal computer 66.
If selected, the interface 68 will be
Perform the select operation so that the
Color image data from the computer 66 side
To the write controller 54 through the
You. The IPU 53 has a basic function.
As is well known, the color scanner 11 side or the
R, G, B input from the personal computer 66
Pixel of interest from the color image data
A determination unit for determining whether the image is an image,
If the image is a black linear image according to the determination result, the black toner Bk is used.
Image data for each pixel of interest so that more images are formed
Function to perform processing and output to write controller 54 side
Having. That is, the image formation as described in FIG.
Function. In addition, the IPU 53 of this embodiment is
One having the function of image presence / absence determination means and image processing means
It is configured. Here, the background image presence determination means
Outputs the black linear image 1 based on the determination result of the determination unit.
If the black linear image 1 is a background image
Image 5 or a white background without the background image 5
To determine whether the paper is present on the transfer paper ground
And the determination can be made according to the determination result of the determination means.
The image processing means here is a means for determining the presence or absence of a background image.
Black linear image 1 determined to have background image 5 by step
At the time of output, the black linear image 1 depends on the background color.
Special image processing to relatively form the base image
Has the ability to perform. Special images by such image processing means
Examples of processing include, for example, the following examples.
I can do it. As a first example, as shown in FIG.
A base image 69 of the same color as the background image 4 for the entire image 1
Write the image data processed so that
The controller 54 is configured to output to the
This corresponds to the invention described in Item 2). That is, with Bk toner
M, C, Y for the entire area of the black linear image 1 on which an image is formed
The background image 69 of the background color by an appropriate combination of color toners
Image processing is performed so as to be formed integrally with the scenery image 4.
Write data is given to the write controller 54 side.
Then, it is subjected to recording in the recording step as described above. By the way, according to the recording process described above,
The image formation on the light body 19 is performed by a black line using Bk toner.
The process related to the shape image 1 is the first, but finally the process
Image transferred onto the transfer paper 3 via the intermediary transfer belt 29
Is formed, black is formed by Bk toner formed first.
The linear image 1 becomes the top image as shown in FIG.
The base image 69 and the background image 4 that are formed with a delay
The image above. According to the first example, the entire area of the black linear image 1 is
Since the background image 69 of the scenery exists,
During recording, a position shift occurs between the black linear image 1 and the background image 4.
Even if it is misaligned, the background image 69 appears in the misaligned portion.
It only shows up, and creates a color missing part where the background can be seen.
I do not. In particular, the position between the black linear image 1 and the background image 4
Even if there is a shift, the base image formed by the background color
Since the image 69 appears, the result is the same as when there is no displacement.
Black linear image with only Bk toner on background color
1 is present, as illustrated in FIG.
High-quality images with good reproducibility
It is. In the first example, the base image 69 is the black linear image 1
Is formed over the entire area of
However, no color missing portion occurs. As a second example, as shown in FIG.
Same as background image 4 only for one dot of the outline of image 1
It is formed by overlapping one color base image 70 so as to bite it.
Image data to be output to the writing controller 54 side.
(Corresponding to the invention described in claim 3)
). That is, a black linear image formed with Bk toner
An appropriate combination of M, C, and Y color toners is applied to the contour of the image 1.
The background image 70 of the background color due to the
Write data that has been subjected to image processing so that
To the embedded controller 54 side, as described above.
Provided for recording in the recording process. According to the second example, the outline 1 of the black linear image 1
The background color base image 70 exists in the dot area
Therefore, the black linear image 1 and the background image 4
Even if there is a displacement of less than 1 dot between
Only the background image 70 appears in the position shift
In addition, no color missing portion that makes the background visible is generated. In particular,
When a position shift occurs between the black linear image 1 and the background image 4
However, the background image 70 formed by the background color appears.
Therefore, the result is the same as when there is no misalignment.
Black linear image 1 using only Bk toner exists on color
And high-quality images with good reproducibility including the outline
Is obtained. In the second example, the base image 70 is a black line.
Since the image is formed only on the outline of the image 1, the background image 7
0 can reduce the amount of toner consumed,
Because the portion of the base of the image 1 becomes the background of the transfer paper,
The color change of the black linear image 1 due to the background is small. Note that in the second example, the contour portion
Only the base image 70 is formed.
If the misalignment is more than one dot, widen it accordingly
What should I do? Further, the thickness (line width) of the black linear image 1 is
The base image formed on the black linear image 1 is
Formed over the entire area as in image 69 or as in base image 70
If it is possible to select whether to form only on the contour part,
For the thick black linear image 1, the base image 69 is
It is possible to suppress the increase in toner consumption by forming
Color change of the black linear image 1 due to the background image
And the entire area of the thin black linear image 1
By forming the base image 69 on the
Life can be reliably prevented. As a third example, as shown in FIG.
Depending on the image densities of the image 1 and the background image 4, the first example
Of the base image 69 formed over the entire area of the black linear image 1
Write image data processed to reduce
It is configured to output to the roller 54 side.
Described invention). In FIG. 6, the background image 6
9 is smaller than the thickness of the background image 4,
Is low. This is a black linear image 1
Depending on the density of the background image 4
The color of the black linear image 1 changes due to the effect of the image 69, and slightly
This is because it may not be black. That is, a black linear image
1 is light and the background color is dark, the background image 6
Forming 9 with a dark background color,
The color of the formed black linear image 1 may not be completely black
is there. Therefore, in such a case, the background image 69
Color is the same as the background color, but its density should be reduced.
With this, the influence of the black linear image 1 due to the base image 69 is reduced.
Is done. For this purpose, the image processing means of the third example comprises:
Density determination for determining the density of black linear image 1 and background image 4
Means and a background image according to the determination result of the density determining means.
A density changing means for changing the density of 69.
No. These are easily realized with existing image processing technology.
obtain. According to the third example, as described above, the background image
69 can reduce the black change of the black linear image 1 as much as possible.
Above, as originally intended, the black linear image 1 and the background image 4
Even if there is a misalignment between them,
Since the image 69 appears, no color missing portion occurs. The third example is an example of application to the first example.
However, the present invention can be similarly applied to the case of the second example. As a fourth example, as shown in FIG.
The line width of the image 1 itself, and therefore its outline, is regarded as the original image.
Write the image data processed so that
The controller 54 is configured to output to the
This corresponds to the invention described in Item 5). That is, the above-mentioned first to third
In the example, the image processing on the background image side (background image side)
A background image of a background color is formed below the linear image 1.
However, in the fourth example, the image processing on the black linear image 1 side is performed.
So that a part of the background image 4 becomes the background image 71
It is configured. About thickening the outline of black linear image 1
Can be set appropriately according to the degree of misalignment that can occur.
Good. According to the fourth example, the original black linear image 1 and the back
Even if there is a misalignment with the scenery image 4, the black linear image
The image 1 has a thickened extension 1a, and this extension 1a
Since the transfer paper 3 is located on the background, the background is directly
There is no visible color missing portion. Also, back
Black linear image 1 using only Bk toner exists on the scene
This means that high-quality images with good reproducibility
An image is obtained. Further, the BK mark is added to the outline of the black linear image 1.
Color expansion prevention by simply expanding the image
Therefore, it is possible to suppress an increase in the amount of toner consumption due to the above. As a modified example, as shown in FIG.
In addition, regarding the boundary between the black linear image 1 and the background image 4, the background
The recording dots on the edge 4a on the image 4 side are blurred.
The processed image data is output to the write controller 54 side.
You may make it do. In FIG. 8, the background image 4
The thickness of the edge portion 4a is tapered.
It is typical that the recording dot is blurred as going to
Is represented in That is, this modified example is different from the first to fourth embodiments described above.
Unlike the example, it is based on the idea of forming a base image.
, But a misalignment between the black linear image 1 and the background image 4
If it occurs, the background of the transfer paper 3 as shown in FIG.
Although a color missing portion 5 in which the image can be seen may occur,
Since the recording dots on the edge 4a are blurred,
The part 5 becomes inconspicuous and does not impair the image quality.
You. Also, the black linear image 1 has no base image.
And there is no change in black color. It should be noted that the above-described color omission prevention processing is performed in the background image.
This is performed only when the black linear image 1 having the image 4 is recorded.
That is, the black linear image 1 does not have the background image 4 and
When formed directly on the ground of the paper 3,
Processing. Even if misalignment occurs, problems such as missing colors may occur.
Because there is no. Also, the black linear image 1 and the background image 4
The positional deviation between the sub-scanning direction and the main scanning direction
May be applied. [0057] The color image forming apparatus according to the first aspect of the present invention.
According to the position, the pixel of interest from the input color image data
Has a determining means for determining whether the image is a neutral color image or a black linear image.
Then, according to the result of the discrimination by the discriminating means, the black linear image is
For each pixel of interest to form an image with black toner
Image data processed and output as images
In the image forming apparatus, the middle of the black linear image
Background image presence / absence to determine the presence / absence of a background image by intercolor image
Determining means for outputting a black linear image having a background image;
The background image based on the background color is relative to this black linear image.
Image processing means for formingThe black linear image and the spine
Density determining means for determining the density with the scenery image;
The density of the background image according to the determination result of the determination means
And a density changing unit, which is provided when the density of the black linear image is low.
In such a case, the density of the base image was reduced.So
Assuming that there is a displacement between the background image and the black linear image
Also, the appearance of the background color will not cause any color loss
In addition, the black linear image is all black toner including its outline.
To reproduce a black linear image with good reproducibilityWhat
In particular, the image density is determined, and the
Since the density of the image is changed, the black
The color change of the linear image is small.You. [0058] [0059] [0060] [0061]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a processing example of a first example in one embodiment of the present invention. FIG. 2 is a schematic front view showing the entire configuration of a full-color copying machine. FIG. 3 is a schematic front view showing the periphery of a photoconductor and an intermediate transfer belt in an enlarged manner. FIG. 4 is a block diagram showing a control system configuration. FIG. 5 is a schematic diagram showing a processing example of a second example in one embodiment of the present invention. FIG. 6 is a schematic diagram showing a processing example of a third example in one embodiment of the present invention. FIG. 7 is a schematic diagram showing a processing example of a fourth example in one embodiment of the present invention. FIG. 8 is a schematic diagram showing a processing example of a modified example in one embodiment of the present invention. FIG. 9 is a schematic diagram showing a conventional example. FIG. 10 is a schematic diagram for explaining a defect according to a conventional example. [Description of Signs] 1 Black linear image 2 Black toner 4 Background image 69 to 71 Base image

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-83540 (JP, A) JP-A-4-14378 (JP, A) JP-A-2-213871 (JP, A) JP-A-3-3 54965 (JP, A) JP-A-61-13261 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/01-15/01 117 H04N 1/46

Claims (1)

(57) [Claims 1] A discriminating means for discriminating whether a pixel of interest is an intermediate color image or a black linear image from input color image data, and according to a discrimination result by the discriminating means. In a color image forming apparatus in which image data processing is performed on each target pixel so as to form an image with a black toner and an image is output using a black toner, a background image based on the intermediate color image is generated with respect to the black linear image. Background image presence / absence determination means for determining the presence or absence of a
Image processing means for forming a base image with a background color relative to the black linear image;
Density determining means for determining the density with the scenery image;
The density of the background image according to the determination result of the determination means
And a density changing unit, which is provided when the density of the black linear image is low.
In this case, the density of the base image is reduced .