JPH04318572A - Color-image forming device - Google Patents

Abstract

PURPOSE:To restrain image omission and image reduction caused by a margin as much as possible by setting the width of a margin which prevents the front end of a sheet from being wound round a fixing roller to the minimum amount necessary according to the amount of toner in the vicinity of the front end of a color picture formed on a sheet. CONSTITUTION:Image data which are color-separated into BGR, read by a line sensor 18, and stored in each area of a VRAM 4, are image-processed and converts them into YMC or YMCK iamge data by CPU 3. Subsequently, the decision range with a width D and an area A set at its front end is determined in such a manner that according to the area ratio R of the area of white base or light color part to A, or the average value M of the total amount of toner by A, the width W of a margin is set narrow when R is large or M is small or wide when R is small or M is large.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly to white edge setting means for providing a white edge at the leading end of a recording medium of a color image forming apparatus.

0002

[Prior art] Video printer, color facsimile,
There are color image forming devices such as color copying machines, color digital copying machines, and color printers that output the final results of computer-generated CAD. Color laser printers, which have particularly excellent resolution and printing speed, are often used in the image forming section. It is being said.

Such a color laser printer (hereinafter simply referred to as a "color printer") uses a sub-scan by moving the photo-conductor and a main-scan by deflecting a laser beam orthogonally to the sub-scan by moving the photo-conductor, thereby scanning the charged photo-conductor. An electrostatic latent monochrome image is formed on the recording medium by optical writing, and the monochrome toner image developed with the corresponding color toner is overlaid several times to finally form a full color image on the recording medium. It is something that forms.

The color overlapping method includes direct transfer, in which a monochrome toner image formed on a photoreceptor is transferred each time to a recording medium set on a transfer drum, and the colors are overlaid on the recording medium. The intermediate transfer method transfers to an intermediate transfer belt each time, superimposes the colors on the intermediate transfer belt, and then transfers them to a recording medium, and the intermediate transfer method transfers monochrome toner images onto a photoreceptor to form a full-color image. There is a single transfer method in which the image is then transferred to a recording medium.

Regardless of the method, when performing dry development using powder toner, there is a fixing step in which the finally formed toner image is fused onto a recording medium such as paper using a high temperature fixing roller. However, due to the stickiness of the molten toner, some of the toner adheres to the fixing roller and stains other parts of the paper, resulting in an offset accident, or the paper wraps around the fixing roller without separating, causing smoke or smoke generation due to the heat generated. There is a risk of serious accidents such as ignition.

[0006] Therefore, countermeasures such as coating the surface of the fixing roller with a resin that has good toner separation properties or applying a thin layer of silicone oil were taken, and the offset accident was resolved.
However, it has not been possible to completely prevent paper wrapping.

Therefore, as shown in Japanese Patent Publication No. 54-36502, there has been a proposal to provide a white light-shielding portion at the reference position of the document table where the leading edge of the document comes into contact with in a copying machine, or to use an eraser. Accordingly, there has been a technique in which a white edge with a width of about 0.5 to 2 mm to which toner does not adhere is provided at the leading edge of the paper, and the leading edge is separated from the fixing roller by the elasticity of the paper.

However, compared to monochrome images that use a single toner, color images use yellow,
Since toner images of three colors magenta and cyan or four colors (hereinafter referred to as "Y, M, C, K") including black are superimposed, the amount of toner becomes much larger and it is difficult to separate the sheets. Generally, a white border with a width of about 7 to 8 mm was provided, although it varied depending on the model, structure, and paper thickness.

Therefore, there is no problem in the case of image output from a video printer or computer, or DTP (desktop publishing) output, etc., where the white border can be widened and edited in advance, but when printing in color without editing the original image, there is no problem. In the case of copying, color facsimile, etc., the part that overlaps the white edge of the image at the leading edge may be missing, or the image at the trailing edge may be removed by shifting the registration of the paper (relative to the formed image) in order to leave the image at the leading edge. There was a problem with it cutting out.

[0010] In order to prevent missing or cut images (hereinafter collectively referred to as "image missing") even if a white border is provided, it is necessary to adjust the document size and paper as shown in, for example, Japanese Patent Laid-Open No. 2-38049. It was also possible to form an image reduced according to the effective size excluding the white edge portion of the paper by applying the proposal of automatically changing the magnification according to the size of the paper.

[0011]

[Problems to be Solved by the Invention] However, if a white border of the same degree is provided at the trailing edge of the paper for balance purposes, the effective length at which an image can be formed without missing data will be reduced by 16 mm, which is a problem for A3 size paper. This is relatively not a problem when using large-sized paper such as B4 or B4 paper in a vertical position where the long side coincides with the transport direction, but it becomes a problem with small-sized paper.

In other words, when B5 size paper is used in the horizontal position, its effective length is 166mm compared to the paper length of 182mm.
mm, the image is reduced by 91%, and psychologically we tend to perceive it based on the area reduction rate, so we feel that it has been reduced to 83%. Therefore, a problem arises in that users who expect a full-size copy with no missing images are disappointed.

However, the 8 mm wide white border was designed so that the paper would separate even in the worst case when all four colors of toner are solid, and the image formed near the leading edge of the paper will be black. If the toner density is low, such as when the toner is composed of only one-color characters or a bright image, a 2 mm wide white border will not cause any problem, as is the case with black-and-white copies.

[0014] This invention was made in view of the above points, and the width of the white edge at the leading edge of the paper (recording medium) is set to the minimum necessary to suppress image loss and image reduction as much as possible. The purpose is to form a color image.

[0015]

[Means for Solving the Problems] In order to achieve the above object, in a color image forming apparatus that forms a color image on a recording medium by overlapping a plurality of color toner images of different colors, a A judgment range of a preset width is set in the transport direction,

[0016] The first invention determines the amount of toner at the leading edge of the recording medium according to the area ratio of the area of a white background or a bright color portion close to it in the image formed within the determination range to the total area of the determination range. A white edge setting means is provided for setting the width of the non-adhesive white edge to be narrow when the area ratio is large and wide when the area ratio is small.

[0017] The second aspect of the invention is to determine whether toner does not adhere to the leading edge of the recording medium in accordance with the average value over the entire determination range of the total amount of each color toner to form an image formed within the determination range. A white edge setting means is provided for setting the edge width to be narrow when the average value is small and wide when the average value is large.

[0018]

[Operation] In the color image forming apparatus configured as described above, the white edge setting means determines the area of the white background or bright color area of the image formed within the determination range provided at the leading end of the recording medium. Depending on the area ratio to the total area or the average value over the entire judgment range of the total amount of each color toner to form the image, the width of the white edge is narrowed when the area ratio is large or the average value is small. , when the area ratio is small or the average value is large, set it wide.

[0019] Therefore, since the set white border has the necessary minimum width depending on each case, it is possible to form a color image in which image loss and image reduction are suppressed as much as possible.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.First, the terms "width and length" will be defined as shown in FIG. That is, for a sheet of paper, which is a recording medium, the conveying direction indicated by the arrow is the "length," the direction perpendicular to that direction is the "width," and the left side is the "tip." On the other hand, the "width" of the white edge and the determination range refers to the width taken from the leading edge of the paper in the conveying direction.

FIG. 4 is a schematic diagram showing the internal mechanism of a color digital copying machine (hereinafter simply referred to as "color copying machine") which is an embodiment of the present invention. Functionally, the mechanical system of this color copying machine can be roughly divided into a scanning photoelectric conversion unit that scans an original and converts it into a digital signal of brightness separated into colors for each pixel, and a monochrome image forming section that forms a color toner image, an intermediate transfer section that superimposes these color toner images to synthesize a full-color image, and transfers and fixes the synthesized full-color image onto paper, which is a recording medium. It consists of a paper transport section.

In the scanning photoelectric conversion section, the original 1 is placed on the glass plate 10 with the original surface facing downward, and set so that the leading edge of the original is in contact with the position regulating plate 11. When a start button (not shown) is pressed, the illumination lamp 12 equipped with a reflector lights up and illuminates the document surface of the document 1, and moves at a constant speed to the right together with the first mirror 13 that is integrally configured. Sub-scan the document surface. At the same time, the second and third mirrors 14 and 15, which are integrally configured and perpendicular to each other, move in the same direction at 1/2 the speed of the first mirror 13. The optical distance to the surface remains constant during scanning.

The photographing lens 16 converts the image (generally a reduced mapped image) of the document surface being sub-scanned into the three additive primary colors of blue, green, and red that constitute the color separation filter group 17.
Each color filter 1 (hereinafter referred to as "B, G, R" respectively)
7b, 17g, and 17r, and an image is formed on a line sensor 18 consisting of a one-dimensional array of CCDs.

The line sensor 18 main-scans the image of the document surface formed on its light-receiving surface using a clock having a preset frequency, and serially outputs an analog signal corresponding to the brightness of each pixel. Output. The analog signals are each converted into a digital signal by an A/D converter (not shown) and stored in each area on the RAM.

The color filters inserted into the photographing optical path of the color separation filter group 17 are the B filter 17b and the G filter 1.
7g and R filter 17r, the above-mentioned main scanning and sub-scanning were repeated each time the filter 7g and R filter 17r were switched, and the digital data of brightness and darkness for each pixel of each image separated into B, G, and R was stored in the memory. It turns out. This B, G, and R image data is converted into Y, M, C, and K image data through image processing that will be described later, and then stored in the memory again.

Next, in the monochrome image forming section,
The surface of the photosensitive drum 20 rotating clockwise is uniformly charged by a charging charger 21, and after the area unnecessary for image formation is removed by an eraser 22, the Y, M, C, It is irradiated by a laser spot that is on/off modulated and main-scanned, which is output from the optical writing unit 23 according to image data of any one of K.
A monochrome electrostatic latent image is formed.

[0027] Downstream of the optical writing unit 23, there is a developing unit consisting of four developing units containing toners of Y, M, C, and K, represented by respective developing drums 24y, 24m, 24c, and 24k. A device 25 is provided, in which a selected one of the four developing drums 24y, 24m, 24c, and 24k develops an electrostatic latent image with its toner in close proximity to the photoreceptor drum 20, and the other three develop the electrostatic latent image with its toner. The developing drums are slidable so that they are far apart from each other so that they do not affect the image. Therefore, the electrostatic latent image formed by the optical writing unit 23 is converted into a monochrome toner image by selecting a developing drum corresponding to the image data.

The monochrome toner image is transferred to an intermediate transfer belt 30 that is in contact with the photosensitive drum 20 and is being fed at the same speed and in the same direction. After the transfer, the toner remaining on the photoreceptor drum 20 has its charge weakened by the static elimination charger 26 and is removed by the cleaning unit 27. The slight amount of charge remaining on the photoreceptor drum 20 is completely eliminated by light irradiation from the charge removal lamp 28, and the photoreceptor drum 20 enters the next cycle starting with charging by the charger 21 again.

In the intermediate transfer section, the intermediate transfer belt 30
The photosensitive drum 20 is driven by two drive rollers 31 and 32.
The photoreceptor drum 20 is driven counterclockwise at the same linear velocity as the photoreceptor drum 20, and is brought into close contact with the photoreceptor drum 20 by two bias rollers 33a and 33b. A transfer roller 34 and a cleaning blade 35, which are capable of coming into contact with each other and detaching from each other and are normally in a detached position, are provided in the moving path.

The intermediate transfer belt 30 has a resistance of about 10 7 to 10 8 Ω, the drive rollers 31 and 32 are grounded, and bias voltages necessary for transfer are applied to the bias rollers 33 a and 33 b and the transfer roller 34, respectively. Therefore, the portion that is in close contact with the photoreceptor drum 20 has the potential of the bias voltage, and the toner image is transferred from the photoreceptor drum 20 to the intermediate transfer belt 30. On the other hand, the intermediate transfer belt 30
The potential of the portion between the drive rollers 31 and 32 is "0".

Each rotation of the intermediate transfer belt 30, the photosensitive drum 20 is moved at a timing such that mutually corresponding portions of the images formed are aligned on the intermediate transfer belt 30.
An image written thereon and converted into a monochrome toner image is transferred. The order of the four colors Y, M, C, and K varies depending on the copying machine model and the performance of each color toner, but the four monochrome images are gradually superimposed on the intermediate transfer belt 30 to synthesize a full-color image. It is being done.

In the paper transport section, the paper 2 fed from a paper cassette (not shown) is passed through a pair of registration rollers 40.
It comes into contact with and stops. When the pair of registration rollers 40 starts conveying in time with the leading edge of the finally synthesized full-color image, the paper 2 passes through the path shown by the broken line, and the transfer roller 34, which has been displaced to the contact position as shown in the figure, has an electric potential. 0 and a full-color image is transferred by the bias voltage of the transfer roller 34. A small amount of toner remaining on the intermediate transfer belt 30 without being transferred is removed by the cleaning blade 35 which has been moved to the illustrated contact position.

The transferred paper 2 is conveyed to a fixing unit 42 by a conveyor belt 41, and is pressed by a pressure roller 43 against a fixing roller 45 which is heated in advance by a built-in heater 44, thereby forming a full color image. The toner is melted onto the paper 2 and the image is fixed. After fixing, the paper 2 is separated from the fixing roller 45 and is ejected onto a paper ejection tray (not shown) by a paper ejection roller 46.

Here, the tip 47a of the separating claw 47 is in contact with the surface of the fixing roller 45, but the separating claw 47 itself is provided to prevent the paper 2 from being wrapped around the fixing roller 45 even if If the operation is normal, the paper 2 is separated from the fixing roller 45 by its own elasticity and moves toward the paper ejection roller 46 without touching the separation claw 47.

This is because if the paper 2 stuck to the fixing roller 45 due to the adhesiveness of the molten toner is attempted to be separated using the tip 47a of the separating claw 47, the molten toner will come into contact with the formed image and cause a large amount of damage in the transport direction. If the paper 2 does not separate by itself due to high toner concentration and therefore strong adhesive force, the formed image will be damaged and defective in order to prevent smoke and fire accidents due to wrapping. The separation claw 47 forcibly separates the paper 2 even if there is a risk that the paper 2 will become separated. Therefore, in order to prevent the separation claw 47 from acting, it is necessary to provide a white edge at the leading end of the paper 2 that is free of toner and therefore has no adhesive properties.

FIG. 1 is a block diagram showing an example of the control system of this color copying machine. The control unit 50 includes a CPU (processing unit) 3 which also serves as a white edge setting means;
A ROM 51 in which programs, constant data, etc. required by the system are stored in advance, a RAM 52 including a VRAM 4 which is an area for storing image data, and an I/O 53 for inputting and outputting data etc. between other units. It consists of
They are connected to each other by bus lines. VRA in RAM52
M4 is an area 4b, 4g, 4r and 4y, 4m for storing image data of B, G, R and Y, M, C, K, respectively.
, 4c, and 4k.

The CPU 3 inputs, via the I/O 53, an A/D converter 54 that digitizes the analog output of the line sensor 18, sensors 55 that detect the operating status and ambient conditions of each part of the color copying machine, and operator instructions. An operation panel 56 for displaying information and displaying various information, and an optical writing unit 2
3 and other sequence equipment group 57, etc., and the ROM
Process control that sets the operating conditions of the optical writing unit 23 and the sequence equipment group 57 according to various signals input from the sensors 55 according to the program stored in the controller 51 and the operator's instructions input to the operation panel 56 In addition to performing sequence control to operate at appropriate timings, it also performs data processing such as image processing and white border width setting.

For example, when the original 1 is placed at a predetermined position on the glass plate 10 shown in FIG. 4 and a start button (not shown) on the operation panel 56 is pressed, the CPU 3 starts sequence control and performs color separation. B filter 17 of filter group 17
b is set in the photographing optical path, the illumination lamp 12 is turned on, and sub-scanning is started. During the sub-scanning, the line sensor 18 repeats the main scanning and outputs an analog signal corresponding to the brightness of each pixel of the B-separated image of the document 1, and the data digitized by the A/D converter 54 is stored in the VRAM 4. B of
Stored in area 4b.

When the first sub-scanning is completed, the illumination lamp 1
2 goes out and returns together with the first to third mirrors 13 to 15, during which time the G filter 17g is set. Next, the second sub-scanning starts, the image data of the G-separated image of the original 1 is stored in the G area 4g, and the third
The data of the R-separated image is stored in the R area 4r by the second sub-scanning, and image data input is completed.

Next, the CPU 3 starts image processing. FIG. 3 is an explanatory diagram showing an example of image processing for converting input image data separated into three colors B, G, and R and stored in a memory into output image data for printing. Input image data (Step 0) is processed as is if it is the same size according to the specified magnification mode, or if it is in enlargement or reduction mode, it is enlarged or reduced at the specified magnification (Step 1) and then subjected to the next color correction. Move on to processing.

In the color correction process (step 2), the image data of B, G, and R, which are the three primary colors of the additive color method, are converted into the primary image data of Y, M, and C, which are the three primary colors of the subtractive color method, by matrix calculation. Convert, then UCR (undercolor removal), BP (
Y, M,
Convert to C and K secondary image data. That is, for each pixel, find the minimum value of Y, M, and C of the primary image data, and subtract the minimum value from the values of each Y, M, and C data to obtain the secondary Y, Set as M, C data (UCR)
. Next, the minimum value is set as K data (BP).

As a result of this color correction processing, the B, G, and R image data had large values in white or bright areas, and small values in black or dark areas, but the converted Y, M, and C image data had white values. Alternatively, the value is small in bright areas and large in black or dark areas. Through the next UCR and BP processing, the density of black or dark areas of the formed image increases and the gradation becomes richer, and a part or most of the Y, M, and C toners are replaced with K toner. Therefore, the total amount of toner representing that pixel decreases, and in the case of achromatic gray or black, the amount of toner becomes approximately 1/3.

Next, image judgment (described later) is performed on the secondary image data of Y, M, C, and K to set the width of the white edge at the leading edge, and depending on the width, the necessary (all image copy mode) ), image reduction processing is performed.

Furthermore, in order to improve the image quality, after performing various filter processing (step 4) such as gradation smoothing or edge emphasis, if it is a binary image such as a character or line drawing, it is directly converted into a binary image, and the halftone image is converted into a binary image. For an image that requires 1 image, the latent image pixels are grouped into 1 x 2 or 2 x 2 to 4 x 4 blocks, depending on the number of gradations to be expressed, to form one image pixel, and the dots of the latent image pixels are Binarize according to the area modulation method that converts the size of image pixel dots, which are a set of (step 5)
. The Y, M, C, and K image data finally binarized in this way are stored again in each area of the VRAM 4 as output image data, and the image processing is completed (step 6).
, wait for optical writing.

[0045] Here, the CC constituting the line sensor 18
One D is a document pixel, the reciprocal of the CCD pitch is converted onto the document surface according to the photographing magnification of the photographing lens 16, and the document pixel density is the document pixel density. The pixels written on 20 are latent image pixels,
One latent image pixel or a set of latent image pixels constituting a block is an image pixel, and the reciprocal of the pixel size of a latent pixel or an image pixel is a latent image pixel density and an image pixel density, respectively.

Subsequently, the CPU 3 starts sequence control for color image formation, and superimposes color toner images in the order of Y, M, C, and K, for example. That is, first, the Y image data stored in the Y area 4y is written onto the photosensitive drum 20 by the optical writing unit 23, and the electrostatic latent image is transferred to the developing drum 24y of the developing device 25 and transferred to the Y toner. After being converted into an image, it is transferred to the intermediate transfer belt 30.

After a delay of the time required for one rotation of the intermediate transfer belt 30 from the start of Y image data writing, the VRAM
Writing of the M, C, and K image data stored in areas 4m, 4c, and 4k of No. 4 starts, and the developing drums 24m, 24c, and 24k are selected in order to perform M, C, and K toner image conversion, respectively. and is transferred to the intermediate transfer belt 30, so that a full-color image is formed on the intermediate transfer belt 30. As already explained, this full-color image is transferred and fixed onto the paper 2, and color copying for one sheet is completed.

The operation of the CPU 3, which is the white edge setting means, will be explained below. First, Y, M, C, K of VRAM4
The image data of is converted into an image formed on paper 2 as shown in FIG. 2, and a diagonal line of width D is applied from the leading edge of the paper to the entire width regardless of the length of the paper. range 5
Set.

The width D varies depending on the configuration of the color copying machine and the thickness and elasticity of the paper used, but is between 10 mm and 5 mm.
It is set to 0 mm, and may be set to 7 to 8 mm depending on the determination method. Here, D = 2 unless otherwise specified.
Set to 0mm and determine the judgment range 5 which is the product of the paper width and D.
The total area of is A, the number of pixels included therein is N, and the gradation T of image data of each color is, for example, 6 bits, that is, T = 0 to 6.
This will be explained as 3.

In the first embodiment according to the first invention, the white edge is adjusted according to the area ratio R (=area of the bright color portion/A) of the area of the bright color portion close to the white background in the determination range 5 to the total area A. However, instead of the area, the area ratio value R is the ratio of the number of pixels Nm constituting the bright color portion to the number N of pixels included in the determination range, that is, R = Nm/N. There is no problem. This CP
The determination of the white edge width W by U3 is performed between steps 2 and 3 of the image processing shown in FIG. 3, that is, for the Y, M, and C primary image data that have undergone color correction processing.

Regarding all pixels within determination range 5 (FIG. 2),
The total value obtained by adding the Y, M, and C image data (gradation T) of each pixel (0 if the pixel is white, 63 if it is black)
x 3 = 189) is below a preset threshold, for example 15, it is determined to be a bright color, and the number of pixels determined to be bright color N
Count m and calculate the ratio (area ratio) to the number of pixels N = Nm/
Find N.

FIG. 5 is a diagram showing an example of the correlation between the area ratio R and the white edge width W, with the horizontal axis representing R (%) and the vertical axis representing W (%).
mm). Therefore, the first step in determining the white edge width W is
In the example, according to FIG. 5, if the judgment range is an image with many dark parts and R = 15%, a wide white border of W = 7 mm is set, and an image with many white areas such as edited characters is set. If R=70%, the width of the white edge is set to be relatively narrow, W=3 mm.

Next, depending on the operator's instruction regarding the copy mode input from the operation panel 56, that is, whether to copy the entire surface, emphasize the leading edge, or emphasize the trailing edge, in the leading edge emphasizing mode and trailing edge emphasizing mode, the entire In the copy mode, reduction processing is performed according to the length of the paper and the white edge width W, and the process moves to step 3 of image processing.

In the second example of determining the white edge width in the first embodiment, first, D=8 mm is set, and the number of pixels determined to be bright within the first determination range is counted. If the pixel is a bright color (assuming that the document has a white edge), W=0 is determined, and the process immediately moves to step 3 of image processing without performing copy mode determination or reduction processing. If there is a pixel that is not a bright color within the first determination range, the same white edge width determination as in the first example is performed for the second determination range further expanded to D=20 mm.

According to this second example, if all the pixels within the first determination range are bright colors, the time required for determination is reduced to 40% compared to the first example, and in the case of full-page copy mode, the time required is further reduced. Time-consuming reduction processing becomes unnecessary. Even if there are pixels that are not bright within the first determination range, D = 8 to 2
Since it is sufficient to investigate the range of 0 mm, the time required for determination is the same as in the first example, and does not exceed it.

The determination of the white edge width W according to the first embodiment is as follows:
There is no problem even if it is performed after step 3 of image processing, and the processing itself is exactly the same except that the threshold value for determining a bright color is changed to, for example, 20, but since it is necessary to add four colors for each pixel, step The time required can be shortened by performing the process between steps 2 and 3.

In addition to determining the white edge width W described above, the CPU 3, which is the white edge setting means, also executes processing for forming a white edge of the determined width W during image formation. That is, depending on the designated copy mode, the eraser 22 may be turned on at a timing corresponding to the width W, or the white border may be written using the optical writing unit 23. Alternatively, by advancing the start of the registration roller pair 40 by a similar timing,
The registration of paper 2 may be shifted with respect to the formed full-color image.

In the second embodiment according to the second invention, the width of the white edge is determined according to the area average value M (=total amount of toner/A) of the total amount of each color toner to form an image formed within the determination range. However, since it is necessary to determine the white edge width W before image formation, the total gradation value T of each pixel of each color or the binarized (latent image) of each color is determined. The total amount of toner is estimated by the total number of pixels that are "1" among the pixels, and the area average value M is determined.

In a solid image, although it varies depending on the type of toner, it is about 0.5 to 1 mg/cm2 on paper, so for example, for a certain color, the gradation T = 63, or all the latent image pixels are "1", the amount of toner for each color can be calculated as 0.7 mg/cm2, and the total amount of toner when superimposed can be found, but in reality, instead of the amount of toner, the area of the amount of toner of a single color solid image is calculated. Taking the average value as 100%,
It is better to find M from the gradation T or the number of dots. Therefore, if it is a white background, M=0, if it is a one-color solid image, M=100.
%, and if it is a four-color solid image, M=400%.

The determination of the white edge width W by the CPU 3 in the second embodiment is performed after the UCR/BP processing in step 3 of the image processing shown in FIG. 3 or after the filter processing in step 4 when the gradation T is used. , if the number of dots of latent image pixels is used, this is done after the binarization process in step 5.

To specifically explain the case where the gradation T is used, Y, M, C,
Calculate the total value of the gradation T of K by 63 (the highest value of T) for all pixels, find the total sum, divide it by the total number of pixels in the judgment range N, and multiply by 100. A percentage display value of the area average value M of the total amount of toner is obtained.

FIG. 6 is a diagram showing an example of the correlation between the average value M (%) and the white edge width W, where M (%) is the horizontal width and W (mm) is the vertical width. The third example of determining the white edge width W is
As shown in FIG. 6, for example, if the image has a large white background or is bright and the amount of toner is small, and M=50%, the white edge will have a narrow width W=2 mm, and a solid image of one color or two colors (M=100% or 20 mm).
0%), W=3 mm or 5 mm, and if M exceeds 280% like a three-color solid image, the width W=8 mm. Next, as explained in the first example, reduction processing is performed as necessary, and the process moves to step 4 or step 5 of image processing.

When using the number of dots, the latent image pixels are divided into "1" pixels to which toner adheres and "0" pixels remaining white by the binarization process in step 5 of image processing. Of these, add the number of pixels that are "1" within the determination range for each of Y, M, C, and K, and divide by the total number of pixels N.
If the value multiplied by 00 is used as the % display value of the area average value M, the subsequent steps are the same as when using the gradation T.

If the white edge width W is determined in this way,
As in the first embodiment, during image formation, the CPU 3 forms a white border with the determined width W.

Also, in this second embodiment, similarly to the second example of the first embodiment, the narrow first determination range (D=
If there is no toner (M = 0) or there is very little toner within 8 mm), W = 0 is determined. Otherwise, the second judgment range with a wider width (D = 20 mm) is determined as in the third example. It goes without saying that the effects described in the second example can be obtained by performing the processing.

As explained above, according to the present invention,
When forming a color image, the width of the white border can be narrowed according to the image to be formed without compromising the safety of the paper from getting wrapped around the fixing roller. It is possible to minimize downscaling and meet user expectations.

The first embodiment is relatively simple because the white edge width W is determined by the area ratio R of a white background or a bright color portion close to it, and the second embodiment is slightly more complicated, but it is determined based on the area average of the toner amount. Since the white edge width W is determined by the value M, the white edge width can be determined more reliably. Because UCR・BP
By creating a black plate (K) through processing, M
This is because it never exceeds 300% and the probability of it exceeding 200% is low.

As is clear from the above explanation, the present invention is applicable not only to full-color copies including Y, M, C or halftones consisting of Y, M, C, and K, but also to full-color images that do not contain halftones. For example, it can also be applied to two-color copying consisting of K and R. Further, although the case of a color digital copying machine has been described, the present invention can also be applied to, for example, a color facsimile, a video printer, or a color printer which is an external output device of a computer.

[0069]

Effects of the Invention As explained above, the color image forming apparatus according to the present invention sets the width of the white edge at the leading edge of the paper, which is the recording medium, to the necessary minimum, so that image deletion and image reduction can be prevented as much as possible. It is possible to form a subdued color image.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a control system of a color copying machine which is an embodiment of the present invention.

FIG. 2 is a plan view of a sheet of paper for explaining definitions of terms.

FIG. 3 is an explanatory diagram showing an example of color image processing by the control system shown in FIG. 1;

FIG. 4 is a schematic configuration diagram showing the internal mechanism of a color copying machine that is an embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of the correlation between the area ratio R of a white background or bright color portion within the determination range and the width W of a white edge.

FIG. 6 is a diagram showing an example of the correlation between the value M corresponding to the area average value of the total amount of toner within the determination range and the width W of the white edge.

[Explanation of symbols]

1 Manuscript
2 Paper (recording medium) 3 CPU (processing unit; white edge setting means) 4 V
RAM (video RAM) 5 Judgment range A Total area of the judgment range
D Width of judgment range M Area average value of total toner amount N
Total number of pixels within the judgment range

Claims (2)

[Claims] 1. A color image forming apparatus that forms a color image on a recording medium by overlapping a plurality of color toner images of different colors, wherein a determination range of a preset width from the leading edge of the recording medium in the conveyance direction is set. of the white edge to which toner does not adhere at the leading edge of the recording medium, depending on the area ratio of the area of a white background or a bright color portion close to it to the total area of the determination range in the image formed within the determination range. A color image forming apparatus characterized in that a white edge setting means is provided for setting the width to be narrow when the area ratio is large and wide when the area ratio is small. 2. In a color image forming apparatus that forms a color image on a recording medium by overlapping a plurality of color toner images of different colors, a determination range of a preset width from the leading edge of the recording medium in the conveying direction is provided. The width of the white edge to which toner does not adhere at the leading edge of the recording medium is set according to the average value of the total amount of each color toner to form an image formed within the determination range over the entire determination range. A color image forming apparatus characterized in that a white edge setting means is provided for setting a narrow edge when the average value is small and wide when the average value is large.