JPH0969935A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compose an image without spoiling the easy visual check of a document image by adjusting a range of gray level used for one image so that when two images are put together, it is made easy to discriminate between both images. SOLUTION: Image data from a scanner part 4 are sent to an image processing part 96 to generate a density historgram. On the basis of the density histogram data, density range conversion of the image data is performed. The image data after the density range conversion are sent to an image composition part 99 or page memory 98. The image composition part 99 puts the two image data together in one. In this case, when a composite image is composed of the two images, the density range of a background image between the two images is varied with the density historgram of the other foreground image. Namely, the density range of the background image is corrected so that the maximum density of the background image is lower than the lowest density of the foreground image except its white ground.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to first and second aspects.
The present invention relates to an image forming apparatus that combines two images.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, two images such as a document image and a background image are combined and formed.

In such an image forming apparatus, since the images are combined by simple superposition or the sum of the densities, there is a problem that when the images having similar densities overlap each other, it is difficult to see the combined image. It was

[0004]

SUMMARY OF THE INVENTION The present invention eliminates the drawback that a composite image becomes difficult to see when the images are combined, and the images are combined without impairing the legibility of the original image. An object of the present invention is to provide an image forming apparatus capable of performing the above.

[0005]

An image forming apparatus according to the present invention is a device for synthesizing two images, a first image and a second image.
When synthesizing the first and second images, an adjusting unit is provided for adjusting the shade range used in at least one of the images so that the two images can be easily distinguished.

In the image forming apparatus of the present invention, in which the first and second images are combined, a density histogram formed by the number of pixels for each density section of the first and second images And a grayscale used in one or both of the images so that the two density histograms generated by the generation unit do not overlap each other when the first and second images are combined. It is composed of adjusting means for adjusting the range.

In the image forming apparatus of the present invention, for combining two images of the foreground image and the background image, when the two images of the foreground image and the background image are combined, it is easy to distinguish the two images. , And has adjusting means for adjusting the range of shading used in the background image.

The image forming apparatus of the present invention includes a foreground image,
In combining two images of a background image, generating means for generating a density histogram formed by the number of pixels for each density division of the foreground image and the background image, and combining the two images of the foreground image and the background image. In order to make it easy to distinguish the two images, the adjusting unit is configured to adjust the range of shades used in the background image so that the two density histograms generated by the generating unit do not overlap.

In the image forming apparatus of the present invention, for synthesizing the first and second images, in order to easily distinguish the two images when synthesizing the first and second images. , And has an inverting means for inverting the contrast of at least one of the images where the images overlap.

In the image forming apparatus of the present invention, for combining two images of the foreground image and the background image, when the two images of the foreground image and the background image are combined, it is easy to distinguish the two images. , The composite image is output by outputting the image data of the higher density of the foreground image and the background image for each pixel, or for the foreground image and the background for the part where the foreground image and the background image do not overlap. The image with the higher density of the image is output for each pixel, and for the part where the foreground image and the background image overlap, the image data with a constant density is output to output a composite image. , The maximum density of the foreground image and the background image is smaller than the density of the foreground image, the background density adjustment for outputting the image data of the higher density of the background images whose density range has been changed for each pixel, or Output the combined image by adding the image data of the foreground image and the background image for each pixel to output the combined image, or use the image data with the higher density or the image data with the lower density of the foreground image and the background image. Selective means for selecting whether to perform gray-scale selective combining for outputting a composite image by outputting for each pixel, judging means for judging whether the foreground image and the background image are character images or photographic images, and the judgment result by the judging means and the selecting means. According to the selection result, the output means outputs the image synthesized by the above-mentioned overlay synthesis synthesis, the above-mentioned overlap inversion synthesis, the above background density adjustment, the above-mentioned addition synthesis, or the above-mentioned grayscale selection synthesis.

In the image forming apparatus of the present invention, for combining two images of the foreground image and the background image, when the two images of the foreground image and the background image are combined, the two images can be easily distinguished from each other. The output means outputs a composite image by outputting, for each pixel, image data having a higher density of the foreground image and the background image.

In the image forming apparatus of the present invention, for combining two images of the foreground image and the background image, when the two images of the foreground image and the background image are combined, it is easy to distinguish the two images. , For the portion where the foreground image and the background image do not overlap, the image data of the higher density of the foreground image and the background image is output for each pixel, and for the portion where the foreground image and the background image overlap, It is composed of output means for outputting a composite image by outputting image data of constant density.

In the image forming apparatus of the present invention, for combining two images of the foreground image and the background image, when the two images of the foreground image and the background image are combined, the two images can be easily distinguished from each other. , The maximum density of the foreground image and the background image is smaller than the density of the foreground image From the output means for outputting a composite image by outputting, for each pixel, the image data of the higher density of the background image whose density range has been changed It is configured.

The image forming apparatus according to the present invention synthesizes two images of the foreground image and the background image, and when the two images of the foreground image and the background image are synthesized, the two images can be easily distinguished from each other. The output means outputs the composite image by outputting the image data obtained by adding the foreground image and the background image for each pixel.

In the image forming apparatus of the present invention, for combining two images of the foreground image and the background image, when the two images of the foreground image and the background image are combined, the two images can be easily distinguished from each other. The output means outputs the composite image by outputting the image data of the higher density or the image data of the lower density of the foreground image and the background image for each pixel.

In the image forming apparatus of the present invention, in which two images of the foreground image and the background image are combined, the judgment means and the combining method for judging whether the foreground image and the background image are character images or photographic images are superposed and combined. Selection means for selecting whether to perform overlap inversion composition, background density adjustment, additive composition, or gradation selection composition, and changing means and judgment means for changing to a density range in which the maximum density of the background image is smaller than the density of the foreground image. When the combination of the character image and the character image is judged by the selection means, and the overlapping composition is selected by the selecting means, the composite image is outputted by outputting the image data of the higher density of the foreground image and the background image for each pixel. However, when the determining unit determines that the character image and the character image are combined and the selecting unit selects the overlapping and inversion combination, the foreground image and the background image are not overlapped. In this case, the image data with the higher density of the foreground image and the background image is output for each pixel, and the image data with a constant density is output for the portion where the foreground image and the background image overlap each other. When the combination of the character image and the character image is judged by the judgment means, and the background density adjustment is selected by the selection means, the density of the background image whose density range is changed by the foreground image and the change means is high. A composite image is output by outputting the other image data for each pixel, and when the combination of the character image and the photographic image is judged by the judgment means and the superposition combination is selected by the selection means, the foreground image and the background image are combined. Of these, the image data with the higher density is output for each pixel to output a composite image, the judgment means judges the combination of the character image and the photographic image, and the selection means overlaps. When transposition is selected, if the density of the character image is lower than the specified density, the image data of the photo image is output, and if the density of the character image is higher than the specified density, the image data of the reverse image of the photo image is output. To output a composite image, the determining unit determines the combination of the character image and the photographic image, and when the selecting unit selects the background density adjustment, the foreground image and the changing unit change the density range of the background image. The composite image is output by outputting the image data of the higher density among the pixels for each pixel, and when the combination of the photographic image and the photographic image is judged by the judgment means and the addition composition is selected by the selection means, the foreground The combined image is output by outputting the image data obtained by adding the image and the background image for each pixel, and the judgment unit judges the combination of the photograph image and the photograph image, and the selecting unit When grayscale selection is selected by, the higher density image data or the lower density image data of the foreground image and the background image is output for each pixel, and the composite image is output by outputting the image data. However, when the combination of the photographic image and the photographic image is judged by the judgment means and the background density adjustment is selected by the selection means, the one of the higher density of the foreground image and the background image whose density range has been changed by the changing means is selected. It is composed of output means for outputting a composite image by outputting image data for each pixel.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic block diagram showing the internal structure of a digital copying machine as an example of the image forming apparatus of the present invention.

As shown in FIG. 2, the digital copying machine comprises an apparatus main body 10 in which a scanner section 4 functioning as a reading means and a printer section 6 functioning as an image forming means, which will be described later, are provided. It is provided.

On the upper surface of the apparatus main body 10, there is provided an original placing table 12 made of transparent glass on which an object to be read, that is, an original D is placed. An automatic document feeder 7 (hereinafter, referred to as an ADF) for automatically feeding a document onto the document table 12 is provided on the upper surface of the apparatus body 10.
The ADF 7 is provided so as to be openable and closable with respect to the document table 12, and transfers the document D placed on the document table 1 to the document table 1.
It also functions as a document holder that is brought into close contact with 2.

The ADF 7 includes a document tray 8 on which the document D is set, an empty sensor 9 for detecting the presence or absence of the document, a pickup roller 14 for taking out the document from the document tray 8 one by one, and a paper feed roller for conveying the taken out document. 1
5. A pair of aligning rollers 16 for aligning the leading edge of the document,
A transport belt 18 is provided so as to cover almost the entire document table 12. The plurality of originals set upward on the original tray 8 are taken out in order from the bottom page, that is, the last page, are aligned by the aligning roller pair 16, and are placed on the original by the transport belt 18. The sheet is transported to a predetermined position on the table 12.

In the ADF 7, a reversing roller 20, a non-reversing sensor 21, a flapper 22, and a paper discharge roller 23 are arranged at the end opposite to the aligning roller pair 16 with the conveyor belt 18 interposed therebetween. The document D whose image information has been read by the scanner unit 4 described below is sent out from the document table 12 by the conveyance belt 18 and
0, flapper 21, and discharge roller 22
The document is discharged onto the document discharge unit 24 on the upper surface of F7. When reading the back surface of the document D, the document D conveyed by the conveyance belt 18 is changed by switching the flapper 22.
After being reversed by the reversing roller 20, it is again conveyed to a predetermined position on the document table 12 by the conveyor belt 18.

The scanner section 4 provided in the apparatus body 10
Has an exposure lamp 25 as a light source for illuminating the document D placed on the document table 12, and a first mirror 26 for deflecting the reflected light from the document D in a predetermined direction. The first mirror 25 and the first mirror 26 are attached to a first carriage 27 disposed below the document table 12.

The first carriage 27 is the original table 12
And is reciprocally moved below the document table 12 by a drive motor via a toothed belt or the like (not shown).

A second carriage 28, which is movable in parallel with the original placing table 12, is disposed below the original placing table 12. Second and third mirrors 30 and 31 for sequentially deflecting the reflected light from the document D deflected by the first mirror 26 are attached to the second carriage 28 at right angles to each other. The second carriage 28 is connected to the first carriage 27 by a toothed belt or the like that drives the first carriage 27.
It is driven by the carriage 27 and is moved parallel to the first carriage along the document table 12 at a speed of 1/2.

Below the document table 12, an image forming lens 32 that focuses the reflected light from the third mirror 31 on the second carriage 28, and the reflected light that is focused by the image forming lens are received. And a CCD sensor 34 for performing photoelectric conversion. The imaging lens 32 is movably disposed via a drive mechanism in a plane including the optical axis of the light deflected by the third mirror 31, and moves the reflected light at a desired magnification by moving itself. Form an image. And the CCD sensor 34
The incident reflected light is photoelectrically converted, and an electric signal corresponding to the read original D is output.

On the other hand, the printer section 6 is provided with a laser exposure section 40 which functions as a latent image forming means. The laser exposure unit 40 includes a semiconductor laser 41 as a light source, a polygon mirror 36 as a scanning member that continuously deflects the laser light emitted from the semiconductor laser 41, and the polygon mirror 36 is rotated at a predetermined rotation number described later. The scanning motor to be driven is also provided with a polygon motor 37 and an optical system 42 which deflects the laser light from the polygon mirror and guides it to a photosensitive drum 44 described later. The laser exposure unit 40 having such a configuration is fixed and supported by a support frame (not shown) of the apparatus main body 10.

The semiconductor laser 41 is on / off controlled according to image information of the document D read by the scanner section 4, facsimile transmission / reception document information, or the like, and this laser light is passed through the polygon mirror 36 and the optical system 42. The electrostatic latent image is formed on the peripheral surface of the photosensitive drum 44 by scanning the peripheral surface of the photosensitive drum 44 toward the photosensitive drum 44.

Further, the printer unit 6 has a rotatable photosensitive drum 44 as an image bearing member disposed substantially at the center of the apparatus main body 10, and the peripheral surface of the photosensitive drum 44 extends from the laser exposure unit 40. To expose a desired electrostatic latent image. Around the photoreceptor drum 44, a charging charger 45 for charging the peripheral surface of the drum to a predetermined charge, and a toner as a developer to supply an electrostatic latent image formed on the peripheral surface of the photoreceptor drum 44 with a desired toner is provided. A developing device 46 for developing at an image density, and a peeling charger 47 for separating a transfer material fed from a paper cassette described later, that is, a copy sheet P from the photosensitive drum 44, A transfer charger 48 for transferring the toner image formed on the photosensitive drum 44 to the paper P, a peeling claw 49 for peeling the copy paper P from the peripheral surface of the photosensitive drum 44, a cleaning unit 50 for cleaning the toner remaining on the peripheral surface of the photosensitive drum 44, A static eliminator 51 for neutralizing the peripheral surface of the photosensitive drum 44 is arranged in order.

An upper cassette 52, a middle cassette 53, and a lower cassette 54, which can be pulled out from the apparatus body, are arranged in a laminated state at the lower part of the apparatus body 10, respectively.
Copy papers of different sizes are loaded in each cassette. Large capacity feeders 5 beside these cassettes
The large-capacity feeder 55 accommodates about 3000 copy sheets P of a frequently used size, for example, A4 size copy sheets P. Further, above the large-capacity feeder 55, a paper feed cassette 57 also serving as a manual feed tray 56 is detachably attached.

In the apparatus main body 10, a conveying path 5 extending from each cassette and the large-capacity feeder 55 through a transfer portion located between the photosensitive drum 44 and the transfer charger 48.
The fixing device 60 is provided at the end of the transport path 58. A discharge port 61 is formed on a side wall of the apparatus main body 10 facing the fixing device 60, and a discharge tray 62 is formed on the discharge port.
Is installed.

Pickup rollers 63 are provided near the upper cassette 52, the middle cassette 53, the lower cassette 54, the paper feed cassette 57, and the large-capacity feeder 55, respectively, to take out the sheets P one by one from the cassette or the large-capacity feeder. Has been. The transport path 58 is provided with a number of paper feed roller pairs 64 for transporting the copy sheet P taken out by the pickup roller 63 through the transport path 58.

A registration roller pair 65 is provided on the upstream side of the photosensitive drum 44 in the transport path 58. The registration roller pair 65 corrects the inclination of the copy paper P taken out, aligns the leading end of the toner image on the photosensitive drum 44 with the leading end of the copy paper P, and adjusts the moving speed of the peripheral surface of the photosensitive drum 44 to The copy paper P is fed to the transfer unit at the same speed. A pre-alignment sensor 66 for detecting the arrival of the copy sheet P is provided in front of the registration roller pair 65, that is, on the side of the feed roller 64.

The copy sheets P taken out one by one from each cassette or the large-capacity feeder 55 by the pickup roller 63 are sent to the registration roller pair 65 by the paper feed roller pair 64. Then, the copy paper P is sent to the transfer section after the leading end is aligned by the registration roller pair 65.

At the transfer portion, the developer image formed on the photosensitive drum 44, that is, the toner image is transferred onto the paper P by the transfer charger 48. The copy sheet P on which the toner image is transferred is peeled off from the peripheral surface of the photosensitive drum 44 by the action of the peeling charger 47 and the peeling claw 49,
The sheet is conveyed to the fixing device 60 via a conveyance belt 67 that forms a part of the conveyance path 52. Then, after the developer image is fused and fixed to the copy paper P by the fixing device 60, the copy paper P
Is discharged onto the paper discharge tray 62 through the discharge port 61 by the paper feed roller pair 68 and the paper discharge roller pair 69.

Below the conveying path 58, the copy sheet P which has passed through the fixing device 60 is reversed and the registration roller pair 65 is again provided.
An automatic double-sided device 70 for sending to is provided. The automatic double-sided device 70 includes a temporary stacking unit 71 for temporarily stacking the copy sheets P, and a reversing path 7 that diverges from the transport path 58 and reverses the copy sheet P that has passed through the fixing unit 60 and guides the copy sheet P to the temporary stacking unit 71.
2, a pickup roller 73 for taking out the copy papers P accumulated in the temporary accumulation section one by one, and a paper feed roller 75 for feeding the taken out paper to a pair of registration rollers 65 through a transport path 74. Further, at a branch portion between the transport path 58 and the reversing path 72, a distribution gate 76 for selectively distributing the copy sheet P to the discharge port 61 or the reversing path 72 is provided.

When performing double-sided copying, the copy sheet P that has passed through the fixing device 60 is guided to a reversing path 72 by a sorting gate 76, temporarily accumulated in a reversed state in a temporary accumulating section 71, and then picked up. The roller 73 and the paper feed roller pair 75 feed the resist roller pair 65 through the conveyance path 74. Then, after the copy paper P is aligned by the registration roller pair 65, the copy paper P is sent to the transfer unit again, and the toner image is transferred to the back surface of the copy paper P. Thereafter, the copy sheet P is discharged onto the discharge tray 62 via the transport path 58, the fixing device 60, and the discharge roller 69.

The digital copying machine further includes an operation panel 80 and a main controller 90 shown in FIG.

The operation panel 80 is provided with a print key 81 for instructing the start of copying, conditions for image output in a digital copying machine, such as the number of copies or prints and magnification.
Alternatively, for example, a plurality of push button switches, a color cathode ray tube, or an input unit 82 provided with a transparent touch sensor panel on a liquid crystal screen for inputting partial copy designation and coordinates of the area, and the operation panel 8.
It includes a panel CPU 83 for controlling 0, and a ten key 84 used for setting the number of copies and the copy magnification.

The input section 82 is arranged in accordance with the operating procedure of the digital copying machine or the conditions to be input, and, for example, touches as a plurality of input keys on which pictograms, numbers, characters or character strings are displayed. It has a sensor. For example, it is a combination mode key and a sort key. Further, the input unit 82 has a display unit 82a for displaying operation guidance and input contents.

On the display section 82a, the number of copies, copy magnification,
The memory capacity at the time of copying, sorting, and the number of readable original documents (standard) corresponding to this memory capacity are displayed.

FIG. 1 is a block diagram schematically showing the flow of signals for electrical connection and control of the digital copying machine shown in FIG. According to FIG. 1, in the digital copying machine, the main CPU 91 in the main controller 90 is
And the scanner CPU 100 of the scanner unit 4 and the printer unit 6
Printer CPU 110.
The main CPU 91 shares the RA with the printer CPU 110.
It performs bidirectional communication via M95,
The PU 91 issues an operation instruction, and the printer CPU 110 returns a status. Printer CPU
110 and the scanner CPU 100 perform serial communication,
The printer CPU 110 issues an operation instruction, and the scanner CP
U100 is adapted to return a status status.

The operation panel 80 is connected to the main CPU 91.

The main control unit 90 includes a main CPU 91, RO
M92, RAM 93, NVM 94, shared RAM 95, image processing unit 96, page memory control unit 97, page memory 98, and image synthesizing unit 99.

The main CPU 91 controls the entire main controller 90. The ROM 92 stores a control program. The RAM 93 temporarily stores data.

NVM (endurance random access memory: n
The on-volatile RAM (94) is a non-volatile memory backed up by a battery (not shown), and retains data on the NVM 94 when the power is turned off.

The shared RAM 95 is used for bidirectional communication between the main CPU 91 and the printer CPU 110. The image processing unit 96 is provided with a circuit that creates a histogram from the image data and corrects the image data based on the histogram. The image processing section 96 has a compression / expansion circuit 96a for compressing or expanding image data. Page memory control unit 97
Is for storing and reading image data in the page memory 98. The page memory 98 has an area capable of storing image data for a plurality of pages, and is formed so that data obtained by compressing image data from the scanner unit 4 can be stored for each page. The image synthesizing unit 99 synthesizes two pieces of image data.

The scanner unit 4 includes a scanner CPU 100 for controlling the entire scanner unit 4, a ROM 101 storing a control program and the like, and a RAM 10 for storing data.
2. CCD driver 10 for driving CCD sensor 34
3. A scan motor driver 104 for controlling the rotation of a motor for moving the exposure lamp 25 and mirrors 26, 27, 28, etc., an A / D conversion circuit for converting an analog signal from the CCD sensor 34 into a digital signal, and the CCD sensor 3.
4 due to variations in temperature or changes in ambient temperature
The shading correction circuit 105 corrects the fluctuation of the threshold level with respect to the output signal from the CD sensor 34, and the image correction unit 105 includes a line memory for temporarily storing the shading-corrected digital signal from the shading correction circuit.

The printer unit 6 includes a printer CPU 110 for controlling the entire printer unit 6, a ROM 111 storing a control program and the like, and a RAM 11 for storing data.
2. Laser driver 113 for turning on / off light emission by semiconductor laser 41, polygon motor driver 11 for controlling rotation of polygon motor 37 of laser unit 40
4. A paper transport unit 115 for controlling the transport of the paper P by the transport path 58, a charging charger 45, a developing unit 46, and a developing process unit 116 for performing charging, development and transfer using the transfer charger 48, and a fixing unit 60 are controlled. The image forming apparatus includes a fixing control unit 117 and an option unit 118.

The image processing section 96 and the page memory 9
8. The image synthesizing unit 99, the image correcting unit 105, and the laser driver 113 are connected by an image data bus 120.

FIG. 3 is a block diagram showing a schematic configuration of the image processing unit 96 including the histogram creating circuit. The histogram creation circuit 130 creates a density histogram from the image data from the scanner unit 4. The density histogram created by the histogram creation circuit 130 is supplied to the correction reference value calculation unit 131, and the main CPU 9
1 is also being supplied. The correction reference value calculation unit 131 calculates a correction reference value (described later) based on the histogram created by the histogram creation circuit 130. The range correction circuit 132 corrects the density range (described later) using the correction reference value from the correction reference value calculation unit 131, and performs automatic density adjustment in real time. Timing signal generator 1
33 generates various timing signals required for each block in the image processing unit 96 based on the clock signal from the clock generating unit 134. The image quality improvement circuit 135 includes a low-pass filter, a high-frequency emphasis circuit, and the like, and further improves the image quality of the image whose range has been corrected by the range correction circuit 132. The enlargement / reduction circuit 136 enlarges / reduces the image as required, and the gradation processing circuit 137 processes the gradation of the image using a dither method or an error diffusion method. The image signal processed in this way is sent to the printer unit 6 to form an image, or is stored in the page memory 98.

4 and 5 show the outline of the density histogram created. For example, in the case of reading one image of A4, assuming that reading is performed at 400 dpi, the total number of pixels G is as follows.

G = 210 × 297 × (400 / 25.4) ² Each pixel of the pixel number G has a density, and here, the density is expressed by 8 bits. The horizontal axis in FIG. 4 indicates the density, that is, the pixel value, and the vertical axis indicates the frequency (number of pixels) indicating how many pixels of which density existed with respect to the density.

As shown in FIG. 4, in this embodiment, the density is 16
The density of 256 steps is simplified to 16 steps.
That is, the lower 4 bits of the 8-bit pixel value are ignored. By adopting 16 divisions, the hardware is greatly simplified. Even with 16 divisions, the amount of information required as a histogram is sufficiently secured in the automatic density adjustment function. FIG. 5 shows a method of evenly dividing into 16 parts, with division number 0.
Is a range of pixel values 0 to F, division number 1 is a pixel value of 10 to 1F
, And the pixel value range up to the division number F is similarly set.

Before describing the histogram creation circuit 130 in detail, the range correction of the correction reference value calculation unit 131 and the range correction circuit 132 will be described. Range correction is a function used for background cutting in an automatic exposure function in an analog copying machine. Generally, when a document is digitally read and a density histogram is created, it becomes as shown in FIG. In the case of a manuscript such as a newspaper, the background density is considerable, so that one peak is formed in the background density portion as shown by M in FIG. 6 and one peak is also formed in the character density portion such as N. Here, in the analog copying machine, the brightness of the exposure lamp is controlled to eliminate the background density portion, but in the digital copying machine, the same effect is obtained by the following signal processing.

Explaining with a simple example, the densities DW and DB corresponding to the peak points of the M peak and the N peak shown in FIG. 6 are obtained, and the following calculation is performed to obtain a density histogram as shown in FIG. Convert to a different distribution. Where density DW
And DB are called correction reference values, and the histogram creation circuit 1
The correction reference value calculation unit 131 calculates the correction reference value calculation unit 131 based on the histogram of each scan line created by the reference numeral 30.

DN = (DI−DW) × FFH / (DB−DW) where DI is the input pixel density, DN is the corrected pixel density, and FFH is the maximum pixel density. That is, the range (density range) between M and N in FIG. 6 is expanded to the range of 0 to FFh.

Next, the histogram creating method in the present invention will be outlined. The following formula is a basic calculation formula for creating a histogram in the present invention, and the histogram is created for each main scanning line. A reference value for range correction is obtained each time the histogram creation processing for one line is completed, and the range correction processing is performed based on the reference value. Further, the total number of data items forming the histogram is always a constant value.

A ′ = A−αA + αB where A ′: corrected frequency (number of pixels) corresponding to each density of the current line A: frequency corresponding to each density calculated up to the previous line B: current line Frequency corresponding to each density of α: Weighting coefficient The weighting coefficient α is a value multiplied by the frequency value accumulated in each line, and indicates the contribution rate to the histogram. This α
Is set in accordance with the number of lines, as shown in FIG. 8, and has 14 values (one power of 2), that is, 1,1 / 1 /
2, 1/4, 1/8, 1/16, 1/32, ..., 1 /
2048, 1/4096, 1/8192 (= 1/2 ¹³ )
To be selected from.

Next, the histogram creating circuit 130 will be described. The histogram creation circuit 130 first calculates A ′ = (A ′) + αB for each input pixel during one line reading, and secondly, between one line reading and the next line reading, that is, the pixel density is input. If not, (A ′) = A−αA is calculated for each density frequency of the histogram. In this way, the histogram creating circuit 130
Is the corrected frequency value for the current line A ′ = A−α
Generate A + αB. The correction reference value calculation unit 131 calculates the reference value for range correction from the histogram thus created.

Two modes, mode 0 and mode 1, are provided for creating the histogram, and one mode is selected as required.

Mode 0: Weighting coefficient variable addition mode depending on the number of sub-scanning lines Mode 1: Constant weighting coefficient addition mode for input pixels In mode 0, as described above, the value of coefficient α depends on the count number of main scanning lines. To create a histogram. Mode 1 creates a histogram with constant coefficients, regardless of the count value of the main scanning line.

FIG. 9 is a block diagram showing a detailed configuration of the histogram creating circuit 130. The pixel density signal IDAT4 from the scanner unit 4 is connected to one terminal of the switch 141.
To IDAT7 are input, and signals CDT00 to CDT03 of output data from the counter 142 are input to the other terminal. The switch 141 is also connected to the timing signal generator 1.
33, one of the input signals is selected according to the selection signal from the selector 33, and the selected signals SLDT0 to SLDT3 are selected by the selector 1
45 and the clock generator 143. Here, the pixel density signals IDAT4 to IDAT7 are the upper 4 bits of the pixel density, and IDAT0 to IDAT3 are ignored for the reason described above. The timing signal CTL0 from the timing signal generator 133 is at a high level between each line, that is, when the pixel density signal is not read,
1 selects and outputs the signal from the counter 142.

The counter 142 uses the clock generator 143 and the selector 145 when calculating (A ') = A-αA.
The required value (count value) is supplied to. Counter 142
Generates a 4-bit count value for generating the 16 outputs of the clock generator 143 in order when the above-mentioned pixel density signal is not read. Counter 1
Reference numeral 42 denotes a timing signal generator 1 to which the counter clock signal CT1CK is input from the timing signal generator 133.
The counter is cleared by the counter clear signal CT1CL from the counter 33. The counter clear signal CT1CL becomes low level when the pixel density signal is read, and the counter 1
Clear 42.

The clock generator 143 selects the selection input signal SL.
In accordance with DT0 to DT3, one of 16 outputs FCK0 to FCK is selected and output at the cycle of the input clock signal MCK. FIG. 10 shows the relationship between the input and output signals of the clock generator 143.

The histogram registers (flip-flops) 144 _{1 to} 144 _F show the corrected frequency (WDAT) for each pixel density as input clock signals FCK0 to FCK0.
It latches and outputs at the rising edge of. Input signal WDAT
Is A′-αA or (A ′) + αB described above. The corrected frequency signals H0 to HF from the histogram registers 144 _{1 to} 144 _F are also output to the correction reference value calculation unit 131.

The selector 145 has 16 levels of density H0 to HF from the histogram registers 144 _{1 to} 144 _F.
Is input, the frequency (the number of pixels) corresponding to
H0 according to input signals SLDT0 to SLDT3 from
1 out of 16 data (each having a bus width of 26 bits)
Data is selected and a signal HSDT is output.

As shown in the timing chart of FIG. 16, the sub-scanning line number counter 153 receives the line synchronization signal HDEN from the timing signal generator 133 and outputs the count value signals FDAT00 to FDAT12 to the clock generator 152. A clear signal CRST from the main CPU 91 clears each page of the document.

The clock generator 152 outputs the output signals FDAT0 to FDAT1 from the sub-scanning line number counter 153.
2, and the pixel synchronization clock signal GC from the scanner unit 4.
K is input and the signal HCK is output to the counter 151 and the added value generation unit 150. The clock generator 152 determines that the value of the signal FDAT is 1, 3, 7, F, 1F, 3F, 7F,
In any one of 1FF, 3FF, 7FF, FFF, and 1FFF, one clock of the input pixel synchronization clock signal is output. The clock generation unit 152 is configured by an AND circuit, and when all the line number signals FDAT are “1”,
DAT = 1, 3 (11), 7 (111), F (111)
When 1) ..., 1 clock is output.

The counter 151 has a clock generator 152.
When the clock signal HCK is input from the controller 14 and the mode 0, the count value signals CDT20 to CDT23 are
Output to 7. The counter 151 is also cleared for each page by the clear signal CRST from the main CPU 91. The count values CDT20 to CDT23 are values for selecting α as shown in FIG.

The fixed coefficient value register 155 outputs the fixed coefficient value in the mode 1. The switch 156 is the CPU 9
It is switched according to the mode signal SL1 from 1 and is set to the counter 151 side in the mode 0 and to the register 155 side in the mode 1.

The subtraction value generating section 146 has (A ') = A-α
“ΑA” for calculating A is output. Subtraction value generator 1
46 receives the output signal HSDT from the selector 145 and generates a value obtained by dividing the signal HSDT by a power of 2 (shifts the signal HSDT).

The selector 147 performs an operation (A ') performed between the lines, that is, when the pixel signal is not read.
= A-αA, the input signals SSL0 to SSL3
Determined according to. That is, when the value of the input signals SSL0 to SSL3 is "1", the selector 147 outputs the signal HS
DT value / 2, when the input value is "2" (signal HSD
(Value of T) / 2 ² , ..., When the input value is C (signal HS
The value of DT) / 2 ¹³ is output.

The subtracting section 149 subtracts (A ') = A-αA.
I do. The subtraction unit 149 receives the density signal HSDT (A in the above equation) from the selector 145, receives the subtraction number signal SDT (αA in the above equation) from the selector 147, and outputs a signal YDAT as a result of the subtraction. .

Addition value generator (shift register) 150
Generates “αB” when calculating A ′ = (A ′) + αB. The addition value generation unit 150 includes a clock generation unit 152
The clock signal HCK from the
Is output to the adding section 148. The addition value generation unit 150 also
It is cleared for each page by a clear signal CRST from the main CPU 91. FIG.
The initial value output is 2000H when the clear signal CRST is input, and the present value becomes 1 each time the clock signal HCK from the clock generator 152 is input thereafter.
/ 2 is output. Since this output is a hexadecimal number, for example, 1/2 of the current value 2000H is 1000H, and 1/2 of the current value 1000H is 800H. FIG. 12 shows a change in each signal corresponding to a change in the signal FDAT.

The adding unit 148 adds A '= (A') + α
Perform B. The addition unit 148 receives the frequency signal HSDT from the selector 145 and the signal XDAT of the addition data from the addition value generation unit 150, and outputs a signal ZDAT as a result of the addition. FIG. 12 shows an example of addition of the signal ZDAT.

The switch 154 switches the calculation of (A ') = A-αA and A' = (A ') + αB. To one terminal of the switch 154, the addition result signal ZDAT from the addition unit 148 is input, and the subtraction result signal YDAT from the subtraction unit 149 is input to the other terminal.
One input is selected according to TL1, and the selection result signal WD
The AT is output to the histogram registers 1441 to 144F.

Next, the creation of a histogram with the configuration shown in FIG. 9 will be described with reference to the timing charts of FIGS. 14, 15 and 16.

FIG. 14 is a timing chart showing how A '= (A') + αB is calculated for each input pixel during one line reading. The signal MCK is a main clock and is synchronized with the pixel signal. The signal VDEN is a page synchronization signal, and the signal HDEN is a line synchronization signal. Pixel density signals IDAT4 to IDAT7 from the scanner unit 4
Are the upper 4 bits of the pixel density and are input to the switch 141. In this case, the sub-scanning valid signal CTL0 is enabled (low level), and the switch 141
DAT4 to IDAT7 are sent to the selector 145 and the clock generator 143.

The selector 145 outputs the pixel signals IDAT4 to IAT
The outputs (frequency) of the histogram registers 144 _{1 to} 144 _F are selected according to the value of DAT7, that is, the selection input signal,
The selected frequency signal HSDT is output. Signal HSDT
Is added by a coefficient (XDAT) weighted according to the number of lines in the adder 148. In this case, the switch 154 is set to the adder 148 side by the input signal CTL1, so that the addition result signal ZDAT returns to the histogram registers 144 ₁ to 144 _F.

Next, the clock generator 143 outputs the pixel signal I
A clock signal FCK0− according to DAT4 to IDAT7
Outputs FCKF. Each histogram register 144 ₁
To 144 _F at the rise of the clock signal FCK0-FCKF, respectively latches i.e. stores the value of the output signal WDAT switch 154. By performing the above processing for each pixel of one line, a histogram of one line is generated, a reference value for pixel density adjustment is calculated, and the reference value is used for the processing of the next line.

Next, between the reading of one line and the reading of the next line, that is, when the pixel density signal is not input, the frequency of each density of the histogram is (A ') = A-αA.
Is calculated.

FIG. 15 is a timing chart showing the state of the subtraction process. The switch 141 has a selection signal CTL.
It is switched to the counter 142 side by 0, and the switch 15
4 is switched to the subtractor 149 side by the selection signal CTL1. The selector 147 subtracts each histogram value by a coefficient (when mode 0) or a fixed coefficient (when mode 1) that is determined by the number of sub-scanning counters. After the subtraction operation is completed, the process proceeds to a normal histogram creation operation. By repeating the above-described operation, a histogram in which the total data amount is variable and constant is created each time each main scanning line is read.

As described above, according to the above embodiment,
A histogram can be obtained for each main scanning line, and real-time automatic density adjustment using the histogram becomes possible. Further, by multiplying the frequency by a weighting coefficient that is changed according to the number of read lines and accumulating the frequency, a histogram with a variable total data amount is created every time each main scanning line is read. When the weighting coefficient is fixed, a histogram corresponding to a sudden change in the density of the document image can be obtained.

FIG. 17 is a block diagram showing a schematic structure of the image synthesizing unit 99.

That is, the image composition unit 99 uses the register 1
61, 162, inversion circuits 163, 164, addition circuit 16
5, the comparator 166, and the selector 167.

The image data A and B from the image processor 96 or the page memory 98 are stored in the registers 161, 1 respectively.
Temporarily stored in 62. The output of the register 161 is
The output of the register 162 is supplied to the inverting circuit 163.
It is supplied to the inverting circuit 164. Inversion circuits 163 and 164
Switches between outputting image data as it is and inverting and outputting it bit by bit in response to a signal from the main CPU 91. The image data inverted bit by bit becomes an image in which black and white are inverted.

The outputs of the inversion circuits 163 and 164 are the addition circuit 165, the comparator 166, and the selector 16 respectively.
7 is supplied. The adder circuit 165 adds two image data. The output image data of the adding circuit 165 is 2
The densities of the pixels of the two input images are added.
In the adder circuit 165, when an overflow occurs due to addition, the output value becomes the maximum value and the selector 167
An overflow signal is output to. Also, the adder circuit 1
One of the image data given to 65 is the inverting circuit 163 or 1
If it is inverted by 64, the output becomes the subtraction result of the original image data. The output of the adder circuit 165 is the selector 16
7 is supplied. The comparator 166 determines, for each pixel, the magnitude relationship between the two image data, in other words, which one has a higher density. The determination result of the comparator 166 is connected to the selector 167.

The selector 167 includes inverting circuits 163, 16
4 is a circuit for selecting one image data for each pixel from the output of 4 and the output of the adding circuit 165.

Which image data the selector 167 selects is determined by the control signal from the main CPU 91 and the determination result of the comparator 166.

For example, the image data A is stored in the register 161.
However, when the image data B is input to the register 162, a control signal from the main CPU 91 is added to set the inversion circuits 163 and 164 to no inversion and select the output of the selector 167 and the addition circuit 165. , The output image data becomes “image data A + image data B”, and 2
It is a composite of the densities of the two images.

The selector 167 switches the image data A according to the judgment output of the comparator 166.
Alternatively, the image data having the higher density of either B can be output. Image data A is output from the comparator 166.
When the main CPU 91 controls the image data B so as to compare a constant value with the image data B instead of comparing
At other times, the image data A can be set to be output.

The image synthesizing method can be specified from the operation panel 80, but for the convenience of the user, it is automatically selected from several synthesizing modes depending on the image. The types of synthesizing methods are shown in FIG.

Histogram creation circuit 1 of the image processing unit 96
The density histogram created by 30 allows the main C
The PU 91 divides the image type into characters and photographs. When the density histogram is divided into high density and low density, it is determined that the image is a clear black and white character center image.
On the contrary, an image in which the density histogram spreads from high density to low density is determined as an image having a halftone such as a photograph. The main CPU 91 makes this determination for the two images A and B to be combined.

Since the images A and B have different priorities depending on the synthesizing method, for example, the image read first by the scanner unit 4 is given high priority as the foreground (front image), and the image read later is given priority as the background. It is decided in advance that the rank will be lowered.

As shown in FIG. 20, there are three combinations of two images: character-character, character-photo, and photograph-photo.

In the case of the character-character combination, the user can select one of the three combining methods of (a) overlapping composition, (b) overlapping inversion composition, and (c) background density adjustment in advance. (A) Comparator 1 of the image synthesizing unit 99 at the time of overlay synthesis
At 66, the two image data A and B are compared, and the selector 1
In 67, the image data having the higher density of the image data A and B is selected for each pixel. As a result, the output image is a superposition of two images as shown in FIG.
(B) When there is no overlap between the two images at the time of overlapping and inverting composition, the image with the higher density is selected by the selector 167 as in the case of (a) overlapping composition, but when the images overlap, the addition circuit 165 An overflow signal is generated, and this signal causes the selector 167 to output a predetermined fixed density, mostly zero density (white). As a result, the output image becomes a white image where the images are overlapped as shown in FIG. (C) In the background density adjustment, the range correction circuit 82 of the image processing unit 96 changes the density range so that the maximum density of the background image becomes smaller than that of the foreground image.
The image synthesizing unit 99 performs the same processing as the (a) overlay synthesis, and the output image is as shown in FIG.

In the case of the character-photograph combination, the user selects from three compositing methods of (d) overlay composition, (e) overlap inversion composition, and (f) background density adjustment. In (d) superposition composition, the same processing as (a) superposition composition in the case of characters is performed. (E) At the time of overlap inversion synthesis, the comparator 166 compares a character image, for example, A, with a constant value, for example, an intermediate value 128 between white and black, and when A is smaller than 128, the selector 167 outputs the photographic image B. Select and A is 128
When it is larger, the inversion circuit 16 inverts the inversion image of the image data B.
Select from 4. (F) The background density adjustment is the same as (c) the background density adjustment, but the photographic image side is automatically selected as the image whose density is changed as the background.

In the case of a photograph-photograph combination, the user selects from three composition methods of (g) additive composition, (h) gradation selection, and (i) background density adjustment. (G) In additive synthesis,
The addition circuit 165 obtains an image in which the two image densities are added. Since the composite image is biased toward the higher density, the range correction circuit 132 corrects the density range before or after the composition. When the original image A shown in FIG. 24 and the original image B shown in FIG. 25 are combined, the output image is as shown in FIG.
(H) In the gradation selection, the two image data are compared by the comparator 166, and the selector 167 selects the higher or lower density for each pixel according to the result.
Also in this case, the density range is corrected if necessary. The output images are as shown in FIG. 27 (dark shade selection) and FIG. 28 (dark shade selection). (I) For background density adjustment, the same processing as (c) or (f) is performed.

There are some items that the user can select and adjust for each synthesizing method. When the user does not perform the setting operation,
Although a predetermined specified value is used, an image closer to the image desired by the user can be output by the user's setting operation. The setting operation is performed using the operation panel 80. The user makes settings with the ten keys, the slide volume, the up / down keys, etc. while looking at the display on the operation panel 80.

Next, an image synthesizing process having such a configuration will be described.

That is, the 8-bit pixel image data from the scanner section 4 is sent to the image processing section 96, and a density histogram is created. The density range conversion of the image data is performed based on this density histogram data. The image data subjected to the density range conversion is sent to the image synthesizing unit 99 or the page memory 98.

The image synthesizing unit 99 synthesizes two image data. The image data is sent from the image processing unit 96 and the page memory 98, or both are sent from different parts of the page memory 98.

The image data synthesized by the image synthesizing unit 99 is sent to the printer unit 6 and stored again in the page memory 98 for forming an image or performing another processing. The image transfer method and the image composition method are performed by the main CPU 9.
Controlled by 1. Further, the user selects and designates image processing such as a combining method through the operation panel 80.

For example, FIG. 18 shows an input section 82 of the operation panel 80 for performing background density adjustment synthesis of a character-character image.
Is a display example of.

That is, in the upper part of FIG. 18, five combining method selection buttons 82a, 82 for selecting a combining method are provided.
b, 82c, 82d, and 82e are lined up. In the figure, a combination method selection button 82d for selecting the background density adjustment is selected, and the selected state is displayed by making the display color (density) of this combination method selection button 82d different from the others.
The synthesizing method selection buttons 82a and 82e are for selecting another synthesizing method, and the synthesizing method selecting button 82a is dimmed because there is nothing to select in the left direction.
It doesn't respond even when pressed.

The display of the interruption and the lower stage differs depending on the combination method selected in the upper stage.

The interruption includes a read-ahead image selection button 82f and a read-ahead image selection button 82g as background image selection buttons for selecting which of the two images is to be used as the background for density adjustment. It is a button for instructing whether the image selected as the background is the image read by the scanner unit 4 first or the image read by the scanner unit 4 later, and the display color (density) of the selected button is different from the other. The selection status is displayed by making a mistake.

The lower part is used for adjusting the density of the background image.
Normally, the density range of the background image is automatically corrected so that the density histograms of the two images do not overlap, but the user can also set the density range.

A scale 82h divided into 16 is displayed on the screen. The division method of the scale 82h corresponds to the division of the pixel values 0 to F when creating the histogram. On the upper side of the scale 82h, the density display 8 of the foreground image is displayed.
2i, the background image density display 82j is displayed in blocks on the lower side. The density displays 82i and 82j are created from histograms. For example, as shown in (b) of FIG. 19, a section having a value of ½ or more of the maximum value of the histogram as shown in (a) of FIG. 19 is displayed. , Is represented by a black block and represents an approximate distribution of the concentration.

When the density adjustment is automatic (AUTO) (AU
The selection state is displayed by making the display color (density) of the TO button 82k different from the others), and the upper and lower density displays 82i, 8
The density range of the background image is adjusted so that 2j does not overlap.

Light button 82l or dark button 82m
When is pressed, the indicator 82n is displayed, and the maximum density setting value of the background image is displayed by the indicator 82n.

When the thin button 82l is pressed, the indicator 82n moves one scale to the 0 side of the scale 82h,
When the dark button 82m is pressed, the indicator 82n moves one scale to the 16 side of the scale 82h, and the value indicated by the indicator 82n at that time becomes the maximum density.
The density range of the background image is adjusted.
As described above, in a digital copying machine that obtains a composite image from two original images, one or both of the original images are created so that the density histograms for the respective original images are not overlapped. The density range is corrected.

As a result, the images can be combined without impairing the visibility of the original images.

That is, when creating a composite image of two images, the density range of the background image of the two images is changed by the density histogram of the other foreground image, that is, the foreground image The density histogram detects the lowest density except the white background of the foreground image, and corrects the background image density range so that the maximum density of the background image is lower than the lowest density of the foreground image excluding the white background. By doing so, a contrast can be provided between the foreground and the background, and a composite image that is easy to see can be obtained.

When making a composite image of two images,
When the images overlap, the shades of one image are reversed, so that the information of the two original images can be retained even after composition.

Further, since the synthesizing method can be selected from the user's selection and the combination of the image types, various synthetic images can be obtained.

[0118]

As described above in detail, according to the present invention,
It is possible to provide an image forming apparatus capable of synthesizing images without impairing the visibility of the original images.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a control circuit of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of an internal mechanism of the image forming apparatus.

FIG. 3 is a block diagram illustrating a schematic configuration of an image processing unit.

FIG. 4 is a diagram for explaining a histogram.

FIG. 5 is a diagram for explaining a histogram.

FIG. 6 is a histogram diagram for explaining correction reference values and range correction.

FIG. 7 is a histogram diagram for explaining correction reference values and range correction.

FIG. 8 is a view for explaining the number of sub-scanning lines in mode 0 and a coefficient α corresponding thereto.

FIG. 9 is a block diagram showing the configuration of a histogram creation circuit.

FIG. 10 is a diagram for explaining the timing of an output clock signal corresponding to the input pixel density in the clock generation unit.

FIG. 11 is a diagram illustrating an output example of an addition value generation unit.

FIG. 12 is a diagram showing a change in each signal corresponding to a change in a signal FDAT.

FIG. 13 is a diagram illustrating an example of addition of a signal ZDAT.

FIG. 14 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 15 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 16 is a timing chart for explaining the operation of the histogram creation circuit.

FIG. 17 is a block diagram showing a schematic configuration of an image composition unit.

FIG. 18 is a diagram showing a display example of the input unit of the operation panel when performing background density adjustment synthesis of a character-character image.

FIG. 19 is a diagram for explaining the relationship between a histogram and density display.

FIG. 20 is a diagram for explaining the types of synthesizing methods.

FIG. 21 is a diagram for explaining an output image.

FIG. 22 is a diagram for explaining an output image.

FIG. 23 is a diagram for explaining an output image.

FIG. 24 is a diagram for explaining an original image A.

FIG. 25 is a diagram for explaining an original image B.

FIG. 26 is a diagram for explaining an output image.

FIG. 27 is a diagram for explaining an output image.

FIG. 28 is a diagram for explaining an output image.

[Explanation of symbols]

 4 ... Scanner section 6 ... Printer section 80 ... Operation panel 82 ... Input section 90 ... Main control section 91 ... Main CPU 96 ... Image processing section 98 ... Page memory 99 ... Image combining section

Claims (12)

[Claims] 1. An image forming apparatus for synthesizing two images, a first image and a second image, at least one of the two images in order to easily distinguish the two images when synthesizing the two images. An image forming apparatus having an adjusting unit for adjusting a range of light and shade used in an image. 2. An image forming apparatus for synthesizing two images, a first image and a second image, for generating a density histogram formed by the number of pixels for each density section of the first and second images. When synthesizing the first image and the second image with each other, the density range used in one or both images is adjusted so that the two density histograms generated by the generating unit do not overlap. An image forming apparatus, comprising: 3. An image forming apparatus for synthesizing two images of a foreground image and a background image, wherein when synthesizing two images of the foreground image and the background image, the background image is An image forming apparatus having an adjusting unit for adjusting a range of light and shade to be used. 4. An image forming apparatus for synthesizing two images of a foreground image and a background image, a generation means for generating a density histogram formed by the number of pixels for each density division of the foreground image and the background image, and a foreground. When synthesizing the two images of the image and the background image, in order to make it easy to distinguish the two images, the density range used in the background image is set so that the two density histograms generated by the generation means do not overlap. An image forming apparatus comprising: an adjusting unit for adjusting. 5. An image forming apparatus for synthesizing two images, a first image and a second image, wherein when synthesizing two images, a first image and a second image are overlapped in order to easily distinguish the two images. An image forming apparatus comprising: a reversing unit for reversing the grayscale of at least one of the image portions. 6. An image forming apparatus for synthesizing two images of a foreground image and a background image, wherein when synthesizing the two images of the foreground image and the background image, the foreground image and The composite image is output by outputting the image data of the higher density of the background image for each pixel, or for the part where the foreground image and the background image do not overlap, the density of the foreground image and the background image Higher image data of each pixel is output for each pixel, and for the portion where the foreground image and the background image overlap, the image data of constant density is output to output a composite image. The maximum density of the background image is smaller than the density of the foreground image.The background image with the higher density of the background image whose density range has been changed is output for each pixel. Is output for each pixel to output a composite image, or an image data having a higher density of the foreground image and the background image or an image data having a lower density is output for each pixel. The selection means for selecting whether to select the grayscale combination for outputting a composite image, the judgment means for judging whether the foreground image and the background image are character images or photographic images, and the judgment result by the judgment means and the selection result by the selection means. Accordingly, an image forming apparatus comprising: an output unit configured to output an image combined by the above-mentioned overlapping composition composition, the above-mentioned overlap inversion composition, the above background density adjustment, the above-mentioned additive composition, or the above-mentioned gradation selection composition. . 7. An image forming apparatus for synthesizing two images, a foreground image and a background image, wherein, when synthesizing the two images, the foreground image and the background image, the two images An image forming apparatus comprising: an output unit that outputs a composite image by outputting image data of a background image having a higher density for each pixel. 8. An image forming apparatus for synthesizing two images of a foreground image and a background image, wherein when the two images of the foreground image and the background image are synthesized, it is easy to distinguish between the two images. For the part where the background image does not overlap, the image data of the higher density of the foreground image and the background image is output for each pixel, and for the part where the foreground image and the background image overlap, an image of constant density is output. An image forming apparatus comprising: an output unit that outputs a composite image by outputting data. 9. An image forming apparatus for synthesizing two images of a foreground image and a background image, wherein when synthesizing two images of the foreground image and the background image, the two images The maximum density of the background image is smaller than the density of the foreground image. The output means for outputting the composite image by outputting the image data of the higher density of the background image whose density range has been changed, for each pixel. An image forming apparatus characterized by the above. 10. In an image forming apparatus for synthesizing two images, a foreground image and a background image, when synthesizing the two images, the foreground image and the background image, in order to easily distinguish the two images, An image forming apparatus comprising: an output unit that outputs a composite image by outputting image data to which a background image is added for each pixel. 11. An image forming apparatus for synthesizing two images, a foreground image and a background image, wherein, when synthesizing the two images, the foreground image and the background image, it is easy to distinguish the two images. An image forming apparatus comprising: an output unit that outputs a composite image by outputting, for each pixel, image data having a higher density or image data having a lower density in a background image. 12. An image forming apparatus for synthesizing two images, a foreground image and a background image, and a deciding means for deciding whether the foreground image and the background image are a character image or a photographic image, and the synthesizing method is an overlay synthesizing method or an overlapping method. Characters are selected by selecting means for selecting reverse composition, background density adjustment, additive composition, and gradation selective composition, changing means for changing to a density range in which the maximum density of the background image is smaller than the density of the foreground image, and the judging means. The combination of the image and the character image is determined,
When the overlay composition is selected by the selection unit, the composite image is output by outputting the image data of the higher density of the foreground image and the background image for each pixel, and the determination unit combines the character image and the character image. When the overlapping inversion composition is selected by the selection means, the image data of the higher density of the foreground image and the background image is output for each pixel for the portion where the foreground image and the background image do not overlap. Then, for a portion where the foreground image and the background image overlap, a composite image is output by outputting image data of a constant density, the determination means determines the combination of the character image and the character image, and the selection means determines the background. When density adjustment is selected,
The maximum density of the foreground image and the background image is smaller than the density of the foreground image.The image data of the higher density of the background images whose density range has been changed is output for each pixel to output a composite image. The combination of text and photo images is determined,
When the overlay composition is selected by the selection unit, the composite image is output by outputting the image data of the higher density of the foreground image and the background image for each pixel, and the determination unit combines the character image and the photographic image. If the density of the character image is smaller than the predetermined density when the overlapping inversion composition is selected by the selection means, the image data of the photographic image is output, and if the density of the character image is higher than the predetermined density, the photographic image is output. The composite image is output by outputting the image data of the reverse image of, and when the combination of the character image and the photographic image is determined by the determination unit and the background density adjustment is selected by the selection unit, the foreground image and the change unit are selected. The composite image is output by outputting the image data of the higher density of the background image of which the density range has been changed for each pixel, and the composite image is output by the judging means. The combination of photographic images is judged,
When the additive composition is selected by the selection unit, the composite image is output by outputting the image data obtained by adding the foreground image and the background image for each pixel, and the composition of the photographic image and the photographic image is judged by the judging unit. When the grayscale selection is selected by the selecting means, the composite image is output by outputting the image data of the higher density or the image data of the lower density of the foreground image and the background image for each pixel, and the determining means When the combination of the photographic image and the photographic image is judged by the selecting means and the background density adjustment is selected by the selecting means, the image data having the higher density of the foreground image and the background image whose density range has been changed by the changing means is selected as a pixel. An image forming apparatus comprising: an output unit configured to output a composite image by outputting each image.