JPH07298033A - Image composite device - Google Patents

Abstract

PURPOSE:To composite an original image and a composite image on purpose and to identify the composite image independently of a density of an original when the composite image is composited with an original image through superimposition. CONSTITUTION:A character signal is converted into a 10-bit multi-value processing signal by a binary/multi-value processing conversion circuit D1, the replaced character signal and a 10-bit original image signal are ORed for each bit by an EXOR (exclusive OR) circuit D2 and an OR circuit D3. A selection control section D4 applies a signal to a selector D5 to select an output of the EXOR circuit D2 in the exclusive OR mode, an output of the OR circuit D3 in the OR mode, an output of the EXOR circuit D2 for a range of the original density of 0 to threshold level th2 and a range of threshold level levels th1-255 and an output of the OR circuit D3 in a range of the original density of a range of threshold level levels th2-th1 in the OR/exclusive OR mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image synthesizing device for a digital copying machine, and more particularly to an image synthesizing device for synthesizing an image such as a character on a document image.

[0002]

2. Description of the Related Art Conventionally, as a digital copying machine of this type, as shown in, for example, Japanese Patent Application Laid-Open No. 62-245774, a specific pattern such as a date or an imprint for approval is combined with an original image and recorded on a recording sheet. What is known is. Also,
When superimposing characters and other images on the original image and combining them,
Two images can be saved by exclusive ORing the two images.

[0003]

By the way, when two images are superimposed and combined, an output image suitable for the purpose of use can be obtained by changing the combining method according to the purpose of use. For example, an image such as date, time, page, etc. should be visible even if it overlaps with an original image, while an image such as a stamp or a stamp should be invisible as it is when overlapping with an original image.

Further, even if an exclusive OR of two images, one of which is an intermediate level and the other is all "1", the effect of the exclusive OR does not appear in the composite image, and the original intermediate level is obtained. There is a problem that the value is close to.

It is an object of the present invention to provide an image synthesizing apparatus capable of synthesizing a synthesizing image on an original image by synthesizing the image according to the purpose of use.

Another object of the present invention is to provide an image synthesizing apparatus capable of synthesizing a synthesizing image in a distinguishable manner regardless of the density of the original when the synthesizing image is superimposed on the original image. .

[0007]

In order to achieve the above object, a first means is to generate a synthesizing image signal for synthesizing an image on a document image, a document image signal and the synthesizing image signal. An exclusive OR means for performing an exclusive OR operation, an OR means for performing an OR operation between the original image signal and the compositing image signal, and a selection for selecting the output of the exclusive OR means and the output of the OR means. And means.

In a second means, the selecting means of the first means selects the output of the logical sum means when the original image has an intermediate density, and when the original image has another density, the exclusive logical sum means of the exclusive OR means. It is characterized by selecting an output.

[0009]

In the first means, the exclusive OR output and the OR output of the original image signal and the image signal for synthesis can be selected, so that the exclusive OR output is performed for images such as date, time, and page. By selecting it, it can be combined so that it can be seen even if it overlaps with the original image, while on the other hand, images such as stamps and seals can be combined so that they will not be visible if they overlap with the original image by selecting logical OR output. be able to. Therefore, when the image for synthesis is superimposed on the original image and is synthesized, it can be synthesized according to the purpose of use.

In the second means, the OR output is selected when the original image has an intermediate density, for example, the density between the preset first threshold value and the second threshold value, and when the original image has another density, Since the exclusive OR output is automatically selected, when the original image has an intermediate density, it can be combined so that the image for combining can be seen even if it overlaps with the original image. Therefore,
When the composition image is superimposed on the document image for composition, the composition image can be composited in a distinguishable manner regardless of the document density.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an image synthesizing apparatus according to the present invention, FIG. 2 is an explanatory view showing a threshold value of document density when switching logical OR and exclusive OR in FIG. 1, and FIG. 3 is digital copying. Diagram showing the image reading device of the machine,
4 is a block diagram for explaining the processing order of image data, FIG. 5 is a block diagram showing a laser printer of a digital copying machine, FIG. 6 is a block diagram showing in detail the spatial filter circuit of FIG. 4, and FIG. 4 is a block diagram showing in detail the gradation processing circuit of FIG. 4, FIG. 8 is an explanatory diagram showing the relationship between the gradation processing output signal and the LD lighting pulse in the gradation processing circuit of FIG. 7, and FIG. 9 is the relationship between the luminance signal and the pulse width. 11 is an explanatory view showing a weighting matrix for distributing requantization error, and FIG.
7 is an explanatory diagram showing a luminance signal allocation process of the error diffusion processing unit of FIG. 7, FIG. 12 is an explanatory diagram showing a 4 × 4 dither matrix of the multilevel dither processing unit of FIG. 7, and FIG. 13 is a multilevel dither of FIG. Explanatory diagram showing the 6 × 6 dither matrix of the processing unit, FIG.
4 is an explanatory view showing the arrangement of threshold values in the dither matrix of FIGS. 12 and 13, FIG. 15 is a block diagram showing in detail the character generation part of FIG. 4, FIG. 16 is an explanatory view showing an example of a composite image, and FIG. It is explanatory drawing which shows the character code data stored in the text RAM of FIG.

First, a digital copying machine to which the image synthesizing apparatus of this embodiment is applied will be described with reference to FIG. In the image reading apparatus shown in FIG. 3, originals (not shown) placed on the contact glass 1 are light sources 2a and 2b.
The reflected light (original image) is illuminated by the mirror 3,
Sequentially reflected by 4, 5, 6, 7 and C by lens 8.
An image is formed on the light receiving surface of the CD image sensor 9 and read by the sensor 9.

The light sources 2a and 2b and the mirror 3 are mounted on a traveling body 10 which moves below the contact glass 1 in parallel with the glass 1 in the sub-scanning direction (horizontal direction in FIG. 3), and the mirrors 4 and 5 are the same. It is mounted on the traveling body 11. Main scanning of the original is performed by solid-state scanning of the CCD image sensor 9, and the entire original is scanned by moving the optical systems 2 to 11. In this embodiment, the reading density is 16 pixels / mm for both main scanning and sub-scanning, and it is possible to read documents up to A3 size (297 mm × 420 mm).

As shown in FIG. 4, the CCD image sensor 9 is driven by a sensor driver 12 to read the original image at the sampling density of 16 pixels / mm. This image signal is amplified to a predetermined voltage amplitude by the amplifier 13, and then 2 times per pixel by the A / D conversion circuit 14.
Is converted into digital data of n-th gradation (256 gradations, 8 bits in the embodiment). The shading correction circuit 15 corrects this digital data for uneven illuminance of the light sources 2a and 2b and sensitivity variations among the elements of the CCD image sensor 9, and then a spatial filter circuit 16 shown in detail in FIG. MTF correction for improving resolution, smoothing processing for removing signal noise and improving reproducibility of photographs and the like are performed.

After that, the main scanning magnification of the image is scaled by the main scanning scaling circuit 17 according to the set scaling ratio, and then the image density is changed by the gamma correction circuit 18 according to the set density.
Is corrected by. After that, halftone processing or the like is performed on the image by the gradation processing circuit 19 shown in detail in FIG. 7 according to the set image quality, and then the synthesizing unit 10 according to the present invention.
At 0, it is combined with the character from the character generation unit 101, and L
It is sent to the D control circuit 20. The LD control circuit 20 generates a lighting signal of a laser diode (LD) according to the image signal to drive the LD.

Next, the structure of the laser printer will be described with reference to FIG. Although this laser printer is often integrated with the image reading apparatus shown in FIG. 3, it may be separated and connected only electrically. The laser printer is roughly composed of a laser writing system, an image reproducing system and a paper feeding system. The laser writing system has a laser output unit 21, an imaging lens 22 and a mirror 23. The laser output unit 21 is a laser diode (LD) which is a laser light source and a polygon (polygon) which is rotated at a constant speed by an electric motor. Have a mirror.

The laser light output from the laser writing system is applied to the photosensitive drum 24 of the image reproducing system. Around the photosensitive drum 24, a charger 25 and an eraser 2 are provided.
6, a developing unit 27, a transfer charger 28, a separation charger 29, a separation claw 30, a cleaning unit 31, etc. are arranged. Although not shown, a beam sensor for obtaining a main scanning synchronization signal (MSSYNC) is arranged at a position near the end of the photosensitive drum 24 where the laser beam is emitted.

The image reproduction process of this laser printer will be briefly described. The peripheral surface of the photoconductor drum 24 is uniformly charged to a high potential by the charging charger 25, and when the peripheral surface is irradiated with the laser beam, the potential of the irradiated area decreases. Therefore, when the laser light is turned on / off according to black / white and the laser irradiation energy on the peripheral surface of the photoconductor drum 24 is controlled by pulse width modulation (PWM) or power modulation (PM), On the peripheral surface of the drum 24, a potential distribution corresponding to the gradation level of the recorded image, that is, an electrostatic latent image is formed.

When the photosensitive drum 24 rotates and the area where the electrostatic latent image is formed passes through the developing unit 27, toner adheres according to the level of the potential, and the electrostatic latent image is visualized and the toner is formed. Become a statue. This toner image is transferred to the recording sheet 32 (32a, 32b) by the transfer charger 28, and the recording sheet 32 is separated from the photoconductor drum 24 by the separation charger 29 and the separation claw 30 and then remains on the photoconductor drum 24. Toner is cleaning unit 3
Removed by 1.

The paper feeding system is composed of two systems. The recording sheet 32a in the upper paper feeding cassette 33a is fed by a paper feeding roller 37a, and the recording sheet 32b in the lower paper feeding cassette 33b is a paper feeding roller. The paper is fed by 37b. Although not shown, a recording sheet size detection sensor for detecting the size of the recording sheets 32a and 32b stored in the cassettes 33a and 33b is provided.

The recording sheet 32a or 32b fed by one of the sheet feeding rollers 37a and 37b is temporarily stopped while being abutted by the registration roller 38, and then the photosensitive drum 24 is synchronized with the image recording process. And the transfer charger 28 to transfer the toner image. The recording sheet 32 is the photosensitive drum 24.
After being separated from the sheet, the sheet is conveyed by the conveying belt 34, the toner image is heat-fixed by the fixing roller 35 having a built-in heater, and the toner image is discharged onto the sheet discharge tray 36.

FIG. 6 shows the spatial filter circuit 16 shown in FIG.
The main scanning magnification / reduction circuit 17, the γ correction circuit 18, and the gradation processing circuit 19 are shown. The shading-corrected signal is input to the spatial filter circuit 16 and the character filter 1 is used.
The MTF correction and the smoothing process are performed in parallel by 61 and the photo filter 162, respectively. Area separation processing unit 16
3 also determines whether it is a character portion or a photograph portion based on this input signal, and the selector 164 outputs the output of the character filter 161 in the character portion and the output of the photograph filter 162 in the photograph portion based on this determination signal. It is selected and output to the main scanning variable magnification circuit 17. Further, the determination signal of the character portion or the photograph portion is applied to the main scanning magnification varying circuit 17 and the gradation processing circuit 19.

The gradation processing circuit 19 performs processing for changing the image quality of the output image according to the image mode in order to transfer the γ-corrected image signal to the printer unit and convert it into the LD lighting signal. In the example shown in FIG. 7, the multi-value processing unit 191
Error diffusion processing unit 192 and multi-value dither processing unit 193
And a binarization processing unit 194 are provided, and the multi-value conversion processing unit 191 and the error diffusion processing unit 192 both perform 1-pixel processing and 2-pixel processing.

Before describing each image quality processing, the format of the image signal output from the gradation processing circuit 19 will be described. As described above, the output signal of the gradation processing circuit 19 is the LD lighting signal, and therefore L
The format of the output signal differs depending on the D lighting method.
In the present embodiment, 256 gradations are configured to be expressed by the PWM method, and the phases of the lighting pulse (left-aligned pulse, center pulse, right-aligned pulse) as shown in FIGS. 8 and 9.
Is used to control the modulation level (0 to 255) and an 8-bit luminance signal and a 2-bit phase signal representing a phase, for a total of 10-bit format.

The multi-value processing unit 191 controls the phase signal and performs one-pixel processing and two-pixel processing. In the phase control, in the case of 1-pixel processing, the phase is shifted to the larger side (blacker side) based on the size relation between the left and right adjacent pixels. However, if the phase is simply changed only by the size relationship of the adjacent pixels on the left and right, texture is generated by random noise, so the phase is controlled only when the density difference (data difference) on the left and right exceeds a certain threshold, and at other times. Fix with central pulse.

In the case of the two-pixel processing, the right pixel is selected as the right pulse and the right pixel is selected as the left pulse so that the black portions of the two target pixels are in contact with each other. That is, for example, odd-numbered pixels in the main scanning are selected as right pulses, and even-numbered pixels are selected as left pulses. Also, the processing of the luminance signal is
In the case of 1-pixel processing, the input signal (γ-corrected image signal) is output as it is, in the case of 2-pixel processing, input data for 2 pixels is added, and each half of the addition result is distributed to both pixels.

The error diffusion processing unit 192 adds the requantization (converted to the LD lighting luminance signal) error generated in the surrounding pixels to the target pixel with a predetermined weighting, and requantizes the addition result to convert it to the luminance signal. At the same time, the error of the pixel is output. Weighting for distributing errors is determined by an error matrix as shown in FIG.

Here, the magnitude of the error depends on the quantization level of the luminance signal, and since the data after γ conversion has 256 gradations, if the luminance signal has 256 gradations, the error is "0", 64.
If it is a gradation, the error is “3”. In this embodiment, the quantization level of the luminance signal is 9 gradations, and the maximum error is "31".
Becomes The maximum error of one pixel is “31”, and the total weighting coefficient of the matrix shown in FIG. 10 is “32”. However, since the total is divided by 1/32, the maximum total error of surrounding pixels is “31”. Becomes

Since this is added to the γ-converted data, the maximum total is "286", and this is divided into 9 gradations in 32 steps. At this time, Data = 3
When 2 × n + c (n and c are integers), n is the error diffusion output,
c is the error. Further, the error diffusion output n is 0 to 8, but the format of the luminance signal is 256 as shown in FIG.
Since the gradation is 0 to 255 as shown in FIG.
To each of n0 to 8 (= 00h to FFh).

The error diffusion processing unit 192 also performs the two-pixel processing similarly to the multi-value quantization processing unit 191. In this case, the error diffusion output n is added in units of 2 pixels, and the addition result is distributed to 2 pixels. Therefore, since the addition result is n0 to 16, the luminance signals 0 to 255 are changed to n0 to 16 (= 00h to FF) as in the case of the one pixel processing as shown in FIG.
Assign to each of h). The error diffusion processing unit 192 also performs phase control similarly to the multilevel halftoning processing unit 191. This phase control is the same as that of the multi-value quantization processing unit 191, although it differs between the one-pixel processing and the two-pixel processing.

Next, the multi-level dither processing section 193 will be described. The multi-value dither process is a dither process in which one pixel is multi-valued, and one pixel is divided in the main scanning direction in consideration of pulse width modulation of the LD lighting signal. The dither matrix is 4 × as shown in FIGS. 12 and 13 in this embodiment.
4 × 6 pixels are used, and in the case of 4 × 4, one pixel is divided into 15 (16-valued) (A0 to A14 in the figure), 4
It becomes possible to express with × 4 × 15 + 1 = 241 gradations. Also,
In the case of 6 × 6, one pixel is divided into eight (9-valued) (aa0 to aa7 in the figure), and 6 × 6 × 8 + 1 = 289 gradations can be expressed.

However, each pixel obtained by dividing one pixel cannot be turned on / off independently, unlike an independent pixel, and the pulse width must be continuously increased from the left end, the right end or the center. That is, when arranging the respective divided threshold values, as shown in FIG. 14, only a monotonic increase from the left, a monotonic increase from the right, or an array gradually increasing from the center to the left and right can be selected. In this case, the pixel is a left pulse in the monotone increase from the left, the pixel is a right pulse in the monotone increase from the right, and the pixel is a center pulse in the increase from the center. Therefore, the phase signal of the pixel is determined according to the array of thresholds, and the luminance signal is determined by how many image data (after γ conversion) of the pixel exceeds the divided threshold.

Next, the binarization processing unit 194 will be described. The binarization is a process of converting the pixel into a binary of white or black (0 or 1), and usually, a threshold is set and binarization is performed depending on whether the image data exceeds the threshold. I do. The binarization processing unit 194 of the present embodiment performs two types of processing, that is, binarization with a fixed threshold and binarization with dither. Two
The result of the binarization is a 1-bit signal, but in order to match the format of the LD signal, the output signal (luminance signal + phase signal) corresponding to the white pixel and the output signal corresponding to the black pixel are previously determined, It is converted into this signal according to the binarization result.

The image signal selection control unit 195 responds to the area signal and the image mode setting signal from the area separation processing unit 163 shown in FIG. 6, and multi-value processing unit 191 and error diffusion processing unit 1
92, a multi-value dither processing unit 193, and a binarization processing unit 194.
A signal for selecting each of the outputs is output to the selector 196, and the selector 196 actually selects by this selection signal. The image mode includes a character mode (a mode for a character document), a photo mode (a mode for a photo document), a character / photo mode (a mode for a document including mixed characters and photos), and the like.

As an example, when the character mode is set, the one-pixel processing output of the multi-value processing unit 191 is selected, and in the photo mode, the multi-value dither processing unit 193 is selected.
In the character / photo mode, the 1-pixel processing output of the multi-value quantization processing unit 191 is selected in the character area, and the 2-pixel processing output of the error diffusion processing unit 192 is selected in the photo area.

Next, the character composition will be described with reference to FIG. What is character composition? In a digital copier, add a page to the copied image, print the date,
This is a process of synthesizing image data of print characters on a normal image signal path when outputting logging data of a machine.

As described above, the signal width of the image signal path is 1 in total, that is, the luminance signal is 8 bits and the phase signal is 2 bits.
It is 0 bit. On the other hand, the printed character image is generally obtained by the character generator ROM, and the image signal is binary data. Therefore, when synthesizing this 2
Replace the value data with 10 bits of the image signal path. That is, a 10-bit signal corresponding to binary black and a 10-bit signal corresponding to white are determined in advance and replaced with them.

The character generator will be described with reference to FIG. The sub-scanning address counter C1 counts the number of lines (main scanning valid period signal Lsync) during which the sub-scanning valid period signal (Fgate) is asserted, and outputs the upper address and the lower address in the sub-scanning direction. C2 counts the number of pixels (pixel clock) during the assertion period of the main scanning effective period signal Lsync and outputs the upper address and the lower address in the main scanning direction.

The memory control section C3 controls the operation of the text RAM C4, and the text RAM C4 has an area corresponding to the position on the original in a one-to-one relationship.
In addition, the character generator ROMC5 is previously stored in the AS.
A character bitmap image is stored at each address in the CII code order.

For example, for an original image as shown in FIG. 16A, a page number (-1
In the case of synthesizing the characters of (-), the CPU preliminarily causes the text RAM C4 via the memory control unit C3 to synthesize the character code, for example, "2D", with the document image data.
FIG. 17 (a) (b) shows "h", "31h", and "2Dh"("h" represents a hexadecimal number, and each code represents "-", "1", "-" in ASCII code). ), And stores it at the address corresponding to the composite position. In addition, the space code “20h” is stored in another address.

When the copying operation is started in this state, the memory control unit C3 causes the main / sub-scanning address counters C1 and C to operate.
The character code data corresponding to the position of the document image is controlled to be read from the text RAM C4 in accordance with each upper address of 2. The bit map image is read using the character code data read from the text RAM C4 as an upper address, and the lower addresses of the main / sub-scanning address counters C1 and C2 as lower addresses, and the synthesizing unit 100 converts the bitmap image into an original image. To be synthesized.

Next, the synthesizing unit 100 according to the present invention will be described with reference to FIGS. The image signal of the image path is input with 10 bits, and the combined character signal is binary (1 = black, 0 = white). Therefore, the character signal is binary /
It is converted into a 10-bit multi-valued signal by the multi-valued conversion circuit D1, and in the simplest example, "1" is the brightness signal "FFh" and the phase signal "00b", and "0" is the brightness signal "0" and the phase signal. One-to-one replacement like "0".

The EXOR (exclusive OR) circuit D2 and the OR (logical sum) circuit D3 perform the respective logical operations on the replaced character signal and the 10-bit original image signal. Three kinds of switching mode signals are input to the selection control unit D4: a mode for exclusive ORing the entire surface, a mode for ORing the entire surface, and a mode for switching between the logical OR and the exclusive OR depending on the image density. The selection control unit D4 outputs the output of the EXOR circuit D2 in the exclusive OR mode, the output of the OR circuit D3 in the logical OR mode, and the original density as shown in FIG. 2 in the logical OR / exclusive OR mode. 0
Range from (white) to threshold th2 and thresholds th1 to 255 (black)
, The output of the EXOR circuit D2 is set to the threshold value th2 to t
In the range of h1, a signal for selecting the output of the OR circuit D3 is applied to the selector D5 (where 0 <th2 <th.
1 <255).

Therefore, for example, images such as date, time and page can be combined so that they can be seen even if they overlap the original image by selecting the output of the EXOR circuit D2, while images such as stamps and seals are ORed. By selecting the output of the circuit D3, it is possible to combine the original image and the original image so that they cannot be seen.

In the logical sum / exclusive logical sum mode, the reason for switching the logical sum and the exclusive logical sum according to the document density is that the binary signal "black" is changed to "FFh" as in the conventional example.
This is because even if the "white" is replaced with "0" and the intermediate level density of the black of the character and the original image is subjected to the exclusive OR, the change in the original density before the exclusive OR is small and the character cannot be seen. In addition, if only the logical sum is performed, the black of the character and the black of the manuscript overlap and the character cannot be seen. Therefore, when the original image has an intermediate density (the range of th2 to th1), the output of the OR circuit D3 can be selected to prevent the characters from becoming invisible.

[0046]

As described above, according to the first aspect of the present invention, the exclusive OR output and the OR output of the original image signal and the image signal for composition can be selected. The image of can be combined so that it can be seen even if it overlaps with the original image by selecting the exclusive OR output, while the images of stamps and seals overlap with the original image by selecting the OR output. Can be composited so that it remains invisible if
When the image for synthesis is superimposed on the original image and is synthesized, it can be synthesized according to the purpose of use.

According to the second aspect of the invention, the OR output is selected when the original image has an intermediate density, and the exclusive OR output is automatically selected when the original image has another density. In the case of density, it can be combined so that the composite image can be seen even if it overlaps with the original image. Therefore, when the composite image is superimposed on the original image, the composite image can be identified regardless of the original density. Can be synthesized.

According to the third aspect of the present invention, since the intermediate density can be freely selected by setting the first and second threshold values,
It is possible to set the threshold appropriately according to the image to define the range of the intermediate density.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image synthesizing apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a threshold value of document density when switching between a logical sum and an exclusive logical sum in FIG.

FIG. 3 is a configuration diagram showing an image reading apparatus of a digital copying machine.

FIG. 4 is a block diagram for explaining a processing order of image data.

FIG. 5 is a configuration diagram showing a laser printer of a digital copying machine.

FIG. 6 is a block diagram showing the spatial filter circuit of FIG. 4 in detail.

FIG. 7 is a block diagram showing the gradation processing circuit of FIG. 4 in detail.

8 is an explanatory diagram showing a relationship between a gradation processing output signal and an LD lighting pulse in the gradation processing circuit of FIG.

FIG. 9 is an explanatory diagram showing a relationship between a luminance signal and a pulse width.

FIG. 10 is an explanatory diagram showing a weighting matrix for distributing requantization errors.

11 is an explanatory diagram showing a luminance signal allocation process of the error diffusion processing unit of FIG. 7. FIG.

12 is an explanatory diagram showing a 4 × 4 dither matrix of the multi-value dither processing unit of FIG. 7. FIG.

13 is an explanatory diagram showing a 6 × 6 dither matrix of the multi-value dither processing unit of FIG. 7. FIG.

FIG. 14 is an explanatory diagram showing an array of threshold values in the dither matrix of FIGS. 12 and 13;

15 is a block diagram showing in detail the character generator of FIG.

FIG. 16 is an explanatory diagram showing an example of a composite image.

17 is an explanatory diagram showing character code data stored in the text RAM of FIG.

[Explanation of symbols]

 100 composition unit 101 character generation unit D1 binary / multi-value conversion unit D2 EXOR (exclusive OR) circuit D3 OR (logical OR) circuit D4 selection control unit D5 selector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Kawamoto 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inoue Arin 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Gouji Tone 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A means for generating a composition image signal for composing an image on a document image, an exclusive OR means for exclusive ORing the document image signal and the composition image signal, and a document image signal An image synthesizing apparatus comprising: a logical sum means for performing a logical sum of the image signals for synthesis; and a selecting means for selecting an output of the exclusive OR means and an output of the logical sum means. 2. The selecting means selects the output of the OR means when the original image has an intermediate density and the output of the exclusive OR means when the original image has another density. Item 1. The image synthesizing apparatus according to item 1. 3. The image synthesizing apparatus according to claim 2, wherein the intermediate density is set to a density between a preset first threshold value and a preset second threshold value.