JPH07123249A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of surely preventing the print out of a data such as a paper money for preventing forgery. CONSTITUTION:At two points of time when an input RGB signal is converted into a YUV signal by a conversion circuit 201, and when the YUV signal is processed y a DCT circuit 203 and quantized by a quantizer 204, whether or not the converted data and the quantized data are data such as a paper money stored in advance in a specific data memory 208 and for preventing forgery are discriminated through the comparison at a comparator 207. When the input signal is the forged data, the data are replaced with invalid data stored in an invalid data memory 206. Thus, the paper money the like is effectively prevented from being forged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, for example, an image forming apparatus that does not form a specific image pattern.

[0002]

2. Description of the Related Art For example, an electrostatic transfer method called a bias roller transfer method or a corona transfer method is generally used in a transfer apparatus of this type used in an electrophotographic copying machine or printer. In the bias roller transfer method, a transfer bias voltage having a polarity opposite to the charge of the toner of the developed image (toner image) on the photoconductor as an image carrier is applied to the transfer roller having a conductive layer to expose the image on the transfer material. The toner image on the body is transferred. As a modification of this, there is also a method of using an endless belt having a conductive layer instead of the transfer roller.

On the other hand, in the corona transfer system, a dielectric film such as a polyester film is used as a transfer material carrier, and this dielectric film wound around a cylinder whose peripheral surface is largely cut is used as a transfer drum.
Corona discharge is applied to the dielectric film from the inside of the transfer drum to transfer the toner image onto the transfer material. As a modification of this, there is a system in which an endless belt made of a dielectric film is used instead of the transfer drum.

In an electrophotographic color laser beam printer, when an electrostatic latent image is formed on a photosensitive drum, which is an image bearing member rotating at a constant speed, through image light, the electrostatic latent image is formed. The image is developed by the developing device and converted into a visible toner image. On the other hand, the transfer material fed by the paper feeding mechanism is wound around the above-mentioned transfer drum which also rotates at a constant speed, and then the toner image on the photosensitive drum is transferred at the transfer position (yellow Y, magenta M). , Cyan C, and black BK are subjected to a total of 4 cycles of exposure-development-transfer process.) When the superimposed transfer of the four-color toner images is completed, the toner images are sent to the fixing device and fixed, and then are transferred to the discharge tray. Is discharged.

The image carrier requires a rotary drive source, and the transfer drum also requires a rotary drive source. And
In many cases, these rotary drive sources are generally composed of one motor.

[0006]

However, the above-mentioned conventional example has the following drawbacks. In recent years, the performance of color printers has improved and high-quality printing has become possible. Along with this, crimes due to forgery of banknotes have been occurring frequently. It is expected that this crime will increase in the future due to higher image quality. It is necessary to prevent this effectively.

[0007]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems, and has the following structure as one means for solving the above problems. Color conversion means for converting the input multi-valued image signal into a specific color signal, and encoding means for encoding the signal converted by the color conversion means,
Quantization means for quantizing the data encoded by the encoding means, specific image storage means for storing specific image data, and a quantized signal quantized by the quantization means in the specific image storage means. A first specific image discriminating means for discriminating whether or not the stored specific image data signal is close to the stored specific image data signal, and the quantized signal is discriminated to be close to the specific image data signal by the first specific image discriminating means. In this case, an image forming means for forming an image by replacing the input multi-valued image signal with a predetermined invalid data signal is provided.

Further, it is determined whether or not the specific color signal converted by the color conversion means is close to the specific image data signal stored by the specific image storage means.
Image forming means by replacing the color signal judged to be approximated by the second specific image judging means among the converted color signals with predetermined invalid data. It is characterized by doing.

For example, the specific image includes images of bills, securities, stamps, etc., and when the input multi-valued image signal is a monochromatic image signal, the first and second specific image discriminating means are It is characterized by not making a judgment. Further, the specific image data signal output from the specific image storage means is a histogram or a quantized signal of the color of the specific image, and the first and second specific image discriminating means output the color of the input multi-valued image signal. It is characterized by measuring the histogram or the quantized signal and the specific image data output from the specific image storage means.

The input multi-valued image signal is a luminance image signal, and the color conversion means converts the input luminance image signal into a density image signal.

[0011]

With the above construction, when the input image is the specific image data of a banknote or the like, the specific image is discriminated at the time of data compression, and the control is performed so as not to form the image of the specific image. It is possible to prevent the image formation. Further, when it is clear that the input image is not the specific image data of a bill or the like, normal image formation is performed, so that more efficient operation is realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail below with reference to the drawings. <First Embodiment> FIG. 1 shows an example of the arrangement of a color laser beam printer according to this embodiment. In FIG. 1, the paper feeding unit 101
The recording paper P fed from the front end of the recording paper P is gripper 103.
It is nipped by f and held on the outer periphery of the transfer drum 103.

The latent image formed on the image carrier 100 by the optical unit 107 for each color is developed by each color developing device Dy, Dc,
It is developed by Dm and Db, and transferred to the recording paper P on the outer periphery of the transfer drum 103 multiple times to form a multicolor image. After that, the recording paper P is separated from the transfer drum 103 and is placed in the fixing unit 104, where it is fixed, and the paper output tray 115 or the paper output tray 105 is used to output the paper output tray unit 1.
It is discharged to 06.

Here, each color developing device Dy, Dc, Dm, D
b has rotation spindles at both ends thereof, each of which is held by the developing device selecting mechanism 108 so as to be rotatable about the shaft, and each developing device Dy, Dc, Dm, Db has a fixed posture. In the maintained state, the developing device selecting mechanism unit 108 for selecting the developing device.
The selected developing device is rotated about the rotation support shaft 110 so as to be at the developing position.

After the selected developing device is moved to the developing position, the developing device selecting mechanism portion 108 is integrated with the selected developing device and the selection mechanism holding frame 109 is centered on the fulcrum 109b toward the image carrier 100 by the solenoid 109a. Moved and positioned. Next, an outline of the operation of the color laser beam printer having the above configuration will be described.

First, the image carrier 10 is charged by the charger 111.
0 is uniformly charged to a predetermined polarity, and a first latent image of magenta, for example, is formed on the image carrier 100 by exposure with the laser beam light L. Next, in this case, the required developing bias voltage is applied only to the magenta developing unit Dm to develop the magenta latent image, and the first toner image of magenta M is formed on the image carrier 100.

On the other hand, the recording paper P is fed at a predetermined timing, and immediately before the leading end of the recording paper P reaches the above-mentioned transfer start position,
A transfer bias voltage (eg, 1.8 KV) having a polarity opposite to that of the toner (eg, positive polarity) is applied to the transfer drum 103, the first toner image on the image carrier 100 is transferred to the recording paper P, and The recording paper P is electrostatically attracted to the surface of the transfer drum 103.

Thereafter, the image carrier 100 is cleaned by the cleaner 112.
Then, the remaining magenta toner is removed to prepare for the next color latent image formation and development process. Next, the image carrier 1
A second latent image of cyan is formed on the image carrier 00 by the laser beam light L, and then the second latent image on the image carrier 100 is developed by the cyan developing device Dc to form a second cyan toner image. , Is transferred onto the recording paper P in alignment with the position of the first magenta toner image previously transferred onto the recording paper P.
In the transfer of the toner image of the second color, a bias voltage (for example, 2.1 KV) higher than that in the case of the first toner image is applied to the transfer drum 103 immediately before the recording paper P reaches the transfer portion.

Similarly, the third of yellow and black,
The fourth latent images are sequentially formed on the image carrier 100, are sequentially developed by the developing devices Dy and Db, and are aligned with the toner images previously transferred to the recording paper P to form yellow and black images. The third and fourth toner images are sequentially transferred, and thus the four color toner images are formed on the recording paper P in an overlapping state.

In the transfer of the toner images of the third and fourth colors, a bias voltage (for example, 2.5 KV and 3) higher than that of the second toner image is applied to the transfer drum 103 immediately before the recording paper P reaches the transfer portion. .0 KV) is applied. The reason why the transfer bias voltage is increased each time the toner image of each color is transferred is to prevent the transfer efficiency from decreasing. The main cause of the decrease in the transfer efficiency is that when the recording paper P is separated from the image carrier 100 after the transfer, the surface of the recording paper P is charged with a polarity opposite to the transfer bias voltage due to the air discharge, and at the same time, the recording paper P is charged. The surface of the transfer drum 103 carrying P is also slightly charged, and this charged charge is accumulated at each transfer. Therefore, if the transfer bias voltage is constant, the transfer electric field is lowered at each transfer. It is in.

During the fourth black toner transfer,
When the front end of the recording paper P reaches the transfer start position and immediately before and after the transfer start position, an AC voltage of 5.5 KV (hereinafter, effective value, frequency is 500 Hz) was applied during transfer of the fourth toner image. The charging device 11 superimposes a DC bias voltage of 3.0 KV having the same polarity and the same potential as the transfer bias voltage.
1 is applied.

In this way, at the time of transferring the fourth color, the recording paper P
The charger 111 is operated when the tip reaches the transfer start position in order to prevent transfer unevenness. In particular, in the transfer of a full-color image, even if a slight transfer unevenness occurs, it is noticeable as a color difference. Therefore, it is necessary to apply a required bias voltage to the charger 111 to perform the discharge operation as described above. Becomes

After that, when the leading end of the recording paper P on which the four color toner images are superposed and transferred approaches the separation position, the separation claw 113 is formed.
Comes closer to the surface of the transfer drum 103, and the recording paper P is separated from the transfer drum 103. The tip of the separation claw 113 keeps contact with the surface of the transfer drum 103 until the rear end of the recording paper P leaves the transfer drum 103.
After that, it is separated from the transfer drum 103 and returns to the original position.

As described above, the charger 111 operates until the trailing edge of the recording paper P reaches the transfer start position of the final color until the trailing edge of the recording paper P leaves the transfer drum 103. The charge (the opposite polarity to the toner) is removed, and the separation claw 11
The recording paper P can be easily separated by the method of 3, and the air discharge at the time of separation is reduced. When the trailing edge of the recording paper P reaches the transfer end position (the exit of the nip portion formed by the image carrier 100 and the transfer drum 103), the transfer drum 103
The transfer bias voltage applied to is turned off (ground potential).
At the same time, the bias voltage applied to the charger 111 is turned off.

Next, the separated recording paper P is conveyed to the fixing unit 104, where the toner image on the recording paper P is fixed, and the paper is discharged onto the paper discharge tray 115 or via the paper discharge unit 105. Discharged onto 106. Next, the image signal will be described. FIG. 2 is a block diagram showing the outline of the entire embodiment.

The printer 302 is a control signal and an image signal 30 from an external device such as a host computer 301.
7 is received by the printer controller 303 and then output to the printer engine 310. Printer engine 310
Then, of the received control signal and image signal 307,
The control signal 308 is sent to the printer control unit 304 and the image signal 3
09 is input to the image processing unit 305. Then, the semiconductor laser 306 is driven by the processing signal from the image processing unit 305.

Next, FIG. 3 shows a block diagram of the image processing unit 305. The image processing unit 305 first receives an RGB 24-bit image signal from the printer controller 303, and the color processing unit 351 outputs a Y signal at one time, an M signal at another time, a C signal at another time, and a K signal at another time. Convert to bit signal. FIG. 4 shows an operation timing chart of the color processing unit 351 described above. In the figure, A1 is a first color processing operation, A2 is a second color processing operation, A3 is a third color processing operation, and A4 is a fourth color processing operation. The section A1 to A4 is the color processing operation for one page.

Y, M, converted by the color processing unit 351
The C and K image signals are γ-corrected by the γ-correction unit 352.
Converted into a bit signal, and the pulse width modulation unit 353 in the next stage
(Hereinafter referred to as “PWM unit”). PWM section 3
In 53, the 8-bit image signal is supplied to the image clock VCLK.
Latched in the latch 354 in synchronization with the rising edge of. Then, the latched image signal is converted into a corresponding analog voltage by the D / A converter 355. Then, it is input to the analog comparator 356.

On the other hand, the image clock VCLK is converted into a triangular wave by the triangular wave generator 358 and the analog comparator 3
56 is input. In the analog comparator 356,
The two signals input as described above are compared with each other and a PWM signal is output. The output signal is inverted by the inverter 357 to obtain the PWM signal.

FIG. 5 shows an operation timing chart of the PWM section 353 described above. The 8-bit image data input to the PWM unit 353 outputs the widest PWM signal at FF [H] and the narrowest P signal at 00 [H].
The WM signal is output. The main parts of this embodiment will be described below, focusing on the signal flow of this embodiment.

FIG. 6 is a block diagram showing the outline of the signal flow of the entire embodiment. The printer 2 receives image information in a predetermined language from the host computer 1 which is an external device, develops the image in the printer controller 3, and sends the image data 7 to the printer engine 4. The printer engine 4 prints based on the image data 7 to form a full-color image.

This embodiment relates to the printer controller 3 and the printer engine 4, and in the following, in the case of transmitting data for three colors of red (R), green (G) and blue (B) as the image data 7. In addition, the printer engine 4 will be described as a printer having a resolution of 600 dpi (dots / inch). In FIG. 6, the main signals exchanged between the printer controller 3 and the printer engine 4 are image signals 7 (RDATA0 to RD
ATA7, GDATA0 to GDATA7, BDATA0
~ BDATA7) and image transfer clock (VCLK)
, PHOTO image designation signal (PHIMG), line synchronization signal (LSYNC), page synchronization signal (PSYNC)
C).

FIG. 7 shows the printer controller 3 shown in FIG.
It is a detailed block configuration diagram of. The printer controller 3 of this embodiment expands the image data 8 of a predetermined format sent from the host computer 1 into a multi-valued image (photo image or color character) by the image expansion unit 5, and expands the multi-valued image. Are stored in the multi-valued image memory 6. For example, when data of R, G, and B colors are stored in the multi-valued image memory 6 as a multi-valued image, the multi-valued image memory 6 outputs a multi-valued image signal of 8 bits for each color and a PHOTO image designation signal. (PH
IMG) is output. For example, the PHOTO image designation signal (PHIMG) is "L" for a photographic image and "H" for a color character. If the PHOTO image designation signal (PHIMG) is "L", 300 lines are printed by the printer engine 4 in the subsequent stage, and if it is "H", 600 lines are printed. Details of these will be described later.

FIG. 8 is a detailed block diagram of the signal processing unit in the printer engine 4 shown in FIG. The multi-valued image data 7 sent from the printer controller 3 is subjected to image compression / expansion processing by the compression / expansion circuit 8 of the signal processing unit, and magenta (M), cyan (C) by the RF (Reproduction Function) circuit 9. ), Yellow (Y), and black (K) image data are converted into M, C, Y, and K image data.
Are output in this order and written in the line memory 10. Then, the multivalued image data 19 read out from the line memory 10 in synchronization with the rising edge of the image clock (PCLK) of the printer engine is output to the γ correction unit 11.

The γ correction unit 11 is a look-up table (LUT) composed of a RAM and a ROM. The image data 19 is at addresses A0 to A7 and PHIMG is A8.
Then, the color designation signal 24 is input to A9 and A10. γ
FIG. 9 shows an example of the address map of the γ correction table of the correction unit 11. As shown in FIG. 9, the γ correction is different depending on the number of PWM lines and the color of the toner.

The γ-corrected 8-bit multi-valued image signal from the γ-correction unit 11 is converted into a corresponding analog voltage by the D / A conversion unit 15 and input to the negative inputs of the comparators 16 and 17 in the next stage. . Output signals from the triangular wave generators 1 and 2 of 13 and 14 are input to the positive inputs of the comparators 16 and 17, respectively. The triangular wave generation unit 1 of 13 converts 1/2 PCLK obtained by dividing the image clock PCLK into a triangular wave by an integration circuit and outputs the triangular wave, and the triangular wave generation unit 2 of 14
Converts the image clock PCLK into a triangular wave by an integrating circuit and outputs the triangular wave.

The comparator 16 outputs the centrally grown PWM signal 21 for 300 lines, and the comparator 17 outputs the centrally grown PWM signal 22 for 600 lines.
Then, the selector 18 selects one of the two PWM signals by PHIMG and outputs it to a laser driver (not shown). The feature of the specific image formation prevention function in this embodiment is best shown in the compression / expansion circuit 8 shown in FIG. 8, but a detailed description of the compression / expansion circuit 8 will be given later. The operation of the RF circuit 9 shown will be described in detail.

FIG. 10 is a detailed block diagram of the RF circuit 9. In FIG. 10, 24, 25, and 26 are logarithmic conversion LUs.
ROM having T, 27, 28, 29 and 34 are switches controlled by a mode switching signal (MODE), 3
0 is UCR (Under Color Removal) part, 3
1 is a masking unit including a product-sum operation circuit, 32 is a ROM having LUTs such as masking coefficients and UCR coefficients, 33
Is a selector. FIG. 11 shows an example of the address map of the ROM 32.

In the address map of the ROM 32 of FIG. 11, the upper 3 bits of each bank represent a control signal and correspond to A8 to A10 of the ROM 32. If the multi-valued image data 7 of 8 bits for each color of R, G, B output from the printer controller 3 is not the monochrome mode,
Switch 2 by the MODE signal sent first
7, 28, 29 and 34 are connected to the A side, the multi-valued image data 7 is logarithmically converted by the LUT stored in the ROMs 24, 25 and 26, and blue (B) is converted to yellow (Y),
The density of green (G) is converted into magenta (M), and the density of red (R) is converted into cyan (C), and these are input to the UCR unit 30.

Next, [100] is first sent to A8 to A10 of the ROM 32 as a 3-bit control signal, the UCR table of magenta (M) is selected as shown in the address map of FIG. 11, and the UCR unit 30 is selected. Then, the minimum value of the input 8-bit data for each color of Y, M, and C is detected. Then, the value of the detected 8-bit data is stored in the ROM 3
2 to A0 to A7 for addressing, and magenta (M) UCR data corresponding to input data is stored in ROM
The data of 32 is output to the UCR unit 30.

Next, a 3-bit control signal [00
0] is sent to A8 to A10 of the ROM 32 to set a bank, and the address data is sent from the register of the masking unit 31 to A0 to A7 of the ROM 32. The ROM 32 outputs the masking coefficient data of the addressed magenta (M). The masking circuit 31 is set. And UCR
The magenta (M) image data output from the unit 30 is
The sum of products is calculated with the masking coefficient set in the masking unit 31, and the result is output to the selector 33.

Next, the selector 33 is switched by the color designation signal to output the magenta (M) image data to the subsequent stage.
By performing the above operation for one screen, the processing of magenta (M) is completed. Next, the 3-bit control signal [101] is sent to A8 to A10 of the ROM 32, the cyan (C) UCR table is selected as shown in the address map of FIG. 11, and the UCR unit 30 receives the input Y. , M, C each color 8-bit data minimum value is detected.

Then, the value of the detected 8-bit data is R
It sends to A0-A7 of OM32 to specify the address,
Ran the cyan (C) UCR data corresponding to the input data
The data of the OM 32 is output to the UCR unit 30. Next, a 3-bit control signal [000] is sent to A8 to A10 of the ROM 32 to set the bank, and the address data is sent from the register of the masking unit 31 to A0 to A7 of the ROM 32, and the ROM 32 is set to the cyan address specified. The masking coefficient data of (C) is masked by the masking unit 3
Set to 1.

Then, the cyan (C) image data output from the UCR unit 30 is subjected to sum-of-products operation with the masking coefficient set in the masking unit 31 and output to the selector 33. Next, the selector 33 is switched by the color designation signal to output the cyan (C) image data to the subsequent stage. The above operation 1
The processing for cyan (C) is completed by performing the processing for the screen.

Next, a 3-bit control signal [11
[0] is sent to A8 to A10 of the ROM 32, and as shown in the address map of FIG.
The R table is selected, and the UCR unit 30 receives the input Y,
The minimum value of 8-bit data for each of M and C is detected. Then, the detected 8-bit data value is set to A0-A of the ROM 32.
7 to perform addressing, and the yellow (Y) UCR data corresponding to the input data is sent to the DAT of the ROM 32.
Output from A to the UCR unit 30.

Next, a 3-bit control signal [00
[0] is sent to A8 to A10 of the ROM 32 to set the bank, and the address data is sent from the register of the masking unit 31 to A0 to A7 of the ROM 32, and the ROM 32 outputs the masking coefficient data of the addressed yellow (Y). Set in the masking section 31. And UCR part 3
The yellow (Y) image data output from 0 is subjected to a product-sum operation with the masking coefficient set in the masking unit 31 and output to the selector 33. Then, the selector 33 is switched by the color designation signal to output the yellow (Y) image data to the subsequent stage. By performing the above operation for one screen, the yellow (Y) process is completed.

Next, a 3-bit control signal [11
1] is sent to A8 to A10 of the ROM 32, and the black (K) UC is displayed as shown in the address map of FIG.
The R table is selected, and the UCR unit 30 receives the input Y,
The minimum value of 8-bit data for each of M and C is detected. Then, the detected 8-bit data value is set to A0-A of the ROM 32.
7 and addressing is performed, and black (K) UCR data corresponding to the input data is DAT of the ROM 32.
Output from A to the UCR unit 30.

The black (K) image data output from the UCR unit 30 is output to the selector 33.
Next, the selector 33 is switched by the color designation signal to output the black (K) image data to the subsequent stage. The black (K) process is completed by performing the above operation for one screen. By the operation of the above-mentioned four processes described above, the RF circuit 9
The color conversion processing of one screen by is completed.

Further, when the multi-valued image data 7 is in the monochrome mode, the switches 27, 28, 2 are switched by the MODE signal.
9, 34 are connected to the B side, and the multi-valued image data of R, G, B are input to the UCR circuit 30 and the masking section 31 as they are. Next, a 3-bit control signal [000] is sent to A8 to A10 of the ROM 32, a bank is set, and address data is sent from the register of the masking unit 31 to A0 to A7 of the ROM 32, and the ROM 3
The coefficient data of the luminance conversion addressed to No. 2 is set in the masking unit 31.

Then, the image data is converted in brightness by the masking section 31 and output from the selector 33 as in the case of not in the monochrome mode. Next, control signal [010]
Is sent to A8 to A10 of the ROM 32, the bank is set to the monochrome mode, the data output from the selector 33 is sent to A0 to A7 of the ROM 32 for addressing, and the logarithmic conversion data corresponding to the input data is stored in the ROM 32.
Output from DATA.

By this operation, a monochrome mode image is output. Next, the operation of the compression / expansion circuit 8 during compression will be described in detail. FIG. 12 is a detailed block diagram of the compression section of the compression / expansion circuit 8 shown in FIG. In FIG. 12, reference numeral 201 is a conversion circuit that has a built-in LUT that converts the input RGB signals into YUV signals and performs thinning, 202 is a page memory that stores each signal, and 203 is a DCT that encodes the input signals. A (discrete cosine transform) circuit and a quantizer 204 performs quantization. Further, 205 is a quantizer 204
Quantization table 206 referred to by the reference numeral 206 is invalid data for accumulating invalid data for converting this data to invalid data when the input data is specific data, for example, data for which it is necessary to prevent forgery. 207 is a memory, 207 is a comparator that compares input data with specific data that needs to prevent forgery of banknotes, and 208 is a specific data memory that stores specific data that needs to prevent forgery of banknotes. is there.

The present embodiment is characterized in that two forgery determinations are carried out: a forgery determination at the time of converting an RGB input signal into a YUV signal and a forgery determination after quantization. R, G, B output from the printer controller 3 described above
The 8-bit multi-valued image data 7 of each color is converted into a YUV signal by the LUT stored in the conversion circuit 201,
Using the characteristics of the human eye, the U signal and the V signal are thinned out in half in the horizontal and vertical directions, and are stored in the page memory 202 for each color signal.

The accumulated image data is the DCT circuit 203.
Is input to, linearly transforms a highly correlated signal into a decorrelated signal as much as possible, and optimizes the amount of information assigned to each coefficient by utilizing the fact that power is concentrated on a specific transform coefficient, and also the overall encoded information amount. In order to delete, the 8 × 8 pixel is converted into a DCT coefficient in 1 unit. The DCT coded signal is input to the quantizer 204 and quantized. Quantizer 204
Then, 8 × 8 quantization table 20 for each YUV signal
5 is assigned, the YUV signal is divided by the value in the quantization table to reduce the effective bits, and encoding is performed.

Next, the forgery judgment when the RGB input signal is converted into the YUV signal will be described. Page memory 20
The YUV signals stored in 2 are read out in the order of YUV points,
At the same time as being input to the comparator 207, a histogram of data required to prevent counterfeiting of banknotes or the like is input to the comparator 207 from the specific data memory 208.

The specific data memory 208 has a histogram range of data for which it is necessary to prevent forgery in advance, such as banknotes and securities, for example, Y = 50 to 8
1 [H], U = 30 to 3F [H], V = 80 to 8F
A YUV histogram such as [H] and data when the YUV histogram is quantized are stored. In the comparator 207, the input YUV signal and the specific data memory 208
Pixels that match the histogram of are counted.

In the comparator 207, when the count number exceeds a predetermined number, it is determined that the input image data is data for forgery (data for which the forgery should be prevented), and the invalid data memory 206 stores it. Send a control signal. Invalid data in which all RGB data is 00 [H] or FF [H] is accumulated in the invalid data memory 206, and when the control signal is received, the invalid data accumulated in the invalid data memory 206 is transferred to the conversion circuit 201. Output.

As described above, when it is determined that the input image data is the data for which it is necessary to prevent the forgery, the actually output data is the white image or the black image. Next, the forgery determination after being quantized by the quantizer 204 will be described. The quantized signal of 8 × 8 pixels accumulated in the quantizer 204 is read out for each 8 × 8 pixel and input to the comparator 207, and at the same time, the specific data memory 208
From the above, a quantized signal of specific data for which it is necessary to prevent forgery of a bill or the like is input to the comparator 207, and the comparator 207 counts the pixels that match these quantized signals.

When the count number exceeds a predetermined number in the comparator 207, it is determined that the input image data is specific data that needs to prevent forgery, and a control signal is sent to the invalid data memory 206. Similarly thereafter, the data actually output becomes a white image or a black image. As described above, according to the present embodiment, the determination as to whether or not the input image is the specific data that needs to prevent counterfeiting of the bill reading data and the like is referred to as color conversion and quantization during data compression. As described above, it is possible to make a more reliable forgery determination because it is performed twice.

<Second Embodiment> A second embodiment according to the present invention will be described below. In the first embodiment, the case where the input image signal is a full-color image is shown, but in this embodiment, in addition to the apparatus configuration of the first embodiment, for example, the printer uses a full-color print mode function of four-color toner overlapping and a single-color toner. In the case of having a mono-color printing (including black characters) mode function, when the mono-color printing mode is selected, it is determined that it is not necessary to operate the forgery prevention function for banknotes, etc. Specific data memory 2 explained
08 is added so that the comparison with 08 is not performed.

As described above, according to the second embodiment, forgery determination is performed when it is clear that the input image is not the specific data for which forgery of banknotes or the like is required, such as in monocolor printing. Since it is not performed, more efficient operation can be realized. In addition, in 1st Example and 2nd Example, although banknote data was mainly assumed and demonstrated as specific data which need to prevent forgery, the specific data used as object in this invention are limited to a banknote, of course. It is also valid for other securities data, including stamps, etc. That is, the specific data memory 208 stores a color histogram of image data of securities such as banknotes and stamps, and quantized data of the histograms.

Although the laser beam printer has been mainly described as the first and second embodiments, the present invention is not limited to this, and may be, for example, an ink jet printer, a thermal transfer printer, a bubble jet printer or the like. Can also be applied in the same manner, and since the forgery determination is performed by comparing with the data memory of a bill or the like at the time of data compression, the printer engine unit of the first embodiment device and the second embodiment device is used for other devices such as a facsimile. Even if it is done, it is possible to make a forgery decision.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0063]

As described above, according to the present invention, when the input image is the specific image data of a bill or the like, the specific image determination is performed at the time of data compression, and the control is performed so that the image formation of the specific image is not performed. Therefore, it is possible to more reliably prevent the image formation of the specific image.

Further, when it is clear that the input image is not the specific image data of a bill or the like, normal image formation is performed, so that more efficient operation is realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a device configuration of a first embodiment according to the present invention.

FIG. 2 is a block diagram showing an outline of the present embodiment.

FIG. 3 is a block diagram showing an image processing unit of the present embodiment.

FIG. 4 is a time chart of signals in the color processing unit of this embodiment.

FIG. 5 is a time chart of signals in the PWM unit of the present embodiment.

FIG. 6 is a block diagram showing an outline of signal processing of this embodiment.

FIG. 7 is a block diagram illustrating a configuration of a printer controller according to the present exemplary embodiment.

FIG. 8 is a block diagram showing a signal processing unit of the printer engine of this embodiment.

FIG. 9 is an address map of a γ correction table according to this embodiment.

FIG. 10 is a block diagram showing a configuration of an RF circuit of this embodiment.

FIG. 11 is an ROM address map in the RF circuit of the present embodiment.

FIG. 12 is a block diagram showing a configuration of a compression / expansion circuit of the present embodiment.

[Explanation of symbols]

 100 image carrier 101 paper feed unit 103 transfer drum 103f gripper 104 fixing unit 105 paper ejection unit 106 paper ejection tray unit 107 optical unit 108 developing device selection mechanism unit 109 selection mechanism holding frame 109a solenoid 110 rotation spindle 111 charger 112 cleaner 113 Separation Claw 115 Paper Discharge Tray Dy, Dc, Dm, Db Developer 201 Conversion Circuit 202 Page Memory 203 DCT Circuit 204 Quantizer 205 Quantization Table 206 Invalid Data Memory 207 Comparator 208 Specific Data Memory

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G06T 1/00 9/00 9287-5L G06F 15/62 410 Z 15/64 400 J 8420-5L 15 / 66 330 A 7459-5L 15/70 310 9061-5L 455 A

Claims (8)

[Claims] 1. A color conversion means for converting an input multi-valued image signal into a specific color signal, an encoding means for encoding the signal converted by the color conversion means, and an encoding means for encoding by the encoding means. Quantization means for quantizing data, specific image storage means for storing specific image data, and a quantized signal quantized by the quantization means approximates to a specific image data signal stored in the specific image storage means. A first specific image discriminating means for discriminating whether or not the input multi-valued image signal is detected when the quantized signal is discriminated by the first specific image discriminating means to be close to the specific image data signal. And an image forming unit for forming an image by replacing the above with a predetermined invalid data signal. 2. A second specific image discriminating means for discriminating whether or not the specific color signal converted by the color converting means is close to the specific image data signal stored by the specific image storage means. However, the image forming unit also forms an image by replacing the color signal determined to be approximated by the second specific image determining unit in the converted color signal with predetermined invalid data. The image forming apparatus according to item 1. 3. The specific image includes an image of banknotes, securities, stamps, or the like.
The image forming apparatus described. 4. The image forming apparatus according to claim 2, wherein when the input multi-valued image signal is a monochromatic image signal, the first and second specific image discriminating means does not make the determination. . 5. The image forming apparatus according to claim 2, wherein the specific image data signal output from the specific image storage means is a color histogram or a quantized signal of the specific image. 6. The first and second specific image discriminating means measure the color histogram or the quantized signal of the input multi-valued image signal and the specific image data output from the specific image storing means. The image forming apparatus according to claim 5, wherein 7. The image forming apparatus according to claim 2, wherein the input multi-valued image signal is a luminance image signal. 8. The image forming apparatus according to claim 2, wherein the color conversion unit converts an input luminance image signal into a density image signal.