JP3176401B2 - Background image removal device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a background image removing apparatus in an image forming apparatus such as a copying machine.

[0002]

2. Description of the Related Art In general, in an image forming apparatus such as a copying machine, a background area of a document image is not required as an output image. ing. That is, for example, in a blue-printed copy original, the density of the background area is high, and in a thin original, the illuminating light is transmitted and the transmission area becomes a background area. Therefore, this background area must be removed. Further, in a document having a low contrast or a document corrected and edited with a thin pencil or the like, it is necessary to prevent the document image from being unnecessarily removed.

Conventionally, this type of background image removing apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-20964. For example, as shown in FIG. 18A, this apparatus detects the background density of the document D by using the image 101 having a width of 50 mm at the center of the reading area in the main scanning direction when reading the image of the document D, for example. This detection signal is processed and applied to the input terminal of the reference level of the A / D converter, so that the A / D converter does not quantize the background area.

As a method of detecting the background of the leading edge region 105 of the document D, for example, as shown in FIG. 19, a fixed value is converted to an A / D converter while scanning and reading a region 105 of 3 mm from the leading edge 105a. Is applied to the input terminal of the reference level. Note that this tip 105a
Can be changed via the operation unit, and by changing the time constant and amplification factor of the background detection circuit via the signal of the image reading circuit and the operation unit, the type of the document image can be changed. The background can be removed.

[0005]

However, FIG.
In the background image removing apparatus as shown in FIG. 18A, for example, an image density having a width of 50 mm at the center of the reading area in the main scanning direction is used. Therefore, as shown in FIG. There is a problem in that when there is an image, for example, a halftone image or the like different from the surroundings, an image having an appropriate density cannot be output. As shown in FIG. 18B, when the black solid image 102 is located at the center of the document, the right and left areas A,
The image of B becomes lighter, and when a halftone image exists, this image becomes lighter.

In a digital copier, a document image can be edited to copy only a specific area or not to be edited. However, as shown in FIG. When it is located outside the background detection area 101 or when a part of the specific area 104 is located outside the background detection area 101, there is a problem that an image having an appropriate density cannot be output.

As shown in FIG. 19, in the background image removing apparatus for detecting the background of the leading edge region 105 of a document, if a sharp change in density exists in the leading edge region 105 of the document, the operator can change the density from the leading edge 105a. Since the distance L to the position 105b must be measured and set, there is a problem that work efficiency is reduced. For example, when the rear part of the tip region 105 has a higher density than the front part, this distance L
Is fixed, the density of the document image 105c from the density change position 105b becomes a thin image signal when the distance L is shorter than the fixed value, and becomes an image signal including the background when the distance L is longer than the fixed value.

The present invention has been made in consideration of the above-described conventional problems, and has as its object to provide a background image removing apparatus capable of appropriately removing a background image of a document to obtain an image having an appropriate density.

[0009]

In order to achieve the above object, a first means is an image reading means for reading an original image and converting the same into an analog signal, and the analog signal read by the image reading means is used as a reference level. A quantizing means for removing the background of the original image by quantizing, and extracting a background area of the original image from the analog signal read by the image reading means to detect a background level, and performing the quantization as a reference level. Background detecting means for applying to the means, and the background detecting means such that the background detecting means conveys the document in the forward direction so as to detect the background level of the leading end area of the document, and the image reading means reads from the leading end of the document. And a document conveying means for conveying the document in the reverse direction after the detection by .

[0010] The second means is characterized by comprising a background level holding means for holding the background level detected by the background detection means of the first means and applying the background level to the quantization means as a reference level.

The third means includes a time constant circuit for holding the background level by charging / discharging the background level holding means of the second means, and the background level detected by the background detection means.
Is changed from low concentration to high concentration,
When the time constant changes from small, high to small, the time constant
Can be greatly changed.

[0012]

[0013]

[0014]

[0015]

The fourth means is to read a document image and analyze it.
Image reading means for converting to a log signal;
Analog signal read by the
Removes background of original image by quantization
Read by the quantization means and the image reading means
Extract the background area of the original image from the analog signal
Background detection means for detecting a level;
The detected background level is held by the time constant circuit,
Background level applied to the quantization means as a reference level
Holding means and a background density detection for detecting the background density of the original image.
Output means, and the background level detected by the background detection means.
If the level changes from low to high,
The time constant of the time constant circuit of the holding means is small, from high concentration to small concentration
If the value changes to the background level, change the time constant to a large value.
And changing means.

[0017]

According to the first means, the original is transported in the forward direction so that the background detecting means reads the leading end area of the original, and the original is transported in the reverse direction so that the image reading means reads from the leading end of the original. After the document is conveyed in the forward direction, the background of the leading edge of the document can be detected in advance, and a black solid image exists in the center of the document even if the position where the background density rapidly changes in the leading edge region of the document varies depending on the document. Even if there is a halftone image different from the surroundings, for example, the background image of the document can be properly removed to obtain an image with an appropriate density.

In the second means, since the background level detected by the background detection means is retained, once the background density can be detected, a black solid exists in the center of the document or a halftone image different from the surroundings, for example. (Example Fig. 1
8 (d)) The background image of the document can be properly removed to obtain an image with an appropriate density.

In the third means, the background detection means
When the detected background level changes from low to high
If the time constant of the time constant circuit is small,
If it changes, the background level retention level is changed so that the time constant becomes large, so even in the case of documents with different background density distributions, the background image of the document is properly removed to obtain an image with the proper density. Obtainable.

[0020]

[0021]

[0022]

[0023]

In the fourth means, the detection is performed by the background detecting means.
If the background level changes from low to high
The time constant of the time constant circuit of the background level holding means is small and high concentration
If the concentration changes from low to high, change the time constant to a large value.
A background level changing unit is provided, and the time constant of the background level holding unit is changed in accordance with the background density. Therefore, even in the case of a document having a different background density distribution, the background image of the document is appropriately removed to obtain the proper density. Images can be obtained.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a background level detection circuit of an embodiment of a background image removing apparatus according to the present invention. FIG. 2 is a side view showing a main part of an image scanner using the background level detection circuit of FIG. Is a perspective view showing the image scanner of FIG. 2, FIG. 4 is a side view showing a book carrier of the image scanner of FIGS. 2 and 3, FIG. 5 is a plan view showing the book carrier of FIG. 4, and FIG. 5 is a side view showing a main part of the book carrier, FIG. 7 is a block diagram showing a circuit for processing an image signal read by the image scanner of FIGS. 2 to 6, and FIG. 8 is a detail of the white level adjustment circuit of FIG. FIG. 9 is a circuit diagram showing a simple configuration, and FIG. 9 is a timing chart for explaining the operation when detecting the background density at the leading edge of the document.
Numeral 0 is a timing chart for explaining the operation in the case where the reading of the original image and the detection of the background density are performed simultaneously.

In FIG. 1, the voltage of the image signal Vin of the original is divided into about 1/2 by the resistors R1 and R2 and is inputted to the + input terminal of the differential amplifier A1. The output terminal of the amplifier A1 is connected to the-input terminal, so that the output signal of the amplifier A1 is output by the capacitor C1 and the resistors R1 and R2.
Attenuation of a component having a relatively high frequency, that is, a density change component having a small width such as a character or a line of a document image is larger than a signal component indicating a density change such as a background.

The output terminal of amplifier A1 also has a series resistor R
3, connected to the + input terminal of the amplifier A2 via R4,
The connection point between the series resistors R3 and R4 is the analog switch AS.
1 can be grounded. Analog switch AS1
Is a logical product signal (AND) of an AEON signal indicating whether the background density is automatically detected (high level) or a fixed level of the background density (low level) and a PEAK signal indicating the detection width of the background density. It is turned on and off by the gate G1).

The output terminal of the amplifier A2 is connected to a diode D1.
And the cathode of the diode D1 is
The resistor R9 and the analog switch AS2, the resistor R10 and the analog switch A
It is grounded through a series circuit of S3, and is connected to the negative input terminal of an amplifier A2 through a resistor R5. The amplifier A2 applies a forward voltage to the diode D1 when the voltage at the connection point between the resistor R3, the resistor R4 and the analog switch AS1 is higher than the applied voltage for charging the capacitor C3.

Therefore, when the output voltage of the amplifier A2 is higher than the charging voltage of the capacitor C3, the output signal of the amplifier A2 first flows to the capacitor C3 via the diode D1, and the charging voltage of the capacitor C3 rises. Then
Since the output signal of the amplifier A2 is fed back to the negative input terminal via the resistor R5, when the charging voltage of the capacitor C3 and the voltage at the connection point of the resistor R3, the resistor R4 and the analog switch AS1 match, the charging voltage of the capacitor C3 is changed. Stop ascent. Therefore, these circuits provide the image signal V
It constitutes a peak level detection circuit of in.

When the voltage at the + input terminal of the amplifier A2 is lower than the charging voltage of the capacitor C3, a reverse bias is applied to the diode D1, so that the charging voltage of the capacitor C3 follows the output voltage of the amplifier A2. do not do. That is, the output voltage of the peak level detection circuit follows the input level instantaneously when the input level shows an increase from before. If the input level decreases,
As described later, a control signal S from the main control unit 100
The analog switches AS2 and AS are respectively operated by S2 and S3.
3 turns on and off, and the operation differs depending on the state of the analog switches AS2 and AS3.

The analog switches AS2 and AS3 are turned on and off by signals S2 and S3 from the main control unit 100, and determine the discharge time constant of the electric charge charged in the capacitor C3. The resistance value of the resistor R10 is larger than that of the resistor R9,
The voltage drops more gently when the analog switch AS3 is turned on than when the analog switch AS2 is turned on. When the analog switches AS2 and AS3 are both off, the charged voltage of the capacitor C3 is held. Note that the signal VCOM is input to the main control unit 100, and the main control unit 100 can determine H and L of the signals S2 and S3 based on the value of the signal VCOM.

The cathode of the diode D1 is connected to a resistor R
6 is connected to the + input terminal of the amplifier A3, and the output terminal of the amplifier A3 is connected to the-input terminal via the connection point of the voltage dividing resistors R7 and R8, and the automatic mode input of the analog switch AS4. Connected to terminal. The other input terminal of the analog switch AS4 has a variable resistor V
A variable voltage is applied via R1, and a ground peak voltage VPK for removing the ground is output from the output terminal.
The variable voltage can be set manually, but when the AEON signal is at a low level, it is output as a fixed value VPK via the analog switch AS4.

The output terminal of the amplifier A3 is also connected to the + input terminal of the differential amplifier COM1 via a resistor R13, and the connection point of the voltage dividing resistors R11 and R12 of the variable resistor VR2 is connected to the-input terminal of the amplifier COM1. Voltage Vs is applied via
The comparison voltage VCOM is output from the output terminal of the differential amplifier COM1. The voltage Vs corresponds to the maximum density of the background area in a normal document. When the background peak voltage VPK does not exceed the voltage Vs, the density of the background area is particularly high.
That is, when the comparison voltage VCOM is at the low level, it is determined that the background density has not been detected yet or the density of the background area is extraordinarily high, and is used in a third mode described later.

Next, an image scanner using the background image removing apparatus of this embodiment will be described with reference to FIGS. In this image scanner, for example, the reading unit is fixed, and the sub-scan is performed by moving the document. As shown in FIGS. 2 and 3, the sheet-shaped document is placed on a document table 5, conveyed in the direction of arrow A, passes over a contact glass 6 serving as a reading surface, and is placed on a discharge tray 14. Is discharged to

Upstream of the contact glass 6, transport rollers 2a and 2b for transporting the original are disposed, and downstream, a transport roller 2c is disposed. Upstream transport rollers 2a, 2b
Can be selectively rotated by a motor M1 (not shown) in a forward direction and a reverse direction, which is the direction of document transport, and the downstream transport roller 2c is driven by a motor M2 (not shown). It can rotate only in the forward direction. When a sheet-shaped document is to be transported, the transport rollers 2a and 2b located upstream until the leading edge of the document passes, for example, about 50 mm from the reading surface.
Then, the sheet is conveyed by the driven rollers 4a and 4b on the side of the upper cover 3, and thereafter, the conveying rollers 2a and 2b are reversed to be retracted in the opposite direction from the position of the light reflection type document detection sensor 45. The insertion of a document is detected by a document insertion detection sensor 13 arranged on the document table 5.

The upper cover 3 of the contact glass 6 also serves as a pressure plate, and has one end supported by an arm 8 so as to be rotatable around a support shaft 9, that is, openable and closable in the vertical direction. Gas springs 10 a and 10 b are attached between the other end of the upper cover 3 and the housing 1.
Oa and 10b are urged to lift the upper cover 3 with respect to the housing 1. When the upper cover 3 is pushed down against the urging force of the gas springs 10a and 10b and reaches a predetermined position on the contact glass 6 and is positioned, the engaging claws 30 of the upper cover 3 are engaged. , And the upper cover 3 is fixed on the contact glass 6 as shown by a dashed line in FIG.

The engaging member 31 has a solenoid S to be described later.
When the OL is attached and the coil of the solenoid SOL is energized, the engagement between the engagement claw 30 and the engagement member 31 is released,
The upper cover 3 is pushed up by the gas springs 10a and 10b. When reading a sheet-shaped document, the upper cover 3 is fixed as shown by a dashed line in FIG. 2, and when reading a book document, the upper cover 3 is pushed up as shown by the solid line in FIG. 2 and FIG. Used. In addition,
A handle 3 is provided on the upper cover 3 to assist the push-up operation.
2 are provided.

Below the contact glass 6, fluorescent lamps 7a and 7b for illuminating the original, an imaging lens 17 and an image sensor 18 are arranged in the main scanning direction (in FIG. 2, orthogonal to the drawing).
The image sensor 18 is a one-dimensional CCD image sensor in which, for example, 7,500 (effective) light receiving elements are arranged in a line in the main scanning direction.
Accordingly, the original image on the contact glass 6 is illuminated by the fluorescent lamps 7a and 7b, the reflected image is formed on the light receiving surface of the image sensor 18 by the lens 17, and a serial image signal is output from the image sensor 18.

Here, a reference density pattern 16 is formed on the upper cover 3 so as to be elongated in the main scanning direction so as to face the contact glass 6. The reference density pattern 16 is white and has a uniform reflectance over the entire surface, and is read by the image sensor 18 at a predetermined timing to perform shading correction as described later.

Next, the book carrier 50 of the image scanner will be described with reference to FIGS. The book carrier 50 is used when reading an original 90 having a thickness that cannot be transported by the transport mechanism, such as a book, and has a carrier sheet 51, a pressure plate 52, and a hinge 53. The original 90 is placed on the carrier sheet 51 such that the reading surface faces downward. The pressure plate 52 is supported at one end so as to be rotatable around the hinge 53 (direction C in the drawing) and to be movable up and down (direction B in the drawing), and the other end is open. That is, the platen 52 is used to hold various types of originals 90.
Is configured to be able to be pressed from above.

The width of the carrier sheet 51 in the main scanning direction is
Both ends protrude so that the book carrier 50 can be conveyed so as to be larger than each width of the document 90 and the pressure plate 52. When reading the original 90 using such a book carrier 50, the upper cover 3 is attached to the book carrier 50.
And is retracted from the contact glass 6 so as not to hinder the movement of the contact glass. For this purpose, as shown in FIGS. 5 and 6, the side rollers 15a, 15b, 1
5c, 15d, 15e and 15f are attached, and the book carrier 5 is held in a state where the carrier sheet 51 is sandwiched between the side rollers 15a and 15d and the transport rollers 2a and 2b.
0 is conveyed. In this case, similarly, the insertion of the book carrier 50 is detected by the document insertion detection sensor 13, and the leading end is detected by the light reflection type document detection sensor 45.

Since a relatively low level signal corresponding to the density of the read image is obtained from the output signal of the image sensor 18, the signal is first amplified by, for example, about 10 times by the amplifier 61 as shown in FIG. . Further, since a scanning clock component of the image sensor 18 and the like are superimposed on this image signal as noise, the noise component is removed by the sampling circuit 62 and then the variable amplifier 23
After being amplified by 1, it is converted into a digital signal by the A / D converter 232. The peak hold circuit 63
The amplification factor of the variable amplifier 231 is automatically adjusted based on the signal converted by the / D converter 232 so that the white level of the image signal becomes constant.

Here, the detailed configuration of the white level adjustment circuit will be described with reference to FIG. 8. The signal VIDEO amplified by the variable amplifier 231 is input to the analog input terminal Vin of the A / D converter 232. , A / D converter 232 is output to peak hold circuit 63 via latch circuit 233. The peak hold circuit 63 includes data selectors 234 and 236, a comparator 235, a latch circuit 237, and the like.
2 (latch circuit 233) is latched by the latch circuit 237 via the data selector 234.
The comparator 235 compares the value latched by the latch circuit 237 with the current value, and does not update the latch circuit 237 when the current value is small, and on the other hand, when the current value is large, Is updated so that is latched.

Here, usually, a value equivalent to the peak value of the image signal appears by the main scanning of several lines, and the peak value is latched by the latch circuit 237 by the main scanning of several lines. This peak value is applied to the control terminal of the variable amplifier 231 via the data selector 236, and the input level of the A / D converter 232 at the time when the peak value appears becomes a predetermined full scale level. The amplification factor is adjusted. Actually, the input signal level of the A / D converter 232 is 3.8 to 4.
It is adjusted to be in the range of 0V.

The A / D converter 232 has a terminal VR + to which a quantization reference voltage is applied, and this reference voltage is set as a full scale level of the A / D converter 232. In this embodiment, the level of the image signal VIDEO increases as the reflectance of the original image increases,
In a normal document, the level of the background of the image, that is, the background area is the maximum. Therefore, the background level detection circuit 67
Generates the background level VPK based on the image signal amplified by the variable amplifier 231 and applies the background level VPK to the terminal VR + to reduce the saturation level of the A / D converter 232, as described in FIG. Set.

Returning to FIG. 7, the signal converted by the A / D converter 232 is also stored in a ROM (read only memory) 6.
4 and an address of a RAM (random access memory) 65, and the ROM 64 and the RAM 65 operate as a shading correction circuit for correcting variations in sensitivity of the image sensor 18 in the main scanning direction and variations in input light amount (illumination). Specifically, when the image sensor 18 reads the reference density pattern 16 described with reference to FIG. 2 and the like, image data for one line in the main scanning direction is stored in the RAM 65 as shading correction data, and then the read image is read. The signal density level is corrected based on the density variation of the shading correction data.

The ROM 64 previously stores input image data and data indicating a combination of shading correction data and corrected data as a conversion table, and converts the data corrected by the RAM 65 and the A / D converter 232. The corrected data is read by simultaneously inputting the input image data into the ROM 64 as an address. The timing signal generation circuit 66 includes the image sensor 18, the sampling circuit 62, and the variable amplifier 23.
1, RAM 65, background level detection circuit 67, address counter and logic circuit 74, main control unit 100
And other various timing signals.

The main control unit 100 is constituted by a microcomputer, and controls the entire background level detection circuit 67 shown in FIG. 1 and the whole image scanner shown in FIGS. That is, the main control unit 100 reads the key input from the operation board 300, controls the display, and drives the motors M1, M2 of the transport rollers 2a to 2c for scanning drive.
On / off control of the fluorescent lamps 7a and 7b for exposure via a solenoid, FL (fluorescent lamp) ballast 400, reading of detection signals from the document insertion detection sensor 13 and the document detection sensor 45, operation of the background level detection circuit 67 It sets conditions, controls the timing signal generation circuit 66, and controls the address counter, the logic circuit 74, and the like.

Address counter and logic circuit 74
Is used when moving an image of a document or reading only a designated area. This designated area can be designated by coordinates on the document via the operation board 300. The X coordinate of the specified area is
The main control unit 100 controls the address (0
７４7499), and the Y coordinate is processed by the number of main scans. That is, the main control unit 100 applies the start address and end address of the designated area in the main scanning direction and the start and end points of the sub-scan, that is, the number of main scans from the leading edge of the document to the address counter and the logic circuit 74. .

The selector 70 selects shading-corrected data from the ROM 64 in the designated area according to a selection signal from the address counter and logic circuit 74, and selects a white level, that is, GND, outside the designated area.
Select a level. The latter-stage selector 71 and RAM 72,
Reference numeral 73 is used when the original image is moved right and left.
For this purpose, the selector 71 alternately outputs image data to the RAMs 72 and 73 for each main scan in accordance with a selection signal from the address counter and the logic circuit 74.
The read timing and the write timing of the RAMs 72 and 73 are alternately controlled by read / write signals from an address counter and a logic circuit 74.

In the RAMs 72 and 73, the write start address and the read start address are changed under the control of the address counter and the logic circuit 74. When the write start address (usually "0") is smaller than the read start address, the image is not read. The image is shifted left and the image is shifted right and read when the write start address is larger than the read start address (usually “0”).

Next, the operation of the first mode for detecting the background density at the leading edge of the document will be described with reference to FIG. This first
Mode, the analog switches AS2, A2 shown in FIG.
S3 is both controlled to be off. First, when the insertion of a document is detected by the document insertion detection sensor 13, the exposure lamps (fluorescent lamps) 7a and 7b are turned on, and the motor M1 is rotated in the forward direction so that the documents are sequentially moved by the transport rollers 2a and 2b. Transport in the direction. Next, when the document detection sensor 45 detects the leading edge of the document, the AEON signal is at a high level for a distance of 50 mm from a position where the leading edge of the document has passed the reading surface by about 3 mm, and the PEAK signal has a detection width of 60 m.
It becomes high level in the range of m. The PEAK signal is not continuously at a high level, but is at a high level only at a portion corresponding to a background density detection width in a part of the width of the document (main scanning direction) as shown in FIG. ing. FIG.
Since the PEAK signal has a shorter cycle than other signals, it cannot be displayed on the same time axis, and is therefore displayed as a continuous high level.

Therefore, the analog switch AS1 is turned off in a rectangular area of 50 mm × 60 mm of the original, and the background density of this rectangular area is determined by the background level detection circuit 6 shown in FIG.
7, the background level VPK is detected, and the saturation level is set by applying the background level VPK to the terminal VR + of the A / D converter 232. In addition, about 3m from the leading edge of the original
The reason why the background density of about m is not detected is that the diazo copy original often shifts from the leading end of the photosensitive paper to the first original during diazo copy, which is different from the actual background.

When the background density is detected, the motor M1 is rotated in the reverse direction to transport the document in the reverse direction by the transport rollers 2a and 2b, and the document detection sensor 45 detects the leading end of the document (in the reverse direction). Is detected, the motor M1 is rotated in the forward direction again to transport the document in the forward direction by the transport rollers 2a and 2b. When the document detection sensor 45 detects the leading edge of the document, the motor M2 is turned on. Rotate forward.
The leading end of the original is read from the first position on the reading surface, the original insertion detecting sensor 13 and the original detecting sensor 45 sequentially detect the rear end of the original, and after a while, the exposure lamps (fluorescent lamps) 7a and 7b are turned on. The light goes off, and the motors M1 and M2 stop.

Therefore, according to the above-described embodiment, the saturation level of the A / D converter 232 is set by detecting the density of the background area at the leading end of the original by transporting the original in the forward direction, After the document is conveyed in the reverse direction, the document is conveyed in the forward direction and the document image is read. Therefore, as shown in FIG. 18E, a black solid image is placed at the front center of the document (in this case, the sub-scanning direction is 60 mm or less). ) Exists, or
Even when there is a halftone image or the like different from the surroundings, an image with an appropriate density can be output. Further, since the background density within about 3 mm from the leading edge of the document is not detected, the background image of the document is properly removed even when there is a sharp density change at the leading edge of the document as shown in FIG. Thus, an image having an appropriate density can be obtained.

Next, the operation of the second mode for simultaneously reading the original image and detecting the background density will be described with reference to FIG. The waveform of the PEAK signal is similar to that of FIG. 9B. In this second mode, FIG.
Is controlled to be off, and the analog switch AS3 is controlled to be on. First, when the insertion of a document is detected by the document insertion detection sensor 13, the exposure lamps (fluorescent lamps) 7a and 7b are turned on, and the motor M1 is rotated in the forward direction so that the documents are sequentially moved by the transport rollers 2a and 2b. Transport in the direction. Next, when the document detection sensor 45 detects the leading edge of the document, the AEON signal is continuously at the high level from the position where the leading edge of the document has passed the reading surface by about 3 mm, and the PEAK signal is within the detection width of 60 mm. High level. Next, the motor M2 is rotated in the forward direction to continuously transport the original.

Accordingly, the analog switch AS1 is continuously turned off in the sub-scanning direction within the range of the original detection width of 60 mm, and the background density is determined by the background level detection circuit 67 shown in FIG.
The background level VPK is detected by the
The saturation level is set by applying the voltage to the terminal VR + of the / D converter 232.

Next, a third mode in which the operation is determined according to the value of the comparison voltage VCOM shown in FIG. 1 will be described. FIG.
Is turned off and the analog switch AS3 is turned on. If the voltage VCOM continues to be at the low level even when the original is scanned in the sub-scanning direction by 60 mm, it is determined that the background density has not been detected yet or the background area density is extraordinarily high. Is P
The detection width of the EAK signal is expanded from 60 mm to 100 mm. The comparison voltage VCO detected with the detection width of 100 mm
When M goes high, the analog switch AS3 is also turned off and the value of the background level VPK is held. As shown in FIG. 9, after the document is conveyed in the reverse direction, the document is conveyed in the forward direction to read the document image. On the other hand, when the comparison voltage VCOM is continuously at the low level, as in the second mode, The reading of the original image and the detection of the background density are performed simultaneously. That is, in the latter case, the original is not transported in the reverse direction,
The analog switch AS3 remains on, and AEO
The N signal and the PEAK signal are turned on at the timing indicated by the broken line in FIG.

Next, a second embodiment will be described with reference to FIGS. FIG. 11 is an explanatory diagram showing a document size detection sensor according to the second embodiment, FIG. 12 is a timing chart for explaining the operation of the second embodiment, and FIG. 13 is a case where the editing area of the document image is not specified FIG. 14 is a timing chart showing main signals when an editing area of a document image is designated.

Next, the configuration of the original size detecting sensor will be described with reference to FIG. 11. The original table 5 shown in FIGS. 14a to 14d are sequentially arranged in the sub-scanning direction. In the example shown in FIG.
When the document size detection sensors 14a to 14c are on and the document size detection sensor 14d is off, the document is determined to be an A2 portrait document or an A3 landscape document.
Reference numeral 15d indicates the side rollers shown in FIGS.

Next, the operation of the second embodiment will be described with reference to FIGS. First, in FIG. 12, when the insertion of a document is detected by the document insertion detecting sensor 13, the exposure lamps (fluorescent lamps) 7a and 7b are turned on, and the motor M1 is rotated in the forward direction to feed the rollers 2a and 2b. Conveys the original in the forward direction. Next, after the document size detection sensors 14a to 14d detect the size of the document, the PEAK signal indicating the background detection width output corresponding to the width of the document shown in FIGS. A certain AEO
The N signal goes high. The details of the PEAK signal in FIG. 12 are as shown in FIG. 9B.

When the editing area of the original image is not designated, the PEAK signal is AEON as shown in FIG.
After the signal goes to a high level from the position where the leading edge of the document has passed the reading surface by about 3 mm, scanning in the main scanning direction
After passing about 0 mm, the level becomes high, and the level becomes low 20 mm before the rear end of the document. That is, in the case of an A2 vertical width document (having a vertical width of 420 mm), the PEAK signal is at a high level in a range of about 380 mm. This range corresponds to the width of the background density detection area. The reason is that a frame or the like is arranged around the original, or the original is not always arranged at the center of the contact glass 6.

On the other hand, when the editing areas a to d of the original image are designated, the AEON signal and the PEAK signal
As shown in (2), control is performed so as to turn on within the detection width of the designated area. Therefore, as shown in FIG. 18C, the designated area 103 is not located outside the background detection area, or a part of the designated area 104 is not located within the background detection area. Can be output. Similarly, in the second embodiment,
Since the background density of about 3 mm from the leading edge of the document is not detected, the background image of the document can be properly removed even if there is a sharp density change at the leading edge of the document as shown in FIG. It is possible to obtain an image having a high density.

Next, a third embodiment will be described. FIG. 15 is a circuit diagram showing an original background density detection circuit, FIG. 16 is a waveform diagram showing a detection signal when there is no significant change in the background level at the leading end of the original, and FIG. 17 is a large change in the background level at the leading end of the original. FIG. 7 is a waveform diagram showing a detection signal in the case where there is a signal.

The document background density detection circuit shown in FIG. 15 is provided separately from the background level detection circuit shown in FIG. 1, and generates an optical current by detecting the LED 13a for illuminating the leading edge of the document and the reflected light of the document D. And a phototransistor 13b. The voltage Vcc is applied to the anode of the LED 13a,
The cathode is grounded via a resistor 13d for determining a current flowing through the LED 13a. The voltage Vcc is applied to the collector of the phototransistor 13b, and the emitter is a resistor 13 for converting a photocurrent into a detection voltage Vout.
c is grounded. The detected voltage Vout is taken into the main control unit 100 shown in FIG. 7 and digitally processed. The CPU in the main control unit 100
It is determined whether or not there is a large change in the background level at the leading edge of the document, and control as described later is performed.

In FIG. 16, when there is no significant change in the background level at the leading edge of the document, the level of the detection voltage Vout does not change significantly. In this case, the main control unit 100 shown in FIG. 7 sets the AEON signal and the PEAK signal for the background level detection circuit shown in FIG. On the other hand, when there is a large change in the background level at the leading edge of the document, the level of the detection voltage Vout greatly changes from the distance L as shown in FIG. In this case, the main control unit 100 detects the background level of the area that has passed the distance L, and changes the time constant at the time of discharging the capacitor C3 by, for example, the analog switches AS2 and AS3 shown in FIG. If the background level changes from low density to high density, reduce the time constant (analog switch A
S2 and AS3 are turned on), and when the density changes from high density to low density, the time constant is increased (analog switches AS2 and AS3 are turned off).

Therefore, according to the third embodiment,
When the original document and the photosensitive paper are displaced in the transport direction, such as a diazo copy document, the latter is effectively removed because it has a white band of about several mm from the leading end and a bluish background thereafter. be able to. In addition, there is an image in the form of a horizontal black band at the leading end of the document, and thereafter the background can be effectively removed even if the document has a normal white background.

[0068]

As described above, according to the first aspect of the present invention, there is provided image reading means for reading an original image and converting it into an analog signal, and quantizing the analog signal read by the image reading means by a reference level. And a quantizing means for removing the background of the original image by extracting the background area of the original image from the analog signal read by the image reading means, detecting the background level, and applying the detected background level to the quantizing means as a reference level. The background detection means performs the detection by the background detection means such that the background detection means conveys the document in the forward direction so as to detect the background level of the front end area of the document, and the image reading means reads from the front end of the document. After the completion, the document is transported in the reverse direction, and thereafter, the document transport means for transporting the document in the forward direction is provided.
Even if there is a black solid image at the front center of the document or a halftone image different from the surroundings, it is possible to properly remove the background image of the document to obtain an image with the proper density. it can.

According to a second aspect of the present invention, there is provided the background level holding means for holding the background level detected by the background detecting means and applying the background level to the quantization means as a reference level. If there is an area where the density can be detected, the background image of the document can be properly removed to obtain an image with an appropriate density.

According to a third aspect of the present invention, the background level holding means has a time constant circuit for holding the background level by charging / discharging, and the background level detected by the background detection means is from low to high. When changing to concentration
When the time constant of the constant circuit changes from small, high concentration to small concentration
In this case, the time constant can be largely changed, so that even in the case of a document having a different background density distribution, the background image of the document can be properly removed to obtain an image with a proper density.

[0071]

[0072]

[0073]

[0074]

According to a fourth aspect of the present invention, the background detecting means is provided.
Of the background level detected by the time constant circuit
And the background level applied to the quantization means as a reference level.
Bell holding means and background density for detecting the background density of the original image
Degree detection means, and the background detected by the background detection means
If the level changes from low to high,
The time constant of the time constant circuit of the bell holding means is small, from high concentration
If the concentration changes, change the time constant to a large value.
Because of the provision of the bell changing means , even in the case of a document having a different background density distribution, the background image of the document can be properly removed to obtain an image with a proper density.

[Brief description of the drawings]

FIG. 1 is a diagram of a background level detection circuit of an embodiment of a background image removing apparatus according to the present invention.

FIG. 2 is a side view showing a main part of an image scanner using the background level detection circuit of FIG. 1;

FIG. 3 is a perspective view showing the image scanner of FIG. 2;

FIG. 4 is a side view showing a book carrier of the image scanner shown in FIGS. 2 and 3;

FIG. 5 is a plan view showing the book carrier of FIG. 4;

FIG. 6 is a side view showing a main part of the book carrier shown in FIGS. 4 and 5;

FIG. 7 is a block diagram showing a circuit for processing an image signal read by the image scanner of FIGS. 2 to 6;

8 is a circuit diagram illustrating a detailed configuration of a white level adjustment circuit in FIG. 7;

FIG. 9 is a timing chart for explaining an operation in a case where background density is detected at the leading edge of a document.

FIG. 10 is a timing chart for explaining an operation when reading a document image and detecting background density are performed simultaneously.

FIG. 11 is an explanatory diagram illustrating a document size detection sensor according to a second embodiment.

FIG. 12 is a timing chart for explaining the operation of the second embodiment.

FIG. 13 is a timing chart showing main signals when an editing area of a document image is not designated in the second embodiment.

FIG. 14 is a timing chart showing main signals when an editing area of a document image is designated in the second embodiment.

FIG. 15 is a circuit diagram showing a document background density detection circuit according to a third embodiment.

FIG. 16 is a waveform diagram showing a detection signal in the case where there is no significant change in the background level at the leading edge of the document in the third embodiment.

FIG. 17 is a waveform diagram showing a detection signal in a case where there is a large change in the background level at the leading edge of the document in the third embodiment.

FIG. 18 is an explanatory diagram showing a background level detection range of the conventional background image removing device.

FIG. 19 is an explanatory diagram showing a background level detection range of another conventional background image removing apparatus.

[Explanation of symbols]

 18 Image sensor 45 Document detection sensor 67 Background level detection circuit 100 Main control unit 232 A / D converter

Claims (4)

(57) [Claims] An image reading unit that reads an original image and converts the analog signal into an analog signal; and a quantizing unit that quantizes the analog signal read by the image reading unit according to a reference level to remove a background of the original image. A background detection unit that extracts a background area of the document image from the analog signal read by the image reading unit, detects a background level, and applies the background level to the quantization unit as a reference level; The original is transported in the forward direction so as to detect the background level of the area, and after the detection by the background detection unit is completed so that the image reading unit reads from the leading edge of the original, the original is transported in the reverse direction. A background image removing device, comprising: a document transport unit configured to transport a document in a forward direction. 2. The background image removing apparatus according to claim 1, further comprising a background level holding unit that holds the background level detected by the background detection unit and applies the background level to the quantization unit as a reference level. 3. The background level holding means includes a time constant circuit for holding the background level by charging / discharging, and the background level detected by the background detection means is changed from a low density to a high density.
If the time constant changes, reduce the time constant of the time constant circuit
3. The background image removing apparatus according to claim 2, wherein the time constant is set to be large when the density changes from low to high . 4. An original image is read and converted to an analog signal.
An image reading means for conversion, an analog signal read by said image reading means
Of the original image by quantizing the
Quantization means for removing skin, and an analog signal read by the image reading means
Extract background area of original image from background to detect background level
Background detection means, and a background level detected by the background detection means is a time constant.
Held by a circuit and used as a reference level by the quantization means.
Background level holding means to be applied, background density detection means for detecting the background density of the original image, and a background level detected by said background detection means having a low density.
If the concentration changes from high to high,
Change the time constant of the time constant circuit from small, high concentration to small concentration
In the case, the background level changing means for changing the time constant to a large value
And a background image removing device comprising: