JP3046030B2 - Document scanner - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document scanner which outputs a document image in which the background of the document has been removed as digital values.

[Conventional technology]

In conventional automatic background removal (AE) control in digital copiers, the center of the scanned document in the main scanning direction is approximately 50 mm.
It is known to detect the white level of a background with a width and use the output as a conversion reference input of an analog / digital (A / D) converter.

[Problems to be solved by the invention]

FIG. 11 and FIG. 12 are explanatory diagrams for explaining document conveyance and reproduction copying in the conventional apparatus, respectively. In FIG. 11, A is a white level detection range, B is a portion where the background is corrected and the background becomes whiter than the others, and C in FIG. 12 is a portion where the background is not removed. In the conventional device, when a white original is pasted on the center of a color original, or when the original in which the center of the second original drawing of the diazo device is corrected (the corrected portion becomes white) is read in the AE mode, the white level is reduced. Since the corrected or bonded portion comes to the detection range (A in FIG. 11), the white level of the corrected or bonded portion is held by the peak hold circuit after the white level detection, and then the background is restored again. ,
Since the time tracking of the time constant is delayed (the delay is 3 to 5 cm), the background is not removed (FIG. 12C), and the correction or the correction is performed in the main scanning direction when the correction portion or the bonded portion starts to be read. There has been a problem that the background of the entire region except for the bonded portion is converted into a signal level.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a document scanner device which performs background detection in the main scanning direction while avoiding a singular point of background density, and enables background removal of an entire region.

[Means for solving the problem]

The above object is to provide a one-dimensional photoelectric conversion that converts an original image into an electric signal by scanning each line in an original scanner device that optically reads an original and outputs a digital image of the original image from which the background of the original has been removed. And an analog / digital converter for converting the output of the photoelectric conversion element into a digital signal, and detecting the white output of the photoelectric conversion element after the start of the original scanning within a document area read by the photoelectric conversion element. This is achieved by performing the detection in an area that can be set at an arbitrary position in the main scanning direction and applying the detected white output to the conversion reference input of the analog / digital converter.

Further, the object is to provide a one-dimensional photoelectric conversion element for converting a document image into an electric signal by scanning each line, and an analog / digital converter for converting an output of the photoelectric conversion element into a digital signal in a document scanner apparatus on the same premise. A digital converter, and detects the background of the document by the photoelectric conversion element after the start of scanning of the document only at the leading end of the document, using a signal having passed through a peak hold circuit having a small rising time constant and a large falling time constant. After the detection of the background of the document, this is achieved by applying a holding signal of the detection output as a conversion reference signal to the conversion reference input of the analog / digital converter.

[Action]

The document scanner device operates to switch the AE detection position in the main scanning direction using the operation unit, and operates so that the operator can select a position avoiding the correction unit or the bonding unit while viewing the document.

Also, the original scanner device operates so that white level detection is performed only at the leading edge of the original, and the background that has become whiter than other portions of the correction portion and the background has been removed without being affected by the cut and pasted portions of the color original. Operate to send a read signal.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an overall block diagram for explaining an embodiment of an original scanner according to the present invention, wherein 1 is an original, 2 is a lens, 3 is a CCD, 4 is a video amplifier, 5 is a sampling circuit, and 6 is a video amplifier. , 7 is a gain control circuit, 8 is a clock / timing generator, 9 is an A / D converter, 10 is a peak hold circuit, 11 is RAM, 12 is ROM, 13, 14, and 17 are analog switch circuits, and 15 is black. Level detection circuit, 16 is a peak hold amplifier, 18 is a fluorescent lamp (FL), 19 is a FL stabilizer, 20 is an operation unit, 21 is a CPU, M is a document transport motor, SOL is a solenoid, and V _CC is a variable resistor. is there.

FIG. 2 is a schematic view showing a scanner unit of a copying machine to which the original scanner according to the present invention is applied, wherein 1 is an original, 2 is a lens, 3 is a CCD, 22 is an original table, and 23, 2
3 ', 24, 24', 27, 27 'are transport rollers, 25 is a document pressure plate, 26 is a contact glass, 28 is a CCD mounted printed board, 29 and 30 are document sensors, 31 is a document registration sensor, and 32 is shading correction It is a board.

Hereinafter, description will be made with reference to FIG. 1 and FIG. When the original 1 on the original table 22 is inserted, the original entrance sensor 29
, The document transport motor M starts rotating, the FL lamp (fluorescent lamp) 18 is turned on, and the transport is started by the rotation of the rollers 23, 23 '. When the leading edge of the document is detected by the document sensor 30, the solenoid SOL is driven, the shading correction plate 32 enters the light blocking the light path, the light of the FL lamp 18 is reflected, the image is formed by the lens 2, and the image is projected onto the CCD 3. Is done. Correction plate
32 is not at the image forming position, but there is no problem if only white output is obtained. Until the leading edge of the document is detected by the document registration sensor 31, shading correction data is taken in. During this time RA
The data stored in M11 and the A / D conversion output are constantly compared, and if the value is higher, the data is controlled to be replaced. During this time, even if there is unevenness in the amount of light at the rising point of the FL lamp 18, it is not affected. Drive the compensator 32 with the solenoid SO
If it is made to move slowly by a motor or the like instead of L, the correction plate 32 will not be affected by dirt or some unevenness. When the document 1 is detected by the document sensor 31, the loading of the shading correction data ends, the solenoid is turned off, and the correction plate 32 is pulled in. Subsequently, information on the document is read, subjected to shading correction, and output. The data transmission ends when the trailing edge of the document is read, and then the document 1 is discharged.

The CCD 3 is a CCD 3 (integrated with 5000 reading elements of 7 μm pitch) (for example, TC106C manufactured by Toshiba Corporation), and the reading density of the original 1 is set to 16 lines / mm on the original surface. CCD3 is 8MH
The drive clock and the SYNC signal are generated by a clock / timing generator 8. Since the output of the CCD 3 is as small as about 50 mV at the white level, if the A / D conversion is performed directly, the conversion error increases due to the influence of noise or the like. Since the driving clock is superimposed on the CCD 3 as noise, sampling is performed to extract only the signal component. The gain control circuit 7 is a variable amplifier for keeping the white level of a signal input to the A / D converter 9 constant, and can be varied from a minimum gain of 8 to a maximum of 40. Prior to the original scan, the white color of the original plate 25 is converted into a pixel signal, and the maximum level is the maximum value of the A / D conversion (3 if it is 6 bits).
FH). The A / D conversion is for converting an analog signal into a digital signal. Here, a 6-bit signal is used, and the signal levels of white to black are converted to data of 64 gradations. The RAM 11 is for storing shading correction data, and is 1 to 5000 when the pressure plate 25 is read.
The CCD output of the pixel is stored as 6-bit data, and is used as reference data for correcting a decrease in peripheral light amount due to the lens 2, a sensitivity unevenness of each element of the CCD 3, and a light amount unevenness of the FL lamp 18. Data is written in the ROM 12 so as to operate as a kind of arithmetic unit, and the output of each element of the CCD 3 when the original 1 is scanned is corrected by the value of the RAM 11, and is subjected to shading correction and taken out as data.

FIG. 3 is a timing chart. When the leading end of the fed original 1 is detected by the original registration sensor 31,
CPU21 is LSYNC generated by clock / timing generator 8.
(Line SYNC) signal is counted, a scan valid signal (SCAN VALID signal) is output in synchronization with the timing of starting exposure of the original 1 (after the delay of Td), and processing of the pixel signal read by the CCD 3 is started. The timing of the start of exposure is corrected by the magnification (document transport speed) in the sub-scanning direction. This is because the LSYNC cycle is constant regardless of the document transport speed. When the sub-scanning scan advances by 2 to 3 mm from the leading edge of the document, an AE signal is output from the CPU 21 to the clock / timing generator 8, and a main-scanning-window-opening signal is transmitted to Q11. The circuit 17 turns on and the peak hold circuit 10
Operates to hold the peak value of the white output of the video amplifier 6 at that time.

FIG. 4 is an explanatory diagram showing a background detection position and a detection width variable range at the time of AE, and FIG.
It is explanatory drawing explaining an original drawing. In FIG. 5, Ad denotes a corrected portion, and A and B denote main scanning window removal signals. FIG. 6 is an explanatory diagram showing the AE output and the background signal in the case of FIG.

The peak value is detected not in the entire area of the CCD 3 in the main scanning direction but in three different widths of 10 mm, 30 mm, and 50 mm in a central area of 200 mm as shown in FIG. The window opening position can be selected in the area of 200 mm in 25 mm steps, and even if the corrected portion Ad as shown in FIG. 5 is at the leading edge of the document, the AE level can be detected at a position avoiding the corrected portion Ad. 20 without window
The reason why it is within the range of 0 mm is that the minimum size of the read document is 210 mm width of A4 length, and when targeting even smaller documents, narrow the variable area or change for each document size I just need to do it. When the original is conveyed with the center as the center, the variable range may be determined based on the center distribution, and with the end face as the reference. The variable range may be determined based on the end face. Is detected, so that AE control is not performed.) The wider the window width is, the less the solid content in the document is affected, but the more easily the modified portion Ad is affected. The choice is based on a balance between both, but the normal is 50mm wide and is selected in the center. The change of the position and the width can be easily performed by a service mode selection switch provided on the operation unit (here, an operator selects by a combination of a touch switch provided on a liquid crystal panel table and a liquid crystal screen).

FIG. 7 is a circuit block diagram showing an example of a windowing signal generation circuit, and FIG. 8 is a timing chart for explaining the operation of the circuit of FIG. In FIG. 7, 33 is a crystal oscillator, 34 is a first counter circuit, 35 is a second counter circuit,
36 is a flip-flop, 37 is a shift register, 38 is a multiplexer, and 39 is a third counter circuit.

The crystal oscillator 33 uses 8 MHz (changed according to the scanning speed), and generates the LSYNC and LGATE signals with a loop counter of 5080 counts per round of the first counter circuit 34, and the D flip-flop 36 at the 500th count from the rise of LGATE. Set,
The second counter circuit 35 is operated to generate pulses (400 counts) at intervals of 25 mm to shift the signal of the shift register 37. Since the shift register 37 has an 8-bit configuration, a timing signal up to 200 mm can be generated.

The multiplexer 38 outputs a 3-bit selection signal from the CPU and outputs a Q signal.
Selecting the timing of the shift register 37 of ₁ to Q _8. The output of the multiplexer 38 activates the third counter circuit 39. The third counter circuit 39 terminates its operation when a windowing signal having a width of 10, 30, 50 mm is generated once. The window width is the same
Can be selected from CPU. If the number of shift registers 37 and multiplexers 38 is increased, finer timing can be obtained. The same applies to the width of the window.

Although the embodiment has a configuration using a counter and a shift register, if a start point counter and an end point counter are provided and a preset address is input from the CPU, detection at an arbitrary width and position is possible.

The DTCC time constant switching signal is output at the same time as the AE switching signal, and the discharge time constant of the peak hold circuit 10 becomes a normal value (about 3 seconds in discharge time constant). At the time of scanning 30 mm in the sub-scanning direction, the main scanning window opening signal and the time constant switching signal are turned off, and the current white peak level is maintained (discharge time constant is about 200 seconds). The document scanning is performed at this holding level. However, even if the sub-scanning scanning time is set to 5 seconds, there is no effect since the level is reduced only by 2.5%.

Peak value of the detected white level is input to the conversion reference voltage V _REF of the A / D converter 9 via the analog switch circuit 17, the video signal at that time is converted to a digital value of 6 bits.

When the AE operation is not performed, the analog switch circuit 17
A / D conversion is performed based on the voltage (about 4 V) divided by the variable resistor V _CC .

FIG. 9 is a circuit diagram showing an example of an automatic white level correction circuit and an AE white level detection circuit. In the figure, the same reference numerals as those in FIG. 1 denote the same parts, and a description thereof will not be repeated.
3,44 is a comparison circuit, 45 is a NAND-OR selector IC, 46,47
An operational amplifier, 48 a transistor, 49 a comparator for peak hold, R ₁ to R ₂₁ are resistors, C ₁ -C ₃ capacitors, D ₁ is a diode. In FIG. 9, a video signal input from CN1 is amplified by a video amplifier 6. The amplification of the video amplifier 6 is equal to the S of the NAND-OR selector IC45.
Since the input is at the H level, the inputs 1B to 4B are selected, so that all the analog switch circuits 13 are turned on, and the minimum magnification is set to 8 times. The output amplified by 8 times
The digital value is converted by the A / D converter 9 and latched once by the latch circuit 41, and the value of the upper 4 bits is encoded in the main scanning direction.
The values are compared by the comparison circuits 42 to 44 and are held at the highest values. After the end of one scan, the 4-bit value held in the comparison circuit 43 is transmitted to the analog switch circuit 13 by setting the S input of the NAND-OR selector IC 45 to L level, thereby switching the amplification degree to a previously calculated amplification degree. For example, Q _1-
Q ₄ are all 8 times at the H level, Q ₄ is the Q ₁ to Q ₃ in H L
13 times at level. The V _IN of the A / D converter 9 varies between 3.8 and 4 V, depending on the input level of CN1. During document scanning (while the SCAN VALID signal is being output), the S input of the NAND-OR selector IC 45 remains at L level so that the amplification of the video amplifier 6 is kept constant.

The output of the video amplifier 6 is divided by 1/2 by the resistors R9 and R10 and extracted as a signal that follows the white level. Amplifier 40 the response of the high band in the general operational amplifier is poor, and in the low frequency of the high frequency component due to the capacitor C _2, a video signal according Kurobe detection such as text is not transmitted. The output of the amplifier 40 is for preventing the white level from being detected except for the resistors R ₁₁ and R ₁₂ and the main scanning direction, and is used as the NAND of the windowing signal and the AE signal from the clock / timing generator 8 (FIG. 1). Driven.

Leftmost analog switch circuit 14 is intended to switch the time constant of the peak hold, resistor R ₁₅ responsiveness to the small time constant by acting on the parallel black level side slightly better, characters, thin lines when the AE operation Has been improved. The three switches on the right side of the analog switch circuit 14 are for switching the gain of the amplifier 47.
The amplification degree of the amplifier 47 is switched between 1.5 times, 1.8 times and 2 times. 1.5x is used when writing newspapers, and V _REF is 3V for 4V video signal to prevent set-off. 1.
Eight times is for a document with a certain level of normal contrast. Twice is when you want to reproduce even thin characters during AE,
Used when scanning low-contrast characters with many white background documents.

As described above, the present invention uses a photoelectric conversion device such as a CCD to convert an original image into an electric signal, processes the original image, processes the original image, converts the original image into a digital signal, and an AE of a digital copying machine that creates a copy image. (Automatic background removal).

FIG. 10 is an explanatory diagram showing the output waveform of CCD3. In the figure, S is the background portion output, T is the black portion on the document, U is the background portion, V is the background portion of the correction portion, W is the solid black portion, and X is the black portion. Indicates a reference white output.

With reference to FIG. 10, the present invention will be further described in comparison with the prior art. In the digital document scanner, the white level of the document is always peak-held as shown in FIG. 10 since the signal must be subjected to background removal when reading the document, and the output is converted by the A / D converter 9 as shown in FIG. The reference signal (V _REF ) is used, and the input signal is A / D converted.
Is always the upper limit of the conversion value, and the white output level can be maintained.
A / D conversion is performed between the background U of the document and the black level 0V.
It is converted to a digital value of 64 bits (64 gradations) or 8 bits (256 gradations), subjected to necessary image processing, and output from a scanner. The background level is always the upper limit of the conversion value (3FH for 6 bits). If the change is slow even if the background level of the document changes, the peak hold circuit 10 follows up, so the background Although it is removed, when reading a document as described in the section of the prior art, since the background level detection is performed at the center of the main scanning direction,
Erase the 2nd original drawing of diazo with the correction liquid and edit the part (the 2nd original drawing of diazo has low sensitivity, so it is necessary to reduce the speed of the copier considerably to skip the background, but considering the productivity, You must copy at medium speed, so the copy will have the background left behind.If this part is corrected, the correction material will dissolve the photosensitive material that has been applied to the background, remove it, and remove it. If you read an original with a white background on a document with a blue or green color background or a white background, the conversion reference input of the A / D converter 9 will have a higher voltage than the surrounding background level. Except for the background of the part or the bonded part, the background of the other part cannot be removed, and is reproduced as a scan signal or as a background stain on a copy.

The present invention provides a mode in which the background detection, which has been performed over the entire area in the sub-scanning direction, is performed only at the leading edge of the original in order to compensate for the disadvantage of the conventional technique. The mode is switched. Since the correction section or the bonding section rarely covers the entire area of the document in the sub-scanning direction and is usually only a partial area, in such a document, the background detection at the leading edge of the document is performed. After that, the detected value is held, and the AE is performed until the end of the original, whereby the background can be removed over the entire area (see FIGS. 4 and 5).

The background detection position at the tip is configured so that a plurality of locations in the main scanning direction can be selected.If the background reading position at the tip also has a stuck part, you can select a position that avoids this. Making it possible.

Next, the reason why the peak hold of the AE is necessary will be described. If there is no peak hold of the white level, the conversion reference input V _REF will respond to the black level of the document, and the black level of characters and thick lines will not be accurately converted. In order to prevent this and follow the fluctuation of the background, the peak hold circuit 10 is provided with a time constant so that the voltage is rapidly charged in the direction in which the voltage increases (the direction in which the background becomes whiter) and lowered in the direction (characters on the document). And a black detection signal of an image) generally have a discharge time constant of 1 to 2 seconds, depending on the scanning speed. This time constant is for preventing the AE level from following the black portion even if the black portion continues for several tens of millimeters on the manuscript (if it follows, all become whiter).

As described above, the peak hold type AE function follows a gradual change in the background level, but cannot follow a direction in which the background becomes rapidly dark. In order to improve the followability, the discharge time constant may be reduced.However, when the black portion is continuous, the background level is drawn to the black portion, so that the background is not stained. Reproducibility of thin lines and the like becomes poor.

In the present invention, since the AE signal is passed through the white level peak hold circuit 10, even if there is an image portion or a thick line image in the white level reading portion, the A / D conversion is performed. The AE signal, which is the reference input signal of the detector 9, is not affected. Therefore, even if a character or a thick solid line portion is present near the leading end of the document, a read signal from which the background has been removed is transmitted.

In addition, since AE detection can be switched to the front end and the entire area in the sub-scanning direction, it is possible to detect an AE control level suitable for each of a unique original and a normal original for correction and bonding, and this can also be performed from the operation unit. With this arrangement, the operator can easily switch the respective directions while viewing the original.

Further, when the white detection is switched, the falling time constant of the peak hold circuit 10 is also switched at the same time, thereby increasing the discharge time constant and maintaining the white level detection value at the tip.

In this way, the white level detection for AE control is performed only at the leading edge, so even if the corrected part of the background is whiter than other parts, or if a color background is cut and pasted, it will not be affected by this part. It is possible to send a read signal from which the background has been removed.

〔The invention's effect〕

As described above, according to the present invention, the position of white level detection for AE control is performed at an arbitrary position in the main scanning direction, is performed only at the leading edge of the document, or can be performed over the entire sub-scanning area. Even if the corrected part is whiter than other background parts, or if a white background is cut and pasted on a color background, the background level can be detected at a position avoiding this position, and the background has been removed. A document scanning device capable of sending a read signal can be provided.

[Brief description of the drawings]

FIG. 1 is an overall block diagram for explaining an embodiment of an original scanner according to the present invention, FIG. 2 is a schematic view showing a scanner unit of a copying machine to which the original scanner according to the present invention is applied, and FIG. FIG. 4 is an explanatory diagram showing a background detection position and a detection width variable range at the time of AE, FIG. 5 is an explanatory diagram illustrating a second original drawing of diazo having a correction portion,
FIG. 6 is an explanatory diagram showing the AE output and the background signal in the case of FIG. 5, FIG. 7 is a block diagram showing the circuit configuration of the windowing signal generating circuit, and FIG. 8 is a diagram explaining the operation of the circuit of FIG. Figure 9 shows the automatic white level correction circuit and AE
Circuit diagram showing an example of a white level detection circuit for CC, FIG.
FIG. 11 and FIG. 12 are diagrams illustrating the output waveform of D, and FIG. 11 and FIG. 12 are diagrams illustrating document conveyance and reproduction copying in the conventional apparatus. 1. Original document, 3. Photoelectric conversion device (CCD), 9. A / D converter, 18. Fluorescent lamp, 23, 23 ', 24, 24'.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (4)

(57) [Claims] An original scanner for optically reading an original and outputting a digital image of the original from which the background of the original has been removed, wherein the original image is converted into an electric signal by scanning each line. A document area, comprising: a conversion element; and an analog / digital converter for converting an output of the photoelectric conversion element into a digital signal. The document area in which detection of white output of the photoelectric conversion element after scanning of a document is started is read by the photoelectric conversion element. A document scanning apparatus which performs the processing in an area which can be set at an arbitrary position in the main scanning direction and applies a detected white output to a conversion reference input of the analog / digital converter. 2. The original according to claim 1, wherein said white output is a photoelectric conversion output which has detected a background of the original and passed through a peak hold circuit having a small rising time constant and a large falling time constant. Scanner device. 3. A one-dimensional photoelectric conversion device for reading a document optically and outputting a document image from which the background of the document has been removed as a digital value, wherein the document image is converted into an electric signal by scanning each line. A conversion element; and an analog / digital converter for converting an output of the photoelectric conversion element into a digital signal. The detection is performed by a signal that has passed through a peak hold circuit having a small constant and a large fall time constant. After the detection of the background of the document, a holding signal of the detection output is applied to a conversion reference input of the analog / digital converter as a conversion reference signal. An original scanner device, characterized in that: 4. The original scanner according to claim 1, wherein the detection of the white output can be switched between a leading end of the original and an entire sub-scanning area of the original.