JPH0654188A - Image reader - Google Patents

Abstract

PURPOSE:To facilitate adjustment after factory shipping by previously storing data obtained by reading a specified white paper and outputting data of the white paper from a memory to use it instead of reading the specified white paper at the time of adjusting a shading correction function. CONSTITUTION:After the specified white paper is set on an original platen glass 105 and the balance and the offset of a CCD linar image sensor 107 is adjusted, a halogen lamp 104 is lighted and mirror table units 101 and 102 are moved. At this time, after adjusting a light quantity and the gain of R, G and B, a white reference board 103 and the white paper is read and each piece of data is stored in the memory. In shading adjustment thereafter, the white paper is not set from the memory but each initial value is set from the memory and at the time of reading the white reference board 103, the level of the white paper is decided for white level adjustment. Thus, the trouble of arranging specified white paper, etc., is omitted so that adjustment at a market after factory shipping is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus such as an image forming apparatus which has a shading correction function for correcting image shading.

[0002]

2. Description of the Related Art In a conventional image reading apparatus, when adjusting the shading of an optical system, a blank sheet of a design standard is set on a platen glass, and the data of the blank sheet and the shading plate are used to determine the optical and electrical characteristics of the image reading apparatus. The correction of the reading data was done.

[0003]

In the conventional image reading apparatus, a blank sheet, which is a design standard, is set on the platen glass when adjusting the shading of the optical system, and the data of the blank sheet and the shading plate are used for the image reading apparatus. Optical and electrical read data were corrected. However, when adjusting the shading in an area where it is difficult to obtain white paper as the design standard, the white standard changes from the design value, and when you read the image, it becomes an image with black as a whole, In some cases, the image will appear white and the image cannot be adjusted as designed.

[0004]

According to the present invention, in order to solve the above-mentioned problems, the blank read data set by the shading adjustment at the time of factory shipment is saved in a storage device, and the read data of the shading plate is stored. By comparison, shading adjustment can be performed without placing a blank sheet on the platen glass.

[0005]

EXAMPLES Example 1 An example of the present invention will be described. FIG. 1 is an example of an image reading apparatus. Reference numeral 101 is a first mirror base unit, 102 is a second mirror base unit, 103 is a shading plate, 104 is a halogen lamp, 105 is a platen glass, 10
Reference numeral 6 is a lens unit, and 107 is a CCD linear image sensor. Here, the first mirror base unit 101 and the second mirror base unit 102 form an optical mirror base, and the first mirror base unit 101 and the second mirror base unit 102 are in the direction of arrow 109 (sub scanning direction). ) To 2) at a speed of 2: 1. Further, the slit 108 is for cutting off the light from the area other than the width of the exposure slit among the reflected light from the original or the shading plate illuminated by the halogen lamp 104. FIG. 2 is an example of the operation unit of the image forming apparatus, which is the base of the image reading apparatus. Here, each function of the operation unit of FIG. 2 will be described.
201 to 203 are density keys of the image forming apparatus.
Reference numerals 4 to 206 denote reduction, equal magnification, and enlargement keys of the variable magnification key. 207 is a display for displaying a message, 208 is an * (asterisk) key, 209 is a main power switch of the image forming apparatus, 210 is an OK key, 21
1-214 cursor keys, 215 preheat key, 216
Is a copy start key, 217 is a stop key, 218
Is a clear key and 219 is a numeric keypad. FIG. 3 is a schematic diagram of the image forming apparatus. The operation of the image forming apparatus will be described with reference to FIG. First, a power cord (not shown) of the image forming apparatus is connected to an outlet, and the main power switch shown in FIG. Then, the heater of the fixing device 315 is turned on, and the fixing device is heated to a preset temperature and enters a standby state in which the temperature is maintained at a substantially constant temperature. In this standby state, a message "ready for copying" is displayed on the display 207. In this state, a document is set on the platen glass 105 and a copy button 216 is pressed. Then, the halogen lamp 104 lights up and 10
Irradiate the shading plate of No. 3 and the reflected light is
BLUE, which is optically transmitted to a lens of 106 through a reflection mirror of 305, and a phase grating for spectroscopy of 307,
The light is split into three color lights of GREEN and RED, and converted into electric signals of BLUE, GREEN, and RED by the line sensors of 107 color 3-line CCD sensors. 107 color 3-line CCD
The document image information converted into an electric signal by the sensor is subjected to image processing by the image processing device 319, and then 30
Projected as laser light from 9 laser transmitters, 3
An image is formed as an image on the photoconductor 313 via the ten polygon mirrors 311, 312 reflection mirrors. The image formed on the photoconductor is transferred to the transfer paper sent from the transfer paper stacking units 317 and 318, sent to the fixing device 315 by the conveyor belt 314, and after being fixed, 31
The sheet is discharged from the sheet discharge unit 6. Next, the structure of the CCD color linear image sensor 107 is shown in FIG. This is CCD linear image sensor 107B, 107G, 1
It shows a structure of three lines of 07R, which is composed of a photodiode which is shielded from light and a dummy pixel which is not connected to the photodiode, and the output of the shield is a reference of the black signal level. Used as. The charges accumulated in the photodiode portion for a certain period of time are transferred to the shift register through the shift gate by the SH signal. The electric signals transferred to the shift register are sequentially transferred by transfer clocks Φ1A1, Φ2A1, Φ2 and are pushed out as output signals by Φ1B, Φ2B. Here, RS1 and RS2 are reset pulses for resetting the residual charges remaining in the output buffer. The color linear image sensor has three line sensors described above, each of which has a color filter or an optical system according to the same so that color reading can be performed. FIG. 7 shows the timing relationship of the drive clocks of the CCD line sensor. Next, FIG.
6 shows a block diagram of the overall configuration of the image processing device 319. In addition to the CCD image sensor 107 described above, it includes an amplifier circuit 1602, an A / D converter 1603, a black correction / white correction circuit 1604, a luminance signal generation unit 1605, a LOG conversion unit 1606, and a CPU 1601.

From the CCD arrays 107R, 107G and 107B of the CCD image sensor 107, analog image signals corresponding to the three primary color components of R, G and B are output respectively, which are amplified by an amplifier circuit 1602, It is converted into a digital signal by the A / D converter 1603. Then, the black correction / white correction circuit 1604
Black level correction and white level correction (shading correction) are performed on each digital image signal corresponding to the three primary color components of R, G, and B. Luminance signal generator 160
5 is R for which black level correction and white level correction have been performed,
A luminance signal corresponding to black and white is generated from each image signal corresponding to the three primary color components G and B. LOG converter 1605
Converts the output signal (luminance signal) from the luminance signal generation unit 1605 into a density signal and outputs it to the printer unit (laser scanner unit 309). In this case, the conversion to the density signal is performed so as to correct the γ characteristic (nonlinearity of sensitivity to exposure). The CPU 1601 controls the black correction / white correction circuit 1604 and the LOG conversion unit 1606. Next, regarding the signal processing of the output signal of the CCD driven by the clock of FIG. 7, the amplifier circuit 1602 and the A / D converter 1
Explaining with reference numeral 603, the analog signal divided into the odd-numbered pixel (ODD) and the even-numbered pixel (EVEN) for each color of R, G, B is converted into a digital signal by the circuit shown in FIG. Here, the amplifier circuit 1602 includes a sample hold circuit 801, clamp circuits 802, 80.
5, MPX switch 803, variable amplifier 804, and gain control device 807. Reference numeral 801 denotes a sample hold circuit for sampling an output signal from the CCD linear image sensor via a coupling capacitor, and both ODD and EVEN outputs are sampled for each pixel. At this time, since the CCD linear image sensor has the configuration as shown in FIG. 6 described above, the shielded photodiode portion shows no change in the output level even when it is irradiated with light. That is, the black level is shown. This level is the output reference signal of the CCD linear image sensor, and it is necessary to make the reference level the same in order to convert the ODD and EVEN signals into one data. Therefore, the clamp circuit 802 clamps at the level of the light shielding portion of the signal. The clamped ODD and EVEN signals are alternately switched in the order of ODD and EVEN by the MPX switch 803, and input as a single signal to the variable amplifier 804. Further, the output signal of the CCD line sensor, which has become a single signal, is re-clamped by the clamp circuit 805 so that the low level of the input range of the A / D converter 1603 becomes the same as the reference level of the signal. . Through the above processing, the output signal of the CCD linear image sensor is converted into a digital signal by the A / D converter 1603.

FIG. 17 is a circuit block diagram of the black correction circuit of the black correction / white correction circuit 1604. The black correction circuit is composed of three identical black correction circuits corresponding to the three primary color components of R, G, and B, but the specific contents thereof are shown only for blue in FIG. This also applies to the white correction circuit described later. A / D
The converted digital color image signal from the CCD image sensor 107 is transferred to the CCD image sensor 107.
When the amount of light input to is very small, the variation between pixels is large as shown in FIG. 18, and if this is directly output as an image, streaks and unevenness occur in the image data portion.
Therefore, the black correction circuit in FIG. 17 corrects variations between pixels. That is, as shown in FIG. 5, the document irradiation lamp 104 and the scanning mirror 30 are placed before the document reading operation.
An original scanning unit 102 composed of 4, 305 is attached to the original table 1
05, the original irradiation lamp 104 is turned off, and a black level image signal is input to the black correction circuit. Regarding the blue component signal Bin, in order to store one line of the black level image signal in the black level RAM 78a, A is selected by the selector 82a (control line d), the gate 80a is closed (control line a), and the gate is closed. 81a is opened (control line b) to connect the data lines 151a, 152a, 153a. On the other hand, A is selected by the selector 83a (control line C) so that the address 155a of the black level RAM 78a is initialized by the inverted HSYNC and the output 154a of the address counter 84a for counting VCLK is input. As a result, the image signal for one line of black level read at the position of the white plate 103 when the original irradiation lamp 104 is turned off is addressed for each pixel and stored in the black level RAM 78a as black reference value data. .

When reading the actual image data of the original, the black level RAM 78a is in the data read mode. That is, by closing the gate 81a (control line b), opening the gate 80a (control line a), and making the selector 86a output A, the black reference value data in the black level RAM 78a is routed through the data lines 153a and 157a. Is input to the B input of the subtractor 79a. At this time, the subtractor 79a
Although the actual image data of the original is input to the A input of, the subtractor 7 outputs one line of the actual image data of the original.
Each time it is input to the A input of 9a, the black reference value data for one line in the black level RAM 78a is repeatedly input to the B input of the subtractor 79a. Further, the above-mentioned two data are input to the subtractor 79a in synchronization with each other for each pixel. Then, the subtractor 79a subtracts the black reference value data from the actual image data of the document to perform the black correction, and outputs the black correction data from the data line 156a. For example, for the i-th pixel of the blue component, if the actual image data of the document is Bin (i) and the black reference value data is DK (i), the black correction data Bout
(I) is Bout (i) = Bin (i) -DK (i)
Becomes Such black correction is similarly performed for the green component and the red component. The control lines a, b, c, d of the respective selector gates for black correction are the CPU 1
It is controlled by the CPU 1601 using the latch 85a assigned as the I / O of 601. Also, by selecting the selectors 82a, 83a, 86a as B selection,
The CPU 1601 can access the black level RAM 78a. FIG. 19 shows a black correction / white correction circuit 1604.
2 is a circuit block diagram of the white correction circuit of FIG. 1, in which white level correction (shading correction) is performed. White level correction (shading correction) is data of a white level when a document scanning unit irradiates a white plate 103 of uniform density arranged in a non-image area at the rear end of a document table with a document irradiation lamp 104 to read the white level. Based on FIG. 20, the illumination system, the optical system, and the CCD image sensor 10 as shown in FIG.
Correct the sensitivity variation of 7.

The basic circuit configuration of the white correction circuit is the same as that of the black correction circuit. In the black correction, the subtractor 79a performs the correction, whereas in the white correction, the multiplier 79b performs the white correction. The description of the same parts will be omitted. CCD image sensor 10 for color correction
When 7 is in the position of the uniform white plate (home position),
That is, before the copying operation or the reading operation, the original irradiation lamp 104 is turned on and the white level image signal reflected by the white plate is stored in the correction coefficient RAM 78b for one line. For example, if the main scanning direction has a longitudinal width of A4 size and the image data is 1 byte, the capacity of the correction coefficient RAM 78b is 4752 at 16 pels / mm.
(= 16 × 297 mm) pixels, which is 4752 bytes, and the correction coefficient RAM 78b stores white level data Wi (i = 1 to 4) for each pixel as shown in FIG.
752) is stored. The storage of the white level data Wi is similarly performed for the blue component, the green component, and the red component.

By the way, with respect to the white level data Wi corresponding to the i-th pixel, the data Do (i) after white correction of the original data Di corresponding to the i-th pixel is Do.
(I) = Di × FFH / Wi should be obtained. That is, as shown in FIG. 20, when the maximum value of the image signal (image data corresponding to the whitest color) is FFH, the shading correction coefficient should be FFH / Wi. Therefore, the CPU 1601 first attaches the correction coefficient RA to the blue component, as shown in Step B of FIG.
The white level data Wi stored in the M78b is sequentially read out, the calculation of FFH / Wi is performed, and the correction coefficient RAM7
The white level data Wi in 8b is rewritten to the shading correction coefficient FFH / Wi which is the above calculation result (see FIG. 21 (b)). Then, similar processing is performed for the green component and the red component. Prior to this processing, the CPU 1601 opens the gates 80b and 81b and outputs a control line signal such that B is selected by the selectors 82b, 83b and 86b to the latch 85b to make the correction coefficient RAM 78b accessible. Keep it.

When reading the actual image data of the document, the CPU 1601 closes the gate 81b (control line b), opens the gate 80b (control line a), and selects the selector 86.
By setting b to A output, the data lines 153b and 153b
The shading correction coefficient FFH / Wi in the correction coefficient RAM 78b is input to the B input of the multiplier 79b via the path 7b. At this time, the actual image data of the document is input to the A input of the multiplier 79b. Therefore, the multiplier 79b is
The actual image data (Di) of the original is multiplied by the shading correction coefficient FFH / Wi to perform white correction, and the white correction data is output from the data line 156a. In this way, the CCD image sensor 10 of the image input system
7 dark current variation, each CCD array 107R, 107
Sensitivity variation between G and 107B, optical system light amount variation,
Image data Bout, Gout, in which variations in black level and white level due to white level sensitivity are corrected and are uniformly corrected for each of the three primary colors in black and white in the main scanning direction.
I am trying to get Rout. This black correction, and
Image data with white correction Bout, Gout, R
out is output to the luminance signal generation circuit 1605.

A luminance signal generation circuit 1605 generates a luminance signal of an image over the entire wavelength region which is not color-separated, that is, a monochrome image, from the color-separated image data (image) read by the CCD image sensor 107. ing. This is because the output means has only a single color output means. In order to generate a luminance signal of a black and white image, the luminance signal generation circuit 1605, as shown in FIG. 23, the black correction output from the black correction / white correction circuit 1604, the blue component after the white correction, the green component, and the red component. Image data of the component Bou
For t, Cout, and Rout, (Bout + Gou
t + Rout) / 3 is calculated to calculate the average of the three primary color components. The luminance signal of this black and white image is L
It is output to the OG conversion unit 1606.

The brightness signal output from the brightness signal generator 1605 is converted into a density signal by the Log converter 1606. This brightness-density conversion is performed by the Log conversion unit 16
Look-up table (L
The image data converted into the density signal is output to the printer unit (laser scanner unit 309). The information in the Log table is written by the CPU 1601 shown in FIG.

In the image processing apparatus 319 having the above-described structure, shading adjustment is performed as shown in FIG. First, the signal from the shading plate 103 is read at the position (A), then the mirror base unit is moved to the position (B), and the signal level of the blank sheet 502 on the platen glass 105 is read. The data at this time is obtained as 8-bit data as shown in FIG. 9, and the data can be sampled for each pixel of the CCD linear image sensor. Based on the pixel data, it is used for correction of read data such as adjustment of white level, correction of sensitivity variation of photodiode of CCD linear image sensor, and correction of light amount distribution of halogen lamp. Further, the reading values of the shading plate and the blank sheet read at the time of the conventional shading adjustment are as shown in FIG. 4 and as shown by 402 and 401, respectively. From this, explaining the shading adjustment example,
As shown in the flowchart of FIG. 12, when the shading adjustment is started after setting a blank sheet on the platen glass of the image forming apparatus, the halogen lamp is not turned on in S1, that is, the ODD of the CCD linear image sensor in the no signal state. , EVEN balance adjustment is performed, and the signal offset is adjusted to 0 level in S2, and then the optical mirror base is moved toward the platen glass in S3 to turn on the halogen lamp. At S4, paying attention to the peak signal level of the output signals of R, G, B of the CCD linear image sensor at this time, S5 to S8
Then, the lighting voltage of the halogen lamp is adjusted so that the peak signal level becomes FFH (256) which is the reading level and the MAX value. After completing the adjustment of the halogen lamp, S9, S
In order to make the output of the CCD linear image sensor obtained by the light amount of the halogen lamp turned on in accordance with the adjustment value in 10, the gain value is changed for each color (by the gain control device 807 in FIG. 8), and the R, G, B Adjust so that the output is uniform for all three colors. This R, G, B
After the adjustment of the three colors is completed, in S11, the data SD of the shading plate necessary for image correction during image reading is read and saved, and in S12, the blank data WD is read and saved. Here, when reading a shading plate and a blank sheet, CC of each color of R, G, and B is used.
Center of 250 pixels of D linear image sensor
During shading adjustment, the average value of the reference read data is read for each of the shading plate and blank paper and stored in the memory. A flow chart for making a copy based on this data is as shown in FIG. Shading during normal copying is performed in conjunction with the copy button, and the data on the shading plate is read for all pixels. Of the read data, the data read by the shading plate has a bumpy output due to the output variations of the photodiodes of the CCD, as shown in FIGS. Shading correction is performed to correct the unevenness, and the shading correction is performed as shown in FIGS.
A correction coefficient for compensating for the shaded area is calculated, and the output of the CCD linear image sensor when a document of constant density is read is converted into a uniform output. Here, FIG. 10 shows a case where the shading target is set high,
The shaded area corresponding to the difference between the shading plate and the target is the correction coefficient, and data is always added for correction. In the case of FIG. 11, since the shading target is set low, the shaded portion is drawn and corrected. In addition, the blank sheet level during normal copying is the data value of the reading level of the shading plate and the blank sheet read during the shading adjustment, SD, WD, or the data ratio (H = WD /
SD) and calculate from readings on the shading plate. This white level is used for white level correction when reading data. That is, even if the output of the CCD linear image sensor is larger than that when a blank sheet is read, signal processing is performed as the MAX signal level (white level).

Here, the actual shading correction coefficient is calculated according to the following formula. Read data for shading plate: SDi, Read data for blank paper: W
Di, maximum value of image signal: T (image level corresponding to the whitest color), data of shading plate read during shading adjustment: SD, data of blank sheet read during shading adjustment: WD, image input during actual reading Signal: Di, image output signal during actual reading: Do (i) H = (WD) / (SD), WDi = (SDi) × H, D
o (i) = Di × T / (WDi) Here, when T = FFH, the same equation as the above-described shading correction is obtained.

In the conventional shading, it is necessary to set a designated blank sheet on the platen glass when adjusting the shading. Therefore, in an area where the designated blank sheet is difficult to obtain, it is necessary to arrange the designated sheet. It was Therefore, in the present invention, the shading adjustment that can be adjusted only by reading the data of the shading plate is shown. As means, at the time of initial setting (for example, when assembling and adjusting the image forming apparatus),
Shading adjustment is performed. At that time, a designated blank sheet is set on the platen glass, the shading adjustment is performed according to the flowchart shown in FIG. 12, and when the shading is adjusted thereafter (for example, installation of the image forming apparatus). Shading adjustment is performed without setting a blank sheet on the platen glass of the image forming apparatus. FIG. 14 is a flowchart at this time. At the start of this adjustment, the balance, offset, ramp, gain, and shading plate data described above are set to the initial values, and the paper data is set to the factory shipment data or the data calculated from the shading plate reading data. Become. The calculation of the blank sheet data at this time is performed by the ratio H = WD of the blank sheet reading level 401WD and the shading plate reading level 402SD shown in FIG.
Set by / SD. If the reading level of 402SD is set to BOH (176), the paper level FF
The ratio with H (256) is about 1.45. If this value of 1.45 is stored, the level of the blank sheet can be determined only by reading the shading plate. This shading adjustment is mainly for correcting the deterioration of the halogen lamp and the accuracy error of the mirror of the optical system, so even if the halogen lamp is deteriorated, the reflection of the shading plate against the irradiation light of the halogen lamp is assumed. Since it is considered that the ratio of the light and the reflected light of the white paper is relatively equal, the white level adjustment according to the present invention has the same effect as the conventional shading adjustment. FIG. 15 shows a control block diagram of shading adjustment.

(Embodiment 2) In the embodiment, as a method for calculating the blank sheet reading data, a data difference between the shading plate reading data adjusted at the time of factory shipment and the blank sheet reading data is calculated, and at the time of adjustment in the market, The same effect can be achieved by adding a differential offset to the shading plate read data. By the way, the offset amount is 4FH (79) from Fig. 4.
Is.

[0018]

In the conventional shading adjustment,
There is a problem that it is difficult to make shading adjustment in areas where it is difficult to obtain the specified blank paper because the specified blank paper is used during the adjustment, but if the blank paper is not used in the shading adjustment, the specified blank paper is not available. Adjustments in the market become very easy without the trouble of making arrangements.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a reading unit according to the present exemplary embodiment.

FIG. 2 is a diagram of an operation unit according to the present embodiment.

FIG. 3 is a schematic diagram of a copying machine using the reading device of the present embodiment.

FIG. 4 is a diagram showing read data of a white reference plate and a blank sheet.

FIG. 5 is a diagram illustrating an operation of a reading unit when adjusting shading.

FIG. 6 is a schematic view of a 3-line color CCD.

FIG. 7 is a diagram showing a drive timing of a CCD.

FIG. 8 is a diagram illustrating an amplification and A / D conversion unit.

FIG. 9 is a diagram in which read data for one pixel is digitally displayed.

FIG. 10 is a diagram illustrating a shading correction operation.

FIG. 11 is a diagram illustrating a shading correction operation.

FIG. 12 is a flowchart showing an operation of shading adjustment using a blank sheet.

FIG. 13 is a flowchart showing a shading correction operation during a copy operation.

FIG. 14 is a flowchart showing a shading correction operation that does not use a blank sheet.

FIG. 15 is a schematic diagram of control of shading adjustment.

FIG. 16 is a schematic diagram of an image processing unit of this embodiment.

FIG. 17 is a diagram illustrating a black level correction circuit.

FIG. 18 is a diagram showing black level read data.

FIG. 19 is a diagram illustrating a white level correction circuit.

FIG. 20 is a diagram illustrating white level read data.

FIG. 21 is a diagram showing how a white level signal and a correction coefficient are stored in a memory.

FIG. 22 is a flowchart showing calculation of a correction coefficient.

FIG. 23 is a diagram illustrating generation of a luminance signal.

[Explanation of symbols]

 103 White Reference Plate 104 Halogen Lamp 107 CCD 216 Copy Key 309 Laser Oscillator 319 Image Processing Unit 401 White Paper Read Signal 402 White Reference Plate Read Signal 1601 CPU 1604 Black Correction / White Correction Unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norimasa Fukuzawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Keizo Isemura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (2)

[Claims] 1. A means for irradiating a document with light, an image sensor for reading an image on the document by receiving reflected light from the document illuminated by the document illuminating means, and an output from the image sensor. In an image reading apparatus having an adjusting means for adjusting a signal level and a white plate serving as a reading reference of the image, a second image reading reference for correcting the reading level of the white plate and the reading level of the white plate. An image reading apparatus having a storage unit for storing a correction coefficient with respect to the reading level, and performing level adjustment of the output signal from the image sensor using the correction coefficient. 2. The image reading apparatus according to claim 1, wherein the adjusting unit includes an irradiation light amount setting unit of the document illuminating unit and a variable amplifying unit that amplifies an output signal from an image sensor.