JP2644487B2 - Image reading device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus that reads a document in pixel units.

(Prior art)

In a facsimile, digital copier, etc., an original is exposed by a light source such as a fluorescent lamp, and the intensity of light reflected from the original is detected by a CCD image sensor or the like to read the original image photoelectrically, and an electrical image signal is output. An image reading device that obtains the following is known.

In such an apparatus, the amount of light emitted from the light source for exposing the document affects the image signal, so that it is necessary to adjust the light so that the amount of light becomes optimal.

As dimming of this type of image reading apparatus, a standard white plate as a reference of the white level is arranged outside the original reading area, and the amount of electricity supplied to the light source so that the data read from the white plate becomes a reference white signal. Has been made to control.

Further, the output of reading an image with a uniform density by the CCD image sensor may not be uniform due to unevenness of the illuminance distribution of the light source, transmission characteristics of the lens, and sensitivity variation of the CCD image sensor. This state is called shading, and in order to correct this, a read signal of an original image is electrically corrected based on an output obtained by reading a standard white plate having a uniform density by a CCD image sensor.

In an apparatus having such a light control function and a shading correction function, a common standard white plate is often used for both functions.

However, there is a problem in that the white level of the standard white plate, particularly the white level having a reflection density of 0.1 or less, is costly because the density control is difficult in manufacturing. Furthermore, even when the device is assembled by controlling this white level, the reflection density of the standard white plate changes due to temperature, humidity, impurities contained in the device and cooling air, discoloration due to temporal changes due to infrared rays and ultraviolet rays of the illumination system, and darkening. There is a problem that the white level of the output image cannot be guaranteed.

Conventionally, when performing shading correction, in order to treat a standard density plate whose density is not controlled as standard white, the shading data is read by increasing the light emission amount of illumination. However, in this method, accurate dimming must be performed so as to obtain a reference white level at the time of reading the shading data. there were.

〔Purpose〕

The present invention has been made in view of the above points, and an image reading apparatus configured to remove non-uniformity of an image signal obtained by reading a document image based on an output obtained by reading a white reference member. Irrespective of the variation in the density of the members and the change with time, the purpose of the present invention is to remove the non-uniformity of the image signal satisfactorily and always obtain a uniform image signal output. Reading means for reading a document image placed on a platen and outputting an image signal; a white reference member serving as a reference for measuring unevenness of the output of the reading means; and reading the white reference member by the reading means. Detecting means for detecting a difference between the output obtained by the reading means and the output obtained by reading the white document of the reference density placed on the platen by the reading means, and a document image placed on the platen. Obtained by reading by the reading means It is an object of the present invention to provide an image reading apparatus having a removing means for removing unevenness of an image signal based on an output obtained by reading the white reference member by the reading means and a difference detected by the detecting means. .

〔Example〕

 Hereinafter, the present invention will be described using preferred embodiments.

FIG. 1 is a schematic diagram of a document reading apparatus to which the present invention is applied. Document platen glass 101
An image sensor 103 such as a CCD having a plurality of light receiving elements arranged in the main scanning direction is used to read the document information of the document 102 placed thereon, and the illumination light from the illumination 104
The lens 10 is reflected on two surfaces and passes through mirrors 105, 106 and 107.
An image is formed on the image sensor 103 by 8. Lighting 104, Mirror 10
The optical unit 113 composed of 5 and the optical unit 114 composed of the mirrors 106 and 107 move at a relative speed of 2: 1. The optical unit moves from left to right at a constant speed while performing PLL control by the DC servo motor 109. This moving speed is variable from 22.5 mm / sec to 360 mm / sec depending on the magnification on the outward path, and is always 800 mm / sec on the return path.

The optical unit is read from the home position at the left end while reading the main scanning direction (hereinafter referred to as Y direction) orthogonal to the sub-scanning direction (hereinafter referred to as X direction) in which the optical unit moves at a resolution of 400 dots / inch by the image sensor. After moving to the right to a predetermined position, it is moved back to the home position again to complete one scan. As a result, the entire area of the original is read and scanned line by line. Reference numeral 111 denotes a light-shielding plate. The light-shielding plate 111 crosses a home position sensor 110 composed of a photo interrupter, thereby detecting that the optical unit is located at the home position. Reference numeral 112 denotes a standard density plate. The standard density plate 112 is used for shading correction and light amount control of the illumination 104. The detection position of the home position sensor 110 is the reading position of the standard density plate 112.

FIG. 2 shows an example of the configuration of an image processing block in the original reading apparatus shown in FIG.

In this embodiment, a fluorescent lamp is used as the illumination 104, and the light is controlled by the light source light amount control unit 201 by a high frequency lighting time control method using a thyristor or the like.

The reading surface 202 reflects the light from the illumination 104 and has document density information read by the CCD line sensor 103. The movement of the optical unit causes the standard density plate 112,
The document 102 becomes a reading surface.

An analog image signal for each line read by the CCD 103 is amplified by an amplifier 203, and then is converted to a multi-valued (8-bit in this embodiment) digital image signal 21 by an A / D converter 204.
It becomes 6.

In this embodiment, the black level of the document is read as "0" and the white level is read as "255". The black reference level and the white reference level of the A / D converter are given fixed values, the illumination 104 is completely turned off, and the output of the A / D converter is completely black when no light enters the CCD 103. The offset of the amplifier 203 is adjusted to be at the level.

The CCD drive signal generation circuit 205 is a CCD signal for reset signal, clock signal, horizontal synchronization signal, etc. necessary for driving the CCD 103.
A drive signal 206 is generated, a clock signal 207 to the A / D converter 204 is generated, and a CCD address 208 which is an address signal for identifying each bit of the CCD is generated. In this embodiment, since the CCD 103 uses a 5000 pixel line sensor, the CCD address is up-counted from 0 to 4999 corresponding to the 5000 pixels read out in synchronization with the horizontal synchronization signal.

Reference numeral 209 denotes a shading data RAM for storing all pixels of the digital image signal for one CCD line from the A / D converter 204
It is.

The address selector 210 is a shading data RAM 209.
Selector for the address signal 211 given to the CPU circuit
With the address switching signal 213 from 212, the CCD address 208
Switching between the CPU address from the address bus 214 of the CPU circuit unit.

The shading correction table RAM 215 is a table for correcting non-uniformity of the read image signal 216 due to uneven light distribution included in the illumination 104 and the lens 108, sensitivity unevenness of each pixel of the CCD 103, an amplification degree setting error of the amplifier 203, and the like. The correction table data is written by the CPU 212 prior to the original reading operation, and the shading data RAM 209 is read at the time of the original reading.
Based on the shading data 217 and the read image signal 216, the correction table RAM 215 is addressed to obtain an image signal 218 in which the read image signal 216 has been corrected for non-uniformity.

Address selector 219 is a shading correction table R
The selector of the address 220 given to the AM 215 switches an address including the CPU address 214, the read image signal 216, and the shading data 217 in accordance with an address switching signal 221 from the CPU 212.

The motor driver 223 performs forward / reverse control and speed control of the optical system drive motor 109.
The forward / reverse / speed data is received from 222, and drive control of the motor 109 is performed using PLL control by an encoder pulse signal 224 synchronized with the motor rotation from the DC servo motor 109. The encoder pulse signal 224 is provided to the CPU 212, and the CPU 212 detects the scanning position of the optical system by counting the encoder pulse signal 224. The home position sensor 110 is a sensor composed of a photo interrupter, is fixed to the reading area of the standard density plate 112, and detects that the light shielding plate 111 fixed to the illumination system 104 is at the location of the home position sensor 110. If detected, scanning surface 1
04 is the standard concentration plate.

The CPU 212 is composed of a micro computer with a built-in ROM storing a control procedure program, a working RAM, an arithmetic unit, and the like, and performs sequence control, image data correction processing, illumination system light amount control, and control of the operation unit of the present embodiment.

The detailed configuration of the operation unit 225 is shown in FIG. This operation unit is C
Under the control of PU212, key input capture and display operation are performed. Reference numeral 301 denotes a key for starting the light control value measurement mode.
02 indicates that the dimming value measurement mode is being executed.
D. Reference numeral 303 denotes a key for starting a reading operation mode of the document 102 placed on the document table 101, and reference numeral 304 denotes an LED that indicates that the document reading mode is being executed.

Reference numeral 305 denotes a key for further setting the measured dimming value to be brighter. Pressing this key increases the dimming value display of the 307. Reference numeral 306 denotes a key for further setting the measured dimming value to be darker. Pressing this key decreases the dimming value adjustment display of 307. The display unit of the dimming value adjustment display of 307 is 1 LSB of the A / D converter 204, and the value displayed here is stored in a battery backup memory (not shown) included in the CPU 212 even when the power of the apparatus is turned off. It is displayed again when the power is turned on again.

With the above configuration, this embodiment has two operation modes. One is to adjust the illumination 104 so that the read image signal 216 from the document whose reflection density is controlled becomes a constant value, and measure the read image signal value 216 from the standard density plate 112 at that light amount. It is a light value measurement mode. The other is to adjust the illumination 104 so that the read image signal value from the standard density plate 112 becomes a value measured in the dimming value measurement mode.
This is a document reading mode in which the upper document 102 is read and scanned, and an image signal 218 corrected for shading is output.

 Hereinafter, these two operation modes will be described.

[Dimming value measurement mode]

As a preparation for the light control value measurement mode, a document 401 is placed on the platen glass 101 as shown in FIG. In this embodiment, as the original 401 whose reflection density is controlled, an A3 size standard white paper immediately after opening, for example, a stack of ten A3 size white papers whose reflection density is controlled to 0.07 is used. Therefore, the reflection density from the document 40 is about 0.07, which is considered as standard white.

After this setup, when the operator inputs the dimming value measurement switch 301 shown in FIG. 3, the CPU 212 turns on the dimming value measurement display 302 and executes the dimming value measurement mode shown in FIG.

In step 501, the original reading surface 202 is
In order to make the original 401 placed on the 101, the optical unit 113
From the position of the home position sensor 110 toward the original 10 cm. At this time, the CPU 212
The stop position of the optical system is determined by counting 2000 encoder pulses of 0.05 mm per pulse.

Next, in step 502, the lighting 104 is turned on to perform A / D
Dimming the lighting 104 so that the converter output 216 becomes "240" (standard dimming). The reason why the standard white is not set to the full-range output of the A / D converter is 255 in order to read a document having a reflection density of 0.07 or less. This is for performing accurate reference dimming while avoiding the use of the output saturation state of the / D converter.

In order to read the A / D converter output 216, the shading data RAM 209 is used.

First, the A input of the address selector 210, that is, the CCD address 208 is selected and set as the address of the shading data RAM 209. Then, light amount data for one CCD line from the reference white document at a certain light amount is written in the RAM 209.

Next, by using the B input of the address selector 210, that is, the address bus 214 of the CPU 212 as the address of the RAM 209, and reading the data written in the RAM 209 by the data bus 222, the CPU 212 measures the light amount data.

Here, the CPU 212 sets 50
The data of the eight pixels at the center, that is, the data of eight consecutive pixels from the 2497th pixel to the 2504th pixel in the data of the 00 pixel CCD licensor 103 are averaged to obtain light amount data.

Then, while increasing or decreasing the illumination light amount data for the light amount control unit 201 so that the light amount data becomes 240,
Repeat writing data to 9 and reading data.

As a result, when the illumination light emission amount at which the light amount data becomes 240 is determined, the optical unit 104 is moved to the home position sensor position in step 503 while maintaining the illumination light emission state, and the standard density plate is determined in step 504. The light amount data from 112 is read from RAM 209. More than 50 steps
A series of operations from 1 to 504 are repeated six times in step 505, and the light amount data from the standard density plate 112 is measured six times.

Next, in step 506, the average value of the four light quantity data obtained by removing the maximum value and the minimum value of the six light quantity data is determined, thereby determining the light control target value in the standard density plate 112.

By setting the light intensity data reflected from the standard density plate to this dimming target value during actual document reading, the reflection density of the document is
0.07 is always “240” in A / D conversion output 216
Will be read with the value.

This dimming target value is stored in a predetermined address of the non-volatile memory that has been backed up in step 507, and a code indicating that the storage has been completed is written. Then, in step 508, the light control value measurement display 302 is turned off, and the light control value measurement mode ends.

Since the light control target value means the ratio of the amount of reflected light between the standard density plate 112 and the standard white 401, when the standard density plate is replaced or the density of the standard density plate changes due to aging, this light control target value is used. Need to execute value measurement mode.

(Image Reading Mode) FIG. 6 shows an operation flow in the image reading mode.

The CPU 212 detects that there is an input from the image reading SW 303 of the operation unit 216, and turns on the image reading display 304.

Next, it is checked in step 601 whether or not the dimming target value in the dimming value measurement mode is set based on the code written in step 507 indicating that the storage is completed. As a result, when the light control target value is not set, the image reading display is blinked in step 602, and a fixed value programmed in advance is used as the light control target value. As the fixed value, a value corresponding to the most frequently used density in the production of the standard density plate is used.

As described above, after the dimming target value or the fixed value in the dimming value measurement mode is adopted as the dimming target, the step 603 is performed.
Then, the shading correction table RAM 215 is written.

In the present embodiment, the shading correction is performed by adjusting the standard density plate output of each pixel of the CCD licensing sensor from the idea of ensuring the standard white of the document by setting the amount of reflected light data from the standard density plate 112 to the dimming target value. Light amount data correction is performed so as to reach the target value.

 FIG. 7 shows a shading correction method.

In this figure, a shading correction is performed on a pixel having a CCD whose standard density plate output is S, and a light control target value N is obtained as a correction output. The horizontal axis is the A / D conversion output before correction, and the vertical axis is the value subjected to shading correction.

When the shading correction is not performed, since the input and output values are a straight line having a slope of 45 ° where the input value and the output value are equal, the pixel of the standard density plate output S is added with the correction amount (N-S) for reading from the standard density plate. Become. In general, the CCD licensor 103 is a device that generates a linear output with respect to the amount of light,
In FIG. 7, the correction amount for the original image read at the value of x is Becomes

 Therefore, the correction output y is given by the following equation.

The shading correction table RAM 215 for outputting the result of the correction operation is configured as shown in FIG. 9, and receives the shading data S of the standard density plate from the upper address and reads the corrected original read in the shading state from the lower address. A signal is input.

Therefore, the CPU 212 selects the B input of the address selector 219 in step 603, and uses the dimming target value N determined in steps 601 and 602, to output the correction output y in all combinations of the shading data S and the original reading signal x. Is written into the shading correction table RAM 215. Then, the A input of the address selector 219 is selected.

Next, the CPU 212 dims the light amount of the illumination 104 to the dimming target value, and moves the optical unit 113 to the position of the home position sensor 110 in order to read the shading data S from the standard density plate 112.

Next, the illumination 104 is turned on in step 605, and light control is performed so that the maximum value of the read signal of one line of the standard density plate becomes the light control target value N.

For this purpose, first, the light amount data read from the standard density plate 112 is written into the shading data RAM 209 using the CCD address 208 with appropriate illumination light amount data.

Next, the CPU 212 supplies the address bus 214 to the shading data RAM 209 by the B input of the address selector 210, and the data at the address corresponding to all the bits of the CCD has reached the saturation level “255” of the A / D converter 204. Check for any. If there is a bit that has reached "255", the illumination light amount data given to the light amount control unit 201 is reduced, the light amount data read from the standard density plate 112 is again written to the shading data RAM 209, and the saturation level is written. Find out if you have reached. After confirming that all the bits have not reached the saturation level in this way, a bit (light control point) indicating the maximum level is searched for.

 The above operation is called a dimming point search.

Next, dimming is performed by the same data sampling operation and illumination light amount data operation such that the average value of eight consecutive pixels including the dimming point substantially at the center becomes the dimming target value N.

Next, in step 606, the shading data S of the standard density plate 112 in the illumination state is written in the shading data RAM 209.

Next, in step 607, the shading correction is performed as the S input and the x input of the shading correction table RAM 215 by using the shading data 217 and the original read image 216 read out from the shading data RAM 209 in synchronization with each CCD. While outputting the output 218, the optical unit 113 is x
Document scanning is performed by sub-scanning at a predetermined speed in the direction.

FIG. 8 shows the shading correction at this time.
That is, since the maximum value of the shading data S from the standard density plate is adjusted so as to become the dimming target value N as shown in FIG. 8 (a), the standard density plate of all the bits of the CCD is subjected to the shading correction. The output becomes N uniformly as shown in FIG. 8 (b), and the original reading signal x becomes a y signal not including shading.

Here, when the shading data S is written into the shading data RAM 209, even if the dimming of the illumination system is insufficient as shown in FIGS. 10 (a) and (b), reading from the standard density plate is performed. The value is used as the shading data, and the original is read in the same dimming state. Therefore, information of the same density as that of the standard density plate on the original always becomes the dimming target value N.

This is because, as is clear from FIG. 7, the shading correction works so as to guarantee the degree of the density of the standard density plate with respect to the reference white density measured in the dimming value measurement mode by a digital signal value. By performing accurate light control in the value measurement mode and accurately measuring the relationship between the reference white density and the density of the standard density plate as the light control target value N, the light control during document reading may be slightly rough.

As described above, in this embodiment, uniform document reading is performed without shading whose density is controlled from the reference black to the standardized white level, but the step is performed using the key inputs 305, 306 and the display 307 in FIG. By adjusting the dimming target value used in 606, the level on the white side of the read image can be adjusted. In other words, by setting the light control level when reading the document higher than the value measured in the light control value measurement mode, the standard document white level becomes equivalently higher, so that the document is read brighter, and by lowering the measured value. The manuscript is read dark.

The key input to enlarge (brighten) is 305,
The key input for reducing (darkening) is 306. CPU21
2 displays a dimming value adjustment display 307 by this key input. The display unit is the minimum resolution level of the A / D converter 204. When increasing, a plus display is performed, and when decreasing, a minus display is performed.

In step 602 in this embodiment, when the light control target value is not set, the reading operation is not performed, and the operator can be alerted by blinking the display.

Further, the present invention is not limited to reading an image using a black-and-white signal. If the standard density plate is configured to reflect white light as white light of a certain density, reading using a color signal is also applicable, and high reflection for light of a specific wavelength is possible. It may have characteristics.

If the dimming value variable operation is performed based on the result of the ground density detecting means of the original by prescanning or the like, the effect of automatic ground skipping can be obtained. In this case, prescanning is performed with a predetermined dimming value, a histogram for each light amount data in the vicinity of white is created, light amount data from the background is obtained, and the light amount data W
By changing the dimming target value N using only N 'shown in the following equation so that the target dimming value becomes the reference white level 240, and scanning the original, the automatic ground skipping is also possible.

The writing of the correction data into the shading correction table RAM 215 does not need to be performed each time the image reading SW 303 is input, but may be performed once when the power of the apparatus is turned on.

According to the configuration of the present embodiment described above, the ratio of the density of the standard density plate to the standard white document is measured using the standard density plate for which the density management is not strict, and the ratio of the density is read when the document is read. In order to ensure shading correction, light adjustment for each document reading may be performed roughly in a relatively short time, so that the document reading time is shortened and the light emission state of the illumination and the density of the standard density plate vary. In addition, uniform original reading with a guaranteed white density can always be performed, and the light source light amount control unit, the density of the standard density plate, and the like do not need to be high-precision, and the cost of the apparatus is reduced.

(Effect)

As described above, according to the present invention, non-uniformity of the image signal obtained by reading the original image is not removed based on only the output obtained by reading the white reference member, but the white reference member is read. The difference between the output obtained by reading the white original of the reference density placed on the platen and the output obtained by
Non-uniformity of the image signal is removed based on the output obtained by reading the white reference member and the detected difference. This makes it possible to always obtain a uniform image signal output.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of an image reading apparatus, FIG. 2 is an electric signal processing block diagram, FIG. 3 is a diagram showing an operation unit controlled by a CPU 212, and FIG. FIG. 5 is a flowchart of the light control value measurement mode, FIG. 6 is a flowchart of the original reading mode, FIG. 7 is a diagram showing a method of shading correction, FIG. 8 and FIG. Fig. 9 is a schematic diagram of the shading correction. Fig. 9 is an input / output diagram of the shading correction table RAM.
D) and 104 are illumination, 112 is a standard density plate, 201 is a light source light amount control unit, 209 is a shading data RAM, and 212 is a CPU.

Claims (1)

(57) [Claims] A document table on which a document is placed; reading means for reading a document image placed on the document table and outputting an image signal; and a reference for measuring unevenness of the output of the reading means. A difference between an output obtained by reading the white reference member by the reading unit and an output obtained by reading the white original having a reference density placed on the platen by the reading unit. Detecting means for detecting the non-uniformity of an image signal obtained by reading the document image placed on the document table by the reading means, by using the output obtained by reading the white reference member by the reading means and the detecting means An image reading device, comprising: a removing unit that removes based on the detected difference.