JPH11220590A - Image reading method and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To read images with no uneven density by keeping the correction data which are introduced based on the data given from a line sensor in a state, set before an image reading operation is started, periodically comparing the data given from the line sensor with the correction data during an image reading operation, and correcting the variance of image data due to the variance of light quantity of an original illumination means, using a 2nd density reference plate. SOLUTION: When an optical system moves to a reading start position, a CPU 1202 fetches the read value of a reference white plate which is set in the vertical scanning direction from an A/D converter 1201 to write the value into a register 1212 and sets the signals 'gate' and 'swoff' to 0 and 1 respectively, so as to control the opening/closing actions of the analog switches 1206 and 1207 by means of the output signal of a comparator 1210. The comparator 1210 compares the latest read value of the reference white plate which is set in the vertical scanning direction that is given from a D-type flip-flop 1211 with the output of the register 1212 and controls both the switches 1206 and 1207. As a result, uneven density of read images can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading method and apparatus for reading a desired image.

[0002]

2. Description of the Related Art In recent years, among flatbed scanners, which are image reading apparatuses that have become widespread as peripheral devices of personal computers, the spread of color scanners has been dramatically improved.

A color scanner includes an R (red) pixel line 30 in a line sensor chip 300 as shown in FIG.
1, G (green) pixel line 302, B (blue) pixel line 3
03, a total of three pixel lines, and the R, G, and B components of the original are read by each pixel line to perform color separation of the original image. Therefore, the amount of data output by the scanner is simply tripled as compared with the conventional monochrome scanner, and the document reading time of the scanner is tripled if the data processing capability of the host computer connected to the scanner does not change. . Generally, a fluorescent tube such as a xenon tube is often used as a light source for illuminating a document used in such a color scanner.

In general, the light quantity characteristics of a fluorescent tube with respect to the time axis are as shown in FIG. That is, when the time t when a predetermined voltage is applied to the fluorescent tube is set to 0, that is, when the light amount at t = 0 is considered as a reference, the light amount increases until a certain time, and thereafter, as shown in FIG. The light quantity gradually decreases, and the light quantity becomes stable after a certain amount of time has elapsed. That is,
In the case of a color scanner, if a document has a uniform density over the entire surface, such as neutral gray, it takes a long time to read, and the difference between the reading density immediately after the start of reading and the reading density immediately before the end of reading is large. There was a defect. Of course, in the case of the conventional monochrome scanner, although there was a difference between the reading density immediately after the start of reading and the reading density immediately before the end of reading, the reading time was short and the density difference was small, so that such a difference was visually confirmed. It was hard to do, and it wasn't a big problem.

For example, in the example of FIG. 5, shading correction is started several seconds (about 5 seconds) after a voltage is applied to the fluorescent tube. At this point, the amount of light of the fluorescent tube shows almost a peak. Assuming that the time required for the conventional printing method is about 30 seconds, the light amount fluctuation between immediately after the start of reading and immediately before the end of reading is indicated by “light amount fluctuation 1”. On the other hand, the color scanner requires about three times the printing time 90 seconds,
The light amount fluctuation between immediately after the start of reading and immediately before the end of reading is indicated by “light amount fluctuation 2”. Obviously, “Light intensity fluctuation 1” <
There is a relationship of “light quantity variation 2”, and the density unevenness when the reading result is viewed is larger in the color scanner, and the reading density unevenness is conspicuous.

In order to solve this problem, a reference white plate is provided in the main scanning direction to correct the output non-uniformity of each pixel of the image sensor, and at the same time, a reference white plate is provided in the sub-scanning direction. A method has been proposed in which, while reading a document image during a reading operation, a reference white plate in the sub-scanning direction illuminated by a document illuminating light source is read at the same time, and the read data is corrected according to the read data of the reference white plate in the sub-scanning direction. ing.

Hereinafter, a method of performing control using such two reference white plates will be described.

FIG. 6 is an external perspective view of the scanner, and FIG.
FIG. 7 is a rear view of the original glass table in the scanner shown in FIG. 6. In FIG. 6, reference numeral 500 denotes a scanner, on which an original glass table 501 on which an original is placed is provided.
A reference white plate 502 is attached to the original glass table 501 in the main scanning direction, and a reference white plate 503 is attached in the sub scanning direction. The two reference white plates 502, 5
Numeral 03 has a role of an index, and a reference abutting position A
The corners of the original. Two reference white plates 502, 5
03 is a uniform white plate having a predetermined whiteness when viewed from the back side.

Next, shading correction using the reference white plate 502 in the main scanning direction will be described with reference to FIGS.

FIGS. 8 and 9 are schematic views of the scanner 500 seen from the side. In both figures, reference numeral 701 denotes an original, reference numeral 702 denotes an original illumination lamp, reference numeral 703 denotes a reflection plate, which reflects the light of the original illumination lamp 702 toward the original 701, reference numeral 704 denotes a first mirror, reference numeral 705 denotes a second mirror, and reference numeral 706.
Is a third mirror, and the light of the original illumination lamp 702 is reflected by these mirrors 704 to 706 toward an image sensor 708 described later. 707 is a lens, and 708 is an image sensor. A first optical unit 709 is configured by the document illumination lamp 702, the reflection plate 703, and the first mirror 704. The second optical unit 710 is configured by the second mirror 705 and the third mirror 706.

In such a configuration, the original 70 illuminated by the original illumination lamp 702 and the reflector 703
The first image is input to an image sensor 708 via a first mirror 704, a second mirror 705, a third mirror 706, and a lens 707, and a line image of the image is read. The first optical unit 709 is moved by a drive system (not shown) in the direction of arrow B in FIG. 8, that is, in the sub-scanning direction, and scans a desired reading range. At the same time as the first optical unit 709, the second optical unit 710 also moves in the direction of arrow B in FIG. 8, and is controlled so that the optical path length is always constant.

When performing shading correction, the first optical unit 709 and the second optical unit 710 are arranged at the positions shown in FIG. 8 and read the image of the reference white plate 502 in the main scanning direction. Although the white density of the reference white plate 502 in the main scanning direction is uniform, the horizontal axis is due to non-uniform sensitivity of each pixel of the image sensor 708, filter characteristics of each pixel of RGB, and uneven illuminance of the document illumination lamp 702. Is the pixel address, and the vertical axis is the output of the image sensor 708.
Reference white plate 502 in the main scanning direction before shading correction
Are as shown in FIG. In the figure, the vertical axis indicates image data in digital values, where 255 indicates the whitest and 0 indicates the blackest. When the shading correction is performed in this state, the reading characteristics of the reference white plate 502 in the main scanning direction after the shading correction are as shown in FIG.

The shading correction is performed by the image sensor 7.
Correction values for all 08 pixels are stored in a RAM (random access memory) not shown. The correction value is calculated from the read value of the reference white plate 502 in the main scanning direction,
For example, if the read value of a certain pixel is 230, the correction value 255/230 = 1.11 corresponds to the RA corresponding to the pixel.
M is written to the address. Then, when the data of the pixel is read, a correction value corresponding to the pixel is read from the RAM, and the pixel data is multiplied by the correction value to perform shading correction.

At the time of such shading correction, if dust or the like is attached to the reference white plate 502 in the main scanning direction,
Since correct shading correction data is not derived, the reading position of the reference white plate 502 in the main scanning direction is usually shifted little by little, and for example, of the five reading values, three points excluding the maximum value and the minimum value are excluded. A method of deriving a shading correction value using an average value is used.

When the shading correction value is calculated, the first optical unit 709 and the second optical unit 710 move to the positions shown in FIG. First optical unit 709 and second optical unit 710
Moves in the direction of arrow B in FIG. 9, line images are sequentially read, and a desired reading range of the document 701 is read.

During reading, the image sensor 708 reads the reference white plate 503 in the sub-scanning direction together with the image of the document 701 placed on the document glass table 501, and corrects the light amount fluctuation during reading. Will be described.

FIG. 12 shows read data immediately after the start of reading, for example, a state of reading a G signal.
In FIG. 12, an area of a range C represents read data of the reference white plate 503 in the sub-scanning direction, and an area of a range D represents data of a document image.

FIG. 13 is a block diagram showing a circuit configuration around the A / D converter. In the figure, reference numeral 1201 denotes an A / D converter; 1202, a CPU (Central Processing Unit); 1203, a time constant circuit, which includes a capacitor 1204 and a resistor 1205. 1206,12
07 is an analog switch, 1208 and 1209 are resistors,
1210 is a comparator, 1211 is a D-type flip-flop, and 1213 and 1214 are OR gates.

The A / D converter 1201 has a terminal Ain
And input analog image data, and output an 8-bit digital image signal from a terminal Dout. The amplitude of the analog image signal is determined by the terminals Vt and Vb. That is, when the voltage applied to the terminal Vt is input to the terminal Ain, ffh = 255 is output, and when the voltage applied to the terminal Vb is input to the terminal Ain, 00h = 0 is output. The voltage applied to the terminal Vb to the voltage applied to the terminal Vt is equally divided into 256 steps, and a digital value of 00h to ffh is output according to the voltage input to the terminal Ain. In the example of FIG. 13, the terminal Vt is connected to the time constant circuit 1203, and the terminal Vb is connected to GND.

The first optical unit 709 and the second optical unit
When the optical unit 710 and the optical unit 710 perform shading correction by the arrangement shown in FIG. 8, the CPU 1202 sets the port signal gate to “1”. gate = 1, OR gate 1
Both the 213 and the OR gate 1214 output “1”, and turn on the analog switch 1206 and the analog switch 1207. In this case, a voltage divided by the resistor 1208 and the resistor 1209 is input to the time constant circuit 1203 including the capacitor 1204 and the resistor 1205.

Assuming that the voltage of the input signal of the A / D converter 1201 when reading the reference white plate 502 in the main scanning direction is about 2 V, the resistance 1208 may be 3 kΩ and the resistance 1209 may be 2 kΩ. Therefore, the time constant circuit 1
A voltage of 2 V is input to 203, and the A / D converter 1201 has a time according to the time constant of the time constant circuit 1203.
2V is input to the terminal Vt. At this point, the read value of the reference white plate 502 in the main scanning direction is approximately ff = 2.
It has a digital value of 55.

When the shading correction processing is completed and the first optical unit 709 and the second optical unit 710 are moved to the positions shown in FIG. 9, the CPU 1202 sets the signal gate to "0", thereby setting the analog switches 1206, 12
The opening and closing of 07 is controlled by the output signal of the comparator 1210.

The output of the A / D converter 1201 is also input to a D-type flip-flop 1211 and the output data is updated at the timing of the sample signal SMP. The sample signal SMP is supplied to the A / D converter 1201
Occurs at the timing when the read value of the reference white plate 503 in the sub-scanning direction is output from the D-type flip-flop 1211. Therefore, the latest read value of the reference white plate 503 in the sub-scanning direction is always output from the D-type flip-flop 1211 during reading. Have been.

To the comparator 1210, the output of the D-type flip-flop 1211 is input to the terminal A,
Is a reference white plate 5 in the sub-scanning direction after shading correction.
A fixed value 254, which is a read value of 03, has been input. Originally, the assumed read value is 255, but 255 is the full scale value of the A / D converter 1201 and is inappropriate as a set value of the control system configured here, so 254 is set to 1 minus 1. . Even if the value is one less than the original set value, the accuracy is only reduced by 1/255 = 0.4%, so it can be said that the effect on the image is small.

The values of the terminals A <B and A> B change depending on the magnitude relationship between the input terminals A and B. If the magnitude relation is as indicated by the terminal name, "1" is output; otherwise, "0" is output.

In the control system configured as described above, the read value of the reference white plate 503 in the sub-scanning direction immediately after the start of document reading is 255 as a digital value as described above. This indicates that approximately 2 V is input as an analog signal. As the reading progresses, the reference white plate 503 in the sub-scanning direction is obtained by the light amount variation characteristics shown in FIG.
Assuming that the voltage corresponding to the read signal of drops to 1.9 V, the instantaneous digital value is 255 × 1.9 / 2 ≒ 24.
2 is output from the A / D converter 1201 and is sampled by the D-type flip-flop 1211. Therefore, the terminal A> B of the comparator 1210 = "0", and the terminal A <B
= “1”, and only the analog switch 1207 is turned on. Therefore, a voltage of 0 V is input to the time constant circuit 1203, and the voltage input to the terminal Vt of the A / D converter 1201 gradually decreases from 2V to 0V according to the time constant. However, when the voltage of the terminal Vt drops to 1.9 V, the digital value 254 is output from the A / D converter 1201 and the D-type flip-flop 1211 is output.
Sampled.

At this time, the terminal A of the comparator 1210
> B = terminal A <B = “0” and analog switch 1
206 and 1207 are turned off. Therefore, the time constant circuit 12
03 enters a floating state, and 1.9 V stored in the capacitor 1204 is input to the terminal Vt of the A / D converter 1201.

Thereafter, if for some reason the voltage corresponding to the read signal of the reference white plate 503 in the sub-scanning direction becomes 1.
When the voltage rises to 9 V or more, for example, to 1.95 V, the instantaneous output of the A / D converter 1201 becomes a digital value of 255.
Is output. The digital value 255 is also sampled by the D-type flip-flop 1211. Therefore, the terminal A> B of the comparator 1210 = “1” and the terminal A <B = “0”
And only the analog switch 1206 is turned on. Therefore, a voltage of 5 V is input to the time constant circuit 1203, and the terminal Vt of the A / D converter 1201 is gradually increased according to the time constant.
, The voltage input to increases from 1.9V toward 5V.

However, when the voltage of the terminal Vt is 1.9 ×
When the voltage rises to 255/254 ≒ 1.91V, A /
A digital value 254 is output from the D converter 1201,
Sampled by the D-type flip-flop 1211.
At this time, terminal A> B of comparator 1210 = terminal A
<B = “0” and the analog switches 1206, 12
07 turns off. Accordingly, the input of the time constant circuit 1203 is in a floating state, and the A / D converter 1203
The terminal 1.t stored in the capacitor 1204 is connected to the terminal Vt.
91V is input.

As described above, by adopting the circuit configuration of FIG. 13, the influence of the light quantity fluctuation is canceled, and the read value of the reference white plate 503 in the sub-scanning direction is always controlled to be 230. The data output of the original image was also uniform, and image reading without unevenness was possible.

[0031]

However, the reference white plate in the main scanning direction and the reference white plate in the sub-scanning direction have not only uniform density but also a uniform white density level for each product lot. In addition, there is a problem that careful management of the manufacturing process is required, and careful management of the members after the manufacturing is required, and the cost is high.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide an inexpensive image reading method and apparatus capable of reading images without unevenness. It is something to offer.

[0033]

According to a first aspect of the present invention, there is provided an image reading method, comprising illuminating an original with original illuminating means, and using a line sensor having a plurality of read pixels arranged linearly. In the image reading method for reading in the main scanning direction and optically reading the original image by moving the reading position in a sub-scanning direction orthogonal to the main scanning direction by a reading position moving means, the main scanning outside the original image reading range is performed. The first reference density plate provided in the direction corrects the output non-uniformity of each pixel of the line sensor and the illumination unevenness of the document illuminating means before the reading of the document image is started, so that the outside of the document image reading range. A second reference density plate provided in the sub-scanning direction corrects a light amount fluctuation of the document illuminating means during a document image reading operation, and outputs data from the line sensor. Alternatively, the correction data guided according to the data is held at a predetermined timing before the start of the reading operation, the data from the line sensor is periodically held at the predetermined timing during the reading operation, and held before the start of the reading operation. The corrected data and the data held during the reading operation are compared, and based on the comparison result, the fluctuation of the image data due to the light amount fluctuation during the reading operation of the original illuminating means using the second reference density plate is determined. It is characterized by correction.

Further, in order to achieve the above object, a second aspect is provided.
The image reading apparatus described above illuminates a document by document illuminating means, reads in the main scanning direction by a line sensor having a plurality of read pixels arranged linearly, and intersects perpendicularly with the main scanning direction by a reading position moving means. In an image reading apparatus for optically reading a document image by moving a reading position in a sub-scanning direction, a first reference density plate provided in a main scanning direction outside a document image reading range; A second reference density plate provided in the sub-scanning direction; and a non-uniform output of each pixel of the line sensor and an illumination unevenness of the document illuminating means before the reading of the document image is started by the first reference density plate. A first control means for controlling the correction of the light amount, and a control for correcting the light quantity fluctuation of the document illuminating means during the document image reading operation by the second reference density plate. Second control means, first data holding means for holding data from the line sensor or correction data derived according to the data at a predetermined timing before the start of the reading operation, and data from the line sensor at a predetermined timing. A second data holding means for periodically holding the data during the reading operation at a timing; a comparing means for comparing the correction data held before the start of the reading operation with the data held during the reading operation; A variation in image data due to a variation in light amount during a reading operation of the document illuminating means using the second reference density plate is corrected based on the comparison result.

In order to achieve the above object, a third aspect is provided.
3. The image reading apparatus according to claim 2, wherein the second reference density plate uses a reference density plate that has been inspected and dropped in a shipping inspection of the first reference density plate. .

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In the present embodiment, description will be given with reference to the drawings described above as necessary.

FIG. 1 is a block diagram showing the configuration of an image reading apparatus according to an embodiment of the present invention. In FIG. 1, the same parts as those in FIGS. 8, 9 and 13 are denoted by the same reference numerals. I have.

In FIG. 1, 708 is a color image sensor, 101 is an analog amplifier (AMP), 1201 is an A / D converter, 102 is a shading correction circuit,
103 is an interface (I / F) circuit.

FIG. 2 shows the A / D converter 1 shown in FIG.
FIG. 2 is a block diagram showing a circuit configuration around 201. In the figure, the same parts as those in FIG. 13 described above are denoted by the same reference numerals.

FIG. 2 is different from FIG. 13 in that one OR gate 1213 and one analog switch 1206 are connected.
And the other OR gate 12
14 and the other analog switch 1207
The gate 202 is inserted, and the port signal s of the CPU 1202 is
The opening and closing of the AND gate 201 and the AND gate 202 are controlled by woff, and the port signal swoff =
When "1", the AND gate 201 and the AND gate 202 are opened, and when the port signal swoff = "0", the AND gate 201 and the AND gate 202 are closed, and both the analog switch 1206 and the analog switch 1207 are turned off. And the output signal of the A / D converter 1201 is C
The configuration is such that a desired image data can be input to the PU 1202 and the register 1212 can be added.

In FIG. 1, the color image sensor 70
The analog image data read by 8 is amplified in the analog amplifier 101 and offset adjustment is performed. Accordingly, the signal amplitude output from the analog amplifier 101 is adjusted so that the black level is 0V and the white level is 2V. The output of the analog amplifier 101 is input to an A / D converter 1201 and is converted into an 8-bit digital signal. Details of the control around the A / D converter 1201 will be described later.

The digital image data output from the A / D converter 1201 is input to a shading correction circuit 102, where shading correction is performed. The algorithm of the shading correction has been described in the section of the above-mentioned “Prior Art”, and thus the description thereof will be omitted.

The image data subjected to the shading correction is input to the interface circuit 103. In the interface circuit 103, the RGB pixel lines 301 to 30 of the color image sensor 708 as shown in FIG.
After correcting the reading position shift occurring due to the distance of each of the two arrangements, for example, the SCSI
(Small computer system interface) is converted into a signal format conforming to the specifications of a general-purpose interface, and the signal is transmitted to an external device such as a host computer.

Next, returning to FIG. 2, the A / D converter 12
The operation around 01 will be described. When the shading correction ends and the first optical system 709 and the second optical system 710 move to the positions shown in FIG. 9, the output of the A / D converter 1201 is input to the CPU 1202. The CPU 1202
The read values of the reference white plate 503 in the sub-scanning direction shown in FIGS. 24 in the reading state of FIG.
0 is that value.

As the reference white plate 503 in the sub-scanning direction, an inexpensive reference white plate which is shipped out because of low whiteness in the inspection of the reference white plate 502 in the main scanning direction is used. Therefore, if the same member as the reference white plate 502 in the main scanning direction is used, the original read value should be 255, but the read value is 240 because the whiteness is low.

Upon recognizing the read value of the reference white plate 503 in the sub-scanning direction, the CPU 1202 stores the read value in the register 12.
Write to 12. Then, the signal gate is set to “0” and the signal swoff is set to “1” at the same time, and the opening and closing of the analog switches 1206 and 1207 are controlled by the output signal of the comparator 1210.

The output of the A / D converter 1201 is also input to the D-type flip-flop 1211 and the output data is updated at the timing of the sample signal SMP. The sample signal SMP is supplied to the A / D converter 1201
Occurs at the timing when the read value of the reference white plate 503 in the sub-scanning direction is output from the D-type flip-flop 1211. Therefore, the latest read value of the reference white plate 503 in the sub-scanning direction is always output from the D-type flip-flop 1211 during reading. Have been.

The output of the D-type flip-flop 1211 is input to the terminal A of the comparator 1210, and the output of the terminal B
Is the output of the register 1212. Terminal A <
For B and terminal A> B, the value of the terminal changes depending on the magnitude relationship between the input terminal A and terminal B. If the magnitude relation is as indicated by the terminal name, "1" is output; otherwise, "0" is output.

In the control system configured as described above, the read value of the reference white plate 503 in the sub-scanning direction immediately after the start of document reading is 240 as a digital value as described above. This is an analog signal of 2V × 240/255 ≒ 1.8V
Indicates that is input. Assuming that the voltage corresponding to the read signal of the reference white plate 503 in the sub-scanning direction drops to 1.7 V due to the light amount fluctuation characteristic shown in FIG. 5 as the reading progresses, the instantaneous digital value becomes 2
55 × 1.7 / 2 ≒ 216 is the A / D converter 1201
And is sampled by a D-type flip-flop 1211. Therefore, the terminal A of the comparator 1210>
B = “0”, terminal A <B = “1”, and only the analog switch 1207 is turned on. Therefore, the time constant circuit 12
03 is supplied with a voltage of 0 V, and A /
The voltage of the terminal Vt of the D converter 1201 is changed from 2V to 0V.
Descend toward. However, when the voltage at the terminal Vt drops to 1.7 × 255/230 ≒ 1.88 V, the digital value 230 is output from the A / D converter 1201 and is sampled by the D-type flip-flop 1211.

At this time, the terminal A of the comparator 1210
> B = terminal A <B = “0” and analog switch 1
206 and 1207 are turned off. Therefore, the time constant circuit 12
03 is in a floating state, and 1.88 V stored in the capacitor 1204 is input to the terminal Vt of the A / D converter 1201.

Thereafter, if for some reason the voltage corresponding to the read signal of the reference white plate 503 in the sub-scanning direction becomes 1.
When the voltage rises to 7 V or more, for example, to 1.75 V, the instantaneous output of the A / D converter 1201 is a digital value 237.
Is output. The digital value 237 is also sampled by the D-type flip-flop 1211. Therefore, the terminal A> B of the comparator 1210 = “1” and the terminal A <B = “0”
And only the analog switch 1206 is turned on. Therefore, a voltage of 5 V is input to the time constant circuit 1203, and the terminal Vt of the A / D converter 1201 is gradually increased according to the time constant.
, The voltage input to increases from 1.88V to 5V.

However, when the voltage at the terminal Vt is 1.75.
× 255/230 ≒ At the time when the voltage rose to 1.94V, A
The digital value 230 is output from the / D converter 1201 and is sampled by the D-type flip-flop 1211. At this time, the terminal A> B of the comparator 1210 = the terminal A <B = “0”, and the analog switches 1206 and
1207 turns off. Accordingly, the input of the time constant circuit 1203 is in a floating state, and the A / D converter 1
1.94V stored in the capacitor 1204 is input to the terminal Vt of 201.

As described above, by adopting the circuit configuration of FIG. 2, the influence of the light quantity fluctuation is canceled, and the reading value of the reference white plate 503 in the sub-scanning direction is always controlled to be 230. The data output of the original image is also uniform, and the image can be read without unevenness.

The reading by the scanner is started /
Controlled by stop control, reading may be interrupted during reading due to data processing in the host computer. If the CPU 1202 in FIG. 2 controls all the operations in a single chip in a scanner embodying the present invention, the CPU 1202 receives an instruction to interrupt reading from an external device, for example, and executes a reading interrupting operation to each control unit. Let it. For example, the operation of the mechanic drive system by the motor (not shown) of the scanner is stopped. At the same time,
The signal swoff is set to “0” and the analog switch 120
6 and the analog switch 1207 are turned off, and the input of the time constant circuit 1203 is set to the floating state.

By performing such control, the reference white plate 50 in the sub-scanning direction when the scanner stops.
Even if dust or the like is attached to the reading position on
Since the voltage value input to the terminal Vt of the / D converter 1201 is fixed, the time constant circuit
03, that is, a voltage drop of the voltage value input to the terminal Vt can be prevented.

Thereafter, when the start operation of the scanner is started again, the CPU 1202 sets the signal swoff to "1".
Then, the analog switch 1206 and the analog switch 1207 are controlled by the output signal of the comparator 1210.

If the CPU used in the scanner
Is a master C using the CPU 1202 as a slave CPU.
When the PU is configured separately, for example, when the master CPU receives an instruction to suspend reading from an external device, an interrupt signal is transmitted from the master CPU to the slave CPU, and the slave CPU performs the above control. You can do it. Since the control is performed after receiving the interrupt signal, the control takes a longer time compared to the configuration of the one-chip CPU, but the time constant of the time constant circuit 1203 is enormous compared to the bus cycle of the CPU in recent years. Therefore, it can be considered that there is no difference in effect due to the difference in the configuration of the CPU.

As described above, according to the image reading apparatus of this embodiment, the original illumination lamp 702 of the scanner fluctuates in the light amount during reading and the reference white plate 5 in the sub-scanning direction.
Even if dust or the like adheres to the surface 03, unevenness in the density of the read image can be prevented, and the quality of the image read by the scanner can be improved. In addition, the reference white plate 503 in the sub-scanning direction is inexpensive because a reference white plate darker than the reference white value that has been inspected and dropped in the shipping inspection of the reference white plate 502 in the main scanning direction is used.

[0059]

As described in detail above, according to the image reading method and apparatus of the present invention, the original illuminating lamp 70 of the scanner is used.
2 can prevent unevenness in the density of the read image and improve the quality of the image read by the scanner even if the light amount fluctuates during reading and dust or the like adheres to the reference white plate 503 in the sub-scanning direction. be able to. Further, since the reference density plate in the sub-scanning direction uses a reference density plate darker than a reference value which has been inspected and dropped in the shipping inspection of the reference density plate in the main scanning direction, it has an effect of being inexpensive.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image reading apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration around an A / D converter in the image reading apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a state of an image signal after reading is started in the image reading apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a color image sensor in a general image reading device.

FIG. 5 is a view showing a light amount variation characteristic of a fluorescent tube in a general image reading apparatus over time.

FIG. 6 is an external perspective view illustrating a configuration of a scanner that is a general image reading apparatus.

FIG. 7 is a back view of a platen glass in a scanner which is a general image reading apparatus.

FIG. 8 is a diagram illustrating an optical system at the time of shading correction of a scanner that is a general image reading apparatus.

FIG. 9 is a diagram illustrating an optical system of a scanner, which is a general image reading apparatus, when reading of a document is started.

FIG. 10 is a diagram illustrating a state of a signal before shading correction in a scanner that is a general image reading apparatus.

FIG. 11 is a diagram illustrating a state of a signal after shading correction in a scanner that is a general image reading apparatus.

FIG. 12 is a diagram illustrating a state of an image signal after reading is started in a scanner that is a general image reading apparatus.

FIG. 13 is a block diagram illustrating a configuration around an A / D converter in a scanner that is a general image reading apparatus.

[Explanation of symbols]

 Reference Signs List 101 analog amplifier 102 shading correction circuit 103 interface (I / F) circuit 201 AND gate 202 AND gate 500 scanner 501 document glass table 502 reference white plate in main scanning direction 503 reference white plate in sub scanning direction 701 document 702 document illumination lamp 703 Reflector 704 First mirror 705 Second mirror 706 Third mirror 707 Lens 708 Image sensor 709 First optical unit 710 Second optical unit 1201 A / D converter 1202 CPU (central processing unit) 1203 Time constant circuit 1204 Capacitor 1205 Resistance 1206 Analog switch 1207 Analog switch 1208 Resistance 1209 Resistance 1210 Comparator 1211 D-type flip-flop 1212 Register 1 13 OR gate 1214 OR gate

Claims (3)

[Claims] An original is illuminated by an original illuminating unit, and reading is performed in a main scanning direction by a line sensor having a plurality of read pixels arranged in a straight line. In the image reading method for optically reading the document image by moving the reading position in the direction, the first reference density plate provided in the main scanning direction outside the document image reading range, before starting reading the document image. The output non-uniformity of each pixel of the line sensor and the illumination unevenness of the original illuminating means are corrected, and a second reference density plate provided in the sub-scanning direction outside the original image reading range is used during the original image reading operation. The light amount fluctuation of the document illuminating means is corrected, and the data from the line sensor or the correction data derived according to the data is read at a predetermined timing. Holds data before the start of operation, periodically holds data from the line sensor during a read operation at a predetermined timing, and compares the correction data held before the start of the read operation with the data held during the read operation. And an image reading method for correcting a change in image data due to a change in light amount during a reading operation of the document illuminating means using the second reference density plate based on the comparison result. An original illuminating means for illuminating the original, reading in a main scanning direction by a line sensor having a plurality of read pixels arranged in a straight line, and sub-scanning orthogonal to the main scanning direction by a reading position moving means; A first reference density plate provided in a main scanning direction outside a document image reading range, and a sub-scanning plate outside a document image reading range. The second reference density plate provided in the direction and the first reference density plate correct the output non-uniformity of each pixel of the line sensor and the illumination unevenness of the document illuminating means before the reading of the document image is started. And a second control means for controlling the second reference density plate to correct the light quantity fluctuation of the original illuminating means during the original image reading operation. Control means, first data holding means for holding data from the line sensor or correction data derived according to the data at a predetermined timing before starting the reading operation, and reading data from the line sensor at a predetermined timing A second data holding unit that periodically holds during the operation, a comparison unit that compares the correction data held before the start of the reading operation with the data held during the reading operation, and a comparison result of the comparison unit. An image reading device for correcting a change in image data due to a light amount change during a reading operation of the document illuminating means using the second reference density plate based on the second reference density plate. 3. The image reading apparatus according to claim 2, wherein the second reference density plate uses a reference density plate that has been inspected and dropped during shipping inspection of the first reference density plate.