JP2001285582A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader that can prevent uneveness in image density and color slurring by stabilizing the light quantity of light from a light source, without increasing the cost. SOLUTION: The image reader is provided with an image signal output means, that employs an image sensor (CCD sensor 3), having linearly arranged pixels to read light reflected from an original and to provide an output of an image signal, and also with a light quantity change correction means (CPU 6 or the like), that corrects the change in the light quantity in a scanning standby state from a scanning stop until scanning restart, when the image signal output means repeats the scanning stop and the scanning restart to read the image information of an original corresponding to one screen worth.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus such as a scanner for reading an image by scanning an original with a line CCD sensor.

[0002]

2. Description of the Related Art Conventionally, there has been known an image reading apparatus provided with a fluorescent lamp as a light source for illuminating an original, and capable of obtaining image information by reading reflected light from the original with a line scanning type image scanner. ing. In such a conventional image reading apparatus, output data becomes uneven due to a difference in light amount distribution in the main scanning direction generated when a uniform original is read, an individual difference between pixels of a CCD sensor, and the like. May be. The non-uniformity of the output data has been solved by performing shading correction.

The amount of data output by a color scanner is extremely large. For example, if an A4 original is output at 300 dpi, 8 bits for each of R, G, and B colors, about 26 Mbytes of information in total is output. Amount. When such an enormous amount of information is reached, data for one screen cannot be stored in the buffer.
Therefore, the image reading operation of the scanner is restricted by the data transfer speed of the scanner to and from other devices that transfer information, the data processing capability of the device that receives data, and the print processing capability of an inkjet printer or the like.
If the processing speed and processing capability of another device to which the scanner transfers information is low, the scanner cannot follow the amount of image information generated from the scanner. For this reason, the scanner must temporarily suspend the scanning operation and wait until the processing of another device catches up.

Further, when a fluorescent lamp is used as a light source, the amount of light immediately after the power is turned on is not stable. Therefore, when a scan is temporarily stopped when reading a document, the output of image reading data before and after the scan is stopped. The value changes, and image quality degradation such as density unevenness and color shift occurs.

To solve such a problem of image quality deterioration, the image reading method and the image reading apparatus disclosed in Japanese Patent Application Laid-Open No. H11-220589 disclose a shading plate in the sub-scanning direction on the back surface of the platen glass of the platen. Is attached, and the gain value of the A / D converter is controlled so that the read output value of the CCD sensor in this portion becomes constant, thereby improving the image quality.

[0006]

In general, when transferring the output from a color scanner to another device, in addition to the time required for the interface handshake,
Requires data processing time for the device receiving the data.
In particular, when a printing process such as an ink jet printer is included, the printing process time must be included.
Unable to predict data processing time. For this reason,
It is necessary to provide a buffer inside the scanner and stop taking in the data when the buffer becomes full, which causes a problem of data continuity when data re-reading is started.

If the wall temperature of the fluorescent tube, which is a light source, is low while the reading operation is on standby, the amount of lamp for illuminating the document slightly changes. For this reason, if the scan is restarted without considering the change in the amount of ramp light, the image read data before and after the stop of the scan becomes discontinuous, and as a result, problems such as uneven density and color shift may occur. .

In the technique disclosed in Japanese Patent Application Laid-Open No. H11-220589, it is necessary to attach a shading plate in the sub-scanning direction on the rear surface of the platen glass of the document table, and there is a problem that the cost increases.

The present invention has been proposed in view of the above-described circumstances, and is capable of preventing unevenness in image density and color shift by stabilizing the amount of light from a light source without increasing costs. It is an object to provide a reading device.

[0010]

The image reading apparatus according to the present invention has the following features in order to achieve the above object.

That is, an image reading apparatus according to the present invention outputs an image signal by reading reflected light from the original using a light source for illuminating the original and an image sensor having a plurality of pixels arranged in a line. An image signal output means for performing the scanning and the sub-scanning means for moving the image signal output means in a sub-scanning direction orthogonal to the main scanning direction. When reading the image information of the original for one screen by repeating stop, scan, and restart, a light amount change correction unit is provided for correcting a light amount change during a scan standby from a scan stop to a scan restart. It is characterized by the following.

The light amount change correction means compares the output value of the image sensor at the time of scanning stop with the output value of the image sensor at the same position as that at the time of scanning stop, which is read during the scan standby. It is characterized by including light amount detecting means for detecting a change in light amount.

The output value of the image sensor is
It is characterized by using output data of several pixels at a predetermined position in the main scanning direction.

The output value of the image sensor is
It is characterized by using output data of one line in the main scanning direction.

The output value of the image sensor is:
It is characterized by using output data of specific components of RGB components or an average value of output data of each component.

Further, the light quantity change correction means controls the light quantity of the light source at the time of scanning stop and at the time of scanning standby to be constant, so that the light quantity at the time of scanning standby from scanning stop to scanning / restarting is maintained. It is characterized in that the change is corrected.

Further, the light quantity change correction means controls the voltage applied to the light source to keep the light quantity during the scan standby constant.

Further, the light quantity change correcting means controls the current of the light source to keep the light quantity during the scan standby constant.

Further, the light quantity change correcting means includes a temperature detecting means for detecting a surface temperature of the light source, and uses a light quantity correction coefficient based on a temperature output value of the temperature detecting means to perform the scan standby during the scan. It is characterized in that the light amount is kept constant.

Further, the light quantity change correcting means controls the gain value when A / D converting the output value of the image sensor to keep the light quantity during the scan standby constant. It is.

Further, the light quantity change correction means is adapted to output an A value corresponding to the output value of each of the RGB components of the image sensor.
By controlling the gain value for each component of the / D converter, the light amount during the scan standby is kept constant.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image reading apparatus according to the present invention will be described below with reference to the drawings. Here, as a typical image reading apparatus, a flat head type scanner capable of reading a color image will be described as an example.

<Schematic Configuration of Scanner> FIG. 1 is a block diagram schematically showing the configuration of a scanner according to an embodiment of the present invention, and FIG. 2 is an array diagram of a color CCD sensor which is a component of an optical unit. It is.

As shown in FIG. 1, a scanner according to an embodiment of the present invention includes a lamp 1 composed of a fluorescent lamp for illuminating a document, an inverter 2 for adjusting the light quantity of the lamp 1, and a scanner. A CCD sensor 3 for modulating the reflected light into a color separation image signal, an A / D converter 4 for modulating an analog signal output from the CCD sensor 3 into a digital signal, and an optical unit in the sub-scanning direction. Motor 5, a CPU 6 for controlling these devices, a memory 7 functioning as a buffer, and a fluorescent lamp surface temperature sensor for detecting the tube surface temperature of the lamp 1 (fluorescent lamp). 8 is provided.

The optical unit of the scanner includes a lamp 1 as a light source, an imaging system (not shown), and a CCD sensor 3. CCD sensor 3 used in this embodiment
Comprises a color CCD sensor 3 capable of reading a color image. As shown in FIG. 2, a line sensor 9 for an R component, a line sensor 10 for a G component, and a line sensor 11 for a B component. It is composed of a line sensor. In the color CCD sensor 3, electrons are excited according to the amount of incident light and the respective spectral sensitivity characteristics,
It is stored as signal charges. Then, at a constant period, the accumulated charges are sequentially transferred through the transfer gate, and the image is output as image information by color-separating the original image.

<Light Source> In many cases, a fluorescent lamp is used as a light source for illuminating a document used in a copying machine for personal use or a popular type scanner. This fluorescent lamp will be described with reference to FIGS. FIG. 3 is a sectional view of a fluorescent lamp, and FIG.
FIG. 2 is a side view of a fluorescent lamp.

This fluorescent lamp is, as shown in FIGS.
Both ends of the glass tube 12 are sealed with a base 13, and the glass tube 1 is sealed.
Mercury gas and a rare gas are sealed in 2. In the glass tube 12, a pair of electrodes 14 made of a tungsten coil is provided. A reflection film 15 for reflecting light generated inside the glass tube 12 is formed inside the glass tube 12, and a phosphor film 16 coated with a phosphor is formed further inside the reflection film 15. I have. The opening on the side surface of the glass tube 12 has a reflective film 15 and a fluorescent film 16.
Are not formed, and light is transmitted.

The light emission process in a fluorescent lamp includes a step of hitting and exciting mercury atoms by electrons accelerated in an electric field, a step of emitting ultraviolet rays from the mercury atoms, and a fluorescent substance coated in a film inside a fluorescent tube. It consists of a total of three stages of photoluminescence in which ultraviolet light is converted into visible light.

Since the light quantity of the fluorescent lamp has a strong correlation with the mercury vapor pressure, the startability is poor. That is, the mercury sealed in the fluorescent lamp exists in a two-phase state of a liquid phase and a gaseous phase at room temperature, and since the vapor pressure of mercury is determined by the temperature of the tube wall, it is turned on at a low temperature (for example, 5 ° C.). Then, it takes about 10 minutes for the light amount to stabilize. For this reason, in many scanners using a mercury fluorescent lamp, the heater controls the tube wall temperature or keeps the light source always on after the power is turned on.

FIG. 5 shows the relative brightness with respect to the lighting time for each mercury lamp tube wall temperature. As shown in FIG. 5, when the tube wall temperature of the fluorescent tube is low, the luminance immediately after lighting is low, and thereafter, the luminance increases with time. When the tube wall temperature is low as described above, it is necessary to spend a long time until a stable light amount is obtained. On the other hand, when the tube wall temperature is high (for example, 35 ° C.), the luminance increases immediately after lighting, but thereafter, the luminance slightly decreases due to the cathode drop.

<Specific Configuration of Scanner> Next, the above-described scanner will be described in more detail with reference to FIGS. FIG. 6 is an external perspective view of the scanner, and FIG. 7 is a sectional view of the scanner.

The scanner shown in FIGS. 6 and 7 is a flat head type scanner, and has a platen glass 17 for placing an original on the upper surface thereof.
The shading plate 18 is stuck on the back surface of. In the scanner having such a configuration, the original is set in accordance with the original reference position 19, the original 20 is pressed by the original cover 21, and then the original 20 is scanned.

When the scanning is started, light from the original illumination lamp 22 is reflected toward the original by the reflector 23. Then, the light emitted from the lamp 22 is reflected on the original surface, enters the CCD sensor 28 as an image sensor via the first mirror 24, the second mirror 25, the third mirror 26, and the lens 27, and Is read in the main scanning direction. Further, the optical unit 29 of the scanner is a driving means (not shown) such as a motor.
, The image can be read in the sub-scanning direction by moving at a constant speed in the direction of the arrow in the figure.

It is ideal for a scanner to monotonously reproduce the image density of a document. However, in actuality, a document having a uniform density is read due to a non-uniform illuminance distribution of light irradiating the document surface, a difference in characteristics of each pixel of the CCD sensor, and the like. The output signal becomes non-uniform for each pixel. For such non-uniform output signals, a correction process called shading correction is performed using a standard white plate so that a flat output value is output when a uniform original is read. .

FIG. 8 is a graph showing an output value of one line when a uniform original is read when the shading correction processing is not performed. FIG. 9 is a graph showing a uniform output value when the shading correction processing is performed. 7 is a graph showing an output value of one line when a document is read. As shown in FIGS. 8 and 9, by performing the shading correction processing, the output signal for each pixel that has been uneven is uniformed.

<Operation of Scanner> Next, the operation of the above-described scanner will be described with reference to the flowchart shown in FIG. In the above-described scanner, when a start button (not shown) is operated, a scanning operation starts (S).
1). The image of the document is scanned by the CCD sensor, and image data is input (S2). Then, C
The reading position of the carriage in the sub-scanning direction is counted by the PU, and it is determined whether the scanning of the reading range is completed (S3). Here, when the scanning of the reading range is completed, a series of scanning operations is completed (S
16).

On the other hand, if the scanning of the reading range has not been completed, the image data output from the CCD sensor is transferred to the buffer, and it is determined whether or not the capacity of this buffer is full (S4). . Here, when the buffer is full, the input of the image data is temporarily suspended (S5), and the carriage is stopped (S6). On the other hand, if the buffer is not full, the process returns to the image data input processing (S2). Subsequently, one line of image data is input as data for light amount correction after the carriage stop processing (S7), and the data is stored in the memory (S8).

Subsequently, a timer for counting the time from the input of the data for one line is monitored (S9). If the count value is 100 msec or more, the current value for one line is monitored. Input the image data (S1
0), the data is stored in the memory (S11). Next, the data when the carriage stops and the current data are compared (S12). If the data when the carriage stops is equal to or larger than the current data, the correction of the increase in the light amount is performed. If the data at the time when the carriage stops is smaller than the current data (S13), the light amount down correction is performed (S14). Subsequently, the capacity of the buffer is checked again (S15), and Em is checked.
In the case of pty, image data input processing (S2)
And the data reading is resumed. On the other hand, if the buffer is not empty, the process returns to the timer monitoring process (S9), and the light amount correction is performed again. By performing such processing, the capacity of the buffer becomes Em
Until the value becomes pty, light amount correction is performed every 100 msec.

<Light Amount Correction> A specific example in the case where a document is read using the scanner according to one embodiment of the present invention will be described below. As described above, the scanner according to one embodiment of the present invention uses a fluorescent tube as a light source means for illuminating the original, and reflects light reflected from the original by a color CCD sensor having a plurality of pixels arranged in a line. It is configured to read and output an image signal.

FIG. 11 shows output values of the CCD sensor when a reading range in the sub-scanning direction is scanned by one pixel of the color CCD sensor. In this case, a halftone full-surface patch covered with a uniform density over the entire surface was used as the document. Since a halftone document is read, the output value should show a constant value. However, as shown in FIG. 11, the output value changes before and after the scan stop. The reason for the change in the output value is that the light intensity of the light source changed when the fluorescent lamp was used as the light source, the tube temperature had not yet risen sufficiently, and the input of image data was temporarily interrupted by a scan stop. Can be determined. For this reason, if it is possible to control the light amount of the light source that changes during the scan stop to be constant, it is possible to prevent the output value from fluctuating.

Next, the carriage movement of the optical system at the time of scanning stop will be described with reference to FIG. In FIG. 12, the horizontal axis shows the position of the carriage in the sub-scanning direction, and the vertical axis shows the moving speed of the carriage.
In addition, the moving speed of the carriage is indicated by a plus when moving in the sub-scanning direction. When the carriage of the scanner receives the scan start command, the carriage starts moving while accelerating. When a predetermined speed is reached, reading starts and image data is transferred. The read image data is temporarily stored in a buffer in order to perform image processing or the like.

Here, if the input speed of the image data from the scanner is faster than the processing speed of the image processing performed after the reading of the image data, the buffer becomes full and the next image data is transferred. You will not be able to remember. Therefore, in order to stop input of new image data, the scanning is temporarily stopped. Upon receiving the stop command, the carriage of the scanner decelerates and stops. At this time, in preparation for the start of re-reading, the carriage is moved back by the sub-scanning line necessary for deceleration stop and re-acceleration, and waits until the buffer becomes empty. Thereafter, when the buffer becomes empty and a command to start rescanning is issued, the carriage of the scanner starts moving while re-accelerated, and when a predetermined speed is reached, reading is resumed from the same line as when the scanning was stopped. .

FIG. 13 shows read data in the case where a change in light amount is corrected during a scan standby from a scan stop to a restart. As shown in FIG. 13, when the light amount change is corrected during the scan standby from the scan stop to the restart, the read output value is kept constant, and density unevenness and color shift can be prevented.

<Detection of Change in Light Amount> As described above, in the scanner according to the embodiment of the present invention, the output value of the CCD sensor at the time of the scan stop and the position at the same position as that at the time of the scan stop, which is read during the scan standby. The configuration is such that the change in light amount is detected by comparing the output value of the CCD sensor.

FIG. 14 shows output values of the CCD sensor at the time of scanning stop and at the time of standby. As shown in FIG. 14, immediately after the carriage moves to the standby position (t = 0 ms)
When the image data of ec) is read, the output value of the first pixel of the G component is “140”, and the output is in a standby state (t = 100 msec).
The output value at the same position in c) was “142”. The change in the light amount can be detected based on the difference between the output values.

At this time, when detecting a change in the amount of light, a CCD
It is preferable to use output data of several pixels at a predetermined position in the main scanning direction as the output value of the sensor. For example, as shown in FIG. 14, the average output value of 32 pixels of the G component was “149”, and the average output value at the same position during standby was “152”. Based on the difference between the average output values, a change in the amount of light can be detected. In consideration of variations in the sensitivity of the CCD sensor and erroneous detection due to the attachment of foreign matter, using the output values of several pixels is more reliable than using the output values of only one pixel, and the density unevenness is more reliable. And color shift can be prevented.

Some pixels located at the end of one line in the main scanning direction are bright (white) as a background area of the document.
In many cases, the data is ideal as data for performing light quantity correction. Therefore, it is preferable to use output data of one line in the main scanning direction as the output value of the CCD sensor. For example, as shown in FIG. 14, the average output value of one line of the G component is “150”, and the average output value at the same position during standby is “153”. Based on the difference between the average output values, a change in the amount of light can be detected.

The output value of the CCD sensor is RGB
The output data of a specific component among the components or the average value of the output data of each component can be used. That is, G
A change in the amount of light can be detected using the output value of only the component and using the R component or the B component. In this case, any of the above-described output value of the specific pixel, the average output value, and the average output value of one line may be used as the output value of the CCD sensor used for detecting the change in light amount.

For example, as shown in FIG. 14, when the average output value of 32 pixels is used, the average output value of the RGB components is “150” immediately after the scan stop, and is “100” in the standby 100 msec. 153 ". When using the average output value of one line,
The average output value of the RGB components was “151” immediately after the stop of the scan, and was “154” after 100 msec during standby.

As described above, the light amount correction control for correcting a change in light amount refers to the CC when scanning is stopped.
This is a control to obtain the difference between the output value of the D sensor and the output value of the CCD sensor during scan standby, and to eliminate this difference. For example, as shown in FIG. 14, when the average output value of 32 pixels is used, the average output value of the RGB components is “150” immediately after the scan stop, and is “153” in the standby 100 msec. there were. Therefore, the amount of change in the amount of light during standby is 153-1.
50 = 3, indicating that the count has increased by 3 counts. The higher the output value, the greater the light intensity, so
If the difference between the output values is positive, control is performed to reduce the light amount, and if the output value is negative, control is performed to increase the light amount, so that the light amount can be controlled to be constant. In order to control the amount of light during scanning standby to be constant, the voltage applied to the light source may be controlled. FIG. 15 shows the lamp voltage with respect to the PWM signal.

As described above, when the average output value of 32 pixels is used, the amount of change in the amount of light during standby is 153-1.
50 = 3, indicating that the count has increased by 3 counts. If the difference between the output values is positive, the light amount has increased, and control must be performed to reduce the light amount. Therefore, the PWM value of the lamp voltage is compared with the PWM value of the lamp voltage when scanning is stopped.
If the value is controlled so as to be decreased by one count, the lamp voltage decreases and the light amount can be reduced.
In addition, in order to control the amount of light during scanning standby to be constant, the fluorescent lamp tube current of the light source may be controlled. FIG. 16 shows the fluorescent lamp tube current with respect to the PWM signal.

As described above, when the average output value of 32 pixels is used, the change in the amount of light during standby is 153-1.
50 = 3, indicating that the count has increased by 3 counts. If the difference between the output values is positive, the light amount has increased, and control must be performed to reduce the light amount. Thus, the PWM value of the fluorescent lamp current when the scan is stopped is compared with the P value of the fluorescent lamp current.
If the WM value is controlled so as to be reduced by one count, the fluorescent lamp current is reduced and the light amount can be reduced.

The memory connected to the CPU stores a correction coefficient table for the output of the temperature sensor.
Therefore, by using the light amount correction coefficient of the correction coefficient table based on the output value from the temperature sensor monitoring the fluorescent lamp surface temperature, the fluorescent lamp current value of the lamp voltage is controlled, and the fluorescent lamp of the light source is controlled. The tube current can be controlled. FIG. 17 shows a correction coefficient table for the temperature sensor output.

As shown in FIG. 17, when the surface temperature of the fluorescent lamp tube is 10 ° C., the correction coefficient is “3”. When the light amount of the light source is controlled based on the PWM value of the lamp voltage, the scan coefficient If the PWM value of the lamp voltage is controlled so as to be lower by the temperature correction coefficient value than the PWM value of the lamp voltage at the time of stopping, the lamp voltage is reduced and the light amount can be reduced. That is, as shown in FIG. 5, even when the surface temperature of the fluorescent lamp is low, by controlling the lamp voltage and the fluorescent lamp current using this correction coefficient, the light amount of the light source can be kept constant in a short time. You can control.

Further, in order to control the amount of light during scanning standby to be constant, a gain value at the time of A / D conversion of an output value from the CCD sensor may be controlled. By performing such control, the apparent light amount can be made constant. That is, the image data output from the CCD sensor is the amount of light accumulated by the photodiodes arranged in a line during the reading time of one main scanning line, and the accumulated charge amount is output as a signal. .

The analog output from the CCD sensor needs to be modulated into a digital signal in order to perform image processing and the like. Therefore, when the analog output from the CCD sensor is A / D converted, the analog output from the CCD sensor when a white original is read in advance is 8b.
The gain value of the A / D converter is adjusted so that the it output becomes "255". FIG. 18 shows the output of the A / D converter with respect to the accumulated charge amount of the CCD sensor.

As shown in FIG. 18, a straight line with a gain value = a is a straight line set when a standard white plate is read in advance, and is represented by an equation of y = ax + b, and a slope a is a gain value. . Here, when y = 0, the value of x is
This is the dark current that occurs when light is not applied to the sensor. This gain value is used when a document is scanned and output as a digital image signal.

As described above, when the average output value of 32 pixels is used, the change in the amount of light during standby is 153-1.
50 = 3, indicating that the count has increased by 3 counts. If the difference between the output values is positive, the light amount has increased, and control must be performed to reduce the light amount. Therefore, in FIG. 18, the gain value = a
As shown by -1, by decreasing the gain value, the apparent lamp light amount decreases, and the signal output value becomes constant, thereby preventing density unevenness and color shift.

Further, in order to control the amount of light during scanning standby to be constant, the gain values of the RGB of the A / D converter may be controlled in accordance with the output values of the RGB components output from the CCD sensor. . By performing such control, the apparent light amount can be made constant. That is, when the analog output from the CCD sensor is A / D converted, the analog output from the CCD sensor when a white original is read in advance is:
What is necessary is just to adjust the gain value of the A / D converter so that “255” is obtained with an 8-bit output.

The fluorescent lamp used as a light source has a different light amount distribution change amount in each wavelength region with respect to a temperature change.
The amount of output change for each of the RGB components of the D sensor is also different. Therefore, by correcting the gain value for each component of the A / D converter, the correction accuracy is improved, and density unevenness and color shift can be more reliably prevented.

[0061]

As described above, in the image reading apparatus according to the present invention, when the buffer or the like becomes full during the scanning of one screen and reading is temporarily interrupted, the lamp light amount during the scanning standby is kept constant. Since the control is performed, it is possible to prevent density unevenness and color shift of an image.

Further, in the image reading apparatus according to the present invention, the light amount of the light source is corrected to be the same as the light amount immediately after the stop of the scan during the scan standby. For this reason, it is possible to eliminate the inconvenience caused when the light amount is corrected just before the scan / restart so as to be equal to the light amount immediately after the scan / stop as in the related art. That is, when the light amount of the light source was corrected by the conventional method, the voltage and tube current applied to the fluorescent lamp had to be rapidly changed, and when the response of the correction was poor, the light amount was corrected. Nevertheless, there has been a disadvantage that density unevenness and color misregistration of the read image occur, but the image reading apparatus according to the present invention can solve such a disadvantage.

Further, in the image reading apparatus according to the present invention, since the correction is performed using the output data of several pixels, the individual difference of each pixel of the image sensor can be absorbed.
Correction accuracy can be improved.

In the image reading apparatus according to the present invention, one line of output data in the main scanning direction is used as data for monitoring a change in the amount of light. However, the correction accuracy can be improved.

Further, in the image reading apparatus according to the present invention, the average value of the output data of the RGB components is used as the output value of the image sensor. Therefore, even when a fluorescent lamp is used as the light source, the correction accuracy is improved. be able to. That is, since the amount of change in the light amount distribution of each wavelength region differs with the temperature change of the fluorescent lamp, the R
The output change amount for each of the GB components will also be different. For this reason, when output data of only a specific component is used, a slight shift occurs with respect to output data of another component, but according to the image reading apparatus according to the present invention,
Such inconvenience can be solved, and the correction accuracy can be improved.

In the image reading apparatus according to the present invention, the light amount of the light source is controlled to be constant at the time of scanning stop and at the time of scanning standby. Therefore, during a scan stop, a relatively short sample rate (eg, 100 m
If the light amount correction is performed every second), it is possible to finely control the voltage applied to the light source and the tube current,
The response of the correction is improved.

Further, in the image reading apparatus according to the present invention, even when the surface temperature of the light source is low, the light quantity correction can be performed reliably. That is, when the tube surface temperature of the fluorescent lamp as the light source is low, the change in the amount of light is large,
In some cases, the amount of light to be corrected is too small to maintain a constant light amount with a normal correction change amount. However, according to the image reading apparatus of the present invention, the tube surface temperature is monitored by a sensor, and the light amount correction is performed based on the result. Since the coefficient is obtained and the correction is performed in accordance with the correction coefficient, the amount of change in the correction becomes large, and the light amount of the light source can be kept constant.

In the image reading apparatus according to the present invention,
By controlling the gain value of each component of the A / D converter in accordance with the output value of each component of the RGB of the image sensor, the light amount during the scan standby is kept constant.
Correction accuracy can be improved. That is, in the method of controlling the voltage or the tube current applied to the fluorescent lamp, which is a photoelectric, the amount of change in the light amount distribution in each wavelength region of the fluorescent lamp is different, so that it is not possible to accurately correct all the RGB components. However, according to the image reading apparatus of the present invention, since the gain value of each of the RGB components of the A / D converter is corrected, the output value can be kept constant, the apparent light amount can be stabilized, Density unevenness and color shift can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of a device configuration of a scanner according to an embodiment of the present invention.

FIG. 2 is a color CCD which is a component of the optical unit.
FIG. 3 is an array diagram of sensors.

FIG. 3 is a cross-sectional view of a fluorescent lamp for an image reading device.

FIG. 4 is a side view of a fluorescent lamp for an image reading device.

FIG. 5 is an explanatory diagram of a lamp light amount with respect to an elapse time at each tube surface temperature of a fluorescent lamp for an image reading device.

FIG. 6 is an external perspective view of a scanner which is an embodiment of the image reading apparatus.

FIG. 7 is a sectional view of a scanner which is an embodiment of the image reading apparatus.

FIG. 8 illustrates a case where shading correction processing is not performed.
9 is a graph showing an output value of one line when a uniform original is read.

FIG. 9 is a graph showing an output value of one line when a uniform original is read when the shading correction processing is performed.

FIG. 10 is a flowchart showing the operation of the image reading apparatus according to the present invention.

FIG. 11 is a graph showing scan data of one pixel when light amount correction is not performed.

FIG. 12 is an explanatory diagram illustrating a moving speed of a reading unit with respect to a position in a sub-scanning direction of a scanner.

FIG. 13 is a graph showing scan data of one pixel when light amount correction is performed.

FIG. 14 is an explanatory diagram of scan data at the time of scanning stop and at the time of standby.

FIG. 15 is a graph showing a lamp voltage with respect to a PWM value.

FIG. 16 is a graph showing a fluorescent lamp current with respect to a PWM value.

FIG. 17 shows A / D with respect to the accumulated charge amount of a CCD sensor.
FIG. 4 is an explanatory diagram illustrating a converter output.

FIG. 18 is a graph showing a light amount correction coefficient with respect to a fluorescent lamp tube surface temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lamp 2 Inverter 3 CCD sensor 4 A / D converter 5 Motor 6 CPU 7 Memory 8 Fluorescent light tube surface temperature sensor 9 R component line sensor 10 G component line sensor 11 B component line sensor 12 Glass tube 13 Base 14 Electrode Reference Signs List 15 reflection film 16 fluorescent film 17 platen glass 18 shading plate 19 document reference position 20 document 21 document cover 22 document illumination lamp 23 reflection plate 24 first mirror 25 second mirror 26 third mirror 27 lens 28 CCD sensor 29 optical unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/407 H04N 1/40 101B (72) Inventor Kenji Ito 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Yukito Nishio 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture F-term (reference) 2H108 AA01 CA01 CA03 CB01 2H110 AC02 AC12 AC17 CD01 CD03 CD18 CE02 5B047 AA01 AB04 BA01 BA02 BB02 BC11 CA07 CA19 CB11 5C072 AA01 BA12 BA13 BA19 CA04 CA10 CA14 EA05 FB13 MB02 NA05 NA09 QA10 QA17 5C077 MM03 MM30 PP31 PP32 PP46 PQ12 PQ18 PQ20

Claims (11)

[Claims] A light source for illuminating a document, image signal output means for reading reflected light from the document by an image sensor having a plurality of pixels arranged in a line, and outputting an image signal; A sub-scanning means for moving the image signal output means in a sub-scanning direction orthogonal to the main scanning direction; wherein the image signal output means repeats scan stop, scan and restart. An image reading apparatus comprising: a light amount change correction unit for correcting a light amount change during a scan standby from a scan stop to a scan restart when reading image information of an original for one screen. 2. The light amount change correction means compares an output value of the image sensor at the time of scanning stop with an output value of the image sensor at the same position as that at the time of scanning stop, which is read during a scan standby. 2. The image reading apparatus according to claim 1, further comprising a light amount detecting unit for detecting a change in light amount. 3. The image reading apparatus according to claim 2, wherein the output value of the image sensor uses output data of several pixels at a predetermined position in a main scanning direction. 4. The image reading apparatus according to claim 2, wherein the output value of the image sensor uses output data of one line in the main scanning direction. 5. An output value of the image sensor is RG.
4. The output data of a specific component of the B component or an average value of output data of each component is used.
Or the image reading device according to 4. 6. The light amount change correction means controls the light amount of the light source at the time of scanning stop and at the time of scanning standby to be constant, so that the light amount at the time of scanning standby from scanning stop to scanning / restarting. The image reading device according to claim 1, wherein the change is corrected. 7. The apparatus according to claim 1, wherein the light quantity change correction unit controls the voltage applied to the light source to keep the light quantity during the scan standby constant. An image reading device according to the item. 8. The apparatus according to claim 1, wherein the light amount change correction unit controls the current of the light source to maintain a constant light amount during the scan standby. Image reading device. 9. The light amount change correcting unit includes a temperature detecting unit for detecting a surface temperature of the light source, and using a light amount correction coefficient based on a temperature output value of the temperature detecting unit, the light amount change correction unit during the scan standby state. The image reading apparatus according to any one of claims 1 to 6, wherein the light amount is kept constant. 10. The apparatus according to claim 1, wherein the light amount change correction unit controls a gain value at the time of A / D conversion of an output value of the image sensor to keep the light amount during the scan standby constant. Item 7. The image reading device according to any one of Items 1 to 6. 11. The light amount change correction means according to claim 1, wherein said light amount change correction means includes an A /
The image reading apparatus according to claim 10, wherein the light amount during the scan standby is kept constant by controlling a gain value for each component of the D converter.