JP3433616B2 - Image reading device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device used in an image scanner, a copying machine, a facsimile machine or the like.

[0002]

2. Description of the Related Art An image reading apparatus irradiates a document with a predetermined amount of light from a lamp and detects the amount of light from the document with an optical sensor.
Here, generally, as shown in FIG. 1, the light quantity of the lamp is highest at the beginning of lighting and tends to gradually decrease with the passage of lighting time. For example, when the light is turned on for about 3 minutes, the light amount decreases to about 90% of the initial light amount.

A light amount correction process for compensating for such a decrease in the light amount of the lamp has been conventionally performed. For example, in a flat bed type image reading apparatus, a white reference plate is provided on the side edge of the platen along the sub-scanning direction, and the amount of light from the white reference plate is updated each time the scanning line is updated in the sub-scanning direction. Is monitored, and the amplification gain of the read signal is adjusted according to the monitored light amount.

[0004]

There are two types of originals handled by the image reading apparatus, a reflective type and a transmissive type. A lamp built in the image reading device is used for the reflective original. The above-described conventional light amount correction method is applied when reading a reflective original.

On the other hand, when reading a transmissive document, an optional device called a transmissive unit, which has an additional lamp built therein, is mounted above the document table, and the lamp in the transmissive unit is used. Therefore, in the image reading apparatus including the transmissive unit, it is necessary to correct the light amount not only in the lamp in the image reading apparatus but also in the lamp in the transmissive unit.

Therefore, it is an object of the present invention to provide an image reading apparatus capable of performing appropriate light amount correction not only when reading a reflective original, but also when reading a transparent original.

[0007]

An image reading apparatus according to the present invention includes a reading sensor for reading an image of an original, a first lamp for irradiating a reflection type original, and a light amount of the first lamp. For illuminating the transmissive original, and a main body having a first detection means for detecting the light quantity and a light quantity correction circuit for performing a light quantity correction process in response to the light quantity detected by the first detection means. A transmissive unit that is detachable from the main body, has a second lamp built in, second detection means for detecting the light quantity of the second lamp, and the second detection means in the light quantity correction circuit. Connection means for connecting the first detection means, the first detection means is arranged in the vicinity of a document table on which a document of the main body is placed, and is provided at a position where the light of the first lamp is illuminated. White reference plate and the first
Detecting the light emitted from the lamp and reflected by the white reference plate, the reading sensor having a portion for reading the white reference plate, wherein the connecting means outputs the output signal of the second detecting means. On the same signal line as the output signal of the reading sensor at a different timing from the output signal of the reading sensor, and the light amount correction circuit outputs the white reference plate from the signal line when reading a reflective original. Read signal is selected, and at the time of reading a transmissive original, the output signal of the second detecting means is selected from the signal line, and the light amount correction process is performed in response to the selected signal.

According to this image reading apparatus, it is possible to perform appropriate light quantity correction by one light quantity correction circuit both when reading a reflective original and when reading a transmissive original. Further, it is possible to use a reading sensor for reading the original so that not only the original but also the white reference plate can be read by the reading sensor at the same time. Then, on the light amount correction circuit side, a signal is picked up from the signal line at a timing selected according to whether a reflective original or a transmissive original is being read, so that the white reference plate of the reflective original is read when the reflective original is read. It is possible to pick up the read signal or the light amount signal from the transmissive unit at the time of reading the transmissive document and use it for the light amount correction processing.

As the second detecting means, for example, a photoelectric sensor can be used, which can be built in the transmission unit. In this case, it is convenient to automatically connect the output of the photoelectric sensor in the transmission unit to the light amount correction circuit in the main body when the transmission unit is attached to the main body.

[0010]

When a white reference plate is read by the reading sensor and is used for light amount correction, the reading sensor is a color sensor and R
If the read signal is output for each of the GB component colors, the signal used in the light amount correction can be only the read signal of the G component color of the white reference plate. By using only the G component color signal, the structure of the light amount correction circuit is simplified, and the temporal change in the light amount of the G component light in the lamp light is RG.
Since it is an intermediate or average of all B3 colors,
Appropriate light quantity correction without extreme bias can be expected.

[0012]

As a method of correcting the light quantity, for example, there is a method of adjusting the amplification gain for the read signal so as to compensate for the change of the light quantity, a method of adjusting the light quantity itself of the lamp, and the like.

[0014]

[0015]

[0016]

[0017]

FIG. 2 shows a basic structure of a flat bed type image scanner according to an embodiment of the present invention in a cross section taken along the sub-scanning direction.

This image scanner has a box-shaped main body 1
And a transmissive unit 3 attached to the upper surface of the main body 1 by a hinge 2 so as to be openable and closable. The transmission unit 3 is the main body 1
It is removable with respect to. A document table 4 made of a transparent plate is provided on the upper surface of the main body 1, and a document 5 can be placed on the document table 4. Inside the main body 1, there is a reading unit 6 that automatically travels in the sub-scanning direction as indicated by the arrow when reading. A lamp 7, a reflecting mirror 8, a lens 9 and a CCD color line sensor 6 are housed in the reading unit 6. A window 11 for transmitting light is provided on the upper surface of the casing of the reading unit 6.

Within the transmissive unit 3 is a lamp unit 13 containing a white lamp 12. A window 14 for transmitting light is provided on the lower surface of the casing of the lamp unit 13. The lamp unit 13 automatically travels in the sub-scanning direction at the same speed as the reading unit 6 as indicated by an arrow so as to maintain the same relative position with respect to the reading unit 6 when reading the transparent original.

FIG. 3 is a sectional view taken along the line AA of FIG.

The original table 4 has a rectangular shape, and an elongated white reference plate 15 is arranged along the sub-scanning direction on the lower surface of the outer frame edge of the original table 4 which is the left side of the original table 4 when viewed from above. It is attached. The lamps 7 and 12 are both elongated discharge lamps that emit white light, and extend over a range slightly wider than the width of the document table 5 along the main scanning direction. Therefore, the lamp 7 in the reading unit 6 can irradiate the range in the main scanning direction in which the white reference plate 25 is added to the entire width of the document table 5 with a uniform light amount, and the lamp 12 in the transmissive unit 3 can be illuminated. Similarly, it is possible to irradiate a range in the main scanning direction over the entire width of the document table 5 with a uniform light amount.

The CCD color line sensor 10 has an R
An array of photocells extending in the main scanning direction is provided for each of the component colors of (red), G (green), and B (blue), and these three cell arrays are arranged very close to each other in the subscanning direction. There is. On each cell array, an image of one line area in the main scanning direction is formed by the lens 9 over the range in which the white reference plate 15 is added to the entire width of the document table 5. The read signal of one line generated in each cell array is sequentially read from the read signal of the pixel on the left side when the document table 4 is viewed from above, that is, from the read signal of the white reference plate 15 sequentially. Is output from.

Further, a photoelectric sensor 16 for detecting the amount of light of the lamp 12 is arranged in the vicinity of the upper portion of the lamp 12 in the transmissive unit 3 which extends outward from the width of the document table 4.

In the above structure, when reading the reflective original 5, the lamp 7 in the reading unit 6 is turned on to illuminate the original 5 from below. And the reading unit 6
Runs in the sub-scanning direction, and at each position in the sub-scanning direction,
The CCD color line sensor 10 reads the image of each line by the reflected light from the document 5. At this time, the lamp 12 in the transmissive unit 3 is not turned on. Every time each line image is read, a light amount correction circuit, which will be described later, performs light amount correction using the read signal of the white reference plate 15 that is first output from the CCD color line sensor 10.

When reading the transparent original 5, the lamp 12 in the transparent unit 3 is turned on to illuminate the original 5 from above. Then, the reading unit 6 and the lamp unit 13
And C run in the sub-scanning direction at the same speed, and at each position in the sub-scanning direction, the image of each line by the transmitted light from the original 5 is C
The CD color line sensor 10 reads. At this time, the lamp 7 in the reading unit 6 is not turned on. At the time of reading each line image, the light amount correction circuit described later uses the signal output from the photoelectric sensor 16 to correct the light amount.

Designation as to whether the original 5 is a reflection type or a transmission type is performed for this image scanner from a scanner driver in a host computer (not shown) connected to this image scanner. The image scanner includes a reading unit 6, a lamp unit 13, and a controller (not shown) that controls a light amount correction circuit described later. Depending on whether the driver specifies a reflection type or a transmission type,
The control mode is selected so that the operation at the time of reading the reflective original or the operation at the time of reading the transparent original is performed.

FIG. 4 shows the configuration of the light quantity correction circuit 30.

The light quantity correction circuit 30 is housed in the main body 1 and is connected to the signal output terminals of the RGB component colors of the CCD color line sensor 10. When the transmission unit 3 is attached to the main body 1, the light amount correction circuit 30 is also connected to the photoelectric sensor 16 in the transmission unit 3 via the connector 40. The connector 40 is provided at the joint between the main body 1 and the transparent unit 3, and is automatically connected when the transparent unit 3 is attached to the main body 1, and is automatically disconnected when the transparent unit 3 is removed from the main body 1.

While the reading is being performed, the reading pulse given from the controller (not shown) is used as a trigger,
The CCD color line sensor 10 outputs a read signal for one line for each color of RGB. The read pulse is repeatedly generated at a constant cycle, and the CCD color line sensor 10 outputs a read signal of each line image each time.

The output RGB line read signals of the three colors are input to the correlated double sampling circuit 21 through the buffer amplifiers 18, 19 and 20, respectively, and are sampled here, and the light amounts of the component colors are sampled in the order of RGB for each pixel. The signal is converted into a read signal sequence in which the signals are serially arranged. This read signal sequence is amplified by the variable gain amplifier 22 and then A / D
It is digitized by the converter 23. This digitized read signal sequence is sent to a known process for output to the host computer and is added to the gain adjustment circuit 50.

The output terminal of the photoelectric sensor 16 in the transmissive unit 3 is connected to the output terminal of the G component color of the CCD color line sensor 10 via the gate 17. When reading a reflective original, the gate 17 is always kept in the off state by a controller (not shown). Therefore, as described above, only the RGB line read signal train from the CCD color line sensor 10 is gain control circuit 5.
Will be sent to 0. On the other hand, when reading a transmissive original, the controller 17 operates only for the time of one pixel immediately after the generation of each reading pulse and immediately before the signal of the first pixel of each line is output from the CCD color line sensor 10. To turn on. As a result, of the RGB line read signal sequence from the CCD color line sensor 10,
The line read signal train of the R component and the B component is the same as that at the time of reading the reflective original, but the light read signal from the photoelectric sensor 16 is added to the head of the line read signal train of the G component. In this case, it is sent to the gain adjusting circuit 50.

The gain adjusting circuit 50 is a circuit for adjusting the gain of the variable gain amplifier 22, and takes 2 levels of "H" and "L" from a controller (not shown).
It receives a control signal of a type, that is, a load signal LOD and a stop signal STP. While the load signal LOD is "L", the up / down counter 28 in the gain adjusting circuit 50 is
The count value of is fixed to the reference gain value registered in the register 27, and as a result, the gain of the variable gain amplifier 22 is fixed to the reference gain. Load signal LO
In response to the rise of D from “L” to “H”, the latch 25 in the gain adjusting circuit 50 latches the output of the averaging circuit 24. Further, while the stop signal STP is “L”, the up / down counter 28 counts up or down according to the output of the comparator 26. While the stop signal STP is “H”, the up / down counter 28
Stops the counting operation and holds a constant count value,
The gain of the variable gain amplifier 22 is held at a value corresponding to the count value.

The operation of each part in the gain adjusting circuit 50 is as follows.

The averaging circuit 24 outputs only the read signal of the G component of the white reference plate (hereinafter referred to as the white reference G signal) from the read signal sequence of each line from the AD converter when reading the reflective original. Further, at the time of reading a transmissive original, only the light amount signal from the photoelectric sensor (hereinafter referred to as photoelectric sensor signal) is selectively picked up. Such selective signal pickup is performed by controlling the timing of signal pickup of the averaging circuit 24 by a controller (not shown). For example, when reading a reflective original, the G component signal of the white reference plate can be picked up at the timing of the G component signal of the first pixel of each line. Further, when reading a transmissive original, the light amount signal from the photoelectric sensor can be picked up at a timing corresponding to the G component signal of the 0th pixel of each line.

The averaging circuit 24 stores the white reference G signals (or photoelectric sensor signals) of the four lines that have been recently picked up, and calculates and outputs the average value. This average value is applied to the comparator 26 and the latch 25. In the latch 25, the load signal LOD is "L" as described above.
The average value from the averaging circuit 24 is latched at the time of rising from "H" to "H", and thereafter the latched value is added to the comparator 26.

The comparator 26 compares the average value of the latest four lines coming from the averaging circuit 24 with the value from the latch 25. As described above, the up / down counter 28 responds to the signal from the comparator 26 while the load signal LOD is “H” and the stop signal STP is “L”, and the latest 4
If the average value of the line is lower than the value of the latch 25, it counts up at a constant speed, if both are the same, the counting operation is stopped, and if the former is higher than the latter, it counts down at a constant speed. Also, as described above, the up-down counter 28 stops the counting operation while the load signal LOD is "H" and the stop signal STP is "H", and while the load signal LOD is "L". The count value of the up / down counter 28 is fixed to the reference gain value registered in the register 27.

The DA converter 29 converts the count value of the up / down counter 28 into an analog voltage signal and applies it to the control terminal of the variable gain amplifier 22. The larger the count value, the larger the gain of the variable gain amplifier 22, and the smaller the count value, the smaller the gain of the variable gain amplifier 22.

FIG. 5 shows the operation of the load signal LOD and the stop signal STP before the start of reading the original.

Both the load signal LOD and the stop signal STP are initially at "H" level, and in this state, an appropriate reference gain value is set in the register 27. At this time, reading of the original has not started yet.

At the same time when the lamp 7 or 12 is turned on and the reading of the original is started, the load signal LOD becomes "L" level, and at least until the read signal train of the first four lines is output from the line sensor 10. Between (that is, at least 5 times the accumulation time of the line sensor 10),
The load signal LOD is held at "L" level. During this period, the count value of the counter 28 is fixed to the reference gain value of the register 27, so that the gain of the variable gain amplifier 22 is fixed to the reference gain. During this time, the lamp 7 or 1
No. 2 has just turned on, so the amount of light is almost maximum. Further, during this period, the averaging circuit 24 outputs the white reference G signal in the case of a reflection type original from the read signal sequence of each line.
In the case of a transmissive original, the photoelectric sensor signal is picked up and the average value of the latest four lines is calculated.

The load signal LOD is raised to the "H" level at least when the read signals of the first four lines have been output from the line sensor 10. In response to this rising, the latch 25 latches the output value of the averaging circuit 24. Since the output value of the averaging circuit 24 at this point is the average value of the white reference G signal or the photoelectric sensor signal of the continuous four lines at the beginning when the lamp 7 or 12 is turned on, the maximum light amount of the lamp 7 or 12 is set. It is substantially represented and hereinafter referred to as "reference light amount value". The reference light amount value held in the latch 25 is added to the comparator 26.

From then on, the load signal LOD is kept at the "H" level. On the other hand, in the read cycle of each line, the stop signal STP is set to "L" level only during the period when the read signal of the white reference plate is input to the variable gain amplifier 22 at the beginning of the cycle, and the read signal of the original document thereafter is set. The period of being input to the variable gain amplifier 22 is set to the “H” level. While the stop signal STP at the beginning of each cycle is at "L" level, the averaging circuit 24 first picks up a new white reference G signal or photoelectric sensor signal to update its output average value, and then the updated average value. The counter 28 counts up or down according to the result of comparison between the average value and the reference light amount value of the latch 25.

In general, since the light quantity of the lamp 7 or 12 gradually decreases with the lapse of time, the output value of the averaging circuit 24 after updating is slightly lower than that before updating. It becomes smaller than the reference light intensity value. In response to this, the up / down counter 28 counts up and increases the count value. As a result, the gain of the variable gain amplifier 22 is increased to compensate for the decrease in the light amount of the lamp 7 or 12.

When the stop signal STP returns to the "H" level, the count value of the counter 28 is fixed to the value increased as described above, so that the gain of the variable gain amplifier 22 also reduces the light amount of the lamp 7 or 12. It is fixed to the compensated value. With this corrected gain, the variable gain amplifier 22 receives and amplifies the original reading signal. Therefore,
The read signal sequence of the document output from the variable gain amplifier 22 has the same level as that when read under a constant lamp light amount.

By the way, in the above-described embodiment, when the reflection type original is read, the light amount is corrected by using the signal value of the G component color of the white reference plate, but it is not always necessary to use the G component color. Component colors may be used, or RG
You may use the integrated value (for example, average value) of the signal values of three colors of B. However, in general, the time-dependent light intensity decrease curve of the discharge lamp is different for each of the RGB color components, and the G component has an intermediate or average decrease curve. Therefore, if the signal of the G component is used, a simple process is appropriate. The result is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a curve of a light amount decrease of a lamp over time.

FIG. 2 is a sectional view taken along the sub-scanning direction of the flatbed image scanner according to the embodiment of the present invention.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a block diagram of a light amount correction circuit.

FIG. 5 is a time chart showing operations of a load signal LOD and a stop signal STP.

[Explanation of symbols]

1 Image scanner body 3 Transmission unit 6 reading unit 7 White lamp 10 CCD color line sensor 12 white lamp 13 Lamp unit 15 White reference plate 16 Photoelectric sensor 17 gates 18, 19, 20 buffer amplifier 21 Correlated double sampling circuit 22 Variable gain amplifier 23 AD converter 24 Averaging circuit 25 latch 26 Comparator 27 registers 28 up-down counter 29 DA converter 30 Light intensity correction circuit 40 connector 50 Gain control circuit

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/04 101 H04N 1/407 H04N 1/48

Claims (4)

(57) [Claims] 1. A reading sensor for reading an image of an original, a first lamp for irradiating a reflective original, a first detecting means for detecting the light amount of the first lamp, and A main body including a light amount correction circuit for performing a light amount correction process in response to the light amount detected by the first detecting means, and a second lamp for irradiating a transmissive original are included.
A transmissive unit detachable from the main body, a second detecting unit for detecting the light amount of the second lamp, and a connecting unit for connecting the second detecting unit to the light amount correction circuit. The first detecting means is arranged in the vicinity of a document table on which a document included in the main body is placed, and a white reference plate provided at a position where the light of the first lamp is illuminated, Detecting the light emitted from the lamp and reflected by the white reference plate, the portion that reads the white reference plate of the reading sensor, the connection means, the output signal of the second detection means. On the same signal line as the output signal of the reading sensor at a different timing from the output signal of the reading sensor, and the light amount correction circuit outputs the white reference plate from the signal line when reading a reflective original. Select the read signal of And, when the reading of the transmission type manuscript selects the output signal of said second detecting means from said signal line, the image reading apparatus characterized by in response to the selected signal performs the light amount correction process. 2. The device according to claim 1, wherein the second detecting means is a photoelectric sensor provided in the transmissive unit, and the connecting means, when the transmissive unit is attached to the main body, An image reading apparatus, wherein the output of the photoelectric sensor is automatically connected to the light amount correction circuit. 3. The reading sensor according to claim 1, wherein the reading sensor outputs a reading signal for each of the RGB component colors, and the light amount correction circuit outputs from the reading sensor when reading a reflective original. An image reading apparatus which performs the light amount correction processing in response to a read signal of the G component color of the white reference plate. 4. The light amount correction circuit according to claim 1, wherein the light amount correction circuit detects a change in the light amount of the first or second lamp from an output signal of the first or second detecting means, and outputs the light amount. The image reading apparatus is characterized in that an amplification gain for a reading signal from the reading sensor is adjusted so as to compensate for the change of