JP2000069285A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce rise time of a reader by changing a clamp period, for extending it in the case of restoration from the energy saving mode to the conventional mode so as to reduce a substantial time until a clamp voltage is made stable. SOLUTION: Functions of a clamp control means, the gain adjustment operation control means, the recognition means and a black level priority processing control means or the like are newly added to a CPU. The clamp control means executes a function of revising a clamp period for extending the clamp period by a line clamp circuit included in sample-and-hold circuits 9, 10 when restoring from the energy saving mode to the conventional mode with respect to a clamp processing to an output from a CCD 1. The gain adjustment operation control means executes the function of re-adjusting an adjusted value of other amplifier 13 with respect to the gain adjustment, when the adjusted value of one fine- adjustment amplifier 12 is deviated from the gain adjustment range set in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital copying machine,
The present invention relates to an image reading apparatus which is applied to a scanner device or the like and reads image information using a linear CCD image sensor.

[0002]

2. Description of the Related Art Generally, in an image reading apparatus using a line-type CCD image sensor of this type, the CCD output is sampled and held, and the gain is adjusted.
By converting, a digital signal corresponding to an image is obtained.

FIG. 4 shows a schematic configuration of an image reading apparatus in a conventional digital copying machine. The light emitted from the light source irradiates the original on the contact glass, and the reflected light from the original is imaged on a linear CCD (CCD image sensor) 1 via a mirror and a condenser lens, and photoelectrically converted to an electric signal. Is converted to The output of the CCD 1 is sampled and held in an analog processing circuit 3 on the same reading substrate 2, and after performing gain adjustment and the like, is converted into a digital signal by an A / D converter 4. The digitized image data is transmitted to the digital processing circuit 6 on the image processing substrate 5, where shading correction processing, filter processing, and the like are performed, and finally transmitted to the writing unit for optical writing. The digital processing circuit 6 is controlled by the CPU 7. Also, the CPU 7
Is connected to a memory 8, and the CPU 7 is in charge of control of each unit on both substrates 2 and 5.

FIG. 5 shows a configuration example of an analog processing circuit 3 and the like mounted on a reading substrate 2. Here, the CCD 1 has two pixels of an even pixel (EVEN) and an odd pixel (ODD).
It is assumed that the output is a two-output type in which the output is divided into systems and output alternately. For this reason, sample hold amplifiers 9 and 10 are provided on the output side of the CCD 1 for each system. The signal components are extracted by these sample and hold amplifiers 9 and 10. The extracted signal components are time-sequentially combined by a multiplexer 11 into a single system output, and are connected in series to two-stage amplifiers 12 and 13 forming a gain adjustment circuit.
Is input to These sample and hold amplifiers 9 and 1
At 0, white level correction (shading correction) is performed.

Here, when sampling and holding the output of the CCD 1, a line clamp is applied to the CCD output. As shown in FIG. 6, the CCD output has a black pixel output period and an effective pixel period for reading actual image data. Conventionally, however, the clamp operation is performed only during the black pixel output period. I have. That is,
Clamping is performed during the black pixel output period (L-level period of the clamp signal) so that the potential during one line is kept constant.

The two-stage amplifiers 12 and 13 can operate independently. For example, the amplifier 12 adjusts the gain (= each scanning line) for each scanning (for each main scanning line).
It is assumed that the amplifier 13 is set to take charge of the gain adjustment of the whole level such as when the power is turned on (of course, the setting may be reversed).

Under such a premise, a conventional gain adjustment process at the time of power-on will be described with reference to a flowchart shown in FIG. First, a default value is set for each of the amplifiers 12 and 13, the carriage is moved, and a white reference plate (not shown), which is a reference document, is read to obtain white data. Here, while the set value of the amplifier 12 is fixed at a default value, the set value of the amplifier 13 is changed from the default value to set an appropriate white level (white data is a standard value).
The adjustment value of the amplifier 13 is set so that When the white data falls within the standard value, the data is set in the memory 8 and the processing is terminated. Thereafter, during normal scanning, the set value of the amplifier 13 is fixed, and only the set value of the amplifier 12 is changed for each scanning so that an appropriate white level is maintained. This is a system that raises or lowers the peak value (that is, the white level) by feeding back the peak value of the shading data performed at the time of scanning to the amplifier 12. One of the amplifiers 12 is designed to have a small gain adjustment range to increase the reflection speed, and the other amplifier 13 has a wide adjustment range so that the reflection speed is relatively slow to continuously light up. Thus, it is possible to correct a decrease in the light amount of the light source due to the above.

Further, when attention is paid to the black level adjustment, if there is a variation in each black level output with respect to the two-output CCD 1 as shown in the figure, the resulting image is inconvenient. For example, shading may be performed on the black level (see, for example,
Adjustment of the black level even-odd difference (difference between even-numbered pixel system and odd-numbered pixel system) is absorbed by adjusting the offset voltage in the analog processing circuit 3 in the subsequent stage. In this case, since the performance of the CCD is improved, the necessity of the black shading which requires a memory and is expensive is reduced, and a system which adjusts the even-odd difference of the black level only when the power is turned on is mainly used.

[0009]

However, regarding such a conventional example, when attention is paid to the line clamp operation, for example, the clamp operation is performed only during the black pixel output period. Including)
In such a situation as return from the normal state, a certain time is required until the clamp voltage is stabilized, which limits the rise time. That is, the sample and hold amplifiers 9 and 1
Since the line clamp circuit (not shown) included in 0 is a circuit utilizing charging / discharging of the capacitor, when the potential of the capacitor is in a completely discharged state such as 0 V,
It takes time to reach a normal clamp potential. By the way, the energy saving mode is a mode in which the power consumption of the unit is smaller than that in the normal mode.
In the circuit as shown in FIG. 5, this means a mode in which all operations including the clamp signal are stopped by stopping the operation clock, and is set when the operation of the machine is not requested (= standby). . By using such an energy saving mode, it is possible to expect effects such as saving of electricity bill, reduction of heat generation, extension of machine life, and the like. Such an energy saving mode is a well-known technique proposed by various companies, and is disclosed in, for example, JP-A-8-2513.
There is a technique disclosed in Japanese Patent Application Laid-Open No. 16-163 and the like.

When attention is paid to the gain adjustment, if the gain adjustment range of the amplifier 12 is exceeded due to a decrease in the light amount of the light source or the like, the power is turned on / off next and the amplifier 1 is turned on.
Until the gain of No. 3 is adjusted, an appropriate gain correction will not be performed. In this regard, a light source having excellent stability with a small decrease in the amount of light may be used. However, such a light source is generally expensive and increases the overall cost. I will.

Further, when attention is paid to the black level adjustment, even if the adjustment of the even / odd difference of the black level of the CCD 1 (balance adjustment) or the overall black level adjustment is performed only when the power is turned on, there is no drift of the offset voltage. Rather, the only way to recover in the event of a difference is to re-adjust by turning on the power again.

An object of the present invention is to provide an image reading apparatus capable of shortening a rise time of the apparatus by shortening a substantial time until the clamp voltage is stabilized even in a situation such as returning from the energy saving mode. That is.

Another object of the invention is to operate independently.
An object of the present invention is to provide an image reading apparatus that can always obtain an appropriate gain adjustment result even when a case where the gain is deviated from one of the gain adjustment ranges occurs in the case of a configuration including various types of gain adjustment circuits.

Still another object of the present invention is to provide an image reading apparatus capable of always obtaining an appropriate black level.

[0015]

According to the first aspect of the present invention,
In an image reading apparatus including a linear CCD image sensor that receives an optical signal corresponding to an image, photoelectrically converts the received optical signal, and outputs the signal, and a line clamp circuit that performs a line clamp on the output of the CCD image sensor, the image reading apparatus is operated in an energy saving mode And a clamp control means for changing the clamp period so as to extend the clamp period by the line clamp circuit when returning to the normal mode.

Therefore, when returning from the energy-saving mode to the normal mode, by changing the clamp period so as to extend the clamp period, the return time until the clamp voltage stabilizes, that is, the rise time, can be shortened.

According to a second aspect of the present invention, there is provided a linear CCD image sensor for receiving an optical signal corresponding to an image, photoelectrically converting and outputting the same, and two types of CCD image sensors which operate independently of the output of the CCD image sensor. And a gain adjustment circuit for adjusting the adjustment value of the other gain adjustment circuit when the adjustment value of one of the gain adjustment circuits deviates from a predetermined gain adjustment range. The control means is provided.

Therefore, the gain adjustment status of one gain adjustment circuit is monitored, and if the adjustment value is out of the gain adjustment range, the adjustment value of the other gain adjustment circuit is adjusted. Therefore, an appropriate gain adjustment result can always be obtained.

According to a third aspect of the present invention, there is provided a linear CCD image sensor for receiving an optical signal corresponding to an image, photoelectrically converting the signal, and outputting the signals in two systems of even-numbered pixels and odd-numbered pixels, and reading a white reference plate. A scanning operation in an image reading apparatus comprising: a shading correction circuit for adjusting a white level with respect to the output of the CCD image sensor based on the image data; and a black level adjusting circuit for adjusting a black level with respect to the output of the CCD image sensor. A recognizing means for recognizing the black levels of the two outputs of the CCD image sensor during standby, and a black level adjusting circuit when there is a difference of not less than a predetermined value between the two levels of black recognized by the recognizing means. Black level priority processing control means for causing the black level to be readjusted by

Therefore, the black level of each of the two systems is monitored during the standby state of the scanning operation. If the difference between the black levels becomes a predetermined value or more and becomes unsuitable, the black level is adjusted again by the black level adjusting circuit. Since the adjustment is performed with priority, an appropriate black level can always be obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. 4 to 7 are denoted by the same reference numerals, and description thereof is omitted. In particular, the schematic configuration shown in FIGS. 4 and 5 is used as it is. In the present embodiment, functions such as a clamp control unit, a gain adjustment operation control unit, a recognition unit, and a black level priority process control unit are newly added to the CPU 7 that controls each unit centering on the digital processing circuit 6. ing. Each of these means will be described schematically. The clamp control means has a function of changing the clamp period so as to extend the clamp period by the line clamp circuits included in the sample and hold amplifiers 9 and 10 when returning from the energy saving mode to the normal mode with respect to the clamp processing for the output from the CCD 1. Execute. The gain adjustment operation control means adjusts the adjustment value of the other amplifier 13 when the adjustment value of one of the fine adjustment amplifiers 12 deviates from a predetermined gain adjustment range set in advance. Execute The recognizing means detects the even-numbered pixels (E) of the CCD 1 during the standby of the scanning operation with respect to the black level adjustment.
VEN) and an odd-numbered pixel (ODD) are monitored and the function of recognizing the black level is executed. The black level priority processing control means automatically resets the black level by the black level adjustment circuit when the even-odd difference of the two systems of black levels recognized by the recognition means is a difference equal to or greater than a predetermined value. Execute the function to shift to the adjustment sequence.

First, the clamp operation for the CCD output will be described with reference to FIG. In FIG. 1 (similarly in the case of FIG. 6), the clamp signal charges the capacitor in the line clamp circuit during the L level period, and discharges by the leak current during the H level period. By repeating such an operation for each main scanning line, the line clamp in the sample hold is properly performed. At this time, in the normal mode, the clamp operation is performed only during the black pixel output period as shown in FIG. 6, but when returning from the energy saving mode (including power-on) to the normal mode, Regardless of other signals, as shown in FIG. 1, the period of the clamp signal (clamp period)
Is extended to the effective pixel period side more than the black pixel output period, so that the recovery time is controlled to be shortened. Incidentally, even in the effective pixel period, when the CCD 1 is not illuminated with light, the same level of output as that of the black pixel output period is normally output even if the clamp period extends to the effective pixel period side. No fluctuation occurs. Such a function is executed under the control of the CPU 7 as a function of the clamp control means. Therefore, even when returning from the energy saving mode to the normal mode, the clamp voltage can be stabilized in a short time, and the rise time of the device can be shortened.

Next, gain adjustment by the amplifiers 12 and 13 will be described. The gain adjustment at the time of turning on the power is performed as a process of adjusting the set value of the amplifier 13 as described with reference to FIG. On the other hand, at the time of fine adjustment in which the set value on the amplifier 13 side is fixed and the set value on the amplifier 12 side is changed for each scanning, control as shown in the flowchart of FIG. 2 is performed. That is, the carriage is moved for each scanning, and a white reference plate (not shown), which is a reference document, is read to obtain white data. Then, it is determined whether or not the peak value of the acquired white data is out of the gain adjustment range set in the amplifier 12, and if not, it is determined whether or not the white data is within the range of the standard value. The original check is made. If not within the range of the standard value, reset the adjustment value for the amplifier 12 and
The process is repeated again from the acquisition of the white data. If the white data falls within the range of the standard value, the data is set in the memory 8 and the processing is terminated. Such a process is performed as a fine adjustment process of the gain for each scanning. On the other hand, when the peak value of the acquired white data is out of the gain adjustment range set in the amplifier 12, the scanning operation is interrupted (or aborted = end), and the memory 12 which has been subjected to the current adjustment is adjusted. Is set to the default value, and the process proceeds to the process of re-adjusting the set value of the memory 13 in the same manner as when power is turned on. Such a function is executed as a function of the gain adjustment operation control means under the control of the CPU 7. Therefore, even when the gain adjustment range of the amplifier 12 is exceeded due to a decrease in the light amount of the light source or the like, an appropriate white level can always be obtained by automatically performing the gain readjustment on the amplifier 13 side. Conversely, an apparatus configuration using an inexpensive light source that causes a decrease in light quantity does not hinder.

Further, the black level adjustment will be described with reference to the flowchart shown in FIG. Roughly speaking, at the time of a scanning operation for shading standby, the value of the black level is also monitored to detect an even-odd difference between the two systems. Is maintained at an appropriate black level at all times. First, ON / OFF of the clamp is appropriately controlled. This process corresponds to the control of the clamp period described above. Next, the reference voltage of the A / D converter 4 is set, and the gains of the amplifiers 9 and 10 are set to the maximum. here,
The gain of the amplifiers 9 and 10 is set to the maximum, and the A / D converter 4
Is set to the minimum to maximize the even-odd difference. In such a situation, when the scanning operation is on standby, the black data is read to recognize two systems of black levels. Such a function is executed as a function of a recognition unit under the control of the CPU 7. Next, it is checked whether the even-odd difference between the recognized black level data is within a predetermined value 1 or less. If the value is within the predetermined value 1 or less, there is no particular problem, and the process is terminated. On the other hand, if the even-odd difference does not fall below the predetermined value 1, the process proceeds to an adjustment value setting process for re-adjusting the black level, and is repeated until the even-odd difference falls below the predetermined value 1. Such a function is executed as a function of the black level priority processing control unit under the control of the CPU 7. Therefore, even when a black level balance difference that cannot be completely corrected by white level adjustment (white shading correction) occurs, an appropriate black level can always be obtained by detecting the balance difference. .

[0025]

According to the first aspect of the present invention, when returning from the energy saving mode to the normal mode, the clamp period is changed so as to extend the clamp period. Therefore, the return time until the clamp voltage is stabilized is reduced. Therefore, the start-up time of the device can be shortened.

According to the second aspect of the present invention, the gain adjustment status of one gain adjustment circuit is monitored, and if the adjustment value is out of the gain adjustment range, the other gain adjustment circuit is monitored. Since the adjustment value of the gain adjustment circuit is readjusted, an appropriate gain adjustment result can always be obtained irrespective of a decrease in the light amount of the light source.

According to the third aspect of the invention, the black level of each of the two systems is monitored during the standby time of the scanning operation, and the difference between the black levels becomes a predetermined value or more, so that the white data correction cannot cope with the difference. If the black level adjustment is no longer appropriate, priority is given to the readjustment of the black level by the black level adjustment circuit, so that an appropriate black level can always be obtained.

[Brief description of the drawings]

FIG. 1 is a time chart showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a gain adjustment process.

FIG. 3 is a flowchart illustrating a black level adjustment process.

FIG. 4 is a block diagram showing a schematic configuration of an image reading apparatus used in a conventional example and the present embodiment.

FIG. 5 is a block diagram showing a schematic configuration on the reading substrate side.

FIG. 6 is a time chart showing a clamp operation.

FIG. 7 is a flowchart illustrating a gain adjustment process when the power is turned on.

[Explanation of symbols]

 1 CCD image sensor

Claims (3)

[Claims] 1. A linear CCD image sensor for receiving an optical signal corresponding to an image, photoelectrically converting the received optical signal, and outputting the signal.
A line clamp circuit for performing line clamp on the output of the D image sensor, wherein the clamp period is changed to extend the clamp period by the line clamp circuit when returning from the energy saving mode to the normal mode. An image reading apparatus comprising a control unit. 2. A linear CCD image sensor for receiving an optical signal corresponding to an image, photoelectrically converting the received optical signal, and outputting the signal.
An image reading apparatus including two types of gain adjustment circuits that operate independently of each other with respect to the output of the D image sensor, wherein an adjustment value of one of the gain adjustment circuits deviates from a predetermined gain adjustment range. An image reading apparatus comprising: a gain adjustment operation control means for adjusting an adjustment value of the other gain adjustment circuit. 3. A linear CCD image sensor for receiving an optical signal corresponding to an image, photoelectrically converting the received light signal into two systems of even pixels and odd pixels and outputting the divided signals, and said CCD image sensor based on reading of a white reference plate. An image reading apparatus comprising: a shading correction circuit for adjusting a white level with respect to the output of the CCD image sensor; and a black level adjustment circuit for adjusting a black level with respect to the output of the CCD image sensor. A recognizing means for recognizing the black levels of the outputs of the two systems, and when the difference between the two black levels recognized by the recognizing means exceeds a predetermined value, readjustment of the black levels by the black level adjusting circuit. An image reading apparatus comprising: