JP3778402B2 - Image reading device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus which is applied to a digital copying machine, a scanner device, and the like and reads image information using a line-shaped CCD image sensor.
[0002]
[Prior art]
In general, in an image reading apparatus using this type of linear CCD image sensor, a CCD output is sampled and held, and after adjusting its gain, A / D conversion is performed to obtain a digital signal corresponding to the image. ing.
[0003]
FIG. 4 shows a schematic configuration of an image reading apparatus in a conventional digital copying machine. The light emitted from the light source is applied to the original on the contact glass, and the reflected light from the original is imaged on a linear CCD (CCD image sensor) 1 through a mirror and a condenser lens, and is photoelectrically converted to an electrical signal. Is converted to The output of the CCD 1 is sampled and held in the analog processing circuit 3 on the same reading substrate 2, and after gain adjustment or the like, it is converted into a digital signal by the A / D converter 4. The digitized image data is transmitted to the digital processing circuit 6 on the image processing board 5 to be subjected to shading correction processing, filter processing, and the like, and finally transmitted to the writing unit for optical writing. The digital processing circuit 6 is controlled by the CPU 7. In addition to the memory 8 being connected to the CPU 7, the CPU 7 is responsible for controlling each part on both the boards 2 and 5.
[0004]
FIG. 5 shows a configuration example of the analog processing circuit 3 and the like mounted on the reading substrate 2. Here, it is assumed that the CCD 1 is a two-output type that outputs alternately in two systems of even pixels (EVEN) and odd pixels (ODD). Therefore, sample hold amplifiers 9 and 10 are provided for each system on the output side of the CCD 1. These sample and hold amplifiers 9 and 10 extract signal components. The extracted signal components are synthesized in time series by the multiplexer 11 into one system output and input to the two-stage amplifiers 12 and 13 connected in series forming a gain adjustment circuit. These sample hold amplifiers 9 and 10 perform white level correction (shading correction).
[0005]
Here, in the sample hold of 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, the clamping operation is limited to the black pixel output period. Yes. In other words, clamping is performed during the black pixel output period (L level period of the clamp signal) to keep the potential between one line constant.
[0006]
The two-stage amplifiers 12 and 13 can operate independently. For example, the amplifier 12 side is responsible for gain adjustment (= fine adjustment) for each scanning (each main scanning line), and the amplifier 13 side is a power source. It is assumed that it is set so as to be responsible for gain adjustment of the entire level such as at the time of input (of course, the reverse setting is also possible).
[0007]
Under such a premise, a conventional gain adjustment process at power-on will be described with reference to a flowchart shown in FIG. First, default values are set in the amplifiers 12 and 13, respectively, the carriage is moved, and white data is acquired by reading a white reference plate (not shown) as a reference document. Here, while the setting value of the amplifier 12 is fixed at the default value, the adjustment value of the amplifier 13 is adjusted so that the setting value of the amplifier 13 is changed from the default value to an appropriate white level (white data is a standard value). Set. When the white data falls within the standard value, the data is set in the memory 8 and the process ends. Thereafter, at the time of 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 as to maintain an appropriate white level. This is a system that raises or lowers the peak value (that is, the white level) by feeding back the peak value of shading data performed during scanning to the amplifier 12. One amplifier 12 is designed to have a small gain adjustment range, thereby increasing the reflection speed, and the other amplifier 13 has a wide adjustment range so that the reflection speed is relatively slow, so that the continuous lighting is performed. It is possible to correct a decrease in the amount of light of the light source due to the above.
[0008]
Further, when attention is paid to black level adjustment, if the black level output varies with respect to the two-output CCD 1 as shown in the figure, the obtained image is inconvenient, so not only the white level but also the black level. Shading (see, for example, Japanese Patent Application Laid-Open No. 9-154016), and adjusting the even / odd difference of black level (difference between even-numbered pixel system and odd-numbered pixel system) in the analog processing circuit 3 in the subsequent stage Absorption is performed by adjusting the offset voltage. In this case, as the performance of the CCD increases, the need for costly black shading that requires a memory is reduced, and a system that adjusts the even / odd difference of the black level only when the power is turned on is the mainstream.
[0009]
[Problems to be solved by the invention]
However, with regard to such a conventional example, for example, when focusing on the line clamp operation, the clamp operation is performed only during the black pixel output period, so that the situation is such as returning from the energy saving mode (including power-on). In, a certain time is required until the clamp voltage is stabilized, which is a limitation on the rise time. That is, since the line clamp circuit (not shown) included in the sample-and-hold amplifiers 9 and 10 is a circuit that uses charging / discharging of the capacitor, when the capacitor potential is completely discharged such as 0V, It takes time to reach the normal clamping potential. Incidentally, the energy saving mode is a mode in which the power consumption of the unit is less than that in the normal mode. In the circuit as shown in FIG. 5, all operations including the clamp signal are stopped when the operation clock is stopped. And is set when the machine operation 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 variously proposed by various companies, for example, a technique disclosed in Japanese Patent Laid-Open No. 8-251316.
[0010]
Further, when paying attention 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 time until the gain of the amplifier 13 is adjusted. Therefore, the gain correction is not performed. In this respect, a light source having excellent stability with little decrease in the amount of light may be used, but such a light source is generally expensive and increases the overall cost, contrary to the demand for cost reduction. End up.
[0011]
Furthermore, when paying attention to the black level adjustment, even when the even / odd difference adjustment (balance adjustment) of the black level of the CCD 1 or the entire black level adjustment is performed only when the power is turned on, the offset voltage drift is not completely eliminated. In the unlikely event that a difference arises, the only way to recover is to re-adjust by turning the power on again.
[0012]
An object of the present invention is to provide an image reading apparatus capable of shortening the 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. .
[0013]
Another object of the present invention is to provide an appropriate gain adjustment result at all times even in the case of a configuration including two types of gain adjustment circuits that operate independently, even when a case deviates from one of the gain adjustment ranges. To provide an image reading apparatus that can be obtained.
[0014]
Still another object of the present invention is to provide an image reading apparatus capable of always obtaining an appropriate black level.
[0015]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a linear CCD image sensor that receives an optical signal corresponding to an image, photoelectrically converts it, and outputs it. The CCD image sensor utilizes a charge of a capacitor for the output of the CCD image sensor. In a normal mode, the clamp period for charging the capacitor is set as the black pixel output period of the CCD image sensor, and the energy saving mode is started. At the time of returning to the normal mode, a clamp control unit is provided for changing the clamp period so that the CCD image sensor is not exposed to light so that it extends beyond the black pixel output period until the effective pixel output period .
[0016]
Therefore, when returning from the energy saving mode to the normal mode, the return time until the clamp voltage is stabilized, that is, the rise time can be shortened by changing the clamp period so as to extend the clamp period.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. The same parts as those shown in FIGS. 4 to 7 are denoted by the same reference numerals, and description thereof is also omitted. In particular, the schematic configuration shown in FIGS. 4 and 5 is used as it is. In the present embodiment, functions such as clamp control means, gain adjustment operation control means, recognition means, and black level priority processing control means are newly added to the CPU 7 that controls each part around the digital processing circuit 6. ing. Each of these means will be schematically described. The clamp control means has a function to change the clamp period so as to widen the clamp period by the line clamp circuit included in the sample hold amplifiers 9 and 10 when returning from the energy saving mode to the normal mode with respect to the clamp process for the output from the CCD 1. Execute. The gain adjustment operation control means is a function for re-adjusting the adjustment value of the other amplifier 13 when the adjustment value of one of the fine adjustment amplifiers 12 deviates from a preset predetermined gain adjustment range. Execute. The recognizing means executes a function of recognizing the black level by monitoring the outputs of the two systems of the even pixel (EVEN) and the odd pixel (ODD) of the CCD 1 when waiting for the scanning operation. The black level priority processing control means automatically resets the black level by the black level adjustment circuit when the even / odd difference between the two black levels recognized by the recognition means is a difference greater than a predetermined value. Executes the function for shifting to the adjustment sequence.
[0022]
First, a clamp operation for CCD output will be described with reference to FIG. In FIG. 1 (the same applies to FIG. 6), the clamp signal charges the capacitor in the line clamp circuit in the L level period, and discharge by the leakage current is performed in the H level period. By repeating such an operation for each main scanning line, line clamping for sample hold is performed properly. At this time, in the normal mode, as shown in FIG. 6, the clamping operation is performed only during the black pixel output period, but when returning from the energy saving mode (including power-on) to the normal mode, Regardless of other signals, as shown in FIG. 1, control is performed to shorten the recovery time by extending the clamp signal period (clamp period) to the effective pixel period side beyond the black pixel output period. Incidentally, even in the effective pixel period, when the CCD 1 is not exposed to light, the output is normally the same level as the black pixel output period, and even if the clamp period extends to the effective pixel period side, There will be no fluctuations. Such a function is executed as a function of the clamp control means under the control of the CPU 7. Therefore, even when returning from the energy saving mode to the normal mode, the clamp voltage can be stabilized in a short time, so that the rise time of the apparatus can be shortened.
[0023]
Next, gain adjustment by the amplifiers 12 and 13 will be described. The gain adjustment when the power is turned on is performed as a process of adjusting the set value on the amplifier 13 side as described with reference to FIG. On the other hand, at the time of fine adjustment in which the setting value on the amplifier 13 side is fixed and the setting value on the amplifier 12 side is changed for each scanning, the control shown in the flowchart of FIG. 2 is performed. That is, the white data is acquired by moving the carriage for each scanning and reading a white reference plate (not shown) as a reference document. Then, it is determined whether or not the peak value of the acquired white data deviates from the gain adjustment range set in the amplifier 12, and if not deviated, whether or not the white data is within the standard value range. Do the original check. If it is not within the range of the standard value, the adjustment value is reset for the amplifier 12, and the process is repeated from the acquisition of the white data again. If the white data falls within the standard value range, the data is set in the memory 8 and the process ends. 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 deviates from the gain adjustment range set in the amplifier 12, the scanning operation is interrupted (or stopped = terminated), and the memory 12 that is the object of adjustment this time Is set to the default value, and the process proceeds to a process of readjusting the set value of the memory 13 in the same manner as when the 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 gain readjustment on the amplifier 13 side. In other words, even an apparatus configuration using an inexpensive light source that causes a decrease in the amount of light does not hinder.
[0024]
Further, black level adjustment will be described with reference to the flowchart shown in FIG. In general, when waiting for the scanning operation for shading, the black level value is also monitored to detect the even / odd difference between the two systems. If the even / odd difference is not appropriate, the black level is automatically shifted to the adjustment sequence. The black level is always maintained at a proper level by resetting. First, the 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 even-odd difference is maximized by setting the gains of the amplifiers 9 and 10 to the maximum and setting the reference voltage of the A / D converter 4 to the minimum. Under such a situation, the black level of the two systems is recognized by reading the black data when waiting for the scanning operation. Such a function is executed as a function of the 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 it is within the predetermined value 1 or less, there is no particular problem, and the processing is terminated as it is. On the other hand, if the even / odd difference does not fall within the predetermined value 1, the process proceeds to an adjustment value setting process in which the black level is readjusted, and is repeated until the even / odd difference falls within the predetermined value 1 or less. Such a function is executed as a function of the black level priority processing control means under the control of the CPU 7. Therefore, even when a black level balance difference that cannot be corrected by white level adjustment (white shading correction) occurs, an appropriate black level can always be obtained by detecting the balance difference. .
[0025]
【The invention's effect】
According to the first aspect of the present invention, since the clamp period is changed so as to widen the clamp period when returning from the energy saving mode to the normal mode, the return time until the clamp voltage is stabilized can be shortened. The rise time of the apparatus can be shortened.
[Brief description of the drawings]
FIG. 1 is a time chart showing an embodiment of the present invention.
FIG. 2 is a flowchart showing a gain adjustment process.
FIG. 3 is a flowchart showing black level adjustment processing;
FIG. 4 is a block diagram showing a schematic configuration of an image reading apparatus used in a conventional example and in the present embodiment.
FIG. 5 is a block diagram showing a schematic configuration on the side of the reading substrate.
FIG. 6 is a time chart showing a clamping operation.
FIG. 7 is a flowchart showing a gain adjustment process at power-on.
[Explanation of symbols]
1 CCD image sensor

Claims (1)

A line-shaped CCD image sensor that receives an optical signal corresponding to an image, photoelectrically converts it, and outputs it, and a line that clamps the output signal of the CCD image sensor using the charging of a capacitor with respect to the output of the CCD image sensor In an image reading apparatus provided with a line clamp circuit that performs clamping,
In the normal mode, the clamp period for charging the capacitor is the black pixel output period of the CCD image sensor, and when returning from the energy saving mode to the normal mode, the CCD image sensor is not exposed to light during the clamp period. An image reading apparatus comprising: a clamp control unit that changes the effective pixel output period to be longer than the black pixel output period .

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