JP2935387B2 - 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 apparatus capable of reading good image data using a charge storage type image sensor despite the performance degradation of a light source.

[0002]

2. Description of the Related Art In an image reading apparatus using a charge accumulation type image sensor, an image on a document illuminated with light from a light source is converted into optical information by a period of an accumulation time control signal output from a clock generation circuit. They are accumulated as signal charges and are sequentially transferred to the output side by charge transfer pulses.

[0003]

However, in such a conventional image reading apparatus, since the period of the accumulation time control signal, that is, the accumulation time is constant, it is not possible to cope with the deterioration of the light source with the passage of time. If the S / N ratio is deteriorated, the quality of the reproduced image is deteriorated, and the output gain must be adjusted in the shipping process.

The present invention has been made in view of such a conventional problem. In spite of a decrease in the amount of light due to the aging of the light source, a good S / N is always obtained, and a desired image quality is obtained. It is another object of the present invention to provide an image reading apparatus that can obtain an optimum output without performing gain adjustment at the time of shipment.

[0005]

According to the present invention, there is provided an image reading apparatus comprising: a charge storage type image sensor for storing optical information as signal charges in a cycle of a storage time control signal; and an output of the charge storage type image sensor. An analog circuit that performs analog processing; a peak level detection circuit that outputs a stop signal when an output level of the charge accumulation type image sensor exceeds a set value based on an output of the analog circuit; and a signal charge accumulation time when reading a white document. The start time is set to be the shortest, and the accumulation time is increased by one cycle until the output level exceeds the set value, and the accumulation time is stopped by the controller so as to stop the increase of the accumulation time when the stop signal is output. This is to control the cycle of the time control signal.

[0006]

The controller according to the present invention increases the accumulation time in the clock generation circuit for each cycle, and uses the stop signal output from the output peak level detection circuit when the output of the charge accumulation type image sensor reaches a set level to store the accumulation time. The function of stopping the increase in time and reading the image in that cycle is performed. As a result, the output of the charge storage type image sensor becomes the maximum value allowed in the circuit system, so that even if the brightness of the light source is deteriorated, the desired good S / N and reproduction can be obtained. I do.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a document, 2 denotes a light source for illuminating the document 1, 3 denotes a charge accumulation type image sensor for accumulating optical information of an image on the document 1 illuminated by the light source 2 as signal charges, and 4 denotes accumulation of signal charges. This is a clock generation circuit that outputs an accumulation time control signal as a clock that determines the period. An analog circuit 5 converts the output of the charge accumulation type image sensor into an analog signal and performs analog processing such as sample hold, offset control, and automatic gain control and outputs the result. An output peak level detection circuit that outputs a stop signal when the level exceeds a set value (peak level).

Further, the reference numeral 7 designates an accumulation time of the signal charges at the time of automatic document reading as the shortest at the start, increases the accumulation time for each cycle until the output level exceeds the set value, and further comprises a stop signal. Is a controller that controls the cycle of the accumulation time control signal so as to stop the increase in the accumulation time at the time of output.

Next, the operation will be described. First, at the time of reading a white reference original, the accumulation time of the charge accumulation type image sensor 3, that is, the period of the accumulation time control signal is started from the shortest (for example, dot clock × 1728 when reading an A4-size original). Thereby, the light source 2
The image data on the document 1 illuminated by the above is accumulated in the charge accumulation type image sensor 3 as signal charges for the accumulation time, and the accumulated signal charges are output by charge transfer pulses and input to the analog circuit 5. The analog circuit 5 converts the output signal of the signal charge into an analog signal, performs analog processing such as sample hold, offset control, and gain control, and performs an output peak level detection circuit 6.
Output to

The output peak level detection circuit 6 detects whether or not the level of the image sensor output has reached a set value (L) as shown in FIG. 2 based on the analog processing output. , A stop signal for fixing the cycle of the accumulation time control signal output from the clock generation circuit 4 is output to the controller 7.

In this case, the controller 7 receives the output from the output peak level detection circuit 6 and increases the accumulation time for each period to the clock generation circuit 4 (for example, dot clock × 1728, 1730, 17
32. As shown in FIG. 2, the signal level is gradually increased from the initial state (a) to the state (b) as shown in FIG. 2, and reaches the set value (L) and receives the stop signal. Stop increasing the accumulation time. Therefore, thereafter, actual image data is read in that cycle. For this reason, the output of the image sensor itself becomes the maximum output allowed in the circuit system, and even if the light amount decreases due to the aging of the light source, a good S / N can always be obtained.
An optimum output can be obtained without performing gain adjustment in the analog circuit system in the initial step.

[0012]

As described above, according to the present invention, a charge accumulation type image sensor for accumulating optical information as signal charges in the cycle of the accumulation time control signal, and an output of the charge accumulation type image sensor are processed by analog processing. An analog circuit, a peak level detection circuit that outputs a stop signal when the output level of the charge accumulation type image sensor exceeds a set value based on an output of the analog circuit, and starts the signal charge accumulation time when reading a white document. Sometimes the shortest,
Until the output level exceeds the set value, the accumulation time is increased by one cycle, and the controller controls the cycle of the accumulation time control signal so that the increase of the accumulation time is stopped when the stop signal is output. Because of the control, the image reading can be realized with high sensitivity and high accuracy while always maintaining a good S / N ratio regardless of the aging of the light source. A practical effect that adjustment work can be omitted is obtained.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram of a signal processed by a controller in FIG. 1;

[Explanation of symbols]

 3 charge storage type image sensor 5 analog circuit 6 output level detection circuit 7 controller

Claims (1)

(57) [Claims] 1. A charge accumulation type image sensor for accumulating optical information as signal charges in a cycle of an accumulation time control signal, an analog circuit for performing analog processing on an output of the charge accumulation type image sensor, and an output of the analog circuit. A peak level detection circuit that outputs a stop signal when the output level of the charge accumulation type image sensor exceeds a set value, and the signal charge accumulation time when reading a white document is minimized at the start, and the output level is set to the set value. An image reading device that controls the cycle of the accumulation time control signal so as to increase the accumulation time in each cycle until the time exceeds a predetermined period, and to stop increasing the accumulation time when the stop signal is output.