JPS6313387B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a document reading device that uses a charge storage type image sensor to stably read a document image regardless of changes in its scanning speed.

[Technical background of the invention and its problems]

2. Description of the Related Art Various document reading devices have been developed that use a charge storage type image sensor such as a CCD to read and scan a document image to obtain time-series document image signals. In facsimile, OCR, copying machines, etc., the original image signal obtained as described above is thermally recorded using a thermal head, or the original image is reproduced using means such as electrostatic recording. There is.

By the way, when reproducing a document image using a thermal head, when all recording lines are white, the recording paper can be simply moved by one line without driving the thermal head, which reduces the time required for recording. It becomes possible to shorten the time. However, in order to perform such control, at least one
It is necessary to store image signals for lines and check the information. Therefore, for example, according to an apparatus equipped with an image memory that stores information for one document,
Since the reading speed and recording speed of information can be matched according to the information, the above-mentioned control can be performed easily. On the other hand, there was a problem in that it required a large capacity image memory.

On the other hand, for devices without image memory,
It is necessary to set the document reading scanning speed in accordance with the recording speed of the recording device. However, when the reading scanning speed is varied in accordance with the recording speed, as mentioned above, if a charge accumulation type image sensor is used, the charge accumulation time will change, and the signal level will eventually change. The problem arose of inviting For this reason, conventionally, changes in signal level have been corrected by varying the amplification gain of the signal processing system in accordance with changes in charge accumulation time, but this has resulted in a considerably complicated device configuration. Moreover, this method involves the inconvenience of varying the frequency of the image sensor drive clock signal in accordance with the scanning speed.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a document reading device using a charge accumulation type image sensor, in which the charge accumulation time is maintained regardless of changes in the document scanning time. It is an object of the present invention to provide a highly practical document reading device that can maintain a constant value and always obtain a good image signal.

[Summary of the invention]

The present invention alternately writes image signals read and output by a charge accumulation type image sensor into first and second memories line by line, and writes these written image signals line by line at a predetermined scanning speed. The structure is such that the charge is accumulated for a certain period of time by the image sensor and all of the original image signals of one line indicated by the accumulated charge are read out alternately every time, within the shortest time of the variably set readout scanning time. The reading is completed.

〔Effect of the invention〕

Thus, according to the present invention, after keeping the charge accumulation time of the image sensor constant for each line, the image signal is written into one memory, and this is read out at a predetermined scanning speed when scanning the next line. ,
During this period, image signals can be written to the other memory under certain conditions, which has great practical effects such as being able to always obtain stable and good image signals regardless of changes in scanning speed. It can be played.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the schematic structure of a typical CCD as a charge accumulation type image sensor. CCD1
For example, it includes a charge storage section 2 that photoelectrically converts an input optical image and stores the resulting charges, and charge transfer sections 5 and 6 provided on both sides of the charge storage section 2 via transfer gates 3 and 4. configured. The transfer gates 3 and 4 convert charges corresponding to the optical images accumulated in each pixel of the charge storage section 2 into sample signals.
It receives SH and transfers it to the charge transfer sections 5 and 6. For example, each odd numbered pixel signal is transferred to the charge transfer section 5, and each even numbered pixel signal is transferred to the charge transfer section 6. The image signals transferred to these charge transfer units 5 and 6 are inverted via an inverter 7 and sequentially transferred in response to clock signals φ ₁ and φ ₂ having opposite phases. , are read out alternately in chronological order. Note that the relationship between the sample signal SH and the clock signals φ ₁ and φ ₂ is as follows.
As shown in the figure. One line of image signals that are read out alternately and output in time series as described above are:
The signal is outputted via the signal amplification section 8.

FIG. 3 is a schematic configuration diagram of this device configured using such a CCD 1, and in the figure, 11 and 12
are first and second memories provided in parallel. The image signals read out from the CCD 1 are gate-controlled via a switch 13, and then passed through a selection switch 14 and sent to the first memory 1 line by line.
The data is written to the first or second memory 12. These first and second memories 11 and 12 alternately write and read data for each line, and the read speed is determined according to the image recording speed. It's summery. The selection switch 15 operates in conjunction with the selection switch 14 and is connected to the memory in read mode.

By the way, the CCD 1 is driven according to the scan start signal ST and the clock signal φ as follows. The scanning start signal ST is given in synchronization with the scanning of image recording, that is, the reading of image signals from the memories 11 and 12, and the period of this scanning start signal ST is determined according to the document recording scanning speed.

The start signal ST triggers the flip-flop (FF) 16 to set it, and is also applied to the counter 17 to reset its count value. By setting the FF 16, a high level signal is given to the FF 18 by its θ output, and when the clock signal φ is applied to the FF 18 in this state, the FF 18 is set. That is, the FF 18 is set in synchronization with the start signal ST and the clock signal φ. By setting the FF 18, the FF 16 is prohibited from inputting the start signal ST, and the FF 19, which inputs the clock signal φ and performs an inversion operation, is permitted to operate.
This FF 19 inputs the clock signal φ and receives the aforementioned clock signal φ ₁ , which drives the CCD 1.
It generates _φ2 .

On the other hand, the clock signal φ is input to a counter 20 and counted. This counter is the FF1
It is reset in response to the sample signal SH output from 8 via the OR circuit 21, and its count value is input to the decoder 22. Each time the count value reaches a predetermined value, the decoder 22
A signal is output, which is passed through the OR circuit 22 as a sample signal SH. Therefore, after receiving the set output of the FF 18, the counter 20 and the decoder 22 generate a sample signal SH of a predetermined period. This sample signal SH is applied to the CCD 1 and also to the counter 17. The counter 17 counts the sample signal SH, and its 4-bit binary output is applied to an AND circuit 26 via inverters 23, 24, and 25. As a result, a gate signal is generated every time the counter 17 counts "2", and the switch 13 is controlled to open or close.

Incidentally, the period determined by the counter 20 and the decoder 22 is set, for example, to 1/2 or less of the variably set shortest period of the start signal ST, that is, the shortest time of the image signal readout scanning time. Depending on this period, the charge accumulation time in the CCD 1,
and one of the image signals represented by the accumulated charge.
The transfer output time for all lines is determined.

According to this device configured in this way, as shown in the operating mode in FIG. , the accumulated image signal is transferred to the CCD over the same amount of time as the above accumulation time.
It will be read from 1. The time required for this is always shorter than the variably set minimum time of the readout scanning time. In this way,
Reading the image signal for each line by CCD1,
The output is done. The switch 13 receives the aforementioned gate signal and becomes conductive only at the timing when one line of image signals is output from the CCD, and guides the image signals to the first and second memories 11 and 12. Then, this image signal is transmitted to the first
Or written in the second memory 11, 12, 1
It is read out at a predetermined readout scanning speed after a line period. Therefore, when one line of image signals is being written into the first memory 11, the image signal of the previous line is read out from the second memory 12, and the image signal from the first memory 11 is read out in the next cycle. When reading is being performed, the image signal of the next line output after being accumulated during that period is stored in the second memory 12.
will be written in.

In this way, according to the present device, the first and second memories 11 and 12 are used to read out image signals in one go.
Since the line period is delayed and the signal speed is converted to generate an image signal at a desired scanning speed, charge accumulation in the CCD 1 and its transfer output can be controlled independently of the readout scanning speed. Moreover, since the charge accumulation and its transfer output are completed within the shortest time that is variably set for the readout scan,
It is possible to always ensure a constant charge accumulation time regardless of the readout scanning speed, and it is possible to stably obtain an image signal, which is a great practical advantage.

Note that the present invention is not limited to the above embodiments. For example, a MOS capacitor type image sensor or the like can be used as a charge accumulation type image sensor. Further, the number of pixels constituting one line may be determined according to specifications. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of the drawing]

The figure shows one embodiment of the present invention, and FIG.
FIG. 2 is a diagram showing the basic configuration of a CCD image sensor, FIG. 2 is a diagram showing drive signals of the CCD, FIG. 3 is a schematic diagram of the configuration of the embodiment device, and FIG. 4 is a diagram showing the operation mode of the embodiment device. 1...CCD image sensor, 11, 12...
Memory, 13, 14, 15...Switch, 16,
18, 19...flip flop, 17, 20...
... Counter, 21 ... OR circuit, 22 ... Decoder, 23, 24, 25 ... Inverter, 26 ...
AND circuit.

Claims (1)

[Claims] 1. A charge accumulation type image sensor that reads a document image line by line, and a first sensor that alternately stores image signals output from this image sensor line by line and reads out the stored image signals line by line. The charge accumulation of the document image by the image sensor is set to 1/2 or less of the readout scanning time within a variably set minimum readout time for reading image signals from the second memory and the first and second memories. and means for controlling the transfer of all of the image signals of one line in which charge has been accumulated to the first or second memory after the charge has been carried out for a certain period of time.