JPH0576170U - Image reader - Google Patents

Abstract

(57) [Abstract] [Purpose] The reading motor has been improved by improving the performance of the CCD.
Focusing on the fact that the same line can be read multiple times during a step, it is an object of the present invention to provide an image reading apparatus that reduces white noise included in read image data of a line as much as possible to improve the S / N ratio. And [Configuration] After the reading motor is driven one step,
In an image reading apparatus configured to read the same line a plurality of times during a document rest period until step driving,
Means (adder 3, buffer memory 4, switch 5, controller 8) for adding the read image data of the same line, and the average value obtained by dividing the added image data of the same line by the number of additions. A means for obtaining image data (switch 5, divider 6, controller 8) is provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an image reading device used in a facsimile machine or the like.

[0002]

[Prior Art]

 The image reading apparatus includes a light source including, for example, an LED (Light Emitting Diode) and a CCD (Charge Coupled Device). The CCD includes a photodiode group for at least pixels and a shift register. The operation of this type of image reading apparatus will be described below. That is, the light source irradiates the original with light, and the reflected light (information light) reflected by the original enters the photodiode group. The photodiode group accumulates optical signal charges corresponding to the reflected light, and the optical signal charges are transferred to the shift register at a predetermined timing. Then, the shift register transfers the density level information (brightness information) based on the optical signal based on a predetermined clock, performs A / D conversion, and sequentially outputs.

Then, for example, in a facsimile apparatus, the output density level information for each pixel is compared with a preset reference value to determine whether it is white or black. That is, if the density level has a value higher (brighter) than the reference value, it is judged as white, and if the density level has a value lower (darker) than the reference value, it is judged as black. And so on.

By the way, in recent years, the performance of each electric device such as the sensitivity of CCD, the operating frequency, and the light amount of the light source has been improved. On the other hand, drive systems (reading motors, printing motors, etc.) can still only operate at low speeds. Further, in the facsimile device, the time required for encoding the image data is relatively long compared to the image reading time, and even if the next line is read before the encoding of one line is completed, that line However, there is a circumstance that the image data processing cannot be performed. Due to these various circumstances, in an image reading apparatus of recent years, the CCD scans the same line several times (2 to 4 times) during the document rest period from step driving of the reading motor to step driving next. (Reading), and one of the line image data is adopted for processing such as encoding.

[0005]

[Problems to be solved by the device]

 By the way, as described above, in the conventional image reading device, the same line is read by the CCD 2 to 4 times, but only one of them is adopted and the rest is discarded. Reading 2 to 4 times is not designed to help improve image quality.

As described above, the present invention focuses on the fact that the same line can be read multiple times during one step of the reading motor due to the improvement of the CCD performance, etc., and white noise included in the read image data of the line can be eliminated. It is an object of the present invention to provide an image reading device which is reduced as much as possible to improve the S / N ratio.

[0007]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, an image reading apparatus according to the present invention comprises a unit for reading the same line a plurality of times during a document rest period from when the reading motor is driven one step to the next step driving. It is characterized by comprising means for adding the read image data on the same line and means for obtaining the average value image data by dividing the added image data on the added same line by the number of additions.

[0008]

[Action]

In the above configuration, one piece of read image data contains white noise having a Gaussian distribution with a mean of 0 and standard deviation σ _x , but M pieces of read image data on the same line are added. By dividing by the number of additions M, the noise contained in the averaged image data is reduced to 1 / M ^1/2 and the S / N ratio is improved.

[0009]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. In FIG. 1, 1 is a CCD, 2 is an A / D converter, 3 is an adder, 4 is a buffer memory, 5 is a switch, 6 is a divider, 7 is a main memory, and 8 is a control unit.

The CCD 1 is provided so that its longitudinal direction coincides with the width direction of a document (not shown), and the image of this document is read and output to the A / D converter 2. In addition, the CCD 1 is driven by a control signal from the control unit 8 from the time when the reading motor (not shown) is driven by one step to the time when the next one step is driven (that is, the original remains stationary). Image reading operation is performed four times each.

The A / D converter 2 converts the analog image data signal received from the CCD 1 into a 6-bit digital image data signal at a predetermined sampling frequency, and outputs this digital image data to the adder 3. It is like this. The adder 3 is configured to add the read image data of four times for the same line output from the A / D converter 2. Specifically, a count value is input from the control unit 8, and when the count value N is N = 1, the 6-bit digital image data from the A / D converter 2 is output to the buffer memory 4 as it is. On the other hand, when the count value N is N> 1, the image data obtained by reading the one already stored in the buffer memory 4 and the 6-bit digital image data output from the A / D converter 2 Are added and output to the buffer memory 4. In the present embodiment, the image reading operation is performed four times on the same line, so that the count value N is repeated within the range of 1 to 4.

The buffer memory 4 holds the image data supplied from the adder 3, and outputs the held image data to the switch 5 in response to a read command from the control unit 8. It should be noted that the digits are increased by the addition, but of course, the digits are set so as not to overflow. The switch 5 is configured to switch, according to a command from the control unit 8, whether the image data output from the buffer memory 4 is supplied to the adder 3 or the divider 6. That is, the switch 5 is connected to the A side in the figure while the addition process is performed in the adder 3, while the switch 5 is connected to the B side in the figure when the division process is performed on the addition image data. To be done.

Here, the relationship between the count value N and the operation contents of the switch 5 and the buffer memory 4 and the command contents of the control unit 8 will be described. When the count value N = 1, the control unit 8 To the buffer memory 4, and the buffer memory 4 stores the image data from the adder 3. In addition, the switch 5 is in a state of being connected to the A side in the drawing according to a command from the control unit 8.

When the count value N = 2, the control unit 8 issues a read command and a write command to the buffer memory 4. In response to the read command, the buffer memory 4 reads the image data already stored, and the read image data is input to the adder 3 via the switch 5. Then, the image data added by the adder 3 is stored again at the same address in the buffer memory 4.

When the count values N = 3 and 4, the same processing as described above is performed, but when the count value N = 4, after the processing is performed, that is, the four read image data for the same line. After the addition is performed, the switch 5 is connected to the B side, a read command is issued to the buffer memory 4, and the read four addition image data is output to the divider 6. Become.

The divider 6 divides the above-mentioned added image data at the count value N = 4 and outputs this average value image data to the main memory 7. In the above configuration, one read image data contains white noise having a Gaussian distribution with an average of 0 and a standard deviation σ _x (variance σ _x ² ) as shown in FIG. , The noise in the averaged image data is reduced to 1 / M ^1/2 by adding multiple (M) read image data on the same line and dividing by the number M of additions. Will be. For example, when M is 4, the noise is reduced to 1/2 and the S / N ratio is improved by 2 times (6 dB).

In this embodiment, a plurality of read image data on the same line are added in the form of digital signals, but as shown in FIG. 3, addition of image data is performed in the form of analog signals. It may be done. As a configuration for realizing the addition in the form of such an analog signal, for example, the digital image data output from the switch 5 is analogized between the contact A side of the switch 5 and an analog adder described later. A D / A converter for converting into a signal is provided, and instead of the adder 4, the analog image data obtained by the above D / A conversion and the analog read image data output from the CCD 1 are added. An analog adder is provided and the added analog image data is converted into a digital signal by the A / D converter 2 and stored again in the buffer memory 4.

Further, in the present embodiment, the number of times of reading on the same line is set to 4, but it may be more or less than 4 if it is plural. Of course, it is not possible to increase the number indefinitely due to the restriction of the coding speed and the capability such as CCD. Also, in the divider 7, if the divisor is 4 as in the present embodiment, it can be performed by shifting (decrease) by 2 bits to the LSB side, and if the divisor is 2, the same applies. This can be done by shifting (decimating) one bit to the LSB side. When the divisor is fixed to 4 or 2, the divider 7 can be eliminated by devising the connection relationship of the data bus connecting the buffer memory 4 and the main memory 7. For example, when the divisor is fixed to 2, as shown in FIG. 4, it is necessary to make a connection so that 1-bit to 7-bit data in the buffer memory 4 becomes 0 to 6-bit data in the main memory 7. Good.

In addition, in the present embodiment, the buffer memory 4 is configured to have a capacity for storing image data for one line, and the capacity of the buffer memory 4 is reduced, but the buffer memory 4 can be used for a plurality of times. All the read image data may be stored, and the addition process may be performed after all the image data are stored.

[0020]

[Effect of the device]

 As described above, according to the present invention, a plurality of read image data is obtained for the same line, and these are added and divided by the number of additions M to be included in the averaged image data. There is an effect that noise can be reduced and the S / N ratio can be improved.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship among read image data, true image data, and white noise.

FIG. 3 is an explanatory diagram showing the concept of performing addition processing in the form of analog signals.

FIG. 4 is an explanatory diagram showing that the divider can be reduced by devising the connection relationship between the buffer memory and the main memory when the divisor is fixed to 2.

[Explanation of symbols]

 1 CCD 2 A / D converter 3 adder 4 buffer memory 5 switch 6 divider 7 main memory 8 controller

Claims (1)

[Scope of utility model registration request] 1. A means for reading the same line a plurality of times during each document rest period from the time the reading motor is driven one step to the next step driving, and means for adding the read image data of the same line. An image reading device comprising means for dividing the added image data on the same line by the number of additions to obtain average value image data.