JP2001203891A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To settle the problem where the read starting time is delayed, when the black level correction is carried out right before the start of a reading operation in a black level correction method by which the black image data equivalent to plural lines are averaged by the software, the averaged data is adjusted to be matched with the black level of an image reader and also the adjustment processing is repeated by plural times. SOLUTION: This image reader is provided with an averaging circuit 50, which fetches the black image data from a CCD image sensor 11 by quantity equivalent to plural continuous lines an averages these image data, an offset adjustment circuit 16 which adjusts the offset voltage of analog image signals according to the data which are averaged by the circuit 20, when the power supply of the image reader is applied or in a period when no image-reading operation is carried out and a correction circuit 18, which corrects the digital image signals according to the data which are averaged by the circuit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital copying machine,
The present invention relates to an image reading device such as a facsimile or a scanner.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus,
A so-called black level correction is performed in which the output corresponding to the black information of the read original is adjusted to match the output black level of the apparatus. In this black level correction, black image data is sampled, and a CCD (Charge Coupled De-charge) is performed so that the black image data matches the black level of the output of the image reading device.
vice) A process of adjusting the offset voltage of the analog signal output from the image sensor is performed. However, due to noise and errors in the amount of adjustment of the offset voltage, etc.,
Precise black level correction cannot be performed.

Therefore, in order to perform accurate black level correction without being affected by noise, errors in the adjustment amount of the offset voltage, and the like, black image data for a plurality of lines is sampled, and black image data for the plurality of lines is obtained. A black level correction method has been proposed in which software is averaged, the average data is adjusted to match the black level of the device, and the process is repeated a plurality of times. See JP-A-6-326867).

[0004]

Since the offset voltage of the analog image signal changes due to a change in the ambient temperature, a change in the temperature of each device, and the like, it is necessary to set the original document so as not to be affected by the change. It is desirable to perform black level correction immediately before the start of reading. However, in the above-described black level correction method, it takes time to repeat the process of adjusting the average data to match the black level of the apparatus a plurality of times. Therefore, if the black level correction is performed immediately before the start of reading, the reading starts. There is a problem that it takes a long time to perform reading, that is, the reading start time is delayed.

In order to perform averaging of black image data for a plurality of lines by software using a CPU,
It is necessary to take a plurality of lines of black image data at predetermined intervals (time). For this reason, there is a problem that accurate averaging processing cannot be performed on periodic noise such as power supply noise, and thus the influence of noise cannot be sufficiently suppressed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to surely correct black level fluctuations caused by temperature fluctuations and the like, and to further reduce periodic noise. An object of the present invention is to provide an image reading apparatus capable of performing black level correction with less influence.

[0007]

An image reading apparatus according to the present invention is an image reading apparatus which converts an analog image signal from an image sensor into a digital image signal and inputs the digital image signal. Averaging means for fetching and averaging the lines, and offset adjusting means for adjusting the offset voltage of the analog image signal based on the data averaged by the averaging means when the apparatus is turned on or during a period in which the reading operation is not performed. When,
Immediately before the start of the reading operation, there is provided correction means for correcting the digital image signal based on the data averaged by the averaging means.

In the image reading apparatus having the above structure, when black image data for a plurality of lines is input from the image sensor, the averaging means averages the black image data for the plurality of lines and offsets the averaged data. It is given to the adjusting means and the correcting means. On the basis of the averaged data, when the apparatus is powered on or during a period in which the reading operation is not performed, the offset adjusting unit performs a process of adjusting the offset voltage of the analog image signal, and immediately before the reading operation starts. Performs a process in which the correction means corrects the digital image signal.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an image reading apparatus according to an embodiment of the present invention. Here, a configuration from the conversion of an analog image signal output from a CCD image sensor into a digital image signal to the execution of shading correction processing is shown.

In FIG. 1, a CCD image sensor 11
Output two data signals of an odd-numbered pixel (hereinafter, referred to as odd-numbered data) and even-numbered pixel data (hereinafter, referred to as even-numbered data) of a pixel column as analog image data signals. Is done. The data of these two systems are supplied to S / H (sample and hold) circuits 12-1 and 12-1.
Sample is held at -2.

The odd-numbered data sampled and held by the S / H circuit 12-1 is a GCA (gain control amplifier).
The signal is amplified by the circuit 14-1 and supplied to the MPX (multiplexer) circuit 15. On the other hand, the even-numbered data sampled and held by the S / H circuit 12-2 is output to the offset adjustment circuit 1
After the offset voltage is adjusted so that the signal level coincides with the odd-numbered data in 3, the signal is amplified by the GCA circuit 14-2 and supplied to the MPX circuit 15.

The MPX circuit 15 combines the odd-numbered data and the even-numbered data and converts them into one-system analog image data corresponding to the pixel rows of the CCD image sensor 11. The offset voltage of the analog image data is adjusted by an offset adjustment circuit 16 for black level correction, and then converted to digital image data by an ADC (analog-digital converter) circuit 17.

The digital image data is supplied to a correction circuit 18
Is corrected (subtracted or added) so as to be the final value of the black image data, and supplied to the shading correction circuit 19 and the averaging circuit 20. The image data that has been subjected to shading correction by the shading correction circuit 19 is supplied to an image processing unit (not shown) at a subsequent stage.

The averaging circuit 20 performs a process of fetching black image data from the CCD image sensor 11 for a plurality of continuous lines and averaging the same. More specifically, the averaging circuit 20 is configured by hardware, takes in a plurality of lines of black image data output from the CCD image sensor 11 in a state where light is not irradiated, and fetches the black image data for the number of lines and the CCD. By averaging with the number of pixels of the image sensor 11, averaged data per pixel (hereinafter, referred to as average data) is calculated.

The average data calculated by the averaging circuit 20 is supplied to a controller 21 comprising a CPU. The controller 21 sets an offset voltage to be adjusted by the offset adjustment circuit 16 and a correction value to be subtracted or added by the correction circuit 18 based on the average data provided from the averaging circuit 20.

FIG. 2 is a block diagram showing an example of the circuit configuration of the averaging circuit 20. The averaging circuit 20 according to this embodiment is configured to read and average black image data from the CCD image sensor 11 for continuous m lines (m is an integer of 2 or more).

In FIG. 2, m adders 201-1 to 201-m are arranged in parallel corresponding to m lines.
The adder circuit 201-1 uses the image data of the first line among the m lines of image data to be taken as one addition input and the output data as the other addition input, thereby obtaining one line worth of image data. The image data is cumulatively added in pixel units. Similarly, for the adders 201-2 to 201-m, 2
The image data for one line from the line to the m-th line is cumulatively added for each pixel.

Here, when the number of pixels of the CCD image sensor 11 is n, the adding circuits 201-1 to 201-m each perform cumulative addition of image data for n pixels. The addition results of these addition circuits 201-1 to 201-m are supplied to the subsequent division circuits 202-1 to 202-m. These division circuits 202-1 to 202-m include addition circuits 201-1 to
Each addition result of 201-m is divided by 1 / n. Thereby, as each division result of the division circuits 202-1 to 202-m,
An average of pixel data in one line is obtained.

Each division result of the division circuits 202-1 to 202-m is supplied to an addition circuit 203. The addition circuit 203
The division results of the division circuits 202-1 to 202-m are added.
The addition result is supplied to the division circuit 204. This division circuit 204 divides the addition result of the addition circuit 203 by 1 / m. As a result, average data per pixel for m lines is obtained as a division result of the division circuit 204.

Next, the processing procedure of the black level correction executed every predetermined time from the previous correction when the power of the apparatus is turned on or during a period in which the reading operation is not performed will be described.
This will be described with reference to the flowchart of FIG.

First, m lines of black pixel data are sampled (step S11), and the averaging circuit 20 calculates average data per pixel in m lines of black pixel data (step S12). Then, the offset voltage is adjusted by the offset adjustment circuit 16 so that the average data becomes the target value (step S13). The target value at this time needs to be a value such that the data of each pixel does not become 0 or less.

After the offset voltage is adjusted in step S13, the processes in steps S11 to S13 are repeated N times. That is, the process of collecting the m-th line of black pixel data again and adjusting the offset voltage based on the averaged data is repeated N times every predetermined time.

After the N repetitions, the final value is determined from the collected average data of N times and the adjusted value of the offset voltage (step S14), and the offset voltage is set to the final value (step S15). . When the CCD image sensor 11 has multiple outputs, the series of processes described above are executed for the number of outputs. Finally, the digital image data is subtracted (or added) by the difference between the target value and the final black image data by the correction circuit 18 so that the digital image data becomes the black level as a system (step S1).
6).

Next, the processing procedure of the black level correction executed immediately before the start of the reading operation will be described with reference to the flowchart of FIG.

First, a set value (for example, a subtraction value) of the correction circuit 18 is cleared (step S21). Thereafter, image data for m lines is collected, and the averaging circuit 20 obtains average data per pixel (step S22). This average data is given to a controller 21 composed of a CPU. Then, the controller 21 calculates a difference between the average data and the target value (step S23), and determines whether the difference is equal to or larger than a predetermined value (step S24).

At this time, if there is a difference equal to or more than a predetermined value, the digital image data is corrected (for example, subtracted) by the difference between the average data and the final black image data in the correction circuit 18 to obtain a system. (Step S25). On the other hand, if there is no difference equal to or greater than the predetermined value, the digital image data is corrected by the difference between the target value and the final black image data (step S26).

Thereafter, an image is read (step S27), and after the reading operation is completed (step S2).
8) It is determined whether or not the difference between the average data at the start of reading and the target value is greater than or equal to a predetermined value (step S29). If there is a difference equal to or larger than the predetermined value, the black level correction described with reference to the flowchart of FIG. 3, that is, the black level correction by offset adjustment of the analog signal is performed (step S30), and the process shifts to the standby state. If there is no difference equal to or more than the predetermined value, the process directly shifts to the standby state.

As described above, when the power of the apparatus is turned on or during the period in which the reading operation is not performed, not only the black level correction is performed by the offset adjustment circuit 16 but also the correction circuit 18 immediately before the reading operation is started. By performing the black level correction, it is possible to reliably correct the fluctuation of the black level due to the temperature fluctuation and the like.

The averaging circuit 20 averages black image data of a plurality of continuous lines by hardware, and performs black level correction using the averaged data. Without giving it, it is possible to perform black level correction with less influence of periodic noise such as power supply noise.

Further, when the correction circuit 18 corrects the digital image data, the black level correction is a simple one. By adjusting the offset voltage, it is possible to perform more accurate black level correction.

In the above embodiment, an image reading apparatus including both the offset adjustment circuit 16 and the correction circuit 18 has been described as an example. However, an image reading apparatus having only one of them may be used.

That is, the image reading apparatus may be configured to take in black pixel data for a plurality of continuous lines and adjust the offset voltage of the analog image signal or correct the digital image signal based on the data.
According to this, it is possible to perform black level correction with less influence of periodic noise such as power supply noise.

[0033]

As described above, according to the present invention,
Black level correction is performed not only at the time of turning on the power of the apparatus or during a period in which the reading operation is not performed, but also immediately before the start of the reading operation. Fluctuations can be reliably corrected. In addition, black image data for a plurality of continuous lines is averaged, and black level correction is performed using the average data. Therefore, black level correction with less influence of periodic noise such as power supply noise can be performed. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image reading device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of a circuit configuration of an averaging circuit.

FIG. 3 is a flowchart illustrating a procedure of a black level correction process performed when the apparatus is turned on or during a period in which a reading operation is not performed.

FIG. 4 is a flowchart showing a procedure of a black level correction process executed immediately before the start of a reading operation.

[Explanation of symbols]

11: CCD image sensor, 15: multiplexer (MPX), 16: offset adjustment circuit, 17: AD converter, 18: correction circuit, 20: averaging circuit, 21 ...
Controller (CPU)

Claims (4)

[Claims] 1. An image reading apparatus for converting an analog image signal from an image sensor into a digital image signal and inputting the digital image signal, and averaging means for fetching and averaging a plurality of lines of black image data from the image sensor. An offset adjusting unit that adjusts an offset voltage of the analog image signal based on data averaged by the averaging unit when the apparatus is powered on or during a period in which a reading operation is not performed; An image reading device comprising: a correction unit configured to correct the digital image signal based on the data averaged by the averaging unit. 2. The image processing apparatus according to claim 1, wherein the averaging means averages black image data for a plurality of lines by the number of lines and the number of pixels of the image sensor, and performs the averaging process by hardware. The image reading device according to claim 1. 3. The apparatus according to claim 1, wherein the offset adjusting unit adjusts the offset voltage after the end of the reading operation when the correction by the correcting unit is performed.
Or the image reading device according to 2. 4. An image reading device for converting an analog image signal from an image sensor into a digital image signal and inputting the digital image signal, wherein a plurality of continuous lines of black image data from the image sensor are fetched and based on the data. An image reading apparatus, comprising: means for adjusting an offset voltage of the analog image signal or correcting the digital image signal.