JP3096914B2 - Digital 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 a digital copying apparatus for digitizing a read signal and performing signal processing.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing the configuration of a conventional reading device. C as a photoelectric converter for reading the original
Two amplifiers 2a and 2b are connected to CD1, and an analog switch 3 is used to select and output one of its outputs.
Is provided. The analog switch 3 has an amplifier 4 for amplifying its output and an output of the amplifier 4 for A / D conversion.
A that converts and converts it to a 6-bit digital signal and outputs it
/ D converter 5 is connected. The CCD 1 is composed of, for example, 5000 sensor elements,
The maximum A3 size can be read with pi. In this case, driving is performed by two channels of EVEN ODD, reset noise of each output is removed, and the output is amplified to a certain level by the amplifiers 2a and 2b. Thereafter, the signals are combined into one channel using the analog switch 3. Further amplifier 4
AGC (automatic gain adjustment) for correcting the light quantity fluctuation for each scan is used for this amplification. The AGC reads a reference white board just before the scanner starts reading an image area, determines an amplification amount (gain) based on the read data, and outputs the amplified signal as AGC data.
Supply to The reference white plate WB is installed as shown in FIG. 7, and is provided at the end of the contact glass CG at the scan start position of the scanner SC.

The CCD 1 used here is of a reduction type, and the sensor is smaller than one pixel on the original and one pixel of the sensor, and the reflected light from the original is converged by a lens. As shown in FIG. 8, the central portion is brighter and the edge portion is darker. Since the AGC data is determined using bright data in the center, the brightest peak value in one line is detected and the peak value is A / D.
In order to approach without exceeding the value of the reference voltage of the converter 5,
Determine AGC data. After the signal is amplified to an appropriate amplitude by AGC, the signal is quantized by the A / D converter 5. In this embodiment, 6-bit quantization is performed. After the conversion into a digital signal, shading correction is performed. As shown in FIG. 9, the shading correction corrects a decrease in the amount of light at an end portion and individual variations in sensor elements. The principle is that the data (D _S ) when the reference white plate is read is stored in each of the 5000 sensor elements, and the read data when the original is actually read is used as the dynamic range of each element. (D _R) is to correct the data where it is in level with respect to D _S. The correction data is represented by the following equation. D = (D _R / D _S ) × (number of quantization levels) If the number of quantization levels is 6 bits, it is 64, and if it is 8 bits, it is 256. One line of memory (RA
M: random access memory), but the data D shown in the above equation has an error due to uneven density or dirt of the reference white plate itself. without deciding the _S, among the read data of several lines, the largest value (maximum white value) so as to leave as D _S. First, RAM the first line of D _S
To write, compared with the D _S it was left until D _S and the previous line newly input from the next line to be written towards the back to RAM larger. RAM writing,
After the AGC data is determined, the period is sufficient to read the reference white board. When the image enters the image reading area, writing to the RAM is stopped and only the output operation is performed.
_S is supplied to the address of the ROM (random access memory) for the operation table. Calculation table ROM
It is the D of the above formula which is determined by a combination of D _S and D _R D
_S and D _R previously written in advance in the ROM address designated by, and outputs the D in the D _R from D _S and the A / D converter 5 from RAM.

[0004]

However, in the above-mentioned prior art, when the peak value of D _S is left, the instantaneous variation of the light source, the microscopic unevenness on the surface of the reference white plate, the electrical There is a problem that a value higher than the actual peak value remains due to excessive noise or the like. This problem is the same in AGC. In the case of AGC, since AGC data is determined by a peak value in one line, if noise is added to the peak value, the AGC data is directly affected. An object of the present invention is to provide a digital image reading device capable of eliminating the influence of noise.

[0005]

In order to achieve the above object, the present invention provides a reading means for optically reading a document image, and a storage for storing an image of a reference white plate read prior to reading the document image. And a processing unit for performing shading correction based on the stored data and the read data at the time of reading a document, wherein a low-pass filter removes noise in the reference white board before storing the image. A filter and the low- pass filter
The peak value is detected from the output data of the
Automatic gain control means for determining the gain of the amplifier from the value.
And it said that there were pictures.

[0006]

According to the above means, before the read image of the reference white board is stored in the RAM, a noise component in the image signal is removed, and the S / N ratio is improved. Therefore, it is possible to prevent the peak value from exceeding the actual value, and to prevent the density unevenness of the output image and the occurrence of linear image noise. The determination of the gain of the amplifier in the AGC is performed on the value passed through the low-pass filter. Therefore,
The AGC data is optimized, and the occurrence of a saturation phenomenon or the like due to the image signal exceeding the reference voltage of the A / D converter can be prevented.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the control unit of the digital image reading device according to the present invention. FIG. 2 is a front view showing a schematic configuration of an image reading device of a digital copying apparatus according to the present invention, and FIG. 3 is a configuration diagram showing a configuration of a printer unit using a laser. First, FIGS. 2 and 3
Will be described. A contact glass 6 on which a document is placed is provided on the upper surface of the apparatus, and a pair of light sources 7a and 7b are arranged as a traveling body 8 so that a lower portion thereof can be moved horizontally (moving in the sub-scanning direction). A mirror 9 for reflecting light from a document in a horizontal direction is provided below the light sources 7a and 7b.
Are integrated with the light sources 7a and 7b. Mirror 9
Mirror 1 to reflect the light from
0 and a mirror 11, the light sources 7a, 7
It is provided so that it can run according to the movement of b. Mirror 1 to reflect light from mirror 11 downward
3 is provided, and a mirror 14 for reflecting the light from the mirror 13 in the opposite direction to the light from the mirror 11 is provided below the mirror 13. In the exit optical path of the mirror 14,
A lens 15 is provided, and a line image sensor 16 is provided at the in-focus position.

In the above configuration, when reading an image, an original is set on the contact glass 6 with the image side down, and a start button (not shown) is pressed. As a result, the traveling body 8 and the traveling body 12 start moving leftward in the figure, and the sub-scanning of the document is performed. At this time, the traveling body 12 moves at half the speed of the traveling body 8. Light source 7a,
The reflected light (reading light) from the original illuminated by 7b is mirror 9 → mirror 10 → mirror 11 → mirror 13 → mirror 1
4 → Line image sensor 1 via lens 15 sequentially
Reach 6. The line image sensor 16 converts the incident light into an electric signal and sends it to a processing circuit.

As shown in FIG. 3, the printer section comprises a laser generator 17, an optical system 18 for focusing laser light from the laser generator 17 on a predetermined position, and a reflection for reflecting output light of the optical system 18. A mirror 19, a photosensitive drum 20 to which a beam from the reflecting mirror 19 is exposed, a charging charger 21 for uniformly charging the photosensitive body before exposure, a developing device 22 for developing an electrostatic latent image by exposure with toner, A registration roller 23 that feeds the transfer paper to the transfer position at a proper timing, a cassette 24 in which a large number of transfer papers are set, a cassette 25 in which paper of a different size from the cassette 24 is set, and only one sheet from the cassette 24 Paper feed roller 26 for feeding paper, paper feed roller 27 for feeding only one sheet from cassette 25, and transfer paper sent from registration roller 23. Transfer charger 28 for transferring the toner image on the optical drum 20, separation charger 29 for peeling the portion where transfer of the paper has been completed from the photoconductor drum 20,
A transport belt 30 that transports the peeled transfer paper, a fixing device 31 that fixes a toner image attached to the transfer paper transported by the transport belt 30, and a residual toner that adheres to the surface of the photosensitive drum 20 is removed. And a discharge tray 33 that stores transfer paper from the fixing device 31.

In FIG. 3, a laser generator 17 is modulated and driven in accordance with image information, and reaches a photosensitive drum 20 which has been charged in advance by a charging charger 21 via an optical system 18 and a reflecting mirror 19. To form a latent image. This latent image reaches a position facing the developing device 22 according to the rotation of the photosensitive drum 20, and toner development is performed on the latent image. The cassette 24 or the cassette 2 is adjusted in timing when the visible image formed by the toner development reaches the transfer position.
5 is fed from the registration rollers 23, and the toner image on the photosensitive drum 20 is attracted to the sheet surface by the transfer charger 28 at the transfer position. The sheet on which the transfer has been completed is discharged from the leading end thereof to the charge removing charger 29.
And is sent out onto the conveyor belt 30.
The sheet on the conveyor belt 30 is carried into the fixing device 31, where heat and pressure are applied to fix the toner image on the sheet. The transfer paper on which the fixing has been completed is sent to a discharge tray 33.

Next, the configuration of FIG. 1 will be described. A /
A low-pass filter (LPF) 35 and a ROM 36 are connected to the D converter 34, and the low-pass filter 35 has a peak detection / AGC circuit 37, a selector 38, and a comparator 39.
Is connected, and a RAM is provided between the ROM 36 and the selector 38.
40 are connected. The low-pass filter 35 is a one-dimensional or two-dimensional spatial filter, and FIGS. 4A and 4B show examples of coefficients of the filter. The center in the figure is the coefficient for the pixel of interest, and for pixels in eight directions adjacent to or before or after the pixel of interest, the coefficient is described at that position. The value of each pixel is multiplied by a coefficient, all are summed, and the value is divided by the sum of the coefficients to become the new value of the pixel of interest. In FIG. 1, the A / D converter 34
After the A / D conversion by the
Selector 38 for writing to 0, comparator 39 and AG
Peak detection / AGC circuit 37 for determining C data
Is passed through a low-pass filter 35 to remove noise components.

FIG. 5 is a timing chart showing the operation of the above embodiment. When the scanner starts, the running body 8
Starts moving from the home position. When the traveling body 8 reaches the reference white board WB shown in FIG. B, first, AGC is performed. AGC may be performed on only one line, but in this embodiment, AGC is performed on two lines. Thereafter, the writing of the shading data is performed on a plurality of lines. This writing can be performed in one line, but as described above, a period as long as the width of the reference white plate WB permits is used in order to leave an appropriate value. When the shading data has been taken and the traveling body 8 enters the document area, the FGATE signal is asserted. After shading correction, the image data is MTF
Correction, scaling, binarization, dithering, and the like are performed, and an image is reproduced by the output device.

[0013]

As described above, according to the present invention, the reference white plate
Filter to remove noise in the image before storing it
Filter and the output data of this low-pass filter
Detect the peak value and determine the amplifier gain from the peak value.
The automatic gain control means for controlling the A / D ratio improves the S / N ratio, prevents the density unevenness of the output image, the generation of linear image noise, and optimizes the AGC data. Therefore, it is possible to prevent the occurrence of a saturation phenomenon or the like due to the image signal exceeding the reference voltage of the A / D converter.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a control unit of a digital image reading device according to the present invention.

FIG. 2 is a front view showing a schematic configuration of an image reading apparatus of the digital copying apparatus according to the present invention.

FIG. 3 is a configuration diagram illustrating a configuration of a printer unit using a laser.

FIG. 4 is an explanatory diagram showing coefficients of the filter shown in FIG. 1;

FIG. 5 is a timing chart showing the operation of the configuration of FIG. 1;

FIG. 6 is a block diagram illustrating a configuration of a conventional reading device.

FIG. 7 is an explanatory diagram showing an installation state of a reference white plate WB.

FIG. 8 is a CCD output characteristic diagram when a reference white plate WB is read.

FIG. 9 is a characteristic diagram showing a result of performing shading correction on the output of FIG. 8;

[Explanation of symbols]

 Reference Signs List 1 CCD 2a amplifier 2b amplifier 3 analog switch 4 amplifier 5 A / D converter 6 contact glass 7a light source 7b light source 8 traveling body 12 traveling body 34 A / D converter 35 low-pass filter 36 ROM 37 peak detection / AGC circuit 38 selector 39 comparison Instrument 40 RAM CG Contact glass SC Scanner WB Reference white board

Claims (1)

(57) [Claims] A reading means for optically reading a document image; a storage means for storing an image of a reference white plate read prior to reading of the document image; and a reading means for reading the document based on the stored data and the read data. In a digital image reading apparatus provided with a processing unit for performing shading correction, a low-pass filter that removes noise in an image of the reference white board before storing the image, and a peak value is detected from output data of the low-pass filter
Automatic gain that determines the amplifier gain from its peak value
Digital image reading apparatus characterized by comprising: a control means.