JP2005260857A - Image reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading device in which irregularities, such as image stripes or spots due to noise are prevented from being generated. <P>SOLUTION: A quantity of light of a lamp 2 is controlled by controlling an inverter 6 by an image processing circuit 5 so that a reference image signal resulting from reading a reference image by an image sensor 1 is converted into a digital signal by an A/D converter 4 by obtaining a maximum output within a range of no saturation in an amplifier circuit 3, and an amplification rate of the amplifier circuit 3 is controlled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus that reads an original using an image sensor.

  Digital copying machines, facsimile machines, and the like are provided with an image reading device that reads an original with an image sensor made up of a CCD element or the like. An image sensor is generally configured by arranging thousands of light receiving elements, and decomposes an image of one line into thousands of pixels and outputs a pixel signal indicating the density of each pixel. In order to read a document stably with such an image sensor, the output of each light receiving element is required to be constant for the same image density.

  However, in the image sensor, not only variation in sensitivity of each light receiving element but also variation in γ characteristic which is linearity of photoelectric conversion characteristic occurs. Shading correction is performed to correct such variations. Shading correction is performed by first reading a reference white original, storing photoelectric conversion output for all white outputs in a memory for each pixel, and reading actual originals based on white output information stored for each pixel. In addition, the output level in each pixel unit is corrected.

However, even if the shading correction is performed, the image output signal when the gray document at the intermediate level is read is not uniform, and a black streak occurs due to the reading of the gray document. For this reason, in Japanese Patent Application Laid-Open No. 9-284550 (Patent Document 1), data is accumulated every predetermined time by a reading means for reading a document, and reading for reading a reference image with respect to the accumulated time. It is described that, by setting the data accumulation time by the means short, the image after binarization is kept good even if the γ characteristic varies.
JP-A-9-284550 (paragraph numbers 0021 to 0025, FIG. 2)

  The read output of the image sensor gradually increases as the amount of light increases as shown in FIG. 7 and changes linearly. However, if the predetermined amount of light indicated by the dotted line is exceeded, the output is saturated and linearity is lost. End up. For this reason, when the light quantity is large, the output of the image sensor is saturated and it becomes impossible to output the gray signal of the image, and when the light quantity is small, the output signal level of the image sensor is low and the S / N becomes worse. As a result, when the light amount correction is performed by the correction method described in Patent Document 1, when an image is read in multiple values, the image may be blown out, or image streaks, spots, and the like may be disturbed due to noise. was there.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image reading apparatus which prevents the occurrence of disturbances such as image streaks and spots caused by noise.

  The present invention includes a light source for illuminating an original, an image reading means for reading an image of the original illuminated by the light source, an amplifying means for amplifying an image signal read by the image reading means, and an image reading The amplifying means controls the light quantity of the light source and maximizes the output voltage of the amplifying means so that the maximum output is obtained in a range where the image signal obtained by reading the reference image by the means is not saturated. And a control means for controlling the amplification factor.

  Preferably, the control means provides an inverter means for driving and turning on the light source, a light source control signal for driving the light source to the inverter means, and an image for giving a control signal for controlling the amplification factor to the amplification means. Processing control means.

  Preferably, the image processing control means sets the offset voltage of the amplifying means so that the output amplitude of the amplifying means becomes a predetermined value with the light source turned off, and then images the reference image with the light source turned on. The light intensity of the light source is adjusted by controlling the inverter means so that the maximum value of the output amplitude of the amplifying means when read by the reading means is a value lower than the saturation voltage by a predetermined voltage value.

  Preferably, conversion means for converting the output signal of the amplification means into a digital signal is included.

  Preferably, the reference image is a white base image.

  The present invention controls the light amount of the light source and the output voltage of the amplifying means so that the maximum output is obtained within a range in which the reference image signal obtained by reading the reference image by the image reading means is not saturated. Since the amplification factor is controlled so as to be maximized, the dynamic range can be utilized to the maximum and the S / N ratio can be improved. It can be prevented from occurring.

  1 is a block diagram of an image reading apparatus according to an embodiment of the present invention, FIG. 2 is a specific block diagram of an amplifier circuit shown in FIG. 1, and FIG. 3 is an A / D converter shown in FIG. It is a figure which shows an example.

  In FIG. 1, an image sensor 1 as an image reading means is configured by arranging a number of CCD elements, and reads an image of a document (not shown) illuminated by a lamp 2 as a light source. The CCD output signal output from the image sensor 1 is given to the amplifier circuit 3 and amplified. The amplifier circuit 3 uses a circuit called an analog front end (AFE), and handles an analog image signal from the image sensor 1 with a digital image signal processing IC such as a DSP (Digital Signal Processor). It consists of an IC circuit for processing into digital signals. As shown in FIG. 2, the amplifier circuit 3 includes an inverting amplifier 31, a sample hold circuit 32, an offset setting amplifier 33, and an amplification factor variable amplifier 34. The amplification factor 3 is controlled by a control signal supplied from the image processing circuit 5. And the offset voltage are controlled.

  The inverting amplifier 31 is provided with a CCD output signal output from the image sensor 1. The inverting amplifier 31 has an amplification factor of −1 and inverts the polarity without amplifying the input CCD output signal. The CCD output signal whose polarity is inverted is sampled and held by the sample and hold circuit 32 and supplied to the offset setting amplifier 33. The offset setting amplifier 33 sets an offset voltage so that the DC voltage appearing at the output becomes 0 V in accordance with the control signal supplied from the image processing circuit 5, and supplies the CCD output signal to the variable gain amplifier 34. The amplification factor variable amplifier 34 is set with an amplification factor according to a control signal supplied from the image processing circuit 5.

  The CCD output signal amplified by the amplifier circuit 3 is converted into a digital signal by the A / D converter 4 and given to the image processing circuit 5. The A / D converter 4 converts an analog CCD output signal into an 8-bit gradation digital signal and outputs it. As shown in FIG. 3, the reference voltage Vref-H is FFh (h indicates hexadecimal). = 2.55V, and 00h = 0V is set as the reference voltage Vref-L. When the input voltage is 0V, the digital output is 00h, and when the input voltage is 2.55V, the digital output is FFh. Also, if 0V to 2.55V is quantized to 256 gradations from 00h to FFh, the output data changes by 1 LSB when the input voltage changes by 0.01V.

  The image processing circuit 5 processes the CCD output signal converted into a digital signal by the A / D converter 4 and outputs image data. The image processing circuit 5 outputs a lamp light amount control signal to the inverter 6 in order to control the light amount of the lamp 2. The inverter 6 controls the light quantity of the lamp 2 according to the lamp light quantity control signal. Further, the image processing circuit 5 outputs a control signal to the amplifier circuit 3 in order to control the amplification factor and the offset voltage of the amplifier circuit 3. The amplifier circuit 3 sets an offset voltage and an amplification factor according to the control signal.

  FIG. 4 is a flowchart for explaining the operation of the image reading apparatus according to the embodiment of the present invention, FIG. 5 is a waveform diagram for explaining the operation for adjusting the lamp light amount, and FIG. 6 is the output of the image sensor. It is a figure which shows an example of a waveform.

  At step SP1 shown in FIG. 4 (abbreviated as SP in the figure), the image processing circuit 5 outputs a control signal to the amplifier circuit 3 when the lamp 2 is turned off and the output amplitude of the image sensor 1 is zero. The offset voltage of the amplifier circuit 3 is set to 0V so that the input signal of the A / D converter 4 is minimized. At this time, the amplification factor of the amplifier circuit 3 is set to 1.

  In step SP2, when the reflected light from a white reference plate (not shown) is read by the image sensor 1 with the lamp 2 turned off, the CCD output signal of the image sensor 1 is amplified by the amplifier circuit 3, and the A / D converter. 4 is converted into a digital signal and supplied to the image processing circuit 5. In step SP3, the image processing circuit 5 can monitor that the input voltage of the A / D converter 4 is always between Vref-L and Vref-H when the lamp 2 is turned off based on the applied digital signal. Thus, the offset voltage is set to 01 h or higher. That is, when a voltage equal to or lower than Vref-L is input to the input terminal of the A / D converter 4, the output digital data is 00h.

  In this state, it cannot be determined whether the input voltage is the same voltage as Vref-L or lower than Vref-L. Therefore, by adjusting the offset voltage of the offset setting amplifier 33 so that the output of the A / D converter 4 becomes 01h, the input voltage of the A / D converter 4 when the lamp 2 is turned off becomes Vref-L. Make sure that the following conditions are not met.

  In step SP4, the brightness of the white reference is read by the image sensor 1 in the lighting state of the lamp 2, the CCD output signal is amplified by the amplifier circuit 3, converted into a digital signal by the A / D converter 4, and the image processing circuit 5 Given to.

  In step SP5, the light quantity of the lamp 2 is set so that the maximum output (8 Dh) is obtained in the range where the image signal obtained when the image sensor 1 reads the white reference brightness is not saturated. That is, assuming that the saturation voltage of the CCD output signal of the A / D converter 4 is 1.5 V as shown in FIG. 5, the image processing circuit 5 causes the CCD output signal in any case, such as when the amount of light varies due to the flickering of the lamp 2. Is set so that the target value of the CCD output signal when the lamp 2 is lit is, for example, 1.5−0.1 = 1.4V. . When 1.4V of the CCD output signal is A / D converted, the digital output becomes 8Ch + 01h = 8Dh.

  As described above, the image processing circuit 5 adjusts the light amount of the lamp 2 by outputting the control signal to the inverter 6 so that the level of the digital signal output from the A / D converter 4 becomes 1.4 V (8 Dh). The saturation voltage is uniquely determined from the specifications of the CCD device.

  In step SP6, the amplification factor of the amplifier circuit 3 is set so that the digital output level becomes FFh. That is, the image processing circuit 5 sees the digital output and can monitor that the input voltage of the A / D converter 4 is always between Vref-L and Vref-H when the lamp 2 is lit. Set to. By performing such control, the output voltage of the image sensor 1 when a bright original is read increases in amplitude as shown in FIG. 6A, and the output of the image sensor 1 when a dark original is read. The amplitude of the voltage decreases as shown in FIG.

  6A and 6B, the triangular waveform appearing on the positive side is generated by the reset pulse of the CCD.

  When the image sensor 1 reads an image by controlling the light amount of the lamp 2 and the amplification factor of the amplifier circuit 3 in this way, the amplitude of the output signal of the image sensor 1 is the same as when a black document is read. When the white original is read, the level becomes −0.1 V lower than the saturation voltage. For this reason, the dynamic range of the output of the image sensor 1 can be utilized to the maximum extent. Accordingly, since the S / N ratio can be improved, the possibility of image disturbance such as streaks / spots due to noise is reduced.

  Further, since the CCD output signal of the image sensor 1 does not saturate, it is possible to prevent whiteout of the image from occurring when reading the image.

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

1 is a block diagram of an image reading apparatus according to an embodiment of the present invention. FIG. 2 is a specific block diagram of the amplifier circuit shown in FIG. 1. It is a figure which shows an example of the A / D converter shown in FIG. 4 is a flowchart for explaining the operation of the image reading apparatus according to the embodiment of the present invention. It is a wave form diagram for demonstrating the operation | movement which adjusts a lamp light quantity. It is a figure which shows an example of the output waveform of an image sensor. It is a figure which shows the relationship of the reading output with respect to the light quantity of the conventional image sensor.

Explanation of symbols

1 image sensor, 2 lamp, 3 amplification circuit, 4 A / D converter, 5 image processing circuit, 6 inverter, 31 inverting amplifier, 32 sample hold circuit, 33 offset setting amplifier, 34 variable amplification factor amplifier.

Claims (5)

A light source for illuminating the document;
Image reading means for reading an image of a document illuminated by the light source;
Amplifying means for amplifying the image signal read by the image reading means;
The light quantity of the light source is controlled and the output voltage of the amplifying means is maximized so that the maximum output is obtained within a range in which the image signal obtained by reading the reference image by the image reading means is not saturated. Thus, an image reading apparatus comprising control means for controlling the amplification factor of the amplification means. The control means includes
Inverter means for driving and turning on the light source;
The image reading apparatus according to claim 1, further comprising: an image processing control unit that supplies a light source control signal for driving the light source to the inverter unit and a control signal for controlling an amplification factor to the amplification unit. .   The image processing control means sets the offset voltage of the amplifying means so that the output amplitude of the amplifying means becomes a predetermined value with the light source turned off, and then becomes the reference when the light source is turned on. The light intensity of the light source is adjusted by controlling the inverter means so that the maximum value of the output amplitude of the amplifying means when the image is read by the image reading means is a value lower than the saturation voltage by a predetermined voltage value. The image reading apparatus according to claim 2.   The image reading apparatus according to claim 1, further comprising conversion means for converting an output signal of the amplification means into a digital signal. The image reading apparatus according to claim 1, wherein the reference image is a white reference image.

Images