JP2006319607A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a color reading speed without causing reduction in image quality. <P>SOLUTION: A clock generator 36 generates clocks inputted to a multiplexer 23 and an A-D conversion circuit 22 on the basis of a drive clock from a read controller, so that output patterns of a plurality of colors per reading pixel of the conversion circuit 22 differ in adjoining pixels, and that the output patterns become periodic at each pixel. An image processor interpolates a color not included in the reading pixel but associated with the reading pixel on the basis of the adjacent reading pixels of the same color as the color. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image reading apparatus that reads an image of a document using an image sensor such as a scanner unit, a digital copying machine, a facsimile machine, or a scanner unit of a digital multifunction peripheral (MFP).

As an image reading apparatus as described above, an image sensor having a plurality of color line sensors that illuminate an image surface of a document, receive a reflected light image from the image surface, and convert it into a plurality of color analog signals (light reception signals). And an A / D converter (A / D conversion circuit) that converts an analog signal output from each color line sensor into a digital signal has been commercialized (for example, Patent Documents 1 to 3). ).
JP 2003-189068 A JP 2002-199232 A JP 2004-040146 A

Such a conventional image reading apparatus will be specifically described with reference to FIGS.
FIG. 15 is a block diagram illustrating a configuration example of a control system of a conventional image reading apparatus.
The CCD 10 is an image sensor having a plurality of color line sensors that output analog signals (light reception signals) respectively corresponding to red, green, and blue colors of a read image.
An analog front end (hereinafter abbreviated as “AFE”) 20 is an IC having a gain and offset adjustment of each analog signal output from the CCD 10 and an A / D conversion function for converting each analog signal into a digital signal. is there.

The image processing unit 30 performs various image processing (shading correction, γ correction, filter processing, etc.) on each digital signal output from the AFE 20.
The reading control unit 40 controls the CCD 10 and the AFE 20. The reading control unit 40 includes a clock generator that generates a clock (drive clock) for driving the CCD 10 and the AFE 20.

FIG. 16 is a block diagram illustrating a configuration example of the AFE 20 in FIG.
In this example, each analog signal corresponding to each color of red (R), green (G), and blue (B) output from the CCD 10 has a separate AFE 20 (20a, 20b, 20c), and each analog signal is analog. A processing circuit 21 (21a, 21b, 21c) and an A / D conversion circuit (ADC) 22 (22a, 22b, 22c) are provided.
Such a configuration of the AFE 20 enables high-speed image processing and is often used in a business color copying machine.

FIG. 17 is a block diagram showing another configuration example of the AFE 20 in FIG. 15, and parts corresponding to those in FIG.
In this example, one AFE 20 is used for each analog signal corresponding to each of red, green, and blue colors output from the CCD 10.
Each analog signal output from each analog processing circuit 21 (21a, 21b, 21c) is sequentially transferred to one A / D conversion circuit 22 by a multiplexer 23, where it is converted into a digital signal.
Such a configuration of the AFE 20 is often used in an inexpensive color image reading apparatus because the circuit scale is small.

  In the configuration of FIG. 17, a high sampling rate is required for the A / D conversion circuit 22 with respect to the drive clock of the CCD 10. For example, when the CCD 10 is driven at 6 MHz, the sampling rate required for the A / D conversion circuit 22 is 6 MSPS (Mega Sample Per Second) in the configuration of FIG. 16, but in the configuration of FIG. 17, A / D conversion is performed. The sampling rate required for the circuit 22 is 18 MSPS.

  Therefore, it is conceivable to use a high-speed A / D conversion circuit as the A / D conversion circuit 22 in FIG. 17, but this leads to an increase in the cost of the AFE 20. For this reason, a case where a low-speed A / D conversion circuit is used and the color reading speed is lowered is often seen. For example, in the configuration of FIG. 17, when the maximum sampling rate of the A / D conversion circuit 22 is 6 MSPS, in color reading, the driving frequency of the CCD 10 is set to 2 MHz, and red, green, and blue analog signals are converted to A / D. The digital signal is converted by the D conversion circuit 22. In monochrome reading, the driving frequency of the CCD 10 is set to 6 MHz, and only the green analog signal is converted into a digital signal by the A / D conversion circuit 22. Therefore, there is a problem that the color reading speed becomes slower than the monochrome reading speed.

  The present invention has been made in view of the above points, and is an image having a configuration in which analog signals output from a CCD (image sensor having a plurality of color line sensors) are sequentially transferred to an A / D converter by a multiplexer. An object of the reading apparatus is to improve the color reading speed without degrading the image quality.

  The present invention provides an image sensor including a plurality of color line sensors, an A / D converter that converts an analog signal output from each color line sensor into a digital signal, and each color line sensor. An image reading apparatus comprising: a multiplexer that sequentially transfers analog signals to the A / D converter; and a clock generator that generates a clock for driving the image sensor, the A / D converter, and the multiplexer. In order to achieve the above object, the present invention is characterized by the following.

  In the image reading apparatus according to the first aspect of the present invention, the output patterns of a plurality of colors per reading pixel of the A / D converter are different in adjacent pixels, and the output pattern is periodic in each pixel. A clock generation unit configured to generate a clock to be input to the multiplexer and the A / D converter based on a clock; and the color applied to a read pixel of a color not included in the read pixel is the same color as the adjacent color. Color pixel interpolation means for interpolating with read pixels is provided.

An image reading apparatus according to a second aspect of the present invention is the image reading apparatus according to the first aspect, wherein the image sensor includes three line sensors for outputting red, green, and blue analog signals, respectively.
An image reading apparatus according to a third aspect of the present invention is the image reading apparatus according to the first or second aspect, wherein output patterns of a plurality of colors per read pixel of the A / D converter are two colors among red, green, and blue. It is a combination of.

An image reading apparatus according to a fourth aspect of the present invention is the image reading apparatus according to any one of the first to third aspects, wherein the monochrome reading mode is selected by the reading mode selecting means for selecting the monochrome reading mode or the color reading mode, and the reading mode selecting means. Output selecting means for selecting only one color output per read pixel from among the respective color outputs from the A / D converter.
According to a fifth aspect of the present invention, there is provided an image reading apparatus according to any one of the first to fourth aspects, further comprising clock changing means for changing a clock for driving the image sensor in accordance with the resolution of the output image. It is a thing.

  According to the image reading apparatus of the present invention, the clock generation means so that the output patterns of a plurality of colors per reading pixel of the A / D converter are different in adjacent pixels and the output pattern is periodic in each pixel. Generates a clock to be input to the multiplexer and the A / D converter, and the color applied to the read pixel of the color not included in the read pixel is interpolated by the read pixel of the same color as the color adjacent to the color pixel interpolation unit Therefore, the color reading speed can be improved without degrading the image quality.

Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration example of a facsimile machine provided with an image reading device (reading unit) for carrying out the present invention.
The facsimile apparatus includes a control unit 101 that controls the entire apparatus, a memory 102, a reading unit 103 that reads an image of a document and converts it into image data, an output image at the time of copying, a transmission image at the time of facsimile transmission, or a facsimile reception time. A writing unit (printing unit) 104 that prints out a received image, an operation unit 105 having a key switch and a display unit, a communication unit 106 that performs communication control, and an encoding unit that has a function of compressing / decompressing transmission / reception image data in a facsimile 107 or the like.

FIG. 2 is a diagram illustrating a configuration example of the optical system of the reading unit 103 in FIG. 1, and portions corresponding to those in FIGS. 15 and 17 are denoted by the same reference numerals.
The reading unit 103 is an image scanner, and includes a scanner housing 110, a contact glass 111 on which a document P is placed, and an optical scanning system. The optical scanning system includes a light source (exposure lamp) 112, a first light source. The mirror 113, the second mirror 114, the third mirror 115, the lens 116, the CCD 10, and the like are included. The light source 112 and the first mirror 113 are fixed on the first carriage 117, and the second mirror 114 and the third mirror 115 are fixed on the second carriage 118.

When reading the image surface (lower surface) of the document P, the first carriage 117 and the second carriage 118 are moved in parallel to the document P. At this time, the distance between the reading surface of the document P and the CCD 10, that is, the optical path length. So that the first carriage 117 and the second carriage 118 are mechanically moved (scanned) at a relative speed of 2: 1.
This optical scanning system is driven by a scanner motor 119. An image of the original P set on the contact glass 111 is read by the CCD 10 and converted into an analog signal which is an electric signal and processed.

That is, the image surface of the original P is illuminated by the light source 112 of the optical scanning system, and the reflected light image from the image surface is transmitted through the first mirror 113, the second mirror 114, the third mirror 115, and the lens 116 to the CCD 10. An image is formed on the light receiving surface and converted into an analog signal by the CCD 10.
The reference white plate 120 is used when capturing shading correction data.

FIG. 3 is a block diagram showing a configuration example of a control system of the reading unit 103 in FIG. 1, and parts corresponding to those in FIG.
The functional outline of the CCD 10, the AFE 20, and the image processing unit 30 has already been described with reference to FIG.
The reading control unit 40 controls the CCD 10, the AFE 20, the light source 112, and the scanner motor 119. The reading control unit 40 includes a clock generator that generates a clock (drive clock) for driving the CCD 10, the AFE 20, and the scanner motor 119.

FIG. 4 is a block diagram showing a configuration example of the AFE 20 in FIG. 3, and parts corresponding to those in FIG.
The AFE 20 is a correlated double sampling circuit (hereinafter abbreviated as “CDS”) 31 (31a, 31b, 31c), an offset adjustment circuit 32 (32a, 32b, 32c), and a programmable gain amplifier (hereinafter abbreviated as “PGA”). ) 33 (33a, 33b, 33c), multiplexer (MUX) 23, A / D converter circuit (ADC) 22, external interface (I / F) 34, AFE controller 35, and clock generator 36 (clock generator) It has.

The clock generation unit 36 outputs from the reading control unit 40 so that the output patterns of a plurality of colors per reading pixel of the A / D converter 22 are different in adjacent pixels and the output pattern is periodic in each pixel. This is clock generation means for generating a clock to be input to the CDS 31, the multiplexer 23, and the A / D converter 22 based on the drive clock.
Note that the CDS 31, the offset adjustment circuit 32, the PGA 33, the external interface 34, and the AFE control unit 35 are well-known and are not directly related to the present invention.

  In the reading unit 103 configured as described above, as a driving mode of the CCD 10 and the AFE 20, a monochrome reading mode (monochrome mode) and three color reading modes, that is, a high resolution color mode, a high speed / high resolution color mode, a high speed / It has a low-resolution color mode, and one of the drive modes can be selected according to the mode of the output image (output image). The function (reading mode selection means) is provided in the reading control unit 40. The reading control unit 40 also has a function (clock changing means) for changing the clock for driving the CCD 10 in accordance with the resolution of the output image.

Hereinafter, the operations of the CCD 10 and the AFE 20 in the monochrome mode, the high resolution color mode, the high speed / high resolution color mode, and the high speed / low resolution color mode will be described.
FIG. 5 is a timing chart showing an example of input / output signals of the CCD 10 in the monochrome mode.
In FIG. 5, φ 1 and φ 2 are transfer clocks, φ RS is a reset pulse, φ CP is a clamp pulse, and R, G, and B are red, green, and blue analog signals output from the CCD 10.
The CCD 10 is driven by a clock having a cycle T (= frequency 1 / T).

FIG. 6 is a timing chart showing an example of input / output signals of the AFE 20 in the monochrome mode.
In FIG. 6, ADCLK is a clock for driving the A / D conversion circuit 22, CLP is a clamp signal for the CDS 31, S / H is a sample hold signal for driving the CDS 31, and R, G and B are red colors output from the CCD 10. , Green and blue analog signals, D is a digital signal output from the AFE 20.
In reading in the monochrome mode (monochrome reading), red and blue analog signals are unnecessary, so only the green analog signal is selected by the reading control unit 40 and A / D converted (converted into a digital signal). ). Therefore, the reading control unit 40 functions as an output selection unit.
The sampling rate of the A / D conversion circuit 22 is 1 / T.

FIG. 7 is a timing chart showing an example of input / output signals of the CCD 10 in the high resolution color mode.
The signal names in FIG. 7 are the same as those in FIG.
The CCD 10 is driven with a clock having a period of 3T. That is, the frequency of the clock for driving the CCD 10 is 1/3 that in the monochrome mode, and the accumulation time of image data for one line is three times that in the monochrome mode.

FIG. 8 is a timing chart showing an example of input / output signals of the AFE 20 in the high resolution color mode.
The signal names in FIG. 8 are the same as those in FIG.
In reading in the high resolution color mode (high resolution color reading), analog signals of three colors of red, green, and blue are A / D converted per pixel. For this reason, the sampling rate of the A / D conversion circuit 22 is the same as that in the monochrome mode, but the sampling rate per pixel is 1/3 that in the monochrome mode. That is, the reading time of image data for one line is three times that in the monochrome mode.

FIG. 9 is a timing chart showing an example of input / output signals of the CCD 10 in the high speed / high resolution color mode.
The signal names in FIG. 9 are the same as those in FIG.
The CCD 10 is driven with a clock having a period of 2T. That is, the frequency of the clock for driving the CCD 10 is ½ that in the monochrome mode, and the storage time of image data for one line is twice that in the monochrome mode.

FIG. 10 is a timing chart showing an example of input / output signals of the AFE 20 in the high speed / high resolution color mode.
The signal names in FIG. 10 are the same as those in FIG.
In reading in the high-speed / high-resolution color mode (high-speed / high-resolution color reading), analog signals of two colors of green and red or two colors of green and blue are A / D converted per pixel. In addition, the color combinations are switched between the odd and even pixels. For this reason, the sampling rate of the A / D conversion circuit 22 is the same as that in the monochrome mode, but the sampling rate per pixel is ½ that in the monochrome mode. That is, the reading time of image data for one line is twice as long as that in the monochrome mode and can be read at a higher speed than in the high resolution color mode.

FIG. 11 shows each output pattern of the AFE 20 in the high speed / high resolution color mode corresponding to the reading position.
The number of red and blue output pixels is half that of green. For this reason, for the pixel data for which red and blue are insufficient, an interpolation calculation value from surrounding image data is substituted (FIG. 12). As an interpolation calculation method, there are a bilinear method in which one pixel is referred to before and after, a bicubic method in which two pixels are referred to before and after, and the bicubic method is suitable as an interpolation method in the present invention. Interpolation calculation is performed by the image processing unit 30. Therefore, the image processing unit 30 functions as a color pixel interpolation unit.

FIG. 13 is a timing chart showing an example of input / output signals of the CCD 10 in the high speed / low resolution color mode.
The signal names in FIG. 13 are the same as those in FIG.
Of the clocks for driving the CCD 10, φ1 and φ2 are periods T, and φRS and φCP are 2T. In this case, the output of the CCD 10 is every other pixel, and the accumulation time of image data for one line is the same as in the monochrome mode.

FIG. 14 is a timing chart showing an example of input / output signals of the AFE 20 in the high speed / low resolution color mode.
The signal names in FIG. 14 are the same as those in FIG.
In reading in the high-speed / low-resolution color mode (high-speed / low-resolution color reading), analog signals of two colors of green and red or two colors of green and blue are A / D converted per pixel. In addition, the color combinations are switched between the odd and even pixels. For this reason, the sampling rate of the A / D conversion circuit 22 is the same as that in the monochrome mode, but the sampling rate per pixel is ½ that in the monochrome mode. However, the number of output pixels of the CCD 10 per line is ½ that in the high-speed / high-resolution color mode.

Accordingly, the reading time of the image data for one line is the same as that in the monochrome mode, and can be read at a higher speed than in the high-speed / high-resolution color mode.
Even in the high-speed / low-resolution color mode, red and blue image data are insufficient.
For this reason, the interpolation calculation is performed by the image processing unit 30 as in the high-speed / high-resolution color mode.

As described above, in the reading unit (image reading apparatus), the number of output pixels per reading line in the A / D conversion is thinned out only for a specific color, and the interpolation is performed to compensate for the thinned out pixels, thereby reducing the image quality. Color reading time can be shortened.
Further, since the CCD drive frequency (drive clock) and the number of output pixels per reading line in A / D conversion are changed according to the reading resolution of the output image, the reading time at the time of low resolution reading Can be shortened.

  As described above, the embodiment in which the present invention is applied to the scanner unit (reading unit) of the facsimile apparatus has been described. However, the present invention is not limited to this, and an image sensor such as a scanner unit, a digital copying machine, or a scanner unit of a digital multifunction machine is used. The present invention can also be applied to an image reading apparatus that reads an image of a document by using it.

  As is apparent from the above description, according to the present invention, the output patterns of a plurality of colors per read pixel of the A / D converter are different in adjacent pixels, and the output pattern is periodic in each pixel. In addition, the clock generation means generates a clock input to the multiplexer and the A / D converter, and the color applied to the read pixel of the color not included in the read pixel is the same color as the color adjacent to the color pixel interpolation means. Therefore, the color reading speed can be improved without degrading the image quality. Therefore, if this invention is used, an image reading apparatus capable of high-quality and high-speed color reading can be provided.

1 is a block diagram illustrating a configuration example of a facsimile apparatus including an image reading apparatus (reading unit) that implements the present invention. FIG. 2 is a diagram illustrating a configuration example of an optical system of a reading unit 103 in FIG. 1. FIG. 2 is a block diagram illustrating a configuration example of a control system of a reading unit 103 in FIG. 1. It is a block diagram which shows the structural example of AFE20 of FIG. FIG. 2 is a timing chart showing an example of input / output signals of a CCD in a monochrome mode in the reading unit 103 in FIG. 1.

FIG. 6 is a timing chart showing an example of AFE input / output signals in the monochrome mode in the same manner. FIG. 6 is a timing chart showing an example of input / output signals of the CCD in the same high resolution color mode. FIG. 6 is a timing chart showing an example of AFE input / output signals in the same high resolution color mode. FIG. 6 is a timing chart showing an example of input / output signals of the CCD in the same high-speed / high-resolution color mode.

FIG. 6 is a timing chart showing an example of AFE input / output signals in the same high-speed / high-resolution color mode. FIG. 6 is an explanatory diagram showing an example of each AFE output pattern in the same high-speed and high-resolution color mode. It is explanatory drawing which shows an example of each output pattern after performing color pixel interpolation with respect to each output pattern shown in FIG. FIG. 2 is a timing chart showing an example of input / output signals of the CCD 10 in the high-speed / low-resolution color mode in the reading unit 103 in FIG. 1.

FIG. 6 is a timing chart showing an example of input / output signals of the AFE 20 in the same high-speed / low-resolution color mode. It is a block diagram which shows the structural example of the control system of the conventional image reading apparatus. It is a block diagram which shows the structural example of AFE20 of FIG. It is a block diagram which shows the other structural example of AFE20 of FIG.

Explanation of symbols

10: CCD 20: Analog front end 21: Analog processing circuit 22: A / D conversion circuit 23: Multiplexer 31: Correlated double sampling circuit 32: Offset adjustment circuit 33: Programmable gain amplifier 34: External interface 35: AFE control unit 36 : Clock generation unit 40: Reading control unit 103: Reading unit

Claims (5)

An image sensor having a plurality of color line sensors, an A / D converter that converts an analog signal output from each color line sensor into a digital signal, and an analog signal output from each color line sensor sequentially An image reading apparatus comprising: a multiplexer for transferring to the A / D converter; and a clock generator for generating a clock for driving the image sensor, the A / D converter, and the multiplexer,
The multiplexer and the A / D are based on the clock so that an output pattern of a plurality of colors per read pixel of the A / D converter is different in adjacent pixels and the output pattern is periodic in each pixel. Clock generating means for generating a clock to be input to the converter;
An image reading apparatus comprising: a color pixel interpolation unit that interpolates the color applied to a read pixel of a color not included in the read pixel by a read pixel having the same color as the adjacent color. The image reading apparatus according to claim 1.
The image sensor includes three line sensors that respectively output red, green, and blue analog signals. The image reading apparatus according to claim 1 or 2,
An image reading apparatus, wherein an output pattern of a plurality of colors per reading pixel of the A / D converter is a combination of two colors of red, green, and blue. The image reading apparatus according to any one of claims 1 to 3,
Reading mode selection means for selecting a monochrome reading mode or a color reading mode;
Output selection means for selecting only one color output per read pixel out of each color output from the A / D converter when the monochrome reading mode is selected by the reading mode selection means is provided. An image reading apparatus. The image reading apparatus according to any one of claims 1 to 4,
An image reading apparatus comprising clock changing means for changing a clock for driving the image sensor according to the resolution of an output image.

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