JP2013038625A - Image reading apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an appropriate gain setting value of amplification means in analog signal processing means in a short time.SOLUTION: By controlling a whole device with an analog signal processing section 17, a CPU of an image reading apparatus exposures a white reference plate by an LED light source, and reads the white reference plate by using a CCD that converts light reflected by the white reference plate to an image signal, and outputs it every main scanning line. The CPU controls a register section 37 in the analog signal processing section 17 and a gain switching circuit 38, and subsequently switches a gain setting value of an amplification circuit 33 in one main scanning line. On the basis of a digital image signal obtained by the switching, a gain table in an image processing section positioned at a rear step of the analog signal processing section 17 calculates an appropriate gain setting value of the amplification circuit 33.

Description

  The present invention relates to an image reading apparatus such as a scanner (an image reading unit or a single image reading apparatus mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine), and an image including the image reading apparatus. More particularly, the present invention relates to a gain adjustment technique for determining an amplification factor of an analog image signal.

The image reading apparatus as described above includes an analog signal processing circuit section (analog signal processing means) and an A / D conversion circuit (A / D conversion means).
The analog signal processing circuit unit exposes a document (actually an image surface) by an exposure unit (exposure unit), converts reflected light from the document into an image signal that is an electrical signal, and outputs the image signal for each main scanning line. A document image (also simply referred to as “document”) is read using a photoelectric conversion element (photoelectric conversion means). Then, analog processing for sampling the image signal from the photoelectric conversion element and amplifying it to a necessary level is performed.
The A / D conversion circuit converts the analog image signal processed in an analog manner by the analog signal processing circuit unit into a digital image signal.

Such a conventional image reading apparatus will be specifically described with reference to FIGS.
FIG. 9 is a longitudinal front view showing a schematic configuration example of an optical system of a conventional image reading apparatus.
The image reading apparatus 1 is a scanner, and as shown in FIG. 9, a contact glass 3, a first carriage 6, a second carriage 9, a CCD linear image sensor (hereinafter abbreviated as “CCD”) 10, and a lens unit 11. , And a white reference plate 12.
The contact glass 3 is a document glass on which the document 2 is placed.

The first carriage 6 includes an LED light source (which may be another light source) 4, which is an exposure unit that exposes the document 2, and a first reflection mirror 5.
The second carriage 9 includes a second reflection mirror 7 and a third reflection mirror 8.
The CCD 10 is a photoelectric conversion element and is provided on the sensor board 13.
The lens unit 11 is a unit having an imaging lens for imaging the reflected light from the third reflecting mirror 8 on the light receiving surface of the CCD 10.
The white reference plate 12 is a member for correcting various distortions caused by the reading optical system or the like, and is arranged at a position (predetermined position) where the LED light source 4 can be exposed.

The sensor board 13 is equipped with a signal processing circuit (described later) for performing various signal processing on an image signal output from the CCD 10 (actually, a digital image signal output from an analog signal processing unit described later). The unit 14 and the signal cable 15 are connected.
The LED light source 4, the first, second and third reflecting mirrors 5, 7, 8 and the lens unit 11 constitute a scanning optical system. The scanning optical system may be a relative type and may be of a type in which the document side moves while the mirror or the like is fixed.

The LED light source 4 irradiates the white reference plate 12 and the reading surface of the contact glass 3 with light at a predetermined angle, and the light reflected by the white reference plate 12 or the original 2 reflects the first, second, and third reflections. The light enters the light receiving surface of the CCD 10 via the mirrors 5, 7, 8 and the lens unit 11.
The CCD 10 outputs a voltage corresponding to the amount of incident light as an image signal.
The first and second carriages 6 and 9 are driven in the sub-scanning direction (arrows) while maintaining a constant distance between the exposure position of the document 2 and the light receiving surface of the CCD 10 by driving a motor such as a stepping motor or servo motor (not shown). A direction) and the original 2 is exposed and scanned.

FIG. 10 is a block diagram illustrating a configuration example of the sensor board 13 and the image processing unit 14 from the output of the CCD 10 of FIG. 9 until a digital image signal is obtained.
The conventional image reading apparatus 1 includes a sensor board 13 and an image processing unit 14 having the circuit configuration shown in FIG.
The sensor board 13 includes a CCD 10, a capacitor 16, an analog signal processing unit (AFE: Analog-Front-End) 17, an interface (I / F) unit 18, an oscillator (OSC) 19, and a timing signal generation circuit unit 20. Yes.
The image processing unit 14 includes an I / F unit 21, an interline correction circuit unit 22, a pixel averaging / peak detection circuit unit 23, a shading correction circuit unit 24, and a γ correction circuit unit 25.

The CCD 10 of the sensor board 13 reads an image of the document 2 on the contact glass 3, and synchronizes with an input drive signal to optically separate colors (in this example, “R, G, B” for each main scanning line). ) Output an image signal for each.
Here, “R” indicates red, “G” indicates green, and “B” indicates blue.

The R, G, and B image signals output from the CCD 10 are AC-coupled by the capacitor 16 and input to the AFE 17.
The AFE 17 generates a continuous analog image signal by sampling an input image signal corresponding to a sample pulse that is a drive signal, converts it into a digital image signal, and outputs it.

FIG. 11 is a circuit diagram showing a configuration example of the AFE 17 in FIG.
The AFE 17 is an analog signal processing means, and as shown in FIG. 11, for each optical separation color (“R, G, B” in this example), a clamp circuit (CLMP) 31 and a sample hold circuit (SH) 32, an amplification circuit (PGA) 33, an A / D conversion circuit (ADC) 34, a black offset correction circuit 35, and a D / A conversion circuit (DAC) 36. Among these, the clamp circuit 31, the sample hold circuit 32, and the amplifier circuit 33 constitute an analog signal processing circuit unit that performs an analog process of sampling the image signal from the CCD 10 and amplifying it to a necessary level.

  Inside the AFE 17, a clamp circuit (CLMP) 31 clamps (determines) a predetermined offset level voltage (offset voltage) for each of R, G, and B, and a sample and hold circuit (SH) 32 resets noise and feedthrough levels. A continuous analog image signal is obtained by sampling and holding the image signal including the above by the sample pulse. The analog image signal is amplified to an A / D conversion reference voltage level by an amplification circuit (PGA) 33, which is an amplification means, and then a predetermined bit (for example, 10 bits) by an A / D conversion circuit (ADC) 34. ) Digital image signal. The amplifier circuit (PGA) 33 is an analog amplifier circuit such as a programmable gain amplifier.

  The digital image signal (also referred to as “digital data” or “image data”) from the A / D conversion circuit 34 is darkened by the black offset correction circuit 35 (before exposure of the original, that is, when no light is incident). The analog offset is added via the D / A conversion circuit (DAC) 36 in an analog manner so that the output of the CCD 10 in FIG. The feedback control is performed so as to be constant at the level.

The digital image signal thus obtained is transmitted to the subsequent image processing unit 14 by the I / F units 18 and 21 in FIG. 10 and subjected to digital processing.
As the digital processing, various correction processes are performed by the inter-line correction circuit unit 22, the shading correction circuit unit 24, and the γ correction circuit unit 25.
The interline correction circuit unit 22 performs interline correction on the digital image signal input from the I / F unit 21 to correct the delay in the sub-scanning direction between the R, G, and B outputs from the CCD 10.

The shading correction circuit unit 24 obtains a predetermined density level by reading (receiving) the reflected light from the white reference plate 12 by the irradiation light from the LED light source 4 in FIG. Shading data is generated and stored in a memory (not shown). Then, based on the shading data, a shading correction (also simply referred to as “shading”) for correcting the sensitivity variation of the CCD 10 and uneven light distribution of the irradiation system is performed on the digital image signal input when reading the image of the document 2. Do.
The γ correction circuit unit 25 performs γ correction on the digital image signal from the shading correction circuit unit 24 to correct an error due to element characteristics.

Here, normally, the output at the edge of the image tends to drop even if the light quantity is the same according to the cos 4 power law by passing through the lens. The cos 4th power law indicates the relationship between the incident angle and the illuminance. When the incident angle of the light incident on the lens (lens incident angle) is θ with respect to the optical axis, the illuminance has the relationship represented by the following equation. . Here, Io represents the illuminance of light before incidence, and I represents the illuminance of light after incidence.
I = Io cos ⁴ θ

A drive signal necessary for driving the CCD 10 and other circuit units is generated by a timing signal generation circuit unit 20 based on a clock signal having a predetermined period input from an oscillator (OSC) 19 and input to each circuit unit.
As shown in FIG. 11, the AFE 17 includes a register unit 37 for determining an operation state. The register unit 37 is controlled by serial communication with an external CPU via a CPU / I / F which is a predetermined I / F unit, and an operation state can be set. Although not shown, a register unit similar to the register unit 37 is also built in the timing signal generation circuit unit 20 and is controlled by serial communication with an external CPU via the CPU / I / F, so that the operation state is It can be set.

In the image reading apparatus 1 configured in this way, two processes are performed using the white reference plate 12.
The first is gain adjustment that determines the amplification factor of the amplifier circuit (PGA) 33. Usually, the pixel level of the digital image signal (image data) read from the white reference plate 12 and A / D converted by the A / D conversion circuit (ADC) 34 (the “density level” of the pixel or the “gradation level” indicating it) The gain of the amplifying circuit 33 is adjusted so as to have a certain size. As a target value for adjustment, an output signal from the A / D conversion circuit 34 expects noise and subsequent fluctuations in the amount of light, and a dynamic value is secured as wide as possible by setting the largest value within a range not saturated. This adjustment is performed at a specific timing, such as when the power is turned on.

  The second is shading correction. As described above, a predetermined density level is obtained by reading the reflected light from the white reference plate 12 irradiated by the LED light source 4 with the CCD 10, and shading data indicating the density level is obtained. Therefore, the sensitivity variation of the CCD 10 and the light distribution unevenness of the irradiation system are corrected based on the shading data. This process is performed every time the document 2 is read. When the document 2 is read, the first and second carriages 6 and 9 move below the white reference plate 12 to read the white reference plate 12 and generate shading data.

Thereafter, the first and second carriages 6 and 9 are moved below the document 2, and one main scanning line in the region of the document 2 (one line in the main scanning direction orthogonal to the sub-scanning direction, simply “1 line”). A read image normalized by the shading data is obtained by performing the following calculation on each pixel data (data constituting the image data).
Document reading data after shading = document reading data / shading data × 1023
Here, the document read data corresponds to a digital image signal input to the image processing unit 14. The post-shading document read data corresponds to a digital image signal after the shading correction circuit unit 24 performs the shading correction.

FIG. 12 is an explanatory diagram for explaining the gain adjustment for determining the amplification factor of the amplifier circuit (PGA) 33 of FIG.
Even when the white reference plate 12 is read, for example, as shown in FIG. 12 (a), the CCD 10 outputs line by line in synchronization with a main scanning synchronization signal which is a synchronization signal in the main scanning direction. Among the digital image signals generated by the output, a digital image signal in a period (effective pixel period) indicating an effective pixel area within a period in which the main scanning synchronization signal is at a high level “H” is an effective pixel signal. Become. When the gain value (amplification factor) is set (gain setting g), the effective pixel signal has a waveform mixed with noise as shown in FIG.

  Therefore, gain adjustment is performed as follows. That is, while changing the gain value (actually the corresponding gain setting code) set in the amplifier circuit 33 in FIG. 11 by setting the register via the CPU / I / F, the data for a plurality of lines captured at that time is obtained. The pixel level of the digital image signal (actually effective pixel signal) is averaged in the main scanning direction (line direction) by the shading correction circuit unit 24. Thereby, for example, as shown in FIGS. 12C and 12D, noise is removed, and the gain is set so that the peak value (peak pixel level) of the pixel level is closest to the target value (target white reading level). The variable value setting is repeated (in this example, “N times”) to determine the optimum gain value.

The gain value is set by switching the amplification factor of the amplifier circuit (PGA) 33 by rewriting the value (register value) in the register unit 37 in the AFE 17 via the CPU / I / F. The pixel level averaging process and peak value detection of the effective pixel signal of one main scanning line are performed by the pixel averaging / peak detection circuit unit 23.
As the image reading apparatus for performing the gain adjustment as described above, those shown in Patent Documents 1 to 4 have been proposed.

  However, in the conventional image reading apparatus, the level determination of the peak value of the pixel level is performed while setting the gain value by incrementing by “1” from the minimum value of the gain setting code. In addition, since the gain value setting change is performed once for each main scanning line, the gain adjustment also takes “gain value setting times × number of average lines”, and the adjustment time is long. In the present day when it is desired to reduce the wait time of the user at the time of input or energy saving return, the length of the adjustment time has been a problem.

There is also a method of calculating the optimum gain value by calculation based on the theoretical value and performing gain adjustment. However, in an analog amplifier circuit such as a programmable gain amplifier, there is a large variation in the amplification factor due to the solid, and it is set. In some cases, linearity and monotonicity between the gain value (gain setting value) and the actual gain are not ensured. In that case, if the optimum gain value is simply obtained by calculation from the theoretical value, the adjustment result vibrates in the vicinity of the target value, and a case where correct adjustment cannot be performed occurs.
The present invention has been made in view of the above points, and an object thereof is to obtain an optimum gain setting value of an amplifying unit in an analog signal processing unit in a short time.

In order to achieve the above object, the present invention provides the following image reading apparatus and image forming apparatus.
The image reading apparatus according to the present invention is an image in which an original is exposed by an exposure unit, and the image of the original is read using a photoelectric conversion unit that converts reflected light from the original into an image signal and outputs the image signal for each main scanning line. The reading apparatus is characterized by the following.

  That is, an analog signal processing unit that has an amplification unit, samples the image signal from the photoelectric conversion unit, and performs an analog process for amplifying the image signal to a required level by the amplification unit, and the analog signal processing unit A / D conversion means for converting the analog image signal into a digital image signal. Further, the photoelectric conversion means that exposes a white reference plate arranged at a predetermined position by the exposure means, converts reflected light from the white reference plate into an image signal, and outputs the image signal for each main scanning line is used. The optimum gain for calculating the optimum gain setting value of the amplifying means based on the digital image signal obtained by reading the white reference plate and sequentially switching the gain setting value of the amplifying means within the one main scanning line. A set value calculating means is also provided.

  According to this invention, the image reading apparatus uses the photoelectric conversion unit that exposes the white reference plate by the exposure unit, converts the reflected light from the white reference plate into an image signal, and outputs the image signal for each main scanning line. An optimum gain setting value of the amplifying means is calculated based on a digital image signal obtained by reading the white reference plate and sequentially switching the gain setting value of the amplifying means in the analog signal processing means within one main scanning line. As a result, the optimum gain setting value of the amplification means in the analog signal processing means can be obtained in a short time.

1 is a block diagram illustrating a configuration example of a main part of a control system in an image reading apparatus which is an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration example of a sensor board and an image processing unit from the output of the CCD of FIG. FIG. 3 is a circuit diagram illustrating a configuration example of an AFE 17 in FIG. 2. FIG. 4 is an explanatory diagram for explaining shading data generation when the gain setting code of the amplifier circuit 33 in FIG. 3 is set to “0”. It is explanatory drawing similarly used for description of gain table preparation. It is explanatory drawing similarly used for description of gain adjustment. FIG. 4 is a diagram illustrating an example of a relationship (gain characteristic) between an ideal and an actual gain for a gain setting code of the amplifier circuit 33 in FIG. 3. FIG. 2 is a schematic diagram illustrating a configuration example of an image forming apparatus equipped with the image reading apparatus of FIG. 1. It is a vertical front view showing a schematic configuration example of an optical system of a conventional image reading apparatus. FIG. 10 is a block diagram illustrating a configuration example of the sensor board 13 and the image processing unit 14 from the output of the CCD 10 of FIG. 9 to obtaining a digital image signal. It is a circuit diagram which shows the structural example of AFE17 of FIG. It is explanatory drawing with which it uses for description of the gain adjustment which determines the gain of the amplifier circuit 33 of FIG.

Hereinafter, embodiments 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 main part of a control system in an image reading apparatus according to an embodiment of the present invention, and FIG. 2 shows a sensor board and an image processing unit for obtaining a digital image signal from the output of the CCD. FIG. 11 is a block diagram illustrating a configuration example, where parts corresponding to those in FIG. 10 are denoted by the same reference numerals, and most of the description thereof is omitted.
Since the schematic configuration of the optical system of the image reading apparatus is the same as that in FIG. 9, it is assumed that FIG. 9 is used again.

As shown in FIG. 1, the image reading apparatus 1 of this embodiment includes a sensor board 13, an image processing unit 14, a CPU 50, an interface (I / F) unit 60, and an operation unit 70.
In addition to the LED light source 4 and the I / F unit 27, the sensor board 13 includes a CCD 10, a capacitor 16, an analog signal processing unit (AFE) 17, an I / F unit 18, an oscillator (OSC) as shown in FIG. 19 and a timing signal generation circuit part (TG) 20. Among them, only the AFE 17 has an internal configuration different from that shown in FIG.
The I / F unit 27 is a CPU / I / F, and controls communication between the AFE 17 and the TG 20 and the CPU 50.

The image processing unit 14 includes an I / F unit 21, an image processing block 41, and an I / F unit 42. Among them, the image processing block 41 includes the inter-line correction circuit unit 22, the pixel averaging / peak detection circuit unit 23, the shading correction circuit unit 24, the γ correction circuit unit 25, and the gain table unit 26 shown in FIG. doing.
The I / F unit 42 is a CPU / I / F, and controls communication between each unit in the image processing block 41 and the CPU 50.
The gain table unit 26 creates a gain table described later.

The CPU 50 is a microcomputer that comprehensively controls the entire image reading apparatus 1, and includes a central processing unit (CPU), a ROM that stores various data including programs executed by the central processing unit, and data temporarily. And a nonvolatile memory for storing and holding data regardless of whether the power of the apparatus is on or off.
The I / F unit 60 is a CPU / I / F, and controls communication between the CPU 50 and the operation unit 70.
The operation unit 70 includes an input unit for inputting various types of information and a display unit for displaying various types of information.

FIG. 3 is a circuit diagram showing a configuration example of the AFE 17 in FIG. 2, and parts corresponding to those in FIG.
As shown in FIG. 3, the AFE 17 is obtained by adding a gain switching circuit 38 to that shown in FIG.

  In the image reading apparatus 1 configured as described above, the CPU 50 performs the AFE 17 and timing signal generation circuit unit (TG) 20 in the sensor board 13, the interline correction circuit unit 22 in the image processing unit 14, the pixel averaging / By controlling the peak detection circuit unit 23, the shading correction circuit unit 24, the gain table 26, etc., the functions as the optimum gain set value calculation means and the gain table creation means are achieved. Further, the shading correction circuit unit 24 functions as normalization means.

Therefore, these functions will be specifically described.
In the image reading apparatus 1, immediately after the power is turned on, the CPU 50 performs register setting for determining the operation state of each circuit unit in the sensor board 13 via the I / F unit 27, and one of them is R, G, B There is gain adjustment for determining the amplification factor of the amplifier circuit (PGA) 33 of FIG.

  The purpose of this gain adjustment is to amplify the output of the sample hold circuit (SH) 32 so that the input dynamic range of the A / D converter circuit (ADC) 34 can be used as wide as possible. However, it is necessary to set the amplification factor such that the output of the A / D conversion circuit 34 does not take full scale “1023” even if noise or light quantity fluctuation of the LED light source 4 of FIG. 9 occurs. To output “1023” means that the image data is saturated in the A / D conversion circuit 34.

Hereinafter, the procedure of gain adjustment will be described with reference to FIGS.
FIG. 4 is an explanatory diagram for explaining generation of shading data when the gain setting code (corresponding to the gain value) of the amplifier circuit (PGA) 33 in FIG. 3 is set to “0”.
FIG. 5 is an explanatory diagram for explaining the creation of the gain table when the gain setting code of the amplifier circuit 33 is set to “0”.
FIG. 6 is an explanatory diagram for explaining gain adjustment when the gain setting code of the amplifier circuit 33 is set to “0”.

  First, the CPU 50 in FIG. 1 can set the gain value in the range of “4 bits”, that is, “0 to 15” by the gain setting code (digital code) corresponding to the amplification circuit 33 via the I / F unit 27. In this case, the gain setting code “0” is first set in the amplifier circuit 33 as the minimum gain value. It is also possible to set a gain value other than the lowest gain value with a corresponding gain setting code.

In this state, the white reference plate 12 shown in FIG. 9 is exposed and read.
At the time of reading the white reference plate 12, for example, as shown in FIG. 4A, output for each line is performed from the CCD 10 in synchronization with the main scanning synchronization signal. Among the digital image signals generated by the output, the digital image signal in the effective pixel period within the period in which the main scanning synchronization signal is at the high level “H” is a digital image signal (effective pixel signal) indicating the effective pixel. It becomes. For example, as shown in FIG. 4B, the effective pixel signal has a waveform in which noise is mixed when the gain setting code “0” is set, that is, when the minimum gain value is set.

  Then, the CPU 50 uses the shading correction circuit unit 24 in FIG. 2 via the I / F unit 42 to perform main scanning reading results for a plurality of lines (16 lines in this example) as shown in FIG. 4C, for example. The (pixel level of the digital image signal) is averaged to remove noise, and stored as shading data in an internal memory as storage means. However, the range held as shading data is only the range corresponding to the effective pixel area.

Next, by rewriting the value (register value) in the register unit 37 of FIG. 3 via the I / F unit 27, the gain switching circuit 38 switches the gain setting value (that is, the corresponding gain setting code) of the amplifier circuit 33. To do. However, during normal operation, a predetermined fixed gain setting value is used.
At the time of gain adjustment, the gain switching circuit 38 is operated as follows.
The gain switching circuit 38 is a logic circuit having a counter function of counting (measuring) pixels, and in synchronization with the main scanning synchronization signal, the gain switching circuit 38 shifts to a switching mode while providing all gain settings during the effective pixel period. . That is, the main scanning synchronization signal is received, waits until the start of effective pixels, and the gain setting code is incremented by one every time 500 pixels are counted.

  Accordingly, for example, as shown in FIG. 5B, for each of 8000 pixels within the effective pixel period shown in FIG. 5A, each gain setting code “0-15” corresponding to each gain setting value is provided. "Is switched evenly every 500 pixels, and the pixel level of the digital image signal (effective pixel signal) is amplified accordingly. The graph shown in FIG. 5B shows the graph after the pixel averaging / peak detection circuit 23 performs the averaging process on the pixel levels of the digital image signals for 16 lines. .

When a digital image signal whose gain setting value is switched to 16 levels is input during one main scanning line, the shading correction circuit unit 24 converts the digital image signal into a gain setting code “0” corresponding to the aforementioned minimum gain value. The shading correction to normalize with the shading data generated by amplification with the amplification factor by the setting of "" is performed. At this time, the calculation is performed using the following equation.
Original reading data after shading
= (Original reading data-Black reference image data) / (Shading data
-Black reference image data) x 1023

Here, the original reading data, the post-shading original reading data, and the black reference image data will be described.
The document read data corresponds to a digital image signal input to the image processing unit 14.
The post-shading document read data corresponds to a digital image signal after the shading correction circuit unit 24 performs the shading correction.
The black reference image data is actually an average value of the pixel level, and corresponds to an average value of the pixel level of the digital image signal in the OPB (optical black) pixel period or the empty transfer pixel period other than the effective pixel period. Since the average values of these pixel levels are equal in level, there is no problem.

An OPB pixel is a pixel in which a pixel (photodiode) physically exists but is optically masked.
Although the empty transfer pixel does not physically exist, the number of transfer clocks in one main scanning line is made larger than the number of effective pixels by the control of the timing signal generation circuit unit 20 by the CPU 50. Thereby, after the digital image signal of the effective pixel period is output by that amount, the digital image signal having the same level as that of the dark digital image signal is continuously output. This output period is called an empty transfer pixel period.

Usually, a certain level of offset is added without setting the dark level of the output (digital image signal) of the image reading apparatus as in this embodiment to “0”. This is because it is not desired to saturate the “0” side including the noise component included in the dark level. Therefore, for example, the above-mentioned “average value of the pixel level of the digital image signal for every 500 pixels at the time of setting each of the 16 stages of gain setting codes” adds an offset corresponding to the black reference image data.
Therefore, it is necessary to generate an average value of the pixel level of the black reference image data before the shading correction, and subtract it from each pixel level of the original reading data, which is reflected in the calculation formula of the original reading data after the shading correction. I am letting.
By using the calculation formula, the digital image signal in which the gain setting value is switched in 16 steps during one main scanning line is corrected for the main scanning unevenness (light distribution unevenness) of the light amount, and FIG. As shown, the output changes stepwise.

Next, the CPU 50 causes the gain table unit 26 to create a gain table including the following calculation.
As shown in FIG. 5 (d), the gain table unit 26 is configured so that each of the 16 stages of gain values subjected to the shading correction by the shading correction circuit unit 24 is sequentially switched and set by the gain setting code. Average values AV_g0 to AV_g15 of the pixel level of the digital image signal (effective pixel signal) are calculated.

The effective pixel signal when the gain setting code “0” corresponding to the lowest gain value g0 is set among the gain setting codes corresponding to the respective gain values (gain setting values) that can be set in the amplifier circuit 33. Pixel level average value AV_gN (AV_g1) and gain setting codes “1” to “15” corresponding to other gain values gN (g1 to g15) are set. ~ AV_g15), the optimum gain setting value is calculated. That is, the relative gain value GAIN_N with respect to the lowest gain value g0 is calculated for each gain value gN from the following equation.
GAIN_N = AV_gN / AV_g0

  When the minimum gain value g0 is 1, the relative gain value GAIN_N = actual amplification factor. The relative gain value GAIN_N means how many times the gain value gN has an amplification factor with respect to the minimum gain value g0. In an actual analog signal processing IC such as the AFE 17, the minimum gain value g 0 may not be “1 ×” depending on the amplifier 33 to be used. If the actual gain of the minimum gain value g0 is twice, the actual gain at the time of the gain value gN is “GAIN_N × 2”. Further, the gain when the gain setting code is “15” becomes the maximum gain value g15.

  The calculated data of the relative gain value GAIN_N for each gain setting value gN is stored and held in a non-volatile memory (not shown) in the gain table unit 26 as a gain table. Thereby, although the creation of the gain table is completed, the gain table is stored and retained in the nonvolatile memory, so that the contents are retained even when the apparatus is turned off. Thereafter, by selectively acquiring the gain value to be set in the amplifier circuit (PGA) 33 from the gain table and setting the corresponding gain setting code in the register unit 37 in the AFE 17 via the I / F unit 27, The amplifier circuit (PGA) 33 can be set.

After creating the gain table, move on to normal gain adjustment.
First, the CPU 50 rewrites the value in the register unit 37 in the AFE 17 through the I / F unit 18, thereby setting the gain setting code of the amplifier circuit (PGA) 33 to the minimum value “0” by the gain switching circuit 38. In this state, for example, as shown in FIGS. 6B and 6C, the pixel averaging of the 16-line digital image signal (actually, effective pixel signal) is performed in the pixel averaging / peak detection circuit unit 23. Processing and peak pixel level detection are performed.

At this time, the maximum relative gain value (GAIN_N) satisfying the relationship of the following equation is set as an appropriate gain value, and a gain setting code corresponding to the gain setting value gN at that time is stored in the AFE 17 via the I / F unit 27. Are set in the register unit 37 of Thereby, the gain switching value of the amplification circuit 33 (corresponding to the gain setting code set in the amplification circuit 33) is switched by the gain switching circuit 38, and the optimum gain setting value is selected as the gain setting value. become.
Peak pixel level when gain setting code is “0” × GAIN_N ≦ target white reading level

Here, as described above, the optimum gain setting value is a gain setting used for actual image reading after obtaining a relative gain value “GAIN_N” with respect to the lowest gain value g0 and holding it in the gain table unit 26. Means value.
Then, as a method of determining the gain value used for actual image reading, “GAIN_N” that does not exceed the preset “target white reading level” and is closest to “AV_gN” is adopted.

  The “target white reading level” is set to a high value so that the dynamic range of the A / D conversion circuit 34 can be used as much as possible in order to secure the gradation of the obtained digital image data. However, in practice, the level at which the output (digital image signal) of the A / D conversion circuit 34 is not saturated, including the noise component included in the signal, is determined in advance. The A / D conversion circuit 34 can output digital image signals up to “1023” if it is 10 bits, but does not achieve “target white reading level = 1023”. Therefore, the “target white reading level” is lowered so as not to take the value “1023” including the noise included in the digital image signal.

When gain adjustment is necessary, such as when the power of a normal apparatus is turned on or when returning from the energy saving mode, only the processing after creating the gain table described above may be performed.
In addition, when the gain table needs to be updated, such as when the sensor board 13 is replaced due to a failure or the like and the AFE 17 is changed, or when the image processing unit 14 is replaced, an operation on the operation unit 70 by the user (external) By issuing a gain table creation execution command by the above operation), it is possible to instruct the CPU 50 to create a gain table via the I / F unit 60 at an arbitrary timing.

  Further, if the actual gain (gain) is obtained theoretically in each gain setting for the amplifier circuit 33 in FIG. 2, a gain table is not necessary. In this case, the ideal amplification factor can be obtained from the peak pixel level obtained when the minimum gain setting value is “0”, for example, only by using the following calculation formula. However, the actual amplification factor (gain characteristic) differs greatly from the ideal amplification factor as shown in FIG. 7, for example.

Next gain setting code =
(Target white scanning level / peak pixel level)
/ Amplification factor when changing gain setting code by 1 (+1) (theoretical value)
+ Current Gain Setting Code Furthermore, in this embodiment, the gain table created by the gain table 26 is created by hardware, but the CPU 50 may create the gain table by software. it can.

  As described above, according to the image reading apparatus 1 of this embodiment, the white reference plate 12 is exposed by the LED light source 4 (exposure means), and the reflected light from the white reference plate 12 is converted into an image signal to obtain one main signal. The white reference plate 12 is read using a CCD 10 (photoelectric conversion means) that outputs each scanning line. Based on the digital image signal obtained by sequentially switching the gain setting value (actually the corresponding gain setting code) of the amplifier circuit 33 (amplifying means) in the analog signal processing unit 17 within one main scanning line, An optimum gain setting value for the amplifier circuit 33 is calculated. Thereby, an optimum gain setting value of the amplifier circuit 33 in the analog signal processing unit 17 can be obtained in a short time. Therefore, even when the gain error of the amplifier circuit 33 is large, the analog processing by the analog signal processing unit 17 can be executed accurately and in a short time.

Further, the following effects (a) to (d) can be obtained.
(A) Before sequentially switching the gain setting value of the amplification circuit 33 within one main scanning line, the digital image signal of one main scanning line when the white reference plate 12 is read in advance with the predetermined gain setting value of the amplification circuit 33 (Shading data) is acquired in advance. Then, a digital image signal obtained by sequentially switching the gain setting value of the amplifier circuit 33 within one main scanning line is used as a digital image signal when the white reference plate 12 is read with the predetermined gain setting value of the amplifier circuit 33. Normalize using. As a result, uneven light distribution of the LED light source 4 is corrected, so that an appropriate digital image signal for gain change can be obtained.

(B) By creating a gain table showing the relationship between the gain setting value of the amplifier circuit 33 and the relative gain value (optimum gain setting value), accurate gain determination can be performed.
(C) By holding the gain table in the non-volatile memory (non-volatile storage means), the gain adjustment is performed without performing the process for obtaining the optimum gain setting value of the amplifier circuit 33 from the next gain adjustment. It can be performed.
(D) By creating (updating) a gain table by an external operation, the gain table is set again even if the sensor board (printed circuit board) 13 on which the CCD 10 or its peripheral circuit is mounted is replaced due to a device failure or the like. It becomes possible to redo.

Normally, there is an influence of the output distribution according to the cos 4 power law by passing through the lens and the light distribution distribution of the exposure unit itself such as an LED light source. is necessary. However, normalization is not necessary when an illumination system or an optical system that does not cause these effects is a problem.
For example, a shading plate is attached to the light receiving surface side of the lens unit 11 in FIG. 9, and the amount of reflected light from the third reflecting mirror 8 is reduced so that the shading plate has an optically flat distribution. Accordingly, when the distribution of the digital image signal in the main scanning direction when the white reference plate 12 is read can be flattened, the normalization calculation at the time of creating the gain table becomes unnecessary.

  The embodiment in which the present invention is applied to an image reading device (scanner) that reads an image of a document with a CCD has been described above. Of course, the present invention can also be applied to various image forming apparatuses such as digital copiers, facsimile machines, and printers equipped with such image reading apparatuses. The image forming apparatus main body can print the image data from the image reading apparatus on a sheet such as paper as a visible image.

FIG. 8 is a schematic diagram showing a configuration example of an image forming apparatus equipped with the image reading apparatus 1 described above, and the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals.
As shown in FIG. 8, the image forming apparatus 200 includes the image reading device (scanner) 1 shown in FIG.
In the image reading apparatus 1, when a parallel 10-bit digital image signal (digital data) is input from the analog signal processing unit (AFE) 17 to the I / F unit 18 in the sensor board 13, Serial transmission to the I / F unit 41 of

The image processing unit 14 is communicably connected to the sensor board 13 by an I / F unit 21 and an I / F unit 18. Further, an interface (I / F) 123 is communicably connected to the printer engine 121 in the printer 120.
When receiving the digital image signal serially transmitted from the I / F unit 18 in the sensor board 13, the I / F unit 21 in the image processing unit 14 converts the digital image signal into a parallel 10-bit digital image signal. , Input to the image processing block 41.

  When a parallel 10-bit digital image signal is input from the I / F unit 21 by reading the white reference plate 12, the image processing block 41 performs the above-described image processing (excluding γ correction) on the digital image signal. Or create a gain table. When a parallel 10-bit digital image signal is input from the I / F unit 21 by reading the document 2, each image process is performed on the digital image signal. Thereafter, the digital image signal subjected to each image processing is output to the printer engine 121 in the printer 120 through the I / F 123, and printing (image formation) is performed on a sheet such as paper.

  The CPU 50 controls not only the image reading device 1 but also the printer engine 121 of the printer 120. That is, the entire image forming apparatus 200 is controlled. Of these, the processing relating to the present invention includes an I / F unit (CPU • I / F) in the sensor board 13 in accordance with an instruction input from the operation unit 70 via the I / F unit (CPU • I / F) 60. F) The analog signal processing unit (AFE) 17 and the timing signal generation circuit unit (TG) 20 are connected via the I / F unit (CPU / I / F) 42 in the image processing unit 14 via the image processing block. The interline correction circuit unit 22, the pixel averaging / peak detection circuit unit 23, the shading correction circuit unit 24, the γ correction circuit unit 25, and the gain table 26 are controlled.

In this image forming apparatus 200, the image quality on the sheet output from the printer engine 121 is improved by mounting the image reading apparatus 1 shown in FIG.
The CPU 50 may be provided on the printer 120 side. Alternatively, it may be provided between the image reading apparatus 1 and the printer 120.
Further, the present invention is not limited to the above-described embodiment, and it goes without saying that all the technical matters included in the technical idea described in the claims are covered.

1: Image reading device 2: Document 3: Contact glass 4: LED light source 5: First reflection mirror 6: First carriage 7: Second reflection mirror 8: Third reflection mirror 9: Second carriage 10: CCD linear image sensor 11: Lens unit 12: White reference plate 13: Sensor board 14: Image processing unit 15: Signal cable 16: Capacitor 17: Analog signal processing unit (AFE)
18, 21, 27, 42, 60: Interface (I / F) section 19: Oscillator (OSC) 20: Timing signal generation circuit section (TG)
22: Interline correction circuit unit 23: Pixel averaging / peak detection circuit unit 24: Shading correction circuit unit 25: γ correction circuit unit 26: Gain table 31: Clamp circuit (CLMP) 32: Sample hold circuit (SH)
33: Amplifier circuit (PGA) 34: A / D converter circuit (ADC)
35: Black offset correction circuit 36: D / A conversion circuit (DAC) 37: Register unit 38: Gain switching circuit 41: Image processing block 50: CPU 70: Operation unit 120: Printer 121: Printer engine 123: Interface 200: Image Forming equipment

Japanese Patent No. 399840 Japanese Patent No. 397367 Japanese Patent No. 4142524 JP 2010-041083 A

Claims (6)

An image reading apparatus that reads an image of an original by using photoelectric conversion means that exposes an original by an exposure unit, converts reflected light from the original into an image signal, and outputs the image signal for each main scanning line;
An analog signal processing unit that includes an amplification unit, samples the image signal from the photoelectric conversion unit, and performs an analog process of amplifying the signal to a required level by the amplification unit;
A / D conversion means for converting an analog image signal from the analog signal processing means into a digital image signal;
The photoelectric conversion means that exposes a white reference plate disposed at a predetermined position by the exposure means, converts reflected light from the white reference plate into an image signal, and outputs the image signal for each main scanning line. An optimum gain setting value for calculating an optimum gain setting value of the amplifying means based on a digital image signal obtained by reading a white reference plate and sequentially switching the gain setting value of the amplifying means within the one main scanning line. An image reading apparatus comprising a calculation unit. The image reading apparatus according to claim 1,
A digital image signal obtained by sequentially switching the gain setting value of the amplifying means within the one main scanning line is used as a digital image signal obtained by reading the white reference plate with a predetermined gain setting value of the amplifying means. An image reading apparatus provided with normalizing means for normalizing the image. The image reading apparatus according to claim 1 or 2,
An image reading apparatus comprising gain table creating means for creating a gain table indicating a relationship between a gain setting value of the amplifying means and the optimum gain setting value.   The image reading apparatus according to claim 3, wherein the gain table is held in a nonvolatile storage unit.   The image reading apparatus according to claim 3, wherein the gain table generation unit creates the gain table by an external operation.   An image forming apparatus comprising the image reading apparatus according to claim 1, wherein an image forming process is performed based on image data read by the image reading apparatus.

Images