JP2001024893A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain image data which are correctly black shading corrected by correcting data of a reference black level to be used at the time of black shading correction in accordance with a ratio of a reference voltage when the reference black level is detected and a specified reference voltage set at the time of reading an original. SOLUTION: In a black shading correction circuit 14, a result of average value processing in an average value circuit 31 for black with respect to digital image data D0 obtained from an inline circuit in detecting a reference black level is stored in a memory 32 as data D0b of the detected reference black level. Also, the device is provided with a subtracting circuit 33 in which the data D0b of the reference black level stored in the memory 32 are subtracted from digital image data D0g obtained from the inline circuit at the time of reading the original and are outputted to a white shading correction circuit at a past step as data Dshb after black shading.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image scanner, a scanner of a digital copying machine, and the like, and more particularly to a CCD.
The present invention relates to an image reading apparatus that reads a document image using a solid-state image sensor such as a 1: 1 close contact sensor using an image sensor.

[0002]

2. Description of the Related Art Generally, in an image reading apparatus of this type, a document is exposed by a light source, and reflected light from the document is focused on a CCD image sensor to convert the reflected light into a voltage value corresponding to the intensity of the reflected light. Then, the voltage value (analog value) is converted into, for example, an 8-bit digital value by an A / D converter and output to an image processing unit or the like. On this occasion,
Even if there is variation in sensitivity of each pixel of the CCD image sensor or variation in signal components due to dark current, a white shading correction function and a black shading correction function are usually provided so that the dynamic range of the A / D converter can be widened. Various proposals have been made for these functions (for example, Japanese Patent Application Laid-Open No. Sho 62-235871,
JP-A-63-18873, JP-A-6-16492
No. 2, JP-A-9-9056, JP-A-11-2
No. 7522).

Here, paying particular attention to black shading correction, the most common type using a CCD image sensor that forms an original image via a reduction optical system has a CC
Since the D image sensor itself has black dummy pixels that are always shielded from light, black dummy output is always possible, and data of the reference black level for black shading is always provided for each line. Will be. Therefore, A /
Even when the reference voltage of the A / D converter is varied, such as when a background removal function is provided to make the upper limit value of the reference voltage of the D converter follow the peak value of the original image, it is varied. The data of the reference black level for black shading can also be changed according to the reference voltage.

[0004]

However, for example, C
In the case of using the same-size close-contact type sensor configured in-line as a CD image sensor, a plurality of chips are arranged without gaps over the entire width of the original document. Cannot have pixels. When a CCD image sensor having no reference black level data for black shading for each line is used, or when the above-described CCD image sensor performs black shading correction for all pixels. The output obtained from each pixel of the CCD image sensor is set to a certain reference voltage while the light source is turned off before the white reference plate is read or before the original image is read.
The data must be converted into digital values by a converter and stored in a memory as reference black level data for black shading.

For this reason, an apparatus for reading an original by varying the reference voltage of an A / D converter (for example, Japanese Patent Application Laid-Open No.
103197), or a device that uses a different reference voltage when reading a white reference plate or reading a document image, has reference black level data for black shading as digital data. Therefore, there is a problem that the black shading correction corresponding to the variable reference voltage cannot be performed.

[0006] This point will be explained in an easy-to-understand manner using mathematical expressions. First, when a black level voltage Vb based on an analog signal is read at a certain reference voltage Vref0 of an 8-bit A / D converter, the digital value D0b of the reference black level is D0b = INT [Vb / Vref0 × 255] ……… (1) where INT []; rounded to the nearest decimal point,
The data is stored in the memory as data of the reference black level for black shading. From equation (1), it can be seen that the reference black level data D0 b depends on the reference voltage Vref of the A / D converter.

On the other hand, image data Dshb after black shading correction is obtained by reading data obtained by reading an original image as D0.
Assuming that g, Dshb is calculated as Dshb = D0g-D0b. At this time, assuming that the reference voltage of the A / D converter when reading the original is Vref 1 and the data of the reference white level by reading the white reference plate is Vw, Dshb = INT [Vw / Vref 1 × 255] −INT [Vb / Vref 0 × 255]... (2), and the calculation is performed between the data read at different reference voltages when the black level is detected and when the document is read. In this case, image data that has been subjected to shading correction cannot be obtained.

Therefore, according to the present invention, in a situation where reference black level data is held as digital data, the reference voltage of an A / D converter for converting the output of the solid-state imaging device into digital data is used for detecting the reference black level. It is an object of the present invention to provide an image reading apparatus capable of accurately obtaining image data that has been subjected to black shading correction even when it is changed from a reference voltage at the time.

[0009]

According to the first aspect of the present invention,
Before reading the document, the output signal for each pixel obtained from the solid-state imaging device in the form of an array is set to a certain reference voltage.
A digital signal is converted by a / D converter to detect reference black levels of all pixels of the solid-state imaging device, data of the detected reference black level is stored in a memory, and obtained from the solid-state imaging device at the time of reading a document. The reference black level data of the corresponding pixel stored in the memory is subtracted from the original data in which the output signal of each pixel is converted into a digital signal by the A / D converter set to a predetermined reference voltage. In the image reading apparatus that performs black shading correction, the reference black level data used at the time of the black shading correction is compared with the certain reference voltage at the time of detecting the reference black level and the predetermined voltage set at the time of reading the document. There is provided a correction means for performing correction in accordance with the ratio to the reference voltage.

Therefore, the data of the reference black level used in the black shading correction is corrected in accordance with the ratio between a certain reference voltage for detecting the reference black level and a predetermined reference voltage set when reading the document. Thus, the data of the reference black level according to the variation of the reference voltage of the A / D converter can be used, and the image data corrected for black shading can be obtained accurately.

According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the image reading apparatus further includes a conversion unit that converts a reference voltage set in the A / D converter into digital data and outputs the digital data, Means for temporarily storing digital data of the certain reference voltage converted by the conversion means when detecting the reference black level, and digital data of the certain reference voltage stored in the latch; A multiplication circuit for multiplying the reference black level data for each pixel stored in the memory,
The reference black level corrected by dividing the reference black level data for each pixel multiplied by the multiplying circuit by the predetermined reference voltage digital data set at the time of reading the original document and converted by the conversion means. And a division circuit that outputs the data of

Therefore, the invention described in claim 1 can be realized with a simple circuit configuration.

According to a third aspect of the present invention, in the image reading apparatus according to the first or second aspect, the solid-state imaging device receives reflected light from a document illuminated by a light source via a 1 × optical system. It consists of a 1: 1 contact type sensor that performs photoelectric conversion.

Therefore, it is possible to solve the problem associated with the variation of the reference voltage of the A / D converter in the type having no reference black level data for black shading correction for each line.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings.

[Principle of the present embodiment] The principle of the present embodiment will be described using mathematical expressions. In the present embodiment, under the conditions such as the above-described equations (1) and (2), even if the reference voltage of the A / D converter is changed, the image data subjected to black shading correction according to the reference voltage is changed. Dshb0 = D0g-D0b * Vref0 / Vref1 (3) so that the following equation can be obtained. That is, Dshb0 = INT [Vw / Vref1 × 255] −INT [Vb / Vref0 × 255] × Vref0 / Vref1 = INT [Vw / Vref1 × 255] −INT [Vb / Vref1 × 255] = INT [(Vw−Vb) / Vref 1 × 255] (4) Black shading correction processing is performed, and image data that has been subjected to black shading correction according to the reference voltage is obtained.

Here, since the reference voltage Vref itself is an analog value, the ratio Vref0 / Vref1 of the reference voltage in the equation (3) is calculated as follows: Vref0 / Vref1 = INT [Vref0 / Vcc × 255] / INT [Vref1 / Vcc × 255] = Dref0 / Dref1 ……………………………………………………………………………………………………………………………………………… (5) This can be easily realized.

[Embodiment] An embodiment utilizing the above principle will be described. The present embodiment is applied to a sheet-through type ADF 2 using a unit-size close-contact type sensor 1 as a solid-state imaging device that photoelectrically reads a document image. FIG. 1 is a front view showing the schematic configuration. The unit-size close-contact type sensor 1 includes an LED array 3 as a light source for slit exposure of a document, and a plurality of in-line CCD image sensor 4a, 4b,..., 4n (see FIG. 2) chips. It is provided facing the document transport path via a 1: 1 imaging optical system such as a lens array. A white reference plate 5 is provided at a position opposed to the unity close-contact type sensor 1, and document conveying rollers 6, 7 are provided before and after the white reference plate. For such a document reading section, a document transport path from the document tray 8 to the document discharge tray 10 via the transport belt 9 and the like is formed.

FIG. 2 is a block diagram showing an example of the configuration of an output processing circuit for processing the output of the unity close-contact type sensor 1 and outputting it to the image processing unit. In brief, each CCD image sensor 4a, 4b,.
The image data output in parallel from each of the 4n pixels is
Sampling / hold circuit (S / H circuit) 11a, 1
After sampling / holding at 1b,..., 11n, A
Are converted into digital data by the / D converters 12a, 12b,..., 12n. Thereafter, these A / D converters 12
a, 12b,..., 12n, the in-line circuit 13 performs in-line processing for aligning the data in the same manner as when the data is read by a CCD image sensor having a one-chip structure, and a black shading correction circuit. 14, black shading correction and white shading correction are sequentially performed by the white shading correction circuit 15 and output to the subsequent image processing unit.

Here, each A / D converter 12a, 12b,
, 12n, a reference control circuit 1 for setting and switching the reference voltage Vref
6 are connected. Further, a gate signal generation circuit 17 for outputting various gate signals for timing control to the reference control circuit 16 and the white shading correction circuit 15 at a predetermined timing is provided.

FIG. 3 shows the reference control circuit 16.
FIG. 3 is a block diagram illustrating a configuration example of FIG. In the present embodiment, the reference control circuit 16 is configured to control the reference voltage V of each of the A / D converters 12a, 12b,.
As ref, any one of three types, Vref g, Vrefw, and Vref AE, is set so as to be freely switchable. In particular,
The analog voltage Vrefg obtained by converting the document voltage by the D / A converter 22a via the switch 21a which is turned on when the document gate signal DOCGT is at the H level is used as a reference voltage as A / D converters 12a, 12b,. 12n. Similarly, an analog voltage Vref w obtained by converting a white reference voltage by a DA converter 22b via a switch 21b that is turned on when the white reference gate signal WTGT is at an H level.
Are A / D converters 12a and 12
, 12n. Further, the analog voltage Vre peak-held by the peak hold circuit (P / H circuit) 23 via the switch 21c which is turned on by an automatic exposure mode signal for providing a background removal function.
f AE is used as a reference voltage for the A / D converters 12a, 1
2b,..., 12n. Note that, for the peak hold circuit 23, the average value circuit 24 for white is used for the digital image signal D0 obtained from the in-line circuit 13.
, A value obtained by comparing the averaged value with a predetermined comparison value by the comparator 25 and converting the result into an analog voltage by the DA converter 26 is given.

On the output side of each of the switches 21a to 21c, the value of the reference voltage Vref set in the A / D converters 12a, 12b,..., 12n is converted into digital data Dref using the power supply voltage Vcc. An A / D converter 27 is provided as a conversion means for outputting to the black shading correction circuit 14.

FIG. 4 is a block diagram showing a configuration example of the black shading correction circuit 14. Basically, when detecting the reference black level, the digital image data D0 obtained from the in-line circuit 13 is applied to the average value circuit 31 for black.
And a memory 32 for storing the result of the average value processing as data D0b of the detected reference black level. Further, the data D0b of the reference black level stored in the memory 32 is subtracted from the digital image data D0g obtained from the in-line circuit 13 at the time of reading a document, and the data Dshb after black shading is subtracted from the digital image data D0b in the latter stage of the white shading correction circuit. 15 is provided.

Such a black shading correction circuit 14
In this embodiment, the memory 32 and the subtraction circuit 3
Correction means 34 is added between the three. This correction means 3
Reference numeral 4 denotes a latch 35 for temporarily storing digital data Dref 0 of a certain reference voltage converted by the A / D converter 27 when the reference black level is detected (when the gate signal BKGT is output); A multiplication circuit 36 for multiplying the digital data Dref stored in the memory 35 and the reference black level data D0 b for each pixel stored in the memory 32
And the reference black level data D1 b for each pixel multiplied by the multiplication circuit 36 are divided by the reference voltage digital data Dref 1 set at the time of reading the original and converted by the A / D converter 27. And a dividing circuit 37 for outputting the reference black level data D2 b corrected in this way.

The operation in such a configuration will be described with reference to a time chart shown in FIG. First,
When the document on the document tray 8 starts to be fed, an LED lighting signal LED ON is activated by a controller (not shown), and the lighting operation of the LED array 3 is started. Here, the reference black level detection gate signal BKGT is active during a period of L1 lines corresponding to the line until the LED array 3 is turned on. During this active period, the CCD image sensors 4a, 4b,. , And converted into digital image data by the A / D converters 12a, 12b,..., 12n, are stored in the memory 32 as reference black level data through averaging processing. That is, during the assertion period of the reference black level detection gate signal BKGT, the averaging circuit 31 performs an averaging process for each pixel by the averaging circuit 31. Eye reference black level data D0 (n): read data of the n-th pixel ΣD0 (n): obtains an added value from the first line to the L1 line of D0 (n) and stores the value in the memory 32 It is.

While the reference black level detection gate signal BKGT corresponding to the LI lines is active, the reference control circuit 16 controls the AEMODE = WTGT = L level.
By setting DOCGT = H level, A / D converter 1
2a, 12b,..., 12n
ref g is selected and set. That is, the A / D converter 12a, when the data of the reference black level shown in the equation (5) is read,
Since the reference voltages Vref 0 of 12b,..., 15n are Vref g in the present embodiment, the A / D converter 27
And is detected as Dref 0 = INT [Vref g / Vin × 255]. The digital data Dref 0 of this reference voltage is latched in the latch 35 at the H-level edge timing of the gate signal BKGT. Then, at the same time when the gate signal BKGT is negated, the detection and generation of the reference black level data is completed, and the LED array 3 is turned on.

Subsequently, when the SLEAD signal indicating the reading operation period of the white reference plate 5 is asserted, the A / D converter 12
, 12n, Vref w based on the white plate voltage is selected, and reading of the white reference plate 5 by the CCD image sensors 4a, 4b, ..., 4n is started. Then, as is well known, shading data is generated during the assertion period of the reference white level detection gate signal WTGT included in the SLEAD signal. At this time, A
Changing the reference voltage of the / D converters 12a, 12b,..., 12n is described in, for example, Japanese Patent Laid-Open No. 5-103197.
This is for absorbing variations in the white reference plate 5 as shown in the publication.

As a result, as described above, it can be seen that data is read using a reference voltage different from that used when the reference black level is detected. That is, the reference voltage Vre of the A / D converters 12a, 12b,..., 15n at the time of reading the original shown in the expression (5) (here, at the time of reading the white reference plate 5).
Since f1 is Vref w in the present embodiment, it is digitized by the A / D converter 27 and detected as Dref1 = INT [Vref w / Vin × 255].

Then, the arithmetic processing of the equation (3) is performed. First,
The multiplication circuit 36 calculates D1b = D0b × Dref0, and the division circuit 37 calculates D2b = D1b / Dref1 = D0b × Dref0 / Dref1. The level data D2 b is obtained. Then, the corrected reference black level data D
By calculating Dshb = D0g-D2b in the subtraction circuit 33 using 2b, data after black shading correction according to the change in the reference voltage can be obtained.

Thereafter, when the SLEAD signal is negated, the reading of the white reference plate 5 ends. And the A / D converter 1
When Vrefg is set again as the reference voltage of 2a, 12b,..., 12n, and the document is conveyed to the reading position facing the close-to-contact type sensor 1, it indicates the document effective range.
The reading of the document is started by asserting the SSCAN signal, and the digital image data converted into digital data by the A / D converters 12a, 12b,. Are subjected to black shading correction and white shading correction, respectively, and output to the image processing unit side.

In this embodiment, the A / D converter 12 detects the reference black level and detects the original document.
Although the same voltage Vref g is used as the reference voltage for a, 12b,..., 12n, as can be seen from equation (3), the reference voltage Vref 1 is used when the original (effective data) is read. Since the black level data is corrected, even if the reference voltages of the A / D converters 12a, 12b,..., 12n differ between when the reference black level is detected and when the original document is read, (Vref 1 = Vr
ef g ≠ Vref 0) or the reference voltage for background removal (Vref 1 = Vref AE) and the reference voltage fluctuates during document reading, the reference black level data is accordingly changed. Corrected and subtracted circuit 3
3 is subjected to a subtraction process. Therefore, the data of the reference black level can be appropriately corrected accurately and in accordance with the level fluctuation of the reference voltage in real time.

[0032]

According to the first aspect of the present invention, the data of the reference black level used in the black shading correction is converted into a reference voltage for detecting the reference black level and a predetermined reference voltage set for reading the document. Since the correction is performed in accordance with the ratio with respect to the voltage, the data of the reference black level according to the variation of the reference voltage of the A / D converter can be used, and the image data corrected with the black shading can be obtained accurately. Can be.

According to the second aspect of the invention, the first aspect of the invention can be realized with a simple circuit configuration.

According to the third aspect of the present invention, the solid-state imaging device is a one-to-one contact type sensor that receives reflected light from a document illuminated by the light source via the one-to-one optical system and performs photoelectric conversion. Therefore, it is possible to solve the problem associated with the variation of the reference voltage of the A / D converter in the type that does not originally have the data of the reference black level for black shading correction for each line.

[Brief description of the drawings]

FIG. 1 is a front view showing a schematic configuration of an ADF according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration example of an output processing circuit of the unity close-contact sensor.

FIG. 3 is a block diagram illustrating a configuration example of the reference control circuit.

FIG. 4 is a block diagram illustrating a configuration example of a black shading correction circuit.

FIG. 5 is a time chart illustrating an operation example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid-state image sensor, 1: 1 contact type sensor 3 Light source 12 A / D converter 27 Conversion means 32 Memory 34 Correction means 35 Latch 36 Multiplication circuit 37 Division circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (3)

[Claims] An output signal for each pixel obtained from an array of solid-state imaging devices before reading a document is converted into a digital signal by an A / D converter set to a certain reference voltage, and the digital signal is output from the solid-state imaging device. Detects the reference black level of all pixels,
Data of the detected reference black level is stored in a memory, and an output signal for each pixel obtained from the solid-state imaging device at the time of reading a document is output from the A / A set at a predetermined reference voltage.
An image reading apparatus that performs black shading correction by subtracting the reference black level data of the corresponding pixel stored in the memory from the original data converted into a digital signal by the D converter, And a correction unit for correcting data of the reference black level in accordance with a ratio between the certain reference voltage at the time of detecting the reference black level and the predetermined reference voltage set at the time of reading the document. Image reading device. 2. A conversion means for converting a reference voltage set in the A / D converter into digital data and outputting the digital data, wherein the correction means performs conversion by the conversion means when detecting the reference black level. A latch for temporarily storing the digital data of the given reference voltage,
A multiplication circuit that multiplies the digital data of the certain reference voltage stored in the latch by the reference black level data of each pixel stored in the memory; and a multiplication circuit for each pixel multiplied by the multiplication circuit. A division circuit that outputs the corrected reference black level data by dividing the reference black level data by the digital data of the predetermined reference voltage set at the time of reading the original and converted by the conversion means. Claim 1 characterized by the following:
The image reading device according to claim 1. 3. The one-to-one contact type sensor for receiving reflected light from a document illuminated by a light source via a one-to-one optical system and photoelectrically converting the reflected light from the original. 3. The image reading device according to 1 or 2.