JP2622039B2 - Reading density correction method for double-sided image scanner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided image scanner capable of reading an image from both sides of a document. The present invention relates to a reading density correction method for correcting a density difference by eliminating variations in the reading density.

[0002]

2. Description of the Related Art The inside of a conventional double-sided image scanner will be described with reference to FIGS. FIG. 5 shows a reading mechanism of a conventional double-sided image scanner.

[0005] In FIG. 5, reference numeral 35 denotes a flatbed for fixing and reading an original. Reference numeral 36 denotes a movable optical reading unit for reading an image on the surface of the document. Reference numeral 37 denotes a white reference plate for reading the front side of the document. Reference numeral 38 denotes a paper feed roller for transporting the original, which is used when performing continuous reading or double-sided reading of the original. Reference numeral 39 denotes a document to be read on both sides, in which the lower surface is the front surface and the upper surface is the back surface. Reference numeral 40 denotes an optical reading unit for reading the back side of the document. Reference numeral 41 denotes a platen that also serves as a white reference for the back surface. Reference numerals 42 and 43 are lamps, and reference numerals 44 and 45 are CCDs.

During the double-sided reading operation, the optical reading unit 36 for reading the front surface is set at the right position with the white reference plate 37.
Has been stopped at the position shown in the figure after reading, and the optical reading unit 40 for reading the back surface includes a platen 41.
After reading the upper white reference, it waits for the original 39 to be sent.

A document 39 is continuously fed to the optical reading units 36 and 40 by a paper feed roller 38, and the reading areas on the front and back sides are irradiated by lamps 42 and 43 in the respective optical reading units. , 45.

FIG. 6 shows an image signal processing circuit. 6, reference numerals 44 and 45 denote CCDs, 4 and 4 shown in FIG.
6, 47 are amplifiers; 48, 49 are A / D conversion circuits;
0 and 51 are white level correction circuits, and 52 and 53 are memories.

[0007] CCD for front side reading and back side reading
The white level of the white reference read first by 44 and 45 is
The white level correction circuits 50 and 51 respectively store and correct the color following the ground color of a document to be read thereafter. The corrected white level is output to A / D conversion circuits 48 and 49. The A / D conversion circuits 48 and 49 use the white level given from the white level correction circuit as the saturation value of the density and convert the analog image signals (video signals) received from the CCDs 44 and 45 via the amplifiers 46 and 47 into the corresponding density. Convert to level image data.

In this manner, the images on the front and back sides of the original are read with appropriate contrast, respectively, and stored in the memories 52 and 53.

[0009]

In the conventional double-sided image scanner, the optical reading units for reading the front surface and reading the back surface generate white levels by using a white reference plate and a unique white reference such as a platen, respectively. Was. For this reason, differences in the reflectivity due to differences in materials and the like are likely to occur in each white reference, and there is a case where the white reference level does not match and there is a density difference between the read image data, so that troublesome level adjustment has to be performed. I had to.

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple means for adjusting the shift between the white references on both sides and eliminating the density difference.

[0011]

According to the present invention, a level variable circuit is provided for each output of a white level correction circuit for the front surface and the back surface, and a white reference sheet having a constant reflectance is used in advance for the front and rear surfaces. The control unit reads and stores the control data necessary to obtain the variation in the white level values of the front and back surfaces, and controls each level variable circuit using the control data during operation, This is to eliminate the variation of the white level for the back and the back.

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, reference numerals 1 and 2 denote optical reading units for reading images on the front and back sides of a document, respectively, and output reading results in a video signal format.

Reference numerals 3 and 4 denote white references for the optical reading units 1 and 2, respectively. Reference numeral 5 denotes a test white reference sheet having a constant reflectance used for adjusting the dispersion of the white level values for the front surface and the back surface.

Reference numerals 6 and 7 denote white level correction circuits for generating white level values for the front side and the back side, respectively. 8, 9
A for converting the input video signal into image data of a corresponding density value based on the white level values for the front side and the back side, respectively.
/ D conversion circuit.

Reference numerals 10 and 11 denote level variable circuits for adjusting the balance between the white level for the front side and the white level for the back side. Reference numeral 12 denotes a memory for storing image data.

Reference numerals 13 and 14 are white level control data for the front side and the back side, respectively. Reference numeral 15 denotes white level control data for creating white level control data 13 and 14 at the time of product shipment and controlling the level variable circuits 10 and 11 for the front and back sides based on the white level control data 13 and 14 during operation. It is an adjustment control unit.

[0017]

The operation of the present invention will be described with reference to FIG. At the time of adjustment at the time of product shipment or maintenance, the white reference 3 and 4 are read by the optical reading units 1 and 2 for front surface reading and back surface reading, respectively, and are set in the white level correction circuits 6 and 7.

Next, a white reference sheet 5 having a constant reflectance on the front and back sides for a test is fed, and each optical reading unit 1 is read.
2 is read, and the level of the image data output from the A / D conversion circuits 8 and 9 is compared with the reflectance of the known white reference sheet 5 by the white level adjustment control unit 15 and the level required for matching the values is obtained. The level adjustment values of the variable circuits 10 and 11, for example, the voltage division ratios are calculated, and the white level control data 13 and 1 are calculated.
4 is retained.

In operation, the white level adjustment control unit 15
The level variable circuits 10 and 11 are controlled using the white level control data 13 and 14, respectively, and the white level correction circuits 6 and 7 are controlled.
Is adjusted so that the white level value is supplied to the A / D conversion circuits 8 and 9.

As a result, the influence of the difference in the reflectance existing between the white references 3 and 4 is removed from the white levels supplied to the A / D conversion circuits 8 and 9, respectively. The quality of the resulting image can be matched.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 2 shows the configuration of the image signal processing circuit according to the embodiment of the present invention.

In FIG. 2, 16 and 17 are CCDs, 1
8 and 19 are amplifiers, 20 and 21 are A / D conversion circuits, 2
2, 23 are white level correction circuits, 22a, 23a are level variable circuits, 24, 25 are RAMs, 26, 27 are latches,
28 is a CPU, 28a is an EEPROM, and 29 is an I / O port. In the figure, the upper circuit portion including the CCD 16 is for reading the front surface, and the lower circuit portion including the CCD 17 is for reading the back surface. Since both circuits have the same circuit configuration, only the upper circuit portion will be described.

The video signal output from the CCD 16 is amplified by the amplifier 18 and input to the white level correction circuit 22 and the A / D conversion circuit 20. The white level correction circuit 22 detects the ground color level of the input video signal, corrects the current white level at a predetermined ratio, and supplies the corrected white level to the A / D conversion circuit 20 through the level variable circuit 22a. The A / D conversion circuit 20 converts the input video signal into digital signal image data using the white level value as a density saturation value (dynamic range value). This image data is stored in the RAM 24 at sequential addresses. Address is n + 1 bit AD
It is shown in the _{0 ~AD n.}

The latches 26 and 27 are three-state latches, and are in a cut-off state while writing image data to the RAMs 24 and 25. The CPU 28 controls an image reading operation or a white level variation adjustment process by executing a control program stored in the EEPROM 28a.

In the adjustment at the time of product shipment, the CPU 28
When the CDs 16 and 17 read the white reference sheet for the test after reading the white reference, the latches 26 and 27
, The read data (image data) of the front and back sides of the white reference sheet are taken in, and the respective density values are obtained to calculate control data necessary for white level adjustment for the level variable circuits 22a and 23a. The control data of the calculation result is E
It is stored in the EPROM 28a. Next, during operation, the CP
U28 reads the control data from the EEPROM 28a, and outputs each level variable circuit 22 through the I / O port 29.
a, 23a to adjust the white level to a predetermined level.

FIG. 3 shows a detailed configuration of the white level correction circuit 22 and the level variable circuit 22a surrounded by a dotted line in FIG. In FIG. 3, a white level memory 30 holds a white level value, and holds a white level pattern (for one line) as indicated by a dotted waveform in the upper right of the figure, and is updated for each line. Reference numeral 31 denotes a D / A conversion circuit that converts a white level value into an analog signal.

Reference numeral 34 denotes a voltage dividing circuit whose voltage dividing ratio is controlled by an analog switch 34a.
4a operates according to the value of the control data output from the I / O port 29 of FIG. Reference numeral 33 denotes a comparator whose positive input terminal has a D / A
The adjusted white level value of the output of the conversion circuit 31 is input, and the video signal from the amplifier 18 of FIG. 2 is input to the negative input terminal.

The comparator 33 compares the magnitudes of the two positive and negative inputs and outputs the result as a binary 1/0. Reference numeral 32 denotes a white level algorithm memory, which stores the white level value of the output of the white level memory 30 and the comparison result value 1 of the comparator 33.
It has a function table that uses / 0 as an address input, and an update value of a white level based on a predetermined algorithm is read as data. The read data from the white level algorithm memory 32 is written to the white level memory 30 and used as the white level of the next line.

The operation of the white level correction circuit 23 and the level variable circuit 23a of FIG. 2 basically operates in the same manner as the circuit of FIG. FIG. 4 shows a flow of the white level control data creation processing executed by the CPU 28 of FIG. The operation will be described below with reference to FIGS.

(1) The level variable circuits 22a and 23 shown in FIG.
The output of a is maximized (all the analog switches 34a in FIG. 3 are turned on), and the white level output is maximized. (2) The white reference is read on each side, and white level correction is performed by the white level correction circuits 22 and 23.

(3) A white reference sheet having a constant front and back reflectance is read. For example, a sheet whose reflectance is known to be 80% is used. (4) The image data of the white reference sheet stored in each of the RAMs 24 and 25 in FIG.

(5) The average value of the density values on each side of the front and back is a level based on the reflectance (80%) of the white reference sheet.
For example, in the case of 256 gradations (0 to 255), 255 ×
A white level adjustment value that satisfies 0.8 = 204, specifically, control data of the analog switch 34a that gives an appropriate voltage dividing ratio of the voltage dividing circuit 34 in FIG. 3 is obtained.

(6) The obtained white level adjustment value is written into the EEPROM 28a of FIG.

[0034]

According to the present invention, it is possible to easily adjust and correct variations in density between front and back sides of a double-sided image scanner, and to adjust different devices using a white reference sheet having the same reflectance. In addition, variations between devices can be eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram showing the basic configuration of the present invention.

FIG. 2 is a configuration diagram of a circuit according to an embodiment of the present invention.

FIG. 3 is a detailed configuration diagram of each level correction and level variable circuit according to the embodiment of the present invention.

FIG. 4 is a flowchart of a white level control data creation process according to the embodiment of the present invention.

FIG. 5 is a configuration diagram of a reading mechanism of a conventional double-sided image scanner.

FIG. 6 is a configuration diagram of a conventional image signal processing circuit.

[Explanation of symbols]

 1, 2 Optical reading unit 3, 4 White reference 5 White reference sheet 6, 7 White level correction circuit 8, 9 A / D conversion circuit 10, 11 Level variable circuit 12 Memory 13, 14 White level control data 15 White level adjustment control Department

Claims (1)

(57) [Claims] 1. An optical reading unit for reading an image on the front side of an original and an optical reading unit for reading an image on a back side of the original, and each of the two optical reading units has a unique white reference and has a ground color of the original. In a double-sided image scanner having a white level correction circuit for generating a corrected white level following the white level correction circuit, a level variable circuit for adjusting the white level is provided at the output of the white level correction circuit, and a white reference sheet for testing is provided in advance. To the optical reading units for the front and back sides, obtain the level control data for each level variable circuit necessary to match each white level on the front and back sides to the target value determined by the white reference sheet, and store it in the memory. Store, at the time of operation, read the level control data stored in the memory to control each level variable circuit,
A reading density correction method for a double-sided image scanner, wherein a white level for a front surface and a white level for a back surface are adjusted to correct a density difference.