JP3489801B2 - Image reading device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus, and more particularly to a linearity correcting means for an image sensor output of an image reading unit such as a scanner or a facsimile machine.

[0002]

2. Description of the Related Art In recent years, image quality has been remarkably improved in facsimile machines, digital copying machines, digital color copying machines, etc.
Solid-state image sensors such as D are often used. To read the original image, CC with the original evenly illuminated.
Receive the reflected light using a solid-state image sensor such as D,
It is common to perform the required processing after converting the optical signal into an electrical signal. When an image sensor such as a CCD is used, a process called shading correction is performed in order to correct the distortion of each gradation output signal due to variations in the characteristics of the pixel sensor and ensure linearity, but prior to that process. At both ends of the gradation, that is, two light receiving levels, that is, a black level at which the light receiving level is zero and a white level at which the light receiving level is maximum are read and stored in a black memory and a white memory, respectively. The image signal read from the original is then [{(pixel data) − (black level)} × 256] / (white level) (1) with reference to the information stored in the black memory and the white memory. The following shading-corrected data is calculated. In order to read the black level, the exposure lamp is turned off and the CCD output in the absence of reflected light is stored in the memory. On the other hand, the white level is stored in the white memory when the exposure lamp is turned on. .

FIG. 9 is a block diagram showing a main configuration of a shading correction circuit in a conventional image reading apparatus. In this figure, for simplification of explanation, only one color element signal of color image signals will be explained. However, the same applies to other color elements. In FIG.
The even line red image signal from the CCD is input to the R / EVEN A / D converter 121, and the odd line red image signal is input to the R-ODD A / D converter 122, respectively, and after being converted into a digital signal, the selector In 127, both are combined. The image signal combined into one system of signals is corrected in the shading gate array 130. At this time, the image signal is read from the original based on the respective reference signals stored in the white memory and the black memory as described above. The shading correction is performed on the image data.

[0004]

However, in the shading correction means in the conventional image reading apparatus as described above, the difference between ODD and EVEN is corrected on the white side and the black side, but as shown in FIG. , ODD and EV
When the linearity differs depending on EN, an error occurs in the correction in the intermediate gradation region, and accurate correction is difficult. Generally, two CCDs are used in an image reading apparatus having a CCD shift register for odd pixels and a CCD shift register for even pixels.
There may be a difference in the output level due to a slight difference in the characteristics of the shift register. Especially, when the number of lines is large like in a 3-line CCD, interference between the registers is unavoidable, and the even-odd difference between ODD and EVEN is inevitable. Was a problem.
That is, since the difference between the odd number and the even number is conventionally detected in the black reference portion, the output difference between the odd and even pixels is unknown in the white portion and the middle portion. May occur and the quality of the formed image may be significantly deteriorated. The present invention has been made in order to solve the problem in such a conventional image reading apparatus, and a fringe caused by interference between odd and even lines in shading correction when a solid-state image sensor such as a CCD is used. It is an object of the present invention to provide an image reading apparatus which prevents generation of patterns and has excellent linearity over the entire gradation range.

[0005]

[Means for Solving the Problems] To achieve the above object
, The present invention includes an original image or shading data
Illuminates the white reference plate used when capturing
An optical system that guides the reflected light to the photoelectric conversion means, and
A / D conversion to convert analog signals from these to digital signals
Means and memory for storing shading data
In an image reading device having shading correction means
The tilt angle of the white reference plate or the white reference plate and the light source
And the distance from the A / D conversion means is changed stepwise.
Means for obtaining pseudo grayscale data as force,
Halftone based on the above pseudo grayscale data
Of the output level between the pixels of the photoelectric conversion means in the part
And a means for correcting the variation.

[0006]

In the present invention, shading data is taken in
The inclination angle of the white reference plate used when
By gradually changing the distance between the reference plate and the light source, C
The amount of light entering the image reading device such as a CD changes,
Pseudo grace as output of A / D conversion means (ADC)
You can get kale data. And in the present invention
Based on this pseudo grayscale data,
The output level between the pixels of the photoelectric conversion means in the intertone section
Correct the roughness. As a result, the characteristics of the CCD, etc. may vary.
In addition to the correction of luck, slight non-linearity of amplifier, ADC, etc.
It is possible to correct it to prevent the occurrence of striped patterns.
It is possible to obtain a high-quality image by correcting a slight difference in each gradation of the number / even lines .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on the illustrated embodiments. FIG. 1 is a block diagram showing an embodiment of an image reading apparatus to which the present invention is applied.
The main functions of the image reading device shown in this example are:
These are a motor control function, an analog automatic setting function, a digital signal processing setting function, a document detection processing function, a communication function with the image forming apparatus main body, a projector compatible function, and the like. In this example, as a large block configuration for fulfilling the above functions, it is composed of a scanner control unit 1, a CCD unit 2, a scanner drive unit 3, and other peripheral blocks. The outline of the configuration and function of each block will be described below. First, the scanner control unit 1 includes a one-chip microcomputer (CPU) 12, and the ROM 1
Various data including image data is generated by executing the program stored in the memory 3, and the data is written to or read from the RAM 14 to control the entire scanner. Further, the main control unit 101 that controls the entire image forming apparatus is connected by, for example, means for serially communicating data (serial communication means), and by transmitting and receiving commands and data, the image forming apparatus is transmitted. Various processes are executed in accordance with instructions from the main control unit.

Further, the main control unit 101 includes an operation display unit 1
02 is connected by serial communication means so that an operation mode and the like can be set according to a user's key operation input. The CPU 12 includes a lamp regulator 4, which performs an I / O function, a document detection sensor 7, and an H, via the scanner driver unit 3 having a relay processing function.
P sensor 9, pressure plate opening / closing sensor 8, and cooling fans 5 and 6
And the scanner opening / closing sensor 10 are controlled. The scanner driver unit 3 generates an excitation pulse sequence by the motor excitation pattern output ROM 42 decoded by the CPU port output to generate the original scanning drive pulse motor 1.
Control 1 Further, the motor driver section 43 is provided with a pre-driver and an FET driver.

The original image is irradiated with the light generated from the halogen lamp 44 controlled and driven by the lamp regulator 4, and the reflected light is C through a plurality of mirrors and lenses.
It is guided to the 3-line CCD 35 of the CD section 2 and converted into an electric signal. The 3-line CCD 35, in accordance with the drive clock from the timing generation gate array 15 of the scanner controller 1, outputs an analog signal corresponding to the original image to the amplifiers 36 to 36.
Output to 41. The timing generating gate array has a built-in FGATE start counter for counting the PMSYNC signal, and starts counting by an output port signal from the CPU 12, thereby generating FGATE of the image reading control signal. A feedback voltage for black level adjustment and dark current correction is applied to the amplifiers 36 to 41 of the CCD unit 2, and this voltage is applied to the CPU 12 via a parallel in serial out. 8ch D / A converter 17 and 12ch by serial data from the data buffer 16
It is driven by the D / A converter 18 of. By this feedback voltage, analog image data whose offsets (DA1, DA2) of black levels "1" and "2" are adjusted from the amplifier output are input to the A / D converters 21 to 26 of the scanner control unit 1. .

The Vref of these A / D converters is adjusted by the voltage from the D / A converter (DA) so as to correspond to the gain (amplitude value) of the analog image data.
3) is done. The A / D converter converts an analog signal into a digital signal, and ODD (odd number signal) and EVEN (even number signal) are digitally combined by the selectors 27 to 29 and input to the shedding gate arrays 30 to 32. The shading gate array has a function of correcting nonuniformity of light of the illumination system and variation of pixel output of CCD. When the lamp is off, output data is set in a black memory (not shown) connected to the shading gate array, black correction processing is performed, and then the lamp is turned on to detect the reflected light from the density reference plate (white reference plate). And this data
Based on the data, white correction is performed to store the data in the white memory connected to the shading gate array. Image data read thereafter is subjected to shading correction processing based on the data of the black memory and the white memory. In addition to the shading correction, the shading gate array has eight continuous lines for each CCD line according to the gate signal.
The maximum value of the arithmetic mean value for pixels is ODD (odd line),
Store in the internal register for every EVEN (even line).
This data can be read from the CPU connected to the bus (maximum value detection function), and it is also possible to output image data without shading calculation (data through mode). The shading-corrected image data is stored in the inter-line correction memories 33 to 34, and the image data of the number of lines of B and G and B and R of the 3-line CCD 35 is read out from the memory and delayed. The read image position of the BGR is adjusted by adjusting the amount and output to the IPU 100. The setting of the line correction memory is controlled by the timing gate array according to the reading speed, that is, the reading magnification.

FIG. 2 is a block diagram showing the essential parts of an embodiment of the shading correction circuit according to the present invention. The shading correction circuit shown in this example is an A / A that converts an analog signal from an image reading sensor such as a CCD into a digital signal.
An even-odd correction circuit 203 is inserted between the D converters 201 and 202 and the selector circuit 204, and the shading gate array 205 reads the reference data stored in the white memory and the black memory in addition to the above-described functions, and reads each reference data. It has a function of reading and correcting variations in each pixel. That is, the circuit shown in this example is an A / D for R-EVEN that inputs an even line red image signal from a CCD.
A converter 201, an R / ODD A / D converter 202 that inputs a red image signal of an odd line, an even-odd difference correction circuit 203, a selector 204, a shading gate array 205, and a black memory 206 connected thereto.
The white block 207, the CPU 12, and the white reference plate moving pulse motor 208 controlled by this CPU are the main blocks. Further, the even-odd difference correction circuit 203 has an R-
The selector circuit 211 that processes the output of the EVEN converter 201, the RAM table 212, and the second selector circuit 213, as well as the R-ODD converter 20.
Second selector circuit 214 for processing the output of the second, second RAM table 215, and fourth selector circuit 216
It consists of and.

To explain the operation in this configuration, first, the black level (sensor dark level when the light source is off) and the white level output from the image sensor are calculated for each bit before performing the shading correction process. Black memory 206
And the white reference data are stored in the white memory 207.
I will As described above, the shading correction is based on the black reference level and the white reference level and follows the above equation (1), and is [{(pixel data)-(black level)} × 256].
÷ (White level) is calculated to obtain the correction data. For example, when the read pixel is white, the above calculation result is the maximum value, and when the read pixel is the black pixel, it is the minimum value, and when the read pixel is an intermediate value, it is one of 256 levels.
Take halftone values.

The shading correction circuit shown in this example has the following five functions. (1) Pixel data processing mode The shading correction of the sensor signal read from the target original is performed. The signal from the image sensor is compared with the black level and the white level, and a predetermined calculation is performed to perform the shading correction. -Get the data. (2) Memory test mode The contents of the black memory 206 and the white memory 207 are read / written from the MPU. (3) Black level processing mode In the mode for generating the black reference level at the time of reading the original, all the contents of the black memory 206 are first set to "0", and the black level signal from the image sensor is read 16 times and averaged to obtain the black level. As a memory. (4) White level processing mode In the mode for generating a white reference level at the time of reading an original, first, all the lower 4 bits of the white memory 207 and the black memory 206 are set to "0", and the white level signal from the image sensor is set. It is read and averaged 16 times and stored as a white level. (5) Data through mode The input sensor output is output as it is.

FIG. 3 is a schematic sectional view in the sub-scanning direction showing an example of the scanner unit section used in the above embodiment. In the scanner unit section shown in this example,
The feature is that the white reference plate 61 is configured to be inclined in the sub-scanning direction. Normally, as shown in FIG. 3 (a), the halogen lamp 6 is placed with the white reference plate 61 horizontal.
The light from 2 is irradiated, and the reflected light is reflected by the plurality of mirrors 63-
After the white correction data is stored in the CCD 67 via the lens 65 and the lens 66 and the white correction data is stored in the CCD 67, the first scanner including the halogen lamp 62 and the mirror 63 and the second scanner including the mirrors 64 and 65 are scanned. The image of the original document placed on the contact glass 68 is read. In the even-odd difference correction processing, the white reference plate drive roller 69 is rotated by supplying a required number of pulses to the white reference plate movement pulse motor 308 connected to the output port of the CPU, and is shown in FIG. Thus, the white reference plate 61 is tilted in the sub-scanning direction. It can be easily understood that when the light from the halogen lamp is irradiated in the state where the white reference plate 61 is inclined, the amount of reflected light from the white reference plate input to the CCD 67 is reduced. Since the amount of reflected light from the white reference plate 61 changes according to its inclination angle, the number of pulses to be supplied to the white reference plate moving pulse motor 308 can be appropriately set to adjust the amount of reflected light in any stepless manner. Is possible. That is, by setting the number of pulses for controlling the inclination angle of the white reference plate 61, there is an effect of obtaining the same gradation output as that obtained by artificially reading the gray scale chart.

With the scanner unit section, the reflected light is detected by the CCD while the white reference plate 61 is tilted and read into the CPU through the shading gate array 205 shown in FIG. 2, and the ODD-EVEN difference for each tilt angle is read. The RAM 21 of the even-odd difference correction circuit 203 is obtained by obtaining (even-odd difference).
5, 212 is written as lookup gamma table data. CPU 12 and RAM of even-odd difference correction circuit 203
Addresses 215 and 212 are connected by the selector circuit 21.
4 and 211 , and the data between them is transferred by switching the CE signals of the selector circuits 213 and 216. The contents of the RAMs 212 and 215 are held by a backup power supply (not shown). In this configuration, the analog signal from the CCD is transferred to the two A / D converters 201,
After inputting into 202 respectively and converting into a digital signal,
In the even-odd difference correction circuit 203, the level difference between even-numbered pixels and odd-numbered pixels
Is corrected, and the selector 204 combines the two. The shading gate array 205 corrects the image signal combined into one system of signals. At this time,
As described above, the image data read from the original is shading-corrected based on the respective reference signals stored in the white memory 207 and the black memory 206.

FIG. 4 is a flowchart showing an example of the processing procedure of the even-odd difference correction processing in the image forming apparatus having the mechanism for inclining the white reference plate as described above. Whether or not the processing described below is executed each time the power is turned on can be selected by setting the dip switch 20 attached to the CPU 12 in FIG. 1 or setting the correction flag by the input of the SP mode. . In FIG. 4, when the even-odd difference correction process starts, it is first determined whether or not the correction flag is set (S1). If it is not set, RET is performed and the process ends, but if the flag is set, The scanner unit is moved to the position of the white reference plate (S2). After setting the exposure lamp voltage, the pulse motor is driven to turn on the white reference plate moving pulse motor (S3), and the lamp is turned on (S4). After the lamp is lit, the timer is reset (S5), and after confirming that the time until the lamp light amount stabilizes, for example, 600 msec has passed (S6), the reflected light from the white reference plate is read and the white memory set in the shading gate array. (S
7). In the white memory set S7, the signal generated by taking in the reflected light from the white reference plate is read 16 times , averaged and stored as a white reference signal (S8). When the above process is completed, the shading gate array is set to the white test mode (S9). The white memory test mode is a function of reading / writing the white memory from the CPU via the register.

As a result, the memory read operation and the averaging process for each even / odd pixel in a predetermined range are performed and stored in the working RAM of the CPU (S10). Then, the white memory test mode is reset (S11), the set number of times n is incremented (S12), and the number of steps of moving the white reference plate, that is, the number of pseudo gradations N is compared (S13). As a result of this comparison, if the number of pseudo gradations N is larger than the set number n, after setting the white reference plate moving motor pulse number (S14), the white reference plate moving motor of S3 is turned on.
Then, the process S3 to S13 described above is repeated. When n = N in the above S13, the γ correction table is set based on the odd / even calculation data (S15), the motor is returned (S17), the motor is stopped (S18), and the post-processing is terminated. The set of the γ correction table has 256 gradations in the case of 8-bit reading, but since it is difficult to obtain the gradation corresponding to the reading resolution by the number of steps of moving the white reference plate, it is difficult to obtain a typical gradation. A value is obtained in several steps, and table data comparable to the reading resolution is calculated by interpolation processing using this even-odd difference data, and is set in the RAM table.

As described above, the white reference plate is tilted to create a pseudo gradation, the even-odd difference of each gradation is calculated, and the look-up table value of the RAM table is set to correct the intermediate gradation part. If this is done, image data without even difference can be obtained. In addition to the examples described above, various uses of this pseudo gray scale are possible. For example, the dynamic range corresponding to the density of the original image data can be secured by loading the halftone white data and the black data into the white memory and the black memory of the shading gate array. Therefore, it is possible to output a good image without increasing the resolution of the A / D converter.

FIG. 5 is a schematic sectional view of the scanner unit section in the sub-scanning direction showing another embodiment of the present invention. The feature of this embodiment is that the inclination angle of the white reference plate 61 is fixed, and instead the first scanner and the second scanner are moved in the sub-scanning direction when reading the reflected light of the white reference plate. It is a point. That is, as is clear by comparing FIGS. 5A and 5B, with the white reference plate 61 tilted by a predetermined angle, the first and second scanners are placed at positions separated by a predetermined length in the sub-scanning direction. If the reflected light from the white reference plate is set and received, the reflected light path length is different and the reflected light amount is different. As a result, the gray scale chart is read in a pseudo manner as in the example described in FIG. There is an effect of obtaining the same gradation output as. The shading correction method in this example is the same as that in the above embodiment.

FIG. 6 and FIG. 7 are schematic sectional structural views in the sub-scanning direction of the scanner unit section showing still another embodiment of the present invention. The feature of this embodiment is that the white reference plate 61 is configured to be inclined in the main scanning direction. That is, when the white reference signal is read, the scanner position is fixed, the white reference plate 61 is horizontal in the main scanning direction as shown in FIG. 6A, and the main scanning as shown in FIG. 7A. The amount of light reflected from the white reference plate 61 is different from that in the case of tilting in the direction. 6 (b) and 7 (b) are respectively the same as in FIG.
(A), white reference plate 6 in the embodiment shown in FIG. 7 (a)
1 is shown in the main scanning direction. As is clear from these figures, even if the white reference plate 61 is tilted in the main scanning direction as in this embodiment, it is possible to create a pseudo gray scale as in the case of the above embodiment. . Also in this example, setting the number of pulses to be supplied to the white reference plate moving pulse motor as means for controlling the inclination angle of the white reference plate 61 and the shading correction method are the same as those in the above-described embodiments.

Further, FIG. 8 is a schematic sectional view of the scanner unit portion in the sub-scanning direction showing another embodiment of the present invention. The feature of this embodiment is that the white reference plate 61 is vertically held and held vertically. That is, as shown in FIG. 8A, the case where the white reference plate 61 and the contact glass 68 are flush with each other,
Since the distance between the halogen lamp and the white reference plate 61 changes when moving in the vertical direction as shown in FIG. 8B, the amount of reflected light differs. That is, since the light from the halogen lamp 62 is diffused, the amount of light guided to the CCD is different if the distance to the white reference plate is different. Therefore, by moving the white reference plate 61 in the vertical direction by the pulse motor, it is possible to realize the gray scale as in the other embodiments described above. The shading correction method in this example is the same as in the above embodiment.

[0022]

According to the present invention, the inclination angle of the white reference plate is
Or, change the distance between the white reference plate and the light source stepwise.
The amount of light input to an image reading device such as a CCD can be adjusted steplessly, and it is possible to easily and inexpensively realize a pseudo gray scale instead of the conventional gray scale chart that is expensive and changes over time. The dynamic range at the time of shading correction can be arbitrarily changed according to the read image density level. Therefore,
Highly accurate image reading is possible without increasing the number of bits of the A / D converter. Furthermore, in the present invention ,
Since it is possible to correct even a slight non-linear distortion of the CCD, the amplifier, the ADC, etc., it becomes possible to form a higher quality image. Further, in the present invention, even-odd difference correction can be performed for all gradations, and therefore, when performing image data separation such as chromatic / achromatic determination and character / dot determination in the subsequent image processing. The accuracy of can be improved.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an image reading apparatus showing an embodiment of the present invention.

FIG. 2 is a block diagram showing an embodiment of a shading correction circuit according to the present invention.

3A and 3B are schematic cross-sectional configuration diagrams showing an example of a scanner unit in the image reading apparatus according to the present invention.

FIG. 4 is a flowchart showing an operation of the image reading apparatus according to the embodiment of the present invention.

5A and 5B are schematic cross-sectional configuration diagrams showing another embodiment example of the scanner unit according to the present invention.

6A and 6B are schematic cross-sectional configuration diagrams showing another embodiment example of the scanner unit according to the present invention.

7A and 7B are schematic cross-sectional configuration diagrams showing another embodiment example of the scanner unit according to the present invention.

8A and 8B are schematic cross-sectional configuration diagrams showing another embodiment example of the scanner unit according to the present invention.

FIG. 9 is a block diagram showing an example of a conventional shading correction circuit.

FIG. 10 is a diagram illustrating a problem in conventional shading correction.

[Explanation of symbols]

1 Scanner Section 2 CCD Section 3 Scanner Driver Section 4 Lamp Regulator 5, 6 Cooling Fan 7 Original Detection Sensor 8 Pressure Plate Open / Close Sensor 9 HP Sensor 10 Scanner Open / Close Sensor 11 Pulse Motor 12 CPU 13 ROM 14, 212, 215 RAM 15 Timing Gate Array 16 parallel serial out data 17, 18 D / A converter 19 serial interface timer 20 DIP switches 21-26, 201, 202 A / D converters 27-29, 211, 213, 214, 216, 204
Selector circuits 30-32, 205 Shading gate array 33, 34 Line memory 35, 67 CCD 36-41 Amplifier 44, 62 Halogen lamp 61 White reference plate 63-65 Mirror 66 Lens 68 Contact glass 100 IPU 101 Main control unit 102 Operation control Part 206 Black memory 207 White memory 208, 308 White reference plate moving pulse motor

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Soga 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Manabu Izumigawa 1-3-6 Nakamagome, Ota-ku, Tokyo Incorporated by Ricoh Co., Ltd. (56) Reference JP-A-6-303391 (JP, A) JP-A-7-307844 (JP, A) JP-A-6-14188 (JP, A) JP-A-7-131665 ( JP, A) JP-A-3-145271 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/04-1/207 H04N 1/40-1/419

Claims (5)

(57) [Claims] 1. An original image or shading data
An optical system that irradiates light on a white reference plate used when capturing light and guides the reflected light to a photoelectric conversion unit, an A / D conversion unit that converts an analog signal from the photoelectric conversion unit into a digital signal, and shading In an image reading apparatus having a shading correction means including a memory for storing data, the inclination angle of the white reference plate is changed stepwise to obtain the A / D.
Pseudo grayscale data as the output of the conversion means
Method and the pseudo-grayscale data above.
Between the pixels of the photoelectric conversion means in the halftone part.
An image reading apparatus comprising: means for correcting variations in output level . 2. The image reading device according to claim 1.
And means for tilting the white reference plate in the sub-scanning direction.
An image reading device characterized in that 3. The image reading device according to claim 1.
And includes means for inclining the white reference plate in the main scanning direction.
An image reading device characterized in that 4. A document image or shading data
Illuminates the white reference plate used when capturing
An optical system that guides the reflected light to the photoelectric conversion means, and
A / D conversion to convert analog signals from these to digital signals
Means and memory for storing shading data
In an image reading device having shading correction means
Then, by gradually changing the distance between the white reference plate and the light source,
A pseudo grayscale data is output as the output of the A / D conversion means.
Data, and the above pseudo grayscale data
Based on the image of the photoelectric conversion means in the halftone part.
And means for compensating for variations in output level between elements
An image reading device characterized by the above. 5. The image reading device according to claim 1 or 2.
Location based on the above pseudo grayscale data.
And the odd pixel of the photoelectric conversion means in the halftone part
The feature is that it corrects the variation in the output level with even-numbered pixels.
Image reading device.