JPH06245066A - Image reader - Google Patents

Abstract

PURPOSE:To read highly accurate image data for shading correction by setting the scanning speed of a scanning means at a value lower than the one in the case of reading normal image data at the time of reading the image data for the shading correction by a scanning control means. CONSTITUTION:At the time of reading the data for the shading correction, the moving speed of a scanner slows down when the first driving clock signal of a low frequency is used. Thus, the received light quantity of a CCD (color image sensor) 201 per unit time increases and there is the possibility of exceeding the allowable received light quantity of the CCD 201. Thus, a voltage V2 lower than the voltage V1 at the time of reading real image data is set for the voltage applied to an exposing lamp 250. Thus, a voltage controllable lamp power source 240 and a CPU 230 are connected and the power source 240 switches an output voltage to V1 and V2 corresponding to the output of selecting signals. Thus, the data for the shading correction with less noise can be read.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device for reading image data of a document image using an image sensor.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus provided in a copying machine or the like, shading correction for correcting illumination unevenness of an original surface by an exposure lamp is performed before reading actual image data of an original image using an image sensor. Image data is read and stored in memory. The image data for shading correction stored in the memory is used for shading correction of actual image data.

[0003]

Since it is desired to increase the processing speed, the moving speed of the image sensor is set near the limit at which the image data can be read. For this reason,
Noise tends to be added to the data of the read image. Even if some noise is added to the actual image data, the effect only appears in a part of the image reproduced on the copy paper.
However, if noise is added to the shading correction data, the entire real image data corrected using this correction data is affected. As a result, remarkable streaks appear in the reproduced image formed based on the actual image data, and the image quality is significantly impaired.

Therefore, an object of the present invention is to provide an image reading device capable of reading image data for shading correction with high accuracy.

According to another aspect of the present invention, there is provided an image reading apparatus including an illuminating means for illuminating an original image, and photoelectrically converting reflected light generated by illuminating the original image by the illuminating means. The scanning control unit includes a reading unit that reads image data of an image, a scanning unit that scans a document image at a predetermined speed, and a scanning control unit that controls a scanning speed of the scanning unit. The scanning control unit outputs image data for shading correction. When reading, the scanning speed of the scanning means is set to a value lower than that when reading normal image data.

An image reading apparatus according to a second aspect is the image reading apparatus according to the first aspect, further comprising illumination control means for controlling the irradiation intensity of the illumination means, and the illumination control means is for shading correction. When the image data for use in reading is read, the irradiation intensity of the illuminating means is set to a value lower than that when the reading means reads normal image data.

An image reading apparatus described in claim 3 is the image reading apparatus described in claim 1 or 2, further comprising smoothing means for smoothing image data of a plurality of lines. The smoothing means is characterized by performing a smoothing process on the image data for shading correction of the plurality of lines read by the reading means.

According to a fourth aspect of the present invention, in the image reading apparatus according to the first, second and third aspects, the image reading device has a predetermined value before the value of the image data read by the reading means becomes stable. A sample and hold circuit for sampling the value of the image data at a timing of, and holding the sampled value for a certain period of time, a selecting means for selecting a line passing through the sample and hold circuit, and a line not passing through the selecting and holding means. When the control means sets the scanning speed of the scanning means to a value lower than that for reading normal image data, the control means selects a line that does not pass through the sample hold circuit.

[0008]

According to the image reading apparatus of the present invention, when the image data for shading correction is read by the reading means, the speed at which the scanning means scans the original image by the scanning control means is higher than that when the normal image data is read. Is also set to a low value.

According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, when the image data for shading correction is read, the intensity at which the illumination means illuminates the original image by the illumination control means. Is set to a lower value than when reading normal image data.

According to a third aspect of the present invention, in the image reading apparatus according to the first aspect or the second aspect, when the image data for shading correction is read, a plurality of lines read by the reading means are read. The image data is subjected to smoothing processing by the smoothing means.

An image reading apparatus according to a fourth aspect is the image reading apparatus according to the first, second and third aspects, wherein the scanning control means sets the scanning speed of the scanning means to a normal image. When setting to a value lower than that for reading data, that is, when reading image data for shading correction, a line that does not pass the sampling and holding circuit is selected by the selecting means.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the image processing apparatus of the present invention, when the image data for shading correction is read by the image sensor, the scanning is performed at a lower speed than when reading the actual image data for copying, and stable image data for shading correction is obtained. To read. Further, when the original image is scanned by the image sensor at a low speed as described above, the intensity of the illumination is set to a low value so that the light amount of the reflected light of the illumination does not exceed the capacity of the image sensor. Furthermore, the image data for shading correction is read for a plurality of lines, and the read image data for a plurality of lines is smoothed. Also, when reading image data for shading correction, a line that does not pass an unnecessary circuit is selected. Hereinafter, the copying machine of the present invention will be described in the following order with reference to the accompanying drawings. (1) Configuration of main body of copying machine (2) Description of image processing unit (3) Switching process of scanner moving speed and lamp voltage (4) Acquisition of data for shading correction and actual image data (5) Description of shading correction

(1) Structure of Copying Machine Main Body FIG. 1 shows an overall structure of a digital color copying machine main body having an image reading apparatus of the present invention. The copying machine is roughly divided into an image reader section 30 and a printer section 20.

The image reader unit 30 includes a document table glass 3
1, a scanner 32 including an exposure lamp 250 and a color image sensor (hereinafter referred to as CCD) 201, a pulse motor 35, an image signal processing unit 330, and a printer head control unit 335. Platen glass 3
The image of the document placed on the sheet 1 is scanned by the scanner 32 while being illuminated by the exposure lamp 250. The CCD 201 provided in the scanner 32 converts the reflected light of the document image into an electric signal. The image signal processing unit 330 performs R processing for driving the laser diode by a predetermined process from the electric signal.
GB digital image data is generated and the image data is transmitted to the print head controller 335. The scanner 3
The second scan is executed by the pulse motor 35.

In the printer control section 20, the laser device 21 forms an electrostatic latent image on the photosensitive drum 4 based on the digital image data obtained by the image reader section 30. The developing unit 6 including toners of cyan, magenta, yellow, and black colors sequentially attaches toners of respective colors to the electrostatic latent image to form a toner image. Transfer charger 14
Transfers the toner image onto the copy paper on the transfer drum 10.
The copy paper chucked on the transfer drum 10 is
It is selected from the storage cassettes 42 to 44 and sent. The transferred toner image is fixed on the copy paper by the fixing device 48. The operation itself of the digital color copier is well known and will not be described in further detail.

(2) Description of Image Processing Unit FIG. 2 shows each process executed in the image processing unit 330 of the digital color copying machine shown in FIG. The CCD 2 which is a photoelectric conversion unit installed in the scanner unit 32 shown in FIG.
At 01, the electric signal of the original image photoelectrically converted, that is, the analog image data is amplified by the amplification unit 202. As shown in FIG. 6, the amplification unit 202 includes two amplifiers 501.
And 502, a sample hold circuit 500, and a selector 600. Sample hold circuit 50
Reference numeral 0 is a circuit for sampling the CCD output at a predetermined timing before the value of the electric signal output from the CCD 201 stabilizes. The selector 600 corresponds to the selection signal, and the amplifier 501 via the sample hold circuit 500.
One of the image data amplified by and the image data amplified without passing through the sample hold circuit 500 is output. The analog image data amplified by the amplification unit 202 is converted into digital image data by the A / D conversion unit 203. Next, the shading correction unit 204 executes the shading correction according to the present invention in order to correct the unevenness of the light quantity of the exposure lamp, the optical system, and the sensitivity of the CCD 201. The shading correction of the present invention will be described later in detail.

The output from the shading correction unit 204 is input to the next reflectance / density conversion unit 205. Here, conversion from a signal proportional to the amount of light reflected on the document surface to a density signal is performed. The reflectance / density conversion unit 205 also simultaneously executes processing such as highlight portion emphasis processing and shadow portion emphasis processing. The respective processes up to the reflectance density conversion 205 are executed in parallel for each of the R, G and B image data.

The next color correction unit 206 generates print output signals of cyan, magenta, yellow, and black by combining the image data of the three colors. Editing control unit 207
Removes unnecessary image data outside the designated area when performing trimming editing, for example. MTF correction unit 208
Performs edge enhancement processing and smoothing processing on the image data. The magnification / moving unit 209 executes changes in pixel density in the main scanning direction, image shifting, repeated output of the same area, and the like. Further, the gamma correction unit 210 corrects the image data using the gamma correction data stored in the gamma correction table. The image data that has been subjected to gamma correction is output to the print head control unit 335.

(3) Switching process of scanner moving speed and lamp voltage Each processing unit operates according to the drive clock signal output from the drive clock signal generation unit 220 and each operation parameter (not shown) output from the CPU 230. To do.

The drive clock signal output from the drive clock signal generator 220 to the selector 221 is used for reading the first drive clock signal of low frequency used for shading correction and the actual image data used for copying operation. There is a high frequency second drive clock signal.
The scanner motor 35 is driven at a speed proportional to the frequency of the drive clock signal.

The selector 221 selects one of the first and second drive clock signals according to the selection signal output from the CPU 230 and outputs it to each processing section. CPU
When reading the data for shading correction, the 230 outputs a signal for selecting the first drive clock signal to the selector 221. Further, the CPU 230 outputs a signal for selecting the second drive clock signal to the selector 221 when reading the actual image data.

When reading the data for shading correction, if the first driving clock signal of low frequency is used, the moving speed of the scanner becomes slow. Therefore, the amount of light received by the CCD 201 per unit time increases, which may exceed the allowable amount of light received by the CCD 201. In order to deal with this, it is necessary to set the voltage applied to the exposure lamp 250 to a voltage V ₂ that is lower than the voltage V _{1 used} when reading the actual image data. Therefore, the voltage controllable lamp power supply 24
0 and the CPU 230 are connected, and the lamp power supply 240 switches the output voltage between V ₁ and V ₂ according to the output of the selection signal.

The CPU 230 is connected via a bus to a second CPU that manages the entire copying machine.
It is set to operate in accordance with an instruction sent from the CPU via the bus. In addition, the second CPU is also connected to an external device via a bus, and thereby it is possible to exchange various data with the external device.

Next, FIG. 3 shows a processing flowchart relating to the switching of the moving speed of the scanner and the lamp voltage in the program executed by the CPU 230. First, in step S3000, an operation check of the copying machine main body is executed,
It is determined whether it is the time of importing the actual image or the time of importing the shading correction data.
If the shading correction data is being fetched (YES in step S3000), a selection signal for selecting the first drive clock signal is output to the selector 221 in the next step S3010, and the next step S3 is performed.
At 020, a selection signal for outputting the voltage V ₁ is output to the lamp power supply 240. Further, in the next step S3025, the sample hold circuit 500 is added to the selector 600 included in the amplification section 202 shown in FIG. 6 as described later.
The input image data is amplified without passing through, and a selection signal for selecting an output line is output.

On the other hand, in step S3000,
If it is determined that the actual image data is being imported,
(NO in step S3000), next step S303
When 0, the selection signal for selecting the second drive clock signal is output to the selector 221, and in the next step S3040, the selection signal for selecting the voltage V ₂ is output to the lamp power supply 240. Further, in the next step S3045, the amplification unit 2
A selection signal for selecting the line passing through the sample hold circuit 500 is output to the selector 600 of No. 02.

(4) Acquisition of data for shading correction and actual image data Next, FIG. 4 shows a motor 35, a CCD 201, and an amplifier 202.
And the drive clock signal input to the A / D conversion unit 203 is the image data of the document image in each processing unit when the drive clock signal is the first drive clock signal used when reading the image data for shading correction.

FIG. 4 shows the first drive clock signal (pixel clock) and the motor 35 that rotates at a speed corresponding thereto.
The electric signal output from the CCD 201 included in the scanner 32 that scans the original image, the analog image data amplified and output by the amplifier circuit 502 of the amplifier 202, and the A / D conversion clock signal (= first drive clock signal) ) And digital image data output from the A / D conversion unit 203.

As shown in the figure, the CCD 201 resets its output in synchronization with the rising timing of the first drive clock signal. At this time, the output of the CCD 201 is
The reset noise shown at the point a is generated. CCD 201
Then generates a voltage proportional to the incident light reflected by the lamp. This voltage does not occur instantaneously, but rather exhibits a predetermined transient as shown. However, the first driving clock signal is a signal having a frequency lower than that of the second driving clock signal used when reading the actual image data, and the output of the CCD 201 is not generated at the falling timing of the first driving clock signal. , A sufficiently stable value. Further, since the frequency is low, noise generated from the drive clock signal generator 220, the scanner motor 35, etc. can be suppressed. The output of CCD 201 is A /
It is taken into the A / D conversion unit 203 at the falling timing of the D conversion clock signal. The output of the CCD 201 captured by the A / D converter 203 at the above timing becomes analog image data as shown in the figure. A / D converter 2
In 03, the input analog image data is converted into digital image data, and this is converted into the shading correction unit 204.
Output to. In the present embodiment, when reading image data for shading correction, a line that does not pass through the sample hold circuit 500 shown in FIG. 6 is selected. By thus preventing unnecessary circuits from passing through, it is possible to suppress the generation of unnecessary noise.

When the image data for shading correction is read, as described with reference to FIG. 4, the scanner 32 is moved at a slower speed by the first drive clock having a lower frequency than the case of reading the actual image data. Read stable image data with low noise. On the other hand, when reading actual image data, the second high frequency
The reading process is executed as fast as possible using the drive clock. As a result, it is possible to suppress the delay in the time required for the entire image reading process, execute accurate shading correction, and obtain a high-quality reproduced image. Traditionally,
When reading the image data for shading correction, the reading process is executed under the same conditions as when reading the actual image data. Image data of a document image in each processing unit when reading actual image data according to the present invention will be described below with reference to FIG.

FIG. 5 shows the second drive clock signal (pixel clock) and the motor 35 that rotates at a speed corresponding thereto.
The electric signal output from the CCD 201 provided in the scanner 32 that scans the original image by the sample and hold timing signal, the analog image data amplified and output by the amplifier circuit 501 of the amplifier 202, and the A / D conversion clock signal ( = Second drive clock signal) and A / D
The digital image data output from the conversion unit 203 is shown.

Similar to the case of reading the image data for shading correction, the CCD 201 generates a voltage proportional to the incident light reflected by the lamp. This voltage does not occur instantaneously, but rather exhibits a predetermined transient as shown. When reading the actual image data, a signal having a frequency about twice that of the first drive clock signal is used.
In this case, as shown in the figure, the output of the CCD 201 is still in a transient state at the falling timing of the second drive clock signal. Therefore, in order to stably capture the output value of the CCD 201 into the A / D conversion unit 203 at the falling timing of the A / D conversion clock signal, the amplification unit 202.
The sample hold circuit 500 provided in the above is used. The sample hold circuit 500 outputs the sample hold timing signal in synchronization with the falling timing of the second drive clock signal, and C at this timing is output.
The output value of the CD 201 is held until the next timing signal is output. In the amplification section 202, the output value of the CCD 201 held by the sample hold circuit 500 is amplified and converted into analog image data by the A / D conversion section 20.
Output to 3. The A / D conversion unit 203 converts the input analog image data into digital image data and outputs the digital image data to the shading correction unit 204.

As can be understood from the above description, at the time of reading the actual image data, the image data can be read at a high speed by using the second drive clock having a high frequency and the sample hold circuit 500. Since the output of the CCD 201 sampled by the sample hold circuit is in a transient state, the sampled value changes with a slight timing shift. Therefore, in the present invention, in reading the image data for shading correction, which requires more stable data, as described above with reference to FIG. It is supposed to read good data.

(5) Description of Shading Correction FIG. 7 shows an example of the configurations of the A / D conversion unit 203 and the shading correction unit 204 shown in FIG.

The A / D converter 1000 includes a CCD 201.
The analog image data fetched by and the A / D conversion clock signal having the same frequency as the first or second drive clock signal are input. The A / D converter 1000 converts the input analog image data into 8-bit digital image data, for example. The output of the A / D converter 1000 is input to the latch 1010. The latch 1010 is
Latched by clock a. Where clock a
Is a clock signal having the same frequency as the A / D conversion clock signal.

When reading data for shading correction, an A / D conversion clock signal having the same frequency as the first drive clock signal is input to the A / D converter 1000. The analog image data input to the A / D converter 1000 is written in the memory 1030 via the buffer 1040. The address of the memory is input from the address counter 1020 which counts based on the clock a.

When reading actual image data, the A / D converter 1000 receives the A / D converted clock signal having the same frequency as the second drive clock signal. A / D converter 1
The analog image data of the actual image input to 000 is input to the address of the memory 1060 via the latch 1010, and the data for shading correction stored in the memory 1030 is input to the address of the memory 1060 via the latch 1050. Input to the terminal. Data of output data corresponding to the address input value is previously input to the memory 1060. Shading correction is executed by passing the image data through this memory. The digital image data of the actual image that has been A / D converted and subjected to shading correction is output to the reflectance / density conversion unit 205.

Unlike the configuration shown in FIG. 7, FIG. 8 captures data for shading correction of a plurality of lines,
It shows an example of the configuration of the A / D conversion unit 203 and the shading correction unit 204 that can obtain more stable data by executing the smoothing process.

The A / D converter 5000 includes a CCD 201.
The analog image data taken in by and the A / D conversion clock signal having the same frequency as the first or second drive clock signal are input. The A / D converter 1000 converts the input analog image data into 8-bit digital image data, for example. The A / D converter 5000 outputs A / D converted data at the falling timing of the input A / D conversion clock signal. Here, when reading data for shading correction, digital image data of different phases is output from the analog image data of one cycle. In the configuration shown in FIG. 8, two digital image data whose phases are different from each other by half a cycle are output.

The output of the A / D converter is the latch 5010,
5015 and the selector 5030. Latch 5
The data input to 010 and 5015 is data for shading correction, and the digital image data input directly from the A / D converter 5000 to the selector 5030 is actual image data. The latch 5010 is latched by the first clock signal. The latch 5015 is latched by the second clock signal of the same frequency that is half the phase shift of the first clock signal. Due to the phase shift of the first and second clock signals input to the latches 5010 and 5015, two digital image data whose phases are different from each other by a half cycle are output. The two pieces of digital image data are input to the adder 5020, and after being added, division processing is executed in the division circuit 5025. In this process, smoothing of image data for shading correction is executed. The selector 5030 has a CPU 2
A selection signal is input from 30, and when outputting data for shading correction, the data output from the division circuit 5025 is selected, and when capturing actual image data,
The data directly input from the A / D converter 5000 is selected.

When the data for shading correction is fetched, the data sent from the selector 5030 via the latch 5035 is stored in the memory 5 via the buffer 5050.
045 is input. The address of the memory is input from the address counter unit 5040 which counts based on the third clock signal having the same frequency as the driving clock signal.

When capturing the actual image data, the selector 50
The data sent from 30 via the latch 5035 is input to the address of the memory 5060. Along with this, the data for shading correction is input from the memory 5040 to the address terminal of the memory 5060 via the latch 5050. In the memory 5060, correction data corresponding to the shading correction data input in advance is set. Therefore, the shading correction is executed by passing the image data of the actual image through the memory 5060. The digital color image data of the actual image on which the shading correction has been performed is processed by the reflectance density conversion unit 2
It is input to 05.

[0042]

By providing the image reading device of the present invention,
Data for shading correction with less noise can be read. This makes it possible to perform highly accurate shading correction.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a digital color copying machine including an image reading apparatus of the present invention.

2 is a diagram showing each processing unit in an image processing unit 330 of the digital color copying machine shown in FIG.

FIG. 3 shows a processing flowchart relating to switching of a moving speed of a scanner and a lamp voltage in a program executed by a CPU 230.

FIG. 4 is a diagram showing a state of each signal when reading data for shading correction.

FIG. 5 is a diagram showing a state of each signal when reading actual image data.

FIG. 6 shows a configuration of an amplification unit 202.

7 is a diagram showing a part of the configuration of an A / D conversion unit 203 and a shading correction unit 204 shown in FIG.

FIG. 8 is a diagram showing a configuration of an A / D conversion unit 203 and a shading correction unit 204 that takes in a plurality of data for shading correction and executes smoothing processing.

[Explanation of symbols]

 35 ... Pulse motor 201 ... CCD 202 ... Amplification unit 203 ... A / D conversion unit 204 ... Shading correction unit 220 ... Drive clock signal generation unit 221 ... Selector 230 ... CPU 240 ... Lamp power supply 250 ... Exposure lamp

Claims (4)

[Claims] 1. A reading unit comprising an illuminating unit for illuminating an original image, photoelectrically converting reflected light generated by illuminating the original image by the illuminating unit to read image data of the original image, and an original image at a predetermined speed. Scanning means for scanning with, and scanning control means for controlling the scanning speed of the scanning means. When the scanning control means reads image data for shading correction, the scanning speed of the scanning means is for reading normal image data. An image reading apparatus characterized in that the value is set to a lower value. 2. The image reading apparatus according to claim 1, further comprising illumination control means for controlling the irradiation intensity of the illumination means, and the illumination control means, when reading the image data for shading correction, the illumination means. The image reading device is characterized in that the irradiation intensity is set to a value lower than that when the reading unit reads normal image data. 3. The image reading device according to claim 1, further comprising a smoothing unit that smoothes the image data of a plurality of lines, and the smoothing unit is read by the reading unit. An image reading apparatus, wherein smoothing processing is performed on image data for shading correction of a plurality of lines. 4. The image reading apparatus according to claim 1, 2, or 3, wherein the value of the image data is sampled at a predetermined timing before the value of the image data read by the reading unit is stabilized. A sampling and holding circuit for holding the sampled value for a certain period of time, and a selecting means for selecting a line passing through the sample holding circuit and a line not passing through the selecting and holding means, wherein the scanning control means controls the scanning speed of the scanning means. An image reading apparatus characterized by selecting a line that does not pass through a sample hold circuit when setting a value lower than that when reading normal image data.