JP4090006B2 - Image processing apparatus and image forming apparatus - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an image processing apparatus that can be applied to an image forming apparatus such as a copying machine or a facsimile machine that reproduces an image based on original read image data, and more specifically, an image read by a line image sensor such as a CCD. The present invention relates to an image processing apparatus and an image forming apparatus that use a timing signal that is frequency-spread as an operation signal for processing the signal.
[0002]
[Prior art]
In an image processing apparatus that can be applied to a copying machine, a facsimile machine, or the like that processes image signals read by a line image sensor such as a CCD as data for image reproduction, the operation clock for controlling and driving the processing circuit is accelerated. In recent years, high-frequency radiation noise caused by the problem has become a problem. As a countermeasure against this, a proposal has been made to avoid the concentration of high-frequency radiation noise at a specific frequency by performing frequency diffusion that periodically changes the oscillation frequency to the operation clock.
However, when the image processing system is operated using the frequency spread technique, a problem that does not occur particularly in the digital signal system due to the use of the frequency spread operation clock (timing signal) occurs in the analog signal system. That is, when processing an analog signal waveform related to the phase relationship and pulse width of the clock signal for driving the device as the output signal of the device, such as a CCD line sensor, the frequency spreading period and the CCD line sensor driving period In response to the frequency spread period, the output signal waveform of the CCD line sensor and the influence of the data fluctuation of the sampling position that change slightly due to the influence of the frequency spread of the drive clock signal of the CCD line sensor, There is a problem that noise asynchronous to the reference signal for line scanning is included in the image data, and when an image is formed using this image data, a stripe pattern due to noise may appear on the image.
[0003]
[Problems to be solved by the invention]
Therefore, the following two methods have been proposed as countermeasures against noise included in the image data. The first method is to reset the frequency spread period by a main scanning synchronization signal for each main scanning line of the CCD and generate noise at a fixed position from the reference point of the main scanning. It is intended to reduce the apparent noise by setting the variation of the noise appearing in the image to a certain position (see Japanese Patent Laid-Open No. 2000-138805). However, according to this method, since the diffusion is performed in a fixed period and asynchronously in the diffusion period, the effect of reducing the stable radiation noise level cannot be maintained.
The second method corrects the generated noise and performs noise removal. The noise component for one line is obtained in advance, and the noise included in the image data is obtained in advance for each line. This is a correction method based on the amount of noise placed (see Japanese Patent Laid-Open No. 2000-22959). However, in recent years, the memory capacity for each line is increasing as the resolution of the CCD increases. In particular, in a color copying machine, for example, the input image signal has three colors RGB and RGB. Therefore, according to this method, a memory for storing one line of noise components is required for each color system, which increases the memory capacity, which is not preferable. Further, since the noise correction data is data corresponding to the scanning line, it must be applied in synchronization with the line synchronization signal (LSYNC), and means for that is required.
[0004]
The present invention has been made in view of the above-described problems of the conventional method, and an object of the present invention is to read an image signal read by a line image sensor such as a CCD using a frequency-spread operation clock (timing signal). In the image processing apparatus that processes the image as data for image reproduction and the image forming apparatus including the image processing apparatus, noise variation occurs by correcting and removing the noise component generated in the image by the frequency spread clock Use a simple circuit that stably reduces the radiation noise level, reduces the memory capacity required to correct and remove noise components, and does not require synchronization with the line synchronization signal Another object of the present invention is to provide an image forming apparatus including the image processing apparatus and the image processing apparatus.
[0005]
[Means for Solving the Problems]
The invention according to claim 1 is an image signal reading means for reading an image signal, a frequency spreading means for generating a frequency spread clock by continuously modulating an oscillation frequency at a predetermined spreading period with respect to a reference clock, and the image signal. Shading data acquisition means for acquiring shading data based on a white reference image signal read when frequency spreading is turned off by a reading means; and shading data holding means for holding shading data acquired by the shading data acquisition means; The image signal reading means acquires noise correction data for correcting noise generated in the image signal by the frequency spread clock generated by the frequency spread means based on the white reference image signal read by the frequency spread clock. And the noise correction data acquisition means A correction data holding means for holding the size correction data, based on the noise correction data shading data and the correction data holding means for the shading data holding means for holding held, frequency spread by the image signal reading means in a normal reading An image processing apparatus comprising correction means for simultaneously correcting image signals read by a clock .
According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the noise correction data held by the correction data holding unit is noise correction data for the diffusion period.
The invention of claim 3 is the image processing apparatus according to claim 1 or 2, wherein the reference noise correction data said correction data holding means for holding on the basis of the spread-period.
According to a fourth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, the correction unit combines the shading data and noise correction data, and performs a correction operation on the image signal as one correction data. It is characterized by having done.
The invention of claim 5 is an image forming apparatus, comprising the construction of a serial mounting image processing apparatus in any one of claims 1 to 4.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described based on the following examples shown with the accompanying drawings.
The present invention uses a timing (operation) signal generated based on a clock (frequency spread clock) signal whose frequency is continuously modulated, and performs analog processing and digital processing of a line image sensor and a sensor output signal. The present invention relates to an image processing apparatus that controls operations. The following embodiments of the present invention show an example of an image processing apparatus applicable to a digital copying machine as an image forming apparatus.
FIG. 1 is a schematic diagram showing the main configuration of an image processing apparatus according to an embodiment of the present invention.
The block configuration and operation of the image processing apparatus according to the embodiment will be described with reference to FIG.
In this embodiment, as is normally done in this type of apparatus, a reference clock is provided for timing the operation of the entire apparatus, and the oscillator 1 generates the reference clock. In this example, based on the generated reference clock, the timing signal generation unit 2 includes an analog signal processing unit 3, an A / D conversion unit 4, a noise correction / shading correction unit 5, which form a processing system for an input image signal, Each block of the digital image processing unit 6 generates a timing signal necessary for processing an image signal and correction data. The operation timing of each processing unit is controlled based on the signal generated by the timing signal generation unit 2.
In the analog signal processing unit 3, a scanner unit using a CCD or the like using the signal of the timing signal generation unit 2 (details are omitted, but it is well known as an image reading unit of a copying machine, a facsimile machine, an image scanner unit, etc. To generate an analog image signal. The generated image signal is converted into a digital image signal by the A / D conversion unit 4 and then subjected to shading correction by the noise correction / shading correction unit 5. In this case, noise (noise generated in the previous processing process by the timing operation using the frequency spread clock), which will be described in detail later, is corrected simultaneously. The corrected image data is processed and output as data for image formation on each medium by the image processing unit 6.
[0010]
FIG. 2 is a diagram showing the timing signal generator 2 shown in FIG. 1 in more detail.
With reference to FIG. 2, the configuration and operation of the timing signal generator 2 will be described below.
The timing signal generation unit 2 includes a frequency spreading circuit 21 and a timing signal generation circuit 22. A reference clock is input to the frequency spreading circuit 21. Here, oscillation is performed while gradually changing the frequency of the clock to perform frequency spreading.
The oscillator 1 normally employs a high-precision (for example, 100 PPM, 50 PPM) reference clock to be generated. The frequency spread circuit 21 outputs the reference clock in a modulated oscillation state having periodicity. An example of a modulation pattern when the frequency is modulated and spread is shown in FIG. In FIG. 3, the vertical axis represents frequency and the horizontal axis represents time.
The modulation pattern in FIG. 3 is smooth with the same pattern in the + direction (the cycle becomes shorter) and the-direction (the cycle becomes longer) with a predetermined width of ± 0.5% or ± 1.0% around the frequency of the reference clock. A unit period is determined so as to change, and a modulation cycle having a constant diffusion period is repeated according to this pattern to control the oscillation frequency.
The timing signals generated by the timing signal generation circuit 22 using the clock frequency-modulated by the frequency spread circuit 21 are all generated based on the frequency-spread clock and output to each processing unit. Thereby, the effect of reducing the radiation noise of the entire system can be obtained.
[0011]
Further, the frequency spreading circuit 21 outputs a spreading cycle SYNC signal. The spreading cycle SYNC signal is a timing signal representing a modulation cycle used for frequency modulation in the frequency spreading circuit 21. For example, when the period used in frequency spreading is as shown in FIG. 3, the spreading period SYNC signal is generated at the timing shown in the figure for each spreading period. At this time, the spreading period SYNC signal is preferably generated at the middle position of the period (generation position in FIG. 3) or at the uppermost part and the lowermost part in the frequency spreading, but it is not limited to this.
The spread period SYNC signal generated here is used as an operation signal when performing noise correction processing (detailed later) by the frequency spread clock, so that the noise correction / shading correction unit 5 is used from the frequency spread circuit 21. To output.
Also, a control signal is input to the frequency spreading circuit 21. This control signal modulates the reference clock by this circuit and operates (ON) the spreading function or does not modulate the reference clock. Controls the OFF / ON operation to either output the signal as it is or not to operate the diffusion function (OFF). This operation is necessary for acquisition processing (described later) of noise correction data used for noise correction.
Here, an embodiment relating to a correction process of noise generated in the image sensor output image by the above-described frequency spread clock will be described in detail.
In this embodiment, a method of removing noise by correcting a sensor output image with noise correction data prepared in advance is adopted. For this purpose, noise data generated in the image is detected by the frequency spread clock when the apparatus is actually operated, noise correction data is generated from the noise data, and stored in the memory. At this time, the noise correction data held in the memory is used as data for only one period of the modulation signal used for diffusion, so that the memory capacity is reduced. At the time of correction, the noise is removed by correcting the sensor output image with the noise correction data read from the memory.
Such a correction method, that is, a correction method for obtaining fluctuation (noise) data and making the output constant is a method similar to a shading correction that is normally performed as a correction process performed on the sensor output image. The present invention focuses on this point, and here, a method is adopted in which correction processing can be performed as a single correction data by combining these correction data, that is, noise correction data and shading data. Therefore, the correction data is referenced from each memory holding the noise correction data and shading data at a timing suitable for each data, and the data used for the correction calculation is made one to correct each image data by one calculation. Try to do it. That is, noise and shading correction processing can be performed simultaneously.
As a method for acquiring data for correcting noise caused by the frequency spread clock, here, the reference white plate is obtained based on a white reference image signal read by an image sensor.
[0013]
FIG. 4 shows in more detail the noise correction / shading correction unit 5 (FIG. 1) that performs processing related to noise correction.
The configuration and operation of the noise correction / shading correction unit 5 will be described below with reference to FIG.
The noise correction / shading correction unit 5 includes a noise correction unit 41, a shading correction unit 42, and a correction calculation unit 43. The noise correction / shading correction unit 5 corrects the image data converted by the A / D conversion unit 4 in the previous stage, removes noise, The image data subjected to the shading correction is output to the subsequent digital image processing unit 6.
The digitally converted image data and its timing signal are input to the noise correction unit 41, the shading correction unit 42, and the correction calculation unit 43, respectively. The shading correction unit 42 has a memory for acquiring shading data therein, and holds shading data generated based on the input image data in the shading data acquisition operation. The noise correction unit 41 includes a memory and a processing unit for acquiring noise correction data therein, and noise correction data generated based on input image data and shading data during the noise correction data acquisition operation (the generation method is Are stored in the memory. The correction calculation unit 43 performs noise correction and shading correction using correction data held in the shading correction unit 42 and the noise correction unit 41 as input image data during a normal image data reading operation such as a document read image. The corrected image data is output to the subsequent digital image processing unit 6. The diffusion period SYNC signal is input to the noise correction unit 41 and the correction calculation unit 43 as a timing signal for the noise correction operation.
[0014]
Here, the data processing during the shading data acquisition operation, the noise correction data acquisition operation and the normal image data reading operation, and the operation of each unit related to the processing will be described in detail.
The shading data is obtained by applying a method conventionally used in a document reading apparatus such as a copying machine. That is, image data from the image sensor that has read the reference white plate is input to the shading correction unit 42 to generate shading data, and is stored in the internal memory of the shading correction unit 42 as a parameter for correction calculation described later. During the shading data acquisition operation, the reference white board is read with no modulation of the spreading frequency applied to the timing signal generated by the timing signal generating unit 2, that is, with the frequency spreading unit 21 turned off. If white reference image data is obtained with this setting, shading data can be generated without being affected by noise due to frequency spreading.
The shading data generated in this way and held in the memory is used for shading correction at the time of normal reading, but is also used when generating noise correction data.
[0015]
Unlike the case of the above-described shading data, the noise correction data is acquired based on image data affected by noise that is detected when the reference white plate is read with a frequency-spread timing signal. That is, when acquiring the noise correction data, the timing signal generation unit 2 turns on the frequency spreading unit 21, reads the reference white plate with the timing signal modulated by the generated spreading frequency, and reads the image data from the read image sensor. Input to the noise correction unit 41. Since the data read at this time is not subjected to shading correction, shading is superimposed in addition to noise.
On the other hand, here, the line-synchronized SYNC signal and the spread modulation cycle SYNC signal are asynchronous, and the unit frequency of the spread frequency (not one line) in order to reduce the memory capacity of the stored noise correction data. Correction data is obtained. Therefore, an operation of extracting noise data from the white reference image data in units of diffusion frequency is required. Therefore, in addition to inputting the shading data previously detected by the shading correction unit 42 to the noise correction unit 41, the frequency is used to perform an operation of extracting noise data for a unit period of the spread frequency. A diffusion period SYNC signal is also input from the diffusion unit 21.
Extraction of noise data is to remove the influence of light source and CCD element variations using shading data acquired with frequency diffusion turned off from white reference image data that can be read at the diffusion frequency. Thus, it is possible to extract noise by pure frequency spreading. At this time, it is possible to extract the read image data by the modulation cycle SYNC signal of the spread frequency and calculate noise correction data for the unit cycle of the spread frequency from the image data. The white reference image data used at this time can be arbitrarily determined from the data extracted by the diffusion cycle SYNC signal, but may be data obtained by applying various averaging processes.
[0016]
Here, a process of calculating noise correction data as a correction calculation parameter used in the correction calculation unit 43 will be described.
FIG. 5 is a signal diagram for explaining the process of calculating the noise correction data.
Referring to FIG. 5, when white reference image data is detected in a state where frequency spreading is applied, and the shading data is used to correct the shading data, the input image data is, for example, the input signal shown in FIG. 5. As shown in (a), the data has diffusion noise that increases and decreases with a frequency spreading period around a uniform level (no spreading).
Therefore, a noise signal included in this input signal is detected and a correction parameter is calculated. As a procedure at this time, the input signal data for the unit period of the modulation period SYNC signal represented by the diffusion period SYNC signal (b) in FIG. 5 is taken (average processing is performed for at least one period). In this case, the necessary number of units) is temporarily stored as correction parameter calculation data. Thereafter, a correction parameter for making the input signal uniform data without noise is calculated using the stored data. In calculating the parameters, the noise signal component is extracted based on the uniform level, and the data as shown in the correction parameter (c) in FIG. 5 obtained by reversing + and − of the noise signal component is obtained as a parameter. When the input image signal is corrected based on the correction parameter obtained by this calculation, a uniform level signal from which noise is removed can be obtained as in the output signal (d) of FIG.
[0017]
An operation during normal image data reading will be described. At the time of normal reading, since the original is read by the frequency-spread timing signal, diffusion noise is included in the input image signal. The diffusion noise correction calculation corrects the input image signal based on the correction parameters. In the example of FIG. 5, by applying the correction parameter (c) to the input signal (a) of FIG. 5 including diffusion noise, a uniform level signal from which noise has been removed as in the output signal (d) is obtained. To obtain the correction calculation.
In this embodiment, diffusion noise correction is performed by the correction calculation unit 43 simultaneously with the shading correction performed on the normal input image signal. That is, the correction calculation unit 43 refers to the correction parameters generated by the noise correction unit 41 and the shading correction correction unit 42 and stored in the internal memory, and simultaneously applies the set correction parameters to the input image signal to perform the correction calculation. And an image signal optimized by the correction is output. At this time, the setting operation of the correction parameter is performed by the operation timing signal based on the line synchronization signal generated by the timing signal generator 2 and the diffusion cycle SYNC signal.
[0018]
At this time, in order to correct accurately, the correction calculation unit 43 may correct the image data and the noise generation based on the diffusion period SYNC signal so that there is no digital delay. is important. By operating with the diffusion period SYNC signal as a reference and by making the timings coincide, the correction parameters and the timing of the image data are matched. Then, an appropriate parameter can be referred to and accurate correction is performed.
In this way, the shading correction such as CCD sensitivity unevenness illuminance unevenness is obtained by using the shading correction parameter obtained from the data at the time of diffusion OFF, and the noise correction parameter obtained by extracting the noise component for correcting the diffusion noise. Highly accurate correction is possible by using the timings suitable for each. Further, by correcting the diffusion noise for each diffusion period, only the parameters corresponding to the diffusion period are required, so that the memory capacity can be reduced.
[0019]
An image forming apparatus equipped with the image processing apparatus of the present invention, for example, in order to constitute a digital copying machine, a document image is read on the input side of the image processing apparatus of the above-described embodiment. It is necessary to provide a scanner unit for performing image processing, and to provide an image forming unit on the output side of the image processing apparatus. Here, the image signal from the CCD line sensor of the scanner unit is used as an input to the image processing apparatus, and these components are arranged so that image data necessary for image formation is sent from the output side of the image processing apparatus to the image forming unit. Combine to form the whole device. The scanner unit and the image forming unit used as components can be implemented by using existing technology.
[0020]
【The invention's effect】
According to the present invention, correction data obtained by referring to a memory that holds shading data and noise correction data corresponding to a diffusion period is simultaneously applied to an input image signal at the time of normal (original) reading to perform correction. by the the like, the shading and diffuse noise properly corrected and removed to reduce the memory capacity required at that time, Ru can be simplified in circuit configuration.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the main configuration of an image processing apparatus according to an embodiment of the present invention.
FIG. 2 shows the timing signal generator shown in FIG. 1 in more detail.
FIG. 3 shows an example of a modulation pattern used when frequency spreading a reference clock.
4 shows the noise correction / shading correction unit shown in FIG. 1 in more detail.
FIG. 5 is a signal line diagram for explaining a process of calculating and applying noise correction data.
[Explanation of symbols]
1 ... oscillator, 2 ... timing signal generator,
21 ... Frequency spread circuit, 22 ... Timing signal generation circuit,
3 ... Analog signal processing unit, 4 ... A / D conversion unit,
41 ... Noise correction unit, 42 ... Shading correction unit,
43 ... correction calculation unit,
5 ... Noise correction / shading correction unit,
6: Digital image processing unit.

Claims (5)

Image signal reading means for reading an image signal;
Frequency spreading means for generating a frequency spread clock by continuously modulating an oscillation frequency with a predetermined spread period with respect to a reference clock;
Shading data acquisition means for acquiring shading data based on the white reference image signal read when the frequency spread is turned off by the image signal reading means ;
Shading data holding means for holding the shading data acquired by the shading data acquisition means;
Means for obtaining noise correction data for correcting noise generated in the image signal by the frequency spread clock generated by the frequency spread means based on the white reference image signal read by the frequency spread clock by the image signal reading means. When,
Correction data holding means for holding noise correction data acquired by the noise correction data acquisition means;
Based on the shading data held by the shading data holding means and the noise correction data held by the correction data holding means, correction for simultaneously correcting the image signal read by the image signal reading means by the frequency spread clock during normal reading Means,
An image processing apparatus comprising:   The image processing apparatus according to claim 1, wherein the noise correction data held by the correction data holding unit is noise correction data for the diffusion period. The image processing apparatus according to claim 1, wherein the correction data holding unit refers to noise correction data held based on the diffusion period.   The image processing apparatus according to claim 1, wherein the correction unit combines the shading data and noise correction data and performs correction calculation on the image signal as one correction data. . Images forming device you comprising the configuration of image processing apparatus according to any one of claims 1 to 4.

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