JP2004166010A - Method for reducing image noise and image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing image noise and an image processor which realize noise reduction without losing information on an image edge with simple constitution. <P>SOLUTION: The image processor has a rearranging part 113 for rearranging a pixel under consideration and its surrounding pixels in the order of pixel values, a subtracter 114 for calculating the difference between the maximum value and the minimum value of the rearranged pixel values, and a selector 116 for replacing the value of the pixel under consideration with the median of the rearranged pixels when the difference is smaller than a threshold. When the difference between the maximum value and the minimum value of the image is larger than the threshold, the image processor judges that the part of an image as an edge part to output the original value of the pixel under consideration and judges that the part as a non-edge part to output the median when the difference is smaller than than the threshold. Thus, the influence of image noise is reduced without losing the information on the image edge with a simple constitution. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image noise reduction method and an image processing apparatus for implementing noise reduction in digital image processing.
[0002]
[Prior art]
In image signal processing, noise reduction is very important for improving image quality. In particular, when the subject is dark, low-level noise is increased by gain amplification, so that the noise is conspicuous and is a major factor in image quality deterioration.
[0003]
Conventionally, a method of applying a median filter to an image to reduce noise and remove impulse noise is known. However, when a median filter is applied to the entire image, there is a problem that thin lines are blurred and the resolution of the image is deteriorated.
In order to cope with this, as shown in FIG. 13, a conventional image noise elimination device that avoids the above-described problem of thin lines by controlling the ON / OFF of a noise filter using a detection result of an image edge. A circuit is disclosed (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-09-200579 (paragraphs 7 to 8, FIG. 1)
[0005]
The conventional image noise elimination circuit shown in FIG. 13 includes median filters 8 and 9, horizontal and vertical edge detection circuits 3 and 2, and signal selection switches 11, 12 and 13. In such a configuration, the image noise elimination circuit switches and outputs the signals subjected to the median filters 8 and 9 and the signals not applied based on the outputs of the horizontal and vertical edge detection circuits 3 and 2. At the edge portion of an image, a signal not subjected to a median filter is output to avoid a problem in which a fine line is blurred, and to reduce noise.
[0006]
[Problems to be solved by the invention]
However, in the method of switching a signal using the output of another function block such as an edge detection circuit as in the above-described conventional image noise elimination circuit, synchronization between the function blocks is necessary, so that timing control becomes complicated, and the circuit There was a problem that the scale increased.
[0007]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described conventional problem, and provides an image noise reduction method and an image processing apparatus which realize noise reduction with a simple configuration without losing edge information of an image. .
[0008]
[Means for Solving the Problems]
The image noise reduction method according to the present invention includes a step of rearranging a target pixel and pixels surrounding the target pixel in the order of pixel values; a step of obtaining a difference between a maximum value and a minimum value of the rearranged pixel values; Is smaller than the threshold value, the pixel value of the target pixel is replaced with the median of the rearranged pixel. With this configuration, when the difference between the maximum value and the minimum value of the image is larger than the threshold value, the image is determined to be an edge portion, and the value of the original pixel of interest is output. By outputting (value), the influence of noise can be reduced with a simple configuration without losing edge information of the image.
[0009]
In the image noise reduction method according to the present invention, a pixel of interest and pixels surrounding the pixel of interest are rearranged in the order of pixel values, and the m-th (m is an integer of 2 or more) value from the maximum value of the rearranged pixel values And calculating a difference between the nth value (n is an integer of 2 or more) from the minimum value and, if the difference is smaller than a threshold value, replacing the pixel value of the pixel of interest with the median of the reordered pixels And a step. With this configuration, it is possible to reduce the influence of noise having a low signal level and the influence of impulse noise occurring in an image with a simple configuration without losing edge information of the image.
[0010]
In the image noise reduction method according to the present invention, the step of rearranging the pixel of interest and the surrounding pixels in the order of pixel values includes a step of recording a pixel value and a column number of the rearranged pixel, and a step of adjoining the pixel of interest. When performing processing on adjacent pixels, only pixels around the pixel of interest are removed from the set of pixel values sorted by the pixel of interest, and pixel values of pixels around only the adjacent pixel are added. And rearranging the images. With this configuration, it is possible to reduce the processing load when the pixels are rearranged in the order of the pixel values.
[0011]
The imaging apparatus according to the present invention has a configuration including a noise reduction unit that executes the image noise reduction method according to any one of claims 1 to 3. With this configuration, it is possible to realize an imaging device that can obtain an image with reduced influence of noise with a simple configuration without losing edge information of the image.
[0012]
An image processing apparatus according to the present invention has a configuration including a noise reduction unit that executes the image noise reduction method according to any one of claims 1 to 3. With this configuration, it is possible to realize an image processing apparatus that can obtain an image with reduced influence of noise with a simple configuration without losing edge information of the image.
[0013]
In the image pickup apparatus according to the present invention, the pixel is converted by amplifying the video signal, and does not make a subtle change in the image into noise according to the amount of amplification of the pixel value, and a value that does not make a large change in the image into noise that becomes an edge. It has a configuration of having a threshold control means for controlling a threshold. With this configuration, it is possible to realize an imaging apparatus that can obtain an image on which favorable noise reduction processing is performed in accordance with an imaging environment, particularly, the brightness of a subject.
[0014]
The image processing apparatus according to the present invention has a configuration including a threshold value control unit that adjusts the threshold value using the recording of the imaging state of the image and the statistical information. With this configuration, it is possible to realize an image processing apparatus that can obtain an image on which favorable noise reduction processing has been performed in accordance with the situation at the time of imaging, particularly the brightness of the subject.
[0015]
A program according to the present invention has a configuration that causes a computer to execute each step described in any one of claims 1 to 3. With this configuration, each step described in any one of claims 1 to 3 can be executed by another computer.
[0016]
A computer-readable recording medium according to the present invention has a configuration in which the program according to claim 8 is recorded. With this configuration, it is possible to read and execute the recording medium on which the program described in claim 8 is recorded by another computer.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, first to eighth embodiments of the present invention will be described in detail with reference to the accompanying drawings.
(First Embodiment)
First, a configuration of an image processing apparatus that realizes the image noise reduction method according to the first embodiment of the present invention will be described with reference to FIGS.
Hereinafter, the present embodiment will be described using an example in which processing is performed using the pixel of interest 221 and its surrounding pixels (3 * 3) 222 as shown in FIG. In the following description, 3 * 3 pixels are used, but the present invention is not limited to 3 * 3 pixels.
[0018]
The image processing apparatus shown in FIG. 1 delays an input image signal by one line to obtain pixel data (pixel values) of lines above and below the pixel of interest 221, and delays the image signal by one pixel Then, the delay circuit 112 that obtains the pixel data (pixel values) on the left and right of the target pixel 221 is compared with the pixel values input from the line memory 111 and the delay circuit 112, and rearranged. A reordering unit 113 that outputs a median and a minimum value; a subtractor 114 that calculates a difference between a maximum value and a minimum value of an output of the reordering unit 113; a comparator 115 that compares the difference with a threshold value; And a selector 116 for selecting either the value of the original pixel of interest 221 or the value of the median (the manner of selection will be described later). The reordering unit 113, the subtractor 114, the comparator 115, and the selector 116 implement a function as a median filter. The reordering unit 113 performs a process of reordering the pixels in the order of the pixel values, and is always necessary when obtaining the median (median value).
[0019]
Next, an operation of the image processing apparatus for realizing the image noise reduction method according to the first embodiment of the present invention will be described with reference to FIGS.
The pixel data of lines above and below the target pixel 221 obtained by delaying the image signal input to the image processing apparatus by one line by the line memory 111 and the pixel data of the target pixel 221 obtained by delaying the image signal by one pixel The left and right pixel data and the target pixel 221 in the image are input to the reordering unit 113. The reordering unit 113 having a part of the function as the median filter compares the magnitudes of the input values to perform reordering, and outputs the maximum value, the median, and the minimum value. The difference between the maximum value and the minimum value of the output of the reordering unit 113 is obtained by the subtractor 114, and the comparator 115 determines the difference between the difference and the threshold value. According to the comparison result, the selector 116 selects whether to output the original value of the target pixel 221 or the median.
[0020]
Next, with reference to FIG. 3, the relationship between the value of the target pixel 221 and the values of the surrounding pixels 222 will be described using a graph. In FIG. 3, the brightness increases as the horizontal axis moves to the right in pixel values, and the vertical axis indicates the number of pixels. FIG. 3A is an image of a non-edge portion, where the difference between the maximum value 333 and the minimum value 331 is small, and this portion of the image can be considered to be a substantially uniform portion of the image, that is, a non-edge portion. Conversely, in FIG. 3B, the difference between the maximum value 336 and the minimum value 334 is large, and can be considered as an edge portion.
Specifically, when the difference between the maximum value and the minimum value is equal to or greater than the threshold value, the surroundings of the target pixel 221 are regarded as an edge portion of the image, and the original value of the target pixel 221 that is not filtered is output. If the value is equal to or smaller than the threshold value, it is determined that the periphery of the pixel of interest 221 is a non-edge of the image, and the value subjected to the median filter is output.
[0021]
With such a configuration, it is possible to determine whether an image is an edge portion or a non-edge portion by using the output of the rearranging section 113 necessary for obtaining a median. It is not necessary to perform control using the result, and noise reduction processing can be realized with a simple configuration.
Performing processing using the value of the target pixel 221 and the surrounding pixels 222 is a general processing in image signal processing. If the line memory 111 and the delay circuit 112 are mounted in other processing blocks, By using it, the line memory 111 and the delay circuit 112 can be deleted from the image processing apparatus shown in FIG.
[0022]
(Second embodiment)
Next, an image processing apparatus that realizes the image noise reduction method according to the second embodiment of the present invention will be described with reference to FIG.
The configuration of the image processing apparatus according to the present embodiment shown in FIG. 4 is the same as that shown in FIG. 1, but the rearrangement section 443 shown in FIG. 4 outputs the m-th value from the maximum value instead of the maximum value. The difference from the first embodiment is that the nth value from the minimum value is output instead of the minimum value.
[0023]
Next, an operation of the image processing apparatus for realizing the image noise reduction method according to the second embodiment of the present invention will be described with reference to FIG.
First, as in the case of the first embodiment, the values of the target pixel 221 and the surrounding pixels 222 are input to the reordering unit 443 using the line memory 441 and the delay circuit 442. The sorting unit 443 performs sorting by comparing the magnitude relationship between the value of the input target pixel 221 and the values of the surrounding pixels 222, and the median, the m-th value from the maximum value, and the n-th value from the minimum value. (M and n are integers of 2 or more).
The difference between the m-th value from the maximum value and the n-th value from the minimum value is obtained by the subtractor 444, and the comparator 445 determines the difference between the difference and the threshold value. According to the determination result, the selector 446 controls whether to output the original value of the target pixel 221 or the median value. When the difference is equal to or larger than the threshold value in the comparator 445, the surrounding pixels 222 of the target pixel 221 are regarded as an edge portion, and the original value of the target pixel 221 is output.
[0024]
When the imaging device is a solid-state imaging device such as a CCD or a CMOS, there may be a pixel having an extremely large pixel value or an extremely small pixel value due to a defective pixel or a temperature flaw. In the inspection in the manufacturing process, if a pixel that is greatly connected is defective or if too many pixels are defective, it is regarded as defective, but if it is less than a certain level, it is regarded as good, and extremely Noises such as salt and pepper noise and impulse noise having large and small values may be scattered.
In such a case, a graph of the value of the pixel of interest 221 and its surrounding pixels 222 is as shown in FIG. 3C. The pixel 310 of the defect has a large (or small) value extremely deviating from the other values, but the difference between the m-th value 339 from the maximum value and the n-th value 337 from the minimum value does not exceed the threshold value. Therefore, even if there is an impulse noise, it can be determined that it is a non-edge portion.
[0025]
In the case of the edge portion of the image, as shown in FIG. 3D, it can be expected that the values are distributed to a large portion and a small portion (FIG. 3D is the same graph as FIG. 3B), and the m-th value from the maximum value Since the difference between 313 and the n-th value 311 from the minimum value exceeds the threshold value, it can be determined to be an edge portion. However, since the ability to determine whether an image is an edge portion or a non-edge portion is worse than that of the first embodiment, the present embodiment is preferably used when impulse noise of an image is conspicuous.
Although m and n depend on the number of surrounding pixels used in the processing, it is preferably about 2 or 3.
[0026]
(Third embodiment)
Next, an image processing apparatus that implements the image noise reduction method according to the third embodiment of the present invention will be described with reference to FIGS. 5 and 6 and the flowchart of FIG.
To implement a median filter, it is necessary to rearrange the data in the order of the values. However, as the number of data to be rearranged increases, the rearrangement process becomes more complicated, and O (n * n) or O (nlog n ), The processing amount increases (here, O means the order).
By the way, image processing is generally performed one pixel at a time from left to right for each line. Then, as shown in FIG. 5, the pixel 551 used for the processing of the N-th column and the pixel 552 used for the processing of the (N + 1) -th column are overlapped. Is used, the value of the leftmost pixel is deleted from the rearrangement result of the Nth column, and the processing amount is reduced by newly adding the pixel of the right column. I can do it. That is, the rearrangement process can be realized as described above by using the list structure (FIG. 6) and the insertion sort (algorithm).
[0027]
FIG. 6A shows a data structure called a list used for sorting. A record, which is one data unit, includes “pixel value 661”, “pixel column number 662”, and “pointer 663 to next record”. The “pointer 663 to the next record” points to the position of the next record, and the records are sequentially connected to form a list structure.
[0028]
Next, with reference to FIG. 7, an operation of the image processing apparatus that realizes the image noise reduction method according to the third embodiment of the present invention will be described.
First, the operation of the insertion sort will be described with reference to FIG. 7A. First, in step S771 (hereinafter, step characters are omitted), data in an old column is deleted from the list. By repeating this deletion process for the number of rows of surrounding pixels used for the process, all data in the old column can be deleted (S772). Thereafter, data of a new column is inserted by the number of rows (S773) (S774).
[0029]
Next, a processing operation for deleting a record from the list will be described with reference to FIG. 7B. First, the pointer is set to the first record (S775). It is determined whether the column number of the pixel of the record is an old column (S776). If not, the value of the pointer is changed to the value of "pointer to next record" (S777), and the determination process (S776) is performed. Return. If it is determined that the data is in the old column, the current record is removed from the list by changing the “pointer to the next record” of the previous record to the “pointer to the next record” of the current record ( S778). FIG. 6B shows an image of deleting a record from the list.
[0030]
Next, a processing operation for adding a record to the list will be described with reference to FIG. 7C. First, the pointer is set to the first record (S779). The value to be added is compared with the "pixel value" (S780), and if smaller, the value of the pointer is changed or set to the value of "pointer to next record" (S781), and the process returns to the comparison process (S780). If it is larger, the "pointer to the next record" of the previous record is set as the pointer to the additional record (S782), and the "pointer to the next record" of the additional record is set to the "pointer to the next record" of the previous record. ", The current record is added to the list (S783). The image of adding a record to the list is as shown in FIG. 6C.
[0031]
Although the order of the insertion sort is O (n * n), the amount of processing can be reduced by reusing the sorted data by using the above method. In the present embodiment, no description has been given of the occurrence of exceptional processing for deletion and addition of the first record and the last record of the list, but a method of preparing dummy records at the beginning and end of the list, etc. Can avoid exceptional processing.
[0032]
(Fourth embodiment)
Next, with reference to FIG. 8, an image pickup apparatus including a noise reduction unit according to a fourth embodiment of the present invention will be described.
The imaging device according to the present embodiment illustrated in FIG. 8 includes an imaging element 881 that photoelectrically converts a video signal into an analog signal, an analog gain unit 882 that amplifies an analog signal, and converts an amplified analog signal into a digital image signal. The image signal processing unit 884 includes an AD conversion unit 883 and an image signal processing unit 884 that performs image processing on a digital image signal. The image signal processing unit 884 includes a pixel value measurement unit 885 that measures the average brightness and distribution of the entire image. Gain control means 886 for calculating the gains of the analog gain means 882 and the digital gain means 887 from the measurement result of the means 885, digital gain means 887 for amplifying the digital image signal, and noise for reducing digital image noise according to the present invention. Reduction means 888 and image processing means for performing various other image processing And a 89.
[0033]
Next, with reference to FIG. 8, an operation of the imaging apparatus including the noise reduction unit according to the fourth embodiment of the present invention will be described.
First, an analog signal photoelectrically converted by the image pickup device 881 is amplified by an analog gain unit 882, digitized by an AD conversion unit 883, and subjected to image processing by an image signal processing unit 884. The pixel value measurement unit 885 measures the average brightness and distribution of the entire image that has been subjected to the image processing, and the gain amount control unit 886 calculates the gain amount of the analog gain unit 882 and the digital gain unit 887 using the measurement result. The noise reduction unit 888 performs noise reduction processing on the digital image signal amplified by the digital gain unit 887 by any one of the first to third embodiments or a combination thereof to reduce the influence of noise. Reduce. Thereafter, various other processes by the image processing means 889 are performed, and by outputting an image signal, a good image with reduced noise can be obtained.
As can be seen from FIG. 8, the noise reduction unit 888 is an independent function block, and does not require the output of the edge detection circuit as in the related art.
[0034]
(Fifth embodiment)
Next, with reference to FIG. 9, a description will be given of a digital image processing apparatus including a noise reduction unit according to a fifth embodiment of the present invention.
The digitized image input signal 991 is measured by the image information collecting means 992 to measure the average brightness and distribution of the entire image, the average and distribution of colors, etc., and the adjustment amount calculating means 993 calculates the brightness and contrast based on the measurement results. , The amount of adjustment such as hue is calculated, and the luminance / contrast adjusting means 994 adjusts the image input signal 991 according to the calculated amount of adjustment. After that, the noise reduction unit 995 performs a noise reduction process on any of the adjusted image signals according to any one of the first to third embodiments or a combination thereof to reduce the influence of noise. After that, various other image processing means 996 performs the processing and outputs an image signal, whereby a good image with reduced noise can be obtained.
[0035]
(Sixth embodiment)
Next, with reference to FIG. 10, an image pickup apparatus including a noise reduction unit according to a sixth embodiment of the present invention will be described.
The imaging device according to the present embodiment shown in FIG. 8 includes an imaging device 101 that photoelectrically converts a video signal into an analog signal, an analog gain unit 102 that amplifies an analog signal, and converts the amplified analog signal into a digital image signal. It has an A / D conversion means 103 and an image signal processing means 104 for performing image processing on a digital image signal. The image signal processing means 104 includes a pixel value measurement means 105 for measuring the average brightness and distribution of the entire image, and a pixel value measurement means. Gain amount control means 106 for calculating the gain amounts of the analog gain means 102 and digital gain means 108 from the measurement result of the means 105, and threshold value control means for controlling the threshold value according to the gain amount obtained by the gain amount control means 106 107, a digital gain means 108 for amplifying the digital image signal, and a threshold control means. A noise reduction unit 109 that determines an edge portion and a non-edge portion of the image by using the threshold value calculated in 107 to reduce noise, and various other types of images that perform various other image processing on the noise-reduced image signal And processing means 1010.
[0036]
Next, with reference to FIG. 10, an operation of the imaging apparatus including the noise reduction unit according to the sixth embodiment of the present invention will be described.
First, an analog signal photoelectrically converted by the image sensor 101 is amplified by an analog gain unit 102, digitized by an AD conversion unit 103, and subjected to image processing by an image signal processing unit 104. The pixel value measurement unit 105 measures the average brightness and distribution of the entire image, and the gain amount control unit 106 calculates the gain amounts of the analog gain unit 102 and the digital gain unit 108 using the results.
The threshold value control means 107 controls the threshold value according to the gain amount obtained by the gain amount control means 106, and the noise reduction means 109 uses the threshold value calculated by the threshold value control means 107 to control the digital gain means 108. The noise is reduced by determining the edge portion and the non-edge portion of the image with respect to the digital image signal amplified in step (1). After that, various other image processing is performed by the various image processing means 1010 and an image signal is output, so that a good image with reduced noise can be obtained.
[0037]
The threshold value used in the noise reduction unit 109 is for determining whether the brightness of an image is a noise or an image when the brightness is changed. If the threshold value is large, subtle changes in the image will be filtered as noise. It causes image quality degradation. Conversely, if the threshold value is small, large noise is erroneously determined as an edge, and noise cannot be removed. Therefore, the determination of the threshold value greatly affects the effect of noise reduction. It is desirable that the threshold value is set to about the noise level upper limit.
Noise is generated by the dark current of the image sensor, analog noise, or digital noise on the video signal, but the noise is also amplified by the analog gain or digital gain. When the subject is dark and the gain amount is large, the noise is large, so the threshold value is large. Conversely, when the subject is bright and the gain amount is small, the threshold value is small, so that a good noise reduction effect can be obtained.
[0038]
(Seventh embodiment)
Next, with reference to FIG. 11, a description will be given of a digital image processing apparatus including a noise reduction unit according to a seventh embodiment of the present invention.
From the digitized image input signal 1110, the image information collecting means 1120 measures the average brightness and distribution of the entire image, the average and distribution of colors, and the like. A recent imaging apparatus can output a shooting state such as an aperture, a shutter speed, and a gain amount at the time of shooting as a shooting state record 1130 together with image information. The adjustment amount calculation unit 1140 calculates an adjustment amount such as brightness, contrast, or hue using the output of the image information collection unit 1120 and the information of the shooting status record 1130, and the brightness / contrast adjustment unit 1160 calculates the image input signal 1110. Make adjustments. The threshold value calculation means 1150 calculates a threshold value from the brightness adjustment amount information of the adjustment amount calculation means 1140. The noise reduction unit 1170 performs an edge determination using the threshold value obtained by the threshold value calculation unit 1150, and executes a noise reduction process. After that, various other image processing means 1180 perform image processing and output image signals.
As described above, by controlling the threshold value based on the information obtained from the input image and the gain state obtained from the recording of the shooting state, a good noise reduction effect can be obtained.
[0039]
(Eighth embodiment)
Next, the procedure of a noise reduction processing method according to the eighth embodiment of the present invention will be described with reference to the flowchart in FIG.
First, when this process is performed using 3 * 3 pixels around the target pixel (221 in FIG. 2), the Y coordinate of the target pixel 221 is set to 1 (S121), and the X coordinate is set to 1 (S122). . The luminance values of the pixel of interest 221 and its surrounding 3 * 3 pixels (222 in FIG. 2) are obtained from a memory or a register (S123), and the rearrangement process (S124) described in the third embodiment is performed. It is determined whether the difference between the rearranged maximum value and the minimum value is larger than a threshold value (S125). If the difference is larger, it is determined that the pixel is an edge portion, and the value of the pixel of interest 221 is output (S126). The median is determined as a part and output (S127). The noise reduction processing is performed from the upper left to the upper right of the image, and then the processing is performed one line down from left to right to the lower right of the image in order (S128) (S129).
[0040]
By executing a program for executing a noise reduction function algorithm for performing such a noise reduction process on a computer such as an MPU or a DSP, the noise reduction process for an image input signal can be realized.
The program for realizing the noise reduction function algorithm can be recorded on a recording medium such as a magnetic disk, a magneto-optical disk, and a ROM. By reading this recording medium with a computer and executing it with an MPU, DSP, or the like, image noise reduction processing can be realized.
[0041]
【The invention's effect】
The image noise reduction method and the image processing device according to the present invention are configured as described above, and in particular, perform rearrangement according to the pixel values of the target pixel and its surrounding pixels, and determine whether the edge portion is determined by the difference between the maximum value and the minimum value. By judging the non-edge portion and switching the output between the pixel value of the pixel of interest and the median, there is no need for an additional edge detection circuit, with a simple configuration, without losing the edge information of the image. , Noise reduction processing can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus that realizes an image noise reduction method according to a first embodiment of the present invention;
FIG. 2 is an image diagram of pixels used in an image noise reduction method according to the first embodiment of the present invention;
FIG. 3 is a graph showing a pixel value of a pixel of interest and its surrounding pixels used in an image noise reduction method according to the first and third embodiments of the present invention;
FIG. 4 is a block diagram illustrating a configuration of an image processing apparatus that implements an image noise reduction method according to a second embodiment of the present invention;
FIG. 5 is an image diagram of pixels used in an image noise reduction method according to a third embodiment of the present invention;
FIG. 6 is a diagram showing an example of a list structure used in an image noise reduction method according to a third embodiment of the present invention;
FIG. 7 is a flowchart for controlling a list structure used in an image noise reduction method according to the third embodiment of the present invention;
FIG. 8 is a block diagram illustrating a configuration of an imaging apparatus using a noise reduction unit according to a fourth embodiment of the present invention;
FIG. 9 is a block diagram showing a configuration of a digital image processing device using a noise reduction unit according to a fifth embodiment of the present invention;
FIG. 10 is a block diagram illustrating a configuration of an imaging apparatus using a noise reduction unit according to a sixth embodiment of the present invention;
FIG. 11 is a block diagram illustrating a configuration of a digital image processing apparatus using a noise reduction unit according to a seventh embodiment of the present invention;
FIG. 12 is a flowchart showing a processing procedure of a noise reduction processing method according to an eighth embodiment of the present invention;
FIG. 13 is a block diagram of a conventional image noise elimination circuit.
[Explanation of symbols]
111, 441 line memory
112,442 delay circuit
113,443 Sorting unit
114,444 subtractor
115,445 comparator
116, 446 Selector
221 pixel of interest
222 surrounding pixels
331,334 Minimum value
332, 335, 338, 312 median
333, 336 maximum value
337, 311 nth value from minimum
339, 313 m-th value from maximum
310 flaw pixel value
551 Pixels used for Nth column processing
552 pixels used in the processing of the (N + 1) th column
553 Pixels commonly used in both processes
661 pixel values
662 column number
663 Pointer to next record
S771 Delete record
S772 Loop by the number of lines in the surrounding image
S773 Add record
S774 Loop by the number of lines in the surrounding image
S775 Set pointer to first record
S776 Determine whether the record is in the old column
S777 Move pointer
S778 Connects the previous record and the next record
S779 Move the pointer to the first record
S780 Pixel value determination
S781 Move pointer
S782 Connect previous record and additional record
S783 Connecting additional record to next record
881, 101 image sensor
882, 102 Analog gain means
883, 103 AD conversion means
884,104 Image signal processing means
885, 105 Pixel value measuring means
886, 106 Gain control means
887,108 Digital gain means
888,995,109,1170 Noise reduction means
889, 996, 1010, 1180 Various image processing means
991, 1110 Image input signal
992, 1120 Image information collecting means
993, 1140 Adjustment amount calculation means
994, 1160 Brightness and contrast adjusting means
107 threshold control means
1130 Imaging information recording means
1150 Threshold value calculation means
S121 Y coordinate initialization
S122 X coordinate initialization
S123: Obtain values of target pixel and surrounding pixels
S124 Rearrangement processing
S125: Determine whether the target pixel is an edge
S126 Output value of target pixel
S127 Output median value
S128 Repeat until X coordinate end
S129 Repeat until the end of Y coordinate
1 input terminal
2 Vertical edge detection circuit
3 Horizontal edge detection circuit
4 Judgment circuit
5, 6, 7, 10 delay circuit
8, 3-line median filter
9,9 pixel median filter
11, 12, 13 signal selection switch
14 Output terminal

Claims (9)

Rearranging the pixel of interest and surrounding pixels of the pixel of interest in order of pixel value; obtaining a difference between a maximum value and a minimum value of the rearranged pixel values; if the difference is smaller than a threshold value, Replacing the pixel value of the pixel of interest with the median of the reordered pixels. Rearranging the pixel of interest and the surrounding pixels of the pixel of interest in the order of pixel values, and n (n is 2) from the m-th (m is an integer of 2 or more) value and the minimum value of the rearranged pixel values. A step of obtaining a difference from the above (integer) -th value; and, if the difference is smaller than a threshold value, a step of replacing the pixel value of the pixel of interest with a median of rearranged pixels. Image noise reduction method. The step of rearranging the pixel of interest and the surrounding pixels in the order of pixel values is a step of recording a pixel value and a column number of the rearranged pixel, and performing processing of an adjacent pixel adjacent to the pixel of interest. Removing only the pixels surrounding the pixel of interest only from the set of pixel values rearranged by the pixel of interest, adding the pixel values of the pixels surrounding only the adjacent pixel, and rearranging the pixels. 3. The image noise reduction method according to claim 1, wherein: An imaging apparatus comprising a noise reduction unit that executes the image noise reduction method according to claim 1. An image processing apparatus comprising a noise reduction unit that executes the image noise reduction method according to claim 1. The pixel is converted by amplifying the video signal, and the threshold value is controlled to a value that does not make a subtle change in the image into noise and does not make a large change in the image into noise that becomes an edge according to the amplification amount of the pixel value. The imaging apparatus according to claim 4, further comprising a threshold control unit. 6. The image processing apparatus according to claim 5, further comprising a threshold value control unit that adjusts the threshold value using recording of an image capturing state and statistical information. A program for causing a computer to execute each step according to claim 1. A computer-readable recording medium on which the program according to claim 8 is recorded.

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