JP2013042343A - Noise removal device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise removal device that effectively removes noise in a small circuit scale mainly comprising an IIR filter and effectively suppresses image spreading and blurring.SOLUTION: The noise removal device includes a filter section 30, and a coefficient setting section 22 for setting a coefficient of a filter included in the filter section 30. The filter section 30 includes a first filter 37 that is an IIR filter. The coefficient setting section 22 computes a difference value between a pixel value 237 of a pixel of interest filtered through the first filter 37 and a pixel value 200 of the pixel of interest yet to be filtered, computes a difference integral value 250 that is an integral value of the difference value, and sets a coefficient 222 of the first filter on the basis of a result of comparison of the difference integral value with a first threshold.

Description

  The present invention relates to a noise removing device, an electronic device, and the like.

  Filter devices are widely used as means for removing noise and unnecessary high-frequency components from data. As the filter device, configurations such as an IIR (Infinite Impulse Response) filter and an FIR (Finite impulse response) filter are generally known.

  Each filter device (hereinafter referred to as “filter”) has its characteristics, but the IIR filter (hereinafter also simply referred to as “IIR”) can reduce the scale of the delay means constituting the filter, and thus is particularly small and low in consumption. It is often used for the purpose of electric power. On the other hand, the FIR filter (hereinafter also simply referred to as FIR) has an unstable pole because it is open loop, and high-frequency processing and the like are easy.

  Here, in the invention of Patent Document 1, noise removal is performed using IIR. At this time, by making the coefficient variable, the value stored in the delay means is rapidly converged to the average value of the input data even for input data having a large variance (fluctuation). That is, the device for converging the value memorize | stored in a delay means by IIR to the value according to an input value at high speed is disclosed.

JP 2007-142893 A

  However, the IIR disclosed in Patent Document 1 has a fixed characteristic of converging to an average value. Therefore, it does not include a mechanism that makes the coefficient variable according to local features. When applied to image data, the edge portion (corresponding to a local feature) may be blurred or blurred, which may result in an unnatural output image.

  The present invention has been made in view of such problems. According to some aspects of the present invention, there is provided a noise removing device that effectively removes noise with a small circuit scale mainly using IIR, and that effectively suppresses blurring, blurring, and the like of an image.

  Also, according to some aspects of the present invention, FIR is used in combination to properly blend the FIR and IIR outputs. At this time, not only the blurring and blurring of the image are effectively suppressed, but it is also possible to finally generate a natural and sharp image even if the outputs of two filters having different properties are used.

(1) The present invention is a noise removing device, including a filter unit and a coefficient setting unit that sets a coefficient of a filter included in the filter unit, wherein the filter unit is an IIR filter. The coefficient setting unit obtains a difference value between a pixel value of the target pixel that has been subjected to the filtering process by the first filter and a pixel value of the target pixel that has not been subjected to the filter process, and A difference integral value that is a value obtained by integrating the difference values is obtained, and a coefficient of the first filter is set based on a result of comparing the difference integral value with a first threshold value.

  The noise removing device of the present invention includes a filter unit including at least a first filter and a coefficient setting unit that sets a coefficient of a filter of the filter unit. Since the first filter is IIR, noise is effectively removed with a small circuit scale. At this time, the coefficient is made variable in accordance with the local characteristics of the image, and blurring, blurring, and the like of the image are effectively suppressed.

  When removing noise from an image, it is preferable that various noises can be removed. There are various types of noise in the input image, such as block noise generated by compression / expansion, gradation noise, mosquito noise, impulse noise generated during imaging, white noise, random noise, and the like.

  For example, for block noise and gradation noise, a filter that removes noise by looking at a wide area of an input image is effective. Here, when FIR is used, a large amount of memory for storing a wide range of pixel values is required. Therefore, the noise removal apparatus of the present invention uses IIR that can increase the effective tap length while suppressing the circuit scale.

  Here, when the IIR is uniformly applied to the entire image, there is a possibility that an effect of reducing the image quality such as blurring, blurring, and pseudo contour may occur. For example, in the input image (hereinafter also referred to as an original image), when IIR is applied to an edge portion that is an outline of an object, the outline may become ambiguous and blurred.

  The coefficient setting unit of the noise removal apparatus of the present invention obtains a difference value between the pixel value of the target pixel and the pixel value of the target pixel filtered by IIR, and calculates a difference integrated value that is a value obtained by integrating the difference value. Ask. Then, based on the difference integral value, it is determined whether or not the original image and the image filtered by the IIR are likely to deviate. Specifically, when the difference integral value is greater than or equal to the first threshold value, it is determined that a deviation from the original image occurs.

  In the previous example, when the target pixel is included in the edge portion of the original image, the value of the difference integral value increases greatly. At this time, the coefficient setting unit can determine that the image based on the pixel value filtered by the IIR is likely to deviate from the original image by comparison with the first threshold value. Then, by setting a new filter coefficient and reducing the effective tap length of the IIR, for example, it is possible to avoid blurring the image.

  As described above, the noise removal apparatus of the present invention feeds back the output of the IIR to the coefficient setting unit, thereby enabling setting of the filter coefficient according to the local feature. At this time, for example, for a gentle area of the original image, it is possible to perform effective noise removal by looking at the wide area. It should be noted that integrating the difference values may be performing cumulative addition of the difference values.

(2) In the noise removal device, a synthesis unit that blends outputs of a plurality of filters included in the filter unit to generate an output pixel value, and the synthesis unit receives the difference integrated value from the coefficient setting unit. The output pixel value may be generated based on a result of receiving and comparing the difference integral value with a second threshold value.

(3) In the noise removal device, the filter unit includes a second filter that is an FIR filter, and the synthesis unit is configured to use the first filter if the difference integral value is smaller than the second threshold value. If the pixel value of the pixel of interest that has been subjected to the filtering process is set as the output pixel value, and the difference integral value is greater than or equal to the second threshold value, the pixel of the pixel of interest that has been subjected to the filtering process by the first filter The output pixel value may be obtained by blending the value and the pixel value of the target pixel subjected to the filtering process by the second filter at a predetermined ratio.

  The noise removal apparatuses of these inventions include a synthesis unit. The synthesizing unit can generate the output pixel value by blending the pixel value filtered by the IIR and the pixel value filtered by another filter. Therefore, if there is a discrepancy from the original image even if a new IIR filter coefficient is set, the output of other filters is blended to suppress the occurrence of blurring, blurring, and false contours. A certain output pixel value can be generated.

  The synthesizing unit receives the differential integral value from the coefficient setting unit, and determines that a deviation from the original image occurs when the differential integral value is equal to or greater than the second threshold value. At this time, it is preferable to set the second threshold value to be larger than the first threshold value. Since the output of other filters is blended only when the IIR filter coefficient is still set and the deviation from the original image still occurs, it occurs when the filters with different characteristics are simply and frequently switched. Generation | occurrence | production of a pseudo contour etc. can be suppressed.

  Here, the blend may be an α blend, for example. The blend value by α blend is given by αA + (1−α) B, where A is a pixel value filtered by IIR and B is a pixel value filtered by another filter. Α is a real number of 0 or more and 1 or less, and indicates a blend ratio.

  Further, the other filter may be a second filter included in the filter unit. The second filter may be FIR. FIR allows adaptive filtering by looking at local features of the image. The ε filter, which is a kind of FIR, can effectively remove, for example, mosquito noise generated at the edge portion while preserving the edge component.

  If the difference integral value is greater than or equal to the second threshold, the synthesizer may include the pixel value of the target pixel that has been subjected to the filter process using the first filter and the pixel of the target pixel that has been subjected to the filter process using the second filter. The values may be blended at a predetermined ratio (for example, α = 0.5 above) to obtain an output pixel value. At this time, for example, since the FIR output from which mosquito noise or the like is effectively removed is blended, a natural and sharp output pixel value can be generated while suppressing a deviation from the original image.

  Note that if the difference integral value is smaller than the second threshold value, the synthesizing unit sets the pixel value of the target pixel subjected to the filtering process using the first filter as the output pixel value.

(4) In this noise removal apparatus, the synthesis unit compares a third threshold value that is larger than the second threshold value and the differential integral value, and the differential integral value is equal to or greater than the third threshold value. If there is, the pixel value of the target pixel that has been filtered by the second filter may be used as the output pixel value.

  According to the present invention, the combining unit compares the third threshold value that is larger than the second threshold value and the difference integral value. At this time, the comparison between the third threshold value and the difference integral value may be performed with priority over the comparison between the second threshold value and the difference integral value. If the difference integral value is equal to or greater than the third threshold value, the pixel value of the target pixel that has been subjected to the filter processing by the second filter that is FIR is set as the output pixel value.

  Therefore, if it is determined that the deviation from the original image is very large, the synthesis unit uses the pixel value filtered by FIR as the output pixel value in order to suppress the occurrence of blurring, blurring, and pseudo contour. can do.

At this time, the coefficient setting unit may initialize the coefficient of the first filter. Here, initialization means that past data of IIR is discarded. For example, when the output Y (n) at the sampling timing n is expressed as Y (n) = α _n * X (n) + (1−α _n ) * Y (n−1), the coefficient setting unit Initialization is performed with _n = 1. X (n) is input data at the sampling timing n, and at this time, the output Y (n) is determined only by X (n).

(5) The noise removal apparatus includes an edge detection unit that performs edge detection based on an input pixel value that is a pixel value of the input original image, and the synthesis unit receives the target pixel from the edge detection unit. When a signal indicating that the edge of the original image is configured is received, a pixel value of a target pixel that has been filtered by the second filter may be used as the output pixel value.

  According to the present invention, the edge detection unit that determines whether or not the target pixel is included in the edge portion based on the input pixel value is included. When the edge detection unit determines that the target pixel is included in the edge portion, the synthesis unit outputs the output of the second filter as the output pixel, as in the case where the difference integral value is equal to or greater than the third threshold value. Value.

  The edge detection unit can make a determination based only on the input pixel value. The judgment of the edge detection unit can be transmitted to the coefficient setting unit and the synthesis unit before the comparison between the difference integral value and the first to third threshold values. For this reason, the noise removal apparatus of the present invention can efficiently generate an output pixel value without performing a calculation other than necessary.

  Note that the input pixel value is not limited to the pixel value of one pixel, and may be, for example, an input of a pixel value of a 3 × 3 pixel region centered on the target pixel. Further, the pixel region is not limited to 3 × 3, and may be 5 × 5 or other pixel regions. At this time, a necessary pixel value may be selected and used from a plurality of pixel values for each processing block or filter.

(6) In this noise removal apparatus, the filter unit may perform filter processing using the first filter in multiple stages for the same target pixel.

(7) In the noise removing device, the filter unit may perform the filtering process using the first filter in at least two stages of a vertical direction and a horizontal direction.

  In these inventions, the same target pixel is subjected to filter processing using the first filter in multiple stages. Therefore, it is possible to reduce the circuit scale of the filter. Here, the multi-stage may be, for example, two stages in the vertical direction and the horizontal direction. In addition, when a frame buffer is provided, filtering between frames may be added.

(8) In the noise removing device, the filter unit may include an IIR filter that satisfies the following formula (1) as the first filter.

However, y (n) is an output at sampling timing n, x (n) is an input at sampling timing n, α _n is a filter coefficient, and y (n−1) is sampling timing n. The output at -1.

(9) In this noise removal apparatus, the coefficient setting unit counts the number of times that the difference integral value is less than the first threshold based on a comparison result between the difference integral value and the first threshold value. A counter may be included, and the filter coefficient α _n in the equation (1) may be the reciprocal of the count value of the counter.

(10) In this noise removal apparatus, the coefficient setting unit may compare the difference integral value with the first threshold value for each color component.

  According to these inventions, the IIR having a small circuit scale according to the equation (1) can change the coefficient according to the local characteristics of the image, and can effectively suppress blurring and blurring of the image.

Further, the filter coefficient calculated by the coefficient setting unit is only α _{n in the} equation (1), and the circuit scale of the coefficient setting unit can be reduced. The coefficient setting unit may include a counter that counts the number of times that the difference integral value is less than the first threshold, and the inverse of the count value may be α _n . At this time, the effect of suppressing the circuit scale can be enhanced by using a counter having a simple configuration.

Here, by comparing the difference integral value and the first threshold value for each color component, it is possible to detect a case where there is a deviation from the original image only in any one of the color components. The comparison is preferably performed for each color component, but the new filter coefficient α _n set when there is a deviation from the original image may be common to all color components in order to avoid the occurrence of color misregistration and the like. preferable.

(11) In this noise removal apparatus, the counter may set an upper limit value for the filter coefficient α _n of the equation (1).

According to the present invention, the upper limit value is set for the filter coefficient α _n in view of the effect of IIR and the calculation accuracy due to the increase in effective tap length. The upper limit value of α _n depends on the input image, but may be 1/9, 1/11, or 1/15, for example.

(12) The present invention is an electronic apparatus including the noise removal device according to any one of the above.

  According to the present invention, it is possible to provide an electronic apparatus including a noise removing device that effectively removes noise with a small circuit scale mainly using IIR, and that effectively suppresses blurring and blurring of an image. Here, the noise removal device included in the electronic device may be hardware such as a noise removal circuit, or a noise removal function may be realized by software.

The block diagram of the noise removal apparatus of 1st Embodiment. FIG. 2A illustrates an image. FIG. 2B illustrates an input pixel value. The detailed block diagram of the noise removal apparatus of 1st Embodiment. The figure for demonstrating the coefficient setting part and filter part of 1st Embodiment. The figure for demonstrating the integrator and 1st comparator of 1st Embodiment. The figure for demonstrating the synthetic | combination part of 1st Embodiment. The detailed block diagram of the noise removal apparatus of a modification. The block diagram of the electronic device of an application example. FIG. 9A illustrates a personal computer which is an example of an electronic device. FIG. 9B illustrates a projector which is an example of an electronic device. FIG. 10A is a diagram for explaining block noise. FIG. 10B is a diagram for explaining noise removal by filter processing.

  Embodiments of the present invention will be described below with reference to the drawings.

1. 1st Embodiment 1st Embodiment of this invention is described with reference to FIGS. 1-6 and FIG.

1.1. FIG. 1 is a block diagram showing an outline of a noise removing device 10 according to the present embodiment. In FIG. 1, only main functional blocks of the noise removal apparatus 10 are shown, and a detailed block diagram will be described later.

  The noise removal apparatus 10 includes a coefficient setting unit 22, a filter unit 30, and a synthesis unit 40. The filter unit 30 includes a first filter 37 that is an IIR and a second filter 38 that is an FIR.

  The noise removal apparatus 10 receives an input pixel value 200 that is a pixel value of the input original image, and generates an output pixel value 202. Here, the original image data is input to the noise removing apparatus 10 while changing the target pixel by scanning. It is assumed that the input pixel value 200 of this embodiment is composed of a plurality of pixel values including the pixel value of the target pixel. Further, it is assumed that the output pixel value 202 is the pixel value of the target pixel after noise is removed by filtering.

  The filter unit 30 includes at least a first filter 37. The first filter 37 is a main filter in the noise removing apparatus 10 and is an IIR that can effectively remove noise with a small circuit scale. For example, block noise, quantization noise, gradation noise, and the like in the original image are preferably removed by looking at a wide area of the original image. IIR can implement a smoothing filter having a large effective tap length (effective tap length) even if the scale of an actual delay means is small by incorporating feedback.

For example, FIG. 10A is a diagram of an original image 300 including block noise. Small circles correspond to pixels, and the original image 300 includes N pixels in the horizontal direction and M pixels in the vertical direction. At this time, it is assumed that, for example, an 8 × 8 block size is used as a unit of compression processing, and block noise is generated in portions indicated by B ₀ and B ₁ in FIG.

FIG. 10B shows the luminance Y of the pixel values of the pixels included in the region 304 of FIG. 10A arranged in correspondence with the pixel order n. Actually, the data is discrete, but is displayed continuously for easy understanding. In the original image, a gap of luminance Y is generated at a portion corresponding to B ₀ and B ₁ in FIG. 10A as x (n) in FIG. That is, block noise is generated.

  In FIG. 10B, y (n) represents the result of filtering (smoothing) by IIR. At this time, the block noise disappears and a smooth gradation is obtained. That is, a natural output image without noise can be obtained.

  Here, if only an original image that has been subjected to compression processing using a fixed block size is input, the occurrence position of block noise is known. At this time, for example, noise can also be removed by FIR that inputs pixel values of a 3 × 3 local area (see area 302 in FIG. 10A).

  However, in order to improve the usability as a noise removing device, it is preferable that various types of original images can be input. For example, H.M. H.264 employs a variable block size, and the position where block noise occurs depends on the image and is unknown unless there is a means for obtaining information from the decoder. Therefore, it is preferable to perform noise removal using IIR while looking at a wide area of the original image. Therefore, the noise removal apparatus 10 of the present embodiment performs a filter process mainly using IIR (first filter 37).

  Here, when the first filter 37 has a fixed characteristic of converging to, for example, an average value, there is a possibility that even an edge portion or the like is smoothed to generate an unnatural output image.

  In the noise removing apparatus 10 of the present embodiment, the coefficient setting unit 22 sets the coefficient 222 of the first filter 37 according to the local characteristics of the original image. Therefore, the characteristics are not fixed. For example, when there is a large deviation from the original image, the past data can be discarded (feedback is cut off), and a natural output image can be generated.

  At this time, the coefficient setting unit 22 selects the pixel value 237 of the target pixel that has been subjected to the filter processing by the first filter 37 and the pixel value of the target pixel before the filter processing (part of the input pixel value 200). ) And the difference value. And the coefficient setting part 22 sets the coefficient 222 adjusted based on the difference integral value which is the value which integrated the difference value. At this time, a local feature of the original image can be indirectly grasped from a difference integral value representing a deviation from the original image, and the characteristic of the first filter 37 can be changed by adjusting the coefficient 222. it can.

  Furthermore, the noise removal apparatus 10 of the present embodiment includes a synthesis unit 40 at the output stage, and the filter unit 30 includes a second filter 38. The synthesizing unit 40 sets the pixel value 237 that is normally the output of the first filter 37 as the output pixel value 202.

  However, the synthesizing unit 40 grasps the state of deviation from the original image based on the difference integral value 250 from the coefficient setting unit 22 and, if necessary, the pixel value 237 that is the output of the first filter 37 and The pixel value 238 that is the output of the second filter 38 is blended to obtain an output pixel value 202. At this time, the synthesis unit 40 may set the pixel value 238 that is the output of the second filter 38 as the output pixel value 202 based on the difference integral value 250.

  When the deviation from the original image is large, the synthesizer 40 generates the output pixel value 202 using the pixel value 238 that is the output of the second filter, thereby generating a more natural and sharp output image. You can make it.

  In the present embodiment, the filter unit 30 includes a second filter 38 that is FIR. FIR allows adaptive filtering by looking at local features of the image. FIR can effectively remove, for example, mosquito noise generated at the edge portion.

1.2. 1st and 2nd filter In the noise removal apparatus 10 of this embodiment, the filter part 30 contains the 1st filter 37 which is IIR, and the 2nd filter 38 which is FIR.

  The first filter 37 is an IIR that satisfies the following formula (1).

However, y (n) is an output at sampling timing n, x (n) is an input at sampling timing n, α _n is a filter coefficient, and y (n−1) is sampling timing n. The output at -1.

  Referring to FIG. 1, x (n) in Expression (1) corresponds to the pixel value of the target pixel in the input pixel value 200. In addition, the pixel value 237 corresponds to y (n) in Expression (1). In the present embodiment, when the sampling timing changes from n to n + 1, the pixel of interest is shifted to an adjacent pixel (or the first pixel in the next row) by scanning.

Here, the coefficient setting unit 22 in FIG. 1 sets the filter coefficient α _n of Expression (1) as the coefficient 222. From the equation (1), on the z plane, the first filter 37 has a response of the equation (2).

Then, the filter coefficient α _n needs to satisfy 0 ≦ α _n ≦ 1 so that the pole becomes a stable pole. Here, when α _n = 1, Expression (1) becomes Expression (3), and past data can be discarded. The present invention is not limited to this example, and the IIR characteristics can be changed by changing the coefficient α _n .

  On the other hand, the 2nd filter 38 is FIR according to Formula (4)-(6). Specifically, it is a kind of ε filter, which is a nonlinear filter.

  Here, k in Expression (4) is a number representing a peripheral pixel in a region centered on the target pixel. Referring again to FIG. 1, the input pixel value 200 of this embodiment is composed of a plurality of pixel values including the pixel value of the target pixel. At this time, x (n) corresponds to the pixel value of the target pixel in the input pixel value 200. Then, x (n + k) corresponds to the pixel values of peripheral pixels other than the target pixel in the input pixel value 200. Further, y (n) in Expression (4) corresponds to the pixel value 238.

In addition, β _k in Equation (4) is a low-pass filter coefficient that satisfies Equation (6). However, the function F (t) satisfies Expression (5), where t is a difference value (here, the difference between the pixel value of the peripheral pixel and the pixel value of the target pixel). ε ₁ and ε ₂ are both positive threshold values and satisfy ε ₁ <ε ₂ . The filter coefficient β _k may be dynamically changed by the coefficient setting unit 22 in FIG. 1, but β _k is determined in advance in the present embodiment.

As another embodiment, the second filter 38 counts k satisfying | x (n + k) −x (n) |> ε _2, and F (t) when the count value is equal to or larger than a certain value. = T may be a non-linear filter.

1.3. Input Pixel Value The noise removal apparatus 10 according to the present embodiment receives original image data as an input pixel value 200. In the present embodiment, in order for the second filter 38 to perform an appropriate output, it is necessary to receive not only one pixel of interest but also the pixel values of its peripheral pixels as the input pixel value 200.

FIG. 2A is a diagram for explaining the correspondence between the original image 300 and the target pixel. The original image 300 includes N pixels in the horizontal direction and M pixels in the vertical direction. The pixel P _ij is suffixed according to the position of the pixel. The subscript i is a natural number up to M and indicates the pixel on the i-th line in the vertical direction. The subscript j is a natural number up to N and indicates the pixel in the jth column in the horizontal direction. In FIG. 2 (B), the pixel value of the pixel _{P ij} is also expressed as _{P ij.}

The pixel value of the pixel P _ij may be, for example, 18-bit data having 6-bit data for each of RGB, or G may be 6-bit data, and R and B may be 16-bit data having 5-bit data. . Also, a data format such as YCbCr may be used as in the present embodiment.

FIG. 2B is a diagram for explaining an input pixel value 200 input to the noise removing device 10 of the present embodiment. For example, when the target pixel is P ₃₄ , the pixel value of the pixel in the 3 × 3 region centered on P ₃₄ (region 302 in FIG. 2A) is the input pixel value 200. Among them, the pixel value of the target pixel P ₃₄ is particularly distinguished as the input pixel value 200A.

In the example of FIG. 2B, the memories REG _{0 to} REG ₈ output the input pixel value 200 to the noise removal device while shifting the pixel value in synchronization with a clock outside the drawing. The line memory 1 and the line memory 2 are line memories that hold the pixel values of the previous line and the previous line, respectively.

In this example, only the case where the target pixel is the pixel P ₃₄ is illustrated, but as described above, the pixel value held in synchronization with a clock (not shown) changes (shifts). For example, after one clock, REG ₄ holds the pixel value of P ₃₅ that has newly become the target pixel.

  Here, input values to the first filter and the second filter will be described with reference to an example illustrated in FIG. First, the first filter, which is an IIR, requires only one pixel value x (n) as shown in Equation (1). That is, in the first filter, only the input pixel value 200A among the input pixel values 200 is received and used as x (n).

The second filter is a FIR, as in equation (4), as well as the input pixel value 200A of the pixel of interest _{P 34} is x (n), peripheral pixels _P 23 in the 3 × 3 _{region, P 24} , P ₂₅ , P ₃₃ , P ₃₅ , P ₄₃ , P ₄₄ , and P ₄₅ pixel values need to be received as x (n + k). In this case, the k of the formula (4) a value of e.g. -4 to 4, the pixel values of x (n-4) is _{P 23, x (n-3} ) is a pixel value of _{P 24,} ..., pixel values of x (n + 3) is _{P 44, x (n + 4} ) may correspond to the pixel values of _{P 45.}

1.4. Details of Noise Removal Device FIG. 3 is a block diagram showing details of the noise removal device 10 of the present embodiment. The main blocks are the same as those in FIG. Therefore, the overlapping description is omitted.

  The noise removal apparatus 10 of this embodiment includes an edge detection unit 20 in addition to the coefficient setting unit 22, the filter unit 30, and the synthesis unit 40 illustrated in FIG. The edge detection unit 20 determines whether or not the target pixel is included in the steep edge portion based only on the input pixel value 200.

  When the target pixel is included in a steep edge portion, control is performed so that the coefficient setting unit 22 and the synthesis unit 40 do not use the pixel value of the IIR output before adjusting and generating the filter coefficient and the output pixel value. Signal 220 can convey. Therefore, the noise removal apparatus 10 of the present embodiment can efficiently generate the output pixel value 202 that does not perform operations other than necessary.

  Here, the filter unit 30 and the synthesis unit 40 of the present embodiment perform IIR filter processing and generation of necessary pixel values in multiple stages. Specifically, it is performed in two stages, the vertical direction and the horizontal direction. This has the effect of reducing the processing load of the filter unit 30 and the synthesis unit 40 and suppressing the increase in circuit scale. If a frame buffer is provided, it is possible to add IIR filtering between frames.

  For this multi-stage processing, as shown in FIG. 3, the filter unit 30 includes a vertical IIR filter 31 (hereinafter also simply referred to as vertical IIR 31) and a horizontal IIR filter 32 (hereinafter also simply referred to as horizontal IIR 32). The FIR filter performs two-dimensional processing, and the filter unit 30 includes one two-dimensional FIR filter 34 (hereinafter also simply referred to as a two-dimensional FIR 34).

Target pixel pixel of interest in the preceding sampling timing in the case of P ₃₄ be treated as a P _{24 (one} on the neighboring pixels) as shown in FIG example is the vertical direction of the process 2 (A) Say. Also, the horizontal processing means that when the pixel of interest is P ₃₄ as shown in FIG. 2A, for example, the pixel of interest at the previous sampling timing is P ₃₃ (one pixel adjacent to the left). Say to handle.

  At this time, the processing in the vertical direction and the processing in the horizontal direction are performed sequentially. Therefore, when executing the processing in the vertical direction, the vertical IIR 31 corresponds to the first filter 37 in FIG. 1, and the pixel value 231 corresponds to the pixel value 237 in FIG. Further, when executing the processing in the horizontal direction, the horizontal IIR 32 corresponds to the first filter 37 in FIG. 1, and the pixel value 232 corresponds to the pixel value 237 in FIG. At this time, physical circuits constituting the IIR may be shared by the vertical IIR 31 and the horizontal IIR 32 as in the present embodiment, or may exist individually.

  The coefficient 222 set by the coefficient setting unit 22 is output to each of the vertical IIR 31 and the horizontal IIR 32. That is, the coefficient setting unit 22 of the present embodiment includes a coefficient setting unit for the vertical IIR 31 and a coefficient setting unit for the horizontal IIR 32 (not shown), and each independently calculates a coefficient as a coefficient 222. Output. The filtered pixel value 230 received by the coefficient setting unit 22 corresponds to the pixel value 237 in FIG. Here, the coefficient setting unit 22 receives the pixel value 231 and the pixel value 232 as the pixel value 230. The two-dimensional FIR 34 corresponds to the second filter 38 in FIG. 1, and the pixel value 234 corresponds to the pixel value 238 in FIG.

  The combining unit 40 includes a vertical combining unit 41 and a horizontal combining unit 42. For the pixel value 231 that is the output of the vertical IIR 31, the vertical composition unit 41 performs blending as necessary. For the pixel value 232 that is the output of the horizontal IIR 32, the horizontal composition unit 42 performs blending as necessary.

  At this time, blending with the pixel value 234 that is the output of the two-dimensional FIR 34 is performed by the horizontal synthesis unit 42 that generates the output pixel value 202. Therefore, the vertical composition unit 41 inputs the input pixel value 200A instead of the pixel value 234.

1.5. Handling of steep edge portion in original image As described above, the noise removal apparatus 10 of the present embodiment performs noise removal mainly by IIR. However, for example, a sharp edge portion in the original image may not be suitable for IIR filtering. That is, even if the filter coefficient is changed, a pixel value that generates an unnatural image may be output.

  In such a case, it is more efficient to perform switching so that only filter processing by FIR is performed immediately. The edge detection unit 20 determines whether or not the target pixel is included in the steep edge portion based only on the input pixel value 200. If included, the control signal 220 can prevent the coefficient setting unit 22 and the combining unit 40 from performing useless calculations.

  The edge detection unit 20 receives the input pixel value 200 and integrates the absolute value of the difference between the pixel values of the target pixel and the surrounding pixels (hereinafter, the difference absolute value).

  In the present embodiment, the input pixel value 200 includes pixel values of pixels in a 3 × 3 region. In Expression (7), k is a number representing a peripheral pixel in a region centered on the target pixel, and is the same as in the case of the FIR.

Edge detection unit 20, if the expression absolute difference a (n) is equal to or larger than the threshold Th _e (7), and outputs a control signal 220 to immediately perform only filtering by FIR. Here, the threshold Th _e may be, for example, various images for previously determined a value obtained by taking statistics, user may set the time of use of the noise removal device.

1.6. Adjustment of IIR Coefficients When the difference absolute value a (n) in Expression (7) is less than the threshold value Th _e , the noise removal apparatus 10 of this embodiment generates an output pixel value using the output of the IIR. At this time, the coefficient setting unit 22 obtains a difference value between pixel values before and after the filter processing by the vertical IIR 31 and the horizontal IIR 32 for the target pixel. Then, based on a difference integral value that is a value obtained by integrating these difference values, it is determined whether or not the original image has deviated.

The coefficient setting unit 22 determines that a deviation from the original image is likely to occur when the differential integral value is equal to or greater than the threshold Th ₁ . Then, the filter coefficient α _n in the equation (1) is adjusted to follow the output of the IIR. The coefficient setting unit 22 will be described below with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same element as FIGS. 1-3, and description is abbreviate | omitted.

  FIG. 4 is a diagram for explaining the configuration of the coefficient setting unit and the IIR. The vertical IIR 31 and the horizontal IIR 32 are physically the same circuit in this embodiment, and appropriate signals are assigned to x (n) and y (n) according to processing.

  That is, with reference to FIGS. 2B and 3 as well, in the case of processing in the vertical direction, the IIR filter is the vertical IIR 31, and the input pixel value 200 A of the target pixel is y (x), The pixel value 231 corresponds to (n). When processing in the horizontal direction, the IIR filter is the horizontal IIR 32, and the pixel value 241 corresponds to x (n) and the pixel value 232 corresponds to y (n). As described above, the coefficient setting unit 22 of this embodiment includes a coefficient setting unit for the vertical IIR 31 and a coefficient setting unit for the horizontal IIR 32 independently (not shown). However, since the respective configurations and calculation processes are the same, the description will be made while avoiding duplication as shown in FIG.

The vertical IIR 31 (or horizontal IIR 32) in FIG. 4 performs the calculation of the above equation (1) by the adders 60 and 61 and the multiplier 65. Here, the coefficient 1-α _n used by the multiplier 65 is given from the coefficient setting unit 22. Further, y (n−1) can be obtained by the delay circuit 70. The delay circuit 70 and the delay circuit 71 of the coefficient setting unit 22 are specifically configured by a register or the like.

  The coefficient setting unit 22 obtains the difference value 262 by the adder 62. The adder 62 receives y (n−1) and x (n−1), which are outputs from the delay circuits 70 and 71, respectively. However, the sign of x (n−1) is inverted. The difference value 262 is a difference between pixel values before and after filtering processing of the vertical IIR 31 (or horizontal IIR 32) at the sampling timing n-1.

  The coefficient setting unit 22 integrates the difference value 262 by the integrator 50. Integration is, for example, cumulative addition. Then, the integrator 50 outputs a difference integral value 250. The difference integral value 250 is obtained by integrating the difference value 262 representing the difference from the original image at each sampling timing, and represents the degree of deviation from the original image. The value increases rapidly, for example, when the pixel of interest is at the edge portion, so that local features in the original image can be grasped.

Then, the coefficient setting unit 22 compares the difference integral value 250 with the threshold Th ₁ by the first comparator 52. The coefficient setting unit 22 determines that there is a deviation from the original image when the difference integral value 250 is equal to or greater than the threshold Th ₁ , adjusts the filter coefficient α _n to reduce the effective tap length, and reduces the vertical IIR 31 (or , The output of the horizontal IIR 32) is made to follow.

As shown in FIG. 4, the counter 54 of the coefficient setting unit 22 determines the filter coefficient α _n based on the comparison signal 252 from the first comparator 52. The counter 54 is, for example, a 4-bit width counter, and the reciprocal of the count value is the filter coefficient α _n . In the present embodiment, the counter 54 outputs the count value “1 / α _n ” and gives “1-α _n ” converted by the coefficient table 56 to the vertical IIR 31 (or horizontal IIR 32).

Based on the comparison signal 252, the counter 54 increments the count value when the difference integration value 250 is less than the threshold Th ₁ . However, if has reached the upper limit value, the count value is also differential integrated value 250 is less than the threshold value Th ₁ is not varied. When the upper limit is a 4-bit width counter, for example, a value such as 9 to 11 may be used. The upper limit value is set in consideration of the effect of the IIR filtering process and the calculation accuracy due to the increase in the effective tap length.

Counter 54, when the differential integrated value 250 is the threshold value Th ₁ or more, changing the count value is forcibly fixed value (e.g. 2 or 3). Changing the count value to a smaller value means reducing the effective tap length of the IIR. If the differential integrated value 250 is the threshold value Th ₁ or more, as the divergence between the original image is generated, the output to reduce the effective tap length of IIR is adjusted to follow.

Incidentally, the counter 54, when the differential integrated value 250 is the threshold value Th ₁ or more, may be allowed to decrement the count value. Moreover, even when changing to a fixed value, you may change in steps. For example, when the difference integral value 250 first becomes equal to or greater than the threshold Th _{1, the} count value is set to 7. Nevertheless, if the differential integrated value 250 is a threshold Th ₁ or more, the count value to 5. And finally, a method of 2 may be taken.

When the control signal 220 informs the counter 54 that the target pixel is included in the steep edge portion, the counter 54 may initialize the filter coefficient by setting the count value to 1 (α _n = 1, see formula (3)). At this time, since the output of the IIR is not used, the coefficient setting unit 22 may stop the above operation.

Here, the comparison signal 252 may reflect the threshold Th ₁ for each color component and the comparison result. FIG. 5 shows details of the configuration of the integrator 50 and the first comparator 52, and corresponds to the region 58 of FIG. Here, it is assumed that the input pixel value 200 has color components of Y, Cb, and Cr, and the difference value 262 that is the calculation result also has the same color component. The integrator 50 includes a Y component integrator 50Y, a Cb component integrator 50Cb, and a Cr component integrator 50Cr, which are integrators for the Y component, Cb component, and Cr component, respectively.

  In this embodiment, the difference value 262 is input to each integrator (50Y, 50Cb, 50Cr) for each color component (262Y, 262Cb, 262Cr), and integrated (for example, cumulative addition) for each color component. . The difference integral value 250 is composed of difference integral values (250Y, 250Cb, 250Cr) for each color component, and is input to the first comparator 52.

The first comparator 52 includes a Y component comparator 52Y, a Cb component comparator 52Cb, and a Cr component comparator 52Cr, which are comparators for the Y component, Cb component, and Cr component, respectively. These comparators, the differential integrated value for each color component respectively (250Y, 250Cb, 250Cr) receives, is compared with a threshold value Th _1. Then, the output of the logical sum 51 of the comparison signals (252Y, 252Cb, 252Cr) for each color component that becomes “1” when the difference integral value is equal to or greater than the threshold Th ₁ is the comparison signal 252 from the first comparator 52. And

By performing such comparison for each color component, it is possible to detect a case where there is a deviation from the original image only in any one of the color components. Note that a common filter coefficient α _n is used instead of each color component. This is because when there is a filter coefficient α _{n for} each color component, a problem such as color misregistration occurs.

1.7. Blending in Combining Unit The combining unit 40 generates an output pixel value 202. At this time, the output of the IIR is normally set to the output pixel value 202. However, when there is a possibility that the output image becomes unnatural due to a deviation from the original image, blending with the output of the FIR or the output of the FIR is performed. Or switch to use only. The synthesizing unit 40 (specifically, the vertical synthesizing unit 41 and the horizontal synthesizing unit 42) will be described below with reference to FIG. In addition, the same code | symbol is attached | subjected to the same element as FIGS. 1-5, and description is abbreviate | omitted.

  FIG. 6 is a diagram for explaining the configuration of the vertical composition unit 41 and the horizontal composition unit 42. The vertical synthesizing unit 41 and the horizontal synthesizing unit 42 are physically the same circuit in this embodiment, and appropriate signals are assigned to y (n), w (n), and g (n) according to processing. To do.

  That is, with reference to FIGS. 2B and 3 as well, the vertical composition unit 41 is used when processing in the vertical direction, the pixel value 231 is represented by y (n), and the pixel value 231 is represented by w (n). The pixel value 241 corresponds to the input pixel value 200A of the target pixel, and g (n). In the case of processing in the horizontal direction, the horizontal combining unit 42 is used. The pixel value 232 is represented by y (n), and the pixel value 234 that is the output of the two-dimensional FIR 34 is represented by g (n ) Corresponds to the output pixel value 202.

  As shown in FIG. 6, the synthesizing circuit 43 of the vertical synthesizing unit 41 (or the horizontal synthesizing unit 42) converts the output signal g (n) into the input signals y (n), w based on the control signal 220 and the comparison signal 282. (N) is generated by blending (including one selection).

The second comparator 82 includes a second threshold Th ₂ and a comparator 82Y, 82Cb, and 82Cr that compare with the third threshold Th ₃ for each color component, and the configuration is the first comparator 52 (FIG. 5). See). Here, detailed description is omitted in order to avoid redundant description.

The vertical composition unit 41 (or the horizontal composition unit 42) has a difference from the original image even when the IIR filter coefficient α _n is changed when the difference integral value 250 is equal to or greater than the second threshold Th _2. Judge. At this time, the synthesis circuit 43 blends the input signals y (n) and w (n) at a predetermined ratio (for example, both 50%) to generate the output signal g (n).

When the difference integration value 250 is equal to or greater than the third threshold value Th ₃ , the vertical synthesis unit 41 (or horizontal synthesis unit 42) includes the pixel of interest in a steep edge portion and has a very large difference from the original image. Is determined to occur. At this time, the synthesis circuit 43 outputs the input signal w (n) as the output signal g (n). For the sake of processing efficiency, it is preferable that the comparison between the difference integral value 250 and the third threshold Th ₃ is performed in preference to the comparison with the second threshold Th ₂ .

Comparison signal 282 may be a 2-bit signal representing the result of comparison between the difference integral value 250 second threshold value Th _2, and the third threshold value Th _3. For example, if the comparison signal 282 is “11b”, the difference integral value 250 is greater than or equal to the third threshold Th ₃ , and if the comparison signal 282 is “01b”, the difference integral value 250 is less than the third threshold Th ₃ and the second threshold value If it is Th ₂ or more and “00b”, the difference integral value 250 may be less than the second threshold Th ₂ .

Here, between the first threshold value Th ₁ used in the first comparator 52 (see FIG. 5), the second threshold value Th ₂ used in the second comparator 82, and the third threshold value Th _3. Is assumed to have a relationship as shown in Expression (8).

  The synthesis circuit 43 receives the control signal 220 and outputs the input signal w (n) as the output signal g (n) when the target pixel is included in the steep edge portion. Note that the processing based on the control signal 220 has priority over the processing based on the comparison signal 282.

1.8. Output Pixel Value As described above, the noise removal device of the present embodiment effectively removes noise with a small circuit scale mainly using IIR, and effectively suppresses blurring and blurring of an image. Further, when a deviation from the original image occurs, the FIR and IIR outputs are appropriately blended using the FIR together. At this time, not only the blurring and blurring of the image are effectively suppressed, but it is also possible to finally generate a natural and sharp image even if the outputs of two filters having different characteristics are used.

The generation of output pixel values is summarized as follows. (1) In a smooth area such as gradation, IIR output is used. (2) If it is determined that the sharp edge region by the edge detection unit (determination using the threshold value Th _e) the output of the FIR is used. (3) In the intermediate region, (3-1) First, the IIR filter coefficient is adjusted by the coefficient setting unit (determination using the threshold Th ₁ ). (3-2) If the synthesis unit is likely to deviate from the original image as a result of the comparison using the _second threshold Th2, the outputs of IIR and FIR are blended. (3-3) If the synthesizer is likely to deviate from the original image as a result of the comparison using the _third threshold value Th3, the FIR output is used.

  Here, when the filters having different characteristics are simply and frequently switched, there arises a problem that, for example, a pseudo contour is generated. In the present embodiment, since the FIR output is blended only when a deviation from the original image still occurs even if a new IIR filter coefficient is set, such a problem is unlikely to occur. In addition, since the output image is subjected to filter processing in consideration of local characteristics, it is possible to generate a natural and sharp image.

In the case of the above (3-2), the difference integrated value is equal to or more than the first threshold Th ₁ from the relationship of the equation (8). Therefore, the output of the IIR to be blended is an output when the filter coefficient α _n is fixed (for example, 1/2). That is, IIR having a small effective tap length is used.

Here, the noise removing apparatus 10 of the present embodiment uses various data in order to appropriately adjust the IIR filter coefficient α _n . Therefore, the noise removal apparatus 10 includes, for example, a line memory, and holds a control signal 220 (see FIG. 3), a comparison signal 252 (see FIG. 4), and a comparison signal 282 (see FIG. 6) that indicate the comparison result with the threshold value. May be. Also, the difference integral value 250 (see FIG. 4), the pixel values before and after executing the IIR filter processing, and the filter coefficient α _n may be held.

  Such a configuration is particularly useful when having independent filters for horizontal processing and vertical processing. If the data held in the line memory can be accessed from the outside, the user can easily check the state.

2. Modification A modification of the present embodiment will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same element as FIGS. 1-6, and description is abbreviate | omitted.

  FIG. 7 is a block diagram of a noise removal apparatus 10A according to a modification. Unlike the case of the first embodiment (see FIG. 3), the FIR included in the filter unit 30A is separated into a vertical FIR filter 35 and a horizontal FIR filter 36. Therefore, the vertical composition unit 41 and the horizontal composition unit 42 receive the pixel value 235 and the pixel value 236 that are the outputs of the vertical FIR filter 35 and the horizontal FIR filter 36, respectively.

  Also for FIR, the circuit scale of the filter can be suppressed by separating the processing in the vertical direction and the processing in the horizontal direction. Other configurations are the same as those in the first embodiment, and a description thereof will be omitted.

3. Application Examples Application examples of the present invention to electronic devices will be described with reference to FIGS. FIG. 8 is a block diagram of the electronic apparatus 1 according to the application example. The electronic device 1 includes a CPU 2, an input unit 3, a storage unit 4, a display unit 5, and an image processing unit 6. The image processing unit 6 performs image processing such as encoding in addition to noise removal. The image processing unit 6 includes a noise removal circuit 10B corresponding to the noise removal device 10 of the first embodiment or the noise removal device 10A of the modification as a part thereof.

  The CPU 2 controls other blocks and performs various calculations and processes. For example, the CPU 2 may read a program from the storage unit 4 and cause the noise removal circuit 10B to perform noise removal according to the program.

  The input unit 3 receives data from the inside or the outside of the electronic device 1. The input unit 3 may receive, for example, input image data and may convert the pixel value into a format suitable for reception by the noise removal circuit 10B.

  The storage unit 4 may be, for example, a memory such as a DRAM or SRAM, or may include a ROM. The program used by the CPU 2 may be written in a ROM included in the storage unit 4, for example.

  The display unit 5 is for outputting an image from which noise has been removed by the noise removing circuit 10B. For example, an LCD or an electrophoretic display device may be used.

  For example, in the electronic device 1, the CPU 2 reads a program from the storage unit 4 after reset, and causes the image processing unit 6 to automatically execute image processing according to a command. At this time, a natural image from which noise has been removed by the noise removal circuit 10B is output to the display unit 5.

  FIG. 9A shows an example of an external view of a personal computer 970 that is one of the electronic devices 1. The personal computer 970 includes an LCD 975 that displays images such as photographs and moving images as the display unit 5. Since the personal computer 970 includes the noise removal circuit 10B, a clean image from which noise has been removed can be displayed on the LCD 975.

  FIG. 9B shows an example of an external view of a projector 980 that is one of the electronic devices 1. The projector 980 enlarges and displays an image on the screen 989 from the projection unit 985 corresponding to the display unit 5. At this time, since the image is enlarged, it is very noticeable if noise is included. By including the noise removal circuit 10B in the projector 980, it is possible to project a clean image from which noise has been removed.

  The noise removal device of the present embodiment is not limited to these examples, and can be applied to various electronic devices that display images. In any case, it is possible to provide an electronic device that performs natural and sharp image display while removing noise.

4). Others The present invention is not limited to these examples, and the present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same purposes and effects). . In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Electronic device, 2 ... CPU, 3 ... Input part, 4 ... Memory | storage part, 5 ... Display part, 6 ... Image processing part, 10, 10A, 10B ... Noise removal apparatus (noise removal circuit), 20 ... Edge detection part , 22 ... Coefficient setting unit, 30, 30A ... Filter unit, 31 ... Vertical IIR filter, 32 ... Horizontal IIR filter, 34 ... Two-dimensional FIR filter, 35 ... Vertical FIR filter, 36 ... Horizontal FIR filter, 37 ... First Filter, 38 ... second filter, 40 ... synthesis unit, 41 ... vertical synthesis unit, 42 ... horizontal synthesis unit, 43 ... synthesis circuit, 50, 50Y, 50Cb, 50Cr ... integrator, 51 ... logical sum, 52, 52Y , 52Cb, 52Cr ... (first) comparator, 54 ... counter, 56 ... coefficient table, 58 ... area, 60, 61, 62 ... adder, 65 ... multiplier, 70, 71 ... Extension circuit, 81 ... logical sum, 82, 82Y, 82Cb, 82Cr ... (second) comparator, 200, 200A ... input pixel value, 202 ... output pixel value, 220 ... control signal, 222 ... coefficient, 230, 231 , 232, 234, 235, 236, 237, 238, 241 ... pixel values, 250, 250Y, 250Cb, 250Cr ... differential integration values, 252, 252Y, 252Cb, 252Cr, 282Y, 282Cb, 282Cr ... comparison signals, 262, 262Y , 262Cb, 262Cr ... difference value, 282 ... comparison signal, 300 ... original image, 302, 304 ... area, 970 ... personal computer, 975 ... LCD, 980 ... projector, 985 ... projection unit, 989 ... screen

Claims (12)

A filter section;
A coefficient setting unit that sets a coefficient of a filter included in the filter unit,
The filter section is
Including a first filter that is an IIR filter;
The coefficient setting unit
Obtaining a difference value between a pixel value of the target pixel subjected to the filtering process by the first filter and a pixel value of the target pixel before the filter process is performed;
Find a difference integral value that is a value obtained by integrating the difference value,
A noise removing device that sets a coefficient of the first filter based on a result of comparing the difference integral value with a first threshold value. In the noise removal apparatus of Claim 1,
Including a combining unit that generates output pixel values by blending outputs of a plurality of filters included in the filter unit;
The synthesis unit is
Receiving the differential integral value from the coefficient setting unit;
A noise removing device that generates the output pixel value based on a result of comparing the difference integral value with a second threshold value. In the noise removal apparatus of Claim 2,
The filter section is
Including a second filter that is an FIR filter;
The synthesis unit is
If the difference integral value is smaller than the second threshold value, the pixel value of the target pixel subjected to the filtering process by the first filter is set as the output pixel value,
If the difference integral value is greater than or equal to the second threshold value, the pixel value of the target pixel that has been subjected to the filtering process by the first filter and the pixel of the target pixel that has been subjected to the filtering process by the second filter A noise removing device that blends values with a predetermined ratio to obtain the output pixel value. In the noise removal apparatus of Claim 3,
The synthesis unit is
A comparison is made between a third threshold value that is greater than the second threshold value and the difference integrated value,
If the difference integral value is equal to or greater than the third threshold value, a noise removing device that uses the pixel value of the target pixel that has been subjected to the filter processing by the second filter as the output pixel value. In the noise removal apparatus in any one of Claims 3 thru | or 4,
Based on the input pixel value that is the pixel value of the input original image, including an edge detection unit that performs edge detection,
The synthesis unit is
When a signal indicating that the target pixel constitutes an edge of the original image is received from the edge detection unit, the pixel value of the target pixel subjected to the filtering process by the second filter is set as the output pixel value. Noise removal device. In the noise removal apparatus in any one of Claims 1 thru | or 5,
The filter section is
A noise removing device that performs filtering using the first filter in multiple stages for the same pixel of interest. In the noise removal apparatus of Claim 6,
The filter section is
A noise removing device that performs filter processing by the first filter in at least two stages of a vertical direction and a horizontal direction. In the noise removal apparatus in any one of Claims 1 thru | or 7,
The filter section is
A noise removing device including an IIR filter satisfying the following formula (1) as the first filter.
However,
y (n) is an output at the sampling timing n,
x (n) is an input at the sampling timing n,
α _n is a filter coefficient,
y (n-1) is an output at the sampling timing n-1. In the noise removal apparatus of Claim 8,
The coefficient setting unit
A counter that counts the number of times that the difference integral value is less than the first threshold based on a comparison result between the difference integral value and the first threshold;
A noise removing device that uses the filter coefficient α _n of the equation (1) as the reciprocal of the count value of the counter. In the noise removal apparatus of Claim 9,
The coefficient setting unit
A noise removing device that compares the difference integral value with the first threshold value for each color component. In the noise removal apparatus in any one of Claims 9 thru | or 10,
The counter is
A noise removing device that sets an upper limit value for the filter coefficient α _n of the formula (1).   An electronic device comprising the noise removal device according to claim 1.