JP2001245298A - Image coder, image coding method and medium storing image coding program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image coder that can enhance its coding efficiency, while preventing deterioration in visual quality in coding of a moving image signal, and to provide an image coding method and a medium storing an image coding program. SOLUTION: A coding deterioration measuring section 17 calculates value denoting the degree of deterioration through coding, on the basis of an image that is received from an image input section 11, the band of which is limited by a pre-filter section 12, and that is stored in a storage section 13 for the image after filtering, and also on the basis of an image resulting from coding the stored image by an image coding section 14, that is decoded by a local decoding section 15, and that is stored in a decoded image storage section 16. A filter control section selects a frequency characteristics C2 to eliminate more high-frequency components for the frequency characteristics of the filter adopted by the per-filter section 12, when the deterioration by the coding is large, but selects a frequency characteristics C1 which does not delete high-frequency components for the frequency characteristics of the filter adopted by the pre-filter section 12, when the deterioration by the coding is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding apparatus for encoding a moving image signal, in particular, encoding with a band limitation, an image encoding method, and a medium storing an image encoding program. is there.

[0002]

2. Description of the Related Art Generally, in moving picture coding such as MPEG-2, DCT (Discrete Cosine Transform) is applied to image information and its coefficient is quantized. Although the quantization efficiency can be improved by this quantization, on the other hand, distortion (quantization distortion) peculiar to the decoded image occurs. The image quality is degraded by the quantization distortion.

In order to reduce such quantization distortion,
Prior to encoding, filtering is performed on an image in advance to limit the band. In general, the high-frequency components of an image have little effect on vision, so that the filter is used to restrict particularly high frequencies, thereby improving coding efficiency without causing visual degradation. In general, as the amount of limiting the high frequency increases, the quantization distortion can be reduced.

The filters for limiting the band include a spatial filter using the correlation between pixels in a screen and a time filter using the correlation between pixels between frames.

[0005] Among them, there is a moving average filter as one of the spatial filters. In this filter, as shown in FIG. 1, a square area of N pixels vertically and N pixels horizontally (N taps) is set around the pixel to be obtained, and the image information of the pixels included in the square is expressed by Expression (1). ) Is performed to obtain image information of the pixel.

[0006]

(Equation 1)

Here, I (x, y): an input image at horizontal x and vertical y pixels, and O (x, y): an output image at horizontal x and vertical y pixels.

By performing this processing on each pixel in the screen, a moving average filter is applied to the entire screen. The frequency characteristic of this filter is characterized by the number of taps N and the weighting coefficient W, and the visual characteristic after band limitation depends on these values. In general, as the number of taps N increases, the average of a wide range of pixels becomes larger, so that the difference between adjacent pixels decreases, and higher frequency components are removed.

As shown in FIG. 2, the temporal filter performs a weighted averaging shown in equation (2) from the image information of the same pixel in the previous frame and the current frame, and uses the value as the image information of the pixel. is there.

[0010]

(Equation 2)

Here, I (x, y): the input image of the current frame in horizontal x, vertical y pixels, PrevI (x, y): the input image of the previous frame in horizontal x, vertical y pixels, O (x , Y): Output image at horizontal x and vertical y pixels.

In general, the function F is used to improve the coding efficiency of inter-frame predictive coding while preventing image lag when the difference between the image information of the previous frame and the current frame is large.
Set. There is a trade-off between preventing this afterimage and improving the coding efficiency. For example, in a temporal filter where priority is given to preventing afterimages, the weighted average value is set to the value of the current frame when the difference between the image information of the previous frame and the current frame is large, and the weighted average value is set to the value of the current frame when the difference is small. Equation (2) to be close to the value of the previous frame
Is set.

Further, it is possible to define a spatio-temporal filter combining the above-described spatial filter and temporal filter. For example, it is possible to define a filter that receives the image information of the current frame vertical N horizontal N pixels and the previous frame vertical N horizontal N pixels and outputs the weighted average value thereof.

Generally, in moving picture coding, variable-length coding is used to improve coding efficiency. Therefore, the generated code amount changes for each frame. Therefore, in order to use the above filter for improving the coding efficiency, a method of changing the frequency characteristic of the filter depending on the generated code amount after coding has been proposed.

In such a method, the frequency characteristic is changed so that the amount of generated code is substantially the same in each frame. That is, when the generated code amount is large, the frequency characteristic is changed so as to restrict more bands, and conversely, when the generated code amount is small, the frequency characteristic is changed so as to restrict a smaller band. I do. This method is effective in a system for transmitting a moving image via a transmission line having a constant transmission speed because the amount of generated codes of each frame can be controlled.

[0016]

However, in the method of controlling the filter so that the generated code amount is the same in each frame, in a frame having a large code amount, the band is remarkably limited by the filter, and only the high frequency component is used. And even the image information of the low frequency component may be deleted. Since the low-frequency component has a large effect on vision, the visual quality is degraded steadily when it is deleted.

Further, when the encoded data stored in a storage medium such as a CD-ROM is decoded and reproduced, or when the encoded data is transmitted, the encoded data is once received and accumulated by a receiving terminal, and the Some systems do not require a constant transmission speed from the encoding side to the decoding side, such as when decoding stored encoded data. In such a system, it is not necessary to make the generated code amount of the encoded data of each frame the same. If the filters are controlled so that the generated code amounts are substantially the same, high frequencies are unnecessarily removed, and the visual quality is degraded.

As described above, in the method of controlling the filters so that the generated code amounts of the respective frames are substantially the same, the visual code quality may be rather deteriorated by making the generated code amounts the same. . It is considered that this problem occurs because the purpose of controlling the filter is to control the generated code amount, and not to control the degree of deterioration of the decoded image of each frame due to coding.

An object of the present invention is to provide an image encoding apparatus, an image encoding method, and a medium storing an image encoding program capable of improving encoding efficiency while preventing visual quality deterioration in encoding of a moving image signal. To provide.

[0020]

In order to solve the above-mentioned problems, in the present invention, in order to control the degree of deterioration of a decoded image of each frame due to encoding, encoded data is decoded once, and the decoded image is decoded. By comparing the image with the image after applying the filter, the degree of image deterioration due to encoding is measured. Then, the degree of deterioration is used for controlling the frequency characteristics of the filter.

As a method of comparing the decoded image with the image after applying the filter, the variance and the standard deviation of the difference of the image information of each pixel can be considered. In this method, when the variance and the standard deviation are large, it is assumed that the deterioration due to the encoding is large. When the screen is divided into small regions and encoding is performed in units of the regions, there is a method of calculating the variance and the standard deviation for each region. For example, there is a method in which a standard deviation is obtained for each macroblock (MB), which is an area of 16 pixels in the vertical and horizontal directions, and when there are many MBs having a large standard deviation, deterioration due to encoding is large. In addition, in an encoding method in which DCT is performed in units of MBs, generally, the degradation of encoding becomes large at a boundary pixel between adjacent MBs.

In this way, the deterioration due to encoding is measured, and if the deterioration is large, the filter applied to the next frame controls the frequency characteristics of the filter so as to further remove high frequency components.

Further, there is also a method of measuring not only the degree of deterioration due to coding but also the degree of deterioration of an image before coding generated by applying a filter, and controlling the filter based on these two kinds of degree of deterioration. Conceivable. This method is suitable for avoiding unnecessary removal of high-frequency components by a filter. For example, consider a case of a filter that controls so that high-frequency components are further removed in the next frame when the degree of deterioration due to encoding is large. When the degree of deterioration due to encoding is large, the degree of deterioration due to the filter is measured. When the degree of deterioration is large, the degree of high-frequency component deletion is reduced, and when the degree of deterioration is small, the degree of high-frequency component deletion is increased. This allows
It is possible to prevent the visual quality from being deteriorated due to the large deterioration caused by the filter.

Further, as described above, a filter controlled by measuring the degree of deterioration due to coding or a filter controlled by measuring the degree of deterioration caused by coding and the degree of deterioration caused by the filter is input to the input image of the next frame. It is also preferable to apply the method to the input image of the current frame and perform the encoding again.

As described above, according to the present invention, the degree of deterioration of the decoded image of each frame due to encoding is measured, and the filter of the input image is controlled using the degree of deterioration. This makes it possible to perform encoding while controlling the degree of deterioration of the decoded image of each frame due to encoding.

[0026]

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

FIG. 3 shows the configuration of the first embodiment of the present invention. Here, the frequency characteristic of the filter is controlled based on the degree of deterioration due to encoding. In FIG. 3, 11 is an image input unit, 12 is a pre-filter unit, 13 is a filtered image storage unit, 14 is an image encoding unit, 15 is a local decoding unit,
16 is a decoded image storage unit, 17 is an encoding deterioration measuring unit, 18
Is a filter control unit.

As a measure for measuring the degree of deterioration due to encoding, a PSNR between a decoded image once decoded from encoded data and an image after applying a filter is used. This value is set to PSNR1. If the value of PSNR1 is 30 or more, it is determined that deterioration due to encoding is small, and 30
If it is less than the above, it is determined that the deterioration is large. P
The equation for calculating SNR1 is shown in equation (3).

[0029]

(Equation 3)

Here, Out (i, j): a decoded image at the pixel of horizontal i and vertical j, Filtered Im (i, j): an image after applying the filter at the pixel of horizontal i and vertical j, M: horizontal direction of the screen N: the number of pixels in the vertical direction of the screen.

In this embodiment, when the degree of deterioration due to encoding is large, the frequency characteristics of the filter are controlled so as to remove more high-frequency components.
Hereinafter, the operation will be described.

The filter control unit 18 is provided with the pre-filter unit 12
Control the frequency characteristics of the filter. The filter of the frequency characteristic C2 removes more high frequency components than the filter of the frequency characteristic C1. The initial state is C1. In the present embodiment, the frequency characteristic of the filter is set to C2 when the deterioration due to coding is large, and the frequency characteristic of the filter is set to C1 when the deterioration due to coding is small.

It is assumed that the image input section 11 acquires image information for one frame and holds the image information until the image information for the next frame is acquired. First, the image input unit 11
The pre-filter unit 12 applies a filter to the image information of the current frame obtained from, and limits the band. The image after the filter application is stored in the filtered image storage unit 13. The image coding unit 14 codes the image stored in the filtered image storage unit 13 as an input image. The encoded data is decoded by the local decoding unit 15 and the decoded image is stored in the decoded image storage unit 16.

The coding deterioration measuring unit 17 calculates P based on the images stored in the filtered image storage unit 13 and the decoded image storage unit 16.
Calculate SNR1. When the value of PSNR1 is less than 30, the filter control unit 18 sets the frequency characteristic of the filter applied by the pre-filter unit 12 to C2, and when it is 30 or more, sets the frequency characteristic to C1. The filter in which this frequency characteristic is set is applied to the next frame.

As in the first embodiment, the degree of deterioration due to coding can be measured by comparing the decoded image with the image after applying the filter. By controlling the frequency characteristics of the filter in accordance with this degree, encoded data that becomes a decoded image with little deterioration due to encoding in the next frame can be obtained.

In the first embodiment, the case where the value of PSNR1 is 30 is shown as a guide for switching between C1 and C2. However, this is an example, and other appropriate values may be set according to the properties of the image. May be taken. Also, the case where only two types of frequency characteristics of the filter are switched, C1 and C2, has been described.
More than one type may be provided, and the degree of high-frequency component deletion may be more finely changed according to the value of PSNR1.

FIG. 4 shows a second embodiment of the present invention, in which the frequency characteristics of a filter are controlled based on the degree of deterioration due to encoding and the degree of deterioration due to a filter. 4, the same components as those of the first embodiment are denoted by the same reference numerals. That is, 11 is an image input unit, 12
Is a pre-filter unit, 13 is a filtered image storage unit, 14
Denotes an image encoding unit, 15 denotes a local decoding unit, 16 denotes a decoded image storage unit, 17 denotes an encoding deterioration measuring unit, 21 denotes a band limit deterioration measuring unit, and 22 denotes a filter control unit.

As a measure for measuring the degree of deterioration due to encoding, the PSNR between the decoded image once decoded from the encoded data and the image after applying the filter is used. This value is set to PSNR1. If the value of PSNR1 is 30 or more, it is determined that deterioration due to encoding is small, and 30
If it is less than the above, it is determined that the deterioration is large.

As a scale for measuring the degree of deterioration due to the filter, the PSNR between the image before the filter application and the image after the filter application is used. This value is called PSNR
Let it be 2. If the value of PSNR2 is 40 or more, it is determined that the deterioration due to the filter is small, and if it is less than 40, it is determined that the deterioration is large. The equation for calculating PSNR1 is the same as equation (3). The equation for calculating PSNR2 is shown in equation (4).

[0040]

(Equation 4)

Where FilteredIm (i, j): the image after applying the filter on the pixels in the horizontal i and vertical j, Im (i, j): the image before applying the filter on the pixels in the horizontal i, vertical j, M: the screen N: the number of pixels in the vertical direction of the screen.

In this embodiment, when the degree of deterioration due to encoding is large, the degree of deterioration due to the filter is measured, and when the degree of deterioration due to the filter is small, the filter is designed to delete more high-frequency components. Is controlled. Even when the degree of deterioration due to encoding is large, if the degree of deterioration due to the filter is large, the frequency characteristics of the filter are not changed. When the degree of degradation due to encoding is small, the frequency characteristics of the filter are controlled so as not to remove high frequency components. Hereinafter, the operation will be described.

The filter control unit 22 includes the pre-filter unit 12
Control the frequency characteristics of the filter. The filter of the frequency characteristic C2 removes more high frequency components than the filter of the frequency characteristic C1. The initial state is C1. In the present embodiment, when deterioration due to encoding is large and deterioration due to the filter is small, the frequency characteristic of the filter is set to C2. When the deterioration due to the encoding is small, the frequency characteristic of the filter is set to C1. In other cases, that is, when deterioration due to encoding is large and deterioration due to the filter is large, the frequency characteristics of the filter are not changed.

It is assumed that the image input unit 11 acquires image information for one frame and holds the image information until image information for the next frame is acquired. First, the image input unit 11
The pre-filter unit 12 applies a filter to the image information of the current frame obtained from, and limits the band. The image after the filter application is stored in the filtered image storage unit 13. The image coding unit 14 codes the image stored in the filtered image storage unit 13 as an input image. The encoded data is decoded by the local decoding unit 15 and the decoded image is stored in the decoded image storage unit 16.

The encoding deterioration measuring unit 17 calculates P based on the images stored in the filtered image storing unit 13 and the decoded image storing unit 16.
Calculate SNR1. If the value of PSNR1 is less than 30, the band-limit degradation measuring unit 21 calculates PSNR2 from the images stored in the image input unit 11 and the filtered image storage unit 13. When the value of PSNR2 is 40 or more, the filter control unit 22 sets the frequency characteristic of the filter applied by the pre-filter unit 12 to C2. When the value of PSNR2 is 4
If it is less than 0, the filter control unit 22 sets the frequency characteristics of the filter to the same characteristics as the current frame. PSNR
If the value of 1 is 30 or more, the frequency characteristic is set to C1. The filter in which this frequency characteristic is set is applied to the next frame.

As in the second embodiment, the decoded image is compared with the image after the filter is applied, and the image before and after the filter is applied is compared. The degree of deterioration by the filter can be measured. By controlling the frequency characteristics of the filter according to these degrees, not only is there little degradation due to coding in the next frame, but also
It is possible to obtain encoded data in which low-frequency components are not deleted by the filter.

In the second embodiment, the case where the values of PSNR1 and PSNR2 are 30 and 40, respectively, is shown as a guide for switching between C1 and C2. However, this is an example, and other values may be used depending on the properties of the image. In some cases, an appropriate value is taken. Also, the case where only two types of filters, C1 and C2, are switched as the frequency characteristics of the filter has been described.
And the degree of high-frequency component deletion may be changed more finely in accordance with the values of PSNR2 and PSNR2.

FIG. 5 shows a third embodiment of the present invention. Here, as in the second embodiment, the frequency characteristic of the filter is determined from the degree of deterioration due to coding and the degree of deterioration due to the filter. Is controlled and, unlike the second embodiment, when the degree of deterioration due to encoding is large, the controlled filter is applied to the image of the current frame. That is, it is determined whether the filter whose frequency characteristic is controlled is applied to the image of the current frame or the image of the next frame, and the filter is applied to the image of the current frame or the next frame. When applied to the image of the current frame, the encoding of the current frame is performed again.

In FIG. 5, the same components as those of the first and second embodiments are denoted by the same reference numerals. That is, 11 is an image input unit, 12 is a pre-filter unit, 13 is a filtered image storage unit, 14 is an image encoding unit, 15 is a local decoding unit, 1
6 is a decoded image storage unit, 17 is an encoding deterioration measurement unit, 21 is a band limit deterioration measurement unit, 22 is a filter control unit, 31 is an input image selection unit, 32 is an image selection unit, 33 is a previous image storage unit, 34 Denotes an encoded data storage unit, and 35 denotes encoded data selection means.

As in the second embodiment, as a scale for measuring the degree of deterioration due to encoding, the PSNR1 between the decoded image obtained by temporarily decoding the encoded data and the image to which the filter has been applied is used. As a scale for measuring the degree of deterioration due to, the PSNR2 between the image before applying the filter and the image after applying the filter is used.

The control method of the frequency characteristic of the filter is the same as that of the second embodiment. Hereinafter, the operation will be described.

It is assumed that the image input unit 11 acquires image information for one frame and holds the image information until image information for the next frame is acquired. First, the image input unit 11
When acquiring the image of the current frame, the previous image storage unit 3
3 stores the image of the previous frame stored in the image input unit 11. The pre-filter unit 12 applies a filter to the image information of the current frame obtained from the image input unit 11 to limit the band. The image after applying the filter is stored in the filtered image storage unit 13. The image coding unit 14 codes the image stored in the filtered image storage unit 13 as an input image. The encoded data is decoded by the local decoding unit 15, and the decoded image is stored in the decoded image storage unit 16. The encoded data is stored in the encoded data storage unit 34.

The coding deterioration measuring section 17 calculates P based on the images stored in the filtered image storing section 13 and the decoded image storing section 16.
Calculate SNR1. If the value of PSNR1 is less than 30, the band-limit degradation measuring unit 21 calculates PSNR2 from the images stored in the image input unit 11 and the filtered image storage unit 13. When the value of PSNR2 is 40 or more, the filter control unit 22 sets the frequency characteristic of the filter applied by the pre-filter unit 12 to C2. When the value of PSNR2 is 4
If it is less than 0, the filter control unit 22 sets the frequency characteristics of the filter to the same characteristics as the current frame. PSNR
If the value of 1 is 30 or more, the frequency characteristic is set to C1.

Here, when the value of PSNR1 is 30 or more, the input image selecting section 31 changes the image selecting means 32,
Next, the image to which the filter is applied is set as the image of the image input unit 11. At the same time, the encoded data selection means 35 is changed,
The setting is made so that the encoded data stored in the encoded data storage unit 34 is output. Since the input image selection unit 31 has set the image to which the filter is applied as the image of the image input unit 11, the image input unit 11 acquires the image of the next frame. The filter is applied to the image of the next frame stored in the image input unit 11, and the image after the filter application is encoded.

That is, when the deterioration due to the encoding is small, the encoded data is output, and the image of the next frame is encoded by applying a filter.

If the value of PSNR1 is less than 30, the PSN
When the value of R2 is 40 or more, the input image selection unit 31 changes the image selection unit 32, and sets the image to which the filter is next applied to the image of the previous image storage unit 33. At the same time, the coded data selection means 35 is changed and the coded data storage section 34 is changed.
Is set so as not to output the coded data stored in. Since the input image selection unit 31 sets the image to which the filter is applied as the image of the previous image storage unit 33, the image input unit 11 does not acquire the image of the next frame. The previous image storage unit 33 stores the image of the current frame stored in the image input unit 11. A filter is applied to the current frame image stored in the previous image storage unit 33, and the image after the filter application is encoded.

That is, when the deterioration due to the coding is large and the deterioration due to the filter is small, the coded data is not output, and the current frame image is coded by applying the filter.

When the value of PSNR1 is less than 30, PSN
When the value of R2 is less than 40, the input image selection unit 31 changes the image selection unit 32, and sets the image to which the filter is to be applied next to the image of the image input unit 11. At the same time, the coded data selection means 35 is changed so that the coded data stored in the coded data storage unit 34 is output. Since the input image selection unit 31 has set the image to which the filter is applied as the image of the image input unit 11, the image input unit 11 acquires the image of the next frame. The filter is applied to the image of the next frame stored in the image input unit 11, and the image after the filter application is encoded.

That is, even when the deterioration due to the encoding is large, when the deterioration due to the filter is large, the encoded data is output, and the image of the next frame is encoded by applying the filter.

In the third embodiment, when the degree of deterioration due to coding is large, whether to apply a filter whose frequency characteristic is controlled to the image of the next frame and perform coding.
It is determined whether to apply the controlled filter to the current frame and encode again. This makes it possible to apply a filter for removing higher frequency components to a frame having a high degree of deterioration due to encoding, and encode the frame again.

In the third embodiment, the frequency characteristic of the filter is changed using both the degree of deterioration due to coding and the degree of deterioration due to the filter. However, the frequency characteristic is changed using only the degree of deterioration due to coding. You may.

In the third embodiment, the case where the values of PSNR1 and PSNR2 are 30 and 40, respectively, is shown as a guide for switching between C1 and C2. However, this is an example, and other values may be used depending on the properties of the image. In some cases, an appropriate value is taken. Also, the case where only two types of filters, C1 and C2, are switched as the frequency characteristics of the filter has been described.
And the degree of high-frequency component deletion may be changed more finely in accordance with the values of PSNR2 and PSNR2.

[0063]

As described above, according to the present invention,
The degree of deterioration of the decoded image of each frame due to encoding and the degree of deterioration of the input image due to the filter are measured, and the filter of the input image is controlled using the degree of deterioration. This makes it possible to control the degree of deterioration of the decoded image of each frame due to encoding. In addition, by applying the filter whose frequency characteristic is controlled to the current frame instead of applying the filter to the next frame, it is possible to reduce the degradation caused by encoding that occurs in the current frame.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a spatial filter.

FIG. 2 is an explanatory diagram showing an example of a time filter.

FIG. 3 is a configuration diagram showing a first embodiment of the present invention.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a third embodiment of the present invention.

[Explanation of symbols]

11: image input unit, 12: pre-filter unit, 13: filtered image storage unit, 14: image coding unit, 15: local decoding unit, 16: decoded image storage unit, 17: coding deterioration measurement unit, 18, 22: Filter control unit, 21: Band limit deterioration measuring unit, 31: Input image selecting unit, 32: Image selecting unit,
33: previous image storage unit, 34: encoded data storage unit, 3
5: Coded data selection means.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C021 PA18 PA34 PA38 PA58 PA62 PA72 PA74 PA79 RB00 RB05 RC01 SA24 XB02 YA00 YC08 YC09 5C059 KK01 KK04 KK23 LA00 MA00 MA05 PP04 SS20 TA69 TB07 TC08 TC33 TD01 TD04 TD05 TD05 UA05 BC01 BC02 BC11 BC18 BC29 BD03 BD04

Claims (9)

[Claims] 1. A moving picture coding apparatus for limiting a band of an image and coding the image, comprising: an image input unit for acquiring an image; a pre-filter unit for limiting a band of the image; A filtered image storage unit for storing the restricted image, an image coding unit for coding the image, a local decoding unit for decoding coded data, a decoded image storage unit for storing the decoded image, and the filtered image A coding deterioration measuring unit that measures the degree of deterioration due to coding from the image stored in the storage unit and the image stored in the decoded image storing unit; and a frequency characteristic of the pre-filter unit based on the degree of deterioration due to coding. And a filter control unit for controlling the image coding. 2. A moving picture coding apparatus for limiting a band of an image and coding the image, comprising: an image input unit for acquiring an image; a pre-filter unit for limiting a band of the image; A filtered image storage unit for storing the restricted image, an image coding unit for coding the image, a local decoding unit for decoding coded data, a decoded image storage unit for storing the decoded image, and the filtered image An image stored in a storage unit, an encoding deterioration measurement unit that measures the degree of deterioration due to coding from the image stored in the decoded image storage unit, an image acquired by the image input unit, and the filter A band-limited degradation measuring unit that measures the degree of degradation due to the filter from the image stored in the post-image storage unit; and a frequency of the pre-filter unit based on the degree of degradation due to the encoding and the degree of degradation due to the filter. An image encoding device, comprising: a filter control unit that controls characteristics. 3. The image coding apparatus according to claim 1, wherein the pre-filter unit whose frequency characteristics are controlled by the filter control unit is selected to be applied to an image of a current frame or to a next frame. An image encoding apparatus comprising: 4. A moving picture coding method for limiting a band of an image and coding the image, comprising: an image inputting step of acquiring an image; a pre-filtering step of limiting a band of the image; A filtered image storing step of storing the restricted image, an image coding step of coding the image, a local decoding step of decoding coded data, a decoded image storing step of storing a decoded image, and the filtered image A coding deterioration measuring step of measuring the degree of deterioration due to coding from the image stored in the storing step and the image stored in the decoded image storing step; and a pre-filtering step based on the degree of deterioration due to coding. A filter control step of controlling frequency characteristics. 5. A moving image coding method for limiting a band of an image and coding the image, comprising: an image inputting step of acquiring an image; a pre-filtering step of limiting a band of the image; A filtered image storing step of storing the restricted image, an image coding step of coding the image, a local decoding step of decoding coded data, a decoded image storing step of storing a decoded image, and the filtered image An image stored in the storing step, an encoding deterioration measuring step of measuring a degree of deterioration due to coding from the image stored in the decoded image storing step, and an image acquired in the image input step; A band-limited deterioration measuring step of measuring the degree of deterioration by the filter from the image stored in the filtered image storing step; An image coding method, comprising: a filter control step of controlling a frequency characteristic of a pre-filter step based on a degree of deterioration due to image formation and a degree of deterioration due to a filter. 6. The image coding method according to claim 4, wherein the pre-filter step of controlling the frequency characteristics in the filter control step is applied to an image of a current frame or to a next frame. An image encoding method, comprising: 7. A medium storing a moving image encoding program for limiting a band of an image and encoding the image, wherein the computer reads the image when the program is read by the computer. An image input step, a pre-filter step for limiting an image band, a filtered image storage step for storing an image with a limited band, an image encoding step for encoding an image, and a local decoding for decoding encoded data Measuring the degree of deterioration due to coding from the decoded image storing step of storing the decoded image, the image stored in the filtered image storing step, and the image stored in the decoded image storing step. A filter that controls the frequency characteristics of the pre-filter step based on the degree of degradation due to encoding and an encoding degradation measurement step A medium storing an image encoding program for executing a process including a control step. 8. A medium storing a moving image encoding program for limiting a band of an image and encoding the image, wherein the computer reads the image when the computer reads the program. An image input step, a pre-filter step for limiting an image band, a filtered image storage step for storing an image with a limited band, an image encoding step for encoding an image, and a local decoding for decoding encoded data Measuring the degree of deterioration due to coding from the decoded image storing step of storing the decoded image, the image stored in the filtered image storing step, and the image stored in the decoded image storing step. An encoding deterioration measuring step, an image acquired in the image input step, and accumulation in the filtered image accumulation step A band-limited degradation measuring step of measuring the degree of degradation due to the filter from the obtained image, and a filter control step of controlling the frequency characteristic of the pre-filter step based on the degree of degradation due to the encoding and the degree of degradation due to the filter. A medium storing an image encoding program for executing processing. 9. A medium storing the image encoding program according to claim 7 or 8, wherein a pre-filter step of controlling frequency characteristics in the filter control step is applied to an image of a current frame or to a next frame. A medium storing an image encoding program, comprising: an input image selecting step of selecting whether to perform the operation.