JP4364422B2 - Video compression encoding method and decoding method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a moving image compression encoding method and a decoding method thereof, and more particularly, to a compression encoding method and a decoding method thereof suitable for a moving image with little temporal change such as surveillance video.
[0002]
[Prior art]
As a compression encoding method of moving images, a method combining DCT (Discrete Cosine Transform) and motion compensation prediction encoding is generally used, and this method is also adopted in the MPEG (Moving Picture Experts Group) method. ing. In general, DCT is applied to intra-frame coding in which coding is performed using only information in a frame (still image) so as to reduce redundancy in the spatial direction. In addition, motion compensation predictive coding (interframe coding) predicts a coding target frame from a frame at another time in order to reduce temporal redundancy, and a difference signal between the coding target frame and the predicted frame. Is subjected to DCT, quantization, or the like. In this case, in order to keep the difference small, the encoding target frame is often predicted from temporally adjacent frames. Such intra-frame coding and motion-compensated prediction coding processes are performed with a block obtained by dividing a frame into a plurality of basic processing units.
[0003]
However, in a moving image such as a monitoring video that has an extremely small temporal change, an input frame is periodically set as a reference image (hereinafter referred to as a key frame), and the interval between the key frame and the input frame is set. Even if a differential encoding method that takes a differential signal is used, it is considered that the difference amount between both frames is small. This method has advantages such as a reduction in calculation load and resistance to errors caused by missing frames, as compared with the above-described motion compensation prediction encoding using adjacent frames. The outline of the conventional differential encoding method will be described with reference to FIG. Assume that a plurality of frames f1, f2,... Sequentially output from the imaging sensor are sequentially input to the encoder. As shown in FIG. 9, when a frame fn (n = 1, 2,...) Is input (ST100), whether or not the input frame fn is a key frame is determined in step ST101. If the frame fn is a key frame, intra-frame encoding processing is executed in step ST102. That is, the frame fn is divided into blocks, DCT is performed for each block, and the transform coefficient is calculated. Next, a quantized coefficient obtained by quantizing the transform coefficient is output. Next, in step ST103, encoded data obtained by variable-length encoding (entropy encoding) the quantization coefficient is generated, converted into a bit stream, and output. The quantization coefficient calculated in step ST102 is stored in the key frame memory 100 after being decoded (inverse quantization and inverse DCT) in step ST104.
[0004]
Next, when the next frame fm (m = n + 1) is input in step ST100, whether or not the frame fm is a key frame is determined in step ST101. If the frame fm is not a key frame, the process proceeds to step ST105. Then, the difference value of the pixel value is calculated for each block between the key frame fn and the frame fm stored in the key frame memory 100. Next, in step ST106, it is determined whether or not the difference value is within a predetermined range. If the difference value is within the predetermined range, inter-frame encoding is performed in step ST107, that is, the difference between the key frame and the input frame fm. The signal is subjected to DCT and quantization. On the other hand, if the difference value exceeds the predetermined range, intra-frame coding is executed in step ST108. As described above, the quantization coefficients calculated in steps ST107 and ST108 are variable-length encoded in step ST103, converted into a bit stream, and then output.
[0005]
An example of such a bitstream decoding process will be described below with reference to FIG. When the bit stream is input (ST110), a compression-coded signal is extracted from the bit stream and subjected to variable length decoding to obtain the quantization coefficient. Next, in step ST111, when the quantized coefficient has been intra-frame encoded in step ST102 of the compression encoding process, the decoding (intra-frame decoding) is performed and stored in the key frame memory 101, If the quantized coefficient has been intra-coded in step ST108, the decoding is performed. On the other hand, if the quantized coefficient has been inter-frame encoded at step ST107, the decoding (inter-frame decoding) is performed with reference to the key frame stored in the key frame memory 101. Then, a decoded image that has been decoded within a frame or between frames is output (ST112).
[0006]
[Problems to be solved by the invention]
However, in the above differential encoding method, since the differential encoding between the key frame and the frame separated in time is performed, the image quality of the key frame is directly related to the image quality of the entire moving image. The key frame is subjected to intra-frame coding in which compression coding is performed using only the information in the frame. As a result, there has been a problem in that the amount of moving picture encoding processing increases rapidly during key frame encoding, and transmission of key frame compressed encoded data is delayed or intermittent. Particularly when moving images are transmitted and reproduced (streamed) in real time through a network, there are cases in which a change in the reproduction speed of the decoded moving images and intermittent images occur.
[0007]
In view of such problems, the present invention intends to solve the problem of suppressing the rapid increase in the amount of encoding processing of key frames, flattening the amount of encoding processing in terms of time, and improving the quality of moving images. The present invention is to provide a compression encoding method and a decoding method for a moving image.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is a compression encoding method of a moving image composed of a plurality of frames that are sequentially input, wherein (a) compression is performed by designating a key frame from the plurality of frames. A step of decoding and storing the compression-encoded key frame, and (b) dividing the frame input after the key frame into a plurality of block areas and selecting a specific area from the block areas. (C) performing intra-frame coding for compressing and encoding only the information in the frame with respect to the specific area, decoding and storing the compression-coded specific area, and (d) ) A difference signal is calculated between the key frame stored in step (a) and each block area excluding the specific area divided in step (b). An intra-frame code that determines the magnitude of the difference between the key frame and each block area based on a difference signal, and compresses and encodes only the information in the frame for the block area when the difference is greater than a predetermined value And if the difference is smaller than a predetermined value, performing inter-frame encoding for compressing and encoding the difference signal; and (e) until a new key frame is designated in step (a). Repeatedly executing the steps (b) to (d), and (c-1) while repeatedly executing the steps (b) to (d) stored in the step (e). A step of accumulating the specific area for one frame in step (c) to generate a reference frame comprising the specific area; and (a-1) the compression encoding of step (a). Then, a difference signal is calculated between the specified key frame and the reference frame, and a difference between the key frame and the reference frame is determined based on the difference signal, and the difference is larger than a predetermined value. If the difference is smaller than a predetermined value, intra-frame encoding for compressing and encoding the difference signal is performed for the key frame. These are provided.
[0009]
The invention according to claim 2 is a decoding method for decoding compressed image data encoded by the compression encoding method according to claim 1, and (f) a compressed image of a key frame according to claim 1. A step of decoding and storing the data; (g) a step of decoding and storing the compressed image data of the specific region according to claim 1; and (h) a block region of each block region excluding the specific region according to claim 1 If the compressed image data has been subjected to the intra-frame coding described in claim 1, the decoding corresponding to the intra-frame coding is executed, and the compressed image data is claimed in claim 1. A step of performing decoding corresponding to the inter-frame encoding with reference to the key frame stored in the step (f) when inter-frame encoding using the described key frame has been performed, and And (g-1) accumulating the specific area stored in the step (g) for one frame to synthesize a reference frame composed of the specific area, and (f-1) the step (f). If the compressed image data of the key frame is subjected to the intra-frame encoding according to claim 1, the decoding corresponding to the intra-frame encoding is executed, and the compressed image data is compressed. If the image data has been subjected to inter-frame encoding using the reference frame according to claim 1, the decoding corresponding to the inter-frame encoding is performed with reference to the reference frame synthesized in step (g-1). And the step of executing.
[0010]
The invention according to claim 3 is the decryption method according to claim 2, wherein (i) between the specific region decrypted in step (g) and the key frame stored in step (f). The difference signal is calculated, and the difference between the specific area and the key frame is determined based on the difference signal. If the difference is smaller than a predetermined value, the difference between the frames according to claim 1 is determined for the specific area. Performing encoding and decoding thereof.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
1 to 3 are flowcharts for realizing the compression coding method according to Embodiment 1 of the present invention. The compression encoding method according to the first embodiment will be described in detail below with reference to this flowchart.
[0012]
A plurality of still images (frames) f1, f2, f3, f4,... Sequentially captured along the time axis by an image sensor such as a CCD (charge coupled device) sensor or a CMOS sensor are encoders according to the first embodiment. (ST1). The key block memory 2 stores a reference frame f0 composed of a key GOB for one frame, which will be described in detail later, before the frame f1 is input. This reference frame f0 is described in the second embodiment to be described later. After being compressed and transmitted, it is decrypted and stored in the key block memory 11 of the decoder. The encoder according to the first embodiment periodically designates key frames from the input frames f1, f2, f3, f4,..., And the input frame f1 is a key frame.
[0013]
First, in step ST2, it is determined whether or not the frame f1 is a key frame. Since the frame f1 is a key frame, the process proceeds to step ST3. As shown in FIG. 2, the difference value of the pixel value between the reference frame f0 and the input frame f1 stored in the key block memory 2 in step ST4, An absolute value sum (difference absolute value sum) S of the difference values is calculated, and then it is determined in step ST5 whether or not the difference absolute value sum is equal to or less than a threshold value. For example, the difference value is ΔP _i When expressed by (i: number corresponding to each pixel), the sum of absolute differences S is S = | ΔP ₁ | + | ΔP ₂ | + ... + | ΔP _n | (N: number of pixels). When the difference absolute value sum S is equal to or smaller than the threshold, the input frame f1 is subjected to interframe coding using the frame f0 because the temporal change between the frames f0 and f1 is small (ST6). Specifically, an orthogonal transform such as DCT (Discrete Cosine Transform) is performed on the difference signal between the input frame f1 and the frame f0, and a quantized coefficient obtained by quantizing the transform coefficient is calculated. Further, such inter-frame coding processing is executed in units of blocks having a size such as 8 × 8 pixels or 16 × 16 pixels. The same applies to the subsequent processing. In this embodiment, orthogonal transform such as DCT is adopted as a transform method, but DWT (discrete wavelet transform) may be employed instead of DCT. In this case, the inter-frame encoding process may be executed in units of frames instead of being performed in units of blocks as described above in consideration of an execution memory capacity or the like, or by dividing a frame into a plurality of areas called tiles.
[0014]
On the other hand, when the difference absolute value sum S calculated in step ST4 exceeds the threshold value in step ST5, the process proceeds to step ST7, and the input frame f1 is subjected to intraframe encoding that encodes only the information in the frame. The Specifically, orthogonal transformation such as DCT is performed on the pixel value of the frame f1, and a quantized coefficient obtained by quantizing the transform coefficient is calculated.
[0015]
From the viewpoint of increasing the compression rate of the frame, color space conversion is performed on the input frame before the intra-frame coding (ST7) or the inter-frame coding (ST6). For example, when the original signal is composed of RGB spaces of “R (red component)”, “G (green component)”, and “B (blue component)”, this is adopted in the NTSC (National Television System Committee) system or the like. YUV coordinate system, YIQ coordinate system, YC _b C _r A coordinate system or the like may be used. For example, YC _b C _r When a coordinate system is used, the RGB components are a luminance signal Y and two color difference signals C. _b , C _r YC consisting of _b C _r Converted to the component coordinate system. YC _b C _r Since the component has a smaller correlation between the components than the RGB component, the image size can be compressed.
[0016]
Next, as shown in FIG. 1, the process proceeds to step ST19, and the quantized coefficients calculated in steps ST6 and ST7 are subjected to entropy coding including Huffman coding, and then the image size and quantization of the frame It is multiplexed with image information such as the number of bits, and compression information such as a quantization table and a coding method (intraframe coding, interframe coding) of each block area, and output as a bit stream. The quantized coefficients calculated in steps ST6 and ST7 are locally decoded (inverse orthogonal transformation such as inverse quantization and inverse DCT) in step ST8 and stored in the key frame memory 1. Therefore, the key frame memory 1 stores the changed key frame including the quantization error through encoding (ST6, ST7) and decoding (ST8). As a result, the image of the key frame becomes the same as the image of the key frame that is referred to when decoding (inter-frame decoding) by a later-described decoder, and the image quality of the moving image to be decoded is not deteriorated. . The compression encoding process for the input frame f1 (key frame) is thus completed.
[0017]
Next, when the frame f2 is input to the encoder following the frame f1, whether or not the frame f2 is a key frame is determined in step ST2. Since the frame f2 is not a key frame, the process shifts to step ST9, and the frame f2 is divided into a plurality of block areas (hereinafter referred to as GOB), and then in step ST9, one or more of these block areas (GOB) are selected. A plurality of specific areas (hereinafter referred to as key GOB) are designated. FIG. 4A schematically shows a frame f2 divided into four GOBs. The frame f2 is divided into four GOBs in units of ten to several tens of pixels in the vertical direction, and the first stage GOB is designated as the key GOB. As shown in FIGS. 2B to 2D, the frames f3 to f5 sequentially input to the encoder following the frame f2 are also divided into a plurality of GOBs, and the second stage GOB of the frame f3 and the frames f4 The third stage GOB and the fourth stage GOB of the frame f5 are designated as the key GOB. As shown in FIG. 5, such frames f1 to f5 are arranged along the time axis.
[0018]
Next, the process proceeds to step ST11, and thereafter, the frame f2 is sequentially processed for each block obtained by further dividing the GOB into basic processing units of about 8 × 8 pixels or 16 × 16 pixels. In step ST11, it is determined whether or not the block to be processed belongs to the key GOB. If the block belongs to the key GOB, the block is subjected to the intra-frame coding in step ST12 and then entropy-coded in step ST19 and multiplexed with the image information and the compression information to form a bit stream. Is output. In addition, the quantization coefficient output by intra-frame encoding the block in step ST12 is stored in the key block memory 2 after being subjected to local decoding (inverse orthogonal transformation such as inverse quantization and inverse DCT) in step ST13. The
[0019]
On the other hand, if the block does not belong to the key GOB in step ST11, the process proceeds to a subroutine of step ST14, and the block of the input frame and the key frame stored in the key frame memory 1 are stored in step ST15 as shown in FIG. And a difference absolute value sum S are calculated. Next, in step ST16, a condition determination is made as to whether or not the difference absolute value sum S is less than or equal to the threshold value. If the difference absolute value sum S is less than or equal to the threshold value, the process proceeds to step ST17, and the block is stored in the key frame memory 1. The inter-frame coding is performed with reference to the stored key frame. On the other hand, when the difference absolute value sum S exceeds the threshold value, the process proceeds to step ST18, and the block is subjected to the intra-frame coding. Thus, the quantized coefficients encoded in steps ST17 and ST18 are subjected to variable length encoding (entropy encoding) and the multiplexing process in step ST19 shown in FIG. 1, and are output as a bit stream. . Thus, the compression encoding process for the input frame f2 is completed.
[0020]
Next, the frames f3, f4,... Input to the encoder subsequent to the frame f2 are processed in the same manner as in the case of the frame f2 until the key frame is input. Accordingly, the keys GOB1 to 4 decrypted in step ST13 are stored in the key block memory 2 for one frame, and the keys GOB1 to 4 are stored in the key block memory 2 as shown in FIG. Is synthesized. This reference frame A is used when a key frame to be input later is inter-frame encoded in the subroutine of step ST3.
[0021]
As described above, in the compression coding method according to the first embodiment, intra-frame coding and inter-frame coding are selectively executed depending on the difference from the reference frame stored in the key block memory 2 in step ST3. In steps ST9 and ST10, the input frame is divided into a plurality of GOBs, a key GOB is designated, and a key GOB for one frame is distributed over a plurality of frames along the time axis. GOB is intra-coded. For this reason, the intraframe encoding processing amount is dispersed in time, the rapid increase in the compression encoding processing amount is suppressed, the encoding processing amount is flattened in time, and the playback speed of the moving image at the transmission destination As a result, it is possible to compress and transmit a high-quality moving image without changing. In particular, the effect is exhibited in a transmission line with a limited bandwidth such as the Internet.
[0022]
In the key block memory 2, the key GOB distributed in a plurality of frames is stored, and a reference frame A composed of these keys GOB is formed. This reference frame A is an accumulation of key GOBs at different times. In the first embodiment, intra-frame coding and inter-frame coding are selectively executed depending on the difference between the reference frame A and the key frame. For this reason, the difference in image quality between GOBs resulting from the use of the reference frame A made up of the key GOBs at different times is alleviated, and it becomes possible to compress and transmit high-quality moving images.
[0023]
Embodiment 2. FIG.
Next, the decoding method according to Embodiment 2 of the present invention will be described in detail below. FIG. 6 is a flowchart for realizing the decoding method according to the second embodiment.
[0024]
The compressed image data encoded in the first embodiment is converted into a bit stream and input to the decoder according to the second embodiment (ST20). The compressed image data is separated from the bit stream and then decoded in step ST21. That is, since the compressed data of the frames f1, f2,... Are sequentially input from the encoder to the decoder according to the second embodiment, the above-described embodiment is applied to the compressed data of the key frame f1 in step ST21. The decoding process of intra-frame coding or inter-frame coding in step ST3 of the form 1 is performed in units of blocks of about 8 × 8 pixels or 16 × 16 pixels. When decrypting the compressed data of the key frame f1, the reference frame f0 stored in advance in the key block memory 11 is used. The decrypted key frame f1 is stored in the key frame memory 10.
[0025]
In addition, intraframe coding or interframe coding in steps ST12 and ST14 to ST18 of the first embodiment is applied to the compressed data of frames f2, f3,. Decoding processing is performed for each block. When performing decoding processing of interframe coding, the key frame f1 stored in the key frame memory 10 is used. When the frames f2, f3,... Are decoded, if the block that is the basic processing unit belongs to the key GOB, the block is stored in the key block memory 11. When the key GOB for one frame is accumulated, the reference frame A composed of these keys GOB is synthesized and used for decoding the compressed data of the key frame to be input to the decoder later. For example, when the compressed data of the frames f2 to f5 shown in FIGS. 4A to 4D are input to the decoder, the compressed data of the blocks constituting each key GOB is subjected to intra-frame decoding. The reference frame A is reconstructed by sequentially accumulating in the key block memory 11.
[0026]
In this way, when the frame groups f1, f2,... Decoded in step ST21 are displayed as a moving image, the image quality of the moving image between the GOB that has been intra-frame encoded by the encoder and the GOB that has been inter-frame encoded. The key GOB encoded in the frame may be clearly seen in the moving image. In order to prevent such a case, the second embodiment includes a key GOB requantization process in which only the key GOB decrypted in step ST21 is re-encoded and decrypted in step ST22 shown in FIG. It is.
[0027]
FIG. 7 is a flowchart showing the key GOB requantization process. As shown in FIG. 7, first, a block of about 8 × 8 pixels or 16 × 16 pixels is input (ST30). Next, in step ST31, it is determined whether or not the block belongs to the key GOB. If the block does not belong to the key GOB, the block is not requantized, and the key GOB requantization processing ends. The process moves to step ST23 shown in FIG. On the other hand, if the block belongs to the key GOB, the process proceeds to step ST32, the difference value between the key frame stored in the key frame memory 10 and the pixel value of the block, and the difference absolute value sum S of the difference values. And are calculated. Next, in step ST33, a condition determination is made as to whether or not the difference absolute value sum S is equal to or smaller than a threshold value. If the difference absolute value sum S exceeds the threshold value, the block is not requantized, and key GOB requantization processing is performed. Is completed, and the process proceeds to step ST23 shown in FIG.
[0028]
On the other hand, if it is determined in step ST33 that the sum of absolute differences S is equal to or less than the threshold, the process proceeds after step ST34. First, in step ST34, the difference signal between the block and the key frame is transform-coded, and then in step ST35, the transform coefficient is quantized. The processes of these steps ST33 to ST35 are performed by a determination process (ST16) of an encoding method (interframe encoding, intraframe encoding) based on the sum of absolute differences S performed by the encoder, orthogonal transformation such as DCT, This is the same as the quantization process (ST17). After that, in step ST36, the quantized coefficient is inversely quantized, and then in step ST37, transform coding decoding (inverse orthogonal transform such as inverse DCT) in step ST34 is performed. As a result, in accordance with the processing in steps ST34 to ST37, the quantization error is the same as when the block signal other than the key GOB is interframe-encoded by the encoder and the encoded signal is decoded by the decoder. An irreversible differential signal including is obtained. Next, a block is reconstructed from the difference signal using the key frame stored in the key frame memory 10 in step ST38 and output.
[0029]
The block subjected to the above key GOB requantization processing is output after being combined with a frame (decoded image) in step ST23 shown in FIG. The above key GOB requantization process will be described by taking the frames f2 to f5 shown in FIG. 4 as an example. As schematically shown in FIG. 8, the keys of the frames f2 to f5 decrypted in step ST21 described above are used. The difference between the GOB and the key frame stored in the key frame memory 10 is taken. Next, in step ST32, it is determined whether or not the difference absolute value sum S of the difference values is equal to or less than a threshold value, that is, whether or not to perform interframe encoding. If the difference absolute value sum S is equal to or less than the threshold value, the key GOB is determined. On the other hand, interframe coding (transform coding and quantization) is performed on the frames, and then decoding of the interframe coding (dequantization and inverse transform decoding) is performed on the frames f2 to f5. Corresponding decoded images F1 to F5 are generated.
[0030]
As described above, according to the second embodiment, if the difference between the key GOB and the key frame is small in the same procedure as the compression coding processing (ST15 to ST17) according to the first embodiment, the key GOB After compressing and encoding the difference signal from the key frame, the decoding is performed and the key GOB is reconstructed. Therefore, the block area other than the key GOB is inter-frame encoded by the encoder and decoded. In the same manner as when the encoded signal is decoded by the coder, the key GOB is mixed with inter-frame encoding and an error associated with the decoding. Therefore, when displaying the decoded moving image, the key GOB does not stand out in the moving image, and there is an effect that the person watching the moving image does not feel uncomfortable.
[0031]
【The invention's effect】
As described above, according to the moving picture compression encoding method according to claim 1 of the present invention, the frame input after the key frame is divided into a plurality of block areas, and a specific area (key GOB) is selected from these block areas. ) Can be specified, and the specific area to be intra-frame encoded can be distributed to a plurality of frames at different times. For this reason, the intra-frame encoding processing amount can be dispersed in time, the rapid increase in the compression encoding processing amount can be suppressed, and the encoding processing amount can be flattened in time. Further, the difference in image quality between the block areas (GOB) caused by using the reference frame in which the specific area is stored for one frame in step (c-1) is the key frame in step (a-1). On the other hand, it can be mitigated by selectively executing intra-frame coding and inter-frame coding. Therefore, at the transmission destination, it is possible to compress and transmit a high quality moving image without changing the reproduction speed of the moving image.
[0032]
According to the moving image decoding method of the second aspect, it is possible to decode the compressed image data encoded by the compression encoding method of the first aspect.
[0033]
According to claim 3, the inter-frame coding is applied to the specific area in the same manner as the inter-frame coding is applied to the block area other than the key block in step (d) according to claim 1, and then the decoding is performed. Therefore, when displaying the decoded moving image, the specific region is not conspicuous in the moving image, and there is an effect that the viewer does not feel uncomfortable.
[Brief description of the drawings]
FIG. 1 is a flowchart for realizing an encoding method according to Embodiment 1 of the present invention;
FIG. 2 is a flowchart for realizing the encoding method according to the first embodiment.
FIG. 3 is a flowchart for realizing the encoding method according to the first embodiment.
FIG. 4 is an explanatory diagram showing each frame divided into four block areas.
5 is a schematic diagram for explaining an encoding method according to Embodiment 1. FIG.
FIG. 6 is a flowchart for realizing a decoding method according to Embodiment 2 of the present invention;
FIG. 7 is a flowchart for explaining requantization processing according to the second embodiment;
FIG. 8 is a schematic diagram for explaining a decoding method according to the second embodiment.
FIG. 9 is a flowchart for explaining a conventional encoding method.
FIG. 10 is a flowchart for explaining a conventional decoding method.
[Explanation of symbols]
1 Key frame memory
2 Key block memory
10 Key frame memory
11 Key block memory

Claims (3)

A method for compressing and encoding a moving image composed of a plurality of frames that are sequentially input,
(A) specifying and compressing and encoding a key frame from the plurality of frames, and decoding and storing the compressed and encoded key frame;
(B) dividing a frame input after the key frame into a plurality of block areas and designating a specific area from the block areas;
(C) performing intra-frame coding for compressing and coding only the information in the frame for the specific area, and decoding and storing the compression-coded specific area;
(D) A difference signal is calculated between the key frame stored in step (a) and each block area excluding the specific area divided in step (b), and the key frame is calculated based on the difference signal. When the difference is larger than a predetermined value, intra-frame coding is performed on the block area using only the information in the frame. Performing inter-frame coding for compressing and coding the difference signal if smaller than a predetermined value;
(E) repeatedly executing steps (b) to (d) until a new key frame is designated in step (a);
In addition,
(C-1) While the steps (b) to (d) are repeatedly executed in the step (e), the specific area stored in the step (c) is accumulated for one frame, and consists of the specific area. Generating a reference frame;
(A-1) In the compression encoding in the step (a), a difference signal is calculated between the designated key frame and the reference frame, and the key frame and the reference frame are calculated based on the difference signal. If the difference is larger than a predetermined value, intra-frame coding is performed on the key frame using only the information in the frame, and if the difference is smaller than the predetermined value, the difference signal is determined. Performing inter-frame encoding to compress-encode
A method for compressing and encoding a moving image, comprising: A decoding method for decoding compressed image data encoded by the compression encoding method according to claim 1, comprising:
(F) decoding and storing the compressed image data of the key frame according to claim 1;
(G) decoding and storing the compressed image data of the specific area according to claim 1;
(H) For the compressed image data of each block area excluding the specific area described in claim 1, when the compressed image data is subjected to the intra-frame encoding described in claim 1, the intra-frame encoding is performed. If corresponding compressed image data is subjected to inter-frame encoding using the key frame according to claim 1, the frame is referred to by referring to the key frame stored in step (f). Performing decoding corresponding to inter-coding;
In addition,
(G-1) accumulating the specific area stored in the step (g) for one frame to synthesize a reference frame composed of the specific area;
(F-1) In the step (f), when the compressed image data of the key frame is subjected to the intra-frame encoding according to claim 1, the intra-frame encoding is performed. If corresponding compressed image data is subjected to interframe coding using the reference frame according to claim 1, refer to the reference frame synthesized in step (g-1). Performing decoding corresponding to the inter-frame coding;
A decoding method comprising: A decoding method according to claim 2, comprising:
(I) A difference signal is calculated between the specific region decoded in step (g) and the key frame stored in step (f), and the specific region and the key frame are calculated based on the difference signal. A decoding method comprising: discriminating a magnitude of a difference, and executing the interframe coding and the decoding thereof according to claim 1 for the specific region when the difference is smaller than a predetermined value.

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