JP2005167655A - Conversion coding method and conversion decoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more improve the coding efficiency for coding after switching over DCT and MP in block units. <P>SOLUTION: The method is composed of a means 101 for dividing image signals composed of a plurality of regions into image blocks with inputs of the image signals and region information, a first and second conversion means 102, 103 for converting the image blocks into code series, a means 104 for selecting either of code series generated by the first and second conversion means 102, 103, and a means 105 for combining the code series selected by the selecting means 104 to generate an output code series. The first conversion means 102 executes a conversion process after determining a conversion base function, based on the region information, and the second conversion means 103 executes a conversion process after determining the conversion base function, irrespective of the region information. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transform encoding method and transform decoding used when encoding or decoding an image signal.

  In a conventional image coding system represented by the JPEG system and the MPEG video system, a screen is divided into predetermined units, and encoding is performed in the divided units. For example, in the MPEG-1 and MPEG-2 systems, motion compensation is performed in units of 16 horizontal pixels and 16 vertical pixels called macroblocks. The residual signal after motion compensation is subjected to discrete cosine transform (hereinafter abbreviated as DCT) in units of 8 horizontal pixels and 8 vertical pixels called blocks included in each macroblock in the screen, and conversion coefficients are obtained. By performing processing such as quantization, a final code string is obtained.

  On the other hand, in recent years, a matching pursuit (hereinafter abbreviated as MP) method has been proposed as a transform coding method for a low bit rate (Non-patent Document 1). In the MP system proposed in Non-Patent Document 1, when encoding a residual signal after motion compensation, a predetermined number of transform bases (non-orthogonal transform bases) are used, This is a method of encoding by repeating the process of placing one transformation base at a position.

Comparing DCT and MP, DCT has high encoding efficiency at a high bit rate, and MP has high encoding efficiency at a low bit rate. Therefore, in order to make use of the characteristics of both, a method of switching between DCT and MP in block units has been proposed (Non-Patent Document 2).
R. Neff et. Al., "Very Low Bit-Rate Video Coding Based on Matching Persuits", IEEE Trans. On Circuits and Systems for Video Technology, Vol. 7, No. 1, pp. 158-171, Feb. 1997 . S. Valente, "Video coding ecology using DCT and block-restricted matching pursuit," International Conference on Image Processing, 2003.

However, in the above conventional method, the conversion process is performed by dividing the entire image into rectangular blocks. When DCT is used, it is generally known that when information on different regions (different objects and different motions) exists in a DCT block, high frequency components increase, and thus encoding efficiency decreases.
The present invention solves the above-described conventional problems, and transform codes that can further improve the coding efficiency when divided into rectangular blocks and switched between DCT and MP for each block. It is an object to provide a conversion method and a conversion decoding method.

  In order to solve this problem, according to a first aspect of the present invention, an image signal composed of M regions and region information indicating the region are input, and a dividing step of dividing the image signal into image blocks; N (N ≧ 2) conversion steps for converting the code string into a code sequence, a selection step for selecting one code sequence from the N code sequences generated by the N conversion steps, and the selection step A code sequence generation step of synthesizing the selected code sequences and generating an output code sequence, wherein the N number of conversion steps determine a conversion basis function based on the region information and perform a conversion process 1 is a transform coding method characterized by including a transform step of 1 and a second transform step of performing transform processing by determining a transform basis function regardless of the region information.

  According to a second aspect of the present invention, a code string generated by encoding an image signal composed of M areas using N (N ≧ 2) conversion methods and area information indicating the area are input, and the code string is input. A code string dividing step for dividing the code string based on the information indicating the conversion method described therein, and reverse decoding the code string divided by the code string dividing step to obtain a decoded image N inverse transformation steps to be generated and a synthesis step for synthesizing the decoded image generated by the inverse transformation step, wherein the N inverse transformation steps determine transformation basis functions based on the region information And a first inverse transform step for performing an inverse transform process and a second inverse transform step for determining a transform basis function regardless of the region information and performing an inverse transform process. Is the method.

  As described above, in the transform coding method and transform decoding method of the present invention, when an image signal having region information is encoded, it is divided into blocks and encoded by two transform methods. The first transform method performs encoding by performing orthogonal transform for each region in the block, and the second transform method performs encoding by performing bi-orthogonal transform without dividing the block into regions (MP Encoding). Then, the block having the higher coding efficiency is selected for each block, and the code string is output. In general, the encoding efficiency of orthogonal transform increases when the encoding rate increases, and the encoding efficiency of bi-orthogonal transform increases when the encoding rate decreases. Also, when transform coding is applied to the residual signal after motion compensation, when there are many residual components, orthogonal transform has higher coding efficiency, and when there are few residual components, bi-orthogonal transform is more efficient. Encoding efficiency is increased. Therefore, by performing the above processing, a high encoding efficiency can be achieved at a wide range of encoding rates from a low encoding rate to a high encoding rate, and a conversion method having a high encoding efficiency according to block characteristics. Can be selected. In addition, in orthogonal transform, it is known that coding efficiency decreases when images of different regions fall within one block. However, by performing orthogonal transform for each region belonging to the same block, Encoding efficiency can be increased. Thus, the transform encoding method and transform decoding method of the present invention have high practical value.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
(Embodiment 1)
FIG. 1 is a block diagram of a moving picture coding apparatus 100 using the transform coding method of the present invention, in which a dividing unit 101, a first transform unit 102, a second transform unit 103, a selection unit 104, a code string The generating unit 105 is configured.

  The image signal and the area information are input to the dividing unit 101. Here, the image signal is a normal image signal or a residual signal after motion compensation. Examples of image signals and area information are shown in FIGS. 2 (a) and 2 (b). The area information is information indicating an area for each object, an area obtained by dividing the image signal at a moving boundary, and the like. Here, as shown in FIG. 2B, it is assumed that the area is divided into four areas 201 to 204.

  The dividing unit 101 divides the input image signal with a predetermined size. Here, the image signal is divided into block shapes, and is divided into blocks of horizontal N pixels × vertical N pixels. For example, N can take values of 4, 8, 16, and the like. The dividing unit 101 outputs the image signal P of each block to the first conversion unit 102 and the second conversion unit 103. Further, the area information R for each block is output to the first conversion means 102.

Processing in the first conversion unit 102 will be described.
FIG. 3 is a block diagram showing the configuration of the first conversion means 102. The first conversion means 102 includes a vertical direction conversion means 301, a horizontal direction conversion means 302, a vertical direction conversion base generation means 303, a horizontal direction conversion base generation means 304, a horizontal direction reverse conversion means 305, a vertical direction reverse conversion means 306, The variable length encoding unit 307, the quantization unit 308, and the inverse quantization unit 309 are configured.

  FIG. 2C is an enlarged view of the vicinity of the area 203 in FIG. 2B, and it is assumed that the vicinity of the area 203 is divided into blocks as indicated by a wavy line. Assume that the block 210 shown in FIG. 2C is input. Also, the area information in this case is shown in FIG. In FIG. 4A, each square indicates a pixel, which indicates a block of 8 horizontal pixels and 8 vertical pixels. Further, the white portion indicates the region 201 and the black portion indicates the region 203.

In the first conversion means 102, the pixels in the region 201 and the pixels in the region 203 in the block 210 are encoded separately. Here, a method for encoding the pixels in the region 203 will be described.
The vertical direction conversion base generation unit 303 generates a conversion base for obtaining a vertical conversion coefficient for the pixels in the area 203 in the block 210. In this case, the number of pixels belonging to the region 203 is counted for each column, and a conversion base is generated based on the result. For example, for column 401, since there are two pixels in region 203, the conversion base is determined with M = 2 in (Equation 1). For column 402, since there are seven pixels in region 203, the conversion base is determined as M = 7 in (Equation 1). Here, in (Equation 1), v is a frequency component in the vertical direction, and y is a spatial coordinate in the vertical direction in the block.

  Based on the region information R in the block, the vertical direction conversion unit 301 moves the encoding target pixel (the pixel in the region 203) in the vertical direction to the block end. In this case, FIG. 4B shows a block in which the encoding target pixel is moved to the block end in the vertical direction. Then, the vertical conversion base input from the vertical direction conversion base generation unit 303 is used to perform vertical conversion for each column to generate a conversion coefficient, which is output to the horizontal direction conversion unit 302. .

  The horizontal direction conversion base generation unit 304 determines a conversion base for obtaining a horizontal direction conversion coefficient. In this case, based on the region information R, the number of vertical direction conversion coefficients belonging to the region 203 is counted for each row in the state of FIG. 4B, and a conversion basis for each row is generated based on the result. For example, for the row 403, since there are five coefficients in the region 203, the conversion base is determined with M = 5 in (Equation 2). For column 404, since there is only one coefficient in region 203, the conversion base is determined with M = 1 in (Equation 2). In (Expression 2), u is a frequency component in the horizontal direction, and x indicates a spatial coordinate in the horizontal direction in the block.

  The horizontal direction conversion unit 302 moves the conversion coefficient block converted in the vertical direction to the block end in the horizontal direction based on the region information R. In this case, FIG. 4C shows a block obtained by moving the conversion coefficient converted in the vertical direction to the block end in the horizontal direction. Then, using the horizontal conversion base input from the horizontal conversion base generation unit 304, horizontal conversion is performed for each row to generate a two-dimensional conversion coefficient.

With the above processing, the horizontal direction conversion means 302 has obtained a two-dimensional conversion coefficient, and the coefficient in this case is the shaded portion in FIG. 4C.
The quantizing unit 308 performs a quantization process on the two-dimensional transform coefficient generated by the horizontal direction transform unit 302, and outputs a quantized transform coefficient block C1. Here, quantization refers to a process of dividing the transform coefficient by a predetermined value (quantized value). The quantization value may be different for each transform coefficient.

The inverse quantization means 309 performs inverse quantization processing and outputs the inversely quantized transform coefficients to the horizontal direction inverse transform means 305. Here, the inverse quantization refers to a process of adding the quantized value to the quantized transform coefficient.
The horizontal inverse transform unit 305 is input from the horizontal direction transform base generation unit 304 with respect to the transform coefficient block in the area 203 of the block 210 (the coefficient at this time is located at the shaded portion in FIG. 4C). Using the horizontal transformation base, horizontal transformation is performed for each row to generate an inverse transformation coefficient block.

  Based on the region information R, the vertical direction inverse transform unit 306 moves the coefficients in the horizontal direction based on the region information R with respect to the inverse transform coefficient block that has been inversely transformed in the horizontal direction. Then, using the vertical direction conversion base input from the vertical direction conversion base generation unit 303, vertical conversion is performed for each column to generate a two-dimensional inverse conversion coefficient (decoded pixel value). Finally, based on the region information R, the decoded pixel is moved in the vertical direction to obtain the state shown in FIG. This is output as a decoding block D1.

The variable length coding means 307 performs variable length coding on the transform coefficient block C1. In this case, as shown in FIG. 4 (d), the coefficients are made one-dimensionally from the low frequency coefficient to the high frequency coefficient, a continuous length of coefficient 0 and a non-zero coefficient value are created, and predetermined. A code string S1 is generated and output using a codebook or arithmetic coding. Also, the code amount B1 at this time is output.
In the above processing, the same processing is performed for the pixels in the area 201 in the block 210, thereby completing the processing of the first conversion unit 102 for the block 210. The code string of the block 210 generated in this case is as shown in FIG.

Subsequently, processing in the second conversion unit 103 will be described.
FIG. 5 is a block diagram showing the configuration of the second conversion means 103. The second transforming unit 103 includes a transforming unit 501, a quantizing unit 502, an inverse quantizing unit 503, an inverse transforming unit 504, a transform base group holding unit 505, and a variable length coding unit 506.
The conversion unit 501 receives the image signal P of each block. Here, it is assumed that the block 210 shown in FIG. In the second conversion unit 103, the pixels in the area 201 and the pixels in the area 203 in the block 210 are encoded without being distinguished.

  The processing target block (here, block 210) is input to the converting unit 501, and the converting unit 501 performs MP encoding on the processing target block. It is assumed that the conversion base used in the conversion unit 501 is held in the conversion base group holding unit 505. In MP encoding, bi-orthogonal basis functions are used. For example, an example of a bi-orthogonal basis function is a Gabor function.

A processing method in the processing of the second conversion means 103 will be described with reference to the flowchart of FIG.
In the flowchart of FIG. 6, an uncoded image signal (initial value is an input image signal) of a block is indicated by f (x, y). Further, the conversion base group holding unit 505 holds the conversion base group gk (x, y).
In step S601, n is set to 1 as an initial value. Thereafter, the processing from step S602 to step S604 is repeated until the end condition is satisfied.

  In step S602, the conversion unit 501 calculates an inner product value for each conversion basis gk ′ (x, y) for each position (dx, dy) in the block of the image signal f (x, y), and calculates the value. Let α (k, dx, dy). Here, the transformation basis gk ′ (x, y) is obtained by normalizing the norm value in the block with respect to the transformation basis group gk (x, y) held by the transformation basis group holding means 505. .

In step S603, the conversion means 501 obtains the maximum value from α (k, dx, dy), the position at that time is dn = (dnx, dny), the conversion base number is kn, and the inner product value is αn. To do. The position dn and the transformation base number kn are output to the variable length encoding unit 506 and the inner product value αn is output to the quantization unit 502.
In step S604, the quantization unit 502 performs a quantization process on the inner product value αn selected in step S603. Here, the quantization process refers to a process of dividing the inner product value αn by a predetermined quantization value. Let qn be the quantized inner product value.

In step S605, the inverse quantization means 503 performs an inverse quantization process on the quantized inner product value qn. Here, the inverse quantization process refers to a process for obtaining a product of the quantization value with respect to an input value. The inversely quantized inner product value is αn ′.
In step S606, the inverse conversion unit 504 obtains gkn (x + dnx, y + dny) × αn ′ and outputs it to the conversion unit 501 as f ′ (x, y). Further, f ′ (x, y) is cumulatively added to generate a decoded image signal.

In step S607, f ′ (x, y) is subtracted from f (x, y), and the uncoded image signal is updated.
In step 608, variable length coding is performed in the variable length coding means 506. The variable length encoding unit 506 outputs the position dn, the conversion base number kn output from the conversion unit 501, and the quantized inner product value qn output from the quantization unit 502. The code string is generated by performing variable length coding.

  As a first method of variable length coding, there is a method of describing in the code string in the order selected by the conversion means 501. By using this method, even when an error is detected during decoding of the code string on the decoding side, the influence on the image quality can be minimized. This is because the conversion unit 501 selects atoms in the order in which the energy of the residual signal can be minimized. An example of the format of the code string in this case is shown in FIG. At this time, as the atom information, a difference value from the previous value may be encoded. For example, a position difference, a base number difference, and an inner product value difference. Thereby, the encoding efficiency can be improved.

  As a second method of variable length coding, atoms are rearranged in a predetermined order based on the positional relationship within the block. The order includes raster order from the upper left to the lower right in the block. Then, the atom information is variable-length encoded in the rearranged order. FIG. 7C shows a code string format example in which the number of atoms and a set of conversion base numbers and inner product values corresponding to the number of atoms are described for each pixel position in the block. Also, for each pixel position in the block, only for the pixel position where an atom exists, a code string format example in which the number of atoms and a set of conversion base numbers and inner product values for the number of atoms are described As shown in FIG. In this case, the number of pixels from the current pixel position to the next pixel position where the atom exists is described. By using a variable-length coded sequence format as shown in FIGS. 7C and 7D, the amount of code of position information can be reduced, and coding efficiency can be improved.

  In step S609, it is determined whether an end condition is satisfied. As an end condition, for example, when the processes of steps S602 to S608 are performed a predetermined number of times (this can be determined by the value of n), or when the energy of the unencoded image signal falls below a predetermined value (this is (Determined when the energy of the unencoded image signal falls below a predetermined threshold value), when the generated code amount reaches a predetermined amount (this is the code amount of the code string generated by the variable length encoding means 506) (Determined based on the counting result) When the decrease value of the energy of the unencoded image signal by one encoding process with respect to the amount of information of 1 bit falls below a predetermined value (this is the energy and code of the unencoded image signal) The code amount of the column is determined from the counting result). If the end condition is not satisfied, n is incremented by 1 in step S610, and then the processing from step S602 is repeated. If the end condition is satisfied, the process of step 611 is performed.

In step 611, the decoded image signal generated by the inverse transform means 504 is output as D2. Also, the code string generated by the variable length coding means 506 is output as S2, and the code amount of the code string is output as B2.
The selection unit 104 includes an input image P of the processing target block, a decoded image D1 of the processing target block processed by the first conversion unit 102, a code string S1, a code amount B1, and a processing performed by the second conversion unit 103. The decoded image D2, the code string S2, and the code amount B2 of the processed block are input. Then, one of the code strings is selected.

As a first selection method, the error energy between the input image P of the processing target block and the decoded images D1 and D2 is obtained, and the one having the smaller error energy is selected.
As a second selection method, error energies between the input image P of the block to be processed and the decoded images D1 and D2 are obtained (referred to as E1 and E2, respectively), E1 + λB1 and E2 + λB2 are calculated, and their values are calculated. Select the smaller one. Here, λ is a weighting coefficient.

The selected code sequence S and selection information L indicating which one of the output of the first conversion unit 102 and the output of the second conversion unit 103 is selected are output to the code sequence generation unit 105. Is done.
In the code string generation means 105, the selection information L and the code string S are connected to form a code string of the processing target block. A format example of the code string is shown in FIG.

  As described above, in the transform encoding method of the present invention, when encoding an image signal having region information, the image signal is divided into blocks and encoded by two transform methods. The first transform method performs encoding by performing orthogonal transform for each region in the block, and the second transform method performs encoding by performing bi-orthogonal transform without dividing the block into regions (MP Encoding). Then, the block having the higher coding efficiency is selected for each block, and the code string is output.

  In general, the encoding efficiency of orthogonal transform increases when the encoding rate increases, and the encoding efficiency of bi-orthogonal transform increases when the encoding rate decreases. Also, when transform coding is applied to the residual signal after motion compensation, when there are many residual components, orthogonal transform has higher coding efficiency, and when there are few residual components, bi-orthogonal transform is more efficient. Encoding efficiency is increased. Therefore, by performing the above processing, a high encoding efficiency can be achieved at a wide range of encoding rates from a low encoding rate to a high encoding rate, and a conversion method having a high encoding efficiency according to block characteristics. Can be selected. In addition, in orthogonal transform, it is known that coding efficiency decreases when images of different regions fall within one block. However, by performing orthogonal transform for each region belonging to the same block, Encoding efficiency can be increased.

In the embodiment of the present invention, the discrete cosine transform base is used as the transform base of the first transform unit, but this may be another transform base. For example, other transform bases include transform bases such as discrete Fourier transform, discrete sine transform, and Hadamard transform.
In the embodiment of the present invention, the case where the transform coefficient is obtained for each area existing in the block has been described. For example, for an area having a small number of pixels existing in the block, It is not necessary to obtain the conversion coefficient. This is because if the number of pixels in the area existing in the block is small, the image quality degradation is considered to be small even if the coding is not performed for each area, and the code amount can be reduced by not obtaining the conversion coefficient of the area. This is because it can. In order to perform such processing, a threshold for the number of pixels is set, and if the number of pixels in a certain area in the block is equal to or greater than the threshold, conversion processing is performed. If there is, conversion processing is not performed. In this case, how to process each block by setting a threshold value in advance on the encoding side and the decoding side, or describing the threshold value in the code string depends on the region. It can be automatically determined from the information.

  In the embodiment of the present invention, the case has been described where one of the first conversion unit 102 and the second conversion unit 103 is selected and processed for each block. Only the luminance component may be performed, and the color difference component may be encoded using only the first conversion unit 102 or the second conversion unit 103. This is because the color difference component has a characteristic that image quality deterioration is less noticeable than the luminance component, and the processing amount can be reduced.

  Further, in the embodiment of the present invention, each block is processed using two conversion units of the first conversion unit 102 and the second conversion unit 103, and a conversion unit with high coding efficiency is selected. However, there may be three or more conversion means. For example, as the third transforming unit, a method of transforming the entire block by orthogonal transform such as discrete cosine transform without considering the region in the block can be used. As a result, the processing amount is further increased, but the encoding efficiency can be further improved.

  In the present embodiment, the second conversion unit 103 has described the case where the conversion unit 501 performs the conversion process using the conversion base group held by the conversion base group holding unit 505. The variable length coding method for atom information may be adaptively converted according to the selection frequency of the conversion base in the conversion means 501. For example, the selection unit 104 sends selection information L indicating which one of the code strings generated by the selection unit 104 generated by the first conversion unit 102 and the second conversion unit 103 to the second conversion unit 103. Output. The second conversion unit 103 receives the selection information L by the variable length encoding unit 506, and when the code sequence generated by the second conversion unit 103 is selected, the second conversion unit 103 is used to generate the code sequence. Count the converted base number of the atom. This operation is performed for a predetermined period (for example, one frame period), and for a conversion base number that is selected a large number of times within that period, an encoding method and an encoding table are set so that the code length is shortened in the next period. Change adaptively. In this process, the conversion base number is counted for each block, and an encoding method or encoding is performed on a block-by-block basis using a cumulative value for a predetermined period (for example, one frame, from the frame head to the sequence head). The table may be changed adaptively. By performing such processing, the encoding method and the encoding table are adaptively changed according to the temporally adjacent frames and the distribution of the transform base numbers used in the current frame. A shorter code can be assigned to a transform base number that is highly likely to be selected when coding a block, and the overall code amount can be reduced. In addition, since the conversion base number used is counted only when the selection unit 104 selects the code sequence generated by the second conversion unit 103, the encoding method and the encoding table can be changed in the code sequence. It is not necessary to describe whether it has been changed, and a code for additional information is not necessary. In addition, when encoding is performed while changing the variable length coding method and the variable length coding table adaptively, the variable length coding method and the variable length coding table are periodically reinitialized. Also good. In addition, a flag indicating whether or not encoding is performed while changing the variable length encoding method or the variable length encoding table may be described adaptively in the header of the code string. As a result, an error occurs during transmission of the code string, and when the code string is decoded halfway (for example, from the beginning of the next frame), the decoding is stopped until the reinitialized frame, By restarting decoding from the initialized frame, the decoding process can be performed correctly.

  Further, in the embodiment of the present invention, the case where each block is encoded using the first conversion method and the second conversion method has been described, but this is performed only for the luminance component of the color image signal, The color difference component may be encoded using only one conversion method. This is because the color difference component has a characteristic that image quality deterioration is less noticeable than the luminance component, and the code amount can be reduced by using only one conversion method for the color difference component. However, image quality degradation can be minimized. FIG. 9 shows the configuration of the encoding apparatus in this case. FIG. 9 shows a configuration in the case where the color difference component is processed by the first conversion means 102.

(Embodiment 2)
FIG. 10 is a block diagram of the moving picture decoding apparatus 1000 using the transform decoding method of the present invention. The code sequence separating means 1001, the first inverse transform means 1002, the second inverse transform means 1003, and the synthesis means 1004 are shown. Consists of

  The code string is input to the code string separation unit 1001. Here, it is assumed that a code string generated by a moving picture coding apparatus using the transform coding method of the present invention described in Embodiment 1 is input. As shown in FIG. 8, it is assumed that the code string is composed of a combination of the selection information L and the code string S of the block for each block. The code string separation unit 1001 decodes the selection information L to determine whether the code string S of the block is generated by the first conversion method or the second conversion method. When the code sequence S of the block is generated by the first conversion method, the code sequence S of the block is output to the first inverse conversion unit 1002. If the code sequence S of the block is generated by the second conversion method, the block code sequence S is output to the second inverse conversion means 1003.

Processing in the first inverse transform unit 1002 will be described.
FIG. 11 is a block diagram showing the configuration of the first inverse conversion means 1002. The first inverse transform unit 1002 includes a variable length decoding unit 1101, an inverse quantization unit 1102, a horizontal direction inverse transform unit 1103, a vertical direction inverse transform unit 1104, a synthesis unit 1105, a vertical direction transform base generation unit 1107, a horizontal direction. It comprises conversion base generation means 1106.

  It is assumed that the variable length decoding unit 1101 receives a code string having the format shown in FIG. Here, it is assumed that the code string of the block 210 is input. The variable length decoding unit 1101 converts the input code string into a transform coefficient for each region (region 201 and region 203), and outputs it to the inverse quantization unit 1102. At this time, it can be obtained from the region information whether the code string of a plurality of regions exists in the block and how many code sequences are present when the code sequences of a plurality of regions exist. .

Inverse quantization means 1102 performs inverse quantization processing, and the inversely quantized transform coefficients are output to horizontal inverse transform means 1103. Here, the inverse quantization refers to a process of adding the quantized value to the quantized transform coefficient.
The horizontal reverse conversion unit 1103 performs reverse conversion on the conversion coefficients of the area 201 and the area 203 of the block 210. For example, in the case of the transform coefficient of the area 203, the horizontal direction transform base generation means 1106 is used with respect to the transform coefficient block of the area 203 of the block 210 (the coefficient at this time is located at the shaded portion in FIG. 4C). Using the input horizontal transformation base (generated using (Equation 2)), horizontal transformation is performed for each row to generate an inverse transformation coefficient block.

  Based on the region information R, the vertical inverse transform unit 1104 moves the coefficients in the horizontal direction based on the region information R with respect to the inverse transform coefficient block that has been inversely transformed in the horizontal direction. Then, using the vertical conversion base (generated using (Equation 1)) input from the vertical direction conversion base generation means 1107, vertical conversion is performed for each column, and a two-dimensional inverse conversion coefficient ( (Decoded pixel value) is generated. Finally, based on the region information R, the decoded pixel is moved in the vertical direction to obtain the state shown in FIG. Decoded pixels are generated for the synthesis unit 1105.

The synthesizing unit 1105 synthesizes the decoded pixels of the respective areas in the block (in the case of the block 210, the decoded pixels of the area 201 and the area 203) and outputs the result as a decoded block D1.
A process in the second inverse transform unit 1003 will be described.
FIG. 12 is a block diagram showing the configuration of the second inverse transform unit 1003, which includes a variable length decoding unit 1201, an inverse quantization unit 1202, an inverse transform unit 1203, and a transform base group holding unit 1204.

  It is assumed that the variable-length decoding unit 1201 is input with a code string in the format shown in FIG. 7B, FIG. 7C, or FIG. Variable length decoding means 1201 performs variable length decoding on the input code string. For example, when the code string is in the format of FIG. 7B, after decoding the number of atoms for each block, information on each atom (position information, conversion base number, inner product value) is sequentially decoded. . If the code string has the format shown in FIG. 7C, the number of atoms for each pixel position in the block is decoded, and then information on each atom (conversion base number, inner product value) is sequentially decoded. Go. If the code string has the format shown in FIG. 7D, after decoding the number of atoms for each pixel position in the block, the information (transformation base number, inner product value) of each atom is decoded in order. Go. In this case, the pixel position is increased by 1 in the case of the format of FIG. 7C, but is increased by the number of pixels described in the code string in the case of the format of FIG. 7D. To go. The decoded position information dn (= (dnx, dny)) and the transform base number kn are output to the inverse transform unit 1203, and the quantized inner product value qn is output to the inverse quantizer 1202. .

The inverse quantization means 1202 performs an inverse quantization process on the quantized inner product value qn. Here, the inverse quantization process refers to a process for obtaining a product of an input value and a quantized value. The inversely quantized inner product value αn ′ is output to the inverse transform means 1203.
The conversion base group holding unit 1204 generates and holds the conversion base group gk (x, y) used in the inverse conversion unit 1203. Here, it is assumed that the inverse transform unit 1203 performs MP decoding, and bi-orthogonal basis functions are used in MP coding. For example, an example of a bi-orthogonal basis function is a Gabor function.

The inverse transforming unit 1203 obtains gkn ′ (x + dnx, y + dny) × αn ′ and cumulatively adds it to generate a decoded image signal. Here, the transformation basis gk ′ (x, y) is obtained by normalizing the norm value in the block with respect to the transformation basis group gk (x, y) held by the transformation basis group holding means 1204. . The decoded image signal is output as a decoded block D2.
The synthesizing unit 1004 selects the decoded block D1 output from the first inverse transform unit 1002 and the decoded block D2 output from the second inverse transform unit 1003 from the selection information L output from the code string separation unit 1001. Based on the above, synthesis is performed in units of blocks, and a decoded image frame is generated and output.

  As described above, in the transform decoding method of the present invention, when encoding an image signal having region information, a code string divided into blocks and encoded by two transform methods is input, Based on the transform coding method described in the column, the transform decoding method (inverse transform method) is switched in units of blocks. The first inverse transform method performs decoding by performing inverse orthogonal transform for each region in the block, and the second inverse transform method performs decoding by performing biorthogonal transform without dividing the block into regions. (MP decoding). Then, the decoded blocks are combined to generate a decoded frame.

Therefore, by using the transform decoding method of the present invention, the code string generated using the transform coding method of the present invention can be correctly decoded.
In the embodiment of the present invention, the discrete cosine transform base is used as the transform base of the first inverse transform unit. However, this may be another transform base. For example, other transform bases include transform bases such as discrete Fourier transform, discrete sine transform, and Hadamard transform.

  Further, in the embodiment of the present invention, the case where the transform coefficient is obtained for each area existing in the block has been described. For example, for an area where the number of pixels existing in the block is small, The conversion coefficient for that region may not be obtained. In this case, a threshold value for the number of pixels is set, and if the number of pixels in a certain area in the block is equal to or greater than the threshold value, the inverse conversion process is performed. Do not give it. In this case, how to process each block by setting a threshold value in advance on the encoding side and the decoding side, or describing the threshold value in the code string depends on the region. It can be automatically determined from the information.

In the embodiment of the present invention, the case has been described where processing is performed using either the first inverse transform unit 1002 or the second inverse transform unit 1003 for each block. Only the luminance component may be performed, and the color difference component may be decoded using only the first inverse conversion unit 1002 or the second inverse conversion unit 1003.
In the embodiment of the present invention, the case has been described in which each block is processed using the two inverse transform units of the first inverse transform unit 1002 and the second inverse transform unit 1003. There may be more than two. For example, as the third inverse transform means, a method of transforming the entire block by inverse orthogonal transform such as discrete cosine transform without considering the area in the block can be used. This may be the same as the processing on the encoding side.

  Further, in the present embodiment, a case has been described in which the second inverse transform unit 1003 performs the inverse transform process by the inverse transform unit 1203 using the transform base group retained by the transform base group retaining unit 1204. However, in this case, the variable length decoding unit 1201 may adaptively convert the variable length decoding method for the atom information according to the appearance frequency of the conversion base in the code string. For example, the variable length decoding unit 1201 counts the conversion base number of the atom obtained by decoding the code string. This operation is performed for a predetermined period (for example, one frame period), and for a transform base number that is selected a large number of times within that period, a decoding method and a decoding table are set so that the code length is shortened in the next period. Change adaptively. In this process, the conversion base number is counted for each block, and the decoding method or decoding is performed on a block-by-block basis using a cumulative value for a predetermined period (for example, one frame, from the frame head to the sequence head). The table may be changed adaptively. In addition, when decoding is performed while changing the variable length decoding method and the variable length decoding table adaptively in this way, the variable length decoding method and the variable length decoding table are periodically reinitialized. Also good. In addition, when a flag indicating whether or not encoding is performed while adaptively changing the variable length coding method or variable length coding table on the encoding side is described in the header of the code string, the flag is referred to. The variable length decoding method and the variable length decoding table may be reinitialized. As a result, an error occurs during transmission of the code string, and when the code string is decoded halfway (for example, from the beginning of the next frame), the decoding is stopped until the reinitialized frame, By restarting decoding from the initialized frame, the decoding process can be performed correctly.

  In the embodiment of the present invention, the case where each block is encoded using the first inverse transformation method and the second inverse transformation method has been described, but this is only for the luminance component of the color image signal. The color difference component may be decoded using only one inverse transformation method. In this case, for example, the code string separation unit 1001 may always output the color difference component code string to the first inverse conversion unit 1002.

(Embodiment 3)
Further, the program for realizing the transform encoding method and transform decoding method shown in each of the above embodiments is recorded on a recording medium such as a flexible disk, thereby showing the above embodiments. Processing can be easily performed in an independent computer system.

FIG. 13 is an explanatory diagram in a case where the transform coding method and the transform decoding method of each of the above embodiments are implemented by a computer system using a program recorded on a recording medium such as a flexible disk.
FIG. 13B shows an appearance, a cross-sectional structure, and a flexible disk when viewed from the front of the flexible disk, and FIG. 13A shows an example of a physical format of the flexible disk that is a recording medium body. The flexible disk FD is built in the case F, and on the surface of the disk, a plurality of tracks Tr are formed concentrically from the outer periphery toward the inner periphery, and each track is divided into 16 sectors Se in the angular direction. ing. Therefore, in the flexible disk storing the program, the program is recorded in an area allocated on the flexible disk FD.

  FIG. 13C shows a configuration for recording and reproducing the program on the flexible disk FD. When the program for realizing the transform encoding method and transform decoding method is recorded on the flexible disk FD, the program is written from the computer system Cs via the flexible disk drive. When the above-described transform encoding method and transform decoding method for realizing the transform encoding method and transform decoding method by a program in a flexible disk are built in a computer system, the program is read from the flexible disk by a flexible disk drive. Transfer to computer system.

  In the above description, a flexible disk is used as the recording medium, but the same can be done using an optical disk. Further, the recording medium is not limited to this, and any recording medium such as an IC card or a ROM cassette capable of recording a program can be similarly implemented.

(Embodiment 4)
Furthermore, application examples of the transform coding method and transform decoding method shown in the above embodiment and a system using the same will be described.

FIG. 14 is a block diagram showing an overall configuration of a content supply system ex100 that implements a content distribution service. The communication service providing area is divided into desired sizes, and base stations ex107 to ex110, which are fixed radio stations, are installed in each cell.
The content supply system ex100 includes, for example, a computer ex111, a PDA (personal digital assistant) ex112, a camera ex113, a mobile phone ex114, a camera via the Internet ex101, the Internet service provider ex102, the telephone network ex104, and the base stations ex107 to ex110. Each device such as the attached mobile phone ex115 is connected.

However, the content supply system ex100 is not limited to the combination as shown in FIG. 14, and any of the combinations may be connected. Further, each device may be directly connected to the telephone network ex104 without going through the base stations ex107 to ex110 which are fixed wireless stations.
The camera ex113 is a device capable of shooting a moving image such as a digital video camera. The mobile phone is a PDC (Personal Digital Communications) system, a CDMA (Code Division Multiple Access) system, a W-CDMA (Wideband-Code Division Multiple Access) system, or a GSM (Global System for Mobile Communications) system mobile phone, Alternatively, PHS (Personal Handyphone System) or the like may be used.

  In addition, the streaming server ex103 is connected from the camera ex113 through the base station ex109 and the telephone network ex104, and live distribution or the like based on the encoded data transmitted by the user using the camera ex113 becomes possible. The encoded processing of the captured data may be performed by the camera ex113 or may be performed by a server or the like that performs data transmission processing. Further, the moving image data shot by the camera 116 may be transmitted to the streaming server ex103 via the computer ex111. The camera ex116 is a device that can shoot still images and moving images, such as a digital camera. In this case, the encoding of the moving image data may be performed by the camera ex116 or the computer ex111. The encoding process is performed in the LSI ex117 included in the computer ex111 and the camera ex116. Note that image encoding / decoding software may be incorporated into any storage medium (CD-ROM, flexible disk, hard disk, etc.) that is a recording medium readable by the computer ex111 or the like. Furthermore, you may transmit moving image data with the mobile telephone ex115 with a camera. The moving image data at this time is data encoded by the LSI included in the mobile phone ex115.

  In this content supply system ex100, the content (for example, video shot of music live) captured by the user with the camera ex113, camera ex116, etc. is encoded and transmitted to the streaming server ex103 as in the above embodiment. On the other hand, the streaming server ex103 distributes the content data to the requested client. Examples of the client include a computer ex111, a PDA ex112, a camera ex113, a mobile phone ex114, and the like that can decode the encoded data. In this way, the content supply system ex100 can receive and reproduce the encoded data at the client, and also realize personal broadcasting by receiving, decoding, and reproducing in real time at the client. It is a system that becomes possible.

The image encoding device or the image decoding device described in the above embodiments may be used for encoding and decoding of each device constituting this system.
A mobile phone will be described as an example.
FIG. 15 is a diagram showing the mobile phone ex115 using the transform coding method and transform decoding method described in the above embodiment. The cellular phone ex115 includes an antenna ex201 for transmitting and receiving radio waves to and from the base station ex110, a camera such as a CCD camera, a camera unit ex203 capable of taking a still image, a video shot by the camera unit ex203, and an antenna ex201. A display unit ex202 such as a liquid crystal display that displays data obtained by decoding received video and the like, a main body unit composed of a group of operation keys ex204, an audio output unit ex208 such as a speaker for audio output, and audio input To store encoded data or decoded data such as a voice input unit ex205 such as a microphone, captured video or still image data, received mail data, video data or still image data, etc. Recording medium ex207, and slot portion ex20 for enabling recording medium ex207 to be attached to mobile phone ex115 The it has. The recording medium ex207 stores a flash memory element which is a kind of EEPROM (Electrically Erasable and Programmable Read Only Memory) which is a nonvolatile memory that can be electrically rewritten and erased in a plastic case such as an SD card.

  Further, the cellular phone ex115 will be described with reference to FIG. The cellular phone ex115 controls the power supply circuit ex310, the operation input control unit ex304, and the image coding for the main control unit ex311 which is configured to control the respective units of the main body unit including the display unit ex202 and the operation key ex204. Unit ex312, camera interface unit ex303, LCD (Liquid Crystal Display) control unit ex302, image decoding unit ex309, demultiplexing unit ex308, recording / reproducing unit ex307, modulation / demodulation circuit unit ex306, and audio processing unit ex305 via a synchronization bus ex313 Are connected to each other.

When the end call and power key are turned on by a user operation, the power supply circuit ex310 activates the camera-equipped digital mobile phone ex115 by supplying power from the battery pack to each unit. .
The mobile phone ex115 converts the voice signal collected by the voice input unit ex205 in the voice call mode into digital voice data by the voice processing unit ex305 based on the control of the main control unit ex311 including a CPU, a ROM, a RAM, and the like. The modulation / demodulation circuit unit ex306 performs spread spectrum processing, and the transmission / reception circuit unit ex301 performs digital analog conversion processing and frequency conversion processing, and then transmits the result via the antenna ex201. In addition, the cellular phone ex115 amplifies the received signal received by the antenna ex201 in the voice call mode, performs frequency conversion processing and analog-digital conversion processing, performs spectrum despreading processing by the modulation / demodulation circuit unit ex306, and analog audio by the voice processing unit ex305. After conversion into a signal, this is output via the audio output unit ex208.

  Further, when an e-mail is transmitted in the data communication mode, text data of the e-mail input by operating the operation key ex204 of the main body is sent to the main control unit ex311 via the operation input control unit ex304. The main control unit ex311 performs spread spectrum processing on the text data in the modulation / demodulation circuit unit ex306, performs digital analog conversion processing and frequency conversion processing in the transmission / reception circuit unit ex301, and then transmits the text data to the base station ex110 via the antenna ex201.

  When transmitting image data in the data communication mode, the image data captured by the camera unit ex203 is supplied to the image encoding unit ex312 via the camera interface unit ex303. When image data is not transmitted, the image data captured by the camera unit ex203 can be directly displayed on the display unit ex202 via the camera interface unit ex303 and the LCD control unit ex302.

  The image encoding unit ex312 has a configuration including the image encoding device described in the present invention, and an encoding method using the image data supplied from the camera unit ex203 in the image encoding device described in the above embodiment. The encoded image data is converted into encoded image data by compression encoding, and sent to the demultiplexing unit ex308. At the same time, the cellular phone ex115 sends the sound collected by the audio input unit ex205 during imaging by the camera unit ex203 to the demultiplexing unit ex308 as digital audio data via the audio processing unit ex305.

  The demultiplexing unit ex308 multiplexes the encoded image data supplied from the image encoding unit ex312 and the audio data supplied from the audio processing unit ex305 by a predetermined method, and the multiplexed data obtained as a result is a modulation / demodulation circuit unit A spectrum spread process is performed in ex306, a digital analog conversion process and a frequency conversion process are performed in the transmission / reception circuit unit ex301, and then the signal is transmitted through the antenna ex201.

When receiving data of a moving image file linked to a home page or the like in the data communication mode, the received signal received from the base station ex110 via the antenna ex201 is subjected to spectrum despreading processing by the modulation / demodulation circuit unit ex306, and the resulting multiplexing is obtained. Is sent to the demultiplexing unit ex308.
In addition, in order to decode the multiplexed data received via the antenna ex201, the demultiplexing unit ex308 separates the multiplexed data to generate an encoded bitstream of image data and an encoded bitstream of audio data. The encoded image data is supplied to the image decoding unit ex309 via the synchronization bus ex313, and the audio data is supplied to the audio processing unit ex305.

  Next, the image decoding unit ex309 is configured to include the image decoding device described in the present invention, and a decoding method corresponding to the encoding method described in the above embodiment for an encoded bit stream of image data. To generate playback moving image data, which is supplied to the display unit ex202 via the LCD control unit ex302, thereby displaying, for example, moving image data included in the moving image file linked to the homepage . At the same time, the audio processing unit ex305 converts the audio data into an analog audio signal, and then supplies the analog audio signal to the audio output unit ex208. Thus, for example, the audio data included in the moving image file linked to the home page is reproduced. The

  Note that the present invention is not limited to the above-described system, and recently, digital broadcasting by satellite and terrestrial has become a hot topic, and as shown in FIG. Any of the decoding devices can be incorporated. Specifically, in the broadcasting station ex409, the encoded bit stream of the video information is transmitted to the communication or broadcasting satellite ex410 via radio waves. Receiving this, the broadcasting satellite ex410 transmits a radio wave for broadcasting, and receives the radio wave with a home antenna ex406 having a satellite broadcasting receiving facility, such as a television (receiver) ex401 or a set top box (STB) ex407. The device decodes the encoded bit stream and reproduces it. In addition, the image decoding apparatus described in the above embodiment can also be implemented in a playback apparatus ex403 that reads and decodes an encoded bitstream recorded on a storage medium ex402 such as a CD or DVD that is a recording medium. is there. In this case, the reproduced video signal is displayed on the monitor ex404. Further, a configuration in which an image decoding device is mounted in a set-top box ex407 connected to a cable ex405 for cable television or an antenna ex406 for satellite / terrestrial broadcasting, and this is reproduced on the monitor ex408 of the television is also conceivable. At this time, the image decoding apparatus may be incorporated in the television instead of the set top box. In addition, a car ex412 having an antenna ex411 can receive a signal from a satellite ex410 or a base station ex107 and the like, and a moving image can be reproduced on a display device such as a car navigation ex413 that the car ex412 has.

  Further, the image signal can be encoded by the image encoding device shown in the above embodiment and recorded on a recording medium. As a specific example, there is a recorder ex420 such as a DVD recorder that records an image signal on a DVD disk ex421 or a disk recorder that records on a hard disk. Further, it can be recorded on the SD card ex422. If the recorder ex420 includes the image decoding device described in the above embodiment, the image signal recorded on the DVD disc ex421 or the SD card ex422 can be reproduced and displayed on the monitor ex408.

For example, the configuration of the car navigation ex413 may be a configuration excluding the camera unit ex203, the camera interface unit ex303, and the image encoding unit ex312 in the configuration illustrated in FIG. 16, and the same applies to the computer ex111 and the television (receiver). ) Ex401 can also be considered.
In addition to the transmission / reception type terminal having both the encoder and the decoder, the terminal such as the mobile phone ex114 has three mounting formats: a transmitting terminal having only an encoder and a receiving terminal having only a decoder. Can be considered.

As described above, the transform coding method and transform decoding method shown in the above embodiment can be used in any of the above-described devices / systems, and as a result, the effects described in the above embodiment can be achieved. Can be obtained.
It should be noted that the present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the scope of the present invention.

  The transform coding method and transform decoding method according to the present invention, when coding an image signal having region information, divides into block units, performs coding by two transform methods, and performs coding efficiency for each block. By selecting the higher one, the encoding efficiency can be improved, which is useful as a transform encoding method and transform decoding method in storage, transmission, communication, and the like.

1 is a block diagram (Embodiment 1) showing the configuration of a transform coding apparatus using the transform coding method of the present invention. It is a schematic diagram (Embodiment 1) which shows the image signal and area | region information for demonstrating the transform coding method of this invention. It is a block diagram (Embodiment 1) which shows the structure of the 1st conversion means in the conversion coding apparatus of this invention. It is a schematic diagram (Embodiment 1) for demonstrating operation | movement of the 1st conversion means in the conversion coding apparatus of this invention. It is a block diagram (Embodiment 1) which shows the structure of the 2nd conversion means in the conversion coding apparatus of this invention. It is a flowchart (Embodiment 1) which shows the operation | movement of the 2nd conversion means in the conversion coding apparatus of this invention. It is a schematic diagram (Embodiment 1) which shows the structural example of the code sequence produced | generated by the conversion coding apparatus of this invention. It is a schematic diagram (Embodiment 1) which shows the structural example of the code sequence produced | generated by the conversion coding apparatus of this invention. It is a block diagram (Embodiment 1) which shows the modification of the transform coding apparatus using the transform coding method of this invention. It is a block diagram (Embodiment 2) which shows the structure of the transform decoding apparatus using the transform decoding method of this invention. It is a block diagram (Embodiment 2) which shows the structure of the 1st reverse conversion means in the conversion decoding apparatus of this invention. It is a block diagram (Embodiment 2) which shows the structure of the 2nd reverse conversion means in the conversion decoding apparatus of this invention. It is explanatory drawing (Embodiment 3) about the recording medium for storing the program for implement | achieving the conversion encoding method and conversion decoding method of said each embodiment by a computer system. FIG. 10 is a block diagram showing the overall configuration of a content supply system (Embodiment 4). It is an example (Embodiment 4) of the mobile phone using the transform coding method and transform decoding method. FIG. 10 is a block diagram of a mobile phone (Embodiment 4). It is an example (Embodiment 4) of the system for digital broadcasting.

Explanation of symbols

101 Separation Unit 102 First Conversion Unit 103 Second Conversion Unit 104 Selection Unit 105 Code String Generation Unit 1001 Code String Separation Unit 1002 First Inverse Conversion Unit 1003 Second Inverse Conversion Unit 1004 Synthesis Unit Cs Computer System FD Flexible disk FDD Flexible disk drive

Claims (21)

With an image signal composed of M areas and area information indicating the areas as inputs,
A dividing step of dividing the image signal into image blocks;
N (N ≧ 2) conversion steps for converting the image block into a code string;
A selection step of selecting one code sequence from the N code sequences generated by the N conversion steps;
A code string generation step of synthesizing the code strings selected in the selection step and generating an output code string;
The N conversion steps include a first conversion step that determines a conversion basis function based on the region information and performs conversion processing, and a first conversion step that determines a conversion basis function regardless of the region information and performs conversion processing. A transform encoding method characterized by comprising two transform steps. 2. The transform coding method according to claim 1, wherein in the code string generation step, an identifier of the code string selected in the selection step is described. The first conversion step includes:
A transform basis determination step for generating a transform basis function based on region information in the block;
The transform coding method according to claim 1, further comprising: a transform step of transforming the pixel value of the block into a transform coefficient using the transform basis function generated by the transform basis determining step. In the second conversion step,
The image signal in the block is expressed by a linear sum of conversion bases selected from a predetermined conversion base group, and the conversion base number, the pixel position in the block in which the conversion base is arranged, and the conversion base are added. The transform encoding method according to claim 1, wherein the weight at the time is described in the code string. In the second conversion step,
The number of the said conversion base, the position in the block which arrange | positions the said conversion base, and the weight at the time of adding the said conversion base are described in a code sequence in the order which selected the said conversion base. Transform coding method. In the second conversion step,
5. The transform coding method according to claim 4, wherein a number of the transform base and a weight for adding the transform base are described in a code sequence in a predetermined pixel order in the block. In the second conversion step,
When the code sequence of the second conversion step is selected by the selection step, the number of the conversion base selected when generating the code sequence is counted, and the code of the number of the conversion base is counted according to the count result The transform encoding method according to claim 4, wherein the conversion method is changed. In the second conversion step,
When the code sequence of the second conversion step is selected by the selection step, the number of the conversion base selected when generating the code sequence is counted, and the code of the number of the conversion base is counted according to the count result Change the conversion method,
In the code string generation step,
The transform coding method according to claim 4, wherein the second transform step describes information indicating that the transform base number coding method has been changed in the code string. A code string generated by encoding an image signal composed of M regions using N (N ≧ 2) conversion methods and region information indicating the region are input,
A code string dividing step of dividing the code string based on information indicating the conversion method described in the code string;
N inverse transform steps for performing inverse transform on the code string divided by the code string dividing step to generate a decoded image;
Combining a decoded image generated by the inverse conversion step,
The N inverse transform steps include a first inverse transform step that performs a transform process by determining a transform basis function based on the region information, and a transform basis function that determines a transform basis function regardless of the region information. A transform decoding method comprising: a second inverse transform step for performing processing. The transform decoding method according to claim 9, wherein in the code string dividing step, the code string is divided based on an identifier described in the code string. The first inverse transformation step includes:
A transform basis determination step for generating a transform basis function based on region information in the block;
The transform decoding method according to claim 9, further comprising: an inverse transform step of transforming transform coefficients of the block into pixel values using the transform basis function generated by the transform basis determining step. In the second inverse transformation step,
The decoded image is generated based on a number of the conversion base described in the code string, a position in a block where the conversion base is arranged, and a weight when adding the conversion base. Item 10. The transform decoding method according to Item 9. In the second inverse transformation step,
13. The decoded image is generated by adding the decoded number of the conversion base and the weight for adding the conversion base based on the position in the block in which the conversion base is arranged. Conversion decoding method. In the second inverse transformation step,
13. The transform decoding method according to claim 12, wherein the decoded image is generated by adding the decoded transform base number and the weight for adding the transform base in a predetermined pixel order in the block. In the second inverse transformation step,
13. The transform decoding method according to claim 12, wherein the number of the transform base selected when generating the code string is counted, and the decoding method of the transform base number is changed according to the count result. . In the second inverse transformation step,
Information indicating whether the code string was generated while changing the encoding method of the conversion base number is acquired from the code string, and the code string is generated while changing the encoding method of the conversion base number When the code base is generated, the number of the transform base selected when generating the code string is counted, and the decoding method of the transform base number is changed according to the count result. 12. The transform decoding method according to 12. A program for performing the transform encoding method according to claim 1 by a computer,
The above program is stored on the computer.
With an image signal composed of M areas and area information indicating the areas as inputs,
A dividing step of dividing the image signal into image blocks;
N (N ≧ 2) conversion steps for converting the image block into a code string;
A selection step of selecting one code sequence from the N code sequences generated by the N conversion steps;
Synthesizing the code strings selected in the selection step, and generating a code string generation step for generating an output code string;
The N conversion steps include a first conversion step that determines a conversion basis function based on the region information and performs conversion processing, and a first conversion step that determines a conversion basis function regardless of the region information and performs conversion processing. And a conversion step. A program for performing the conversion decoding method according to claim 9 by a computer,
The above program is stored on the computer.
A code string generated by encoding an image signal composed of M regions using N (N ≧ 2) conversion methods and region information indicating the region are input,
A code string dividing step of dividing the code string based on information indicating the conversion method described in the code string;
N inverse transform steps for performing inverse transform on the code string divided by the code string dividing step to generate a decoded image;
Performing a synthesizing step of synthesizing the decoded image generated by the inverse transformation step;
The N inverse transform steps include a first inverse transform step that performs a transform process by determining a transform basis function based on the region information, and a transform basis function that determines a transform basis function regardless of the region information. And a second inverse conversion step for performing processing. A recording medium storing data, wherein the data is
With an image signal composed of M areas and area information indicating the areas as inputs,
A dividing step of dividing the image signal into image blocks;
N (N ≧ 2) conversion steps for converting the image block into a code string;
A selection step of selecting one code sequence from the N code sequences generated by the N conversion steps;
Generated by the code sequence generation step of synthesizing the code sequences selected in the selection step and generating an output code sequence;
The recording medium, wherein the data describes an identifier of a code string selected in the selection step in the code string generation step. A recording medium storing data, wherein the data is
With an image signal composed of M areas and area information indicating the areas as inputs,
A dividing step of dividing the image signal into image blocks;
N (N ≧ 2) conversion steps for converting the image block into a code string;
A selection step of selecting one code sequence from the N code sequences generated by the N conversion steps;
Generated by the code sequence generation step of synthesizing the code sequences selected in the selection step and generating an output code sequence;
The N conversion steps represent an image signal in the block by a linear sum of conversion bases selected from a predetermined conversion base group, the number of the conversion base, and the pixel in the block in which the conversion base is arranged. A conversion step for describing a position, a weight for adding the conversion bases in a code string,
The data describes the number of the conversion base, the position in the block in which the conversion base is arranged, and the weight for adding the conversion base in the order in which the conversion bases are selected. . A recording medium storing data, wherein the data is
With an image signal composed of M areas and area information indicating the areas as inputs,
A dividing step of dividing the image signal into image blocks;
N (N ≧ 2) conversion steps for converting the image block into a code string;
A selection step of selecting one code sequence from the N code sequences generated by the N conversion steps;
Generated by the code sequence generation step of synthesizing the code sequences selected in the selection step and generating an output code sequence;
The N conversion steps represent an image signal in the block by a linear sum of conversion bases selected from a predetermined conversion base group, the number of the conversion base, and the pixel in the block in which the conversion base is arranged. A conversion step for describing a position, a weight for adding the conversion bases in a code string,
The recording medium is characterized in that the data describes a number of the conversion base and a weight for adding the conversion base in a predetermined pixel order in the block.

Images