Image processing apparatus and image processing method

An image processing apparatus includes an input unit that inputs image data; and an analysis filtering unit that generates coefficient data of a plurality of subbands by performing analysis filtering of the image data input by the input unit for each predetermined number of lines from an upper-end line to a lower-end line such that analysis filtering of a lower-end line of the current picture is completed before analysis filtering of an upper-end line of the next picture starts.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese Patent Application JP 2006-136876 filed in the Japanese Patent Office on May 16, 2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a band analysis apparatus and method for performing, using a filter bank, band analysis of each of a plurality of pictures forming a moving image and dividing each of the pictures into a plurality of subbands, to a band synthesis apparatus and method for performing, using a filter bank, band synthesis of each of a plurality of pictures divided into a plurality of subbands, to an image encoding apparatus and method for performing, using a filter bank, band analysis of each of a plurality of pictures forming a moving image and encoding each of the pictures that has been subjected to band analysis to generate an encoded code-stream, to an image decoding apparatus and method for decoding an encoded code-stream and performing, using a filter bank, band synthesis of the decoded code-stream to reconstruct a moving image, to a program, and to a recording medium.

2. Description of the Related Art

As a typical method for compressing images, a Joint Photographic Experts Group (JPEG) method, which is standardized by the International Organization for Standardization (ISO), is available. The JPEG method uses discrete cosine transform (DCT) and provides excellent encoded images and decoded images at a relatively high bit rate. However, when the encoding bit rate is reduced to a predetermined value or less, block noise, which is specific to DCT transform, is significantly increased. Thus, deterioration becomes conspicuous from a subjective point of view.

In recent years, research and development of methods for dividing an image into a plurality of subbands using a filter bank, which is a combination of a low-pass filter and a high-pass filter, and performing encoding of each of the plurality of subbands has been actively conducted. In such circumstances, wavelet-transform encoding has been regarded as a new promising technique that will take the place of DCT transform since wavelet-transform encoding does not have a disadvantage that block noise becomes conspicuous at high compression, unlike DCT transform.

The JPEG 2000, for which international standardization was completed in January 2001, adopts a method in which the above-mentioned wavelet transform and high-efficiency entropy coding (bit modeling and arithmetic coding for each bit-plane) are combined together. The JPEG 2000 achieves a significant improvement in encoding efficiency, compared with any other JPEG method.

For example, a technique described in Japanese Unexamined Patent Application Publication No. 2001-197499 has been suggested.

SUMMARY OF THE INVENTION

Basically, the JPEG 2000 is a standard for encoding static images. Application of the JPEG-2000 technology to satellite images, map images, images for identification photographs, and the like has been expected. The Motion JPEG 2000, which encodes each of a plurality of pictures forming a moving image in accordance with the JPEG 2000, has been standardized as Part3 of the JPEG 2000 standard.

However, in order to encode moving images, such as video signals, using the JPEG 2000 technique, it is necessary to encode each of a plurality of continuously input pictures in real time. In particular, in wavelet transform used in the JPEG 2000, in order to improve compression efficiency, subband division of each of a plurality of pictures is generally performed until a desired division level is reached. Thus, it is necessary to complete analysis filtering of the current picture at the final division level before the next picture is input.

Not only the JPEG 2000 method but also other image compression methods for dividing each of a plurality pictures forming a moving image into a plurality of subbands in accordance with wavelet transform and performing encoding of each of the plurality of subbands are performed taking into consideration the above-mentioned condition.

For dedicated hardware, this condition can be satisfied by increasing the number of processing clocks of the hardware to increase the operation speed of wavelet transform. However, increasing the number of processing clocks causes an increase in power consumption. In addition, since the number of processing clocks of programmable hardware, such as a field programmable gate array (FPGA) or a programmable logic device (PLD), is small, such programmable hardware does not satisfy the condition.

Accordingly, it is desirable to provide a band analysis apparatus and method for performing wavelet transform of a moving image signal in real time, a band synthesis apparatus and method for performing inverse wavelet transform of a moving image in real time, an image encoding apparatus and method for performing encoding while performing wavelet transform of a moving image signal in real time, an image decoding apparatus and method for performing decoding while performing inverse wavelet transform of a moving image signal in real time, a program, and a recording medium.

An image processing apparatus according to an embodiment of the present invention includes input means for inputting image data; and analysis filtering means for generating coefficient data of a plurality of subbands by performing analysis filtering of the image data input by the input means for each predetermined number of lines from an upper-end line to a lower-end line such that analysis filtering of a lower-end line of the current picture is completed before analysis filtering of an upper-end line of the next picture starts.

An image processing apparatus according to another embodiment of the present invention includes input means for inputting coefficient data generated by performing filtering of image data for each predetermined number of lines from an upper-end line to a lower-end line; and synthesis filtering means for generating the image data by performing vertical and horizontal synthesis filtering of the coefficient data input by the input means for each predetermined number of lines from an upper-end line to a lower-end line of each of a plurality of subbands such that synthesis filtering of a lower-end line of the current picture is completed before synthesis filtering of an upper-end line of the next picture starts.

Accordingly, since wavelet transform or inverse wavelet transform of the current picture is completed before wavelet transform or inverse wavelet transform of the next picture starts, wavelet transform or inverse wavelet transform of a moving image signal can be performed in real time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A band analysis apparatus according to a first embodiment that performs, using an analysis filter bank, band analysis of an input video signal to divide the video signal into a plurality of subbands will be described.

FIG. 1schematically shows a configuration of a band analysis apparatus10according to the first embodiment. Referring toFIG. 1, the band analysis apparatus10includes an image line input unit11, a line buffer unit12, a vertical analysis filter unit13, and a horizontal analysis filter unit14.

The image line input unit11receives a video signal D10for each line, and supplies a data stream D11for the image line to the line buffer unit12.

Video signals are normally defined by a standard. For example, currently, television broadcasting is performed in accordance with a National Television Standards Committee (NTSC) system. In addition, a high definition television (HDTV) system is standardized as a standard number “SMPTE 274M” by the Society of Motion Picture and Television Engineers (SMPTE), which is a standard-setting organization in the United States. In the description below, the HDTV system (a resolution of 1920×1080) will be described as an example.

FIG. 2includes signal distribution diagrams showing an interlace signal from among signals based on the SMPTE 274M standard of the HDTV system. Referring toFIG. 2, an upper diagram shows a first field and a lower diagram shows a second field. An actual signal in the first field is located in an area from the 21st line to the 560th line (560−21+1=540 (lines)), the area being disposed subsequent to a vertical blank signal (V_BLK1) for 22 lines shown as “22H” inFIG. 2. An actual signal in the second field is located in an area from the 584th line to the 1123rd line (1123−584+1=540 (lines)), the area being disposed subsequent to a vertical blank signal (V_BLK2) for 23 lines shown as “23H” inFIG. 2.

As described above, concerning a video signal, vertical blank signals are disposed before and after actual data.FIG. 3shows an actual image area of the first field, an actual image area of the second field, and blank areas. The above-mentioned vertical blank signals V_BLK1and V_BLK2are also shown inFIG. 3.

Since the band analysis apparatus10performs wavelet transform in units of pictures (fields/frames) forming a video signal, it is necessary to detect an end point of a picture and to reset an operation of analysis filtering. Thus, the image line input unit11detects the end point of the picture by detecting a vertical blank signal for the video signal.

The line buffer unit12stores and holds data streams D11for individual lines. The line buffer unit12continues to store and hold data streams D11until data streams D11for the number of lines (N lines) necessary for vertical filtering are stored, as shown inFIG. 4.

The vertical analysis filter unit13sequentially reads line data D12for N lines, and performs vertical low-pass analysis filtering and vertical high-pass analysis filtering. Due to the vertical filtering, a low-frequency component (L) and a high-frequency component (H) D13, which are obtained by vertical division, are generated, as shown inFIG. 5.

Immediately after the number of samples in a horizontal direction of low-frequency and high-frequency components D13reaches M necessary for horizontal filtering, the horizontal analysis filter unit14performs horizontal low-pass analysis filtering and horizontal high-pass analysis filtering. Due to the horizontal filtering, a low-frequency component (1LL) D14and high-frequency components (1HL,1LH, and1HH) D15, which are obtained by horizontal division, are generated, as shown inFIG. 6. Concerning the order of letters “L” and “H” inFIG. 6, the first letter indicates a band obtained after horizontal filtering is performed, and the last letter indicates a band obtained after vertical filtering is performed. In addition, the numeral disposed before the letter “L” or “H” indicates division level.

As a result of analysis filtering at division level1, the horizontal analysis filter unit14generates the low-frequency component (1LL) D14and the high-frequency components (1HL,1LH, and1HH) D15, as described above.

In wavelet transform, normally, a low-frequency component is hierarchically divided until a desired division level is reached. Thus, in the first embodiment, the low-frequency component (1LL) D14is supplied to the line buffer unit12so as to be further divided by an analysis filter bank. Immediately after the number of lines necessary for vertical analysis filtering is buffered in the line buffer unit12, analysis filtering at division level2is performed. A low-frequency component is repeatedly divided as described above since most of the energy of an image signal is concentrated in the low-frequency component.

In the analysis filtering at division level2, the vertical analysis filter unit13sequentially reads line data D12for N/2 lines, and performs vertical low-pass analysis filtering and vertical high-pass analysis filtering, as shown inFIG. 6. Then, immediately after the number of samples in the horizontal direction of low-frequency and high-frequency components D13reaches M, the horizontal analysis filter unit14performs horizontal low-pass analysis filtering and horizontal high-pass analysis filtering. Due to the horizontal filtering, a low-frequency component (2LL) and high-frequency components (2HL,2LH, and2HH) are generated, as shown inFIG. 7. Referring toFIG. 7, a subband1LL obtained at division level1is divided into four subbands,2LL,2HL,2LH, and2HH, and seven subbands are obtained in total.

In order to further increase the division level, analysis filtering can be repeatedly performed for a low-frequency component.FIG. 8shows an example in which subband division by analysis filtering is performed for an actual image until division level3.

The number N of lines of each of subbands stored and held in the line buffer unit12becomes twice every time the division level is decreased by 1. Thus, as shown inFIG. 8, when the number of lines of a subband at division level3is 1, a subband at division level2has two lines and a subband at division level1has four lines. This is based on the principle of wavelet transform.

As the most general arithmetic method of the above-mentioned analysis filtering, a method called convolutional operation is available. The convolutional operation is the most fundamental procedure for achieving a digital filter. As the convolutional operation, convolution multiplication of a filter tap coefficient by actual input data is performed. However, the convolutional operation generates a problem in which the calculation load increases as the tap length increases.

FIG. 9shows a lifting structure of a 9×7-analysis filter, which is adopted in the JPEG 2000 standard. Analysis filtering in which the lifting technique is applied to the 9×7-analysis filter will be schematically explained with reference toFIG. 9.

Referring toFIG. 9, input image samples are shown in the first row from the top (that is, the top row), and components generated by processing of steps S1and S2are shown in the second row from the top and the third row from the top, respectively. In addition, high-frequency component outputs generated by processing of step S3are shown in the fourth row from the top, and low-frequency component outputs generated by processing of step S4are shown in the fifth row from the top (that is, the bottom row). Input image samples are not necessarily shown in the first row. Coefficients obtained by the above-mentioned analysis filtering may be shown in the first row. In this embodiment, input image samples are shown in the first row. Even-numbered samples or lines are represented as squares, and odd-numbered samples or lines are represented as circles.

Due to analysis filtering in which the lifting technique is applied to the 9×7-analysis filter, high-frequency components are obtained by the processing of step S3and low-frequency components are obtained by the processing of step S4. The processing of steps S1to S4is expressed using the following equations:
StepS1:di1=di0+α(si0+si+10)
StepS2:si1=si0+β(di−11+di1)
StepS3:di2=di1+γ(si1+si+11)
StepS4:si2=si1+δ(di−12+di2)

Since analysis at a division level can be performed by analysis filtering using the lifting structure shown inFIG. 9, analysis filtering until a desired division level can be achieved by performing a plurality of steps of analysis filtering.

In the description below, for example, in a display device or the like, scanning is started from the pixel in the upper-left corner of the screen. When scanning from the leftmost pixel to the rightmost pixel in a line is completed, a line is formed. When scanning from the uppermost line to the lowest line is completed, a screen is formed.

FIG. 10shows an example in which analysis filtering in which the lifting technique is applied to the 9×7-analysis filter is performed until division level2. UnlikeFIG. 9, input image lines are shown in the longitudinal direction inFIG. 10. That is, in the analysis filtering, scanning of samples on the screen is vertically performed using a vertical analysis filter.

In the analysis filtering at division level1, components are generated in the order of a high-frequency component (1), a low-frequency component (2), a high-frequency component (3), a low-frequency component (4), etc. in a direction from the top to the bottom inFIG. 10. In addition, in the analysis filtering at division level2, components are generated in the order of a high-frequency component (1), a low-frequency component (2), a high-frequency component (3), a low-frequency component (4), etc. in the direction from the top to the bottom inFIG. 10. Although the analysis filtering at division level2is performed while the analysis filtering at division level1is performed, the explanation of this is omitted here.

As is clear fromFIG. 10, a timing at which a high-frequency component or a low-frequency component is generated at division level2is delayed by a factor of two with respect to a timing at which a high-frequency component or a low-frequency component is generated at division level1. This delay is a feature of analysis filtering using the lifting structure.

As described above, in wavelet transform, in general, subband division of a picture is performed until a desired division level is reached. However, a timing at which a high-frequency component or a low-frequency component is generated is delayed by a factor of two as the division level increases, as described above. Thus, when wavelet transform is performed for a video signal D10, wavelet transform of the current picture may not be completed within the vertical blank period shown inFIG. 2, and the next picture may be input before wavelet transform of the current picture is completed.

FIG. 11shows an example in which the next picture is input before wavelet transform of the current picture is completed.FIG. 11shows processing of wavelet transform from division level1to division level4in chronological order when wavelet transform is performed for the current picture and the next picture. Line numbers shown inFIG. 11are the same as the line numbers used in accordance with the SMPTE 274M standard inFIG. 2. As shown inFIG. 11, analysis filtering of the current picture at division levels3and4is not completed by the time when analysis filtering of the next picture at division level1is performed.

In order to solve the above-mentioned problem, in analysis filtering of the current picture at each division level, the band analysis apparatus10according to the first embodiment advances the timing of analysis filtering of a lower-end line, as shown inFIG. 12. Thus, analysis filtering of the current picture until division level4can be completed before analysis filtering of the next picture at division level1starts.

A method for advancing the timing of analysis filtering of a lower-end line of the current picture at each division level is described next.

FIG. 13shows an example in which analysis filtering in which the lifting technique is applied to the 9×7-analysis filter is performed until division level4, as in the example shown inFIG. 10.FIG. 13shows the 1123rd line, which is the lower end of the current picture, a 22-line vertical blank signal disposed subsequent to the current picture, and samples of the next picture from the 21st line.

In analysis filtering of the lower-end line at division level1, components (10), (11), and (12) are generated in that order, and then, a high-frequency component (13) and a low-frequency component (14) are generated, as shown inFIG. 13. Similarly, in analysis filtering of the lower-end line at division level2, components (20), (21), and (22) are generated in that order, and then, a high-frequency component (23) and a low-frequency component (24) are generated, as shown inFIG. 13. In analysis filtering of the lower-end line at division level3, components (30), (31), and (32) are generated in that order, and then, a high-frequency component (33) and a low-frequency component (34) are generated, as shown inFIG. 13. In analysis filtering of the lower-end line at division level4, components (40), (41), and (42) are generated in that order, and then, a high-frequency component (43) and a low-frequency component (44) are generated, as shown inFIG. 13.

Arrows pointing from the current picture to pixels in the blank period indicate that samples are expanded symmetrically. “Symmetric expansion” means that a supplementary sample is provided from an image area to a portion where a sample does not actually exist by symmetric expansion when analysis filtering is performed at a boundary between pictures or subbands. Thus, the provided supplementary sample and the original sample are in a mirror-image relationship with respect to each other. As shown inFIG. 13, for example, a component (10′) located in an area of the current picture is an original component with respect to a supplementary component (10) located in the blank period. Similarly, at division level1, symmetrical expansion from a component (11′) to a component (11), from a component (12′) to a component (12), from a component (13′) to a component (13), and from a component (14′) to a component (14) is performed. The same applies to other division levels.

Although analysis filtering at division level4is completed within the blank period inFIG. 13, if analysis filtering is performed until division level5, analysis filtering at division level5is not completed within the blank period. In addition, when the number of lines in the blank period is smaller, a similar problem occurs.

In order to solve the above-mentioned problem, the band analysis apparatus10according to the first embodiment advances the timing of symmetric expansion at the lower-end line, and thus advances the timing of analysis filtering of the lower-end line of the current picture. That is, as shown inFIG. 14, immediately after an original sample to be subjected to symmetric expansion for supplementation at the lower-end line of the current picture and the lower-end line of each subband of the current picture is generated, symmetric expansion processing is performed and analysis filtering at each division level is performed.

Accordingly, even when the number of division levels is larger, the band analysis apparatus10is capable of completing analysis filtering of the current picture until the final division level before starting analysis filtering of the upper-end line of the next picture.

Second Embodiment

An image encoding apparatus according to a second embodiment that compresses and encodes coefficient data generated by wavelet transform will be described.

FIG. 15schematically shows a configuration of an image encoding apparatus20according to the second embodiment. Referring toFIG. 15, the image encoding apparatus20includes an analysis filter bank21, a quantization unit22, an entropy-coding unit23, and a rate controller24.

The analysis filter bank21has a configuration similar to the band analysis apparatus10shown inFIG. 1. That is, the analysis filter bank21performs analysis filtering for an input video signal D20, and supplies coefficient data D21obtained by analysis to the quantization unit22. In particular, immediately after an original sample to be subjected to symmetric expansion for supplementation at the lower-end line of the current picture and the lower end of each subband of the current picture is generated, the analysis filter bank21performs symmetric expansion processing and performs analysis filtering at each division level. Thus, analysis filtering of the current picture until the final division level is completed before analysis filtering of the first line of the next picture starts.

The quantization unit22performs quantization by dividing the coefficient data D21generated by the analysis filter bank21by, for example, a quantization step size, and generates quantized coefficient data D22.

The entropy-coding unit23performs source encoding of the quantized coefficient data D22generated by the quantization unit22, and generates a compressed encoded code-stream D23. As source encoding, for example, Huffman coding adopted in the JPEG and the Moving Picture Experts Group (MPEG) or high-precision arithmetic coding adopted in the JPEG 2000 can be used.

The rate controller24performs control so as to achieve a desired bit rate or compression rate. After performing rate control, the rate controller24outputs an encoded code-stream D24whose rate has been controlled. For example, in order to achieve a higher bit rate, the rate controller24transmits to the quantization unit22a control signal D25for decreasing the quantization step size. In contrast, in order to achieve a lower bit rate, the rate controller24transmits to the quantization unit22a control signal D25for increasing the quantization step size.

Third Embodiment

A band synthesis apparatus according to a third embodiment that corresponds to the band analysis apparatus10according to the first embodiment will be described.

FIG. 16schematically shows a configuration of a band synthesis apparatus30according to the third embodiment. Referring toFIG. 16, the band synthesis apparatus30includes a column buffer unit31, a horizontal synthesis filter unit32, a line buffer unit33, a vertical synthesis filter unit34, and a vertical blank signal insertion unit35.

The column buffer unit31stores and holds a low-frequency component D30and a high-frequency component D31for each column. The column buffer unit31continues to store and hold low-frequency components D30and high-frequency components D31until low-frequency components D30and high-frequency components D31for M samples are stored. A low-frequency component D30only for a lowest-frequency subband is input to the column buffer unit31. Then, low-frequency components D35generated by synthesis filtering are supplied from the vertical synthesis filter unit34.

The horizontal synthesis filter unit32sequentially reads column data D32for M samples, and performs horizontal low-pass synthesis filtering and horizontal high-pass synthesis filtering. Due to the horizontal filtering, low-frequency and high-frequency components D33, which are obtained by horizontal synthesis, are generated.

The line buffer unit33stores and holds low-frequency and high-frequency components D33, which are obtained by horizontal synthesis, for individual lines, and continues to store and hold low-frequency and high-frequency components D33until low-frequency and high-frequency components D33for N lines are stored.

The vertical synthesis filter unit34sequentially reads line data D34for N lines, and performs vertical low-pass synthesis filtering and vertical high-pass synthesis filtering. Due to the vertical filtering, a low-frequency component D35, which is obtained by vertical synthesis, is generated. The low-frequency component D35is supplied to the column buffer unit31, and stored and held in the column buffer unit31until synthesis filtering at the next division level is performed.

In inverse wavelet transform, synthesis filtering is performed in a direction, for example, from division level4to division level1, which is opposite to the direction of wavelet transform. By repeatedly performing processing for generating a low-frequency signal at a division level lower by one than the previous level from the low-frequency component D35and the high-frequency component D31, image data stream is generated. The generated image data stream is supplied to the vertical blank signal insertion unit35.

As shown inFIG. 2, the vertical blank signal insertion unit35inserts a vertical blank signal into the image data stream at a predetermined timing, and outputs a generated video signal D36.

A lifting technique can also be applied to synthesis filtering. However, in synthesis filtering adopting a lifting structure, the timing at which a high-frequency component or a low-frequency component is generated is delayed by a factor of two as the division level increases. Thus, inverse wavelet transform of the current picture may not be completed within the vertical blank period shown inFIG. 2, and the next picture may be input before the inverse wavelet transform of the current picture is completed.

FIG. 17shows an example in which the next picture is input before inverse wavelet transform of the current picture is completed.FIG. 17shows processing of inverse wavelet transform from division level4to division level1in chronological order when inverse wavelet transform is performed for the current picture and the next picture. Line numbers shown inFIG. 17are the same as the line numbers used in accordance with the SMPTE 274M standard inFIG. 2. As shown inFIG. 17, synthesis filtering of the current picture at division levels2and1is not completed by the time when synthesis filtering of the next picture at division level4is performed.

In order to solve the above-mentioned problem, the band synthesis apparatus30according to the third embodiment advances the timing of synthesis filtering of the lower-end line of the current picture at each division level, as shown inFIG. 18. Thus, synthesis filtering of the current picture until division level1can be completed before synthesis filtering of the next picture at division level4starts. In addition, as shown inFIG. 18, the timings of synthesis filtering of the next picture at predetermined one or more division levels (division levels4and3) are delayed.

A method for advancing the timing of synthesis filtering of the lower-end line of the current picture at each division level is described next.

FIG. 19shows an example in which synthesis filtering in which a lifting technique is applied to a 9×7-synthesis filter is performed from division level4to division level1.

In synthesis filtering of the lower-end line at division level4, components (40), (41), and (42) are generated in that order, and then, a high-frequency component (43) and a low-frequency component (44) are generated, as shown inFIG. 19. Similarly, in synthesis filtering of the lower-end line at division level3, components (30), (31), and (32) are generated in that order, and then, a low-frequency component (33) and a high-frequency component (34) are generated, as shown inFIG. 19. In synthesis filtering of the lower-end line at division level2, components (20), (21), and (22) are generated in that order, and then, a low-frequency component (23) and a high-frequency component (24) are generated, as shown inFIG. 19. In synthesis filtering of the lower-end line at division level1, components (10), (11), and (12) are generated in that order, and then, a low-frequency component (13) and a high-frequency component (14) are generated, as shown inFIG. 19.

As shown inFIG. 19, synthesis filtering at division level4is not completed within the blank period. Thus, inverse wavelet transform of the current picture is not completed before the next picture is input.

In order to solve the above-mentioned problem, the band synthesis apparatus30according to the third embodiment advances the timing of symmetric expansion processing at the lower-end line, and thus advances the timing of synthesis filtering of the lower-end line of the current picture. That is, as shown inFIG. 20, immediately after an original sample to be subjected to symmetric expansion for supplementation at the lower-end line of each subband of the current picture is generated, the band synthesis apparatus30performs symmetric expansion processing and performs synthesis filtering at each division level.

In addition, since the band synthesis apparatus30according to the third embodiment delays the timing of synthesis filtering of the next picture at predetermined one or more division levels, inverse wavelet transform of the current picture is prevented from temporally overlapping with inverse wavelet transform of the next picture, as shown inFIG. 18. That is, for example, by stopping synthesis filtering of one or more upper-end lines at division levels4and3, temporal overlapping with inverse wavelet transform of the current picture is prevented, as shown inFIG. 21. Then, by advancing the timings of synthesis filtering processing including synthesis filtering of the above-mentioned one or more lines, temporal overlapping with the next picture is prevented.

Thus, even when the number of division levels is larger, the band synthesis apparatus30is capable of completing synthesis filtering of the current picture until division level1before starting synthesis filtering of the upper-end line of the next picture.

If temporal overlapping between inverse wavelet transform of the current picture and inverse wavelet transform of the next picture is prevented only by advancing the timing of symmetric expansion at the lower-end line, the timing of synthesis filtering of the next picture at a predetermined division level may not be delayed as shown inFIG. 21.

Fourth Embodiment

An image decoding apparatus according to a fourth embodiment that corresponds to the image encoding apparatus20according to the second embodiment will be described.

FIG. 22schematically shows a configuration of an image decoding apparatus40according to the fourth embodiment. Referring toFIG. 22, the image decoding apparatus40includes an entropy-decoding unit41, a dequantization unit42, and a synthesis filter bank43.

The entropy-decoding unit41performs source decoding of a received encoded code-stream D40, and generates quantized coefficient data D41. As source decoding, Huffman decoding or high-efficiency arithmetic decoding can be used, as described above.

The dequantization unit42performs dequantization by multiplying the quantized coefficient data D41by a quantization step size, and generates coefficient data D42. Normally, the quantization step size is described in the header of an encoded code-stream.

The synthesis filter bank43has a configuration similar to the band synthesis apparatus30shown inFIG. 16. That is, the synthesis filter bank43performs synthesis filtering for the coefficient data D42to generate an image data stream, inserts a vertical blank signal into the generated image data stream, and outputs a generated video signal D43. In particular, immediately after an original sample to be subjected to symmetrical expansion for supplementation at the lower-end line of each subband of the current picture is generated, the synthesis filter bank43performs synthesis filtering at each division level. Thus, synthesis filtering of the current picture until division level1is completed before synthesis filtering of the first line of the next picture starts. The synthesis filter bank43may delay the timings of synthesis filtering of the next picture at predetermined one or more division levels, as described above.

The present invention is not limited to any of the first to fourth embodiments described above. Various changes and modification can be made to the present invention without departing from the spirit and scope of the present invention.

For example, although a case where the band analysis apparatus10according to the first embodiment performs horizontal filtering after performing vertical filtering has been described, the band analysis apparatus10may perform vertical filtering after performing horizontal filtering.FIG. 23schematically shows a configuration of a band analysis apparatus50that performs vertical filtering after performing horizontal filtering.

In the band analysis apparatus50, an image line input unit51receives a video signal D50for each line, and supplies a data stream D51for the image line to a column buffer unit52. The column buffer unit52stores and holds data streams D51for individual columns, and continues to store and hold data streams D51until data streams D51for M samples are stored. A horizontal analysis filter unit53sequentially reads column data D52for M samples, and performs horizontal low-pass analysis filtering and horizontal high-pass analysis filtering. Due to the horizontal filtering, low-frequency and high-frequency components D53, which are obtained by horizontal division, are generated. Immediately after the number of lines of the low-frequency and high-frequency components D53reaches N, a vertical analysis filter unit54performs vertical low-pass analysis filtering and vertical high-pass analysis filtering. Due to the vertical filtering, a low-frequency component (1LL) D54and high-frequency components (1HL,1LH, and1HH) D55, which are obtained by vertical division, are generated. The low-frequency component (1LL) D54is supplied to the column buffer unit52to be subjected to analysis filtering at level2.

As described above, a subband that is generated when horizontal filtering is performed after vertical filtering is performed is the same as a subband that is generated when vertical filtering is performed after horizontal filtering is performed.

Although hardware configurations have been described in the foregoing embodiments, a series of processing may be performed by software. In this case, a program constituting the software may be incorporated in advance in dedicated hardware of a computer, such as a read-only memory (ROM) or a hard disk, or installed from a network or a recording medium on a general-purpose personal computer capable of performing various functions by installing various programs. As the recording medium, for example, a package medium including a magnetic disk (flexible disk), an optical disk, such as compact disk-read only memory (CD-ROM) or a digital versatile disc (DVD), a magnetic optical disk, such as mini-disk (MD) (trademark), or a semiconductor memory can be used.