decoding device and method for images encoded with VOP fixed rate flags

TECHNICAL FIELD

0001The present invention relates to an image decoding device and an image decoding method which perform image processing.

BACKGROUND ART

0002Conventionally, it is always necessary at the decoding side that the analysis of VOP header information be preceded by analyses of a VOP start code, a modulo time base and a VOP time increment which are contained in each VOP header, because no distinction can be made between VOP not to be analyzed (information to be decimated in the case of a low speed shot of an image signal) and VOP to be analyzed (information not to be decimated in the case of a low speed shot of an image signal); hence, there is a problem that the processing involved is cumbersome and low in accuracy.

0003For decoding and synthesizing encoded signals respectively corresponding to a subject, a background, a log and similar objects which form a pictorial image, it is necessary that each object be added with a synthesizing timing signal (information representing absolute time) necessary for decoding and synthesizing the object. Without the information indicative of absolute time, an image decoding device cannot synthesize the object, and hence it is incapable of image reconstruction. In short, in the case of generating one pictorial image from a plurality of objects including those having no information representative of absolute time, it is impossible with the prior art to combine objects having the required information with those having no such information.

0004Moreover, the bit length of the modulo time base increases until the next GOV header is multiplexed--this raises a problem that the bit length of the modulo time base keeps on increasing when the GOV header, which is an option, is not multiplexed.

0005With a view to solving such problems as referred to above, the present invention is to provide an image decoding device and an image decoding method whose processing accuracies improve through simple processing. Another object of the present invention is to provide an image decoding device and an image decoding method which permit the generation of a pictorial image composed of a plurality of objects based on a time code. Still another object of the present invention is to prevent the generation of an unnecessary amount of information.

DISCLOSURE OF THE INVENTION

0006The present invention solves the above mentioned objects by an image decoding device comprising the features of claim 1 and by an image decoding method comprising the features of claim 2.

BRIEF DESCRIPTION OF THE DRAWINGS

0007<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a diagram depicting the video data structure in MPEG-4; <figref idref="f0002">Fig. 2</figref> is a diagram showing a concrete example of VOP; <figref idref="f0003">Fig. 3</figref> is a block diagram illustrating a VOP encoder part according to Example 1 not covered by the present invention, but useful for understanding the invention; <figref idref="f0004">Fig. 4</figref> is a block diagram illustrating an example of the configuration of a header multiplexing part of the VOP encoder part according to Example 1; <figref idref="f0001">Fig. 5</figref> is a diagram for explaining a modulo time base and a VOP time increment; <figref idref="f0005">Fig. 6</figref> is a block diagram illustrating an example of the configuration of the header multiplexing part of the VOP encoder part according to Example 1; <figref idref="f0006">Fig. 7</figref> is a block diagram depicting a VOP encoder part according to Example 2 not covered by the present invention, but useful for understanding the invention; <figref idref="f0007">Fig. 8</figref> is a block diagram depicting an example of the configuration of the header multiplexing part of the VOP encoder part according to Example 2; <figref idref="f0008">Fig. 9</figref> is a diagram showing an example of a bit stream; <figref idref="f0008">Fig. 10</figref> is block diagram showing an example of the configuration of a VOP header multiplexing part of a header multiplexing part according to Example 2; <figref idref="f0009">Fig. 11</figref> is a block diagram depicting the internal configuration of a VOP decoder part according to Example 3 not covered by the present invention, but useful for understanding the invention; <figref idref="f0010">Fig. 12</figref> is a block diagram depicting an example of the configuration of a header analysis part of the VOP decoder part according to Example 3; <figref idref="f0011">Fig. 13</figref> is a block diagram depicting a system for synthesizing a plurality of objects according to Example 3; <figref idref="f0012">Fig. 14</figref> is a block diagram illustrating an example of the configuration of a header analysis part of a VOP decoder part according to Example 4 not covered by the present invention, but useful for understanding the invention; <figref idref="f0013">Fig. 15</figref> is a block diagram illustrating an example of the configuration of the header analysis part of the VOP decoder part according to Example 4; <figref idref="f0014">Fig. 16</figref> is a block diagram showing the internal configuration of a VOP decoder part according to an Embodiment of the present invention; <figref idref="f0015">Fig. 17</figref> is a block diagram illustrating an example of the configuration of a header analysis part of the VOP decoder part according to the Embodiment of the present invention; and <figref idref="f0016">Fig. 18</figref> is a block diagram illustrating an example of the configuration of a VOP header analysis part of the VOP decoder part according to the Embodiment of the present invention.</li></ul>

BEST MODE FOR CARRYING OUT THE INVENTION

0008To facilitate a better understanding of the present invention, a description will be given, with reference to the accompanying drawings, of the best mode for carrying out the invention.

EXAMPLE 1

0009In Example 1 a VOP encoder for the MPEG-4 video encoding system disclosed in ISO/IEC JTC11 SC29/WG11/N1796 will be described which is provided with constituents of this embodiment, i.e. means for encoding an image on the basis of object display speed information and means for multiplexing the display speed information onto an encoded bit stream by adding the information for each object.

0010The MPEG-4 system is a system that regards a moving picture sequence as a set of moving picture objects taking arbitrary forms temporally and spatially and performs encoding and decoding for each moving picture object. In <figref idref="f0001">Fig. 1</figref> there is depicted the video data structure in MPEG-4. In MPEG-4 the moving picture object containing the time axis is referred to as a video object [Video Object (VO)], a component of the VO as a video object layer {Video Object Layer (VOL)], a component of the VOL as a group of video object plane (Group of Video Object Plane (GOP)], and image data which represents the state of the GOP at each time and forms the basic unit of encoding as a video object plane [Video Object Plane (VOP)]. The VO corresponds, for example, to each speaker or his background in a video conference scene; the VOL forms the basic unit having inherent temporal and spatial resolutions of the speaker or background; and the VOP is image data of such a VOL at each time (corresponding to a frame). The GOP is a data structure that forms the basic unit for editing a plurality of VOLs or random access thereto; this data structure need not always be used for encoding.

0011A concrete example of VOP is shown in <figref idref="f0002">Fig. 2</figref>. In <figref idref="f0002">Fig. 2</figref> there are depicted two VOPs (VOP1 indicating a man and VOP2 a picture on the wall). Each VOP is composed of texture data representing the color gradation level and shape data representing the shape of the VOP. The texture data is composed of a luminance signal of 8 bits per pixel and a color difference signal (of a size subsampled to 1/2 that of the luminance signal in the horizontal and vertical directions), and the shape data is the same binary matrix data as the image size of the luminance signal which sets the inside and outside of the VOP at 0 and 1, respectively.

0012In the VOP-based moving picture representation a conventional frame image is obtained by arranging a plurality of VOPs in the frame. When the moving picture sequence contains only one VO, each VOP is synonymous with the frame.

0013In this instance, no shape data exists and only the texture data is encoded.

0014A description will be given below of an image encoding device of Example 1. This is based on an MPEG-4 video encoder; the MPEG-4 video encoder will hereinafter be referred to as a VOP encoder since it performs encoding for each VOP. Since the operation of the existing VOP encoder is disclosed, for example, in ISO/IEC JTC1/SC29/WG11/N1796, no description will be given of the existing VOP encoder itself, but a description will be given of a VOP encoder that contains constituents of Example 1. <figref idref="f0003">Fig. 3</figref> depicts an example of he configuration of the VOP encoder in Example 1; reference numeral 110 denotes a VOP-to-be-encoded determination part, 111 a shape encoding part, 113 a motion estimation part, 115 a motion compensation part, 118 a texture encoding part, 122 a memory, 124 a header multiplexing part, 126 a video signal multiplexing part, 128 a subtractor, and 129 an adder.

0015Next, the operation of the encoder will be described. Based on VOP rate 7 that is set externally or in accordance with the encoding condition, the VOP-to-be-encoded determination part 110 determines the VOP to be encoded in the input object images, and outputs the VOP to be encoded to the shape encoding part 111, the motion estimation part 113 and the subtractor 128. The VOP rate 7 mentioned herein refers to a value that represents how many VOPs in each VOL or GOV are to be displayed per second. And the VOP rate information also mentioned herein is a code word corresponding to the VOP rate 7, and it is equivalent to what is called the display speed information.

0016A concrete example of the operation of the VOP-to-be-encoded determination part 110 will be described. When the input object images are 30/sec and the VOP rate 7 is 15/sec, the VOP-to-be-encoded determination part 110 judges that alternate ones of the VOPs contained in the input object images are to be encoded, and outputs every other VOPs to be encoded.

0017The VOPs specified by the VOP-to-be-encoded determination part 110 as those to be encoded have their shape data encoded for each area with 16 by 16 pixels, which is commonly called an alpha block, and have their texture data encoded for each area with 16 by 16 pixels which is called a macro block.

0018The shape encoding part 111 encodes the alpha block input thereinto and outputs encoded shape information 112 and locally decoded shape information 109. The encoded shape information 112 is fed to the video signal multiplexing part 126, whereas the locally decoded shape information 109 is input into the motion estimation part 113, the texture encoding part 115 and the texture encoding part 118. The motion estimation part 113 reads reference data 123a from the memory 122 and performs block matching for each macro block to obtain motion information 114. In this case, the motion information is obtained by block matching for only the objects contained in the macro block based on the locally decoded shape information 109.

0019The motion compensation part 115 reads out of the memory 122 reference data 123b on the position indicated by the motion information 114 and generates a predictive image based on the locally decoded shape information 109. The predictive image 116 created in the motion estimation part 115 is input into the subtractor 128 and the adder 129. The subtractor 129 calculates the difference between the predictive image 116 and the input macro block to provide a prediction-error image 117.

0020In the texture encoding part 118 the prediction-error image 117 input thereinto is encoded by a predetermined method prescribed by MPEG-4 to obtain encoded texture information 119 and locally-decoded prediction-error image 120. In this instance, only the objects contained in the block are encoded based on the locally decoded shape information 109. The encoded texture information 119 is sent to the video signal multiplexing part 126, and the locally-decoded prediction-error image 120 is output to the adder 129.

0021The adder 129 adds the predictive image 116 and the locally-decoded prediction-error image 120 to create a decoded image 121, which is written in the memory 122.

0022In the header multiplexing part 124 respective pieces of header information are multiplexed, and a bit stream 125 obtained by multiplexing the header information is input into the video signal multiplexing part 126.

0023The video signal multiplexing part 126 multiplexes the encoded shape information 112, the motion information 114 and the encoded texture information 119 onto the bit stream 125 formed by multiplexing respective header information, and outputs an encoded VOP bit stream.

0024<figref idref="f0004">Fig. 4</figref> is a block diagram depicting the configuration of the header multiplexing part shown in <figref idref="f0003">Fig. 3</figref>. In <figref idref="f0004">Fig. 4</figref>, reference numeral 1 denotes a VO header multiplexing part, 2 a VOL header multiplexing part, 3 a GOV header e multiplexing selection part, 4 a GOV header multiplexing part, 5 a VOP header multiplexing part, 6 GOV multiplexing information, and 7 VOP rate.

0025Next, the operation of this embodiment will be described. The VO header multiplexing part 1 creates a bit stream by multiplexing VOP header information, and outputs the bit stream to the VOL header multiplexing part 2.

0026The VOL header multiplexing part 2 multiplexes VOL header information onto the input bit stream, and outputs the bit stream to the GOV header multiplexing selection part 3.

0027Based on the GOV multiplexing information 6 indicating whether to perform the multiplexing of the GOV header, the GOV header multiplexing selection part 3 determines the destination of the bit stream fed from the VOL header multiplexing part 2. When the GOV multiplexing information 6 indicates that no multiplexing of the GOV header takes place, the bit stream is output to the VOP header multiplexing part 5, whereas when the GOV multiplexing information 6 indicates that the multiplexing of the GOV header is performed, the bit stream is output to the GOV header multiplexing part 4.

0028Table 1 exemplifies the abovesaid VOP rate information, showing four kinds of VOP rates. When the VOP rate is 30/sec, "01" is multiplexed. When the VOP to be encoded is the same as the VOP encoded immediately previously, VOP information "00" is multiplexed but the subsequent VOP header information and VOP data information are not multiplexed. When the VOP rate is variable, VOP rate information "11" is multiplexed. That is, the VOP rate 7 indicates whether the VOP rate is fixed or variable, and represents the value of the rate when it is fixed.

0029A VOP start code multiplexing part 8 in the VOP header multiplexing part 5 outputs to a modulo time base (modulo-time-base) multiplexing part 9 and a VOP time increment (VOP-time-increment) multiplexing part 10 a bit stream obtained by multiplexing a VOP start code onto the input bit stream. The modulo time base 13 mentioned herein is information that represents what number of seconds will pass until the VOP concerned is displayed after a certain reference time as depicted in <figref idref="f0001">Fig. 5</figref>, and the VOP time increment 14 is information by which the display time defined by the modulo time base is fine-adjusted with an accuracy of 1/1000th of a second as similarly depicted in <figref idref="f0001">Fig. 5</figref>. That, is, MPEG-4 permits defining the VOP display time with a precision of 1/1000th of a second.

0030A management time generating part 12 in the VOP header multiplexing part 5 generates the modulo time base 13 and the VOP time increment 13 based on the VOP rate 7, and outputs the modulo time base 13 to the modulo time base multiplexing part 9 and the VOP time increment 14 to the VOP time increment multiplexing part 10. When the VOP rate 7 represents a variable VOP rate, the modulo time base 13 and the VOP time increment 14 are set independently of the VOP rate 7.

0031The abovementioned modulo time base multiplexing part 9 multiplexes the modulo time base 13 onto the bit stream provided from the VOP start code multiplexing part, and outputs the multiplexed bit stream to the VOP time increment multiplexing part 10. The VOP time increment multiplexing part 10 multiplexes the VOP time increment 14 fed thereto from the management time generating part 12 onto the bit stream fed from the modulo time base multiplexing part 9, and outputs the multiplexed bit stream to a video information header multiplexing part 11. The video information header multiplexing part 11 multiplexes a video information header onto the bit stream provided thereto from the VOP time increment multiplexing part 10, and outputs the multiplexed bit stream to the video signal multiplexing part 126.

0032As described above, according to Example 1, since the VOP rate information is multiplexed onto the GOP header, a bit stream can be created which enables the decoder side to determine whether or not to require the decoding of the VOP concerned, or to synthesize a plurality of objects, simply by analyzing only the VOP start code of each VOP header.

0033It is also possible to define the VOP rate 7 for each VOL and perform encoding and multiplexing of the VOP rate information as shown in <figref idref="f0005">Fig. 6</figref>. In this instance, the VOP rate information is determined for each VOL and is multiplexed in the VOL header multiplexing part 2. Based on this, the modulo time base 13 and the VOP time increment 14 are determined.

0034As described above, Example 1 has disclosed an example of the image encoding device which encodes images on an objectwise basis and which is provided with encoding means for encoding the images on the basis of predetermined display speed information and multiplexing means for multiplexing the abovesaid predetermined display speed information onto the image signals encoded by the encoding means and for outputting the multiplexed signals.

0035Furthermore, Example 1 has disclosed an example of the multiplexing means of the type that multiplexes the abovementioned display speed information on an object-by-object basis.

EXAMPLE 2

0036Example 2 is directed to another example of the VOP encoder described above in Example 1. The VOP encoder of Example 2 is provided with means for encoding a 1-bit VOP rate flag that indicates as the display speed information whether the object display speed is a fixed or variable speed and the VOP rate that indicates the value of the object display speed, and for multiplying the encoded information onto the bit stream.

0037When the abovementioned VOP rate flag indicates a variable speed, the VOP rate corresponds to "variable" in Table 1 referred to previously in respect of Example 1, whereas when the VOP rate flag indicates a fixed speed, the VOP rate corresponds to 30/sec or 15/sec in Table 1 mentioned above with respect to Example 1.

0038<figref idref="f0006">Fig. 7</figref> shows an example of the configuration of the VOP encoder according to Example 2. Reference numeral 1000 denotes a header multiplexing part, 1001 the VOP rate flag, and 1026 the VOP rate. Since the VOP encoder according to Example 2 differs from the VOP encoder described previously in connection with Example 1 only in the configuration and operation of the header multiplexing part 1000 that corresponds to the header multiplexing part 124 of the latter, a description will be given in this respect alone.

0039<figref idref="f0007">Fig. 8</figref> is a block diagram depicting the configuration of the header multiplexing part 1000 of the VOP encoder part according to Example 2. In <figref idref="f0007">Fig. 8</figref>, reference numeral 1002 denotes a VOL header multiplexing part, and 1003 a VOP header multiplexing part. Next, the operation will be described.

0040The VOP header multiplexing part 1 creates a bit stream by multiplexing VO header information, and outputs the thus created bit stream to the VOL header multiplexing part 1002. The VOL header multiplexing part 1002 multiplexes VOL header information onto the input bit stream, and outputs the multiplexed bit stream to the GOV header multiplexing selection part 3. In this case, the VOL rate information and the VOP rate flag are also multiplexed.

0041Table 3 shows examples of multiplexing of the VOP rate 1026. In this instance, when the VOP rate 1026 is 2/sec, "000" is multiplexed as the VOP rate information; when the VOP rate is 5/sec, "001" is multiplexed; when the VOP rate is 25/sec, "001" is multiplexed; when the VOP rate is 30/sec, "011" is multiplexed; and in the cases of other VOP rates (for example, when the VOP rate is 10/sec), "100" is multiplexed. Incidentally, a decision as to whether to multiplex the VOP rate information is made independently of the VOP flag value described later on. The multiplexing of the VOP rate may also be such as exemplified in Table 4. In this case, when all VOPs are those of exactly the same images in the VOL, the display is regarded as a still picture and "010" is multiplexed as the VOP rate information.

0042As regards the VOP rate flag, "1" or "0" is multiplexed depending on whether the VOP rate flag indicates a fixed or variable speed. <figref idref="f0008">Fig. 9</figref> depicts an example of the bit stream provided from the VOL header multiplexing part 1002.

0043Based on the GOV multiplexing information 6 indicating whether to multiplex the GOV header, the GOV header multiplexing selection part 3 determines the destination of the bit stream fed thereto from the VOL header multiplexing part 102. When the GOV multiplexing information 6 does not indicates the multiplexing of the GOV header is performed, the bit stream is output to the VOP header multiplexing part 1003, whereas when the GOV multiplexing information 6 indicates the multiplexing of the GOV header, the bit stream is provided to the GOV header multiplexing part 4. The GOV header multiplexing part 4 multiplexes the GOV header information onto the input bit stream, and outputs the multiplexed bit stream to the VOP header multiplexing part 1003. <figref idref="f0008">Fig. 10</figref> illustrates the VOP header multiplexing part 1003 in detail. In <figref idref="f0008">Fig. 10</figref>, reference numeral 1004 denotes a management time generating part.

0044Next, the operation of this example will be described. The management time generating part 1004 generates a modulo time base and a VOP time increment based on the VOP rate 1026 when the input VOP rate flag 1001 indicates a fixed speed, and based on a timer contained in the VOP encoder when the input VOP rate flag 1001 indicates a variable speed. The modulo time base and the VOP time increment thus created are fed to the modulo time base multiplexing part 9 and the VOP time increment multiplexing part 10, respectively.

0045The VOP time increment multiplexing part 10 multiplexes the VOP time increment onto the input bit stream, and outputs the multiplexed bit stream to the video information header multiplexing part 11. The video information header multiplexing part 11 multiplexes the video information header onto the bit stream provided thereto from the VOP time increment multiplexing part 10, and outputs the multiplexed bit stream to the video signal multiplexing part 126.

0046As described above, according to Example 2, since the VOP rate flag and the VOP rate information are multiplexed onto the VOL layer, a bit stream can be created which enables the user to specify his desired VOP in a moment through utilization of the VOP rate flag and the VOP rate on the decoder side--this allows him to determine whether or not to require the decoding of the VOP concerned, or to synthesize a plurality of objects, simply by analyzing only the VOP start code of the corresponding VOP header.

0047Incidentally, since it is possible to distinguish between variable and fixed speeds even if only the VOP rate flag is multiplexed, the VOP desired to decode can be decoded.

0048As described above, Example 2 has shown an example of the image encoding device which encodes images on an objectwise basis and which is provided with: means for encoding the flag indicating whether the object display speed is fixed or variable; multiplexing means for multiplexing the flag onto the encoded image signal encoded by the encoding means and for outputting the multiplexed signal; encoding means for encoding the images on the basis of predetermined display speed information; and multiplexing means for multiplexing the predetermined display speed information onto the image signals encoded by the encoding means and for outputting the multiplexed signals.

EXAMPLE 3

0049Example 3 will be described as being applied to a system wherein an image decoding device for decoding from an encoded bit stream the VOP rate information mentioned previously in connection with Example 1 and for outputting it, that is, an MPEG-4 video decoder (hereinafter referred to as a VOP decoder) is provided for each of a plurality of objects and a plurality of decoded objects are synthesized to reconstruct a pictorial image.

0050A description will be given first of the configuration and operation of the image decoding device (VOP decoder) in Example 3. Since the operation of the existing VOP decoder is disclosed, for example, in ISO/IEC JTC1/SC29/WG11/N1796, the VOP decoder containing constituents of Example 3 will be described without referring to the existing VOP decoder itself. The VOP decoder in Example 3 is a decoder that is able to decode an encoded bit stream generated by the VOP encoder described previously with reference to Example 1.

0051<figref idref="f0009">Fig. 11</figref> depicts an example of the internal configuration of the VOP decoder in Example 3. The VOP decoder is supplied with compressed-encoded data composed of texture data and shape data as described previously with reference to Example 1 and shown in <figref idref="f0002">Fig. 2</figref>, and decodes the individual pieces of data. In <figref idref="f0009">Fig. 11</figref>, reference numeral 150 denotes encoded VOP bit stream, 151 a header analysis part, 152 a bit stream with the header information analyzed,153 a video signal analysis part, 154 encoded shape data, 155 a shape decoding part, 156 decoded shape data, 157 encoded texture data, 158 motion information, 159 a motion compensation part, 160 predictive texture data, 161 a texture decoding part, 162 decoded texture data, 164 a memory, and 165 reference data.

0052Referring to <figref idref="f0009">Fig. 11</figref>, the operation of the decoder will be described in detail. The encoded VOP bit stream 150 is input into the header analysis part 151, wherein the header information is analyzed following a predetermined syntax. The bit stream having the header information analyzed in the header analysis part 151 is fed into the video signal analysis part 153, wherein it is analyzed into the encoded shape data 154, the encoded texture data 157 and the motion information 158. The shape decoding part 155 decodes the encoded shape data input thereinto, and outputs the decoded shape data 156.

0053The motion compensation part 159 generates the predictive texture data 160 from the reference data 165 in the memory 164 and the motion information 158 provided from the video signal analysis part 153. Based on the encoded texture data 157 and the predictive texture data 160, the texture decoding part 161 reconstructs image data by the method prescribed in MPEG-4, generating the decoded texture data 162. The decoded texture data 162 is used for subsequent VOP decoding, and hence it is written in the memory 164.

0054<figref idref="f0010">Fig. 12</figref> depicts the internal configuration of the header analysis part 151 that is characteristic of Example 3. In <figref idref="f0010">Fig. 12</figref>, reference numeral 51 denotes a start code analysis part, 52 a VO header analysis part, 53 a VOL header analysis part, 54 GOV header analysis part, 58 VOP rate, and 55 a VOP header analysis part. The header analysis part 151 in Example 3 is characterized in that the GOV header analysis part 54 decodes the VOP rate of VOP contained in the GOV concerned from the bit stream and outputs to the outside. A description will be given later of how to use the VOP rate 58.

0055The start code analysis part 51 analyzes the start code contained in the encoded VOP bit stream 150 input thereinto. A bit stream is output to the VO header analysis part when the analyzed start code is indicative of VOL, to the VOL header analysis part 53 when the analyzed start code is indicative of VOL, to the GOV header analysis part 54 when the analyzed start code is indicative of GOV, and to the VOP header analysis part 55 when the analyzed start code is indicative of VOP Incidentally, upon completion of the analysis in the VOP header analysis part 55, the bit stream is output to the video signal analysis part 153.

0056The VO header analysis part 52 analyzes VO header information from the input bit stream, and outputs the resulting bit stream to the start code analysis part 51. The VOL header analysis part 53 analyzes VOL header information from the input bit stream, and outputs the resulting bit stream to the start code analysis part 51. The GOV header analysis part 54 analyzes GOV header information from the input bit stream, and outputs the resulting bit stream to the start code analysis part 51. At this time, the VOP rate information contained in the GOV header information is decoded and output. The VOP header analysis part 55 analyzes VOP header information from the input bit stream, and outputs the resulting bit stream via the start code analysis part 51 to the video signal analysis part 153.

0057With the VOP decoder of the above configuration of operation, it is possible to output, for each GOV, the VOP rate of VOPs contained therein. <figref idref="f0011">Fig. 13</figref> illustrates a system that uses this information to synthesize a plurality of objects. In <figref idref="f0011">Fig. 13</figref>, reference numeral 200 denotes an encoded VOP bit stream a, 201 an encoded VOP bit stream b, 202 an encoded VOP bit stream c, 203a a VOP decoder part for decoding the encoded VOP bit stream 200 a200, 203b a VOP decoder part for decoding the encoded VOP bit stream b201, 203c a VOP decoder part for decoding the encoded bit stream c202, 204 a decoded object image a, 205 a decoded object image b, 206 a decoded object image c, 207 VOP rate a, 208 VOP rate b, 209 VOP rate c, 210 a composition part, and 211 a decoded pictorial image. The decoded object image herein mentioned refers to an image that is obtained by combining the decoded shape data 154 and the corresponding decoded texture data 162 for each of VOPs and then integrating such combined pieces of data for each group of VOPs (for example, GOV or VOL).

0058The encoded VOP bit streams a200 to c202 are decoded by the VOP decoder parts 203a to 203c corresponding thereto, respectively, by which the decoded VOP images a204 to c206 are generated. At this time, the VOP decoder parts decode the corresponding VOP rate a207 to c209, and output them to the composition part 210. Based on the VOP rate a207 to c209, the composition part 210 determines the time of the frame where to synthesize the decoded VOP images in the decoded image 211, and maps them into the frame corresponding to the determined time. Let it be assumed, for example, that the decoded image 211 is displayed at a rate of 30 video object planes per sec (which corresponds to a ordinary TV signal display speed). Furthermore, assume the following situations.

0059The decoded VOP image a204 is displayed at a rate of 5/sec (that is, the VOP rate a207 indicates the 5/sec rate).

0060The decoded VOP image b205 is displayed at a rate of 10/sec (that is, the VOP rate indicates the 10/sec rate).

0061The decoded VOP image c206 is displayed at a rate of 15/sec (that is, the VOP rate c209 indicates the 15/sec rate).

0062In this instance, the decoded VOP images a204 to c206 are all mapped into the first image frame at each second in the decoded image 211; the decoded VOP image a204 is mapped into every five image frames including the first at each second; the decoded VOP image b205 is mapped into every 10 image frames including the first at each second; and the decoded VOP image c206 is mapped into every 15 images frames including the first at each second. By this, it is possible to display a pictorial image with a plurality of objects synthesized in the image frames in accordance with their display speeds. As described-above, by using VOP decoder which decodes the encoded bit stream having the VOP rate encoded in the GOV layer, a system which synthesizes a plurality of object into a reconstructed image can be implemented with a simple structure.

0063The VOP rate may also be encoded for each VOL at the image encoding device side. In this case, it is possible, at the image decoding device side, to decode the VOP rate encoded for each VOL and easily synthesize a plurality of objects for each VOL as described above.

0064While Example 3 employs the VOP decoder as a system for synthesizing a plurality of objects, it is also feasible to use only one VOP decoder for a system that decodes only one object to reconstruct an image.

0065As described above, according to Example 3, the image decoding device which decodes the bit stream encoded from an image on an object-by-object basis is provided with display speed information decoding means for decoding display speed information from the encoded bit stream and control means for controlling the reconstruction of the image encoded on the object-by-object basis through utilization of the display speed information decoded by the display speed information decoding means.

0066In Example 3 the display speed information decoding means has been described to decode the display speed information object by object.

EXAMPLE 4

0067Example 4 is directed to another modification of the VOP decoder described above in Example 3. The VOP decoder according to Example 4 has a function of specifying the VOP to be decoded on the basis of the value of the VOP rate that the decoder assumes.

0068Since the VOP decoder of Example 4 differs from Example 2 only in the configuration and operation of the header analysis part 151, a description will be given only in this respect.

0069<figref idref="f0012">Fig. 14</figref> is a block diagram illustrating the configuration of the header analysis part of the VOP decoder part according to Example 4, in which the VOP rate at the encoder side and the VOP rate at the decoder side do not match. In <figref idref="f0012">Fig. 14</figref>, reference numeral 59 denotes a VOP-to-be-decoded selection part, which compares a VOP rate from the GOV header analysis part 54 and a VOP rate assumed at the decoder side, and outputs VOP select information 62. And the VOP header analysis part 55 has a counter 60 has a counter part 60 in addition to a time management information header analysis part 56 and a video information header analysis part 57.

0070Next, the operation of this example will be described. The VOP-to-be-decoded selection part 59 outputs to the counter part 60 of the VOP header analysis part 55 the VOP select information that indicates information about the VOP to be decoded according to the result of comparison between the VOP rate 58 analyzed in the GOV header analysis part 54 and the VOP rate 61 assumed at the decoder side. The counter part 60 uses the VOP select information 62 to determined whether to decode the VOP header information that follows the VOP start code contained in the input bit stream.

0071More specifically, when the VOP rate 58 analyzed in the GOV header analysis part 55 is 30 planes/sec and the VOP rate assumed at the decoder side is 15 planes/sec, the VOP select information 62 indicating that every other VOPs are analyzed is output to the counter part 60 in the VOP header analysis part 55. The counter part 60 first counts every VOP header input thereinto by a counter 60a.

0072Then, based on the count value input thereinto from the counter 60a and the VOP rate select information 62 from the VOP-to-be-decoded selection part 59, decision means 60b decides whether the input VOP needs to be analyzed. When it is decided that the input VOP needs to be analyzed, the input bit stream is output to the time management information header analysis part 56. When it is decided that the input VOP need not be analyzed, the input bit stream is output to the start code analysis part 51.

0073A concrete example will be described below. When the VOP rate select information 62 is one that one VOP needs to be analyzed for every three VOPs, the decision means 60b judges that the VOP needs to be analyzed for which the count value from the counter 60a can be divided by 3 without a remainder, and that the VOP need not be analyzed for which the count value from the counter 60a is divided by 3, with a remainder of 1 or 2. Incidentally, while the VOP decoder of Embodiment 4 has been described to be adapted for use in the case where the VOP rate information is contained in the GOV header, the VOP rate information may also be contained in the VOL header as described previously with reference to Embodiment 2. In such an instance, the VOL header analysis part 300 needs only to be equipped with the function of decoding the VOP rate information. Moreover, the VOP decoder of Example 4 can be used not only in a system which synthesizes a plurality of objects but also in a system which decodes and reconstructs only one object.

0074As described above, the decoder according to Example 4 has control means which is provided with: decoding time specifying means for specifying the time when to decode an object on the basis of the object display information decoded by the display speed information decoding means and the object display speed information preset in the decoding device; and decoding means for decoding the object at the decoding time specified by the decoding time specifying means.

EMBODIMENT

0075The Embodiment will is directed to another example of the VOP decoder described above in Example 4. The VOP decoder according to the Embodiment is equipped with a function of specifying a VOP to be decoded on the basis of: the VOP rate flag indicating whether the object display speed is fixed or variable; the VOP rate information indicating the object display speed; externally-set display control information indicating time information externally set by a user; and a time code.

0076Since the VOP decoder according to the Embodiment differs, as shown in <figref idref="f0014">Fig. 16</figref>, from Example 3 only in the configuration and operation of a header analysis part 1005 corresponding to the header analysis part 151 of the VOP decoder of the latter, a description will be given in this respect alone. <figref idref="f0015">Fig. 17</figref> is a block diagram illustrating the configuration of the header analysis part 1005 of the VOP decoder part according this embodiment. In <figref idref="f0015">Fig. 17</figref>, reference numeral 1006 denotes a VOL header analysis part, 1007 a GOV header analysis part, 1008 a VOP header analysis part, 1009 an externally-set display control information, 1010 a VOP rate flag, and 1011 a time code. Incidentally, the externally-set display control information 1009 may be information indicating absolute time or VOP select information indicating the number of VOPs from which one VOP to be decoded is selected.

0077Next, the operation of this embodiment will be described. The start code analysis part 51 analyzes the start code contained in the input encoded VOP bit stream. The start code analysis part outputs the bit stream to the VO header analysis part 52 when the analyzed start code indicates VO, to the VOL header analysis part 1006 when the analyzed start code indicates VOL, to the GOV header analysis part 1077 when the analyzed start code indicates GOV, and to the VOP header analysis part 1008 when the analyzed start code indicates VOP. Incidentally, the bit stream is output to the video signal analysis part 153 after completion of the analysis in the VOP header analysis part 1008.

0078Next, the VO header analysis part 52 analyzes the VO header, the VOP rate 58 and the VOP rate flag 1011 contained in the input bit stream, and outputs the analyzed bit stream to the start code analysis part 51 and, at the same time, outputs the VOP rate 58 to the composition part 210 and the VOP header analysis part 1008 and the VOP rate flag 1010 to the VOP header analysis part 1008.

0079The GOV header analysis 1007 analyzes the GOV header contained in the input bit stream, and outputs the analyzed bit stream to the start code analysis part 51 and, at the same time, outputs the time code 1011 contained in the analyzed GOV header to the VOP header analysis part 1008.

0080<figref idref="f0016">Fig. 18</figref> is a block diagram illustrating the VOP header analysis part 1008 in detail. Reference numeral 1012 denotes a VOP-to-be-decoded determining part (1), which has a counter part 1012a and decision means 1012b. Reference numeral 1013 denotes a modulo time base analysis part, 1014 a VOP time increment analysis part, 1015 a VOP-to-be-decoded determining part (2), and 1016 a VOP-to-be-decoded determining method select part. Next, the operation of this embodiment will be described. The VOP-to-be-decoded determining method select part 1016 uses the VOP rate flag 1010 to determine the destination of the input bit stream. When the VOP rate flag 1010 indicates a fixed speed, the VOP-to-be-decoded determining part (1) 1012 is selected as the destination of the bit stream, and when the VOP rate flag 1010 indicates a variable speed, the modulo time base analysis part 1013 is selected.

0081A description will be given first of the case where the VOP rate flag 1010 indicates a fixed speed. The counter part 1012a in the VOP-to-be-decoded determining part (1) 1012 increments its count value upon each input of the bit stream into the VOP header analysis part 1006 when the VOP start code is detected-in the start code analysis part 51, and outputs the count value and the bit stream to the decision means 1012b.

0082Then the decision means 1012b decides whether the VOP to be decoded needs to be decoded. The operation of the decision means 1012b will be described in respect of first and second cases where the externally-set display control information 1009 is provided as absolute time and where the externally-set display control information 1009 is provided as VOP select information.

(First Case)

0083Based on the count value and the VOP rate fed thereto from the counter part 1012a and the time code 1011, the decision means calculates the absolute time that the VOP candidate for decoding has. For example, in the case where the count value is 4, the VOP rate is 2/sec and the absolute time is 0h10m0sec0msec, the absolute time that the VOP candidate for decoding has is calculated to be 0h10m02sec0msec. If the thus calculated absolute time of the VOP candidate for decoding and the externally-set display control information 1009 are equal to each other, it is decided that decoding needs to be done.

0084On the other hand, when they are not equal, the absolute time of the next VOP candidate for decoding is calculated. This is intended to make comparison between the absolute time of the next VOP candidate for decoding and the absolute time of the current VOP candidate for decoding so as to ensure decoding the VOP of the absolute value closer to the externally-set display control information 1009. The absolute time of the next VOP candidate for decoding is calculated from the already calculated absolute time of the current VOP candidate for decoding and the VOP rate 58. When this calculated value is smaller or equal to the externally-set display control information 1009, it is decided that the next VOP candidate for decoding is to be decoded, and the current VOP candidate for decoding is not decoded. When the calculated value exceeds the externally-set display control information 1009, any of the following methods may be chosen. Decode the current VOP candidate for decoding; Decode the next VOP candidate for decoding (=not decode the current VOP candidate for decoding); Decode the VOP of an absolute time which has a small difference between it and the externally-set display control information 1009, that is, which is close to the externally-set display control information 1009.

(Second Case)

0085This is the case where the display speed is controlled at the VOP decoder side; for example, the user is allowed to determine the display speed or designate the optimum display speed according to CPU resources.

0086Next, the operation in this case will be described. Let it be assume that the VOP select information indicating the necessity for decoding one for every three VOPs. In this instance, the decision means 1012b judges that decoding needs to be done when the count value fed thereto from the counter part 1012a can be divided by 3 without a remainder and that decoding need not be done when the count value from the counter part 1012a is divided by 3 with a remainder 1 or 2.

0087In either of the first and second cases, when it is judged that the VOP candidate for decoding must be decoded, the decision means outputs a bit stream to the modulo time base analysis part 1013, and to the start code analysis part 51 when it is judged that no decoding is necessary. The modulo time base analysis part 1013 analyzes the modulo time base, and outputs a bit stream to the VOP time increment analysis part 1014.

0088The VOP time increment analysis part 1014 analyzes the VOP time increment, and outputs a bit stream to the video information header analysis part 57. The video information header analysis part 57 analyzes the video information header, and outputs a bit stream to the start code analysis part 51.

0089Next, a description will be given of the case where the VOP rate flag 1010 indicates a variable speed. The modulo time base analysis part 1013 analyzes the modulo time base, and outputs a bit stream to the VOP time increment analysis part 1014. The VOP time increment analysis part 1-14 analyzes the VOP time increment, and outputs a bit stream to the VOP-to-be-decoded determining part (2) 1015.

0090Based on the modulo time base analyzed in the modulo time base analysis part 1013, the VOP time increment analyzed in the VOP time increment analysis part 1014 and the time code 1011, the VOP-to-be-decoded determining part (2) 1015 generates the absolute time of the VOP candidate for decoding, and based on the generated absolute time and the externally-set display control information 1009, determines whether the VOP candidate for decoding needs to be decoded. When it is determined that the VOP needs to be decoded, a bit stream is output to the video information header analysis part 57, and to the start code analysis part 51 when it is judged that no decoding is necessary. The video information header analysis part 57 analyzes the video information header, and outputs a bit stream to the start code analysis part 51.

0091As described above, according to the embodiment, since the bit stream with the encoded VOP rate flag and VOP rate is multiplexed onto the VOL layer, it is possible for the user to specify his desired VOP in a moment through utilization of the VOP rate flag and the VOP rate--this allows him to determine whether the VOP concerned needs to be decoded, or to synthesize a plurality of objects, simply by analyzing only the VOP start code contained in the corresponding VOP header information.

0092Incidentally, when the VOPs contained in the encoded VOP bit stream input into the VOP decoder are all intra-encoded, the user can specify his desired VOP in a moment and cause it to be displayed.

0093As described above, the decoder according to the Embodiment is characterized by control means which controls the image reconstruction by specifying the display time of the image at each time for decoding on the basis of the display speed information when the display speed identification information decoded by the display speed information decoding means indicates a fixed speed and on the basis of display time information multiplexed for each image at each time in the case where the display speed identification information indicates a variable speed. <tables id="tabl0001" num="0001"><table frame="all"><title><b>TABLE.1</b></title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="28mm" /><colspec colnum="2" colname="col2" colwidth="44mm" /><thead><row><entry align="center" valign="top">VOP RATE</entry><entry align="center" valign="top">VOP RATE INFORMATION</entry></row></thead><tbody><row><entry align="center">30/SEC</entry><entry align="center">01</entry></row><row><entry align="center">15/SEC</entry><entry align="center">10</entry></row><row><entry align="center">STllL PICTURE</entry><entry align="center">00</entry></row><row><entry align="center">VARIABLE</entry><entry align="center">11</entry></row></tbody></tgroup></table></tables><tables id="tabl0002" num="0002"><img file="EP1585342B1_D0001.tif" /></tables><tables id="tabl0003" num="0003"><table frame="all"><title><b>TABLE.3</b></title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="118mm" /><colspec colnum="2" colname="col2" colwidth="44mm" /><thead><row valign="middle"><entry align="center">VOP RATE</entry><entry align="center">VOP RATE INFORMATION</entry></row></thead><tbody><row valign="middle"><entry align="center">2/SEC</entry><entry align="center">000</entry></row><row valign="middle"><entry align="center">5/SEC</entry><entry align="center">001</entry></row><row valign="middle"><entry align="center">25/SEC</entry><entry align="center">010</entry></row><row valign="middle"><entry align="center">30/SEC</entry><entry align="center">011</entry></row><row valign="middle"><entry align="center">FIXED VOP RATES OTHER THAN THE ABOVE (2/SEC, 5/SEC, 25/SEC, 30/SEC)</entry><entry align="center">100</entry></row></tbody></tgroup></table></tables><tables id="tabl0004" num="0004"><table frame="all"><title><b>TABLE.4</b></title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="118mm" /><colspec colnum="2" colname="col2" colwidth="44mm" /><thead><row valign="middle"><entry align="center">VOP RATE</entry><entry align="center">VOP RATE INFORMATION</entry></row></thead><tbody><row valign="middle"><entry align="center">2/SEC</entry><entry align="center">000</entry></row><row valign="middle"><entry align="center">5/set</entry><entry align="center">001</entry></row><row valign="middle"><entry align="center">25/SEC</entry><entry align="center">010</entry></row><row valign="middle"><entry align="center">30/SEC</entry><entry align="center">011</entry></row><row valign="middle"><entry align="center">FIXED VOP RATES OTHER THAN THE ABOVE (2/SEC, 5/SEC, 25/SEC, 30/SEC)</entry><entry align="center">100</entry></row><row valign="middle"><entry align="center">STILL PICTURE</entry><entry align="center">101</entry></row></tbody></tgroup></table></tables>