Video decoding apparatus for decoding shape and texture signals using inter/intra modes

Abstract: An image decoding apparatus which receives an encoded signal and decodes the encoded signal, comprising: first decoding means for decoding the input encoded signal to obtain mode identifying information indicating respective encoding modes for the shape information and for the pixel value information; second decoding means for decoding, according to the obtained mode identifying information, blocked shape information and blocked pixel value information, respectively; and reverse blocking means for integrating the blocked shape information and the blocked pixel value information which are output from the second decoding means to obtain a decoded image signal. An image decoding apparatus according to Claim 1 wherein, the first decoding means obtains the mode identifying information which indicates intra-frame encoding and the inter-frame encoding, alternatively, as the encoding mode.

Description: Field of Technology This invention relates to an image decoding apparatus. Prior Art The image encoding technology has a long history. There has been established excellent standard proposals such as ITU-T H.261, ITU-T H263, ISO MPEG1/2 and so on. Roughly speaking, the image encoding method has two approaches: an encoding method using the orthogonal transform and a prediction encoding method encoding the error of predicted values with the use of the prediction function. Although the encoding method using the orthogonal transform needs complicated calculation, when encoded signals of small bit numbers are obtained, it is possible to keep better picture quality than the prediction encoding method. The ordinary encoding method using orthogonal transform such as JPEG, MPEG and the like utilizes the DCT(Discrete Cosine Transform). Though it is known that DCT enables encoding by a small number of bits, it has own problems in that it needs high-precision multiplication, resulting in complicated calculation, and in that the reversible encoding is impossible. Accordingly, DCT calculation can not be used in the fields in which the reversibility is required. As opposed to this, the prediction encoding method needs simple calculations and can do the reversible encoding. MMR(Modified Modified Read) used in facsimiles is famous as an image coding method having reversibility. MMR is used according to CCITT Rec.T6 "Facsimile Coding Schemes and Coding Control Functions for Group 4 Facsimile Apparatus". In this method, the difference value in the horizontal direction between the change points of pixel values on the immediately previous already-coded scanning line and the change points of pixel value on the not-yet-coded scanning line is variable-length encoded. MMMR(Modified MMR) which is a further improved MMR is used as the evaluation model for MPEG4 (ISO/IEC/JTC/SC29/WG11 N1277, July 1996). Incidentally, if image signals are separated into the objects and then the objects are processed as arbitrary shapes, image can be operated and synthesized, object by object, which leads to the effective signal-transmission. For applications which restrict bit number, by using such information, it is possible to selectively assign priority to important objects to transmit and record the same. However, the prior art technology has not taken into account the encoding of objects having arbitrary shapes. And the standardization of coding for image signals having arbitrary shapes has been proceeding in the ISO MPEG4. In MPEG4, the evaluation model called VM3.0 (printed in ISO/IEC/JTC1/SC29/WG11 N1277) is created, which is now a unique image encoding method that can encode image signals having arbitrary shapes. An image signal having arbitrary shapes ordinarily consists of the shape information indicating the shape of an object and the pixel value information (color information) representing pixel values within an object. Concerning the shape information, the two-valued shape information indicating whether each pixel is significant(on the inside of the shape) or insignificant(on the outside of the shape), or the transparency information indicating the ratio(how much the object occludes the background) of respective pixels which is used in synthesizing with other images. When the transparency has only two levels, 0% and 100%, the shape information is identical-to the transparency information and thereby the arbitrary-shape-having image signal is represented by the two of the two-valued shape information and the pixel value information. Fig.31 is a drawing for explaining these information. The transparency information is an information representing how much ratio of each pixel is used for synthesis when a fish shown in figure 31(a) is synthesized with the other image. In figure 31(b), there is shown the value of transparency information in the horizontal scanning line indicated by a dotted line in the figure. The outside of the fish is perfectly transparent. Here, the transparency 0 is defined as being perfectly transparent for simplification. Hence, on the outside of the fish the transparency information has a value of 0, while on the inside of the fish it has a value of non-0. Fig.31(c) shows the transparency which is made two-valued as having two of 0 and non-0. In figure 31(c), the pixels having the non-0 transparency require encoding of the pixel value information, while the pixels having the 0 transparency do not need the pixel value information, so that the two-valued transparency information is very important to the pixel value information encoding. On the other hand, the component of the transparency information which can not be represented by two-valued information, as shown in figure 31(d), is multi-valued information which is called gray scale. The shape information represented by multi-valued information as described above can be treated by the waveform encoding similar as that for the pixel value information. While performing the image encoding, the intra-frame encoding based on the spacial correlation or the temporal correlation is separately used, both of the two are employed. In the inter-frame encoding, the motion in the close frames is detected, and the motion compensation is carried out for the detected motion. The motion vector is generally used for the motion compensation. In the above-mentioned VM3.0, the intra-frame encoding and the inter-frame encoding are adaptively switched each other block by block, and the motion compensation similar as in MPEG1/2 is carried out, whereby the efficiency of encoding is improved. As described above, when performing encoding to the image consisting of the shape information and the pixel value information, if the motion compensation encoding of a shape information is carried out using the motion vector of the pixel value information for the shape information to be used for the image synthesis, the efficiency of encoding is further improved than when the shape information is directly encoded. This is reported by ISO/IEC/JTC1/SC29/WG11 N1260 March 1996. Further, when the motion detection and motion compensation are executed, it is considered that it is efficient that the shape information is separated into the two-valued shape information component and the multi-valued information component, and the multi-valued information component as well as the pixel value information are subjected to the same waveform encoding together, which has been actually practiced. In the above-described prior art image encoding and the image decoding accompanying to this, there exist the following problems. Though MMR encoding is a representative one of the reversible (loss-less) encoding as described above, because of the reversibility, it is impossible to largely improve the compression rate by allowing the visually less-important picture-quality degradation. In addition, MMR is an intra-frame encoding method, and does not take into account the improvement of the compression rate by utilizing the inter-frame correlation. In MMR and MMMR which a modified version of MMR, only the difference between the change point of the current scanning line and the change point of the immediately previous scanning line is utilized, and the redundancy by the correlation as a straight line in the vertical direction is not sufficiently removed. Accordingly, the encoding efficiency is good when the change of the pixel value happens along the scanning line, but the encoding efficiency is bad when the change of the pixel value does not happen along the scanning line. MMR and MMMR also includes the horizontal encoding mode which does not utilize the correlation in the vertical direction at all in order to encode the pixels which can not be encoded as the difference of the change point of the immediately previous scanning line. This horizontal encoding mode has a room for further improving the efficiency with the use of the correlation in the vertical direction. Further, in the prior art MMR and MMMR, the hierarchical image reproduction by decoding part of bit stream is impossible. The other methods in which the hierarchical image reproduction is possible have no good encoding efficiency and have demerit of increasing the encoding bit number. Accordingly, there exists no encoding method which enables the effective hierarchical image reproduction. Further, when encoding the image consisting of shape information and image information by the motion compensation, the shape information is motion-compensated using the same motion vector as that for the image information in the prior art. However, similarly as that, if a sphere rotates, the figure drawn on the sphere moves, though the shape of the sphere does not change, the motion vector of the image information is not identical to that of the shape information. Therefore, in such a case no good encoding is carried out, which is a problem in the prior art encoding method. Furthermore, while in VM3.0, there is a method which tries to improve the encoding efficiency by adaptively switching the intra-frame encoding and the inter-frame encoding block by block as described, the judgment against intra-frame/inter-frame encoding is based on the pixel value information similarly as in the adaptive switching in MPEG1/2, so that it is difficult to appropriately and efficiently encode the shape information which is largely different from the pixel value information in its nature. The document "A region based motion compensated video codec for very low bitrate applications", Ebrahimi T. et al., IEEE International symposium on circuits and systems, 1-3 May, 1995, New Orleans, US, New York, NY, pages 457-461 discloses a method for transmitting a coded image signal which is obtained by coding an image signal including a shape information and a pixel value information. An intra-frame encoding mode or an inter-frame encoding mode may be used for encoding the image signal. The intra-frame encoding mode is used when encoding the shape signal. Disclosure of invention The present invention relates to an image decoding apparatus as defined in the appended claim. Brief description of drawings Fig.12 is a block diagram showing the structure of an image encoding apparatus according to an first embodiment not forming part of this invention. Fig.13 is a block diagram showing the structure of an image encoding apparatus according to a 2nd embodiment not forming part of this invention. Fig.14 is a block diagram showing the structure of an image encoding apparatus according to a 3rd embodiment not forming part of this invention. Fig.15 is a block diagram showing the structure of an image decoding apparatus according to a 4th embodiment not forming part of this invention. Fig.16 is a block diagram showing the structure of an image decoding apparatus according to a 5th embodiment not forming part of this invention. Fig.17 is a block diagram showing the structure of an image encoding apparatus according to a 6th embodiment not forming part of this invention. Fig. 18 is a block diagram showing the structure of an image encoding apparatus according to a 7th embodiment not forming part of this invention. Fig.19 is a block diagram showing the structure of an image encoding apparatus according to a 8th embodiment not forming part of this invention. Fig.20 is a block diagram showing the structure of an image encoding apparatus according to a 9th embodiment not forming part of this invention. Fig.21 is a block diagram showing the structure of an image encoding apparatus according to a 10th embodiment not forming part of this invention. Fig.22 is a block diagram showing the structure of an image encoding apparatus according to an 11th embodiment not forming part of this invention. Fig.23 is a block diagram showing the structure of an image encoding apparatus according to a 12th embodiment not forming part of this invention. Fig.24 is a block diagram showing the structure of an image encoding apparatus according to a 13th embodiment not forming part , of this invention. Fig.25 is a block diagram showing the structure of an image decoding apparatus according to a 14th embodiment of this invention. Fig.26 is a block diagram showing the structure of an image encoding apparatus according to a 15th embodiment not forming part of this invention. Fig.27 is a block diagram showing the structure of an image encoding apparatus according to a 16th embodiment not forming part of this invention. Fig.28 is a block diagram showing how the number of motion vectors is selected in an image encoding apparatus according to a 16th embodiment. Fig.29 is a block diagram showing the structure of an image encoding apparatus according to a 17th embodiment Fig. 30 is a drawing showing a floppy disk as an example of recording media for a image encoding program and a image decoding program according to a 18th embodiment not forming part of this invention. Fig.31 is a drawing for explaining the shape information of an image in an image encoding. Best Embodiments of Invention Embodiment 1 An image encoding apparatus according to a first embodiment not forming part of this invention receives an image signal consisting of a transparency signal indicating the ratio for synthesizing an image and a pixel value signal, as an input signal, and encodes the input signal with reference to a reference image. Fig.12 is a block diagram showing the structure of the image decoding apparatus according to the first embodiment. In the figure, 60a indicates a pixel value signal. 60b indicates a transparency signal. The pixel value signal and the transparency signal constitute a image signal and are input to the image encoding apparatus according to the 8th embodiment as input signals. 61 indicates a memory which temporarily stores data such as previously encoded and decoded image signals used as reference images. 62a and 62b indicate motion detectors which detect motion with the reference images to output motion vectors. 63a and 63b indicate motion compensation units which perform motion compensation with the image signal of the already encoded and decoded reference frame to generate reference pixel values. 64a and 64b indicate difference value calculators which calculate the difference value between the input signal and the motion-compensated signal, and output the difference value. 65a and 67b indicate encoders which encode the motion vectors. 67a and 65b indicate encoders which encode the difference values. 66a and 68b indicate encoded signals into which the motion vectors are encoded. 67a and 65b indicate encoded signals into which the difference values are encoded. A description is given of the image encoding apparatus according to the first embodiment as constructed above. The image encoding apparatus according to the 8th embodiment receives image signals, as the pixel value signal 60a and the transparency signal 60b. Here, the transparency signal is such a signal as shown in Fig.53(b) used for explaining the prior art, and indicates what ratio is used for synthesizing each pixel when it is combined with the other image. The pixel value signal 60a is input to the memory 61, the motion detector 62a and the difference value calculation means 64a. The transparency signal 60b is input to the memory 61, the motion detector 62b and the difference value calculation means 64b. The motion detectors 62a and 62b perform detecting motions by comparing the input signals with the already encoded and decoded pixel values contained by the reference image read out from the memory 61, and obtain motion vectors of each input signal. The motion vectors of the pixel value signals obtained by the motion detector 62a are output to the encoder 65a, the motion compensation unit 63a and the memory 61. The motion compensation unit 63a reads out the pixel value indicated by the motion vector of the pixel value signal from the memory 61, and outputs the motion-compensated value of the pixel value signal into the difference calculator 64a. The difference calculator 64a calculates the difference value between the input pixel value signal and motion-compensated value and obtains the same, and outputs the difference value to the encoder 67a. The motion vector of the pixel value signal is encoded in the encoder 65a to become encoded signal 66a, while the difference value is encoded in the encoder 67a to become encoded signal 68a. Similarly, the motion vector of the transparency signal obtained from the motion detector 62b is output to the encoder 67b, the motion compensation unit 63b and the memory 61. The motion compensation unit 63b performs motion compensation for the transparency signal, and outputs the obtained motion compensated value to the difference value calculator 64a. On the other hand, the difference value calculator 64b outputs the obtained difference value to the encoder 67a similarly to the 64a. Similar to the pixel value signal, the motion vector of the transparency signal is encoded in the encoder 67b to become the encoded signal 68b, and the difference value is encoded in the encoder 65b to become the encoded signal 66b. The first embodiment is an example of a reversible encoding, so that the encoded input signal is stored in the memory 61 and is used for encoding subsequent image signals(not shown). As described above, the image encoding apparatus according to the first embodiment has the motion detector 62a, motion compensation unit 63a, difference value calculator 64a, encoder 65a and encoder 67a, all of which process the pixel value signal 60a, and has the motion detector 62b, the motion compensation unit 63b, the difference value calculator 64b, the encoder 65b and the encoder 67b, all of which process the transparency signal 60b, whereby the pixel value signal and the transparency signal are separately subjected to the motion detection to obtain the motion vectors and are also subjected to the motion compensation. As described in the Prior Art section, in the prior art image encoding, when the image consisting of the shape information and pixel value information is encoded, concerning the shape information used for the image synthesis, in order to improve the encoding efficiency, the motion compensation for the shape information is carried out using the motion vector of the pixel value information. Accordingly, when encoding such a signal as the input image signal of the first embodiment, the motion compensation encoding for the transparency signal is performed using the motion vector of the pixel value signal. However, although the transparency signal is a signal representing the shape of the object, the motion vector does not always agree with the motion vector of the pixel value signal. For example, although the shape of a rotating disc is invariable, the drawings on the disc move. Hence, in this case, as the motion vector of the pixel value signal is much different from that of the transparency signal, when the motion compensation is performed for the transparency signal using the motion vector of the pixel value signal, the motion error becomes large and the code length of the difference value increases, resulting in the reduction of the encoding efficiency. As opposed to this, the image encoding apparatus according to the first embodiment performs motion compensation using another detected motion vectors rather than the motion vector of the pixel value signal and thereby obtains a more precise approximation to the input transparency signal by the motion compensated signal and improves the encoding efficiency as a result of the reduction of the motion compensation error. Also, in the image encoding apparatus according to the 8th embodiment, the input signal can be input block by block, and the motion compensation and the encoding can be performed for respective blocks, whereby the above-mentioned effect is obtained. Embodiment 2 An image encoding apparatus according to a 2nd embodiment not forming part of this invention, similarly to the first embodiment, receives an image signal consisting of a transparency signal and a pixel value signal, as input signals, and encodes the input signal with reference to a reference image. Fig.13 is a block diagram showing the structure of the image decoding apparatus according to the 2nd embodiment. In the figure, the numerals indicate the same as those in Fig.12, and the description is similar to that for the embodiment 1. The difference from the structure of the image encoding apparatus according to the first embodiment is that, in the image encoding apparatus according to the 2nd embodiment, the motion detector 62a obtains the motion vector from the pixel value signal 60a and outputs the motion vector to the motion detector 62b for the transparency signal 60b, and the motion detector 62b detects the motion from in the vicinity of the motion vector of the input pixel value signal. Also, the operation of the image encoding apparatus according to the 2nd embodiment is similar to that of the first embodiment except the motion detector 62a performs the above-mentioned output and the motion detector 62b performs the above-mentioned detection. As described above, in.the image encoding apparatus according to the 2nd embodiment, based on the structure of the first embodiment, the motion detector 62a obtains the motion vector from the pixel value signal 60a and outputs the motion vector to the motion detector 62b for the transparency signal 60b, and the motion detector 62b detects the motion of the transparency from in the vicinity of the motion vector of the input pixel value signal. That is, it is possible that when the motion of the transparency signal is detected, the result of the motion detection of the pixel value signal is used. Although the motion vectors of the pixel value signal and the transparency signal are sometimes largely different from each other as shown in the first embodiment, they are almost the same in most images. Therefore, when the motion vector of the transparency signal is detected, if the motion vector of the transparency signal is detected only in the vicinity of the motion vector of the pixel value signal, compared to the case of detecting independently of the pixel value signal, the calculation times required for the motion detection is reduced. Note that, compared to the case of the motion detection independent of the pixel value signal the number of motion vectors which can be selected is restricted, so that the motion compensation error of the transparency signal is more or less increased, but the ratio is slight. Accordingly, the image encoding apparatus according to the 2nd embodiment as well as the first embodiment performs the appropriate motion compensation for each signal, resulting in improving the encoding efficiency and reducing the calculation times of the motion detection. Note that, in the image encoding apparatus according to the 9th embodiment, although the motion vector of the pixel value signal is used for the motion detection of the transparency signal, it is possible that based on the structure of the 8th embodiment, the motion detector 62b obtains the motion vector from the transparency signal 60b and outputs the motion vector to the motion detector 62a for the pixel value signal 60a, and the motion detector 62a detects the motion of the pixel value signal from in the vicinity of the motion vector of the input transparency signal. That is, it is possible that when the motion of the pixel value signal is detected, the result of the motion detection of the transparency signal is used. Also, the calculation times of the motion detection can be reduced. Also, similarly to the first embodiment, the block-by-block encoding is possible. Embodiment 3 An image encoding apparatus according to a 3rd embodiment not forming part of this invention, similarly to the first and 2nd embodiments, receives an image signal consisting of a transparency signal and a pixel value signal, as an input signal, and encodes the input signal with reference to a reference image. Fig.14 is a block diagram showing the structure of the image decoding apparatus according to the 3rd embodiment. In the figure, 70 indicates a difference calculator for motion vectors which obtains the difference vector between the motion vector of the pixel value signal obtained from the motion detector 62a and the motion vector of the transparency signal obtained from the motion detector 62b. Though the encoder 67b encodes the motion vector of the transparency signal in the 8th embodiment, the encoder 67b encodes the difference vector of the motion vector obtained by the difference value calculator 70 in the 3rd embodiment. The other numerals indicate the same as those in Fig.12, and the description is similar to that in the first embodiment. The operation of the image encoding apparatus according to the 3rd first embodiment is similar to that of the first embodiment except that the motion detectors 62a and 62b output motion vectors to the difference value calculator 70, and the difference value calculator 70 obtains the above-mentioned difference vector to the encoder 67b and outputs the same, and the encoder 67b encodes the difference vector of the motion vector. As described above, in the image encoding apparatus according to the 3rd embodiment, based on the structure of the image encoding apparatus according to the first embodiment, the difference value calculator 70 for motion vectors is added to the structure, and thereby, instead of encoding the motion vector of the transparency signal, the difference vector between the motion vectors of the pixel value and the transparency vectors is encoded. As described in the 9th embodiment, since the motion vectors of both the signals often correlate, if the difference vector between the motion vectors of both the signals is encoded, the frequency of occurrence of the difference vector is concentrated in the neighborhood of 0 vector, whereby, performing the variable-length encoding which gives a code of a short code length to the difference vector in the neighborhood of 0 vector, the encoding efficiency is improved and the encoding can be performed with a smaller bit number. Note that, in the image encoding apparatus according to the 3rd embodiment, although the difference vector of the motion vectors of both the signals are encoded instead of the motion vectors of the transparency signal, there can be provided the structure in which the difference vector obtained by the difference value calculator 70 is output to the encoder 65a instead of 67b. If the difference vector of the motion vectors of both the signals is encoded instead of encoding the motion vector of the pixel value signal, the same result can be obtained. Also, similar to the first embodiment, the block-by-block encoding is possible. Embodiment 4 An image decoding apparatus according to a 4th embodiment not forming part of this invention appropriately decodes the encoded signal efficiently encoded by the image encoding apparatus according to the first embodiment. Fig.15 is a block diagram showing the structure of the image decoding apparatus according to the 4th embodiment. In the figure, 82a and 82b indicate encoded signals corresponding to the encoded signals 68a and 66b in Fig.12, respectively, into which the difference values in the pixel value signal and in the transparency signal are encoded respectively. 80a and 80b indicate encoded signals corresponding to the encoded signals 66a and 68b in Fig.12, respectively, into which the motion vectors in the pixel value signal and in the transparency signal are encoded respectively. 83a and 83b indicate encoders which encode the difference values in the pixel value signal and in the transparency signal, and output the encoded difference values in the pixel value signal and in the transparency signal, respectively. 81a and 81b indicate encoders which encode the motion vectors of the pixel value signal and of the transparency signal, and output the encoded motion vectors of the pixel value signal and of the transparency signal, respectively. 61 indicates a memory which temporarily stores data such as the already encoded and decoded image signal used as a reference image. 63a and 63b indicate motion compensation units which perform the motion compensation using the encoded motion vectors. 84a and 84b indicate difference value adders which perform the addition processing using the encoded difference values. 85a and 85b indicate encoded image signals. The operation of the image decoding apparatus according to the 4th embodiment as constructed above is explained. The signals 68a and 66b into which the difference values of the pixel value signal and of the transparency signal are encoded by the image encoding apparatus according to the first embodiment respectively, are input to the image decoding apparatus according to the 11th embodiment as the input signals 82a and 82b, and are decoded by the decoders 83a and 83b, and are output to the difference value calculators 84a and 84b as the difference values of the pixel value signal and the transparency signal, respectively. The signals 66a and 68b into which the motion vectors of the pixel value signal and of the transparency signal are encoded by the image encoding apparatus according to the first embodiment respectively, are input to the image decoding apparatus according to the 4th embodiment as the input signals 80a and 80b, and are decoded by the decoders 81a and 81b, and are output to the motion compensation units 63a and 63b as the motion vectors of the pixel value signal and the transparency signal, respectively. The motion compensation units 63a and 63b read out pixel values indicating the respective input motion vectors from the memory 61, and perform the motion compensation, and output the motion compensated values into the difference value adder 84a and 84b, respectively. The difference value adders 84a and 84b add the respectively input encoded difference value and motion compensated value, and output the decoded image signals 85a and 85b, respectively, which are stored in the memory 61. As described above, the image decoding apparatus according to the 11th embodiment has the decoder 81a, the decoder 83a, the motion compensation unit 63a, and the difference value calculator 84a, all of which perform the process of the encoded signal of the pixel value signal, and has the decoder 81b, the decoder 83b, the motion compensation unit 63b, and the difference value calculator 84b, all of which perform the process of the encoded signal of the transparency signal, whereby the encoded signals 80a and 82a of the pixel value signal, and the encoded signals 80b and 82b of the transparency signal can be separately subjected to the decoding process, whereby decoding can be appropriately performed to obtain the image signal. Note that, in the image decoding apparatus according to the 4th embodiment, although the encoded signal encoded by the image encoding apparatus according to the first embodiment is encoded, the encoded signal obtained by the image encoding apparatus according to the 2nd embodiment can be appropriately decoded. Also, the signals which have been input block by block and encoded for respective blocks in the first and 2nd embodiment can be received block by block to be appropriately decoded. Embodiment 5 An image decoding apparatus according to a 5th embodiment not forming part of this invention appropriately decodes the encoded signal efficiently encoded by the image encoding apparatus according to the 3rd embodiment. Fig.16 is a block diagram showing the structure of the image decoding apparatus according to the 5th embodiment. In the figure, 86 indicates a difference value adder for motion vectors which adds a decoded motion vector and a decoded difference motion vector. The other numerals are similar to those in Fig.15, and the description is similar to that in the 4th embodiment and is therefore omitted here. The operation of the image decoding apparatus according to the 5th embodiment as constructed above is described. The decoder 81a outputs the decoded motion vector of the pixel value signal obtained by decoding the input signal 80a, to the motion compensation unit 63a and the difference adder 86 for motion vectors. The decoder 80b receives, not the encoded signal of the motion vector of the transparency signal in the 4th embodiment, but the encoded signal 68b of the difference motion vector in the 3rd embodiment. The decoder 80b obtains, not the motion vector of the transparency signal by decoding in the 4th embodiment, but the difference vector, and outputs the decoded difference motion vector to the difference adder 86 for motion vectors. The output decoded difference motion vector is the difference vector between the motion vectors of the pixel value signal and the transparency signal. Therefore, by adding the difference vector with the decoded motion vector of the pixel value signal in the difference value adder 86, the motion vector of the transparency signal is obtained. The decoded motion vector of the transparency signal is output to the motion compensation unit 63b. The other part of the operation is the same as the process of the image decoding apparatus according to the 4th embodiment. The decoded signal 85a of the pixel value signal and decoded signal 85b of the transparency signal are the outputs of the apparatus. As described above, the image decoding apparatus according to the 5th embodiment has the structure which is based on the structure of the image decoding apparatus according to the 4th embodiment and which is added to the difference value adder 86 for motion vectors, and thereby performs addition of the decoded motion vector and the decoded difference vector, whereby the encoded signal output by the 3rd embodiment which outputs the encoded signal of the difference vector as an encoded signal can be appropriately decoded. Also, it is possible to respond in the situation whereby the encoding is performed block by block as in the 3rd embodiment, similar to in the 4th embodiment. Embodiment 6 An image encoding apparatus according to a 6th embodiment not forming part of this invention receives an image signal with blocked shapes which consists of the shape signal indicating the shape of the object and whether the pixel value of pixels is significant or not, and the pixel value signal, as an input signal, and encodes the input signal with reference to a reference image. Fig.17 is a block diagram showing the structure of the image encoding apparatus according to the 6th embodiment. In the figure, 60a indicates a pixel value signal. 60b indicates a shape signal. 60a and 60b constitute the image signal and are input to the image encoding apparatus according to the first embodiment as input signals. 69a and 69b indicate decoders which decode the encoded signals of the difference values output by the encoders 67a and 65b. 75a and 75b indicate difference value .adders which add the decoded difference value and the motion compensated value, and the result is stored in the memory 61. The other numerals are similar to those in Fig.12, and the description is similar to that in the first embodiment and is therefore omitted here. A description is given of the operation of the image encoding apparatus according to the 6th embodiment as constructed above. The image signal with blocked shapes, the input signal, is input to the image encoding apparatus according to the 6th embodiment as the pixel value signal 60a and the shape signal 60b. Here, the shape signal is the one shown in Fig. 31 used in the Prior Art section, consisting of the two-valued information shown in Fig.31(c) or multi-valued information shown in Fig.31(d). In the case of the multi-valued information, it is similar to the transparency signal in the first embodiment. In the image encoding apparatus according to the 6th embodiment, by the process similar to that in the first embodiment, the pixel value signal and the shape signal are encoded, and thereby the encoded signal 66a of the motion vector of the pixel value signal, the encoded signal 68a of the difference value of the pixel value signal, the encoded signal 66b of the motion vector of the shape signal and the encoded signal 68b of the difference value of the shape signal are obtained. Although the encoded signal is input to the memory 61 in the apparatus according to the first embodiment, in the 6th embodiment the encoded difference values are respectively decoded in the decoders 69a and 69b, and are output to the difference value adders 75a and 75b, and are added to the motion compensated values output by the motion compensation units 63a and 63b in the difference value adders 75a and 75b, and are input to the memory 61. Accordingly, the reference image used for the encoding is encoded and decoded, and is added to the motion compensated value, which is the difference from the 8th embodiment. As described above, the image encoding apparatus according to the 6th embodiment has the structure which is based on the structure of the image encoding apparatus according to the first embodiment and which is added to the decoders 69a and 69b and the difference value adders 75a and 75b, and therefore, similarly to the first embodiment, by reducing the motion compensation error the improvement of the encoding efficiency is realized, and moreover, though there accompanies a slight increase in the processing load, with the use of the more appropriate signal which is encoded and decoded as a reference image, and is added to the motion compensated value, a further reduction of the motion compensation error can be realized. Note that, the encoded signal output by the image encoding apparatus according to the 6th embodiment, similarly to the first embodiment, in the image decoding apparatus according to the 4th embodiment, is appropriately encoded. Embodiment 7 An image encoding apparatus according to a 7th embodiment not forming part of this invention, similar to the 6th embodiment, receives an image signal consisting of a shape signal and a pixel value signal as an input signal, and referring to a reference image, encodes this input signal. Fig.18 is a block diagram showing the structure of the image encoding apparatus according to the 7th embodiment of this invention. In the figure, the numerals are the same as those in Fig.17, and the description is similar to that in the 6th embodiment. In the image encoding apparatus according to the 7th embodiment, similar to the 2nd embodiment, the motion detector 62a for the pixel value signal 60a outputs the motion vector of the obtained pixel value signal to the motion detector 62b for the transparency signal 60b, and the motion detector 62b performs the motion detection of the transparency signal in the vicinity of the motion vector of the input pixel value signal, which is the difference from the structure of the image encoding apparatus according to the 6th embodiment. Also, the operation of the image encoding apparatus according to the 7th embodiment is similar to that of the 6th embodiment, except that the motion detector 62a performs the above-mentioned output and the motion detector 62b performs the above-mentioned detection. As described above, in the image encoding apparatus according to the 7th embodiment, based on the structure of the 6th embodiment, the motion detector 62a for the pixel value signal 60a outputs the motion vector of the obtained pixel value signal to the motion detector 62b for the shape signal 60b, and the motion detector 62b performs the motion detection of the shape signal in the vicinity of the motion vector of the input pixel value signal, and thereby similar to the 2nd embodiment, at the time of the motion detection of the shape signal, using the result of the motion detection of the pixel value signal, the calculation times of the motion detection can be reduced. Note that, the possible structure in which the motion vector of the pixel value signal can be detected in the vicinity of the motion vector of the shape signal, is similar to that of the 2nd embodiment, and it is similar to the 6th embodiment in which the encoded signal is obtained by the image encoding apparatus according to the 7th embodiment. Embodiment 8 An image encoding apparatus according to an 8th embodiment, similarly to the 6th and 7th embodiments, receives an image signal consisting of a shape signal and a pixel value signal as an input signal, and referring to a reference image, encodes this input signal. Fig.19 is a block diagram showing the structure of the image encoding apparatus according to the 8th embodiment. In the figure, the difference calculator 70 of the motion vector is similar to that of the 3rd embodiment shown in Fig. 13. And, the encoder 67b, similarly to that in the 3rd embodiment, encodes the difference vector of the motion vector obtained by the difference value calculator 70. The other numerals indicate the same as those in Fig.17, and the description is similar to that of the 6th embodiment. Concerning the operation of the image encoding apparatus according to the 8th embodiment, the motion detectors 62a and 62b output the motion vectors to the difference value calculator 70, and the difference value calculator 70 obtains the above-mentioned difference vector to output to the encoder 67b, and the encoder 67b encodes the difference vector of the motion vector, which is similar to that of the 3rd embodiment, while the other operations are similar to those of the 6th embodiment. As described above, the image encoding apparatus according to the 8th embodiment is based on the structure of the image encoding apparatus according to the 6th embodiment and is added to the difference value calculator 70 of the motion vector, and thereby encodes the difference vector between the motion vector of the pixel value signal and the motion vector of the shape signal instead of encoding the motion vector of the shape signal. Accordingly, similar to the 3rd embodiment, the performance of the variable-length encoding enables the further improvement of the encoding efficiency to be realized. Note that the case of encoding the difference vector instead of encoding the motion vector of the pixel value signal is possible, which is similar to the 3rd embodiment. Also, the encoded signal output by the image encoding apparatus according to the 8th embodiment can be, similarly to that in the 3rd embodiment, appropriately decoded by the image decoding apparatus according to the 5th embodiment. Embodiment 9 An image encoding apparatus according to a 9th embodiment, similar to the 6th to 8th embodiments, receives an image signal consisting of a shape signal and a pixel value signal as an input signal, and referring to a reference image, encodes this input signal. Fig.20 is a block diagram showing the structure of the image encoding apparatus according to the 9th embodiment. In the figure, 90 indicates the motion detector judgment unit which receives the input shape signal 60b and the motion vectors of the pixel value signal output by the motion detector 62a, and judges the propriety of the motion compensation of the shape signal with the motion vector of the pixel value signal, and according to the judgment, outputs the instruction whether the motion detection will be performed or not, to the motion detector 62b. The operation of the above-constructed image encoding apparatus according to the 9th embodiment is described. The processing of the pixel value signal 60a input to the image encoding apparatus according to the 9th embodiment, except for the point that the motion vector of the pixel value signal obtained in the motion detector 62a is also output to the motion detection judgment unit 90, is similar to the 6th embodiment, and thereby the encoded signal 66a of the motion vector of the pixel value signal and the encoded signal 68a of the difference value of the pixel value signal are obtained. On the other hand, the input shape signal 60b is first input to the motion detection judgment unit 90. The motion detection judgment unit 90 performs the motion compensation of the input shape signal 60b using the motion vector of the input pixel value signal, and compares the motion-compensated shape signal with the input shape signal 60, and judges whether both the shape signals have agreement or not. Thereafter, if there exists agreement, the motion vector of the pixel value signal is output to the motion detector 61b, and the motion detector 61b does not perform the motion detection of the shape signal and the input motion vector of the pixel value signal is substituted for the motion vector of the shape signal. As opposed to this, if there does not exist agreement in the result of the comparison of the motion detection judgment 90, the motion detection judgment 90 outputs such an instruction to the motion detector 61b that the motion detector 61b performs the motion detection, and the motion vector is calculated by the motion detector 61b. For the shape signal, the remaining processes are similar to those of the 6th embodiment, and the encoded signals 66b and 68b are obtained. As described above, the image encoding apparatus according to the 9th embodiment has the structure of the image encoding apparatus according to the 6th embodiment which is added to the motion detection judgment unit 90, and judges the propriety of the performance of the motion compensation of the input shape signal using the motion vector of the input pixel value signal, and if the result of the judgment is that it is possible, the motion detection for the input shape signal is not performed and thereby the omission of the calculation realizes the reduction of the processing load. If the result of the judgment is that it is impossible, the motion detection for the input shape signal is performed similarly to the 6th embodiment and thereby the encoding efficiency and picture quality of the encoded signal are not affected. Note that, in the 9th embodiment, although the detection of the shape signal is not performed when the motion-compensated shape signal and the input shape signal have agreement, if the slight degradation of the encoding efficiency due to the increase in the motion compensation error is tolerable, it is also possible that the motion detection is not performed when the error due to the motion compensation in the judgment is equal to or smaller than the given value, and thereby a further reduction of the processing load can be realized. Embodiment 10 An image encoding apparatus according to a 10th embodiment, similar to the 6th to 9th embodiments, receives an image signal consisting of a shape signal and a pixel value signal as an input signal, and referring to a reference image, encodes this input signal. Fig.21 is a block diagram showing the structure of the image encoding apparatus according to the 10th embodiment. In the figure, 93 indicates the switching judgment unit which receives the motion vectors of the pixel value signal and shape signal, and similarly to 9th embodiment, judges the propriety of the motion compensation of the shape signal using the motion vector of the pixel value signal, and according to the judgment, gives an instruction to the switching unit 94. The switching unit 94, according to the instruction of the switching judgment unit 93, switches the motion vector of the pixel value signal and the motion vector of the shape signal for the output to the difference value calculator 70. The memory 95 for the motion vector performs the temporal storage in order to input the motion vector output by the switching unit 94 to the difference value detector 70 after a delay. The other numerals are similar to those of Fig.19, and the description is similar to that of the 8th embodiment. The operation of the image encoding apparatus according to the 10th embodiment is similar to that of the 8th embodiment, except for that according to the judgment of the switching judgment unit 93, the two embodiments differ in the difference motion vector to be obtained by the difference value calculator 70, so the operation of that alone is described. The switching judgment unit 93 receives and compares the encoded signal of the motion vector of the pixel value signal and the motion vector of the shape signal, both of which are of the immediately previous encoded input signal, and checks whether the motion vector of the shape signal of the immediately previous encoded input signal is already encoded or not. That is, by processing the immediately previous encoded input signal, it is' checked whether the encoded signal of the difference motion vector obtained from the encoder 67b has been the difference vector between the motion vector of the pixel value signal and the motion vector of the shape signal, or the difference vector between the motion vectors of the shape signals. Thereafter, when the difference vector of the motion vectors of the shape signals has been encoded, by sending an instruction to the switching unit 94, the motion vector detected from the shape signal is input to the memory 95 for delay. Accordingly, in this case, the encoder 67b obtains the difference vector between the immediately previous encoded motion vector of the shape signal obtained from the memory 95 for delay and the motion vector detected from the input shape signal, and encodes the difference vector. On the other hand, when the difference vector between the motion vectors of the pixel value and shape signals of the immediately previous input signal has been encoded, by sending an instruction to the switching unit 94, similarly to the 8th embodiment, the difference vector of the motion vectors of both the signals is to be encoded. As described above, the structure of the image encoding apparatus according to the 10th embodiment is based on the structure of the image encoding apparatus according to the 8th embodiment and is added to the switching judgment 93, the switching unit 94 and the memory 95 for delay, and thereby when the motion vector of the immediately previous shape signal is encoded, the difference vector between the motion vector and detected motion vector are obtained and encoded, and the encoding efficiency can be improved by utilizing the difference between the motion vectors of the shape signals which highly correlate. Note that, in the 10th embodiment, although the judgment and the encoding of the difference vector are performed for the motion vector of the shape signal, the judgment and the encoding of the difference vector can be also performed for the motion vector of the pixel value signal, and similarly, an improvement of the encoding efficiency can be realized. Embodiment 11 An image encoding apparatus according to an 11th embodiment not forming part of this invention receives image signals consisting of at least one of either the shape information or the transparency information, and the pixel information, as input image signals, and encodes the image signals according to the mode suitable for respective image signals. Fig.22 is a block structure showing the structure of the image encoding apparatus according to the 11th embodiment. In the figure, 101 indicates the input image signal which consists of at least one of either the shape information or the transparency information, and the pixel information. 102 indicates the blocking unit which blocks the input image signal 101 and outputs the blocked shape signal 103, the blocked transparency signal 105 and the blocked pixel value signal 107. 110 indicates the shape encoding mode judgment unit, and 114 indicates the transparency encoding mode judgment unit, and 116 indicates the pixel value encoding mode judgment unit, which judges the respective encoding modes suitable for the shape signal 103, the transparency signal 105 and the pixel value signal 107, and outputs the shape encoding mode 111, the transparency encoding mode 115 and the pixel value encoding mode 119. 112 indicates the shape encoder, 116 indicates the transparency encoder and 120 indicates the pixel value encoder, all of which encode respective signals according to each judgment unit, and output the shape encoded signal 113, the transparency encoded signal 117 and the pixel value encoded signal 121, respectively. 122 indicates the mode encoder which collectively encodes all of the encoding modes 111, 115 and 119, and outputs the encoded mode signal 123. The operation of the above-constructed image encoding apparatus according to the 11th embodiment is explained. Initially, the input image signal 101 consisting of the shape information, the transparency information and the pixel value information is input to the image encoding apparatus according to the 11th embodiment. Here, the transparency information and the shape information are explained referring to Fig.31 used in the Prior Art section. The transparency information represents the ratio of each pixel to be synthesized when the image shown in Fig.31(a) is combined with another image, and basically is multi-valued information such as what is shown in Fig.31(d). The shape information is two-valued information such as what is shown in Fig.31(c), which is two-valued transparency information with 0 and non-0 indicating that the object "exists/non-exists". Note that when the transparency information has only two of the perfect transparency and the perfect opacity, the information can be represented only by the shape signal as described above and thereby the transparency information is not required. Accordingly, in this case, only the shape information and the pixel value information are encoded or decoded. The blocking unit 102 blocks the input image signal 101 by integrating a plurality of pixels based on the corresponding relation between the pixels of the shape information·transparency information and the pixel value information, and outputs the blocked shape signal 103, the blocked transparency signal 105 and the blocked pixel value signal 107. The shape signal 103 is output to the shape encoding mode judgment unit 110 and the shape encoder 112, and the transparency signal 105 is output to the transparency encoding mode judgment unit 114 and the transparency encoder 116, and the pixel value signal 107 is output to the pixel value encoding mode judgment unit 118 and the pixel value encoder 120. The shape encoding mode judgment unit 110, the transparency encoding mode judgment unit 114 and the pixel value encoding mode judgment unit 118 judge suitable encoding modes for the input shape signal 103 respectively, the transparency signal 105 and the pixel value signal 107 respectively, and output the shape encoding mode 111, the transparency encoding mode 115 and the pixel value encoding mode 119. Each encoding mode is output to each encoding mode unit, and to the mode encoding unit 122. The shape encoder 112, the transparency encoder 116 and the pixel value encoder 120 output the respective input signals according to each of the input encoding modes, and output the shape encoded signal 113, the encoded transparency signal 117 and the encoded pixel value signal 121. On the other hand, the mode encoder 122 collectively encodes all of the input encoding modes, and outputs the encoded mode signal 123. The shape encoded signal 113, the encoded transparency signal 117, the encoded pixel value signal 121 and the encoded mode signal 123 are the encoded outputs of the image encoding apparatus according to the 11th embodiment. As described above, the encoded outputs of the image encoding apparatus according to the 11th embodiment has the blocking unit 101 which blocks the input image signal and separates the input image signal into the shape signal, the transparency signal and the pixel value signal and outputs these signals, and the encoding mode judgment units 110, 114 and 118 which judge the respective encoding modes suitable for each signal, and the encoder 112, 116 and 120 which encode each signal according to each encoding mode, and the mode encoder 122 which collectively encodes all of the encoding modes, and thereby it is possible that the encoding is performed according to the mode suitable for each separated signal and all of the information related to the selected mode is collectively encoded. Since the shape information, the transparency information and the pixel value information often have mutual correlation, the same encoding mode is likely to be selected. Therefore, by performing the variable-length encoding wherein the codes given the same mode are to have the short code length, which results in the possible reduction of the bit number of the encoded signal. Embodiment 12 An image encoding apparatus according to a 12th embodiment not forming part of this invention receives image signals consisting of at least one of either the shape information or the transparency information, and the pixel information, as input image signals, and encodes the image signals according to the respective modes suitable for each image signal. Fig.23 is a block structure showing the structure of the image encoding apparatus according to the 12th embodiment. In the figure, the shape encoding mode judgment unit 110 judges the encoding mode suitable for the shape signal 103, and outputs the result of the judgment as the encoding mode to the shape encoder 112 and the mode encoder 122, and also to the transparency encoding mode judgment 130 and the pixel value encoding mode judgment unit 132. Thereafter, the transparency encoding mode judgment 130 carries out judgment, referring to the input shape encoding mode 111, and outputs the result of the judgment as the encoding mode to the transparency encoder 116 and the mode encoder 122, and also to the pixel value encoding mode judgment unit 132. The pixel value encoding mode judgment unit 132 carries out judgment, referring to the input shape encoding mode 111 and the transparency encoding mode 115. The operation of the image encoding apparatus according to the 12th embodiment is similar to that of the 11th embodiment except the judgments of the respective mode judgment units, and similarly, outputs the shape encoded signal 111, the encoded transparency signal 117, the encoded pixel value signal 121 and the encoded mode signal 123. As described above, the image encoding apparatus according to the 12th embodiment has the transparency encoding mode judgment unit 130 which judges the encoding mode of the transparency signal with reference to the shape encoding mode, and the pixel value encoding mode judgment unit 132 which judges the encoding mode of the pixel value signal with reference to both the shape encoding mode and the transparency encoding mode, and thereby the selected modes are likely to be the same. Accordingly, in the mode encoder 122 in which a shorter code is given in the case that the modes are the same, the efficiency of the variable-length encoding can improve more than in the 11th embodiment and can reduce the bit number of the encoded mode signal, which is the obtained result. Embodiment 13 An image encoding apparatus according to a 13th embodiment improves the encoding efficiency of the encoded mode signal, similarly to that of the 12th embodiment. Fig.24 is a block structure showing the structure of the image encoding apparatus according to the 13th embodiment. In the figure, the pixel value encoding mode judgment unit 118 judges the encoding mode suitable for the pixel value signal 107, and outputs the result of the judgment as the encoding mode to the pixel value encoder 120 and the mode encoder 122, and also to the transparency encoding mode judgment 136 and the shape encoding mode judgment unit 138. Thereafter, the transparency encoding mode judgment 136 carries out judgment, referring to the input pixel value encoding mode 119, and outputs the result of the judgment as the encoding mode to the transparency encoder 116 and the mode encoder 122, and also to the shape encoding mode judgment unit 138. The shape encoding mode judgment unit 138 carries out judgment, referring to the input pixel value encoding mode 119 and the transparency encoding mode 115. The operation of the image encoding apparatus according to the 13th embodiment is similar to that of the 11th embodiment except the judgments of the respective mode judgment units, and similarly, outputs the shape encoded signal 113, the encoded transparency signal 117, the encoded pixel value signal 121 and the encoded mode signal 123. As described above, the image encoding apparatus according to the 13th embodiment has the transparency encoding mode judgment unit 136 which judges the encoding mode of the transparency signal with reference to the pixel value encoding mode, and the shape encoding mode judgment unit 138 which judges the encoding mode of the shape signal with reference to both the pixel value encoding mode and the transparency encoding mode, and thereby the selected modes are likely to be the same. Accordingly, in the mode encoder 122 in which shorter codes are given in the case that the modes are the same, the efficiency of the variable-length encoding can improve more than in the 11th embodiment and can reduce the bit number of the encoded mode signal, which is the obtained result. Embodiment 14 An image decoding apparatus according to a 14th embodiment of this invention appropriately decodes the encoded signal encoded by the image encoding apparatus according to the 11th embodiment. Fig.25 is a block structure showing the structure of the image decoding apparatus according to the 14th embodiment. In the figure, input signals 113, 117, 119 and 123 are the shape encoded signal 113, the encoded transparency signal 117, the encoded pixel value signal 119 and the encoded mode signal 123, respectively, all of which are output by the image encoding apparatus according to the 18th embodiment. 150 indicates the mode decoder which decodes the encoded mode signal 123, and outputs the shape encoding mode 151, the transparency encoding mode 153, and the pixel value encoding mode 155. 156 indicates the shape decoder, 158 indicates the transparency decoder and 160 indicates the pixel value decoder, which encode the shape encoded signal 113, the encoded transparency signal 117 and the encoded pixel value signal 119, respectively, according to the encoding modes input from the mode decoder 150, and output the decoded shape signal 157, the decoded transparency signal 159 and the decoded pixel value signal 161, respectively. 162 indicates the reverse blocking unit which receives and integrates the decoded shape signal 157, the decoded transparency signal 159 and the decoded pixel value signal 161, and outputs the decoded image signal 163. The operation of the above-constructed image decoding apparatus according to the 14th embodiment is described. The image decoding apparatus according to the 14th embodiment receives the shape encoded signal 113, the encoded transparency signal 117, the encoded pixel value signal 119 and the encoded mode signal 123, to be output into the shape decoder 156, the transparency decoder 158, the pixel value decoder 160 and the mode decoder 150, respectively. The mode decoder 150 decodes the encoded mode signal 123, and outputs the shape encoding mode 151, the transparency encoding mode 153, and the pixel value encoding mode 155 into the shape decoder 156, the transparency decoder 158 and the pixel value decoder 160, respectively. The shape decoder 156, the transparency decoder 158 and the pixel value decoder 160 decode the input encoded signals according to the input encoding mode respectively, and output the decoded shape signal 157, the decoded transparency signal 159 and the decoded pixel value signal 161 into the reverse blocking unit 162. The reverse blocking unit 162 integrates the input decoded signals and outputs the decoded image signal 163. As described above, the image decoding apparatus according to the 14th embodiment has the mode decoder 150, the shape decoder 156, the transparency decoder 158, the pixel value decoder 160 and the reverse blocking unit 162, and thereby appropriately decodes the encoded signal obtained by the image encoding apparatus according to the 11th embodiment, and performs the integration, and can obtain the decoded image signal 163. Note that, in the image decoding apparatus according to the 14th embodiment, although the encoded signal obtained by the image encoding apparatus according to the 11th embodiment, the encoded signals obtained by the image encoding apparatuses according to the 12th and 13th embodiments can be also appropriately decoded. Embodiment 15 An image encoding apparatus according to a 15th embodiment not forming parts of this invention performs encoding of an input signal, switching the intra-/inter-frame encodings adaptable to the input signal. Fig.26 is a block structure showing the structure of the image encoding apparatus according to the 15th embodiment. In the figure, 178 indicates an intra-/inter-frame encoding judgment unit of the pixel encoding which judges the intra- or inter- for the encoding mode of the pixel value signal, and outputs the encoding mode 119 of the pixel value signal. 138 indicates the shape encoding mode judgment unit which corresponds to the shape encoding mode judgment unit in the 13th embodiment indicated by 138 in Fig.24. 170 and 176 indicate the switches which are switched according to the output of the judgment unit 178 and decide the encoding mode of the shape signal. 172 indicates the intra-/inter-frame encoding judgment unit which judges the intra- or inter- for the encoding mode of the shape signal, and outputs the encoding mode 173 of the shape signal. The other numerals are similar to those in Fig.22, and the description is similar to that of the 11th embodiment. A description is given of the above-constructed image encoding apparatus according to the 15th embodiment. Initially, the input image signal 101 is input to the image encoding apparatus according to the 15th embodiment, and then the blocking unit 102, similarly to the 11th embodiment, performs the blocking and the signal separation, and outputs the pixel value signal and the shape signal. When the separated pixel value signal 107 is input to the intra-/inter-frame encoding judgment unit of the pixel value encoding, the judgment unit 178 judges whether the encoding is performed by the intra-frame encoding or inter-frame encoding, and outputs the result of the judgment as the pixel value encoding mode indicating "intra" or "inter" to the pixel value encoder 120, the mode encoder 122 and the shape encoding mode judgment 138. In the shape encoding mode judgment unit 138, the switch 170 and 176 are switched according to the pixel value encoding mode 119. The switching is performed in such a manner that the judgment unit 178 does not receive the input when the pixel value encoding mode indicates "intra", while the judgment unit 178 receives the input when the pixel value encoding mode indicates "inter". Accordingly, when the pixel value encoding mode 119 indicates the intra-frame encoding, the shape judgment mode 111 indicating the intra-frame encoding is output from the judgment unit 138. On the other hand, when the pixel value encoding mode 119 indicates the inter-frame encoding, the intra-/inter-frame encoding judgment unit 172 judges whether the encoding of the particular shape signal is performed by the intra-frame encoding or the inter-frame encoding for the shape signal 105, and outputs the result of the judgment as the shape encoding mode 111. In either of the cases, the shape encoding mode 111 is output to the shape encoder 112 and the mode encoder 122. And, the operations of the pixel value encoder 120, the shape encoder 112 and the mode encoder 122 are similar to those of the 11th embodiment, all of which output respective encoded signals. As will be apparent from the above-described operation, in the image encoding apparatus according to the 15th embodiment, when the pixel value signal is intra-frame encoded, the shape signal is always intra-frame encoded. In general, since when the pixel values do not have agreement, the shapes do not have agreement, either, and therefore when the pixel value signal should be intra-frame encoded; that is, the pixel value signal has a small temporal correlation, even if the number of the encoding mode for encoding, the shape signal is restricted similarly to the 22nd embodiment, the encoding efficiency in encoding the shape signal is scarcely degraded. Also, there is the case that the pixel values to be synthesized will change though the shape signal in the synthesis is constant such as like a fixed picture(synthesized picture) and the like, and in this case, even if the inter-frame encoding is selected according to the pixel value signal, the inter-frame encoding for the shape signal is not always appropriate. In the image encoding apparatus according to the 15th embodiment, when the inter-frame encoding is selected for the pixel value signal, which of the intra-/inter-frame encodings to be selected is judged and thereby it is also possible to select the intra-frame encoding for the shape signal, and therefore it is possible to prevent the encoding efficiency from seriously degrading due to the inappropriate inter-frame encoding for encoding the shape signal. Also, when at least either the shape signal or the pixel value signal is inter-frame encoded, a lot of additional information is required for the motion compensation and so on to be carried out in the inter-frame encoding. In the image encoding apparatus according to the 22nd embodiment, there is no case that only the shape signal is inter-frame encoded, so that when the intra-frame encoding is selected for the pixel value signal, the bit number can be saved. Generally, the above-mentioned additional information has the smaller bit number than when the pixel value signal is intra-frame encoded, but if compared to the bit number required for intra-frame encoding the shape signal, the bit number is of an amount that can not be ignored and this has a big effect. As described above, the image encoding apparatus according to the 15th embodiment has the intra-/inter-frame encoding judgment unit 178 for the pixel value signal and the shape encoding mode judgment unit 138 containing the intra-/inter-frame encoding judgment unit 172 for the shape signal, and thereby the intra-frame encodes the encoding mode of the shape signal when the encoding mode of the pixel value signal is the intra-frame encoding, while judges and selects the encoding mode for the shape signal when the encoding mode of the pixel value signal is the inter-frame encoding, which causes the correlation between the encoding mode 119 for the pixel value signal and the encoding mode 111 for the shape signal to be higher and. thereby realizes the reduction of the bit number of the encoded mode signal, and makes it possible that the bit number of the additional information for the motion compensation is reduced as a result of the prevention of the choice for carrying out inter-frame encoding. Embodiment 16 An image encoding apparatus according to a 16th embodiment not forming part of this invention performs the encoding of the input signal, switching the number of the motion vectors in encoding adapting to the input signal. Fig.27 is a block structure showing the structure of the image encoding apparatus according to the 16th embodiment. In the figure, 188 indicates the motion vector number judgment unit for encoding the pixel value, which judges what number of motion vectors should be and outputs the encoding mode 119 for the pixel value signal. 138 indicates the shape encoding mode judgment unit which corresponds to the shape encoding mode judgment unit according to the 20th embodiment indicated by 138 in Fig.24. 180 and 186 are switches which switch according to the output of the judgment unit 188 and determine the encoding mode for the shape signal. 182 indicates the motion vector number judgment unit for encoding the shape, which judges what number of motion vectors should be and outputs the encoding mode 183 for the shape signal according to the result of the judgment. The other encodings are similar to those in Fig.22, and the description is similar to that for the 11th embodiment. The description is given of the image encoding apparatus according to the 16th embodiment as constructed above. Initially, the image encoding apparatus according to the 16th embodiment receives the input image signal 101, and the blocking unit 102, similar to the 11th embodiment, performs the blocking and separation of the signal and outputs the pixel value signal and the shape signal. The motion vector number judgment unit 188 for encoding the pixel value receives the separated pixel value signal 107, and then judges the signal to be encoded for what number of the motion vectors for the pixel value signal 107 is, and then outputs the result of the judgment as the pixel value encoding mode 119 to the pixel value encoder 120, the mode encoder 122 and the shape encoding mode judgment 138. Fig.28 is a drawing for explaining the number of the motion vectors. Since the motion is complicated in the vicinity of the contour of an object, it is very difficult to sufficiently reduce the motion compensation error by employing one motion vector(MV) per block. In this case, it is known that it is desirable to divide the block, and then give the divided blocks to the motion vectors, and this changing of the number of the motion vectors adaptively according to the nature of the image improves the encoding efficiency. Accordingly, the image encoding apparatus according to the 16th embodiment adaptively switches the motion compensation with the use of one motion vector(MV1) per block as shown in the figure and the motion compensation with the use of a total of 4 pieces of motion vectors (MV1,MV2,MV3,MV4) which are given respectively to one of the divided blocks which the particular block is divided into. Therefore, the judgment unit 188 judge whether the number of the motion vectors is 1 piece or 4 pieces, and outputs "1" or "4" as the encoding mode for encoding the pixel value. In the shape encoding mode unit 138, the switches 180 and 186 are switched according to the pixel value encoding mode. The switching is performed so that the judgment unit 182 can't receive the input when the pixel value encoding mode indicates "1", while the judgment unit 182 can receive the input when the pixel value encoding mode indicates "4". Accordingly, when the. pixel value encoding mode 119 is "1", the minimum number "1" of the motion vectors as the shape judgment mode 111 is output. On the other hand, when the pixel value encoding mode 119 indicates "4", the motion vector number judgment unit 182 judges whether the number of the motion vectors should be 1 piece or 4 pieces for the shape signal 105, and outputs the result of the judgment as the shape encoding mode 111. In either of the cases, the shape encoding mode 111 is output to the shape encoder 112 and the mode encoder 122. And, the operations of the pixel value encoder 120, the shape encoder 112 and the mode encoder 122 are similar to those of the 11th embodiment, and the respective encoded signals are output. As a result of the above-described operation, in the image encoding apparatus according to the 16th embodiment, when the pixel value signal is encoded using the minimum number of the motion vectors, the shape signal is always encoded using the minimum number of the motion vectors. As the number of the motion vectors is increased, the information required for encoding the motion vectors adversely becomes larger. In this case, by the reduction of the number of the motion vectors for encoding the shape signal, an increase of the load is prevented. As described above, the image encoding apparatus according to the 16th embodiment has the motion vector number judgment unit 188 for encoding the pixel value and shape encoding mode judgment unit 138 containing the motion vector number judgment unit 182 for encoding the shape. Thereby when the encoding mode for the pixel value signal uses the minimum number of motion vectors the encoding mode for the shape signal uses the minimum number. And when the encoding mode for the pixel value signal uses a lot of motion vectors the encoding mode for the shape signal is judged and then selected. This causes the correlation between the encoding mode 119 for the pixel value signal and the encoding mode 111 for the shape signal and makes it possible that the bit number of the encoded mode signal is reduced, and which causes the prevention of the selection when the number of the motion vectors is increased and thereby makes it possible that the bit number is prevented from increasing due to the increase in the additional information. Embodiment 17 An image encoding apparatus according to a 17th embodiment not forming part of this invention performs encoding of the input signal, switching the changing and non-changing of the quantizing step adapting to the input signal. Fig.27 is a block structure showing the structure of the image encoding apparatus according to the 17th embodiment. In the figure, 198 indicates the quantizing step change/non-change judgment unit for encoding the pixel value which judges whether the quantizing step is performed or not for the encoding mode for the pixel value signal, and outputs the encoding mode 119 for the pixel value signal. 138 indicates the shape encoding mode judgment unit which corresponds to the shape encoding mode judgment unit according to the 13th embodiment indicated by 138 in Fig.24. 190 and 196 indicate the switches which are switched according to the output of the judgment 198 and determine the encoding mode for the shape signal. 192 indicates the quantizing step change/non-change judgment unit for encoding the shape which judges whether or not the quantizing step is performed for the encoding mode for the shape signal, and outputs the encoding mode 113 for the shape signal depending on the result of the judgment. The other encodings are similar to those in Fig.22, and the description is similar to that for the 11th embodiment. The description is given of the image encoding apparatus according to the 17th embodiment as constructed above. Initially, the image encoding apparatus according to the 24th embodiment receives the input image signal 101, and the blocking unit 102, similar to the 18th embodiment, performs the blocking and separation of the signal and outputs the pixel value signal and the shape signal. The quantizing step change/non-change judgment unit 198 receives the separated pixel value signal 107, and then judges whether or not the quantizing step is performed for the pixel value signal 107, and then outputs the result of the judgment as the pixel value encoding mode 119 to the pixel value encoder 120, the mode encoder 122 and the shape encoding mode judgment 138. In the shape encoding mode unit 138, the switches 190 and 196 are switched according to the pixel value encoding mode. The switching is performed so that the judgment unit 192 can't receive the input when the pixel value encoding mode indicates "non-change", while the judgment unit 192 can receive the input when the pixel value encoding mode indicates "change". Accordingly, when the pixel value encoding mode 119 indicates that the quantizing step is not changed, the shape judgment mode 111 indicating "non-change" is output. On the other hand, when the pixel value encoding mode 119 indicates that the quantizing step is changed, the judgment unit 192 judges whether or not the quantizing step is performed for the shape signal 105, and outputs the result of the judgment as the shape encoding mode 111. In either of the cases, the shape encoding mode 111 is output to the shape encoder 112 and the mode encoder 122. And, the operations of the pixel value encoder 120, the shape encoder 112 and the mode encoder 122 are similar to those of the 11th embodiment, and the respective encoded signals are output. Since the value of the quantizing step is directly related to the compression rate, namely the transmission rate of encoded signals, generally, in order that the transmission rate or recording rate of the encoded signal into which the image is encoded should be constant, the quantizing step is coarsely controlled if the transmission rate is equal to or larger than the given value, while the quantizing step is finely controlled if the transmission rate is less than the given value. And, since the value of the quantizing step also directly influences the picture quality of the encoded signal, when the image is one in which there exist step-like changes of the pixel values, as the degradation of the picture quality in the amplitude direction is difficult to be visually detected, it is possible to make the compression rate higher by making the quantizing step larger. In this case, the changing of the quantizing step is usually performed according to the change of the pixel value. When control of the changing of the quantizing step as described above is performed, the information indicating "the quantizing step has been changed" is added to each block and encoded along with the image data. However, it is often that the change of the quantizing step should be performed in such a manner that the pixel value signal and the shape signal are simultaneously changed, so that when the quantizing step for the pixel value signal is not changed, even if the change of the quantizing step for the shape signal is prevented, the degradation of the picture quality caused by the restriction is small, meanwhile the additional information indicating the change of the quantizing step is reduced to a large extent. As described above, the image encoding apparatus according to the 17th embodiment has the quantizing step change/non-change judgment unit 198 for encoding the pixel value, and the shape encoding mode judgment unit 138 containing the quantizing step change/non-change judgment unit 192 for encoding the shape, and thereby when the encoding mode for the pixel value signal is "quantizing step non-change", the encoding mode for the shape signal is "quantizing step non-change", while when the encoding mode for the pixel value signal is "quantizing step change", the encoding mode for the shape signal is judged and selected, which causes the correlation between the encoding mode 119 for the pixel value signal and the encoding mode 111 for the shape signal, and makes it possible for the bit number of the encoded mode signal to be reduced, and which causes the prevention of the selection of the changing the quantizing step and thereby makes it possible that the increase in the additional information due to the change of the quantizing step is prevented and the bit number is reduced. Note that, although the structures of the image encoding apparatuses according to the 15th to 17th embodiments are based on the 13th embodiment shown in Fig.24, it is also possible for them to be based on the 12th embodiment shown in Fig.23, and also, the correlation of the encoding modes becomes higher and the additional information is prevented from increasing, which realizes the reduction of the bit number. Also, it is possible to base it on the 11th embodiment shown in Fig.20, and the bit number is reduced, realizing the encodings suitable for the respective signals. Also, the encoded signals obtained by the image encoding apparatuses according to the 15th to 17th embodiments can be appropriately decoded by the image decoding apparatus according to the 14th embodiment. Also, although in the 11th to 14th embodiments the input image signal consists of the transparency information and the shape information in addition to the pixel value information and is separated into the pixel value signal, the transparency signal and the shape signal, in the 15th to 17th embodiments the input image signal is separated into the pixel value signal and the shape signal. Concerning this, when also in the 15th to 17th embodiments the transparency information and the shape information have agreement, it is possible to use only the shape information, while when there is not agreement, if the transparency information is made the shape signal, or the transparency information which is a multi-valued signal is processed along with the pixel value information in the blocking unit, the shape signal and the pixel value signals are obtained. Embodiment 18 An image encoding program recording medium and an image decoding program recording medium realize the image encoding apparatuses and the image decoding apparatuses according to the 1st to 17th embodiments. Fig.30 shows a floppy disk which is an example of a recording medium which records the program. The image encoding program is recorded in the floppy disk shown in Fig.30, and is executed on a personal computer or a work station or the like, and thereby realizes the image encoding apparatus . Similarly, the image decoding program is recorded on the floppy disk shown in Fig.30, and is executed on a personal computer or a work station or the like, and thereby realizes the image decoding apparatus. As described above, the program recording media according to the 18th embodiment record the image decoding program, and thereby on a computer system such as an ordinary personal computer and the like, the image decoding apparatus according to this invention can be realized. Further, in the 18th embodiment, although the floppy disk is presented as a recording medium, an IC card, a CD-ROM, an optical disc and a cassette tape or the like can be similarly employed, if it is a medium which can record the programs.

Claims: An image decoding apparatus which receives an encoded signal including shape information indicating a shape of an object, pixel value information indicating a pixel value of each of pixels constituting the object, and mode identifying information indicating respective encoding modes for the shape information and for the pixel value information and decodes the encoded signal, comprising: a first decoding unit (150) operable to decode the encoded signal to obtain mode identifying information indicating respective encoding modes for the shape information and for the pixel value information, the shape information and the pixel value information being encoded according to respective encoding modes for the shape information and the pixel value information, the respective encoding mode being selected from one of intra-coding mode and inter-coding mode; a second decoding unit (156, 160) operable to subject the shape information to a shape decoding process corresponding to the obtained mode identifying information and the pixel value information to a pixel value decoding process corresponding to the obtained mode identifying information; and a reverse blocking unit (162) operable to integrate the shape information and the pixel value information which are output from the second decoding unit to obtain a decoded image signal.

Inventors: KADONO SHINYA, KADONO, SHINYA
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: H04N7
IPC codes: H04N7, G06T9