Interframe predicting method and picture signal coding/decoding apparatus

Abstract: In an interframe move predicting method for prediction of the move in a bidirectionally predictive-coded frame (B0) from an intra-coded frame (I0) and a predictive-coded frame (P0), the improvement predicts the move in another bidirectionally predictive-coded frame (B1) from the preceding motion compensated interpolated frame (B0) and the predictive-coded frame (P0). Also disposed is a picture signal coding apparatus capable of executing orthogonal transformation of a picture signal, then quantizing the transformed data, and coding the data thus quantized. The apparatus comprises a local decoder (8,9,10) for the quantized data; first and second memories (11,12) for storing the decoded picture data of an intra-coded or bidirectionally predictive-coded frame, and that of a predictive-coded frame respectively; a predictive picture generator (14) for generating a predictive picture of the other bidirectionally predictive-coded frame; and a difference calculator (2) for calculating the difference between the predictive picture and the original picture signal corresponding thereto. Further disclosed is a picture signal decoding apparatus which comprises an inverse multiplexer (16) for separating the coded data into interframe predictive error data and vector coded data; a decoder (18,19,20) for generating decoded picture data on the basis of such error data; first and second memories (21,22) for storing the decoded picture data of the intra-coded frame and the predictive-coded frame respectively; a predictive picture generator (23) for generating a predicted picture of the other bidirectionally predictive-coded frame; and a frame switching selector (24) for selectively rearranging the decoded picture data in the order of reproduction.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interframe move predicting method concerned with moving pictures, and also to a picture signal coding/decoding apparatus based particularly on the MPEG (moving picture experts group) system. 2. Description of the Prior Art A conventional interframe move predicting method based on the MPEG system will be described below with reference to Fig. 7 and is disclosed in EP-A- 424 026. In this diagram, first a predictive-coded frame P0 is predicted from an intra-coded frame I0. Subsequently a bidirectionally predictive-coded frame B0 is predicted from the two frames I0 and P0. And similarly another bidirectionally predictive-coded frame B1 is predicted from the intra-coded frame I0 and the predictive-coded frame P0. For prediction of the bidirectionally predictive-coded frames B0 and B1, there are known three modes such as forward prediction from the predictive-coded frame P0, backward prediction from the intra-coded frame I0, and interpolative prediction executed bidirectionally as mentioned above. And in practice, the most adequate one for data compression is selected out of such three modes. In the illustration of Fig. 7, two bidirectionally predictive-coded frames B0 and B1 are existent between the frames I0 and P0. However, desired prediction can be performed by the same method even in case there are three or more bidirectionally predictive-coded frames between the frames I0 and P0. When two or more bidirectionally predictive-coded frames are existent between the frames I0 and P0 as described, the precision of move prediction relative to the bidirectionally predictive-coded frame B temporally apart from the frame I0 or P0 is lowered in accordance with the time difference therebetween, and such precision is deteriorated particularly with a rise in the degree of the move. OBJECT AND SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved interframe move predicting method, as defined in claim 1, which is capable of enhancing the precision in the prediction of the move in any bidirectionally predictive-coded frame to consequently raise the efficiency in compressing the moving picture data. According to a first aspect of the present invention, there is provided an improvement in an interframe move predicting method for prediction of the move in a bidirectionally predictive-coded frame from an intra-coded frame and a predictive-coded frame. The improvement predicts the move in another bidirectionally predictive-coded frame from the first-mentioned bidirectionally predictive-coded frame and the predictive-coded frame. When three or more bidirectionally predictive-coded frames are existent between the intra-coded frame and the predictive-coded frame, the move in any of the bidirectionally predictive-coded frames other than the first one is predicted from the preceding adjacent bidirectionally predictive-coded frame and the predictive-coded frame. In a modification of such method, the move in the other bidirectionally predictive-coded frame is predicted on the additional basis of the intra-coded frame as well. According to a second aspect of the present invention, there is provided a picture signal coding apparatus, as defined in claim 4, capable of executing orthogonal transformation of a picture signal where each of block groups consists of a plurality of unitary blocks, then quantizing the transformed data, and coding the data thus quantized. The apparatus comprises a local decoder for locally decoding the quantized data; a first memory for storing the decoded picture data obtained by locally decoding an intra-coded frame or a bidirectionally predictive-coded frame; a second memory for storing the decoded picture data obtained by locally decoding the predictive-coded frame; a predictive picture generator for generating a predictive picture of the other bidirectionally predictive-coded frame from the decoded picture data obtained by locally decoding the said one bidirectionally predictive-coded frame and also from the decoded picture data obtained by locally decoding the predictive-coded frame; and a difference calculator for calculating the difference between the predictive picture formed by the predictive picture generator and the original picture signal corresponding to such predictive picture. According to a third aspect of the present invention, there is provided a picture signal coding apparatus capable of executing orthogonal transformation of a picture signal where each of block groups consists of a plurality of unitary blocks, then quantizing the transformed data, and coding the data thus quantized. This apparatus comprises a local decoder for locally decoding the quantized data; a first memory for storing the decoded picture data obtained by locally decoding an intra-coded frame; a second memory for storing the decoded picture data obtained by locally decoding a predictive-coded frame; a third memory for storing the decoded picture data obtained by locally decoding one bidirectionally predictive-coded frame; a predictive picture generator for generating a predictive picture of the other bidirectionally predictive-coded frame from the decoded picture data obtained by locally decoding the intra-coded frame, the decoded picture data obtained by locally decoding the said one bidirectionally predictive-coded frame, and also from the decoded picture data obtained by locally decoding the predictive-coded frame; and a difference calculator for calculating the difference between the predictive picture formed by the predictive picture generator and the original picture signal corresponding to such predictive picture. In the picture signal coding apparatus mentioned, the local decoder comprises an inverse quantizer for inversely quantizing the quantized data, and an inverse orthogonal transformer for executing an inverse orthogonal transformation of the inversely quantized data. According to a fourth aspect of the present invention, there is provided a picture signal decoding apparatus as defined in claim 7, comprising: an inverse multiplexer for separating the coded data into interframe predictive error data and vector coded data; a decoder for generating decoded picture data on the basis of the interframe predictive error data; a first memory for storing the decoded picture data of the intra-coded frame; a second memory for storing the decoded picture data of the predictive-coded frame; a predictive picture generator for generating a predictive picture of the other bidirectionally predictive-coded frame from both the decoded picture data of one bidirectionally predictive-coded frame and the decoded picture data of the predictive-coded frame; and a frame switching selector for selectively rearranging the decoded picture data in the order of reproduction and outputting the rearranged data. According to a fifth aspect of the present invention, there is provided a picture signal decoding apparatus comprising: an inverse multiplexer for separating the coded data into interframe predictive error data and vector coded data; a decoder for generating decoded picture data on the basis of the interframe predictive error data; a first memory for storing the decoded picture data of the intra-coded frame; a second memory for storing the decoded picture data of the predictive-coded frame; a third memory for storing the decoded picture data of one bidirectionally predictive-coded frame from the decoded picture data of the intra-coded frame, the decoded picture data of the said one bidirectionally predictive-coded frame, and the decoded picture data of the predictive-coded frame; and a frame switching selector for selectively rearranging the decoded picture data in the order of reproduction and outputting the rearranged data. In the picture signal decoding apparatus mentioned, the decoder generates a predictive picture from the decoded picture data obtained by adding the interframe predictive error data to the predictive picture data outputted from the predictive picture generator. Thus, in the interframe move predicting method of the present invention, the move in the other bidirectionally predictive-coded frame is predicted from one bidirectionally predictive-coded frame and the predictive-coded frame, or from one bidirectionally predictive-coded frame, the predictive-coded frame and the intra-coded frame. The above and other features and advantages of the present invention will become apparent from the following description which will be given with reference to the illustrative accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A, 1B and 1C illustrate exemplary embodiments of the interframe move predicting method according to the present invention; Fig. 2 is a block diagram of a coding apparatus to which the method of Figs. 1A and 1B is applied; Fig. 3A through 3G are timing charts of signals for explaining in detail the method of Figs. 1A and 1B; Fig. 4 is a block diagram of a decoding apparatus correlative to the coding apparatus of Fig. 2; Fig. 5 is a block diagram of a coding apparatus to which the method of Fig. 1C is applied; Fig. 6A through 6H are timing charts of signals for explaining in detail the method of Fig. 1C; and Fig. 7 illustrates a conventional interframe move predicting method. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter exemplary embodiments of the interframe move predicting method of the present invention will be described in detail with reference to the accompanying drawings. Fig. 2 is a block diagram of a coding apparatus where the method of the present invention is applied. This coding apparatus is of a general type equipped with a combination of a DCT (discrete cosine transformer) and an interframe predictor. To a video input terminal T1 shown in Fig. 2, picture frames I0, B0, B1, P0, B2, B3 and P1 are sequentially inputted in this order. Such picture frames a are rearranged in a frame memory 1 in the order to be encoded, and then are supplied to a subtracter 2 as picture frames a (Fig. 3A). Subsequently from the subtracter 2, there is outputted interframe predictive error data which is the difference between the picture data inputted to a positive terminal and the predictive picture data inputted to a negative terminal. The interframe predictive error data is branched into two transmission lines via a DCT 3 and a quantizer 4. The data delivered to one transmission line is inputted to a variable length coder 5 and then is multiplexed with vector data and so forth in a multiplexer 6, so that the multiplexed data is obtained as the output e of the coding apparatus from an output terminal T2 via a buffer 7. Meanwhile, the data delivered to the other transmission line is processed via an inverse quantizer 8 and an inverse DCT 9, and then is outputted as decoded picture data b (Fig. 3B) from an adder 10. The decoded picture data b is inputted via a frame memory selector switch SW1 to a frame memory 11 or 12. A move vector calculator 13 generates a move vector from the data inputted from the frame memory 1, 11 or 12. A predictive picture generator 14 generates predictive picture data c from the move vector data obtained by the move vector calculator 13 and also from the picture data stored in the frame memory 11 or 12. The predictive picture data c is inputted via a switch SW2 to the negative terminal of the subtracter 2 while being inputted also to the adder 10 via a switch SW3. Now a description will be given on an embodiment of the interframe move predicting method of the present invention with reference to Figs. 1A and 1B. In Fig. 1A, a bidirectionally predictive-coded frame B0 is predicted from an intra-coded frame I0 and a predictive-coded frame P0 as in the conventional method. However, another bidirectionally predictive-coded frame B1 is predicted from the preceding frames B0 and P0. And the most adequate mode of prediction is selected out of forward prediction, backward prediction and interpolative prediction. The same operation as the above is performed also in the case of Fig. 1B where three bidirectionally predictive-coded frames B (B0, B1, B2) or more are existent between the frames I0 and P0. And with the exception of the first frame B0, the successive frames B1, B2, .... are predicted from the respective preceding adjacent frames B0, B1, .... and the frame P0. Thus, prediction from each preceding adjacent bidirectionally predictive-coded frame can be performed to enhance the precision of prediction in comparison with the known method that executes prediction from the intra-coded frame I0 temporally apart from the relevant bidirectionally predictive-coded frame, hence further raising the efficiency in compression of the picture data. Particularly in any picture with great moves, the precision of prediction relative to the bidirectionally predictive-coded frame is raised to consequently achieve a higher picture-data compression efficiency. The above embodiment will now be explained in further detail below with reference to Figs. 2 and 3. First a picture frame I0 shown in Fig. 3A is inputted to the subtracter 2 in the coding apparatus of Fig. 2. Subsequently the picture frame I0 is outputted from the adder 10 in the form of a decoded picture frame I0' (Fig. 3B). Since the switch SW1 is connected to the frame memory 11 (as shown in Fig. 3D), the frame I0' is inputted to the frame memory 11 and is stored therein. At this time, the switches SW3 and SW2 are both in an off-state as shown in Fig. 3D and 3E, so that the predictive picture data c obtained from the predictive picture generator 14 is not supplied to the subtracter 2 or the adder 10 either. Subsequently a picture frame P0 is inputted to the subtracter 2. At this time the switches SW2 and SW3 are both in an on-state, so that a predictive-coded frame P0'' (Fig. 3C) predicted from the decoded picture data I0' is outputted from the predictive picture generator 14. The decoded picture data P0' shown in Fig. 3B is generated in the adder 10 on the basis of the frames P0'' and P0. At the input time of the picture frame P0, the switch SW1 is connected to the frame memory 12, so that the decoded picture data P0' is inputted to and stored in the frame memory 12. At the input time of the next picture frame B0, the predictive picture generator 14 is supplied with the data I0', P0' stored in the frame memories 11, 12 and the move vector d , and then outputs the predictive picture data B0'' shown in Fig. 3C. The adder 10 generates decoded picture data B0' from the picture frames B0 and B0''. Since the switch SW1 is connected to the frame memory 11 at this time, the data B0' is inputted to and stored in the frame memory 11. The above operation is shown in Fig. 3F. First the data I0' is stored in the frame memory 11, and then the data B0' is stored therein. Meanwhile in the frame memory 12, first the data P0' is stored as shown in Fig. 3G. The data P0' is continuously retained even at the instant the storage content in the frame memory 11 has been updated from the data I0' to the data B0'. Subsequently a picture frame B1 is inputted. At this time, the data P0' and B0' from the frame memories 11, 12 have already been inputted to the predictive picture generator 14, so that predictive picture data B1'' is outputted from the predictive picture generator 14, and decoded picture data B1' is produced in the adder 10 on the basis of the data B1'' and the picture frame B1. Since the switch SW1 is in its off-state at this instant, the data B1' is not stored in any of the frame memories 11 and 12. The same operation as the above is performed when the next predictive-coded frame P1 is inputted. Predictive picture data P1'' predicted from the data P0' (Fig. 3G) stored in the frame memory 12 is outputted from the predictive picture generator 14, and then the adder 10 produces decoded picture data P1' from the predictive picture data P1'' and the frame P1. Subsequently the same operation is performed with respect to unshown successive picture frames B2 and B3. Regarding the picture frame B2, predictive picture data B2'' is predicted from the data P0' and P1', and decoded picture data B2' is obtained from the picture frame B2 and the data B2". Meanwhile, regarding the picture frame B3, predictive picture data B3'' is predicted from the data P1' and B2', and decoded picture data B3' is obtained from the picture frame B3 and the data B3". Fig. 4 is a block diagram of a decoding apparatus correlative to the coding apparatus shown in Fig. 2. The output signal delivered from the coding apparatus to an input terminal T3 is supplied via a buffer 15 to an inverse multiplexer 16, which then outputs inter-frame predictive error data and move vector data processed through discrete cosine transformation and quantization. The interframe predictive error data thus obtained is decoded by a variable length decoder 17, an inverse quantizer 18 and an inverse DCT, and then is inputted to an adder 20. To the adder 20, there is also inputted, simultaneously with such interframe predictive error data, the predictive picture data produced by the predictive picture generator 23 on the basis of the data obtained from frame memories 21, 22 via a switch SW5, and the input data are added to each other to become decoded picture data. The decoded picture data is inputted to the frame memory 21 or 22 to produce data for generation of desired predictive picture data while being inputted also to a frame switching selector 24. In the frame switching selector 24, the picture frame are rearranged in the initial order of I0, B0, B1, P0, B2, B3, P1. Fig. 1C illustrates a modification of the method shown in Figs. 1A and 1B. In Fig. 1C, a bidirectionally predictive-coded frame B1 is predicted not merely from frames P0 and B0 but also from a frame I0 as well. Hereinafter the modification of Fig. 1C will be described in detail with reference to Figs. 5 and 6. In Fig. 5, the difference from the aforementioned embodiment of Fig. 2 resides in the additional provision of a frame memory 15, so that a total of three frame memories are employed. Meanwhile in Fig. 6, the difference from the example of Fig. 3 resides in the connection state (Fig 6E) of the frame memory 15 selected by the switch SW1, and the storage contents (Fig. 6F and H) of the frame memories 11 and 15. Since any other component parts in Figs. 5 and 6 are the same as those in Figs. 2 and 3, a repeated explanation thereof is omitted here. In response to input of a picture frame B0 shown in Fig. 6A, the switch SW1 in Fig. 6E connects the frame memory 15 (or the frame switch 11 in Fig. 3), whereby decoded picture data B0' is stored in the frame memory 15 as shown in Fig. 6H while the decoded picture data I0' is still stored in the frame memory 11 continuously as shown in Fig. 6F. Therefore it becomes possible to obtain a bidirectionally predictive-coded frame B1'' from the data I0', P0' and B0' stored respectively in the frame memories 11, 12 and 15, hence attaining a higher precision of prediction than the value in predicting the data B1'' merely from the picture data P0' and B0'. According to the interframe move predicting method of the present invention, as described hereinabove, any move in the other bidirectionally predictive-coded frame is predicted from one bidirectionally predictive-coded frame and a predictive-coded frame, or from one bidirectionally predictive-coded frame, a predictive-coded frame and an intra-coded frame, so that it is rendered unnecessary to use any temporally apart intra-coded frame or predictive-coded frame, hence enhancing the precision in prediction of the other bidirectionally predictive-coded frame to consequently raise the efficiency in compressing the moving picture data. Furthermore, the method eliminates the necessity of the move vector calculation based on any temporally apart intra-coded frame or predictive-coded frame, thereby achieving another advantage of curtailing the time required for the move vector calculation.

Claims: An interframe move predicting method, wherein the move in a predictive-coded frame (P0) is predicted from an intra-coded frame (I0), and the move in a first bidirectionally predictive-coded frame (B0), being existent between said intra-coded frame (I0) and said predictive-coded frame (P0), is predicted from said intra-coded frame (I0) and said predictive-coded frame (P0), characterized in that the move in a second bidirectionally predictive-coded frame (B1, B2, ...), being existent between said first bidirectionally predictive-coded frame (B0) and said predictive-coded frame (P0), is predicted from said predictive-coded frame (P0) and said first bidirectionally predictive-coded frame (B0). The interframe move predicting method according to claim 1, characterized in that when three or more bidirectionally predictive-coded frames (B0, B1, B2, ...) are existent between said intra-coded frame (I0) and said predictive-coded frame (P0), the move in any of the bidirectionally predictive-coded frames (Bi) other than the first one (B0) is predicted from the preceding adjacent bidirectionally predictive-coded frame (Bi-1) and said predictive-coded frame (P0). The interframe move predictive method according to claim 1 or 2, characterized in that the move in said bidirectionally predictive-coded frame (Bi) other than said first one (B0) is predicted on the additional basis of said intra-coded frame (I0) as well. A picture signal coding apparatus capable of executing orthogonal transformation of a picture signal, then quantizing the data corresponding to said transformed signal, and coding the data thus quantized, said apparatus comprising: a local decoder (8, 9, 10) for inversely quantizing said quantized data and executing the inverse orthogonal transformation of said inversely quantized data; a first memory (11) for storing decoded picture data obtained by locally decoding an intra-coded frame (I0) or a first bidirectionally predictive-coded frame (B0); a second memory (12) for storing decoded picture data obtained by locally decoding a predictive-coded frame (P0); a predictive picture generator (14) for generating a predictive picture of a second bidirectionally predictive-coded frame (B1, B2, ...) from said decoded picture data obtained by locally decoding said first bidirectionally predictive-coded frame (B0) and from said decoded picture data obtained by locally decoding said predictive-coded frame (P0); and a difference calculator (2) for calculating the difference between said predicted picture signal correspnding to said predicted picture formed by said predictive picture generator (14) and the original picture signal corresponding to such predictive picture. A picture signal coding apparatus according to claim 4, wherein said picture signal coding apparatus further comprises: a third memory (15) for storing decoded picture data obtained by locally decoding an intra-coded frame (I0) or a bidirectionally predictive-coded frame; wherein said predictive picture generator (14) generates said predictive picture of said second bidirectionally predictive-coded frame (B1) from said decoded picture data obtained by locally decoding said intra-coded frame (I0), said decoded picture data obtained by locally decoding said first bidirectionally predictive-coded frame (B0), and from said decoded picture data obtained by locally decoding said predictive-coded frame (P0). A picture signal coding apparatus according to claim 4 or 5, wherein said local decoder comprises an inverse quantizer (8) for inversely quantizing said quantized data; and an inverse orthogonal transformer (9) for executing said inverse orthogonal transformation of said inversely quantized data. A picture signal decoding apparatus comprising: an inverse multiplexer (16) for separating predictive-coded picture data received by said picture signal decoding apparatus into interframe data indicating an predictive error of an interframe move and data indicating a vector of said interframe move; a decoder (18, 19, 20) for generating decoded data on the basis of said interframe predictive error data and said move vector data and for inversely quantizing said decoded data and executing an inverse discrete cosine transformation of said inversely quantized data, thus obtaining decoded picture data; a first memory (21) for storing decoded picture data of an intra-coded frame (I0); a second memory (22) for storing decoded picture data of a predictive-coded frame (P0); a predictive picture generator (23) for generating a predictive picture of a second bidirectionally predictive-coded frame (B1) from both decoded picture data of a first bidirectionally predictive-coded frame (B0) and said decoded picture data of said predictive-coded frame (P0); and a frame switching selector (24) for selectively rearranging and outputting said decoded picture data in the initial order of said intra-coded frame (I0), said first bidirectionally predictive-coded frame (B0), said second bidirectionally predictive-coded frame (B1), and said predictive-coded frame (P0). A picture signal decoding apparatus according to claim 7, wherein said picture signal decoding apparatus further comprises: a third memory for storing said decoded picture data of said second bidirectionally predictive-coded frame (B1); and wherein said predictive picture generator (23) generates said predictive picture of said second bidirectionally predictive-coded frame (B1) from said decoded picture data of said intra-coded frame (I0), said decoded picture data of said first bidirectionally predictive-coded frame (B0), and said decoded picture data of said predictive-coded frame (P0). A picture signal decoding apparatus according to claim 7 or 8, wherein said decoder (18, 19, 20) produces a predictive picture from said decoded picture data obtained by adding said interframe predictive error data to said predictive picture data output from said predictive picture generator (23).

Inventors: RYUICHI IWAMURA, VELTMAN MARK, RYUICHI, IWAMURA, VELTMAN, MARK, Ryuichi, Iwamura, c/o Sony Corporation, Veltman, Mark, c/o Sony Corporation
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: H04N7
IPC codes: H04N7, G06T9