Title of Invention

METHOD & SYSTEM FOR THE CODING & DECODING OF A DIGITIZED PICTURE

Abstract

Method and arrangement for the coding and decoding of a digitized picture A shape adapted transform coding is proposed in which different shape adapted transform codings are carried out during intra picture coding and inter picture coding. A first shape adapted transform coding is carried out during intra picture coding and a second shape adapted transform coding which is different from the first shape adapted transform coding is carried out during inter picture coding.

Full Text

Description The coding of video signals in accordance with the picture coding standards H.261, H.2 63, MPEG1 and MPEG2 is based on a block-oriented discrete cosine transform (DCT). These methods generally use the principle of block-based picture coding. A further approach to picture coding is the so-called principle of object-based picture coding. In the case of object-based picture coding, the original pictures are segmented in accordance with the objects occurring in the scene, and these objects are coded separately. Figure 2 gives a general illustration of an arrangement for picture coding and picture decoding. Figure 2 illustrates a camera K which is used to record pictures. The camera K may be, for example, any desired analogue camera K which records pictures of a scene and either digitizes the pictures in the camera K or else transmits them in analogue form to a first computer R1, in which then either the digitized pictures B are processed or the analogue pictures are converted into digitized pictures B and the digitized pictures B are processed. The camera K may also be a digital camera K with which digitized pictures B are recorded directly and are fed to the first computer R1 for further processing. The first computer R1 may also be configured as a dedicated arrangement which is used to carry out the method steps described below, for example as a dedicated computer card installed in a computer. The first computer R1 has a processor unit P which is used to carry out the method steps of picture coding or of picture decoding that are described below. The processor unit P is coupled for example via a bus BU to a memory SP in which the video data are stored. - 2 - In general, the methods described below can be realized either using software or using hardware or else partly using software and partly using hardware. Once picture coding has been effected in the first computer R1 and the compressed video data have been transmitted via a transmission medium ##UM to a second computer R2, picture decoding is carried out in the second computer R2. The second computer R2 may have the same structure as the first computer R1, that is to say the memory SP which is coupled via the bus BU to the processor unit P. Figure 3 gives a more detailed illustration of a possible arrangement in the form of a basic circuit diagram for picture coding and/or for picture decoding which can be used in the context of block-based picture coding and, in some instances, as explained below, in the context of object-based picture coding. In block-based picture coding methods, a digitized picture B is divided into normally square blocks having a size of 8x8 pixels BP or 16x16 pixels BP and fed to the arrangement for picture coding. Usually, coding information is uniquely assigned to a pixel, for example brightness information (luminance values) or colour information (chrominance values). In the block-based picture coding methods, a distinction is made between various picture coding modes. In the so-called intra picture coding mode, in each case the entire picture with the entire coding information assigned to the pixels of the picture is coded and transmitted (I picture). In the so-called inter picture coding mode, in each case only the difference picture information between two chronologically succeeding pictures is coded and transmitted (P picture, B picture). In order to change over between the intra picture coding mode and the inter picture coding mode, two switch units SE are provided. In order to carry out the inter picture coding mode, a subtraction unit S is provided in - 3 - which the difference in the picture information of two succeeding pictures B is formed. The entire picture coding is controlled by means of a picture coding control unit ST. The picture blocks BB or difference picture blocks BB to be coded are in each case fed to a transform coding unit DCT, in which transform coding, for example the discrete cosine transform {DCT), is applied to the coding information assigned to the pixels. In general, however, it is possible to carry out any desired transform coding, for example a discrete sine transform or else a discrete Fourier transform. The spectral coefficients formed by the transform coding are quantized in a quantization unit Q and fed to a picture coding multiplexer (not illustrated) for example for channel coding and/or for entropy coding. In an internal reconstruction loop, the quantized spectral coefficients are subjected to inverse quantization in an inverse quantization unit IQ and to inverse transform coding in an inverse transform coding unit IDCT. Furthermore, in the case of inter picture coding, picture information of the respective chronologically preceding picture is added in an adder unit AE. The pictures reconstructed in this way are stored in a frame memory SP. A unit for motion compensation MC is illustrated symbolically in the frame memory SP in order to simplify the illustration. Furthermore, a loop filter LF is provided which is connected to the memory SP and also to the subtraction unit S. In addition to the video data to be transmitted, a mode flag p is fed to the picture coding multiplexer, which flag in each case specifies whether intra or inter picture coding has been performed. Furthermore, quantization indices q for the spectral coefficients are fed to the picture coding multiplexer. A motion vector v is also assigned in each case to a picture block and/or a macroblock having 4 picture blocks, for example, and is fed to the picture coding _ 4 _ multiplexer. Furthermore, an information item f for the activation or deactivation of the loop filter LF is provided. After the transmission of the picture information via the transmission medium ##UM, the transmitted data can be decoded in the second computer R2. For this purpose, a picture decoding unit is provided in the second computer R2 and, for example, has the structure of the reconstruction loop of the arrangement illustrated in Figure 2. In the case of object-based picture coding methods, each picture object is firstly split into blocks having a fixed size, for example likewise 8x8 pixels. After this splitting, some of the resulting picture blocks are located completely within a picture object BO. This situation is illustrated in Figure 4. The picture B contains at least one picture object BO, which is bounded by an object edge OK of the picture object BO. Furthermore, picture blocks BB having 8x8 pixels BP are illustrated. Picture blocks BB which contain at least part of the object edge OK are designated as edge picture blocks RBB below. Picture blocks BB which are located completely within the picture object BO after the splitting operation can be coded in a manner following the above-mentioned block-based picture coding methods using a customary block-based discrete cosine transform. However, the edge picture blocks RBB are partly filled with picture information and have to be coded using a special method. Two fundamental approaches exist to date for coding the edge picture blocks RBB. Document [1] discloses supplementing the picture information of the picture object BO within the edge picture block RBB by means of a suitable extrapolation method of the coding information to the area of the complete edge picture block RBB. This procedure is referred to as padding. The supplemented area is then - 5- coded using a customary 2-dimensional discrete cosine transform. As an alternative to this, documents [1] and [2] disclose transforming the given picture object BO separately according to rows and columns. This procedure is referred to as shape adapted transform coding, and as shape adapted DCT in the specific case of the use of a DCT. The DCT coefficients assigned to the picture object BO are determined in such a way that those pixels BP of an edge picture block RBB which do not belong to the picture object BO are masked out. A transform is then firstly applied line by line to the remaining pixels BP, the length of which transform corresponds to the number of pixels remaining in this row. The resulting coefficients are horizontally aligned and then subjected to a further one-dimensional DCT in the vertical direction with a corresponding length. In this case, the same method is employed both for the intra picture coding and for the inter picture coding. The known method of shape adaptive transform coding, which has been described above, primarily has the disadvantage that only a relatively poor compression factor of the video data to be compressed is achieved. In this case, the value holds true for the case p=0, and y = 1 for all other cases. N designates a magnitude of the picture vector The known specification for coding prediction error pictures in shape adapted transform coding is based on a transform matrix DCT - N having the following structure: - 6 - which is to be transformed and in which the transformed pixels are contained. DCT - N designates a transform matrix having the size N x N. p, k designate indices, where p,k e [0, N-1]. According to the known procedure, the shape adapted PCT of a picture segment is determined in that firstly each column of the segment is vertically transformed in accordance with the specification and afterwards the same specification (2) is applied to the resulting data in the horizontal direction. However, the specification in accordance with formula (2) is not optimal for coding prediction error pictures. Principles of block-based picture coding are disclosed in (3). Thus, the invention is based on the problem of specifying methods for picture coding and for picture decoding and arrangements for picture coding and for picture decoding with which shape adapted transform coding is achieved with an improved compression factor for the video data. The problem is solved by the method according to Patent Claim 1, by the method according to Patent Claim 6 and by the arrangement according to Patent Claim 11. In the method according to Patent Claim 1 for the coding of a digitized picture, the picture coding is carried out in an intra picture coding mode or in an inter picture coding mode. The picture information of the pixels is transformed in the intra picture coding mode, and difference picture information between picture information of two succeeding pictures is transformed in the inter picture coding mode. A first shape adapted transform coding is carried out in the inter picture coding mode and a second shape adapted transform coding - 7 - which is different from the first shape adapted transform coding is carried out in the intra picture coding mode. This procedure has the particular advantage that it becomes possible, by using two different transform codings, for the quantization error during the subsequent quantization of the spectral coefficients resulting from the transformation to be distributed uniformly over all of the pixels BP, and for the quantization error to have the same average value as in the case of a normal 8x8 picture block. This method is primarily suitable for the coding of edge picture blocks of a picture segment. Overall, the method enables a distinctly improved coding efficiency, i.e. with the same data rate, the picture quality that can be achieved rises. As is described below, in contrast to the known procedure of using the same transform for intra picture coding and for inter picture coding in the case of shape adapted picture coding, it is possible to achieve a considerably improved signal/noise power ratio of approximately one dB without any additional computing outlay. In the method according to Patent Claim 6, a first inverse shape adapted transform coding is carried out in the case of decoding in the intra picture coding mode. A second inverse shape adapted transform coding is carried out in the intra picture coding mode. The first inverse shape adapted transform coding and the second inverse shape adapted transform coding are different. This method likewise has the advantages for picture coding that have been correspondingly illustrated above. In the arrangement according to Patent Claim 11 for carrying out the methods, provision is made of a transform coding unit for the shape adapted transform coding of the pixels, and/or of a transform decoding unit for the inverse shape adapted transform coding. The transform coding unit and/or the transform decoding unit is configured in such a way that a first shape adapted transform coding and/or a first inverse shape adapted - 8 - transform coding is carried out in the intra picture coding mode. A second shape adapted transform coding and/or a second inverse shape adapted transform coding is carried out in the inter picture coding mode. The first shape adapted transform coding, and/or the first inverse shape adapted transform coding, and the second shape adapted transform coding, and/or the second inverse shape adapted transform coding, are different. The advantages described above also apply to the arrangement. Advantageous developments of the invention emerge from the dependent claims. In a development of the methods, it is advantageous that at least one of the shape adapted transform codings and/or at least one of the inverse shape adapted transform codings are carried out in such a way that the signal energy of the pixels to be transformed in the space domain is approximately identical to the signal energy of the transformed pixels in the frequency domain. In other words, this means that the corresponding shape adapted transform coding and/or inverse shape adapted transform coding is orthonormalized. This procedure has the particular advantage that the quantization error during the subsequent quantization of the spectral coefficients resulting from the transformation is distributed uniformly over all of the pixels, and the quantization error has the same average value as in the case of a normal 8x8 picture block. where In a development of the method for picture coding, it is furthermore advantageous to form the transform coefficients Cj of the pixels Xj to be transformed in accordance with the following specification: - 9 - - N designates a magnitude of the picture vector which is to be transformed and in which the transformed pixels are contained, - DCT - N designates a transform matrix having the size N x N, - p, k designate indices, where p, k e [0, N-l]. As can be discerned in the specification (3) , the considerable improvement is achieved merely by a different scaling of the transform specification relative to the known procedure. The above-described developments for the method for picture coding are likewise provided as developments for the picture decoding, in the specification for inverse transform coding with the correspondingly inverse specification. The developments of the methods are likewise advantageous for refinements of the transform coding unit of the arrangement for picture coding. These methods are primarily suitable for the coding and decoding of edge picture blocks of a picture segment. The figures illustrate an exemplary embodiment of the invention which is explained in more detail below. In the figures, Figure 1 shows a flow diagram in which the individual method steps are symbolically represented; Figure 2 shows a customary arrangement for picture coding having a camera, two computers and a transmission medium; Figure 3 shows a sketch of a customary arrangement for block-based picture coding; Figure 4 symbolically shows a representation of a picture with a picture object and picture blocks and edge picture blocks. In the context of object-based picture coding, the digitized picture B is segmented in accordance with the picture obj ects BO occurring in the scene, and the picture objects BO are coded separately. For this purpose, each picture object BO is - 10 - usually firstly split into picture blocks BB having a fixed size, for example 8x8 pixels BP. After the splitting operation, some of the resulting picture blocks BB are located completely within the picture object BO. These blocks BB can be coded in a manner following the cited methods explained above using a customary block-based transform coding. As described above, the edge picture blocks RBB are, however, only partly filled with picture information and have to be coded using a special method. In the method, edge picture blocks RBB are preferably fed, in the first computer R1, to the transform coding unit DCT in a first step 101. The first computer Rl is configured in such a way that the modules represented symbolically in Figure 3 can be implemented. In a second step 102, for each edge picture block RBB transform coefficients Cj of the pixels Xj to be transformed are formed for the coding information of the pixels BP of the respective edge picture block RBB, in accordance with the following specification: where - N designates a magnitude of the picture vector which is to be transformed and in which the transformed pixels are contained, - DCT - N designates a transform matrix having the size N x N, - p, k designate indices, where p, k e [0, N-1]. Clearly, the specification for transform coding (3) signifies that the signal energy of the coding information of the pixels to be transformed in the space domain is identical to the signal energy of the coding information of the transformed pixels in the frequency domain. - 11 - The shape adapted discrete cosine transform is preferably used as the shape adapted transform coding. The specification (3) is preferably employed for transform coding when the picture coding is carried out in the inter picture coding mode. When the picture coding is carried out in the intra picture coding mode, the transform coefficients cj of the transformed pixels Xj are preferably formed in accordance with the following specification: After the transmission of the coded picture information (step 105), i.e. after quantization (step 103), possibly entropy coding (step 104) of the transmitted video data for example according to the method described in [1] , via the transmission medium ##UM, picture decoding is carried out in the second computer R2. In the case of picture decoding, entropy decoding is carried out in a first step 106 and an inverse quantization of the quantized spectral coefficients is carried out in a second step 107. The spectral coefficients Cj are furthermore fed to the inverse shape adapted transform coding (IDCT). In a manner corresponding to the method for picture coding, for picture decoding a shape adapted transform coding is once again carried out in such a way that the signal energy of the coding information of the transformed pixels in the frequency domain is approximately identical to the signal energy of the coding information of the pixels in the space domain. For the purpose of inverse shape adapted transform coding, the pixels Xj are formed from the spectral transform coefficients cj in accordance with the following specification (step 108): - 12 - where - N designates a magnitude of the picture vector which is to be transformed and in which the transformed pixels are contained, - DCT - N designates a transform matrix having the size N x N, - p, k designate indices, where p, k e [0, N-l] - ( )" designates inversion of a matrix. The inverse shape adapted transform coding in accordance with specification (4) is preferably carried out in the context of picture decoding in the inter picture decoding mode. In the intra picture decoding mode, the shape adapted inverse transform coding is preferably carried out in accordance with the following specification: In the arrangement for picture coding, provision is made of a transform coding unit DCT for the shape adapted transform coding of the pixels BP. The transform coding unit DCT is configured in such a way that a signal energy of the coding information of the pixels to be transformed in the space domain is approximately identical to the signal energy of the coding information of the transformed pixels in the frequency domain. The transform coding unit is preferably configured in such a way that the method steps illustrated in the context of the method for picture coding are realized in the transform coding unit DCT. Of course, the method can also be realized, in the arrangement, using software which is processed by the processor P. - 13 - The same applies to the arrangement for picture decoding, which has an inverse transform coding unit IDCT. In a corresponding manner, the inverse transform coding unit IDCT is configured in such a way that the method steps for picture decoding, in particular for inverse shape adapted transform coding, are realized. Both the method and the arrangements can preferably be applied to edge picture blocks RBB of picture objects BO of a digitized picture B. Clearly, the method means that different shape adapted transform codings are carried out during intra picture coding and inter picture coding. A first shape adapted transform coding is carried out during intra picture coding and a second shape adapted transform coding which is different from the first shape adapted transform coding is carried out during inter picture coding. The way in which the transformed pixels, i.e. the spectral coefficients, are used further in the context of picture coding, i.e. the type of quantization, of entropy coding and/or of channel coding, is not essential to the invention. The following publications have been cited in the context of this document: [1] ISO/IEC JTC1/SC29/WG11, MPEG-4 Video Verification Model Version 5.0 Doc. N1469, Nov. 1996, pp. 55-59. [2] T. Sikora and B. Makai, Shape Adaptive DCT for Generic Coding of Video, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 5, pp. 59-62, Feb. 1995 [3] A. K. Jain, Image Data Compression: A Review, Proceedings of the IEEE, Vol. 69, No. 3, pp. 349-389, March 1981 -14-WE CLAIM 1. Method for the coding of a digitized picture which has picture objects having any desired number of pixels, in which the picture coding is carried out in an intra picture coding mode or in an inter picture coding mode, in which the picture information of the pixels is transformed in the intra picture coding mode, in which difference picture information between picture information of two succeeding pictures is transformed in the inter picture coding mode, in which a first shape adapted transform coding is carried out in the inter picture coding mode, and in which a second shape adapted transform coding which is different from the first shape adapted transform coding is carried out in the intra picture coding mode. 2. Method as claimed in claim 1, in which a variant of a shape adapted discrete cosine transform is used as the First shape adapted transform coding, in which a shape adapted discrete cosine transform is used as the second shape adapted transform coding. 3. Method as claimed in claim 1 or 2, in which the first shape adapted transform coding and/or the second shape adapted transform coding is carried out in such a way that a signal energy of the pixels to be transformed in the space domain is approximately identical to a signal energy of the transformed pixels in the frequency domain. 4. Method as claimed in one of the preceding claims, in which the transform coefficients cj of the pixels xj which are transformed in accordance with the first shape adapted transform coding are formed in accordance with the following specification : -15- where N designates a magnitude of the picture vector which is to be transformed and in which the transformed pixels are contained, DCT-N designates a transform matrix having the size N x N, p, k designate indices, where p, k s [ 0, N-1]. 5. Method as claimed in one of the preceding claims, in which the first shape adapted transform coding is applied only to edge picture blocks. 6. Method for the decoding of a digitized picture which has picture objects having any desired number of pixels which has been coded by the method as claimed in claim 1, in which the picture decocting is carried out In an intra picture decoding mode or in an inter picture decoding mode, in which the picture information of the pixels is transformed in the intra picture decoding mode, in which difference picture information between picture information of two succeeding pictures is transformed in the inter picture decoding mode, in which a first inverse shape adapted transform coding is carried out in the inter picture decoding mode, and in which a second inverse shape adapted transform coding which is different from the first inverse shape adapted transform coding is carried out in the intra picture decoding mode. 7. Method as claimed in claim 6, in which a variant of a shape adapted inverse discrete cosine transform is used as the first inverse shape adapted transform coding, in which an inverse shape adapted discrete cosine transform is used as the second inverse shape adapted transform coding. 8. Method as claimed in claim 6 or 7, in which the first inverse shape adapted transform coding and/or the second inverse shape adapted transform coding is carried out in such a way that a signal energy of the pixels to be transformed in the space domain is -16- approximately identical to a signal energy of the transformed pixels in the frequency domain. 9. Method as claimed in one of claims 6 to 8, in which pixels xj that are transformed during the first inverse shape adapted transform coding are formed from transform coefficients cj in accordance with the following specification: where N designates a magnitude of the picture vector which is to be transformed and in which the transformed pixels are contained, - DCT-N designates a transform matrix having the size N x N, p, k designate indices, where p, k s [0, N-l] ( )-designates inversion of a matrix. 10. Method as claimed in one of claims 6 to 9, in which the first inverse shape adapted transform coding is applied only to edge picture blocks. 11. A system for carrying out the method for the coding of a digitized picture which has picture objects with any desired number of pixels as claimed In claim 1, having a processor unit which is set up in such a way that the picture coding is carried out in an intra picture coding mode or in an inter picture coding mode; the picture information of the pixels in the intra picture coding mode; difference picture information between picture information of two succeeding pictures is transformed in the inter picture coding mode; a first shape adapted transform coding is carried out in the inter picture coding mode, and - a second shape adapted transform coding which is different from the first shape adapted transform coding is carried out in the intra picture mode. -17- 12. The system as claimed in claim 11, in which the processor unit is set up in such a way that - a variant of a shape adapted discrete cosine transform is used as the first shape adapted transform coding; a shape adapted discrete cosine transform is used as the second shape adapted transform coding. 13. The system as claimed in claim 11 or 12, in which the processor unit is set up in such a way that the first shape adapted transform coding and/or the second shape adapted transform coding is carried out in such a way, that a signal energy of the pixels to be transformed in the space domain is approximately identical to a signal energy of the transformed pixels in the frequency domain. 14. The system as claimed in one of claims 11 to 13, in which the processor unit is set up in such a way that the transform coefficients cj of the pixels xj which are transformed In accordance with the first shape adapted transform coding are formed in accordance with the following specification : where N designates a magnitude of the picture vector which is to be transformed and in which the transformed pixels are contained, DCT - N designates a transform matrix having the size N x N, p, k designate indices, where p, k c [0, N-l]. 15. The system as claimed in one of claims 11 to 14, in which the processor unit is set up in such a way that the first shape adapted transform coding is applied only to edge picture blocks. 18 16. A system for carrying out the method for the decoding of a digitized picture which has picture objects with any desired number of pixels, as claimed in claim 6, having a processor unit which Is set up in such a way that the picture decoding is carried out in an intra picture decoding mode or in an inter picture decoding mode, the picture information of the pixels is transformed in the intra picture decoding mode, difference picture information between picture information of two succeeding pictures is transformed in the inter picture decoding mode a first inverse shape adapted transform coding is carried out in the inter picture decoding mode, and - a second inverse shape adapted transform coding which is different from the first inverse shape adapted transform coding is carried out in the intra picture decoding mode. 17. The system as claimed in claim 16, in which the processor unit is set up in such a way that a variant of a shape adapted inverse discrete cosine transform is used as the first inverse shape adapted transform coding, an inverse shape adapted discrete cosine transform s used as the second inverse shape adapted transform coding. 18. The system as claimed in claim 16 or 17 in which the processor unit is set up in such a way that the first inverse shape adapted transform coding and/or the second inverse shape adapted transform coding is carried out in such a way that a signal energy of the pixels to be transformed in the space domain is approximately identical to a signal energy of the transformed pixels in the frequency domain. 19 19. The system as claimed in one of claims 16 to 18 in which the processor unit is set up in such a way that pixels xj that are transformed during the first inverse shape adapted transform coding are formed from transform coefficients cj in accordance with the following specification : where - N designates a magnitude of the picture vector which is to be transformed and in which the transformed pixels are contained, DCT-N designates a transform matrix having the size N x N, p, k designate indices, where p, k s [0, N-1] - ( )- designates inversion of a matrix. 20. The system as claimed in one of claims 16 to 19, in which the processor unit is set up in such a way that the first inverse shape adapted transform coding is applied only to edge picture blocks. Dated this 20th day of January, 1998 Method and arrangement for the coding and decoding of a digitized picture A shape adapted transform coding is proposed in which different shape adapted transform codings are carried out during intra picture coding and inter picture coding. A first shape adapted transform coding is carried out during intra picture coding and a second shape adapted transform coding which is different from the first shape adapted transform coding is carried out during inter picture coding.

Documents:

00105-cal-1998 abstract.pdf

00105-cal-1998 claims.pdf

00105-cal-1998 correspondence.pdf

00105-cal-1998 description(complete).pdf

00105-cal-1998 drawings.pdf

00105-cal-1998 form-1.pdf

00105-cal-1998 form-2.pdf

00105-cal-1998 form-3.pdf

00105-cal-1998 form-5.pdf

00105-cal-1998 gpa.pdf

00105-cal-1998 priority document.pdf

105-CAL-1998-(08-10-2012)-FORM-27.pdf

105-CAL-1998-CORRESPONDENCE.pdf

105-CAL-1998-FORM-27.pdf

105-CAL-1998-PA.pdf