METHODS AND DEVICES FOR CODING AND DECODING A DATA FLOW REPRESENTATIVE OF AT LEAST ONE IMAGE 1. Field of the invention The field of the invention is that of coding and decoding of images or sequences of images, and in particular of video streams. More precisely, the invention relates to the compression of images or sequences of images using a representation by blocks of the images. The invention can in particular be applied to the image or video coding implemented in current or future coders (JPEG, MPEG, H.264, HEVC, etc. and their amendments), and to the corresponding decoding. 2. Prior Art The images and sequences of digital images occupy a lot of space in terms of memory, which makes it necessary, when these images are transmitted, to compress them in order to avoid congestion problems on the network used for this transmission. Numerous video data compression techniques are already known. Among these, the HEVC compression standard ("High Efficiency Video Coding, Coding Tools and Specification", Matthias Wien, Signais and Communication Technology, 2015) proposes to implement a prediction of pixels of a current image compared to other pixels belonging to the same image (intra prediction) or to a previous or next image (inter prediction). More precisely, the intra prediction exploits the spatial redundancies within an image. To do this, the images are cut into blocks of pixels. The blocks of pixels are then predicted using information already reconstructed, corresponding to the blocks previously encoded / decoded in the current image according to the order in which the blocks are traversed in the image. Moreover, conventionally, the coding of a current block is carried out using a prediction of the current block, called the predictor block, and of a prediction residue or “residual block”, corresponding to a difference between the current block and the predictor block. The residual block obtained is then transformed, for example using a DOT-type transform (discrete cosine transform). The coefficients of the transformed residual block are then quantized, then encoded by entropy coding and transmitted to the decoder, which can reconstruct the current block by adding this residual block to the predictor block. The decoding is done image by image, and for each image, block by block. For each block, the corresponding elements of the stream are read. The inverse quantization and the inverse transformation of the coefficients of the residual block are performed. Then, the prediction of the block is calculated to obtain the predictor block and the current block is reconstructed by adding the prediction (ie the predictor block) to the decoded residual block. In the HEVC standard, it is possible to perform an intra prediction of a current block according to 35 different intra prediction modes. To encode the intra prediction mode selected to encode a current block, the HEVC standard defines two lists of prediction modes: a first list called the MPM list (for Most Probable Mode in English) comprising the 3 most probable intra prediction modes for the current block, such an MPM list being defined from the prediction modes previously selected during the coding of the neighboring blocks the current block, a second list called the non-MPM list comprising the other 32 remaining intra prediction modes, ie the intra prediction modes not included in the MPM list. According to the HEVC standard, the MPM list is constructed as a function of the intra prediction modes used to code the neighboring blocks of the current block located respectively to the left and above the current block. However, the mechanism for constructing the MPM list of the HEVC standard does not require that an intra prediction mode be systematically available for the neighboring blocks. When at least one of the neighboring blocks has not been coded beforehand using an intra prediction mode, the mechanism for constructing the MPM list populates the MPM list using one or more modes of intra prediction by default. It appears that according to this mechanism for coding an intra prediction mode (use of an MPM list), when the neighboring blocks are not coded according to an intra prediction mode, the cost of coding an intra prediction mode for the current block is high. In addition, when new intra prediction modes are used in addition to the existing classic intra prediction modes (for example those of the HEVC standard, or H.264, or others), the use of a new intra prediction mode or of an inter prediction mode for the current block impacts the coding cost of an intra prediction mode for the following blocks of the image which are coded in intra mode. There is therefore a need for a novel encoding and decoding method to improve the compression of image or video data. 3. Disclosure of the invention The invention improves the state of the art. For this purpose, it relates to a method of decoding a coded data stream representative of at least one image cut into blocks. The decoding method comprises the following steps, for at least one block of the image, called the current block: - determination if the current block is coded according to an intra coding mode or another coding mode, the intra coding mode being a coding mode using an intra prediction mode selected from a group of intra prediction modes, as a function of 'at least one intra prediction mode associated with a neighboring block of the current block, - when the current block is coded according to said intra coding mode: determination, for the current block, of an intra prediction mode in said group of intra prediction modes, as a function of at least one intra prediction mode associated with a previously decoded block of the image, - decoding of said current block as a function of said determined intra prediction mode, - association with said current block of said determined intra prediction mode, - when the current block is coded according to said other coding mode: - decoding of said current block according to said other coding mode, - determination, for the current block, of an intra prediction mode, in said group of intra prediction modes, - association with said current block of said determined intra prediction mode. According to the invention, when a block is coded according to a coding mode different from a so-called classic intra coding mode, ie an intra coding mode, such as that defined for example in the HEVC standard, an intra prediction mode is determined and associated with the block. Such an intra prediction mode associated with a current block is “fictitious” since it is not used, in this case, for decoding the current block. Such an intra prediction mode associated with the current block can be used subsequently to decode a next block in the image if the latter is coded according to the so-called classic intra coding mode, or else to associate an intra prediction mode with the. next block if the next block is coded according to another coding mode. The so-called classic intra coding mode corresponds to any type of intra coding mode using an intra prediction mode selected from a group of intra prediction modes, as a function of an intra prediction mode which has been used to predict a block previously. decoded and neighbor of the current block. For example, it may be an intra coding mode according to the H.264 / AVC standard, or HEVC, or others. The other coding mode can correspond to any type of coding mode distinct from the so-called classic intra coding mode, for example an inter coding mode, another type of intra coding mode (based on DPCM - for Differential pulse-code modulation. in English or ILR - for In-Loop Residual in English -, based on a "template matching" technique (pairing of models in English, ...). The invention also relates to a method of encoding an encoded data stream representative of at least one image divided into blocks, the encoding method comprises the following steps, for at least one block of the image, called the current block: - determination whether the current block is coded according to an intra coding mode or another coding mode, the intra coding mode being a coding mode using an intra prediction mode selected from a group of intra prediction modes as a function of at least one intra prediction mode associated with a neighboring block of the current block, - when the current block is coded according to said intra coding mode: - determination, for the current block, of an intra prediction mode in a group of intra prediction modes, as a function of at least one intra prediction mode associated with a previously decoded block of the image, - coding of said current block as a function of said determined intra prediction mode, - association with said current block of said determined intra prediction mode, - when the current block is coded according to said other coding mode: - coding of said current block according to said other coding mode, - determination, for the current block, of an intra prediction mode in said group of intra prediction modes, - association with said current block of said determined intra prediction mode. Selon un mode particulier de réalisation de l'invention, la détermination d'un mode de prédiction intra dans un groupe de modes de prédiction intra, en fonction d'au moins un mode de prédiction intra associé à un bloc précédemment décodé de l'image, comprend la construction d'une liste comprenant un sous-ensemble de modes de prédiction intra sélectionnés dans ledit groupe de modes de prédiction intra en fonction dudit au moins un mode de prédiction intra associé à un bloc précédemment décodé de l'image. Par exemple une telle liste peut correspondre à la liste des modes de prédiction les plus probables telle que définie selon le standard HEVC. In addition, according to this particular embodiment of the invention, when the current block is encoded according to said other encoding mode, the determination of an intra prediction mode in said group of intra prediction modes comprises the construction of at at least a part of said list for the current block, and the determined intra prediction mode corresponds to the first intra prediction mode of the list. According to this particular embodiment of the invention, a list comprising a subset of intra prediction modes is created, for example to predict an intra prediction mode used to predict the current block when the latter is coded according to the mode. intra coding, for example in a similar way to the list construction mechanism MPM of the HEVC standard. When the current block is coded according to another coding mode, a similar list construction mechanism is implemented, according to which at least part of the list is created, so as to select the first intra prediction mode of this list to associate it with the current block. According to another particular embodiment of the invention, when the current block is coded according to said other coding mode, the determined intra prediction mode corresponds to a predetermined prediction mode. According to this particular embodiment of the invention, the association of an intra prediction mode not used to encode / decode the current block is fast, since it is a predetermined prediction mode, for example it can be the intra PLANAR prediction mode of the HEVC standard. It can also be an intra prediction mode by default and transmitted in the stream, at the image or sequence level. According to another particular embodiment of the invention, when the current block is coded according to said other coding mode, the intra prediction mode determined for the current block corresponds to an intra prediction mode selected from at least one subset. of the group of intra prediction modes as providing a predicted block for the current block for which a distortion calculated between said predicted block and the decoded current block is minimal. According to this particular embodiment of the invention, a selection is made of the intra prediction mode approximating the decoded current block as closely as possible, from among the possible intra prediction modes, or from only some of these intra prediction modes. For example, all the intra prediction modes can be tested or else only those included in the list of the most probable intra prediction modes. According to another particular embodiment of the invention, when the current block is coded according to said other coding mode, the decoding of said current block comprising a prediction of said current block providing a first predicted current block, the intra prediction mode determined for the current block corresponds to an intra prediction mode selected from at least a subset of the group of intra prediction modes as providing a second predicted block for the current block for which a distortion calculated between said second predicted block and said first current block predicted is minimal. According to this particular embodiment of the invention, the intra prediction mode which is selected is that which best approximates the predicted current block obtained during the decoding of the current block. According to another particular embodiment of the invention, the prediction of said current block providing a first predicted current block comprises, for each pixel of the current block, obtaining a prediction of said pixel from another previously decoded pixel , said other previously decoded pixel belonging to said current block or to a previously decoded block of the image, and - when said other previously decoded pixel belongs to said current block, said other previously decoded pixel is obtained by: - the decoding of a prediction residue associated with said other pixel, the reconstruction of said other pixel by adding a prediction of said other pixel to the decoded residue. According to this variant embodiment of the invention, the prediction of the current block is obtained by coding / decoding the block pixel by pixel, for example according to a DPCM or ILR technique. According to another particular embodiment of the invention, when the current block is coded according to said other coding mode, the decoding of said current block comprising: - determining a local prediction function for the current block in a group of predetermined local prediction functions, the prediction of said current block comprising, for each pixel of the current block: obtaining a prediction of said pixel according to said local prediction function using at least one previously decoded pixel neighboring said pixel, said previously decoded pixel belonging to said current block or to a previously decoded block of the image, the intra prediction mode determined for the current block corresponds to an intra prediction mode selected from the group of intra prediction modes as a function of the local prediction function. According to this particular embodiment of the invention, the prediction of the current block is obtained by encoding / decoding the current block pixel by pixel as a function of a local prediction function using previously decoded pixels, neighbors of the current pixel. The intra prediction mode is then selected as a function of the local prediction function. According to another particular embodiment of the invention, the intra prediction mode for the current block is determined from a correspondence table associating an intra prediction mode with a local prediction function of the group of local prediction functions predetermined. According to another particular embodiment of the invention, for a neighboring block of the current block, located after the current block in an order of traversal of the blocks of the image for coding or decoding, the neighboring block being coded according to said intra coding mode, the method comprises: the determination, for the neighboring block, of an intra prediction mode in a group of intra prediction modes, as a function of at least the intra prediction mode associated with the current block, - decoding or coding of said neighboring block as a function of said determined intra prediction mode, - association with said neighboring block of said determined intra prediction mode. According to another particular embodiment of the invention, for a neighboring block of the current block, located after the current block in an order of traversal of the blocks of the image for coding or decoding, the neighboring block being coded according to said another coding mode, the method comprises: - decoding or coding of said neighboring block according to said other coding mode, the determination, for the neighboring block, of an intra prediction mode in said group of intra prediction modes, as a function of the intra prediction mode associated with the current block, - association with said neighboring block of said determined intra prediction mode. The invention also relates to a decoding device configured to implement the decoding method according to any one of the particular embodiments defined above. This decoding device could of course include the various characteristics relating to the decoding method according to the invention. Thus, the characteristics and advantages of this decoding device are the same as those of the decoding method, and are not further detailed. The decoding device comprises in particular a processor configured for, for at least one block of the image, said current block: - determine whether the current block is coded according to an intra coding mode or another coding mode, the intra coding mode being a coding mode using an intra prediction mode selected from a group of intra prediction modes as a function of at least one intra prediction mode associated with a neighboring block of the current block, - when the current block is coded according to said intra coding mode: determining, for the current block, an intra prediction mode in a group of intra prediction modes, as a function of at least one intra prediction mode associated with a previously decoded block of the image, - decode said current block according to said determined intra prediction mode, - associate with said current block said determined intra prediction mode, - when the current block is coded according to said other coding mode: - decode said current block according to said other coding mode, - determining, for the current block, an intra prediction mode in said group of intra prediction modes, - Associating with said current block said determined intra prediction mode. According to a particular embodiment of the invention, such a decoding device is included in a terminal. The invention also relates to an encoding device configured to implement the encoding method according to any one of the particular embodiments defined above. This coding device could of course include the various characteristics relating to the coding method according to the invention. Thus, the characteristics and advantages of this coding device are the same as those of the coding method, and are not further detailed. The coding device comprises in particular a processor configured for, for at least one block of the image, said current block: - determine whether the current block is coded according to an intra coding mode or another coding mode, the intra coding mode being a coding mode using an intra prediction mode selected from a group of intra prediction modes as a function of at least one intra prediction mode associated with a neighboring block of the current block, - when the current block is coded according to said intra coding mode: determining, for the current block, an intra prediction mode in a group of intra prediction modes, as a function of at least one intra prediction mode associated with a previously decoded block of the image, - coding said current block as a function of said determined intra prediction mode, - associate with said current block said determined intra prediction mode, - when the current block is coded according to said other coding mode: - coding said current block according to said other coding mode, - determining, for the current block, an intra prediction mode in said group of intra prediction modes, - Associating with said current block said determined intra prediction mode. According to a particular embodiment of the invention, such a coding device is included in a terminal, or a server. The decoding method, respectively the encoding method, according to the invention can be implemented in various ways, in particular in wired form or in software form. According to a particular embodiment of the invention, the decoding method, respectively the encoding method, is implemented by a computer program. The invention also relates to a computer program comprising instructions for implementing the decoding method or the encoding method according to any one of the particular embodiments described above, when said program is executed by a processor. Such a program can use any programming language. It can be downloaded from a communications network and / or recorded on a computer readable medium. This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other. desirable shape. The invention also relates to a recording medium or information medium readable by a computer, and comprising instructions of a computer program as mentioned above. The recording media mentioned above can be any entity or device capable of storing the program. For example, the medium can include a storage means such as a memory. On the other hand, the recording media can correspond to a transmissible medium such as an electrical or optical signal, which can be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can in particular be downloaded from an Internet type network. Alternatively, the recording media can correspond to an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question. 4. List of figures Other characteristics and advantages of the invention will emerge more clearly on reading the following description of a particular embodiment, given by way of simple illustrative and non-limiting example, and the appended drawings, among which: - Figure 1 shows steps of the coding method according to a particular embodiment of the invention, FIG. 2 illustrates an example of position of neighboring blocks of a current block to determine an intra prediction mode according to a particular embodiment of the invention, FIG. 3 illustrates an example of the position of the reference pixels used to predict pixels of a current block according to a particular embodiment of the invention, - Figure 4 shows steps of the decoding method according to a particular embodiment of the invention, FIG. 5 illustrates an example of a signal comprising coded data representative of at least one block of an image according to a particular embodiment of the invention, FIG. 6 shows the simplified structure of a coding device suitable for implementing the coding method according to any one of the particular embodiments of the invention, FIG. 7 shows the simplified structure of a decoding device suitable for implementing the decoding method according to any one of the particular embodiments of the invention. 5. Description of an embodiment of the invention 5.1 General principle The general principle of the invention is to associate an intra prediction mode determined in a group of intra prediction modes defined for an intra coding mode, with a block of an image coded according to another coding mode distinct from the mode. intra coding. Conventionally, when a block of the image is coded according to the intra coding mode, the prediction mode used to code this block is coded in the stream. Such a prediction mode defined for an intra coding mode is predicted from the intra prediction modes used for coding neighboring blocks of the block. According to the invention, when a neighboring block has not been coded according to the intra coding mode, and therefore no intra prediction mode defined for the intra coding mode has been used to code this neighboring block, the neighboring block still has an intra prediction mode associated with this neighboring block. The intra prediction mode associated with the neighboring block can thus be used to predict the intra prediction mode of a block coded according to an intra coding mode, The invention thus makes it possible to improve the performance in compression. 5. 2 Examples of implementation FIG. 1 shows steps of the coding method according to a particular embodiment of the invention. For example, we encode a sequence of images l 1; l 2 , ..., Iisi b in the form of a STR coded data stream according to a particular embodiment of invention. For example, such a coding method is implemented by a coding device as described below in relation to FIG. 6. A sequence of images l1 , l 2 , lisi b , Nb being the number of images of the sequence to be coded, is supplied at the input of the coding method. The encoding method delivers at output an encoded data stream STR representative of the sequence of images supplied at input. In known manner, the coding of the sequence of images h, l 2 , ..., lisi b is carried out image by image according to a coding order established beforehand and known to the decoder. For example, the images can be coded in the time order 1 ; l 2 , ..., l N b or in another order, for example I s, l 2, ..., l Nb . During a step E0, an image I to be encoded from the sequence of images l, l 2 , ..., l Nb is cut into blocks, for example into blocks of size 32 × 32, or 64 × 64 pixels or more. Such a block can be subdivided into square or rectangular sub-blocks, for example of size 16x16, 8x8, 4x4, 16x8, 8x16, .... During an optional step E10, according to a particular embodiment of the invention, a quantization parameter QP is encoded in the data stream STR, at the level of the data encoded for the image I, or else at the level of the data encoded for the sequence of images. Then, during a step E1, a first block or sub-block X b to be encoded of the image I is selected according to a direction of travel of the image I, which is predetermined. For example, it may be the first block in the lexicographical order of the image browsing. During a step E2, the encoder chooses the encoding mode for encoding the current block X b . According to the particular embodiment described here, the encoder selects the coding mode for coding the current block X b from a first coding mode M1 and a second coding mode M2. Additional coding modes (not described here) can be used. According to the particular embodiment described here, the first coding mode M1 corresponds to the coding of the current block by intra-classical prediction, for example as defined according to the HEVC standard and the second coding mode M2 ​​corresponds to coding by prediction In Loop Residual (ILR). The principle of the invention can be extended to other types of coding modes, whether for the first coding mode M1 or the second coding mode M2. For example, the first coding mode can correspond to any type of intra coding mode according to which the intra prediction mode used to encode a block is coded by prediction from the intra prediction mode of the neighboring blocks previously decoded when there is . This is for example the case with the intra coding mode according to the H.264 or HEVC standards or even in the experimental JEM software available at the internet address (https://ivet.hhi.fraunhofer.de/). The second coding mode can correspond to any type of coding mode available to the coder / decoder, for example an inter-picture coding mode, a coding mode by template matching,. During step E2, the encoder can perform bit rate / distortion optimization to determine the best encoding mode for encoding the current block. During this bit rate / distortion optimization, additional coding modes distinct from the first and second coding modes can be tested, for example a coding mode in inter mode. During this bit rate / distortion optimization, the encoder simulates the coding of the current block X b according to the different coding modes available in order to determine the bit rate and the distortion associated with each coding mode and, select the coding mode offering the best bit rate / distortion compromise, for example according to the D + R function, where R represents the bit rate necessary to code the current block according to the coding mode evaluated and D the distortion measured between the decoded block and the original current block and a Lagrangian multiplier, for example entered by the user or defined in the encoder. During a step E20, information indicating the coding mode selected for the current block is coded in the data stream STR. If the current block X b is coded according to the first coding mode M1, the method goes to step E21 for coding the block according to M1. If the current block X b is coded according to the second coding mode M2, the method goes to step E22 for coding the block according to M2. The step E21 of coding the block according to the first coding mode M1, according to a particular embodiment of the invention, is described below. According to the particular mode described here, the first coding mode corresponds to an intra-classical prediction, such as that defined in the HEVC standard. According to a particular embodiment of the invention, during a step E210, a quantization step ¾ is determined. For example, the quantization step ¾ can be fixed by the user, or else calculated using a quantization parameter fixing a compromise between compression and quality and entered by the user or defined by the encoder. Thus, such a quantization parameter can be the parameter L, used in the bit rate-distortion cost function D + 1. R where D represents the distortion introduced by the coding and R the bit rate used for coding. This function is used to make coding choices. Conventionally, we are looking for a way to code the image which minimizes this function. As a variant, the quantization parameter can be the QP, corresponding to the quantization parameter conventionally used in the AVC or HEVC standards. Thus, in the HEVC standard, the quantization step ¾ is determined by the equation 5 1 = levelScale [QP% 6] “(QP / 6)) where levelScale [k] = {40, 45, 51, 57, 64 , 72} for k = 0..5. During a step E21 1, a prediction of the current block is determined using an intra-classic prediction mode. According to this intra-classical prediction, each predicted pixel is calculated only from the decoded pixels resulting from the neighboring blocks (reference pixels) located above the current block, and to the left of the current block. How the pixels are predicted from the reference pixels depends on a prediction mode which is transmitted to the decoder, and which is chosen by the encoder from a predetermined set of modes known to the encoder and the decoder. Thus, in HEVC, there are 35 possible prediction modes: 33 modes which interpolate the reference pixels in 33 different angular directions, and 2 other modes: the DC mode in which each pixel of the predicted block is produced from the average reference pixels, and PLANAR mode, which performs plane, non-directional interpolation. This so-called “intra-classical prediction” approach is well known and also used in the ITU-T H.264 standard (where there are only 9 different modes) as well as in the JEM experimental software available at the internet address (https : //ivet.hhi.fraunhofer.de/), where there are 67 different prediction modes. In all cases, the intra-classical prediction respects the two aspects mentioned above (prediction of the pixels from neighboring blocks and transmission to the decoder of During step E21 1, the encoder therefore chooses one of the prediction modes available from the predetermined list of prediction modes. One way of choosing consists for example in evaluating all the prediction modes and in keeping the prediction mode which minimizes a cost function such as, conventionally, the bit rate-distortion cost. During a step E212, the prediction mode chosen for the current block is coded from the neighboring blocks of the current block. FIG. 2 illustrates an example of the position of neighboring blocks A b and B b of the current block X b to code the prediction mode of the current block X b . During step E212, the intra prediction mode chosen for the current block is coded using the intra prediction modes associated with the neighboring blocks. According to the particular embodiment of the invention described here, the intra prediction mode associated with a block is: - the intra prediction mode which was used to predict the block, if the block was coded by a conventional intra prediction coding mode, the intra prediction mode which has been associated with the block, if the block has been coded by another coding mode distinct from the coding mode by conventional intra prediction. An example of such an association is described below with reference to step E229. Thus, the approach described in the HEVC standard for encoding the prediction mode of the current block can be used. Such an approach consists, in the example of FIG. 2, in identifying the intra m A prediction mode associated with the block A b located above the current block, and the intra m B prediction mode associated with the block B b located just to the left of the current block. As a function of the value of m A and of m B , a list called MPM (for Most Probable Mode), containing 3 intra prediction modes, and a list called non-MPM, containing the 32 other prediction modes, are created. Selon le mode particulier décrit ici, le mécanisme de création de la liste MPM spécifié selon la norme HEVC est adapté afin de prendre en compte l'association d'un mode de prédiction intra à un bloc lors de son codage, lorsque ce bloc n'est pas codé selon le mode de codage intra classique (étape E229 décrite plus loin). Ainsi, un bloc voisin du bloc courant a toujours un mode de prédiction intra qui lui est associé, que ce bloc ait été codé selon un mode de codage intra ou selon un autre mode de codage (ILR, inter, etc....). The rest of the mechanism for creating the MPM list remains similar to that specified according to the HEVC standard. If m A and m B are both equal to the same intra prediction mode and that this intra prediction mode is the DC or PLANAR prediction mode, the MPM list includes the following prediction modes: MPM [0] = PLANAR, MPM [1] = DC, MPM [2] = A (26) corresponding to the angular prediction mode at index 26 of the table of intra HEVC prediction modes. If m A and m B are both equal to the same angular prediction mode m (n), the list MPM includes the following prediction modes: MPM [0] = m (n), MPM [1] = m (2+ (n + 29) mod32), MPM [2] = m (2+ (n-1) mod32). If m A and m B are different, the MPM list includes the following prediction modes: MPM [0] = m B , MPM [1] = m A , MPM [2] = Mlast, where Mlast is defined by: - if m B is not equal to PLANAR mode and m A is not equal to PLANAR mode, then Mlast is equal to PLANAR mode, - if not, if m B is not equal to DC mode and m A is not equal to DC mode, then Mlast is equal to DC mode, - otherwise Mlast is equal to the angular mode A (26). The non-MPM list includes all other intra prediction modes not included in the MPM list. According to the HEVC standard, in order to encode the intra prediction mode of the current block, syntax elements are transmitted: a binary indicator indicating whether the prediction mode to be coded for the current block is in the MPM list or not, -if the prediction mode of the current block belongs to the MPM list, an index in the MPM list corresponding to the prediction mode of the current block is coded, - If the prediction mode of the current block does not belong to the MPM list, an index in the non-MPM list corresponding to the prediction mode of the current block is coded. During a step E213, the prediction residue R for the current block is constructed. During step E213, conventionally, a predicted block P is constructed as a function of the prediction mode chosen in step E21 1. Then the prediction residue R is obtained by calculating the difference for each pixel, between the predicted block P and the original current block. At a step E214, the prediction residue R is converted to R T . During step E214, a frequency transform is applied to the block of residue R so as to produce the block R T comprising transformed coefficients. The transform may be a DCT type transform for example. It is possible to choose the transform to be used from a predetermined set of transforms E T and to signal the transform used to the decoder. During a step E215, the block of transformed residue R T is quantized using, for example, a scalar quantization of quantization steps. This produces the block of transformed quantized prediction residue R TQ . During a step E216, the coefficients of the quantized block R TQ are encoded by an entropy encoder. For example, the entropy coding specified in the HEVC standard can be used. According to the variant embodiment described here, during a step E217, the prediction mode determined in step E21 1 is associated with the current block. In a known manner, the current block is decoded by de-quantizing the coefficients of the quantized block R TQ , then by applying the inverse transform to the de-quantized coefficients to obtain the decoded prediction residue. The prediction is then added to the decoded prediction residue in order to reconstruct the current block and to obtain its decoded version. The decoded version of the current block can then be used subsequently to spatially predict other neighboring blocks of the image or else to predict blocks of other images by inter-image prediction. The step E22 of coding the block according to the second coding mode M2, according to a particular embodiment of the invention, is described below. According to the particular mode described here, the second coding mode corresponds to coding by ILR prediction. During a step E220, a local predictor PL for the current block is determined. According to the coding mode described here, the pixels of the current block are predicted by previously reconstructed pixels of a block neighboring the current block or of the current block itself. Preferably, to predict, pixels are chosen which are as close as possible to the pixel to be predicted. For this reason, we speak of a local predictor. The local predictor PL can also be likened to a mode of prediction of the current block associated with the second coding mode M2. According to this interpretation, in the particular embodiment described here, the first coding mode uses a first group of intra prediction modes, for example the intra prediction modes defined by the HEVC standard, and the second mode coding, here the ILR mode, uses a second group of prediction modes distinct from the first group of intra prediction modes. According to an alternative embodiment described below, a correspondence between these two groups of prediction modes can be determined. The local predictor PL can be unique or it can be selected from a set of predetermined local predictors (second group of prediction modes). According to an alternative embodiment, 4 local predictors are defined. Thus, if we call X a current pixel to be predicted from the current block, A the pixel located immediately to the left of X, B the pixel located immediately to the left and above X, C the pixel located immediately above X, as illustrated in FIG. 3 showing a current block X b . 4 local predictors PL1, PL2, PL3, PL4 can be defined as follows: PL1 (X) = min (A, B) if C> max (A, B) max (A, B) if C