A method, an apparatus and a computer program product for video encoding and video decoding

Abstract

The embodiments relate to a method and technical equipment for implementing the method. The method comprises forming an intra prediction for a current block of a video frame using an intra-prediction process, wherein the intra-prediction process comprises: forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters, being computed using reconstructed samples in a template.

Description

[0001] A METHOD, AN APPARATUS AND A COMPUTER PROGRAM PRODUCT FOR VIDEO ENCODING AND VIDEO DECODING

[0002] Technical Field

[0003] The present solution generally relates to video encoding and video decoding.

[0004] Background

[0005] Video encoding is a process, where input video is transformed into a compressed format suited for storage or transmission. In video decoding, the opposite is performed, i.e., compressed video is uncompressed back into a viewable form. The encoding process comprises prediction, where pixel values of a certain picture area are predicted. Then a prediction error, i.e., difference between the predicted pixels and the original pixels is coded.

[0006] Summary

[0007] The embodiments discussed in the present description provides an improved prediction solution to be used in video encoding and decoding.

[0008] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0009] Various aspects include a method, an apparatus and a computer readable medium comprising a computer program stored therein, which are characterized by what is stated in the independent claims. Various embodiments are disclosed in the dependent claims.

[0010] According to a first aspect, there is provided an apparatus comprising means for forming an intra prediction for a current block of a video frame using an intra-prediction process, where for the intraprediction process the apparatus comprises: means for forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and means for forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and means for blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template.

[0011] According to a second aspect, there is provided a method, comprising forming an intra prediction for a current block of a video frame using an intra-prediction process, wherein the intra-prediction process comprises: forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template.

[0012] According to a third aspect, there is provided an apparatus comprising at least one processor, memory including computer program code, the memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: form an intra prediction for a current block of a video frame using an intra-prediction process, where for the intra-prediction process comprises: forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template.

[0013] According to a fourth aspect, there is provided computer program product comprising computer program code configured to, when executed on at least one processor, cause an apparatus or a system to: form an intra prediction for a current block of a video frame using an intra-prediction process, where for the intra-prediction process comprises: forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template.

[0014] According to an embodiment, the computed parameters comprise at least one cost between predicted and reconstructed samples in the template.

[0015] According to an embodiment, blending the main predictor and the one or more additional predictors comprises computing a weighted average.

[0016] According to an embodiment, weights for the weighted average are computed depending on the at least one cost between the predicted and the reconstructed samples in the template. According to an embodiment, the weights are computed based on measuring a cost between the predicted and the reconstructed samples in the template against a fixed threshold value.

[0017] According to an embodiment, the weights for the weighted average are computed as the sum of an initial value and an offset value.

[0018] According to an embodiment, offset values are computed depending on the at least one cost between the predicted and the reconstructed samples in the template

[0019] According to an embodiment, the different Multiple Reference Line indices are determined based on the given Multiple Reference Line index.

[0020] According to an embodiment, the blending of the main predictor and the one or more additional predictors depends on a given intra-prediction mode.

[0021] According to an embodiment, the blending of the main predictor and the one or more additional predictors depends on the size of the current block.

[0022] According to an embodiment, the reconstructed samples are adjacent to the current block.

[0023] According to an embodiment, the computer program product is embodied on a non-transitory computer readable medium.

[0024] Description of the Drawings

[0025] In the following, various embodiments will be described in more detail with reference to the appended drawings, in which

[0026] Fig. 1 shows an example of an encoding process;

[0027] Fig. 2 shows an example of a decoding process;

[0028] Fig. 3 shows an example of a current block and multiple reference lines; Fig. 4 shows an example of a template for a current block;

[0029] Fig. 5 is a flowchart illustrating a method according to an embodiment; and

[0030] Fig. 6 shows an apparatus according to an embodiment.

[0031] Description of Example Embodiments

[0032] The following description and drawings are illustrative and are not to be unnecessarily construed as limiting. The specific details are provided for a thorough understanding of the disclosure. However, in certain instances, well- known or conventional details are not described in order to avoid obscuring the description. Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure.

[0033] The present embodiments relate to encoding and decoding of digital video material. In the following, several embodiments will be described in the context of one video coding arrangement. It is to be noted, however, that the present embodiments are not necessarily limited to this particular arrangement. In particular, the present embodiments relate to tuning of arithmetic coding contexts with bin grouping. The arithmetic coding is a process where syntax elements are compressed or decompressed based on probability estimates for the syntax elements.

[0034] Before describing the embodiments further, a brief reference to evolution of video coding standardization is given. The present embodiments are suited within the context of next generation video coding standardization, e.g., H.267 video coding standard and the ECM (Enhanced Compression Model) exploration.

[0035] A video codec comprises an encoder and a decoder. The encoder transforms the input video into a compressed representation suited for storage / transmission. The decoder can un-compress the compressed video representation back into a viewable form. The encoder may discard some information in the original video sequence in order to represent the video in a more compact form (i.e. , at lower bitrate).

[0036] Figure 1 shows an example of an encoding process for two-dimensional (2D) pictures, and Figure 2 shows an example of a decoding process for 2D pictures. In Figure 1 , the following have been illustrated:

[0037] - an image to be encoded (ln);

[0038] - a predicted representation of an image block (P'n);

[0039] - a prediction error signal (Dn);

[0040] - a reconstructed prediction error signal (D'n);

[0041] - a preliminary reconstructed image (l'n);

[0042] - a final reconstructed image (R'n);

[0043] - a transform (T) and inverse transform (T-1);

[0044] - a quantization (Q) and inverse quantization (Q-1);

[0045] - entropy encoding (E);

[0046] - a reference frame memory (RFM);

[0047] - inter prediction (Pinter);

[0048] - intra prediction (Pintra);

[0049] - mode selection (MS), and

[0050] - filtering (F).

[0051] In Figure 2 the following have been illustrated:

[0052] - a predicted representation of an image block (P'n);

[0053] - a reconstructed prediction error signal (D'n);

[0054] - a preliminary reconstructed image (l'n);

[0055] - a final reconstructed image (R'n); an inverse transform (T1);

[0056] - an inverse quantization (Q-1);

[0057] - an entropy decoding (E-1);

[0058] - a reference frame memory (RFM);

[0059] - a prediction (either inter or intra) (P);

[0060] - and filtering (F).

[0061] An elementary unit for the input to an encoder and the output of a decoder, respectively, in most cases is a picture (also referred to as “an image”). A picture given as an input to an encoder may also be referred to as a source picture, and a picture decoded by a decoded may be referred to as a decoded picture or a reconstructed picture. The source and decoded pictures are each comprised of one or more sample arrays, such as one of the following sets of sample arrays:

[0062] - Luma (Y) only (monochrome).

[0063] - Luma and two chroma (YCbCr or YCgCo).

[0064] - Green, Blue and Red (GBR, also known as RGB).

[0065] - Arrays representing other unspecified monochrome or tristimulus color samplings (for example, YZX, also known as XYZ).

[0066] A picture may be defined to be either a frame or a field. A frame comprises a matrix of luma samples and possibly the corresponding chroma samples. A field is a set of alternate sample rows of a frame and may be used as encoder input, when the source signal is interlaced. Chroma sample arrays may be absent (and hence monochrome sampling may be in use) or chroma sample arrays may be subsampled when compared to luma sample arrays.

[0067] The Advanced Video Coding standard (which may be abbreviated AVC or H.264 / AVC) was developed by the Joint Video Team (JVT) of the Video Coding Experts Group (VCEG) of the Telecommunications Standardization Sector of International Telecommunication Union (ITU-T) and the Moving Picture Experts Group (MPEG) of International Organization for Standardization (ISO) I International Electrotechnical Commission (IEC). The H.264 / AVC standard is published by both parent standardization organizations, and it is referred to as ITU-T Recommendation H.264 and ISO / IEC International Standard 14496-10, also known as MPEG-4 Part 10 Advanced Video Coding (AVC). There have been multiple versions of the H.264 / AVC standard, each integrating new extensions or features to the specification. These extensions include Scalable Video Coding (SVC) and Multiview Video Coding (MVC).

[0068] The High Efficiency Video Coding standard (which may be abbreviated HEVC or H.265 / HEVC) was developed by the Joint Collaborative Team - Video Coding (JCT-VC) of VCEG and MPEG. The standard is published by both parent standardization organizations, and it is referred to as ITU-T Recommendation H.265 and ISO / IEC International Standard 23008-2, also known as MPEG-H Part 2 High Efficiency Video Coding (HEVC). Extensions to H.265 / HEVC include scalable, multiview, three-dimensional, and fidelity range extensions, which may be referred to as SHVC, MV-HEVC, 3D-HEVC, and REXT, respectively. The references in this description to H.265 / HEVC, SHVC, MV-HEVC, 3D-HEVC and REXT that have been made for the purpose of understanding definitions, structures or concepts of these standard specifications are to be understood to be references to the latest versions of these standards that were available before the date of this application, unless otherwise indicated.

[0069] Versatile Video Coding (which may be abbreviated WC, H.266, or H.266 / VVC) is a video compression standard developed as the successor to HEVC. WC is specified in ITU-T Recommendation H.266 and equivalently in ISO / IEC 23090-3, which is also referred to as MPEG-I Part 3.

[0070] Some key definitions, bitstream and coding structures, and concepts of H.264 / AVC, HEVC, WC, and / or AV1 and some of their extensions are described in this section as an example of a video encoder, decoder, encoding method, decoding method, and a bitstream structure, wherein the embodiments may be implemented. The aspects of various embodiments are not limited to H.264 / AVC, HEVC, WC, and / or AV1 or their extensions, but rather the description is given for one possible basis on top of which the present embodiments may be partly or fully realized.

[0071] Hybrid video codecs, for example ITU-T H.263, H.264 / AVC, HEVC, and WC, may encode the video information in two phases. At first, pixel values in a certain picture area (or “block”) are predicted for example by motion compensation means or by spatial means.

[0072] In motion compensation based prediction (which may be referred to as inter prediction, temporal prediction or motion-compensated temporal prediction or motion-compensated prediction or MCP) an area in one of the previously coded frames that corresponds closely to the block being coded is found and used for prediction. Inter prediction may reduce temporal redundancy.

[0073] In spatial prediction pixel values around the block to be coded are used. In the first phase, predictive coding may be applied, for example, as so-called sample prediction and / or so-called syntax prediction. In the sample prediction, pixel or sample values in a certain picture area or "block" are predicted. These pixel or sample values can be predicted, for example, using one or more of motion compensation or intra prediction mechanisms.

[0074] Intra prediction, where pixel or sample values can be predicted by spatial mechanisms, involve finding and indicating a spatial region relationship. Intra prediction utilizes the fact that adjacent pixels within the same picture are likely to be correlated. Intra prediction can be performed in spatial or transform domain, i.e. , either sample values or transform coefficients can be predicted. Intra prediction is typically exploited in intra coding, where no inter prediction is applied.

[0075] In the syntax prediction, which may also be referred to as parameter prediction, syntax elements and / or syntax element values and / or variables derived from syntax elements are predicted from syntax elements (de)coded earlier and / or variables derived earlier. Non-limiting examples of syntax prediction are provided below.

[0076] In motion vector prediction, motion vectors e.g., for inter and / or inter-view prediction may be coded differentially with respect to a block-specific predicted motion vector. In many video codecs, the predicted motion vectors are created in a predefined way, for example by calculating the median of the encoded or decoded motion vectors of the adjacent blocks. Another way to create motion vector predictions, sometimes referred to as advanced motion vector prediction (AMVP), is to generate a list of candidate predictions from adjacent blocks and / or co-located blocks in temporal reference pictures and signalling the chosen candidate as the motion vector predictor. In addition to predicting the motion vector values, the reference index of previously coded / decoded picture can be predicted. The reference index is typically predicted from adjacent blocks and / or co-located blocks in temporal reference picture. Differential coding of motion vectors is typically disabled across slice boundaries.

[0077] The block partitioning, e.g., from a coding tree unit (CTU) to coding units (CUs) and down to prediction units (PUs), may be predicted. In filter parameter prediction, the filtering parameters e.g., for sample adaptive offset may be predicted. Prediction approaches using image information from a previously coded image can also be called as inter prediction methods which may also be referred to as temporal prediction and motion compensation. Prediction approaches using image information within the same image can also be called as intra prediction methods.

[0078] In the second phase of encoding, the prediction error, i.e., the difference between the predicted block of pixels and the original block of pixels, is coded. This may be done by transforming the difference in pixel values using a specified transform (e.g., Discrete Cosine Transform (DCT) or a variant of it), quantizing the coefficients and entropy coding the quantized coefficients. By varying the fidelity of the quantization process, encoder can control the balance between the accuracy of the pixel representation (picture quality) and size of the resulting coded video representation (file size of transmission bitrate).

[0079] In some video codecs, such as H.265 / HEVC, video pictures are divided into coding units (CU) covering the area of the picture. A CU consists of one or more prediction units (Pll) defining the prediction process for the samples within the CU and one or more transform units (TU) defining the prediction error coding process for the samples in the said CU. A CU may consist of a square block of samples with a size selectable from a predefined set of possible CU sizes. A CU with the maximum allowed size is typically named as LCU (largest coding unit) or CTU (coding tree unit) and the video picture is divided into non-overlapping CTUs. A CTU can be further split into a combination of smaller CUs, e.g., by recursively splitting the CTU and resultant CUs. Each resulting CU typically has at least one PU and at least one TU associated with it. Each PU and TU can be further split into smaller PUs and TUs in order to increase granularity of the prediction and prediction error coding processes, respectively. Each PU has prediction information associated with it defining what kind of a prediction is to be applied for the pixels within that PU (e.g., motion vector information for inter predicted PUs and intra prediction directionality information for intra predicted PUs). Similarly, each TU is associated with information describing the prediction error decoding process for the samples within the said TU (including e.g., DCT coefficient information). It is typically signaled at CU level whether prediction error coding is applied or not for each CU. In the case there is no prediction error residual associated with the CU, it can be considered there are no TUs for the said CU. The division of the image into CUs, and division of CUs into PUs and TUs is typically signaled in the bitstream allowing the decoder to reproduce the intended structure of these units.

[0080] The decoder reconstructs the output video by applying prediction means similar to the encoder to form a predicted representation of the pixel blocks (using the motion or spatial information created by the encoder and stored in the compressed representation) and prediction error decoding (inverse operation of the prediction error coding recovering the quantized prediction error signal in spatial pixel domain). After applying prediction and prediction error decoding means the decoder sums up the prediction and prediction error signals (pixel values) to form the output video frame. The decoder (and encoder) can also apply additional filtering means to improve the quality of the output video before passing it for display and / or storing it as prediction reference for the forthcoming frames in the video sequence.

[0081] Instead, or in addition to approaches utilizing sample value prediction and transform coding for indicating the coded sample values, a color palette based coding can be used. Palette based coding refers to a family of approaches for which a palette, i.e. , a set of colors and associated indices, is defined and the value for each sample within a coding unit is expressed by indicating its index in the palette. Palette based coding can achieve good coding efficiency in coding units with a relatively small number of colors (such as image areas which are representing computer screen content, like text or simple graphics). In order to improve the coding efficiency of palette coding different kinds of palette index prediction approaches can be utilized, or the palette indices can be run-length coded to be able to represent larger homogenous image areas efficiently. Also, in the case the CU contains sample values that are not recurring within the CU, escape coding can be utilized. Escape coded samples are transmitted without referring to any of the palette indices. Instead, their values are indicated individually for each escape coded sample.

[0082] In many video codecs, including H.264 / AVC, HEVC, and WC, motion information is indicated by motion vectors associated with each motion compensated image block. Each of these motion vectors represents the displacement of the image block in the picture to be coded (in the encoder) or decoded (at the decoder) and the prediction source block in one of the previously coded or decoded images (or pictures). In order to represent motion vectors efficiently those are typically coded differentially with respect to block specific predicted motion vectors. In typical video codecs the predicted motion vectors are created in a predefined way, for example calculating the median of the encoded or decoded motion vectors of the adjacent blocks. Another way to create motion vector predictions is to generate a list of candidate predictions from adjacent blocks and / or co-located blocks in temporal reference pictures and signaling the chosen candidate as the motion vector predictor. In addition to predicting the motion vector values, the reference index of previously coded / decoded picture can be predicted. The reference index is typically predicted from adjacent blocks and / or or co-located blocks in temporal reference picture. Moreover, typical high efficiency video codecs employ an additional motion information coding / decoding mechanism, often called merging / merge mode, where all the motion field information, which includes motion vector and corresponding reference picture index for each available reference picture list, is predicted and used without any modification / correction. Similarly, predicting the motion field information is carried out using the motion field information of adjacent blocks and / or colocated blocks in temporal reference pictures and the used motion field information is signaled among a list of motion field candidate list filled with motion field information of available adjacent / co-located blocks.

[0083] Video codecs may support motion compensated prediction from one source image (uni-prediction) and two sources (bi-prediction). In the case of uniprediction a single motion vector is applied whereas in the case of bi-prediction two motion vectors are signaled and the motion compensated predictions from two sources are averaged to create the final sample prediction. In the case of weighted prediction, the relative weights of the two predictions can be adjusted, or a signaled offset can be added to the prediction signal.

[0084] In addition to applying motion compensation for inter picture prediction, similar approach can be applied to intra picture prediction. In this case the displacement vector indicates where from the same picture a block of samples can be copied to form a prediction of the block to be coded or decoded. This kind of intra block copying methods can improve the coding efficiency substantially in presence of repeating structures within the frame - such as text or other graphics.

[0085] In video codecs the prediction residual after motion compensation or intra prediction may be first transformed with a transform kernel (like DCT) and then coded. The reason for this is that often there still exists some correlation among the residual and transform can in many cases help reduce this correlation and provide more efficient coding.

[0086] Many video encoders utilize Lagrangian cost functions to find optimal coding modes, e.g., the desired Macroblock mode and associated motion vectors. This kind of cost function uses a weighting factor A to tie together the (exact or estimated) image distortion due to lossy coding methods and the (exact or estimated) amount of information that is required to represent the pixel values in an image area:

[0087] C = D + AR (Eq. 1 )

[0088] Where C is the Lagrangian cost to be minimized, D is the image distortion (e.g., Mean Squared Error) with the mode and motion vectors considered, and R the number of bits needed to represent the required data to reconstruct the image block in the decoder (including the amount of data to represent the candidate motion vectors).

[0089] The phrase along the bitstream (e.g., indicating along the bitstream) may be defined to refer to out-of-band transmission, signaling, or storage in a manner that the out-of-band data is associated with the bitstream. The phrase decoding along the bitstream or alike may refer to decoding the referred out- of-band data (which may be obtained from out-of-band transmission, signaling, or storage) that is associated with the bitstream. For example, an indication along the bitstream may refer to metadata in a container file that encapsulates the bitstream.

[0090] Scalable video coding refers to coding structure where one bitstream can contain multiple representations of the content at different bitrates, resolutions or frame rates. In these cases, the receiver can extract the desired representation depending on its characteristics (e.g., resolution that matches best the display device). Alternatively, a server or a network element can extract the portions of the bitstream to be transmitted to the receiver depending on e.g., the network characteristics or processing capabilities of the receiver. A scalable bitstream may consist of a “base layer” providing the lowest quality video available and one or more enhancement layers that enhance the video quality when received and decoded together with the lower layers. In order to improve coding efficiency for the enhancement layers, the coded representation of that layer typically depends on the lower layers. E.g., the motion and mode information of the enhancement layer can be predicted from lower layers. Similarly, the pixel data of the lower layers can be used to create prediction for the enhancement layer.

[0091] A scalable video codec for quality scalability (also known as Signal-to-Noise or SNR) and / or spatial scalability may be implemented as follows. For a base layer, a conventional non-scalable video encoder and decoder is used. The reconstructed / decoded pictures of the base layer are included in the reference picture buffer for an enhancement layer. In H.264 / AVC, HEVC, and similar codecs using reference picture list(s) for inter prediction, the base layer decoded pictures may be inserted into a reference picture list(s) for coding / decoding of an enhancement layer pictures similarly to the decoded reference pictures of the enhancement layer. Consequently, the encoder may choose a base-layer reference picture as inter prediction reference and may indicate its use e.g., with a reference picture index in the coded bitstream. The decoder decodes from the bitstream, for example from a reference picture index, that a base-layer picture is used as an inter-prediction reference for the enhancement layer. When a decoded base-layer picture is used as a prediction reference for an enhancement layer, it is referred to as an inter-layer reference picture.

[0092] In addition to quality scalability following scalability modes exist:

[0093] • Spatial scalability: Base layer pictures are coded at a lower resolution than enhancement layer pictures.

[0094] • Bit-depth scalability: Base layer pictures are coded at lower bit-depth (e.g., 8 bits) than enhancement layer pictures (e.g., 10 or 12 bits).

[0095] • Chroma format scalability: Enhancement layer pictures provide higher fidelity in chroma (e.g., coded in 4:4:4 chroma format) than base layer pictures (e.g., 4:2:0 format). In all of the above scalability cases, base layer information could be used to code enhancement layer to minimize the additional bitrate overhead.

[0096] Scalability can be enabled in two basic ways. Either by introducing new coding modes for performing prediction of pixel values or syntax from lower layers of the scalable representation or by placing the lower layer pictures to the reference picture buffer (decoded picture buffer, DPB) of the higher layer. The first approach is more flexible and thus can provide better coding efficiency in most cases. However, the second approach, i.e., reference frame based scalability, can be implemented very efficiently with minimal changes to single layer codecs while still achieving majority of the coding efficiency gains available. A reference frame based scalability codec can be implemented by utilizing the same hardware or software implementation for all the layers, just taking care of the DPB management by external means.

[0097] There are number of intra-prediction modes available for existing video codecs. These intra-prediction modes comprise different directional intra- prediction modes, as well as prediction modes such as DC or Planar intra- prediction.

[0098] In Planar intra-prediction interpolation processes in both the vertical and horizontal directions are performed to obtain vertical and horizontal predictors, respectively. Then, sample-by-sample mean of these two predictors can be computed. Each interpolation process may be carried out by computing weighted averages of the reference samples. As an example, when computing the vertical predictor, each predicted sample at a given horizontal coordinate is obtained as the weighted average between the two reference samples at the same horizontal coordinate extracted from the top row and bottom row of the current block, respectively. Due to the fact the samples located on the bottom row of the current block are not reconstructed when predicting the current block, these are padded using the sample on the bottom-left of the current block. Similarly, the horizontal predictor is computed as the weighted average of the reference samples extracted from the columns on the left and right of the current block.

[0099] In coding solutions prior to present embodiments, the reference samples used in intra-prediction modes, such as Planar prediction, have been extracted from the immediate neighbourhood of the current block. For instance, the samples located on the row directly above the current block, and the column directly on the left of the current block may be used.

[0100] In some cases though, these reference samples may not be ideal, and other reference samples may be used instead. As an example, reference samples located on columns and / or rows further away from the current block may be used. However, when using these techniques that involve usage of reference samples located further away from the current block, the conventional Planar intra prediction process is not ideal, due to the fact that the resulting prediction block may inefficiently represent the content of the current block, as the spatial location of reference samples with respect to the current block is not taken into account.

[0101] The usage of intra-prediction reference lines located further away from the current block is well-known in video coding. The usage of these reference lines may be indicated by means of signalling. In WC, usage of these reference lines is indicated by means of a Multiple Reference Line (MRL) index, where MRL index 0 corresponds to using the conventional reference line formed of samples extracted directly above and on the left of the current block. Each increasing MRL index corresponds to using samples located further away from the current block in the vertical and horizontal direction. The MRL index is then signaled in the bitstream.

[0102] Recently, more advanced techniques have been proposed to better signal usage of MRL. An example of this is Template-based Multiple Reference Line (TMRL). TMRL consists in computing a list of possible combinations of intra- prediction modes and MRL indexes. The list is computed based on distortion costs obtained using a template, where the template is formed of the reference samples located at MRL index 0. An index is then signaled in the bitstream identifying the correct element in the TMRL list to use for the current block. The TMRL index replaces signalling of both the specific intra mode as well as the MRL index, thus improving the coding efficiency.

[0103] In ECM, intra prediction can be performed using different reference lines, where each reference line corresponds to a set of already decoded samples at a given distance from the current block. Each reference line is identified by a given Multiple Reference Line (MRL) index, where for instance MRL 0 corresponds to using samples that are directly adjacent to the current block (namely, at a distance of 0 samples from the current block), MRL 1 corresponds to samples located at a distance of 1 samples from the current block, and so on, where each increasing MRL index corresponds to increasing the distance from the current block in the above and left directions. Figure 3 illustrates an example showing a current block 301 , wherein the location of the current block 301 is defined within the frame as xcurrand ycurrwhich indicate the location of the top-left sample within the block 301 . The different reference lines are illustrated in Figure 3 with indices MRL 0 - MRL 3.

[0104] Multiple Reference Line (MRL) Fusion is a method implemented in ECM to improve the intra-prediction for a current block, combining an intra predictor obtained using a given MRL index L (L = 0, 1, 2, 3, ...), with a predictor obtained using MRL index L+l. The two predictors are combined together using fixed weights set to 3 / 4 and 1 / 4 respectively.

[0105] In ECM, a “one-size-fits-all” approach is used, where if MRL Fusion is inferred to be used, then it is applied with the same fixed weights and using the same fixed MRL lines. This may not be ideal, as the correlation between the current block and neighboring samples may differ depending on local characteristics. In certain cases, if spatial correlation quickly decreases, it may be beneficial to reduce the weights assigned to predictors obtained with higher MRL indices, corresponding to reference samples further away from the current block. Conversely, in some other cases, if for instance the content of the current reference line is particularly noisy, it may be more beneficial to assign higher weights to predictors obtained using higher MRL indexes to smoothen out the final predictor. In general, adapting the MRL Fusion parameters may lead to better predictors which adapt to the actual characteristics of the current block being predicted.

[0106] It is an aim of the present embodiments to provide a solution that produces an intra-prediction for a given block using at least one intra-prediction process, where the intra-prediction process comprises applying a Multiple Reference Line (MRL) Fusion process. The application of the MRL Fusion process is adapted depending on characteristics of the current block and / or on characteristics of other blocks in the current picture. It is also the aim of the present embodiments to provide a solution that produces an intra-prediction for a given block using at least one intra-prediction process, where the intra- prediction process comprises applying a Multiple Reference Line (MRL) Fusion process, where the application of the MRL Fusion process is based on computing parameters, where the parameters are computed using reconstructed samples in a template, where the template is formed of already reconstructed samples. According to an embodiment, the MRL Fusion process is based on the computation of a cost between predicted and reconstructed samples in a template, where the template is formed of already reconstructed samples. As another embodiment, the MRL Fusion process is based on the computation of Decoder-side Intra Mode Derivation (DIMD) parameters on reconstructed samples in a template, where the template is formed of already reconstructed samples.

[0107] According to an embodiment, a method produces an intra-prediction for a given block using at least one intra-prediction process, where the intra- prediction process comprises applying a Multiple Reference Line (MRL) Fusion process, where the application of the MRL Fusion process is adapted to utilize one main predictor and two additional predictors, where each predictor is obtained using reference samples extracted from two different reference lines.

[0108] The MRL fusion process according to present embodiments comprises performing intra prediction so that each predicted sample is computed as the weighted average of two or more predictors, where each predictor is obtained using a selected set of reference samples extracted from different reference lines. For example, in intra prediction direction corresponds to an angle that goes from top-right to bottom-left, then the reference samples located on the left of the current block may not be used at all. The MRL Fusion process can be applied at a reference sample level or at a block level.

[0109] When the MRL Fusion process is applied at a reference sample level, for each sample within the block, a main intra-predicted sample predictor and one or more additional intra-predicted sample predictors are computed. The main intra-predicted sample predictor (later referred to as “main predictor”) is obtained using the current MRL index used for the block. Each of the one or more additional predictors is obtained using a different MRL index. The one or more additional predictors are blended together with the main predictor to obtain the final predictor for the given sample within the current block.

[0110] When the MRL Fusion process is applied at a block level, the main predictor and one or more additional predictors are computed. The main predictor is obtained using the current MRL index, and each of the one or more additional predictors is obtained using a different MRL index. The one or more additional predictors are then blended together with the main predictor to obtain the final predictor for the given block.

[0111] As an example, the MRL Fusion process according to present embodiments may depend on a number of parameters, e.g., the MRL fusion indices for computing the additional predictors, and / or the weights for blending the additional predictors with the main predictor. As an example, the determination of at least one of these parameters may depend on characteristics of the current block. As an example, the determination of the MRL fusion indices to compute the additional predictors may depend on the current MRL index used for the block. As an example, in case the MRL index is greater than zero, then at least one of the MRL fusion indices may be determined to be smaller than the MRL index. As an example, the determination of the weights to blend the additional predictors with the main predictor may depend on the current MRL index.

[0112] A method according to the present embodiments produces an intra-prediction for a given block using at least one intra-prediction process, where the intra- prediction process comprises applying a Multiple Reference Line (MRL) Fusion process. The MRL Fusion process comprises forming the main predictor and two additional predictors. When forming a given predictor using a given MRL index, an intra-prediction process is applied to predict the content of the current block utilizing a set of reference samples extracted from the current reference line (corresponding to the given MRL index). This process may follow a variety of different methodologies, depending on the current intra- prediction mode being used. As an example, Planar intra-prediction may be used. As an example, DC intra-prediction may be used. As an example, directional intra-prediction may be used. The main predictor PLis obtained using the current MRL index L, and the two additional predictors are obtained using two different reference lines extracted using two different MRL Fusion indices. As an example, MRL Fusion index L+l and MRL Fusion index L+2 can be used for the additional predictors PL+iand PL+2. As an example, in case, where L > 0, MRL Fusion index L+l and MRL Fusion index L-l can be used to compute the additional predictors PL+I and PL-I . AS an example, fixed weights can be used for blending in case, where L > 0. As an example, weights may be computed depending on characteristics of the current block and / or on characteristics of other blocks in the current picture. As an example, in case, where L > 0, a weighted average can be used for determining the final predictor P as follows:

[0113] P = WO x PL+ W1 x PL+1 + W2 X PL-I

[0114] As an example, the weights WO, W1 and W2 can be fixed to values W0=5 / 8, Wl=2 / 8 and W2=l / 8. As an example, the weights WO, W1 and W2 can be fixed to values W0=6 / 8, Wl=2 / 8 and W2=0.

[0115] A method according to the present embodiments produces an intra-prediction for a given block using at least one intra-prediction process, where the intra- prediction process comprises applying a Multiple Reference Line (MRL) Fusion process, where the application of the MRL Fusion process is based on an analysis of already reconstructed samples in a template. As an example, the application of the MRL Fusion process is based on the computation of a cost between predicted and reconstructed samples in a template, where the template is formed of already reconstructed samples.

[0116] Figure 4 illustrates an example of a current block 401 . A template may be considered, formed of already reconstructed samples in the surrounding of the current block 401 . As an example, the template may be formed of a line 405 of samples of the same width of the current block 401 , located immediately above the current block, and a column 403 of samples of the same height as the current block 401 , located immediately on the left of the current block 401 . As an example, a template may be formed of more than one line and / or more than one column of samples. As an example, two lines and two columns of samples may be used.

[0117] As an example, the samples within the template may be predicted using an intra-prediction process. As an example, a given MRL index may be used to extract reference samples to predict the samples within the template. As an example, in case the template is formed of one line and one column of already reconstructed reference samples, MRL index 1 may be used to predict the samples within the template. As an example, in case the template is formed of one line and one column of already reconstructed reference samples, MRL index 2 may be also used to predict the samples within the template.

[0118] The samples within the template can be predicted using conventional intraprediction modes. As an example, a set of intra-prediction modes can be considered, where a prediction of the template is obtained for each intra- prediction mode. As an example, the set of intra-prediction modes may correspond to any intra-prediction mode that is signaled to be used at the decoder side. As an example, the set of intra-prediction modes may include all available intra-prediction directions.

[0119] Upon computing a prediction of the samples within the template for a given intra-prediction mode, a cost can be computed, based on the distortion between the reconstructed samples within the template, and the predicted samples obtained with the given intra-prediction mode. As an example, the Sum of Absolute Differences (SAD) may be used to compute the cost. As an example, the Sum of Absolute Transformed Differences (SATD) may be used to compute the cost. As an example, a combination of SAD and SATD may be used to compute the cost.

[0120] As an example, considering that the current MRL index L = 0, then two MRL Fusion indices equal to 1, 2 may be used, respectively. As an example, the obtained two additional predictors Pl and P2 are blended together with the main predictor P0, to form a final predictor P for the current block. As an example, a weighted average can be used for determining the final predictor P as follows:

[0121] P = WO x P0 + W1 x Pl + W2 x P2

[0122] As an example, a number of template costs may be computed, using MRL indexes corresponding to those MRL indexes used in the MRL fusion process. As an example, in case one additional MRL predictor is used in the MRL fusion process, then one template cost is computed using the given additional MRL index to predict the template samples. As an example, in case two additional MRL predictors are used in the MRL fusion process, then two template costs are computed using the two given additional MRL indexes to predict the template samples. As an example, a first cost Cl may be computed using reference samples extracted with MRL index equal to 1; a second cost C2 may be computed using reference samples extracted with MRL index equal to 2 (as presented e.g., in Figure 4). As an example, Cl may be used to determine weight Wl; correspondingly, C2 may be used to determine weight W2. As an example, a given template cost can be computed, and the given template cost can be used to determine the weights used in the MRL Fusion process, where the cost associated with a given MRL index can be used to modify the weight associated to the predictor obtained with that given MRL index.

[0123] As an example, a starting weight Wl_start may be defined. The definition of the starting weight may be determined based on characteristics of the current block and / or on characteristics of other blocks in the current picture. As an example, the current intra-prediction direction may be used. As an example, the size of the current block may be used. As an example, the determination of whether the slope corresponding to the current intra-prediction direction is integer or not may be used. As an example, the determination of whether the current block makes use of the Intra Sub Partition (ISP) mode may be used. As an example, Wl_start = 2 may be used. As an example, Wl_start = 0 may be used.

[0124] As an example, a set of thresholds may be defined. Then, the cost Cl may be compared against such set of thresholds to determine an offset 01. Finally, the final weight Wl may be determined as:

[0125] Wl = Wl_start + 01.

[0126] As an example, given thresholds T_min and T_max may be defined, where:

[0127] If Cl <= T_min, 01 = +1,

[0128] Else if Cl <= T_max, 01 = 0

[0129] Else 01 = -1

[0130] As an example, given thresholds T_min and T_max may be defined, where:

[0131] If Cl <= T_min, 01 = +L, Else if Cl <= T_max, 01 = 0

[0132] Else 01 = -L

[0133] As an example, different values may be assigned to 01 depending on the thresholds. As an example, the threshold may be used to determine the values of Wl directly. As an example, a given value may be computed for W1 depending on whether the template cost is smaller or equal than a given threshold.

[0134] As an example, T_min may be equal to a power of 2. As an example, T_min may depend on the current block size. As an example, T_min may depend on the block area A. As an example, T_min may be computed as A x K. As an example, a fixed parameter K may be determined. As an example, K = 16. As an example, K may be equal to a power of 2.

[0135] As an example, T_max may be equal to a power of 2. As an example, T_ max may depend on the current block size. As an example, T_ max may depend on the block area A. As an example, T_ max may be computed as A x K. As an example, a fixed parameter K may be determined. As an example, K = 32. As an example, K may be equal to a power of 2.

[0136] As an example, L may be equal to 1 . As an example, L may be equal to 2.

[0137] The same process may be applied to C2, to determine:

[0138] W2 = W2_start + 02

[0139] As an example, given thresholds T2_min and T2_max may be defined, where: If C2 <= T2_min, 02 = +1, Else if C2 <= T2_max, 02 = 0 Else 02 = -1

[0140] Finally, a new main weight WO may be computed based on Wl, W2 and the total sum sumW, so that

[0141] WO = sumW - Wl - W2. A method according to present embodiments produces an intra-prediction for a given block using at least one intra-prediction process, where the intra- prediction process comprises applying a Multiple Reference Line (MRL) Fusion process, where the application of the MRL Fusion process is based on already reconstructed samples surrounding the current block. As an example, a texture analysis of the reconstructed samples surrounding the current block may be performed, where smaller weights may be assigned to blend the additional predictors with the main predictor in case the content is classified as highly textured. As an example, the amount of texture in the surrounding of the block may be determined based on estimating the number of edges. As an example, the difference between consecutive reconstructed samples in the surrounding of the current block can be computed and used to determine the weights used to blend the additional predictors with the main predictor.

[0142] A method according to present embodiments produces an intra-prediction for a given block using at least one intra-prediction process, where the intra- prediction process comprises applying a Multiple Reference Line (MRL) Fusion process, where the application of the MRL Fusion process is based on parameters computed within a Decoder-side Intra Mode Derivation (DIMD) process. As an example, the MRL Fusion weights may be computed based on the computation of DIMD modes and DIMD weights. As an example, if the DIMD weight associated with the main DIMD mode is above a given threshold, then a given MRL fusion weight may be used for the current block.

[0143] Thus, the apparatus implementing a method according to various embodiments comprises means for processing, e.g., one or more processors; and means for storing, e.g., a memory, computer readable instructions. The means for processing executes the computer readable instructions to cause the apparatus form an intra prediction for a current block of video using an intra-prediction process, where the intra-prediction process comprises: forming a main predictor using a set of reference samples where a process for identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming at least one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending the main predictor and the additional predictors to form a final prediction, where a final predictor is formed on the basis of the computation of a cost between predicted and reconstructed samples in a template.

[0144] The method according to an embodiment is shown in Figure 5. The method generally comprises forming 510 an intra prediction for a current block of a video frame using an intra-prediction process, wherein the intra-prediction process comprises: forming 520 a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming 530 one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending 540 the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template. Each of the steps can be implemented by a respective module of a computer system.

[0145] An apparatus according to an embodiment comprises means for forming an intra prediction for a current block of a video frame using an intra-prediction process, where for the intra-prediction process the apparatus comprises: means for forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and means for forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and means for blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template. The means comprises at least one processor, and a memory including a computer program code, wherein the processor may further comprise processor circuitry. The memory and the computer program code are configured to, with the at least one processor, cause the apparatus to perform the method of Figure 5 according to various embodiments.

[0146] Figure 6 illustrates an example of an electronic apparatus 600, being an example of video coding system. In some embodiments, the apparatus may be a mobile terminal or a user equipment of a wireless communication system or a camera device. The apparatus 600 may also be comprised at a local or a remote server or a graphic processing unit of a computer. The apparatus may also be comprised as part of a head-mounted display device

[0147] The apparatus may be configured to perform various functions, such as for example, gathering information by one or more sensors, encoding and / or decoding information, receiving and / or transmitting information, analyzing information gathered or received by the apparatus. An apparatus configured to encode a video scene may optionally comprise one or more microphones for capturing the scene and / or one or more cameras for capturing information about the physical environment in which the scene is captured. Alternatively, the apparatus configured for encoding may be configured to receive information about an environment in which a scene is captured and / or a simulated environment. An apparatus configured to decode and / or render the video scene may be configured to receive a bitstream comprising encoded video. An apparatus configured to decode and / or render the video scene may comprise one or more speakers / audio transducers and / or displays, and / or may be configured to transmit a decoded scene or signals to a device comprising one or more speakers / audio transducers and / or displays. An apparatus configured to decode and / or render the video scene may comprises a user equipment , a head-mounted display, or another device capable of rendering to a user an AR; VR and / or MR experience.

[0148] The apparatus 600 comprises one or more processors 610 and one or more memories 620 and one or more transceivers interconnected through one or more buses. The one or more memories 620 store computer instructions, for example in respective modules (Modulel , Module2, ModuleN). The one or more memories may store data in the form of image, video and / or audio data, and / or may also store instructions to be executed by the processors or the processor circuitry. The one or more processors may comprise a central processing unit (CPU) and / or a graphical processing unit (GPU). The one or more buses may be address, data or control buses, and may include interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment. The apparatus also comprises a codec 630 that is configured to implement various embodiments relating to present solution. According to some embodiments, the apparatus may comprise an encoder or a decoder. The apparatus 600 also comprises a communication interface 640 which is suitable for generating wireless communication signals for example for communication with a cellular communications network, a wireless communications system, or a wireless local area network, and thus enabling data transfer over data transfer network 650.

[0149] The apparatus 600 may comprise a display in the form of a liquid crystal display. In other embodiments of the invention the display may be any suitable display technology suitable to display an image or video. The apparatus 600 may further comprise a keypad. In other embodiments of the invention any suitable data or user interface mechanism may be employed. For example, the user interface may be implemented as a virtual keyboard or data entry system as part of a touch-sensitive display. The apparatus 600 may comprise a microphone or any suitable audio input which may be a digital or analogue signal input. The apparatus 600 may further comprise an audio output device which in embodiments of the invention may be any one of: an earpiece, speaker, or an analogue audio or digital audio output connection. The apparatus 600 may also comprise a battery (or in other embodiments of the invention the device may be powered by any suitable mobile energy device such as solar cell, fuel cell or clockwork generator). The apparatus may further comprise a camera capable of recording or capturing images and / or video. The camera may be a multi-lens camera system having at least two camera sensors. The camera is capable of recording or detecting individual frames which are then passed to the codec 630 or to processor 610. The apparatus may receive the video and / or image data for processing from another device prior to transmission and / or storage.

[0150] The apparatus 600 may further comprise e.g., the other functional units disclosed in any of the Figures 1 - 2 for implementing any of the present embodiments.

[0151] The various embodiments can be implemented with the help of computer program code that resides in a memory and causes the relevant apparatuses to carry out the method. For example, a device may comprise circuitry and electronics for handling, receiving and transmitting data, computer program code in a memory, and a processor that, when running the computer program code, causes the device to carry out the features of an embodiment. Yet further, a network device like a server may comprise circuitry and electronics for handling, receiving and transmitting data, computer program code in a memory, and a processor that, when running the computer program code, causes the network device to carry out the features of various embodiments.

[0152] The various embodiments can be implemented in a system comprising multiple communication devices which can communicate through one or more networks. The system may comprise any combination of wired or wireless networks including, but not limited to a wireless cellular telephone network, a wireless local area network (WLAN) such as defined by any of the IEEE 802.x standards, a BLUETOOTH™ personal area network, an Ethernet local area network, a token ring local area network, a wide area network, and / or the Internet. A wireless network may implement network virtualization, which is the process of combining hardware and software network resources and network functionality into a single, software based administrative entity, a virtual network.

[0153] It may also be noted that operations of example embodiments of the present disclosure maybe carried out by a plurality of cooperating devices (e.g. centralized Radio Access Network “cRAN”).

[0154] The system may include both wired and wireless communication devices and / or electronic devices suitable for implementing example embodiments of the present disclosure.

[0155] For example, the system may comprise a mobile telephone network and a representation of the internet. Connectivity to the internet may include, but is not limited to, long range wireless connections, short range wireless connections, and various wired connections including, but not limited to, telephone lines, cable lines, power lines, and similar communication pathways.

[0156] The example communication devices of the system may include, but are not limited to, an apparatus, a combination of a personal digital assistant (PDA) and a mobile telephone, a PDA, an integrated messaging device (IMD), a desktop computer, a notebook computer, and a head-mounted display (HMD). The apparatus according to present embodiments may comprise any of such example communication devices. In an example embodiment of the present disclosure, more than one of these devices, or a plurality of one or more of these devices, may perform the method according to various embodiments.

[0157] If desired, the different functions discussed herein may be performed in a different order and / or concurrently with other. Furthermore, if desired, one or more of the above-described functions and embodiments may be optional or may be combined.

[0158] Although various aspects of the embodiments are set out in the independent claims, other aspects comprise other combinations of features from the described embodiments and / or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims. It is also noted herein that while the above describes example embodiments, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications, which may be made without departing from the scope of the present disclosure as, defined in the appended claims.

Claims

Claims:

1. An apparatus, comprising means for forming an intra prediction for a current block of a video frame using an intra-prediction process, where for the intraprediction process the apparatus comprises: means for forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and means for forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and means for blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template.

2. The apparatus according to claim 1 , wherein the computed parameters comprise at least one cost between predicted and reconstructed samples in the template.

3. The apparatus according to claim 1 or 2, wherein means for blending the main predictor and the one or more additional predictors is configured to compute a weighted average.

4. The apparatus according to claim 3, further comprising means for computing weights for the weighted average depending on the at least one cost between the predicted and the reconstructed samples in the template.

5. The apparatus according to claim 4, comprising means for computing the weights based on measuring a cost between the predicted and the reconstructed samples in the template against a fixed threshold value.

6. The apparatus according to claim 3 further comprising means for computing the weights for the weighted average as the sum of an initial value and an offset value.

7. The apparatus according to any of the claim 1 to 6, comprising means for computing offset values depending on the at least one cost between the predicted and the reconstructed samples in the template.

8. The apparatus according to any of the claim 1 to 7, further comprising means for determining the different Multiple Reference Line indices based on the given Multiple Reference Line index.

9. The apparatus according to any of the claim 1 to 8, where the blending of the main predictor and the one or more additional predictors depends on a given intra-prediction mode.

10. The apparatus according to any of the claim 1 to 9, where the blending of the main predictor and the one or more additional predictors depends on the size of the current block.

11. The apparatus according to any of the claims 1 to 10, wherein the reconstructed samples are adjacent to the current block.

12. A method, comprising: forming an intra prediction for a current block of a video frame using an intra-prediction process, wherein the intra-prediction process comprises: forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending the main predictor and the one or more additional predictors to form a final predictor, where the blending isbased on parameters, being computed using reconstructed samples in a template.

13. The method according to claim 6, wherein the computed parameters comprise at least one cost between predicted and reconstructed samples in the template.

14. An apparatus comprising at least one processor, memory including computer program code, the memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: form an intra prediction for a current block of a video frame using an intra-prediction process, where for the intra-prediction process comprises: forming a main predictor using a set of reference samples, where a process of identifying the set of reference samples is determined on the basis of a given Multiple Reference Line index, and forming one or more additional predictors using different sets of reference samples determined on the basis of different Multiple Reference Line indices, and blending the main predictor and the one or more additional predictors to form a final predictor, where the blending is based on parameters being computed using reconstructed samples in a template.

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