Method and apparatus for intra prediction within display screen

An apparatus of decoding a video signal, the apparatus comprising:

• a video decoder configured to derive reference samples based on neighboring samples adjacent to a current block, the reference samples being used for intra prediction of the current block, and configured to obtain a prediction sample of the current block based on the reference samples adjacent to the current block,
• wherein when the neighboring samples adjacent to the current block include an unavailable sample which is not used for the intra prediction of the current block, the video decoder is further configured to perform a substitution of the unavailable sample using a sample which is present on one side of the unavailable sample,
• wherein when the unavailable sample is a left neighboring sample of the current block and is not a top-left neighboring sample, the substitution of the unavailable sample is performed using only a bottom neighboring sample of the unavailable sample, without referring to a top neighboring sample of the unavailable sample,
• wherein when the unavailable sample is a top neighboring sample of the current block, the substitution of the unavailable sample is performed using only a left neighboring sample of the unavailable sample, without referring to a right neighboring sample of the unavailable sample, and
• wherein when an intra prediction mode of the current block is a planar mode, the prediction sample is obtained from linear interpolation of the reference samples adjacent to the current block.