According to a Scalable Video Codec (SVC) scheme, a video signal is encoded with a best video quality in such a manner that a low quality video can be presented even though parts of picture sequences (frame sequences intermittently selected from among the picture sequences) derived from the encoding are decoded. A motion compensated temporal filter (or filtering) (MCTF) is one of encoding schemes suggested for the SVC scheme.
However, although picture sequences encoded through the SVC scheme can present a low quality image even if only parts of received picture sequences are processed, image quality is seriously degraded if a bit rate is lowered. In order to overcome the image quality degradation, an additional assistant picture sequence having a low transmission rate, such as a small-sized video and/or a picture sequence having the smaller number of frames per second, may be provided in a hierarchy structure having at least one layer
On the assumption that two sequences are processed, an assistance sequence (a lower layer sequence) and a main picture sequence (an upper layer sequence) are called a base layer and an enhancement layer, respectively. However, since the base layer and the enhanced layer are obtained by encoding the same video source, redundancy information exists in video signals of both layers. Accordingly, in order to improve the coding rate of the enhanced layer, the video signal of the enhanced layer is coded using coding information of the base layer. This is one of inter-layer prediction schemes.
For example, when the type of a current macro block in the enhanced layer is determined as an intra mode macro block, the current macro block is coded into residual data using image data of a corresponding block in an intra mode of the base layer (this corresponding block temporarily simultaneous with and identical to the macro block of the enhanced layer).
The coded macro block is called an ‘intra BL mode block’, and the specification of the intra BL mode for the macro block may be limited or not. For example, as shown in FIG. 1A, the inter-layer prediction may be constrained by allowing the inter-layer prediction only when the corresponding block of the base layer is coded in the intra mode. In addition, as shown in FIG. 1B, the inter-layer prediction may not be constrained by allowing the inter-layer prediction when the corresponding block of the base layer is coded in an inter mode as well as in an intra mode.
A encoding mode (in the side of an encoder) or a decoding mode (in the side of a decoder) is determined from one of modes shown in FIGS. 1A and 1B based on the value of a ‘constrained_intra_pred_flag’ of the base layer. When a macro block having residual data coded in an intra mode is reconstructed, this flag is used for indicating that a fixed value (constrained_intra_pred_flg=1) or a reconstructed pixel value (constrained_intra_pred_flg=0)) is employed for the adjacent inter mode block.
However, when a video signal is encoded in three layers as shown in FIG. 2, and when both the upper layer (L1) and the middle layer (L2) are coded by employing the lower layer (L3) as a prediction layer and then are provided to the decoder, both the upper layer (L1) and the middle layer (L2) are constrained in a coding scheme for an intra mode block of the lower layer (L3). In other words, when the constrained_intra_pred_flag of the lower layer (L3) is ‘1’, prediction-constraint is assigned to the upper layer (L1) and the middle layer (L2) so that the upper layer (L1) and the middle layer (L2) are coded through a constrained scheme as shown in FIG. 1A. In addition, when the constrained_intra_pred_flag is ‘0’, prediction-unconstraint is assigned to the upper layer (L1) and the middle layer (L2) so that the upper layer (L1) and the middle layer (L2) are coded through an unconstraint scheme as shown in FIG. 1B. In other words, when inter-layer prediction is performed based on the lower layer (L3), the upper layers of the lower layer cannot individually select the inter-layer prediction constraint or the inter-layer prediction unconstraint.
In addition, since inter-layer prediction constraint (unconstraint) is determined for “constrained_intra_pred_flag” having a different attribute, if the “constrained_intra_pred_flag” of a lower layer has a specific value from among a plurality of layers, the upper layer may loss the degree of freedom for the inter-layer prediction constraint. In other words, only one of inter-layer prediction constraint and inter-layer prediction unconstraint is forcibly determined for the upper layer.