Transmitting and receiving a composite image

摘要

Disclosed is a method of transmitting and of decoding a composite image that comprises at least a foreground image and a transparency mask. When transmitting an image a video encoder encodes the foreground image and the transparency mask and transmits these encoded images together with a flag signifying whether or not the encoded transparency mask is to be decoded as a binary transparency mask in which each pixel can take only two values. On the decoder side on receipt of the encoded foreground image, encoded transparency mask and flag, the decoded will decode the foreground image and, where indicated by the flag, decode the transparency mask as a binary transparency mask. Clipping values may be signalled to the decoder for use in clipping of a decoded binary transparency mask. Also disclosed is a system for transmitting and receiving a video sequence using the above method. The method may be used in systems in which the images are encoded according to the H.264/AVC or High Efficiency Video Coding (HEVC) standards and the flag may be represented in the syntax header element Sequence Parameter Set (SPS) of these standards.