| 摘要 |
<p>The current frame of the picture is compared (2) block-by-block with the previous frame to identify changed picture elements (pixels). The resulting matrix is matched (''vector quantised'') (4) to one of a set of standard matrices (''VQ shapes''). Only those pixels flagged by the selected VQ shape are transmitted plus a ''VQ shape code''. This technique is modified in that the current frame is also compared (30) with a ''background'' frame stored (31) at the transmitter and at the receiver. Where, for any block, all the pixels flagged by the VQ shape are indicated by the second comparison as being the same as the background, the pixels are not sent - instead a shape code plus a ''copy background'' instruction is transmitted.</p> |
