| 摘要 |
Video data compression apparatus in which video data are compressed on a block-by-block basis comprises a frequency-transformer that generates corresponding groups of coefficient values representing spatial frequency components of the image blocks; a quantisation factor selector for deriving a quantisation factor for use in quantising the frequency-transformed data in dependence on properties of the frequency-transformed data and/or corresponding data from preceding images, the derived quantisation factor then being rounded to one of a predetermined set of quantisation factors, and for generating a range boundary parameter in dependence on the amount by which the derived quantisation factor deviates from the selected one of the predetermined set of quantisation factors; and a quantiser operable on the groups of coefficient values to map each of a contiguous plurality of ranges of coefficient values onto respective quantised data values, the extent of each range being controlled by the quantisation factor selected by the quantisation factor selector, and the first non-zero range boundary being defined by the range boundary parameter generated by the quantisation factor selector. |
