Compression enhancement in graphics system

摘要

Disclosed is an arrangement which lessens the effects of compression artifacts resulting from the compression of graphic images having high spatial frequency components. Such graphic images are typically text related in view of the high contrast required for text outlines. The arrangement includes a text detector configured to detect cells of a source image which are likely to create compression artifacts when each of the cells is compressed by a compressor for storage in a compressed image store. The text detector creates a bit table in a text detect store of those cells which include high spatial frequency components. Upon expansion, of the compressed image by an expander, the cells are passed through a pixel saturator which, if the cell is a "text" cell referenced in the text detect store, all pixels within that text cell are saturated to colours from a predetermined set of colours. The expanded image is then restored to an image store.