7. A compression device for use in a system as claimed in claim 5 wherein said memory cycle is a read-before-write operation under direct-memory access (DMA) control.
7. A compression device for use in a system as claimed in claim 5 wherein said memory cycle is a read-before-write operation under direct-memory access (DMA) control. 8. A scanning device for a document, comprising a compression device as claimed in claim 7, further comprising a picture buffer which is fed by a scanning element in order to accommodate all data of a picture field before further processing.