HP 4 FAMILY - Manual (Page 173)

Raster Graphics
Adaptive
Compression
(Method 5)
Raster Graphics Adaptive Compression (Set Compression
Method Command, mode 5) is implemented on the HP
LaserJet IIIP, Color LaserJet, all LaserJet 4, 5, and 6
family printers, and the DeskJet 1200C and 1600C printers.
This compression method allows the host to compress data
using a combination of PCL compression modes to obtain
optimum compression (refer to the PCL 5 Printer Language
Technical Reference manual, Set Compression Method
Command, for details).
An added benefit of this method for the HP LaserJet 4L and
LaserJet IIIP printers is that the data is not decompressed
upon entry to the printer provided the image is portrait,
300 dpi, transparent print model and no patterns are being
used. This allows the LaserJet 4L and IIIP to print many
pages which would otherwise require more memory. As an
added benefit these pages print faster. The other HP
LaserJet 4, 5, and 6 family printers decompress the data
upon entry to the printer and rely upon ADC or MEt to
compress the data if required.
For the HP LaserJet 4L printer it is critical that the image
actually compress (not expand) if Adaptive Compression is
used since MEt does not operate upon images meeting the
requirements for delayed decompression.
Memory Usage 5-7