Operation of ADC and MEt
The goal of ADC is to automatically and transparently reduce Memory
Out errors caused by raster graphics pages. MEt extends this goal to
reducing all Memory Out errors and eliminating Print Overrun errors.
During the printing of a page, if available printer memory becomes
low, all HP LaserJet 4, 5, and 6 family printers and the HP Color
LaserJet printer have the ability to automatically compress any
already-stored raster graphics data using a variety of compression
techniques. This allows the printing of many raster graphics pages
which would have caused a Memory Out error on previous
HP LaserJet printers having the same amount of memory.
With ADC or MEt, PCL 5 printers can typically print a full page of
raster graphics in base memory without a memory out. This is
especially true for line art and typical business graphics. Other types
of graphics such as scanned photographs (especially if a technique
called error-diffusion is used), cannot always be printed as easily by
ADC or MEt as can line art graphics. Fortunately, another internal
printer feature, Image Adapt, can be called upon to make the page fit
Image Adapt is only used as a last resort for compressing raster
graphics data and as such will rarely be seen. It reduces a raster
graphic image to one-fourth its original size by trading off some of the
image's fine detail. This loss of fine detail is often not noticeable.
Image Adapt can be disabled on some of the HP LaserJet 4, 5, and 6
family printers if required, but the technique varies. On the
HP LaserJet 4, 4M and 4Si the user will have to add more memory to
effectively remove the need for Image Adapt. Image Adapt can be
disabled on some of the other HP LaserJet 4, 5, and 6 family printers
by using a PJL command (refer to the respective printer user manuals
for further information—the Color LaserJet printer does not utilize
Image Adapt). If Image Adapt is turned off, more pages will cause
Memory Out errors.
All HP LaserJet 4, 5, and 6 family printers also include enhancements
to improve the internal storage of raster graphics data.
5-2 Memory Usage