HP 4 FAMILY - Manual (Page 168)

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 in memory.
Image Adapt 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.
5-2 Memory Usage