HP PCL/PJL reference (PCL 5 Color) - Technical Reference Manual

6-24 Raster Graphics EN
Run-length Encoding
?*r1A
?*b1m6W(3)U(0)A(1)T
?*rC
TIFF Encoding
?*r1A
?*b2m6W(-3)U(0)A(-1)T or ?*b2m6W(-3)U(2)ATT
?*rC
In the TIFF encoding example above, parenthetical expressions are
used to identify control bytes. For example, the byte (-3) is shown to
represent the control byte for a repetition (minus value) of 3. The
actual value for this position is the decimal value 253. Additional
“encoded” control bytes in this sequence include: (0) for decimal 0,
(-1) for decimal 255, and (2) for decimal 2. The raster data (pattern)
bytes are represented by the ASCII character.
Delta Row Compression (Method 3)
Delta row compression identifies a section of bytes in a row that is
different from the preceding row, and then transmits only that data
that is different (the delta data). If a row is completely different from its
preceding row, then the entire row must be sent as the delta, which is
not very efficient; if only one bit is different, then only one byte is
identified and sent. To reassemble the raster data rows, the printer
takes the current row (the seed row) and makes the changes
indicated by the delta data, to create the new row. The new row
(which becomes the new seed row) is used by the next delta
compression data to create another row.
A delta compression row consists of two parts, a command byte and
the replacement bytes, as shown below:
[(Command byte)(1 to 8 Replacement bytes)]