HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part I

EN Set Compression Method Command 15-19
TIFF encoding also allows you to include a non-operative (NOP)
control byte, represented by the value –128. This byte is ignored,
and the subsequent byte is treated as the new control byte.
Note It is more efficient to code two consecutive identical bytes as a
repeated byte. If these bytes are preceded and followed by literal
bytes, however, it is more efficient to code the entire group as literal
bytes.
Examples: Run-length and TIFF Compression
The following examples show how a raster row can be coded
using run-length and TIFF compression methods. Note that the
compression examples use characters to represent the binary
data stream.
Unencoded
E
C
*r1A
E
C
*b0m7WUUUUATT
E
C
*rC
Run-length Encoding
E
C
*r1A
E
C
*b1m6W(3)U(0)A(1)T
E
C
*rC
Table 15-6
Byte
Number
#1 #2 #3 #4 #5 #6 #7
Bits
01010101 01010101 01010101 01010101 01000001 01010100 01010100
ASCII UUUUATT