HP deskjet 600 User Manual

The following data is compressed using method 3. Italicized bytes are those needing replace-
ment, i.e., bytes different from the seed row. Graphics data is binary.

Esc * r 1 A

 initializes the seed row to all zeros.

Row 1 - Esc * b 3 m 2 W (00000001 )( 11111111 )

3m selects method 3, and 2W indicates that 2 bytes of data will follow. The upper three bits of
the command byte are zero, indicating that one byte will be replaced. The lower five bits con-
tain a relative offset of 1, indicating that the replacement occurs one byte in from the current
position. The replacement byte follows and contains 11111111.

Row 2 - Esc * b 2 W (00000010)(11110000)

The first three bits of the command bye are 0 indicating one byte will be replaced. The lower
five bits contain a relative offset of 2; so the replacement will occur 2 bytes from the current
position. The replacement byte 11110000 follows.

Row 3 - Esc * b 5 W (00000000)(00001111)(00100010)(10101010)(1010 1010)

Three bytes are replaced using two commands. The first three bits of the first command byte
are zero, indicating a single byte replacement, and the next five bits are zero, indicating a rela-
tive offset of zero. The replacement byte 00001111 follows.

The first three bits of the second command byte are 001, indicating the replacement of two
bytes; and the lower five bits contain a relative offset of two. The two replacement bytes
(10101010)(10101010) follow the command byte.

Like Method 3, this method replaces only bytes in the current row that differ from the preced-
ing (seed) row. Unlike Method 3, the replacement (delta) bytes may be encoded.

A delta compression string consists of a command byte, optional offset bytes, optional
replacement count bytes, and the replacement data.

The command byte itself has three parts:

Row 1

00000000

00000000

00000000

00000000

Row 2

00000000

11111111

00000000

00000000

Row 3

11111111

11110000