# = 5 indicates that adaptive compression is to be used.
•
This compression compresses multiple rows (a block) into one transfer graphics command.
Most other compression methods compress only one row to one transfer graphics command.
One transfer graphic command (ESC *b##W) can contain only up to 32,767 bytes.
As mode 5 compression compresses multiple rows, the amount of transferred data may become large.
If compressed data exceeds this limit, reduce the number of rows in the block.
We can use mode 0 to mode 3 compression to compress each row. We can even compress empty (white)
rows and duplicate rows with these compression methods.
Command byte
Mode 5 compressed data consists of multiple elements. Each element contains 3 header bytes at the
beginning.
The first byte of the header bytes is a command byte.
First byte
0
Unencoded
1
Run-length Encoding
2
TIFF
3
Delta Row compression
4
Empty Row
5
Duplicate Row
Command byte
0 -
This element is an uncompressed row. The next two bytes contain the byte count of the uncompressed
data. Uncompressed data follows the header.
1 -
This element identifies a compressed row. Compression method is mode 1. The next two bytes
(upper byte first) contain the byte count of the compressed data. Compressed data follows the header.
2 -
This element identifies a compressed row. Compression method is mode 2. The next two bytes
(upper byte first) contain the byte count of the compressed data. Compressed data follows the header
3 -
This element identifies a compressed row. Compression method is mode 3. The next two bytes
(upper byte first) contain the byte count of the compressed data. Compressed data follows the header
4 -
This element identifies multiple empty rows. The next two bytes (upper byte first) contain the empty
row count.
5 -
This element identifies duplicate rows. The next two bytes (upper byte first) contain the duplicate
row count.
• # = 9 Mode 9 compression
Like mode 3 compression, this mode 9 compression data contains only the difference of the current row
from the preceding row.
Replacement data often consists of a repetition of a particular byte in mode 3 compression.
Mode 9 compression is effective in such cases.
Simple mode 9 compression data consists of a command byte and the replacement data.
A Command byte consists of 3 parts. These are the control bit, the offset count and the replacement count.
The Control bit is the most significant bit (bit 7) of a control byte.
Command byte for mode 9 compression (non repeated replacement data)
7
0
Second, third byte
Number of bytes of data
Number of empty row or repetition
6
5
4
3
Offset count
Replacement count-1
Control bit
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