Brother HL-1070 - B/W Laser Printer Technical Reference Manual page 110

2001/10/02
<Compressed Image Data>
Data compression compresses the original image data word by word (16 bits).
The comp ressed data consists of both horizontal compression which uses 16 bit, 8 bit and 4 bit repeating patterns
within 1 word or 2 words of data and vertical compression which indicates how many times to repeat the same
data as in the previous line within 1 word of data.
Ÿ Non-compressed data
When the most significant bit in the first 2 bytes is 0, the printer goes into non-compression mode. The following
11 bits then indicate the number of words of data, the least significant 4 bits are not used. After that, the image
data follows word by word.
15 14
0
Ÿ 16 bit repeating compressed data
When the most significant 3 bits in the first 2 bytes are in the order 1, 0, 0, the remaining 13 bits indicate the
number of times to repeat 16 bit data. The following 2 bytes should be the 16 bit data to repeat.
15
1
Ÿ 8 bit repeating comp ressed data
When the most significant 3 bits in the first 2 bytes are in the order 1, 1, 0, the following 5 bits indicate the number
of times to repeat 16 bit (two by 8 bits) data. The remaining 8 bits should be the 8 bit data to repeat.
15 14 13 12
1
Ÿ 4 bit repeating compression data
When the most significant 3 bits in the first 2 bytes are in the order 1, 0, 1, the following 4 bits are the 4 bit data to
repeat. The remaining 9 bits indicate the number of times to repeat the 16 bit (4 by 4 bits) data.
15 14 13 12
1
Ÿ Vertical repeating compressed data
When the most significant 3 bits in the first 2 bytes are in the order 1, 1, 1, the remaining 13 bits indicate the same
data words as in the previous line.
15 14 13 12
1
The printer cannot support the APT and HRC function in the 1200 dpi printing mode.
data word count (11 bits)
data 1 (16 bits)
data n (16 bits)
14 13 12
0 0
data to repeat(16 bits)
1 0 number of repeats
(5 bits)
0 1 data to repeat
(4 bits)
1 1 the same data words as in the previous line (13 bits)
4 3
:
number of repeats(13 bits)
8 7 0
data to repeat(8 bits)
9 8 0
number or repeats(9 bits)
CHAPTER 2 "PCL" - 90
0
not used
0
0