Single Progression Sequential Bi-Level Image Compression Method - Canon FAX-L350 Service Manual

The characteristics of Progressive Bi-level Image Compression are explained below as a
reference. First of all, after the original image has been read in at high resolution, it is
converted to low resolution, and this low resolution image data proceeds to be encoded
NOTE
(compressed). On the receiving end, the overall original image can be quickly recognized
by the steps in which this low resolution image compression data is received.
Next, to improve the quality of the low resolution image already sent, only information
needed to improve the resolution is forwarded. The previous low resolution image is
decoded on the receiving side with this information, and following this, the high
resolution image is displayed on top of the previous low resolution image.
It is easy to quickly recognize the original image in the process of displaying the image
from low resolution to high resolution in order by using this method, with a CRT display
for example. Also, according to the situation, it is possible to interrupt the image transfer
at the point where the original image is recognized to some degree by the receiving side.
This method requires a page buffer memory for the low resolution image because the low
resolution images are used for the purpose of high resolution image encoding.

7.2.2 Single progression sequential bi-level image compression method

The Single Progression Sequential Bi-level Image Compression Method used in this fax is explained below.
The Progressive Bi-level Image Compression Method uses multiple resolution layers on a single page (multi-
level layers, low resolution layers~high resolution layers) to perform encoding/decoding. In the Single Pro-
gression Sequential Bi-level Image Compression Method, encoding is done in units of horizontal bands (a
number of lines) called stripes, and is performed from left to right, top to bottom (this condition is called
sequential), and in one resolution layer (single layer).
In this method, the encoding is done in stripe units, so it is completed with a buffer
memory much smaller than a page buffer memory.
NOTE
The methods by which encoding takes place and by which image data is constructed after encoding are
explained below.
FAX-L350 Chapter 2: Technical Reference
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