Single Progression Sequential Bi-Level Image Compression Method - Canon FAX L1000 Service Manual

FAX-L1000 Chapter 3: Technical Reference
NOTE

3.2.2 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 Progression 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).
NOTE
The methods by which encoding takes place and by which image data is constructed after
encoding are explained below.
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 (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.
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.
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