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4.5.3 Encoding scheme
In the JBIG encoding used in the Single Progression Sequential Bi-level
Image Compression Scheme, uses in the encoder shown below to encode
to the original the results of comparison of the line currently being pro-
cessed and the previous line, as well as the predicted value of an image
pixel (white or black) used in a model template.
The study table used in the prediction makes the next prediction more
accurate by learning and correcting the study table every time the model
template moves to the adjoining pixel. It is characteristic of this scheme
that if the prediction is accurate the amount of encoding will not increase,
and if the prediction is off the amount of encoding increases, so the
increase in prediction accuracy of this study table is very important.
An outline of the encoding procedure is shown below.
5–32
Comparison of current
and previous lines
Image
TYPICAL
data
PREDICTION
input
No-match path
Prediction
of pixel
to be
encoded
MODEL
TEMPLATE
Prediction of pixel using
10-bit pixel pattern
Next prediction based
on prediction results
Fig. 5-26 Encoder and Flow of JBIG Encoding
ENCODER
Output of
match/no match ARITHMETIC
ENCODING
Pixel to be encoded
(For comparison
against prediction)
10-bit pixel
pattern
Prediction and
status reference
and prediction
results
STUDY
TABLE
Refer to the next
status and pixel
prediction based
on the prediction
results (Learnig)
Relevant
status
PROBABILITY
area reference
ESTIMATION
TABLE
Output of
image data
encoded
by JBIG
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