ISO/IEC 10918-1 : 1993(E)
Renormalization driven estimation
The change in state in Table D.3 occurs only when the arithmetic coder interval register is renormalized. This must always
be done after coding an LPS, and whenever the probability interval register is less than X'8000' (0.75 in decimal notation)
after coding an MPS.
When the LPS renormalization is required, Next_Index_LPS gives the new index for the LPS probability estimate. When
the MPS renormalization is required, Next_Index_MPS gives the new index for the LPS probability estimate. If
Switch_MPS is 1 for the old index, the MPS symbol sense must be inverted after an LPS.
Estimation following renormalization after MPS
The procedure for estimating the probability on the MPS renormalization path is given in Figure D.5. Index(S) is part of
the information stored for context-index S. The new value of Index(S) is obtained from Table D.3 from the column labeled
Next_Index_MPS, as that is the next index after an MPS renormalization. This next index is stored as the new value of
Index(S) in the context storage at context-index S, and the value of Qe at this new Index(S) becomes the new Qe(S).
MPS(S) does not change.
Figure D.5 Probability estimation on MPS renormalization path
I = Index(S)
I = Next_Index_MPS(I)
Index(S) = I
Qe(S) = Qe_Value(I)
Figure D.5 [D43], = 7 cm = 273.%
CCITT Rec. T.81 (1992 E)