Method and apparatus for range derivation in context adaptive binary arithmetic coding
View Patent ↗A method and apparatus of entropy coding of coding symbols using Context-Based Adaptive Binary Arithmetic Coder (CABAC) are disclosed. According to the present invention, a math formula is used for calculating the LPS range for deriving rangeOne value and rangeZero value. For example, the LPS range is derived using one or more mathematical operations comprising calculating a multiplication of a first value and a second value, in which the first value is related to (2*the LPS probability index+1) or the LPS probability index, while the second value is related to (2*the range index+1) or the range index. Besides, the LPS range can be derived by using a look-up-table including table contents corresponding to values of LPS range associated with a set of LPS probability indexes and a set of range indexes for encoding or decoding a binary value of the current bin.
1. A method of entropy coding of coding symbols, the method comprising:
applying context-adaptive arithmetic encoding or decoding to a current bin of a binary data of a current coding symbol according to a current probability for a binary value of the current bin and a current range associated with a current state of the context-adaptive arithmetic encoding or decoding, wherein the current probability is generated according to one or more previously coded symbols before the current coding symbol;
deriving an LPS probability index corresponding to an inverted current probability or the current probability depending on whether the current probability for the binary value of the current bin is greater than 0.5;
deriving a range index for identifying one range interval containing the current range; and
deriving an LPS range using one or more mathematical operations comprising calculating a multiplication of a first value related to (2*the LPS probability index+1) or the LPS probability index and a second value related to (2*the range index+1) or the range index, or deriving the LPS range using a look-up-table including table contents corresponding to values of LPS range associated with a set of LPS probability indexes and a set of range indexes for encoding or decoding a binary value of the current bin, wherein the range index corresponds to a result of right-shifting the current range by mm and mm is a non-negative integer and each value of LPS range corresponds to one product of (2*one LPS probability index+1) and (2*one range index+1) or deriving an LPS range corresponds to an offset and one product of one LPS probability index and one range index.
2. The method of claim 1 , wherein when the current probability for the binary value of the current bin is greater than 0.5, an LPS (least-probably-symbol) probability is set equal to (1−the current probability) and otherwise, the LPS probability is set equal to the current probability; and the LPS probability index is determined based on a target index indicating one probability interval containing the current probability or the LPS probability.
3. The method of claim 1 , wherein when the current probability for the binary value of the current bin is greater than 2 k−1 or is greater than or equal to 2 k−1 , an LPS probability is set equal to (2 k −1−the current probability) and the LPS probability index is set equal to (2 n+1 −1) minus a result of right-shifting the current probability by (k−n−1) bits; otherwise, the LPS probability is set equal to the current probability and the LPS probability index is set equal to the result of right-shifting the current probability by (k−n−1) bits; and wherein the current probability is represented by k-bit values, and n and k are positive integers.
4. The method of claim 3 , wherein k is equal to 15, and n is equal to 5.
5. The method of claim 3 , wherein the LPS range is derived by multiplying (2*the LPS probability index+1) with (2*the range index+1) to obtain a multiplication result, and right-shifting the multiplication result by x bits and x is a positive integer.
6. The method of claim 5 , wherein x is equal to 3.
7. The method of claim 3 , wherein the LPS range is derived by multiplying the LPS probability index with the range index to obtain a multiplication result, and right-shifting the multiplication result by x bits plus an offset and x is a positive integer, the offset is an integer.
8. The method of claim 7 , wherein x is equal to 1, and the offset is equal to 2, 3, or 4.
9. The method of claim 1 , wherein the look-up-table corresponds to a two-dimensional table with the LPS probability index as a first table index in a first dimension and a clipped range index as a second table index in a second dimension, where the clipped range index corresponding to the range index.
10. The method of claim 9 , wherein the LPS probability index has a first value range from 0 to 31, the clipped range index has a second value range from 0 to 7 and the LPS range has a third value range from greater than or equal to 0 to smaller than or equal to 255.
11. The method of claim 10 , wherein the look-up-table corresponds to:
probIdx,
(range >> 5)&7
(ProbLPS >>
rangeIdx
9)
0
1
2
3
4
5
6
7
31
133
149
165
181
196
212
228
244
30
129
144
160
175
190
205
221
236
29
125
140
154
169
184
199
213
228
28
121
135
149
163
178
192
206
220
27
116
130
144
158
171
185
199
213
26
112
125
139
152
165
178
192
205
25
108
121
133
146
159
172
184
197
24
104
116
128
140
153
165
177
189
23
99
111
123
135
146
158
170
182
22
95
106
118
129
140
151
163
174
21
91
102
112
123
134
145
155
166
20
87
97
107
117
128
138
148
158
19
82
92
102
112
121
131
141
151
18
78
87
97
106
115
124
134
143
17
74
83
91
100
109
118
126
135
16
70
78
86
94
103
111
119
127
15
65
73
81
89
96
104
112
120
14
61
68
76
83
90
97
105
112
13
57
64
70
77
84
91
97
104
12
53
59
65
71
78
84
90
96
11
48
54
60
66
71
77
83
89
10
44
49
55
60
65
70
76
81
9
40
45
49
54
59
64
68
73
8
36
40
44
48
53
57
61
65
7
31
35
39
43
46
50
54
58
6
27
30
34
37
40
43
47
50
5
23
26
28
31
34
37
39
42
4
19
21
23
25
28
30
32
34
3
14
16
18
20
21
23
25
27
2
10
11
13
14
15
16
18
19
1
6
7
7
8
9
10
10
11
0
2
2
2
2
3
3
3
3
wherein “rangeIdx” corresponds to the range index or the clipped range index, “probIdx” corresponds to the LPS probability index, and “rangeIdx” is derived according to (range >>5)&7 and “range” corresponds to the current range.
12. The method of claim 10 , wherein the look-up-table corresponds to:
probIdx,
(range >> 5)&7
(ProbLPS >>
rangeIdx
9)
0
1
2
3
4
5
6
7
31
128
143
159
174
190
205
221
236
30
124
139
154
169
184
199
214
229
29
120
134
149
163
178
192
207
221
28
116
130
144
158
172
186
200
214
27
112
125
139
152
166
179
193
206
26
108
121
134
147
160
173
186
199
25
104
116
129
141
154
166
179
191
24
100
112
124
136
148
160
172
184
23
96
107
119
130
142
153
165
176
22
92
103
114
125
136
147
158
169
21
88
98
109
119
130
140
151
161
20
84
94
104
114
124
134
144
154
19
80
89
99
108
118
127
137
146
18
76
85
94
103
112
121
130
139
17
72
80
89
97
106
114
123
131
16
68
76
84
92
100
108
116
124
15
64
71
79
86
94
101
109
116
14
60
67
74
81
88
95
102
109
13
56
62
69
75
82
88
95
101
12
52
58
64
70
76
82
88
94
11
48
53
59
64
70
75
81
86
10
44
49
54
59
64
69
74
79
9
40
44
49
53
58
62
67
71
8
36
40
44
48
52
56
60
64
7
32
35
39
42
46
49
53
56
6
28
31
34
37
40
43
46
49
5
24
26
29
31
34
36
39
41
4
20
22
24
26
28
30
32
34
3
16
17
19
20
22
23
25
26
2
12
13
14
15
16
17
18
19
1
8
8
9
9
10
10
11
11
0
4
4
4
4
4
4
4
4
wherein “rangeIdx” corresponds to the range index or the clipped range index, “probIdx” corresponds to the LPS probability index, and “rangeIdx” is derived according to (range>>5)&7 and “range” corresponds to the current range.
13. The method of claim 1 , wherein the LPS probability is set equal to a result of bitwise exclusive or (XOR) for a value of (current probability >>(k−1)) and the current probability, or the LPS probability index is set equal to the result of bitwise exclusive or for the value of (current probability >>(k−1)) and the value of (current probability >>(k−n−1)); and wherein the current probability is represented by k-bit values, and n and k are positive integers.
14. The method of claim 1 , further comprising deriving, from the current range, a rangeOne value and a rangeZero value for the current bin having a value of one and a value of zero respectively, wherein if the current probability for the binary value of the current bin is greater than 0.5 or is greater than or equal to 0.5, the rangeOne value is set to (the current range−the LPS range) and the rangeZero value is set to the LPS range; and otherwise, the rangeZero value is set to (the current range−the LPS range) and the rangeOne value is set to the LPS range.
15. An entropy coding apparatus for an image or video encoder or decoder, the entropy coding apparatus comprising:
apply context-adaptive arithmetic encoding or decoding to a current bin of a binary data of a current coding symbol according to a current probability for a binary value of the current bin and a current range associated with a current state of the context-adaptive arithmetic encoding or decoding, wherein the current probability is generated according to one or more previously coded symbols before the current coding symbol;
derive an LPS probability index corresponding to an inverted current probability or the current probability depending on whether the current probability for the binary value of the current bin is greater than 0.5;
derive a range index for identifying one range interval containing the current range; and
derive an LPS range using one or more mathematical operations comprising calculating a multiplication of a first value related to (2*the LPS probability index+1) or the LPS probability index and a second value related to (2*the range index+1) or the range index, or deriving the LPS range using a look-up-table including table contents corresponding to values of LPS range associated with a set of LPS probability indexes and a set of range indexes for encoding or decoding a binary value of the current bin, wherein the range index corresponds to a result of right-shifting the current range by mm and mm is a non-negative integer and each value of LPS range corresponds to one product of (2*one LPS probability index+1) and (2*one range index+1) or deriving an LPS range corresponds to an offset and one product of one LPS probability index and one range index.
16. The entropy coding apparatus of claim 12 , wherein when the current probability for the binary value of the current bin is greater than 0.5, an LPS (least-probably-symbol) probability is set equal to (1−the current probability) and otherwise, the LPS probability is set equal to the current probability; and the LPS probability index is determined based on a target index indicating one probability interval containing the current probability or the LPS probability.
17. The entropy coding apparatus of claim 12 , wherein when the current probability for the binary value of the current bin is greater than 2 k−1 or is greater than or equal to 2 k−1 , an LPS probability is set equal to (2 k −1−the current probability) and the LPS probability index is set equal to (2 n+1 −1) minus a result of right-shifting the current probability by (k−n−1) bits; otherwise, the LPS probability is set equal to the current probability and the LPS probability index is set equal to the result of right-shifting the current probability by (k−n−1) bits; and wherein the current probability is represented by k-bit values, and n and k are positive integers.
18. The entropy coding apparatus of claim 14 , wherein the LPS range is derived by multiplying (2*the LPS probability index+1) with (2*the range index+1) to obtain a multiplication result, and right-shifting the multiplication result by x bits and x is a positive integer.
19. The entropy coding apparatus of claim 14 , wherein the LPS range is derived by multiplying the LPS probability index with the range index to obtain a multiplication result, and right-shifting the multiplication result by x bits plus an offset and x is a positive integer, the offset is an integer.
20. The entropy coding apparatus of claim 12 , wherein the look-up-table corresponds to a two-dimensional table with the LPS probability index as a first table index in a first dimension and a clipped range index as a second table index in a second dimension, where the clipped range index corresponding to the range index.
21. The entropy coding apparatus of claim 12 , wherein the LPS probability is set equal to a result of bitwise exclusive or (XOR) for a value of (current probability >>(k−1)) and the current probability, or the LPS probability index is set equal to the result of bitwise exclusive or for the value of (current probability >>(k−1)) and the value of (current probability >>(k−n−1)); and wherein the current probability is represented by k-bit values, and n and k are positive integers.
22. The entropy coding apparatus of claim 12 , further comprising deriving, from the current range, a rangeOne value and a rangeZero value for the current bin having a value of one and a value of zero respectively, wherein if the current probability for the binary value of the current bin is greater than 0.5 or is greater than or equal to 0.5, the rangeOne value is set to (the current range−the LPS range) and the rangeZero value is set to the LPS range; and otherwise, the rangeZero value is set to (the current range−the LPS range) and the rangeOne value is set to the LPS range.