Game Development Reference
In-Depth Information
Table 4.3
Chroma
intraprediction modes
Mode index
Prediction modes
0
Derived mode (DM)
1
DC mode
2
Horizontal mode
3
Vertical mode
4
Bilinear modes
It should be pointed out that all interpolated prediction sample
P
[
x
,
y
]
should be
2
BitDepth
clipped in to the sample bit-depth range, e.g.
[
0
..
−
1
]
, assuming BitDepth
is the sample bit-depth.
4.2.2 Chroma Prediction
Different from luma prediction, onlyN
2N
CU, and only 5 prediction modes are supported which are exhibited in Table
4.3
.For
DMmode, the chroma prediction mode derived from the prediction mode of the first
luma prediction unit in the current coding unit (Piao et al.
2013
).
Assuming col
×
Nprediction block is allowed for a 2N
×
[
i
]
and row
[
i
]
(
i
=
0..2
L
) are the neighboring top and left chroma
samples for a
L
L
chroma prediction unit, similar prediction samples derivation
is used for chroma as luma. But as the block size is square, it would be simpler for
chroma prediction than for luma prediction. For example, if the coded or derived
mode is bilinear, a prediction sample
Pc
×
[
x
,
y
]
for chroma is calculated as follows,
(
x
val
+
y
val
+
1
) >>
1
,
if
(
x
val
+
y
val
)
≥
0
Pc
[
x
,
y
]
=
,
(4.31)
(
x
val
+
y
val
−
1
) >>
1
,
otherwise
where
x
val and
y
val are computed as follows,
col [
y
+
1]
+
((
kx
×
(
x
+
1
)
+
(
L
>>
1
)) >>
Log
(
L
)) ,
if
kx
≥
0
x
val
=
col [
y
+
1]
+
((
kx
×
(
x
+
1
)
−
(
L
>>
1
)) >>
Log
(
L
)) ,
otherwise
(4.32a)
row [
x
+
1]
+
((
ky
×
(
y
+
1
)
+
(
L
>>
1
)) >>
Log
(
L
)) ,
if
ky
≥
0
y
val
=
row [
x
+
1]
+
((
ky
×
(
y
+
1
)
−
(
L
>>
1
)) >>
Log
(
L
)) ,
otherwise
(4.32b)
and
kx
,
ky
are computed as follows,
