H.264 Prediction

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Revision as of 01:01, 7 August 2007 by Kostya (talk | contribs) (Correct information about H.264 plane prediction and merge with RV40 plane prediction)
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This page documents the various prediction methods used in H.264 and related formats such as Sorenson Video 3 and RealVideo 4.

4x4 Prediction Modes

4x4 prediction modes vary between different codecs. While they are almost the same for H.264 and Sorenson Video 3, RealVideo 4 has a different order for these modes and some of them significantly differ from H.264 counterparts (by using left predictors where H.264 does not and down left predictors which are not used elsewhere).

Vertical

  • H.264: mode 0
  • SVQ3: mode 0
  • RV40: mode 1
 LT | T0  T1  T2  T3
---------------------
 L0 | T0  T1  T2  T3
 L1 | T0  T1  T2  T3
 L2 | T0  T1  T2  T3
 L3 | T0  T1  T2  T3

Horizontal

  • H.264: mode 1
  • SVQ3: mode 1
  • RV40: mode 2
 LT | T0  T1  T2  T3
---------------------
 L0 | L0  L0  L0  L0
 L1 | L1  L1  L1  L1
 L2 | L2  L2  L2  L2
 L3 | L3  L3  L3  L3

DC

  • H.264: mode 2
  • SVQ3: mode 2
  • RV40: mode 0
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   a   a   a
 L1 |  a   a   a   a
 L2 |  a   a   a   a
 L3 |  a   a   a   a

where:

a = (T0 + T1 + T2 + T3 + L0 + L1 + L2 + L3 + 4) / 8

Diagonal Down/Left

  • H.264: mode 3
  • SVQ3: not used
  • RV40: not used
 LT | T0  T1  T2  T3  T4  T5  T6  T7
-------------------------------------
 L0 |  a   b   c   d
 L1 |  b   c   d   e
 L2 |  c   d   e   f
 L3 |  d   e   f   g

where:

 a = (T0 + 2*T1 + T2 + 2) / 4
 b = (T1 + 2*T2 + T3 + 2) / 4
 c = (T2 + 2*T3 + T4 + 2) / 4
 d = (T3 + 2*T4 + T5 + 2) / 4
 e = (T4 + 2*T5 + T6 + 2) / 4
 f = (T5 + 2*T6 + T7 + 2) / 4
 g = (T6 + 3*T7      + 2) / 4

Diagonal Down/Left (SVQ3)

  • H.264: not used
  • SVQ3: mode 3
  • RV40: not used
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   b   c   c
 L1 |  b   c   c   c
 L2 |  c   c   c   c
 L3 |  c   c   c   c

where:

 a = (L1 + T1) / 2
 b = (L2 + T2) / 2
 c = (L3 + T3) / 2

Diagonal Down/Left (RV40)

  • H.264: not used
  • SVQ3: not used
  • RV40: mode 4
 LT | T0  T1  T2  T3  T4  T5  T6  T7
-------------------------------------
 L0 |  a   b   c   d
 L1 |  b   c   d   e
 L2 |  c   d   e   f
 L3 |  d   e   f   g
 L4 |
 L5 |
 L6 |
 L7 |


where:

 a = (T0 + 2*T1 + T2 + L0 + 2*L1 + L2 + 4) / 8
 b = (T1 + 2*T2 + T3 + L1 + 2*L2 + L3 + 4) / 8
 c = (T2 + 2*T3 + T4 + L2 + 2*L3 + L4 + 4) / 8
 d = (T3 + 2*T4 + T5 + L3 + 2*L4 + L5 + 4) / 8
 e = (T4 + 2*T5 + T6 + L4 + 2*L5 + L6 + 4) / 8
 f = (T5 + 2*T6 + T7 + L5 + 2*L6 + L7 + 4) / 8
 g = (T6 +   T7      + L6 +   L7      + 2) / 4

Diagonal Down/Right

  • H.264: mode 4
  • SVQ3: mode 4
  • RV40: mode 3
 LT | T0  T1  T2  T3
---------------------
 L0 |  d   e   f   g
 L1 |  c   d   e   f
 L2 |  b   c   d   e
 L3 |  a   b   c   d

where:

 a = (L3 + 2*L2 + L1 + 2) / 4
 b = (L2 + 2*L1 + L0 + 2) / 4
 c = (L1 + 2*L0 + LT + 2) / 4
 d = (L0 + 2*LT + T0 + 2) / 4
 e = (LT + 2*T0 + T1 + 2) / 4
 f = (T0 + 2*T1 + T2 + 2) / 4
 g = (T1 + 2*T2 + T3 + 2) / 4

Vertical/Right

  • H.264: mode 5
  • SVQ3: mode 5
  • RV40: mode 5
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   b   c   d
 L1 |  e   f   g   h
 L2 |  i   a   b   c
 L3 |  j   e   f   g

where:

 a = (LT + T0 + 1) / 2
 b = (T0 + T1 + 1) / 2
 c = (T1 + T2 + 1) / 2
 d = (T2 + T3 + 1) / 2
 e = (L0 + 2*LT + T0 + 2) / 4
 f = (LT + 2*T0 + T1 + 2) / 4
 g = (T0 + 2*T1 + T2 + 2) / 4
 h = (T1 + 2*T2 + T3 + 2) / 4
 i = (LT + 2*L0 + L1 + 2) / 4
 j = (L0 + 2*L1 + L2 + 2) / 4

Horizontal/Down

  • H.264: mode 6
  • SVQ3: mode 6
  • RV40: mode 8
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   b   c   d
 L1 |  e   f   a   b
 L2 |  g   h   e   f
 L3 |  i   j   g   h

where:

 a = (LT + L0 + 1) / 2
 b = (L0 + 2*LT + T0 + 2) / 4
 c = (LT + 2*T0 + T1 + 2) / 4
 d = (T0 + 2*T1 + T2 + 2) / 4
 e = (L0 + L1 + 1) / 2
 f = (LT + 2*L0 + L1 + 2) / 4
 g = (L1 + L2 + 1) / 2
 h = (L0 + 2*L1 + L2 + 2) / 4
 g = (L2 + L3 + 1) / 2
 j = (L1 + 2*L2 + L3 + 2) / 4

Vertical/Left

  • H.264: mode 7
  • SVQ3: mode 7
  • RV40: mode 6
 LT | T0  T1  T2  T3  T4  T5  T6  T7
-------------------------------------
 L0 |  a   b   c   d
 L1 |  f   g   h   i
 L2 |  b   c   d   e
 L3 |  g   h   i   j

where:

 a = (T0 + T1 + 1) / 2
 b = (T1 + T2 + 1) / 2
 c = (T2 + T3 + 1) / 2
 d = (T3 + T4 + 1) / 2
 e = (T4 + T5 + 1) / 2
 f = (T0 + 2*T1 + T2 + 2) / 4
 g = (T1 + 2*T2 + T3 + 2) / 4
 h = (T2 + 2*T3 + T4 + 2) / 4
 i = (T3 + 2*T4 + T5 + 2) / 4
 j = (T4 + 2*T5 + T6 + 2) / 4

For RV40 two coefficients differ:

 a = (2*T0 + 2*T1 + L1 + 2*L2 +   L3 +      4) / 8
 f = (  T0 + 2*T1 + T2 +   L2 + 2*L3 + L4 + 4) / 8

Horizontal/Up

  • H.264: mode 8
  • SVQ3: mode 8
  • RV40: not used
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   b   c   d
 L1 |  c   d   e   f
 L2 |  e   f   g   g
 L3 |  g   g   g   g

where:

 a = (L0 + L1 + 1) / 2
 b = (L0 + 2*L1 + L2 + 2) / 4
 c = (L1 + L2 + 1) / 2
 d = (L1 + 2*L2 + L3 + 2) / 4
 e = (L2 + L3 + 1) / 2
 f = (L2 + 2*L3 + L3 + 2) / 4
 g = L3

Horizontal/Up (RV40)

  • H.264: not used
  • SVQ3: not used
  • RV40: mode 7
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   b   c   d
 L1 |  c   d   e   f
 L2 |  e   f   g   h
 L3 |  g   h   i   j
 L4 |
 L5 |
 L6 |
 L7 |

where:

 a = (T1 + 2*T2 + T3 + 2*L0 + 2*L1 +      4) / 8
 b = (T2 + 2*T3 + T4 +   L0 + 2*L1 + L2 + 4) / 8
 c = (T3 + 2*T4 + T5 + 2*L1 + 2*L2 +      4) / 8
 d = (T4 + 2*T5 + T6 +   L1 + 2*L2 + L3 + 4) / 8
 e = (T5 + 2*T6 + T7 + 2*L2 + 2*L3 +      4) / 8
 f = (T6 + 3*T7 +        L2 + 3*L3 +      4) / 8
 g = (T6 +   T7 +        L3 +   L4      + 2) / 4
 h = (                   L3 + 2*L4 + L5 + 2) / 4
 i = (                   L4 +   L5      + 1) / 2
 j = (                   L4 + 2*L5 + L6 + 2) / 4

Left/DC

  • H.264: mode 9
  • SVQ3: mode 9
  • RV40: not used
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   a   a   a
 L1 |  a   a   a   a
 L2 |  a   a   a   a
 L3 |  a   a   a   a

where:

a = (L0 + L1 + L2 + L3 + 2) / 4

Top/DC

  • H.264: mode 10
  • SVQ3: mode 10
  • RV40: not used
 LT | T0  T1  T2  T3
---------------------
 L0 |  a   a   a   a
 L1 |  a   a   a   a
 L2 |  a   a   a   a
 L3 |  a   a   a   a

where:

a = (T0 + T1 + T2 + T3 + 2) / 4

DC-128

  • H.264: mode 11
  • SVQ3: mode 11
  • RV40: not used
 LT |  T0   T1   T2   T3
------------------------
 L0 | 128  128  128  128
 L1 | 128  128  128  128
 L2 | 128  128  128  128
 L3 | 128  128  128  128

16x16 Prediction Modes

DC

  • H.264: mode 0
  • SVQ3: mode 0
  • RV40: mode 0

Using the 16 top predictors (T0..T15) and the 16 left predictors (L0..L15), set all 256 elements to the mean, computed as:

 mean = (sum(T0..T15) + sum(L0..L15) + 16) / 32

Vertical

  • H.264: mode 1
  • SVQ3: mode 1
  • RV40: mode 1
  LT | T0  T1  T2  T3  T4  ..  T15
-------------------------- .. -----
  L0 | T0  T1  T2  T3  T4  ..  T15
  L1 | T0  T1  T2  T3  T4  ..  T15
  L2 | T0  T1  T2  T3  T4  ..  T15
 ......
 L15 | T0  T1  T2  T3  T4  ..  T15

Horizontal

  • H.264: mode 2
  • SVQ3: mode 2
  • RV40: mode 2
  LT |  T0  T1  T2  T3  T4  ..  T15
--------------------------- .. -----
  L0 |  L0  L0  L0  L0  L0  ..   L0
  L1 |  L1  L1  L1  L1  L1  ..   L1
  L2 |  L2  L2  L2  L2  L2  ..   L2
 ......
 L15 | L15 L15 L15 L15 L15  ..  L15

Plane

  • H.264: mode 3
  • SVQ3: mode 3
  • RV40: mode 3

Notice that SVQ3 and RV40 follow a slightly different method here.

Given the top predictors (T0..T15), left predictors (L0..L15) and the left-top corner predictor (LT) arranged as follows:

  LT |    T0        T1        T2     ..    T15
-----------------------------------  ..  --------
  L0 | c[ 0, 0]  c[ 1, 0]  c[ 2, 0]  ..  c[15, 0]
  L1 | c[ 0, 1]  c[ 1, 1]  c[ 2, 1]  ..  c[15, 1]
 ......
 L15 | c[ 0,15]  c[ 1,15]  c[ 2,15]  ..  c[15,15]

Compute H and V as:

H' = 1* (T8 - T6) +
     2* (T9 - T5) +
     3*(T10 - T4) +
     4*(T11 - T3) +
     5*(T12 - T2) +
     6*(T13 - T1) +
     7*(T14 - T0) +
     8*(T15 - LT)
V' = 1* (L8 - L6) +
     2* (L9 - L5) +
     3*(L10 - L4) +
     4*(L11 - L3) +
     5*(L12 - L2) +
     6*(L13 - L1) +
     7*(L14 - L0) +
     8*(L15 - LT)

For H.264, compute H and V as:

 H = (5*H' + 32) / 64
 V = (5*V' + 32) / 64

For SVQ3, compute H and V as:

 V = (5*(H'/4)) / 16
 H = (5*(V'/4)) / 16 
 (notice that V and H are computed from H' and V', respectively)

For RV40, compute H and V as:

 H = (5*(H' >> 2)) >> 4
 V = (5*(V' >> 2)) >> 4 
 (like SVQ3 but without swapping and it's important to use shifts here instead of divisions)

The final process for filling in the 16x16 block is:

 a = 16 * (L15 + T15 + 1) - 7*(V+H)
 for (j = 0..15)
   for (i = 0..15)
     b = a + V * j + H * i
     c[i,j] = SATURATE_U8(b / 32)

The SATURATE_U8() function indicates that the result of the operation should be bounded to an unsigned 8-bit range (0..255).

Left/DC

  • H.264: mode 4
  • SVQ3: mode 4
  • RV40: not used

Using 16 left predictors (L0..L15), set all 256 elements to the mean, computed as:

 mean = (sum(L0..L15) + 8) / 16

Top/DC

  • H.264: mode 5
  • SVQ3: mode 5
  • RV40: not used

Using the 16 top predictors (T0..T15), set all 256 elements to the mean, computed as:

 mean = (sum(T0..T15) + 8) / 16

DC-128

  • H.264: mode 6
  • SVQ3: mode 6
  • RV40: not used

Set all 256 elements to 128.