FAST MULTI-BLOCK SELECTION FOR

H.264 VIDEO CODING

Chang, A.; Wong, P.H.W.; Yeung, Y.M.; Au, O.C.;

Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on , Volume: 3 , 23-26 May 2004

OnlineOnline Introduction of H.264.Introduction of H.264. Introduction of FMBME. Introduction of FMBME. FMBME: a fast multi-block motion FMBME: a fast multi-block motion

estimation.estimation. The best match function of multi-block The best match function of multi-block

motion estimation.motion estimation. The useful multi-block motion estimation.The useful multi-block motion estimation.

Object movement.Object movement. Texture regions.Texture regions.

The proposed fast multi-block selection The proposed fast multi-block selection algorithm.algorithm.

Experimental result.Experimental result. Conclusion.Conclusion.

Introduction of H.264Introduction of H.264 The JVT/H.264 is the new video coding standThe JVT/H.264 is the new video coding stand

ard which additional features concludes:ard which additional features concludes: Intra prediction mode for I-frames.Intra prediction mode for I-frames. Different mode decision including multiple block Different mode decision including multiple block

size.size.

MacroblockMacroblock TypesTypes

Sub macroblockSub macroblock TypesTypes

Multiple reference frame motion estimation.Multiple reference frame motion estimation.

16 * 16

4 * 44 * 88 * 48 * 8

8 * 88 * 16

16 * 8

00

00

00

00

11

1

11

12

2 3

3

Introduction of FMBMEIntroduction of FMBME

We propose a fast multi-block selection scheme We propose a fast multi-block selection scheme ::

16*16 (mode 1), 16*8 (mode 2), 8*16 (mode 3), 8*16*16 (mode 1), 16*8 (mode 2), 8*16 (mode 3), 8*8 (mode 4) which can efficiently reduce the com8 (mode 4) which can efficiently reduce the computational cost while achieving similar visual qputational cost while achieving similar visual quality and bit-rate.uality and bit-rate.

The sequence of a fast multi-block selection schThe sequence of a fast multi-block selection scheme is :eme is :

Mode

4 ( 8 * 8 )

Mode

1 ( 16 * 16 )

Mode

2 ( 16 * 8 )

Mode

3 ( 8 * 16 )

The best match function of The best match function of multi-block motion multi-block motion

estimationestimation The best match is found by minimizing the cost funThe best match is found by minimizing the cost function:ction:

J(m,J(m,λλ MOTIONMOTION)=SAD(s,c(m))+)=SAD(s,c(m))+λλ MOTIONMOTION *R(m-p) *R(m-p) m=(mm=(mxx,m,myy))TT is the motion vector. is the motion vector. p=(pp=(pxx,p,pyy))TT is the prediction for the motion vector. is the prediction for the motion vector. λλMOTION MOTION is the Lagrangle multiplier.is the Lagrangle multiplier. R(m-p) is the bits rate.R(m-p) is the bits rate. SAD ( Sum of Absolute Differences ):SAD ( Sum of Absolute Differences ):

B=16, 8 or 4 is the original video signal.B=16, 8 or 4 is the original video signal. c is the coded video signal.c is the coded video signal.

BB,

1y,1x|]

ymy,

xmx[c]y,x[s|))m(c,s(SAD

The useful multi-block The useful multi-block motion estimation.motion estimation.

There are two situations : Object movement and texture rThere are two situations : Object movement and texture regions.egions.

Object movement :Object movement : This means more than one object in a macroblock and are

moving in different directions. This included objects moving over a background with different velocity.

Fig. 2 the object is moving against a static background. In this case, the current block should be divided into two 8x16 sub-blocks such that the cost function can be minimized.

The useful multi-block The useful multi-block motion estimation.motion estimation. Texture regions:Texture regions:

If the edges have a integer-pixel offset as shown in Fig. 3a. If the edges of texture have a half-pixel or a quarter-pixel offse

t relative to the senor, the edges may be blurred as shown in Fig. 3b, 3c.

The pixel at the blurred edges may have only ½ , 3/4 or ¼ the intensity of the original one, which can lead to difficulty in motion estimation.

Since it is possible for a macroblock to contain more than one kind of texture, using only one integer, half or quarter pixel motion vector will not be sufficient to describe the texture content.

The proposed fast multi-The proposed fast multi-block selection algorithm.block selection algorithm.

The proposed FMBME it analysis the informaThe proposed FMBME it analysis the information obtained from 8*8 block size ME to predition obtained from 8*8 block size ME to predict the mode 1 macroblock.ct the mode 1 macroblock.

As a result, computation can be saved for moAs a result, computation can be saved for mode 2 and mode 3 block size ME and in some side 2 and mode 3 block size ME and in some situation mode as well.tuation mode as well.

Three decisions are set up in different video aThree decisions are set up in different video area:rea:

general area, slow moving area general area, slow moving area andand fast mo fast moving area.ving area.

The proposed fast multi-The proposed fast multi-block selection algorithm.block selection algorithm.

<General Area Decision><General Area Decision> Defining MV0, MV1, MV2, MV3 is the motion vector of Defining MV0, MV1, MV2, MV3 is the motion vector of

8*8 subblock of the macroblock.8*8 subblock of the macroblock.C1: If MV0=MV1=MV2=MV3 then

- choose mode 1 (16x16) as final block type- no ME will be further performed- 16x16 MV = 8x8 MV0

C2: If three subblock MV are the same AND the forth unequal MV only differ by one quarter pixel (1/4) distance

then- choose mode 1 (16x16) as final block type- no ME will be further performed- 16x16 MV = dominated 8x8 MV

The proposed fast multi-The proposed fast multi-block selection algorithm.block selection algorithm.

The proposed fast multi-The proposed fast multi-block selection algorithm.block selection algorithm.

<Slow Moving Area Decision>C3: If collocate MB in previous frame is mode1 AND

{MV0, MV1, MV2, MV3} < 4 (i.e. one integer pixel distance) AND MV0, MV1, MV2, MV3 has the same direction then

- choose mode 1 (16x16) as final block type- 8 point local search around MV = {0, 0}

The proposed fast multi-The proposed fast multi-block selection algorithm.block selection algorithm.

The proposed fast multi-The proposed fast multi-block selection algorithm.block selection algorithm.

<Fast Moving Area Decision>C4: If all magnitude of 8x8 MVx >= 3 integer distance OR

all agnitude of 8x8 MVy >= 3 integer distance- choose mode 1 (16x16) as final block type- local search for surrounding 24 points of

MV0

The proposed fast multi-The proposed fast multi-block selection algorithm.block selection algorithm.

Experimental result.Experimental result.

Experimental result.Experimental result.

Experimental result.Experimental result.

Experimental result.Experimental result.

Conclusion.Conclusion.

In this paper, a novel fast multi-block motion estimation called FMBME is proposed for H.264 video coding.

Experiment results suggest that FMBME can reduce the computation cost significantly with little change to PSNR and bit rate.