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MPEG's coded_block_pattern problem?

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davyzhu

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Hi all,

I am reading MPEG-2's spec. It has a VLC coded_block_pattern_420. The spec said we can get cbp from coded_block_pattern_420. But what's cbp's function? Is it a important parameter?

Any suggestions will be appreciated!
Best regards,
Davy
 

Hi,
In MPEG2 the Picture is divided into slices which inturn into MacroBlocks which inturn into Blocks.
For a 4:2:0 (yuv) format encoding, each macroblock contains 4 blocks of Y (luminance) 1 block of Cr and 1 block of Cb(Chrominance) thus 6 Blocks.

The Coded Block pattern specifies that whether that particular block in the Macroblock is coded (DCT + quantisation) or not i.e if the cbp for that block is 1 then it is coded and is present in bitstream.

Hope this was useful.

Regards,
KJN
 

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    davyzhu

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Hi nitthilan,

Happy to talk with you!

I understand the answer.
There is a further problem: I read the coded_block_pattern VLC table.
The shortest VLC is 111 and cbp=60. You said "if the cbp for that block is 1 then it is coded and is present in bitstream".

And I think it maybe the most common situation. But Why the cbp=60 be the most common situation?

Any suggestions will be appreciated!

Best regards,
Davy
 

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