RE: [WM]: Parameters in MPEG-2 compression

["Buisson Alexandre" <Alexandre.Buisson@thomson.net>]

In MPEG2, the quantizer_scale_code describe to slice and macroblock is the current quality factor. It can be the same for the slice
or change at each macroblock (see the slice and macroblock in 13818 document). The quantization use the following formula : Cij =
((2*Qij + k)*Wij*quantizer_scale)/32, where Cij is the unquantized coefficient, Qij the quantized, k equal 0 if intra block or sign
of qij in the non-intra block case, Wij is the coefficient of your quantization matrix, and quantizer_scale (1..112) is deduce from
quantizer_scale_code
(1..31) and q_scale_type(0 or 1 to linear and no-linear scale) following table 7-6 of ISO/IEC 13818-2.

Good luck

_____________________________________
 
Alexandre Buisson - R&D Team
Thomson Content Security - Nextamp 
Tel: +33 299 22 61 62
Fax: +33 299 22 61 63
Email : a.buisson@nextamp.com
www.nextamp.com
_____________________________________
 
     
 
 

-----Original Message-----
From: watermarking-owner@watermarkingworld.org
[mailto:watermarking-owner@watermarkingworld.org] On Behalf Of Anindya Sarkar
Sent: samedi 29 avril 2006 06:38
To: watermarking@watermarkingworld.org
Subject: [WM]: Parameters in MPEG-2 compression

Hi
 I have a query about MPEG 2 encoder..When you run a MPEG encoder program, you have to specify a .par file.
In the par file (parameter file), what are the parameters that you can play around with? (e.g. you can specify your own GOP size
(6/8/12), the distance between I-P frames (2/3)).. can we also specify the intra-quantization matrix..
E.g. in the standard MPEG-2 code, we have:
EXTERN unsigned char
default_intra_quantizer_matrix[64]
#ifdef GLOBAL
=
{
   8, 16, 19, 22, 26, 27, 29, 34,
  16, 16, 22, 24, 27, 29, 34, 37,
  19, 22, 26, 27, 29, 34, 34, 38,
  22, 22, 26, 27, 29, 34, 37, 40,
  22, 26, 27, 29, 32, 35, 40, 48,
  26, 27, 29, 32, 35, 40, 48, 58,
  26, 27, 29, 34, 38, 46, 56, 69,
  27, 29, 35, 38, 46, 56, 69, 83
}
#endif
;

Now, we all know that in JPEG, depending on the quality factor at which we want to compress, we can specify a different quality
factor matrix. What will be the corresponding case for MPEG-2 compression?
Depending on our requirements, hou will the choice of intra-quantizer matrix vary?

Thanks in advance
Anindya 





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