[MPEG] reference picture question

Hi all,

I am reading MPEG's MSSG software implementation.

fullsearch() function in motion.c input includes "source reference
picture" and "reconstructed reference picture".

AFAIK, all the reference picture(including I frame and P frame) should
be reconstructed (by IDCT) before be used as reference. So what's these
two reference's difference?

Any suggestions will be appreciated!
All the best!
Davy

"Davy" <zhushenli@gmail.com> a &#4294967295;crit dans le message de news: 1125913029.237183.322320@g14g2000cwa.googlegroups.com...
| Hi all,
|
| I am reading MPEG's MSSG software implementation.
|
| fullsearch() function in motion.c input includes "source reference
| picture" and "reconstructed reference picture".
|
| AFAIK, all the reference picture(including I frame and P frame) should
| be reconstructed (by IDCT) before be used as reference. So what's these
| two reference's difference?
|
| Any suggestions will be appreciated!
| All the best!
| Davy
|

I do not know this MPEG's MSSG software implementation but
i maybe guess what they are talking about.

I suppose that fullsearch() is related to motion estimation. (?)

Motion estimation can be done either relatively to the "source"
pictures or to the "reconstructed" pictures.

"Source" pictures are original pictures without any change and
"reconstructed" pictures are pictures which have been compressed
and uncompressed locally at the encoder side.

Motion estimation is sometimes done relatively to the source picture
at low bitrate because it yields to a more homogenous motion vector
field which is the better compressed when vectors are differentially
encoded in the bitstream.

Of course, motion compensation is then always done relatively to the
reconstructed picture since coder and decoder shall do the
same things.

Hi ast,

Thank you for your help!

Yes,  fullsearch() is related to motion estimation ;-)

MPEG's MSSG (http://www.mpeg.org/MPEG/MSSG/) is a stardard MPEG1/2
implementation I could find on Internet. Its comments are
poor. Oh, my God. And I haven't any dollar to buy their author's
expensive book.

I have one more question:
You said" "Source" pictures are original pictures without any change",
Is "Source" pictures must be I frame? And is "reconstructed" pictures
must be P frame?
IMHO, P frame will be stored for future usage by reconstruct.

Any suggestions will be appreciated!
Best regards,
Davy

"Davy" <zhushenli@gmail.com> a &#4294967295;crit dans le message de news: 1125970682.993747.265840@g43g2000cwa.googlegroups.com...
| Hi ast,
|
| Thank you for your help!
|
| Yes,  fullsearch() is related to motion estimation ;-)
|
| MPEG's MSSG (http://www.mpeg.org/MPEG/MSSG/) is a stardard MPEG1/2
| implementation I could find on Internet. Its comments are
| poor. Oh, my God. And I haven't any dollar to buy their author's
| expensive book.
|
| I have one more question:
| You said" "Source" pictures are original pictures without any change",
| Is "Source" pictures must be I frame?

I call source pictures all the movie pictures before encoding.

| And is "reconstructed" pictures
| must be P frame?

Reconstructed pictures are those pictures which are encoded and then
decoded at the encoder side because they are used by motion
compensation for further picture. Only I and P pictures needs to be
reconstructed.

| IMHO, P frame will be stored for future usage by reconstruct.

Yes, and I pictures too.

|
| Any suggestions will be appreciated!
| Best regards,
| Davy
|