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RE: Lossless Compression Help!



Title: Message
To hopefully clear things up
 
to quote you 'OK, the PC capture of whatever feed is lossless...'
 
this is not the case as the PC capture involves a Analogue to Digital conversion, the only way around this is to use Sky + as Ken said.
 
 
LNB to Digibox - Digital Connection
 
Digibox to RBG or S-Vid out put invloves a D/A Conversion
 
so we are now in the anlogue domain and now you have to do another A/D conversion to get the feed into SS, this will be done by the TV capture card.
 
all of these A/D conversions are NOT good.
 
 
 
What you do with the captured file may well, be lossless, but you have already degraded the signal by the A/D conversion.
 
Regards
 
Ben
-----Original Message-----
From: Jason Lee [mailto:jasonjlee@xxxxxxx]
Sent: 28 May 2002 11:54
To: ukha_d@xxxxxxxSubject: Re: [ukha_d] Lossless Compression Help!

Oh Jesus!
 
I keep putting things as simply as I can and still people jump down my throat.
 
I've got lots of books as well. No really I have.
 
If I send you a zipped file and you unzip it. Do you get the same file? Or is it different?
 
THAT IS LOSSLESS COMPRESSION. Go look up huffyuv. Its here...http://math.berkeley.edu/~benrg/huffyuv.html
 
I'm not sure if the you will *apologise* for spouting utter nonsense about compression.
 
Now that fact is dealt with...
 
The point of using lossless is not to produce more artifacts. I understand that the digital feed is already compressed. I just don't want to add more noise until the end.
 
People work in lossless and then compress down at the last stage.
 
I suggest you try reading some of your books sometime :)
 
Jason
 
 
 
----- Original Message -----
Sent: Tuesday, May 28, 2002 11:37 AM
Subject: RE: [ukha_d] Lossless Compression

The point being Jason that any form of compression and manipulation of the file *will* introduce loss and affect the quality of the image. If your digibox un-compresses the stream then there is a loss in that, then you are re-compressing it for storage (loss again), then decompressing it to view (still more loss)…NOT lossless!

 

Any form of capture, compression or manipulation will introduce certain artefacts into the picture whether you notice them or not, although there is many a software “trick” to minimise the impact of such manipulation. If you like I can loan you a couple of good books that explain this but it isn’t exactly light reading material.

 

K.

 

-----Original Message-----
From: Jason Lee [mailto:jasonjlee@xxxxxxx]
Sent: 28 May 2002 11:27
To: ukha_d@xxxxxxxSubject: Re: [ukha_d] Lossless Compression

 

OK, the PC capture of whatever feed is lossless...

 

Like taking a file and using zip to compress it. The file when uncompressed is exactly the same as the source. Lossless

 

As opposed to using jpeg/mpeg/mjpeg which uses tricks to compress images down. When the image is uncompressed it is not identical to the source. Not lossless.

 

Look at matroxusers web site vcdhelper, any big video editors website for details as to why this is a good idea...

 

I don't only capture from tv, I capture from dv and my s-vhs deck.

 

Jason

 

 

----- Original Message -----

From: Kenneth Watt

Sent: Tuesday, May 28, 2002 11:19 AM

Subject: [ukha_d] Lossless Compression

 

Jason,

This is really a question for you...

How are you achieving lossless compression with SS?

I was thinking about this last night and the only way I can see of doing
this is to take a feed into a SAT card in the PC direct from the LNB to
catch the digital stream before it is decoded thus achieving a lossless
compressed file. The problem with that is that there is no CAM available
for Sky Digital to enable this to be done with a SAT card or TV.

AFAIK the only way to do this, or more accurately, the only system that
can do this, is Sky+ as it actually records the stream directly and
plays back as it would be presented straight off the air.

If you are running it through the STB and then transferring that signal
to your SS machine then that is not lossless, you are in fact, doing
what any PVR or VHS machine would do.

K.


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