RE: Lossless Compression Help!

["Ben McCormack" <ben.mccormack@xxxxxxx>]

Title: Message

I think that we have simply been confused by your post that stated

 

'I am capturing to a raid array in a silencing enclosure.  I can capture from my S-vhs deck or ntl digibox losslessly or with compression.'

 

All Ken was asking was how can you say that you can capture losslessly when you have an A/D conversion in there? The A/D is going to degrade the signal

 

I hope that this will be cleared up now

 

regards

 

ben

 

-----Original Message-----
From: Jason Lee [mailto:jasonjlee@xxxxxxx]
Sent: 28 May 2002 12:22
To: ukha_d@xxxxxxxSubject: Re: [ukha_d] Lossless Compression Help!

I never mentioned having anything extraordinary in this setup!

 

Im now attributed sky digital I don't even have!

 

Those are all things ken has thrown in.

 

I understand that the feed into my pc is not straight from the back of the camera the taking pictures.

Thats obvious. I never stated any different.

 

All I said is that once I have the signal inside the PC compression is lossless.

 

I don't pretend to defy the laws of a/d d/a conversion. I took that as read.

 

If you look back at my original post, I also capture from the s-vhs deck which has no digital artifacts as its not digital.

 

Again I'll attempt to clarify the value of lossless compression.

 

Mpeg is based on the same concept as jpeg.

 

If you take a jpeg and uncompress it and compress it again and uncompress it.

 

You have more noise than the original. You even probably have more noise than the 1st jpeg.

 

Thats my point.

 

Once it reaches where I can control it, I don't immediately add noise by capturing in a compressed format.

 

I edit, crop, and titles, effects all losslessly. Please, this is common practice!

 

The Last stage is mpeg2 compression. Sometimes I keep the lossless compressed material as well, which is big but thats life.

 

Now, surely this is clear now guys.

 

Jason

 

 

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

From: Ben McCormack

To: ukha_d@xxxxxxx

Sent: Tuesday, May 28, 2002 12:02 PM

Subject: RE: [ukha_d] Lossless Compression Help!

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 -----

From: Kenneth Watt

To: ukha_d@xxxxxxx

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

To: ukha_d@xxxxxxx

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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