[opendtv] Re: JPEG2000?
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 26 Jul 2006 08:46:04 -0400
At 6:19 PM -0400 7/14/06, Manfredi, Albert E wrote:
>Cliff Benham wrote:
>
>> The compression rate for JPEG2000 is incredible. An
>> over 2 hour theatrical release takes only 250 G. All
>> I frames, so no time fractured macro blocking.
>
>JPEG2000 uses a wavelet transform vs discrete cosine transform, and it
>offers a lot of flexibility, like scalability. But, as we saw on here in
>previous threads from time to time, it doesn't seem to be any slam dunk
>for compression efficiency, compared with alternatives. Or for
>complexity in encoding and decoding.
Compression efficiency must be assessed based upon the application.
Clearly, it is unlikely that an INTRA-frame codec - designed to
maintain pristine image quality - will produce bitstreams that are as
compact as an INTER-frame codec designed for limited bandwidth
emission channels.
As for complexity, intra-frame codecs typically use only a small
fraction of the computational power needed for inter-frame codecs.
This is true for the new chips that are being used for JPEG-2000 and
other wavelet variants, just as it was true for the original JPEG
chips, which were fast enough to allow their use for Motion-JPEG
encoding of video at 30p/60i, more than a decade ago.
It is worth noting that analog devices developed a wavelet codec chip
in the early '90s, but DCT based JPEG won the day in early non-linear
editing systems. It is also worth noting that storage efficiency has
grown so dramatically that it is commonplace for non-linear editing
systems to use uncompressed source today, even for HD projects - a
250 GB drive costs little more than $100 today.
>
>This suggests that its use for motion pictures would not result in
>better compression efficiency than M-JPEG, which of course is less good
>(in that regard) than MPEG-2 (H.262). And less good than H.264, as well.
There are certainly trade-offs when looking at the compression
efficiency and delivered image quality of DCT-based M-JPEG versus
wavelet-based JPEG 2000 and related codecs optimized for video/film.
In my personal experience, these codecs are roughly comparable at
similar data rates, however the compression artifacts of the DCT are
more visible than the loss of detail that occurs with the wavelet
transform. Hollywood has voted, and wavelets have won when it comes
to theatrical exhibition.
M-JPEG is NOT less good that MPEG-2 when operating as an INTRA-frame
codec - they are essentially identical. If you use some inter-frame
compression it may be possible to produce a slightly more compact
bitstream, at the cost of added computational complexity. Frankly, it
is not worth it to add this complexity, given the cheap cost of
storage. HDV is the exception to this rule; it uses inter-frame
MPEG-2 compression to squeeze HD (rather poorly in my opinion) onto a
25 Mbps tape-based recording format.
>
>Here's an article that compares the coding efficiency of various
>still-image codecs:
>
>http://jj2000.epfl.ch/jj_publications/papers/004.pdf
>
>The conclusions paragraphs say:
>
>"The results presented in previous sections show that new standards do
>not provide any truly substantial improvement in compression efficiency
>and are significantly more complex
>than JPEG, with the exception of JPEG-LS for lossless compression.
>However, from a functionality point of view JPEG 2000 is a true
>improvement, providing lossy and lossless compression, progressive and
>parseable bitstreams, error resilience, random access, region of
>interest and other features in one integrated algorithm.
Agreed. the compression efficiency is similar, but the added features
are VERY significant. We will soon see these features exploited in
many web applications, especially the region of interest feature,
which allows only the bits needed for more detail in the region of
interest selected to be sent to the browser requesting the
information.
>As to the 250 GB storage for a 2 hour movie, using JPEG2000. I would
>expect the result to be good for quality, and JPEG2000 is probably great
>as a future-proof digital format in archives. But compared with a 2 hour
>HDTV show, where HD uses every bit of the 19.39 Mb/s the entire time,
>the MPEG-2 file would be just 17.45 GB.
Apples and oranges. The article failed to mention that the resolution
for the movie may be significantly higher than the 1920 x 1080 used
for emission formats today. 4K x 2K is the goal here, and wavelets
deal very efficiently with whatever information may exist at these
higher frequencies.
>
>So you're talking about over 14X the size of the MPEG-2 file. Depending
>on how much greater the resolution of that JPEG2000 file was meant to
>be, a 14X increase may or may not be impressive.
I'll agree with Bert that there is nothing impressive about a 250GB
movie file. We have understood these trade-offs and where each
compression technology is best used for more than a decade.
Regards
Craig
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