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View Full Version : MPEG-2 / avc / vc-1 picture quality question

jcar
30th August 2007, 14:24
I don't know if this is the correct place for this thread, please move it if it's not!


I've been reading a lot of stuff regarding the whole BD vs HD-DVD and noticed a couple of people complaining about "noise" in blu-ray movies. I have a ps3 but only 4 titles so I can't really compare with hd-dvd or other BD titles.

Anyway, one of them even said that this was due to MPEG-2.


This "noise" everybody talks about is like little "dots" you can notice in the picture. Casino royale is almost perfect but in Pearl Harbour I can notice such things.

Anyway, I've been wondering if the codec used has anything to do with it. And I would like the most scientific explanation possible, hehe.

If I'm not mistaken, the picture quality doesn't depend on the codec but on the compression rate. A raw video can be stored in less space, and quality is loss is to be expected, and it's related to the bitrates and I suppose the spatial/time frequency in the video. The faster and more detailed the picture, the more artifacts will be noticeable at a given bitrate, right?

But since bd and hd-dvd are designed for 1080p high bitrates and have enough storage space, how can people claim there's noise?

If you have the same source, and encode it in the three formats to achieve a comparable quality in the three formats, can any encode look better than the others? The file sizes of avc and vc-1 are smaller, but that doesn't mean mpeg-2 will look bad.

So ... if anybody knows something about this, please explain it to me! :stupid:
Sharktooth
30th August 2007, 15:01
hint: ever heard of DCT noise?;)
jethro
30th August 2007, 16:45
Lossy nature of codecs in next-gen DVD means they encode pixels with digital noise (error, difference from original). That is what Sharktooth said.
There is also noise in movies which may result from bad transfer or bad original copy in case of older films and finally noise can be purposefully added by the studio.There is also film grain.

I think you misunderstood something about codecs quality - quality does depend on the codec - new codecs, like x264, are more efficient than for example mpeg2 - they are more optimal and better at finding ways to save bitrate. This means that at the same bitrate they should look better (because they can use the saved bits to improve picture).
Also, codecs have different looks and their specific artefacts (but it may be hard to see at these bitrates because codecs often reach transparency).
jcar
30th August 2007, 19:21
I know what you mean hethro, at a given bitrate, the new codecs will have better picture quality than mpeg-2 at that bitrate. Because of the better compression.

But that doesnt mean mpeg-2 can't achieve that picture quality with a higher bitrate, even if it's double the bitrate.


About the DCT noise. Is it noise per se, or a distortion due to the compression?
Sharktooth
30th August 2007, 19:51
it is noise due to quantization.
however, yes, mpeg-2 can reach the same quality at a higher bitrate... but what's the point? at that bitrate a more advanced codec would provide an even better quality...
there's no reason in using an old tech when you have a better one. infact BDs made using MPEG-2 look like shit.
Sagittaire
30th August 2007, 20:09
there's no reason in using an old tech when you have a better one. infact BDs made using MPEG-2 look like shit.

Well in this case it's perhaps (certainely in fact) because MPEG2 implementation is not really good.
jcar
30th August 2007, 20:40
That's why I mean. HD-DVD fans seem to believe that MPEG-2 blurays look like shit because it's mpeg-2. But I think it's a sad coincidence. MPEG-2 is perfectly capable of delivering the same picture quality, albeit the higher bitrates, and there are mpeg-2 that look perfect that go unnoticed.
jcar
30th August 2007, 20:41
it is noise due to quantization.
however, yes, mpeg-2 can reach the same quality at a higher bitrate... but what's the point? at that bitrate a more advanced codec would provide an even better quality...
there's no reason in using an old tech when you have a better one. infact BDs made using MPEG-2 look like shit.

THat's true, and that's what I believe. But the reason those bds look bad isn't mpeg-2 blame. It's more like due to bad transfers and bad compression.
Golgot13
30th August 2007, 22:31
there's no reason in using an old tech when you have a better one. infact BDs made using MPEG-2 look like shit.

Hi all,

Yes and no for old technology. BD using MPEG2 was shit because the video source and
preprocessing video of encoding used by authoring studio was shit, "rubbish"...
At 25Mbps-30Mbps, MPEG2 is near of VC1 and H264.

And about MPEG2 with movie grain, yes it's possible to have good MPEG2HD file with grain preserve
at 9Mbps ( 1920x1080 at 24P ) with HDDVD or BD restrictions. Some good expert (I think best experts)
can made this "challenge"....

I hope MS will put some video with grain to see really what it's the difference
between best encoders of different codecs.

Last: yes VC1 and H264 can do better than MPEG2 but VC1 and H264 are not optimized like best MPEG2 encoder... ;)
Sharktooth
31st August 2007, 02:13
Yes, maybe i should have added that MPEG-2 can be able to deliver a comparable to VC-1/h.264 picture with the BD/HD-DVD limitations, but not on long movies.