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Old 04-18-2008, 11:30 PM   #1
DocNovak DocNovak is offline
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Default "lossless" video compression

With all of this talk about DTS-HDMA (a "lossless" audio compression) v. uncompressed PCM, I started to think about video. So my question to all of the people out there that are much smarter than I is this: Is it possible to have a "lossless" video compression? As far as I understand it from my own research, with current encodeing methods you would need an extremely high bitrate to end up with anything anywhere near "lossless", but it might be possible in the future to develope a new codec that could result in lower bitrate (similar to those we see in video today) "lossless" video compression. So am I way off here? I searched the forums here to see if I could find anything about it but came up with zilch. So if anyone knows the answer I would appreciate it.


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Old 04-18-2008, 11:54 PM   #2
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Don't really know much about it, but here is a good read/start. See the video section.
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Old 04-19-2008, 04:23 AM   #3
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I have given some basic calculations in this thread.

http://forum.blu-ray.com/showthread.php?t=3338&page=7
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Old 04-19-2008, 03:03 PM   #4
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Thanks for the info. So it is possible, but not practical at this time given that a 2 hour movie would be around 300Gb using a "lossless" video codec. So my next question is, where do we go from where we are currently for the next home video format. Do you go for 4k resolution or do we go for lossless video compression, or for some compremise between the two?
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Old 04-19-2008, 03:25 PM   #5
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Quote:
Originally Posted by DocNovak View Post
Thanks for the info. So it is possible, but not practical at this time given that a 2 hour movie would be around 300Gb using a "lossless" video codec. So my next question is, where do we go from where we are currently for the next home video format. Do you go for 4k resolution or do we go for lossless video compression, or for some compremise between the two?
As it stands people aren't see a lot of compression artifacts in Blu-ray. So, what would lossless gain?

I think the first step is to improve colour by going 4:4:4/36-bit/expanded gamut. Expanding the resolution, gamut and depth of colour would be a big boost. And it's far more accessible for common sized sets and sitting distances than higher luminance resolution.

Low resolution colour has been the compromise all along. NTSC has lower resolution colour too (4.2 MHz luma combed with 1.1/1 MHz for colours) (hence VHS and Laserdisc) and DVD uses 4:2:0 the same as Blu-ray.

With colour improved, then any move to 4K would incorporate that. If we were to move to 4K first I'd expect them to cheat on the colour again.

Gary

Last edited by dialog_gvf; 04-19-2008 at 03:28 PM.
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Old 04-19-2008, 04:31 PM   #6
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Quote:
Originally Posted by dialog_gvf View Post
Low resolution colour has been the compromise all along. NTSC has lower resolution colour too (4.2 MHz luma combed with 1.1/1 MHz for colours) (hence VHS and Laserdisc) and DVD uses 4:2:0 the same as Blu-ray.
BD uses 4:2:2, last I checked.


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Old 04-19-2008, 06:29 PM   #7
dialog_gvf dialog_gvf is offline
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Quote:
Originally Posted by WriteSimply View Post
BD uses 4:2:2, last I checked.


fuad
Nope.

4:4:4 - Colour is same resolution as luminance.
4:2:2 - Colour has same vertical resolution and half horizontal
4:2:0 - Colour has half vertical and half horizontal resolution.

Basically, with 4:2:0 there is a U and V sample for the middle point of a 2 x 2 luminance pixel block.

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Old 04-20-2008, 02:05 PM   #8
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What does this mean? Blu-ray is 4:2:2 colour or not. In some HD specs, I could remember seen 4:2:2.
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Old 04-20-2008, 02:26 PM   #9
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Quote:
Originally Posted by DocNovak View Post
Thanks for the info. So it is possible, but not practical at this time given that a 2 hour movie would be around 300Gb using a "lossless" video codec. So my next question is, where do we go from where we are currently for the next home video format. Do you go for 4k resolution or do we go for lossless video compression, or for some compremise between the two?
Video would be always compressed for a foreseeable future as disk storage requirement do not permit uncompressed video. Anyhow, it is debatable whether the quality gain could be justified for a home environment to go beyond blu-ray. Yes, very large commercial screens would gain from higher bit rates and resolutions. Even for commercial applications, there are many steps to take before uncompressed video.

IMO blu-ray would be around for some time for home use. I have seen many threads related to this:

http://forum.blu-ray.com/showthread....050#post777050
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Old 04-20-2008, 09:07 PM   #10
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Quote:
Originally Posted by syncguy View Post
What does this mean? Blu-ray is 4:2:2 colour or not. In some HD specs, I could remember seen 4:2:2.
Sometimes, players reference 4:2:2 color, such as the upcoming Panasonic BD50 which claims that it "upsamples" to 4:2:2, but BD on-disc is 4:2:0 (just like DVD before it). This is partially why they are able to compress the video stream to the degree they are. Apple's ProRes 422 codec, for example, uses 4:2:2 color, takes up around 220Mbps at 1080p resolution (in its highest quality mode) -- and that's just for a so-called "visually lossless" format... not a truly lossless one.

HDCAM SR records 4:2:2 color 1080p to tape at a video bitrate of 440Mbps, and also isn't even lossless, though at that bitrate it's about as close as you can get.
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Old 04-22-2008, 02:05 AM   #11
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Just some speculation off the top of my head. As far as I know, all video compression codecs are lossy in SOME way, just like JPEG pics. .GIF, on the other hand used a lossless compression, which why they tend to be larger than JPEG. But .GIF was MANY times smaller than .BMP, .TIFF, .PCX, or any other non compressed format.

With that being said, digital film is about 4096 lines of resolution, so some detail gets lost in compressing down the video stream to 1080p. Even the transfer of 4000 line film to blu-ray still yields some loss in quality.

To be technical, we are still only seeing about 1/4 of the potential picture. But how much of that are we going to notice? I still believe holographic disc can bring us lossless video, or something near it.

Sony demoed a 4K HDTV screen, so it may be an indicator of the industry leaning in that direction. At least on a pro-sumer level. The general consumer won't see it any time soon.

In reality, all we are really watching are stunning approximations.
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Old 04-22-2008, 07:30 AM   #12
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The amount of data reduction in video compression does not directly relate to the amount of quality reduction. For example, if the compressed video is 50% smaller than the original, that does not mean the quality reduction is 50%. The quality reduction could be only 10% for some cases and in some other cases it could be 30%. The quality reduction is mainly depend on the amount of motion involved in the content because compression algorithms determines the data for a frame based on the amount of change of that frame in comparison to the previous frame. Due to this reason, fast moving content requires less compression (e.g. sports) in comparison to a talking-head to achieve same level of perceivable picture quality.
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Old 04-22-2008, 08:53 AM   #13
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All DVDs, HD DVDs and Blu-ray discs store video in YCbCr 4:2:0 format, which is described very well by Dialog.

When the decoder performs the video decoding, it also perfroms the first of two stages of chroma up-sampling and actually outputs 4:2:2 video. This is always done within the player.

A second stage of up-sampling brings this up to YCbCr 4:4:4, then this is transcoded to RGB for display. These processes may be performed in the player, or externally, but this shouldn't make much difference.

The level of video compression on BD is very high (around 20:1 to 50:1) so lossless is probably a very long way off. It may not even be desirable. Where there is a limit on how many bits you can use, you want to make best use of them to achieve the best picture, not necessarily the least amount of compression.

I agree that we would want to use greater depth of modulation before we improve anything else.

regards, Nick
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Old 04-22-2008, 09:16 AM   #14
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The most of perceivable picture quality depends on the resolution of the luminance but not colour. Hence could get away with higher amount of colour compression and still produce a better quality picture. If luminance resolution is reduced to a level of colour the perceivable quality will degrade.
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