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RE: dvd colour sampling question

picknmix — Sun, 17 Aug 2008 14:42:24 GMT

I'm curious. Why do you think this aspect of Mpeg-2 has any bearing on why ITV looks so bad?

RE: dvd colour sampling question

Slipstreem — Sun, 17 Aug 2008 00:39:00 GMT

I don't have an answer to that one although, looking at the problem from a purely mathematical point of view, there's no logical reason why it couldn't be. I'd expect the noise level to be slightly higher as it would contain the dither and quantisation noise from the two other channels added together. I'm only guessing though. It's something I've never looked into. :)

Cheers, Slipstreem. :cool:

RE: dvd colour sampling question

maticus2 — Sat, 16 Aug 2008 23:51:34 GMT

I might look in to the FFshow app as Im going to be toying with VGA on my TV in the near future. hers another thing If green isn't sampled and is worked out later is it subject to the same colour sampling resolution as red and blue?

RE: dvd colour sampling question

Slipstreem — Fri, 18 Jul 2008 15:52:02 GMT

The idea may have been formulated around the way the human eye works in relation to colour perception. We only need roughly one-third as much luminance accuracy in the colour content of a signal (the chrominance as it's officially termed) as in the luminance region. Analogue broadcast TV does the same thing. I guess that digital Freeview is probably doing the same thing as it uses MPEG-2 so is almost identical to DVD but at a slower bitrate. Domestic analogue VCRs rely on a similar technique to enable them to encode colour to magnetic tape efficiently at relatively low tape speeds.

The lowering of colour detail still allows for the same general crispness if the luminance signal still has enough bandwidth to play with. After all, you see just as much detail in a black-and-white film (potentially more actually) as you do in a colour film, so it obviously works. DVD would probably look much worse if it didn't do this to be honest.

One of the handy side-effects of bringing this topic up is that ffdshow can perform pretty much any image correction you're likely to need if you think that the master has minor deficiencies. That's why it's a wise move for the fussier of us to use a PC media centre as a DVD player. It gives you an enormous amount of control over the image quality in real-time once you've learned how to use ffdshow. :)

Cheers, Slipstreem. :cool:

dvd colour sampling question

maticus2 — Fri, 18 Jul 2008 15:27:19 GMT

I`ve been swoting up on how DVD`s work and I was surprised to find that dvds only show colour at half to one quarter the resolution of the original image (witch now explanes why ITV1 looks so bad). so I was wondering why does colour sampling rates have to be cut by factors of 2? isn't there a more flexible and forgiving system in use?