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h264 compression issues

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ben rollason
h264 compression issues
on Oct 28, 2005 at 3:07:46 pm

Has anyone had a chance to work with H.264 compression? This is the new mpeg 4 based compression format that is included as part of Quicktime 7 and is much touted as the industry standard for everything video, from 3G mobile phones to Blu-Ray - HD DVD.

I've just got Quicktime 7 and have been running some tests. I've found however that despite astoundingly low data rates and clear, sharp video there are problems.

The most obvious is the well documented gamma problem while compressing RGB files, where the images appear to become washed out and desaturated. I've found that first rendering the source material into a YUV format then compressing overcomes this problem. It is time consuming though.

Also there's the issue that the codec is sharp enough to render artefacts from prior compressions rather clearly. This means that it's easy to notice the difference between something compressed from a digibeta master and something compressed from a DV copy of the same. While H.264 seems to add its own fair share of compression artefacts (undesirable visual side effects), these somehow don't mask the artefacts already present from other codecs. This means we're going to have to start archiving the uncompressed digital files if we want to go that extra quality mile.

But the main problem I've found is that of banding - the effect where gentle gradients are rendered as discernable bands of colour, due to a limited colour palette. It doesn't seem to make any difference how high you raise the data rate, the effect doesn't really disappear. It appears to be inherent in the codec. Nor are preprocessing tricks, such as dithering the image using grain or noise especially effective, although they help. I wonder if there's any kind of intelligent dithering that can be done to minimise the banding.

Any ideas anyone?



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Ben Waggoner
Re: h264 compression issues
on Oct 31, 2005 at 4:26:06 pm

Color space issues seem to have been improved from 7.0 to 7.0.3 - do you have the current version?

I've been using Popwire's Compression Master for H.264 encoding, which doesn't have that issue.

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