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Don't the discrete cosine transforms that underlie most video codecs automatically remove noise, as noise is generally high frequency?
by suzumer 4y ago
Don't the discrete cosine transforms that underlie most video codecs automatically remove noise, as noise is generally high frequency?
- brucethemoose2 4y agoNot as well as more computationally expensive algorithms that take more frames/wider areas into account. And as the blog mentions, noise "tricks" the encoder into blowing its bitrate budget on preserving noise that looks like detail, instead of something more useful.
- psychphysic 4y agoDon't think so, I read somewhere (like HN) that Netflix purposefully removes noise, transmits it and readds it locally saving some 30% bandwidth. And the HBO intro is a nightmare.
- deleted 4y ago[deleted]
- bob1029 4y agoThe DCT is lossless. It's the subsequent quantization step that chops certain frequency components.
- orlp 4y agoFurthermore it is a common (even logical) misbelief that chopping out the higher frequencies after a Fourier transform is filtering them out. Unfortunately this merely zeroes the exact frequencies used to define the bins but leaves a lot of high frequency signals. You need a proper low-pass filter.