[x264-devel] [PATCH]adaptive lowpass

[Eric Viscito]

> Loren Merritt a écrit :
> Aside from being adaptive, does lowpass provide any benefit over a CQM
> which quantizes the high frequencies more?

I don't think this question was directly answered.  Your question sounds a
bit general, so please pardon me for a general response not directly
related to the particular patch.

If I understand it correctly (I haven't looked at the patch), the LPF
reduces the magnitude of high frequencies, reducing the energy in the
quantizer's output (hence fewer bits), but smoothing the image.

The CQM quantizer reduces bits by injects more quantization noise into the
high frequencies without changing the magnitude of those frequencies.

The reduction in bits in the two schemes comes with different types of
distortions.

So the *adaptive* LPF provides a means to trade off the two types of
distortions.  If the adaptive filter control is sound, this can be a
benefit.  My guess is that the right kind of adaptive filter control would
have a model of human visual perception built into it.  Roughly speaking,
this would filter "noisy textures" more and doesn't touch edges, lines and
other (admittedly hard to define ) "structure".

Eric Viscito

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