[x264-devel] [PATCH]adaptive lowpass

[Loren Merritt]

Is it better to multiply the coeffs by some fraction, rather than 
subtracting a constant (in the case of deadzone) or increasing lambda (in 
the case of trellis)? That wouldn't be strictly a lowpass, but it would 
also reduce the bits in high frequencies by changing coefficient magnitude 
rather than step size, and would be closer to RD optimal.

On Wed, 27 Jun 2007, Eric Viscito wrote:

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

The quantizer almost always rounds down, so increasing the quantization 
step size also reduces the average coefficient magnitude.

> 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.

It can adapt the amount of bits spent in high vs low freqs. But the CQM is 
still constant, so the LPF vs quantization noise is still not adaptive.

--Loren Merritt
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