[M4IF Technotes] Downsample filters

[Yossi Shain]

Gentlemen,
Looking at the filter taps for downsampling the luminance componenet of an
image by 1/2 or 1/4, the mpeg4 Pisa document (ISO/IEC JTC1/SC29/WG11 N3908,
January 2001/Pisa, Section 2.2.2, page 17) recommends using a 13-tap or
15-tap filter. I wanted to know whether these filters offered noticable
improvement in quality over other filters for qcif video?
If yes, was this a result of a crisp downsampled image, or a reduction in
noise that enabled better compression?