Here you are your avisynth function:
function lowchromanoise (clip clip) {
clip
SeparateFields
Spline16Resize(clip.width/4,clip.height/2)
Spline16Resize(clip.width,clip.height/2)
Weave
MergeLuma(clip)
}
don't know if using other spline, or different resizer at all, will increase the quality, though... hope to find out some other capture to test it...