HQDering mod v0.3

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### HQDering mod v0.3 by mawen1250
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### Requirements: masktools v2.0a48, RemoveGrain v1.0pre, dfttest v1.9.2
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### Applies derining by using a smart smoother near edges (where ringing occurs) only.
###
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Function HQDeringmod(clip input, clip "smoother", int "mthr", int "mrad", float "sigma", float "sigma2", int "sbsize", int "sosize") {

 mthr     = Default(mthr,   80     )   # threshold of edge mask, lower  value means more aggressive processing.
 mrad     = Default(mrad,   2      )   # radius    of ring mask, higher value means more aggressive processing.

 sigma    = Default(sigma,  64.0   )   # dfttest: sigma.
 sigma2   = Default(sigma2, sigma/8)   # dfttest: sigma2.
 sbsize   = Default(sbsize, 4      )   # dfttest: length of the sides of the spatial window.
 sosize   = Default(sosize, 3      )   # dfttest: spatial overlap amount.

 smoothed = Defined(smoother) ? smoother : input.dfttest(Y=true, U=false, V=false, sigma=sigma, sigma2=sigma2, sbsize=sbsize, sosize=sosize, tbsize=1, lsb_in=false, lsb=false)

 prewittm      = input.mt_edge("prewitt", mthr, 255, 0, 0, V=1, U=1)
 fmask         = mt_hysteresis(prewittm.RemoveGrain(4, -1), prewittm, U=1, V=1)
 omask         = mrad > 1 ? fmask.mt_expand(U=1, V=1) : fmask
 omask         = mrad > 2 ? omask.mt_expand(U=1, V=1) : omask
 omask         = mrad > 3 ? omask.mt_expand(U=1, V=1) : omask
 omask         = mrad > 4 ? omask.mt_expand(U=1, V=1) : omask
 imask         = fmask.mt_inflate(U=1, V=1).mt_inpand(U=1, V=1)
 ringmask      = omask.mt_lutxy(imask.mt_invert(U=1, V=1), "x y * 255 /", U=1, V=1)

 return mt_merge(input, smoothed, ringmask, luma=false, Y=3, U=2, V=2)

}