- -hwa.min-s Filter - Filmhwa

def filmhwa_min_s(I, r=4, sigma_s=2.0, sigma_c=0.1, s=0.25, alpha=0.6, beta=0.15):
    I_lin = to_linear(I)
    O = zeros_like(I_lin)
    for p in pixels(I_lin):
        W = window(p, r)
        ws = exp(-dist2(p,W)/(2*sigma_s**2))
        dc = color_dist(I_lin[p], I_lin[W])
        wc = exp(-dc**2/(2*sigma_c**2))
        w = ws * wc
        S1 = w.sum()
        S2 = (w**2 / I_lin[W]).sum(axis=0)  # channel-wise
        H = (S1**2) / (S2 + 1e-8)
        m = H.min(axis=channel)
        for c in channels:
            O[c,p] = (1-s)*H[c] + s*(m + alpha*(I_lin[c,p]-m))
    if beta>0:
        guided = guided_blur(I_lin, r=2)
        residual = I_lin - guided
        O = O + beta * residual
    return to_srgb(O)

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