Before I post a bug report, I'd like some confirmation of what I've found. There
seems to be a (very conspicuous) bug in the various noise functions. It exhibits
itself as banding after a certain _negative_ distance, along any axis, from the
origin. This distance varies depending on the noise function: it is around
78.125 for 1/f noise (granite), 312.5 (78.125*4) for DNoise and Agate noise, and
around 10000 for Perlin noise (bozo, bumps, spotted).
Furthermore, in 1/f and DNoise the bug seems to become more pronounced at
78.125*2 and 78.125*4
I've tested this on POVWin 3.1g (Watcom and VC compile) and the Superpatch (3.1e
codebase)

//BEGIN EXAMPLE SCENE

camera{
    orthographic
    location y*5
    up y*5*.75 right x*5
    look_at 0
}

//1/f noise (granite)
#declare Tex1=
pigment{
    granite
    color_map{[0 rgb 0][1 rgb 1]}
    translate 78.13*x //First signs of banding
    //translate 156.25*x //More pronounced
    //translate 312.5*x //Even more pronounced
    scale 5
}

//Perlin noise (Bozo & Bumps & Spotted)
#declare Tex2=
pigment{
    bozo
    color_map{[0 rgb 0][1 rgb 1]}
    translate 10000*x
    scale 1
}

//DNoise (turbulence)
#declare Tex3=
pigment{
    gradient x
    color_map{[0 rgb 0][1 rgb 1]}
    translate 312.5*x //Banding starts
    //translate 625*x //Becomes more pronounced
    scale 1
    turbulence 1
}

//Agate turbulence
#declare Tex4=
pigment{
    agate
    color_map{[0 rgb 0][1 rgb 1]}
    translate 312.5*x //Banding starts
    scale 5
}


plane{
    y,0
    pigment{Tex1}
    finish{ambient 1}
}

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