plrgbhls: Convert RGB color to HLS 

DESCRIPTION:

    Convert RGB color coordinates to HLS 

SYNOPSIS:

plrgbhls(r, g, b, p_h, p_l, p_s)

ARGUMENTS:

    r (PLFLT, output) :    Red intensity (0.0-1.0) of the colour 

    g (PLFLT, output) :    Green intensity (0.0-1.0) of the colour 

    b (PLFLT, output) :    Blue intensity (0.0-1.0) of the colour 

    p_h (PLFLT *, input) :    Pointer to hue, in degrees on the colour
    cone (0.0-360.0) 

    p_l (PLFLT *, input) :    Pointer to lightness, expressed as a
    fraction of the axis of the colour cone (0.0-1.0) 

    p_s (PLFLT *, input) :    Pointer to saturation, expressed as a
    fraction of the radius of the colour cone (0.0-1.0)