x, y)</code> specify the desired interpolation point. Then define: <pre>
    XF = floor(x)
    YF = floor(y)
</pre> </dd></dl>
<dl class="section user"><dt></dt><dd>The interpolated output point is computed as: <pre>
 f(x, y) = f(XF, YF) * (1-(x-XF)) * (1-(y-YF))
          + f(XF+1, YF) * (x-XF)*(1-(y-YF))
          + f(XF, YF+1) * (1-(x-XF))*(y-YF)
          + f(XF+1, YF+1) * (x-XF)*(y-YF)
</pre> Note that the coordinates (x, y) contain integer and fractional components. The integer components specify whic