interpolation rectangle 120 a diagonal interpolation is conducted to find d the interpolated value at the point 140 on the diagonal line 145 according to as described below the diagonal interpolation is conducted whether the interpolation target 110 is below or above the diagonal line 145 in fig1 a t gt f indicating that the interpolation target 110 is above the diagonal line 145 in addition a horizontal interpolation is conducted along the top horizontal line 150 to find h the interpolated value at the point 155 a final interpolation is then conducted to find the final gl value f using the earlier results d and h fig1 b is a graph illustrating an embodiment of the novel interpolation technique when the interpolation target is not above the diagonal i e when t u2266 f as before a diagonal interpolation is conducted to find d the interpolated value at the point 160 on the diagonal line 145 in addition a vertical interpolation is conducted along the vertical line 170 to find v the interpolated value at the point 175 a final interpolation is then conducted to find the final gl value f at the target interpolation point 190 using the earlier results d and v fig2 is a flow diagram of one embodiment of a method of interpolating a final gl using entries taken from a from to lut the method begins in a start step 210 in a step.