k32u kSpot_InterpolateSobelvZcSpotCentre	(	kSize	lastPositiveIndex,
		k16s	lastPositiveGradient,
		kSize	firstNegativeIndex,
		k16s	firstNegativeGradient
	)

Integer math Focalspec spot centre interpolation.

Parameters

lastPositiveIndex	Last index at which gradient filter value > 0
lastPositiveGradient	Gradient value at lastPositiveIndex
firstNegativeIndex	First index at which gradient filter value < 0
firstNegativeGradient	Gradient value at firstNegativeIndex

Returns

interpolatedCentre Interpolated centre position. 11 MSBs are integer component & 9 LSBs are fractional