Sum-of-absolute-difference calculator for motion estimation using inversion and carry compensation with full and half-adders

摘要

A specialized Sum-of-Absolute-Difference (SAD) calculator for motion estimation uses inversion rather than 2's complementing. The absolute-value operation of each pixel-pair difference is performed by a bit-wise inversion rather than a complement. This reduces delay since the adder/incrementer propagation is eliminated. The increment needed to adjust for inversion rather than 2's complementing is accomplished by using the carry inputs to the summing and final adders that generate the sum of the absolute differences. When 2-input final adders are used for summing, a total of k−1 adders are used to sum k absolute differences. One additional increment is needed since only k−1 adders are available. A reduced half-adder rather than a full adder is inserted between the summing and final adder for this remaining increment. Propagation of carries between bit positions in a full adder can be avoided using the half adder. The final adder generates the final sum (the SAD) by adding the sum and carry bits from the half-adder array and propagating the carries.