The paste stage spent its host time on three full-canvas passes per frame. The face warp now runs on the device with cv2's own fixed-point convention (the matrix inversion of warpAffine, the 1/1024 pre-scale, the 1/32 tap grid, the (+512)>>10 rounding), the mask warp reuses the one batched grid sliced to the face ROI, and the blend and the quantizing tail run inside that ROI. The frame-global maximum branch is kept: a near-black frame falls back to the full-canvas path, which stays bit-exact by construction.
Measured over 48 frames at 720p on CUDA: the paste call's process CPU time falls 20% (38.74 -> 30.92 ms/frame), the host-device transfers shrink 6.66x (the blended canvas download by 85%), and the result is bit-identical to the full-canvas path on the smooth and the noise corpus, at interior and edge-touching ROIs.
WildAi
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