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Denoise can attempt to use GPU acceleration. You can activate this mode by adding --override gpuIndex 0 to the command line, where the number indicates which GPU to use.  In a single-GPU system, this will always be 0. If no compatible hardware is found it will failover to CPUs. Using the GPU requires CUDA 7.0 5 (compute capability 2.0 or later) and a capable graphics card with support.

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