open-source NEON optimizations

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Well, this is true that OpenCV may get open-source NEON optimizations someday. But they should be contributed by somebody (company or individual), and core team doesn't have plans (and more importantly resources) to work on these optimizations. So, no guarantees, but the possibility exists...

So, if you need open-source NEON code for you demos, I wouldn't wait on your place... It may take years to get them to the OpenCV. Instead, you can work on your own, and become a first contributor =) Prefetches and vectorizations are able to give you a good speedup, typically 3x in comparison to the original code. But of course it depends on algorithm.

If you don't need the source, you can use NEON optimizations that are available in binary form as a part of OpenCV for Tegra (official docs, introductory talk, sample app, relevant article). This way you can try to estimate what speedup is expected in your application, but you'll need a Tegra 3 device for these experiments. Alternatively, you can try to use FastCV, but again, you need a Qualcomm device, and you'll have to rewrite your application.

That's basically all I have to say. NEON code contribution is not going to happen in a short term, but we have a chance to see it in 3.0. In the meantime I would recommend you to experiment with your own code, or try optimized libraries like OpenCV for Tegra, provided in the binary form.