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I am trying to find out which algorithm is used to resize image when I called sips -z function from the terminal mac os x yosemite.

It seems Lanczos algorithm used in vImage framework. And it is claimed as "vImage’s geometry transforms usually look better than what you get from Quartz 2D or Core Image". Does SIPS uses Quartz 2D, Core Image, vImage or something else?

https://developer.apple.com/library/prerelease/content/documentation/Performance/Conceptual/vImage/GeometricOperations/GeometricOperations.html

user2616232
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  • It's odd that it claims vImage's Lanczos geometry transforms usually look better than ... Core Image, as you can use a [Lanczos scale transform](https://developer.apple.com/library/mac/documentation/GraphicsImaging/Reference/CoreImageFilterReference/index.html#//apple_ref/doc/filter/ci/CILanczosScaleTransform) in Core Image. – user1118321 Jul 01 '16 at 05:07
  • Don't know much about sips, but you can usually answer questions like this by running a Time Profile in Instruments on a heavy workload and look at the backtraces of the heavy time using functions to find out who is doing what. (If the workload is on the GPU, you might need to run system trace instead to see it.) – Ian Ollmann Jul 06 '16 at 02:10

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