Running multiple CascadeClassifiers - possible to reuse scaling?

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I'm throwing the kitchen sink at recognising faces by running every *face*.xml CascadeClassifier on every frame of a video (and the eyes, mouth, and smile finders!) to see which performs the best. I noticed that the docs mentioned the scaling as a large chunk of the CPU effort, which got me wondering:

1. Is it really? Or is the majority of the time in the actual face-detecting steps for each scaled size?
2. If it IS a big part of the time, can I somehow reuse the scaling step across all my various classifiers?

If there is an easy way to do it (like pre-calculating a pyramid?) - great! If not, no worries, this doesn't have to be realtime.

Java/Kotlin,OpenCV 3.x