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You don't have to actually do any scaling of dimensions with -vf scale - just set width, height =-1
There are other ways, such as using -pix_fmt (e.g. yuvj420p "j" would be full range) , sws flags, -vf colormatrix (to change in YUV, it's like avisynth's colormatrix). I don' t know if any of them are the "proper" way
But it's always changing in ffmpeg land - it's hard to keep up unless you're actively checking it. At one point those scale options didn't work properly, but maybe 1/2 year ago they did, and there was at least 1 build in between where it didn't work. There are slight "gotchas" for each method, sometimes quality issues. For example, even though -vf colormatrix is ported from avisynth, it tends to yield lower quality. And produces slightly different results from ffmbc's -vf colormatrix yet all are derived from the same code! Theoretically it should have given the same results. All the ffmpeg conversions are 8bit currently. Higher quailty way, without a doubt, is to use higher bit depth conversion in vapoursynth or stack16 in avisynth. It's easy to demonstrate how your output values deviate more compared to output when using any of the 8bit conversion methods
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