What is stereo subpixel matching/interpolation precision?

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Hello,

I'm trying to figure out what the subpixel stereo matching precision is (that is, how many pixels/subpixels of disparity can the stereo matching algorithm interpolate to). I looked at the code a bit, and I think it's 1/4-pixel, but I've also heard it's 1/8-pixel. Do you which it is (or maybe a different value altogether)? Thanks!