I think the notion of fractional pixels is rare indeed. But I can think of one example from astrophotography. After taking a photo, we use software to analyze t

I think the notion of fractional pixels is rare indeed. But I can think of one example from astrophotography. After taking a photo, we use software to analyze the size of stars - for features like autofocus, auto-guiding, and detecting smeared images. Describing the full width at half maximum (FWHM) of stars with decimal pixels is normal practice. It's akin to fitting a Gaussian function to a measured peak, and letting the Gaussian have a fractional standard deviation that isn't constrained by the integer pixel grid. I guess on that note, video compression motion estimation/compensation can also make use of fractional pixels.