Pixel is a unit of length and area
nayuki.ioPrevious discussion: https://news.ycombinator.com/item?id=43769478 (176 comments) [2025-04-23]
If you consider that a pixel is a container for RGB value, then the length and area collapse into simple storage requirement.
When an image is some px wide and some px high, it provides a shape (ratio between them), because a camera of 12mega px isn't 1px x 12M px in shape, but it does occupy 12M storage units nevertheless.
I agree though that like many IT related terms, their usage is twisted and simplified to amplify the buzz. Because it is more marketing friendly to put a bigger number than exact dimensions and proper terminology.
Is there any context where it makes sense to have fractional pixels? Like millipixels, micropixels, nanopixels, etc.? There is of course sub-pixel text rendering; does anyone refer to numerical fractional pixels in that field (333.33 mpx)?
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.