The reason our vision never pixelates is that we compensate by moving our eyes. In other words, we scan and rescan the image as many times as necessary.
The electric signals produced in the eyes are sent to the brain where they are processed. The various scans are combined into the final image.
Whatever pixelation may still remain is then "discarded" by the mind by combining the "bitmap" into the illusion of a continuous tone image.
Human mind is very good at picking up essential information and discarding any redundancy.