 Pixel pitch

Pixel pitch is the physical spacing between corresponding centres of neighbouring pixels on a display or sensor grid. For an axis-aligned rectangular grid it can have separate horizontal and vertical values $p_x,p_y$. The pixel pitch describes the grid spacing, rather than the number of bits used for each pixel value.^[ref]

For square pixels on a uniform grid, linear pixel density $\rho$ and pixel pitch $p$ are reciprocal. If $\rho$ is measured in pixels per inch,For example, a hypothetical matrix with 2400 columns occupying a $600\mathrm{mm}$ active width has $p_x=600/2400=0.25\mathrm{mm}$ and horizontal pixel density $25.4/0.25=101.6$ pixels per inch. This calculation treats the width as the edge-to-edge extent of 2400 equal pixel cells; the distance from the first centre to the last centre is instead $2399p_x$.

Doubling the column count over the same width halves the horizontal pixel pitch. Doubling both row and column counts quadruples the number of pixels per unit area. The dimensions and the direction being measured therefore matter when comparing specifications.

A smaller pixel pitch provides a finer sampling grid, but it cannot recover detail already lost from the input image. Optical blur, aliasing and the viewing geometry also affect visible detail. A CSS pixel is a layout unit, so its size must be mapped through the device pixel ratio before it can be related to this physical grid.