= Pixel pitch
{title2=$p$}
<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.<Pixel Pitch and Enlarged Mode by EIZO>[Opening definition of pixel pitch and comparison of physical text size at different densities]{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>,
$$
p=\frac{25.4}{\rho}\,\mathrm{mm}.
$$
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.
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