Monitor and display test tools

Monitor test tools display carefully designed images that reveal how well a screen reproduces brightness, colour and geometry. By showing solid colours, gradients, grids and fine patterns, they make faults visible that are hard to judge with ordinary content. Such tools are used to check a display when it is bought, to compare settings, and to calibrate a screen so that what appears on it matches a known reference as closely as possible.

The two main display technologies need different checks. A CRT, or cathode-ray tube, forms its image by scanning electron beams across a phosphor-coated screen, and its typical faults concern geometry and convergence: straight lines may bow, the picture may not fill the screen evenly, or the red, green and blue beams may not align, producing coloured fringes. Test grids and crosshatch patterns expose these problems so they can be corrected with the monitor's controls.

A flat-panel LCD uses a fixed grid of liquid-crystal cells backlit from behind, so its geometry is inherently stable, but it has its own characteristic faults. Solid-colour screens reveal stuck or dead pixels that fail to change, while uniform grey fields show backlight unevenness or clouding. Sharpness patterns confirm that the panel is running at its native resolution, and grey-scale steps help set brightness and contrast so that both dark and light detail remain visible. Many of these test utilities are distributed as freeware, and some run directly in a web browser.

Frequently asked questions

What is a dead pixel?

It is a point on an LCD that no longer changes colour, usually staying black or one fixed colour. Solid-colour test screens make such pixels easy to spot against the uniform background.

Why do CRT and LCD monitors need different tests?

A CRT scans beams across a tube and can suffer geometry and convergence errors, while an LCD has a fixed pixel grid and instead shows faults like stuck pixels and uneven backlighting.

What is convergence on a CRT?

It is how precisely the red, green and blue beams align on the screen. Poor convergence produces coloured fringes around edges, which crosshatch patterns help reveal.