Wallpaper Contrast & Legibility Checker

The most common reason a wallpaper fails is not that it looks bad — it is that your clock or your icon labels stop being readable on top of it. Drop an image in and this measures exactly that, in the three places it actually matters.

🔒 Your image is measured directly in your browser. It is never uploaded or stored anywhere.

How to read the numbers

Each zone is scored twice: once against white text and once against black text. The number is a WCAG contrast ratio, which runs from 1:1 (invisible) to 21:1 (black on white). The thresholds used here are the standard accessibility ones — 4.5:1 for small text such as icon labels, and 3:1 for large text such as the lock-screen clock.

Crucially, each zone is judged on its worst patch rather than its average. A wallpaper whose clock area is mostly dark sky but has one bright cloud in the corner will read as fine on average and still swallow the last two digits of the time. The tool takes the brightest 5% of the zone when scoring white text and the darkest 5% when scoring black text, which is the part that actually breaks.

Why 9:19.5, and why centre-cropped

Android does not show your image as you framed it. It scales the picture to cover the screen and crops whatever does not fit, so a wide photograph loses its sides and a very tall one loses its top and bottom. The preview above applies that crop first, because measuring the uncropped image would score parts of it nobody will ever see.

What the tool cannot see

• Text shadows and scrims. Most launchers put a subtle shadow behind the clock and a gradient behind the dock, which buys perhaps one extra point of contrast. A zone that scores just under threshold will often still be readable in practice; a zone at 1.5:1 will not be rescued by anything.
• Your icon grid. A denser grid pushes the first row of labels higher up the image than the band measured here.
• Dynamic colour. Android may tint your labels based on the wallpaper rather than using pure white or pure black, which shifts both scores.
• Always-on and lift-to-wake states, which dim the whole image and improve every score.

If a zone fails

Usually the fix is a crop rather than a different picture. Moving the frame down so the busy part falls below the icon grid solves most clock failures, and it is exactly what the wallpaper preview mockup is for — check the change there before you commit to it. If you want the reasoning behind why negative space in the top third matters more than the subject, the colour-theory guide covers it, and how to choose a wallpaper puts it in a wider routine.

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