Dead Pixel Test
Fill the screen with flat colour to find dead and stuck pixels.
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About the Dead Pixel Test converter
A single failed pixel is nearly invisible against a photograph and glaringly obvious against a flat colour. That is the whole technique: fill the screen with one colour at a time and look.
Worth doing the day a monitor or phone arrives, because manufacturers allow a certain number of faulty pixels before a warranty claim succeeds, and the window for returning it is short.
What each colour reveals
Black finds pixels stuck on — they appear as bright dots on an otherwise dark field. White finds pixels stuck off, which show as dark specks, though dust on the panel looks much the same.
The pure primaries are the interesting ones. A pixel is three subpixels, and one failing shows only on its own colour: a pixel with a broken red subpixel looks perfectly normal until the screen turns red, at which point it is a black dot.
The grey field is for something different — uneven backlighting, clouding and the brighter patches near the edges of some panels, none of which show against black or white.
Dead, stuck, or dust
A dead pixel is black on every colour, because it receives no power at all. It will not recover. A stuck pixel shows the same colour constantly, because a subpixel is jammed on, and those sometimes free themselves after a while or with gentle pressure.
Anything that appears on every colour, sits on top of the image rather than in it, and shifts as you tilt the screen is dust or a mark on the surface — worth cleaning before assuming a fault.
What the browser can tell you about the display
Alongside the test, the page reports the resolution, the usable area, the device pixel ratio and the colour depth. On a scaled display the resolution reported is the logical one, so multiply by the pixel ratio to get the real number of pixels.
The refresh rate is measured by counting animation frames over half a second. That reflects what the browser is actually receiving, which is occasionally lower than the display can manage — a useful thing to know in itself.
Frequently asked questions
Can a stuck pixel be fixed?
Sometimes. A stuck pixel is jammed rather than dead, and cycling colours rapidly or applying very gentle pressure with a soft cloth occasionally frees it. A genuinely dead pixel, black on every colour, cannot be revived.
How many faulty pixels before I can return it?
It depends entirely on the manufacturer and the panel grade, and the thresholds are often higher than people expect. Check the specific warranty — but do it quickly, because return windows are usually much shorter than warranty periods.
Why does my resolution look wrong?
Browsers report the logical resolution, which on a scaled or high-density display is smaller than the physical one. Multiplying by the pixel ratio shown alongside it gives the real pixel count.
The refresh rate seems low.
It is measured from frames the browser actually delivered, so a busy machine, a power-saving mode or a browser throttling background work can all pull it below what the display supports.
Is anything recorded or sent anywhere?
No. Everything is measured by the page itself and forgotten when you close it. Nothing is uploaded, and no permission is asked for, because none of these tests need one.