Dead & Stuck Pixel Test and Fixer

Find dead, stuck and hot pixels and screen lines, log their exact position, try the stuck-pixel fixer and check the warranty rules.

Tester Utilities Updated Oct 7, 2026
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How to Use
  1. Clean the screen with a dry microfibre cloth so dust is not mistaken for a fault, and set browser zoom to 100 %.
  2. Press Start full-screen test. The screen fills with black; tap, swipe or press Space or → for white, red, green, blue and three greys. Esc returns here.
  3. Press M and tap a faulty dot to mark it; press L to mark a vertical or horizontal line instead. Arrow keys nudge a mark by one device pixel and [ ] change a line’s width. Back on the page, answer the two questions under each mark.
  4. A line from top to bottom? Open Line on my screen? and answer four questions (menu, self-test, cable, video mode) to see whether it is the panel, the cable or the signal.
  5. For a stuck pixel, open Fix stuck pixel, read the warning, put a square (or a strip, for a line) over it and run it for 10 to 30 minutes. The flashing area is checked against the WCAG limit, and any key or tap stops it.
  6. Use Screen tests (refresh rate, motion, black crush, chroma 4:4:4, sub-pixels, uniformity), Camera scan, OLED care and Warranty for the rest, and copy the report for a claim.
Display test

Black, white, red, green, blue and greys. Tap or Space for the next colour, M to mark a pixel, Esc to exit. No flashing.

8 test colours
Order: Black → White → Red → Green → Blue → 25 % grey → 50 % grey → 75 % grey
  • Next colour: tap, swipe left, Space or →. Back: ←. Jump: 1–8.
  • M marks; L switches pixel / vertical line / horizontal line; arrows nudge the last mark one device pixel (Shift = 10); [ ] line width; Z undoes. Esc exits.
Presets
Screen preview

Screen
—
Pixel ratio
—
Refresh rate
60.0Hzexample
Marked faults
1example

Marked faults

Example — press Start test to check your own screen.

Line on my screen?

A line that runs the full height or width of the screen means a whole column or row of pixels is wrong. Makers treat it as a hardware or signal problem, test it with the monitor's built-in self-test, and send monitors whose lines show in the self-test for repair. No maker page we read says pixel-flashing software fixes a line.

What the makers say (9 sources)

Warranty: None of the 14 pixel policies in the Warranty table counts a line in its dead-pixel limits; Dell lists lines as a symptom that is not a pixel defect. A line that shows in the monitor's self-test is handled as a hardware fault under the normal warranty: contact the maker with the self-test result.

We found no maker statement that a line over the on-screen menu proves a panel fault, and none that says flashing software fixes lines. HP's support pages timed out and were not read.

Pixel map history: is it still there tomorrow?

Save your marks as dated sessions for this screen resolution and compare them over days: still there, gone or new. Saved only in this browser, only when you press Save; export a PNG map or JSON to keep or share.

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Your screens

On a computer with several monitors, Chrome and Edge can list them and open the test full screen on the one you choose (the browser asks for permission first). Elsewhere, drag this window to the monitor you want to test.

Worked Example

Finding and logging a dead pixel. A 27-inch 2560 × 1440 monitor runs at 125 % scaling in Windows, so the browser reports a device pixel ratio of 1.25 and a screen of 2048 × 1152 CSS pixels (2048 × 1.25 = 2560, 1152 × 1.25 = 1440). On the white test screen there is a black dot. Marking it records x = 812, y = 344 CSS px. The panel pixel is ⌊812 × 1.25⌋ = 1015 across and ⌊344 × 1.25⌋ = 430 down. It is black on white and stays black on black, so it is a dead pixel: an ISO 9241-307 Type 2 (dark) fault.

Is one dead pixel enough for a claim? The panel has 2560 × 1440 = 3,686,400 pixels, 3.6864 million. ISO Class II allows 2 dark pixels per million: 2 × 3.6864 = 7.37. One dark pixel is within Class II (and within Class I, which allows 1 per million, 3.69 here), so a claim depends on the brand’s own policy, not on the ISO class.

A vertical RGB line on a 144 Hz monitor. The line is marked with L and nudged to device column 1,203, 3 pixels wide. It crosses the monitor’s own menu and shows in the built-in self-test, so the fault is inside the monitor: Dell’s advice for a line in the self-test is to contact support for repair. A fixer strip over it would be 3 + 2 = 5 px wide and 1,440 px tall, 7,200 px², 33.0 % of the 21,824 px² WCAG limit, so it could run at full speed; but no maker says flashing fixes lines. Measured refresh: 1000 ÷ 6.944 ms = 144.0 Hz, and the motion test moves round(960 ÷ 144) = 7 pixels a frame, 7 × 144 = 1,008 px/s.

The common mistake: reporting the position in CSS pixels. Telling the manufacturer “812, 344” sends the technician 203 pixels left of the fault (1015 − 812) and 86 pixels too high (430 − 344). Quote the device-pixel position, 1015, 430, counted from the top-left corner of the screen, which is what the copied report gives.

Show Work

Mark a pixel, start the fixer or measure the refresh rate to see the working.

Formulas

Device pixel from a tap
xdevice = ⌊xCSS × devicePixelRatio⌋
812 × 1.25 = 1015. At 100 % scaling the ratio is 1 and the two are equal.
Refresh rate (vsync fit)
f = 1000 ÷ slope of ti against ki
ki is each frame’s whole refresh number. A late frame skips a number instead of counting as one slow frame. 6.944 ms → 144.0 Hz; 16.667 ms → 60.0 Hz.
Jitter
σ = √( Σ(ti − t̄)² ÷ (n − 1) )
Standard deviation of the steady frame intervals (0.5 to 1.5 × the median).
Motion per frame (frame-locked)
d = round(speed × DPR ÷ f) device px
960 px/s at 144 Hz is 6.67 px, rounded to 7 px a frame = 1,008 px/s, so every step is the same size. At 60 Hz: 16 px.
Flash area (WCAG 2.3.1)
A = Σ wi × hi ≤ 0.25 × 341 × 256 = 21,824 px²
Every square and strip is added up. 64 × 64 = 4,096 (18.8 %); a 3 × 1,440 strip = 4,320 (19.8 %). Over the limit: 3 changes a second at most.
Camera scan: perspective and threshold
(x, y) = H · (u, v, 1); flag |r| > 6σ, σ = 1.4826 × MAD
H maps the monitor grid onto the four corners in the photo. r is the image minus a wide background; MAD is the median absolute deviation.
Gamma check square
v = 255 × 0.51/γ
Matches 50 % black/white stripes: γ 1.8 → 174, 2.0 → 180, 2.2 → 186, 2.4 → 191, 2.6 → 195.
ISO 9241-307 allowance
N = limit per million × (width × height ÷ 106)
Class II dark pixels on 2560 × 1440: 2 × 3.6864 = 7.37. Type 3 counts 2 × lit + dark sub-pixels: 10 × 3.6864 = 36.86.

How Screen Pixels Fail

Pixels and sub-pixels. Each pixel of an LCD is three sub-pixels, red, green and blue, each behind a colour filter. A thin-film transistor (TFT) on the glass sets the voltage across the liquid crystal of each sub-pixel, and the crystal decides how much backlight passes. An OLED pixel has three tiny light-emitting diodes instead, each driven by its own transistor circuit. A 3840 × 2160 panel has 8,294,400 pixels and 24,883,200 sub-pixels, so a handful of faults is a manufacturing reality rather than a rare defect.

Dead, stuck and hot. When a transistor or its connection fails, the sub-pixel is stuck in one state. On a normally-black panel (IPS and VA LCDs, and every OLED) a sub-pixel that gets no drive stays dark, so a fully failed pixel is a black dot: a dead pixel. A sub-pixel stuck at full drive shows as a red, green or blue dot on a black screen: a stuck sub-pixel. All three stuck on is a white dot, a hot or bright pixel. On older twisted-nematic (TN) panels, which are normally white, a pixel with no drive lets light through, so failures there tend to show as bright dots.

Lines. The rows and columns of a panel are driven by driver chips along its edges, connected to the glass by fine flexible connections. When a whole column or row gets the wrong signal, the result is a line from edge to edge, often coloured when only one sub-pixel column is affected. Makers test this with the monitor’s built-in self-test, which draws a pattern inside the monitor: Dell’s advice is that if the lines appear in the self-test, contact support for repair, and if not, check the cable, the graphics card and the computer. Lenovo has fixed lines on two monitors with firmware updates, and Microsoft points out that lines visible in a Surface’s UEFI screen suggest hardware rather than a Windows driver.

Why a fixer sometimes works. Some stuck sub-pixels are not broken outright: the liquid crystal or the drive circuit is stuck, and switching the sub-pixel hard on and off many times can free it. That is the idea behind flashing fixers. It works on some pixels and not others, and nothing makes a dead pixel light again.

OLED retention and burn-in. OLED sub-pixels dim slowly with use, so a logo or taskbar shown for many hours can leave a lasting shadow. LG describes temporary retention as a faint ghost that fades and burn-in as retention that lasts much longer and shows over other content; Samsung calls burn-in a static image that becomes a permanent fixture. OLED monitors run their own compensation while switched off: ASUS starts pixel cleaning after five minutes in standby, and LG’s Image Cleaning runs after more than four hours of use.

The standards. ISO 13406-2, published in 2001, introduced pixel-fault classes for flat panels. It was replaced in 2008 by ISO 9241-307, which keeps the idea: three fault types (Type 1 bright pixels, Type 2 dark pixels, Type 3 lit or dark sub-pixels) and classes 0 to III giving how many of each are allowed per million pixels, with a lit sub-pixel counting twice and separate limits for faults clustered in a 5 × 5 pixel area. Monitor makers state different classes: ISIC and MEDION manuals say Class II, AOC’s US warranty and Lenovo say Class I or better. Each maker then publishes its own dead-pixel policy, usually stricter than its ISO class, and that policy decides a warranty claim.

About This Tool

This tool tests a screen in six ways. Test pixels fills the screen with eight solid colours and lets you mark pixels and whole lines, recording each position in CSS pixels and in the panel’s own device pixels, with a guided check for lines. Fix stuck pixel flashes squares or strips over the faults you marked for 10, 20 or 30 minutes, adds up their area against the WCAG limit and keeps the screen awake with the Screen Wake Lock API where supported. Screen tests covers refresh rate, motion and pursuit, backlight bleed, banding, gamma, sharpness, black crush and white clipping, chroma 4:4:4, sub-pixel layout, LCD inversion, uniformity and viewing angle, and reads what the browser reports about the display. Camera scan finds specks and lines in a photo or camera view of the screen. OLED care has retention check screens and a slow, non-flashing refresher. Warranty turns your marks into ISO 9241-307 counts, shows what each class and 14 brands allow, and copies a report; the full brand comparison is in Dead pixel warranty policies by brand.

Safety: flashing follows WCAG 2.2 Success Criterion 2.3.1 (Three Flashes or Below Threshold). It never starts on its own, shows a warning first, stops on any key, click or tap, and adds up the area of every square and strip: under 21,824 px² any speed is allowed, above it the speed drops to 3 changes a second, and whole-screen flashing needs a second confirmation.

Privacy: everything runs in your browser and nothing is uploaded. Marks and measurements are lost when you close the tab unless you press Save in the pixel map, which keeps them in this browser’s local storage only. The camera, full screen, the wake lock and the list of screens are only requested when you press their buttons; camera frames stay in memory and the camera stops when you press Stop, leave the mode or hide the tab.

Sources: W3C WCAG 2.2 (2.3.1 and the general flash and red flash thresholds), the WHATWG Fullscreen and HTML standards (requestAnimationFrame), the W3C Screen Wake Lock, Window Management, Media Capture and Streams and Media Capabilities specifications, CSS Media Queries Levels 4 and 5, CSSOM View, MDN Web Docs, RTINGS: Chroma Subsampling 4:4:4 vs 4:2:2 vs 4:2:0, RTINGS: Text Clarity test (sub-pixel layouts), Lagom LCD test: Inversion (pixel walk), Blur Busters: Pursuit camera HOWTO, and the manufacturers’ ISO 9241-307 summaries, pixel policies, line troubleshooting and OLED care pages linked above.

Related tools: Touchscreen Test, Contrast Checker, and Keyboard Tester.

Frequently Asked Questions

How do I test a monitor for dead pixels?

Clean the screen, set zoom to 100 % and show full-screen solid colours one at a time: black shows stuck and hot pixels, white shows dead pixels, and red, green and blue show single dead sub-pixels. Look at the whole panel from about 30 cm. On a 2560 × 1440 monitor there are 3,686,400 pixels, so take your time on each colour, and mark each fault so you have its exact position.

What is the difference between a dead, stuck and hot pixel?

A dead pixel stays black on every colour, because no light gets through it. A stuck pixel has one or two sub-pixels stuck on, so it shows as a red, green or blue dot on black. A hot pixel has all three sub-pixels stuck on and shows white on black. ISO 9241-307 calls these Type 2 (dark), Type 3 (sub-pixel) and Type 1 (bright) faults.

Can a stuck pixel or a line on the screen be fixed?

A stuck sub-pixel sometimes starts working again, on its own or after being switched on and off rapidly, which is what the fixer does; a dead pixel cannot be fixed by software. A line from edge to edge is a whole row or column: Dell says to check whether it shows in the monitor’s built-in self-test and to contact support for repair if it does, and no maker we checked says flashing software fixes lines. Check the warranty first: Dell advises against pixel-fixing software, while one bright pixel already qualifies for an exchange under Dell Premium Panel Exchange.

How many dead pixels are allowed under warranty?

The brand’s own policy decides, and the Warranty table quotes 14 of them: Dell Premium Panel Exchange allows 0 bright and up to 5 dark sub-pixels, for example. The ISO 9241-307 standard sets classes instead. Class II allows 2 bright pixels, 2 dark pixels and a sub-pixel total of 10 per million pixels, where a lit sub-pixel counts twice. On a 2560 × 1440 panel (3.6864 million pixels) that is 7.37 bright, 7.37 dark and a sub-pixel total of 36.86 (18.43 lit or 36.86 dark sub-pixels).

Is the stuck pixel fixer safe for people with photosensitive epilepsy?

Anyone with photosensitive epilepsy should not use it or be in the room. The fixer warns before it starts, never starts by itself and stops on any key, click or tap. By default it flashes one 64 × 64 pixel square, 4,096 px², which is 18.8 % of the WCAG 2.3.1 flash-area limit of 21,824 px² (a quarter of 341 × 256). Squares and strips are added together: a 3 × 1,440 px strip is 4,320 px² (19.8 %). Above the limit the fixer slows to 3 colour changes a second, and whole-screen flashing needs a second confirmation.

Common Use Cases

Checking a new monitor in the return window

Run all 8 colours on day one. A 27-inch 1440p panel has 3,686,400 pixels; one bright pixel found now is easier to return than after 30 days.

Buying a used laptop or phone

Ten seconds of black and white in full screen shows any dead or stuck pixel before you pay.

Trying to revive a stuck green sub-pixel

Place the 64 px square over it at 10 changes per second for 20 minutes: 12,000 colour changes, then re-test on black.

A vertical line down the screen

Mark it with L (for example column 1,203, 3 px wide), then answer the four questions. If it shows in the monitor’s self-test, it is a hardware fault for the warranty, not something to flash.

Checking a high-refresh gaming monitor

Measure the refresh rate: a 144 Hz panel left at 60 Hz in Windows shows 16.667 ms per frame instead of 6.944 ms.

Filing a warranty claim

Mark each pixel and line, answer the questions, and copy the report: device-pixel positions, counts by ISO type, line diagnosis and the class they fit.

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