Before starting, clean the screen and lower the ambient light: dirt is mistaken for defective pixels. A dead pixel appears black on all colors; a locked one stays fixed on one color.
How it works
Scroll the screen with fourteen full-screen patterns. Flat colors—red, green, blue, white, black, gray, cyan, magenta, and yellow—are those that reveal dead and stuck pixels: a dead pixel looks black on all backgrounds, while a stuck pixel stays fixed on one color and stands out on the opposite background.
The technical patterns point to other flaws: the gradient shows banding when the panel has low color depth, the one-pixel panel betrays scaling or interpolation, the thin lines evaluate sharpness, and the moving bar reveals the trail that produces a high response time.
It also measures the refresh rate by counting the frames that the browser draws in a second, reports the estimated logical and physical resolution, pixel density, depth and color range, and allows you to verify how many fingers a touch screen recognizes simultaneously.
Examples
Black dot on white, red, green and blue backgrounddead pixelThe subpixel does not receive power on any channel: this is a permanent defect and is usually covered by the warranty when several appear.Fixed red dot on black backgroundstuck pixelThe subpixel stayed on. Sometimes it recovers by alternating colors for a few minutes, something this tour does naturally.120 Hz8.3 ms per frameOn screens with variable refresh rate the value drops when there is no movement: measure again while the wake pattern bar is running.Use cases
- Check a newly purchased monitor, notebook or cell phone before the exchange deadline expires.
- Document defective pixels with photos for a warranty claim.
- Confirm that the monitor is operating at the refresh rate configured in the system.
- Detect image retention or burn-in in OLED panels used as signage.
- Check the digitizer of a tablet or cell phone after changing the screen.
Frequently asked questions
What is the difference between a dead pixel and a stuck pixel?
The dead pixel never lights up: it looks like a black dot on any colored background. The lock stays on in a fixed color, so it disappears on a background of that same color and stands out against the others. That is why it is advisable to go through all the patterns before drawing conclusions.
Can a stuck pixel be repaired?
Sometimes. Rapidly alternating colors over that area for several minutes manages to unblock some subpixels, and this tour serves that purpose. The dead pixel, on the other hand, is a physical defect of the panel and is not recovered by software.
Why doesn't the measured frequency match that of my monitor?
The browser draws a maximum of one frame per refresh, but may draw less if the tab is in the background, if the computer is in power save, or if the screen uses variable refresh. There are also browsers that limit the animation to 60 Hz. Close the rest of the tabs and measure again to get closer to the real value.
Why doesn't it go into full screen on iPhone?
Safari on iOS does not allow a page to go full screen. In that case, the pattern appears the same, covering the entire browser window: it is enough to review the panel, even if the system bars are visible.
How many fingers should my touch screen recognize?
Most modern cell phones and tablets handle ten simultaneous contacts, and many touch monitors stay at ten or five. The navigator also reports a theoretical maximum in the screen data: if the maximum detected in the test is much below, there may be areas of the digitizer that do not respond.