Screen Test Tool
Detect dead pixels, bright spots, and test color display quality
What is Screen Test?
The Screen Test helps detect visible display problems such as dead pixels, bright spots, dark spots, uneven backlight, color shifts, banding, and line defects. It shows solid colors, gradients, grids, and high-contrast patterns so flaws stand out more clearly than they would on a normal desktop or web page. Use it when buying a new monitor, checking a laptop after transport, preparing a warranty claim, or investigating a screen that suddenly looks wrong. A careful test takes more than one glance: clean the panel, set a reasonable brightness, view from different angles, and cycle through several colors because some defects only appear on specific backgrounds.
How to Use
How to use
- Select a test mode or click 'Enter Fullscreen Test' button
- In fullscreen mode, carefully observe all areas of the screen for abnormal bright or dark spots
- Use arrow keys or click buttons to switch between different test colors
- Press Esc to exit fullscreen mode
Detection Tips
- It's recommended to test in a dimly lit environment to better detect screen anomalies
- White background can detect dead pixels (always-on black dots)
- Black background can detect bright spots
- Solid colors can detect color abnormalities
Use Cases
Technical Principle
Each test mode renders a full-viewport overlay with position: fixed and inset: 0 so the chosen color or pattern covers every pixel the panel can address. Solid-color tests use sRGB primaries at full intensity, namely #FF0000 red, #00FF00 green, #0000FF blue, plus #FFFFFF, #000000, cyan, magenta, and yellow. Pure backgrounds make sub-pixel defects stand out because the human eye notices a single off-color dot against a uniform field much faster than against textured desktop wallpaper. Fullscreen presentation runs through element.requestFullscreen() so browser chrome, the taskbar, and notification banners disappear during inspection. Keyboard navigation listens for arrow keys to cycle between modes and Escape to exit, which is the only practical control scheme when the screen under test is a ceiling-mounted projector or a wall TV several meters from the keyboard. Gradient and grayscale-ramp modes are rendered with CSS linear-gradient, while checkerboard and grid patterns are drawn as 1-pixel CSS repeating-linear-gradient or background-image tiles. The defect categories follow ISO 9241-307: a bright (stuck) sub-pixel is always lit on a black background, a dark (dead) sub-pixel is always off on a white background, and a fully dead pixel is dark on every test color. Class I displays allow zero defects per million pixels, Class II permits a small per-million quota, and Class III is the consumer baseline. On OLED panels, additional artifacts such as PWM flicker at low brightness and dark-corner uniformity drift can also surface on a solid gray field that a desktop wallpaper would have hidden.
- Fullscreen overlay: position: fixed; inset: 0 with a single background-color or background gradient; no browser chrome or notifications visible
- Test colors: sRGB primaries #FF0000 / #00FF00 / #0000FF plus #FFFFFF, #000000, cyan, magenta, yellow as full-intensity backgrounds
- Fullscreen API: element.requestFullscreen() to suppress the taskbar; Escape exits, arrow keys cycle modes for remote-display use
- Defect taxonomy: stuck (bright) sub-pixel on black, dead (dark) sub-pixel on white, fully dead pixel dark on every color
- ISO 9241-307 grading: Class I = zero defects per million pixels, Class II = limited quota, Class III = consumer-grade tolerance
- Pattern tests: gradient ramp 0-255 reveals 6-bit / 8-bit / 10-bit banding; 1-pixel checkerboard exposes 4:2:0 chroma subsampling and HDMI scaler artifacts
- OLED-only artifacts: PWM dimming flicker at low brightness and panel non-uniformity visible only on solid gray fields
Examples
New monitor unboxing inspection
Brightness: 80%, room: dimly lit
1. White fullscreen -> scan for stuck-off (black) pixels
2. Black fullscreen -> scan for stuck-on (bright) dots & backlight bleed
3. Red / Green / Blue -> per-subpixel defects
4. Result: 0 dead pixels, slight IPS glow at bottom-left corner (within spec)Checkerboard test for 4K HDMI signal
Mode: Checkerboard (1 px black + 1 px white)
View from arm's length distance
Expected: uniform gray blend
Fail signal: visible color fringing or moire = chroma 4:2:0 path, scaler issue, or wrong HDMI source format
Fix: switch cable to certified 18 Gbps HDMI 2.0 or set source to RGB FullGradient banding check on 8-bit panel
Mode: Gradient (grayscale ramp 0-255)
Look for: visible stripes (banding) in the dark quarter
Clean 10-bit panel: smooth ramp
8-bit + FRC: very faint stepping
8-bit only / cheap TN: visible 6-8 step bands
Tip: turn off all dynamic contrast settings before judgingWarranty claim defect log
Date: 2026-06-10
Model: 27-inch IPS, S/N: ABC123
Bright dots: 2 (top-left zone, top-right zone) on Black test
Dead pixels: 0
Backlight bleed: moderate, bottom edge on Black test
ISO 9241-307 class II permits 2 bright + 2 dead per million pixels; 2560 x 1440 ~= 3.7 million pxFAQ
What does the screen test cover?
Pure-color fullscreen (red, green, blue, white, black, and gray gradient) for dead-pixel and backlight-bleed checks; geometry patterns (grid, alignment, convergence); contrast strips for gamma and banding; text rendering at multiple sizes; aspect-ratio test patterns. Cycle through them at fullscreen.
How do I find dead or stuck pixels?
Display each primary color (red/green/blue) at fullscreen, then white, then black. A pixel that shows the wrong color, refuses to change, or stays dark on a white screen is dead or stuck. Check at low brightness too - some defects only appear at certain levels.
How do I check for backlight bleed?
Display pure black at fullscreen in a dark room. Even, uniform black is good. Bright glow at edges or corners is backlight bleed (LCD) or off-axis emission (OLED). A small amount is normal on LCD; severe bleed is a defect worth a warranty claim.
Can it detect ghosting or motion blur?
Some builds include a moving box pattern that shows ghosting trails on slow-response panels. For serious motion-clarity testing, dedicated tools like Blur Busters' UFO Test (testufo.com) are more thorough.
Does it test color calibration?
It can show color gradients and known reference colors, but real calibration needs a hardware colorimeter (X-Rite, Datacolor) plus profiling software. A web tool only tells you what your display is currently rendering, not whether it matches a target color space.
How do I exit fullscreen?
Press Esc or F11. The page does not lock the OS; you can always switch tabs or close the browser.
Is anything uploaded?
No. The page is pure rendering. Nothing is logged or transmitted.