Dead Pixel Test
Cycles through 8 solid colors to reveal stuck or dead pixels that stand out against a uniform background.
Device
On-device · No upload
Screen Test
Test your display for dead pixels, backlight bleed, black level, white clipping, gamma, color banding, and more.
Screen Test detects display issues with ten fullscreen modes: Dead Pixel (8 solid colors), Gradient, Checkerboard at three densities, Backlight Bleed, Color Uniformity, Black Level (RGB 0–32), White Level (RGB 223–255), Gamma (1.8–2.6 per channel), Stuck Pixel Fixer, and Response Time. Includes a monitor and NVIDIA settings guide. Runs entirely in your browser — no download required. Made by FreeToolHub.
Photosensitivity warning: Some test modes contain rapidly flashing lights. Do not use the Stuck Pixel Fixer or Response Time Test if you have epilepsy or photosensitivity.
How to Use
- Clean your screen gently to remove dust and fingerprints that could be mistaken for dead pixels.
- Click "Start Test" on any mode below. The test will open in fullscreen (or a full-page overlay on mobile).
- Click, tap, or press the arrow keys to cycle through patterns. Press ESC or the back button to exit.
Gradient Test
Displays smooth color gradients to reveal banding, bit-depth issues, and poor calibration.
Checkerboard Pattern
Black and white checkerboard at three pixel densities to test sharpness, pixel crosstalk, and scaling artifacts.
Backlight Bleed Test
Pure black screen to reveal light leaking from edges and corners on LCD panels.
Color Uniformity Test
Solid grey levels to check for uneven brightness, IPS glow, or color tinting across the panel.
Black Level Test
33 near-black patches from RGB 0 to 32 to check shadow detail and crushed blacks.
White Level Test
33 near-white patches from RGB 223 to 255 to check for clipped highlights.
Gamma Test
Striped and solid patches for gamma 1.8 to 2.6 in grey, red, green, and blue.
Stuck Pixel Fixer
A rapidly color-cycling square you drag over a stuck pixel. Leave it running for 10-20 minutes to attempt repair.
Response Time Test
Alternates black and white frames at configurable speeds to assess monitor ghosting and response time.
How to Adjust Your Monitor
Run the Black Level, White Level, and Gamma tests in a dimly lit room after the monitor has warmed up for about 30 minutes. Switch the monitor to its Standard or sRGB picture mode and turn off dynamic contrast, eco, and auto-brightness features first. These tests target standard (SDR) output: with Windows HDR turned on, use the Windows HDR Calibration app and the SDR content brightness slider instead.
Black level (RGB 0–32)
Patch 0 is identical to the background, and patches from about 2–4 upward should be just visible. If patches up to 8 or higher vanish into the background, blacks are crushed: raise the monitor's Black Level, Black Stabilizer, or Shadow Boost setting, or raise Brightness slightly. If the background looks dark grey rather than black and every patch is obvious, blacks are raised: lower that setting again. Slight flicker or smearing of near-black patches on VA and OLED panels is normal.
White level (RGB 223–255)
Patches up to about 250–254 should be distinguishable from the 255 background. If the brightest patches merge into the background, highlights are clipped: lower the monitor's Contrast setting one step at a time until they reappear. On most LCD monitors Brightness only changes the backlight, so set it for comfort (around 120 cd/m² in a normally lit room) once contrast is correct.
Gamma
Each column pairs fine black-and-white stripes with a solid center patch. Step back or squint until the stripes blur: the column where the center blends into the stripes shows your effective gamma. 2.2 is the standard for Windows, macOS, and the web. If the match is at 2.0 or lower, mid-tones are too bright: pick a higher gamma preset in the monitor menu. If it is at 2.4 or higher, mid-tones are too dark: pick a lower one. If the red, green, and blue views match at different values, the panel has a color tint in the mid-tones. Use 100% browser zoom and 100% display scaling, or the stripes will blur and the result is unreliable.
NVIDIA Control Panel settings
Open NVIDIA Control Panel → Display → Change resolution. Select “Use NVIDIA color settings”, set Output color format to RGB and Output dynamic range to Full. Over HDMI the driver may default to Limited (16–235): a monitor expecting full range then shows grey blacks and dull whites, while full range sent to a monitor set to limited crushes patches below 16 and clips everything above 235. Set the monitor's own HDMI black level or RGB range option to match. Also pick the highest Output color depth the monitor supports (8 or 10 bpc) to reduce banding in the Gradient test.
Under Display → Adjust desktop color settings, keep Brightness and Contrast at 50%, Gamma at 1.00, and Digital vibrance at 50%, and make corrections on the monitor first; use the gamma slider there only if the monitor has no gamma presets. On AMD Radeon the matching option is Pixel Format (RGB 4:4:4 Full RGB) in AMD Software, and on Intel it is Quantization Range (Full Range) in Intel Graphics Command Center.
Frequently Asked Questions
What is a dead pixel?
A dead pixel is a permanently dark pixel that receives no power and appears as a black dot on your screen. Unlike stuck pixels which display a fixed color, dead pixels cannot be fixed by software. They appear clearly against bright solid-color backgrounds.
What is a stuck pixel and can it be fixed?
A stuck pixel is a pixel locked to a single color — red, green, blue, or white. Unlike dead pixels, stuck pixels may be repaired. The Stuck Pixel Fixer mode rapidly cycles colors to stimulate and unstick the pixel. Leave the flashing square over the affected area for 10-20 minutes.
How do I test for backlight bleed?
Use the Backlight Bleed test mode. It fills the screen with pure black. In a dark room, look for any light leaking from the edges or corners of your display. Some backlight bleed is normal on LCD panels, but excessive bleed can be distracting during dark scenes.
What does the gradient test reveal?
The gradient test shows smooth black-to-white and color gradients. If you see visible banding (distinct steps instead of a smooth transition), your display may have limited bit depth or poor calibration. A well-calibrated display should show perfectly smooth gradients.
Why does the cursor disappear in fullscreen mode?
The cursor hides automatically after 2 seconds of inactivity so it does not obscure the test pattern. Move your mouse or touch the screen to make it reappear. The HUD (heads-up display) also reappears when you move the mouse.
Does this tool work on mobile devices?
Yes. All test modes support touch — tap to advance, swipe left or right to navigate. The Stuck Pixel Fixer square can be dragged by touch. Fullscreen mode uses the browser Fullscreen API where supported, with a CSS full-overlay fallback on browsers that do not support it.
Why are my blacks crushed or my picture washed out?
The most common cause is an RGB range mismatch between the graphics card and the monitor. If the Black Level test shows no difference until patch 16 or higher, the PC is sending full range to a monitor set to limited. If black looks grey and contrast is flat, the PC is sending limited range (16–235) to a monitor expecting full range. Set both sides to Full: in NVIDIA Control Panel this is Output dynamic range under Change resolution.
What gamma should my monitor use?
Gamma 2.2 is the standard for Windows, macOS, web content, and most games, so it is the right target for a normal room. Gamma 2.4 (BT.1886) is used for video mastering in a dark room. Run the Gamma test, find the column where the solid center blends into the stripes, and change the monitor's gamma preset until the match sits at 2.2 in the grey view.