Monitor Test — Dead Pixels, Bleed, Ghosting

Written and reviewed by the BroBroGo editorial team.Last updated: 2026-07-30

The Monitor Test Suite is a browser-based tool designed to help users inspect, evaluate, and adjust their displays using fullscreen visual patterns. Operating entirely within the user's web browser, the tool renders specialized test patterns that make physical screen defects, color rendering issues, motion artifacts, and display capabilities visible to the naked eye.

Every test pattern is drawn locally on the user's device. The tool does not see, record, or upload what is displayed on the screen.

Interactive Controls and Interface Behavior

The tool provides a selection of test modes and pattern variants to evaluate different aspects of a display. Depending on the active mode, users can adjust settings or interact with the interface using the following controls:

Steps: Adjusts the number of steps in step-based patterns.
Speed: Adjusts the speed of motion patterns.
Start motion / Pause: Toggles the movement of animated patterns.
Measure again: Restarts the refresh rate measurement.
Enter fullscreen / Exit: Toggles native fullscreen mode.
Navigation: Users can press the ← → keys to change patterns and Esc to exit on desktop devices, or tap the screen to change patterns on touch devices.

System and Browser Edge Cases

The tool adapts its behavior based on system settings and browser permissions:

System Reduced Motion: If the user's operating system has a "reduced motion" setting enabled, animations remain paused by default. The interface displays the message: "The animation stays paused because your system asks for reduced motion. Start it only if that is comfortable for you.".
Fullscreen Blocking: If the browser blocks the transition to native fullscreen mode, the tool falls back to filling the browser window and displays the message: "Fullscreen was blocked here, so the pattern fills the window instead.".
Refresh Rate Measurement Interruption: If the user switches tabs or minimizes the browser during a refresh rate test, the measurement pauses and displays: "Measurement paused — come back to this tab and measure again.".

Screen Defects and Panel Uniformity

Evaluating physical defects is critical during a new monitor's return window. The tool provides specific modes to isolate these issues:

Solid Colors & Dead Pixels

This mode allows users to cycle through fullscreen variants including White, Black, Red, Green, Blue, Cyan, Magenta, Yellow, and Custom color. Users should scan the entire screen, including the corners, to identify pixel defects. A dead pixel remains dark on every color background because its subpixels never switch on. A stuck subpixel is frozen lit, glowing in a specific color (such as red, green, or blue) on backgrounds where it should not, and vanishing on others. Physical dust can be distinguished from pixel defects if the speck moves when wiped.

Backlight Bleed vs. IPS Glow

Using a solid black screen in a dimmed room, users can inspect the display for light leakage. Backlight bleed appears as bright patches leaking in from the edges or corners of the panel. This physical defect remains in a fixed position regardless of the viewing angle. In contrast, IPS glow is a normal characteristic of In-Plane Switching (IPS) technology; it appears as a faint glow that shifts or disappears as the user moves their head. Twisted Nematic (TN) and Vertical Alignment (VA) panels behave differently, while Organic Light-Emitting Diode (OLED) panels switch pixels off entirely, resulting in zero backlight bleed.

Uniformity

This mode displays a single mid-gray field (with 25% and 75% brightness variants) to check for uneven brightness or color reproduction across the panel. Users should look for darker or tinted zones, vertical or horizontal bands, and corners falling off in brightness. Some panels exhibit excellent uniformity at one brightness level but show patchiness at another.

Color, Tone, and Contrast Calibration

Achieving accurate color and contrast requires evaluating how a display handles gradients, saturation, and gamma curves.

Test Mode	Pattern Variants	What to Look For
Grayscale steps	Step-based gray bars	Every step should be distinct from its neighbors from darkest to brightest. If the first steps merge into black, shadow detail is crushed; if the last steps merge into white, highlights are clipping.
Gradients & banding	Gray (horizontal/vertical), RGB bars	A smooth ramp should show no visible stripes. Distinct bands indicate gradient banding, which is common on 6-bit panels or displays utilizing aggressive image processing.
Saturation	Color saturation bars	Each bar should ramp evenly from gray to its most vivid color without sudden jumps or flat stretches. If the vivid end collapses into a solid block, the screen or its color profile is clipping saturated tones.
Gamma	Striped and solid patches	Users should step back or squint until the striped halves blend into even tones, then find the column where the stripes and solid patch match. Most screens target a 2.2 gamma curve. A higher match indicates deeper shadows, while a lower match indicates a washed-out picture.
Contrast detail	Near black, Near white	In the near-black pattern, each numbered square should be barely but visibly different from the background. In the near-white pattern, the brightest squares must still separate from pure white.

Sharpness, Resolution, and Motion

Sharpness and Moiré

Using Line pairs, Checkerboard, Text sample, Fine grid, Concentric rings, and Pixel stripes, users can verify if the display is running at its native resolution. Single-pixel lines and checkerboards should look crisp without smearing or halos. Blurriness or scaling artifacts like wavy rainbows, shimmer, or rippling (moiré) indicate that the picture is being scaled away from its native resolution or that display sharpening settings are overprocessing the image.

Ghosting and Response Time

By following moving blocks at adjustable speeds, users can evaluate pixel response times. Trails or shadows behind the moving blocks indicate ghosting caused by slow pixel transitions. Conversely, bright leading or trailing edges point to overshoot artifacts caused by aggressive monitor overdrive settings.

Refresh Rate Accuracy

The tool measures the display's refresh rate based on how fast the browser is allowed to draw frames. The interface displays the Measured refresh rate in Hz, the Average frame time in ms, or a Measuring… status.

This measurement is bound to browser performance. The reading will drop below the screen's actual hardware specification if:

The browser window is placed on a slower secondary display.
System power-saving modes cap the frame rate.
Background tabs or applications consume system resources.

Display Info Panel

The tool detects and displays system-reported parameters under the Display Info panel:

HDR output: Displays Active, Not active, or Cannot detect.
P3 wide color: Displays Active, Not active, or Cannot detect.
Rec. 2020 color: Displays Active, Not active, or Cannot detect.
Color depth: Detected depth value.
Screen resolution: Detected resolution.
Pixel ratio: Detected device pixel ratio.

If HDR reads as inactive on an HDR-capable monitor, it is usually switched off in the operating system's display settings.

Limitations of Visual Testing

Visual checks performed with this tool are subjective. What you see depends on ambient light, viewing distance, your eyes and how the browser and system handle color. These checks help you inspect a screen by eye — they are not a substitute for a hardware colorimeter, professional calibration or the manufacturer’s own quality control.

Frequently Asked Questions

Can a browser test really judge a monitor?

It puts on screen exactly the pattern each defect needs to become visible — a black field for bleed, single-pixel lines for sharpness, moving blocks for ghosting — and your eyes do the judging. What it cannot do is put numbers on color accuracy or brightness; that takes a colorimeter and a controlled room. Use it to spot defects while a return window is open or to sanity-check picture settings.

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

A dead pixel stays black on every color because its subpixels never switch on. A stuck subpixel is frozen lit, so the dot glows red, green, blue or another color on some backgrounds and vanishes on others. Most makers tolerate a few defects before a warranty replacement applies, and the thresholds differ by brand and panel class — count and photograph what you find before contacting support.

Why does the measured refresh rate read lower than the spec?

The reading tracks how fast the browser is allowed to draw, which normally equals the refresh rate of the screen the window sits on. It drops when the window is on a slower secondary display, a power-saving mode caps the rate, or heavy tabs and apps steal frame time. Rule those out and measure again before blaming the monitor.

Is some backlight bleed normal?

Nearly every LCD leaks a little light on a black frame in a dark room; at normal brightness with the lights on it is usually invisible. Corner glow that moves when you shift your head is IPS glow, a property of the panel technology rather than a defect. Fixed bright patches visible at everyday settings are worth an exchange while you can still return the screen. OLED panels switch pixels off entirely and show no bleed.