desktest.net
guide

Display Test Guide

A reference for the desktest.net Display Test. Explains what the browser can and cannot tell you about a monitor, how to read the verdict, and what to do about each failure. Read this before you swap a panel that might only need a cable or a color profile.

Open the Display Test ->

What does the Display Test check?

The browser exposes very little information about the physical display. There is no API for dead pixels, no API for panel bit depth, and no API for color accuracy. The Display Test combines the few values that are readable with a guided visual check, then turns your yes/no answers into a verdict. Three steps run in order:

  1. Display capabilities. Reads screen.width, screen.height, screen.availWidth, screen.availHeight, screen.colorDepth, screen.pixelDepth, and window.devicePixelRatio. Also reads system preferences through matchMedia: prefers-color-scheme, prefers-reduced-motion, and prefers-contrast. A width under 1024px or a color depth under 24-bit is flagged as a warning, not a hard fail.
  2. Color reproduction. You click each pattern button to fill the screen: solid red, green, blue, white, black, plus CMYK bars, RGB bars, and a black-to-white grayscale gradient. Press Esc or click to exit. Two yes/no questions follow: did the solid colors match their names, and did the gradient look smooth with no banding?
  3. Dead-pixel and uniformity scan. Auto-cycles through red, green, blue, white, and black for about two seconds each. Watch for a single dot that stays the wrong color (stuck pixel), a single dot that stays black (dead pixel), or dim and bright patches across the surface (backlight or burn-in). Two yes/no questions follow: did you see any dead or stuck pixels, and did the screen look uniform?
What this tool cannot do: it cannot measure absolute color accuracy, cannot detect a 6-bit panel pretending to be 8-bit, and cannot tell whether "white" looks white to you. Color-critical workflows still need a hardware colorimeter.

When should I run this?

Reading the results

Each step renders a row with a status badge: Pending (grey), Running (yellow), Pass (green), Partial (yellow), or Fail (red). On fail or partial, the row expands and shows the recorded answers plus a fix block per issue.

The verdict panel at the top summarises the run with a likely cause and a recommended next step. It is opinionated and reflects the common real-world reason for each failure. If the verdict is wrong for your case, the per-failure fix block under the failing row covers the rest.

Copy Diagnostic Report copies a plain-text report to the clipboard: screen metrics, browser user-agent, per-step results, yes/no answers, named diagnosis per step, timestamp. Paste it into a ticket or email.

Reminder: Esc or a single click exits any full-screen overlay at any time. You are never trapped in a pattern, even mid-scan.

Common failures and fixes

The tool produces a specific named diagnosis for every failure path. Each diagnosis maps to a fix. Here they are, in the order the steps run.

low-resolution: reported width is below 1024px

The probe came back with a screen.width below 1024. Modern hardware rarely runs that low. Usual causes:

  1. The display is in a Windows fallback mode (640x480 or 800x600) after a driver crash. Reboot, then in Settings, System, Display, set the panel to its native resolution.
  2. The graphics driver is missing or generic. Install the vendor driver: NVIDIA, AMD, or Intel.
  3. The cable cannot carry the panel's native mode. HDMI 1.4 tops out around 4K30 or 1440p60. For 4K60 or 1440p144 you need HDMI 2.0 or higher, or DisplayPort. For 4K120 or 8K, HDMI 2.1 or DisplayPort 1.4 with DSC.
  4. The system is a constrained kiosk or thin client locked to a low mode by group policy.

low-color-depth: reported color depth under 24-bit

The probe returned a screen.colorDepth below 24. Modern desktops should be 24-bit (8 bits per channel) at minimum, and most are 32-bit (8 bpc + alpha). Below that means visible banding on photos and gradients.

  1. Windows: Settings, System, Display, Advanced display settings. The bit depth is shown per output. If it is stuck at 16-bit, update the graphics driver.
  2. On a remote desktop session (RDP), the host may downgrade to 16-bit for bandwidth. Check the RDP client's Experience tab and set color depth to highest available.
  3. Some old VGA outputs cap at 16-bit at high resolutions. Switch to DVI, HDMI, or DisplayPort.

color-fail: solid colors did not match their names

Red looked pink, blue looked purple, white was tinted, or one channel was missing. Most likely cause is the color profile or the cable.

  1. Check the cable first. Reseat both ends. DisplayPort connectors have lock-tabs that must engage; press them while pulling to release, and listen for the click when reseating. A loose DP cable is a top cause of missing-channel symptoms. A bent HDMI pin or damaged shield can drop a color channel too.
  2. ICC profile. On Windows, open Settings, Display, Advanced display settings, then Color Management. Make sure the assigned profile is for this exact monitor and not a leftover from a previous panel. If unsure, set to sRGB IEC61966-2.1 as a generic baseline.
  3. Run Display Color Calibration. In Start, search for "Calibrate display color" (dccw.exe). Step through gamma, brightness, contrast, and color balance. It writes a new ICC profile.
  4. Reset the monitor. Use the on-screen menu factory reset. Pre-set picture modes ("Cinema," "Game," "Vivid") often crush or shift colors.
  5. Swap the cable. Cheap HDMI cables that pass at 1080p often fail at 4K60 with sparkles or missing red.

banding: visible bands in the grayscale gradient

The black-to-white ramp showed stripes instead of a smooth fade. Three usual causes:

  1. 6-bit panel. Many cheap LCDs are 6-bit and use frame-rate-control dithering to fake 8-bit. Mild banding is expected. Check the panel spec sheet.
  2. Driver downsampling. In NVIDIA Control Panel, AMD Radeon Settings, or Intel Graphics Command Center, raise output color depth to the highest available (10-bit if supported, otherwise 8-bit). Set Output Dynamic Range to Full; Limited range crushes the bottom of the gradient.
  3. Lower the refresh rate and test. Some monitors run 10-bit only below 120Hz. Drop to 60Hz in Windows display settings and re-check the gradient.

dead-pixels: dead or stuck pixels reported

A stuck pixel is always on one color (a tiny red, green, or blue dot). A dead pixel is always black on every pattern.

  1. Massage and rapid cycle. Rapidly cycle solid colors over the affected area (the Display Test color patterns work for this) for 10 to 30 minutes, and combine with gentle finger pressure through a microfibre cloth on the stuck pixel. Recovers a fair share of stuck (not dead) pixels.
  2. Truly dead pixels do not recover in software.
  3. Warranty replacement. If you can see more than one or two dead pixels, file a warranty claim. Most vendor policies allow return at that point.
  4. On a customer-facing display, replace the monitor outright.

non-uniform: dim or bright patches across the screen

Patches of different brightness on the solid-white pattern, or color tinting on solid-gray. Almost always a panel issue.

  1. LCD backlight failure. A bright patch at one edge means the diffuser is failing or an edge LED has shifted. Worsens over time. Not fixable in software.
  2. OLED burn-in. A faint ghost of a previously displayed image on solid colors. Permanent. Lower brightness and enable pixel-shift to slow further damage.
  3. Confirm in a dark room. View solid-white with the lights off; backlight bleed at corners is much easier to spot.
  4. Warranty. File a claim with photos of the solid-white and solid-gray patterns.

user-cancel: diagnostic was aborted

You clicked Cancel on the color or pixel questions before answering any. Not a hardware failure, just an incomplete run. Click Run Display Test again and answer through to the end.

limited: some questions were skipped (partial pass)

You clicked Skip remaining questions with some answers still empty. The verdict shows what was answered, but the picture is incomplete. Rerun for a definitive result.

For IT admins

Display config differs per OS. Document the steps for your fleet so the helpdesk does not have to look them up each call.

Windows. ICC profile assignment lives in Settings, Display, Advanced display settings, Display adapter properties, Color Management. The calibration wizard is dccw.exe. Graphics driver settings (output color depth, dynamic range) live in NVIDIA Control Panel, AMD Radeon Settings, or Intel Graphics Command Center. For Group Policy, ICC profiles can be deployed per user with Add-PrinterColorProfile style PowerShell, or pushed as part of the OS image.

macOS. System Settings, Displays, then the Color tab. Color profile per display. Calibrate opens the Display Calibrator Assistant (hold Option when clicking for expert mode with white-point and gamma controls). Profiles live in /Library/ColorSync/Profiles for shared, ~/Library/ColorSync/Profiles for per-user. Deploy via MDM with a configuration profile that copies the ICC into the shared folder.

Bulk monitor QA workflow. When deploying a batch of new monitors:

  1. Connect each unit to a test workstation before it is racked or shipped.
  2. Run the Display Test and the dead-pixel scan with the room lights off.
  3. Save the diagnostic report with the monitor serial number and the receiving date.
  4. Flag and return any unit with: more than two dead pixels, any dead pixel within the central third of the screen, banding visible on the gradient, or backlight patches visible on solid white.
  5. Keep a per-vendor failure rate. If one supplier averages above 2 percent rejection, escalate to procurement.

Warranty escalation criteria. Manufacturer policies vary. Dell's Premium Panel Exchange covers a single bright pixel. LG, Samsung, ASUS, and BenQ each publish dead-pixel thresholds based on ISO 9241-307 panel class. Class II (the common consumer class) allows up to 2 bright, 2 dark, and 5 stuck subpixels per million. Class I allows zero. For monitors above 1080p, that is "any visible defect" in practice. Keep the policy text bookmarked per vendor; the support line will not always quote it back accurately.

Behind the scenes

The probe reads screen.width, screen.availWidth (the area not covered by the taskbar or dock), screen.colorDepth, and window.devicePixelRatio. A 1.0 ratio means logical pixels equal physical pixels; 2.0 is the typical high-DPI macOS Retina or Windows 200% scale. The matchMedia queries surface the user's system preferences (dark mode, reduced motion, contrast) so a kiosk you ship can honor them without extra config.

Full-screen patterns use a position: fixed overlay with width and height set to 100vw and 100vh. The overlay sits at z-index: 1000 and covers the viewport. The Fullscreen API is not used as a primary mechanism, because users must be able to press Esc to exit at any time and some kiosk shells block requestFullscreen entirely. The browser's address bar still hides on most platforms because the overlay grabs the full viewport.

The dead-pixel cycle uses setTimeout to advance every two seconds. Each step is a single CSS background change driven by a class swap on the overlay element, one solid color at a time. There is no requestAnimationFrame loop or animation involved; the class swap repaints the whole overlay in the next color.

Nothing is uploaded. The probe values, the answers, and the report all live in this tab. View source on the page to confirm.