Web & Diagnostics
Screen Colour Test
Fill the screen with solid colours, greys and gradients to find dead pixels and banding.
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Keyboard: ← and → step, Space starts and stops the cycle, F toggles full screen, Esc leaves it.
A dead pixel is easy to miss in normal use and impossible to miss once you know it is there — which matters if the screen is inside its return window. The test is simple: fill the panel with each primary colour in turn and look closely.
This page shows solid colours, a full grey ramp for spotting banding and uneven backlighting, and a full-screen mode so browser chrome is out of the way. A cycling mode sweeps through the colours automatically while you watch for stuck pixels, which are often easier to spot in motion than standing still.
How to use it
- Choose a preset. RGB and white is the standard dead-pixel sweep; greyscale ramp is the one that exposes banding and backlight bleed.
- Press Full screen (or the F key) so nothing but the colour is on the panel.
- Use the arrow keys to step through colours one at a time, or press Cycle to sweep automatically.
- Set the cycle speed. Slow for inspecting one area, fast for spotting a stuck pixel that flashes against different backgrounds.
- Clean the screen first and look from normal viewing distance as well as up close — dust looks exactly like a dead pixel until you wipe it.
- Switch to the gradient mode to check for banding: smooth ramps should be smooth, not stepped.
Questions
What is the difference between a dead, stuck and hot pixel?
A dead pixel stays black on every colour because no light is coming through. A stuck pixel is fixed on one colour — often bright red, green or blue — and shows up on dark backgrounds. A hot pixel is stuck white. Stuck pixels occasionally recover after a long video or a press-and-release, but a truly dead one does not.
How do I check backlight bleed?
Use the solid black screen in a dark room. On an LCD, look for light leaking in at the edges and corners; that is backlight bleed and it is normal to a degree. On an OLED, black should be indistinguishable from the screen being off, and any grey haze there is a fault rather than a characteristic.
Is the banding I see the monitor's fault?
Usually, though not always. Most 8-bit displays show some stepping in very smooth gradients, and cheap panels show much more. It can also come from a compressed source image or an aggressive colour profile in the operating system. The gradient preset uses every stop at full range, so if it is smooth here, that is the panel's best case.