Screen Soft Light / Diagnostics / UNIFORMITY TEST

Grey 20% (RGB 51, 51, 51), step 4 of 9

Arrow keys or Space step the grey, R toggles the ramp, F goes fullscreen.

No. 001 · UNIFORMITY TEST

Screen uniformity test with full-screen grey levels

  • 01 Grey steps 5% to 75%
  • 02 Banding ramp
  • 03 Keyboard and tap controls

Flat grey screens show what white and black hide: blotches, bands, colour tints and the dirty screen effect. Step through nine grey levels fullscreen with the arrow keys or a tap, then check a smooth ramp for banding.

§ 01

What each grey level reveals

Very dark greys (5 to 15%) expose the weak points of OLED panels, where each pixel turns on at a barely-there current: you may see vertical stripes, a green or magenta tint, or a blotchy pattern. On LCDs the same levels show clouding and backlight zones. Mid greys (25 to 50%) are the best for dirty screen effect and for comparing the left and right sides of a panel. Light greys (75%) show edge vignetting and colour shifts across the screen.

§ 02

OLED panels are made of millions of independent light sources, and the first few percent of brightness is the hardest range to control.

OLED and AMOLED uniformity

OLED panels are made of millions of independent light sources, and the first few percent of brightness is the hardest range to control. Some phones show a faint vertical line or tint at 5 to 10% grey, particularly at low brightness. Dirty screen effect appears as a mottled or streaky look on a flat grey, and can be stronger on new displays. Compare at your normal brightness, and run the test again after a few weeks if the unit is new, since some panels settle in.

§ 03

IPS and VA uniformity

IPS panels are prone to corner glow and clouding on dark greys, and brightness falloff towards the edges on light greys. VA panels can show a darker centre or dark edges depending on how the panel is stretched. Small variations of a few percent are normal. A visible patch, a clear tint on one side or a bright band across the screen is worth documenting.

§ 04

How to read the results

Write down the grey level at which you first notice each problem, and take a photo of the worst one. If a defect only appears at a grey that you rarely see in real content, such as 5%, it may not matter in use. If it shows on 25 to 50% grey, you will see it in sports, skies and documents. Always compare against another screen of the same model before deciding it is a fault.

Procedure

Three moves to peak output

  1. 01

    Set up the room

    Dim the lights, turn off night-shift or colour filters, and use the brightness you normally work at.

  2. 02

    Start dark and go fullscreen

    Press F, then use Space or the arrow keys to move through the greys. On a phone, tap the grey to step to the next level.

  3. 03

    Scan each level

    Look for blotches, bands, tinted corners and grain. Stay on each grey for a few seconds, because your eyes need time to adapt.

  4. 04

    Finish with the ramp

    Press R for the black to white ramp. Smooth, even steps are good. Wide bands or sudden jumps are worth investigating.

Inquiries

Questions worth asking

Q.01 How do I check screen uniformity?
Open the grey test, go fullscreen and step through the grey levels from 5% up to 75%. At each level look for blotches, vertical or horizontal bands, tinted corners and a mottled grain. Dark greys such as 5% to 25% show the problems best. Run it in a dim room at the brightness you normally use.
Q.02 What is OLED grey uniformity or the dirty screen effect?
Dirty screen effect (DSE) is a faint mottled or streaky pattern on a flat grey image, most visible on panels that pan sideways across a scene such as sports. Some OLED phones and TVs also show vertical banding or a green or pink tint at very low grey levels. A grey test makes both visible, since a photo or a dark film scene would hide them.
Q.03 What is the banding ramp for?
The ramp is a smooth black to white gradient. A good 8-bit panel shows fine, even steps. Wide visible bands, or steps that jump suddenly, point to a limited colour depth setting, a low-bit panel or a driver and cable problem. Note that a browser may dither or colour-manage gradients, so use it as a hint.
Q.04 Why do the greys look different on my second monitor?
Panels vary in gamma, colour temperature and brightness, and the grey levels are sent as the same RGB values to both. If one monitor shows a tint or blotches that the other does not, that points to a panel difference. Check both monitors on the same input type and with the same colour profile.
Cross-reference

Try adjacent plates