Black level test
A near-black ladder at known code values. Count how many patches you can separate from the background, and you know whether your shadows are being crushed.
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The patches are at sRGB code values 0, 1, 2, 3, 4, 5, 8, 12 and 16, left to right, on a background of code 0. Code 16 is the floor of the limited RGB range, which is why it is the last rung on the ladder.
How to run this test
- Dim the room. Near-black detail is the one thing genuinely worth checking in low light, because ambient light washes it out completely.
- Go full screen and let your eyes adapt for a good minute. This test is useless in the first ten seconds.
- Count how many patches you can separate from the black background, starting from the left.
- If the first few are invisible, raise your display brightness a little, or lower contrast, and count again.
- If they are still invisible, check your RGB range setting. A full-range source feeding a limited-range display crushes everything below code 16.
What a problem looks like
- Everything below code 5 is invisible
- Mild crushing, and very common. Usually a brightness setting that is slightly too low for the room. Raise brightness a step at a time and recount; the patches should start appearing one by one.
- Everything below code 16 is invisible
- The signature of an RGB range mismatch. Limited range uses codes 16 to 235, so a display expecting limited range that receives full range throws away everything under 16. Check the range setting on your GPU, your console or your television HDMI input.
- The background is not actually black
- On an LCD this is normal: the backlight is still on. If it looks noticeably grey, check whether the opposite range mismatch is in play, which lifts black off the floor instead of crushing it. The backlight bleed test covers the leakage side.
- The patches appear but the steps look uneven
- Code 1 to 2 looking like a bigger jump than 4 to 5, for example, points at the gamma curve near black rather than at clipping. Common, and mostly a characteristic rather than a fault.
- All nine patches are clearly visible
- A good result. Your display is passing shadow detail through rather than throwing it away, which is what you want for dark film scenes and for games with any night content.
What to do next
If something looks wrong, check it again in a normally lit room and from straight on, then check whether it appears on a second device. If it only happens on this screen and you are still inside the return window, that is the time to contact the retailer.
Questions people actually ask
What is a PLUGE pattern?
PLUGE stands for Picture Line-Up Generation Equipment, a broadcast test pattern with patches just above and around black. It exists so an engineer can set brightness to the point where the just-above-black patches are visible and true black stays black. The ladder here is the same idea in a form you can run at home.
How many patches should I be able to see?
On a well-adjusted display in a dim room, all of them, including code 1. Seeing everything from code 2 upwards is a perfectly good result. If you cannot see anything below code 8, something in your chain is crushing shadow detail.
What is limited versus full RGB range?
Full range uses all 256 code values from 0 to 255. Limited range uses 16 to 235, a convention inherited from broadcast video. If the source and the display disagree about which one is in use, you either lose all shadow detail below 16 or get washed-out, greyish blacks. It is a single setting on most GPUs and televisions, and it is one of the most common causes of the problem this test reveals.
Can this measure my black level?
No. Black luminance is measured in candelas per square metre with a photometer in a dark room, which no browser can do. What this shows is whether detail near black survives the journey to your panel, which is the part you can actually act on.
Why does my OLED show all the patches easily?
Because its black really is black, so the contrast between the background and even code 1 is enormous. OLED panels tend to do well here. The flip side is that some OLEDs handle very dark near-black transitions unevenly, which shows as blotchiness rather than as missing patches.