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Black Level Test
Near-identical black blocks that reveal how many dark tones your screen genuinely resolves.
A great deal of the detail in any dark scene lives at the very bottom of the greyscale: the folds of a curtain in shadow, the outline of a figure in an unlit corridor, the texture of a wall out of the light. If your setup crushes those tones, they all collapse into one flat black and the information simply disappears. That phenomenon is called black crush, and it is one of the most common image problems and one of the easiest to overlook, because it produces no eye-catching artefacts — it just quietly stops you seeing things.
This test shows a row of black blocks with values very close to one another, from absolute black to a barely hinted grey. The question is simple: how many can you separate from the background and from each other? If you see them all, your video chain is reproducing the low tones correctly. If the first few merge into a single black smear, you have black crush, and it is worth finding out where it comes from, because more often than not the cause is a setting rather than the panel.
How to Run the Test and What It Cannot Tell You
Switch the room lights off and go full screen. Wait two or three minutes before judging: dark adaptation completely changes what you will see, and many users conclude their monitor crushes blacks when in reality their own pupils have not yet opened. Then scan the blocks from left to right and count where you begin separating them from the background. Work at your usual brightness and note the result; afterwards you can repeat with higher brightness to see how much it changes. Be clear about the limits. Visual adaptation, reflections from any light source on the glass and your viewing angle all matter enormously, especially on VA panels, where black near the edges lightens noticeably when viewed off-axis. It is also not a contrast measurement: it tells you nothing about the panel's contrast ratio or minimum luminance, only whether the incoming signal still carries the shadow information. And on HDR displays the result can vary with the active mode, so run it in standard mode.
How Many Blocks You Should See
Count how many blocks you can separate from the black background in a dark room with your eyes adapted. The table turns that count into a diagnosis and the setting worth checking first.
| Distinguishable blocks | Diagnosis | Suggested adjustment |
|---|---|---|
| All visible | The whole chain reproduces the low tones without losses. Your setup preserves every scrap of available shadow detail. | None. Save this configuration as a reference before touching any of the monitor's picture modes. |
| 1 block missing | Minimal loss at the very bottom of the scale. This is common and rarely noticeable in real content. | Acceptable as is. If it bothers you, raise brightness a step or two and see whether the block appears. |
| 2-3 blocks missing | Moderate black crush. In dark game scenes you will start losing silhouettes and shadow texture. | Check brightness and, above all, verify the RGB range on both the graphics output and the monitor. |
| 4-5 blocks missing | Severe crushing. The entire lower portion of the scale has collapsed into one black smear. | Almost certainly a configuration issue: limited RGB range, high gamma or a cinema picture mode. |
| Black only | You cannot separate a single block. The shadow information was lost before it ever reached the panel. | Repeat with dark-adapted eyes. If it persists, factory reset the monitor and force full RGB range. |
Why Black Level Matters
In games, black crush is not merely an aesthetic issue but a competitive one. On a night map or in an unlit interior, an opponent crouched in a dark corner is separated from the background by a difference of two or three grey levels. If your setup flattens that part of the scale, that opponent simply does not exist for you until they open fire. The same goes for environmental details the designer placed as cues: a half-open door, a descending staircase, the shadow of an interactive object. The game becomes harder for a reason that has nothing to do with your skill.
The most frequent and least understood cause is RGB range. A video signal can carry the full set of values, 0 to 255, or the limited range inherited from consumer video, 16 to 235. If your graphics card sends full range while the monitor or television expects limited, everything below 16 is clipped and blacks crush; if the reverse happens, blacks look grey and washed out. The problem crops up very often over HDMI, where the graphics driver spots a television and switches to limited mode on its own, sometimes after nothing more than a routine update.
Fixing it is usually quick once you know where to look. The graphics card control panel has an output dynamic range setting that must match what the display expects: for a computer monitor, full range is the norm. The monitor or television menu usually has an equivalent option, sometimes labelled black level, with values such as low and high, or normal and expanded. Align both sides and run the test again. If nothing changes, check gamma and the picture mode next, and only then start suspecting the panel itself.
Tips for an Accurate Diagnosis
- Give yourself three minutes in the dark before counting blocks: your pupils need that time to open.
- Look straight on, especially on VA panels, where black near the edges lightens sharply off-axis.
- Check the RGB range in both the graphics driver and the monitor menu, and make them match.
- Turn off HDR, local dimming and cinema picture modes before drawing any conclusions.
- Try another cable or port if the range keeps changing on its own; some combinations negotiate badly.
- Write down how many blocks you see before and after each change, so you know which fix actually helped.
Frequently Asked Questions
What exactly is black crush?
It is the loss of detail in the darkest tones of an image. Several distinct levels of black and very dark grey are displayed as one flat black, so all the information they carried disappears. It shows up most in night scenes, unlit interiors and deep shadows, where instead of textures and silhouettes you see a uniform smear. It produces no visible artefacts or flicker, which is why many people live with it for years without realising their screen is hiding information from them.
What is the difference between limited and full RGB range?
It is the span of values the signal uses to represent black through white. Full range uses the entire scale, 0 to 255, and is the norm in computing. Limited range uses 16 to 235, a convention inherited from consumer video. If sender and receiver disagree, the scale gets stretched or clipped: when the graphics card sends full and the display expects limited, everything below 16 is lost and black crush appears. In the opposite case blacks look greyish and the image loses contrast.
How do I fix black crush on my monitor?
Start with RGB range. In the graphics card control panel find the output dynamic range setting and set it to full if you are using a computer monitor; then check whether the display menu has an equivalent black level option and align it. If that is not enough, look at gamma: too high a value closes up shadows. Next check the picture mode, because cinema presets and contrast-enhancement modes flatten the bottom of the scale. Brightness should be the last thing you touch, since it affects the whole image.
Should I raise brightness to see more blocks?
Only if brightness is genuinely the problem, and often it is not. Raising panel brightness lifts the whole scale evenly, so you will see an extra block but also a greyer black, less overall contrast and more eye strain. If blocks are missing because the signal arrives clipped by a badly negotiated RGB range, more brightness does not recover that information — it merely lightens what is left without restoring detail. Diagnose the cause first and leave brightness at whatever level is comfortable for your eyes.
Does an OLED panel always show every block?
Not necessarily. An OLED reaches perfect black because it switches the pixel off, which gives it an enormous contrast advantage, but how it reproduces the tones just above black depends on how the panel handles those minimum values, and some models struggle precisely in that region. On top of that, a misconfigured RGB range clips the signal before it ever reaches the panel, so an OLED with a badly negotiated limited range suffers exactly the same black crush as any LCD.