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What is “Black Crush” on a screen?



A scene that could cause

Have you heard the term “black crush” while watching TV or monitor reviews? The issue is gaining attention as display manufacturers attempt to improve blacks, especially on LED-lit LCD models. So what are ‘crushed blacks’ and should you be concerned about them?

Black Crush means loss of shadow detail

Black crush refers to the loss of fidelity in particularly dark areas of an image. The term can apply to both photography and video, but is most commonly used to describe the loss of shadow detail in moving images such as movies and games.

You may not immediately notice Black crush until you see the “correct”

; image next to it (for example, on another screen that has been properly calibrated). You can see a simulated example in the image below, where the right side has lost detail in the bricks under the shadow. In other words, this image has “crushed blacks”.

Black Crush Example
Tim Brookes

The issue is unlikely to make the content unwatchable, but it detracts from the overall presentation. In movies, you might miss subtle details around the edge of the frame, while the problem can make it far too difficult to see what’s happening in some games (especially in brightly lit rooms).

There are all kinds of reasons why black infatuation can occur, and not all of them are due to the display. If the shadow detail wasn’t captured in the first place because the camera wasn’t set up for it, blacks will appear crushed. Some directors and photographers use this technique to intentionally create negative space.

Your TV or monitor makes the difference

All too often the problem lies with the display or source device (such as a game console). Many games require the player to calibrate gamma and white point when the software is first launched, and setting this incorrectly (or setting it incorrectly at the system level) can lead to loss of shadow detail. Sometimes games implement HDR poorly, which also causes black crush.

Most consumer displays are never calibrated when they leave the factory and without proper calibration by a professional they will always produce an image that differs from the source. This is why content creators and photographers are strongly encouraged to use a calibrated screen when editing their work.

LG G1 OLED Evo
LG

Sometimes the TV is really the problem. OLED is a self-emitting display technology, meaning the pixels can be turned off to display “true” black. Unfortunately, OLED also struggles to get out of black, which can lead to a loss of shadow detail in some models as the TV struggles to reproduce the subtle tones that exist between the “on” and “off” states at the pixel level.

Many LED-lit LCD TVs now use dimming algorithms to turn off or reduce the light behind dark or black scenes. This helps the TV produce a much deeper black level, but it almost always comes at the cost of shadow detail. In general, the more dimming zones a display has, the less serious the problem will be.

How to test your own display for Black Crush

An easy way to test for black crush is to use a starfield test. On a black crush display, many of the stars will not be visible. On an OLED, the vast majority of stars should be visible, as a bright white pixel can sit next to a pure black one without a dimming algorithm interfering with the image.

If you’ve just realized what you’ve been missing, read our guide to buying a TV (or a TV for gaming) before parting with your money.

RELATED: Buying a TV: what you need to know




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