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Why HDR looks too dark on TV and how to fix it



4K aside: Since the transition to HD, high dynamic range (HDR) has been the most exciting jump in image quality, and it has unprecedented popularity on TV. However, if you take home a shiny new HDR TV and find that the show is too dark to see, you might think this is problematic-after all, is HDR more than just brightness? This is what is happening, what can you do to make the picture brighter.

Why HDR looks dark on some TVs

The movies and TV shows you’ve been watching for years are in what we now call standard dynamic range (SDR) and are actually quite dim, with only a peak brightness level of about 100 nits. However, most modern LCD TVs can output 300 nits or more when playing the SDR content, so if you are in a brightly lit room, you can increase the brightness of the backlight, thereby increasing the brightness of all content in the image . -From dark shadows to bright highlights.

HDR is different. As the name suggests, its main purpose is to create a higher dynamic range, that is, the gap between the dark and bright parts of the scene is larger. In HDR, depending on the function of the TV, the highlight part can be 1

000 nits or more. In HDR, the sunlight passing through the forest will indeed suddenly appear in the dark foreground, or the campfire will glow like a warm oasis in the dark desert night. On the right TV, this would produce an incredible image, but it doesn’t mean that the entire image is brighter than its SDR counterpart-only those highlights are. In theory, the average brightness of an HDR scene should be similar to the same scene in SDR (although different movies may be different depending on how they are graded).

However, there is a problem: Many TVs use the maximum backlight and contrast level by default in HDR mode, so for content like SDR, you can’t adjust them higher in a well-lit living room.This is not true all TV, but this is very common, and it will annoy you.

To make matters worse, some TVs actually darken This image makes up for the lack of HDR. “The light output of many valuable 4K HDR TVs is usually no different from the light output of many non-HDR TVs,” said professional TV calibrator and host Robert Heron. AVExcel Home theater podcast. This is most common on cheap TVs, but some mid-range and even high-end models may reduce brightness. Combine it with the wider color palette of HDR, which cannot be reproduced by many poorly-performing TVs, so TVs must take some measures to compensate for their shortcomings.

When the TV cannot reproduce these bright highlights at the specified level, it will perform a process called “tone mapping” to adapt the content to its function. Suppose you have a low-end TV that can only play 350 nits of HDR. When playing a scene with 1,000 nits of highlights, the scene must be adjusted so that the highlights are only 350 nits. TV engineers have two main methods:

  • Some TVs will “cut” the highlights, thereby keeping the average brightness of the scene in place. The picture will not darken too much, but the highlights may be slightly discolored.

  • Other TVs will lower the average brightness of the scene, retaining the details in the highlights, but making the overall image darker than the original image.


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