Step aside, 4K: High dynamic range (HDR) is the most interesting leap in image quality since the transition to HD and is available on more TVs than ever before. But if you bring home your new bright HDR TV just to find that the shows are too dark to see, you might think there’s something wrong – after all, isn’t HDR just brightness? Here’s what happens and what you can do to brighten the picture.
Why HDR looks dark on some TVs
The movies and shows you’ve been watching for years have been mastered in what we now call standard dynamic range or SDR – and it’s actually quite weak, controlled with a maximum brightness level of only about 100 nits. Most modern LCD TVs, however, are capable of outputting 300 nits or more when playing SDR content, so if you are in a brightly lit room, you can carry the backlight, which raises the brightness of everything in the picture. . “From dark shadows to bright lights.”
HDR is different. Its main purpose is, as its name suggests, to create a higher dynamic range – that is, a larger gap between the dark parts of a scene and the light parts. In HDR, the bright lights can be 1,000 nits or more, depending on the capabilities of the TV. In HDR, a sun shining through the forest will really appear in the shady foreground or a campfire will shine like an oasis of warmth in the dark night of the desert. On the right TV, this creates an incredible picture, but it doesn’t mean that the whole picture is brighter than its SDR counterpart – it’s just those important moments. The average brightness of the HDR scene should, in theory, be similar to the same scene in SDR (although this may vary from movie to movie, depending on how it was graded).
However, there is a problem: Many TVs set the maximum backlight and contrast level in HDR mode, so you can’t open them above for the well-lit living room, as you can, with SDR content. Not true all TVs, but it is common and can leave you in a pickle.
Even worse, some TVs actually darken image to compensate for HDR defects. “The light output of many valuable 4K HDR TVs is often no different from that of many non-HDR TVs,” says Robert Heron, a professional TV calibrator and host of AVExcel home theater podcast. This is most common on cheaper TVs, but can happen with certain midrange or even high-end models that cut corners on brightness. Combine it with the wider color palette of HDR, which many of these low-performance TVs can’t reproduce, and the TV needs to do something to make up for its shortcomings.
When a TV cannot reproduce those bright lights at the specified levels, it performs a process called tone mapping to match the content to its capabilities. Suppose you have a state-of-the-art TV that can only have 350 rivets in HDR. When playing a scene that has a 1,000-rivet highlight, you need to adjust the scene so that the highlight is only 350 rivets. There are two main ways to approach TV engineers:
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Some TVs will “flash” the bright lights, keeping the average brightness of the scene in which they are. The image will not darken too much, but the highlights may be a little blown.
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Other TVs will reduce the average brightness of the scene, keeping the details in highlights, but making the overall picture darker than it was originally mastered.