Set aside, 4K: High Dynamic Range (HDR) is the most exciting image leap since the transition to HD and is available on more TVs than ever before. But if you take home your shiny new HDR TV just to find that the programs are too dark to watch, you might think there’s something wrong, after all, isn’t HDR just shine? This is what is happening and what you can do to brighten the image.
Why HDR looks dark on some TVs
The movies and shows you’ve been watching for years were dominated in what we now call standard dynamic range or SDR, and it’s actually quite weak, dominated with maximum brightness levels of just 100 nights. Most modern LCD TVs, however, are capable of shooting 300 nights or more when playing this SDR content, so if you’re in a brightly lit room, you can only turn on the backlight, which increases the brightness of everything shown in the image. —From dark shadows to bright reflections.
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 bright parts. In HDR, highlights can be 1,000 nights or more, depending on the capabilities of the TV. In HDR, a sun shining through the woods will really appear against the gloomy foreground or a bonfire will shine like an oasis of heat against the dark desert night. On the right TV, it creates an amazing picture, but that doesn’t mean the whole picture is brighter than its SDR counterpart, they just are. The average brightness of the HDR scene should, in theory, be similar to the same scene in SDR (although it can vary from movie to movie, depending on how it is rated).
However, there is a problem: many TVs set the maximum contrast and backlight levels in HDR mode, so they cannot be increased for the well-lit living room as can be done with SDR content. This is not true all TVs, but it’s common and can leave you pickled.
Even worse, some TVs actually to darken the image to compensate for your HDR errors. “The light output of many valuable 4K HDR TVs is often no different than that of many non-HDR TVs,” says Robert Heron, a professional TV calibrator and host of AVExcel home theater podcast. This is more common on cheaper TVs, but can happen with certain mid-range or even high-end models that reduce brightness. Combine that with HDR’s wider color palette, which many of these low-performance TVs can’t play, and the TV needs to do something to make up for its shortcomings.
When a TV cannot reproduce these bright aspects at the specified levels, it performs a process called tone mapping to adjust the content to its functions. Suppose you have a low-end TV that can only have 350 nights in HDR. When playing a scene that has a bounce of 1,000 nights, you must adjust the scene so that the bounce is only 350 nights. There are two main ways to deal with television engineers:
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Some TVs will “trim” bright tones, maintaining the average brightness of the scene where it is located. The image doesn’t darken much, but the highlights can be a bit blown away.
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Other TVs will reduce the average brightness of the scene, retaining the details in the highlights, but making the overall picture darker than originally dominated.