Tuesday, April 20, 2021

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

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Step aside, 4K: High dynamic range (HDR) is the most exciting jump in picture quality since the transition to HD, and it’s available at more televisions than ever. But if you take home your shiny new HDR TV to find that the shows are too dark to see, you might think there’s something wrong – after all, HDR isn’t just about brightness? Here’s what’s going on and what you can do to brighten up 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 pretty low, overpowered with peak brightness levels of just around 100. slow. However, most modern LCD TVs are capable of producing 300 nits or more when playing this SDR content, so if you are in a well-lit room you can just turn up the backlight, which increases the brightness of everything. which is in the picture. “From dark shadows to highlights.

HDR is different. Its main purpose is, as the name suggests, to create a higher dynamic range, i.e. a larger gap between the dark parts of a scene and the bright parts. In HDR, highlights can be 1000 nits or more, depending on the capabilities of your TV. In HDR, a sun shining through the forest will truly appear against the shaded foreground, or a campfire will shine like an oasis of heat against the dark desert night. On the right TV, this creates an amazing picture, but that doesn’t mean the entire image is brighter than its SDR counterpart – only those reflections are. The average brightness of the HDR scene should, in theory, be similar to that same scene in SDR (although this could vary from movie to movie, depending on how it was rated).

However, there’s a catch: many TVs default to the maximum backlight and contrast levels in HDR mode, so you can’t increase them for that well-lit living room like you can with SDR content. It is not true of all TVs, but it’s common, and it can leave you confused.

Worse still, some televisions darken the image to compensate for their HDR failures. “The light output of many valuable 4K HDR televisions is often no different than that of many non-HDR televisions,” says Robert Heron, a professional TV calibrator and host of AVExcel home theater podcast. This is more common on cheaper TVs, but it can happen with some mid-range or even high-end models that lower the brightness. Combine that with HDR’s wider color palette, which a lot of these lower-performing TVs can’t reproduce, and the TV has to do something to make up for its shortcomings.

When a TV cannot reproduce these highlights at specified levels, it performs a process called tone mapping to tailor the content to its capabilities. Suppose you have a low-end TV capable of just 350 nits in HDR. When playing a scene that has 1000 nits highlight, it should adjust the scene so that the highlight is only 350 nits. TV engineers approach this in two main ways:

  • Some TVs “cut” highlights, keeping the scene’s average brightness where it is. The image will not darken much, but the highlights can be blown out a bit.

  • Other TVs will reduce the average brightness of the scene, preserving highlight detail but making the overall picture darker than it originally was.

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