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Why does HDR look dim on your TV? Tone mapping, explained

The critic

HDR is not a brighter picture so much as a bigger range. Films can be mastered as high as 10,000 nits, but even good TVs peak far below that and projectors lower still, so the set has to squeeze the highlights to fit. How well it squeezes decides whether HDR looks dim, flat or glorious.

Set the content and the display below to see what a given peak does to a bright cloud, then run through the short list of settings that most often hold a picture back.

Explainer · 5 min read

Switch on HDR and some films look brighter and deeper than the standard version. Others look darker. Both can be a TV doing exactly what it was built to do. The difference is a step called tone mapping, and it explains most of the "HDR looks dim" complaints.

HDR is a bigger range, not a brighter picture

A standard-range (SDR) picture is graded around a peak of roughly 100 to 120 nits, a nit being a unit of brightness (candelas per square metre). HDR content is encoded on a curve called PQ that tracks all the way up to 10,000 nits. Very little is mastered anywhere near that, and no home display gets close: many TVs reach about 1,000 nits in highlights, few reach 4,000, and one engineering write-up says consumer displays rarely exceed 2,000. Home projectors manage a couple of hundred at most.

Those peaks are for small highlights only. A bright patch can cover a fraction of the screen, and a full-screen maximum would overheat a set. So a good HDR picture is mostly ordinary brightness with small hot spots: a lamp, a sun-lit window, a spark.

What the TV does with the rest

When a film's highlights go higher than the display can reach, the set has to decide what to do with them. With no tone mapping they are hard clipped: everything above the display's limit becomes the same white, and the detail in a cloud or a sunlit wall goes with it. With tone mapping, the set compresses the top of the range so the detail survives, at the cost of squeezing it together.

Why one curve for a whole film is a compromise

Basic HDR10 sends one set of brightness values for the entire film, worked out from its single brightest moment. A quiet, dim scene then gets squeezed by a curve built with the brightest scene in mind. Dolby Vision and HDR10+ send fresh instructions scene by scene, or even frame by frame, so each scene gets a curve that fits it.

Many sets also analyse the picture themselves and adjust on the fly. It can help, especially on a dimmer display, but one reviewer found the result inconsistent, with dark scenes sometimes too bright or too flat. It is a taste setting, not a cure.

Six things to try before blaming the film

Menu names change from brand to brand, so look for the idea rather than the exact words.

  • Leave Eco mode. Many TVs ship in an energy-saving picture mode that mainly cuts brightness. A Cinema or Movie mode is brighter and still accurate; Vivid is the one to avoid.
  • Switch off the room-light sensor. Automatic brightness settings read the room and can hold the picture back even when you want it bright.
  • Find the peak-brightness control. Some sets, mini-LED models especially, hide a peak brightness or peak luminance setting. Reviewers suggest keeping it at its highest.
  • Turn off energy-saving steps. A few sets cap their output by default.
  • Try the tone-mapping option both ways. If your set has dynamic tone mapping, watch a familiar bright scene and a familiar dark one with it on and off, and keep the one that holds shadows and keeps the highlights shaped.
  • Dim the room and cut the glare. A bright, sunny room works against dark content. See why a dim light behind the TV helps.

Filmmaker Mode, where your set has it, keeps tone mapping closer to the original curve; our piece on which picture settings to switch off covers it.

When the dark is intended

Not every dim scene is a settings problem. Filmmakers still favour dark palettes and moody lighting, and some showrunners have defended a dim look as deliberate. If shadows hold detail and bright objects keep their shape, the TV is probably doing its job. If shadows are black blobs or clouds are white blanks, the numbers above are the place to start. And if your TV is among the many that support HDR but not very brightly, a dim result is the honest result: the standard version may look better.

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