What is HDR and How Does It Work?

HDR TVs are making headlines all around the world. However, many among us are still confused about what HDR actually is. 

Manufacturers don't take the pain to explain concepts, and you are left on your own. We thought of providing a helping hand and making things clear for our readers. 

Today, we will explain how HDR for TV works and why it's becoming so popular. We will also share a few words on HDR TVs, and considerations for picking the best one. 

What is HDR

The images you see on your TV don't represent what you see with your eyes. The real-life play of light and shadows, dark and bright, and endless shades of colors seldom appear realistically on TVs. 

In technical terms, how bright or dark hues a TV can produce is referred to as the contrast ratio. A TV that can produce a higher range of dark and bright highlights will appear closer to life. 

The same is applicable to color. A TV with good color accuracy will produce images with colors we see in real life. 

These are the two most important factors that determine the picture quality of a TV. 

Till now, TVs were not able to produce such vivid colors or highlights. HDR or high-dynamic-range enables TVs to produce a wider range of contrast and colors. Images appear more bright or dark, giving you a feel of depth. 

One important thing to note here is HDR doesn't necessarily mean the highest levels of brightness or blacks. Rather, it's about representing the exact levels of contrast that we see in real life. 

Colors are also enhanced, and you can see brighter and crisp colors. This is made possible by an accompanying technology called wider color gamut or WCG. 

HDR also enables content creators to create the color palette they want successfully. Think of the dull and dark hues popularly used for post-apocalyptic movies. Compare that to an adventure movie like Indiana Jones, where colors are bright and warm. 

Additionally, the TV is also able to produce more colors, thanks to HDR. 

The Components of HDR

You can now buy a 4K HDR TV to stream Netflix HDR content for a few hundred dollars. However, buying HDR-enabled TV is only a part of the equation. You also need HDR content to go along to enjoy realistic images and videos. 

So, HDR = HDR TV + HDR Content

If you take anyone out of the equation, you will end up without HDR. That means an HDR TV will not convert standard content to HDR. You will just see what normal TVs show. 

In the same way, HDR content will not play out on a non-HDR TV. Additionally, not all HDR TVs are of the same quality. A cheap HDR TV might even produce a poorer visual experience compared to a regular TV. 

Most of the HDR content is now in 4K. You can also stream HDR content from platforms like Amazon or watch an HDR Blu-ray disc on your gaming console. 

Next, we will go into how HDR works. But we will clear one doubt before we proceed. 

Camera HDR and TV HDR Are Not the Same

Cameras and smartphones come with an HDR mode to shoot images. You can use the mode to capture brighter pictures with richer colors. But the technology is entirely different than HDR TVs. 

In the case of cameras, HDR attempts to create a high dynamic range by combining the elements of different exposures. The end result is an image that appears closer to life. 

HDR TVs don't work the same way. They increase the range of contrast ratio and color accuracy to create realistic results. 

How HDR Works

HDR uses a few technologies to deliver the real-life viewing experience-

1. Electro-Optical Transfer Function

Electro-Optical Transfer Function or EOTF, is the key technology behind HDR. The term refers to the action of transforming data to specific brightness levels on TVs. 

The HDR data contains an EOTF value that directs your TV to produce a particular brightness level on the screen. For example, an HDR EOTF value of 1,024 will produce five nits of brightness or light on the screen. 

Content creators can incorporate the electronic value in HDR content quite easily. HDR TVs can also decode the value very easily and produce real-world brightness.

Before HDR, TVs were not able to produce realistic brightness. The content would only tell the TV to generate a percentage of brightness, without any specific value. 

As a result, you will end up with a brighter picture, but not necessarily one that represents real-life conditions. EOTF changes that and enables content creators to have full control over the visual results on your TV.

2. Dynamic Range

Dynamic range is another name for the contrast ratio of a TV. As we already said, it's how brightest and blackest your TV can get. A TV with a high contrast ratio or dynamic range will produce a wide level of brightness. 

HDR TVs do exactly that and create more real-life brightness compared to regular TVs. This is true for both OLED and LCD HDR TVs and can be many times brighter than non-HDR TVs. The additional brightness is the secret behind the realistic and crisp images of HDR.

How different types of TVs create this dynamic range of brightness is also interesting. They don't actually make dark parts of the screen darker but make the brighter parts brighter. 

OLED TVs have an advantage over LCD TVs in this respect. They have already achieved near-perfect blacks because of their mechanism. As a result, OLED HDR TVs only need to make brighter parts more bright. 

OLED TVs have an intrinsic high contrast ratio that even makes non-HDR content appear luxurious. LCD TVs have a bit of hard work to do. They generally leak a lot of light and compromise the dark areas, which look gray. So, you will have to increase the brightness of the lightest areas on the screen to achieve HDR effects.

However, not all HDR TVs will be able to reach the same peak brightness. This is true for most entry-level HDR TVs. 

3. Wide Color Gamut

Most HDR TVs started using wide color gamut or WCG since CES 2016. WCG helps HDR TVs create realistic colors that were not possible before. Your HDR TV can now accurately produce the cherry red of cherries, purple of eggplants, and so on. 

In short, you will be able to create a range of deeper and vibrant colors. Color gamut and contrast ratio go hand-in-hand to create the best HDR experience. 

How do HDR TVs create such vivid colors?

Till now, TVs could display many colors, but they didn't always turn out the way content creators expected. HDR changes all of that by generating better light for an improved range of colors. 

OLED TVs create RGB colors using yellow and blue OLED components. HDR allows OLED TVs to brighter lights using the same amount of energy. As a result, manufacturers can offer more deep colors without many hassles.

Most LCD TVs use color filters to create a range of colors. You can make the colors deep only by dimming the backlights, which defeats the purpose of HDR. The problem is more prominent in conventional LCD panels and even regular white backlit LED TVs. 

For this reason, modern HDR LCD TVs use quantum dots to create HDR effects. Quantum dots are semiconductor nanocrystals that can generate blue, green, and red lights. The technology is a bit of improvement over regular LCD TVs but still uses a backlight. 

Quantum dots can be easily controlled using HDR values on the content. You can easily create deeper colors without compromising the brightness, the hallmark of HDR. 

The dynamic range of colors is also facilitated by the HDR format itself. In the case of non-HDR TVs, you get 8 bits to create varying levels of brightness and colors. You can think of each bit as a token that you can associate with various elements of an image or footage. 

Let's say you are dealing with a frame of a cityscape. You have several elements, like the sky, buildings, cars, people, shops, streetlights, and so on. Content creators can use the 8 bits to represent the brightness levels of each element. 

However, in reality, 8 bit falls short when you consider the countless elements in the frame. As a result, content creators have to make compromises and lose out on details. 

HDR breaks the limitations and provides 10 bits for dedicating brightness levels. You might think 2 more bits are not that significant, but that's only on paper. 

8 bit TVs can create up to 256 shades. When it comes to 10 bit of HDR, you can take advantage of 1,024 shades. 

Coming to colors, 8 bit allowed content creators to use 16.78 million color options. When you use HDR, the 10 bits translates to almost 1.07 billion colors. 

As you can see, HDR can increase both the number and shades of colors. This helps HDR TVs to display what you see with your real eyes perfectly. You can enjoy a whole new range of deeper, vibrant, and brighter colors. 

However, to enjoy these features, your content must be HDR-ready. 

4. Suitable HDR Content

You can't enjoy a real-life viewing experience even on an HDR TV if your content doesn't support it. So, creating HDR content is another part of the equation. 

Many 4K TV shows and videos are now made in HDR. The content creators can include HDR metadata or values in the content that tell the TV how to tune the picture. According to Technicolor, even old movies and shows shot in standard dynamic range can be converted into HDR

HDR content will increase in the coming years, whether they are new production or remastered version of old ones. 

Popular HDR Formats

HDR10/10+

HDR10 is taken as the standard for HDR. All HDR TVs and players can play HDR10 content. However, you can only use static HDR metadata in the case of HDR10. That means you can only tell the TV once how to present the HDR effects, which will apply to all scenes. 

The limitations of static HDR metadata is eliminated with the coming of HDR10+. Content creators can use dynamic HDR data for each scene of the movie. Or, you can tell a TV how to tune the picture for each scene. 

As a result, HDR10+ is able to provide a richer viewing experience as bright scenes differ from dark ones strikingly. 

HDR10+ is still not that popular, and most content use HDR10.

Dolby Vision

Dolby Vision is Dolby's version of HDR. It supports dynamic HDR metadata and is considered the best format for HDR effects. 

Unlike HDR10 or 10+, Dolby Vision is a paid technology. Not many manufacturers go for this format even though streaming services like Amazon and Netflix support Dolby Vision.

Final Thoughts

The basic principle of HDR is really simple. HDR TVs come with a wide range of contrast levels, colors, and shades. The HDR metadata on the HDR content tells your HDR TV how to present the picture matching the provided values. Additionally, you get more bits to enjoy deeper and more vibrant colors. HDR is a worthy technology that can increase the pleasure of watching your favorite TV shows and movies without exceptions. 

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