HDR - Simple explanation ( 2 min read )

HDR.

You may have come across this term several times, perhaps even in the course of just today. It seems it is everywhere now and everyone is talking about it. But what is HDR? It's in your TV, it's in your phone. It may even be in your camera but is that even the same? And what even is color gamut? What do people mean when they say "whites are whiter and blacks are blacker" and who is this Dolby Vision person? It's time to find all that out.

Understanding Dynamic Range

To understand HDR or High Dynamic Range, we must first understand dynamic range.

Dynamic range of anything is the difference between the highest and the lowest value of something. While it is used in multiple applications, the dynamic range we will be discussing today pertains to light.

The dynamic range of an optical system is the difference between the highest and lowest value or intensity of light it can detect. The wider this range, the more detail the system can capture. A system with a particularly wide range is called a high dynamic range system.

The human eye has a reasonably wide dynamic range. With our eyes, we can look at a scene and see the details in the brightly lit and the dimly lit areas with relative ease. It's only when a scene has an intensely bright object that our eyes have to adjust by narrowing the iris, at which point it can only really see the bright object and everything in the darker areas of the scene fades away. If our eyes had a wider dynamic range, we wouldn't have to squint at bright objects and could see them comfortably. Similarly, we wouldn't have to strain our eyes so much in the dark while animals such as mice can comfortably see in much less light.

Now let's apply the same logic to a camera system. Just like with the eye, the dynamic range of a camera system is the highest and lowest values of light the system can capture at any given moment. Cameras with wide dynamic range are obviously better but they also tend to be more expensive. Conversely, cheaper cameras or those that are physically smaller (smartphone cameras, for example) generally have worse dynamic range.

Understanding the HDR mode in your phone's camera

We have all come across this button in our phone's camera app. Pretty much every phone these days has an HDR option and most of us just choose to leave it on or on Auto.

This HDR mode is actually a misnomer for a technology called tone mapping. What this does is create an image that has details in the brightest as well as the darkest areas of the scene. It can do this by processing a single high-quality image or more commonly, by capturing multiple images at different exposures and combining them.

In the latter method, the photographer first sets the exposure (essentially the brightness levels) of the image low and takes a shot. Then several more shots are taken, gradually increasing the exposure levels while keeping the camera steady. Now you have multiple set of images, with the low exposure shots having great detail in the brightly lit areas of the image but all the darker parts are completely black and the high exposure shots having great detail in the darker areas but all the bright parts are blown out. You can probably see where this is going from here. The photographer then puts all these images in an image editor and superimposes them, which creates a final image that has detail in both, the dark as well as bright images.

Understanding an HDR display

You must have seen television manufacturers claiming HDR support on their latest 4K televisions. Even smartphones are now starting to ship with HDR displays. The first one was the ill-fated Samsung Galaxy Note7 last year but since then we have had the Galaxy S8 and the Galaxy Tab S3, the Xperia ZX Premium and Xperia XZ1, the LG G6 and V30 and most recently, the iPhone X. So what is an HDR display?

An HDR display has three advantages over a standard dynamic range display (let's just call it SDR, even though that's not an official term):

• Wider dynamic range
• Higher peak brightness
• Wider color gamut

The first and the second are closely related. The display is capable of showing more detail in the brighter and darker areas of the screen. This is where the often touted but seldom explained "whites are whiter and blacks are backer" adage comes in.

When you look at HDR content (more on this later) on an HDR display and compare it side by side with SDR content on SDR display, you will notice that the brighter areas of the image are brighter. However, at the same time you can actually see more detail there.

For example, if there is a shot of someone standing next to a window with bright light coming in, the side of the face facing the window will look overexposed on the SDR display and will just appear white. The same spot on the HDR display will look brighter but even through that you will be able to see the texture and details on the skin without the bright area just looking like a white glowing spot.

Same thing is with the shadows. A dark night shot on an SDR display will have some areas of the image, such as hair or a dark jacket, just appear black but on the HDR display you will be able to make out more details and see the texture.

This is where the high brightness helps. The increased brightness elevates the whole image and lets you see more details. You can ask why can't they do the same with SDR display but with an SDR display, increasing the brightness will just make the image wash out without adding any more detail.

The third aspect is wider color gamut. Our eyes can see a certain range of colors. Unfortunately, due to various restrictions in transmitting data, whether it's over the television or the internet, the images we see on our screen use a significantly smaller subset of colors than what our eyes can see. With a wider gamut of color, we are effectively increasing the range of colors the image has. It's still not close to the limits of what our eyes can see but it's still better than an SDR image.

To clarify, a wider gamut is not more saturated colors. It's not the same as increasing the saturation on your display. Increasing the saturation simply increases the intensity of the color. It does not show you more color. A wider color gamut lets you see more shades of color, which increasing saturation cannot achieve. This is the difference between an oversaturated display and a wide color gamut display.

Acquiring HDR content

Two of the main ways to acquire HDR content today is via Blu-ray discs and streaming services. Blu-ray, specifically 4K Blu-ray, is where you will get the best quality. Blu-ray discs have uncompressed video and audio and is just the absolute best way to enjoy your movies or television shows.

However, what most people will end up using is streaming services, especially since that is the only option available on mobile. Here, companies like Netflix, Amazon and YouTube rule. Netflix, in particular, has one of the largest libraries of HDR content on the internet. Netflix is also the only one to have HDR-10 as well as Dolby Vision content.

Amazon would be a close second along with Hulu. YouTube recently started supporting HDR content and Google also added some HDR movies to its Google Play Movies services. This week, Apple also threw its hat in the 4K HDR ring with the announcement of the Apple TV 4K, iPhone X and iTunes 4K content.

Wrapping it up

In summary, HDR is all about increasing the quality of your content. Previous advancements in video technology were primarily about increasing the resolution but HDR is where the advancement happens on the pixel level, meaning it's less about more pixels and more about better pixels. The brighter, more dynamic and vibrant HDR image is far more obvious even to the novice eye than a resolution bump, which may or may not be obvious depending upon your visual acuity or distance from the screen.

It must be said that it still depends upon two major factors, quality of the HDR panel and mastering of the content. Cheaper HDR televisions are obviously nowhere as good as the most expensive ones and just like with 3D, some of the HDR content is clumsily mastered with absurd colors and contrast to make it pop more.

I hope this helped clear some of the confusion surrounding HDR. In the coming days we will be seeing a lot more of this technology but for once, it is actually useful and not a gimmick so I personally will be looking forward to it.

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