We’ve all seen those TV commercials claiming how their new TV or digital camera offers 4K UltraHD QLED HDR with 8 million pixels resolution. But have you ever wondered about the science behind those numbers and letters and how they make a screen more appealing? How to know if you need an HDR display or a UHD one? Let us discuss this in detail.
To put it simply, HDR and UHD are properties of content-storing devices (digital cameras, mobile phones, CCTV) and content-displaying hardware (TVs, monitors, projectors) that improve the visual quality of images or video on a display screen.
To make things easier to understand, we shall focus on UHD first.
WHAT IS UHD?
UHD is short for Ultra High Definition. UHD describes the dimensions of a screen (width and height) in terms of pixels.
Pixels are minuscule squares on a digital screen that make up an image. Each pixel contains red, green and blue (RGB) color-emitting mechanisms that interact with each other to produce dynamic shades of colors in an image.
Display screens have a fixed number of pixels. The first HD display, the 720p, has a resolution of 1280x720p meaning 1280 pixels horizontally (screen width) and 720 pixels vertically (screen height).
When multiplied, this gives the total number of pixels on the screen i.e., 921600 pixels in this case. The ‘p’ here stands for ‘progressive’ and not ‘pixel’.
Next to 720p is 1080p. A 1080p display has a screen resolution of 1920x1080p and is called Full High Definition (FHD). Next in line is the 2160p display with 3840x2160p called the Ultra High Definition (UHD).
If we tweak the 1080p a little in horizontal pixels and make it 2048x1080p instead, it is now called a 2K resolution (2K being short for 2048 pixels).
Similarly, tweaking the UHD to make it 4096x2160p makes it a 4K display resolution.
The 2K and 4K are in reality ‘cinema’ resolutions. Owing to marketing gimmicks, FHD/2K and UHD/4K are now interchangeably used.
Why Is UHD The In-Thing Nowadays?
The simple answer is that it is the latest technology.
The more technical answer is that a screen with a greater resolution has more pixels per inch and will provide a more detailed and sharp image. A UHD video can be cropped while still retaining most of its details.
It can also be projected on a larger scale without losing picture quality. An important benefit of UHD is that content can be downscaled to FHD or HD meaning that you can still view HD or FHD content on your UHD output device.
WHAT IS HDR?
High Dynamic Range, as the name suggests, is a high dynamic range. So what is dynamic range?
Dynamic Range, sometimes called Contrast Ratio, is a property of a display system. It is defined as the ratio of the luminance of the brightest shade to that of the darkest shade in an image.
Instead of a resolution, HDR is based on the contrast, brightness and color properties of a screen. In the science of displays:
HDR is not a singularity. It includes a wide range of video format technologies namely HDR10, HDR10+, Dolby Vision and HLG.
Of all formats, Dolby Vision and HDR10 are the most widely adopted by electronics and game manufacturers, and streaming platforms. All these formats are unique in their way. But the result is that all essentially enhance picture quality.
HDR is a 10-bit color system compared to traditional 8-bit SDR (Standard Dynamic Range). 8-bit SDR offers 256 shades each of RGB and, consequently, 16.8 million colors.
10-bit HDR now offers at least 1024 shades each of RGB and over a billion colors, meaning more colors to choose from. Increasing one bit increases the maximum Bit Depth by a factor of 8.
What is Bit Depth?
Bit Depth is the number of digital bits used to encode each color of the image. It is color info stored as the number of bits per pixel of an image. More bit depth means more color info per pixel and more file size.
An HDR technology particularly aims to target three aspects of content:
This leads the content to display fine details in the lightest and darkest regions of the image, wider and more realistic color shades, and an overall life-like viewing experience.
More vivid details can be seen in the darkest and lightest regions of the screen instead of just dark or light patches. A wider gradient of shades can be told apart.
How Is HDR Better Than SDR?
SDR devices only portray 100 nits of luminance values with zero being pure black and 100 being pure white. Any value beyond these limits would not be comprehendible resulting in clipping i.e., pixels appearing as pure black or pure white patches with no digital color info.
HDR technology widens the luminance range to at least 1000 nits meaning more details can be stored and viewed in these patches.
Dynamic Range is measured in “stops”. SDR cameras offer 6.5 stops. HDR devices now offer 15 stops. The human eye can perceive up to 20 stops of dynamic range. A higher dynamic range in modern devices means the image or video is near to what a human eye can perceive.
While SDR offers a rec709 color gamut, HDR widens the color gamut to rec2020 color space (i.e., more vibrant and saturated colors, true to life). It is worth mentioning that the human eye can perceive more than the rec2020 color gamut.
CONCLUSION: COMPARING HDR AND UHD
Ideally, comparing HDR with UHD is like comparing apples and oranges, as both are unrelated. HDR displays can have a resolution of Full HD, Quad HD or 4K. Though HDR and UHD combined offer a more realistic visual experience paired with more vivid and variable colors in every frame, the devices consume more power, demand greater storage capacity, transfer data slowly and are costly.
Additionally, the advancements in the UHD and HDR technologies have not yet been widely adopted by manufacturers because of high cost, limiting the scope of this field.