Charting the Evolution of TV Displays from HD, 4K and Even Further

To an average consumer, the acronyms, terminology and numerals which are utilized to describe today’s television displays can be confusing. First, there are the display technologies: OLED, QLED (QDEF), LCD, LED, plasma, etc.

There is also screen resolution: 4K, 8K, HDTV, HDR, Full HD, 1420 x 1080, 4406, Ultra HD (UHD), etc. This is because consumer electronics manufacturers compete to supply ever-higher visual realism and image resolution.

How can manufacturers ensure they deliver on customer expectations for high-end TV displays and what do these labels mean for performance, display quality and real-life viewing experiences?

The Resolution Race

The drive to increase screen resolution can, in part, be attributed to the mainstreaming of digital television images, beginning in the 1990s. The U.S. Government mandated that broadcasters move to entirely digital signals by June 2009.

This shift has included pixels at the heart of every television screen, the tiny, illuminated elements of digital displays.

A typical pixel consists of three subpixels, one each of red, blue and green, which are controlled with a thin-film transistor (TFT) and deposited on a thin backplane of glass or other substrates.

Developers have inevitably found ways to make pixels smaller and more powerful, increase the amount of them and their density (pixels/dots per inch, ppi or dpi), sometimes accomplishing all at once.

 Television display pixels viewed under a microscope, each with a red, green, and blue subpixel. Image Credit: Radiant Vision Systems

 Evolving TV Technology & Terminology

To begin with, some definitions: HDTV means “high-definition television,” which became commonplace in the mid aughts, replacing SDTV (standard-definition TV), which is an earlier digital format.

The number of pixels is the main difference. SDTVs usually possess 480 rows of pixels and 640 pixels in each row (480 x 640). By comparison, HDTVs usually have 720 or 1080 rows of pixels, supplying up to double the resolution of an SDTV screen.

Essentially, the more pixels, the higher the resolution, corresponding to a more crisp, detailed image on the screen. Most HDTVs today are described as Full HD (FHD): they utilize 1080 rows of pixels and 1920 columns, making roughly 2 million pixels (2 megapixels) in total.¹ These are often just referred to as “1080p” displays.

The “HD” in “HDR” does not mean high definition; it means “high dynamic range.” Dynamic range is a screen’s capability to display sharp contrast, a larger range of vivid colors, and light level gradations from deep black to bright white.

As manufacturers strive to provide the best performance across multiple device parameters, high-resolution televisions often supply a better dynamic range, just as they usually supply higher frame rates and other enhanced specifications.

Television sets were created that provided 3840x2160 pixels in the early 2010s, known as “4K”. Technically “4K” started out referring to 4,096 x 2,160, the format used for movie theaters, and 3,840 isn’t quite 4,000.

The 4K terminology is also applied to 3840 x 2160 television displays as those dimensions had to be resized to a 16:9 ratio. In fact, most televisions which are bigger than 50-inches sold today are this type of “4K”.²

To confuse things further, the term Ultra HD (UHD) was originally used for 3849 x 2160 display screens (to distinguish them from “true” 4096 that applies to 4K cameras). Today it is common to hear UHD employed for any extremely high-resolution TVs, like “4K UHD”.

New 8K screens are also being coined as UHD, and 4K is also the specification for professional cameras and projectors which do have 4096 x 2160 pixels, usually known as 4K x 2K.³

Table 1. Different screen resolutions and pixels. While a 4K television is roughly twice the dimensions (measurement), it has four times the number of pixels, thus can display comparatively higher-resolution images. Source: Synopi

The Dawn of 8K

8K displays are much anticipated in the market today. They boast 7,680 x 4,320 pixels. Sharp released the first commercial 8K television in 2015, and LG display’s 88-inch screen was the first OLED 8K TV, released in 2019. ⁴

8K promises to offer significant performance enhancements and can be seen as the next stage in the SD/HD/4K/8K trend. It includes elements of HDR and creates a “looking through the window” image quality, almost like 3D. In addition, capturing content in 8K format can enhance image quality even on 2K and 4K televisions.⁵

For example, capturing content in 8K format also allows a wider field of view, filming the action across an entire sports field. The 2021 Tokyo Olympics was captured and broadcast in 8K for more of a “you are there” viewing experience on 8K screens.

LG Display’s 88Z9 has an 88-inch OLED panel with 8K Ultra HD resolution (7680 x 4320) — four times more pixels than 4K. The OLED panel itself is the largest that LG has ever shipped in a TV. Image Credit: LG

What Do Viewers See?

Human vision is not unlimited, but it is highly acute. Our eyes can perceive between 250 and 290 dots per inch under normal contrast and within minimum focus distance. It has been found in recent research that the human eye can distinguish around 576 megapixels.⁶

Yet, with areas of increased focus at the center (fovea) and less focus on the periphery, human vision is not uniform. As a viewer is located farther away from a screen, individual pixels blur together more, so distance also makes a difference.

Spatial resolution dramatically decreases when increasing the viewing distance (after 1 meter, it’s just under 75 DPI), and it even falls in situations of low contrast.⁷

So for viewing high-resolution displays, for instance, up close, the difference between regular HD and 4K is discernible. Yet, a typical person cannot tell much difference in image clarity beyond a distance of around one meter from the screen.

Both screens might appear to possess almost identical resolution when sitting on a sofa across the room. But it is on extra-large screens greater than 85 inches where 8K makes a difference for image quality.

Some analysts argue that, to the average viewer, 8K does not make a huge difference.⁸ Many other experts foresee that consumers seeking a more immersive and vivid experience will respond to the technology. However, there is also little 8K content available for viewing at present.

The pace of technology change will continue if we are to go off the previous history, consumer expectations will continue to grow, and 8K will become commonplace in time. As future generations of technology and new breakthroughs usher in viewing experiences we can hardly imagine today, eventually, it might even feel obsolete.

Comparison of image content displayed at different panel resolutions. Image Credit: Geoffrey Morrison/CNET

Quality Considerations

Consumers expect a near-flawless performance and appearance from these high-priced, high-end screens, whether they’ve purchased a television billed as 4K, 8K or UHD. Manufacturers have to rigorously inspect displays at numerous stages in the production process to ensure quality.

Advanced, high-resolution inspection systems are needed as pixel density and screen resolution increase (and pixels shrink to microLED sizes of just a few micrometers wide).

Proven Imaging Performance, Higher Resolution

Image-based display measurement systems must also increase in precision and resolution as displays evolve to supply higher and higher resolution.

Radiant has long provided some of the premier low-noise, high-resolution imaging photometers and colorimeters in the industry, with accessories and software designed to optimize system performance.

With Radiant’s latest generation of display inspection solutions, new imaging systems achieve resolutions up to 61MP, helping manufacturers apply measurement to keep pace with the display resolution evolution.

References

1. Woodford, C., “HDTV (High-definition television).” ExplainThatStuff!, last updated January 28, 2021. (Retrieved April 28, 2021).
2. Morrison, G., “4K vs 8K vs 1080p: TV Resolutions Explained.” CNET, April 22, 2021.
3. Pendlebury, T., “What is 4K UHD? Next-generation resolution explained.” CNET, January 29, 2014.
4. “The Evolution of Resolution” on Corning.com, The Glass Age / Science of Glass. (Retrieved April 28, 2021)
5. Chinnock, C., “The Status of 8K & Light Field/Holographic Development”, SID-LA One-Day Conference 2021, March 25, 2021
6. Hamer, Ashley, “How Many Megapixels Is the Human Eye?” Discovery.com, April 1, 2019.
7. “TV and Monitors HD 4K: Resolution / Resolution of the Human Eye.” on Stari.co. (Retrieved April 29, 2021).
8. Wilkinson, S., “8K vs. 4K TVs: Double blind study by Warner Bros. et al. reveals most consumers can’t tell the difference.” TechHive, February 28, 2020.

Acknowledgments

Produced from materials originally authored by Anne Corning from Radiant Vision Systems.

This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.

For more information on this source, please visit Radiant Vision Systems.