If you've bought a TV or chosen a movie to watch in recent years, you've probably come across the terms Ultra HD or 4K. Behind these letters lies a whole world of improved picture and sound quality, but it can be difficult to understand all the technologies involved.
It often seems that, in addition to high resolution, new TVs are required to support HDR, wide color gamut, and sometimes high frame rates. What does all this mean in practice and how does it affect what we see on the screen?
In this article, we will explain in simple terms the main “building blocks” of modern image quality. We will look at how HDR differs from a simple bright picture, why not only pixels but also colors are important, and how new audio formats complement the movie experience.
Spatial resolution
Video resolution is the most straightforward aspect, although confusion over terminology still exists. It is commonly referred to as 4K, which is how companies such as Sony referred to it when announcing their first UHD products in 2012.
In the same year, the Consumer Electronics Association or CEA (now the Consumer Technology Association or CTA) proposed the term Ultra HD to refer to a resolution of 3840 × 2160, which is not coincidentally consonant with Full HD, as it is twice as large horizontally and vertically as the HDTV resolution of 1920 × 1080 with the same aspect ratio of 16:9 (1.78:1).
Perhaps the CEA chose the name Ultra HD to distinguish it from the term 4K DCI (Digital Cinema Initiative), which implies a resolution of 4096 × 2160, corresponding to an aspect ratio of 17:9 or 1.90:1. However, this format is often misunderstood.
As a rule, movies are not made with a resolution of 4096 × 2160. This is, so to speak, a “container” format. The image in it usually has a real resolution of 4096 × 1716 (2.35:1 or CinemaScope) or 3996 × 2160 (1.85:1 or Vista Vision). That is, in order to fit it to the TV screen format, some cropping of the video width is required.
However, the Ultra HD format was initially described by only one resolution. Now it has many more parameters, so organizations such as the Ultra HD Forum have started to refer to the 3840 × 2160 resolution as 4K. The other components of this standard are the five pillars mentioned above. Which of these can be considered decisive for a video to qualify as Ultra HD? The debate on this topic is still ongoing, although the following has been briefly defined:
— Ultra HD is a resolution of 4K and above.
— 1080p video with HDR is also Ultra HD;
— the presence of only one next-generation audio format from the list above does not make a video Ultra HD-compatible.
However, many other combinations are possible. For example, is HD video with a resolution of 1080p but with HFR 100 frames per second also Ultra HD? We have yet to find out.
Keep in mind that 8K is also called Ultra HD. The CEA/CTA chose this name for 4K and 8K resolutions, while the DVB Project refers to 8K as UHD2. For televisions, this means a resolution of 7680 × 4320, which is again twice as high as 4K resolution, both horizontally and vertically.
In film production, 8K refers to a resolution of 8192 × 4320. Some films have already been (partially) shot in this resolution, but have not been completed in it. Instead of 8K, they are saved in 2K Digital Intermediate format or, at best, in 4K due to the high cost and time required to develop visual effects.
But the situation is changing. While 4K television content—with the exception of some specialty channels such as Insight TV and Travel XP—is still rare, 4K production is gradually becoming more common in Hollywood.
However, if you're looking for a rich selection of 4K content, you'll inevitably come across streaming platforms like Netflix, Amazon, and Disney+. Disney is currently remastering its back catalog in 4K to make it available via OTT, while Netflix insists that all its content is originally produced in 4K and HDR.
Ultra HD Blu-ray discs are more complicated. They can be made from material shot and finished entirely in 4K, from 4K scans of film stock, or from 2K transfers when the film was finished in that resolution. Either because it was shot in that resolution or because the visual effects were rendered in that resolution.
Will companies such as Netflix start producing content in 8K format in the near future? Perhaps. They are the most likely providers of 8K content, as just a few years ago they were the pioneers in the field of 4K. But it is unlikely that we will ever see 8K discs — read more about this here.
You are probably aware that there are various display technologies competing on the market, especially OLED and LCD displays (often mistakenly referred to as LED TVs and monitors). They are not tied to specific Ultra HD formats — they are agnostic.
There are many articles that discuss the differences between them, their pros and cons, in detail, so we will not go into this in detail in this article. All that matters to us is that, in general, LCD displays can have higher peak brightness, while OLED displays can have higher contrast thanks to deeper blacks.
Extended dynamic range
First, it is worth dispelling a common misconception: HDR video is something completely different from HDR photography. Photography is a kind of “exposure synthesis” where two images taken with different exposures are combined into one.
The resulting image is usually intended for display on a standard range display or for printing on paper, so it is easy to see that this is incorrect HDR. The only thing that has a high dynamic range in HDR photography is the scene itself.
What we call HDR in video includes a greater dynamic range between the darkest and brightest parts of the image, expressed in F-stops or stops. The standard dynamic range covers seven stops, while the extended range covers about 14 stops. This dynamic range is also captured in photography, usually in RAW format, whose files need to be pre-processed for display.
One of the few cases where photos and videos can converge on this issue is with still images in HLG HDR format, which can be captured with the latest Panasonic Lumix cameras and displayed in HDR on Panasonic TVs without prior conversion. In general, the HLG or Hybrid Log Gamma format deserves special attention, as do others in the Perceptual Quantizer (PQ) family of standards.
HLG is a so-called scene-referred HDR format, meaning it does not use any metadata. It was developed by the BBC and NHK broadcasting companies with the aim of delivering a signal that is compatible with HDR as well as SDR TVs (the latter must work with a wide color gamut to reproduce the correct image). In addition, it was supposed to offer a high level of compatibility with existing production processes and equipment. They achieved this. As already mentioned, not many TV broadcasts are in HDR today, but those that are mainly use HLG.
The PQ format, developed by Dolby and described by SMPTE in the ST.2084 standard, can use metadata, but this is not mandatory. The variant with static metadata is specified in the ST.2086 standard and is called HDR10. The HDR ST.2084 variant without metadata is referred to as PQ10. The difference between them is not as significant as it seems.
For example, although ST2086 defines what metadata must comply with, it does not provide strict guidelines on how it should be used. Therefore, TV manufacturers can make their own adjustments when decoding, and some prefer to simply ignore the metadata and apply their own secret processing — which, naturally, leads to different results.
In addition to static metadata, HDR video can also be provided with dynamic metadata, which allows content creators to change settings from scene to scene (and even from frame to frame — translator's note). There are three variants of this HDR, specified in a set of standards combined in SMPTE ST.2094:
1. Dolby Vision (ST.2094-10).
2. Advanced HDR by Technicolor.
3. HDR10+ (ST.2094-40), developed by Samsung and Panasonic.
Today, the Dolby Vision format is the most widespread. Technicolor HDR is the dark horse in this race. It was chosen as the HDR format for Brazil, was recently implemented in ATSC 3.0 broadcasts in the US, and is being considered by Chinese authorities as the basis for a broadcast HDR format.
If we don't take TV broadcasting into account, HDR10 reigns supreme in all other areas. It is supported by all HDR-enabled TVs, as well as all consumer HDR monitors for PCs. In the field of PC gaming, when HDR support is claimed, HDR10 is meant.
All streaming services that offer HDR support at least HDR10 — and this is the mandatory HDR format for UHD Blu-ray (this means that all players must be able to decode it, while Dolby Vision, HDR10+, and ST-2094-20 standards are not mandatory for them).
Wide color gamut
Around the same time that standards for 4K resolution were being established, the television industry adopted a new color space with a wider color gamut, which flat-panel displays (LCD and OLED) were already capable of generating at that time.
In the days of standard-definition analog television, when we all used cathode ray tube (CRT) televisions, the color space (in PAL, SECAM, and NTSC) was described by the Rec.601 standard. For HDTV, which appeared immediately after the transition to digital television, this color space was slightly expanded to Rec.709.
The capabilities of modern displays in terms of coverage can vary greatly, but they are significantly wider and usually correspond to the so-called DCI-P3 format, which is also defined by the Digital Cinema Initiative, as is the DCI-4K resolution. The Rec.2020 color space, defined for UHD TV, far exceeds the capabilities of most displays currently on the market. And it is not certain that full Rec.2020 coverage will ever be achieved in commercial products.
Virtually all UHD TVs currently available, with the exception of the very first generations of 4K models from 2012/2013, can support Rec.2020 in the sense that they accept such signals and process them accordingly. None of them offer 100% coverage of this color space. The actual coverage of different models can vary significantly — and most often depends on the price.
The newer Rec.2100 standard does not imply a larger color space than Rec.2020, but rather the same area with specifications for HDR (both PQ and HLG), resolutions (Full HD, 4K, or 8K) and frame rates (all standards from 24 to 120 frames per second, including fractional frame rates). In essence, it is a summary standard.
Color depth
Color depth is expressed in terms of the number of bits per subpixel. Each pixel in an image consists of three subpixels: red, green, and blue. Thus, so-called 8-bit video actually uses 24 bits per pixel.
The HDTV format (and SDTV before it) uses 8 bits, which allows for 2^8 gradations or 256 color options (shades of red, green, and blue—so 24 bits per pixel give 2^24 gradations or 256^3—16.8 million colors. This seems like a lot, but today it is no longer enough.
Why? Because of HDR. It's not that our eyes have gotten better, but our displays have. They can display a much wider range of colors, and if we continue to use the same number of bits, they will need to cover a larger color range, where the differences between borderline shades will be greater and easily distinguishable. This results in an effect known as “color banding” (stepped color transitions).
When you see an illustration of this effect, it is usually greatly exaggerated in the image. If you like, it's a kind of fake. The fact is that you are most likely reading this article on an SDR (standard dynamic range) display. There is no other way, because trying to show the difference between SDR and HDR on an SDR display is like trying to show the difference between a color and a black-and-white image on a black-and-white TV.
That's why most materials attempting to compare SDR and HDR illustrate with images in which the contrast of one image has been artificially reduced. Some go even further, showing three images with reduced brightness levels, suggesting that they represent SDR, HDR with static metadata, and HDR with dynamic metadata.
For example, this image (from another excellent article) at the top shows a spectrum of 32 colors, including black and white, that you can construct with 5 bits per pixel (2^5 = 32). So, with 2 bits per subpixel, you already have 64 colors — twice as many as in this image. 8-bit color gives you 2^18 = 262,144 times more colors.
The number of colors in the image at the bottom, which looks like a fairly smooth gradient in SDR, is about 1,300 — significantly less than the 2,048 that can be achieved with 11 bits per pixel or 4 bits per subpixel. In fact, 4-bit color gives 4,096 colors — more than three times as many as shown here.
Now back to real numbers: 10-bit color gives us 2^10 = 1,024 shades per subpixel, so 2^30 = 1,024^3 = over 1 billion colors. Unfortunately, I can't show you the difference between 8-bit and 10-bit color on the 8-bit panel you're probably looking at right now, but you can see it on an HDR TV with a 10-bit panel. And you don't need well-trained eyes to notice it.
Note that not all HDR TVs use 10-bit panels. 8-bit panels are still too common in them, and even more so in computer monitors. You are more likely to find panels that use 8-bit conversion + FRC or Frame Rate Control — a method of simulating 10-bit colors.
12-bit color with two additional bits provides four times more shades per subpixel, resulting in 4,096 gradations and 2^36 = over 68 billion colors. It is unclear when we will see 12-bit panels in televisions, but we already have the signal for them. For example, Dolby Vision outputs 12-bit color on UHD Blu-ray discs.
Japan's public broadcaster NHK, which has been broadcasting programs in 8K since November 2018, advocates 12-bit color, while the 8K Association sticks to 10-bit color. At the same time, they offer different frame rates. More on that below.
By and large, Ultra HD Blu-ray is currently the only form of consumer media that supports 12-bit color. Discs without Dolby Vision use 10-bit color and the Rec.2020 color space, while regular 1080p Blu-ray discs use 8-bit color and the Rec.709 color space.
Ultra HD is not just about image clarity, but a whole set of technologies that together make the image more realistic and vivid. This includes high resolution (4K), brighter and more saturated colors, extended dynamic range (HDR), smooth motion thanks to high frame rate (HFR), and high-quality surround sound. Together, they create a sense of presence: the picture looks natural, as if outside the window, and the sound envelops you from all sides. To truly appreciate Ultra HD, you need to understand how these elements work together, rather than just chasing the “4K” number on the TV packaging.
HDR + WCG + extended color depth
It is widely believed that HDR inherently has a wide color gamut and a color depth of at least 10 bits. In practice, these three technologies are usually combined with each other, and there is a good reason for that — their combination provides a significant improvement in color. For example, more bits help prevent color transitions from becoming rough, which can easily happen when the dynamic range is expanded.
In fact, all three technologies can exist independently of each other and can offer certain advantages. 10-bit and 12-bit color have already been tested on Full HD Blu-ray in Japan. Several years ago, Panasonic launched the Master Grade Video Coding (MGVC) format, which contains a kind of enhancement layer with two or four additional bits to achieve 10- or 12-bit color. However, only special Panasonic BD players could decode the added bits. Several Studio Ghibli animated films were released in this format.
The sound is deep, with rich, saturated, but at the same time high-quality bass, a rich, completely transparent midrange, and moderately bright high frequencies. The overall presentation is slightly warm, but this is almost imperceptible, only at the level of nuances. The detail is high, but not excessive, and the reverberations are long and clear. The soundstage is wide and deep, with images slightly larger than usual and somewhat crowded. Both quiet passages and rich, dynamic, and complex passages are equally audible. However, quiet passages often lack lightness and grace. The sound signature, while somewhat graceful, is still powerful, more suited to rock music. Vocal parts are reproduced with high quality and fullness in almost all genres, including large choral works.
So, our tests clearly showed that even in a simple analog connection, a cable is not just a “wire.” There are differences between models, and sometimes they are very noticeable. More expensive and higher-quality cables often demonstrate better detail, clarity, and coherence of sound. The cable is thin and quite stiff, not the most convenient to use. All markings are in order. The cable has very high-quality ferrules, but their central contacts require careful handling. The conductors are made of ultra-pure copper tubes with a silver coating. The dielectric is fluoroplastic. The cable is shielded. The break-in period is long, and the sound stabilizes slowly.
High frame rate
It's confusing, but high frame rate means different things in different fields. In movies, anything above 24 frames per second is considered HFR. Examples are rare. Most people will remember movies such as The Hobbit trilogy (shot at 48 frames per second), Billy Lynn's Long Halftime Walk, and Gemini Man (both shot at 120 frames per second and shown at either 60 or 120 frames per second).
But in reality, there are no other feature films with HFR, because frame rates that deviate from the 100-year-old standard of 24 frames per second are perceived too ambiguously. Some people like it, but many find it very annoying — probably because for decades we have been accustomed to perceiving images shot at such a non-standard frame rate only in the genre of epic cinema.
It's somewhat similar to film grain: one could argue that it's an artifact that should be avoided, but for most people it helps to dispel mistrust. It instructs the brain to switch to movie viewing mode. A higher degree of realism is useless — on the contrary, it destroys the magic.
Many questions about how these mechanisms work in the brain remain unanswered. Perhaps the norm will not be with us forever, but it may take a long time for higher frame rates to become commonplace and widely accepted.
Meanwhile, on television, frame rates of 50 and 60 Hz have been the norm since their introduction in the middle of the last century. In recent years, we have reached a point where interlaced video (50i, 60i) is gradually being replaced by progressive video (50p, 60p). However, this does not make it HFR — after all, in TV, this means a higher frame rate of 100p or 120p. As you may have guessed, this frame rate is rarely used in movies. On the other hand, sports is the video genre that will benefit most from HFR.
Currently, TV broadcasts in 1080p50 (in Europe) and 1080p60 (in North America) are quite common, especially for sports. In addition, such frame rates are the norm for broadcasts in 2160p (4K). But HFR has not yet been used, except for a few trial broadcasts.
This is probably because very few TVs currently support HFR. Only LG's 2020 OLED TV lineup and a few other models are HFR-ready, because the new generation of game consoles will be able to output HFR video.
This brings us to the third area of application: video games. What is considered HFR in games is not clearly defined. But we can say with confidence that it is more than 60 frames per second. Today, there is something of a refresh rate race going on in computer gaming monitors, where 144 Hz is considered normal and 240 Hz is considered outstanding.
Next-generation audio
The only non-video-related requirement for UHD is sound. Next-Gen Audio (NGA) is considered to be sound that goes beyond traditional multi-channel formats such as Dolby Digital, DTS-HD, and the like. Specifically, this refers to immersive object-based audio systems that can use overhead channels to make sound truly three-dimensional. Three formats compete in this area: Dolby Atmos, DTS:X, and MPEG-H (nactually, there are four, including Auro-3D — translator's note).
Dolby Atmos for home works a bit differently than in movie theaters, but it aims to do the same thing: precisely place sounds anywhere in the three-dimensional space where you're watching movies. Where a theater system can process up to 128 audio objects and address 64 different channels (speakers), a home system adds a spatially encoded sub-stream to the Dolby Digital Plus and Dolby TrueHD signal or is recognized as metadata in Dolby MAT 2.0 format (transmission of sound with enhanced metadata). Streaming services use the lossy Dolby Digital Plus format. Ultra HD Blu-ray discs and the Kaleidescape platform, which allows you to download movies in Ultra HD, use the lossless Dolby TrueHD format.
A more detailed description of how it works is beyond the scope of this article, but Dolby Atmos has found its way into home systems mainly through streaming video platforms, movie downloads, Blu-ray, and Ultra HD Blu-ray—and to a lesser extent through broadcast television. BT TV in the UK is one of the very few operators using Dolby Atmos in live football broadcasts. They have been doing this since 2017.
Video games are another important source of Dolby Atmos sound. Xbox One already supports Atmos in games, as does Xbox Series S/X. On the other hand, PS5 uses Sony's proprietary object-oriented 3D audio system called “Tempest Engine.”
In terms of practical use, of course, you don't need to install 64 speakers in your living room like in a movie theater. You can have a set of regular floor-standing speakers that make up a 7.1- or 9.1-channel configuration with the addition of two or four overhead channels — this will give you what is called 9.1.4.
There are more practical alternatives, including speakers with upward-facing drivers that eliminate the need for ceiling speakers. And since every sound is essentially created using computational mathematics known as psychoacoustics, Atmos support is now even available on TVs, soundbars, and smart speakers.
DTS:X is a similar system from Xperi, the company behind DTS. It is supported by all modern AV receivers, as well as TVs and soundbars. Like Atmos, DTS:X is available on Blu-ray and UHD Blu-ray discs. However, you won't find it on streaming services, and it is not used for TV broadcasts.
Broadcast television will likely be the main resource targeted by MPEG-H. This format with the least memorable name was developed by the Fraunhofer Institute, which has played a key role in many compression standards up to MP3. It is used by various UHD broadcasters in South Korea in combination with ATSC 3.0 video.
So, we've broken down the key elements that make up modern Ultra HD content. It's not just an increase in the number of pixels, but a whole complex of technologies working together.
4K resolution makes the picture detailed, HDR adds vibrancy and contrast, and the expanded color palette makes the image more natural. High frame rates can make motion incredibly smooth, especially in dynamic scenes.
Don't forget about sound. Formats such as Dolby Atmos create a truly immersive sound space, complementing the visual experience.
Ultimately, to fully enjoy Ultra HD, it is important that all components in the chain — from the signal source to the TV and speakers — support these technologies. Only then will you get that “wow effect” from watching.
