# 7 Concept Series : What is the difference between HD and UHD
Walk past a TV display section in any large electronic store and Ultra HD screens makes you stop and take notice. The screen looks stunning and the display experience makes you think – Is it time to switch to 4K UHD? 2015 marks the year when UHD and 4K have flooded the floors in CES, IBC and TV OEMs are not leaving any stones unturned to market the UHD magic. Recent CEA report predicts revenue for 4K televisions is projected to reach $5.3 billion with 4.4 million unit shipments of 4K UHD displays in 2015. Few years back when HD entered the scene, many marketing terms like true HD, HD ready, full HD surfaced and gradually millions of living rooms across the world had an upgrade. Today the next avatar of TV technology stands on the horizon with new marketing acronyms UHD, 4K, True 4K, 4K UHD, 8k UHD and True UHD etc. hitting us hard from all corners and the risks of confusion is even more. While enough is already written on (non) availability of UHD content, there remains little understanding on UHD itself. Do we really understand what is 4K or UHD or 4K UHD ? Are we as consumers aware of what advantages UHD brings – does the higher quality means we need to increase existing screen size or reduce the viewing distance in order to get the benefits? So let us take a step back and go beyond the marketing jargons to understand if UHD is a real game changer and how UHD differs from HD.
What is HD?
HD or High Definition is a digital video standard and an upgrade from Standard definition (480i, 480p). SD was largely an analog standard and HD introduced digital delivery bringing better picture colors, greater depth and increased clarity. High definition exists in two variants of HD Ready and Full HD
So what is UHD?
Ultra High Definition, or UHD for short, is the next upgrade from full HD (1920×1080). Ultra HD is about the immersive viewing experience. It is important to understand that UHD is not a single resolution increment but a family of specifications, which is still evolving. UHD not only brings larger pixel set and hence more details but also overall enhanced viewing experience. UHD offers host of incredible features like High dynamic range (HDR), higher frame rates (HFR) and wider color gamut (WCG). The two key UHD categories are UHD -1 and UHD -2
The first and only standardized member of the UHD family is UHD-1 or more precisely UHD-1, Phase 1, which is based on SMPTE 2036-1. UHD-1 Phase 1 has no significant incremental features apart from larger spatial resolution (number of pixels) in comparison to full HD. A host of UHD features including HDR, immersive audio, HFR, WCG etc. are still under discussion for UHD-1 Phase 2 and UHD-2. Represented below is currently available specification from DVB.
What is 4K ? Is it same as UHD?
Unfortunately not. A gross misrepresentation exists when describing 4K. Technically speaking, 4K is not the same as UHD and is not even a Television standard. “4K” is derived from Digital Cinema and specifies a resolution of 4096 × 2160. Since Digital Cinema resolution is not available in a consumer television, the term “4K Ultra HD” (3840 × 2160 ) or simply 4K got introduced and is now famously used for all marketing and branding activities.
4K relates to Digital cinema and a 4K stream uses JPEG2000 codec for compression, employs 12-bit 4:4:4 color depth and high bitrate of 200 – 250 Mbps.
But UHD Television is named as 4K UHD TV ?
4K has become the consumer friendly name for Ultra HD TV available in market today, but as we know it is not same as “4K”. 4K is a marketing name and essentially based on first generation UHD namely UHD 1 Phase 1 and only has a subset of core UHD features.
The Pixel Game
Pixels are at the heart of TV resolution and UHD brings significant upgrade to pixel set. More pixels bring richer viewing experience on a large screen TV. Below representation provides a quick guide to various resolution variants which exists today in SD, HD and UHD.
What is the difference between HD and UHD
The most commonly understood difference between HD and UHD is larger pixel set, full HD offering around 2 million pixels and 4K UHD with approx. four times more at 8 million and 8K UHD with approx. 32 million pixels. For most of us this remains the only reason for why UHD is better. The current and the first wave towards UHD is just about providing more pixels, but there are other developments which put altogether are much more exciting. UHD as we have today maps to a UHD-1 Phase 1 (4k UHD) specification but there are more in the family (UHD-1 Phase 2, UHD-2, and more). UHD brings entire spectrum of enhancements across the domain of bit depth, HDR, HFR, Wide color gamut and more. Let us understand the key differences between HD and UHD.
Difference between HD and UHD
|High Definition HD||Ultra High Definition UHD|
|Current state of affairs - 2015||Established standard in consumer devices and media workflows. Most major networks distributing HD content (720p/1080i)||Evolving standard, early adopter in consumer devices. Limited workflow support. Limited trials from Broadcast and OTT players, especially for sports content. End to End UHD workflow is still few years away|
|Definition and Unique Proposition||Next upgrade from SD, (576i and 480p/480i). Introduced wide screen aspect ratio 16:9, higher frame rate and progressive scan.. Key variants|
- 720p 1280x720
- 1080i 1920x1080
- 1080p 1920 x 1080
|Next upgrade from full HD (1080p). Ultra HD is an umbrella term for new high resolution video format. Removes Interlaced scan and 4:3 aspect ratio. Introduced HDR, HFR, WCG and higher bit depth. |
Ultra HD covers two different resolutions: 4K and 8K. Key Variants
4K UHD 3840x2160
8K UHD 7580x4320
|Temporal Resolution or Frame Rates||23.97/24/25/29.97/30/50/59.94/ 60 fps||23.97/24/25/29.97/30/50/59.94/60/100/120 fps|
|Quantization or Bit Depth||Full HD - 8 bit||4K UHD – 10 Bit, 8 bit still supported|
8K UHD 2 - 10, 12, 16 bit
|Min viewing Distance||3 x Picture Height||1.5 x Picture Height|
|Video Compression||MPEG4 H.264. Support in both SW and HW||HEVC and VP9 most popular. Support in SW only|
|Signal Details (Scanning Format and Aspect Ratio)||Interlaced and Progressive|
4:3 and 16:9
Analog and Digital
|Progressive format only|
|Color Spectrum||Rec.709 color gamut |
Rec. 709 covers 35.9% of CIE 1931 color space
|UHD Ph1 – Rec 709|
UHD Ph2 - Rec.2020 color gamut
Rec. 2020 covers 75.8%, of CIE 1931 color space
|Display Connection||HDMI||4K UHD - HDMI 2.0|
8K UHD - Newer technology -e.g. MHT, Super MHT
|Bit Rates||Full HD - 6-15 Mbit/s||4K UHD 30-40 + Mbit/s|
|Contrast or Dynamic Range||Standard Dynamic Range, Rec. ITU-R BT.1886||4K UHD - SDR|
8K UHD - HDR
|Audio||5.1 surround sound system and stereo||5.1 surround sound system and stereo. Expandable to 24 channels, channel and 3D object based audio|
|Field of vision||Full HD - 30 degree||4K UHD - 60 degree|
8k UHD - 100 degree
|Key Challenges||Visual artifacts and motion blur. Lack of Immersive experience, limited color space, low bit depth, lower frame rate||Lack of standards, Increased size of file, streaming and increased processing power to render the content. Higher cost of production, processing and delivery|
|Future Improvements||Enhanced HD (HDR, WCG and HFR in 1080p)||Encoding in HW, higher compression technology, Cost reduction and integration across entire media supply chain|
It took more than a decade before HD technology and availability got settled from resolutions (1080i, 1080p, 720p..) to the codecs and getting the content produced, processed and delivered. Even today, full HD is broadcasted or streamed for a limited content and the number dips further if we account the percentage of devices which can play full HD. UHD is in the scene and is getting attention but there is still more to be discussed and debated. Several standard bodies including ITU, EBU/DVB, SMPTE, MPEG, CEA, UHD alliance have UHD on their roadmap and are contributing towards standards interpretation. UHD is not only about larger pixel set but also smarter pixels, clearly the emphasis is shifting away from resolution to enrichment and UHD has a lot in its bag to offer. We are in inception years for UHD and it will take many years before practical implementation of UHD across production, management, distribution and play-out is achieved. We can only hope that the journey will be shorter this time.