Why 4K TV is about more than just pixels.

posted in: Blog

4k or UHD (Ultra High Definition) is now well established as a consumer technology. Visit any electronics retailer and you will find a variety of UHD TV’s from various manufacturers available for purchase right now. What is not so common though is actual 4k content to watch on these latest and greatest screens. Due to the much higher bandwidth requirements of 4k and UHD material we will have to wait a bit longer for the content to catch up with the hardware.

4k UHD screens provide a more immersive experience for the viewer. The higher pixel count means viewers can be closer to larger screens, filling more of the viewers visual field and increasing the sense of reality and “being there”.

Currently there are a few options to fill all those pixels on your new UHD TV. In the world of HDTV Blu-ray has traditionally provided the best picture reproduction for consumers. Currently the best quality discs you can purchase are the “Mastered in 4k” Blu-ray movies. These are movies that have been encoded at a higher bit-rate than standard Blu-ray discs and with ‘expanded colour’ which requires a xvYCC-compatible TV and player to view. However the discs are still only HDTV 1080p resolution. The extra quality provided by the better encoding means the image looks better when up-scaled (or stretched) to fill a 4k UHD screen. True 4k Blu-rays are due to hit the market towards the end of 2015 so until then this is the best physical media can deliver.

These days more and more people receive there content at home via streaming services. Most providers now offer some 4k content. The quality varies greatly and there is still a long way to go to optimise the video compression codecs to provide that balance between quality and file size. An uncompressed 4k movie of around 90 minutes duration will occupy around 11TB’s of storage and at its highest quality can require a bandwidth approaching 16GB/sec. In order to make 4k streaming viable the content has to be compressed. Currently there are a few different codecs in use for 4k material; H.265 MPEG4 is typically used for content storage on PC’s, VP9 is an open source codec commonly used for streaming services, and HEVC is now being used in trials for broadcasting.

Broadcast television is obviously a big part of the drive within television technology. The transition from SD broadcasts to HD broadcasts is still ongoing. The transition from HD to 4k and beyond will probably take even longer. One of the biggest hurdles in any emerging technology is to ensure everyone is working towards a common standard. The major players in this market are keen to avoid a repetition of the VHS vs Betamax, or more recently the Blu-ray vs HD-DVD format war.

The European Broadcasting Union (EBU) have a timeline in place for bringing 4k formats into the mainstream. Currently HDTV broadcast signals adhere to Rec. ITU-R BT.709, or more commonly referred to as REC-709. This covers HDTV signals with a resolution of 1920 x 1080, at 24, 25, 30, 50 and 60 frames per second (Hz), 8 or 10 bits colour depth, and in progressive or interlaced format. The move to 4k requires a new standard and that standard is Rec. ITU-R BT.2020 or REC-2020. REC-2020 covers resolutions up to 8k, frame rates up to 120Hz, a colour depth of up to 12 bits and a wider colour gamut for better colour reproduction.

Current monitor technology limits the amount of colours a screen can reproduce accurately. REC. 709 covers approx. 35.9% of the visible gamut. Adobe RGB is a standard that is designed to replicate the colours produced by a CMYK printing process. It covers approx. 52% of the visible gamut. Rec. 2020 looks to improve on both of these standards and will cover approx. 75.8% of the visible gamut. This improved colour reproduction will help with the immersion of these higher resolution formats.

REC.709 vs Adobe RGB vs REC. 2020

Currently though there is no screen technology available which can reproduce the full range of colour required by REC. 2020. The OLED screens currently shipping can hit approx. 80% of the required range. However there are still a few years for a technological break-through to come along.

Along with better colour reproduction the new UHD formats will bring higher frame rates. Faster refresh rates give smoother looking motion and reduce screen jitter when objects pass quickly from one side of the screen to another. Current LCD technology means the response time of each pixel is the same whether it is in a HD screen or a 4k screen. As the pixels in the 4k UHD screens are smaller the amount of blur appears reduced when compared to the larger pixels on a HD screen.

Broadcasters are already testing 4k transmissions and working towards 8k. Japan is leading the way with a goal of 8k broadcasting in time for the 2020 Olympics in Tokyo. In the meantime the advent of the new 4k Blu-ray standard should ensure some fantastic looking content for all those who have already invested in this technology.