I’ve been considering buying a UHD 4k TV and the current crop of TV’s look exceptional. This year a number of specifications have officially become a baseline for manufacturers to work with. For buyers this is an important milestone that brings compatibility to devices that record, store, transmit and display video.
- 1 The Baseline Specification for 4K TV’s
- 2 OLED or LED Displays
- 3 Human Perception
- 4 How Are 4K TV’s Better?
- 5 Putting it Together
- 6 References
- 7 Disclaimer
- 8 Related Posts
The Baseline Specification for 4K TV’s
The baseline specifications have been developed by the ‘UHD Alliance’. The Alliance is composed of a group of 47 big name companies who all have a vested interest in agreeing on what the targets should be. This includes companies such as Sony, LG, Samsung, Dolby, Disney, Netflix, Nvidia, Microsoft and many more. You can find those members here. The Ultra HD logo tells you that the TV it’s attached to meets or surpasses the Alliance standards.
The meaning of the specs are well illustrated on their ‘consumers’ page. They set targets for all manufacturers to meet and a baseline for testing the finished systems against. An overview can be found here. Inevitably this means that the players, disks and transmission protocols will need upgrading to provide support for the higher data rates and formats needed to drive the displays.
OLED or LED Displays
Although LG’s OLED 4k TV’s are seriously superior to their LED counterparts and have a much simpler construction, OLEDs they do have a significant known flaw. The luminosity decreases over time and the blue hue will decay much faster than the other colours. It’s completely possible that the luminance and colour imbalance may become noticeable after not many years. However, LG says their OLED screen should give 20 years of high-quality use. I’m not really convinced as I’ve seen this problem being mentioned repeatedly and I tend to believe it.
If the potential for a less durable display isn’t a problem for you then OLED displays are so good they can seem almost 3D to look at, simply stunning. However, I stopped considering OLEDs as a safe route to 4k and the rest of this article is just about LED displays. I’m biased towards Samsung, but when it comes to 4K screens all the manufacturers seemed to have really good products.
As a reality check, I thought it would be worthwhile comparing what is on offer with what human vision is capable of.
The standard for visual acuity as defined by Nist.gov is better than 20/20 vision, they use 20/12 vision as a benchmark. This is equivalent to an angular resolution of 1 arc minute, which is 1/60th of 1 degree. So if you sit 2 meters away from a TV, the smallest discernible dimension for a person with very good eyesight will be approximately 1.16 mm.
A 40 inch UHD 4k TV panel containing 3840 x 2160 pixels will have space for pixels of about 0.23 mm square. On an 80 inch TV at the same distance, the pixels will be twice as big but still half the discernible threshold defined by Nist.gov. There is a little more to it though, as the human visual system is also good at detecting motion, contrast, colour and edges.
How Are 4K TV’s Better?
Better refresh rates and faster CPU’s make difference but there have been some advances in picture quality that are less straightforward:
- Wide Colour Gamut
- 10 Bit Panels
- High Dynamic Range
WCG – Wide Colour Gamut for Natural Colours
New tech provides a much wider range of colours than before. Manufacturers are using quantum dots / nano-crystals to achieve this. Nanocrystals are light emitting particles on the scale of 5 to 20 NM, larger than molecules and smaller than a virus which range in size from 30 to 50 NM.
Nanocrystals can be manufactured very precisely, and their dimensions are proportional to the wavelength of light that they emit. They work by absorbing light provided by the TV back-light and re transmit the energy as light of a specific wavelength according to their dimensions.
Samsung uses a strong blue back-light and adds in the red and green light via nano particles to make a very bright, very white light source. This method for producing colour is what gives a much wider range of colours than before.
10 Bit Panels for Smooth Colour Gradation
In order to manipulate pixels on a display, the colour range needs to be divided into discrete values that can be selected by digital circuits. The current system for representing colours uses 8 bits for each of the red, green and blue pixel elements. 8 bits provides 256 settings so that means 256 x 256 x 256 different RGB colour shades are possible, making 16,777,216 or roughly 16.8 million colours.
The new tech uses a similar method but increases the number of bits per RGB pixel element to 10. That provides 1073,741,824 different colours, or roughly 1 billion. This is an increase by a factor of 64 in the number of uniquely selectable colours. The increase in resolution prevents the bands in such things as sunsets that you will have seen in previous generations.
HDR – High Dynamic Range for Realistic Contrast
A dynamic range is the ratio between the maximum and minimum measurable values for something. A high dynamic range simply means a wider range. When light travels from an object, to a camera and then a display device, the camera and display device each have dynamic ranges that are limited by their design. The goal is to reduce those limitations so more of the real values provided by the subject reach the display, making it look more natural.
The display device achieves a larger dynamic range by boosting the luminosity of the back-light using newly available bright LEDs. Images that are supposed to contain bright lights such as the sun at sunset will gain an increase in intensity. This widens the difference between the brightest and darkest colours to a more realistic degree.
Putting it Together
The new image quality comes from increasing the following:
- the pixel density
- the range of colours
- the resolution of the steps within the colour range
- the brightness of the display
- The frame rate
Note: The sound quality has also been improved.
The badge that wraps up these features is Ultra HD, short for Ultra High Definition. If you have that then the TV will support an agreed set of standards and work with UHD players. Interoperability might be something you assumed was always there, but it’s not – and that’s what having a standard is all about.
Care has been taken to keep the information in this article as accurate as possible but errors are possible, so be aware of the full disclaimer here.