4K Digital Video: Truth and Myth

4K is a term to describe a maximum video resolution of 4096x2400 pixels. However, the most commonly used resolution is UHD (Ultra High Definition) at 3840x2160 pixels. This resolution basically allows for four full HD signals of 1920x1080 pixels to be displayed on a single screen. Unfortunately, the pure pixel count doesn't tell the complete the story and this is what makes things a bit tricky – at least for now! The following overview will look into some key differences to provide you with a better understanding of potential requirements to help you select the most suitable solutions.

Technical Details

• Resolution (max.): 4096x2400 respectively 3840x2160 reflecting between 8.3 Megapixel and 9.8 Megapixel
• Refresh rate: 24p/30p/60p

Typical Interfaces

DVI-D

The DVI specification allows 1920x1200 pixels to be transmitted in SingleLink format or 2560x1600 (2048x2048) pixels in DualLink. Typically, the SingleLink is supported by 23/24" displays, commonly called Full HD panels. The DualLink resolutions require larger screen sizes of typically 27" (2560x1440), 30" (2560x1600) or square ATC displays of 2048x2048 pixels.

Full 4K resolutions 3840x2160 or higher over DVI-DL are possible, but only at <=30Hz due to bandwidth limitations. The bandwidth required for professional AV and PC environments can come to 4.95 Gbps (165Mhz) for Single Link or 9.9Gbps (2x 165Mhz) for DualLink DVI.

HDMI and DVI share the same digital video signal format, but HDMI allows for higher pixel clock frequencies, resulting in higher bandwidth or resolutions and deeper color!

The specifications vary based on the different HDMI versions. Up to HDMI 1.2 the specs more or less reflect those of DVI video. HDMI 1.3 and especially 1.4 even exceed the dual link DVI specs although it only uses a single link. HDMI 1.3/1.4 bandwidth is 10.2 Gbps (single link 340Mhz).

Most HDMI 4K appliances and displays currently on the market are limited to 30Hz. The recently released HDMI 2.0 standard increases bandwidth to 18 Gbps (600 Mhz), effectively matching the bandwidth of DisplayPort for supporting 4k at up to 60 fps! The first HDMI 2.0 displays supporting this full specification are presently showing up on the market. HDMI is commonly used on almost all consumer and professional AV equipment.

DisplayPort 1.2

DisplayPort is a slightly different, micro packet-based, video standard supporting a maximum bandwidth of approximately 17 Gbits. This currently makes it the only suitable single-connect option for full UHD (3840x2160) at 60 fps.

DisplayPort is mainly used on PC graphic adapter cards. Note: all current graphics cards with DisplayPort support the full DisplayPort 1.2a specification of 5.4 Gbps per lane and therefore only support 30 fps rather than 60 fps 4k resolutions.

Thunderbolt is an Apple-only interface for multi-purpose use, including video. The interface plays a niche role because it is limited to Apple devices.

Thunderbolt is compatible with DisplayPort 1.1 and capable of natively outputting DisplayPort signals. It can deliver full 4k resolution at 60 fps on a single connector.

Different ways of delivering 4k

Depending on the specifications of the equipment being used, a 4k signal may be delivered in the following ways:

• Display/projector with four SingleLink DVI interfaces and synchronized channels. Acts like a video wall in just a single large device.
• Display/projector with two DualLink DVI interfaces and synchronized channels. Acts like a video wall in just a single large device. (MPT : Multiple Protocol Transport)
• Display/projector with either two DualLink DVI or HDMI 1.4 inputs. The term used to describe this method is MPT (Multiple Protocol Transport).
• Display with either DisplayPort, Thunderbolt or upcoming HDMI 2.0 full spec interfaces.

• Display/projector with either one DualLink DVI or HDMI 1.4 input. The term used to describe this method is MPT (Multiple Protocol Transport).
• Display with either DisplayPort, Thunderbolt or upcoming HDMI 2.0 full spec interfaces.