HDR stands for High Dynamic Range and is a feature being touted on many new TVs, PC monitors, and even mobile phones. Unfortunately, there are a number of competing HDR standards that make it difficult to understand what HDR actually does and why it’s better than the standard dynamic range.
SDR or Standard Dynamic Range is the default experience for most devices. SDR monitors use an 8-bit colour depth, meaning that 8 bits of data are used to specify the value for each of the three colour channels. The standard colour scheme for SDR content is known as sRGB (standard Red Green Blue) and is a standard agreed by HP and Microsoft in 1996, before being standardised by the IEC in 1999.
The sRGB colour scheme is based on the colours that could be represented on the CRT monitors of the day. Typically, SDR monitors operate at a brightness between 120 to 300 nits.
Tip: cd/m^2 is the SI unit for luminance. It’s based on the candela, the SI unit for luminous intensity and the square metre. The candela per square metre is also popularly referred to as the “nit”, which comes from the Latin “Niter” which means “to shine”.
HDR improves on SDR by using a broader colour spectrum known as WCG, Wide Colour Gamut. HDR can make the best use of this by increasing the colour depth from 8-bits to 10-bits. This allows for much more colours to be specified, allowing greater colour accuracy.
HDR also has at least a peak brightness of 450 nits, although some TVs can go up to 10,000 nits. Extra data about brightness is transmitted as metadata and allows greater bright/dark contrast making colours appear more vivid.
Tip: Metadata is a secondary stream of data that provides “data about other data”.
HDR10 is the most common HDR standard, it uses 10bit colour. Brightness is transmitted as metadata but only at the start of a transmission, meaning that only one brightness setting can be used rather than dynamically changing the brightness in relation to the scene. The HDR10 standard also allows for a peak brightness of 1000 nits.
HDR10+ builds on the HDR10 standard by supporting up to 12-bit colour depth, 8K video and peak brightness of up to 10,000 nits. HDR10+ also allows for frame-by-frame or scene-by-scene brightness allowing for greater contrast when switching between bright and dark locations.
The other popular standard is Dolby Vision which supports a similar feature set to HDR10+ but is proprietary, and costs $3 per device to support rather than the free HDR10+ standard.