An Introduction to High Dynamic Range (HDR)
The industry has
been constantly working towards improving the user experience in terms of video
content consumption. The efforts have been multi-pronged and one of the key
areas so far has been to focus on higher resolutions. While ten years ago, HD
was a big thing, 4K has now become a common resolution in many production
workflows. 4K is also delivered to consumers in many scenarios though it needs
to penetrate better especially on the broadcast side.
Industry is now at a stage where it needs to decide what will bring the next significant improvement in user experience. Some of the key contenders are:-
· Higher resolution. Going to 8K?
· Higher frame rate. Use more of 50 fps or 100 fps?
· Wider color range
· HDR (High Dynamic Range)
Tests have been
conducted by many organizations including IRT, EBU etc. and they conclude that
HDR probably offers a higher improvement in quality of experience compared to
other technological improvements.
Read more at:-
Benefits of High Dynamic Range (HDR)
The holy grail of
quality is reproducing a video experience on user’s display device as close as
possible to what a human being will perceive when they watch the same scene in
nature with their eyes. While this still is an ambitious goal, HDR brings us
closer to the reality by offering a wider brightness range (very close to human
perception range) and thereby a more realistic experience.
It is known that
human visual system (HVS) is more sensitive towards brightness than colors and
for the same reason we have color spaces like YUV420, YUV422 that does
subsampling for color but retain the brightness information for all the pixels.
Regular SDR
(Standard Dynamic Range) monitors available in the market have a range of 1-400
Nits (cd/m2) while HDR allows the representation range of 0-10,000 Nits, which
is a significantly wider range of brightness than offered by SDR devices.
Currently, available HDR TVs have a range of up to approximately 2,000 Nits.
Wider brightness range in HDR simply means that the brightness of each pixel
can be more accurately represented rather than being transformed with a higher
quantization factor resulting into inaccurate pixel representation (poor
quality). The quality improvement with HDR is usually more visible in plain
areas with gradients where minor degradation is easily perceived by human eyes.
In essence – HDR means more accurate
pixels in terms of their brightness!
Read the next article on transfer functions and how they help in
representing a wider brightness range for HDR
Definitions
cd/m2 – The
candela (cd) is the base unit of luminous intensity in the International System
of Units (SI); that is, luminous power per unit solid angle emitted by a point
light source in a particular direction. A common wax candle emits light with a
luminous intensity of roughly one candela.
Nits – A
non-SI unit used to describe the luminance. 1 Nit = 1 cd/m2.
HDR – High
Dynamic range. It is a technology that improves the brightness & contrast
range in an image (up to 10,000 cd/m2)
SDR – Standard
Dynamic range. It refers to the brightness/contrast range that is usually
available in regular, non-HDR televisions usually with range of up to 100
cd/m2. This term came into existence after HDR was introduced
Originally published at http://www.veneratech.com on June 17, 2019.
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