Ed’s AV Handbook
Saving the world from poor fidelity
HDR Ultra-HDTV (2/17)
Part 2 Buzzword Noise Reduction
This is an outline of the technologies that support the stunning images on HDR Ultra-HDTV screens. The objective is to clarify their definition and reduce the ‘buzzword-noise’ that obscures their significance and misleads many to pitch an HDR Ultra-HDTV as simply a brighter TV.
High Dynamic Range
High Dynamic Range is primarily about an expanded range of luminance – the difference between black and the brightest white light – that allows for a simultaneous display of bright highlights and dark shadow detail. But this breakthrough that “changes the nature of television as we know it” is achieved via three additional inter-weaved video elements: color space, gray-scale, and color gamut.
The Illuminating Details
The following sheds more light on the ‘interweaved elements. It also introduces many of their
underlying building blocks and video allies. This includes Color Volume, Color Depth, Bit Depth, Deep Color, DCI P3, the Nit, Gamma, EOTF, frame rate, HEVC, and the CIE Color Chart.
The CIE Color Chart is the official chart of visible color. It is defined by the red, green, blue X, Y color mix points and their Z grayscale amplitude (brightness) points. D65 specifies the brightest Z-point goal. Envision the illustration as a three-dimensional cone. The CIE is an international organization.
Color Space is simply the total referenced space within the Color Chart cone.
Color Gamut is the color space allocated to video technology. For example; the larger triangle defines REC 2020 Ultra-HDTV color gamut. The smaller triangle defines REC709 HDTV color gamut.
Color Volume measures color gamut as a percentage of the total color space. For example; Ultra-HDTV covers 75.8% of the total color space. HDTV covers 35.9% of the color space
Color Depth or Bit Depth is the number of computer bits allocated to create a video color sub-pixel. The number of bits determines the possible range of color shades. For example; 8-bit color provides up to 255 shades per red-green-blue sub-pixel for a total of 16.78 million colors. 10-bit color provides up to 1024 shades for a total of 1.07 billion colors. 12- bit as employed by Dolby Vision provides even more shades.
Deep Color describes 10 bit or more color depth. For example, 10 bit HDR10 and 12 bit Dolby Vision offer Deep Color potential. Many new TVs can be enabled to reproduce Deep Color.
DCI P3 – The Digital Cinema Initiative P3 spec defines the color gamut of commercial digital cinema that covers 53.6% of the CIE Color Chart.
Note: Current TVs are limited to the DCI P3 specification. Although we may look forward to the full CIE 2020 color space spec; the current library of movies is limited to DCI P3. The good news is DCI P3 is a significant improvement over HDTV.
NIT – The NIT is a unit of TV screen brightness. This is different from the ANSI lumen that measures the reflected screen brightness produced by a video projector. As a reference; the ISF’s Silver and Paullin stated; “Our old TV content was created thinking in terms of brightness at 100 Nits; this is what NTSC CRT reference monitors were capable of. HDR monitors will be capable of 4,000 to 10,000 Nits.”
HDR LCD TVs and HDR OLED TVs are defined by different brightness standards. An HDR LCD TV must be capable of over 1,000 Nits peak brightness and less than 0.05 nits black level. An HDR OLED TV must be capable of 540 Nits brightness and less than 0.0005 nits black level.
The LCD brightness spec is near twice the OLED spec. This will lead many to claim LCD is better than OLED. However HDR OLED black level is 100 times lower. If you want the TV with the largest dynamic range – the difference between peak brightness and black level; then HDR OLED crushes HDR LCD.
Note: The NIT is too light as the decibel is to the sound pressure level.
Similar to hearing, human vision is not evenly sensitive to the entire bandwidth of light.
The eye is most sensitive to green light, less to red, and even less to blue. This subjective visual response is defined as luminance. The subjective response to sound is called loudness.
Gamma is a fixed gray-scale luminance correction to accommodate human perception. If you are an old audio pro – gamma is similar to Fletcher/Munson loudness correction.
EOTF or Electro-Optical Transfer Function is a dynamic (not fixed as gamma) frame by frame luminance adjustment. The Hybrid Log-Gamma and Phillips/Technicolor HDR formats use this technology. (More on this later)
Frame Rates [frames per second] – The REC 2020 HDR UltraHD specification provides for 120fps or 60fps. The 120fps option is significant because it exceeds the frame rate requirement for Virtual Reality and Augment Reality.
HEVC – Ultra-HDTV broadcast and Blu-ray discs require High-Efficiency Video Coding compression. HEVC ‘squeezes’ video data within their limited bandwidth. Unaltered, Ultra-HD cannot fit within Blu-ray disc space or via future off-air broadcast bandwidth. This is not a consumer issue. Content and hardware providers’ products will comply.
In an HDR nutshell
HDR luminance sets the table for an extended gray scale that creates a broader space of color. The expansive gray-scale/color-space lays the foundation for a wider color gamut Ultra-HDTV specification.
The HDR breakthrough is derived from the combination of concurrent dark/bright light plus the expanded shades of color. This is not about more pixels or a brighter screen. This is about better pixels.
That concludes Part 2. Coming Soon Part 3 – The possible format war.