High Dynamic Range: An Introduction
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Transcript of High Dynamic Range: An Introduction
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SDR
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HDR
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Contents Introduction What is Dynamic Range Why High Dynamic Range is matter
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Improving Video Qual-ity
More pixels: SD – HD –UHD (4k, 8K)
Increase spatial resolution
HDTVUHDTV
SDTV
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Improving Video Qual-ity
Increase temporal resolution
More frame: 24 ~ 300 Fps (sport,
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Improving Video Qual-ity
More View (3D): Stereo, Multiple view, free view
Increase views – 3DTV
1 view 2 views M views
…
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Improving Video Qual-ity
More pixel’s info (Better pixel)
Higher contrast: SDR vs. HDR
Standard(SDR)
Enhanced(EDR)
High(HDR)
10 16 f-stops
n f-stops = a difference of 2n : 1 contrast ratio
Quantization bit: 8 – 10 – 12
strong contrast between the bright parts and the dark parts of an image
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Why? better-looking images/videos
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Problem of Dynamic Range
The Grandma Problem
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Long Exposure
10-6 106
10-6 106
Picture
High dynamic rangeReal world
0 to 255
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Short Exposure
10-6 106
10-6 106
Picture
High dynamic rangeReal world
0 to 255
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Problem Dynamic The real world is high dynamic range
A nit is a unit used to measure brightness
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High Dynamic Range Making the bright pixels on a TV as bright and vibrant
as possible while making the dark pixels as dark as possible.
Especially valuable for outdoor scenery and sharp contrast movie scenes.
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High Dynamic Range Need around 10.000 nits to satisfied 90% viewer at
ideal range
Current Color Space (Color Gamut) is not enough
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Moving to HDR UHD Alliance: with mission to create (Jan. 2015
at CES) New standard to support video technologies including 4K,
Higher resolution, high dynamic range, wider color gamut, and 3D audio
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Moving to HDR (Netflix) HDR is more important for video quality
than 4K
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Moving to HDR (Netflix) HDR is more important for video quality
than 4K “We kind of ran out of more pixels to add,” Neil Hunt,
Can notice HDR from any distance and screen size, at once
Resolution is only apparent when you are close
Dramatic better visual quality
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Moving to HDR Who interested?
TV manufacturers
…. ...TV manufactures mainlyTV manufacturers + Content creators
Optimistic future
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Moving to HDR 4K (UHD) will support HDR standard in the end of
2015. 4K + HDR (10/12bit) give less data overhead than 8K itself
(8bit)
MPEG Exploration: HDR and WCM content distribution
HDMI 2.0a (Apr. 2015): spec update fro HDR support in 4K
Ultra HD Blu-ray: will support HDR
Technicolor and Sinclair Demo HDR UHD Live Over-the-Air Broadcast (Apr. 9, 2015)
NAB Labs to Demo Super Hi-Vision, LDM, HDR HFR (NHK’s SHTV). (Apr. 11, 2015)
HDMI 2.0a: 18Gbps
SMPTE 2014: Doing HDR With HEVC
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HIGH DYNAMIC RANGEMore on
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HDR in Digital Photog-raphy
Dynamic range describes the ratio between the maxi-mum and minimum measurable light intensities (white and black, respectively)
Ratio between lightest and darkest regions (contrast ratio)
Never have true white or black Dynamic range’s concept depends on:
Capture device (camera, scanner)
Display devices(screen, printer)
Subject
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Influence of Light Light intensity as incident and reflected light
Real world is high dynamic range
Accurate measure luminance is critical for dynamic range
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Digital Cameras Light is measured at each pixel in a well (photosite)
Each photo’s size determine a digital camera dynamic range
Define darker and white level based on its capacity
(idea camera) Contrast ratio is dynamic range is generally higher for digital SLR cameras compared to compact cameras due to larger pixel sizes.
Maximum light intensity measurable ( at pixel
saturation)Minimum light intensity
measurable (above read-out noise)
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Comparison Dynamic range is commonly measured on a logarithmic
scale
Printed Media
f-stopsDensity
Scanner
Display devices
Scanners
Digital Camera
f-stopsDensity
Scanner
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The Human Eye Human eye uses the pupil to see darker or brighter im-
ages Turn smaller to limit coming light to see the brighter But cannot see darker & brighter region at same time it around 10 – 14 f-stops
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Bit depth & Dynamic Range
(bit per pixel)Quantifies how many unique colors are available
How many unique shades are available in grayscale im-age
Most digital cameras us a 10 – 14 bit A/D ~ 10-15 f-stops Higher precision A/D converter does not necessarily mean
greater dynamic range
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Wider Color Gamut Current color gamut is limited
Current HDTV (BT.709) – 1990 Created for CRT, and HDTV Around 100 nits. 8 bpp
Today we have better display technology: Plasma, LCD, OLED …
More Colors: REC. 2020 for UHDTV 10, 12 bpp.
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What the viewer gets? Distorts the image from what the director create
Content creator see 100 nits
Viewer see – 300-500 nits
Gamma correction
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What the viewer gets? Distorts the image from what the director create
Unpredictable distortion
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Color and Brightness
Luminance dynamic range for various technologies
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Dolby Vision & dual layer HDR
“dual-codec” technology that uses the HEVC 10-bit base layer plus an 8-bit AVC enhancement layer or two 8-bit AVC encodes.
Encoder
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Dolby Vision & dual layer HDR
Decoder
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HDR Related SEI in HEVC
HEVC version 2 include three SEI messages to HDR data
Chroma resampling filter hint: info for changing color space
Info: some transformation information to reduce artifact
Knee function information: info about transform one brightness or luminance dynamic range to another
Mastering display color volume: info on color primaries and luminance dynamic rage of the display tha was used to author the source
e.g: from REC 2020 (10-12bit) to REC 708 (8bit)
e.g. convert HDR for 500 nits to 120 nits
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HDR Develop ? Update gamma function: maps linear light to a spe-
cific code value for a display screen. Current system was originally designed to support CRT
display
Standardized signaling a television receiver for HDR’s contents
New metadata sets, how system delivery and response that.
Standardized HDR mapping …
How new HDR signals are carried Layered approach – which create different levels of video
quality Similar to SD/HD enable device?
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HDR Develop ? HEVC compatible to HDR contents (HEVC extension)
HDR – capable display devices with HEVC decoder
Workflow to create, encoded and distributable HDR video
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Conclusion High dynamic range is current trends in video technol-
ogy as well as industry (broadcasting operator, con-tent provider, TV manufactures)
Better visual perception with significant different to SDR Small bit overhead New HDR-enabled display device is coming
Very optimistic future – just around the corner
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References R. Diaz, An introduction to High dynamic range HDR and its
support within the H.265/HEVC Standard Extension, Dec. 2014.
Dolby Laboratories, Dolby vision white paper, 2014. http://www.cambridgeincolour.com/tutorials
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Appendix What’s remain
How to capture HDR? How to compress/encode HDR content? How to display HDR ? Dynamic range convert – Tone mapping ?
SDR to HDR HDR to SDR