High Dynamic Range: An Introduction
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High Dynamic Range: An Introduction
- 1. High Dynamic Range April. 2015 Presented by Thuong Nguyen tnguyen@humaxdigital.com 1
- 2. 2 SDR
- 3. 3 HDR
- 4. Contents 4 Introduction What is Dynamic Range Why High Dynamic Range is matter
- 5. Improving Video Quality 5 More pixels: SD – HD –UHD (4k, 8K) Increase spatial resolution HDTV UHDTV SDTV
- 6. Improving Video Quality 6 Increase temporal resolution More frame: 24 ~ 300 Fps (sport,
- 7. Improving Video Quality 7 More View (3D): Stereo, Multiple view, free view Increase views – 3DTV 1 view 2 views M views …
- 8. Improving Video Quality 8 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
- 10. Problem of Dynamic Range The Grandma Problem 10
- 11. Long Exposure 11 10-6 106 10-6 106 Picture High dynamic range Real world 0 to 255
- 12. Short Exposure 12 10-6 106 10-6 106 Picture High dynamic range Real world 0 to 255
- 13. Problem Dynamic The real world is high dynamic range 13 A nit is a unit used to measure brightness
- 14. High Dynamic Range Making the bright pixels on a TV as bright and vibrant as possi ble while making the dark pixels as dark as possible. 14 Especially valuable for outdoor scenery and sharp contrast movie scenes.
- 15. High Dynamic Range Need around 10.000 nits to satisfied 90% viewer at ideal range 15 Current Color Space (Color Gamut) is not enough
- 16. 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 16
- 17. Moving to HDR (Netflix) HDR is more important for video quality than 4K 17
- 18. 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, 18 Can notice HDR from any distance and screen size, at once Resolution is only apparent when you are close Dramatic better visual quality
- 19. Moving to HDR Who interested? 19 TV manufacturers …. ... TV manufactures mainlyTV manufacturers + Content creators Optimistic future
- 20. 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) 20 HDMI 2.0a: 18Gbps SMPTE 2014: Doing HDR With HEVC
- 21. HIGH DYNAMIC RANGE More on 21
- 22. HDR in Digital Photography Dynamic range describes the ratio between the maximum 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: 22 Capture device (camera, scanner) Display devices (screen, printer) Subject
- 23. Influence of Light Light intensity as incident and reflected light Real world is high dynamic range 23 Accurate measure luminance is critical for dynamic range
- 24. 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 24 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)
- 25. Comparison Dynamic range is commonly measured on a logarithmic scale 25 Printed Media f-stops Density Scanner Display devices Scanners Digital Camera f-stops Density Scanner
- 26. The Human Eye Human eye uses the pupil to see darker or brighter images 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 26
- 27. Bit depth & Dynamic Range (bit per pixel)Quantifies how many unique colors are available How many unique shades are available in grayscale image 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 27
- 28. Wider Color Gamut Current color gamut is limited Current HDTV (BT.709) – 1990 Created for CRT, and HDTV Around 100 nits. 8 bpp 28 Today we have better display technology: Plasma, LCD, OLED … More Colors: REC. 2020 for UHDTV 10, 12 bpp.
- 29. What the viewer gets? Distorts the image from what the director create 29 Content creator see 100 nits Viewer see – 300-500 nits Gamma correction
- 30. What the viewer gets? Distorts the image from what the director create 30 Unpredictable distortion
- 31. Color and Brightness 31 Luminance dynamic range for various technologies
- 32. Dolby Vision & dual layer HDR 32 “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
- 33. Dolby Vision & dual layer HDR 33 Decoder
- 34. 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 lumin ance dynamic rage of the display tha was used to author the source 34 e.g: from REC 2020 (10-12bit) to REC 708 (8bit) e.g. convert HDR for 500 nits to 120 nits
- 35. HDR Develop ? Update gamma function: maps linear light to a specific 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? 35
- 36. HDR Develop ? HEVC compatible to HDR contents (HEVC extension) HDR – capable display devices with HEVC decoder Workflow to create, encoded and distributable HDR video 36
- 37. Conclusion High dynamic range is current trends in video technology as well as industry (broadcasting operator, content 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 37
- 38. 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 38
- 39. 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 39
Notas del editor
- 10 f-stops = a difference of 210 = 1024: 1 contrast ratio. 14 f-stops = a difference of 214 = 16,384: 1 contrast ratio. 16 f-stops = a difference of 216 = 65,536: 1 contrast ratio. 100,000:1 is normally regarded as approximately the range that the eye can see in a scene with no adaptation. 20 f-stops = a difference of 220 = 1,048,576: 1 contrast ratio. 1,000,000:1 is normally regarded as approximately the range that the eye can see in a scene with minimal (no noticeable) adaptation.
- The candela per square metre (cd/m2) is the derived SI unit of luminance. The unit is based on the candela, the SI unit of luminous intensity, and the square metre, the SI unit of area. As a measure of light emitted per unit area, this unit is frequently used to specify the brightness of a display device.
- “I would much rather have a dynamic 2K HDTV than more pixels. Something with great blacks or great HDR, that is more impactful. Resolution is only apparent when you are close” Fundamentally, the video expert believes that 4K is just the tip of the iceberg and the least impressive part of what we should soon be seeing with video display technology.
- “I would much rather have a dynamic 2K HDTV than more pixels. Something with great blacks or great HDR, that is more impactful. Resolution is only apparent when you are close” Fundamentally, the video expert believes that 4K is just the tip of the iceberg and the least impressive part of what we should soon be seeing with video display technology.
- Therefore the concept of dynamic range becomes more complicated, and depends on whether you are describing a capture device (such as a camera or scanner), a display device (such as a print or computer display), or the subject itself. In fact, another device not shown above is our eyes, which also have their own dynamic range.
- Scenes with high variation in reflectivity, such as those containing black objects in addition to strong reflections, may actually have a greater dynamic range than scenes with large incident light variation. Photography under either scenario can easily exceed the dynamic range of your camera — particularly if the exposure is not spot on.
- Photosites can be thought of as buckets which hold photons as if they were water. Therefore, if the bucket becomes too full, it will overflow. A photosite which overflows is said to have become saturated, and is therefore unable to discern between additional incoming photons — thereby defining the camera's white level.
- Scanner express dynamic range in terms of density This is useful because it is conceptually similar to how pigments create tones in printed media, as shown below.
- For example, a light bulb can have more than 10,000 cd/m2, surfaces lit in the sunlight can have brightness upwards of hundreds of thousands of cd/m2, while the night sky can be 0.005 cd/m2 or lower. In color reproduction, including computer graphics and photography, the gamut, or color gamut /ˈɡæmət/, is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a certain output device.
- The human eye uses the pupil to allow it to see darker or brighter images. If the pupil gets smaller, then less light enters the eye. This means that the eye can look at brighter areas without overwhelming the eye with too much light. But this comes with a tradeoff: when the pupil is small, less light means that the eye cannot see dark areas as well. The total range from darkest to brightest visible at the same time does not change significantly for the eye, but the eye can adjust the pupil to optimize the overall viewing conditions and adjust to varying amounts of light.