HDR Demystified
Version 1.0, March 2016HDR DemystifiedEMERGING UHDTV SYSTEMSBy Tom Schulte, with Joel BarsottiThe CE industry is currently migrating from HighDefinition TV (HDTV) to Ultra High Definition TV(UHDTV). In addition to higher resolution, UHDTVbenefits greatly from additional visual qualityenhancements like Higher Dynamic Range (HDR)and Wide Color Gamut (WCG).These enhanced features have been received verypositively by consumers, and CE manufacturers aremoving very quickly to introduce equipment to themarket with various levels of UHD capability. Thisfast movement in the industry has left many of usconfused about UHDTV capabilities, proposedsystem features, system compatibility, and standards.In this preliminary draft document, we attempt toshed some light on High Dynamic Range and WideColor Gamut, the two significant features of UHDTVthat will affect how we test and calibrate the imageaccuracy of these new generation TVs.We cover the different industry proposals related toHDR and WCG and we briefly discuss how CalMANdisplay calibration software addresses these newtechnologies.UHDTV CapabilitiesThe new UHDTV system comprises a number ofadvanced technologies. Those technologies include:High Resolution Video – Higher spatial resolutionwas the first promoted feature of UHDTV. A UHDTV's native resolution will be 3840x2160 pixels. Thisis four times the total number of pixels produced byHDTV at 1920x1080. However, the visible resolutionimprovement over HDTV could be less pronouncedin a home environment, due to the limitations ofhuman visual acuity, screen size, and home viewingdistances.High Dynamic Range (HDR) – The dynamic rangeof a TV refers to its luminance, the maximum andminimum amount of light the TV is capable ofproducing.High Dynamic Range is the capability to represent alarge luminance variation in the video signal, i.e.,from very dark values (0.00005 cd/m2) to very brightvalues (greater than 1000 cd/m2). Existing systems,now referred to as Standard Dynamic Range (SDR),support luminance values only in the range of 0.0002to 100 cd/m2.HDR creates brighter whites, darker blacks, andbrighter colors that better match images we see in thereal world. The enhanced image quality due to HDRis appreciable under virtually any viewing condition.Wide Color Gamut (WCG) – A TV’s color gamutindicates the level of saturation and number of colorsthat a TV can produce. Wide Color Gamut indicatesthe capability of displaying images with a wider rangeof colors than have been supported by conventionalsystems.Video systems up to now have been based on theBT.709 and BT.601 color spaces, which contain onlya small percentage (about 33.5%) of all 1976 CIEvisible chromaticity values. This legacy color spaceleaves a large set of visible colors that cannot berendered on SDTV or HDTV displays.Note: The NTSC color gamut was never used, evenfor the NTSC system, and is totally irrelevant.Larger color spaces, such as DCI-P3 and BT.2020 canrepresent a much larger set of visible colors (about41.8% and 57.3% respectively). Displays capable ofproducing a majority of these color spaces can rendermore colorful and realistic content.The UHD spec will call for a wider color gamut,creating more vivid colors and more detailed colorgradation than with HDTVs.Page 1
HDR DemystifiedVersion 1.0, March 2016High Dynamic Range (HDR)High dynamic range will potentially provide the mostsignificant UHD picture quality improvement overHDTV. HDR provides a more lifelike range of imagelight levels than previously possible.The average picture level (APL) of UHD images willremain fairly consistent with HDTV images, but theblack level detail will be enhanced and the highestluminance levels will occur only in specularhighlights within the HDR images.The contrast range and light levels in specularhighlights will increase dramatically, coming closerto reproducing the rich contrast, tonal details, andbright picture highlights that we see in the real world.HDR, along with wide color gamut, enables a morenatural saturation of bright colors, without theartificially muted saturation inherent in the BT.709HDTV system (figure 1).Figure 1: HDR produces bright highlights, but italso yields brighter, natural colors and improvedshadow detail. Image credit: Scott Wilkinson,AVS Forum postHigh Dynamic Range Photography – The firstexperience many of us had with HDR was with asmartphone camera that provided an HDR function.HDR photography is about overcoming thelimitations of consumer image sensors to increase animage’s exposure range. It typically does this byautomatically capturing three images, at differentexposures, then combining the best exposed parts ofthe three images into a single HDR photo. This resultsin a captured image with increased tonal detail in boththe dark and bright areas of the photo. However, thereis no expanded range; it does not make the dark areasof the photo darker or the bright areas of the photobrighter.HDR photography entirely involves optimizing theimage exposure capture process, basically to tonemap an HDR image into an SDR container. It doesnot increase an image’s dynamic range, nor does itinvolve the method with which the image istransmitted to a display device or the method withwhich the image is rendered on the display.High Dynamic Range TV – HDR TV is not aboutovercoming limitations on the capture end, as withconsumer photography. Professional film and digitalvideo cameras have long had greater dynamic rangethan the 6 exposure stops (or a few more with cameras-curves and grading correction) supported by theBT.709 HDTV SDR system. (An exposure stop is adoubling or halving of light.) Most digital cinemacameras today can capture at least 14 stops ofexposure range, but this wide dynamic range is notcurrently preserved, even for cinema presentation.HDR grading for the home can be delivered with 810 stops of exposure range.HDR TV is also not primarily about overcominglimitations on the playback end. Late model TVs havebecome capable of displaying much brighter imagesthan the current BT.709 HDTV luminance spec of100 cd/m2 (now commonly known as nits).Even before the push to HDR, many TVs with LEDbacklights could produce brighter colors than theBT.709 standard and could produce peak luminancelevels over 400 nits. Current displays can producegreater dynamic range than the current specificationsfor the content distribution chain can handle. Trendssuggest that HDR-capable consumer TVs should beable to produce "specular highlights" with luminanceof 1,000-1,500 nits or brighter in the next few years.Page 2Figure 2: The original dynamic range of capturedcontent will be able to be substantially preservedby a new HDR TV system, compared to thecurrent SDR TV system. Image credit: Dolby
HDR DemystifiedVersion 1.0, March 2016Dual modulation backlights and zone LEDbacklighting were both introduced prior to HDR andare prime enablers of HDR, but until now we couldn’tfully take advantage of these technologies.TVs with LED backlights, OLED displays, orquantum dots can also produce a wider range ofcolors, including more highly saturated colors, whichalso look brighter. To accurately render BT.709images, HDTVs currently need to limit any of theseenhanced capabilities.The main challenges that need to be addressed toenable HDR TV are primarily the specifications andsystems for the middle processes of mastering,encoding and delivering TV images to consumerdisplay devices.HDR TV StandardsStandards have been and continue to be formulatedfor every aspect of HDR content creation, communications Union (ITU), Society of MotionPicture and Television Engineers (SMPTE),Consumer Electronics Association (CEA), MotionPicture Experts Group (MPEG), and the Blu-ray DiscAssociation (BDA) have all developed standardsrelating to some aspect of UHDTV and HDR.SMPTE – SMPTE ST2084:2014 (and CEA-861-3)standardizes an Electro-Optical Transfer Function(EOTF) for HDR that was developed by Dolby Labsto define the process by which digital code words areconverted into visible light.SMPTE – SMPTE standard ST2086:2014 definesstatic metadata; metadata that does not change duringplayback of the associated video content.SMPTE standard ST2094, which is being consideredin committee, along with CEA-861-G/HDMI 2.x, willdefine content-dependent (dynamic) metadata.ITU – ITU-R Recommendation BT.2020 defines awide gamut color space, among other aspects of aUHDTV system.ITU-R Report BT.2381-0 (07/2015), Requirementsfor High Dynamic Range Television (HDR-TV)Systems, is a summary of performance criteria thatshould be met by a newly implemented HDR TVdelivery system that includes the criterion ofbackward compatibility of HDR content with SDRdisplays.CTA – The Consumer Technology Association(CTA), formerly the Consumer ElectronicsAssociation (CEA), has defined the followingminimum guidelines for a TV, monitor, or projectorto be referred to as an HDR-Compatible Display: Includes at least one interface that supportsHDR signaling. Receives and processes static HDR metadata.(An HDMI input needs to be HDMI 2.0a to passHDR metadata.) Receives and processes the HDR10 MediaProfile from IP, HDMI or other video deliverysources. This requires HDMI 2.0a. Other mediaprofiles may additionally be supported. Appliesan appropriate Electro-OpticalTransfer Function (EOTF) before rendering theimage.UHD Alliance – The UHD Alliance is a multiindustry alliance that formed to promote UHDstandards development and UHD branding andcertification. The alliance members include all majorproduction studios, content distributors, and displaymanufacturers.The UHD Alliance has defined an ULTRA HDPREMIUM certification and logo for devices, contentand services that meet the following minimum UHDspecs. Resolution:3840x2160forcontent,distribution, and playback displays. Color bit depth: 10 bits minimum for contentand distribution, 10 bits for playback displays. Color representation: BT.2020 for content,distribution, and playback displays. Mastering display; transfer function: SMPTEST2084 inverse EOTF; color space: minimum100% of P3; peak luminance more than 1,000nits; black level: less than 0.03 nits. Content transfer function: SMPTE ST2084 Playback display; transfer function: SMPTEST2084 EOTF; color space: minimum 90% ofP3; peak luminance more than 1,000 nits andblack level less than 0.05 nits OR peakluminance more than 540 nits and black levelless than 0.0005 nitsPage 3
HDR DemystifiedVersion 1.0, March 2016One goal of the UHD Alliance is that UHD contentwill be backwards compatible with SDR displays.This is a key challenge for HDR delivery systems.BDA - The Blu-ray Disc Association has released itsnew Ultra HD Blu-ray Disc specification, whichincludes provision for base layer HDR10 video andoptional Dolby Vision.HDR Transfer FunctionThe image content of a video signal is defined bywhat is seen on the mastering reference display, sincecolorists adjust and make decisions on the appearanceof the content based on the look of the referencedisplay.In the case of live production, this may be performedby a creative at a camera control unit or by theapplication of a simple look-up table (LUT) for tonemapping. For off-line production, this usuallyinvolves artistic color grading of the content in a postproduction suite.The reference display’s EOTF determines how videosignal values are converted to linear light values.Since the production of both live and off-line contentis guided by a reference display, the EOTF of thereference display always defines the content.Figure 3: ST2084 HDR EOTF vs. legacy gammapower function. Image credit: IBC/Litwic et.al.The legacy BT.709 and BT.1886 power law gammacurves are a quantization of relative brightness. Thesecurves are relative luminance, allowing eachplayback display to map a video signal’s maximumcode word to the peak luminance of that specificdisplay.The traditional gamma curves (e.g. BT.709 orBT.1886) were based on CRT physics and are similarto human perception at relatively low light levels.They cover luminance values up to 100 nits.When conventional EOTFs are stretched beyond afew hundred nits, even with a 10-bit signal, they startto produce image contouring, due to the inefficientway they use bits relative to the human visual system.The SMPTE ST2084 EOTF curve is a 10 or 12-bitquantization of absolute brightness. It is an absoluteluminance function, requiring the EOTF of theplayback display to exactly match the EOTF of themastering reference display.The ST2084 EOTF was designed with headroom forfuture expansion and covers a range of luminancefrom 0.00005 nits up to 10,000 nits (figure 3). ST2084maps each video signal code word to the sameabsolute luminance and chromaticity in every display(i.e. 10-bit code word 691 always maps to 500 nits).This allows each playback display to exactly matchthe luminance and chromaticity of the masteringreference display.This HDR EOTF, standardized as SMPTE ST2084, isbased on the contrast sensitivity function of thehuman eye, as measured by Barten and referenced inITU-R Report BT.2246-5. It is called a perceptualquantizer (PQ) curve.Since SMPTE ST2084 corresponds closely to thehuman perceptual model, it makes the most efficientuse of signal bits throughout the entire luminancerange. An ST2084 encoded signal can representluminance levels up to 10,000 nits at the cost ofrelatively few extra code words (figure 3). A majorityof the ST2084 codes represent lower luminancelevels, to complement the human visual system’sgreater contrast sensitivity at lower luminance levelsand to minimize visible banding at those lower levels.Half of the HDR codes are in the SDR range, meaningthat 10-bit HDR doubles the number of code valuesin the SDR range, compared to traditional 8-bit video.If a display system were to simply reproduce a linearrepresentation of the scene light, it would produce lowcontrast, washed out images. This is because scenesthat are viewed at brightness levels much lower thanthe original scene are perceived to have much lowercontrast than the original scenePage 4
HDR DemystifiedVersion 1.0, March 2016To optimize the images, an S-curve function is usedto map scene light to display light. This Optical toOptical Transfer Function (OOTF - often referred toas rendering intentor systemgamma)compresses/clips the extreme highlights and darkareas and contrast enhances the mid-range light levelswith a gamma 1 characteristic (typically 1.1 to 1.6).The SMPTE ST2084 PQ system, which is defined byits EOTF, was designed to have the OOTF applied inthe camera or the production process (figure 4).Figure 4: In an ST2084 PQ system, the OOTF(rendering intent) is applied in the productionprocess. Image credit: ITUHDR MetadataSMPTE ST2086 defines static metadata that issupported by HDMI 2.0a, and is included withmastered HDR content to convey the color volume ofthe mastering display and the luminance of thecontent. This is described by the chromaticity of thered, green, and blue display primaries and white pointof the mastering display, plus its black level and peakluminance level. ST2086 also conveys the followingluminance attributes of the mastered content(calculated in linear light domain): MaxCLL (Maximum Content Light Level)The MaxCLL cd/m2 level is the luminance of thebrightest pixel in the content. MaxFALL (Maximum Frame-Average LightLevel)The average luminance of all pixels in eachframe is first determined (frame-averagemaxRGB). The MaxFALL cd/m2 level is thenthe maximum value of frame-average maxRGBfor all frames in the content.SMPTE ST2094 (pending) will define contentdependent (dynamic) metadata, to be supported inHDMI 2.1. Dynamic metadata will convey frame-byframe or scene-by-scene Color RemappingInformation (CRI), developed by Technicolor, whichwill enable color transformation to be variable alongthe content timeline.Samsung has also proposed a standard for contentdependent dynamic metadata and color volumemapping of HDR content to displays with a smallerdynamic range and narrower color gamut (morebelow on color volume mapping).Wide Color Gamut (WCG)From CES 2016, it appears that almost all UHDcontent that is HDR will also be wide color gamut.Wide color gamut describes content or displays withthe capability of representing a larger volume ofcolors than have been supported by existing colorstandards.Wide color gamut enables more true-to-life hues andsaturation levels, especially in very bright and verydark image areas. It allows you to see more lifelikecolor representations of vividly colored objects likeflowers and eggplants, sports jerseys, or stained glass.To produce a wider color gamut, a display needs tohave higher saturation, narrow spectral bandwidthRGB primary colors that measure closer to the edgesof the CIE Chromaticity Diagram (figure 5). The edgecolors on the diagram are pure, monochromatic,100% saturated colors; created by light energy that isconcentrated at a single wavelength.The current color gamut standard for HDTV isspecified by ITU-R Rec. BT.709. As seen in figure 5,the P3 color gamut that is currently specified by theDCI for cinema presentation is significantly largerthan the BT.709 HDTV gamut. The recently specifiedcolor space for HDR, ITU-R Rec. BT.2020, withabsolutely pure RGB primary colors, is the ultimatelimit of the UHDTV system.The BT.2020 color space is a large container for colorgamut information, but the size of the container doesnot define the color gamut of any particular content.The color gamut volume within the BT.2020container, as specified by HDR metadata, can be anygamut content that is no larger than the BT.2020 colorspace container. As wide color gamut is beingimplemented within the UHDTV system, the DCI P3gamut (legacy cinema content) is a popular contentgamut.Page 5
HDR DemystifiedVersion 1.0, March 2016Figure 5: The BT.2020 color gamut is the goal forUHD TV. The P3 gamut is currently used forcinema theater presentations and will be anintermediate gamut for UHD content. The BT.709color gamut, with much lower saturation colors,is the current HDTV standard. Image credit: W3CUntil recently, RGB LED and RG phosphor-dopedLED backlights have been the principal source ofhighly saturated primary colors, getting close to theP3 gamut. OLED emissive displays, primarily fromLG, are now available with color gamuts also veryclose to the P3 gamut.Quantum Dot red and green nanocrystals, which emitlight at very narrow bandwidths when excited by blueLED photon energy, are now beyond DCI-P3 and aregetting narrower and wider as the technologymatures.Laser light sources, as recently implemented in theDolby Cinema and IMAX Laser projection systems,produce narrow bandwidth, highly saturated colorsand are able to precisely reproduce the BT.2020 colorgamut.Pointer’s gamut is an approximation of the gamut of4,000 diffuse surface colors found in nature, as seenby the human eye and measured by Dr. Michael R.Pointer in 1980 (figure 6). Every color that can bereflected by the surface of an object of any natural orman-made material is inside Pointer’s gamut.Figure 6: Pointer’s gamut, containing the colorsof all real surfaces, is mostly contained within theBT.2020 color gamut. Image credit: BBCAs indicated in figure 6, BT.2020 covers 99.9% ofPointer’s gamut. Hence, there are very few naturallyoccurring colors that could not be described withinthe BT.2020 color space. So, BT.2020 would appearto be a sufficient color space for television systems todisplay realistic images (including neon lights, LEDlights, and computer generated images).The chromaticities of the BT.2020 color space areplotted in figure 7, as compared to the smaller HDTVBT.709 color gamut.The BT.2020 primaries, which are represented at thevery edges of the CIE Diagram, are maximumsaturation pure colors, created by extremely narrowspectral slices of light energy. As with all otherconsumer color standards, BT.2020 specifies a D65white point.Page 6
HDR
ITU – ITU-R Recommendation BT.2020 defines a wide gamut color space, among other aspects of a UHDTV system. ITU-R Report BT.2381-0 (07/2015), Requirements for High Dynamic Range ST2084Television (HDR-TV) Systems, is a summary P3; of performance crite
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Images HDR et rendu HDR Images HDR Rendu HDR Définitions Principes Comparaison avec les images classiques Construction des images HDR Logiciels Formats. Historique Utilisation des images HDR pour le rendu 3D Intérêt du rendu HDR Limitations Solutions pour l'affichage.
by the HDR technology which is a combination of High Dynamic Range, Wide Color Gamut and Higher Bit-depth (10/12-bit sampling). HDR components[10] are shown in Figure 2-1. HDR improves the pixels and enables viewer to see a more realistic image and have an immersive visual experience. Figure 2-1 Component of HDR technology
The Atlona AT-HDR-H2H-88MA is an 8 8 HDMI matrix switcher for high dynamic range (HDR) formats. It is HDCP 2.2 compliant and supports 4K/UHD video @ 60 Hz with 4:4:4 chroma sampling, as well as HDMI data rates up to 18 Gbps. The AT-HDR-H2H-88MA is ideal for professional HDMI signal rout
brightness and contrast on a TV to produce a more realistic image. Brightness: A normal TV puts out around 100 - 300 "nits" of brightness. An HDR TV can in theory produce up to 5,000 nits. Note: Generally TVs that claim to be HDR or "HDR compatible" may be able to only play HDR content, but not have full HDR picture quality.
