Summer 2020 length of akilometer,length of of andtheduration we havemakes sense if clearly defined the the freeway at100km/h, thatnumber only color space. Isay thatIamtraveling If down to colormapped anunderlying gamut and the color are model unless notmeaningful numbers. However, thenumbers defined by howdescribes colors are represented with defines that model amathematicalmodel gamut. acolorcombination andacolor model of thesR beyond thescope of rates,frame andresolutions, topics thatare go beyond thatandalso define bit depths, define a color space), butboth standards color gamuts andcolor (andthus models (hencetelevision “R 709 are international recommendations for atthispointthatR noting P3,DCI- R color model. color spacesan thatmake useof Y’CbCr color space,” there although are of plenty there isnosuch thingasasingle “Y’CbCr color toused describe models. For example, ambiguous incorrectly andissometimes T Color spaces reasonably sized message or file format. representing dynamic into range a awide or storing data transferring waysvarious of color spaces anddynamic range, along with models, andbit depths. N color representation, R In part one, we considered color what is Part two The dynamicsofdigital colors: he term issomewhat color space P E art of what makes what upacolor of space isthe art xamples of color spaces arexamples of R A s previously discussed,s previously thecolor ec. 709 2 , andsR ec.”) define thatindeed GB and Y’CbCr color ow we move on to GB. It’s worth ec. 2020andR GB standard. ec. 2020 By Marcus Bengtsson ec. 1 , there that agiven isnoguarantee of set and the end result iscompletely arbitrary color gamut), andanabsolute color space, model, colors theavailable (the of range relationship (mapping) between thecolor meaningless. providedinformation is aboutourvelocity an hour. Without thosedefinitions, the Similarly, having aclearly defined without Summer 2020 28 Figure 1– CIE1931chromaticity diagram with wavelengthswith innanometers, shown locus(or monochromaticthe spectral locus), diagram. T such astheFigure 1 CIE1931chromaticity space isthrough achromaticity diagram, gamut anditsrelationship to agiven color different display devices. R GB values will ever thesameacross look GB values will A rguably, way thebest to acolor visualize he outermost boundary is called iscalled he outermost boundary Summer 2020 his only his only his refers to to his refers eference white is white eference ec. 709 incorporates a 709 incorporates ec. hese values are considered considered are hese values his seemingly arbitrary limitation s we’ve previously discussed, the minimum the minimum previously discussed, s we’ve xtended range or Extended range video range A is 0 and the (8 bits) byte one for value black pure 0 represents is 255. maximum that is But white. pure and 255 represents R the case. not always as to also referred called legal levels, concept T swing.” “studio video range or withinthe range stay the digital has to value legal In compliant. standard be considered to video is black range studio-swing, or levels, is at white 16 and reference at value placed 235 (the range is 64 – 940 when using 10-bit called 0 – 16 are from Values depth). color called 236 – 255 are and from black super T white. super ofoutside range nominal the should not and T be used. a time when analog video from is a remnant a digital into signals, converted signals were ofdetailed explanation is considered which of T the scope outside this article. R the digital to levels. refers is still black still and reference 100% white of regardless range which is 100% black, being used. work together in an end-to-end content content end-to-end in an together work transmission delivery and acquisition, is called an Opto-Optical the result system, F. OOT or , Function Transfer GB values is GB values ec. 2020 and 2020 ec. 29 F describes how F describes how he EOT he coordinates for D65 for he coordinates PROTOCOL Figure 2 – Linear input vs. non-linear output with a gamma of 2.2 2 – Linear input vs. Figure GB or Y’CbCr values and vice values Y’CbCr GB or his stems from the fact that from his stems y = 0.329 GB at x = 0.3127, he value 255 means fullhe value intensity his mathematical function is generally he most commonly used reference white is white used reference he most commonly R 709/s ec. xactly how x/y coordinates are converted converted are x/y coordinates xactly how Digital representation E digitalinto R math beyond complicated involves versa however, of is, It the scope article. this conversion that the important know to R to coordinates x/y from not linear. T not linear. almost visionhuman is highly non-linear, intensity are at low Changes logarithmic. significantto us more as much perceived Because of at highthan changes intensity. about 22% to attenuated a light source this, of as half its original intensity is perceived T as bright. on an 8-bit system; the value 128 (50% of the value system; an 8-bit on as 50% as bright 255) will be not perceived 78% as bright. approximately but as 255, T , Function called an Electro-Optical Transfer T short. F for EOT or the display converts from data to screen screen data to from converts the display an Opto-Electrical Conversely, brightness. (OETF) describes how Function Transfer brightness scene converts a camera sensor transfer functions these two When data. into R T T as D65. to referred both R for is the same of balance a white to 6,504 K, equates which daylight. to close GB. GB. ec. 709 and sR ec. he three triangleshe three GB on the other hand, hand, the other GB on ec. 2020, the center triangle the center 2020, ec. GB. ec. 2020 specifies a minimum of 2020 specifies a minimum ec. ec. 709 and sR ec. s we can see on both the chromaticity both can see on the chromaticity s we he available color gamut is then defined defined is then gamut color he available A Rec. 709/sRGB Rec. 0.330 0.640, Red: 0.600 0.300, Green: 0.060 Blue: 0.150, DCI-P3 0.320 0.680, Red: 0.690 0.265, Green: 0.060 Blue: 0.150, T 2020 Rec. 0.292 0.708, Red: 0.797 0.170, Green: 0.046 Blue: 0.131, side from defining the chromaticity of chromaticity the defining from side ec. 2020 and DCI- a significantly P3 offer ec. ec. 709 and sR ec. o enable this wider gamut to be efficiently be efficiently this widero enable to gamut White point A also needs to space a color the primaries, white. reference or point, the define white diagram and the corresponding numbers, diagram numbers, and the corresponding R with saturated gamut wider more color R to primaries compared require a minimum of a minimum allow but bits 8 require It’s be used. to depths color 10-bit for important that the absolute point out to of the wavelengths) (monochromatic colors primaries on depending not change does of the number only or steps depth, the bit variations the primaries between change. 10-bit color depth and allows up to 12 up to and allows depth color 10-bit R bits. T R used, 3, and the innermost DCI-P3, represents triangle used in both gamut is the color R of the chromaticity x/y coordinates the by the spaces, the various color For diagram. used: are following coordinates depicting the chromaticity visible an depicting the chromaticity to T eye. human average the spectralinside different three locus are triangle the outer gamuts; is the color color used in R gamut Summer 2020 least 1% of theincoming light. least 1%of 100:1. of T range white hasanapproximate paper dynamic For example, image aprinted on apiece of darkest color (blackest black) inanimage. colorbrightest (whitest white) andthe concept dynamic range. R “High Dynamic understand that, we to theterm need dissect does itmeanandhow does it work? T SDR,. Range or Standard But Dynamic what improvements andtangible significant over whites.blacks and brighter HDRprovides deeper with images or videos describes ,Range which simply put isaterm that T Dynamic range andHDR High Dynamic for Dynamic High he term HDRisshort Dynamic range isusually measured range Dynamic inso between the istheratio range Dynamic he black ink will reflect at he black inkwill ange.” Let’s the with start o Figure 3–Leftside: SDR exposure, rightside:R exposure HD called stops called than 16stops. For reference, ahealthy more aboutadynamic of can brag range cinema cameras the linedigital Some top of and aprofessional DSLRupto 14stops. dynamic range between sixand10stops of monitor or T ≈7stops.log2(100) an example thus has adynamic of range T thecontrast ratio. of function logarithmic anddarkest asabase2 its brightest sections image (or display contains device) between stops,with we measure how many stops our available describing when dynamic range thelight. onelight; stop So lessmeanshalf or half. Onestop more meansdouble the let’s simplifyitto define one stop as double work thisarticle, isbeyond thescope so of he printed imagehe printed we as used previously . E V may have somewhere xplaining indetailhow stops Summer 2020 A standard computer 30 that camera needs to needs configuredthat camera be to dynamic range, wide avery with camera created HDRinmind. you with have If a entire chainmust be andpipeline signal in thedarkest sections. more alsoadding theimage while detail of able parts to maintaindetailinthebrightest With theextended dynamic we range are approximately dynamic range. 14steps of side isasimulated HDRexposure right with dynamic range.around steps of eight T image, theleft side isaSDRexposure with we cansee. OntheFigure 3 St. Louis content than thathasalarger contrast ratio HDR pipeline, we cancapture anddisplay stops. upto 14 human eye hasa dynamic of range T In essence, usingan thismeansthatwhen o effectively HDR, make useof the A rch he

Photo Courtesy Kevin McCoy / CC BY-SA Summer 2020

hus, there there hus, echnology he standard uses he standard significantly PQ differs he device also be of capable must in that it is a so-called PQ is unique in 2017 and HDR10+ was introduced HDR10+ also supports luminance supported Both are HDR10 and HDR10+ ssociation in 2015. T ssociation in 2015. ec. 2020 color space and a 10-bit color color and a 10-bit space 2020 color ec. HDR10/HDR10+ R standard HD HDR10 and is an open T Consumer by created A PQ as its transfer function and defines that a device requirements the minimum as HDR10 capable: qualify meet to must R T depth. transmitting static metadata and decoding characteristics define the for whole used to video. color increased upon HDR10 by improves scene-based and it includes 12 bits, to depth brightness for metadata that allows and the display be to made adjustments to color frame-by-frame or a scene-by-scene on basis. oflevels HDR10 10,000 nits whereas up to 4,000 nits. to was limited a wideby range of and manufacturers are the standards but producers, content entertainment home used for mainly services.devices streaming and online SMPTE ST 2084. as it was not designed for HLG from T cinema. for but broadcast, backwards maintain was no need to is compatibility; the standard instead quality image maximize to designed purely the characteristicsbased on of human vision. meaning it encodes F, EOT display-referred pixel each for values luminance absolute the capabilities ofbased on not the device, brightness. relative just n s the A A ransfer ptical T 31 able, is usually a file or a a file is usually able, PROTOCOL Vision , or Lookup T Lookup or , • Log-Gamma Hybrid • Quantizer Perceptual • HDR10 (and HDR10+) • Dolby ec. 2100) and several open or proprietary or open 2100) and several ec. standard HDR standard international is one here he reason for this, as with most things this, for he reason Perceptual Quantizer Perceptual (PQ) is an HDR Quantizer Perceptual O and Electro- standard by Dolby curve that was defined Function as standardized Laboratories and later Hybrid-Log Gamma is short, for “HLG” or Gamma, Hybrid-Log and BBC by that was developed a standard purposes. broadcast for NHK mainly HDR standards and functions transfer T (R of distribution which and transfer systems, are: most common the four . . . wider color gamuts . . . and HDR . . . color gamuts wider . . . the most some of are workflows that have innovations exciting technical years. in the last couple of emerged T LU HLG encoded signal can be displayed on on signal can be encoded displayed HLG any not require and does an SDR screen it of makes which metadata, exchange production. event live for suitable name suggests, it defines a hybrid non-linear a it defines name suggests, transfer function a gamma in which curve half the lower is used of for the signal values and a logarithmic half. the upper curve for T compatibility. is backwards broadcast, predefined software function statically that software predefined rangemaps one ofrange another to values applying color, input a given For of values. a known willT treatment produce a LU color. output A/D ecording or or ecording . In this context a this context In . he second stop gets stop he second his value is read, converted converted is read, his value he end result is a washed out is a washed out result he end o combat this, camera manufacturers camera manufacturers this, o combat T raditional digital used in compact sensors 25% of data (values 64 – 127); the third stop 25% of stop the third 64 – 127); data (values down we’re When and so on. 12.5% of data, less than 1% of have we our sixth stop, to makes which data range left, our available shadow extract impossible to any to it next detail. log curves to different introduced have range of use the dynamic better camera each a the log curve is apply does What sensor. logarithmic transfer the function to the camera after that happens conversion dynamic in the camera’s stop so each sensor, range amounts equal gets allocated roughly T of data. this is but without contrast, image much by applying an HDR fix easily something we T transfer function LU or into a digital exposure value, and stored and stored value, digital a into exposure not this does most cases, In somewhere. range of as the dynamic problems, pose any the limitations for narrow is too the sensor apparent. become of to this process with of the introduction wider However, range that can cameradynamic sensors incoming recording 16 stops, up to record Cameras issues. some light linearly presents and we’ve in f-stops, exposure measure is a doubling that a stop concluded already If count we halvingor of light intensity. our brightest (255 white from backwards the first this represents system), an 8-bit on 50% of taking up data the available stop, T 128 – 255). (values s, camcorders, and cell and cell camcorders, Rs, DSL cameras, If the in a linear fashion. work phones intensity of on the light that hits a pixel is that the voltage increases, the sensor that particular for being outputted pixel T also increases. T Log-Format Recording Log-Format capture imagery capture in a format that can later so that it R content as HD beon processed R compatible an HD on can be displayed it is R content, HD recording When display. R Log-Format use to common Log Video to maximize the camera sensor. maximize to Video Log Summer 2020 living room,living streaming service, and every where HDRisnow inavailable inevery around cinema or home entertainment recommendations are mostly focused T Conclusion are functions allowed.transfer refresh rates. or 12bits for resolutions upto 8Kand120p space asR functions.transfer It usesthesamecolor subsampling, bit depth, color space, and as display resolution, rate, frame chroma such HDRvideo of several aspects specifies called, isaninternational standard that R Finally, R Rec. 2100 as HDR10+, thesameluminancealso supports levels dynamic based or metadata. frame It scene 12bits andsupport color depth of function, PQ transfer conform to R arethey almostidentical; have devices to Vision. From view atechnical pointof maincompetitorThe to HDR10+isDolby Dolby V become Dolby Vision Certified. assurance procedures andcalibration to pay royalty quality fees andundergo strict to Dolby integrate wishes who Vision must any manufacturer or content provider bymaintained Dolby Laboratories. standard developeda proprietary and main difference isthatDolby Vision is ecommendation B he aforementioned standards and ec. 2100, or “ITU-R ec. 10 acolor 2020with depth of upto 10,000nits. HLG Both andPQoptical ec. 2020color space, usethe ision T .2100” asitisofficially display aminimum The A s such, Both DisplayBoth P HDRmetadata. any kindof transport SDIisnotable toand infrastructure: industry. standards specific to our of new set whole entertainment, we to need develop or a if recommendations are applicable to live theexisting standards and to seen if be making their way into live shows, itremains thesetechnologies slowly butwith surely gamut required for R accurately color displaying thefull of any production-ready products capable inthatregard, lagging is still few if with gamut support, but LEDdisplay technology coming close to reaching R full innovations inlaser projection isalso professional HDRstandards.R color profiles in time,real with and work color gamuts, 10-bit color depths, apply wide servers thatcanplayback with video recently have we seen professional media theworld. therestbehind of Only very entertainment, we are for once afew years it isHDRcapable. live In theworld of than five-years old, there’s a good chance youris notatypo.less smartphone If even devices. inmosthandheld N about Video over IP? Well, SMPTEST failover systems are necessities. what So scenario where redundancy andautomatic that isabsolutely inalive critical show compatible routers available—something professional Display P addition, there are no(to my knowledge) challenges.an entirely of new set In over pose integrity long distances will andmaintainingsignal transporting dynamic metadata,can transport but Some obvious challengesSome obvious are bandwidth ort 1.4andHDMI2.1 ort Summer 2020 32 ec. 2020. However, ort 1.4or HDMI2.1 ort ecent ec. 2020color o, that reached [email protected] . diving, goodfood, andgoodwine. Hecanbe enjoys rockclimbing, mountainbiking, scuba not tryingtosolveimpossibleproblems, Marcus and challengerofthestatusquo. When heis winning engineer, inventorofseveral patents, generation of live shows?generation of How canwe usethem to enhance thenext have years. emerged inthelastcouple of the mostexciting technical innovations that depths, andHDRworkflows are some of color gamuts, than8-bit color higher usingimage sequences.with mention theinherent challenges thatcome manufacturer support,necessary notto O HDR standards. Image such formats as incorporate theaforementioned any of files today video do not use for delivery of another challenge; thecodecs we typically to afew be years away. Content delivery is HLG, but mainstream looks adoption still PQand HDRusingboth 2110 supports Endnotes EXR dowepen what need, but lack the 2 1 N evertheless, itismy opinion thatwider Officially “ITU-R RecommendationBT.709” Officially “ITU-R RecommendationBT.2020” published author, award- Management andisa Engineering and a degreeinSoftware Angeles. Marcusholds based insunnyLos Specialist fordisguise, a TechnicalSolutions Marcus Bengtssonis n