- From: Tim Borer <tim.borer@bbc.co.uk>
- Date: Tue, 19 Jun 2018 17:44:22 +0100
- To: Lars Borg <borg@adobe.com>, Craig Revie <Craig.Revie@FFEI.co.uk>, Phil Green <green@colourspace.demon.co.uk>
- Cc: Leonard Rosenthol <lrosenth@adobe.com>, Max Derhak <Max.Derhak@onyxgfx.com>, Simon Thompson-NM <Simon.Thompson2@bbc.co.uk>, "public-colorweb@w3.org" <public-colorweb@w3.org>
- Message-ID: <31217eb4-c94e-0807-4f07-fa36f378c46a@bbc.co.uk>
Hi Lars, The reason I discussed the consumer display was to show that there was little sense in archiving broadcast content in a display referred format when there was no single reference monitor on which it should be displayed. HLG is defined in ITU-R Recommendation BT.2100. Nowhere in that specification is there a defined luminance for a reference display. The reference display for HLG may, in principle, be any peak luminance. BT.2100 does mention a 1000nit display for HLG, but that is by no means a defined reference peak luminance. The recommendation makes it clear that the display may have a wide range of peak luminances. What BT.2100 does define is a reference view condition, which is basically a dim environment with surround luminance (i.e. the backdrop for the display) of 5 nits. Of course Planet Earth II was graded. It was graded on a Dolby PRM 4220 monitor (I think that was the model number). The Dolby monitor used a custom (internal) LUT so that it functioned as an HLG display. The peak luminance was 600nits. Actually that seemed a bit bright (according to the colourist). As you well know many people now use a, 1000nit, Sony BVM X300 for HDR grading (and, of course, other grading monitors are available). In general programmes may be graded (or shaded for live) on a variety of monitors. Parts of the programme may well be graded/shaded on different monitors (at different peak luminance). That is a difference from movie production. Consequently there is no one single reference monitor to which the programme is naturally display referred. Since television programmes do not have a specific reference monitor (which is also true, though to a lesser extent, with SDR), it makes good sense to use a scene referred signal, and to archive in that scene referred format. This is what has always been done for broadcast TV. Best regards, Tim On 19/06/2018 16:06, Lars Borg wrote: > The consumer display is of no interest here. > Compare with a printed catalog. The D50 light booth is the reference > viewing condition for the catalog. - the catalog print is carefully > verified in a D50 light booth, but is actually used in completely > different viewing environments, just as happens for TV viewing. > > Was Planet Earth II HLG produced without color grading? > > Thanks, > > *Lars Borg*|Principal Scientist |Adobe |p. 408.536.2723|c. > 408.391.9479|borg@adobe.com <mailto:borg@adobe.com> > > > > On 6/18/18, 11:43 AM, "Tim Borer" <tim.borer@bbc.co.uk > <mailto:tim.borer@bbc.co.uk>> wrote: > > Hi Craig and all, > > What Lars says sounds very logical, but I think it is incorrect > both in general and for HLG. > > The key to what he says is broadcast material, by which I assume > he means finished programmes. The key part is “broadcast”. To > understand this it is useful to reprise the difference between > movies and television, which has become more greatly accentuated > with the development of HDR. > > With movies (not my specialist field) the viewer is always in a > standardised movie theatre. A conventional movie theatre is > specified to have a peak luminance of 48 cd/m^2. Since movie > theatres are standardised it does make sense both to grade and to > archive a display referred signal, which is what is done. > > TV, on the other hand, does not control the display or the viewing > environment. Modern CRT displays, before their replacement by flat > panels, had a peak brightness of about 200 cd/m^2 (hereafter > “nits” to simplify my typing). Modern SDR flat panels went up to > as high as 600nits. Now, with the advent of HDR, consumer HDR TVs > can be as bright as 1600 nits and increasing. Mobile phones may be > a few hundred nits and perhaps as much as 600nits. At the same > time the viewing environment can vary greatly from a dim living > room (on a “movie night”) to a bright daytime living room for live > sport (think Wimbledon Tennis in the UK), to a train in the dark > or a bus in bright sunlight for mobiles. In short, a broadcast > programme, in contrast to a movie, does not know how brightly the > programme will be shown, not the viewing environment. But with TV > the display does “know” its own brightness and either “knows” or > can estimate the viewing conditions (as I said previously this is > a second order effect, and so precise knowledge is not required). > It therefore makes sense for the programme to be stored in a > display referred format and for the display to render to its > capabilities and the viewing environment. > > With TV, unlike movies, content may be graded under a variety of > conditions on displays with different luminances. Obviously the > ideal is a controlled grading suite, but this is not always > available particularly for live and for news. For example news is > quite often shaded using (carefully selected) consumer monitors in > a relatively bright environment. > > So when archiving movie content it makes sense that it should be a > display referred signal. > > With broadcast material archiving a scene referred signal makes > more sense. Indeed this is what has been done for the history of > TV where the recording of the scene referred signal (e.g. Ree.709) > has been archived. HLG simply continues conventional broadcast > practice. > > Best regards, > Tim > > ------------------------------------------------------------------------ > *From:* Lars Borg [borg@adobe.com <mailto:borg@adobe.com>] > *Sent:* 18 June 2018 15:04 > *To:* Craig Revie; Tim Borer; Phil Green > *Cc:* Leonard Rosenthol; Max Derhak; Simon Thompson-NM; > public-colorweb@w3.org <mailto:public-colorweb@w3.org> > *Subject:* Re: Help with HLG profile > > Hi Craig, > > If you’re archiving already broadcast material, then a display > referred profile seems the most appropriate, as it tells you what > the approver saw. > If you’re archiving original footage that has not been broadcast, > nor approved on a display, then a camera profile would be > appropriate for future processing. > These would be general recommendations, not specific to HLG. > Is HLG an exception to these general rules? > > Thanks, > > *Lars Borg*|Principal Scientist |Adobe |p. 408.536.2723|c. > 408.391.9479|borg@adobe.com <mailto:borg@adobe.com> > > > > On 6/18/18, 5:51 AM, "Craig Revie" <Craig.Revie@FFEI.co.uk > <mailto:Craig.Revie@FFEI.co.uk>> wrote: > > Hi Tim, > > Thanks for this detailed response which I hope will be helpful > in the PQ/HLG discussion. From the perspective of someone only > peripherally involved in the motion picture or broadcast > television industry, it seems that HLG provides a good > solution for live broadcasts whereas PQ provides a better > model for motion picture production. Is that a reasonable > assumption? How do you expect that HDR BBC and NHK dramas will > be produced? > > I also see a statement on the World Cup 2018 link: “The > production workflow for the World Cup is not native HLG as > Host Broadcaster Services have defined their own HDR > workflow.” Can you provide more details about this? > > @Lars, given Tim’s description, it would seem that a > ‘scene-referred’ profile would make more sense than a display > referred profile if the intent is to allow archival of images > encoded as HLG. > > Best regards, > > _Craig > > *From:*Tim Borer <tim.borer@bbc.co.uk > <mailto:tim.borer@bbc.co.uk>> > *Sent:* 18 June 2018 10:17 > *To:* Lars Borg <borg@adobe.com <mailto:borg@adobe.com>>; > Craig Revie <Craig.Revie@FFEI.co.uk > <mailto:Craig.Revie@FFEI.co.uk>>; Phil Green > <green@colourspace.demon.co.uk > <mailto:green@colourspace.demon.co.uk>> > *Cc:* Leonard Rosenthol <lrosenth@adobe.com > <mailto:lrosenth@adobe.com>>; Max Derhak > <Max.Derhak@onyxgfx.com <mailto:Max.Derhak@onyxgfx.com>>; > Simon Thompson-NM <Simon.Thompson2@bbc.co.uk > <mailto:Simon.Thompson2@bbc.co.uk>>; public-colorweb@w3.org > <mailto:public-colorweb@w3.org> > *Subject:* Re: Help with HLG profile > > P.S. For more information see: > World Cup 2018 in UHD HDR on BBC iPlayer > (https://www.bbc.co.uk/rd/blog/2018-05-uhd_hdr_world_cup_2018 > <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.bbc.co.uk%2Frd%2Fblog%2F2018-05-uhd_hdr_world_cup_2018&data=02%7C01%7Cborg%40adobe.com%7Cac8c6af30bfe4b1fc2dd08d5d5011d01%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636649123133564877&sdata=vj4UwJMsC3OUMJXl1T%2BTQmhMp9YNYJhfhi1oddW%2FXCE%3D&reserved=0>). > The Royal Wedding in High Dynamic Range > (https://www.bbc.co.uk/rd/blog/2018-05-ultra-high-definition-dynamic-range-royal-wedding-uhd-hdr > <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.bbc.co.uk%2Frd%2Fblog%2F2018-05-ultra-high-definition-dynamic-range-royal-wedding-uhd-hdr&data=02%7C01%7Cborg%40adobe.com%7Cac8c6af30bfe4b1fc2dd08d5d5011d01%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636649123133564877&sdata=CnJQNiixcSmCIi%2Bsl%2Buuh7HdzpRdeqDE%2Fp30I0AAXp0%3D&reserved=0>) > Tim > > On 18/06/2018 09:46, Tim Borer wrote: > > There are one or two inaccuracies in the thread. So I > though it worthwhile to introduce a few facts to correct > these. Hope this is useful. > > It IS reasonable to describe HLG as relative scene > luminance. There has been a lot of debate by proponents of > PQ (which is absolute/non-relative display referred > encoding) that this is not really so. Nevertheless we > designed HLG precisely as relative scene luminance (just > like Rec.709). > > I have often heard it said that there is no standard > Rec.709 production (because camera operators, it is > claimed, universally adjust their cameras). The claim is > that by tweaking the camera the picture somehow becomes > display referred. Even if it were true that cameras are > always adjusted (not so) this would not make the signal > display referred. If you doubt this simply look at the > dimensions of the signal. HLG is dimensionless (a relative > signal) and PQ has dimensions of candelas per square metre > (nits). All that adjusting a 709/HLG camera does is to > produce an “artistic” modification to the signal. The > signal still represents relative scene referred light, > just not the actual scene (but, rather, one that the > producer wished had existed). Adjusting the camera does > not convert a dimensionless signal into a dimensional one. > > In fact a great deal of live television is produced using > a standard Rec709 OETF. This includes almost all live > sport (especially soccer), live light entertainment, and > news. This encompasses a large part of broadcast > television output. In sport it is often a contractual > obligation to use the Rec 709 OETF. In other instances the > producers often do not like knees because, as typically > implemented, then can distort flesh tones. A further > consideration it that in a multicamera shoot it is > essential to match all the cameras. This is difficult if > they don’t use a standard Rec 709 setting (often cameras > may have different firmware versions, which means that > setting up a camera does not necessarily mean the same > thing even on the same model of camera). It is not the > case that “the camera’s linearity response is tweaked by > the operator for various reasons”. This is not really > viable in a multicamera live shoot, and the shaders don’t > have time to do it live. Similarly for live production the > gamut is standard Rec 709 (if necessary clipped from the > wider camera taking gamut). This is necessary to ensure > consistent colours for sporting strips both between > cameras and at different venues and different games. It is > not unusual for sporting strips to be outside 709, and it > is important that such colours are treated in a consistent > way, so gamut mapping, other than simple clipping, is not > viable (bear in mind that footage from different games > may often be shown as part of the commentary). So, to > emphasise, the fact is that a great deal of television IS > produced using the standard Rec 709 OETF using standard > 709 gamut (without gamut mapping). > > Scene referred conversions need to be used appropriately. > When used appropriately they do not create significant > colour shifts. Scene referred conversion should be used > when matching camera outputs (as opposed to matching the > picture that is seen on the display – they are not the > same). Display referred conversions are used to ensure > that the displayed image is the same. There are different, > distinct, use cases for these two types of conversion. It > is a mistake to assume that all conversions should be > display referred. As an example consider the recent > coverage of the Royal Wedding. This was shot using a > mixture of HLG HDR cameras and HD cameras (using Rec 709). > The production architecture was that shown in ITU-R Report > BT.2408-1 2018 (note the -1 version) (freely available at > https://www.itu.int/pub/R-REP-BT.2408-1-2018 > <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.itu.int%2Fpub%2FR-REP-BT.2408-1-2018&data=02%7C01%7Cborg%40adobe.com%7Cac8c6af30bfe4b1fc2dd08d5d5011d01%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636649123133564877&sdata=AqwlwS97EBGMkSeszU18HBpEuyXD%2F7nanzK5GqVNJ%2Fs%3D&reserved=0>), > figure 4, page 14. In this workflow you will note that > there are many scene referred Rec 709 to HLG conversions. > This is so that pictures can be shaded using standard Rec > 709 monitors (which is a requirement when the majority of > viewers are watching in 709). Note, in particular, that > the final Rec 709 SDR output is converted from the HLG > signal using a scene referred conversion. We estimate that > the Royal Wedding was viewed by 1.8 billion viewers. The > international feed was derived from the HLG signal as > described, using a scene referred conversion. The colour > was NOT distorted using this conversion (and, clearly, the > producers would not have allowed distortion for such a > prestigious broadcast). On the other hand if one were > producing primarily for an HDR audience then you would use > the alternative architecture in BT.2408 (fig 3, page 12). > Here shading is performed primarily on the HDR monitor > (with an SDR monitor fed by a DISPLAY referred conversion, > so that the shader can check that nothing untoward is > happening on the SDR signal). Note that in a joint HDR SDR > production you can give primacy to either shading in HDR > (for a majority HDR audience) or to shading in SDR (for a > mainly SDR audience – the current situation). But you > cannot prioritise both. We have found that shading in SDR > gives very good quality HDR as well as SDR. NHK have in > mind producing for a primarily HDR audience and, > therefore, they favour the production workflow of figure > 3. To summarise scene referred conversion do not produce > significant colour shifts when they are used properly. > Indeed without using scene referred conversions it is not > possible to match the look of HDR and SDR output when > shading in SDR. > > There are few HDR broadcasts in Europe yet though a number > are in the pipeline. To the best of my knowledge all these > broadcasts will be using HLG. Similarly broadcasters that > produce live content (such as sport) in the US also favour > HLG. The BBC has made our Planet Earth II series available > in UHD HDR HLG on catch up (OTT) television, and are > showing some of the Soccer World Cup matches is HLG HDR > OTT. Most OTT movie distribution currently uses PQ > (HDR10). This is possible because of the non-live > workflow. I am unaware of live sporting events broadcast > using PQ. YouTube distribute in both HLG and HDR10. Since > production is easier in HLG (particularly with pro-summer > equipment) most of the user generated HDR content on > YouTube is HLG. > > Best regards, > Tim > > Dr Tim Borer MA, MSc, PhD, CEng, MIET, SMIEEE, Fellow SMPTE > > Lead Engineer > > Immersive & Interactive Content > > BBC Research & Development > > BBC Centre House, 56 Wood Lane, London W12 7SB > > T: +44 (0)30304 09611 M: +44 (0)7745 108652 > > On 12/06/2018 05:20, Lars Borg wrote: > > Hello Craig, > > See below. > > On 6/9/18, 9:12 PM, "Craig Revie" > <Craig.Revie@FFEI.co.uk > <mailto:Craig.Revie@FFEI.co.uk>> wrote: > > Hi Lars, > > Thanks for your reply. > > First of all on terminology, is it reasonable to > describe HLG as encoding relative scene luminance? > > Not really. I wouldn’t. > > It’s an approximation of scene colorimetry just like > 709 or 2020. > > How accurate is it in real production? > > And what accuracy do you need? Why? > > I haven’t seen any published tests. > > But here’s what we know from 709 production. > > I’ve yet to find anyone that sets their camera in > reference 709 mode in real production. > > Typically 709 productions do not use the standard OETF > found in the 709 spec. > > The camera’s linearity response is tweaked by the > operator for various reasons. > > Extra suppression of the darks as a means to reduce noise. > > And the typical knee for highlight rolloff. (Which HLG > now includes in a standard way) > > Maybe there are options for gamut mapping (which is > non-linear) > > We usually do’t call these tweaks color grading, but > rather camera setup. > > Either tweak changes the contrast relations from true > scene colorimetry. > > These tweaks are not indicated in metadata (as HLG has > no such, and other formats seem to be proprietary or > incomplete), so you have no knowledge on how to undo > them in post. > > I am not very familiar with the technical details > of the cameras used for broadcast television but > my assumption was that the controls allow white > balance, aperture control and selection of > filters. I also assume that the sensor is linear > > So far I agree with you. > > and that there is minimal processing of the > signal. If so, the assumption of relative scene > luminance (as described in a number of papers) > would seem to be at least a reasonable > approximation. Are these assumptions incorrect? > > I doubt it. As I noted above, there are many in-camera > processing options. So the signal might be non-linear. > > I think that for the uses outlined by Simon on > this thread, it would be helpful to have a V4 ICC > profile even if there are some limitations (which > there may well be). Is this something you could > provide? It seems to me that the more useful of > the two profiles would be the ‘HLG scene profile’ > although depending on the result of our discussion > about terminology this may need a different > description. > > I have yet to find a use case for an HLG scene profile. > > Please explain how you would use it, and what workflow. > > Primarily I see post production uses for an HLG > reference display profile. > > With this profile I can mix display-referred content > across HLG, PQ, 709 media. > > For example, the colors in a commercial are > display-referred and the repurposing to another media > should preserve those colors. Scene-referred > conversions wouldn’t cut it, so I would not use an HLG > scene profile for this. > > On the point about ‘grading’, in talking to people > from the BBC and NHK, I understand that the main > reason to develop HLG was that for many use cases > there is no opportunity for grading, for example > for live broadcasts. > > Grading, no. > > But camera matching, yes, also for live broadcasts. > > It is the rare event where all cameras are of the same > make, model, and revision, including lens and lights. > > In practice, cameras at major sports events include > both HDR and 709 cameras, different sensors, multiple > brands, different light setups, different codecs. > > Same sports jersey => very different colors. > > So some effort is often spent to make cameras produce > similar colors on output. > > Same sports jersey => similar colors. > > Most likely that matching process undermines true > scene colorimetry. > > BT.2087 shows conversions from 709 to 2020. > > My study shows that doing this ‘scene’-referred (case > 2) creates significant color shifts. > > In practice, I would have thought that PQ would be > used for grading of film production and would be > converted to HLG at the time of broadcast. > > Are there movie HLG broadcasts in Europe yet? > > PQ for movie grading, yes. > > Although Adobe Premiere is agnostic and lets you grade > (display-referred) HLG content as well. > > But it seems movie distribution is mostly PQ (HDR10), > not HLG. Think Netflix, etc. > > I like this diagram from Yoeri Geutskens > <https://www.linkedin.com/in/yoerigeutskens/ > <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.linkedin.com%2Fin%2Fyoerigeutskens%2F&data=02%7C01%7Cborg%40adobe.com%7Cac8c6af30bfe4b1fc2dd08d5d5011d01%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636649123133564877&sdata=pRjL8L1MQvG%2FJsLHjH9QrOVnyjpFqithv326FVuunVg%3D&reserved=0>> > > More names in the PQ circle than in the HLG circle. > > Lars > > Best regards, > > _Craig > > ________________________________ > > From: Lars Borg <borg@adobe.com > <mailto:borg@adobe.com>> > > Sent: 10 June 2018 04:53:58 > > To: Craig Revie; Phil Green > > Cc: Leonard Rosenthol; Max Derhak; Simon > Thompson-NM; public-colorweb@w3.org > <mailto:public-colorweb@w3.org> > > Subject: Re: Help with HLG profile > > Hi Craig, > > A very sensible question. > > Rec. 2100 gives you two reference decodings for > HLG media: scene referred and display referred @ > 1000 nits. > > Scene versus display is not a metadata item, but > rather a choice by the reader. > > Presumably the camera operator optimized the > camera rendering for a pleasing appearance on the > reference display, so ‘scene’ is a misnomer, as > it’s always been also with Rec. 709. > > At the consumer end, each HDR TV set (PQ or HLG) > is expected to apply some form of re-rendering > based on its assumed luminance (assumed as it is > not actually measured or calibrated). That would > be your metadata source. However, we should not > expect that they implement anything like what’s > indicated in Rec. 2100. Power limits, motion > enhancements, user preferences, etc. are out of > scope for Rec.2100. This makes it rather > meaningless to try to model anything other than > the reference display. > > In a separate expert forum, a majority stated that > even the best consumer HDR TV sets are so bad, > they should never be used of color grading. > > So this begs the question, who would need a > parameterized HLG decoder? > > BTW, the HLG scene profile is trivially > implementable in V4. The reference display profile > is a little bit more complex in V4, but doable. > > Thanks, > > Lars Borg | Principal Scientist | Adobe | p. > 408.536.2723 | c. 408.391.9479 | borg@adobe.com > <mailto:borg@adobe.com> > > On 6/8/18, 9:46 PM, "Craig Revie" > <Craig.Revie@FFEI.co.uk > <mailto:Craig.Revie@FFEI.co.uk><mailto:Craig.Revie@FFEI.co.uk> > <mailto:Craig.Revie@FFEI.co.uk%3E>> wrote: > > Hi Max and Phil, > > I hesitate to ask as this may show my ignorance > but I had thought that HLG encodes relative scene > luminance and does not carry any metadata. In my > understanding the choice of the reference white is > made by the camera/cameraman shooting the scene > and the camera signal is encoded as HLG which > makes this model ideal for broadcast television. > > You seem to anticipate having max and min > luminance values - where do these come from? > > What does the profile represent and how do you > anticipate it being used? > > As I say, this may just show my ignorance... > > _Craig > > On 8 Jun 2018, at 23:18, Phil Green > <green@colourspace.demon.co.uk > <mailto:green@colourspace.demon.co.uk><mailto:green@colourspace.demon.co.uk> > <mailto:green@colourspace.demon.co.uk%3E>> wrote: > > In my understanding yes, but you would not be able > to pass in the max and min luminance so would need > a different profile for each condition supported. > > Phil > > On 08/06/2018 16:28, Leonard Rosenthol wrote: > > Can this profile be defined WITHOUT the calculator? > > Leonard > > From: Max Derhak <Max.Derhak@onyxgfx.com > <mailto:Max.Derhak@onyxgfx.com>><mailto:Max.Derhak@onyxgfx.com> > > Date: Wednesday, June 6, 2018 at 2:43 PM > > To: Simon Thompson-NM <Simon.Thompson2@bbc.co.uk > <mailto:Simon.Thompson2@bbc.co.uk>><mailto:Simon.Thompson2@bbc.co.uk>, > "public-colorweb@w3.org > <mailto:public-colorweb@w3.org>"<mailto:public-colorweb@w3.org> > <public-colorweb@w3.org > <mailto:public-colorweb@w3.org>><mailto:public-colorweb@w3.org> > > Subject: RE: Help with HLG profile > > Resent-From: <public-colorweb@w3.org > <mailto:public-colorweb@w3.org>><mailto:public-colorweb@w3.org> > > Resent-Date: Wednesday, June 6, 2018 at 2:43 PM > > Simon has indeed helped me, and I’m very grateful > for his assistance. As it turns out there was a > small bug in my matlab/octave code. > > Based on my matlab/octave code I have been able to > create iccMAX profiles for both narrow range and > full range encoding of Rec 2100 using Hgl curves. > I created XML representations of the profiles and > used the iccFromXML tool from the reference > implementation to create the profiles for testing > using the iccMAX reference implementation CMM. > > Significant features of these prototype profiles > include: > > * Full floating point based algorithmic > encoding of RGB to XYZ and XYZ to RGB tags using > calculator processing elements > > * Uses a D65 based PCS > > * Max and min luminances can be passed in as > CMM environment variables to adjust Hlg curves > > * The profiles use display relative Y=100 for > max white for default relative intent processing > > * Scene relative luminances can be supported > with CMM luminance matching using the spectral > viewing conditions tag (part of Profile Connection > Conditions – PCC) illuminant white point > luminance. (Note: Using CMM control options for > luminance based matching by CMM allows for scene > relative luminances to be used and adjusted > for. The PCC can be externally substituted to > define an alternate white point luminance for > luminance scaling, but matching values for CMM > environment variables are also needed to ensure > that the corresponding Hlg curves are used). > > An Interoperability Conformance Specification > (ICS) is needed to help define specific profile > and CMM requirements for this type of > profile. That is something that the ICC display > working group will work on. > > None of this can be directly accomplished using a > single V4 profile. V4 uses display relative with > a D50 PCS (with chromatic adaptation applied). By > playing around with defining the media white point > one can achieve a level of luminance scaling using > absolute intent with some possible > interoperability issues to contend with. The Hlg > algorithm cannot be directly encoded in v4, and > LUTs and inverse LUTs using interpolation need to > be populated for a fixed scene luminance condition > with different profiles created for different > scene luminances. > > Regards, > > Max Derhak (PhD) > > Principal Scientist > > From: Simon Thompson-NM > [mailto:Simon.Thompson2@bbc.co.uk] > > Sent: Tuesday, May 29, 2018 8:52 AM > > To: public-colorweb@w3.org > <mailto:public-colorweb@w3.org><mailto:public-colorweb@w3.org> > > Subject: Re: Help with HLG profile > > Hi Chris, all, > > I’ve already sent a code correction to Max, so > hopefully that will fix the issue he was seeing. > > I’ll comment further inline, below. > > From: Chris Lilley [mailto:chris@w3.org] > > On 17-May-18 23:25, Max Derhak wrote: > > Hi, > > I have an action item in the ICC Display Working > group to develop an HLG based iccMAX display > profile. In order to understand how to go about > it I’ve first prototyped functionality in > Matlab/Octave. > > The attached zip file has my code along with the > BT2100 document that I’m using to implement.. The > problem is that for a display profile you need to > have both device to PCS as well as PCS to device > transforms. > > The device to PCS transform is conceptually > implemented in HLG_FullToXYZ.m, and the PCS to > device is conceptually implemented in > HLG_XYZToFull.m (I’m using full 0.0 to 1.0 range > encoding in this case). Alternatively one could > use the HLG_Narrow12ToXYZ.m and > HLG_XYZToNarrow12.m to use the narrow 12-bit > integer encoding. > > The problem is that the OOTF (implemented in > HLG_EOTF.m) and inverse OOTF (implemented in > HLG_invEOTF) functions are not logical inverses of > each other (from what I can tell from the docs). > > I recall hearing that these are not round-trippable. > > The equations for HLG are reversible and we have > used the reverse transforms for converting other > HDR formats to HLG, converting SDR camera feeds to > HLG and converting HLG to SDR. An example use > case is given in: > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.bbc.co.uk%2Frd%2Fblog%2F2018-05-ultra-high-definition-dynamic-range-royal-wedding-uhd-hdr&data=02%7C01%7Cborg%40adobe.com%7Cc687232c3775491b340f08d5cea18e1c%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636642115681164772&sdata=eICRO%2Fa3ISG%2Fxm50j3UznDG5HMD1Ekf5YHc6uCxp5%2F4%3D&reserved=0<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.bbc.co.uk%2Frd%2Fblog%2F2018-05-ultra-high-definition-dynamic-range-royal-wedding-uhd-hdr&data=02%7C01%7Clrosenth%40adobe.com%7Cb810dc2b06c24735603308d5cbdd749e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C1%7C636639074360711277&sdata=R%2BFSqmXWBTIxF8EfODM8ZR83S4jkiC8YwMpWTlFzi4Q%3D&reserved=0> > <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.bbc.co.uk%2Frd%2Fblog%2F2018-05-ultra-high-definition-dynamic-range-royal-wedding-uhd-hdr&data=02%7C01%7Cborg%40adobe.com%7Cc687232c3775491b340f08d5cea18e1c%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C0%7C636642115681164772&sdata=eICRO%2Fa3ISG%2Fxm50j3UznDG5HMD1Ekf5YHc6uCxp5%2F4%3D&reserved=0%3Chttps://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.bbc.co.uk%2Frd%2Fblog%2F2018-05-ultra-high-definition-dynamic-range-royal-wedding-uhd-hdr&data=02%7C01%7Clrosenth%40adobe.com%7Cb810dc2b06c24735603308d5cbdd749e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C1%7C636639074360711277&sdata=R%2BFSqmXWBTIxF8EfODM8ZR83S4jkiC8YwMpWTlFzi4Q%3D&reserved=0%3E> > > On the other hand the BBC claim that the transcode > looks "identical" > > A more complete description of the process of > transcoding between HDR formats is given in ITU-R > BT.2390 section 7: > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.itu.int%2Fdms_pub%2Fitu-r%2Fopb%2Frep%2FR-REP-BT.2390-4-2018-PDF-E.pdf&data=02%7C01%7Cborg%40adobe.com%7Cc687232c3775491b340f08d5cea18e1c%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C1%7C636642115681164772&sdata=ZLkH19GPIpEJ3v48wDdMaoIkMDT8aGfgOleSjeXPVoI%3D&reserved=0<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.itu.int%2Fdms_pub%2Fitu-r%2Fopb%2Frep%2FR-REP-BT.2390-4-2018-PDF-E.pdf&data=02%7C01%7Clrosenth%40adobe.com%7Cb810dc2b06c24735603308d5cbdd749e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C1%7C636639074360711277&sdata=cXEstDUoMa2r2vIP1fmlx57urfV5uyxbR2hOEjEFbQc%3D&reserved=0> > <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.itu.int%2Fdms_pub%2Fitu-r%2Fopb%2Frep%2FR-REP-BT.2390-4-2018-PDF-E.pdf&data=02%7C01%7Cborg%40adobe.com%7Cc687232c3775491b340f08d5cea18e1c%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C1%7C636642115681164772&sdata=ZLkH19GPIpEJ3v48wDdMaoIkMDT8aGfgOleSjeXPVoI%3D&reserved=0%3Chttps://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.itu.int%2Fdms_pub%2Fitu-r%2Fopb%2Frep%2FR-REP-BT.2390-4-2018-PDF-E.pdf&data=02%7C01%7Clrosenth%40adobe.com%7Cb810dc2b06c24735603308d5cbdd749e%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C1%7C636639074360711277&sdata=cXEstDUoMa2r2vIP1fmlx57urfV5uyxbR2hOEjEFbQc%3D&reserved=0%3E> > > *Also it would be incredibly helpful to better > understand what is the purpose of having an HLG > ICC profile? > > There are a few general use cases that we’ve > thought of so far which apply equally to all HDR > variants: > > · Storage of subtitles and other still images – > currently still formats like PNG can only store a > gamma value in the header files – the only way to > store non-gamma encoded images is to embed an ICC > Profile. Currently for PQ HDR, there’s a draft > proposal that looks for a given ICC Profile > filename in the header which then over-rides both > the header and profile. We would prefer to have > the correct ICC profiles available. > > · Allowing operating systems to correctly display > images on non-gamma displays. > > · IP disptribution platforms (both PC based > and Set-top box will need to display video and > background images) – e.g. a video embedded in a > webpage, you may have a video box in HDR and a > surrounding webpage in sRGB, both of which need to > be correctly displayed and need an ICC profile > description. > > Any transforms from SDR to HDR will need to place > the SDR diffuse white at the correct signal level > (given in ITU-R BT.2408) – I’m not sure how this > is encoded in to the transforms. > > Best Regards > > Simon > > -- > > Simon Thompson MEng CEng MIET > > Project R&D Engineer > > BBC Research and Development South Laboratory > > ________________________________ > > [FFEI > Limited]<https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.ffei.co.uk&data=02%7C01%7Cborg%40adobe.com%7C95e992930a4b4a0f85c308d5cddd420a%7Cfa7b1b5a7b34438794aed2c178decee1%7C0%7C1%7C636641272535313819&sdata=Q1alNsLsCwIaIzgnNuFnw45OG31IyZE1TqVlXo8XBCM%3D&reserved=0> > > CONFIDENTIALITY AND DISCLAIMER NOTICE > > This message and any attachment is confidential > and is protected by copyright. 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Received on Tuesday, 19 June 2018 16:44:52 UTC