- From: Rik Cabanier <cabanier@gmail.com>
- Date: Thu, 15 Sep 2016 11:25:46 -0700
- To: Mark Watson <watsonm@netflix.com>
- Cc: Rossen Atanassov <Rossen.Atanassov@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
- Message-ID: <CAGN7qDCawt+H0e9WLSutKGCeZMh2Tz-yZUyGinbzOxgdahNJHQ@mail.gmail.com>
On Thu, Sep 15, 2016 at 11:01 AM, Mark Watson <watsonm@netflix.com> wrote: > > > On Thu, Sep 15, 2016 at 10:41 AM, Rik Cabanier <cabanier@gmail.com> wrote: > >> >> >> On Thu, Sep 15, 2016 at 10:21 AM, Mark Watson <watsonm@netflix.com> >> wrote: >> >>> >>> >>> On Thu, Sep 15, 2016 at 9:58 AM, Rik Cabanier <cabanier@gmail.com> >>> wrote: >>> >>>> >>>> >>>> On Thu, Sep 15, 2016 at 7:35 AM, Mark Watson <watsonm@netflix.com> >>>> wrote: >>>> >>>>> > On Sep 14, 2016, at 10:05 PM, Rossen Atanassov < >>>>> Rossen.Atanassov@microsoft.com> wrote: >>>>> > >>>>> >> On Wed, Sep 14, 2016 at 16:53:53, Mark Watson wrote: >>>>> >> >>>>> >> I have some use-cases and issues / questions related to High >>>>> Dynamic Range >>>>> >> graphics / images and how they could be supported in CSS. I >>>>> wondered if this >>>>> >> topic was or could be on the agenda for next week ? >>>>> > >>>>> > Are you referring to our TPAC agenda? If so, we don't have the topic >>>>> scheduled and looking through everything we have it is doubtful we could >>>>> get to it. >>>>> > >>>>> > Could you summarize your proposal? Is this something proposed at >>>>> WICG already? >>>>> >>>>> Yes, TPAC. I've raised the issue of HDR a few times on the CSS list, >>>>> but with no real response. We had a breakout at TPAC last year, but no >>>>> one from CSS attended. I imagine that is because people do not yet >>>>> have real hardware / platform APIs with which to play with this >>>>> functionality. Those will soon be available, so it seemed good timing >>>>> to raise it again and explain the various problems. >>>>> >>>>> I only have problems, not a proposal. The basic problem (as I >>>>> understand it) is that with HDR displays, users are unlikely to want >>>>> the peak white for regular sRGB to map to the peak luminance of the >>>>> display. That would make desktops blindingly bright. So there needs to >>>>> be a way for pages to signal when they are providing data in the sRGB >>>>> luminance space (where peak white is what the user has set as a >>>>> comfortable luminance for their desktop according to current ambient >>>>> light) and when they are providing data in a different luminance >>>>> space, where peak white is brighter (exactly how bright is one of he >>>>> questions to be answered.) >>>>> >>>> >>>> This is defined in the CSS color spec [1]. If no profile is provided, >>>> peak white is peak sRGB white. >>>> The fact that you get blindingly white is a browser bug. (I believe >>>> only Safari does this right today) >>>> >>> >>> I think there is a mis-understanding here and that is why I think the >>> issue deserves discussion. >>> >>> As far as I can tell, [1] is entirely about color gamut. Whilst there >>> are many ways to identify colors, the specification does not seem to treat >>> dynamic range. The section you reference regarding profiles, says "Others >>> are more human-friendly to write and understand, *and are converted to >>> an sRGB color by CSS*". >>> >>> sRGB peak white will appear at the brightness the user prefers for their >>> environment (because most of the graphics they see are sRGB and they will >>> adjust the brightness control on their display). >>> >>> My point is that for capable displays, it should be possible to make >>> graphics brighter than that. >>> >> >> Yes, you can by either providing an image with an embedded profile that >> has a higher gamut than sRGB, or by specifying a CSS color [1] with an HDR >> profile. >> > > Could you give an example of how you would specify an HDR profile with > CSS ? For example, if I wanted some white text that was twice as bright as > sRGB(255,255,255) text ? I don't see that in the css-color specification. > Dean wrote a blog about this: https://webkit.org/blog/6682/improving-color-on-the-web/ I don't know what profile is twice as bright as sRGB, but color(rec2020 255 255 255) would be brighter than rgb(255, 255, 255) > Note that I am not talking about a wider gamut - that seems to be well > covered - but a different dynamic range (i.e. a larger color volume, not > just larger color gamut). > What do you mean by "color volume". Are you talking about higher bit depths for compositing? > Those colors are then mapped to the "device" color which usually is the >> monitor's colorspace. If you have an HDR monitor and specify an HDR image, >> you will get colors that are brighter than sRGB white. >> >> Safari is already doing this for images so you can try this for yourself >> if you have a capable device. >> >> >>> >>>> If you do provide a profile, it will be used to map to the display. >>>> Is there a way to embed a profile in a video stream? >>>> >>> >>> Here I am not talking about video. But, yes, video metadata specifies >>> not only color gamut (primaries) but a transfer function which is used to >>> map between encoded luminance and actual luminance and is different for HDR >>> and SDR video. >>> >> >> I think we need to specify what is done with video. It seems that this >> information needs to be used so the browser knows how to manage the video's >> colors. >> what happens today with video? >> > > Well, this is all rather new, so I doubt there is any consistency. On the > various devices we have seen which composite sRGB graphics with HDR video > it's highly variable. I expect when we see this on devices with > desktop-class browsers, the operating system will have made some decision > as to what luminance to map sRGB to, relative to the HDR images. I've heard > 80 nits. I've also heard of people planning to map sRGB peak white to panel > peak white. > > > >> >> >>> To obtain CSS use-cases, imagine first a still image extracted from an >>> HDR video, encoded in some still image format which carries HDR metadata >>> and which is supported by the browser. >>> >>> It should be possible to specify in CSS any color+luminance that appears >>> in that image. If the video or still image pixels are constrained to be no >>> brighter than the sRGB peak white (the luminance the user prefers for their >>> desktop), then you will not get any improvement in appearance: for example >>> specular highlights in the video / image would be no brighter than for an >>> SDR video / image, even though the display may be capable of that. >>> >> >> Yes, extract the transfer function and other information from the video >> stream and use it to construct a profile. Then embed that profile in your >> still image. >> > > What about actually specifying one of those colors in CSS ? So that I can > have text or graphics matching the colors in the image ? > You can place the profile on your web server,load it with css using @color-profile and use the name with the css color property. > >> >>> >>>> >>>>> If the WICG is the appropriate place to raise these problems, I can do >>>>> that, but the experts are in CSS WG so I wondered if there was >>>>> interest in learning about these issues. >>>>> >>>>> Thanks ... Mark >>>>> >>>> >>>> 1: https://drafts.csswg.org/css-color/#color-type >>>> >>>> >>> >> 1: https://drafts.csswg.org/css-color/#icc-colors >> >> > 1: https://drafts.csswg.org/css-color/#at-profile
Received on Thursday, 15 September 2016 18:26:16 UTC