KDE Takes First Steps Towards Linux HDR Support

Key Takeaways

with Katie aiming to make whale in default for kde6 you should expect a lot of the major whale and pain points to get a lot of develop retention over the next coming months for example X whale and Video Bridge addressing the fact that a lot of applications don't support Whalen video capture so you can't share your screen share application windows and things like this which is a serious problem if you're making a video call application and now we're seeing early support for HDR now I want to be very clear that KDE are definitely not the only ones working on this for quite a while now gnome has been doing some stuff they've got some very experimental code available in Gnome valve with the steam deck has been doing some really cool stuff since earlier this year and actually has some games working which is kind of crazy and I know that for some reason a lot of people just don't like red hat but they've also been a major driving force here so all the way back in February they organized the red hat display HDR hack Fest this was scheduled to take place on the 24th to the 26th of April in the Czech Republic which seems like a completely random place for it to happen but that's where it happened nonetheless this would include developers from all over the Linux world people from Red Hat KDE system 76 AMD egalia collabora canonical W root and a bunch of other people all attended in person with additional people from Nvidia Intel and Google that participated remotely now it's funny that those are the ones that came remotely when they are the companies that could very easily afford to send someone there in person but regardless they were still there in some form or another whilst HDR was certainly a major Topic at this event with it literally being in the name and a lot of discussions rolling around things like mixing SDR and HDR content together because you're not always just going to be playing hdr on a full screen window sometimes it's going to be in a smaller window and you still want the SDR content to look the way it should be looking it was also about General display Tech as well with discussions around things like variable refresh rate kernel mode setting properties a vendor neutral API for compositors to control the color Pipeline and even things like screen recording brightness adjustment night light and I know NightLight is a serious problem when it comes to Nvidia users all of this and more was covered really well in Simon Says blog post to the event he was there in person he is the current head developer of Sway and W or Roots if you want to see everything they discussed this is probably be one of the better places to go whoa not much actual programming coding was done at the event a lot of really important discussions were had and these discussions could then be taken back home shared with your individual teams and over time be implemented into your respective code bases hopefully improving things and shaping Linux better into the future I really do hope that this event becomes like a yearly or by yearly thing where people can get together and discuss how to make display Tech better on Linux because frankly this is one of the areas where Linux seriously lags behind windows and even Mac OS they've had support for HDR even game consoles have support for HDR for years now and only just now starting to make a little bit of Headway into that space and that is what takes us into what's happening over on KDE so this is a blog post from Xavier's blog okay HDR and color Management in kwin this is from one of those developers that attended that event in the Czech Republic and this developer realized that someone had an HDR display and uh they were like hey what can I actually do with it and they managed to make K win actually display HDR content now heavy emphasis on display this is not something you're using on like a day-to-day basis for running HDR content this is very early very Alpha stuff that is basically a proof of concept but it's possible now to understand what's Happening Here we need to have a basic level of understanding of how colors work on a display luckily the author does explain this the only problem is he explains a lot so I'm going to shorten this down so we're not here all day so traditionally when an application wants to show something on your screen the color data for that content will be sent down the display pipeline in three separate channels the red the green and the blue Channel but this is just data it needs to be converted into a form that the display can actually use and show this is then converted into brightness using an electro Optical transfer function and this is used to light up the color emitting element on the display now as I said we are simplifying it I'm well aware that color emitting element can mean vastly different things depending on the display Tech being used it's not super important for this video so we're going to ignore it now assume you're at a reasonable viewing distance by lighting up this element you are going to see the color the application is intending to show you assuming that the application and the display agree on what colors mean now we're not getting metaphysical here what I mean is the way that you encode color doesn't always have to be the same this is known as your color space with the most common being srgb but even in that case of a consistent color space sometimes build constraints you'll especially notice this on the cheaper displays will make the display show Colors a little bit differently sometimes it'll be a warmer color sometimes it'll be a cooler color and things like that now srgb is also by no means the full spectrum of colors you can actually see you've probably seen a diagram look something like this before the triangle in the middle represents the color space of srgb the thing around it wrap represents the colors you can actually see a great example of this is Tom Scott's video on the pinkest pink this is a color so pink that there is absolutely nowhere to show it to you in a YouTube video this is just not able to be captured in the srgb color space but as I said there are more color spaces but if you just change the color space of the display and then have a different color space for the content things start to get a little bit weird and colors can be shown incorrectly this is a mismatch of your color gamut the way that this is addressed is with color management if you have content using a smaller color space then what is able to be shown by your display this is pretty easy to fix all you do is map the smaller color space onto the larger one going in the other direction is a little bit harder now you're going from a larger space to a smaller one and this can lead to some loss in colors some loss in detail that can be partially overcome by doing more complex operations more complex conversions but no matter what you're doing there is always going to be loss now all of that is a long way to say basically the exact same problem exists with HDR as well HDR is high dynamic range SDR is standard dynamic range basically it is the range of brightness that can be shown on the display now when we're talking about srgb brightness is from 0 to 80 nits of brightness compare this to the thousands of nits you'll see on an HDR display and there are multiple different ways that this brightness can be encoded so if you have mismatched encoding things are going to look weird as well one such method being perceptual quantizer but there's a bunch of others as well here is the problem with KD color currently on kde5 you can select a color profile this is going to include the color correction curves and everything needed to make the colors show correctly on your display and on X this allows wide color gamma displays wide color space displays with apps that use the profile to show correctly the problem is um many apps just ignore the profile so it doesn't matter if you said it also while 10-bit color is technically possible on X it does break a couple of important applications so realistically you are limited to 8-bit color so even if it is using the color profile you might still have color banding Endo from the Whelan side theoretically the exact same thing as possible the problem is there's no protocol for applications to request the color profile so even if you set it in KDE there is no way for applications to know what the color profile is supposed to be also HDR support just doesn't exist on X and at the moment doesn't really exist generally on Weyland either but there is a new approach being worked on X no one cares about X that's never going to have HDR support unless someone feels like going and rewriting the entire EXO display server on the whale inside however there is some progress being made and this is where the support is coming in for Katie eager gnome for what valve is doing and all of this stuff so the new approach is for applications to tag the content with the color space it is supposed to be using and any other metadata that's important and then the compositor is going to do any of the needed conversions and if the content isn't tagged it's assumed to just be srgb content basically you get support for these wide color gamut displays and also HDR without affecting anything that's not using those features it just displays regularly like it already would have been doing but today we are a little bit far away from this fully being realized right now we're in very early stages we didn't do a lot of hacking at the hack Fest but I did manage to drive an HDR screen with a wide color gamut and with HDR mode enabled while having K win do the required color conversions to make SDR content look correct don't get your hopes up too much last week I was also at plasmusic Sprint in Augsburg which was also amazing and while it was mostly unrelated to HDR Kai I'm not trying to say that last name Kai happened to have a portable OLED monitor so of course I immediately started testing kwin with hdr on it piling some more hacks on top of what I put together a hackfest I could show a video in HDR surrounded by SDR content I write HDR in quotes because I didn't actually have the time to implement a proper HDR test client yet and only hard-coded K win to boost the brightness range of the video player even this super simple hack already looks amazing though especially on the OLED display but since then I polished up the code fixed a lot of K1 effects to do required color conversions and now the first bit of basic HDR and color management support emerged in K win and if you have a screen capable of HDR or a wide color gamut you can test it right now with the get build of plasma 6 but after all that you're probably wondering when will it actually be useful enabling HDR in wide color gamut just to get an image that looks the same is pretty lame for an end user the actual interesting parts are when it comes to actually gaming in HDR playing HDR videos or painting and Critter for those use cases however a lot more has to fall in place than just K when able to do color conversions there is no way to give a good estimate for when the Weyland protocol will be ready let alone when applications will be using it so I'm not even going to try it but I am however quite optimistic about the future of HDR and color Management on Linux it's all progressing pretty quickly and even just being able to fix the colors for srgb content on wide color gamut displays with a single click solution is already a pretty good step up over what we had before and I pretty much agree we are a while away from HDR just being turn on HDR and you're good to go but we are going to get there one day and there are a lot of incredible developers trying to make that happen so with that let me know your thoughts in the comment section down below are you excited for HDR do you have an HDR display that you just can't use properly on Linux or would you consider buying one if Linux does properly support it I would love to know and if you happen to be like a digital artist or something in that field let me know is HDR really important to you or is it just a trend you think is going to die out so if you like the video like the video and if you really like the video and you want to become one of them these amazing people over here check out the patreon scrubs liberope Linked In the description down below that's gonna be it for me and KDA good going bad [Music] [Music]