HDR support in Wayland/Weston
Sharma, Shashank
shashank.sharma at intel.com
Fri Jan 11 03:24:37 UTC 2019
Hello Ole,
On 1/10/2019 9:31 PM, Niels Ole Salscheider wrote:
> Hello,
>
> on a first glance this sounds sensible. Would it work well with the last color
> management protocol proposal that I made or do you see issues there?
> We could add REC2020 as another predefined profile.
>
> https://lists.freedesktop.org/archives/wayland-devel/2017-January/032769.html
> I think the last proposal was mostly sane and usable for everybody, but there
> was not much interest afterwards. However, there was a lot of discussion with
> wishes from different sides that went into this. The relevant mailing list
> threads are the following, but you have to follow the discussion over the next
> months:
>
> https://lists.freedesktop.org/archives/wayland-devel/2016-November/031728.html
> https://lists.freedesktop.org/archives/wayland-devel/2014-March/013951.html
Thanks for sharing the links, let me go through the discussion history,
I will come back with my feedback for this stack, soon.
- Shashank
> Best regards,
> Ole
>
> Am Donnerstag, 10. Januar 2019, 16:02:18 CET schrieb Sharma, Shashank:
>> Hello All,
>>
>> This mail is to propose a design for enabling HDR support in
>> Wayland/Weston stack, using display engine capabilities, and get more
>> feedback and input from community.
>> Here are few points (you might already know these), about HDR
>> framebuffers, videos and displays:
>> - HDR content/buffers are composed in REC2020 colorspace, with bit depth
>> 10/12/16 BPC. Some of the popular formats are P010,P012,P016.
>> - HDR content come with their own Metadata to be applied to get the
>> right luminance at the display device.
>> - The metadata can be of two type 1. static 2. dynamic . For
>> simplicity, this solution is focusing on static HDR only (HDR10 standard)
>> - HDR content also provide its supported EOTF (electro optical transfer
>> function) information, which is a curve (like SRGB gamma curve). One
>> popular EOTF is PQ(ST2084).
>> - HDR capable displays mention their EOTF and HDR metadata support
>> information in EDID CEA-861-G blocks.
>> - Normal SRGB buffers are composed in SRGB color space following REC709
>> specifications.
>> - For accurate blending in display engines, we need to make sure following:
>> - All the buffers are in same colorspace (Rec 709 or Rec 2020)
>> - All the buffers are liner (gamma/EOTF removed)
>> - All the buffers are tone mapped in same zone (HDR or SDR)
>>
>> Please refer to the block diagram below, which presents a simple case of
>> a HDR P010 movie playback, with HDR buffers as video buffers, and SDR
>> buffers as subtitles. The subsystem looks and works like this:
>> - A client decodes the buffer (using FFMpeg for example) and gets the
>> two buffers, one with video (HDR) and one subtitles (SDR)
>> - Client passes following information to the compositor:
>> - The actual buffers
>> - Their colorspace infromation, BT2020 for HDR buffer, REC709 for
>> SDR buffer (planning to add a new protocol extension for this)
>> - The HDR metadata of the content (planning to add new protocol
>> for this)
>>
>> - Compositors actions:
>> - Reads the End display's HDR capabilities from display EDID. Assume
>> its an HDR HDMI monitor.
>> - Compositor tone maps every view's framebuffer to match tone of end
>> display, applying a libVA filter. In this example:
>> - The SDR subtitles frame will go through SDR to HDR tone
>> mapping (called S2H)
>> - The HDR video frame will go through HDR to HDR tone mapping
>> (called H2H) if the HDR capabilities of monitor and content are different.
>> - Now both the buffers and the monitor are in the same tone
>> mapped range.
>> - As the end display is HDR capable, and one of the content frame
>> is HDR, the compositor will prepare all other planes for color space
>> conversion (CSC) from REC709->REC2020 using plane CSC property.
>> - As the CSC and blending should be done in liner space, compositor
>> will also use plane level degamma to make the buffers linear.
>> - These actions will make sure that, during blending:
>> - All the buffers are in same colorspace (REC2020)
>> - All the buffers are linear
>> - All the buffers are tone mapped (HDR)
>> - The plane level color properties patch, for DRM can be found
>> here: https://patchwork.freedesktop.org/series/30875/
>> - Now, in order to re-apply the HDR curve, compositor will apply
>> CRTC level gamma, so that the output buffer is non-linear again.
>> - To pass the output HDR information to kernel, so that it can
>> create and send AVI-info-frames to HDMI, compositor will set Connector
>> HDR metadata property.
>> - Code for the same can be found here:
>> https://patchwork.freedesktop.org/series/25091/
>> - And they will ever live happily after :).
>>
>> Please provide inputs, feedbacks and suggestions for this design and
>> plan, so that we can improve out half cooked solution, and start sending
>> the patches.
>>
>> +------------------+ +-------------------+
>>
>> | SDR Buffer subtitles | HDR Buffer video
>> | (REC 709 colorsp) | (REC 2020 colorsp |
>>
>> +-------+----------+ +-------+-----------+
>>
>>
>>
>> +------v---------------------------v------------+ +--------------+
>>
>> | Compositor: v | |
>>
>> LibVA |
>>
>> | - assigns views to overlays
>>
>> +---------> Tone mapping |
>>
>> | - prepare plane/CRTC color properties
>>
>> <---------+ SDR to HDR |
>>
>> | for linear blending in display
>> | |
>> | | HDR to SDR |
>>
>> +------+-----------------------------+----------+ +--------------+
>>
>> | Tone mapped | Tone mapped
>> | non-linear-Rec709 | non-linear
>>
>> Rec2020
>> +------v------+ +-------v--------+
>> SRGB Degamma | |EOTF as degamma |
>>
>> |(Plane) | |(Plane) |
>>
>> +------+------+ +-------+--------+
>> Tone mapped linear Rec 709 | |
>> +------v------+ | Tone mapped
>>
>> | CSC/CTM | | non-linear
>>
>> Rec2020
>>
>> | REC709->2020| |
>>
>> +------+------+ |
>>
>> | Tone mapped linear |
>> | Rec 2020 |
>>
>> +------v-----------------------------v---------+
>>
>> | Blender |
>>
>> +--------------------+-------------------------+
>>
>> | Tone mapped linear Rec2020
>>
>> +--------------------v-------------------------+ Tone mapped
>>
>> | OETF(CRTC Gamma, post blending) |
>>
>> non-linear Rec2020 +------------------+
>>
>> | +----------------> | HDMI monitor |
>>
>> +----------------------------------------------+ +------------------+
>
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