Re: [RFC PATCH v3 1/6] drm/doc: Color Management and HDR10 RFC

[Harry Wentland <harry.wentland@amd.com>]

On 2021-09-22 04:31, Pekka Paalanen wrote:
> On Tue, 21 Sep 2021 14:05:05 -0400
> Harry Wentland <harry.wentland@amd.com> wrote:
> 
>> On 2021-09-21 09:31, Pekka Paalanen wrote:
>>> On Mon, 20 Sep 2021 20:14:50 -0400
>>> Harry Wentland <harry.wentland@amd.com> wrote:
>>>   

...

> 
>> Did anybody start any CM doc patches in Weston or Wayland yet?
> 
> There is the
> https://gitlab.freedesktop.org/swick/wayland-protocols/-/blob/color/unstable/color-management/color.rst
> we started a long time ago, and have not really touched it for a while.
> Since we last touched it, at least my understanding has developed
> somewhat.
> 
> It is linked from the overview in
> https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/14
> and if you want to propose changes, the way to do it is file a MR in
> https://gitlab.freedesktop.org/swick/wayland-protocols/-/merge_requests
> against the 'color' branch. Patches very much welcome, that doc does
> not need to limit itself to Wayland. :-)
> 

Right, I've read all that a while back.

It might be a good place to consolidate most of the Linux CM/HDR discussion,
since gitlab is good with allowing discussions, we can track changes, and
it's more formatting and diagram friendly than text-only email.

> We also have issues tracked at
> https://gitlab.freedesktop.org/swick/wayland-protocols/-/issues?scope=all&utf8=%E2%9C%93&state=opened
> 
>>> Pre-curve for instance could be a combination of decoding to linear
>>> light and a shaper for the 3D LUT coming next. That's why we don't call
>>> them gamma or EOTF, that would be too limiting.
>>>
>>> (Using a shaper may help to keep the 3D LUT size reasonable - I suppose
>>> very much like those multi-segmented LUTs.)
>>>   
>>
>> AFAIU a 3D LUTs will need a shaper as they don't have enough precision.
>> But that's going deeper into color theory than I understand. Vitaly would
>> know better all the details around 3D LUT usage.
> 
> There is a very practical problem: the sheer number of elements in a 3D
> LUT grows to the power of three. So you can't have very many taps per
> channel without storage requirements blowing up. Each element needs to
> be a 3-channel value, too. And then 8 bits is not enough.
> 

And those storage requirements would have a direct impact on silicon real
estate and therefore the price and power usage of the HW.

Harry

> I'm really happy that Vitaly is working with us on Weston and Wayland. :-)
> He's a huge help, and I feel like I'm currently the one slowing things
> down by being backlogged in reviews.
> 
> 
> Thanks,
> pq
>