[RFC PATCH v2 0/1] Color manager calibration protocol

Sebastian Wick sebastian at sebastianwick.net
Tue May 21 19:07:28 UTC 2019

On 2019-05-21 19:32, Erwin Burema wrote:
> Hi,
> This is the second version of my color manager calibration protocol,
> biggest change is that I now use a surface this surface is set up in a
> similar way to the touch screen calibration protocol. Another big
> change is more (and hopefully better) documentation and the last big
> one is a new way to set the calibration curve (plus some info needed
> to use it). There are some other smaller changes many regarding
> formatting.
> One thing I am not entirely satisfied with is the way I am setting the
> calibration curve but decided to not wait for a brilliant idea to
> strike me out of the blue and put it out here so more eyeballs can
> have a look. And more brains can think about it.

Hi Erwin,

the approach still doesn't make sense to me. Why expose this specific
part of the color pipeline, the VCGT, to the client? What is the
advantage over simply passing e.g. a double to the compositor and the
compositor then does the best to display that value at the highest
precision it can.

In previous discussions there was two arguments:
1. the VCGT might have higher precision than the frame buffer
2. so you can measure the thing you later actually use to show

None of them seem to be valid. The compositor should know how to get the
best precision out of the whole pipeline. The latter argument ignored
that the compositor can use combinations of framebuffers, shaders,
plane/crtc gamma, csc and degamma properties all with different
precision for different parts of the screen in normal operation. And who
knows, maybe we'll get more sophisticated scanout hardware.

So what's the rationale behind this?

> For those wondering why this is needed see here:
> https://www.argyllcms.com/doc/monitorcontrols.html although with the
> color manager protocol the first reason becomes moot (although it
> wouldn't surprise me if a compositor would only implements this
> protocol and not that one for reasons of simplicity or memory/disk
> space savings) the other 2 are still valid.
> If this is seen as acceptable I will see if I can implement it in
> Weston, although seeing as my day job is something completely
> different (doing this as a hobbyist) and I am actually a physicist not
> a software engineer I will probably need some help with that.
> Erwin Burema (1):
>   Adding color calibration protocol
>  .../wp_wayland_calibration.xml                | 247 ++++++++++++++++++
>  1 file changed, 247 insertions(+)
>  create mode 100644 
> unstable/color_calibration/wp_wayland_calibration.xml

More information about the wayland-devel mailing list