Roughly speaking, a color profile describes the color space of content
or an output. Under the hood, the description includes one or more ways
to map colors between the profile space and some standard profile
connecting space (PCS).
This object is not called a color space. A color space has a unique
definition, while a color profile may contain multiple different
mappings depending on render intent. Some of these mappings may be
subjective, with an artistic touch.
When a source color profile and a destination color profile are combined
under a specific render intent, they produce a color transformation.
Color transformations are already preresented by weston_color_transform.
This patch adds the basic API for color profile objects. Everything
worthwhile of these objects is implemented in the color managers:
color-noop never creates these, and in color-lcms they are basically a
container for cmsHPROFILE, the Little CMS object for color profiles.
Color profile objects will not be interpreted outside of the color
managers, unlike color transformations.
For a start, the color manager API has one function to create color
profiles: from ICC profile data. More creation functions for other
sources will be added later.
The API has errmsg return parameter for error messages. These are not
simply weston_log()'d, because CM&HDR protocol will allow clients to
trigger errors and the protocol handles that gracefully. Therefore
instead of flooding the compositor logs, the error messages will
probably need to be relayed back to clients.
Color-lcms is expected to create a cmsHPROFILE for all kinds of color
profiles, not just for those created from ICC profile data. Hence,
color-lcms will fingerprint color profiles by the MD5 hash which Little
CMS computes for us. The fingerprint is used for de-duplication: instead
of creating copies, reference existing color profiles.
This code is very much based on Sebastian Wick's earlier work on Weston
color management, but structured and named differently.
Co-authored-by: Sebastian Wick <sebastian@sebastianwick.net>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Initialize LittleCMS and use it to generate the sRGB EOTF and inverse
curves. Use these curves to define the blending color space as optical
(linear) sRGB by assuming that both content and output color spaces are
sRGB.
As a consequence, this causes Weston to do "gamma correct blending", as
in, blend in light linear space which should avoid distorting colors in
alpha gradients, when color-lcms is active.
This makes use of the 3x1D LUT support added in gl-renderer earlier, and
shows how the color manager is responsible for re-using existing color
transformation objects.
Co-authored-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
This creates the color-lcms plugin that in the future will be using
Little CMS as the color matching module, processing ICC profiles, and
producing HDR tone mappings.
Right now, this new plugin is functionally equivalent to the no-op color
manager, except it already links to lcms2 and checks that the renderer
supports color operations.
Color-lcms is a libweston plugin that is loaded with explicit
weston_compositor API. This does not currently allow loading alternative
color manager plugins. External color manager plugins might be
considered in the future when the libweston APIs around color management
stabilize.
This libweston plugin uses the same build option as the old cms-static
Weston plugins, as they both need lcms2. The minimum version for lcms2
was chosen by what Debian Buster provides today and for no other reason.
This plugin intends to support the Wayland CM&HDR protocol extension and
hence sets supports_client_protocol to true. This will expose the
protocol extension to clients when it gets implemented.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Pekka Paalanen