EXT_surface_CTA861_3_metadata

EGL_EXT_surface_CTA861_3_metadata

Courtney Goeltzenleuchter (courtneygo 'at' google.com)

James Jones
Weiwan Liu

No known IP claims.

Complete

Version 5 - Nov 29, 2016

EGL Extension #117

This extension requires EGL 1.5 and EGL_EXT_surface_SMPTE2086_metadata.

This extension is written against the wording of the EGL 1.5 specification
(August 27, 2014).

This extension adds additional EGL surface attributes for the metadata
defined by the CTA (Consumer Technology Association) 861.3 standard.
This metadata, in addition to the SMPTE 2086 metadata, is used to define the
color volume of the mastering display as well as the content (CTA-861.3),
The mastering display is the display where creative work is done and creative
intent is established. To preserve such creative intent as much as possible
and achieve consistent color reproduction on different viewing displays,
it is useful for the display pipeline to know the color volume of the
original mastering display where content is created or tuned.  This avoids
performing unnecessary mapping of colors that are not displayable on the
original mastering display.

This extension adds the ability to pass the CTA-861.3 metadata via EGL,
from which the color volume can be derived. While the general purpose of the
metadata is to assist in the transformation between different color volumes
of different displays and help achieve better color reproduction, it is not
in the scope of this extension to define how exactly the metadata should be
used in such a process. It is up to the implementation to determine how to
make use of the metadata.

None.

Accepted as attribute by eglSurfaceAttrib and eglQuerySurface:

EGL_CTA861_3_MAX_CONTENT_LIGHT_LEVEL_EXT            0x3360
EGL_CTA861_3_MAX_FRAME_AVERAGE_LEVEL_EXT            0x3361

Add the following paragraph before the "Errors" section on page 43,

    If attribute is EGL_CTA861_3_MAX_CONTENT_LIGHT_LEVEL_EXT or EGL_CTA861_3_-
MAX_FRAME_AVERAGE_LEVEL_EXT, then value indicates the corresponding
maximum content light level and maximum frame average level.
    The unit of value is 1 nit (candela per square meter). The
    floating-point luminance values should be multiplied by
    EGL_METADATA_SCALING, a constant scaling factor of 50000, before being
    passed into eglSurfaceAttrib as integers.

    Exactly how the color volume information is used to assist the color
reproduction process is implementation dependant.

    The initial values of EGL_CTA861_3_MAX_CONTENT_LIGHT_LEVEL_EXT and
EGL_CTA861_3_MAX_FRAME_AVERAGE_LEVEL_EXT are EGL_DONT_CARE, which causes the
    hints to be ignored. If value is not in the implementation's supported
    range for attribute, a EGL_INVALID_VALUE error is generated, and some or
    all of the metadata fields are ignored.

Change the original footnote 12 at the end of section "3.5.6 Surface
Attributes" on page 45 to,

        [13] EGL_DISPLAY_SCALING (10000) and EGL_METADATA_SCALING_EXT (50000)
    are used where EGL needs to take or return floating-point attribute
    values, which would normally be smaller than 1, as integers while still
    retaining sufficient precision to be meaningful.

Addition to Table 3.5 "Queryable surface attributes and types",

                  Attribute                   Type
    ------------------------------------------------
EGL_CTA861_3_MAX_CONTENT_LIGHT_LEVEL_EXT     integer
EGL_CTA861_3_MAX_FRAME_AVERAGE_LEVEL_EXT     integer

                  Description
    --------------------------------------------------------------------------------------
    Maximum content light level in nit multiplied by EGL_METADATA_SCALING_EXT
    Maximum frame average light level in nit multiplied by EGL_METADATA_SCALING_EXT

Add the following paragraph at the end of section "3.5.6 Surface Attributes"
on page 45,

    Querying EGL_CTA861_3_MAX_CONTENT_LIGHT_LEVEL_EXT EGL_CTA861_3_MAX_-
FRAME_AVERAGE_LEVEL_EXT returns respectively the maximum content light level
and maximum frame average level respectively. The values returned are
in units of 1 nit (candela per square meter), multiplied by the constant
value EGL_METADATA_SCALING_EXT (50000). The value of EGL_CTA861_3_MAX_-
CONTENT_LIGHT_LEVEL_EXT and EGL_CTA861_3_MAX_FRAME_AVERAGE_LEVEL_EXT can
be set via eglSurfaceAttrib as described above.

Described in the body text above.

Version 1, 2017/02/28
  - Initial draft