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SubjectRe: [PATCH 2/3] docs: media: Document CLL and Mastering display
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On 09/11/2020 18:31, Stanimir Varbanov wrote:
> Document Content light level and Mastering display colour volume.
>
> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
> ---
> .../media/v4l/ext-ctrls-codec.rst | 61 +++++++++++++++++++
> 1 file changed, 61 insertions(+)
>
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index ce728c757eaf..39d0aab5ca3d 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -4382,3 +4382,64 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
> - Selecting this value specifies that HEVC slices are expected
> to be prefixed by Annex B start codes. According to :ref:`hevc`
> valid start codes can be 3-bytes 0x000001 or 4-bytes 0x00000001.
> +
> +``V4L2_CID_MPEG_VIDEO_HEVC_CLL_INFO (struct)``
> + The Content Light Level defines upper bounds for the nominal target
> + brightness light level of the pictures.
> +
> +.. c:type:: v4l2_ctrl_hevc_cll_info
> +
> +.. cssclass:: longtable
> +
> +.. flat-table:: struct v4l2_ctrl_hevc_cll_info
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 1 1 2
> +
> + * - __u16
> + - ``max_content_light_level``
> + - An upper bound on the maximum light level among all individual
> + samples for the pictures of coded video sequence, cd/m2.
> + * - __u16
> + - ``max_pic_average_light_level``
> + - An upper bound on the maximum average light level among the
> + samples for any idividual picture of coded video sequence, cd/m2.

idividual -> individual

In the CTA-861-G spec value 0 is used to indicate that this information is
not present. How is that handled here? Can it be 0 as well in an HEVC stream?

Same for the next control.

> +
> +``V4L2_CID_MPEG_VIDEO_HEVC_MASTERING_DISPLAY (struct)``
> + The mastering display defines the colour volume (the colour primaries,
> + white point and luminance range) of a display considered to be the
> + mastering display for current video content.
> +
> +.. c:type:: v4l2_ctrl_hevc_mastering_display
> +
> +.. cssclass:: longtable
> +
> +.. flat-table:: struct v4l2_ctrl_hevc_mastering_display
> + :header-rows: 0
> + :stub-columns: 0
> + :widths: 1 1 2
> +
> + * - __u16
> + - ``display_primaries_x[3]``
> + - Specifies the normalized x chromaticity coordinate of the colour
> + primary component of the mastering display.

CTA-861-G defines this as: "coded as unsigned 16-bit values in units
of 0.00002, where 0x0000 represents zero and 0xC350 represents 1.0000."

Is that true here as well? If so, then this should be documented because
"normalized x chromaticity coordinate" doesn't say anything meaningful.

> + * - __u16
> + - ``display_primaries_y[3]``
> + - Specifies the normalized y chromaticity coordinate of the colour
> + primary component of the mastering display.
> + * - __u16
> + - ``white_point_x``
> + - Specifies the normalized x chromaticity coordinate of the white
> + point of the mastering display.
> + * - __u16
> + - ``white_point_y``
> + - Specifies the normalized y chromaticity coordinate of the white
> + point of the mastering display.
> + * - __u32
> + - ``max_luminance``
> + - Specifies the nominal maximum display luminance of the mastering
> + display.

In CTA-861-G this is in 1 cd/m^2 units.

> + * - __u32
> + - ``min_luminance``
> + - specifies the nominal minimum display luminance of the mastering
> + display.

And this in units of 0.0001 cd/m^2.

Regards,

Hans

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