linux-kernel - Re: [PATCH v4 11/12] [media] Documentation: Add HSV encodings

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Message-ID: <47e24b8b-3ad2-90a5-41f6-bc99f05df872@xs4all.nl>
Date:	Fri, 12 Aug 2016 15:51:52 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Markus Heiser <markus.heiser@...marIT.de>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Helen Mae Koike Fornazier <helen.koike@...labora.co.uk>,
	Antti Palosaari <crope@....fi>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Shuah Khan <shuahkh@....samsung.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org
Subject: Re: [PATCH v4 11/12] [media] Documentation: Add HSV encodings

On 07/18/2016 02:42 PM, Ricardo Ribalda Delgado wrote:
> Describe the hsv_enc field and its use.
> 
> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> ---
>  Documentation/media/uapi/v4l/pixfmt-002.rst        | 12 ++++++-
>  Documentation/media/uapi/v4l/pixfmt-003.rst        | 14 ++++++--
>  Documentation/media/uapi/v4l/pixfmt-006.rst        | 38 ++++++++++++++++++++++
>  Documentation/media/uapi/v4l/pixfmt-packed-hsv.rst |  3 +-
>  Documentation/media/videodev2.h.rst.exceptions     |  4 +++
>  5 files changed, 67 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/media/uapi/v4l/pixfmt-002.rst b/Documentation/media/uapi/v4l/pixfmt-002.rst
> index fae9b2d40a85..9a59e87b590f 100644
> --- a/Documentation/media/uapi/v4l/pixfmt-002.rst
> +++ b/Documentation/media/uapi/v4l/pixfmt-002.rst
> @@ -177,6 +177,16 @@ Single-planar format structure
>  
>      -  .. row 13
>  
> +       -  enum :ref:`v4l2_hsv_encoding <v4l2-hsv-encoding>`
> +
> +       -  ``hsv_enc``
> +
> +       -  This information supplements the ``colorspace`` and must be set by
> +	  the driver for capture streams and by the application for output
> +	  streams, see :ref:`colorspaces`.
> +
> +    -  .. row 14
> +
>         -  enum :ref:`v4l2_quantization <v4l2-quantization>`
>  
>         -  ``quantization``
> @@ -185,7 +195,7 @@ Single-planar format structure
>  	  the driver for capture streams and by the application for output
>  	  streams, see :ref:`colorspaces`.
>  
> -    -  .. row 14
> +    -  .. row 15
>  
>         -  enum :ref:`v4l2_xfer_func <v4l2-xfer-func>`
>  
> diff --git a/Documentation/media/uapi/v4l/pixfmt-003.rst b/Documentation/media/uapi/v4l/pixfmt-003.rst
> index 25c54872fbe1..f212d1feaaa0 100644
> --- a/Documentation/media/uapi/v4l/pixfmt-003.rst
> +++ b/Documentation/media/uapi/v4l/pixfmt-003.rst
> @@ -138,6 +138,16 @@ describing all planes of that format.
>  
>      -  .. row 10
>  
> +       -  enum :ref:`v4l2_hsv_encoding <v4l2-hsv-encoding>`
> +
> +       -  ``hsv_enc``
> +
> +       -  This information supplements the ``colorspace`` and must be set by
> +	  the driver for capture streams and by the application for output
> +	  streams, see :ref:`colorspaces`.
> +
> +    -  .. row 11
> +
>         -  enum :ref:`v4l2_quantization <v4l2-quantization>`
>  
>         -  ``quantization``
> @@ -146,7 +156,7 @@ describing all planes of that format.
>  	  the driver for capture streams and by the application for output
>  	  streams, see :ref:`colorspaces`.
>  
> -    -  .. row 11
> +    -  .. row 12
>  
>         -  enum :ref:`v4l2_xfer_func <v4l2-xfer-func>`
>  
> @@ -156,7 +166,7 @@ describing all planes of that format.
>  	  the driver for capture streams and by the application for output
>  	  streams, see :ref:`colorspaces`.
>  
> -    -  .. row 12
> +    -  .. row 13
>  
>         -  __u8
>  
> diff --git a/Documentation/media/uapi/v4l/pixfmt-006.rst b/Documentation/media/uapi/v4l/pixfmt-006.rst
> index 987b9a8a9eb4..ef7518077e8a 100644
> --- a/Documentation/media/uapi/v4l/pixfmt-006.rst
> +++ b/Documentation/media/uapi/v4l/pixfmt-006.rst
> @@ -19,6 +19,15 @@ colorspace field of struct :ref:`v4l2_pix_format <v4l2-pix-format>`
>  or struct :ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>`
>  needs to be filled in.
>  
> +.. _hsv-colorspace:
> +
> +On :ref:`HSV formats <hsv-formats>` the *Hue* is defined as the angle on
> +the cylindrical color representation. Usually this angle is measured in
> +degrees, i.e. 0-360. When we map this angle value into 8 bits, there are
> +two basic ways to do it: Divide the angular value by 2 (0-179), or use the
> +whole range, 0-255, dividing the angular value by 1.41. The
> +`v4l2_hsv_encoding <v4l2-hsv-encoding>` field specify which encoding is used.
> +
>  .. note:: The default R'G'B' quantization is full range for all
>     colorspaces except for BT.2020 which uses limited range R'G'B'
>     quantization.
> @@ -286,3 +295,32 @@ needs to be filled in.
>         -  Use the limited range quantization encoding. I.e. the range [0…1]
>  	  is mapped to [16…235]. Cb and Cr are mapped from [-0.5…0.5] to
>  	  [16…240].
> +
> +
> +
> +.. _v4l2-hsv-encoding:
> +
> +.. flat-table:: V4L2 HSV Encodings
> +    :header-rows:  1
> +    :stub-columns: 0
> +
> +
> +    -  .. row 1
> +
> +       -  Identifier
> +
> +       -  Details
> +
> +    -  .. row 2
> +
> +       -  ``V4L2_HSV_ENC_180``
> +
> +       -  For the Hue, each LSB is two degrees.
> +
> +    -  .. row 3
> +
> +       -  ``V4L2_HSV_ENC_256``
> +
> +       -  For the Hue, the 360 degrees are mapped into 8 bits, i.e. each
> +          LSB is roughtly 1.41 degrees.

s/roughtly/roughtly/

> +

It is cleaner if this goes before the quantization list and after the ycbcr encoding.

The quantization description should also be updated: HSV is full range. Limited range
makes no sense for this encoding.

Regards,

	Hans