linux-kernel - Re: [PATCH v2 2/6] [media] Documentation: Add HSV format

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Date:	Sat, 16 Jul 2016 17:28:08 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Antti Palosaari <crope@....fi>,
	Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>,
	Helen Mae Koike Fornazier <helen.koike@...labora.co.uk>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Shuah Khan <shuahkh@....samsung.com>,
	linux-media <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] [media] Documentation: Add HSV format

On 07/16/2016 04:32 PM, Ricardo Ribalda Delgado wrote:
> Hi
> 
> On Sat, Jul 16, 2016 at 4:12 PM, Laurent Pinchart
> <laurent.pinchart@...asonboard.com> wrote:
> 
>> I'd still like to know about it for my personal information :-)
> 
> Maybe it is just a very cheap gamma.
> 
>>
>>> Anyway, I am inclined to use ycbcr_enc as well.
>>
>> I'm glad we agree.
>>
> 
> Are you thinking about something like this:
> 
> 
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index c7fb760386cf..3e613fba1b20 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -330,6 +330,16 @@ enum v4l2_ycbcr_encoding {
>         V4L2_YCBCR_ENC_SMPTE240M      = 8,
>  };
> 
> +enum v4l2_hsv_encoding {
> +       V4L2_HSV_ENC_180        = 16,
> +       V4L2_HSV_ENC_256        = 17,
> +};

Yes.

> +
> +enum v4l2_rgb_encoding {
> +       V4L2_RGB_ENC_FULL       = 32,
> +       V4L2_HSV_ENC_16_235     = 33,
> +};

No.

The starting point is RGB, so there is nothing to encode. YCbCr and HSV
are transformations from RGB (or R'G'B' to be precise).

The basic chain is:

XYZ -> colorspace conversion -> RGB -> transfer function -> R'G'B'

and after this there is an optional step that converts R'G'B' to
Y'CbCr or HSV (ycbcr_enc or hsv_enc). The final step is the quantization
step where you end up with the actual color component values.

There doesn't seem to be something like limited range HSV, so I'd say it's
full range only.

Regards,

	Hans

> +
>  /*
>   * Determine how YCBCR_ENC_DEFAULT should map to a proper Y'CbCr encoding.
>   * This depends on the colorspace.
> @@ -455,7 +465,11 @@ struct v4l2_pix_format {
>         __u32                   colorspace;     /* enum v4l2_colorspace */
>         __u32                   priv;           /* private data,
> depends on pixelformat */
>         __u32                   flags;          /* format flags
> (V4L2_PIX_FMT_FLAG_*) */
> -       __u32                   ycbcr_enc;      /* enum v4l2_ycbcr_encoding */
> +       union {
> +               __u32                   ycbcr_enc;      /* enum
> v4l2_ycbcr_encoding */
> +               __u32                   hsv_enc;        /* enum
> v4l2_hsv_encoding */
> +               __u32                   rgb_enc;        /* enum
> v4l2_rgb_encoding */
> +       };
>         __u32                   quantization;   /* enum v4l2_quantization */
>         __u32                   xfer_func;      /* enum v4l2_xfer_func */
>  };
> @@ -1988,7 +2002,11 @@ struct v4l2_pix_format_mplane {
>         struct v4l2_plane_pix_format    plane_fmt[VIDEO_MAX_PLANES];
>         __u8                            num_planes;
>         __u8                            flags;
> -       __u8                            ycbcr_enc;
> +       union {
> +               __u8                    ycbcr_enc;      /* enum
> v4l2_ycbcr_encoding */
> +               __u8                    hsv_enc;        /* enum
> v4l2_hsv_encoding */
> +               __u8                    rgb_enc;        /* enum
> v4l2_rgb_encoding */
> +       };
>         __u8                            quantization;
>         __u8                            xfer_func;
>         __u8                            reserved[7];
> 
>> --
> 
> 
> Best regards!
>