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

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Date:	Sat, 16 Jul 2016 15:38:24 +0300
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
	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@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/6] [media] Documentation: Add HSV format

Hi Hans,

On Saturday 16 Jul 2016 10:19:29 Hans Verkuil wrote:
> On 07/15/2016 08:11 PM, Laurent Pinchart wrote:
> > On Friday 15 Jul 2016 18:13:15 Ricardo Ribalda Delgado wrote:
> >> Describe the HSV formats
> >> 
> >> Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> >> ---
> >> 
> >>  Documentation/media/uapi/v4l/hsv-formats.rst       |  19 ++
> >>  Documentation/media/uapi/v4l/pixfmt-packed-hsv.rst | 253 +++++++++++++++
> >>  Documentation/media/uapi/v4l/pixfmt.rst            |   1 +
> >>  Documentation/media/uapi/v4l/v4l2.rst              |   5 +
> >>  4 files changed, 278 insertions(+)
> >>  create mode 100644 Documentation/media/uapi/v4l/hsv-formats.rst
> >>  create mode 100644 Documentation/media/uapi/v4l/pixfmt-packed-hsv.rst
> >> 
> >> diff --git a/Documentation/media/uapi/v4l/hsv-formats.rst
> >> b/Documentation/media/uapi/v4l/hsv-formats.rst new file mode 100644
> >> index 000000000000..f0f2615eaa95
> >> --- /dev/null
> >> +++ b/Documentation/media/uapi/v4l/hsv-formats.rst
> >> @@ -0,0 +1,19 @@
> >> +.. -*- coding: utf-8; mode: rst -*-
> >> +
> >> +.. _hsv-formats:
> >> +
> >> +***********
> >> +HSV Formats
> >> +***********
> >> +
> >> +These formats store the color information of the image
> >> +in a geometrical representation. The colors are mapped into a
> >> +cylinder, where the angle is the HUE, the height is the VALUE
> >> +and the distance to the center is the SATURATION. This is a very
> >> +useful format for image segmentation algorithms.
> >> +
> >> +
> >> +.. toctree::
> >> +    :maxdepth: 1
> >> +
> >> +    pixfmt-packed-hsv
> >> diff --git a/Documentation/media/uapi/v4l/pixfmt-packed-hsv.rst
> >> b/Documentation/media/uapi/v4l/pixfmt-packed-hsv.rst new file mode 100644
> >> index 000000000000..b297aa4f7ba6
> >> --- /dev/null
> >> +++ b/Documentation/media/uapi/v4l/pixfmt-packed-hsv.rst
> >> @@ -0,0 +1,253 @@
> >> +.. -*- coding: utf-8; mode: rst -*-
> >> +
> >> +.. _packed-hsv:
> >> +
> >> +******************
> >> +Packed HSV formats
> >> +******************
> >> +
> >> +*man Packed HSV formats(2)*
> >> +
> >> +Packed HSV formats
> >> +
> >> +
> >> +Description
> >> +===========
> >> +
> >> +The HUE (h) is meassured in degrees, one LSB represents two degrees.
> > 
> > Is this common ? I have a device that can handle HSV data, I need to check
> > how it maps the hue values to binary, but I'm pretty sure they cover the
> > full 0-255 range. We would then have to support the two formats. Separate
> > 4CCs are an option, but reporting the range separately (possibly through
> > the colorspace API) might be better. Any thought on that ?
> 
> It's either a separate 4cc or we do something with the ycbcr_enc field
> (reinterpreted as hsv_enc). I'm not sure, I would have to think some more
> about that.

I'm inclined to use the ycbcr_enc field, especially given that a similar usage 
could be useful for RGB as well (don't ask me what it's supposed to be used 
for, but I have hardware that support limiting the RGB values range to 
16-235).

-- 
Regards,

Laurent Pinchart