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

[Hans Verkuil]

On 07/16/2016 02:38 PM, Laurent Pinchart wrote:
> 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@xxxxxxxxx>
>>>> ---
>>>>
>>>>  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).

Limited vs full range quantization is handled by the quantization field. It's
there already.

Limited range RGB is needed for HDMI due to a brain-dead spec when dealing with
certain kinds of TVs and configurations. Don't ask, it's horrible.

Anyway, I am inclined to use ycbcr_enc as well.

Regards,

	Hans