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From: Jacopo Mondi <jacopo@jmondi.org>
To: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	tfiga@google.com, pavel@ucw.cz,
	"open list:MEDIA INPUT INFRASTRUCTURE (V4L/DVB)" 
	<linux-media@vger.kernel.org>
Subject: Re: [PATCH v3 04/11] media: v4l2-ctrl: Document V4L2_CID_CAMERA_SENSOR_ROTATION
Date: Tue, 24 Sep 2019 17:53:17 +0200
Message-ID: <20190924155317.nd7f5bp2ey2rkb54@uno.localdomain> (raw)
In-Reply-To: <20190913184906.6tpl374n4anzja5c@uno.localdomain>

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Hi Hans,

On Fri, Sep 13, 2019 at 08:49:06PM +0200, Jacopo Mondi wrote:
> Hi Hans,
>
> On Fri, Sep 13, 2019 at 04:02:45PM +0200, Hans Verkuil wrote:
> > On 9/12/19 10:10 PM, Jacopo Mondi wrote:
> > > Add documentation for the V4L2_CID_CAMERA_SENSOR_ROTATION camera
> > > control. The newly added read-only control reports the camera device
> > > mounting rotation.
> > >
> > > Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
> > > ---
> > >  .../media/uapi/v4l/ext-ctrls-camera.rst       | 117 ++++++++++++++++++
> > >  1 file changed, 117 insertions(+)
> > >
> > > diff --git a/Documentation/media/uapi/v4l/ext-ctrls-camera.rst b/Documentation/media/uapi/v4l/ext-ctrls-camera.rst
> > > index f879dcc9409c..74991522ca3a 100644
> > > --- a/Documentation/media/uapi/v4l/ext-ctrls-camera.rst
> > > +++ b/Documentation/media/uapi/v4l/ext-ctrls-camera.rst
> > > @@ -542,6 +542,123 @@ enum v4l2_scene_mode -
> > >
> > >
> > >
> > > +``V4L2_CID_CAMERA_SENSOR_ROTATION (integer)``
> > > +    This read-only control describes the sensor orientation expressed as
> > > +    rotation in counterclockwise degrees along the axis perpendicular to the
> > > +    device mounting plane, and directed away from the sensor lens. Possible
> > > +    values for the control are 90, 180 and 270 degrees. To compensate the device
> >
> > compensate -> compensate for
> >
> > > +    mounting rotation on the captured images, a rotation of the same amount of
> > > +    degrees, in the same counterclockwise rotation direction should be applied
> > > +    along the axis directed from the observer to the captured image when
> > > +    displayed on a screen.
> >
> > Is this right? Shouldn't that be "in the clockwise direction"? If the sensor is
> > mounted 90 degrees counterclockwise, then I need to rotate by 90 degrees clockwise
> > to compensate for that, right?
> >
>
> It really depend along which axis direction you are applying the mounting
> rotation and the compensation rotation... See below...
>
> > > +
> > > +    To better understand the effect of the sensor rotation on the acquired
> > > +    images when displayed on a screen, it is helpful to consider a fictional
> > > +    scan-out sequence of the sensor's pixels, assuming the pixel array having
> > > +    its top-left pixel at position (0, 0) with values on the 'x' axis increasing
> > > +    towards the right direction, and values on the 'y' axis increasing towards
> > > +    the bottom. The effect of sensor rotation could be easily visualized
> > > +    considering the sequence of captured pixels.
> > > +
> > > +    Assuming the following scene has to be captured::
> > > +
> > > +                o
> > > +               -|-
> > > +               / \
> > > +
> > > +    An upright mounted sensor has its pixel array displaced as follow::
> > > +
> > > +                                      x
> > > +            (0,0)---------------------->
> > > +              ! 0,0 0,1 0,2 ... 0,line-len
> >
> > Isn't that 0,0 ... 0,num-col?
>
> Yes indeed sorry
>
> > line-len is a weird name, shouldn't that be num-lines?
> >
> > line-len sounds like it is the same as num-col.
> >
> > I'm totally confused.
> >
>
> num-col is totally wrong, that should have been num-lines
>
> In general
> s/line-len/num-col
> s/num-col/num-lines
>
> > > +              ! 1,0 1,1 1,2 ...
> > > +              ! ...
> > > +              ! ...
> > > +              ! (num-col,0)...  (num-col,line-len)
> > > +            y V
> > > +
> > > +
> > > +    Assuming pixels are scanned out from (0,0) to (num-col,line-len)
> > > +    progressively::
> > > +
> > > +             (0,0) ---->-------------> (0,line-len)---!
> > > +             !------------------------------------<a--!
> > > +             V
> > > +             (1,0) ---->-------------> (1,line-len)---!
> > > +             !------------------------------------<---!
> > > +             V
> > > +             (...) .-->--------------> ( ,,,, )    ---!
> > > +             !------------------------------------<---!
> > > +             V
> > > +             (num-col,0)------------->(num-col,line-len)
> > > +
> > > +
> > > +    If a rotation of 90 degrees counterclockwise along the axis perpendicular to
> > > +    the sensor's lens and directed towards the scene to be captured is applied
> > > +    to the sensor, the pixel array would then be rotated as follows::
> > > +
> > > +            x ^  0,line-len,,,(num-col,line-len
> > > +              !  ....
> > > +              !  0,2 1,2      ...
> > > +              !  0,1 1,1      ...
> > > +              !  0,0 1,0 ... num-col,0
> > > +             (0,0)------------------------>
> > > +                                   y
> > > +
> > > +    And the pixel scan-out sequence would then proceed as follows::
> > > +
> > > +            (0,line-len)            (num-cols,line-len)
> > > +                 ^\    ^\    ^\    ^\    ^
> > > +                 ! \   ! \   ! \   ! \   !
> > > +                 !  \  !  \  !  \  !  \  !
> > > +                 !   \ !   \ !   \ !   \ !
> > > +                 !    \!    \!    \!    \!
> > > +               (0,0)  (1,0) ....      (num-cols,0)
> > > +
> > > +    Which when applied to the capture scene gives::
> > > +
> > > +            (0,line-len)            (num-cols,line-len)
> > > +                ^\    ^\    ^\    ^\    ^
> > > +                ! \   ! \   0 \   ! \   !
> > > +                !  \  !  \ -|- \  !  \  !
> > > +                !   \ !    / \  \ !   \ !
> > > +                !    \!    \!    \!    \!
> > > +              (0,0)  (1,0) ....      (num-cols,0)
> > > +
> > > +    Producing the following image once captured to memory and
> > > +    displayed to the user::
> > > +
> > > +             \ !
> > > +               --0
> > > +             / !
> > > +
> > > +    Which has a rotation of the same amount of degrees applied on the opposite
> > > +    rotation direction along the axis that goes from the observer to the
> > > +    displayed image.
> > > +
> > > +    In order to compensate the sensor mounting rotation, when expressed
> > > +    as counterclockwise rotation along the axis directed from the sensor to
> > > +    the captured scene, a rotation of the same amount of degrees in the
> > > +    same counterclockwise rotation direction but applied along the axis
> > > +    directed from the observer to the captured image, has to be applied.::
> >
> > .:: -> :
> >
>
> Don't I need the :: to mark the following block of text as verbatim ?
>
> > > +
> > > +                -------   90 degree counterclockwise
> > > +                |   o  |  mounting rotation applied
> > > +                |  -|- |  along the axis directed
> > > +                |  / \ |  away from the sensor lens
> > > +                -------
> > > +                -------
> > > +                | \ !  |  Resulting captured
> > > +                |  --0 |  image when displayed
> > > +                | / !  |  on screen
> > > +                -------
> >
> > Trying this with my webcam turning it 90 degrees counterclockwise, I
> > and up with my head to the left, not to the right.
> >
>
> Along which axis direction are you rotating the camera counterclockwise ?
>
> If you see your face, and you rotate the camera counterclockwise while
> looking at it, you're actually rotating along the axis directed -towards-
> the sensor.
>
> The rotation here in the example and in the 'rotation' property
> description has to be applied along the axis pointing aways from the
> sensor, so what you're actually doing is rotating clockwise along that
> direction (I guess)... So yes, to compensate that, you need to rotate
> clockwise when you look at the image on the screen... Confusing,
> right?
>

Does it work for you? Can I send a new iteration with your comments on
the previous patches taken in ?

Thanks
  j

> > > +                -------
> > > +                |   o  |  Rotation compensation
> > > +                |  -|- |  is 90 degrees counterclockwise
> > > +                |  / \ |  along the axis directed to the
> > > +                -------   displayed image
> > > +
> > > +
> > >  .. [#f1]
> > >     This control may be changed to a menu control in the future, if more
> > >     options are required.
> > >
> >
> > Regards,
> >
> > 	Hans



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  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-12 20:10 [PATCH v3 00/11] media: Report camera sensor properties Jacopo Mondi
2019-09-12 20:10 ` [PATCH v3 01/11] dt-bindings: video-interfaces: Document 'location' property Jacopo Mondi
2019-09-13 13:45   ` Hans Verkuil
2019-09-27 15:27   ` Pavel Machek
2019-09-28 12:48     ` Jacopo Mondi
2019-09-12 20:10 ` [PATCH v3 02/11] media: v4l2-ctrl: Document V4L2_CID_CAMERA_SENSOR_LOCATION Jacopo Mondi
2019-09-13 13:48   ` Hans Verkuil
2019-09-12 20:10 ` [PATCH v3 03/11] dt-bindings: video-interfaces: Expand rotation description Jacopo Mondi
2019-09-13 13:50   ` Hans Verkuil
2019-09-12 20:10 ` [PATCH v3 04/11] media: v4l2-ctrl: Document V4L2_CID_CAMERA_SENSOR_ROTATION Jacopo Mondi
2019-09-13 14:02   ` Hans Verkuil
2019-09-13 18:49     ` Jacopo Mondi
2019-09-24 15:53       ` Jacopo Mondi [this message]
2019-09-27 11:20       ` Hans Verkuil
2019-09-12 20:10 ` [PATCH v3 05/11] media: v4l2-ctrls: Add camera location and rotation Jacopo Mondi
2019-09-12 20:10 ` [PATCH v3 06/11] media: v4l2-fwnode: Add helper to parse device properties Jacopo Mondi
2019-09-13 14:08   ` Hans Verkuil
2019-09-13 19:04     ` Jacopo Mondi
2019-09-27 10:57       ` Hans Verkuil
2019-09-12 20:10 ` [PATCH v3 07/11] include: v4l2-ctrl: Sort forward declarations Jacopo Mondi
2019-09-12 20:10 ` [PATCH v3 08/11] media: v4l2-ctrls: Sort includes alphabetically Jacopo Mondi
2019-09-12 20:10 ` [PATCH v3 09/11] media: v4l2-ctrls: Add helper to register properties Jacopo Mondi
2019-09-13 14:25   ` Hans Verkuil
2019-09-12 20:10 ` [PATCH v3 10/11] media: i2c: ov5670: Parse and " Jacopo Mondi
2019-09-12 20:10 ` [PATCH v3 11/11] media: i2c: ov13858: " Jacopo Mondi

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