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 <[email protected]>
> ---
> .../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?
> +
> + 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?
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.
> + ! 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.::
.:: -> :
> +
> + ------- 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.
> + -------
> + | 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
