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media: v4l2-ctrl: Document V4L2_CID_CAMERA_SENSOR_ROTATION

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Add documentation for the V4L2_CID_CAMERA_SENSOR_ROTATION camera
control. The newly added read-only control reports the rotation
correction to be applied to images before displaying them to the user.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Jacopo Mondi 2020-05-09 11:04:47 +02:00 committed by Mauro Carvalho Chehab
parent 9397a83f40
commit 9926c22487
1 changed files with 121 additions and 0 deletions
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121
Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
View file

@ -540,6 +540,127 @@ enum v4l2_scene_mode -
``V4L2_CID_CAMERA_SENSOR_ROTATION (integer)``
This read-only control describes the rotation correction in degrees in the
counter-clockwise direction to be applied to the captured images once
captured to memory to compensate for the camera sensor mounting rotation.
For a precise definition of the sensor mounting rotation refer to the
extensive description of the 'rotation' properties in the device tree
bindings file 'video-interfaces.txt'.
A few examples are below reported, using a shark swimming from left to
right in front of the user as the example scene to capture. ::
0 X-axis
0 +------------------------------------->
!
!
!
! |\____)\___
! ) _____ __`<
! |/ )/
!
!
!
V
Y-axis
Example one - Webcam
Assuming you can bring your laptop with you while swimming with sharks,
the camera module of the laptop is installed on the user facing part of a
laptop screen casing, and is typically used for video calls. The captured
images are meant to be displayed in landscape mode (width > height) on the
laptop screen.
The camera is typically mounted upside-down to compensate the lens optical
inversion effect. In this case the value of the
V4L2_CID_CAMERA_SENSOR_ROTATION control is 0, no rotation is required to
display images correctly to the user.
If the camera sensor is not mounted upside-down it is required to compensate
the lens optical inversion effect and the value of the
V4L2_CID_CAMERA_SENSOR_ROTATION control is 180 degrees, as images will
result rotated when captured to memory. ::
+--------------------------------------+
! !
! !
! !
! __/(_____/| !
! >.___ ____ ( !
! \( \| !
! !
! !
! !
+--------------------------------------+
A software rotation correction of 180 degrees has to be applied to correctly
display the image on the user screen. ::
+--------------------------------------+
! !
! !
! !
! |\____)\___ !
! ) _____ __`< !
! |/ )/ !
! !
! !
! !
+--------------------------------------+
Example two - Phone camera
It is more handy to go and swim with sharks with only your mobile phone
with you and take pictures with the camera that is installed on the back
side of the device, facing away from the user. The captured images are meant
to be displayed in portrait mode (height > width) to match the device screen
orientation and the device usage orientation used when taking the picture.
The camera sensor is typically mounted with its pixel array longer side
aligned to the device longer side, upside-down mounted to compensate for
the lens optical inversion effect.
The images once captured to memory will be rotated and the value of the
V4L2_CID_CAMERA_SENSOR_ROTATION will report a 90 degree rotation. ::
+-------------------------------------+
| _ _ |
| \ / |
| | | |
| | | |
| | > |
| < | |
| | | |
| . |
| V |
+-------------------------------------+
A correction of 90 degrees in counter-clockwise direction has to be
applied to correctly display the image in portrait mode on the device
screen. ::
+--------------------+
| |
| |
| |
| |
| |
| |
| |\____)\___ |
| ) _____ __`< |
| |/ )/ |
| |
| |
| |
| |
| |
+--------------------+
.. [#f1]
This control may be changed to a menu control in the future, if more
options are required.