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@xxxxxxxxxx>
---
.../media/v4l/ext-ctrls-camera.rst | 121 ++++++++++++++++++
1 file changed, 121 insertions(+)
diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
index 01a9042d53a6..140f985c7f06 100644
--- a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
+++ b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
@@ -542,6 +542,127 @@ 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.
--
2.26.1
