Struct libcamera::properties::Rotation
source · pub struct Rotation(pub i32);Expand description
The camera rotation is expressed as the angular difference in degrees between two reference systems, one relative to the camera module, and one defined on the external world scene to be captured when projected on the image sensor pixel array.
A camera sensor has a 2-dimensional reference system ‘Rc’ defined by its pixel array read-out order. The origin is set to the first pixel being read out, the X-axis points along the column read-out direction towards the last columns, and the Y-axis along the row read-out direction towards the last row.
A typical example for a sensor with a 2592x1944 pixel array matrix observed from the front is
2591 X-axis 0
<------------------------+ 0
.......... ... ..........!
.......... ... ..........! Y-axis
... !
.......... ... ..........!
.......... ... ..........! 1943
V
The external world scene reference system ‘Rs’ is a 2-dimensional reference system on the focal plane of the camera module. The origin is placed on the top-left corner of the visible scene, the X-axis points towards the right, and the Y-axis points towards the bottom of the scene. The top, bottom, left and right directions are intentionally not defined and depend on the environment in which the camera is used.
A typical example of a (very common) picture of a shark swimming from left to right, as seen from the camera, is
0 X-axis
0 +------------------------------------->
!
!
!
! |\____)\___
! ) _____ __`<
! |/ )/
!
!
!
V
Y-axis
With the reference system ‘Rs’ placed on the camera focal plane.
¸.·˙!
¸.·˙ !
_ ¸.·˙ !
+-/ \-+¸.·˙ !
| (o) | ! Camera focal plane
+-----+˙·.¸ !
˙·.¸ !
˙·.¸ !
˙·.¸!
When projected on the sensor’s pixel array, the image and the associated reference system ‘Rs’ are typically (but not always) inverted, due to the camera module’s lens optical inversion effect.
Assuming the above represented scene of the swimming shark, the lens inversion projects the scene and its reference system onto the sensor pixel array, seen from the front of the camera sensor, as follow
Y-axis
^
!
!
!
! |\_____)\__
! ) ____ ___.<
! |/ )/
!
!
!
0 +------------------------------------->
0 X-axis
Note the shark being upside-down.
The resulting projected reference system is named ‘Rp’.
The camera rotation property is then defined as the angular difference in the counter-clockwise direction between the camera reference system ‘Rc’ and the projected scene reference system ‘Rp’. It is expressed in degrees as a number in the range [0, 360[.
Examples
0 degrees camera rotation
Y-Rp
^
Y-Rc !
^ !
! !
! !
! !
! !
! !
! !
! !
! 0 +------------------------------------->
! 0 X-Rp
0 +------------------------------------->
0 X-Rc
X-Rc 0
<------------------------------------+ 0
X-Rp 0 !
<------------------------------------+ 0 !
! !
! !
! !
! !
! !
! !
! !
! V
! Y-Rc
V
Y-Rp
90 degrees camera rotation
0 Y-Rc
0 +-------------------->
! Y-Rp
! ^
! !
! !
! !
! !
! !
! !
! !
! !
! !
! 0 +------------------------------------->
! 0 X-Rp
!
!
!
!
V
X-Rc
180 degrees camera rotation
0
<------------------------------------+ 0
X-Rc !
Y-Rp !
^ !
! !
! !
! !
! !
! !
! !
! V
! Y-Rc
0 +------------------------------------->
0 X-Rp
270 degrees camera rotation
0 Y-Rc
0 +-------------------->
! 0
! <-----------------------------------+ 0
! X-Rp !
! !
! !
! !
! !
! !
! !
! !
! !
! V
! Y-Rp
!
!
!
!
V
X-Rc
Example one - Webcam
A camera module installed on the user facing part of a laptop screen casing 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.
Y-Rp
Y-Rc ^
^ !
! !
! ! |\_____)\__
! ! ) ____ ___.<
! ! |/ )/
! !
! !
! !
! 0 +------------------------------------->
! 0 X-Rp
0 +------------------------------------->
0 X-Rc
The two reference systems are aligned, the resulting camera rotation is 0 degrees, no rotation correction needs to be applied to the resulting image once captured to memory buffers to correctly display it to users.
+--------------------------------------+
! !
! !
! !
! |\____)\___ !
! ) _____ __`< !
! |/ )/ !
! !
! !
! !
+--------------------------------------+
If the camera sensor is not mounted upside-down to compensate for the lens optical inversion, the two reference systems will not be aligned, with ‘Rp’ being rotated 180 degrees relatively to ‘Rc’.
X-Rc 0
<------------------------------------+ 0
!
Y-Rp !
^ !
! !
! |\_____)\__ !
! ) ____ ___.< !
! |/ )/ !
! !
! !
! V
! Y-Rc
0 +------------------------------------->
0 X-Rp
The image once captured to memory will then be rotated by 180 degrees
+--------------------------------------+
! !
! !
! !
! __/(_____/| !
! >.___ ____ ( !
! \( \| !
! !
! !
! !
+--------------------------------------+
A software rotation correction of 180 degrees should be applied to correctly display the image.
+--------------------------------------+
! !
! !
! !
! |\____)\___ !
! ) _____ __`< !
! |/ )/ !
! !
! !
! !
+--------------------------------------+
Example two - Phone camera
A camera installed on the back side of a mobile 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.
0 Y-Rc
0 +-------------------->
! Y-Rp
! ^
! !
! !
! !
! ! |\_____)\__
! ! ) ____ ___.<
! ! |/ )/
! !
! !
! !
! 0 +------------------------------------->
! 0 X-Rp
!
!
!
!
V
X-Rc
The two reference systems are not aligned and the ‘Rp’ reference system is rotated by 90 degrees in the counter-clockwise direction relatively to the ‘Rc’ reference system.
The image once captured to memory will be rotated.
+-------------------------------------+
| _ _ |
| \ / |
| | | |
| | | |
| | > |
| < | |
| | | |
| . |
| 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.
+--------------------+
| |
| |
| |
| |
| |
| |
| |\____)\___ |
| ) _____ __`< |
| |/ )/ |
| |
| |
| |
| |
| |
+--------------------+Tuple Fields§
§0: i32