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@xxxxxxxxxx> > --- > .../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
