Hi Jacopo, Sorry for the late reply, it fell through the cracks... On 9/13/19 8:49 PM, Jacopo Mondi wrote: > Hi Hans, > > On Fri, Sep 13, 2019 at 04:02:45PM +0200, Hans Verkuil wrote: >> 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? >> > > It really depend along which axis direction you are applying the mounting > rotation and the compensation rotation... See below... > >>> + >>> + 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? > > Yes indeed sorry > >> 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. >> > > num-col is totally wrong, that should have been num-lines > > In general > s/line-len/num-col > s/num-col/num-lines > >>> + ! 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.:: >> >> .:: -> : >> > > Don't I need the :: to mark the following block of text as verbatim ? Ah, sorry, this is for the markup. I missed that. > >>> + >>> + ------- 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. >> > > Along which axis direction are you rotating the camera counterclockwise ? > > If you see your face, and you rotate the camera counterclockwise while > looking at it, you're actually rotating along the axis directed -towards- > the sensor. > > The rotation here in the example and in the 'rotation' property > description has to be applied along the axis pointing aways from the > sensor, so what you're actually doing is rotating clockwise along that > direction (I guess)... So yes, to compensate that, you need to rotate > clockwise when you look at the image on the screen... Confusing, > right? I think you are right, but let me take another look at this when v4 is posted. The line-len/num-col confusion didn't help :-) Regards, Hans > >>> + ------- >>> + | 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
