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 <jac...@jmondi.org>
>>> ---
>>> .../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
