Mobile appratus, in particular a rotary-wing drone, provided with a video camera delivering sequences of images dynamically corrected for the wobble effect
The apparatus comprises a camera ( 10 ) with a digital sensor read by a mechanism of the rolling shutter type delivering video data (S cam ) line by line. An exposure control circuit ( 22 ) adjusts dynamically the exposure time (t exp ) as a function of the level of illumination of the scene that is captured. A gyrometer unit ( 12 ) delivers a gyrometer signal (S gyro ) representative of the instantaneous variations of attitude (φ, θ, ψ) of the camera, and a processing circuit ( 18 ) that receives the video data (S cam ) and the gyrometer signal (S gyro ) delivers as an output video data processed and corrected for artefacts introduced by vibrations specific to the apparatus. An anti-wobble filter ( 24 ) dynamically modifies the gain of the gyrometer signal as a function of the exposure time (t exp ), so as to reduce the gain of the filter when the exposure time increases, and vice versa.
1. A mobile apparatus, in particular a motorized flying device such as a drone, including:
a camera comprising a lens, a digital sensor on which is formed an image of a scene during a given exposure time (t exp ), and a mechanism for reading the sensor of the rolling-shutter type delivering as an output. line by line, video data (S cam );
an exposure control circuit, comprising a servomechanism adapted to dynamically adjust the exposure time (t exp ) as a function of the level of illumination of the scene that is captured;
a gyrometer unit adapted to deliver a gyrometer signal (S gyro ) representative of the instantaneous variations of the attitude (φ, θ, ψ) of the mobile apparatus; and
an image processing circuit, comprising an anti-wobble filter, receiving as an input the video data (S cam ) and the gyrometer signal (S gyro ), and delivering as an output video data processed and corrected for artefacts introduced by vibrations specific to the mobile apparatus,
characterized in that the anti-wobble filter is adapted to dynamically modify the gain of the gyrometer signal applied at the input of the image processing circuit as a function of the exposure time (t exp ) determined by the exposure control circuit, so as to reduce the gain of the filter when the exposure time increases, and vice versa.
2. The mobile apparatus of claim 1 , wherein the gain variation law of the filter is a monotonic variation law.
3. The mobile apparatus of claim 2 , wherein the gain variation law of the filter is a variation law that is bound between a maximum gain of one and a minimum gain of zero.
4. The mobile apparatus of claim 2 , wherein the anti-wobble filter ( 24 ) is a digital filter adapted to generate, for a given image, a low-pass Butter-worth filter whose order is predefined and whose cut-off frequency (F c ) varies as a function of the exposure time (t exp ) determined for said given image.
5. The mobile apparatus of claim 4 , wherein the law of variation of the cut-off frequency (F c ) of the Butterworth filter as a function of the exposure time (t exp ) is a law of the type F c =1/2.t exp .
6. The mobile apparatus of claim 4 , wherein the digital filter is applied twice to the gyrometer signal, in the forward direction and in the return direction.
7. The mobile apparatus of claim 1 , wherein the camera is adapted to deliver as an output the video data for the duration of an acquisition window (A),
and wherein means are provided. which are adapted to apply the anti-wobble filter for a given image for the duration of a processing window (P, A, P′) starting before the window of acquisition of this image.
8. The mobile apparatus of claim 7 , wherein said means are adapted to apply the anti-wobble filter for the duration of said processing window (P, A, P′) ending after the window of acquisition of the image.