Relative Position Estimation Using Cross Filter for Rolling-Shutter Cameras

We propose an estimation method of the relative position of a light emitting diode (LED) from a rolling-shutter (RS) camera with a cross filter (CF). The CF is set in front of the camera lens so that incident light can be scattered into two straight lines extending about $\pm \pi /4$ from the horizontal row of the CMOS RS image sensor (IS). With the geometry of a right-angled isosceles triangle, our method makes it possible to estimate the coordinates of the LED in the IS plane when the scattered light is captured at two points in a scanline. With the CF, our method continues to update the estimated coordinate of the LED as long as the row captures scattered light at two points. Naturally, our method makes it possible row by row when multiple LEDs are used or when they are moving. In contrast, without the CF, estimation is not possible until the scanline reaches the row which captures the whole LED, and the estimated coordinates are not updated once it is done for that frame. Experiments verify that our estimation method works with the estimation error less than five pixels, and extends the region of a frame in which estimated coordinates are output, even in a moving environment, while the conventional method (without CF) does the estimated coordinates only once per frame.