Selecting an Optimal Exposure Time for Estimating the Distance Between a Camera and an Infrared Emitter Diode Using Pixel Grey-Level Intensities

摘要

The problem of estimating the distance between a camera and an infrared emitter diode (IRED), using image pixels grey-levels values is analysed. An implementation of the method for estimating the distance between a camera and an IRED demonstrated that the accuracy of distance estimation depends on camera exposure times, for a fixed radiant intensity. A graph of distance estimation errors as a function of camera exposure resulted in a curve that resembles a bathtub curve, with a range of camera exposure times in which minimum errors are located. This curve was obtained after images for distance estimation, over a 200 to 380 cm range were acquired and processed. In addition, several camera exposure times were taken into account in this experiment. However, if model calibration errors are analysed, a similar bathtub curve is obtained. This implies that an optimal range for camera exposure time can be selected after the calibration process has been completed, thus a reduction in exposure times in the distance estimation process could be obtained. The error analysis for a bathtub curve was tested for calibration images captured at respective distances of 402.5, 350, 300 and 250 cm between the IRED and the camera, and the extracted optimal exposure times were used to estimate the distance in the 200 to 380 cm range. Besides these, other distances for model calibration and distance estimation were considered with equivalent results being obtained.