Abstract

Images acquired with a long exposure time using a camera embedded on UAVs (Unmanned Aerial Vehicles) exhibit motion blur due to the erratic movements of the UAV. The aim of the present work is to be able to acquire several images with a short exposure time and use an image processing algorithm to produce a stacked image with an equivalent long exposure time. Our method is based on the feature point image registration technique. The algorithm is implemented on the light-weight IGN (Institut national de l’information géographique) camera, which has an IMU (Inertial Measurement Unit) sensor and an SoC (System on Chip)/FPGA (Field-Programmable Gate Array). To obtain the correct parameters for the resampling of the images, the proposed method accurately estimates the geometrical transformation between the first and the N-th images. Feature points are detected in the first image using the FAST (Features from Accelerated Segment Test) detector, then homologous points on other images are obtained by template matching using an initial position benefiting greatly from the presence of the IMU sensor. The SoC/FPGA in the camera is used to speed up some parts of the algorithm in order to achieve real-time performance as our ultimate objective is to exclusively write the resulting image to save bandwidth on the storage device. The paper includes a detailed description of the implemented algorithm, resource usage summary, resulting processing time, resulting images and block diagrams of the described architecture. The resulting stacked image obtained for real surveys does not seem visually impaired. An interesting by-product of this algorithm is the 3D rotation estimated by a photogrammetric method between poses, which can be used to recalibrate in real time the gyrometers of the IMU. Timing results demonstrate that the image resampling part of this algorithm is the most demanding processing task and should also be accelerated in the FPGA in future work.

Highlights

  • Over the last decade, Unmanned Aerial Vehicles (UAVs) have been widely used for civil applications [1], especially for environmental surveys [2,3]

  • Images acquired with a long exposure time using a camera embedded on UAVs may exhibit motion blur due to the erratic movements of the UAV

  • An image processing stacking algorithm has been presented, which consists of several steps

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Summary

Introduction

Over the last decade, Unmanned Aerial Vehicles (UAVs) have been widely used for civil applications [1], especially for environmental surveys [2,3] Their growing popularity has led the LOEMI (Laboratoire d’Opto-électronique, de Métrologie et d’Instrumentation) team of Institut national de l’information géographique (IGN)/LaSTIG (Laboratoire des Sciences et Technologies de l’Information Géographique) to design and produce an ultra-light smart digital aerial camera, more suitable for photogrammetric applications than consumer cameras. This camera was originally used to exploit photogrammetric and metrological surveys using. An initial presentation of this work has been done in [6]

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