Digital cameras are increasingly used for measurement tasks within engineering scenarios, often being part of metrology platforms. Existing cameras are well equipped to provide 2D information about the fields of view (FOV) they observe, the objects within the FOV, and the accompanying environments. But for some applications these 2D results are not sufficient, specifically applications that require Z dimensional data (depth data) along with the X and Y dimensional data. New designs of camera systems have previously been developed by integrating multiple cameras to provide 3D data, ranging from 2 camera photogrammetry to multiple camera stereo systems. Many earlier attempts to record 3D data on 2D sensors have been completed, and likewise many research groups around the world are currently working on camera technology but from different perspectives; computer vision, algorithm development, metrology, etc. Plenoptic or Lightfield camera technology was defined as a technique over 100 years ago but has remained dormant as a potential metrology instrument. Lightfield cameras utilize an additional Micro Lens Array (MLA) in front of the imaging sensor, to create multiple viewpoints of the same scene and allow encoding of depth information. A small number of companies have explored the potential of lightfield cameras, but in the majority, these have been aimed at domestic consumer photography, only ever recording scenes as relative scale greyscale images. This research considers the potential for lightfield cameras to be used for world scene metrology applications, specifically to record absolute coordinate data. Specific interest has been paid to a range of low cost lightfield cameras to; understand the functional/behavioural characteristics of the optics, identify potential need for optical and/or algorithm development, define sensitivity, repeatability and accuracy characteristics and limiting thresholds of use, and allow quantified 3D absolute scale coordinate data to be extracted from the images. The novel output of this work is; an analysis of lightfield camera system sensitivity leading to the definition of Active Zones (linear data generation good data) and In-active Zones (non-linear data generation poor data), development of bespoke calibration algorithms that remove radial/tangential distortion from the data captured using any MLA based camera, and, a light field camera independent algorithm that allows the delivery of 3D coordinate data in absolute units within a well-defined measurable range from a given camera.

L'imagerie plénoptique est souvent présentée comme une révolution par rapport à l'imagerie standard. En effet, elle apporte plus de contrôle à l'utilisateur sur l'image finale puisque les dimensions spatiales et angulaires du champ de lumière offrent la possibilité de changer le point de vue ou de refaire la mise au point après coup ainsi que de calculer la carte de profondeur de la scène. Cependant, cela complique le travail du concepteur optique du système pour deux raisons. La première est qu'il existe une multitude d'appareils de capture plénoptique différents, chacun avec sa propre spécificité. La deuxième est qu'il n'existe pas de modèle qui relie le design de la caméra à ses propriétés optiques d'acquisition et qui puisse guider le concepteur dans sa tâche. Cette thèse répond à ces observations en proposant un modèle optique du premier ordre pour représenter n'importe quel appareil d'acquisition plénoptique. Ce modèle abstrait une caméra plénoptique par un réseau équivalent de caméras virtuelles existant en espace objet et qui effectue un échantillonnage identique de la scène. Ce modèle est utilisé pour étudier et comparer plusieurs caméras plénoptiques ainsi qu'un microscope plénoptique monté en laboratoire, ce qui révèle des lignes directrices pour la conception de systèmes plénoptiques. Les simulations du modèle sont aussi validées par l'expérimentation avec une caméra et le microscope plénoptique. / Light field imaging is often presented as a revolution of standard imaging. Indeed, it does bring more control to the user over the final image as the spatio-angular dimensions of the light field offer the possibility to change the viewpoint and refocus after the shot and compute the scene depth map.However, it complicates the work of the optical designer of the system for two reasons. The first is that there exist a multitude of different light field acquisition devices, each with its own specific design. The second is that there is no model that relates the camera design to its optical properties of acquisition and that would guide the designer in his task. This thesis addresses these observations by proposing a first-order optical model to represent any light field acquisition device. This model abstracts a light field camera as en equivalent array of virtual cameras that exists in object space and that performs the same sampling of the scene. The model is used to study and compare several light field cameras as well as a light field microscope setup which reveals guidelines for the conception of light field optical systems. The simulations of the model are also validated through experimentation with a light field camera and a light field microscope that was constructed in our laboratory.

This work presents the development and analysis of a system that combines the concepts of light field microscopy and particle image velocimetry (PIV) to measure three-dimensional velocities within a microvolume. Rectanglar microchannels were fabricated with dimensions on the order of 350-950 micrometers using a photolithographic process and polydimethylsiloxane (PDMS). The flow was seeded with fluorescent particles and pumped through microchannels at Reynolds numbers ranging from 0.016 to 0.028. Flow at Reynolds numbers in the range of 0.02 to 0.03 was seeded with fluorescent particles and pumped through microchannels. A light field microscope with a lateral resolution of 6.25 micrometers and an axial resolution of 15.5 micrometers was designed and built based on the concepts described by Levoy et al. Light field images were captured continuously at a frame rate of 3.9 frames per second using a Canon 5D Mark II DSLR camera. Each image was post processed to render a stack of two-dimensional images. The focal stacks were further post processed using various methods including bandpass filtering, 3D deconvolution, and intensity-based thresholding, to remove effects of diffraction and blurring. Subsequently, a multi-pass, three-dimensional PIV algorithm was used to measure channel velocities. Results from PIV analysis were compared with an analytical solution for fully-developed cases, and with CFD simulations for developing flows. Relative errors for fully-developed flow measurements, within the light field microscope refocusing range, were approximately 5% or less. Overall, the main limitations are the reduction in lateral resolution, and the somewhat low axial resolution. Advantages include the relatively low cost, ease of incorporation into existing micro-PIV systems, simple self-calibration process, and potential for resolving instantaneous three-dimensional velocities in a microvolume.