Range sensors have drawn much interest for human activity related research since they provide explicit 3D information about the shape that is invariant to clothing, skin color and illumination changes. However, triangulationbased systems like structured-light sensors generate occlusions in the image when parts of the scene cannot be seen by both the projector and the camera. Those occlusions, as well as missing data points and measurement noise, depend on the structured-light system design. These artifacts add a level of difficulty to the task of human body segmentation that is typically not addressed in the literature. In this work, we design a segmentation model that is able to reason about 3D spatial information, to identify the different body parts in motion and is robust to artifacts inherent to the structured-light system, such as triangulation occlusions, noise and missing data. First, we build the first realistic sensor-specific training set by closely simulating the actual acquisition scenario with the same intrinsic parameters as our sensor and the artifacts it generates. Second, we adapt a state-of-the-art fully convolutional network to range images of the human body in order for it to transfer its learning toward 3D spatial information instead of light intensities. Third, we quantitatively demonstrate the importance of simulating sensor-specific artifacts in the training set to improve the robustness of the segmentation of actual range images. Finally, we show the capability of the model to accurately segment human body parts on real range image sequences acquired by our structured light sensor, with high inter-frame consistency and in real-time.
Proc. SPIE. 9897, Real-Time Image and Video Processing 2016
KEYWORDS: Image compression, Digital image processing, Data storage, Digital filtering, Denoising, Linear filtering, Image analysis, Image filtering, Image enhancement, Video processing, Embedded systems
Spatial Averaging Filters (SAF) are extensively used in image processing for image smoothing and denoising. Their latest implementations have already achieved constant time computational complexity regardless of kernel size. However, all the existing O(1) algorithms require additional memory for temporary data storage. In order to minimize memory usage in embedded systems, we introduce a new two-dimensional recursive SAF. It uses previous resultant pixel values along both rows and columns to calculate the current one. It can achieve constant time computational complexity without using any additional memory usage. Experimental comparisons with previous SAF implementations shows that the proposed 2D-Recursive SAF does not require any additional memory while offering a computational time similar to the most efficient existing SAF algorithm. These features make it especially suitable for embedded systems with limited memory capacity.
Improving the appearance of the trunk is an important goal of scoliosis surgical treatment, mainly in patients' eyes. Unfortunately, existing methods for assessing postoperative trunk appearance are rather subjective as they rely on a qualitative evaluation of the trunk shape. In this paper, an objective method is proposed to quantify the changes in trunk shape after surgery. Using a non-invasive optical system, the whole trunk surface is acquired and reconstructed in 3D. Trunk shape is described by two functional measurements spanning the trunk length: the lateral deviation and the axial rotation. To measure the pre and postoperative differences, a correction rate is computed for both measurements. On a cohort of 36 scoliosis patients with the same spinal curve type who underwent the same surgical approach, surgery achieved a very good correction of the lateral trunk deviation (median correction of 76%) and a poor to moderate correction of the back axial rotation (median correction of 19%). These results demonstrate that after surgery, patients are still confronted with residual trunk deformity, mainly a persisting hump on the back. That can be explained by the fact that current scoliosis assessment and treatment planning are based solely on radiographic measures of the spinal deformity and do not take trunk deformity into consideration. It is believed that with our novel quantitative trunk shape descriptor, clinicians and surgeons can now objectively assess trunk deformity and postoperative shape and propose new treatment strategies that could better address patients' concern about their appearance.