Browsing by Author "Yao, Ming, Ph. D."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Fabric wrinkling and pilling evaluation by stereovision and three-dimensional surface characterization(2011-12) Yao, Ming, Ph. D.; Xu, Bugao; Chen, Jonathan Y.Wrinkling and pilling caused in wear and care procedures are vital performance characteristics of fabric. The advance of three-dimensional (3D) imaging techniques has made it possible to develop a convenient, reliable and low cost tool for automatic and efficient evaluation of fabric wrinkling and pilling. We suggest that 3D imaging and measurement system can provide a convenient, accommodating and comprehensive mean to fabric surface assessment. A 3D imaging system based on stereo vision technology is developed. To make it more affordable and portable, the system consists of a pair of consumer grade high resolution digital cameras with mounting hardware. The system is calibrated with classic camera calibration technique. The calibration procedure is relatively complicated, but there is no need to repeat frequently as long as the relative positions between cameras are not changed. In this system, image acquisition can be completed in less than one second. This efficient surface capturing feature is important for a large amount of measurement tasks. However, the computation in stereo vision is complex and intensive, thus it remains a challenge. A two-phase multi-resolution stereo matching algorithm is developed. In the first phase, a discrete disparity map is generated by block matching. In the second phase, local least-squares matching is performed in combination with global optimization within a regularization framework, so as to ensure both accuracy and reliability. To make the 3D imaging system ready for practical use, detection and measurement modules for wrinkling and pilling were developed to take advantage of the depth information in the 3D surface data. The practical feasibility of the 3D imaging system in fabric surface assessment was demonstrated in comparison with human visual ratings. The results showed agreement between the 3D automatic assessment and subjective visual assessment.Item High-quality dense stereo vision for whole body imaging and obesity assessment(2015-05) Yao, Ming, Ph. D.; Xu, BugaoThe prevalence of obesity has necessitated developing safe and convenient tools for timely assessing and monitoring this condition for a broad range of population. Three-dimensional (3D) body imaging has become a new mean for obesity assessment. Moreover, it generates body shape information that is meaningful for fitness, ergonomics, and personalized clothing. In the previous work of our lab, we developed a prototype active stereo vision system that demonstrated a potential to fulfill this goal. But the prototype required four computer projectors to cast artificial textures on the body which facilitate the stereo-matching on texture-deficient images (e.g., skin). This decreases the mobility of the system when used to collect a large population data. In addition, the resolution of the generated 3D~images is limited by both cameras and projectors available during the project. The study reported in this dissertation highlights our continued effort in improving the capability of 3Dbody imaging through simplified hardware for passive stereo and advanced computation techniques. The system utilizes high-resolution single-lens reflex (SLR) cameras, which became widely available lately, and is configured in a two-stance design to image the front and back surfaces of a person. A total of eight cameras are used to form four pairs of stereo units. Each unit covers a quarter of the body surface. The stereo units are individually calibrated with a specific pattern to determine cameras' intrinsic and extrinsic parameters for stereo matching. The global orientation and position of each stereo unit within a common world coordinate system is calculated through a 3Dregistration step. The stereo calibration and 3Dregistration procedures do not need to be repeated for a deployed system if the cameras' relative positions have not changed. This property contributes to the portability of the system, and tremendously alleviates the maintenance task. The image acquisition time is around two seconds for a whole-body capture. The system works in an indoor environment with a moderate ambient light. Advanced stereo computation algorithms are developed by taking advantage of high-resolution images and by tackling the ambiguity problem in stereo matching. A multi-scale, coarse-to-fine matching framework is proposed to match large-scale textures at a low resolution and refine the matched results over higher resolutions. This matching strategy reduces the complexity of the computation and avoids ambiguous matching at the native resolution. The pixel-to-pixel stereo matching algorithm follows a classic, four-step strategy which consists of matching cost computation, cost aggregation, disparity computation and disparity refinement. The system performance has been evaluated on mannequins and human subjects in comparison with other measurement methods. It was found that the geometrical measurements from reconstructed 3Dbody models, including body circumferences and whole volume, are highly repeatable and consistent with manual and other instrumental measurements (CV < 0.1$%, R2>0.99). The agreement of percent body fat (%BF) estimation on human subjects between stereo and dual-energy X-ray absorptiometry (DEXA) was found to be improved over the previous active stereo system, and the limits of agreement with 95% confidence were reduced by half. Our achieved %BF estimation agreement is among the lowest ones of other comparative studies with commercialized air displacement plethysmography (ADP) and DEXA. In practice, %BF estimation through a two-component model is sensitive to body volume measurement, and the estimation of lung volume could be a source of variation. Protocols for this type of measurement should still be created with an awareness of this factor.