RESUMEN
In target detection of optical remote sensing images, two main obstacles for aircraft target detection are how to extract the candidates in complex gray-scale-multi background and how to confirm the targets in case the target shapes are deformed, irregular or asymmetric, such as that caused by natural conditions (low signal-to-noise ratio, illumination condition or swaying photographing) and occlusion by surrounding objects (boarding bridge, equipment). To solve these issues, an improved active contours algorithm, namely region-scalable fitting energy based threshold (TRSF), and a corner-convex hull based segmentation algorithm (CCHS) are proposed in this paper. Firstly, the maximal variance between-cluster algorithm (Otsu's algorithm) and region-scalable fitting energy (RSF) algorithm are combined to solve the difficulty of targets extraction in complex and gray-scale-multi backgrounds. Secondly, based on inherent shapes and prominent corners, aircrafts are divided into five fragments by utilizing convex hulls and Harris corner points. Furthermore, a series of new structure features, which describe the proportion of targets part in the fragment to the whole fragment and the proportion of fragment to the whole hull, are identified to judge whether the targets are true or not. Experimental results show that TRSF algorithm could improve extraction accuracy in complex background, and that it is faster than some traditional active contours algorithms. The CCHS is effective to suppress the detection difficulties caused by the irregular shape.
RESUMEN
Computer-generated holograms (CGHs) provide an approach to high-precision metrology of aspherics. A CGH is designed under the trade-off among size, mapping distortion, and line spacing. This paper describes an optimal design method based on the parametric model for tilt carrier frequency CGHs placed outside the interferometer focus points. Under the condition of retaining an admissible size and a tolerable mapping distortion, the optimal design method has two advantages: (1) separating the parasitic diffraction orders to improve the contrast of the interferograms and (2) achieving the largest line spacing to minimize sensitivity to fabrication errors. This optimal design method is applicable to common concave aspherical surfaces and illustrated with CGH design examples.
RESUMEN
Dependences of the spectral profiles on the both Tm(3+)- and Yb3+ additive amounts were presented. Further, the temporal evolution of Tm3+ luminescence in the nanocrystals was explored. Enhanced ultraviolet emissions with Tm3+ upconversion were investigated in the Y(0.800-x)Fa:Yb(3+)0.200, Tm3+(x), nanocrystal samples following excitation with 980 nm. The emissions can be attributed to the transitions of 1G4 --> 3H6, 1D2 --> 3F4 or 3H6 and (3P0 and 1I6) --> 3F4 or 3H6. A detailed energy-transition scheme was proposed and described well the ultraviolet-enhanced upconversion of Tm3+ and the energy-transfer processes from Yb3+ to Tm3+ based on energy-matching conditions.