Probing photospheric magnetic fields with new spectral line pairs

The magnetic line ratio (MLR) method has been extensively used in the measurement of photospheric magnetic field strength. It was devised for the neutral iron line pair at 5247.1 A and 5250.2 A (5250 A pair). Other line pairs as well-suited as this pair been have not been reported in the literature. The aim of the present work is to identify new line pairs useful for the MLR technique and to test their reliability. We use a three dimensional magnetohydrodynamic (MHD) simulation representing the quiet Sun atmosphere to synthesize the Stokes profiles. Then, we apply the MLR technique to the Stokes V profiles to recover the fields in the MHD cube both, at original resolution and after degrading with a point spread function. In both these cases, we aim to empirically represent the field strengths returned by the MLR method in terms of the field strengths in the MHD cube. We have identified two new line pairs that are very well adapted to be used for MLR measurements. The first pair is in the visible, Fe I 6820 A - 6842 A (whose intensity profiles have earlier been used to measure stellar magnetic fields), and the other is in the infrared (IR), Fe I 15534 A - 15542 A. The lines in these pairs reproduce the magnetic fields in the MHD cube rather well, partially better than the original 5250 A pair. The newly identified line pairs complement the old pairs. The lines in the new IR pair, due to their higher Zeeman sensitivity, are ideal for the measurement of weak fields. The new visible pair works best above 300 G. The new IR pair, due to its large Stokes V signal samples more fields in the MHD cube than the old IR pair at $1.56\,\mu$m, even in the presence of noise, and hence likely also on the real Sun. Owing to their low formation heights (100-200 km above tau_5000=1), both the new line pairs are well suited for probing magnetic fields in the lower photosphere.Comment: Accepted for publication in Astronomy & Astrophysic

Text Localization in Video Using Multiscale Weber's Local Descriptor

In this paper, we propose a novel approach for detecting the text present in videos and scene images based on the Multiscale Weber's Local Descriptor (MWLD). Given an input video, the shots are identified and the key frames are extracted based on their spatio-temporal relationship. From each key frame, we detect the local region information using WLD with different radius and neighborhood relationship of pixel values and hence obtained intensity enhanced key frames at multiple scales. These multiscale WLD key frames are merged together and then the horizontal gradients are computed using morphological operations. The obtained results are then binarized and the false positives are eliminated based on geometrical properties. Finally, we employ connected component analysis and morphological dilation operation to determine the text regions that aids in text localization. The experimental results obtained on publicly available standard Hua, Horizontal-1 and Horizontal-2 video dataset illustrate that the proposed method can accurately detect and localize texts of various sizes, fonts and colors in videos.Comment: IEEE SPICES, 201