Light sheet fluorescence microscopy (LSFM) with fluorescence emission difference (FED) obtains axial resolution-enhanced images by the subtraction of signals excited by different light sheets, Gaussian light sheet and negative light sheet. Negative values are inevitable in FED LSFM with conventional subtraction coefficient, due to mismatches in the outer contours of the raw signals excited by different light sheets, causing image distortion. In this paper, we propose a method based on tangent-function subtraction coefficient to reduce image distortion. This tangent-function subtraction coefficient is introduced to minimize image distortion without lowering the axial resolution. The value of the variable subtraction coefficient is obtained from the intensity value of raw signals. We performed experiments using fluorescent beads with a diameter of 1 micron and compared the subtraction results with constant and tangent-function subtraction coefficient. The experimental results demonstrated that the proposed tangent-function subtraction coefficient has an advantage over the conventional constant coefficient.
We introduce a phase mask with a left-handed azimuthal polarization to generate a special shape of point spread function. The proposed point spread function has low-intensity and small size in the central lobe. This central lobe of the point spread function is used to obtain an image on the detector, and therefore the lateral resolution is improved. The proposed method can achieve a remarkable improvement in the lateral resolution and the depth of field compared with conventional confocal scanning microscopy. The image simulation demonstrated that the images obtained by this proposed method have better imaging quality.
KEYWORDS: Optical transfer functions, Wavefronts, Image restoration, Imaging systems, Signal to noise ratio, Digital signal processing, Image compression, Phase shift keying, Modulation transfer functions, Point spread functions
The random selection of phase mask parameters will cause the degradation of imaging quality, which can be fixed through the optimization process. We introduce an evaluation function based on the use of multitarget optimization to obtain optimal phase mask parameters. The proposed method gives the optimal phase mask parameters, which produce together an imaging quality at all defocus positions as best as possible. The cubic phase mask and the general cubic phase mask are both used to perform optimization with a proposed evaluation function. The simulation result gives quite interesting values for the two types of these phase masks.
We proposed a radially symmetrical conjugate phase mask (PM) pair to yield an invariant imaging property for extending depth-of-field imaging. This conjugate PM pair is a two-radially symmetrical phase function with opposite orientation of the phase modulation. Compared with a single-radially symmetrical PM, the proposed conjugate PM pair shows a symmetrically imaging property on both sides of the focal plane and high magnitude of modulation transfer function (MTF). The quartic phase mask (QPM) with optimized phase parameters is employed to demonstrate our concept. Several evaluation approaches, including point-spread function, MTF, and image simulation, are used to realize the performance comparison among a traditional imaging system, an original QPM system, and a conjugate QPM. The results are proof that the proposed conjugate PM has a superior performance in extending depth of field imaging.
The random volume over ground (RVoG) model has been extensively applied to polarimetric interferometry SAR (PolInSAR) data for the retrieval of forest geophysical parameters. The complex interferometric coherence of the RVoG model was originally derived in a simplified way by neglecting one of the two possible contributions of the ground response: direct return from the ground or double-bounce interaction with the stems or trunks. In many cases, their influence depends on both the system and scene parameters, and none of them should be ignored a priori. Therefore, a more general model accounting for the simultaneous retrieval of the both ground contributions should be considered. Based on the characteristics of the scattering progress in the forest area, a general three-layer scattering model (GTLSM) is proposed to extract forest parameters using L-band single-baseline PolInSAR data. The proposed model assumes the vertical structural forest composed of three layers: canopy, tree-trunk, and ground layer, which account for the simultaneous effects of three scattering components on complex coherence. The GTLSM performance is evaluated with simulated data from PolSARProSim software and spaceborne data acquired by the SIR-C/X-SAR system. Experimental results indicate that forest parameters could be effectively extracted by the proposed GTLSM.
Wavefront coding involves the use of an asymmetrical phase mask to extend the depth of field of incoherent imaging systems. The performance of wavefront coding systems depends on designing a suitable phase profile to generate the defocus-invariant imaging characteristic. We proposed a square-root phase mask with two profile factors for achieving a steadier defocused modulation transfer function (MTF). Several evaluation methods are employed for the purpose of performance comparison between the proposed phase mask and the previously suggested phase masks under the constraint condition that the phase parameters are optimized at the same level of noise gain. Numerical results show that the square-root phase mask yields better properties in extended depth of field imaging, especially in acquiring defocus-invariant MTFs and eliminating image artifacts associated with the decoded images.
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