Contrast enhancement for image by WNN and GA combining PSNR with information entropy

A new contrast enhancement algorithm for image is proposed combining genetic algorithm (GA) with wavelet neural network (WNN). In-complete Beta transform (IBT) is used to obtain non-linear gray transform curve so as to enhance global contrast for an image. GA determines optimal gray transform parameters. In order to avoid the expensive time for traditional contrast enhancement algorithms, which search optimal gray transform parameters in the whole parameters space, based on gray distribution of an image, a classification criterion is proposed. Contrast type for original image is determined by the new criterion. Parameters space is, respectively, determined according to different contrast types, which greatly shrink parameters space. Thus searching direction of GA is guided by the new parameter space. Considering the drawback of traditional histogram equalization that it reduces the information and enlarges noise and background blur in the processed image, a synthetic objective function is used as fitness function of GA combining peak signal-noise-ratio (PSNR) and information entropy. In order to calculate IBT in the whole image, WNN is used to approximate the IBT. In order to enhance the local contrast for image, discrete stationary wavelet transform (DSWT) is used to enhance detail in an image. Having implemented DSWT to an image, detail is enhanced by a non-linear operator in three high frequency sub-bands. The coefficients in the low frequency sub-bands are set as zero. Final enhanced image is obtained by adding the global enhanced image with the local enhanced image. Experimental results show that the new algorithm is able to well enhance the global and local contrast for image while keeping the noise and background blur from being greatly enlarged.     

Luminance contrast, a new illumination technique in light microscopy: Optical basics, practical evaluations, further developments

Luminance contrast is a new illumination technique in light microscopy recently developed by the author, which leads to extraordinary contrast effects, enhanced focal depth and supramicroscopic resolution when transparent stained or unstained specimens are examined.This method is characterized by a small illuminating light beam running centrically to the specimen, so that the specimen is illuminated very homogenously. Within the objective, the illuminating beam is blocked by a small light stop. When all parts of the illuminating light are totally blocked, the background is completely dark; when small parts of the illuminating light pass the light stop, the background is moderately brightened.The microscopic image is a result of scattered light components, which are bent or reflected by the specimen. When the illuminating light is not completely blocked by the light stop, the transmitted illuminating components interfere with the scattered light components coming from the specimen.Additional three-dimensional effects are achievable when the illuminating light passes the specimen obliquely.The resulting variants of illumination are similar to dark field, negative phase contrast and interference contrast. In all modes of luminance contrast the specimen is illuminated very homogenously so that it appears as a self-luminous, fluorescent body – similar to fluorescence microscopy.Luminance contrast can be carried out when mirror objectives are used or common objectives containing glass lenses are equipped with individually adjusted light stops.Further aspects of technical developments are discussed in full details.     

Polarimetry group theory analysis in biological tissue phantoms by Mueller coherency matrix

The characterization of biological tissues by optical techniques provides several advantages over other techniques. Optical techniques enable to perform high resolution and contrast imaging, in a non-invasive way and with no-contact. Biological tissues are turbid media that strongly scatter light. The ultrastructure of some tissues makes them present a certain degree of anisotropy. Both scattering and anisotropy affect light polarization. Some pathologies alter these characteristics of the tissue. As a consequence polarized light can be used to extract additional information and achieve a better diagnosis.In this work, Group Theory is applied to analyse the polarization behavior of several samples. Firstly, the Mueller matrix for each sample is measured. Then, the Mueller Coherency matrix is obtained by means of the SU(4)-O + (6) homomorphism. Finally, the target decomposition theorem is applied by analyzing the eigenvalues and eigenvectors, and subsequently the different polarimetric effects are separated. In this way, the contrast of tissue imaging can be increased. This analysis is applied to biological tissue phantoms, which consisted on glucose suspensions of polystyrene spheres with different scatterer concentrations. Their behaviour can be modeled by means of single or multiple scattering depending on the concentration, either in the Rayleigh or Mie regimes. The same procedure could be used in a wide range of applications, like the study of cancerous cells that grow without control in cell cultures, or erythrocytes monitoring in anemia. The technique also has a great potential to be applied in Polarization Sensitive Optical Coherence Tomography (PS-OCT).     

Bounds for visual cryptography schemes

In this paper, we investigate the best pixel expansion of various models of visual cryptography schemes. In this regard, we consider visual cryptography schemes introduced by Tzeng and Hu (2002) [13]. In such a model, only minimal qualified sets can recover the secret image and the recovered secret image can be darker or lighter than the background. Blundo et al. (2006) [4] introduced a lower bound for the best pixel expansion of this scheme in terms of minimal qualified sets. We present another lower bound for the best pixel expansion of the scheme. As a corollary, we introduce a lower bound, based on an induced matching of hypergraph of qualified sets, for the best pixel expansion of the aforementioned model and the traditional model of visual cryptography scheme realized by basis matrices. Finally, we study access structures based on graphs and we present an upper bound for the smallest pixel expansion in terms of strong chromatic index.     

Visualisation of the fibrillar and pore morphology of cellulosic fibres applying transmission electron microscopy

Applying transmission electron microscopy (TEM) on ultra-thin cross-sections of fibres, the main characteristics of the internal morphology of cotton and the main man-made cellulosic fibres (modal, viscose and lyocell) could be visualised. To obtain an appropriate contrast for TEM, isoprene was polymerised into the swollen fibres after a stepwise solvent exchange from water to acetone. The included polymer is stainable with osmium tetraoxide. Significant differences in distribution of pore sizes and pore arrangements in the cellulosic fibres were seen. Cotton showed very small pores in the bulk of the fibre, but drying cracks and flat pores between the sheets of the secondary wall appear as larger pores. Lyocell contains only nanopores in the bulk of the fibre with a slight gradient in pore density, and a very porous skin layer. In viscose and modal, a very wide pore size distribution from nanometer to micrometer size can be seen.     

The dependence of nuclear magnetic resonance (NMR) image contrast on intrinsic and pulse sequence timing parameters

In Nuclear Magnetic Resonance (NMR) the image pixel value is governed by at least three major intrinsic parameters: the spin density N (H), the spin-lattice relaxation time T1, and the spin-spin relaxation time T2. The extent to which the signal is weighted toward one or several parameters is related to the history of the spin system preceding detection. On the simplifying, though not generally warranted assumption that the spin density does not vary significantly in soft tissues, relative tissue contrast can be predicted quantitatively provided the relaxation times are known. Signal intensities and contrast were computed on the basis of the Bloch equations and experimentally determined relaxation times as a function of pulse timing parameters and the data compared with those in images recorded at 0.5T field strength. Significant deviations from the equal density hypothesis were found for gray and white substance. Notably partial saturation but also spin echo and inversion-recovery images are not in full accordance with predictions made on the basis of relaxation times alone.     

The oral administration of MnCl2: A potential alternative to IV injection for tissue contrast enhancement in magnetic resonance imaging

Mn⁺² (as MnCl₂) was administered to rabbits intravenously and orally (a route of administration which based upon our previous experiments in rats⁷ promises to give selective hepatobiliary enhancement with less systemic toxicity). Nuclear magnetic relaxation dispersion or T₁ (NMRD) was performed on selected tissues (heart, liver, kidney, serum, and bile) in both animal groups to examine possible qualitative and semiquantitative differences in T₁ relaxation at equivalent sacrifice times. One animal was given an oral dose of MnCl₂ (620 micromoles/kg) and imaged sequentially (T₁ weighted sequence, .12T) for 30 minutes. The NMRD curves for organ tissues show an increase in relaxation efficacy in the 10–20MHz range characteristic of Mn-macromolecular complexes and are similar irrespective of the route of administration. The lack of increased relaxation enhancement for bile in this frequency range reflects cleavage of this complex upon excretion. Decreased overall relaxation in the liver is observed when oral Mn⁺² is compared to IV Mn⁺² due to the small fraction of administered dose that is absorbed. However, the images document a significant increase in the intensity of liver signal after the oral dose. We suspect this dose may ultimately be adjusted downward to give selective hepatobiliary effects.     

Magnetic resonance imaging of molecular transport in living morning glory stems

MRI was applied to investigate the transport pathways in Morning Glory plant stems. The study was carried out on living plants without affecting their integrity. The architecture of a dicotyledonous plant was deeply characterized: the root system structure and the vascular bundle location were identified, the presence of central voids caused by cell maturation and loss were observed in the stem. Molecular transport components were recognized, by observing the concentration profile of a tracer, which changed with time after its absorption by the plant roots. MRI analysis revealed the presence of an axial transport as the progress of the tracer front through the vascular bundles and a radial molecular transport from the vascular bundles toward the surface of the stem. As a result, the tracer molecular transport formed the parabolic tracer front (PTF). A model was built up through the analysis of the PTF that consisted of an axial front at the peak position and a radial front at the width of the parabolic tail. PTF analysis revealed differences between the tracer transport velocities in the axial and the radial directions in the plant stem. The model revealed that the width of the parabolic tail reflected the magnitudes of diffusion and permeation of the tracer in the plant stem.     

Impact of wavefront specifications of optical elements on the characteristics of short pulses in multi-pass stretcher

The relationship between the wavefront errors of optical elements in multi-pass stretcher and the compressed pulse characteristics has been studied. Low-frequency spatial modulation leads to pulse width enlarging. High-frequency spatial modulation leads to contrast reduction. The pedestal is linked to the power spectral density of the wavefront error. The analytic relationship between these factors is derived.