Adapting the Spatial-frequency Bandpass of In-focus Phase-contrast Apertures for Biologcal Applications

2007 ◽  
Vol 13 (S02) ◽  
Author(s):  
RM Glaeser ◽  
D Typke ◽  
KH Downing ◽  
PC Tiemeijer ◽  
R Cambie ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Phase Contrast

Form-Colour Aftereffects: Selectivity to Local Luminance Contrast

Perception ◽  
1978 ◽  
Vol 7 (4) ◽  
pp. 407-415 ◽  
Author(s):  
Charles F Stromeyer ◽  
Benjamin M Dawson
Keyword(s):  
Spatial Frequency ◽  
Phase Contrast ◽  
Luminance Contrast ◽  
Spatial Phase ◽  
Black And White ◽  
White Test

For long periods observers fixated low spatial frequency coloured gratings. Black and white test gratings of the same spatial frequency and orientation as the adapting gratings appeared coloured with the hue complementary to the adapting patterns when the dark test stripes fell on retinal areas previously occupied by the dark adapting stripes; no colour or very weak colour was seen when the test gratings were reversed in phase (contrast reversed). No colour aftereffects were produced with coloured gratings that lacked luminance contrast. This selectivity to the polarity of local luminance contrast can be explained by mechanisms that respond conjointly to colour and luminance contrast. The aftereffects are selective to spatial phase.

Single Element Detection Phase Contrast Spatial Frequency Modulation Imaging

2018 ◽  
Author(s):  
Nathan Worts ◽  
Jeff Field ◽  
Randy Bartels ◽  
Jason Jones ◽  
Jeff Broderick ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Frequency Modulation ◽  
Phase Contrast ◽  
Single Element

scholarly journals Spatial frequency-based image reconstruction to improve image contrast in multi-offset adaptive optics ophthalmoscopy

2020 ◽  
Author(s):  
Pedro Mecê ◽  
Elena Gofas ◽  
Yuhua Rui ◽  
Min Zhang ◽  
José-Alain Sahel ◽  
...  
Keyword(s):  
Image Reconstruction ◽  
Spatial Frequency ◽  
Retinal Ganglion Cells ◽  
Adaptive Optics ◽  
Phase Contrast ◽  
Ganglion Cells ◽  
Image Contrast ◽  
Detection Methods ◽  
Retinal Ganglion

Off-axis detection methods in adaptive optics (AO) ophthalmoscopy can enhance image contrast of translucent retinal structures such as cone inner segments and retinal ganglion cells layer neurons. Here, we propose a 2D optical model showing that the phase contrast produced by these methods depends on the offset orientation. While one axis provides an asymmetric light distribution, hence a high phase contrast, the perpendicular axis provides a symmetric one, thus a substantially lower contrast. We support this model with in-vivo human data acquired with a multi-offset AO scanning light ophthalmoscope. Then, using this finding, we provide a post-processing method, named Spatial frequency-based iMAge ReconsTruction (SMART), to optimally combine images from different off-axis detector orientations, significantly increasing the structural cellular contrast of in-vivo human retinal neurons such as conne inner segment, putative rods and retinal ganglion cells.

Observation of biological macromolecules using various electron microscopic methods

1978 ◽  
Vol 36 (2) ◽  
pp. 170-171
Author(s):  
Mitsuo Ohtsuki ◽  
Michael Sogard
Keyword(s):  
Electron Microscope ◽  
Phase Contrast ◽  
Image Interpretation ◽  
Density Lipoprotein ◽  
Biological Macromolecules ◽  
Contrast Effects ◽  
Biological Structure ◽  
Electron Microscopic ◽  
Structural Investigations ◽  
Staining Techniques

Structural investigations of biological macromolecules commonly employ CTEM with negative staining techniques. Difficulties in valid image interpretation arise, however, due to problems such as variability in thickness and degree of penetration of the staining agent, noise from the supporting film, and artifacts from defocus phase contrast effects. In order to determine the effects of these variables on biological structure, as seen by the electron microscope, negative stained macromolecules of high density lipoprotein-3 (HDL3) from human serum were analyzed with both CTEM and STEM, and results were then compared with CTEM micrographs of freeze-etched HDL3. In addition, we altered the structure of this molecule by digesting away its phospholipid component with phospholipase A2 and look for consistent changes in structure.

Analysis of STEM micrographs of thick objects

1978 ◽  
Vol 36 (2) ◽  
pp. 106-107
Author(s):  
S. Golladay
Keyword(s):  
Inelastic Scattering ◽  
Multiple Scattering ◽  
Mass Distribution ◽  
Cross Sections ◽  
Phase Contrast ◽  
Image Point ◽  
Contrast Effects ◽  
Total Cross Sections ◽  
Elastic And Inelastic Scattering

The theory of multiple scattering has been worked out by Groves and comparisons have been made between predicted and observed signals for thick specimens observed in a STEM under conditions where phase contrast effects are unimportant. Independent measurements of the collection efficiencies of the two STEM detectors, calculations of the ratio σe/σi = R, where σe, σi are the total cross sections for elastic and inelastic scattering respectively, and a model of the unknown mass distribution are needed for these comparisons. In this paper an extension of this work will be described which allows the determination of the required efficiencies, R, and the unknown mass distribution from the data without additional measurements or models. Essential to the analysis is the fact that in a STEM two or more signal measurements can be made simultaneously at each image point.

The Imaging of Crystal Structures and Crystal Defects

1978 ◽  
Vol 36 (3) ◽  
pp. 207-217
Author(s):  
J.M. Cowley
Keyword(s):  
Electron Microscope ◽  
Crystal Structures ◽  
Phase Contrast ◽  
Crystal Defects ◽  
Atom Density ◽  
Lack Of Information ◽  
Spatial Frequencies

The problem of "understandinq" electron microscope imaqes becomes more acute as the resolution is improved. The naive interpretation of an imaqe as representinq the projection of an atom density becomes less and less appropriate. We are increasinqly forced to face the complexities of coherent imaqinq of what are essentially phase objects. Most electron microscopists are now aware that, for very thin weakly scatterinq objects such as thin unstained bioloqical specimens, hiqh resolution imaqes are best obtained near the optimum defocus, as prescribed by Scherzer, where the phase contrast imaqe qives a qood representation of the projected potential, apart from a lack of information on the lower spatial frequencies. But phase contrast imaqinq is never simple except in idealized limitinq cases.

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