Speckle photography technique [1] is an optical diagnostic method to measure nonintrusively the refractive index gradients of inhomogeneous medium, also called a phase object, based on light ray refraction and deflection. The dislocations of speckle images result from the flow-particle displacement in PIV.
How does speckle imaging work?
Speckle imaging recreates the original image through image processing techniques. In images at this time scale, or smaller, the movement of the atmosphere is too sluggish to have an effect; the speckles recorded in the image are a snapshot of the atmospheric seeing at that instant.
Who invented speckle imaging?
In the 1970s, Antonine Laberyrie first developed the method for developing high-resolution astronomical photos that were limited by blurring from the atmosphere. Labreyrie demonstrated quick, short exposures produced ‘speckled’ grainy results.
How does laser speckle imaging work?
Laser Speckle Contrast Imaging (LSCI) is a simple yet powerful technique that is used for full-field imaging of blood flow. The technique analyzes fluctuations in a dynamic speckle pattern to detect the movement of particles similar to how laser Doppler analyzes frequency shifts to determine particle speed.
What is speckle noise in image?
Speckle noise is the noise that arises due to the effect of environmental conditions on the imaging sensor during image acquisition. Speckle noise is mostly detected in case of medical images, active Radar images and Synthetic Aperture Radar (SAR) images.
Who introduced the principle of speckle interferometry in 1970?
A noisy, random granular speckle pattern is also a carrier of important information. The first metrolog- ical application using a speckle pattern was published by Groh [23. 4] in 1970. Today, speckle metrology is an important and rapidly growing area of optical metrology in experimental mechanics.
How do you stop a laser speckle?
The speckle generated by the diffuser is used to vary the phase of the illumination of the rough object. One method to reduce speckle involves scanning a beam on a diffuser rather than scanning the diffuser on the beam.
What causes speckle in laser?
When laser light illuminates a diffuse object, it produces a random interference effect known as a speckle pattern. If there is movement in the object, the speckles fluctuate in intensity. These fluctuations can provide information about the movement.
How does speckle interferometry work?
The basic principle of speckle interferometry involves the comparison of speckle patterns recorded before and after a load or displacement is applied to the component under test. Correlation of the speckle patterns produces a fringe pattern, with the fringes representing a contour map of the measurand.
How do I stop speckle?
Speckle reduction A second method involves using adaptive and non-adaptive filters on the signal processing (where adaptive filters adapt their weightings across the image to the speckle level, and non-adaptive filters apply the same weightings uniformly across the entire image).
How do you stop the speckle artifact?
Speckle can be decreased with proprietary postprocessing algorithms (speckle reduction imaging) on most modern US units (Fig 5). Spatial compounding and THI also reduce speckle.
What causes laser speckle?
Speckle occurs because the laser light is temporally coherent and is scattered from a random surface. The random surface causes a large number of wavelets to leave the object and overlap in space, each wavelet having a random phase relationship to all the others.
What is speckle imaging and how does it work?
Speckle imaging describes a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add (” image stacking “) method and the speckle interferometry methods.
How do speckles appear on a star image?
The speckles move around rapidly, so that each star appears as a single fuzzy blob in long exposure images. Slow-motion speckle imaging movie, showing how a high-magnification (negative) image of a star breaks up into multiple blobs (speckles), entirely an atmospheric effect.
What is Fourier analysis ( speckle analysis)?
In 1970, the French astronomer Antoine Labeyrie showed that Fourier analysis ( speckle interferometry) can obtain information about the high-resolution structure of the object from the statistical properties of the speckle patterns. Methods developed in the 1980s allowed simple images to be reconstructed from this power spectrum information.
