During recent years, the use of fringe projection techniques for generating three-dimensional (3D) surface information has become one of the most active research areas in optical metrology. Its applications range from measuring the 3D shape of MEMS components to the measurement of flatness of large panels (2.5 m × .45 m). The technique has found various applications in diverse fields: biomedical applications such as 3D intra-oral dental measurements [1], non-invasive 3D imaging and monitoring of vascular wall deformations [2], human body shape measurement for shape guided radiotherapy treatment [3,4], lower back deformation measurement [5], detection and monitoring of scoliosis [6], inspection of wounds [7,8] and skin topography measurement for use in cosmetology [9,10, 11]; industrial and scientific applications such as characterization of MEMS components [12,13], vibration analysis [14,15], refractometry [16], global measurement of free surface deformations [17,18], local wall thickness measurement of forced sheet metals [19], corrosion analysis [20,21], measurement of surface roughness [22,23], reverse engineering [24,25,26], quality control of printed circuit board manufacturing [27,28,29] and heat-flow visualization [30]; kinematics applications such as measuring the shape and position of a moving object/creature [31,32] and the study of kinematical parameters of dragonfly in free flight [33,34]; biometric identification applications such as 3D face reconstruction for the development of robust face recognition systems [35,36]; cultural heritage and preservation [37,38,39] etc.One of the outstanding features of some of the fringe projection techniques is their ability to provide high-resolution, whole-field 3D reconstruction of objects in a non-contact manner at video frame rates. This feature has backed the technique to pervade new areas of applications such as security systems, gaming and virtual reality. To gain insights into the series of contributions that have helped in unfolding the technique to acquire this feature, the reader is referred to the review articles in this special issue by Song Zhang, and Xianyu Su et al.A typical fringe projection profilometry system is shown in Fig 1. It consists of a projection unit, an image acquisition unit and a processing/analysis unit. Measurement of shape through fringe projection techniques involves (1) projecting a structured pattern (usually a sinusoidal fringe pattern) onto the object surface, (2) recording the image of the fringe pattern that is phase modulated by the object height distribution, (3) calculating the phase modulation by analyzing the image with one of the fringe analysis techniques (such as Fourier transform Figure 1: Fringe projection profilometry system method, phase stepping and spatial phase detection methodsmost of them generate wrapped phase distribution) (4) using a suitable phase unwrapping algorithm to get continuous phase distribution which is proportional to the object height variations, and finally (5) calibrating the system for m...

The combination of microscopy and flow cytometry enables image based screening of large collections of cells. Despite the proposition more than thirty years ago, adding high resolution wide-field imaging to flow cytometers remains challenging. The velocity of cells in flow cytometry can surpass a meter per second, requiring either sub-microsecond exposure times or other sophisticated photodetection techniques. Instead of faster detectors and brighter sources, we demonstrate that by imaging multiple channels simultaneously, a high throughput can be maintained with a flow velocity reduced in proportion to the degree of parallelization. The multi-field of view imaging flow cytometer (MIFC) is implemented with parallel arrays of microfluidic channels and diffractive lenses that produce sixteen wide field images with a magnification of 45 and submicron resolution. Using this device, we have imaged latex beads, red blood cells, and acute myeloid leukemia cells at rates of 2,000-20,000 per second.

This letter introduces a fluidics-based focus-stack collecting microscope. A microfluidic device transports cells through the focal plane of a microscope, resulting in an efficient method to collect focus stacks of large collections of single cells. Images from the focus stacks are used to reconstruct the quantitative phase of cells with the transport-of-intensity-equation method. Using the phase imaging flow cytometer, we measure three-dimensional shape variations of red blood and leukemia cells.

Illumination plays an important role in optical microscopy. Köhler illumination, introduced more than a century ago, has been the backbone of optical microscopes. The last few decades have seen the evolution of new illumination techniques meant to improve certain imaging capabilities of the microscope. Most of them are, however, not amenable for wide-field observation and hence have restricted use in microscopy applications such as cell biology and microscale profile measurements. The method of structured illumination microscopy has been developed as a wide-field technique for achieving higher performance. Additionally, it is also compatible with existing microscopes. This method consists of modifying the illumination by superposing a well-defined pattern on either the sample itself or its image. Computational techniques are applied on the resultant images to remove the effect of the structure and to obtain the desired performance enhancement. This method has evolved over the last two decades and has emerged as a key illumination technique for optical sectioning, super-resolution imaging, surface profiling, and quantitative phase imaging of microscale objects in cell biology and engineering. In this review, we describe various structured illumination methods in optical microscopy and explain the principles and technologies involved therein.

Imaging fluorescence in moving cells is fundamentally challenging because the exposure time is constrained by motion-blur, which limits the available signal. We report a method to image fluorescently labeled leukemia cells in fluid flow that has an effective exposure time of up to 50 times the motion-blur limit. Flowing cells are illuminated with a pseudo-random excitation pulse sequence, resulting in a motion-blur that can be computationally removed to produce near diffraction-limited images. This method enables observation of cellular organelles and their behavior in a fluid environment that resembles the vasculature.