Tomographic Diffraction Microscopy (TDM) is a technique that makes it possible to assess for 3D complex refractive index of the investigated sample without fluorescent labeling. Therefore, TDM is a method of choice for the characterization of biological samples or functionalized surfaces. TDM is a generalization of Digital Holographic Microscopy with a full control of the angle of illumination over the object. Angle can be modified either by sweeping the illumination on the object, or by rotating the object while maintaining the angle of illumination. Combining several hundreds of acquisition, it is possible to retrieve a full 3D information about both refraction and absorption of the object. Nevertheless, the time needed for data acquisition might become prohibitive for routine investigations, or dynamic sample imaging. Moreover, simultaneous reflection and transmission characterization of sample remains an experimental challenge. Recently a method called “Mirror-Assisted Tomographic Diffraction Microscopy” (MA-TDM) have been proposed [Opt. Lett. 35, 1857 (2010)], which theoretically allows to achieved isotropic 3D resolution by combining, in a simpler fashion, reflection and transmission modes. When transparent sample are considered, one can take benefits of this mirroring effect to limit the amount of acquired holograms, while maintaining the resolution of TDM. We propose to demonstrate this concept, using a specific preparation of the sample. It will be shown that, using an adequate data processing scheme, it is possible to reconstruct 3D objects using an annular illumination sweep, thus limiting the amount of acquisition. This study paves the way to a versatile TDM configuration allowing for both reflection and transmission acquisitions from a single image acquisition.
This work shows the interests of the refocusing technics in the domain of industrial vision. A prototype of light field camera is used for computing refocused images, which are calibrated in depth. These images are computed with a method previously presented, using a multi-view camera modeled following the “variable homography” principles. The camera prototype is composed by 4 mini-lenses placed behind a single CCD sensor, calibrated and able to perform 3D measurements. As the device is calibrated in depth, we link refocused images to a selected depth. Contrary to the conventional imaging, with refocused depth calibrated images, it is possible to highlight planes of interest to facilitate vision inspection. Objects can be distinguished from others according to their depths. We also show that a pixel metric scale can be estimated at different depths, avoiding the use of other measurement devices. Two standard vision examples are presented to illustrate the interests of this approach.
KEYWORDS: Image resolution, Time division multiplexing, Spatial resolution, 3D image processing, Image resolution, 3D acquisition, Digital holography, Microscopes, 3D displays
Tomographic diffractive microscopy allows for imaging unlabeled specimens, with a better resolution than conventional microscopes, giving access to the index of refraction distribution within the specimen, and possibly at high speed. Principles of image formation and reconstruction are presented, and progresses towards realtime, three-dimensional acquisition, image reconstruction and final display, are discussed, as well as towards three-dimensional isotropic-resolution imaging.
We propose a model of depth camera based on a four-lens device. This device is used for validating alternate approaches for calibrating multiview cameras and also for computing disparity or depth images. The calibration method arises from previous works, where principles of variable homography were extended for three-dimensional (3-D) measurement. Here, calibration is performed between two contiguous views obtained on the same image sensor. This approach leads us to propose a new approach for simplifying calibration by using the properties of the variable homography. Here, the second part addresses new principles for obtaining disparity images without any matching. A fast algorithm using a contour propagation algorithm is proposed without requiring structured or random pattern projection. These principles are proposed in a framework of quality control by vision, for inspection in natural illumination. By preserving scene photometry, some other standard controls, as for example calipers, shape recognition, or barcode reading, can be done conjointly with 3-D measurements. Approaches presented here are evaluated. First, we show that rapid calibration is relevant for devices mounted with multiple lenses. Second, synthetic and real experimentations validate our method for computing depth images.
In previous works, we have extended the principles of “variable homography”, defined by Zhang and Greenspan, for measuring height of emergent fibers on glass and non-woven fabrics. This method has been defined for working with fabric samples progressing on a conveyor belt. Triggered acquisition of two successive images was needed to perform the 3D measurement. In this work, we have retained advantages of homography variable for measurements along Z axis, but we have reduced acquisitions number to a single one, by developing an acquisition device characterized by 4 lenses placed in front of a single image sensor. The idea is then to obtain four projected sub-images on a single CCD sensor. The device becomes a plenoptic or light field camera, capturing multiple views on the same image sensor. We have adapted the variable homography formulation for this device and we propose a new formulation to calculate a depth with plenoptic cameras. With these results, we have transformed our plenoptic camera in a depth camera and first results given are very promising.
The 3-D fluorescence microscope is a powerful method for imaging and studying living cells. However, the data
acquired with conventional 3-D fluorescence microscope are not quantitatively significant for spatial distribution or
volume evaluation of fluorescent areas in reason of distortions induced on data by the acquisition process.
Theses distortions must be corrected for reliable measurements. The knowledge of the impulse response
characterizing the instrument permits to consider the backward process retrieving the original data. One realize a
deconvolution opposed to the convolution process induced by the microscope, projecting the 'object' space in the
'image' space. However, when the response of the system is not invariant in the observation field, the classical
algorithms using Fourier Transform for computations are not usable.
The contribution of this work is to present several approaches making it possible to use the Fourier Transform
in non-invariance conditions and to simulate it's application in the 3-D fluorescence microscope problems.
3-D optical fluorescent microscopy becomes now an efficient tool for volume investigation of living biological samples.
Developments in instrumentation have permit to beat off the conventional Abbe limit, in any case the recorded image
can be described by the convolution equation between the original object and the Point Spread Function (PSF) of the
acquisition system. If the goal is 3-D quantitative analysis, whether you improve the instrument capabilities, or (and)
you restore the data. These last is until now the main task in our laboratory. Based on the knowledge of the optical
Transfer Function of the microscope, deconvolution algorithms were adapted to automatic determine the regularisation
threshold in order to give less subjective and more reproducible results. The PSF represents the properties of the image
acquisition system; we have proposed the use of statistical tools and Zernike moments to describe a 3-D system PSF and
to quantify the variation of the PSF. This first step toward standardization is helpful to define an acquisition protocol
optimizing exploitation of the microscope depending on the studied biological sample.
We have pointed out that automating the choice of the regularization level; if it facilitates the use, it also greatly
improves the reliability of the measurements. Furthermore, to increase the quality and the repeatability of quantitative
measurements a pre-filtering of images improves the stability of deconvolution process. In the same way, the PSF pre-filtering
stabilizes the deconvolution process. We have shown that Zernike polynomials can be used to reconstruct
experimental PSF, preserving system characteristics and removing the noise contained in the PSF.
Fluorescent microscopes suffer from limitations; photobleaching and phototoxicity effects, or influence of the sample
optical properties to 3-D observation. Amplitude and phase of the object can be reached with optical tomography based
on a combination of microholography with a tomographic illumination. So indices cartography of the specimen can be
obtained, and combined with fluorescence information it will open new possibilities in 3-D optical microscopy.
KEYWORDS: Point spread functions, Deconvolution, Luminescence, Microscopes, Image processing, 3D acquisition, 3D image processing, Microscopy, Image acquisition, Algorithm development
3-D optical fluorescent microscopy now becomes an efficient tool for the volume investigation of living biological
samples. Developments in instrumentation have permitted to beat off the conventional Abbe limit. In any case the
recorded image can be described by the convolution equation between the original object and the Point Spread Function
(PSF) of the acquisition system. Due to the finite resolution of the instrument, the original object is recorded with
distortions and blurring, and contaminated by noise. This induces that relevant biological information cannot be
extracted directly from raw data stacks.
If the goal is 3-D quantitative analysis, then to assess optimal performance of the instrument and to ensure the data
acquisition reproducibility, the system characterization is mandatory. The PSF represents the properties of the image
acquisition system; we have proposed the use of statistical tools and Zernike moments to describe a 3-D PSF system and
to quantify the variation of the PSF. This first step toward standardization is helpful to define an acquisition protocol
optimizing exploitation of the microscope depending on the studied biological sample.
Before the extraction of geometrical information and/or intensities quantification, the data restoration is mandatory.
Reduction of out-of-focus light is carried out computationally by deconvolution process. But other phenomena occur
during acquisition, like fluorescence photo degradation named "bleaching", inducing an alteration of information
needed for restoration. Therefore, we have developed a protocol to pre-process data before the application of
deconvolution algorithms.
A large number of deconvolution methods have been described and are now available in commercial package. One
major difficulty to use this software is the introduction by the user of the "best" regularization parameters. We have
pointed out that automating the choice of the regularization level; also greatly improves the reliability of the
measurements although it facilitates the use. Furthermore, to increase the quality and the repeatability of quantitative
measurements a pre-filtering of images improves the stability of deconvolution process. In the same way, the PSF prefiltering
stabilizes the deconvolution process. We have shown that Zemike polynomials can be used to reconstruct
experimental PSF, preserving system characteristics and removing the noise contained in the PSF.
KEYWORDS: Point spread functions, Deconvolution, Luminescence, Microscopy, 3D image processing, Data acquisition, 3D acquisition, Signal to noise ratio, Optical microscopy, Spindles
3-D optical fluorescence microscopy is an efficient tool for volumic investigation of biological samples. Nevertheless the image acquired by this way is altered by the properties of the microscope, according to its Point Spread Function (PSF). The aim of deconvolution algorithms is the reassignment of defocused information. This method provides an improvement in data quality and the possibility to compare specimens acquired using different systems. But deconvolution requires making a compromise between the precision of the result and the stability of the process, since this stability is directly related to the noise level of the data. This noise can be of different types, mainly electronic noise due to the sensors but we also include in the term "noise" the variation of fluorescence during the acquisition. Numerous deconvolution algorithms exist, giving variable results according to specimen characteristics. For the cases where deconvolution is not enough to obtain usable data, we developed some pre-process treatments. These tools can be used separately or consecutively depending on the application needs and specimen requirements.
3-D optical fluorescent microscopy becomes now an efficient tool for volumic investigation of living biological samples. The 3-D data can be acquired by Optical Sectioning Microscopy which is performed by axial stepping of the object versus the objective. For any instrument, each recorded image can be described by a convolution equation between the original object and the Point Spread Function (PSF) of the acquisition system. To assess performance and ensure the data reproducibility, as for any 3-D quantitative analysis, the system indentification is mandatory. The PSF explains the properties of the image acquisition system; it can be computed or acquired experimentally. Statistical tools and Zernike moments are shown appropriate and complementary to describe a 3-D system PSF and to quantify the variation of the PSF as function of the optical parameters. Some critical experimental parameters can be identified with these tools. This is helpful for biologist to define an aquisition protocol optimizing the use of the system. Reduction of out-of-focus light is the task of 3-D microscopy; it is carried out computationally by deconvolution process. Pre-filtering the images improves the stability of deconvolution results, now less dependent on the regularization parameter; this helps the biologists to use restoration process.
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