96,675 research outputs found
Image enhancement methods and applications in computational photography
Computational photography is currently a rapidly developing and cutting-edge topic in applied optics, image sensors and image processing fields to go beyond the limitations of traditional photography. The innovations of computational photography allow the photographer not only merely to take an image, but also, more importantly, to perform computations on the captured image data. Good examples of these innovations include high dynamic range imaging, focus stacking, super-resolution, motion deblurring and so on. Although extensive work has been done to explore image enhancement techniques in each subfield of computational photography, attention has seldom been given to study of the image enhancement technique of simultaneously extending depth of field and dynamic range of a scene. In my dissertation, I present an algorithm which combines focus stacking and high dynamic range (HDR) imaging in order to produce an image with both extended depth of field (DOF) and dynamic range than any of the input images. In this dissertation, I also investigate super-resolution image restoration from multiple images, which are possibly degraded by large motion blur. The proposed algorithm combines the super-resolution problem and blind image deblurring problem in a unified framework. The blur kernel for each input image is separately estimated. I also do not make any restrictions on the motion fields among images; that is, I estimate dense motion field without simplifications such as parametric motion. While the proposed super-resolution method uses multiple images to enhance spatial resolution from multiple regular images, single image super-resolution is related to techniques of denoising or removing blur from one single captured image. In my dissertation, space-varying point spread function (PSF) estimation and image deblurring for single image is also investigated. Regarding the PSF estimation, I do not make any restrictions on the type of blur or how the blur varies spatially. Once the space-varying PSF is estimated, space-varying image deblurring is performed, which produces good results even for regions where it is not clear what the correct PSF is at first. I also bring image enhancement applications to both personal computer (PC) and Android platform as computational photography applications
Multi-plane super-resolution microscopy
Understanding cell functions is the major goal of molecular biology, which intends to elucidate the interactions between biomolecules at a subcellular level. One of the widely used techniques in molecular biology is fluorescence microscopy, which offers high specificity and sensitivity at the submicrometer spatial scale but is limited by diffraction to about 200nm lateral resolution, which is insufficient for the observation of many molecular processes. During the last two decades several super-resolution techniques overcoming the diffraction limit have been developed. However, imaging samples in three dimensions (3D) at high speed remains a challenging and not yet resolved task. This thesis focuses on enhancing super-resolution imaging towards fast, live-cell and 3D imaging. Super-resolution optical fluctuation imaging (SOFI) is a technique based on the stochastic fluctuations of photoswitchable fluorescent markers. It possesses several unique features such as background reduction, capability of increased pixel grid generation, i.e. spatial oversampling, as well as tolerance and robustness to a wide range of photoswitching conditions. In this thesis SOFI was extended to perform 3D analysis. As a result, the resolution in all three spatial dimensions can be improved and the depth sampling increased. We present a novel design of a 3D fluorescence microscope capable of acquiring images of eight depth planes simultaneously. This design incorporates an image-splitting prism, a single optical element allowing to achieve in-depth image separation. The optical performance of the 3D microscope was described and experimentally verified. The simultaneous depth plane acquisition allows to fully exploit the 3D capabilities of SOFI while generating additional virtual depth planes. An algorithm for the extraction of switching kinetics of fluorescent markers is presented. Using appropriate imaging conditions, we demonstrate the applications of 3D SOFI on several examples of fixed and living cells. We also present the potential of the 3D microscope for phase retrieval in transparent samples
Plasmonic photoconductive terahertz focal-plane array with pixel super-resolution
Imaging systems operating in the terahertz part of the electromagnetic
spectrum are in great demand because of the distinct characteristics of
terahertz waves in penetrating many optically-opaque materials and providing
unique spectral signatures of various chemicals. However, the use of terahertz
imagers in real-world applications has been limited by the slow speed, large
size, high cost, and complexity of the existing imaging systems. These
limitations are mainly imposed due to the lack of terahertz focal-plane arrays
(THz-FPAs) that can directly provide the frequency-resolved and/or
time-resolved spatial information of the imaged objects. Here, we report the
first THz-FPA that can directly provide the spatial amplitude and phase
distributions, along with the ultrafast temporal and spectral information of an
imaged object. It consists of a two-dimensional array of ~0.3 million plasmonic
photoconductive nanoantennas optimized to rapidly detect broadband terahertz
radiation with a high signal-to-noise ratio. As the first proof-of-concept, we
utilized the multispectral nature of the amplitude and phase data captured by
these plasmonic nanoantennas to realize pixel super-resolution imaging of
objects. We successfully imaged and super-resolved etched patterns in a silicon
substrate and reconstructed both the shape and depth of these structures with
an effective number of pixels that exceeds 1-kilo pixels. By eliminating the
need for raster scanning and spatial terahertz modulation, our THz-FPA offers
more than a 1000-fold increase in the imaging speed compared to the
state-of-the-art. Beyond this proof-of-concept super-resolution demonstration,
the unique capabilities enabled by our plasmonic photoconductive THz-FPA offer
transformative advances in a broad range of applications that use hyperspectral
and three-dimensional terahertz images of objects for a wide range of
applications.Comment: 62 page
Acoustical structured illumination for super-resolution ultrasound imaging.
Structured illumination microscopy is an optical method to increase the spatial resolution of wide-field fluorescence imaging beyond the diffraction limit by applying a spatially structured illumination light. Here, we extend this concept to facilitate super-resolution ultrasound imaging by manipulating the transmitted sound field to encode the high spatial frequencies into the observed image through aliasing. Post processing is applied to precisely shift the spectral components to their proper positions in k-space and effectively double the spatial resolution of the reconstructed image compared to one-way focusing. The method has broad application, including the detection of small lesions for early cancer diagnosis, improving the detection of the borders of organs and tumors, and enhancing visualization of vascular features. The method can be implemented with conventional ultrasound systems, without the need for additional components. The resulting image enhancement is demonstrated with both test objects and ex vivo rat metacarpals and phalanges
The Devil is in the Decoder: Classification, Regression and GANs
Many machine vision applications, such as semantic segmentation and depth
prediction, require predictions for every pixel of the input image. Models for
such problems usually consist of encoders which decrease spatial resolution
while learning a high-dimensional representation, followed by decoders who
recover the original input resolution and result in low-dimensional
predictions. While encoders have been studied rigorously, relatively few
studies address the decoder side. This paper presents an extensive comparison
of a variety of decoders for a variety of pixel-wise tasks ranging from
classification, regression to synthesis. Our contributions are: (1) Decoders
matter: we observe significant variance in results between different types of
decoders on various problems. (2) We introduce new residual-like connections
for decoders. (3) We introduce a novel decoder: bilinear additive upsampling.
(4) We explore prediction artifacts
Light Field Super-Resolution Via Graph-Based Regularization
Light field cameras capture the 3D information in a scene with a single
exposure. This special feature makes light field cameras very appealing for a
variety of applications: from post-capture refocus, to depth estimation and
image-based rendering. However, light field cameras suffer by design from
strong limitations in their spatial resolution, which should therefore be
augmented by computational methods. On the one hand, off-the-shelf single-frame
and multi-frame super-resolution algorithms are not ideal for light field data,
as they do not consider its particular structure. On the other hand, the few
super-resolution algorithms explicitly tailored for light field data exhibit
significant limitations, such as the need to estimate an explicit disparity map
at each view. In this work we propose a new light field super-resolution
algorithm meant to address these limitations. We adopt a multi-frame alike
super-resolution approach, where the complementary information in the different
light field views is used to augment the spatial resolution of the whole light
field. We show that coupling the multi-frame approach with a graph regularizer,
that enforces the light field structure via nonlocal self similarities, permits
to avoid the costly and challenging disparity estimation step for all the
views. Extensive experiments show that the new algorithm compares favorably to
the other state-of-the-art methods for light field super-resolution, both in
terms of PSNR and visual quality.Comment: This new version includes more material. In particular, we added: a
new section on the computational complexity of the proposed algorithm,
experimental comparisons with a CNN-based super-resolution algorithm, and new
experiments on a third datase
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