24,723 research outputs found
High Dynamic Range Imaging with Context-aware Transformer
Avoiding the introduction of ghosts when synthesising LDR images as high
dynamic range (HDR) images is a challenging task. Convolutional neural networks
(CNNs) are effective for HDR ghost removal in general, but are challenging to
deal with the LDR images if there are large movements or
oversaturation/undersaturation. Existing dual-branch methods combining CNN and
Transformer omit part of the information from non-reference images, while the
features extracted by the CNN-based branch are bound to the kernel size with
small receptive field, which are detrimental to the deblurring and the recovery
of oversaturated/undersaturated regions. In this paper, we propose a novel
hierarchical dual Transformer method for ghost-free HDR (HDT-HDR) images
generation, which extracts global features and local features simultaneously.
First, we use a CNN-based head with spatial attention mechanisms to extract
features from all the LDR images. Second, the LDR features are delivered to the
Hierarchical Dual Transformer (HDT). In each Dual Transformer (DT), the global
features are extracted by the window-based Transformer, while the local details
are extracted using the channel attention mechanism with deformable CNNs.
Finally, the ghost free HDR image is obtained by dimensional mapping on the HDT
output. Abundant experiments demonstrate that our HDT-HDR achieves the
state-of-the-art performance among existing HDR ghost removal methods.Comment: 8 pages, 5 figure
Modeling and removal of optical ghosts in the PROBA-3/ASPIICS externally occulted solar coronagraph
Context: ASPIICS is a novel externally occulted solar coronagraph, which will
be launched onboard the PROBA-3 mission of the European Space Agency. The
external occulter will be placed on the first satellite approximately 150 m
ahead of the second satellite that will carry an optical instrument. During 6
hours per orbit, the satellites will fly in a precise formation, constituting a
giant externally occulted coronagraph. Large distance between the external
occulter and the primary objective will allow observations of the white-light
solar corona starting from extremely low heights 1.1RSun. Aims: To analyze
influence of optical ghost images formed inside the telescope and develop an
algorithm for their removal. Methods: We implement the optical layout of
ASPIICS in Zemax and study the ghost behaviour in sequential and non-sequential
regimes. We identify sources of the ghost contributions and analyze their
geometrical behaviour. Finally we develop a mathematical model and software to
calculate ghost images for any given input image. Results: We show that ghost
light can be important in the outer part of the field of view, where the
coronal signal is weak, since the energy of bright inner corona is
redistributed to the outer corona. However the model allows to remove the ghost
contribution. Due to a large distance between the external occulter and the
primary objective, the primary objective does not produce a significant ghost.
The use of the Lyot spot in ASPIICS is not necessary.Comment: 14 pages, 13 figure
Temporal phase unwrapping using deep learning
The multi-frequency temporal phase unwrapping (MF-TPU) method, as a classical
phase unwrapping algorithm for fringe projection profilometry (FPP), is capable
of eliminating the phase ambiguities even in the presence of surface
discontinuities or spatially isolated objects. For the simplest and most
efficient case, two sets of 3-step phase-shifting fringe patterns are used: the
high-frequency one is for 3D measurement and the unit-frequency one is for
unwrapping the phase obtained from the high-frequency pattern set. The final
measurement precision or sensitivity is determined by the number of fringes
used within the high-frequency pattern, under the precondition that the phase
can be successfully unwrapped without triggering the fringe order error.
Consequently, in order to guarantee a reasonable unwrapping success rate, the
fringe number (or period number) of the high-frequency fringe patterns is
generally restricted to about 16, resulting in limited measurement accuracy. On
the other hand, using additional intermediate sets of fringe patterns can
unwrap the phase with higher frequency, but at the expense of a prolonged
pattern sequence. Inspired by recent successes of deep learning techniques for
computer vision and computational imaging, in this work, we report that the
deep neural networks can learn to perform TPU after appropriate training, as
called deep-learning based temporal phase unwrapping (DL-TPU), which can
substantially improve the unwrapping reliability compared with MF-TPU even in
the presence of different types of error sources, e.g., intensity noise, low
fringe modulation, and projector nonlinearity. We further experimentally
demonstrate for the first time, to our knowledge, that the high-frequency phase
obtained from 64-period 3-step phase-shifting fringe patterns can be directly
and reliably unwrapped from one unit-frequency phase using DL-TPU
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