2,153 research outputs found
Precise correction of lateral chromatic aberration in images
International audienceThis paper addresses the problem of lateral chromatic aberration correction in images through color planes warping. We aim at high precision (largely sub-pixel) realignment of color channels. This is achieved thanks to two ingredients: high precision keypoint detection, which in our case are disk centers, and more general correction model than what is commonly used in the literature, radial polynomial. Our setup is quite easy to implement, requiring a pattern of black disks on white paper and a single snapshot. We measure the errors in terms of geometry and of color and compare our method to three different software programs. Quantitative results on real images show that our method allows alignment of average 0.05 pixel of color channels and a residual color error divided by a factor 3 to 6
Calibration and removal of lateral chromatic aberration in images
This paper addresses the problem of compensating for lateral chromatic aberration in digital images through colour plane realignment. Two main contributions are made: the derivation of a model for lateral chromatic aberration in images, and the subsequent calibration of this model from a single view of a chess pattern. These advances lead to a practical and accurate alternative for the compensation of lateral chromatic aberrations. Experimental results validate the proposed models and calibration algorithm. The effects of colour channel correlations resulting from the camera colour filter array interpolation is examined and found to have a negligible magnitude relative to the chromatic aberration. Results with real data show how the removal of lateral chromatic aberration significantly improves the colour quality of the image
Diffractive X-ray Telescopes
Diffractive X-ray telescopes using zone plates, phase Fresnel lenses, or
related optical elements have the potential to provide astronomers with true
imaging capability with resolution several orders of magnitude better than
available in any other waveband. Lenses that would be relatively easy to
fabricate could have an angular resolution of the order of micro-arc-seconds or
even better, that would allow, for example, imaging of the distorted space-
time in the immediate vicinity of the super-massive black holes in the center
of active galaxies What then is precluding their immediate adoption? Extremely
long focal lengths, very limited bandwidth, and difficulty stabilizing the
image are the main problems. The history, and status of the development of such
lenses is reviewed here and the prospects for managing the challenges that they
present are discussed.Comment: 46 pages, 15 figures, invited review paper to be published in a
special issue on "X-Ray Focusing: Techniques and Applications" of the online
journal "X-Ray Optics & Instrumentation
Correction of spherical single lens aberration using digital image processing for cellular phone camera
制度:新 ; 報告番号:甲3276号 ; 学位の種類:博士(工学) ; 授与年月日:2011/2/21 ; 早大学位記番号:新558
Removing lateral chromatic aberration in bright field optical microscopy
"We present an efficient alternative to remove lateral chromatic aberration (LCA) in bright field light microscopy images. Our procedure is based on error calibration using time-sequential acquisition at different wavelengths, and error correction through digital image warping. Measurement of the displacements of fiducial marks in the red and green images relative to blue provide calibration factors that are subsequently used in test images to realign color channels digitally. We demonstrate quantitative improvement in the position and boundaries of objects in target slides and in the color content and morphology of specimens in stained biological samples. Our results show a reduction of LCA content below the 0.1% level.
Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. II. Concept validation with ZELDA on VLT/SPHERE
Warm or massive gas giant planets, brown dwarfs, and debris disks around
nearby stars are now routinely observed by dedicated high-contrast imaging
instruments on large, ground-based observatories. These facilities include
extreme adaptive optics (ExAO) and state-of-the-art coronagraphy to achieve
unprecedented sensitivities for exoplanet detection and spectral
characterization. However, differential aberrations between the ExAO sensing
path and the science path represent a critical limitation for the detection of
giant planets with a contrast lower than a few at very small
separations (<0.3\as) from their host star. In our previous work, we proposed a
wavefront sensor based on Zernike phase contrast methods to circumvent this
issue and measure these quasi-static aberrations at a nanometric level. We
present the design, manufacturing and testing of ZELDA, a prototype that was
installed on VLT/SPHERE during its reintegration in Chile. Using the internal
light source of the instrument, we performed measurements in the presence of
Zernike or Fourier modes introduced with the deformable mirror. Our
experimental and simulation results are consistent, confirming the ability of
our sensor to measure small aberrations (<50 nm rms) with nanometric accuracy.
We then corrected the long-lived non-common path aberrations in SPHERE based on
ZELDA measurements. We estimated a contrast gain of 10 in the coronagraphic
image at 0.2\as, reaching the raw contrast limit set by the coronagraph in the
instrument. The simplicity of the design and its phase reconstruction algorithm
makes ZELDA an excellent candidate for the on-line measurements of quasi-static
aberrations during the observations. The implementation of a ZELDA-based
sensing path on the current and future facilities (ELTs, future space missions)
could ease the observation of the cold gaseous or massive rocky planets around
nearby stars.Comment: 13 pages, 12 figures, A&A accepted on June 3rd, 2016. v2 after
language editin
Fast Two-step Blind Optical Aberration Correction
The optics of any camera degrades the sharpness of photographs, which is a
key visual quality criterion. This degradation is characterized by the
point-spread function (PSF), which depends on the wavelengths of light and is
variable across the imaging field. In this paper, we propose a two-step scheme
to correct optical aberrations in a single raw or JPEG image, i.e., without any
prior information on the camera or lens. First, we estimate local Gaussian blur
kernels for overlapping patches and sharpen them with a non-blind deblurring
technique. Based on the measurements of the PSFs of dozens of lenses, these
blur kernels are modeled as RGB Gaussians defined by seven parameters. Second,
we remove the remaining lateral chromatic aberrations (not contemplated in the
first step) with a convolutional neural network, trained to minimize the
red/green and blue/green residual images. Experiments on both synthetic and
real images show that the combination of these two stages yields a fast
state-of-the-art blind optical aberration compensation technique that competes
with commercial non-blind algorithms.Comment: 28 pages, 20 figures, accepted at ECCV'22 as a poste
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