172,235 research outputs found
Spectrally Based Material Color Equivalency: Modeling and Manipulation
A spectrally based normalization methodology (Wpt normalization) for linearly transforming cone excitations or sensor values (sensor excitations) to a representation that preserves the perceptive concepts of lightness, chroma and hue is proposed resulting in a color space with the axes labeled W , p, t. Wpt (pronounced “Waypoint ) has been demonstrated to be an effective material color equivalency space that provides the basis for defining Material Adjustment Transforms that predict the changes in sensor excitations of material spectral reflectance colors due to variations in observer or illuminant. This is contrasted with Chromatic Adaptation Transforms that predict color appearance as defined by corresponding color experiments. Material color equivalency as provided by Wpt and Wpt normalization forms the underlying foundation of this doctoral research. A perceptually uniform material color equivalency space (“Waypoint Lab or WLab) was developed that represents a non-linear transformation of Wpt coordinates, and Euclidean WLab distances were found to not be statistically different from ∆E⋆94 and ∆E00 color differences. Sets of Wpt coordinates for variations in reflectance, illumination, or observers were used to form the basis of defining Wpt shift manifolds. WLab distances of corresponding points within or between these manifolds were utilized to define metrics for color inconstancy, metamerism, observer rendering, illuminant rendering, and differences in observing conditions. Spectral estimation and manipulation strategies are presented that preserve various aspects of “Wpt shift potential as represented by changes in Wpt shift manifolds. Two methods were explored for estimating Wpt normalization matrices based upon direct utilization of sensor excitations, and the use of a Wpt based Material Adjustment Transform to convert Cone Fundamentals to ”XYZ-like Color Matching Functions was investigated and contrasted with other methods such as direct regression and prediction of a common color matching primaries. Finally, linear relationships between Wpt and spectral reflectances were utilized to develop approaches for spectral estimation and spectral manipulation within a general spectral reflectance manipulation framework – thus providing the ability to define and achieve “spectrally preferred color rendering objectives. The presented methods of spectral estimation, spectral manipulation, and material adjustment where utilized to: define spectral reflectances for Munsell colors that minimize Wpt shift potential; manipulate spectral reflectances of actual printed characterization data sets to achieve colorimetry of reference printing conditions; and lastly to demonstrate the spectral estimation and manipulation of spectral reflectances using images and spectrally based profiles within an iccMAX color management workflow
The Connection between Star-Forming Galaxies, AGN Host Galaxies and Early-Type Galaxies in the SDSS
We present a study of the connection between star-forming galaxies, AGN host
galaxies, and normal early-type galaxies in the Sloan Digital Sky Survey
(SDSS). Using the SDSS DR5 and DR4plus data, we select our early-type galaxy
sample in the color versus color-gradient space, and we classify the spectral
types of the selected early-type galaxies into normal, star-forming, Seyfert,
and LINER classes, using several spectral line flux ratios. We investigate the
slope in the fundamental space for each class of early-type galaxies and find
that there are obvious differences in the slopes of the fundamental planes
(FPs) among the different classes of early-type galaxies, in the sense that the
slopes for Seyferts and star-forming galaxies are flatter than those for normal
galaxies and LINERs. This may be the first identification of the systematic
variation of the FP slope among the subclasses of early-type galaxies. The
difference in the FP slope might be caused by the difference in the degree of
nonhomology among different classes or by the difference of gas contents in
their merging progenitors. One possible scenario is that the AGN host galaxies
and star-forming galaxies are formed by gas-rich merging and that they may
evolve into normal early-type galaxies after finishing their star formation or
AGN activities.Comment: 5 pages with emulateapj, 2 figures, accepted for publication in the
Astrophysical Journal Letter
The Spitzer-IRAC Point Source Catalog of the Vela-D Cloud
This paper presents the observations of the Cloud D in the Vela Molecular
Ridge, obtained with the IRAC camera onboard the Spitzer Space Telescope at the
wavelengths \lambda = 3.6, 4.5, 5.8, 8.0 {\mu}m. A photometric catalog of point
sources, covering a field of approximately 1.2 square degrees, has been
extracted and complemented with additional available observational data in the
millimeter region. Previous observations of the same region, obtained with the
Spitzer MIPS camera in the photometric bands at 24 {\mu}m and 70 {\mu}m, have
also been reconsidered to allow an estimate of the spectral slope of the
sources in a wider spectral range. A total of 170,299 point sources, detected
at the 5-sigma sensitivity level in at least one of the IRAC bands, have been
reported in the catalog. There were 8796 sources for which good quality
photometry was obtained in all four IRAC bands. For this sample, a preliminary
characterization of the young stellar population based on the determination of
spectral slope is discussed; combining this with diagnostics in the
color-magnitude and color-color diagrams, the relative population of young
stellar objects in the different evolutionary classes has been estimated and a
total of 637 candidate YSOs have been selected. The main differences in their
relative abundances have been highlighted and a brief account for their spatial
distribution is given. The star formation rate has been also estimated and
compared with the values derived for other star forming regions. Finally, an
analysis of the spatial distribution of the sources by means of the two-point
correlation function shows that the younger population, constituted by the
Class I and flat-spectrum sources, is significantly more clustered than the
Class II and III sources.Comment: Accepted by Ap
Radiometric responsivity determination for Feature Identification and Location Experiment (FILE) flown on space shuttle mission
A procedure was developed to obtain the radiometric (radiance) responsivity of the Feature Identification and Local Experiment (FILE) instrument in preparation for its flight on Space Shuttle Mission 41-G (November 1984). This instrument was designed to obtain Earth feature radiance data in spectral bands centered at 0.65 and 0.85 microns, along with corroborative color and color-infrared photographs, and to collect data to evaluate a technique for in-orbit autonomous classification of the Earth's primary features. The calibration process incorporated both solar radiance measurements and radiative transfer model predictions in estimating expected radiance inputs to the FILE on the Shuttle. The measured data are compared with the model predictions, and the differences observed are discussed. Application of the calibration procedure to the FILE over an 18-month period indicated a constant responsivity characteristic. This report documents the calibration procedure and the associated radiometric measurements and predictions that were part of the instrument preparation for flight
Hyperspectral Image Processing Using Locally Linear Embedding
We describe a method of processing hyperspectral images of natural scenes that uses a combination of k-means clustering and locally linear embedding (LLE). The primary goal is to assist anomaly detection by preserving spectral uniqueness among the pixels. In order to reduce redundancy among the pixels, adjacent pixels which are spectrally similar are grouped using the k-means clustering algorithm. Representative pixels from each cluster are chosen and passed to the LLE algorithm, where the high dimensional spectral vectors are encoded by a low dimensional mapping. Finally, monochromatic and tri-chromatic images are constructed from the k-means cluster assignments and LLE vector mappings. The method generates images where differences in the original spectra are reflected in differences in the output vector assignments. An additional benefit of mapping to a lower dimensional space is reduced data size. When spectral irregularities are added to a patch of the hyperspectral images, again the method successfully generated color assignments that detected the changes in the spectra
How good are RGB cameras retrieving colors of natural scenes and paintings?—A study based on hyperspectral imaging
RGB digital cameras (RGB) compress the spectral information into a trichromatic system capable of approximately representing the actual colors of objects. Although RGB digital cameras follow the same compression philosophy as the human eye (OBS), the spectral sensitivity is different. To what extent they provide the same chromatic experiences is still an open question, especially with complex images. We addressed this question by comparing the actual colors derived from spectral imaging with those obtained with RGB cameras. The data from hyperspectral imaging of 50 natural scenes and 89 paintings was used to estimate the chromatic differences between OBS and RGB. The corresponding color errors were estimated and analyzed in the color spaces CIELAB (using the color difference formulas ΔE*ab and CIEDE2000), Jzazbz, and iCAM06. In CIELAB the most frequent error (using ΔE*ab) found was 5 for both paintings and natural scenes, a similarity that held for the other spaces tested. In addition, the distribution of errors across the color space shows that the errors are small in the achromatic region and increase with saturation. Overall, the results indicate that the chromatic errors estimated are close to the acceptance error and therefore RGB digital cameras are able to produce quite realistic colors of complex scenarios.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the
framework of the Strategic Funding UIDB/04650/2020
Morphologies and Spectral Energy Distributions of Extremely Red Galaxies in the GOODS-South Field
Using U'- through Ks-band imaging data in the GOODS-South field, we construct
a large, complete sample of 275 ``extremely red objects'' (EROs; K_s<22.0,
R-K_s>3.35; AB), all with deep HST/ACS imaging in B_435, V_606, i_775, and
z_850, and well-calibrated photometric redshifts. Quantitative concentration
and asymmetry measurements fail to separate EROs into distinct morphological
classes. We therefore visually classify the morphologies of all EROs into four
broad types: ``Early'' (elliptical-like), ``Late'' (disk galaxies),
``Irregular'' and ``Other'' (chain galaxies and low surface brightness
galaxies), and calculate their relative fractions and comoving space densities.
For a broad range of limiting magnitudes and color thresholds, the relative
number of early-type EROs is approximately constant at 33-44%, and the comoving
space densities of Early- and Late-type EROs are comparable. Mean rest-frame
spectral energy distributions (SEDs) at wavelengths between 0.1 and 1.2 um are
constructed for all EROs. The SEDs are extremely similar in their range of
shapes, independent of morphological type. The implication is that any
differences between the broad-band SEDs of Early-type EROs and the other types
are relatively subtle, and there is no robust way of photometrically
distinguishing between different morphological types with usual
optical/near-infrared photometry.Comment: Submitted to the ApJL. A version with full-resolution figures, all
GOODS data and all GOODS collaboration papers may be found at
http://www.stsci.edu/science/goods
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