11,816 research outputs found
Gloss Management for Consistent Reproduction of Real and Virtual Objects
A good match of material appearance between real-world objects and their digital on-screen representations is critical for many applications such as fabrication, design, and e-commerce. However, faithful appearance reproduction is challenging, especially for complex phenomena, such as gloss. In most cases, the view-dependent nature of gloss and the range of luminance values required for reproducing glossy materials exceeds the current capabilities of display devices. As a result, appearance reproduction poses significant problems even with accurately rendered images. This paper studies the gap between the gloss perceived from real-world objects and their digital counterparts. Based on our psychophysical experiments on a wide range of 3D printed samples and their corresponding photographs, we derive insights on the influence of geometry, illumination, and the displayâs brightness and measure the change in gloss appearance due to the display limitations. Our evaluation experiments demonstrate that using the prediction to correct material parameters in a rendering system improves the match of gloss appearance between real objects and their visualization on a display device
Multi-scale roughness transfer in cold metal rolling
We report on a comparative Atomic Force Microscope (AFM) multi-scale roughness analysis of cold rolled Al alloy and steel roll, in order to characterize the roughness transfer from the steel roll to the workpiece in cold strip rolling processes. More than three orders of length-scale magnitudes were investigated from 100 microns to 50 nanometers on both types of surfaces. The analysis reveals that both types of surfaces are anisotropic self-afïŹne surfaces. Transverse and longitudinal height proïŹles exhibit a different roughness exponent (Hurst exponent) zÖ=0.93±0.03 and zÊ=0.5±0.05 Different length-scale cut-offs are obtained in each direction lsup=50mm, lsupŐ100mm. Height and slope distributions are also computed to complement this study. The above mentionned self-afïŹne characteresitics are found to be very similar for the roll and the strip surfaces, which suggest that roughness transfer takes place from the macroscopic (100 ”m) to the very small scale (50 nm)
Inconsistencies in the Notions of Acoustic Stress and Streaming
Inviscid hydrodynamics mediates forces through pressure and other, typically
irrotational, external forces. Acoustically induced forces must be consistent
with arising from such a pressure field. The use of "acoustic stress" is shown
to have inconsistencies with such an analysis and generally arise from
mathematical expediency but poor overall conceptualization of such systems.
This contention is further supported by the poor agreement of experiment in
many such approaches. The notion of momentum as being an intrinsic property of
sound waves is similarly found to be paradoxical. Through an analysis that
includes viscosity and attenuation, we conclude that all acoustic streaming
must arise from vorticity introduced by viscous forces at the driver or other
solid boundaries and that calculations with acoustic stress should be replaced
with ones using a nonlinear correction to the overall pressure field
Investigation and computer modelling of the pore structure of paper and of consolidated pigment coatings
Merged with duplicate record 10026.1/839 on 27.02.2017 by CS (TIS)The aim of this project was to enhance the current state of knowledge of the void structure
of paper, and pigments used to coat paper. The porosities and pore size distributions of
consolidated pigments were measured using mercury porosimetry. Prior to this work,
mercury porosimetry was rarely used in this field due to problems associated with the
conventional interpretation of mercury porosimetry data. These problems were examined
and two limitations of mercury porosimetry were addressed. Firstly, the shrinkage of
compressible samples causes an apparent increase in void volume and secondly, large void
spaces shielded by smaller ones are not intruded until anomalously high applied pressures of
mercury are reached. The first limitation was overcome by means of a new correction
procedure which, uniquely, also allows the measurement of the bulk modulus of the
continuous solid phase of a porous sample. Shielding effects have been taken into account by
means of a software package known as Pore-Cor, which generates a three dimensional
structure which has both a mercury intrusion curve and porosity in close agreement with
experiment. It has also been possible to calculate the permeabilities and tortuosity of the
simulated structure and this provides realistic and useful values, which may not be measured
experimentally.
Mercury porosimetry and a range of specialised absorption techniques, including liquid
porosimetry, were used to characterise the porous structures of a highly filled paper which
had been calendered using a range of different conditions. A unique feature of this work is
that for the first time it has been shown that two porosimetric techniques which measure
overlapping pore size distributions may be combined to give a better indication of the total
pore size distribution.ECC International plc
Redefining A in RGBA: Towards a Standard for Graphical 3D Printing
Advances in multimaterial 3D printing have the potential to reproduce various
visual appearance attributes of an object in addition to its shape. Since many
existing 3D file formats encode color and translucency by RGBA textures mapped
to 3D shapes, RGBA information is particularly important for practical
applications. In contrast to color (encoded by RGB), which is specified by the
object's reflectance, selected viewing conditions and a standard observer,
translucency (encoded by A) is neither linked to any measurable physical nor
perceptual quantity. Thus, reproducing translucency encoded by A is open for
interpretation.
In this paper, we propose a rigorous definition for A suitable for use in
graphical 3D printing, which is independent of the 3D printing hardware and
software, and which links both optical material properties and perceptual
uniformity for human observers. By deriving our definition from the absorption
and scattering coefficients of virtual homogeneous reference materials with an
isotropic phase function, we achieve two important properties. First, a simple
adjustment of A is possible, which preserves the translucency appearance if an
object is re-scaled for printing. Second, determining the value of A for a real
(potentially non-homogeneous) material, can be achieved by minimizing a
distance function between light transport measurements of this material and
simulated measurements of the reference materials. Such measurements can be
conducted by commercial spectrophotometers used in graphic arts.
Finally, we conduct visual experiments employing the method of constant
stimuli, and derive from them an embedding of A into a nearly perceptually
uniform scale of translucency for the reference materials.Comment: 20 pages (incl. appendices), 20 figures. Version with higher quality
images: https://cloud-ext.igd.fraunhofer.de/s/pAMH67XjstaNcrF (main article)
and https://cloud-ext.igd.fraunhofer.de/s/4rR5bH3FMfNsS5q (appendix).
Supplemental material including code:
https://cloud-ext.igd.fraunhofer.de/s/9BrZaj5Uh5d0cOU/downloa
fMRI evidence for areas that process surface gloss in the human visual cortex.
Surface gloss is an important cue to the material properties of objects. Recent progress in the study of macaque's brain has increased our understating of the areas involved in processing information about gloss, however the homologies with the human brain are not yet fully understood. Here we used human functional magnetic resonance imaging (fMRI) measurements to localize brain areas preferentially responding to glossy objects. We measured cortical activity for thirty-two rendered three-dimensional objects that had either Lambertian or specular surface properties. To control for differences in image structure, we overlaid a grid on the images and scrambled its cells. We found activations related to gloss in the posterior fusiform sulcus (pFs) and in area V3B/KO. Subsequent analysis with Granger causality mapping indicated that V3B/KO processes gloss information differently than pFs. Our results identify a small network of mid-level visual areas whose activity may be important in supporting the perception of surface gloss.This project was supported by fellowships to H.B. from the Japan Society for the Promotion of Science (H22.290), KAKENHI26870911
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Optical and material properties of varnishes for paintings
Clear varnish coatings are applied to the surface of historic paintings to provide a protective barrier layer and/or change their appearance. The natural varnishes used by the original artist would have given the painting its original finished appearance. Over a period of years these varnish layers degrade with age, which changes the appearance. Then it becomes necessary to remove and replace the coating. This removal and replacement is undesirable as it can lead to damage of the painting. Synthetic alternatives can provide a much longer life coating but may not give the same appearance. This thesis details research into the soft matter physics and fluid mechanisms that determine the relationships between the material properties of varnishes and their effect on the appearance of paintings
Perceptual Modeling and Reproduction of Gloss
The reproduction of gloss on displays is generally not based on perception and as a consequence does not guarantee the best visualization of a real material. The reproduction is composed of four different steps: measurement, modeling, rendering, and display. The minimum number of measurements required to approximate a real material is unknown. The error metrics used to approximate measurements with analytical BRDF models are not based on perception, and the best visual approximation is not always obtained. Finally, the gloss perception difference between real objects and objects seen on displays has not sufficiently been studied and might be influencing the observer judgement.
This thesis proposes a systematic, scalable, and perceptually based workflow to represent real materials on displays. First, the gloss perception difference between real objects and objects seen on displays was studied. Second, the perceptual performance of the error metrics currently in use was evaluated. Third, a projection into a perceptual gloss space was defined, enabling the computation of a perceptual gloss distance measure. Fourth, the uniformity of the gloss space was improved by defining a new gloss difference equation. Finally, a systematic, scalable, and perceptually based workflow was defined using cost-effective instruments
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